Flooding Mechanisms and Timers

IS-IS floods link state information in response to connected link information changes. Link changes that cause IS-IS to flood link state information include

  • An adjacency changing state (either coming up or going down)

  • The cost of the attached link changing

  • A change in the areas configured on the system

  • A change in the node's system ID

  • A change in the designated intermediate system for an attached broadcast network

In these cases a new level 1 or level 2 LSP is flooded, including any new reachable IS or ES neighbors and leaving out any IS or ES neighbors which are no longer reachable.


Two flags are used by IS-IS to control the propagation of information: the Send Routing Message (SRM) and the Send Sequence Numbers ...

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