Answers: EIGRP and Bandwidth

This lab asks you to configure EIGRP, with a small twist – a change to the link bandwidth on one of the links. As a result, some of the routes will follow a two-hop path rather than a one-hop path. Otherwise, the configuration is relatively straightforward. As usual, if you haven’t looked at the original lab post yet, do that first, and then check your own answer here!

Answers

Example 4: R1 Config

Example 5: R2 Config

Example 6: R3 Config

Commentary

When configuring EIGRP it is important to have an idea of how the metric is calculated to determine how it will be selecting the best path through the network. EIGRP by default uses both a bandwidth and a delay component to calculate the metric.

EIGRP calculates metrics in part based on the bandwidth. Specifically, EIGRP uses the worst (slowest) bandwidth for all the links in a route. EIGRP also uses link delay to calculate the metric, but EIGRP uses the cumulative delay rather than slowest bandwidth.

If this lab were completed with all default bandwidth settings, comparing each router’s two paths to reach another router, the slowest bandwidth settings would tie. However, by configuring one link (the link between R2 and R3) with a slower link bandwidth of 100Mbps, any routes that use the R2-R3 link will have the slowest bandwidth. As a result, routes between R2 and R3 will now use only the path through R1, rather than the direct link between R2 and R3.