[ovs-dev] [PATCH] Add OpenFlow support for 802.1AD Ethertype

Thomas F Herbert thomasfherbert at gmail.com
Sat Oct 18 13:55:57 UTC 2014


On 10/17/14, 4:54 PM, Ben Pfaff wrote:
> On Fri, Oct 17, 2014 at 01:19:33PM -0400, Dave Benson wrote:
>> On Fri, Oct 10, 2014 at 6:43 PM, Ben Pfaff<blp at nicira.com>  wrote:
>> ...

> My first thought is to define a new NXM_NX_VLAN_TPID that matches the
> TPID, and for backward compatibility to imply a match on 0x8100 if it
> is not given.
I think the assumption in OF is that the vlan-vid match is always on the 
outermost tag  but the description in the spec is not explicit. The 
802.1ad spec requires that the outer TPID must be 0x88a8 so in spite of 
some legacy use of 0x9100 or 0x8100 for the outer tpid, I think it is OK 
to assume that 0x88a8 is the TPID for the outer tag and 0x8100 is the 
TPID for the inner tag.

However, an ambiguity in the OF spec is that the behavior for 802.1q and 
802.1ad is implied and not explicitly stated.For example,  the entry in 
the OF in table 11 (page 57, version 1.4,) the line about vlans should 
say that the prerequisite of a VLAN_ID should be a TPID of 0x8100 OR 
0x88a8 and the description should be changed to include both 802.1q and 
802.1ad and that the match is on on the outer tag.

802.1ah is in a similar situation in this respect. Notice in contrast, 
the entry for OXM_OF_PBB_ISID  in the same table in the OF spec states 
explicitly that 0x88E7 is the prerequisite and that the match is on the 
outer ISID.

Your proposal, Ben of adding a match on the TPID to OF is a way to end 
the ambiguity but I don't think it  absolutely necessary. My opinion is 
that it would be sufficient to change in the language  in the spec to  
explicitly state that the match is on the outer tag.
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-- 
Thomas F. Herbert
Network Implementation Engineer
Entry Point LLC




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