ovs-fields(7)                 Open vSwitch Manual                ovs-fields(7)



NAME
       ovs-fields - protocol header fields in OpenFlow and Open vSwitch

INTRODUCTION
       This  document aims to comprehensively document all of the fields, both
       standard and non-standard,  supported  by  OpenFlow  or  Open  vSwitch,
       regardless of origin.

   Fields
       A  field  is  a  property of a packet. Most familiarly, data fields are
       fields that can be extracted from a packet. Most data fields are copied
       directly  from  protocol  headers, e.g. at layer 2, the Ethernet source
       and destination addresses, or the VLAN ID; at layer 3, the IPv4 or IPv6
       source  and  destination;  and  at layer 4, the TCP or UDP ports. Other
       data fields are computed, e.g. ip_frag describes whether a packet is  a
       fragment but it is not copied directly from the IP header.

       Some  data  fields,  called root fields, are always present as a conse‐
       quence of the basic networking technology in use. The  Ethernet  header
       fields  are  root  fields  in  current versions of Open vSwitch, though
       future versions might support other roots. (Currently, to support  LISP
       tunnels, which do not encapsulate an Ethernet header, Open vSwitch syn‐
       thesizes one.)

       Other data fields are not always present. A packet contains ARP fields,
       for  example, only when its Ethernet header indicates the Ethertype for
       ARP, 0x0806. In this documentation, we say that a field  is  applicable
       when it is present in a packet, and inapplicable when it is not. (These
       are not standard terms.) We refer  to  the  conditions  that  determine
       whether  a  field  is  applicable  as  prerequisites. Some VLAN-related
       fields are a special case: these fields are always applicable, but have
       a  designated  value  or  bit  that  indicates whether a VLAN header is
       present, with the remaining values or bits indicating the VLAN header’s
       content (if it is present).

       An  inapplicable  field  does  not  have  a  value,  not even a nominal
       ``value’’ such as all-zero-bits. In many  circumstances,  OpenFlow  and
       Open  vSwitch  allow references only to applicable fields. For example,
       one may match (see Matching, below) a given field  only  if  the  match
       includes  the  field’s prerequisite, e.g. matching an ARP field is only
       allowed if one also matches on Ethertype 0x0806.

       Sometimes a packet may contain multiple  instances  of  a  header.  For
       example,  a  packet may contain multiple VLAN or MPLS headers, and tun‐
       nels can cause any data field to recur. OpenFlow and  Open  vSwitch  do
       not  address these cases uniformly. For VLAN and MPLS headers, only the
       outermost header is accessible, so that inner headers may  be  accessed
       only by ``popping’’ (removing) the outer header. (Open vSwitch supports
       only a single VLAN header in any case.) For tunnels, e.g. GRE or VXLAN,
       the  outer  header  and  inner  headers  are  treated as different data
       fields.

       Many network protocols are built in layers as a stack  of  concatenated
       headers.  Each  header  typically  contains  a ``next type’’ field that
       indicates the type of the protocol header that follows,  e.g.  Ethernet
       contains  an Ethertype and IPv4 contains a IP protocol type. The excep‐
       tional cases, where protocols are layered but an outer layer  does  not
       indicate  the  protocol  type  for  the  inner  layer, or gives only an
       ambiguous indication, are troublesome. An  MPLS  header,  for  example,
       only  indicates whether another MPLS header or some other protocol fol‐
       lows, and in the latter case the inner protocol must be known from  the
       context.  In  these exceptional cases, OpenFlow and Open vSwitch cannot
       provide insight into the inner protocol data fields without  additional
       context,  and  thus  they  treat  all later data fields as inapplicable
       until an OpenFlow action explicitly specifies what protocol follows. In
       the  case  of  MPLS,  the OpenFlow ``pop MPLS’’ action that removes the
       last MPLS header from a packet provides this context, as the  Ethertype
       of the payload. See Layer 2.5: MPLS for more information.

       OpenFlow  and  Open vSwitch support some fields other than data fields.
       Metadata fields relate to the origin or treatment of a packet, but they
       are not extracted from the packet data itself. One example is the phys‐
       ical port on which a packet arrived at the switch. Register fields  act
       like  variables: they give an OpenFlow switch space for temporary stor‐
       age while processing a packet. Existing metadata  and  register  fields
       have no prerequisites.

       A  field’s  value  consists  of  an  integral number of bytes. For data
       fields, sometimes those bytes are taken directly from the packet. Other
       data  fields  are copied from a packet with padding (usually with zeros
       and in the most significant positions). The remaining data  fields  are
       transformed  in other ways as they are copied from the packets, to make
       them more useful for matching.

   Matching
       The most important use of fields in OpenFlow is matching, to  determine
       whether  particular field values agree with a set of constraints called
       a match. A match consists of zero or  more  constraints  on  individual
       fields,  all  of  which must be met to satisfy the match. (A match that
       contains no constraints is always satisfied.) OpenFlow and Open vSwitch
       support a number of forms of matching on individual fields:

              Exact match, e.g. nw_src=10.1.2.3
                     Only  a  particular  value  of  the field is matched; for
                     example, only one particular  source  IP  address.  Exact
                     matches  are  written  as field=value. The forms accepted
                     for value depend on the field.

                     All fields support exact matches.

              Bitwise match, e.g. nw_src=10.1.0.0/255.255.0.0
                     Specific bits in the field must  have  specified  values;
                     for  example,  only  source  IP addresses in a particular
                     subnet. Bitwise matches are written as  field=value/mask,
                     where  value  and mask take one of the forms accepted for
                     an exact match on field. Some fields accept  other  forms
                     for       bitwise       matches;       for       example,
                     nw_src=10.1.0.0/255.255.0.0   may   also    be    written
                     nw_src=10.1.0.0/16.

                     Most  OpenFlow switches do not allow every bitwise match‐
                     ing on every field (and before OpenFlow 1.2, the protocol
                     did  not  even  provide  for  the  possibility  for  most
                     fields). Even switches that do allow bitwise matching  on
                     a  given  field  may restrict the masks that are allowed,
                     e.g. by allowing matches only on contiguous sets of  bits
                     starting from the most significant bit, that is, ``CIDR’’
                     masks [RFC 4632]. Open vSwitch does  not  allows  bitwise
                     matching  on every field, but it allows arbitrary bitwise
                     masks on any field that does  support  bitwise  matching.
                     (Older  versions  had some restrictions, as documented in
                     the descriptions of individual fields.)

              Wildcard, e.g. ``any nw_src’’
                     The value of the field  is  not  constrained.  Wildcarded
                     fields  may be written as field=*, although it is unusual
                     to mention them  at  all.  (When  specifying  a  wildcard
                     explicitly  in  a  command  invocation,  be sure to using
                     quoting to protect against shell expansion.)

                     There is a tiny difference between  wildcarding  a  field
                     and  not  specifying  any match on a field: wildcarding a
                     field requires satisfying the field’s prerequisites.

       Some types of matches on individual fields cannot be expressed directly
       with OpenFlow and Open vSwitch. These can be expressed indirectly:

              Set match, e.g. ``tcp_dst ∈ {80, 443, 8080}’’
                     The value of a field is one of a specified set of values;
                     for example, the TCP destination  port  is  80,  443,  or
                     8080.

                     For  matches  used  in flows (see Flows, below), multiple
                     flows can simulate set matches.

              Range match, e.g. ``1000 ≤ tcp_dst ≤ 1999’’
                     The value of the field must lie within a numerical range,
                     for example, TCP destination ports between 1000 and 1999.

                     Range matches can be expressed as a collection of bitwise
                     matches. For example, suppose that the goal is  to  match
                     TCP source ports 1000 to 1999, inclusive. The binary rep‐
                     resentations of 1000 and 1999 are:

                     01111101000
                     11111001111


                     The following series of bitwise matches will  match  1000
                     and 1999 and all the values in between:

                     01111101xxx
                     0111111xxxx
                     10xxxxxxxxx
                     110xxxxxxxx
                     1110xxxxxxx
                     11110xxxxxx
                     1111100xxxx


                     which can be written as the following matches:

                     tcp,tp_src=0x03e8/0xfff8
                     tcp,tp_src=0x03f0/0xfff0
                     tcp,tp_src=0x0400/0xfe00
                     tcp,tp_src=0x0600/0xff00
                     tcp,tp_src=0x0700/0xff80
                     tcp,tp_src=0x0780/0xffc0
                     tcp,tp_src=0x07c0/0xfff0


              Inequality match, e.g. ``tcp_dst ≠ 80’’
                     The  value  of  the field differs from a specified value,
                     for example, all TCP destination ports except 80.

                     An inequality match on an n-bit field can be expressed as
                     a  disjunction  of  n  1-bit  matches.  For  example, the
                     inequality match ``vlan_pcp ≠ 5’’  can  be  expressed  as
                     ``vlan_pcp  =  0/4 or vlan_pcp = 2/2 or vlan_pcp = 0/1.’’
                     For matches used in flows (see Flows,  below),  sometimes
                     one  can  more  compactly express inequality as a higher-
                     priority flow that matches the  exceptional  case  paired
                     with a lower-priority flow that matches the general case.

                     Alternatively,  an inequality match may be converted to a
                     pair of range matches, e.g. tcp_src  80 may be expressed
                     as ``0 ≤ tcp_src tcp_src ≤ 65535’’, and then
                     each range match may in turn be converted  to  a  bitwise
                     match.

              Conjunctive  match, e.g. ``tcp_src ∈ {80, 443, 8080} and tcp_dst
              ∈ {80, 443, 8080}’’
                     As an OpenFlow extension, Open vSwitch supports  matching
                     on conditions on conjunctions of the previously mentioned
                     forms of matching. See the documentation for conj_id  for
                     more information.

       All  of  these supported forms of matching are special cases of bitwise
       matching. In some cases this influences the  design  of  field  values.
       ip_frag  is  the  most prominent example: it is designed to make all of
       the practically useful checks for IP fragmentation possible as a single
       bitwise match.

     Shorthands

       Some  matches are very commonly used, so Open vSwitch accepts shorthand
       notations. In some cases, Open vSwitch also  uses  shorthand  notations
       when  it  displays  matches. The following shorthands are defined, with
       their long forms shown on the right side:

              ip     eth_type=0x0800

              ipv6   eth_type=0x86dd

              icmp   eth_type=0x0800,ip_proto=1

              icmp6  eth_type=0x86dd,ip_proto=58

              tcp    eth_type=0x0800,ip_proto=6

              tcp6   eth_type=0x86dd,ip_proto=6

              udp    eth_type=0x0800,ip_proto=17

              udp6   eth_type=0x86dd,ip_proto=17

              sctp   eth_type=0x0800,ip_proto=132

              sctp6  eth_type=0x86dd,ip_proto=132

              arp    eth_type=0x0806

              rarp   eth_type=0x8035

              mpls   eth_type=0x8847

              mplsm  eth_type=0x8848

   Evolution of OpenFlow Fields
       The discussion so far applies to all OpenFlow  and  Open  vSwitch  ver‐
       sions.  This section starts to draw in specific information by explain‐
       ing, in broad terms, the treatment of fields and matches in each  Open‐
       Flow version.

     OpenFlow 1.0

       OpenFlow  1.0  defined  the  OpenFlow  protocol  format of a match as a
       fixed-length data structure that could match on the following fields:

              ·      Ingress port.

              ·      Ethernet source and destination MAC.

              ·      Ethertype (with a special value to match frames that lack
                     an Ethertype).

              ·      VLAN ID and priority.

              ·      IPv4 source, destination, protocol, and DSCP.

              ·      TCP source and destination port.

              ·      UDP source and destination port.

              ·      ICMPv4 type and code.

              ·      ARP IPv4 addresses (SPA and TPA) and opcode.

       Each supported field corresponded to some member of the data structure.
       Some members represented multiple fields, in the case of the TCP,  UDP,
       ICMPv4,  and ARP fields whose presence is mutually exclusive. This also
       meant that some members were poor fits for their fields: only the low 8
       bits of the 16-bit ARP opcode could be represented, and the ICMPv4 type
       and code were padded with 8 bits of zeros to fit in the 16-bit  members
       primarily  meant  for  TCP  and  UDP ports. An additional bitmap member
       indicated, for each member, whether its field should be an ``exact’’ or
       ``wildcarded’’  match  (see Matching), with additional support for CIDR
       prefix matching on the IPv4 source and destination fields.

       Simplicity was recognized early on as the main virtue of this approach.
       Obviously,  any fixed-length data structure cannot support matching new
       protocols that do not fit. There was no room, for example, for matching
       IPv6 fields, which was not a priority at the time. Lack of room to sup‐
       port matching the Ethernet addresses inside ARP packets actually caused
       more  of  a  design problem later, leading to an Open vSwitch extension
       action specialized for dropping ``spoofed’’ ARP packets  in  which  the
       frame  and  ARP Ethernet source addressed differed. (This extension was
       never standardized. Open vSwitch dropped support for it a few  releases
       after it added support for full ARP matching.)

       The  design  of the OpenFlow fixed-length matches also illustrates com‐
       promises, in both directions, between the strengths and  weaknesses  of
       software  and  hardware that have always influenced the design of Open‐
       Flow. Support for matching ARP fields that do fit in the data structure
       was  only  added  late  in the design process (and remained optional in
       OpenFlow 1.0), for example, because common switch ASICs did not support
       matching these fields.

       The compromises in favor of software occurred for more complicated rea‐
       sons. The OpenFlow designers did not know how to implement matching  in
       software  that  was  fast, dynamic, and general. (A way was later found
       [Srinivasan].) Thus, the designers sought to support  dynamic,  general
       matching  that  would be fast in realistic special cases, in particular
       when all of the matches were microflows, that is, matches that  specify
       every  field  present  in  a packet, because such matches can be imple‐
       mented as a single hash table lookup. Contemporary  research  supported
       the  feasibility of this approach: the number of microflows in a campus
       network had been measured to peak  at  about  10,000  [Casado,  section
       3.2]. (Calculations show that this can only be true in a lightly loaded
       network [Pepelnjak].)

       As a result, OpenFlow 1.0 required switches to treat microflow  matches
       as  the  highest  possible priority. This let software switches perform
       the microflow hash table lookup first.  Only  on  failure  to  match  a
       microflow did the switch need to fall back to checking the more general
       and presumed slower matches. Also, the OpenFlow 1.0 flow match was min‐
       imally  flexible,  with no support for general bitwise matching, partly
       on the basis that this seemed more likely amenable to relatively  effi‐
       cient  software  implementation.  (CIDR  masking for IPv4 addresses was
       added relatively late in the OpenFlow 1.0 design process.)

       Microflow matching was later discovered to aid some hardware  implemen‐
       tations.  The  TCAM  chips used for matching in hardware do not support
       priority in the same way as OpenFlow but instead tie priority to order‐
       ing  [Pagiamtzis]. Thus, adding a new match with a priority between the
       priorities of existing matches can require reordering an arbitrary num‐
       ber  of  TCAM  entries.  On the other hand, when microflows are highest
       priority, they can be managed  as  a  set-aside  portion  of  the  TCAM
       entries.

       The  emphasis  on  matching  microflows also led designers to carefully
       consider the bandwidth requirements between switch and  controller:  to
       maximize  the  number of microflow setups per second, one must minimize
       the size of each flow’s description. This favored the fixed-length for‐
       mat in use, because it expressed common TCP and UDP microflows in fewer
       bytes than more flexible ``type-length-value’’  (TLV)  formats.  (Early
       versions  of OpenFlow also avoided TLVs in general to head off protocol
       fragmentation.)

       Inapplicable Fields

       OpenFlow 1.0 does not clearly specify how to treat inapplicable fields.
       The  members  for  inapplicable  fields are always present in the match
       data structure, as are the bits that indicate whether  the  fields  are
       matched,  and  the  ``correct’’  member and bit values for inapplicable
       fields is unclear. OpenFlow 1.0 implementations changed their  behavior
       over time as priorities shifted. The early OpenFlow reference implemen‐
       tation, motivated to make every flow a  microflow  to  enable  hashing,
       treated  inapplicable  fields  as  exact  matches on a value of 0. Ini‐
       tially, this behavior was implemented in the reference controller only.

       Later, the reference switch was also  changed  to  actually  force  any
       wildcarded  inapplicable  fields  into  exact  matches on 0. The latter
       behavior sometimes caused problems, because the modified flow  was  the
       one  reported back to the controller later when it queried the flow ta‐
       ble, and the modifications sometimes meant that  the  controller  could
       not  properly recognize the flow that it had added. In retrospect, per‐
       haps this problem should have alerted the designers to a design  error,
       but  the  ability to use a single hash table was held to be more impor‐
       tant than almost every other consideration at the time.

       When more flexible match formats were introduced much later, they  dis‐
       allowed  any  mention  of  inapplicable fields as part of a match. This
       raised the question of how to translate between this new format and the
       OpenFlow 1.0 fixed format. It seemed somewhat inconsistent and backward
       to treat fields as exact-match in one format and forbid  matching  them
       in  the  other,  so instead the treatment of inapplicable fields in the
       fixed-length format was changed from exact match on 0  to  wildcarding.
       (A  better  classifier had by now eliminated software performance prob‐
       lems with wildcards.)

       The OpenFlow 1.0.1 errata (released only in 2012) added some additional
       explanation  [OpenFlow 1.0.1, section 3.4], but it did not mandate spe‐
       cific behavior because of variation among implementations.

     OpenFlow 1.1

       The  OpenFlow  1.1  protocol   match   format   was   designed   as   a
       type/length/value  (TLV)  format  to  allow for future flexibility. The
       specification standardized only a single type OFPMT_STANDARD (0) with a
       fixed-size  payload,  described here. The additional fields and bitwise
       masks in OpenFlow 1.1 cause this match structure to be  over  twice  as
       large as in OpenFlow 1.0, 88 bytes versus 40.

       OpenFlow 1.1 added support for the following fields:

              ·      SCTP source and destination port.

              ·      MPLS label and traffic control (TC) fields.

              ·      One 64-bit register (named ``metadata’’).

       OpenFlow  1.1 increased the width of the ingress port number field (and
       all other port numbers in the protocol) from 16 bits to 32 bits.

       OpenFlow 1.1 increased matching flexibility  by  introducing  arbitrary
       bitwise  matching  on  Ethernet  and IPv4 address fields and on the new
       ``metadata’’ register field. Switches were not required to support  all
       possible masks [OpenFlow 1.1, section 4.3].

       By  a strict reading of the specification, OpenFlow 1.1 removed support
       for matching ICMPv4 type and code [OpenFlow 1.1,  section  A.2.3],  but
       this  is  likely  an  editing  error because ICMP matching is described
       elsewhere [OpenFlow 1.1, Table 3, Table 4, Figure 4]. Open vSwitch does
       support ICMPv4 type and code matching with OpenFlow 1.1.

       OpenFlow  1.1 avoided the pitfalls of inapplicable fields that OpenFlow
       1.0 encountered, by requiring the switch to ignore the specified  field
       values  [OpenFlow  1.1, section A.2.3]. It also implied that the switch
       should ignore the bits that  indicate  whether  to  match  inapplicable
       fields.

       Physical Ingress Port

       OpenFlow  1.1 introduced a new pseudo-field, the physical ingress port.
       The physical ingress port is only a pseudo-field because it  cannot  be
       used  for  matching.  It appears only one place in the protocol, in the
       ``packet-in’’ message that passes a packet received at the switch to an
       OpenFlow controller.

       A  packet’s ingress port and physical ingress port are identical except
       for packets processed by a switch feature such as bonding or  tunneling
       that  makes  a packet appear to arrive on a ``virtual’’ port associated
       with the bond or the tunnel. For such packets, the ingress port is  the
       virtual  port and the physical ingress port is, naturally, the physical
       port. Open vSwitch implements both bonding and tunneling, but its bond‐
       ing implementation does not use virtual ports and its tunnels are typi‐
       cally not on the same OpenFlow switch as their physical  ingress  ports
       (which  need not be part of any switch), so the ingress port and physi‐
       cal ingress port are always the same in Open vSwitch.

     OpenFlow 1.2

       OpenFlow 1.2 abandoned the fixed-length approach to matching. One  rea‐
       son  was size, since adding support for IPv6 address matching (now seen
       as important), with bitwise masks, would have added  64  bytes  to  the
       match  length,  increasing it from 88 bytes in OpenFlow 1.1 to over 150
       bytes. Extensibility had also become important  as  controller  writers
       increasingly  wanted  support  for  new fields without having to change
       messages throughout the OpenFlow protocol. The challenges of  carefully
       defining  fixed-length  matches  to  avoid  problems  with inapplicable
       fields had also become clear over time.

       Therefore, OpenFlow 1.2 adopted a flow format using  a  flexible  type-
       length-value  (TLV) representation, in which each TLV expresses a match
       on one field. These TLVs were in turn encapsulated inside the outer TLV
       wrapper  introduced  in  OpenFlow 1.1 with the new identifier OFPMT_OXM
       (1). (This wrapper fulfilled  its  intended  purpose  of  reducing  the
       amount  of churn in the protocol when changing match formats; some mes‐
       sages that included matches remained unchanged from OpenFlow 1.1 to 1.2
       and later versions.)

