Subject: what is the fundamental difference between OSPF and IS-IS?

From: "Liu B." <[email-masked]>
Date: Thu, 22 Aug 2002 15:20:18 +0100

Hello everyone,

Thanks for answering my previous questions. I am reading RFC 1142 (OSI IS-IS
Intra-domain Routing Protocol), in order to compare OSPF with IS-IS. There
are so many common things between two of them, such as area routing, virtual
link, designated router ... what is the fundamental difference (or
improvement?) between OSPF and IS-IS?

Thanks again for all your helps.

Bin Liu

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From: Arthur Dimitrelis <[email-masked]>
Date: Fri, 23 Aug 2002 10:09:49 +1000

Hi,

there is a paper by Radia Perlman that answers your question, entitled "A
Comparison Between Two Routing Protocols: OSPF and IS-IS". It appeared in the
September 1991 issue of the IEEE Network Magazine. Contact me off list if you
need help finding it (it's freely available in electronic form).

cheers,
Arthur

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From: Arthur Dimitrelis <[email-masked]>
Date: Fri, 23 Aug 2002 10:49:02 +1000

Sorry, I take that last point back. The said paper is available in electronic
form, but I have no idea if it's free (in a monetary sense) or not.

arthur

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From: Felix Lin <[email-masked]>
Date: Thu, 22 Aug 2002 19:20:48 -0700

Arthur,

I tried searching for this paper on Internet but was unsuccessful. Is it
available publicly? How do I find it?

Thx
Felix

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From: Barry Friedman <[email-masked]>
Date: Thu, 22 Aug 2002 21:21:30 -0700

There's not much fundamental difference, but plenty of divergence
in the details:

http://www.nanog.org/mtg-0006/katz.html

Regards,
Barry

--
Barry Friedman
Cisco Systems Inc.  mailto:[email-masked]

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From: Arthur Dimitrelis <[email-masked]>
Date: Fri, 23 Aug 2002 16:08:58 +1000

Felix,

it is publicly available, but as far as I can tell, you will need an IEEE
subscription in order to download it, from IEEE Xplore at least.

Those who have the necessary IEEE subscription can go to:
http://ieeexplore.ieee.org

Failing this, I'd expect to find a hard copy at a university library.

cheers,
Arthur

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From: Erblichs <[email-masked]>
Date: Fri, 23 Aug 2002 09:49:12 -0700

Bin Liu,

        I will assume that

        The two biggest differences in my opinion are:

        1)  IS-IS is a pure SPF computation based LS protocol.

           IS-IS : Routes computed between L2 to L2 routes in
           IS-IS are link-state / SPF computations. L1 routers
           have no direct outside area connection. L2 routers
           have that direct connection. Yes, a router can be
           a L1/L2 router.

            OSPF : Like routes (non-local) within OSPF are distance
            vector computation.

        2)  Neighbor to adjacency formation process.

           OSPF : Uses a heavy weight process to initially synchronize
           its link state databases for adjacencies. Then it uses
           flooding to keep them synchronized.

           IS-IS : Uses complete and partial link-state protocol data
           units which describe every LSP in the database and are
           periodicly multicasted.

        Mitchell Erblich
        Ex-Extreme Networks IS-IS Software Developer.
        =============================================