[ovs-dev] [PATCH 3/9] Add OF11 set IP ECN action.

Ben Pfaff blp at nicira.com
Thu Oct 17 18:47:13 UTC 2013


On Wed, Oct 16, 2013 at 04:16:05PM -0700, Jarno Rajahalme wrote:
> Signed-off-by: Jarno Rajahalme <jrajahalme at nicira.com>

This raises an issue that I had resolved one way, and you resolved
another (even if you did not realize it).  I am not certain that I chose
the right way, so let me present the issue for discussion.

The definition of the "set-ecn" action in OpenFlow 1.1 is:

    Replace the existing IP ECN value and up-
    date the IP checksum. Only applies to IPv4
    packets.

It's the "only applies to IPv4" that concerns me.  According to a plain
reading of the specification, this makes the action do nothing (or be
invalid) for IPv6.  But a spec standards lawyer[*] would notice that
OF1.1 did not support IPv6, and so "only applies to IPv4" could be read
as meaning that the action does not apply to the other protocols that
OF1.1 does support (e.g. it is meaningless for ARP, MPLS, ...).

   [*] Catch me playing a spec standards lawyer in a special guest
       appearance on an upcoming episode of "CSI: OpenFlow", next
       Wednesday at ten (nine central)!
  
I interpreted this according to the plain wording in other cases, and
so, for example, OFPAT_SET_DSCP only sets the DSCP for IPv4 and becomes
a no-op for IPv6.  Maybe I was wrong.  Either way, I would like to be
consistent here.

Thanks,

Ben.



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