       OpenFlow 1.2 added support for the following fields:

              ·      ARP hardware addresses (SHA and THA).

              ·      IPv4 ECN.

              ·      IPv6  source and destination addresses, flow label, DSCP,
                     ECN, and protocol.

              ·      TCP, UDP, and SCTP port numbers when encapsulated  inside
                     IPv6.

              ·      ICMPv6 type and code.

              ·      ICMPv6  Neighbor  Discovery target address and source and
                     target Ethernet addresses.

       The OpenFlow 1.2 format, called OXM (OpenFlow  Extensible  Match),  was
       modeled  closely  on  an  extension  to OpenFlow 1.0 introduced in Open
       vSwitch 1.1 called NXM (Nicira Extended Match). Each OXM or NXM TLV has
       the following format:

               type
        gt;
             16        7   1    8      length bytes
       +------------+-----+--+------+ +------------+
       |vendor/class|field|HM|length| |    body    |
       +------------+-----+--+------+ +------------+


       The most significant 16 bits of the NXM or OXM header, called vendor by
       NXM and class by OXM, identify an organization  permitted  to  allocate
       identifiers  for  fields.  NXM  allocates  only two vendors, 0x0000 for
       fields supported by OpenFlow 1.0 and 0x0001 for fields  implemented  as
       an Open vSwitch extension. OXM assigns classes as follows:

              0x0000 (OFPXMC_NXM_0).
              0x0001 (OFPXMC_NXM_1).
                   Reserved for NXM compatibility.

              0x0002 to 0x7fff
                   Reserved  for  allocation  to  ONF  members,  but  none yet
                   assigned.

              0x8000 (OFPXMC_OPENFLOW_BASIC)
                   Used for most standard OpenFlow fields.

              0x8001 (OFPXMC_PACKET_REGS)
                   Used for packet register fields in OpenFlow 1.5 and later.

              0x8002 to 0xfffe
                   Reserved for the OpenFlow specification.

              0xffff (OFPXMC_EXPERIMENTER)
                   Experimental use.

       When class is 0xffff, the OXM header is extended to 64  bits  by  using
       the  first 32 bits of the body as an experimenter field whose most sig‐
       nificant byte is zero and whose remaining bytes are an Organizationally
       Unique  Identifier  (OUI)  assigned  by  the  IEEE [IEEE OUI], as shown
       below. OpenFlow says that support for experimenter fields is  optional.
       Open  vSwitch 2.4 and later does support them, primarily so that it can
       support the ONFOXM_ET_* code points defined by official Open Networking
       Foundation  extensions  to  OpenFlow 1.3 in e.g. [TCP Flags Match Field
       Extension].

            type                 experimenter
        gt;             gt;
          16     7   1    8        8     24     (length - 4) bytes
       +------+-----+--+------+ +------+-----+ +------------------+
       |class |field|HM|length| | zero | OUI | |       body       |
       +------+-----+--+------+ +------+-----+ +------------------+
        0xffff                    0x00


       Taken as a unit, class  (or  vendor),  field,  and  experimenter  (when
       present) uniquely identify a particular field.

       When  hasmask (abbreviated HM above) is 0, the OXM is an exact match on
       an entire field. In this case, the  body  (excluding  the  experimenter
       field, if present) is a single value to be matched.

       When  hasmask is 1, the OXM is a bitwise match. The body (excluding the
       experimenter field) consists of a value to match, followed by the  bit‐
       wise  mask to apply. A 1-bit in the mask indicates that the correspond‐
       ing bit in the value should be matched and a 0-bit that  it  should  be
       ignored.  For  example, for an IP address field, a value of 192.168.0.0
       followed by  a  mask  of  255.255.0.0  would  match  addresses  in  the
       196.168.0.0/16 subnet.

              ·      Some  fields  might  not support masking at all, and some
                     fields that do support masking might restrict it to  cer‐
                     tain  patterns.  For example, fields that have IP address
                     values might be restricted to CIDR  masks.  The  descrip‐
                     tions of individual fields note these restrictions.

              ·      An  OXM  TLV  with a mask that is all zeros is not useful
                     (although it is not forbidden), because  it  is  has  the
                     same effect as omitting the TLV entirely.

              ·      It  is not meaningful to pair a 0-bit in an OXM mask with
                     a 1-bit in its value, and Open vSwitch  rejects  such  an
                     OXM  with  the error OFPBMC_BAD_WILDCARDS, as required by
                     OpenFlow 1.3 and later.

       The length identifies the number of bytes in the  body,  including  the
       4-byte  experimenter header, if it is present. Each OXM TLV has a fixed
       length; that is, given class, field,  experimenter  (if  present),  and
       hasmask,  length  is  a  constant. The length is included explicitly to
       allow software to minimally parse OXM TLVs of unknown types.

       OXM TLVs must be ordered so that a field’s prerequisites are  satisfied
       before  it  is parsed. For example, an OXM TLV that matches on the IPv4
       source address field is only allowed following an OXM TLV that  matches
       on  the  Ethertype  for IPv4. Similarly, an OXM TLV that matches on the
       TCP source port must follow a TLV that matches an Ethertype of IPv4  or
       IPv6  and  one  that matches an IP protocol of TCP (in that order). The
       order of OXM TLVs is not otherwise restricted; no canonical ordering is
       defined.

       A given field may be matched only once in a series of OXM TLVs.

     OpenFlow 1.3

       OpenFlow  1.3 showed OXM to be largely successful, by adding new fields
       without making any changes to how flow  matches  otherwise  worked.  It
       added OXMs for the following fields supported by Open vSwitch:

              ·      Tunnel  ID  for ports associated with e.g. VXLAN or keyed
                     GRE.

              ·      MPLS ``bottom of stack’’ (BOS) bit.

       OpenFlow 1.3 also added OXMs for the following  fields  not  documented
       here and not yet implemented by Open vSwitch:

              ·      IPv6 extension header handling.

              ·      PBB I-SID.

     OpenFlow 1.4

       OpenFlow  1.4  added  OXMs for the following fields not documented here
       and not yet implemented by Open vSwitch:

              ·      PBB UCA.

     OpenFlow 1.5

       OpenFlow 1.5 added OXMs for the  following  fields  supported  by  Open
       vSwitch:

              ·      TCP flags.

              ·      Packet registers.

              ·      The output port in the OpenFlow action set.

       OpenFlow  1.5  also  added OXMs for the following fields not documented
       here and not yet implemented by Open vSwitch:

              ·      Packet type.

FIELDS REFERENCE
       The following sections document the fields that Open vSwitch  supports.
       Each  section  provides  introductory  material  on  a group of related
       fields, followed by information on each individual field.  In  addition
       to  field-specific  information,  each  field  begins with a table with
       entries for the following important properties:

              Name   The field’s name, used for  parsing  and  formatting  the
                     field,  e.g.  in  ovs-ofctl commands. For historical rea‐
                     sons,  some  fields  have  an  additional  name  that  is
                     accepted  as  an  alternative in parsing. This name, when
                     there is one, is listed as well,  e.g.  ``tun  (aka  tun
                     nel_id).’’

              Width  The  field’s  width,  always  a  multiple of 8 bits. Some
                     fields don’t use all of the bits, so this may be accompa‐
                     nied  by an explanation. For example, OpenFlow embeds the
                     2-bit IP ECN field as as the low bits in an  8-bit  byte,
                     and  so  its  width  is  expressed  as ``8 bits (only the
                     least-significant 2 bits may be nonzero).’’

              Format How a value for the field  is  formatted  or  parsed  by,
                     e.g., ovs-ofctl. Some possibilities are generic:

                     decimal
                            Formats  as  a  decimal  number. On input, accepts
                            decimal numbers or hexadecimal numbers prefixed by
                            0x.

                     hexadecimal
                            Formats as a hexadecimal number prefixed by 0x. On
                            input, accepts decimal numbers or hexadecimal num‐
                            bers  prefixed  by 0x. (The default for parsing is
                            not hexadecimal: only a 0x prefix causes input  to
                            be treated as hexadecimal.)

                     Ethernet
                            Formats  and  accepts  the common Ethernet address
                            format xx:xx:xx:xx:xx:xx.

                     IPv4   Formats  and  accepts   the   dotted-quad   format
                            a.b.c.d.  For bitwise matches, formats and accepts
                            address/length  CIDR  notation  in   addition   to
                            address/mask.

                     IPv6   Formats  and  accepts the common IPv6 address for‐
                            mats, plus CIDR notation for bitwise matches.

                     OpenFlow 1.0 port
                            Accepts 16-bit port numbers in decimal, plus Open‐
                            Flow  well-known  port  names  (e.g.  IN_PORT)  in
                            uppercase or lowercase.

                     OpenFlow 1.1+ port
                            Same syntax as OpenFlow 1.0 ports but  for  32-bit
                            OpenFlow 1.1+ port number fields.

                     Other,  field-specific  formats  are explained along with
                     their fields.

              Masking
                     For most fields, this says ``arbitrary  bitwise  masks,’’
                     meaning  that a flow may match any combination of bits in
                     the field. Some fields instead say ``exact match  only,’’
                     which  means  that a flow that matches on this field must
                     match on the whole field instead of  just  certain  bits.
                     Either  way,  this reports masking support for the latest
                     version of Open vSwitch using OXM or NXM (that is, either
                     OpenFlow  1.2+  or  OpenFlow  1.0  plus  Open vSwitch NXM
                     extensions). In particular, OpenFlow  1.0  (without  NXM)
                     and 1.1 don’t always support masking even if Open vSwitch
                     itself does; refer to the OpenFlow 1.0 and  OpenFlow  1.1
                     rows to learn about masking with these protocol versions.

              Prerequisites
                     Requirements that must be met to match on this field. For
                     example, ip_src has IPv4 as a prerequisite, meaning  that
                     a match must include eth_type=0x0800 to match on the IPv4
                     source address. The following prerequisites,  with  their
                     requirements, are currently in use:

                     none   (no requirements)

                     VLAN VID
                            vlan_tci=0x1000/0x1000  (i.e.  a  VLAN  header  is
                            present)

                     ARP    eth_type=0x0806 (ARP) or eth_type=0x8035 (RARP)

                     IPv4   eth_type=0x0800

                     IPv6   eth_type=0x86dd

                     IPv4/IPv6
                            IPv4 or IPv6

                     MPLS   eth_type=0x8847 or eth_type=0x8848

                     TCP    IPv4/IPv6 and ip_proto=6

                     UDP    IPv4/IPv6 and ip_proto=17

                     SCTP   IPv4/IPv6 and ip_proto=132

                     ICMPv4 IPv4 and ip_proto=1

                     ICMPv6 IPv6 and ip_proto=58

                     ND solicit
                            ICMPv6 and icmp_type=135 and icmp_code=0

                     ND advert
                            ICMPv6 and icmp_type=136 and icmp_code=0

                     ND     ND solicit or ND advert

                     The TCP, UDP, and SCTP prerequisites also have  the  spe‐
                     cial requirement that nw_frag is not being used to select
                     ``later fragments.’’ This is because only the first frag‐
                     ment  of  a fragmented IPv4 or IPv6 datagram contains the
                     TCP or UDP header.

              Access Most fields are ``read/write,’’ which means  that  common
                     OpenFlow  actions  like set_field can modify them. Fields
                     that are ``read-only’’ cannot be modified in  these  gen‐
                     eral-purpose  ways, although there may be other ways that
                     actions can modify them.

              OpenFlow 1.0
              OpenFlow 1.1
                   These rows report the level of support that OpenFlow 1.0 or
                   OpenFlow  1.1,  respectively, has for a field. For OpenFlow
                   1.0, supported fields are reported as either  ``yes  (exact
                   match  only)’’  for  fields that do not support any bitwise
                   masking or ``yes (CIDR match only)’’ for fields  that  sup‐
                   port  CIDR  masking.  OpenFlow  1.1 supported fields report
                   either ``yes (exact match only)’’  or  simply  ``yes’’  for
                   fields that do support arbitrary masks. These OpenFlow ver‐
                   sions supported a fixed collection of fields that cannot be
                   extended,  so  many  more fields are reported as ``not sup‐
                   ported.’’

              OXM
              NXM  These rows report the OXM and NXM code points  that  corre‐
                   spond to a given field. Either or both may be ``none.’’

                   A field that has only an OXM code point is usually one that
                   was standardized before it was added  to  Open  vSwitch.  A
                   field  that  has only an NXM code point is usually one that
                   is not yet standardized. When a field has both OXM and  NXM
                   code points, it usually indicates that it was introduced as
                   an Open vSwitch extension under the NXM  code  point,  then
                   later  standardized  under  the OXM code point. A field can
                   have more than one OXM code point if it was standardized in
                   OpenFlow  1.4  or  later  and additionally introduced as an
                   official ONF extension for OpenFlow 1.3. (A field that  has
                   neither  OXM  nor  NXM  code point is typically an obsolete
                   field that is supported in some other  form  using  OXM  or
                   NXM.)

                   Each  code  point  in  these  rows is described in the form
                   ``NAME (number) since OpenFlow spec and Open  vSwitch  ver
                   sion,’’  e.g.  ``OXM_OF_ETH_TYPE (5) since OpenFlow 1.2 and
                   Open vSwitch 1.7.’’ First, NAME, which specifies a name for
                   the  code  point,  starts  with  a prefix that designates a
                   class and, in some cases, a vendor, as listed in  the  fol‐
                   lowing table:

                   Prefix           Vendor       Class
                   ───────────────  ───────────  ───────
                   NXM_OF           (none)       0x0000
                   NXM_NX           (none)       0x0001
                   OXM_OF           (none)       0x8000
                   OXM_OF_PKT_REG   (none)       0x8001
                   NXOXM_ET         0x00002320   0xffff
                   ONFOXM_ET        0x4f4e4600   0xffff

                   For  more information on OXM/NXM classes and vendors, refer
                   back to OpenFlow 1.2 under Evolution  of  OpenFlow  Fields.
                   The number is the field number within the class and vendor.
                   The OpenFlow spec is the version of OpenFlow that standard‐
                   ized  the  code  point.  It  is omitted for NXM code points
                   because they are nonstandard. The version is the version of
                   Open vSwitch that first supported the code point.

CONJUNCTIVE MATCH FIELDS
   Summary:
       Name      Bytes   Mask   RW?   Prereqs   NXM/OXM Support
       ────────  ──────  ─────  ────  ────────  ────────────────
       conj_id   4       no     no    none      OVS 2.4+

       An  individual  OpenFlow  flow  can  match only a single value for each
       field. However, situations often arise where one wants to match one  of
       a  set  of values within a field or fields. For matching a single field
       against a set, it is straightforward  and  efficient  to  add  multiple
       flows  to  the  flow table, one for each value in the set. For example,
       one might use the following  flows  to  send  packets  with  IP  source
       address a, b, c, or d to the OpenFlow controller:

             ip,ip_src=a actions=controller
             ip,ip_src=b actions=controller
             ip,ip_src=c actions=controller
             ip,ip_src=d actions=controller


       Similarly,  these  flows send packets with IP destination address e, f,
       g, or h to the OpenFlow controller:

             ip,ip_dst=e actions=controller
             ip,ip_dst=f actions=controller
             ip,ip_dst=g actions=controller
             ip,ip_dst=h actions=controller


       Installing all of the above flows in a single flow table yields a  dis‐
       junctive  effect:  a  packet  is  sent  to  the  controller if ip_src ∈
       {a,b,c,d} or ip_dst ∈ {e,f,g,h} (or both). (Pedantically,  if  both  of
       the above sets of flows are present in the flow table, they should have
       different priorities, because OpenFlow says that the results are  unde‐
       fined  when  two  flows  with  same  priority  can  both match a single
       packet.)

       Suppose, on the other hand, one wishes to match conjunctively, that is,
       to  send a packet to the controller only if both ip_src ∈ {a,b,c,d} and
       ip_dst ∈ {e,f,g,h}. This requires 4 × 4 = 16 flows, one for each possi‐
       ble  pairing  of  ip_src  and  ip_dst. That is acceptable for our small
       example, but it does not gracefully extend to larger  sets  or  greater
       numbers of dimensions.

       The  conjunction  action  is a solution for conjunctive matches that is
       built into Open vSwitch. A conjunction action ties groups of individual
       OpenFlow flows into higher-level ``conjunctive flows’’. Each group cor‐
       responds to one dimension, and each flow within the group  matches  one
       possible  value  for the dimension. A packet that matches one flow from
       each group matches the conjunctive flow.

       To implement a conjunctive flow with conjunction, assign  the  conjunc‐
       tive  flow  a 32-bit id, which must be unique within an OpenFlow table.
       Assign each of the n ≥ 2 dimensions a unique number from 1  to  n;  the
       ordering  is  unimportant.  Add one flow to the OpenFlow flow table for
       each possible value of each dimension with conjunction(id, k/n) as  the
       flow’s actions, where k is the number assigned to the flow’s dimension.
       Together, these flows specify the conjunctive flow’s  match  condition.
       When  the conjunctive match condition is met, Open vSwitch looks up one
       more flow that specifies the conjunctive flow’s  actions  and  receives
       its  statistics. This flow is found by setting conj_id to the specified
       id and then again searching the flow table.

       The following flows provide an example. Whenever the IP source  is  one
       of  the values in the flows that match on the IP source (dimension 1 of
       2), and the IP destination is one of the values in the flows that match
       on  IP destination (dimension 2 of 2), Open vSwitch searches for a flow
       that matches conj_id against the conjunction  ID  (1234),  finding  the
       first flow listed below.

             conj_id=1234 actions=controller
             ip,ip_src=10.0.0.1 actions=conjunction(1234, 1/2)
             ip,ip_src=10.0.0.4 actions=conjunction(1234, 1/2)
             ip,ip_src=10.0.0.6 actions=conjunction(1234, 1/2)
             ip,ip_src=10.0.0.7 actions=conjunction(1234, 1/2)
             ip,ip_dst=10.0.0.2 actions=conjunction(1234, 2/2)
             ip,ip_dst=10.0.0.5 actions=conjunction(1234, 2/2)
             ip,ip_dst=10.0.0.7 actions=conjunction(1234, 2/2)
             ip,ip_dst=10.0.0.8 actions=conjunction(1234, 2/2)


       Many subtleties exist:

              ·      In  the  example  above, every flow in a single dimension
                     has the same form, that is, dimension 1 matches on ip_src
                     and dimension 2 on ip_dst, but this is not a requirement.
                     Different flows within a dimension may match on different
                     bits  within a field (e.g. IP network prefixes of differ‐
                     ent lengths, or TCP/UDP port ranges as bitwise  matches),
                     or even on entirely different fields (e.g. to match pack‐
                     ets for TCP source port 80 or TCP destination port 80).

              ·      The flows within  a  dimension  can  vary  their  matches
                     across  more  than one field, e.g. to match only specific
                     pairs of IP source and destination addresses or  L4  port
                     numbers.

              ·      A  flow  may have multiple conjunction actions, with dif‐
                     ferent id values. This is useful for multiple conjunctive
                     flows  with  overlapping  sets.  If  one conjunctive flow
                     matches packets with both ip_src ∈  {a,b}  and  ip_dst  ∈
                     {d,e}  and  a  second  conjunctive  flow matches ip_src ∈
                     {b,c} and ip_dst ∈ {f,g}, for example, then the flow that
                     matches  ip_src=b would have two conjunction actions, one
                     for each  conjunctive  flow.  The  order  of  conjunction
                     actions within a list of actions is not significant.

              ·      A  flow  with  conjunction  actions may also include note
                     actions for  annotations,  but  not  any  other  kind  of
                     actions.  (They  would  not  be useful because they would
                     never be executed.)

              ·      All of the flows that constitute a conjunctive flow  with
                     a  given  id must have the same priority. (Flows with the
                     same id but different priorities are currently treated as
                     different conjunctive flows, that is, currently id values
                     need only be unique within an OpenFlow table at  a  given
                     priority. This behavior isn’t guaranteed to stay the same
                     in later releases, so please use id values unique  within
                     an OpenFlow table.)

              ·      Conjunctive  flows must not overlap with each other, at a
                     given priority, that is, any given packet must be able to
                     match  at  most one conjunctive flow at a given priority.
                     Overlapping   conjunctive   flows   yield   unpredictable
                     results.

              ·      Following  a  conjunctive  flow match, the search for the
                     flow with conj_id=id is done in the same  general-purpose
                     way  as  other  flow table searches, so one can use flows
                     with conj_id=id to act differently depending  on  circum‐
                     stances.  (One  exception  is  that  the  search  for the
                     conj_id=id flow  itself  ignores  conjunctive  flows,  to
                     avoid  recursion.)  If  the search with conj_id=id fails,
                     Open vSwitch acts as if  the  conjunctive  flow  had  not
                     matched  at  all,  and continues searching the flow table
                     for other matching flows.

