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List:       ms-ospf
Subject:    Re: what is the fundamental difference between OSPF and IS-IS?
From:       Erblichs <erblichs () EARTHLINK ! NET>
Date:       2002-08-23 16:49:12
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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.
        =============================================


"Liu B." wrote:
>
> 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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