SPF or Dijkstra algorithm gives the routing table to link-state routing protocols from the topological table.
The drawback is that the routing table must be recomputed with SPF after every LSA.
To optimize the ressources of the router, Cisco has made a new feature "incremential SPF" : instead recomputing the entire routing table, the router will compute only the part of the routing table concerned by the topological changement.
Another thing to know, routers using incremential SPF can work with non-incremential SPF routers.
To enable this feature, the command is ispf in routing protocol configuration.
This commande can also work with IS-IS with arguments level-1 / level-2 / level-1-2 to specify on which level using the feature (only L1 / only L2 / L1 and L2)
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