              ·      OpenFlow prerequisite checking occurs for the  flow  with
                     conj_id=id  in the same way as any other flow, e.g. in an
                     OpenFlow 1.1+ context, putting a mod_nw_src  action  into
                     the  example above would require adding an ip match, like
                     this:

                               conj_id=1234,ip actions=mod_nw_src:1.2.3.4,controller


              ·      OpenFlow prerequisite checking also occurs for the  indi‐
                     vidual  flows  that  comprise  a conjunctive match in the
                     same way as any other flow.

              ·      The flows that constitute a conjunctive flow do not  have
                     useful  statistics.  They  are never updated with byte or
                     packet counts, and so on. (For such  a  flow,  therefore,
                     the idle and hard timeouts work much the same way.)

              ·      Sometimes there is a choice of which flows include a par‐
                     ticular match. For example,  suppose  that  we  added  an
                     extra  constraint  to  our  example, to match on ip_src ∈
                     {a,b,c,d} and ip_dst ∈ {e,f,g,h} and tcp_dst = i. One way
                     to  implement  this  is  to add the new constraint to the
                     conj_id flow, like this:

                               conj_id=1234,tcp,tcp_dst=i actions=mod_nw_src:1.2.3.4,controller


                     but this is not recommended because of the  cost  of  the
                     extra  flow  table lookup. Instead, add the constraint to
                     the individual flows, either in one of the dimensions  or
                     (slightly better) all of them.

              ·      A conjunctive match must have n ≥ 2 dimensions (otherwise
                     a conjunctive  match  is  not  necessary).  Open  vSwitch
                     enforces this.

              ·      Each dimension within a conjunctive match should ordinar‐
                     ily have more  than  one  flow.  Open  vSwitch  does  not
                     enforce this.

       Conjunction ID Field

       Name:            conj_id
       Width:           32 bits
       Format:          decimal
       Masking:         not maskable
       Prerequisites:   none
       Access:          read-only

       OpenFlow 1.0:    not supported
       OpenFlow 1.1:    not supported
       OXM:             none
       NXM:             NXM_NX_CONJ_ID (37) since Open vSwitch 2.4

       Used for conjunctive matching. See above for more information.

TUNNEL FIELDS
   Summary:
       Name                   Bytes            Mask   RW?   Prereqs   NXM/OXM Support
       ─────────────────────  ───────────────  ─────  ────  ────────  ─────────────────────

       tun_id aka tunnel_id   8                yes    yes   none      OF 1.3+ and OVS 1.1+
       tun_src                4                yes    yes   none      OVS 2.0+
       tun_dst                4                yes    yes   none      OVS 2.0+
       tun_ipv6_src           16               yes    yes   none      OVS 2.5+
       tun_ipv6_dst           16               yes    yes   none      OVS 2.5+

       tun_gbp_id             2                yes    yes   none      OVS 2.4+
       tun_gbp_flags          1                yes    yes   none      OVS 2.4+
       tun_metadata0          124              yes    yes   none      OVS 2.5+
       tun_metadata1          124              yes    yes   none      OVS 2.5+
       tun_metadata2          124              yes    yes   none      OVS 2.5+

       tun_metadata3          124              yes    yes   none      OVS 2.5+
       tun_metadata4          124              yes    yes   none      OVS 2.5+
       tun_metadata5          124              yes    yes   none      OVS 2.5+
       tun_metadata6          124              yes    yes   none      OVS 2.5+
       tun_metadata7          124              yes    yes   none      OVS 2.5+

       tun_metadata8          124              yes    yes   none      OVS 2.5+
       tun_metadata9          124              yes    yes   none      OVS 2.5+
       tun_metadata10         124              yes    yes   none      OVS 2.5+
       tun_metadata11         124              yes    yes   none      OVS 2.5+
       tun_metadata12         124              yes    yes   none      OVS 2.5+

       tun_metadata13         124              yes    yes   none      OVS 2.5+
       tun_metadata14         124              yes    yes   none      OVS 2.5+
       tun_metadata15         124              yes    yes   none      OVS 2.5+
       tun_metadata16         124              yes    yes   none      OVS 2.5+
       tun_metadata17         124              yes    yes   none      OVS 2.5+

       tun_metadata18         124              yes    yes   none      OVS 2.5+
       tun_metadata19         124              yes    yes   none      OVS 2.5+
       tun_metadata20         124              yes    yes   none      OVS 2.5+
       tun_metadata21         124              yes    yes   none      OVS 2.5+
       tun_metadata22         124              yes    yes   none      OVS 2.5+

       tun_metadata23         124              yes    yes   none      OVS 2.5+
       tun_metadata24         124              yes    yes   none      OVS 2.5+
       tun_metadata25         124              yes    yes   none      OVS 2.5+
       tun_metadata26         124              yes    yes   none      OVS 2.5+
       tun_metadata27         124              yes    yes   none      OVS 2.5+

       tun_metadata28         124              yes    yes   none      OVS 2.5+
       tun_metadata29         124              yes    yes   none      OVS 2.5+
       tun_metadata30         124              yes    yes   none      OVS 2.5+
       tun_metadata31         124              yes    yes   none      OVS 2.5+
       tun_metadata32         124              yes    yes   none      OVS 2.5+

       tun_metadata33         124              yes    yes   none      OVS 2.5+
       tun_metadata34         124              yes    yes   none      OVS 2.5+
       tun_metadata35         124              yes    yes   none      OVS 2.5+
       tun_metadata36         124              yes    yes   none      OVS 2.5+
       tun_metadata37         124              yes    yes   none      OVS 2.5+

       tun_metadata38         124              yes    yes   none      OVS 2.5+
       tun_metadata39         124              yes    yes   none      OVS 2.5+
       tun_metadata40         124              yes    yes   none      OVS 2.5+
       tun_metadata41         124              yes    yes   none      OVS 2.5+
       tun_metadata42         124              yes    yes   none      OVS 2.5+

       tun_metadata43         124              yes    yes   none      OVS 2.5+
       tun_metadata44         124              yes    yes   none      OVS 2.5+
       tun_metadata45         124              yes    yes   none      OVS 2.5+
       tun_metadata46         124              yes    yes   none      OVS 2.5+
       tun_metadata47         124              yes    yes   none      OVS 2.5+

       tun_metadata48         124              yes    yes   none      OVS 2.5+
       tun_metadata49         124              yes    yes   none      OVS 2.5+
       tun_metadata50         124              yes    yes   none      OVS 2.5+
       tun_metadata51         124              yes    yes   none      OVS 2.5+
       tun_metadata52         124              yes    yes   none      OVS 2.5+

       tun_metadata53         124              yes    yes   none      OVS 2.5+
       tun_metadata54         124              yes    yes   none      OVS 2.5+
       tun_metadata55         124              yes    yes   none      OVS 2.5+
       tun_metadata56         124              yes    yes   none      OVS 2.5+
       tun_metadata57         124              yes    yes   none      OVS 2.5+

       tun_metadata58         124              yes    yes   none      OVS 2.5+
       tun_metadata59         124              yes    yes   none      OVS 2.5+
       tun_metadata60         124              yes    yes   none      OVS 2.5+
       tun_metadata61         124              yes    yes   none      OVS 2.5+
       tun_metadata62         124              yes    yes   none      OVS 2.5+

       tun_metadata63         124              yes    yes   none      OVS 2.5+
       tun_flags              2 (low 1 bits)   yes    yes   none      OVS 2.5+

       The fields in this group relate to tunnels, which Open vSwitch supports
       in several forms (GRE, VXLAN, and so  on).  Most  of  these  fields  do
       appear  in  the  wire  format of a packet, so they are data fields from
       that point of view, but they are metadata from an OpenFlow  flow  table
       point  of view because they do not appear in packets that are forwarded
       to the controller or to ordinary (non-tunnel) output ports.

       Open vSwitch supports a spectrum of usage models for mapping tunnels to
       OpenFlow ports:

              ``Port-based’’ tunnels
                     In this model, an OpenFlow port represents one tunnel: it
                     matches a particular type of tunnel traffic  between  two
                     IP  endpoints,  with a particular tunnel key (if keys are
                     in use). In this situation, in_port suffices  to  distin‐
                     guish  one  tunnel  from  another,  so  the tunnel header
                     fields have little importance  for  OpenFlow  processing.
                     (They are still populated and may be used if it is conve‐
                     nient.) The tunnel header fields play no role in  sending
                     packets  out  such  an OpenFlow port, either, because the
                     OpenFlow port itself fully specifies the tunnel headers.

                     The following  Open  vSwitch  commands  create  a  bridge
                     br-int,  add  port tap0 to the bridge as OpenFlow port 1,
                     establish a port-based GRE tunnel between the local  host
                     and  remote IP 192.168.1.1 using GRE key 5001 as OpenFlow
                     port 2, and arranges to forward all traffic from tap0  to
                     the tunnel and vice versa:

                     ovs-vsctl add-br br-int
                     ovs-vsctl add-port br-int tap0 -- set interface tap0 ofport_request=1
                     ovs-vsctl add-port br-int gre0 --
                         set interface gre0 ofport_request=2 type=gre \
                                            options:remote_ip=192.168.1.1 options:key=5001
                     ovs-ofctl add-flow br-int in_port=1,actions=2
                     ovs-ofctl add-flow br-int in_port=2,actions=1


              ``Flow-based’’ tunnels
                     In  this model, one OpenFlow port represents all possible
                     tunnels of a given type with an endpoint on  the  current
                     host,  for  example,  all GRE tunnels. In this situation,
                     in_port only indicates that traffic was received  on  the
                     particular  kind  of  tunnel.  This  is  where the tunnel
                     header fields are most important: they allow the OpenFlow
                     tables  to  discriminate  among tunnels based on their IP
                     endpoints or keys. Tunnel header  fields  also  determine
                     the IP endpoints and keys of packets sent out such a tun‐
                     nel port.

                     The following  Open  vSwitch  commands  create  a  bridge
                     br-int,  add  port tap0 to the bridge as OpenFlow port 1,
                     establish a flow-based GRE tunnel port 3, and arranges to
                     forward  all  traffic  from tap0 to remote IP 192.168.1.1
                     over a GRE tunnel with key 5001 and vice versa:

                     ovs-vsctl add-br br-int
                     ovs-vsctl add-port br-int tap0 -- set interface tap0 ofport_request=1
                     ovs-vsctl add-port br-int allgre --
                         set interface gre0 ofport_request=3 type=gre \
                                            options:remote_ip=flow options:key=flow
                     ovs-ofctl add-flow br-int \
                         in_port=1 actions=set_tunnel:5001,set_field:192.168.1.1->gt;>gt;tun_dst,3
                     ovs-ofctl add-flow br-int in_port=3,tun_src=192.168.1.1,tun_id=5001 actions=1


              Mixed models.
                     One may define both flow-based and port-based tunnels  at
                     the same time. For example, it is valid and possibly use‐
                     ful to create and configure both gre0 and  allgre  tunnel
                     ports described above.

                     Traffic  is  attributed  on  ingress to the most specific
                     matching tunnel. For example, gre0 is more specific  than
                     allgre.  Therefore,  if both exist, then gre0 will be the
                     ingress  port  for  any   GRE   traffic   received   from
                     192.168.1.1 with key 5001.

                     On  egress,  traffic  may  be directed to any appropriate
                     tunnel port. If both gre0 and allgre  are  configured  as
                     already  described,  then  the  actions  2  and  set_tun
                     nel:5001,set_field:192.168.1.1->gt;>gt;tun_dst,3 send  the  same
                     tunnel traffic.

              Intermediate models.
                     Ports  may  be  configured  as  partially flow-based. For
                     example, one may define an OpenFlow port that  represents
                     tunnels  between  a pair of endpoints but leaves the flow
                     table to discriminate on the flow key.

       ovs-vswitchd.conf.db(5) describes all the details of tunnel  configura‐
       tion.

       These fields do not have any prerequisites, which means that a flow may
       match on any or all of them, in any combination.

       These fields are zeros for packets that did not arrive on a tunnel.

       Tunnel ID Field

       Name:            tun_id (aka tunnel_id)

       Width:           64 bits
       Format:          hexadecimal
       Masking:         arbitrary bitwise masks
       Prerequisites:   none
       Access:          read/write
       OpenFlow 1.0:    not supported
       OpenFlow 1.1:    not supported
       OXM:             OXM_OF_TUNNEL_ID (38)  since  OpenFlow  1.3  and  Open
                        vSwitch 1.10
       NXM:             NXM_NX_TUN_ID (16) since Open vSwitch 1.1

       Many kinds of tunnels support a tunnel ID:

              ·      VXLAN and Geneve have a 24-bit virtual network identifier
                     (VNI).

              ·      LISP has a 24-bit instance ID.

              ·      GRE has an optional 32-bit key.

              ·      STT has a 64-bit key.

       When a packet is received from a tunnel, this field holds the tunnel ID
       in its least significant bits, zero-extended to fit. This field is zero
       if the tunnel does not support an ID, or if no ID is in use for a  tun‐
       nel  type  that has an optional ID, or if an ID of zero received, or if
       the packet was not received over a tunnel.

       When a packet is output to a  tunnel  port,  the  tunnel  configuration
       determines whether the tunnel ID is taken from this field or bound to a
       fixed value. See the earlier description of ``port-based’’ and  ``flow-
       based’’ tunnels for more information.

       The following diagram shows the origin of this field in a typical keyed
       GRE tunnel:

          Ethernet            IPv4               GRE           Ethernet
        gt;   gt;   gt;   gt;
        48  48   16           8   32  32    16    16   32    48  48   16
       +---+---+-----+ +---+-----+---+---+ +---+------+---+ +---+---+----+
       |dst|src|type | |...|proto|src|dst| |...| type |key| |dst|src|type| ...
       +---+---+-----+ +---+-----+---+---+ +---+------+---+ +---+---+----+
                0x800        47                 0x6558


       Tunnel IPv4 Source Field

       Name:            tun_src
       Width:           32 bits
       Format:          IPv4
       Masking:         arbitrary bitwise masks
       Prerequisites:   none
       Access:          read/write
       OpenFlow 1.0:    not supported

       OpenFlow 1.1:    not supported
       OXM:             none
       NXM:             NXM_NX_TUN_IPV4_SRC (31) since Open vSwitch 2.0

       When a packet is received from a  tunnel,  this  field  is  the  source
       address  in  the  outer IP header of the tunneled packet. This field is
       zero if the packet was not received over a tunnel.

       When a packet is output to a flow-based tunnel port, this field  influ‐
       ences  the  IPv4 source address used to send the packet. If it is zero,
       then the kernel chooses an appropriate IP address based using the rout‐
       ing table.

       The following diagram shows the origin of this field in a typical keyed
       GRE tunnel:

          Ethernet            IPv4               GRE           Ethernet
        gt;   gt;   gt;   gt;
        48  48   16           8   32  32    16    16   32    48  48   16
       +---+---+-----+ +---+-----+---+---+ +---+------+---+ +---+---+----+
       |dst|src|type | |...|proto|src|dst| |...| type |key| |dst|src|type| ...
       +---+---+-----+ +---+-----+---+---+ +---+------+---+ +---+---+----+
                0x800        47                 0x6558


       Tunnel IPv4 Destination Field

       Name:            tun_dst
       Width:           32 bits
       Format:          IPv4
       Masking:         arbitrary bitwise masks
       Prerequisites:   none

       Access:          read/write
       OpenFlow 1.0:    not supported
       OpenFlow 1.1:    not supported
       OXM:             none
       NXM:             NXM_NX_TUN_IPV4_DST (32) since Open vSwitch 2.0

       When a packet is received from a tunnel, this field is the  destination
       address  in  the  outer IP header of the tunneled packet. This field is
       zero if the packet was not received over a tunnel.

       When a packet is output to a flow-based tunnel port, this field  speci‐
       fies the destination to which the tunnel packet is sent.

       The following diagram shows the origin of this field in a typical keyed
       GRE tunnel:

          Ethernet            IPv4               GRE           Ethernet
        gt;   gt;   gt;   gt;
        48  48   16           8   32  32    16    16   32    48  48   16
       +---+---+-----+ +---+-----+---+---+ +---+------+---+ +---+---+----+
       |dst|src|type | |...|proto|src|dst| |...| type |key| |dst|src|type| ...
       +---+---+-----+ +---+-----+---+---+ +---+------+---+ +---+---+----+
                0x800        47                 0x6558


       Tunnel IPv6 Source Field

       Name:            tun_ipv6_src
       Width:           128 bits
       Format:          IPv6
       Masking:         arbitrary bitwise masks
       Prerequisites:   none

       Access:          read/write
       OpenFlow 1.0:    not supported
       OpenFlow 1.1:    not supported
       OXM:             none
       NXM:             NXM_NX_TUN_IPV6_SRC (109) since Open vSwitch 2.5

       Similar to tun_src, but for tunnels over IPv6.

       Tunnel IPv6 Destination Field


       Name:            tun_ipv6_dst
       Width:           128 bits
       Format:          IPv6
       Masking:         arbitrary bitwise masks
       Prerequisites:   none
       Access:          read/write
       OpenFlow 1.0:    not supported
       OpenFlow 1.1:    not supported
       OXM:             none
       NXM:             NXM_NX_TUN_IPV6_DST (110) since Open vSwitch 2.5

       Similar to tun_dst, but for tunnels over IPv6.

   VXLAN Group-Based Policy Fields
       The VXLAN header is defined as follows [RFC 7348], where the I bit must
       be set to 1, unlabeled bits or those labeled reserved must be set to 0,
       and Open vSwitch makes the VNI available via tun_id:

          VXLAN flags
        gt;
        1 1 1 1 1 1 1 1    24    24     8
       +-+-+-+-+-+-+-+-+--------+---+--------+
       | | | | |I| | | |reserved|VNI|reserved|
       +-+-+-+-+-+-+-+-+--------+---+--------+


       VXLAN Group-Based Policy [VXLAN Group Policy Option] adds new interpre‐
       tations to existing bits in the VXLAN header, reinterpreting it as fol‐
       lows, with changes highlighted:

           GBP flags
        gt;
        1 1 1 1 1 1 1 1       24        24     8
       +-+-+-+-+-+-+-+-+---------------+---+--------+
       | |D| | |A| | | |group policy ID|VNI|reserved|
       +-+-+-+-+-+-+-+-+---------------+---+--------+


       Open vSwitch makes GBP fields and flags available through the following
       fields.  Only  packets  that  arrive  over  a VXLAN tunnel with the GBP
       extension enabled have these fields set. In other packets they are zero
       on receive and ignored on transmit.

       VXLAN Group-Based Policy ID Field

       Name:            tun_gbp_id
       Width:           16 bits
       Format:          decimal
       Masking:         arbitrary bitwise masks
       Prerequisites:   none
       Access:          read/write
       OpenFlow 1.0:    not supported
       OpenFlow 1.1:    not supported
       OXM:             none

       NXM:             NXM_NX_TUN_GBP_ID (38) since Open vSwitch 2.4

       For  a  packet  tunneled  over  VXLAN with the Group-Based Policy (GBP)
       extension, this field represents the GBP policy ID, as shown above.

       VXLAN Group-Based Policy Flags Field

       Name:            tun_gbp_flags
       Width:           8 bits
       Format:          hexadecimal

       Masking:         arbitrary bitwise masks
       Prerequisites:   none
       Access:          read/write
       OpenFlow 1.0:    not supported
       OpenFlow 1.1:    not supported
       OXM:             none
       NXM:             NXM_NX_TUN_GBP_FLAGS (39) since Open vSwitch 2.4

       For a packet tunneled over VXLAN  with  the  Group-Based  Policy  (GBP)
       extension, this field represents the GBP policy flags, as shown above.

       The field has the format shown below:

           GBP Flags
        gt;
        1 1 1 1 1 1 1 1
       +-+-+-+-+-+-+-+-+
       | |D| | |A| | | |
       +-+-+-+-+-+-+-+-+


       Unlabeled bits are reserved and must be transmitted as 0. The VXLAN GBP
       draft defines the other bits’ meanings as:

              D (Don’t Learn)
                     When set, this bit indicates that the egress tunnel  end‐
                     point  must  not learn the source address of the encapsu‐
                     lated frame.

              A (Applied)
                     When set, indicates that the  group  policy  has  already
                     been applied to this packet. Devices must not apply poli‐
                     cies when the A bit is set.

   Geneve Fields
       These fields provide access to additional features in the  Geneve  tun‐
       neling  protocol [Geneve]. Their names are somewhat generic in the hope
       that the same fields could be reused for other protocols in the future;
       for  example, the NSH protocol [NSH] supports TLV options whose form is
       identical to that for Geneve options.

