Case Study Unequal Cost Load Balancing Again

The entire internetwork of Figure 6.20 is routed with a single IGRP process, and the bandwidths for the serial links are configured to the numbers shown. Default delays are used. Notice that the addresses of the link between Lovett and Harriman are different from the previous examples. Because network 10.0.0.0 can be reached from Acheson not only by the two serial links but also via the Ethernet to Lovett, the network administrator wants to distribute the traffic proportionately among all three routes:

Figure 6.20. This internetwork has three paths from Acheson to network 10.0.0.0.

Figure 6.20. This internetwork has three paths from Acheson to network 10.0.0.0.

The access points to network 10.0.0.0 are:

• Kennnan's Token Ring interface

• Kennan's Ethernet interface

• Harriman's Token Ring interface

Of Kennan's two interfaces to network 10.0.0.0, the lowest delay will be advertised, which is on the Token Ring interface. The minimum bandwidths of all three routes are the bandwidths of the serial interfaces. The metrics of the three routes from Acheson are:

The highest metric is 4.8 times the lowest metric, so variance will be five.

The variance is configured, but the administrator finds that load balancing is not working as expected (Figure 6.21). The routing table shows only the two routes via Kennan; the route via Lovett is between the highest and lowest metrics, but is not included.

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