Subject: Re: MPLS Performance analysis.....

From: [email-masked] (Sean Doran)
Date: Thu, 25 May 2000 01:06:11 +0200 (CEST)

Several people write:

> [lots of commentary about how wonderful MPLS is at making forwarding fast]

You are analysing the performance of MPLS using the wrong metric.
I think MPLS performs exactly as intended.
Ipsilon basically died, and not even Nokia could revive it.
UUNET found a new layer-2 religion, essentially killing backbone ATM.
Many companies are distracted from actually learning how to do IP routing.

Score: MPLS 3, Rest Of World 0.

	Sean.

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From: Yakov Rekhter <[email-masked]>
Date: Mon, 29 May 2000 04:14:22 -0700

Sean,
 
> Many companies are distracted from actually learning how to do IP routing.

Of course, for some folks the *one and only* way to move data is by
looking at the IP header, and executing the longest match algorithm on
the destination address in that header (aka "destination based
routing"). Anything else (e.g., MPLS), *regardless* of its pragmatic
value, is viewed as "religion", "distraction", etc... 

Yakov.

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From: "Loa Andersson" <[email-masked]>
Date: Mon, 29 May 2000 23:14:57 +0200

> > [lots of commentary about how wonderful MPLS is at making forwarding fast]
So comments are basically wrong, HW forwarding on IP header is exactly
as fast as Label based forwarding- wired speed!

BTW - who were the people that made those comments?

< snip>

> Many companies are distracted from actually learning how to do IP routing.

Poor UU-net - they were converted to a non-sense religion. MPLS is not
L2
it is L3. Or is the misunderstanding by those who try to explain what 
UU-net believes?

/Loa

-- 

Loa Andersson
Director Routing Architecture Lab, EMEA
St Eriksgatan 115A, PO Box 6701
113 85 Stockholm, Sweden
phone: +46 8 50 88 36 34,   mobile + 46 70 522 78 34
e-mail: [email-masked]

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From: Curtis Villamizar <[email-masked]>
Date: Tue, 30 May 2000 17:38:40 -0400

> BTW - who were the people that made those comments?

Loa,

I was one of those people.  Doing the IP destination lookup is no
longer a limiting factor for modern routers.

Curtis

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From: David Charlap <[email-masked]>
Date: Tue, 30 May 2000 18:51:42 -0400

> longer a limiting factor for modern routers.

Depends on the speed.  If you up the number and type of interfaces so
that your fabric has to forward billions or trillions of packets per
second, you will once again find differences in how the two forwarding
engines (IP destination vs. label) perform.

Regardless of how fast the chips run, an IP best-match lookup is an
inherently more complicated operation than the integer-matching lookup
required by something that forwards based on label (or VC or DLC).

-- David

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From: Grenville Armitage <[email-masked]>
Date: Tue, 30 May 2000 16:24:50 -0700

David Charlap wrote:
	[..]
> required by something that forwards based on label (or VC or DLC).

And regardless how much faster your label lookup is, if both
approaches can fill the pipes one is interested in the issue
is moot. Which I thought we'd already concluded.

cheers,
gja

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From: Curtis Villamizar <[email-masked]>
Date: Wed, 31 May 2000 09:43:50 -0400

> engines (IP destination vs. label) perform.

The forwarding decision needs to be made independently on each
forwarding card if you want to build a scalable router.  This way the
amount of parallelism grows as the number of interfaces grows.  If the
IP forwarding decision is part of the fabric, that's simply a design
mistake if very large scalability is a design goal.

> required by something that forwards based on label (or VC or DLC).

If you can do it in a few clock cycles in an microprogammed engine,
and its faster than the packet arrival rate it doesn't matter.  As
Greg Mirsky already pointed out, its been done in routers (from
multiple sources).

Curtis