What Are Domains and Why Are They Used?

First of all, what is a domain? A domain is a logically contiguous group of intermediate systems which all have the same set of topology information, or link state packets. All the intermediate systems within a domain share a common view of the world. But since IS-IS is a link state protocol, shouldn't every intermediate system in the network have the same topology, or link state information? If every intermediate system in the network simply records the information it receives, and then passes it on to every other neighboring IS, wouldn't every intermediate system have, through the flooding process, the same information in their databases?

For reasons we'll soon discover, not all intermediate systems simply ...

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