       Generic Tunnel Option 0 Field


       Name:            tun_metadata0
       Width:           992 bits (124 bytes)
       Format:          hexadecimal
       Masking:         arbitrary bitwise masks
       Prerequisites:   none
       Access:          read/write
       OpenFlow 1.0:    not supported
       OpenFlow 1.1:    not supported
       OXM:             none
       NXM:             NXM_NX_TUN_METADATA0 (40) since Open vSwitch 2.5

       The above information specifically covers generic tunnel option 0,  but
       Open  vSwitch  supports  64  options,  numbered 0 through 63, whose NXM
       field numbers are 40 through 103.

       These fields provide OpenFlow access to the  generic  type-length-value
       options  defined  by  the  Geneve tunneling protocol or other protocols
       with options in the same TLV format as Geneve options.  Each  of  these
       options has the following wire format:

               header                 body
        gt; gt;
         16    8    3    5    4×(length - 1) bytes
       +-----+----+---+------+--------------------+
       |class|type|res|length|       value        |
       +-----+----+---+------+--------------------+
                    0


       Taken together, the class and type in the option format mean that there
       are about 16 million distinct kinds of TLV options, too  many  to  give
       individual  OXM  code  points.  Thus, Open vSwitch requires the user to
       define the TLV options of interest, by binding up to 64 TLV options  to
       generic  tunnel  option NXM code points. Each option may have up to 124
       bytes in its body, the maximum allowed by the  TLV  format,  but  bound
       options may total at most 252 bytes of body.

       Open  vSwitch  extensions  to the OpenFlow protocol bind TLV options to
       NXM code points. The ovs-ofctl(8) program offers one way to  use  these
       extensions,  e.g.  to  configure a mapping from a TLV option with class
       0xffff, type 0, and a body length of 4 bytes:

       ovs-ofctl add-tlv-map br0 "{class=0xffff,type=0,len=4}->gt;>gt;tun_metadata0"


       Once a TLV option is properly bound, it can be  accessed  and  modified
       like any other field, e.g. to send packets that have value 1234 for the
       option described above to the controller:

       ovs-ofctl add-flow br0 tun_metadata0=1234,actions=controller


       An option not received or not bound is matched as all zeros.

       Tunnel Flags Field

       Name:            tun_flags
       Width:           16 bits (only the least-significant 1 bits may be nonzero)
       Format:          tunnel flags
       Masking:         arbitrary bitwise masks
       Prerequisites:   none
       Access:          read/write
       OpenFlow 1.0:    not supported
       OpenFlow 1.1:    not supported
       OXM:             none

       NXM:             NXM_NX_TUN_FLAGS (104) since Open vSwitch 2.5

       Flags indicating various aspects of the tunnel encapsulation.

       Matches on this field are most conveniently written in  terms  of  sym‐
       bolic names (given in the diagram below), each preceded by either + for
       a flag that must be set, or - for a flag that must  be  unset,  without
       any  other  delimiters between the flags. Flags not mentioned are wild‐
       carded. For example, tun_flags=+oam matches only OAM  packets.  Matches
       can also be written as flags/mask, where flags and mask are 16-bit num‐
       bers in decimal or in hexadecimal prefixed by 0x.

       Currently, only one flag is defined:

              oam    The tunnel protocol indicated that this is an OAM (Opera‐
                     tions and Management) control packet.

       The switch may reject matches against unknown flags.

       Newer  versions of Open vSwitch may introduce additional flags with new
       meanings. It is therefore not recommended to use an exact match on this
       field  since  the  behavior of these new flags is unknown and should be
       ignored.

       For non-tunneled packets, the value is 0.

METADATA FIELDS
   Summary:
       Name            Bytes   Mask   RW?   Prereqs   NXM/OXM Support

       ──────────────  ──────  ─────  ────  ────────  ─────────────────────
       in_port         2       no     yes   none      OVS 1.1+
       in_port_oxm     4       no     yes   none      OF 1.2+ and OVS 1.7+
       skb_priority    4       no     no    none

       pkt_mark        4       yes    yes   none      OVS 2.0+
       actset_output   4       no     no    none      OF 1.3+ and OVS 2.4+

       These fields relate to the origin or treatment of a  packet,  but  they
       are not extracted from the packet data itself.

       Ingress Port Field

       Name:            in_port

       Width:           16 bits
       Format:          OpenFlow 1.0 port
       Masking:         not maskable
       Prerequisites:   none

       Access:          read/write
       OpenFlow 1.0:    yes (exact match only)
       OpenFlow 1.1:    yes (exact match only)
       OXM:             none

       NXM:             NXM_OF_IN_PORT (0) since Open vSwitch 1.1

       The  OpenFlow port on which the packet being processed arrived. This is
       a 16-bit field that holds an OpenFlow 1.0 port number. For receiving  a
       packet, the only values that appear in this field are:

              1 through 0xfeff (65,279), inclusive.
                     Conventional OpenFlow port numbers.

              OFPP_LOCAL (0xfffe or 65,534).
                     The ``local’’ port, which in Open vSwitch is always named
                     the same as the bridge itself. This represents a  connec‐
                     tion  between the switch and the local TCP/IP stack. This
                     port is where an IP address is most  commonly  configured
                     on an Open vSwitch switch.

                     OpenFlow  does not require a switch to have a local port,
                     but all existing versions of  Open  vSwitch  have  always
                     included a local port. Future Directions: Future versions
                     of Open vSwitch might be  able  to  optionally  omit  the
                     local  port,  if someone submits code to implement such a
                     feature.

              OFPP_NONE (OpenFlow 1.0) or OFPP_ANY (OpenFlow 1.1+) (0xffff  or
              65,535).
              OFPP_CONTROLLER (0xfffd or 65,533).
                   When  a controller injects a packet into an OpenFlow switch
                   with a ``packet-out’’ request, it can specify one of  these
                   ingress  ports  to  indicate  that the packet was generated
                   internally rather than having been received on some port.

                   OpenFlow 1.0 specified OFPP_NONE for this purpose.  Despite
                   that,  some  controllers  used  OFPP_CONTROLLER,  and  some
                   switches only accepted OFPP_CONTROLLER, so  OpenFlow  1.0.2
                   required  support  for  both  ports. OpenFlow 1.1 and later
                   were more clearly drafted to  allow  only  OFPP_CONTROLLER.
                   For  maximum  compatibility, Open vSwitch allows both ports
                   with all OpenFlow versions.

       Values not mentioned above will never appear when receiving  a  packet,
       including the following notable values:

              0      Zero is not a valid OpenFlow port number.

              OFPP_MAX (0xff00 or 65,280).
                     This  value  has  only  been clearly specified as a valid
                     port number as of OpenFlow 1.3.3. Before that, its status
                     was  unclear,  and  so  Open  vSwitch  has  never allowed
                     OFPP_MAX to be used as a port  number,  so  packets  will
                     never be received on this port. (Other OpenFlow switches,
                     of course, might use it.)

              OFPP_UNSET (0xfff7 or 65,527)
              OFPP_IN_PORT (0xfff8 or 65,528)
              OFPP_TABLE (0xfff9 or 65,529)
              OFPP_NORMAL (0xfffa or 65,530)
              OFPP_FLOOD (0xfffb or 65,531)
              OFPP_ALL (0xfffc or 65,532)
                   These port numbers are used  only  in  output  actions  and
                   never appear as ingress ports.

                   Most  of  these  port numbers were defined in OpenFlow 1.0,
                   but OFPP_UNSET was only introduced in OpenFlow 1.5.

       Values that will never appear when receiving  a  packet  may  still  be
       matched  against  in  the  flow table. There are still circumstances in
       which those flows can be matched:

              ·      The resubmit Open vSwitch extension action allows a  flow
                     table lookup with an arbitrary ingress port.

              ·      An  action  that  modifies  the  ingress  port field (see
                     below), such as e.g. load or set_field,  followed  by  an
                     action  or  instruction  that performs another flow table
                     lookup, such as resubmit or goto_table.

       This field is heavily used for matching in  OpenFlow  tables,  but  for
       packet egress, it has only very limited roles:

              ·      OpenFlow  requires suppressing output actions to in_port.
                     That is, the following two flows both  drop  all  packets
                     that arrive on port 1:

                     in_port=1,actions=1
                     in_port=1,actions=drop


                     (This  behavior  is occasionally useful for flooding to a
                     subset of ports. Specifying actions=1,2,3,4, for example,
                     outputs  to  ports  1,  2, 3, and 4, omitting the ingress
                     port.)

              ·      OpenFlow has a  special  port  OFPP_IN_PORT  (with  value
                     0xfff8) that outputs to the ingress port. For example, in
                     a switch that  has  four  ports  numbered  1  through  4,
                     actions=1,2,3,4,in_port  outputs to ports 1, 2, 3, and 4,
                     including the ingress port.

       Because the ingress port field has so little influence on  packet  pro‐
       cessing,  it  does not ordinarily make sense to modify the ingress port
       field. The field is writable only to support the  occasional  use  case
       where  the  ingress  port’s  roles  in  packet egress, described above,
       become troublesome. For example,  actions=load:0->gt;>gt;NXM_OF_IN_PORT[],out
       put:123  will  output  to  port  123 regardless of whether it is in the
       ingress port. If the ingress port is important, then one may  save  and
       restore it on the stack:

       actions=push:NXM_OF_IN_PORT[],load:0->gt;>gt;NXM_OF_IN_PORT[],output:123,pop:NXM_OF_IN_PORT[]


       or,  in  Open  vSwitch  2.7  or later, use the clone action to save and
       restore it:

       actions=clone(load:0->gt;>gt;NXM_OF_IN_PORT[],output:123)


       The ability to modify the ingress port is an Open vSwitch extension  to
       OpenFlow.

       OXM Ingress Port Field

       Name:            in_port_oxm
       Width:           32 bits
       Format:          OpenFlow 1.1+ port

       Masking:         not maskable
       Prerequisites:   none
       Access:          read/write
       OpenFlow 1.0:    not supported
       OpenFlow 1.1:    yes (exact match only)
       OXM:             OXM_OF_IN_PORT (0) since OpenFlow 1.2 and Open vSwitch
                        1.7
       NXM:             none

       OpenFlow 1.1 and later use a 32-bit port number, so this field supplies
       a  32-bit  view  of  the ingress port. Current versions of Open vSwitch
       support only a 16-bit range of ports:

              ·      OpenFlow 1.0 ports 0x0000 to 0xfeff,  inclusive,  map  to
                     OpenFlow 1.1 port numbers with the same values.

              ·      OpenFlow  1.0  ports  0xff00 to 0xffff, inclusive, map to
                     OpenFlow 1.1 port numbers 0xffffff00 to 0xffffffff.

              ·      OpenFlow 1.1  ports  0x0000ff00  to  0xfffffeff  are  not
                     mapped and not supported.

       in_port  and  in_port_oxm are two views of the same information, so all
       of the comments on in_port apply to in_port_oxm too. Modifying  in_port
       changes in_port_oxm, and vice versa.

       Setting  in_port_oxm  to an unsupported value yields unspecified behav‐
       ior.

       Output Queue Field

       Name:            skb_priority
       Width:           32 bits
       Format:          hexadecimal
       Masking:         not maskable
       Prerequisites:   none
       Access:          read-only
       OpenFlow 1.0:    not supported

       OpenFlow 1.1:    not supported
       OXM:             none
       NXM:             none

       Future Directions: Open vSwitch implements the output queue as a field,
       but  does  not currently expose it through OXM or NXM for matching pur‐
       poses. If this turns out to be a useful feature,  it  could  be  imple‐
       mented  in  future versions. Only the set_queue, enqueue, and pop_queue
       actions currently influence the output queue.

       This field influences how packets in the flow will be queued, for qual‐
       ity  of  service (QoS) purposes, when they egress the switch. Its range
       of meaningful values, and their meanings, varies greatly from one Open‐
       Flow  implementation  to  another. Even within a single implementation,
       there is no guarantee that all OpenFlow ports have the same queues con‐
       figured  or that all OpenFlow ports in an implementation can be config‐
       ured the same way queue-wise.

       Configuring queues on OpenFlow is not well standardized. On Linux, Open
       vSwitch  supports  queue  configuration via OVSDB, specifically the QoS
       and Queue tables (see ovs-vswitchd.conf.db(5) for  details).  Ports  of
       Open  vSwitch  to  other  platforms  might  require queue configuration
       through some separate protocol (such as a CLI).  Even  on  Linux,  Open
       vSwitch  exposes  only  a  fraction  of  the  kernel’s queuing features
       through OVSDB, so advanced or unusual uses might require use  of  sepa‐
       rate  utilities  (e.g.  tc).  OpenFlow switches other than Open vSwitch
       might use OF-CONFIG or  any  of  the  configuration  methods  mentioned
       above.  Finally,  some  OpenFlow switches have a fixed number of fixed-
       function queues (e.g. eight queues with  strictly  defined  priorities)
       and others do not support any control over queuing.

       The only output queue that all OpenFlow implementations must support is
       zero, to identify a default queue, whose properties are implementation-
       defined. Outputting a packet to a queue that does not exist on the out‐
       put port yields unpredictable behavior:  among  the  possibilities  are
       that  the  packet  might  be dropped or transmitted with a very high or
       very low priority.

       OpenFlow 1.0 only allowed output queues to be specified as part  of  an
       enqueue action that specified both a queue and an output port. That is,
       OpenFlow 1.0 treats the queue as an argument to an  action,  not  as  a
       field.

       To increase flexibility, OpenFlow 1.1 added an action to set the output
       queue. This model was carried forward, without change, through OpenFlow
       1.5.

       Open  vSwitch implements the native queuing model of each OpenFlow ver‐
       sion it supports. Open vSwitch also includes an extension  for  setting
       the output queue as an action in OpenFlow 1.0.

       When  a  packet  ingresses into an OpenFlow switch, the output queue is
       ordinarily set to  0,  indicating  the  default  queue.  However,  Open
       vSwitch  supports  various  ways  to forward a packet from one OpenFlow
       switch to another within a single host. In these  cases,  Open  vSwitch
       maintains the output queue across the forwarding step. For example:

              ·      A  hop  across an Open vSwitch ``patch port’’ (which does
                     not actually involve queuing) preserves the output queue.

              ·      When a flow sets the output  queue  then  outputs  to  an
                     OpenFlow  tunnel  port,  the  encapsulation preserves the
                     output queue. If  the  kernel  TCP/IP  stack  routes  the
                     encapsulated  packet  directly  to  a physical interface,
                     then that output honors the output queue.  Alternatively,
                     if  the  kernel routes the encapsulated packet to another
                     Open vSwitch bridge, then the output queue set previously
                     becomes the initial output queue on ingress to the second
                     bridge and will thus be used for further  output  actions
                     (unless overridden by a new ``set queue’’ action).

                     (This  description  reflects the current behavior of Open
                     vSwitch on Linux. This behavior relies on details of  the
                     Linux  TCP/IP  stack. It could be difficult to make ports
                     to other operating systems behave the same way.)

       Packet Mark Field

       Name:            pkt_mark
       Width:           32 bits
       Format:          hexadecimal
       Masking:         arbitrary bitwise masks
       Prerequisites:   none
       Access:          read/write
       OpenFlow 1.0:    not supported
       OpenFlow 1.1:    not supported
       OXM:             none
       NXM:             NXM_NX_PKT_MARK (33) since Open vSwitch 2.0

       Packet mark comes to Open vSwitch from the Linux kernel, in  which  the
       sk_buff  data structure that represents a packet contains a 32-bit mem‐
       ber named skb_mark. The value of skb_mark  propagates  along  with  the
       packet it accompanies wherever the packet goes in the kernel. It has no
       predefined semantics but various kernel-user  interfaces  can  set  and
       match  on  it,  which  makes it suitable for ``marking’’ packets at one
       point in their handling and then acting on the mark later.  With  ipta
       bles,  for  example, one can mark some traffic specially at ingress and
       then handle that traffic differently at  egress  based  on  the  marked
       value.

       Packet  mark  is an attempt at a generalization of the skb_mark concept
       beyond Linux, at least through more generic naming. Like  skb_priority,
       packet  mark  is  preserved  across  forwarding steps within a machine.
       Unlike skb_priority, packet mark has no direct effect  on  packet  for‐
       warding: the value set in packet mark does not matter unless some later
       OpenFlow table or switch matches on packet mark, or unless  the  packet
       passes  through some other kernel subsystem that has been configured to
       interpret packet mark in specific ways, e.g. through iptables  configu‐
       ration mentioned above.

       Preserving packet mark across kernel forwarding steps relies heavily on
       kernel support, which ports to  non-Linux  operating  systems  may  not
       have.  Regardless  of  operating  system support, Open vSwitch supports
       packet mark within a single bridge and across patch ports.

       The value of packet mark when a packet ingresses into  the  first  Open
       vSwich  bridge  is typically zero, but it could be nonzero if its value
       was previously set by some kernel subsystem.

       Action Set Output Port Field

       Name:            actset_output
       Width:           32 bits
       Format:          OpenFlow 1.1+ port
       Masking:         not maskable
       Prerequisites:   none
       Access:          read-only
       OpenFlow 1.0:    not supported
       OpenFlow 1.1:    not supported

       OXM:             ONFOXM_ET_ACTSET_OUTPUT (43) since  OpenFlow  1.3  and
                        Open  vSwitch  2.4;  OXM_OF_ACTSET_OUTPUT  (43)  since
                        OpenFlow 1.5 and Open vSwitch 2.4
       NXM:             none

       Holds the output port currently in the OpenFlow action set  (i.e.  from
       an  output  action within a write_actions instruction). Its value is an
       OpenFlow port number. If there is no output port in the OpenFlow action
       set,  or  if  the output port will be ignored (e.g. because there is an
       output group in the OpenFlow  action  set),  then  the  value  will  be
       OFPP_UNSET.

       Open  vSwitch  allows any table to match this field. OpenFlow, however,
       only requires this field to be matchable from within an OpenFlow egress
       table (a feature that Open vSwitch does not yet implement).

CONNECTION TRACKING FIELDS
   Summary:
       Name          Bytes   Mask   RW?   Prereqs   NXM/OXM Support

       ────────────  ──────  ─────  ────  ────────  ────────────────
       ct_state      4       yes    no    none      OVS 2.5+
       ct_zone       2       no     no    none      OVS 2.5+
       ct_mark       4       yes    yes   none      OVS 2.5+

       ct_label      16      yes    yes   none      OVS 2.5+
       ct_nw_src     4       yes    no    CT        OVS 2.8+
       ct_nw_dst     4       yes    no    CT        OVS 2.8+
       ct_ipv6_src   16      yes    no    CT        OVS 2.8+

       ct_ipv6_dst   16      yes    no    CT        OVS 2.8+
       ct_nw_proto   1       no     no    CT        OVS 2.8+
       ct_tp_src     2       yes    no    CT        OVS 2.8+
       ct_tp_dst     2       yes    no    CT        OVS 2.8+

       Open  vSwitch  2.5  and  later  support  ``connection tracking,’’ which
       allows bidirectional streams of packets to be statefully  grouped  into
       connections.  Open vSwitch connection tracking, for example, identifies
       the patterns of TCP packets that  indicates  a  successfully  initiated
       connection,  as  well as those that indicate that a connection has been
       torn down. Open vSwitch connection tracking can also  identify  related
       connections, such as FTP data connections spawned from FTP control con‐
       nections.

       An individual packet passing through the pipeline may be in one of  two
       states,  ``untracked’’  or  ``tracked,’’ which may be distinguished via
       the ``trk’’ flag in ct_state. A packet is untracked at the beginning of
       the Open vSwitch pipeline and continues to be untracked until the pipe‐
       line invokes the ct action. The  connection  tracking  fields  are  all
       zeroes in an untracked packet. When a flow in the Open vSwitch pipeline
       invokes the ct action, the action initializes the  connection  tracking
       fields and the packet becomes tracked for the remainder of its process‐
       ing.

       The connection tracker stores connection state in  an  internal  table,
       but  it  only adds a new entry to this table when a ct action for a new
       connection invokes ct with the commit parameter. For  a  given  connec‐
       tion,  when  a  pipeline  has executed ct, but not yet with commit, the
       connection is said to be uncommitted. State for an uncommitted  connec‐
       tion is ephemeral and does not persist past the end of the pipeline, so
       some features are only available to committed connections. A connection
       would typically be left uncommitted as a way to drop its packets.

       Connection tracking is an Open vSwitch extension to OpenFlow.

       Connection Tracking State Field

       Name:            ct_state
       Width:           32 bits

       Format:          ct state
       Masking:         arbitrary bitwise masks
       Prerequisites:   none
       Access:          read-only

       OpenFlow 1.0:    not supported
       OpenFlow 1.1:    not supported
       OXM:             none
       NXM:             NXM_NX_CT_STATE (105) since Open vSwitch 2.5

       This  field holds several flags that can be used to determine the state
       of the connection to which the packet belongs.

       Matches on this field are most conveniently written in  terms  of  sym‐
       bolic  names  (listed below), each preceded by either + for a flag that
       must be set, or - for a flag that must  be  unset,  without  any  other
       delimiters  between  the flags. Flags not mentioned are wildcarded. For
       example, tcp,ct_state=+trk-new matches TCP packets that have  been  run
       through  the  connection tracker and do not establish a new connection.
       Matches can also be written as flags/mask, where  flags  and  mask  are
       32-bit numbers in decimal or in hexadecimal prefixed by 0x.

