Introduction

The exercise is part of case study describing IPX routing in Great Coals network shown below:

To improve the EIGRP convergence and stability in the network, the network design uses hierarchical default routing. Please refer to "Case Study - GreatCoals network" in Chapter 10 for more details.

Exercise

When the new network design was implemented, the number of routes in all routers drastically decreased, and the number of SIA events was reduced. SIA events still occurred occasionally, though, and the network was still converging slowly. Why? Simulate what happens when a regional WAN connection in Germany fails.

Solution

When a regional WAN connection in Germany fails, the Frankfurt router will start diffusing computation and query the Austin router, which will in turn query all of its neighbors, including the routers reachable through low-speed international links. These links slow down convergence as every international sales office router has to respond to the query before the network convergence is complete. They could also become a bottleneck and cause SIA event somewhere else in the network.