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.
Note
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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