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packet that lists this information along with new neighbors, changes in link costs, and links that
are no longer valid. The LSA packet then is sent out so that all other routers receive it.

Figure 6-19shows an example of link-state topology changes.

Figure 6-19 shown a Link-State Topology Changes

When the router receives an LSA packet, the database is updated with the most recent
information. The accumulated data is used to compute a map of the internetwork, and the SPF
algorithm calculates the shortest path to other networks. Each time an LSA packet changes the
link-state database, SPF recalculates the best paths and updates the routing table. Every router
takes the topology change into account to determine the shortest path to use for packet routing.
Three Link-State Concerns

Running link-state protocols brings up three primary concerns:

■ Processor overhead ■ Memory requirements ■ Bandwidth consumption

Routers running link-state protocols require more memory and perform more processing
than distance vector routing protocols.

Routers must have enough memory to hold all the information from the various
databases, the topology tree, and the routing table, as shown in Figure 6-20. Initial link-state
packet flooding consumes bandwidth. During the initial discovery process, all routers using link-
state routing protocols send LSA packets to all other routers.

This action floods the internetwork and temporarily reduces the bandwidth available for
routed traffic carrying user data.
After this initial flooding, link-state routing protocols generally require only minimal
bandwidth to send infrequent or event-triggered LSA packets reflecting topology changes.

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