From: Peter van Oene (pvo@usermail.com)
Date: Tue Mar 11 2003 - 12:09:55 GMT-3
Hi all,
Here is a quick post from Dave Katz on ISIS vs OSPF in large networks
dealing with the issue of which protocol inherently scales better. This is
from a thread in the IETF OSPF WG mailing list for those looking for the
full thread. Dave has participated significantly in the development of
routing protocol software for both Cisco and Juniper.
Thought some folks might find it interesting
Pete
>Date: Sun, 9 Mar 2003 21:05:14 -0800
>Reply-To: Mailing List <OSPF@DISCUSS.MICROSOFT.COM>
>Sender: Mailing List <OSPF@DISCUSS.MICROSOFT.COM>
>From: Dave Katz <dkatz@JUNIPER.NET>
>Subject: Re: ospf limits...
>To: OSPF@DISCUSS.MICROSOFT.COM
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>For all practical purposes, the designs of the OSPF and ISIS protocols
>will not be the limiting factor in the size of an area, unless (a) you
>have a really good implementation, and (b) you feel the need to dump
>excessive numbers (many thousands) of external and stub routes into
>the protocol.
>
>Most implementations will crash and burn before the topology gets
>big enough to become an issue, and most people don't dump externals
>into their IGPs (they use BGP instead.)
>
>Architecturally, OSPF limits the inter-router topology and stub routes
>due to the 64KB limit on the Router LSA, and ISIS limits the total amount
>of information due to the 256 LSP "fragment" limit. One could come up
>with various hacks for either protocol if these limits were actually,
>well, limiting, but this has never been the case in (sane) practice.
>
>Historically, the ISIS implementation from a particular major vendor has
>had better scaling characteristics than the OSPF implementation of that
>particular major vendor, but this this isn't really the case for another
>major vendor. ;-)
>
>--Dave
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