Enhanced Interior Gateway Routing Protocol (EIGRP)

Enhanced Interior Gateway Routing Protocol (EIGRP) is a unique Cisco innovation. Highly valued for its ease of deployment and fast convergence, EIGRP is commonly used in many large Enterprise networks. EIGRP maintains all of the advantages of distance-vector protocols, while avoiding the concurrent disadvantages.

EIGRP scales effectively in a well-designed network and provides extremely quick convergence times with minimal network traffic. EIGRP advantages include:

• Very low usage of network resources during normal operation; only hello packets are transmitted on a stable network.
• Only routing table changes, not the entire routing table, are propagated, whenever a change occurs; this reduces the amount of load the routing protocol itself places on the network.
• Rapid convergence times for changes in the network topology (convergence can be almost instantaneous in some situations)

EIGRP is an enhanced distance-vector protocol, relying on the Diffused Update Algorithm (DUAL) to calculate the shortest path to a network.