Subject: [Isis-wg] Simple question about IS-IS mixed domains

From: Cyndi Jung <[email-masked]>
Date: Thu, 14 Sep 2000 11:50:36 -0700

If you can't mix dual and non-dual routers in the same area and
have routing work for the non-OSI protocols supported (IP and IPv6),
then how can it work at Level 2 if all the Level 2 routers do not
support all the same non-OSI protocols?  It seems to have the same
problem - routes will be computed through routers that do not support
the protocol of the data, just because the link costs are lowest.

Am I missing something?

Cyndi

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From: Tony Li <[email-masked]>
Date: Thu, 14 Sep 2000 23:15:33 -0700 (PDT)

| If you can't mix dual and non-dual routers in the same area and
 | have routing work for the non-OSI protocols supported (IP and IPv6),
 | then how can it work at Level 2 if all the Level 2 routers do not
 | support all the same non-OSI protocols?  It seems to have the same
 | problem - routes will be computed through routers that do not support
 | the protocol of the data, just because the link costs are lowest.
 | 
 | Am I missing something?

If one Really Wanted to do this, then one would have to SPF independently
for each protocol.  

Plus, because adjacency information is not carried on a per-protocol basis,
you would still have the restriction that any link between two routers
supporting a protocol would have to have the protocol working on that
link.  So for example, the link between two IPv6 routers had better be
configured for IPv6.

This seems like more complexity than it's worth.  After all, there's only
one important network layer.  ;-)

Tony

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From: Cyndi Jung <[email-masked]>
Date: Fri, 15 Sep 2000 10:47:07 -0700

Of course, there is really only one important network layer, IP,
but it has taken over the only routing protocol that CLNP ever had :-)

So, it's most prevalent use is in IP-only networks, or purely dual
domains.  In fact, without the SPF per-protocol (assuming there were
some information in the LSPs that they could use to imply the missing
Supported Protocol field), a "mixed" domain is a misconfiguration,
just as a mixed area is.

Cyndi