[rbridge] encoding of TRILL IS-IS frames
Radia.Perlman at sun.com
Fri Oct 10 15:43:37 PDT 2008
Someone asked me why IS-IS frames need to be TRILL-encapsulated, and I
don't remember. I do know we
were somewhat concerned about differentiating TRILL IS-IS frames from
layer 3 IS-IS frames. But assuming
we use a different multicast address for TRILL IS-IS than layer 3 IS-IS,
with the additional safeguard of
using a different "area ID" (for TRILL, area ID=0), it seems like there
would be no danger of confusion.
Perhaps we were concerned about possible unicast of IS-IS frames, like
for instance, a PSNP that one might
send just to the DR? I think I verified with the IS-IS people that there
are no IS-IS frames that are unicast.
So why doesn't the following work?
For core IS-IS frames, no encapsulation, but a special multicast address
the destination address.
For ESADI, TRILL encapsulation like with ordinary data packets, but
having as the destination
address in the inner Ethernet header a different multicast address
The advantage of this is that for core TRILL IS-IS, we'd save header
room and probably work for
RBridges to parse IS-IS packets.
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