Case Study

The following case study illustrates the point that there is no right or wrong choice to use when deciding which routing protocol to use as each has its own advantages and disadvantages. It is up to the network administrator to make the determination based on the best information available at the time.

Figure 11-4 illustrates a five-node, fully-meshed, wide area network (WAN).

Figure 11-4. Routing (Full-Mesh) Topology

The network administrator can elect one of two routing protocol types to use here: distance vector or link-state.

A distance vector protocol is a viable option because the network is small enough that the routes are manageable with this protocol in that the hop count does not exceed 15 hops (a destination network is considered unreachable at 16 hops). If one or more links were to fail, the amount of time it would take each WAN router to converge on the new network can result in significant delay and dropped sessions. Network stability/reliability can be used to determine whether distance vector should be used in this network.

A link-state protocol is a viable option if the network administrator questions network stability/reliability. If the network administrator feels that stability/reliability is an issue, the convergence time of link-state protocols would better serve the users in that the likelihood of significant delay and dropped sessions is reduced.