       The following flags are defined:

              new (0x01)
                     A new connection. Set to 1 if this is an uncommitted con‐
                     nection.

              est (0x02)
                     Part of an existing connection. Set to 1  if  this  is  a
                     committed connection.

              rel (0x04)
                     Related  to an existing connection, e.g. an ICMP ``desti‐
                     nation unreachable’’ message or an FTP data  connections.
                     This  flag will only be 1 if the connection to which this
                     one is related is committed.

                     Connections identified as rel are separate from the orig‐
                     inating  connection and must be committed separately. All
                     packets for a related connection will have the  rel  flag
                     set, not just the initial packet.

              rpl (0x08)
                     This packet is in the reply direction, meaning that it is
                     in the opposite direction from the packet that  initiated
                     the  connection.  This flag will only be 1 if the connec‐
                     tion is committed.

              inv (0x10)
                     The state is invalid, meaning that the connection tracker
                     couldn’t  identify  the connection. This flag is a catch-
                     all for problems in  the  connection  or  the  connection
                     tracker, such as:

                     ·      L3/L4  protocol handler is not loaded/unavailable.
                            With the Linux kernel datapath, this may mean that
                            the nf_conntrack_ipv4 or nf_conntrack_ipv6 modules
                            are not loaded.

                     ·      L3/L4 protocol handler determines that the  packet
                            is malformed.

                     ·      Packets are unexpected length for protocol.

              trk (0x20)
                     This  packet  is  tracked, meaning that it has previously
                     traversed the connection tracker. If  this  flag  is  not
                     set,  then  no  other  flags will be set. If this flag is
                     set, then the packet is tracked and other flags may  also
                     be set.

              snat (0x40)
                     This packet was transformed by source address/port trans‐
                     lation by a preceding ct action. Open vSwitch  2.6  added
                     this flag.

              dnat (0x80)
                     This  packet  was transformed by destination address/port
                     translation by a preceding ct action.  Open  vSwitch  2.6
                     added this flag.

       There  are  additional constraints on these flags, listed in decreasing
       order of precedence below:

              1.
                If trk is unset, no other flags are set.

              2.
                If trk is set, one or more other flags may be set.

              3.
                If inv is set, only the trk flag is also set.

              4.
                new and est are mutually exclusive.

              5.
                new and rpl are mutually exclusive.

              6.
                rel may be set in conjunction with any other flags.

       Future versions of Open vSwitch may define new flags.

       Connection Tracking Zone Field

       Name:            ct_zone
       Width:           16 bits
       Format:          hexadecimal
       Masking:         not maskable
       Prerequisites:   none
       Access:          read-only
       OpenFlow 1.0:    not supported
       OpenFlow 1.1:    not supported
       OXM:             none
       NXM:             NXM_NX_CT_ZONE (106) since Open vSwitch 2.5

       A connection tracking zone, the zone value passed to the most recent ct
       action.  Each  zone  is  an independent connection tracking context, so
       tracking the same packet in multiple contexts  requires  using  the  ct
       action multiple times.

       Connection Tracking Mark Field

       Name:            ct_mark
       Width:           32 bits
       Format:          hexadecimal
       Masking:         arbitrary bitwise masks

       Prerequisites:   none
       Access:          read/write
       OpenFlow 1.0:    not supported
       OpenFlow 1.1:    not supported
       OXM:             none
       NXM:             NXM_NX_CT_MARK (107) since Open vSwitch 2.5

       The  metadata  committed, by an action within the exec parameter to the
       ct action, to the connection to which the current packet belongs.

       Connection Tracking Label Field

       Name:            ct_label
       Width:           128 bits
       Format:          hexadecimal
       Masking:         arbitrary bitwise masks
       Prerequisites:   none
       Access:          read/write
       OpenFlow 1.0:    not supported
       OpenFlow 1.1:    not supported
       OXM:             none
       NXM:             NXM_NX_CT_LABEL (108) since Open vSwitch 2.5

       The label committed, by an action within the exec parameter to  the  ct
       action, to the connection to which the current packet belongs.

       Open vSwitch 2.8 introduced the matching support for connection tracker
       original direction 5-tuple fields.

       For non-committed non-related connections the conntrack original direc‐
       tion  tuple  fields  always  have  the same values as the corresponding
       headers in the packet itself. For any other packets of a committed con‐
       nection  the conntrack original direction tuple fields reflect the val‐
       ues from that initial non-committed non-related packet, and thus may be
       different  from the actual packet headers, as the actual packet headers
       may be in reverse direction (for reply  packets),  transformed  by  NAT
       (when \fBnat\fR option was applied to the connection), or be of differ‐
       ent protocol (i.e., when an ICMP response is sent to an UDP packet). In
       case of related connections, e.g., an FTP data connection, the original
       direction tuple contains the original direction headers from the master
       connection, e.g., an FTP control connection.

       The  following  fields  are  populated  by the ct action, and require a
       match to a valid connection tracking state as a prerequisite, in  addi‐
       tion  to  the  IP or IPv6 ethertype match. Examples of valid connection
       tracking      state      matches      include      \fBct_state=+new\fR,
       \fBct_state=+est\fR, \fBct_state=+rel\fR, and \fBct_state=+trk-inv\fR.

       Connection Tracking Original Direction IPv4 Source Address Field

       Name:            ct_nw_src
       Width:           32 bits
       Format:          IPv4
       Masking:         arbitrary bitwise masks
       Prerequisites:   CT
       Access:          read-only
       OpenFlow 1.0:    not supported
       OpenFlow 1.1:    not supported
       OXM:             none

       NXM:             NXM_NX_CT_NW_SRC (120) since Open vSwitch 2.8

       Matches IPv4 conntrack original direction tuple source address. See the
       paragraphs above for general  description  to  the  conntrack  original
       direction tuple. Introduced in Open vSwitch 2.8.

       Connection Tracking Original Direction IPv4 Destination Address Field

       Name:            ct_nw_dst
       Width:           32 bits
       Format:          IPv4

       Masking:         arbitrary bitwise masks
       Prerequisites:   CT
       Access:          read-only
       OpenFlow 1.0:    not supported
       OpenFlow 1.1:    not supported
       OXM:             none
       NXM:             NXM_NX_CT_NW_DST (121) since Open vSwitch 2.8

       Matches  IPv4  conntrack  original direction tuple destination address.
       See the paragraphs above for general description to the conntrack orig‐
       inal direction tuple. Introduced in Open vSwitch 2.8.

       Connection Tracking Original Direction IPv6 Source Address Field

       Name:            ct_ipv6_src
       Width:           128 bits
       Format:          IPv6
       Masking:         arbitrary bitwise masks
       Prerequisites:   CT
       Access:          read-only
       OpenFlow 1.0:    not supported
       OpenFlow 1.1:    not supported
       OXM:             none

       NXM:             NXM_NX_CT_IPV6_SRC (122) since Open vSwitch 2.8

       Matches IPv6 conntrack original direction tuple source address. See the
       paragraphs above for general  description  to  the  conntrack  original
       direction tuple. Introduced in Open vSwitch 2.8.

       Connection Tracking Original Direction IPv6 Destination Address Field

       Name:            ct_ipv6_dst
       Width:           128 bits
       Format:          IPv6

       Masking:         arbitrary bitwise masks
       Prerequisites:   CT
       Access:          read-only
       OpenFlow 1.0:    not supported
       OpenFlow 1.1:    not supported
       OXM:             none
       NXM:             NXM_NX_CT_IPV6_DST (123) since Open vSwitch 2.8

       Matches  IPv6  conntrack  original direction tuple destination address.
       See the paragraphs above for general description to the conntrack orig‐
       inal direction tuple. Introduced in Open vSwitch 2.8.

       Connection Tracking Original Direction IP Protocol Field

       Name:            ct_nw_proto
       Width:           8 bits
       Format:          decimal
       Masking:         not maskable
       Prerequisites:   CT
       Access:          read-only
       OpenFlow 1.0:    not supported
       OpenFlow 1.1:    not supported
       OXM:             none

       NXM:             NXM_NX_CT_NW_PROTO (119) since Open vSwitch 2.8

       Matches  conntrack  original direction tuple IP protocol type, which is
       specified as a decimal number between 0 and 255, inclusive (e.g.  1  to
       match ICMP packets or 6 to match TCP packets). In case of, for example,
       an ICMP response to an UDP packet, this may be different  from  the  IP
       protocol  type  of the packet itself. See the paragraphs above for gen‐
       eral description to the conntrack original direction tuple.  Introduced
       in Open vSwitch 2.8.

       Connection  Tracking  Original  Direction  Transport  Layer Source Port
       Field

       Name:            ct_tp_src
       Width:           16 bits
       Format:          decimal
       Masking:         arbitrary bitwise masks
       Prerequisites:   CT
       Access:          read-only
       OpenFlow 1.0:    not supported
       OpenFlow 1.1:    not supported
       OXM:             none
       NXM:             NXM_NX_CT_TP_SRC (124) since Open vSwitch 2.8

       Bitwise match on  the  conntrack  original  direction  tuple  transport
       source,  when  MFF_CT_NW_PROTO  has value 6 for TCP, 17 for UDP, or 132
       for SCTP. When MFF_CT_NW_PROTO has value 1 for ICMP, or 58 for  ICMPv6,
       the lower 8 bits of MFF_CT_TP_SRC matches the conntrack original direc‐
       tion ICMP type. See the paragraphs above for general description to the
       conntrack original direction tuple. Introduced in Open vSwitch 2.8.

       Connection  Tracking  Original  Direction  Transport  Layer Source Port
       Field

       Name:            ct_tp_dst

       Width:           16 bits
       Format:          decimal
       Masking:         arbitrary bitwise masks
       Prerequisites:   CT
       Access:          read-only
       OpenFlow 1.0:    not supported
       OpenFlow 1.1:    not supported
       OXM:             none
       NXM:             NXM_NX_CT_TP_DST (125) since Open vSwitch 2.8

       Bitwise match on the conntrack original direction tuple transport  des‐
       tination port, when MFF_CT_NW_PROTO has value 6 for TCP, 17 for UDP, or
       132 for SCTP. When MFF_CT_NW_PROTO has value 1  for  ICMP,  or  58  for
       ICMPv6,  the lower 8 bits of MFF_CT_TP_DST matches the conntrack origi‐
       nal direction ICMP code. See the paragraphs above for general  descrip‐
       tion  to  the  conntrack  original  direction tuple. Introduced in Open
       vSwitch 2.8.

REGISTER FIELDS
   Summary:
       Name       Bytes   Mask   RW?   Prereqs   NXM/OXM Support

       ─────────  ──────  ─────  ────  ────────  ─────────────────────
       metadata   8       yes    yes   none      OF 1.2+ and OVS 1.8+
       reg0       4       yes    yes   none      OVS 1.1+
       reg1       4       yes    yes   none      OVS 1.1+

       reg2       4       yes    yes   none      OVS 1.1+
       reg3       4       yes    yes   none      OVS 1.1+
       reg4       4       yes    yes   none      OVS 1.3+
       reg5       4       yes    yes   none      OVS 1.7+

       reg6       4       yes    yes   none      OVS 1.7+
       reg7       4       yes    yes   none      OVS 1.7+
       reg8       4       yes    yes   none      OVS 2.6+
       reg9       4       yes    yes   none      OVS 2.6+

       reg10      4       yes    yes   none      OVS 2.6+
       reg11      4       yes    yes   none      OVS 2.6+
       reg12      4       yes    yes   none      OVS 2.6+
       reg13      4       yes    yes   none      OVS 2.6+

       reg14      4       yes    yes   none      OVS 2.6+
       reg15      4       yes    yes   none      OVS 2.6+
       xreg0      8       yes    yes   none      OF 1.3+ and OVS 2.4+
       xreg1      8       yes    yes   none      OF 1.3+ and OVS 2.4+

       xreg2      8       yes    yes   none      OF 1.3+ and OVS 2.4+
       xreg3      8       yes    yes   none      OF 1.3+ and OVS 2.4+
       xreg4      8       yes    yes   none      OF 1.3+ and OVS 2.4+
       xreg5      8       yes    yes   none      OF 1.3+ and OVS 2.4+

       xreg6      8       yes    yes   none      OF 1.3+ and OVS 2.4+
       xreg7      8       yes    yes   none      OF 1.3+ and OVS 2.4+
       xxreg0     16      yes    yes   none      OVS 2.6+
       xxreg1     16      yes    yes   none      OVS 2.6+

       xxreg2     16      yes    yes   none      OVS 2.6+
       xxreg3     16      yes    yes   none      OVS 2.6+

       These fields give an OpenFlow switch space for temporary storage  while
       the  pipeline is running. Whereas metadata fields can have a meaningful
       initial  value  and  can  persist  across  some  hops  across  OpenFlow
       switches,  registers are always initially 0 and their values never per‐
       sist across inter-switch hops (not even across patch ports).

       OpenFlow Metadata Field

       Name:            metadata
       Width:           64 bits
       Format:          hexadecimal

       Masking:         arbitrary bitwise masks
       Prerequisites:   none
       Access:          read/write
       OpenFlow 1.0:    not supported

       OpenFlow 1.1:    yes
       OXM:             OXM_OF_METADATA  (2)  since  OpenFlow  1.2  and   Open
                        vSwitch 1.8
       NXM:             none

       This  field  is the oldest standardized OpenFlow register field, intro‐
       duced in OpenFlow 1.1. It was introduced to model the limited number of
       user-defined bits that some ASIC-based switches can carry through their
       pipelines. Because of hardware limitations, OpenFlow allows switches to
       support  writing  and  masking only an implementation-defined subset of
       bits, even no bits at all. The Open vSwitch software switch always sup‐
       ports  all 64 bits, but of course an Open vSwitch port to an ASIC would
       have the same restriction as the ASIC itself.

       This field has an OXM code point, but OpenFlow 1.4 and earlier allow it
       to  be  modified only with a specialized instruction, not with a ``set-
       field’’ action. OpenFlow 1.5 removes  this  restriction.  Open  vSwitch
       does not enforce this restriction, regardless of OpenFlow version.

       Register 0 Field

       Name:            reg0
       Width:           32 bits
       Format:          hexadecimal

       Masking:         arbitrary bitwise masks
       Prerequisites:   none
       Access:          read/write
       OpenFlow 1.0:    not supported

       OpenFlow 1.1:    not supported
       OXM:             none
       NXM:             NXM_NX_REG0 (0) since Open vSwitch 1.1

       This  is the first of several Open vSwitch registers, all of which have
       the same properties. Open vSwitch 1.1 introduced registers 0, 1, 2, and
       3,  version 1.3 added register 4, version 1.7 added registers 5, 6, and
       7, and version 2.6 added registers 8 through 15.

       Extended Register 0 Field

       Name:            xreg0
       Width:           64 bits
       Format:          hexadecimal

       Masking:         arbitrary bitwise masks
       Prerequisites:   none
       Access:          read/write
       OpenFlow 1.0:    not supported

       OpenFlow 1.1:    not supported
       OXM:             OXM_OF_PKT_REG0  (0)  since  OpenFlow  1.3  and   Open
                        vSwitch 2.4
       NXM:             none

       This is the first of the registers introduced in OpenFlow 1.5. OpenFlow
       1.5 calls these fields just the ``packet registers,’’ but Open  vSwitch
       already  had  32-bit  registers  by that name, so Open vSwitch uses the
       name ``extended registers’’ in an  attempt  to  reduce  confusion.  The
       standard  allows  for  up to 128 registers, each 64 bits wide, but Open
       vSwitch only implements 4 (in versions 2.4 and 2.5) or  8  (in  version
       2.6 and later).

       Each of the 64-bit extended registers overlays two of the 32-bit regis‐
       ters: xreg0 overlays reg0 and reg1, with reg0 supplying  the  most-sig‐
       nificant bits of xreg0 and reg1 the least-significant. Similarly, xreg1
       overlays reg2 and reg3, and so on.

       The OpenFlow specification says, ``In most cases, the packet  registers
       can  not be matched in tables, i.e. they usually can not be used in the
       flow entry match structure’’  [OpenFlow  1.5,  section  7.2.3.10],  but
       there  is no reason for a software switch to impose such a restriction,
       and Open vSwitch does not.

       Double-Extended Register 0 Field

       Name:            xxreg0
       Width:           128 bits
       Format:          hexadecimal

       Masking:         arbitrary bitwise masks
       Prerequisites:   none
       Access:          read/write
       OpenFlow 1.0:    not supported

       OpenFlow 1.1:    not supported
       OXM:             none
       NXM:             NXM_NX_XXREG0 (111) since Open vSwitch 2.6

       This is the first of the double-extended registers  introduce  in  Open
       vSwitch  2.6.  Each  of the 128-bit extended registers overlays four of
       the 32-bit registers: xxreg0 overlays reg0 through reg3, with reg0 sup‐
       plying  the most-significant bits of xxreg0 and reg3 the least-signifi‐
       cant. xxreg1 similarly overlays reg4 through reg7, and so on.

LAYER 2 (ETHERNET) FIELDS
   Summary:
       Name                   Bytes   Mask   RW?   Prereqs   NXM/OXM Support

       ─────────────────────  ──────  ─────  ────  ────────  ─────────────────────
       eth_src aka dl_src     6       yes    yes   none      OF 1.2+ and OVS 1.1+
       eth_dst aka dl_dst     6       yes    yes   none      OF 1.2+ and OVS 1.1+
       eth_type aka dl_type   2       no     no    none      OF 1.2+ and OVS 1.1+

       Ethernet is the only layer-2 protocol that Open  vSwitch  supports.  As
       with  most software, Open vSwitch and OpenFlow regard an Ethernet frame
       to begin with the 14-byte header and end with the  final  byte  of  the
       payload;  that  is,  the frame check sequence is not considered part of
       the frame.

       Ethernet Source Field

       Name:            eth_src (aka dl_src)

       Width:           48 bits
       Format:          Ethernet
       Masking:         arbitrary bitwise masks
       Prerequisites:   none

       Access:          read/write
       OpenFlow 1.0:    yes (exact match only)
       OpenFlow 1.1:    yes


       OXM:             OXM_OF_ETH_SRC (4) since OpenFlow 1.2 and Open vSwitch
                        1.7
       NXM:             NXM_OF_ETH_SRC (2) since Open vSwitch 1.1

       The Ethernet source address:

          Ethernet
        gt;
        48  48   16
       +---+---+----+
       |dst|src|type| ...
       +---+---+----+


       Ethernet Destination Field

       Name:            eth_dst (aka dl_dst)
       Width:           48 bits
       Format:          Ethernet

       Masking:         arbitrary bitwise masks
       Prerequisites:   none
       Access:          read/write
       OpenFlow 1.0:    yes (exact match only)

       OpenFlow 1.1:    yes
       OXM:             OXM_OF_ETH_DST (3) since OpenFlow 1.2 and Open vSwitch
                        1.7
       NXM:             NXM_OF_ETH_DST (1) since Open vSwitch 1.1

       The Ethernet destination address:

          Ethernet
        gt;
        48  48   16
       +---+---+----+
       |dst|src|type| ...
       +---+---+----+


       Open vSwitch 1.8 and later support arbitrary masks  for  source  and/or
       destination. Earlier versions only support masking the destination with
       the following masks:

              01:00:00:00:00:00
                     Match     only     the     multicast      bit.      Thus,
                     dl_dst=01:00:00:00:00:00/01:00:00:00:00:00   matches  all
                     multicast (including  broadcast)  Ethernet  packets,  and
                     dl_dst=00:00:00:00:00:00/01:00:00:00:00:00   matches  all
                     unicast Ethernet packets.

              fe:ff:ff:ff:ff:ff
                     Match all bits except the multicast bit. This is probably
                     not useful.

              ff:ff:ff:ff:ff:ff
                     Exact match (equivalent to omitting the mask).

              00:00:00:00:00:00
                     Wildcard all bits (equivalent to dl_dst=*).

