Subject: [rbridge] Revisiting the TRILL header

From: Radia Perlman <[email-masked]>
Date: Mon, 11 Feb 2008 19:29:16 -0800

Now that people are getting into implementing TRILL...

An implementor said that he found looking beyond the options for things 
like VLAN and destination address
in the inner header annoying.

Don Eastlake had proposed a format moving the VLAN and destination 
address into the TRILL header (and removing
them from the inner packet). I liked it at the
time and still do, and thought I'd give it one more chance on the 
mailing list.

The format that the implementor proposed was that without options, all 
that would change is that the
Ethertype would be removed from the 802.1q tag, so the format would be

current header + Ethernet DA + Ethernet SA + 16 bits of VLAN info 
(priority, drop eligibility, VLAN tag) + options (if any) +
rest of packet.

The arguments, I think, were that then core RBridges don't have to look 
beyond the TRILL header, and also,
that the core RBridges don't have to understand both Ethertypes (IEEE 
changed the Ethertype on the VLAN tag when
changing the meaning of the "format indicator" bit to "drop eligibility".

Can other people who are implementing this comment on:
a) whether changing the header at this point is really a problem, even 
if it were a good idea, and
b) whether this is a good idea.

Thanks,

Radia

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