EIGRP

Cisco's Advanced Distance-Vector Protocol

Enhanced Interior Gateway Routing Protocol (EIGRP) is Cisco's advanced routing protocol, originally proprietary but partially standardized in RFC 7868 (2016). EIGRP combines the low overhead of distance-vector protocols with rapid convergence using the Diffusing Update Algorithm (DUAL), which guarantees loop-free paths at every instant during topology changes — a major advantage over RIPRouting Information Protocol. One of the oldest distance-vector routing protocols, using hop count (max 15) as its metric. Largely superseded by OSPF and EIGRP in enterprise networks due to slow convergence and limited scalability. and classic distance-vector protocols.

Composite Metric and DUAL

EIGRP's metric is a composite formula using bandwidth, delay, reliability, load, and MTU — though in practice, only bandwidth and delay are used by default. DUAL maintains a Feasibility Condition: a neighbor's route is a Feasible Successor (backup path) if its reported distance is less than the current best metric to the destination. When the primary path fails, EIGRP instantly promotes the Feasible Successor without recomputing, achieving sub-second convergence compared to OSPFOpen Shortest Path First. An interior gateway routing protocol that uses link-state advertisements and Dijkstra's algorithm to compute the shortest path within an autonomous system.'s SPF recalculation.

EIGRP vs. OSPF

EIGRP is simpler to configure than OSPFOpen Shortest Path First. An interior gateway routing protocol that uses link-state advertisements and Dijkstra's algorithm to compute the shortest path within an autonomous system. — no area design required, no DR/BDR election, and automatic summarization at classful boundaries (though best disabled). However, OSPF is a fully open standard, supported by all vendors, making it the preferred IGP in multi-vendor environments. EIGRP's Named Mode (introduced in IOS 15.x) unifies IPv4, IPv6Internet Protocol version 6. The successor to IPv4 using 128-bit addresses (e.g., 2001:0db8::1), providing a virtually unlimited address space of 3.4 x 10^38 addresses. Designed to solve IPv4 address exhaustion., and address-family configuration under a single process, simplifying management in dual-stack networks. Ping Test