> o How is the forwarding mechanism on the router making use of
> that IP forwarding table. In some cases (e.g. when using a
> "route cache"), the router will pick a single next-hop for
> each new entry it puts in the "route cache", so unless there
> is a cache invalidation all the traffic to a given destination
> will travel over over same wire to the same next-hop. In
> recent route-cache code the "destination" is generally a
> "prefix", not a host (eh, remember good old times? ;-). In
> other cases, the forwarding engine can be made to do a "per-
> packet" choice of next hop (process switching on old gear and
> apparently CEF switching with new software), since no
> simplified route cache (with only a single next-hop) is
> involved in those cases. I'm sure there can be variations on
> these themes, e.g. source-dest hash, as you mention (anyone
> know how cisco's netflow-based route cache does this?),
> although I can see that anything host-based will tend to scale
> badly in backbone routers.
>
Would you agree that any type of 'route caching' wouldn't scale well on
a backbone router? I think that you have to have full table with all
best paths on a forwarding engine. (I might be off topic cause it's not
about
some today's HW.) The penalty for doing multiple lookups can be minimal
when it'll be done in ASIC.
Regards,
Greg
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