The L1 router will use the default route to forward all interarea or interdomain traf?¬?c
to the ABR, or L1/L2, router. This behavior can be different for OSPF, depending on how the
OSPF nonbackbone area is con?¬?gured (stub area, totally stubby area, or not-so-stubby area).
Link-State Routing Protocol Algorithms
Link-state routing algorithms, known collectively as SPF protocols, maintain a complex database
of the network topology. Unlike distance vector protocols, link-state protocols develop and
maintain full knowledge of the network routers and how they interconnect. This is achieved
through the exchange of link-state packets (LSP) with other routers in a network.
Each router that has exchanged LSPs constructs a topological database using all received LSPs.
An SPF algorithm is then used to compute reachability to networked destinations. This
information is employed to update the routing table. The process can discover changes in the
network topology caused by component failure or network growth.
In fact, the LSP exchange is triggered by an event in the network, instead of running periodically.
This can greatly speed up the convergence process because it is unnecessary to wait for a series of
timers to expire before the networked routers can begin to converge.
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