EIGRP Introduction

Enhanced Interior Gateway Routing Protocol (EIGRP) is a distance vector protocol often used in Cisco networks.

For many years it was a Cisco proprietary protocol, but was released to the Internet Engineering Task Force with RFC 7868 and ratified in May 2016.

EIGRP has some advantages over lesser distance vector protocols such as RIP, such as including features like unequal-cost load balancing, support for networks up to 255 hops away (15 hops for RIP), and rapid convergence.

Other distance vector protocols use hop count as their main metric for routing decisions, EIGRP diverges from this by taking into account link bandwidth and delay, and optionally other factors.

EIGRP uses a diffusing update algorithm (DUAL) to identify available network paths and allows rapid convergence using loop-free backup paths that are pre-calculated.