> I agree that terminology is confusing sometimes. How about
> 'route balancing' or 'prefix balancing' for a routing protocols
> which distributes its routes among known equal cost paths. Then
> for the forwarding we can accept 'traffic balancing' or 'load
> balancing' refering to the true distribution of bytes and
> packets.
Well, you can call them what you like for me, but I think that
the terminology in itself doesn't really assist all that much in
furthering the understanding of the separation of the issues.
Just to rephrase what Dorian said:
To do "load balancing" between (typically) "equal-cost" paths you
need to think of a couple of separate things:
o Does your routing protocol permit the selection of more than
one parallel paths (next-hops) to a given destination?
o Can the resulting IP forwarding table (which is normally
constructed based on the collected routing information from
allt he routing protocols active on the router) hold more than
one next-hop address for each given destination? (The answer
to this is normally "yes" nowadays.)
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.
Regards,
- Håvard
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