[ovs-dev] NSH Option 2 implementation

Simon Horman simon.horman at netronome.com
Thu Aug 11 13:03:39 UTC 2016


Hi Jan,

On Thu, Aug 11, 2016 at 12:58:44PM +0000, Jan Scheurich wrote:
> Hi Simon
> 
> > > The implicit push_eth action introduced by Simon in his L3 tunnel port
> > > patch mainly ensures the presence of the 14 byte MAC header on ports
> > > where this is a must for syntactic interpretation of the packet. It
> > > did not worry about if the resulting packet was semantically useful or not.
> > 
> > In the context of my patchset it is possible to set the MAC addresses (to something non-zero) using a set-field (or similar) action. Is that
> > facility of use here?
> 
> I don't understand how this can work. The implicit push_eth action is inserted just before sending an L3 packet to an L2 port by means of an output action. How can the OF controller modify the newly inserted SMAC and DMAC fields with set_field actions after the output action?

I can double check and possibly its conceptually a bit broken but at least
in the context of the l3 VPN patchset I believe you can set the ethernet
fields (e.g. just before output) even though the packet has no ethernet
header at that point.

Given the way translation works in ovs-vswtichd this makes some sense.
>From an OpenFlow point of view perhaps less so.



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