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RE: The Gorgon's Knot. Was: Re: Verio Peering Question
From: "Deepak Jain" <deepak () ai net>
Date: Sun, 30 Sep 2001 18:46:23 -0400



There are two separate problems I think with core routers.

A number of router platforms, like Juniper, have lots of core memory on
their main CPU [like 768MB I think]. This is fine to hold all the views of
all your peers, etc. Even a PC can handle this task and calculate
convergence.

The problem is where the RIB, or forwarding table is exported to the line
cards which frequently have less than 128MB of usable RAM/SRAM/memory
storage/etc. This essentially means that the line cards can only directly
talk to other line cards for a specified, limited number of routing
prefixes. I do not know the algorithms used when the line card is out of
memory, but in many cases this memory is not field upgradeable beyond a
certain point.

This causes operators of this sort of a equipment difficulties in longer
convergence times and less than ideal routing performance.

While its great to say we can all upgrade our core routing equipment every
9-12 months, which is often the case for business reasons, not all of us
want the OBLIGATION to, and filtering is one way to ensure  increased
longevity of your equipment.

We can always bring up the idea of using PCs for peering, and real routers
for forwarding/packet filtering, but you are essentially asking the
operators of backbones to absorb additional operations expense [in terms of
maintaining multiple platforms] for reason that benefits _their_ business
model.

Many smaller networks can and do use PCs for BGP and for forwarding because
their total forwarding needs at their core are say sufficiently less than
800mb/s upto which PCs seem to handle. However, the desires and models of
these smaller networks don't scale much beyond this level with currently
available PC technology.

You can put many interfaces in a PC, or several PCs and not need a dedicated
16 slot chassis, but when you are aggregating many interfaces and they are
moving well over 800mb/s, there aren't too many options.

This completely ignores the fact that a core router doesn't want to be
touched under any circumstance, and engineers come up with LOTS and LOTS of
good reasons why you need to wait until the router is ready to fall over
before scheduling a maintenance window on it.

Just my opinion, YMMV.

Deepak Jain
AiNET

-----Original Message-----
From: owner-nanog () merit edu [mailto:owner-nanog () merit edu]On Behalf Of
Joseph T. Klein
Sent: Sunday, September 30, 2001 11:34 AM
To: Stephane Bortzmeyer
Cc: nanog () merit edu
Subject: Re: The Gorgon's Knot. Was: Re: Verio Peering Question



At 13:54 +0200 30-09-2001, Stephane Bortzmeyer wrote:
On Friday 28 September 2001, at 20 h 6,
"Joseph T. Klein" <jtk () titania net> wrote:

 Yeah right. I suggest you look at real world loaded 7200s. They have
 problems with full routing tables.

I don't know, I don't use Ciscos and I don't regret it.

 >Any Taiwan-made PC can swallow much more. The limit is not clear but is
 >certainly far away from us.

 I want to you to put a couple of channelized DS-3s, an ATM OC12c,
 and a POS OC48c to your backbone plus all the BGP peers you can sign
 up at AADS on a PC.

Come on, I did not say that a PC can handle everything, just that it can
handle easily 100k routes.

I don't know the limit but neither do you (did you try the funny experiment
you suggest or are you just guessing?) The only thing I'm sure, because I
run
it daily, is that 100k routes is not a lot for today's machines.

 The black and white simplicity expressed by people on this forum is
 unbelievable.

The ability of some people to continue the discussion about the "routing
table
explosion" legend as if we were still in a world of 64 mega-bytes routers
(with a Motorola 68020) is unbelievable.

Muck through the archives ... you will find me on the other side of the
argument.

A PC with the big interfaces is called a Juniper. ;-)

The problem is at the core, not at the edge. You can put a PC in
many places but not in a high bandwidth, peer rich location.

--
Joseph T. Klein                                         +1 414 915 7489
Senior Network Engineer                                 jtk () titania net
Adelphia Business Solutions                joseph.klein () adelphiacom com

     "... the true value of the Internet is its connectedness ..."
                                                  -- John W. Stewart III


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