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 ...