Recall from Chapter 3, "Structuring and Modularizing the Network," that the modules in the Cisco Enterprise Architecture correspond to places in the network. The choice of routing protocols depends on the network design goals. Therefore, the routing protocol decision should be made only after the network goals and topology are determined. Running multiple routing protocols might be necessary in large enterprise networks, for example, when a network upgrade is performed; the old routing protocol usually coexists with the new one during the transition period.
As discussed in previous sections of this chapter, routing protocols differ in many ways. For example, how routing information is exchanged, convergence times, metrics used for optimal route determination, required amount of processing power and memory, and availability of a routing protocol on various platforms can determine whether a routing protocol is more or less suitable for a network or parts of a network. The following sections explain why certain protocols are suitable for specific modules in the Enterprise Architecture, and the advantages and disadvantages of individual protocols.
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