Dynamic Routing: Link State

Link state protocols exchange information about individual objects in the topology and their mutual interconnections.  The objects normally consist of routers, multiaccess networks, routers on borders of areas, or an entire autonomous system, or networks from other areas and outside the autonomous system.

Primarily routers are used as the objects in the link state routing protocols and their links.  IPs are treated as attributes or properties of these objects.  Once a router generates a message that describes itself and its links to neighbors…that message is flooded without any modification to every area’s topology.  The router is aware of every other router, and every network, and every link.  Having this information allows the router to construct it’s own topology based on the advertisements and detailed information within them and use an algorithm to compute a tree of shortest paths to each of the networks reported to the router.  Usually the SPF algorithm is used for this computation.

The SPF algorithm will not create a looped network, however temporary changes in topology could cause temporary loops before the algorithm is calculated to update the new shortest path to affected networks.

The downside of this type of protocol is the potential to be CPU intensive in environments where topologies change constantly however this is mostly negated by the improved hardware and memory of newer routing devices on the market today.

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