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CCIE Practical Studies: Security (CCIE Self-Study) by Raymond Morrow, Andrew G. Mason, Dmitry Bokotey

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IS-IS Building Blocks

Now that you have a functioning IS-IS network, you are ready for a more detailed examination of the IS-IS routing protocol.

A Level-1 IS delivers and receives adjacency information packets from other ISs and also route based on their ID portion of their address, or within their native areas. Level-1 ISs forward other area traffic to the nearest Level-2 router in the local area. A Level-2 IS routes data traffic based on its area address toward other areas in the same domain or to other domains. Level-2 routers do not need to know anything about the internal structure of an area to route toward them. Level-1 routing occurs between Level-1 ISs, and Level-2 routing occurs between Level-2 ISs.

Internodal connections are referred ...

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