EIGRP
acronymnetworking
Stands for: Enhanced Interior Gateway Routing Protocol
Enhanced Interior Gateway Routing Protocol - Cisco's advanced distance-vector protocol: the DUAL algorithm keeps loop-free backup routes precomputed, so convergence is nearly instant.
EIGRP grew out of Cisco's earlier IGRP (whose composite bandwidth-plus-delay metric it kept and refined) and stayed proprietary for two decades until Cisco published it as informational RFC 7868 in 2016. Its heart is the Diffusing Update Algorithm from J.J. Garcia-Luna-Aceves: for each destination, a router tracks feasible successors - neighbors mathematically proven loop-free - so when the best path dies, the backup is promoted without recomputation or flooding. That is why the classic praise is 'fast convergence'. The trade: superb inside Cisco shops, historically a lock-in lever, and still the exam counterweight to OSPF's open link-state model.
EIGRP is Cisco's distance-vector protocol with features borrowed from link-state designs, converging quickly by keeping precomputed backup routes it can switch to without recalculating. It was proprietary for most of its life and later published as an informational specification.
The practical consideration is that publication is not the same as multi-vendor support. Real interoperability remains limited, so choosing EIGRP is largely choosing a single-vendor network, which is a legitimate decision made deliberately and a trap made accidentally. OSPF is the standards-based alternative with genuine multi-vendor implementation, and the comparison is the same one DECnet lost: an integrated stack against an open one.
Also known as: eigrp, igrp, dual algorithm