What is EIGRP?

EIGRP (Enhanced Interior Gateway Routing Protocol) is a Cisco-proprietary advanced distance-vector routing protocol that uses features of both distance-vector and link-state protocols. It is often called a "hybrid" or "balanced hybrid" protocol. EIGRP uses the DUAL (Diffusing Update Algorithm) to calculate loop-free paths and maintain backup routes (feasible successors) so it can instantly switch to a backup path without waiting for reconvergence. EIGRP sends partial, bounded updates only when the topology changes (not periodic full table updates like RIP), making it bandwidth-efficient. The composite metric uses bandwidth, delay, reliability, and load (by default only bandwidth and delay). EIGRP maintains three tables: neighbor table (adjacent routers), topology table (all learned routes), and routing table (best paths). It supports VLSM, CIDR, and supports IPv4, IPv6, and other Layer 3 protocols. EIGRP converges faster than OSPF in most scenarios and is simpler to configure for smaller networks.