Reviewing Dynamic Routing 119
If the network shown in Figure 3-28 uses a link-state routing protocol, connectivity between New
York City and San Francisco is not a concern. Depending on the actual protocol employed and the
metrics selected, it is highly likely that the routing protocol could discriminate between the two
paths to the same destination and try to use the best one.
Figure 3-28 Link-State Algorithms
Table 3-2 summarizes the contents of the routing database of each router in the ?¬?gure.
Table 3-2 Link-State Routing Database
Router Destination Next Hop Cost
A 185.134.0.0 B 1
192.168.33.0 C 1
192.168.157.0 B 2
192.168.157.0 C 2
B 10.0.0.0 A 1
192.168.33.0 C 1
192.168.157.0 D 1
Network
10.0.0.0
Network
185.134.0.0
A
B
New York
San Francisco
Cost = 1
Network
192.168.33.0
Network
192.168.157.0
C
D
Boston
Los Angeles
Cost = 1
Cost = 1
Cost = 1
Cost = 1
continues
120 Chapter 3: Medium-Sized Routed Network Construction
As shown in the table link-state database entries for the New York (Router A) to Los Angeles
(Router D) routes, a link-state protocol would remember both routes. Some link-state protocols
can even provide a way to assess the performance capabilities of these two routes and bias toward
the better-performing one.
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