Chapter 2. EIGRP Theory and Operation

Enhanced Interior Gateway Protocol (EIGRP) is a widely used advanced distance vector routing protocol. This chapter provides a high-level overview of the theory and operation of EIGRP.

Neighbor Relationships

EIGRP forms neighbor relationships for two primary reasons:

• To maintain state about reachable destinations and paths without periodically retransmitting this information

• To provide a reliable mechanism to process the loss of reachability information

EIGRP uses a three-way handshake process to build a neighbor adjacency, as shown in Figure 2-1.

FIGURE 2-1 EIGRP Neighbor Formation

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Once EIGRP neighbors ...

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