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Re: number of hops != performance

  • From: Petri Helenius
  • Date: Tue Nov 05 15:20:20 2002

> Of course L3 forwarding is not by itself "bad" for the packets. However...
> If you have a network with "excessive" hops (for some definition of
> excessive), it probably means one or more of the following:
>
> A) you have a poor (or at least non-elegant) network design.

If your L3 topology is well aligned with your L1 topology, you usually
end up with more hops. The less intermediate gear, like SONET you
use but do L3 instead, the more L3 hops you have.

> B) you have more places for things to go wrong in both hardware and
>    software.

This is specifically true for the hop-hiders using MPLS or other mostly
pointless multihop recursive switching systems.

> C) you're busy gratifying your architectural ego instead of designing
>    the simplest thing possible which gives you the necessary performance
>    and reliability.

Hop-hiding is usually going the other way from the simplest thing.

> D) you're buying so much unnecessary hardware that you are either not
>    not financially healthy or you're not passing on as much savings as you
>    could be to your customer.
>
Eliminating n+1 kinds of gear and replacing it with a smaller number of
different kind of boxes makes your network simpler and saves nicely
on OPEX. Might be somewhat more CAPEX intensive on the start but
not by a large margin.

> Now while I'm sure that you don't fit into that definition of "excessive",
> I can think of a few people who do, and they try to use that "but more L3
> hops are never bad" argument.

This would translate to that "hops are bad", regardless of the layer. Many
people
mess with L4 to L7 generating unneccesary hops on application protocols.
These usually seem to be the same growd that does other hiding things.

Pete





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