Basic understanding of IS-IS

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Dec 31st, 2008
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I just want to clear some confusion!

IS-IS is ISO protocol that doesn't have native support of IP, is that correct?

To add the support of IP IS-IS use different TLV which represent the IP characteristics required for IP communication as well as to support IP link state routing protocol characteristics! right?

Now IS-IS does use the NET to in routing process so it is required to have NET even in IP only routing domain so it is necessary to encapsulate the IP related routing packets into original ISO IS-IS encapsulation, is that correct?


Devang Patel

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Giuseppe Larosa Thu, 01/01/2009 - 13:00
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Hello Devang,

the answer is yes to all of your questions your understanding is good.

RFC1195 defines the TLVs for IPv4, later TLVs for IPv6 have been added.

The NET is the CLNP address of the node: only one regardless of the number of interfaces (this is a big difference from IP)

and yes the IS-IS data structures travel inside IS-IS PDUs including IPvX related TLVs

Happy new Year

Hope to help



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