       Ethernet Type Field

       Name:            eth_type (aka dl_type)
       Width:           16 bits
       Format:          hexadecimal
       Masking:         not maskable

       Prerequisites:   none
       Access:          read-only
       OpenFlow 1.0:    yes (exact match only)
       OpenFlow 1.1:    yes (exact match only)
       OXM:             OXM_OF_ETH_TYPE   (5)  since  OpenFlow  1.2  and  Open
                        vSwitch 1.7

       NXM:             NXM_OF_ETH_TYPE (3) since Open vSwitch 1.1

       The most commonly seen Ethernet frames today use a format called ``Eth‐
       ernet  II,’’ in which the last two bytes of the Ethernet header specify
       the Ethertype. For such a frame, this field is copied from those  bytes
       of the header, like so:

             Ethernet
        gt;
        48  48      16
       +---+---+----------+
       |dst|src|   type   | ...
       +---+---+----------+
                ≥0x600


       Every Ethernet type has a value 0x600 (1,536) or greater. When the last
       two bytes of the Ethernet header have a value too small to be an Ether‐
       net  type,  then the value found there is the total length of the frame
       in bytes, excluding the Ethernet header. An 802.2 LLC header  typically
       follows the Ethernet header. OpenFlow and Open vSwitch only support LLC
       headers with DSAP and SSAP 0xaa and control byte 0x03,  which  indicate
       that  a  SNAP header follows the LLC header. In turn, OpenFlow and Open
       vSwitch only support a SNAP header with organization 0x000000. In  such
       a  case,  this  field is copied from the type field in the SNAP header,
       like this:

           Ethernet           LLC                SNAP
        gt;   gt;   gt;
        48  48    16      8    8    8        24        16
       +---+---+------+ +----+----+----+ +--------+----------+
       |dst|src| type | |DSAP|SSAP|cntl| |  org   |   type   | ...
       +---+---+------+ +----+----+----+ +--------+----------+
                gt;   gt;   gt;
         48  48      16   16        16
       +----+---+ +------+---+ +----------+
       |dst |src| | TPID |TCI| |   type   | ...
       +----+---+ +------+---+ +----------+
                   0x8100       ≥0x600


       LLC and SNAP encapsulation look like this with an 802.1Q header:

        Ethernet     802.1Q     Ethertype        LLC                SNAP
        gt;   gt;   gt;   gt;   gt;
         48  48      16   16       16        8    8    8        24        16
       +----+---+ +------+---+ +---------+ +----+----+----+ +--------+----------+
       |dst |src| | TPID |TCI| |  type   | |DSAP|SSAP|cntl| |  org   |   type   | ...
       +----+---+ +------+---+ +---------+ +----+----+----+ +--------+----------+
                   0x8100        0x5ff
       (OFP_DL_TYPE_NOT_ETH_TYPE).

VLAN FIELDS
   Summary:
       Name          Bytes             Mask   RW?   Prereqs    NXM/OXM Support

       ────────────  ────────────────  ─────  ────  ─────────  ─────────────────────
       dl_vlan       2 (low 12 bits)   no     yes   none
       dl_vlan_pcp   1 (low 3 bits)    no     yes   none

       vlan_vid      2 (low 12 bits)   yes    yes   none       OF 1.2+ and OVS 1.7+
       vlan_pcp      1 (low 3 bits)    no     yes   VLAN VID   OF 1.2+ and OVS 1.7+
       vlan_tci      2                 yes    yes   none       OVS 1.1+

       The  802.1Q  VLAN  header causes more trouble than any other 4 bytes in
       networking. OpenFlow 1.0, 1.1, and 1.2+ all  treat  VLANs  differently.
       Open  vSwitch  extensions  add another variant to the mix. Open vSwitch
       reconciles all four treatments as best it can.

   VLAN Header Format
       An 802.1Q VLAN header consists of two 16-bit fields:

          TPID        TCI
        gt; gt;
           16      3   1  12
       +---------+---+---+---+
       |Ethertype|PCP|CFI|VID|
       +---------+---+---+---+
         0x8100        0


       The first 16 bits of the VLAN header, the TPID  (Tag  Protocol  IDenti‐
       fier), is an Ethertype. When the VLAN header is inserted just after the
       source and destination MAC addresses in a  Ethertype  frame,  the  TPID
       serves  to  identify  the  presence of the VLAN. The standard TPID, the
       only one that Open vSwitch supports, is 0x8100. OpenFlow 1.0 explicitly
       supports  only TPID 0x8100. OpenFlow 1.1, but not earlier or later ver‐
       sions, also requires support for TPID 0x88a8  (Open  vSwitch  does  not
       support this). OpenFlow 1.2 through 1.5 do not require support for spe‐
       cific TPIDs (the ``push vlan header’’ action does say that only  0x8100
       and  0x88a8 should be pushed). No version of OpenFlow provides a way to
       distinguish or match on the TPID.

       The remaining 16 bits of the VLAN header, the TCI (Tag Control Informa‐
       tion), is subdivided into three subfields:

              ·      PCP (Priority Control Point), is a 3-bit 802.1p priority.
                     The lowest priority is  value  1,  the  second-lowest  is
                     value 0, and priority increases from 2 up to highest pri‐
                     ority 7.

              ·      CFI (Canonical Format Indicator), is a 1-bit field. On an
                     Ethernet  network,  its value is always 0. This led to it
                     later being repurposed under the name DEI (Drop Eligibil‐
                     ity Indicator). By either name, OpenFlow and Open vSwitch
                     don’t provide any way to match or set this bit.

              ·      VID (VLAN IDentifier), is a 12-bit VLAN. If the VID is 0,
                     then  the  frame is not part of a VLAN. In that case, the
                     VLAN header is called a priority tag because it  is  only
                     meaningful  for assigning the frame a priority. VID 0xfff
                     (4,095) is reserved.

       See eth_type for illustrations of a complete Ethernet frame with 802.1Q
       tag included.

   Multiple VLANs
       Open vSwitch can match only a single VLAN header. If more than one VLAN
       header is present, then eth_type holds  the  TPID  of  the  inner  VLAN
       header.  Open vSwitch stops parsing the packet after the inner TPID, so
       matching further into the packet (e.g. on the inner TCI or  L3  fields)
       is not possible.

       OpenFlow only directly supports matching a single VLAN header. In Open‐
       Flow 1.1 or later, one OpenFlow table can match on the  outermost  VLAN
       header and pop it off, and a later OpenFlow table can match on the next
       outermost header. Open vSwitch does not support this.

   VLAN Field Details
       The four variants have three different levels of expressiveness:  Open‐
       Flow  1.0  and  1.1  VLAN matching are less powerful than OpenFlow 1.2+
       VLAN matching, which is less powerful than Open vSwitch extension  VLAN
       matching.

   OpenFlow 1.0 VLAN Fields
       OpenFlow  1.0  uses two fields, called dl_vlan and dl_vlan_pcp, each of
       which can be  either  exact-matched  or  wildcarded,  to  specify  VLAN
       matches:

              ·      When  both  dl_vlan  and  dl_vlan_pcp are wildcarded, the
                     flow matches packets without an 802.1Q header or with any
                     802.1Q header.

              ·      The  match  dl_vlan=0xffff  causes  a  flow to match only
                     packets without an 802.1Q header. Such a flow should also
                     wildcard  dl_vlan_pcp,  since  a packet without an 802.1Q
                     header does not have a PCP.  OpenFlow  does  not  specify
                     what  to  do  if  a match on PCP is actually present, but
                     Open vSwitch ignores it.

              ·      Otherwise, the flow matches only packets with  an  802.1Q
                     header.  If dl_vlan is not wildcarded, then the flow only
                     matches packets with the VLAN ID specified  in  dl_vlan’s
                     low  12  bits. If dl_vlan_pcp is not wildcarded, then the
                     flow only matches packets with the priority specified  in
                     dl_vlan_pcp’s low 3 bits.

                     OpenFlow  does  not  specify  how to interpret the high 4
                     bits of dl_vlan or the high 5 bits of  dl_vlan_pcp.  Open
                     vSwitch ignores them.

   OpenFlow 1.1 VLAN Fields
       VLAN  matching  in  OpenFlow  1.1  is  similar to OpenFlow 1.0. The one
       refinement is that when dl_vlan matches  on  0xfffe  (OFVPID_ANY),  the
       flow  matches  only packets with an 802.1Q header, with any VLAN ID. If
       dl_vlan_pcp is wildcarded, the flow matches any packet with  an  802.1Q
       header,  regardless of VLAN ID or priority. If dl_vlan_pcp is not wild‐
       carded, then the flow only matches packets with the priority  specified
       in dl_vlan_pcp’s low 3 bits.

       OpenFlow 1.1 uses the name OFPVID_NONE, instead of OFP_VLAN_NONE, for a
       dl_vlan of 0xffff, but it has the same meaning.

       In OpenFlow 1.1, Open vSwitch reports  error  OFPBMC_BAD_VALUE  for  an
       attempt  to  match  on  dl_vlan between 4,096 and 0xfffd, inclusive, or
       dl_vlan_pcp greater than 7.

   OpenFlow 1.2 VLAN Fields
       OpenFlow 1.2+ VLAN ID Field

       Name:            vlan_vid
       Width:           16 bits (only the least-significant 12 bits may be nonzero)
       Format:          decimal
       Masking:         arbitrary bitwise masks
       Prerequisites:   none
       Access:          read/write

       OpenFlow 1.0:    yes (exact match only)
       OpenFlow 1.1:    yes (exact match only)
       OXM:             OXM_OF_VLAN_VID (6) since OpenFlow 1.2 and Open vSwitch 1.7
       NXM:             none

       The OpenFlow standard describes this field as  consisting  of  ``12+1’’
       bits.  On  ingress,  its value is 0 if no 802.1Q header is present, and
       otherwise it holds the VLAN VID in its least significant 12 bits,  with
       bit  12  (0x1000 aka OFPVID_PRESENT) also set to 1. The three most sig‐
       nificant bits are always zero:

        OXM_OF_VLAN_VID
        gt;
         3  1     12
       +---+--+--------+
       |   |P |VLAN ID |
       +---+--+--------+
         0


       As a consequence of this field’s format, one may use it  to  match  the
       VLAN ID in all of the ways available with the OpenFlow 1.0 and 1.1 for‐
       mats, and a few new ways:

              Fully wildcarded
                     Matches any packet, that is, one without an 802.1Q header
                     or with an 802.1Q header with any TCI value.

              Value 0x0000 (OFPVID_NONE), mask 0xffff (or no mask)
                     Matches only packets without an 802.1Q header.

              Value 0x1000, mask 0x1000
                     Matches  any  packet with an 802.1Q header, regardless of
                     VLAN ID.

              Value 0x1009, mask 0xffff (or no mask)
                     Match only packets with an 802.1Q header with VLAN ID 9.

              Value 0x1001, mask 0x1001
                     Matches only packets that have an 802.1Q header  with  an
                     odd-numbered  VLAN  ID. (This is just an example; one can
                     match on any desired VLAN ID bit pattern.)

       OpenFlow 1.2+ VLAN Priority Field

       Name:            vlan_pcp
       Width:           8 bits (only the least-significant 3 bits may be nonzero)
       Format:          decimal

       Masking:         not maskable
       Prerequisites:   VLAN VID
       Access:          read/write
       OpenFlow 1.0:    yes (exact match only)
       OpenFlow 1.1:    yes (exact match only)


       OXM:             OXM_OF_VLAN_PCP (7) since OpenFlow 1.2 and  Open  vSwitch
                        1.7
       NXM:             none

       The  3  least  significant bits may be used to match the PCP bits in an
       802.1Q header. Other bits are always zero:

        OXM_OF_VLAN_VID
        gt;
           5       3
       +--------+------+
       |  zero  | PCP  |
       +--------+------+
           0


       This field may only be used when vlan_vid is not  wildcarded  and  does
       not  exact  match  on  0  (which  only  matches when there is no 802.1Q
       header).

       See VLAN Comparison Chart, below, for some examples.

   Open vSwitch Extension VLAN Field
       The vlan_tci extension can describe more kinds of VLAN matches than the
       other variants. It is also simpler than the other variants.

       VLAN TCI Field

       Name:            vlan_tci
       Width:           16 bits
       Format:          hexadecimal
       Masking:         arbitrary bitwise masks
       Prerequisites:   none
       Access:          read/write

       OpenFlow 1.0:    yes (exact match only)
       OpenFlow 1.1:    yes (exact match only)
       OXM:             none
       NXM:             NXM_OF_VLAN_TCI (4) since Open vSwitch 1.1

       For a packet without an 802.1Q header, this field is zero. For a packet
       with an 802.1Q header, this field is the TCI  with  the  bit  in  CFI’s
       position  (marked  P  for  ``present’’  below) forced to 1. Thus, for a
       packet in VLAN 9 with priority 7, it has the value 0xf009:

        NXM_VLAN_TCI
        gt;
         3   1   12
       +----+--+----+
       |PCP |P |VID |
       +----+--+----+
         7   1   9


       Usage examples:

              vlan_tci=0
                     Match packets without an 802.1Q header.

              vlan_tci=0x1000/0x1000
                     Match packets with an 802.1Q header, regardless  of  VLAN
                     and priority values.

              vlan_tci=0xf123
                     Match packets tagged with priority 7 in VLAN 0x123.

              vlan_tci=0x1123/0x1fff
                     Match packets tagged with VLAN 0x123 (and any priority).

              vlan_tci=0x5000/0xf000
                     Match packets tagged with priority 2 (in any VLAN).

              vlan_tci=0/0xfff
                     Match packets with no 802.1Q header or tagged with VLAN 0
                     (and any priority).

              vlan_tci=0x5000/0xe000
                     Match packets with no 802.1Q header or tagged with prior‐
                     ity 2 (in any VLAN).

              vlan_tci=0/0xefff
                     Match packets with no 802.1Q header or tagged with VLAN 0
                     and priority 0.

       See VLAN Comparison Chart, below, for more examples.

   VLAN Comparison Chart
       The following table describes each of several possible matching  crite‐
       ria  on  802.1Q header may be expressed with each variation of the VLAN
       matching fields:

       Criteria   OpenFlow 1.0   OpenFlow 1.1   OpenFlow 1.2+         NXM
       ─────────  ─────────────  ─────────────  ──────────────  ──────────

            [1]    ????/1,??/?    ????/1,??/?    0000/0000,--   0000/0000
            [2]    ffff/0,??/?    ffff/0,??/?    0000/ffff,--   0000/ffff
            [3]    0xxx/0,??/1    0xxx/0,??/1    1xxx/ffff,--   1xxx/1fff
            [4]    ????/1,0y/0    fffe/0,0y/0    1000/1000,0y   z000/f000
            [5]    0xxx/0,0y/0    0xxx/0,0y/0    1xxx/ffff,0y   zxxx/ffff
            [6]         (none)      (none)      1001/1001,--    1001/1001
            [7]         (none)      (none)         (none)       3000/3000
            [8]         (none)      (none)         (none)       0000/0fff
            [9]         (none)      (none)         (none)       0000/f000
           [10]         (none)      (none)         (none)       0000/efff

       All numbers in the table are expressed in hexadecimal. The  columns  in
       the table are interpreted as follows:

              Criteria
                     See the list below.

              OpenFlow 1.0
              OpenFlow 1.1
                   wwww/x,yy/z  means  VLAN  ID match value wwww with wildcard
                   bit x and VLAN PCP match value yy with wildcard  bit  z.  ?
                   means that the given bits are ignored (and conventionally 0
                   for wwww or yy, conventionally 1 for x  or  z).  ``(none)’’
                   means  that  OpenFlow  1.0 (or 1.1) cannot match with these
                   criteria.

              OpenFlow 1.2+
                   xxxx/yyyy,zz means vlan_vid with value xxxx and mask  yyyy,
                   and  vlan_pcp  (which  is  not  maskable) with value zz. --
                   means that vlan_pcp is omitted. ``(none)’’ means that Open‐
                   Flow 1.2 cannot match with these criteria.

              NXM  xxxx/yyyy means vlan_tci with value xxxx and mask yyyy.

       The matching criteria described by the table are:

              [1]    Matches any packet, that is, one without an 802.1Q header
                     or with an 802.1Q header with any TCI value.

              [2]    Matches only packets without an 802.1Q header.

                     OpenFlow 1.0 doesn’t define the behavior  if  dl_vlan  is
                     set  to  0xffff  and dl_vlan_pcp is not wildcarded. (Open
                     vSwitch always ignores dl_vlan_pcp when dl_vlan is set to
                     0xffff.)

                     OpenFlow  1.1  says explicitly to ignore dl_vlan_pcp when
                     dl_vlan is set to 0xffff.

                     OpenFlow 1.2 doesn’t say how to interpret  a  match  with
                     vlan_vid  value 0 and a mask with OFPVID_PRESENT (0x1000)
                     set to 1 and some other bits in the mask set to  1  also.
                     Open  vSwitch  interprets  it  the  same way as a mask of
                     0x1000.

                     Any NXM match with vlan_tci value 0 and the CFI  bit  set
                     to  1  in the mask is equivalent to the one listed in the
                     table.

              [3]    Matches only packets that have an 802.1Q header with  VID
                     xxx (and any PCP).

              [4]    Matches  only packets that have an 802.1Q header with PCP
                     y (and any VID).

                     OpenFlow 1.0 doesn’t clearly define the behavior for this
                     case. Open vSwitch implements it this way.

                     In the NXM value, z equals (y LAYER 2.5: MPLS FIELDS
   Summary:
       Name         Bytes             Mask   RW?   Prereqs   NXM/OXM Support

       ───────────  ────────────────  ─────  ────  ────────  ──────────────────────
       mpls_label   4 (low 20 bits)   no     yes   MPLS      OF 1.2+ and OVS 1.11+
       mpls_tc      1 (low 3 bits)    no     yes   MPLS      OF 1.2+ and OVS 1.11+

       mpls_bos     1 (low 1 bits)    no     no    MPLS      OF 1.3+ and OVS 1.11+
       mpls_ttl     1                 no     yes   MPLS      OVS 2.6+

       One or more MPLS headers (more commonly called MPLS labels)  follow  an
       Ethernet  type  field  that specifies an MPLS Ethernet type [RFC 3032].
       Ethertype 0x8847 is used for all unicast.  Multicast  MPLS  is  divided
       into  two  specific classes, one of which uses Ethertype 0x8847 and the
       other 0x8848 [RFC 5332].

       The most common overall packet format is Ethernet II, shown below (SNAP
       encapsulation  may  be used but is not ordinarily seen in Ethernet net‐
       works):

           Ethernet           MPLS
        gt;   gt;
        48  48    16      20   3  1  8
       +---+---+------+ +-----+--+-+---+
       |dst|src| type | |label|TC|S|TTL| ...
       +---+---+------+ +-----+--+-+---+
                0x8847


       MPLS can be encapsulated inside an 802.1Q header,  in  which  case  the
       combination looks like this:

        Ethernet     802.1Q     Ethertype        MPLS
        gt;   gt;   gt;   gt;
         48  48      16   16       16        20   3  1  8
       +----+---+ +------+---+ +---------+ +-----+--+-+---+
       |dst |src| | TPID |TCI| |  type   | |label|TC|S|TTL| ...
       +----+---+ +------+---+ +---------+ +-----+--+-+---+
                   0x8100        0x8847


       The fields within an MPLS label are:

              Label, 20 bits.
                     An identifier.

              Traffic control (TC), 3 bits.
                     Used for quality of service.

              Bottom of stack (BOS), 1 bit (labeled just ``S’’ above).
                     0 indicates that another MPLS label follows this one.

                     1  indicates  that this MPLS label is the last one in the
                     stack, so that some other protocol follows this one.

              Time to live (TTL), 8 bits.
                     Each hop across an MPLS network decrements the TTL by  1.
                     If it reaches 0, the packet is discarded.

                     OpenFlow  does not make the MPLS TTL available as a match
                     field, but actions are available to set and decrement the
                     TTL. Open vSwitch 2.6 and later makes the MPLS TTL avail‐
                     able as an extension.

   MPLS Label Stacks
       Unlike the other encapsulations supported by OpenFlow and Open vSwitch,
       MPLS  labels  are  routinely  used  in ``stacks’’ two or three deep and
       sometimes even deeper. Open vSwitch  currently  supports  up  to  three
       labels.

       The OpenFlow specification only supports matching on the outermost MPLS
       label at any given time. To match on the second label, one  must  first
       ``pop’’  the  outer  label and advance to another OpenFlow table, where
       the inner label may be matched. To match on the third label,  one  must
       pop  the two outer labels, and so on. The Open Networking Foundation is
       considering support for directly matching on multiple MPLS  labels  for
       OpenFlow 1.6.

   MPLS Inner Protocol
       Unlike  all other forms of encapsulation that Open vSwitch and OpenFlow
       support, an MPLS label does not indicate what inner protocol it  encap‐
       sulates.  Different deployments determine the inner protocol in differ‐
       ent ways [RFC 3032]:

              ·      A few reserved label values do indicate an  inner  proto‐
                     col. Label 0, the ``IPv4 Explicit NULL Label,’’ indicates
                     inner IPv4. Label 2, the ``IPv6  Explicit  NULL  Label,’’
                     indicates inner IPv6.

              ·      Some  deployments  use  a  single  inner protocol consis‐
                     tently.

              ·      In some deployments, the inner protocol must be  inferred
                     from the innermost label.

              ·      In  some deployments, the inner protocol must be inferred
                     from the innermost label and the encapsulated data,  e.g.
                     to  distinguish  between  inner  IPv4  and  IPv6 based on
                     whether the first nibble of the inner protocol data are 4
                     or  6. OpenFlow and Open vSwitch do not currently support
                     these cases.

