[ovs-dev] [RFC v4] Add TCP encap_rcv hook (repost)
jesse at nicira.com
Thu Apr 26 09:13:50 PDT 2012
On Thu, Apr 26, 2012 at 12:13 AM, Simon Horman <horms at verge.net.au> wrote:
> On Wed, Apr 25, 2012 at 10:17:25AM -0700, Jesse Gross wrote:
>> On Wed, Apr 25, 2012 at 1:39 AM, Simon Horman <horms at verge.net.au> wrote:
>> > Hi Kyle,
>> > the component that is of most interest to me is enabling OVS to use in-tree
>> > tunnelling code - as it seems that makes most sense for an implementation
>> > of STT. I have taken a brief look over your vxlan work and it isn't clear
>> > to me if it is moving towards being an in-tree implementation. Moreover,
>> > I'm a rather unclear on what changes need to be made to OVS in order for
>> > in-tree tunneling to be used.
>> > My recollection is that OVS did make use of in-tree tunnelling code
>> > but this was removed in favour of the current implementation for various
>> > reasons (performance being one IIRC). I gather that revisiting in-tree
>> > tunnelling won't revisit the previous set of problems. But I'm unclear how.
>> > Jesse, is it possible for you to describe that in a little detail
>> > or point me to some information?
>> This was what I had originally written a while back, although it's
>> more about OVS internally and less about how to connect to the in-tree
>> In order to flexibly implement support for current and future tunnel
>> protocols OVS needs to be able to get/set information about the outer
>> tunnel header when processing the inner packet. At the very least
>> this is src/dst IP addresses and the key/ID/VNI/etc. In the upstream
>> tunnel implementations those are implicitly encoded in the device that
>> sends or receives the packet. However, this has a two problems:
>> number of devices and ability to handle unknown values. We addressed
>> part of this problem by allowing the tunnel ID to be set and matched
>> through the OVS flow table and an action. In order to do this with
>> the in-tree tunneling code, we obviously need a way of passing this
>> information around since it would currently get lost as we pass
>> through the Linux device layer.
>> The plan to deal with that is to add a function to the in-tree
>> tunneling code that allows a skb to be encapsulated with specific
>> parameters and conversely a hook to receive decapsulated packets along
>> with header info. This would make all of the kernel tunneling code
>> common, while still giving OVS userspace the ability to implement
>> essentially any type of tunneling policy. In many ways, this is very
>> similar to how vlans look in OVS today.
>> While it would be possible to implement the hook to use the in-tree
>> tunnel code today without a lot of changes, we already know that we
>> want to move away from port-based model in the OVS kernel module
>> towards the flow model. As we push this upstream the userspace/kernel
>> API should be the correct one, so that's why these two things are tied
> Thanks, that explanation along with Kyle's response helps a lot.
> It seems to me that something I could help out with is the implementation
> of the set_tunnel action which extents and replaces the tun_id action.
> It seems that is a requirement for the scheme you describe above.
I agree that's probably the best place to start unless Kyle has some
specific plans otherwise.
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