The focus of this chapter is on how EIGRP works so that those networks can be designed to maximize efficiency and truly scale the network.
The major concern in scaling an organizational network is controlling the network overhead that is sent, in particular over slow WAN links. The less information about the network, its services, and networks that need to be sent, the greater the capacity available for the data between clients and servers. Although sending less routing information relieves the network, it gives the routers less information with which to make decisions. Every designer of routing protocols and every network administrator must deal continually with this trade-off. As seen with summarization, static and default routes can lead to poor routing decisions and loss of connectivity.
OSPF was the first protocol to attempt to address these problems. Alternatives to OSPF that offer the capability to scale to the size of modern networks are few. Static routing is one possibility, but it demands so much from the network administrator that it would never scale. IGRP offers another alternative; as a proprietary distance vector protocol, IGRP has solved many of the problems. However, it does face some issues with regard to scaling because of the inherent nature of distance vector. Although still distance vector and proprietary, EIGRP addresses many of the problems related to scaling the network that IGRP never anticipated.
This chapter discusses EIGRP. As a proprietary routing protocol, EIGRP can solve many problems seen in standards-based protocols that have to please all of the devices all of the time.
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