Figure 86 Hop counts are modified to differentiate between primary and alternative routes

Figure 8-6 presents a slightly modified version of the WAN depicted in Figure 8-5. This illustration adds low-bandwidth redundant links to the topology depicted in Figure 8-5. The network administrator, to ensure that the alternate routes remained alternate routes, set the metric value of these alternate routes to 10. These higher costs preserve the bias toward the higher- bandwidth T1 transmission facilities. In the event of a failure of one of those T1 lines, the internetwork can continue to function normally; although there may be some degraded performance levels due to the lower available bandwidth on the 56 kbps backup facility. Figure 8-7 illustrates how the internetwork will react to a failure of a T1 line between the gateway and Router A.

Figure 8-6 presents a slightly modified version of the WAN depicted in Figure 8-5. This illustration adds low-bandwidth redundant links to the topology depicted in Figure 8-5. The network administrator, to ensure that the alternate routes remained alternate routes, set the metric value of these alternate routes to 10. These higher costs preserve the bias toward the higher- bandwidth T1 transmission facilities. In the event of a failure of one of those T1 lines, the internetwork can continue to function normally; although there may be some degraded performance levels due to the lower available bandwidth on the 56 kbps backup facility. Figure 8-7 illustrates how the internetwork will react to a failure of a T1 line between the gateway and Router A.

Figure 8-7: Hop counts add up quickly, but the network remains functional.

Figure 8-7: Hop counts add up quickly, but the network remains functional.

The alternative 56 kbps transmission facility becomes the only way for A and the rest of the network to communicate. Router A's routing table, after the network converges upon a common understanding of this new topology, is summarized in Table 8-4.

Table 8-4:

Router Name

Host Name

Next Hop

Number of Hops

A

A.10

Local

0

A.15

Local

0

B.2

Gateway

11

B.9

Gateway

11

C.5

Gateway

11

C.20

Gateway

11

0 0

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