Subject: [Isis-wg] Computing routes with wide (TE Draft) metrics

From: Neal Castagnoli <[email-masked]>
Date: Wed, 10 Jan 2001 14:30:08 -0800

In reviewing the ISIS TE draft, I'm wondering how to mix wide (TE draft) and
narrow (original) links and routes.

One way to build a migration path would be to run two SPF computations, once
on each metric space (using only "narrow" or "wide" metrics in each run).
This method has the disadvantage that during migration wildly suboptimal
routes can occur, because during migration computations only use a subset of
the links.

Other options include administrative control. For example:

New routers compute using both "old" and/or "new" metrics.  New routers can
have paths composed of links with old and new metrics in it.

Start:
   . all old routers, only reporting old metric
   . one by one change to new routers, also reporting only old metrics.
   . When all routers are "new", reconfigure each router so it repots only
new metrics on each of its links.

This method has disadvantages, including that the administrator needs to be
extremely careful with the router versions and that routes can also be
suboptimal.

I don't think either of these are great solutions.  Perhaps someone would
like to suggest others.  But at any rate, it seems like how to compute hop
by hop routes needs to be specified as a part of the TE document.

  --Neal
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