[ovs-discuss] ARP Behavior in XenServer Host

David Erickson derickso at stanford.edu
Thu Dec 1 13:11:04 PST 2011

On 12/1/2011 12:05 PM, Ben Pfaff wrote:
> On Thu, Dec 01, 2011 at 12:02:46PM -0800, David Erickson wrote:
>> On 12/1/2011 12:01 PM, Ben Pfaff wrote:
>>> On Wed, Nov 30, 2011 at 06:18:15PM -0800, David Erickson wrote:
>>>> I think I've run into another semi-related issue with inband.  I
>>>> recently changed the fail mode of my OVS instances from standalone
>>>> to secure because I wanted them to continue using the rules that had
>>>> been set in the event the controller died or needed restarting.
>>>> This had the unfortunate side effect that if the controller is down
>>>> long enough then the box can lose its DHCP lease, and be unable to
>>>> get a new one because DHCP requests are trying to be sent to the
>>>> controller, but the switch isn't able to connect to the controller
>>>> without an address, ie:
>>>> Nov 30 21:04:52 localhost dhclient: DHCPDISCOVER on xenbr0 to
>>>> port 67 interval 4
>>>> Nov 30 21:04:56 localhost dhclient: No DHCPOFFERS received.
>>>> Nov 30 21:04:56 localhost dhclient: No working leases in persistent
>>>> database - sleeping.
>>>> Nov 30 21:04:58 localhost ovs-vswitchd:
>>>> 789878|stream_tcp|ERR|tcp: connect: Network is
>>>> unreachable
>>>> What is the behavior of the inband rules when the switch is in
>>>> secure mode and has lost connection to the controller?
>>> No different from any other time.
>>>> It seems to me like they are being ignored, or at least the DHCP
>>>> rule doesn't seem to be working.
>>> Please investigate further.  I would start by finding out whether the
>>> DHCP requests are making it out on the wire, then if they are, whether
>>> DHCP replies are visible coming back across the wire.
>> Ya the requests aren't making it onto the wire.
> Please capture the kernel flow that matches the request with
> "ovs-dpctl dump-flows", then feed that flow back into "ofproto/trace"
> to see what OVS is actually doing with it.

So in the base case where dump-flows returns no flows at all, the host 
has lost its dhcp lease it had previously, and the controller had gone 
unreachable so the switch moved to fail secure mode:

ovs-appctl ofproto/trace xenbr0 0 65534 

Packet: 00:c0:9f:9f:fe:d8 > Broadcast, ethertype IPv4 (0x0800), length 
96: truncated-ip - 246 bytes missing! > BOOTP/DHCP, Request from 00:c0:9f:9f:fe:d8, 
length: 300
Flow: tunnel0:in_port0000:tci(0) mac00:c0:9f:9f:fe:d8->ff:ff:ff:ff:ff:ff 
type0800 proto17 tos16 ip0.0.0.0-> port68->67
Rule: table=0 cookie=0 
OpenFlow actions=NORMAL

Final flow: unchanged
Datapath actions: drop

Any ideas?


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