       Open vSwitch and OpenFlow do not infer  the  inner  protocol,  even  if
       reserved  label values are in use. Instead, the flow table must specify
       the inner protocol at the time it pops the bottommost MPLS label, using
       the Ethertype argument to the pop_mpls action.

   Field Details
       MPLS Label Field

       Name:            mpls_label
       Width:           32 bits (only the least-significant 20 bits may be nonzero)

       Format:          decimal
       Masking:         not maskable
       Prerequisites:   MPLS
       Access:          read/write
       OpenFlow 1.0:    not supported
       OpenFlow 1.1:    yes (exact match only)


       OXM:             OXM_OF_MPLS_LABEL  (34) since OpenFlow 1.2 and Open vSwitch
                        1.11
       NXM:             none

       The least significant 20 bits hold the ``label’’ field  from  the  MPLS
       label. Other bits are zero:

        OXM_OF_MPLS_LABEL
        gt;
           12       20
       +--------+--------+
       |  zero  | label  |
       +--------+--------+
           0


       Most  label  values  are  available  for any use by deployments. Values
       under 16 are reserved.

       MPLS Traffic Class Field

       Name:            mpls_tc
       Width:           8 bits (only the least-significant 3 bits may be nonzero)

       Format:          decimal
       Masking:         not maskable
       Prerequisites:   MPLS
       Access:          read/write
       OpenFlow 1.0:    not supported
       OpenFlow 1.1:    yes (exact match only)


       OXM:             OXM_OF_MPLS_TC (35) since OpenFlow 1.2 and  Open  vSwitch
                        1.11
       NXM:             none

       The  least  significant  3  bits hold the TC field from the MPLS label.
       Other bits are zero:

        OXM_OF_MPLS_TC
        gt;
           5       3
       +--------+-----+
       |  zero  | TC  |
       +--------+-----+
           0


       This field is intended  for  use  for  Quality  of  Service  (QoS)  and
       Explicit Congestion Notification purposes, but its particular interpre‐
       tation is deployment specific.

       Before 2009, this field was named EXP and reserved for experimental use
       [RFC 5462].

       MPLS Bottom of Stack Field

       Name:            mpls_bos
       Width:           8 bits (only the least-significant 1 bits may be nonzero)
       Format:          decimal
       Masking:         not maskable
       Prerequisites:   MPLS
       Access:          read-only

       OpenFlow 1.0:    not supported
       OpenFlow 1.1:    not supported
       OXM:             OXM_OF_MPLS_BOS  (36) since OpenFlow 1.3 and Open vSwitch
                        1.11
       NXM:             none

       The least significant bit holds the BOS  field  from  the  MPLS  label.
       Other bits are zero:

        OXM_OF_MPLS_BOS
        gt;
           7       1
       +--------+------+
       |  zero  | BOS  |
       +--------+------+
           0


       This  field  is  useful as part of processing a series of incoming MPLS
       labels. A flow that includes a pop_mpls action should  generally  match
       on mpls_bos:

              ·      When mpls_bos is 1, there is another MPLS label following
                     this one, so the Ethertype passed to pop_mpls  should  be
                     an  MPLS Ethertype. For example: table=0, dl_type=0x8847,
                     mpls_bos=1, actions=pop_mpls:0x8847, goto_table:1

              ·      When mpls_bos is 0, this MPLS label is the last  one,  so
                     the  Ethertype  passed  to  pop_mpls should be a non-MPLS
                     Ethertype   such   as   IPv4.   For   example:   table=1,
                     dl_type=0x8847,    mpls_bos=0,   actions=pop_mpls:0x0800,
                     goto_table:2

       MPLS Time-to-Live Field

       Name:            mpls_ttl
       Width:           8 bits
       Format:          decimal
       Masking:         not maskable

       Prerequisites:   MPLS
       Access:          read/write
       OpenFlow 1.0:    not supported
       OpenFlow 1.1:    not supported
       OXM:             none
       NXM:             NXM_NX_MPLS_TTL (30) since Open vSwitch 2.6

       Holds the 8-bit time-to-live field from the MPLS label:

        NXM_NX_MPLS_TTL
        gt;
               8
       +---------------+
       |      TTL      |
       +---------------+

LAYER 3: IPV4 AND IPV6 FIELDS
   Summary:
       Name                    Bytes             Mask   RW?   Prereqs     NXM/OXM Support

       ──────────────────────  ────────────────  ─────  ────  ──────────  ─────────────────────
       ip_src aka nw_src       4                 yes    yes   IPv4        OF 1.2+ and OVS 1.1+
       ip_dst aka nw_dst       4                 yes    yes   IPv4        OF 1.2+ and OVS 1.1+

       ipv6_src                16                yes    yes   IPv6        OF 1.2+ and OVS 1.1+
       ipv6_dst                16                yes    yes   IPv6        OF 1.2+ and OVS 1.1+
       ipv6_label              4 (low 20 bits)   yes    yes   IPv6        OF 1.2+ and OVS 1.4+

       nw_proto aka ip_proto   1                 no     no    IPv4/IPv6   OF 1.2+ and OVS 1.1+
       nw_ttl                  1                 no     yes   IPv4/IPv6   OVS 1.4+
       ip_frag                 1 (low 2 bits)    yes    no    IPv4/IPv6   OVS 1.3+

       nw_tos                  1                 no     yes   IPv4/IPv6   OVS 1.1+
       ip_dscp                 1 (low 6 bits)    no     yes   IPv4/IPv6   OF 1.2+ and OVS 1.7+
       nw_ecn aka ip_ecn       1 (low 2 bits)    no     yes   IPv4/IPv6   OF 1.2+ and OVS 1.4+

   IPv4 Specific Fields
       These fields are applicable only to IPv4 flows,  that  is,  flows  that
       match on the IPv4 Ethertype 0x0800.

       IPv4 Source Address Field

       Name:            ip_src (aka nw_src)

       Width:           32 bits
       Format:          IPv4
       Masking:         arbitrary bitwise masks

       Prerequisites:   IPv4
       Access:          read/write
       OpenFlow 1.0:    yes (CIDR match only)

       OpenFlow 1.1:    yes
       OXM:             OXM_OF_IPV4_SRC  (11)  since  OpenFlow  1.2  and  Open
                        vSwitch 1.7

       NXM:             NXM_OF_IP_SRC (7) since Open vSwitch 1.1

       The source address from the IPv4 header:

          Ethernet            IPv4
        gt;   gt;
        48  48   16           8   32  32
       +---+---+-----+ +---+-----+---+---+
       |dst|src|type | |...|proto|src|dst| ...
       +---+---+-----+ +---+-----+---+---+
                0x800


       For historical reasons, in an ARP or RARP flow, Open vSwitch interprets
       matches on nw_src as actually referring to the ARP SPA.

       IPv4 Destination Address Field

       Name:            ip_dst (aka nw_dst)

       Width:           32 bits
       Format:          IPv4
       Masking:         arbitrary bitwise masks

       Prerequisites:   IPv4
       Access:          read/write
       OpenFlow 1.0:    yes (CIDR match only)

       OpenFlow 1.1:    yes
       OXM:             OXM_OF_IPV4_DST  (12)  since  OpenFlow  1.2  and  Open
                        vSwitch 1.7

       NXM:             NXM_OF_IP_DST (8) since Open vSwitch 1.1

       The destination address from the IPv4 header:

          Ethernet            IPv4
        gt;   gt;
        48  48   16           8   32  32
       +---+---+-----+ +---+-----+---+---+
       |dst|src|type | |...|proto|src|dst| ...
       +---+---+-----+ +---+-----+---+---+
                0x800


       For historical reasons, in an ARP or RARP flow, Open vSwitch interprets
       matches on nw_dst as actually referring to the ARP TPA.

   IPv6 Specific Fields
       These fields apply only to IPv6 flows, that is, flows that match on the
       IPv6 Ethertype 0x86dd.

       IPv6 Source Address Field

       Name:            ipv6_src

       Width:           128 bits
       Format:          IPv6
       Masking:         arbitrary bitwise masks

       Prerequisites:   IPv6
       Access:          read/write
       OpenFlow 1.0:    not supported

       OpenFlow 1.1:    not supported
       OXM:             OXM_OF_IPV6_SRC  (26)  since  OpenFlow  1.2  and  Open
                        vSwitch 1.1

       NXM:             NXM_NX_IPV6_SRC (19) since Open vSwitch 1.1

       The source address from the IPv6 header:

           Ethernet            IPv6
        gt;   gt;
        48  48    16          8   128 128
       +---+---+------+ +---+----+---+---+
       |dst|src| type | |...|next|src|dst| ...
       +---+---+------+ +---+----+---+---+
                0x86dd


       Open  vSwitch  1.8 added support for bitwise matching; earlier versions
       supported only CIDR masks.

       IPv6 Destination Address Field

       Name:            ipv6_dst

       Width:           128 bits
       Format:          IPv6
       Masking:         arbitrary bitwise masks

       Prerequisites:   IPv6
       Access:          read/write
       OpenFlow 1.0:    not supported

       OpenFlow 1.1:    not supported
       OXM:             OXM_OF_IPV6_DST  (27)  since  OpenFlow  1.2  and  Open
                        vSwitch 1.1

       NXM:             NXM_NX_IPV6_DST (20) since Open vSwitch 1.1

       The destination address from the IPv6 header:

           Ethernet            IPv6
        gt;   gt;
        48  48    16          8   128 128
       +---+---+------+ +---+----+---+---+
       |dst|src| type | |...|next|src|dst| ...
       +---+---+------+ +---+----+---+---+
                0x86dd


       Open  vSwitch  1.8 added support for bitwise matching; earlier versions
       supported only CIDR masks.

       IPv6 Flow Label Field

       Name:            ipv6_label

       Width:           32 bits (only the least-significant 20 bits may be nonzero)
       Format:          hexadecimal
       Masking:         arbitrary bitwise masks

       Prerequisites:   IPv6
       Access:          read/write
       OpenFlow 1.0:    not supported

       OpenFlow 1.1:    not supported
       OXM:             OXM_OF_IPV6_FLABEL (28) since OpenFlow 1.2 and Open vSwitch
                        1.7

       NXM:             NXM_NX_IPV6_LABEL (27) since Open vSwitch 1.4

       The  least  significant 20 bits hold the flow label field from the IPv6
       header. Other bits are zero:

        OXM_OF_IPV6_FLABEL
        gt;
           12       20
       +--------+---------+
       |  zero  |  label  |
       +--------+---------+
           0


   IPv4/IPv6 Fields
       These fields exist with at least approximately the same meaning in both
       IPv4  and IPv6, so they are treated as a single field for matching pur‐
       poses. Any flow that matches on the IPv4 Ethertype 0x0800 or  the  IPv6
       Ethertype 0x86dd may match on these fields.

       IPv4/v6 Protocol Field

       Name:            nw_proto (aka ip_proto)
       Width:           8 bits
       Format:          decimal
       Masking:         not maskable

       Prerequisites:   IPv4/IPv6
       Access:          read-only
       OpenFlow 1.0:    yes (exact match only)
       OpenFlow 1.1:    yes (exact match only)

       OXM:             OXM_OF_IP_PROTO  (10)  since  OpenFlow  1.2  and  Open
                        vSwitch 1.7
       NXM:             NXM_OF_IP_PROTO (6) since Open vSwitch 1.1

       Matches the IPv4 or IPv6 protocol type.

       For historical reasons, in an ARP or RARP flow, Open vSwitch interprets
       matches  on  nw_proto  as actually referring to the ARP opcode. The ARP
       opcode is a 16-bit field, so for matching purposes ARP opcodes  greater
       than  255  are  treated as 0; this works adequately because in practice
       ARP and RARP only use opcodes 1 through 4.

       IPv4/v6 TTL/Hop Limit Field


       Name:            nw_ttl
       Width:           8 bits
       Format:          decimal
       Masking:         not maskable

       Prerequisites:   IPv4/IPv6
       Access:          read/write
       OpenFlow 1.0:    not supported
       OpenFlow 1.1:    not supported

       OXM:             none
       NXM:             NXM_NX_IP_TTL (29) since Open vSwitch 1.4

       The main reason to match on the TTL or hop limit  field  is  to  detect
       whether a dec_ttl action will fail due to a TTL exceeded error. Another
       way that a  controller  can  detect  TTL  exceeded  is  to  listen  for
       OFPR_INVALID_TTL ``packet-in’’ messages via OpenFlow.

       IPv4/v6 Fragment Bitmask Field

       Name:            ip_frag
       Width:           8 bits (only the least-significant 2 bits may be nonzero)
       Format:          frag
       Masking:         arbitrary bitwise masks

       Prerequisites:   IPv4/IPv6
       Access:          read-only
       OpenFlow 1.0:    not supported
       OpenFlow 1.1:    not supported

       OXM:             none
       NXM:             NXM_NX_IP_FRAG (26) since Open vSwitch 1.3

       Specifies  what  kinds  of  IP fragments or non-fragments to match. The
       value for this field is most conveniently specified as one of the  fol‐
       lowing:

              no     Match only non-fragmented packets.

              yes    Matches all fragments.

              first  Matches only fragments with offset 0.

              later  Matches only fragments with nonzero offset.

              not_later
                     Matches  non-fragmented  packets  and fragments with zero
                     offset.

       The field is internally formatted as 2 bits: bit 0 is 1 for an IP frag‐
       ment  with any offset (and otherwise 0), and bit 1 is 1 for an IP frag‐
       ment with nonzero offset (and otherwise 0), like so:

        NXM_NX_IP_FRAG
        gt;
         6     1    1
       +----+-----+---+
       |zero|later|any|
       +----+-----+---+
         0


       Even though 2 bits have 4 possible values, this field only  uses  3  of
       them:

              ·      A packet that is not an IP fragment has value 0.

              ·      A  packet that is an IP fragment with offset 0 (the first
                     fragment) has bit 0 set and thus value 1.

              ·      A packet that is an IP fragment with nonzero  offset  has
                     bits 0 and 1 set and thus value 3.

       The switch may reject matches against values that can never appear.

       It  is  important to understand how this field interacts with the Open‐
       Flow fragment handling mode:

              ·      In OFPC_FRAG_DROP mode, the OpenFlow switch drops all  IP
                     fragments  before  they  reach  the  flow table, so every
                     packet that is available for matching will have  value  0
                     in this field.

              ·      Open vSwitch does not implement OFPC_FRAG_REASM mode, but
                     if it did then IP fragments would be  reassembled  before
                     they reached the flow table and again every packet avail‐
                     able for matching would always have value 0.

              ·      In OFPC_FRAG_NORMAL mode, all three values are  possible,
                     but OpenFlow 1.0 says that fragments’ transport ports are
                     always 0, even for the first fragment, so this  does  not
                     provide much extra information.

              ·      In  OFPC_FRAG_NX_MATCH  mode, all three values are possi‐
                     ble. For fragments with offset 0, Open vSwitch  makes  L4
                     header information available.

       Thus, this field is likely to be most useful for an Open vSwitch switch
       configured in OFPC_FRAG_NX_MATCH  mode.  See  the  description  of  the
       set-frags command in ovs-ofctl(8), for more details.

     IPv4/IPv6 TOS Fields

       IPv4  and IPv6 contain a one-byte ``type of service’’ or TOS field that
       has the following format:

        type of service
        gt;
           6       2
       +--------+------+
       |  DSCP  | ECN  |
       +--------+------+


       IPv4/v6 DSCP (Bits 2-7) Field

       Name:            nw_tos

       Width:           8 bits
       Format:          decimal
       Masking:         not maskable
       Prerequisites:   IPv4/IPv6
       Access:          read/write
       OpenFlow 1.0:    yes (exact match only)

       OpenFlow 1.1:    yes (exact match only)
       OXM:             none
       NXM:             NXM_OF_IP_TOS (5) since Open vSwitch 1.1

       This field is the TOS byte with the two ECN bits cleared to 0:

        NXM_OF_IP_TOS
        gt;
          6      2
       +------+------+
       | DSCP | zero |
       +------+------+
                 0


       IPv4/v6 DSCP (Bits 0-5) Field

       Name:            ip_dscp
       Width:           8 bits (only the least-significant 6 bits may be nonzero)
       Format:          decimal

       Masking:         not maskable
       Prerequisites:   IPv4/IPv6
       Access:          read/write
       OpenFlow 1.0:    yes (exact match only)
       OpenFlow 1.1:    yes (exact match only)


       OXM:             OXM_OF_IP_DSCP (8) since OpenFlow 1.2  and  Open  vSwitch
                        1.7
       NXM:             none

       This  field is the TOS byte shifted right to put the DSCP bits in the 6
       least-significant bits:

        OXM_OF_IP_DSCP
        gt;
           2      6
       +-------+------+
       | zero  | DSCP |
       +-------+------+
           0


       IPv4/v6 ECN Field

       Name:            nw_ecn (aka ip_ecn)
       Width:           8 bits (only the least-significant 2 bits may be nonzero)

       Format:          decimal
       Masking:         not maskable
       Prerequisites:   IPv4/IPv6
       Access:          read/write
       OpenFlow 1.0:    not supported
       OpenFlow 1.1:    yes (exact match only)

       OXM:             OXM_OF_IP_ECN (9) since OpenFlow 1.2 and Open vSwitch 1.7
       NXM:             NXM_NX_IP_ECN (28) since Open vSwitch 1.4

       This field is the TOS byte with the DSCP bits cleared to 0:

        OXM_OF_IP_ECN
        gt;
           6      2
       +-------+-----+
       | zero  | ECN |
       +-------+-----+
           0


LAYER 3: ARP FIELDS
   Summary:
       Name      Bytes   Mask   RW?   Prereqs   NXM/OXM Support
       ────────  ──────  ─────  ────  ────────  ─────────────────────

       arp_op    2       no     yes   ARP       OF 1.2+ and OVS 1.1+
       arp_spa   4       yes    yes   ARP       OF 1.2+ and OVS 1.1+
       arp_tpa   4       yes    yes   ARP       OF 1.2+ and OVS 1.1+
       arp_sha   6       yes    yes   ARP       OF 1.2+ and OVS 1.1+
       arp_tha   6       yes    yes   ARP       OF 1.2+ and OVS 1.1+

       In theory, Address Resolution Protocol, or ARP, is a  generic  protocol
       generic  protocol  that can be used to obtain the hardware address that
       corresponds to  any  higher-level  protocol  address.  In  contemporary
       usage,  ARP  is  used  only in Ethernet networks to obtain the Ethernet
       address for a given IPv4 address. OpenFlow and Open vSwitch  only  sup‐
       port  this  usage of ARP. For this use case, an ARP packet has the fol‐
       lowing format, with the ARP fields exposed as Open vSwitch fields high‐
       lighted:

          Ethernet                      ARP
        gt;   gt;
        48  48   16     16   16    8   8  16 48  16  48  16
       +---+---+-----+ +---+-----+---+---+--+---+---+---+---+
       |dst|src|type | |hrd| pro |hln|pln|op|sha|spa|tha|tpa|
       +---+---+-----+ +---+-----+---+---+--+---+---+---+---+
                0x806    1  0x800  6   4


       The  ARP  fields are also used for RARP, the Reverse Address Resolution
       Protocol, which shares ARP’s wire format.

       ARP Opcode Field


       Name:            arp_op
       Width:           16 bits
       Format:          decimal
       Masking:         not maskable
       Prerequisites:   ARP

       Access:          read/write
       OpenFlow 1.0:    yes (exact match only)
       OpenFlow 1.1:    yes (exact match only)
       OXM:             OXM_OF_ARP_OP (21) since OpenFlow 1.2 and Open vSwitch
                        1.7

       NXM:             NXM_OF_ARP_OP (15) since Open vSwitch 1.1

       Even  though  this is a 16-bit field, Open vSwitch does not support ARP
       opcodes greater than 255; it treats them to zero. This works adequately
       because in practice ARP and RARP only use opcodes 1 through 4.

       ARP Source IPv4 Address Field

       Name:            arp_spa
       Width:           32 bits
       Format:          IPv4

       Masking:         arbitrary bitwise masks
       Prerequisites:   ARP
       Access:          read/write
       OpenFlow 1.0:    yes (CIDR match only)
       OpenFlow 1.1:    yes

       OXM:             OXM_OF_ARP_SPA   (22)  since  OpenFlow  1.2  and  Open
                        vSwitch 1.7
       NXM:             NXM_OF_ARP_SPA (16) since Open vSwitch 1.1

       ARP Target IPv4 Address Field

       Name:            arp_tpa
       Width:           32 bits
       Format:          IPv4
       Masking:         arbitrary bitwise masks
       Prerequisites:   ARP

       Access:          read/write
       OpenFlow 1.0:    yes (CIDR match only)
       OpenFlow 1.1:    yes
       OXM:             OXM_OF_ARP_TPA  (23)  since  OpenFlow  1.2  and   Open
                        vSwitch 1.7

       NXM:             NXM_OF_ARP_TPA (17) since Open vSwitch 1.1

       ARP Source Ethernet Address Field

       Name:            arp_sha

       Width:           48 bits
       Format:          Ethernet
       Masking:         arbitrary bitwise masks
       Prerequisites:   ARP
       Access:          read/write

       OpenFlow 1.0:    not supported
       OpenFlow 1.1:    not supported
       OXM:             OXM_OF_ARP_SHA   (24)  since  OpenFlow  1.2  and  Open
                        vSwitch 1.7
       NXM:             NXM_NX_ARP_SHA (17) since Open vSwitch 1.1

       ARP Target Ethernet Address Field

       Name:            arp_tha
       Width:           48 bits
       Format:          Ethernet

       Masking:         arbitrary bitwise masks
       Prerequisites:   ARP
       Access:          read/write
       OpenFlow 1.0:    not supported
       OpenFlow 1.1:    not supported

       OXM:             OXM_OF_ARP_THA  (25)  since  OpenFlow  1.2  and   Open
                        vSwitch 1.7
       NXM:             NXM_NX_ARP_THA (18) since Open vSwitch 1.1

LAYER 4: TCP, UDP, AND SCTP FIELDS
   Summary:
       Name                 Bytes             Mask   RW?   Prereqs   NXM/OXM Support

       ───────────────────  ────────────────  ─────  ────  ────────  ─────────────────────
       tcp_src aka tp_src   2                 yes    yes   TCP       OF 1.2+ and OVS 1.1+
       tcp_dst aka tp_dst   2                 yes    yes   TCP       OF 1.2+ and OVS 1.1+
       tcp_flags            2 (low 12 bits)   yes    no    TCP       OF 1.3+ and OVS 2.1+

       udp_src              2                 yes    yes   UDP       OF 1.2+ and OVS 1.1+
       udp_dst              2                 yes    yes   UDP       OF 1.2+ and OVS 1.1+
       sctp_src             2                 yes    yes   SCTP      OF 1.2+ and OVS 2.0+
       sctp_dst             2                 yes    yes   SCTP      OF 1.2+ and OVS 2.0+

       For  matching  purposes, no distinction is made whether these protocols
       are encapsulated within IPv4 or IPv6.

   TCP
       The following diagram shows TCP within IPv4. Open vSwitch also supports
       TCP  in  IPv6.  Only  TCP fields implemented as Open vSwitch fields are
       shown:

          Ethernet            IPv4                   TCP
        gt;   gt;   gt;
        48  48   16           8   32  32    16  16       12
       +---+---+-----+ +---+-----+---+---+ +---+---+---+-----+---+
       |dst|src|type | |...|proto|src|dst| |src|dst|...|flags|...| ...
       +---+---+-----+ +---+-----+---+---+ +---+---+---+-----+---+
                0x800         6


       TCP Source Port Field

       Name:            tcp_src (aka tp_src)
       Width:           16 bits
       Format:          decimal
       Masking:         arbitrary bitwise masks

       Prerequisites:   TCP
       Access:          read/write
       OpenFlow 1.0:    yes (exact match only)
       OpenFlow 1.1:    yes (exact match only)


       OXM:             OXM_OF_TCP_SRC  (13)  since  OpenFlow  1.2  and   Open
                        vSwitch 1.7
       NXM:             NXM_OF_TCP_SRC (9) since Open vSwitch 1.1

       Open vSwitch 1.6 added support for bitwise matching.

       TCP Destination Port Field

       Name:            tcp_dst (aka tp_dst)
       Width:           16 bits
       Format:          decimal

       Masking:         arbitrary bitwise masks
       Prerequisites:   TCP
       Access:          read/write
       OpenFlow 1.0:    yes (exact match only)
       OpenFlow 1.1:    yes (exact match only)

       OXM:             OXM_OF_TCP_DST   (14)  since  OpenFlow  1.2  and  Open
                        vSwitch 1.7
       NXM:             NXM_OF_TCP_DST (10) since Open vSwitch 1.1

       Open vSwitch 1.6 added support for bitwise matching.

       TCP Flags Field

       Name:            tcp_flags
       Width:           16 bits (only the least-significant 12 bits may be nonzero)
       Format:          TCP flags

       Masking:         arbitrary bitwise masks
       Prerequisites:   TCP
       Access:          read-only
       OpenFlow 1.0:    not supported
       OpenFlow 1.1:    not supported

       OXM:             ONFOXM_ET_TCP_FLAGS  (42)  since  OpenFlow  1.3  and   Open
                        vSwitch  2.4;  OXM_OF_TCP_FLAGS (42) since OpenFlow 1.5 and
                        Open vSwitch 2.3
       NXM:             NXM_NX_TCP_FLAGS (34) since Open vSwitch 2.1

       This field holds the TCP flags. TCP currently defines 9 flag  bits.  An
       additional  3  bits  are reserved. For more information, see [RFC 793],
       [RFC 3168], and [RFC 3540].

       Matches on this field are most conveniently written in  terms  of  sym‐
       bolic names (given in the diagram below), each preceded by either + for
       a flag that must be set, or - for a flag that must  be  unset,  without
       any  other  delimiters between the flags. Flags not mentioned are wild‐
       carded. For example, tcp,tcp_flags=+syn-ack matches TCP SYNs  that  are
       not  ACKs,  and  tcp,tcp_flags=+[200]  matches  TCP  packets  with  the
       reserved [200] flag set. Matches can also  be  written  as  flags/mask,
       where  flags  and  mask are 16-bit numbers in decimal or in hexadecimal
       prefixed by 0x.

       The flag bits are:

                 reserved      later RFCs         RFC 793
             gt; gt; gt;
         4     1     1     1   1   1   1   1   1   1   1   1   1
       +----+-----+-----+-----+--+---+---+---+---+---+---+---+---+
       |zero|[800]|[400]|[200]|NS|CWR|ECE|URG|ACK|PSH|RST|SYN|FIN|
       +----+-----+-----+-----+--+---+---+---+---+---+---+---+---+
         0


   UDP
       The following diagram shows UDP within IPv4. Open vSwitch also supports
       UDP  in  IPv6.  Only UDP fields that Open vSwitch exposes as fields are
       shown:

          Ethernet            IPv4              UDP
        gt;   gt;   gt;
        48  48   16           8   32  32    16  16
       +---+---+-----+ +---+-----+---+---+ +---+---+---+
       |dst|src|type | |...|proto|src|dst| |src|dst|...| ...
       +---+---+-----+ +---+-----+---+---+ +---+---+---+
                0x800        17


       UDP Source Port Field

       Name:            udp_src

       Width:           16 bits
       Format:          decimal
       Masking:         arbitrary bitwise masks
       Prerequisites:   UDP
       Access:          read/write

       OpenFlow 1.0:    yes (exact match only)
       OpenFlow 1.1:    yes (exact match only)
       OXM:             OXM_OF_UDP_SRC  (15)  since  OpenFlow  1.2  and   Open
                        vSwitch 1.7
       NXM:             NXM_OF_UDP_SRC (11) since Open vSwitch 1.1

       UDP Destination Port Field

       Name:            udp_dst
       Width:           16 bits
       Format:          decimal

       Masking:         arbitrary bitwise masks
       Prerequisites:   UDP
       Access:          read/write
       OpenFlow 1.0:    yes (exact match only)
       OpenFlow 1.1:    yes (exact match only)

       OXM:             OXM_OF_UDP_DST   (16)  since  OpenFlow  1.2  and  Open
                        vSwitch 1.7
       NXM:             NXM_OF_UDP_DST (12) since Open vSwitch 1.1

   SCTP
       The following diagram shows SCTP within IPv4. Open  vSwitch  also  sup‐
       ports  SCTP  in  IPv6.  Only  SCTP  fields that Open vSwitch exposes as
       fields are shown:

          Ethernet            IPv4             SCTP
        gt;   gt;   gt;
        48  48   16           8   32  32    16  16
       +---+---+-----+ +---+-----+---+---+ +---+---+---+
       |dst|src|type | |...|proto|src|dst| |src|dst|...| ...
       +---+---+-----+ +---+-----+---+---+ +---+---+---+
                0x800        132


       SCTP Source Port Field


       Name:            sctp_src
       Width:           16 bits
       Format:          decimal
       Masking:         arbitrary bitwise masks
       Prerequisites:   SCTP
       Access:          read/write

       OpenFlow 1.0:    not supported
       OpenFlow 1.1:    yes (exact match only)
       OXM:             OXM_OF_SCTP_SRC  (17)  since  OpenFlow  1.2  and  Open
                        vSwitch 2.0
       NXM:             none

       SCTP Destination Port Field

       Name:            sctp_dst
       Width:           16 bits
       Format:          decimal
       Masking:         arbitrary bitwise masks
       Prerequisites:   SCTP

       Access:          read/write
       OpenFlow 1.0:    not supported
       OpenFlow 1.1:    yes (exact match only)
       OXM:             OXM_OF_SCTP_DST  (18)  since  OpenFlow  1.2  and  Open
                        vSwitch 2.0
       NXM:             none

LAYER 4: ICMPV4 AND ICMPV6 FIELDS
   Summary:
       Name          Bytes   Mask   RW?   Prereqs      NXM/OXM Support
       ────────────  ──────  ─────  ────  ───────────  ─────────────────────

       icmp_type     1       no     yes   ICMPv4       OF 1.2+ and OVS 1.1+
       icmp_code     1       no     yes   ICMPv4       OF 1.2+ and OVS 1.1+
       icmpv6_type   1       no     yes   ICMPv6       OF 1.2+ and OVS 1.1+
       icmpv6_code   1       no     yes   ICMPv6       OF 1.2+ and OVS 1.1+
       nd_target     16      yes    yes   ND           OF 1.2+ and OVS 1.1+

       nd_sll        6       yes    yes   ND solicit   OF 1.2+ and OVS 1.1+
       nd_tll        6       yes    yes   ND advert    OF 1.2+ and OVS 1.1+

   ICMPv4
          Ethernet            IPv4             ICMPv4
        gt;   gt;   gt;
        48  48   16           8   32  32     8    8
       +---+---+-----+ +---+-----+---+---+ +----+----+---+
       |dst|src|type | |...|proto|src|dst| |type|code|...| ...
       +---+---+-----+ +---+-----+---+---+ +----+----+---+
                0x800         1


       ICMPv4 Type Field

       Name:            icmp_type
       Width:           8 bits

       Format:          decimal
       Masking:         not maskable
       Prerequisites:   ICMPv4
       Access:          read/write
       OpenFlow 1.0:    yes (exact match only)

       OpenFlow 1.1:    yes (exact match only)
       OXM:             OXM_OF_ICMPV4_TYPE (19) since OpenFlow  1.2  and  Open
                        vSwitch 1.7
       NXM:             NXM_OF_ICMP_TYPE (13) since Open vSwitch 1.1

       For  historical  reasons,  in  an  ICMPv4 flow, Open vSwitch interprets
       matches on tp_src as actually referring to the ICMP type.

       ICMPv4 Code Field

       Name:            icmp_code

       Width:           8 bits
       Format:          decimal
       Masking:         not maskable
       Prerequisites:   ICMPv4
       Access:          read/write

       OpenFlow 1.0:    yes (exact match only)
       OpenFlow 1.1:    yes (exact match only)
       OXM:             OXM_OF_ICMPV4_CODE (20) since OpenFlow  1.2  and  Open
                        vSwitch 1.7
       NXM:             NXM_OF_ICMP_CODE (14) since Open vSwitch 1.1

       For  historical  reasons,  in  an  ICMPv4 flow, Open vSwitch interprets
       matches on tp_dst as actually referring to the ICMP code.

   ICMPv6
           Ethernet            IPv6            ICMPv6
        gt;   gt;   gt;
        48  48    16          8   128 128    8    8
       +---+---+------+ +---+----+---+---+ +----+----+---+
       |dst|src| type | |...|next|src|dst| |type|code|...| ...
       +---+---+------+ +---+----+---+---+ +----+----+---+
                0x86dd        58


       ICMPv6 Type Field

       Name:            icmpv6_type
       Width:           8 bits

       Format:          decimal
       Masking:         not maskable
       Prerequisites:   ICMPv6
       Access:          read/write
       OpenFlow 1.0:    not supported

       OpenFlow 1.1:    not supported
       OXM:             OXM_OF_ICMPV6_TYPE (29) since OpenFlow  1.2  and  Open
                        vSwitch 1.7
       NXM:             NXM_NX_ICMPV6_TYPE (21) since Open vSwitch 1.1

       ICMPv6 Code Field

       Name:            icmpv6_code
       Width:           8 bits
       Format:          decimal
       Masking:         not maskable

       Prerequisites:   ICMPv6
       Access:          read/write
       OpenFlow 1.0:    not supported
       OpenFlow 1.1:    not supported


       OXM:             OXM_OF_ICMPV6_CODE  (30)  since  OpenFlow 1.2 and Open
                        vSwitch 1.7
       NXM:             NXM_NX_ICMPV6_CODE (22) since Open vSwitch 1.1

   ICMPv6 Neighbor Discovery
           Ethernet            IPv6              ICMPv6            ICMPv6 ND
        gt;   gt;   gt;   gt;
        48  48    16          8   128 128      8     8          128
       +---+---+------+ +---+----+---+---+ +-------+----+---+ +------+----------+
       |dst|src| type | |...|next|src|dst| | type  |code|...| |target|option ...|
       +---+---+------+ +---+----+---+---+ +-------+----+---+ +------+----------+
                0x86dd        58            135/136  0


       ICMPv6 Neighbor Discovery Target IPv6 Field

       Name:            nd_target
       Width:           128 bits
       Format:          IPv6
       Masking:         arbitrary bitwise masks

       Prerequisites:   ND
       Access:          read/write
       OpenFlow 1.0:    not supported
       OpenFlow 1.1:    not supported
       OXM:             OXM_OF_IPV6_ND_TARGET (31) since OpenFlow 1.2 and Open
                        vSwitch 1.7

       NXM:             NXM_NX_ND_TARGET (23) since Open vSwitch 1.1

       ICMPv6 Neighbor Discovery Source Ethernet Address Field

       Name:            nd_sll
       Width:           48 bits

       Format:          Ethernet
       Masking:         arbitrary bitwise masks
       Prerequisites:   ND solicit
       Access:          read/write
       OpenFlow 1.0:    not supported
       OpenFlow 1.1:    not supported

       OXM:             OXM_OF_IPV6_ND_SLL  (32)  since  OpenFlow 1.2 and Open
                        vSwitch 1.7
       NXM:             NXM_NX_ND_SLL (24) since Open vSwitch 1.1

       ICMPv6 Neighbor Discovery Target Ethernet Address Field


       Name:            nd_tll
       Width:           48 bits
       Format:          Ethernet
       Masking:         arbitrary bitwise masks
       Prerequisites:   ND advert
       Access:          read/write

       OpenFlow 1.0:    not supported
       OpenFlow 1.1:    not supported
       OXM:             OXM_OF_IPV6_ND_TLL (33) since OpenFlow  1.2  and  Open
                        vSwitch 1.7
       NXM:             NXM_NX_ND_TLL (25) since Open vSwitch 1.1

REFERENCES
              Casado M. Casado, M. J. Freedman, J. Pettit, J. Luo, N. McKeown,
                     and S. Shenker, ``Ethane: Taking Control  of  the  Enter‐
                     prise,’’ Computer Communications Review, October 2007.

              EXT-56 J.  Tonsing,  ``Permit  one  of a set of prerequisites to
                     apply, e.g. don’t preclude non-Ethernet media,’’
                     ⟨https://rs.opennetworking.org/bugs/browse/EXT-56⟩   (ONF
                     members only).

              EXT-112
                     J. Tourrilhes, ``Support non-Ethernet packets  throughout
                     the pipeline,’’ ⟨https://rs.opennetworking.org/bugs/
                     browse/EXT-112⟩ (ONF members only).

              EXT-134
                     J. Tourrilhes, ``Match first  nibble  of  the  MPLS  pay‐
                     load,’’ ⟨https://rs.opennetworking.org/bugs/browse/
                     EXT-134⟩ (ONF members only).

              Geneve J. Gross, I. Ganga, and T.  Sridhar,  editors,  ``Geneve:
                     Generic Network Virtualization Encapsulation,’’ ⟨https://
                     datatracker.ietf.org/doc/draft-ietf-nvo3-geneve/⟩ .

              IEEE OUI
                     IEEE Standards Association,  ``MAC  Address  Block  Large
                     (MA-L),’’ ⟨https://standards.ieee.org/develop/regauth/
                     oui/index.html⟩ .

              NSH    P.  Quinn  and  U.  Elzur,  editors,  ``Network   Service
                     Header,’’ ⟨https://datatracker.ietf.org/doc/
                     draft-ietf-sfc-nsh/⟩ .

              OpenFlow 1.0.1
                     Open Networking  Foundation,  ``OpenFlow  Switch  Errata,
                     Version 1.0.1,’’ June 2012.

              OpenFlow 1.1
                     OpenFlow Consortium, ``OpenFlow Switch Specification Ver‐
                     sion 1.1.0 Implemented (Wire Protocol  0x02),’’  February
                     2011.

              OpenFlow 1.5
                     Open  Networking Foundation, ``OpenFlow Switch Specifica‐
                     tion Version 1.5.0 (Protocol  version  0x06),’’  December
                     2014.

              OpenFlow Extensions 1.3.x Package 2
                     Open  Networking  Foundation, ``OpenFlow Extensions 1.3.x
                     Package 2,’’ December 2013.

              TCP Flags Match Field Extension
                     Open  Networking  Foundation,  ``TCP  flags  match  field
                     Extension,’’ December 2014. In [OpenFlow Extensions 1.3.x
                     Package 2].

              Pepelnjak
                     I. Pepelnjak, ``OpenFlow and Fermi Estimates,’’ ⟨http://
                     blog.ipspace.net/2013/09/openflow-and-fermi-esti‐
                     mates.html⟩ .

              RFC 793
                     ``Transmission Control Protocol,’’ ⟨http://www.ietf.org/
                     rfc/rfc793.txt⟩ .

              RFC 3032
                     E.  Rosen,  D.  Tappan, G. Fedorkow, Y. Rekhter, D. Fari‐
                     nacci, T. Li, and A. Conta,  ``MPLS  Label  Stack  Encod‐
                     ing,’’ ⟨http://www.ietf.org/rfc/rfc3032.txt⟩ .

              RFC 3168
                     K.  Ramakrishnan,  S. Floyd, and D. Black, ``The Addition
                     of Explicit Congestion Notification (ECN) to IP,’’
                     ⟨https://tools.ietf.org/html/rfc3168⟩ .

              RFC 3540
                     N.  Spring,  D.  Wetherall, and D. Ely, ``Robust Explicit
                     Congestion Notification (ECN) Signaling with Nonces,’’
                     ⟨https://tools.ietf.org/html/rfc3540⟩ .

              RFC 4632
                     V.  Fuller  and  T.  Li, ``Classless Inter-domain Routing
                     (CIDR): The Internet Address Assignment  and  Aggregation
                     Plan,’’ ⟨https://tools.ietf.org/html/rfc4632⟩ .

              RFC 5462
                     L.  Andersson and R. Asati, ``Multiprotocol Label Switch‐
                     ing (MPLS) Label Stack Entry: ``EXP’’  Field  Renamed  to
                     ``Traffic Class’’ Field,’’ ⟨http://www.ietf.org/rfc/
                     rfc5462.txt⟩ .

              RFC 6830
                     D. Farinacci, V. Fuller, D. Meyer, and  D.  Lewis,  ``The
                     Locator/ID Separation Protocol (LISP),’’ ⟨http://
                     www.ietf.org/rfc/rfc6830.txt⟩ .

              RFC 7348
                     M. Mahalingam, D. Dutt, K. Duda, P. Agarwal, L.  Kreeger,
                     T. Sridhar, M. Bursell, and C. Wright, ``Virtual eXtensi‐
                     ble Local Area Network (VXLAN): A Framework for  Overlay‐
                     ing  Virtualized  Layer 2 Networks over Layer 3 Networks,
                     ’’ ⟨https://tools.ietf.org/html/rfc7348⟩ .

              Srinivasan
                     V. Srinivasan, S. Suriy, and G. Varghese, ``Packet  Clas‐
                     sification using Tuple Space Search,’’ SIGCOMM 1999.

              Pagiamtzis
                     K.  Pagiamtzis  and A. Sheikholeslami, ``Content-address‐
                     able memory (CAM) circuits and architectures: A  tutorial
                     and  survey,’’ IEEE Journal of Solid-State Circuits, vol.
                     41, no. 3, pp. 712-727, March 2006.

              VXLAN Group Policy Option
                     M. Smith and L. Kreeger, `` VXLAN Group Policy  Option.’’
                     Internet-Draft.  ⟨https://tools.ietf.org/html/
                     draft-smith-vxlan-group-policy⟩ .

AUTHORS
       Ben Pfaff, with advice from Justin Pettit and Jean Tourrilhes.



Open vSwitch                        2.7.90                       ovs-fields(7)