Enhanced Interior Gateway Routing Protocol (EIGRP) is an advanced distance-vector routing protocol that is used on a computer network for automating routing decisions and configuration. Developed by Cisco Systems in the early 1990s, EIGRP was designed to offer significant improvements over its predecessors, such as Interior Gateway Routing Protocol (IGRP). Unlike traditional distance-vector protocols, EIGRP incorporates features typically found in link-state protocols, making it a hybrid routing protocol. EIGRP was proprietary to Cisco systems but has been partially opened up to the public in 2013 through an informational RFC 7868.
EIGRP is known for its efficiency and scalability, offering fast convergence times and low network traffic overhead.
Features of EIGRP:
- Diffusing Update Algorithm (DUAL): EIGRP uses the DUAL algorithm to guarantee loop-free and reliable routing decisions. DUAL allows for rapid convergence across large and complex networks by computing the shortest path and a feasible successor as a backup route, ensuring continuous data forwarding even if the primary route fails.
- Protocol-Independent Operation: EIGRP can support multiple network layer protocols, such as IPv4, IPv6, and IPX, because it is protocol-independent. This is achieved through the use of protocol-dependent modules.
- Advanced Metric Calculation: EIGRP uses a composite metric based on bandwidth, delay, load, and reliability of the source route. This composite metric provides a more nuanced route selection process compared to simpler metrics like hop count.
- Partial and Bounded Updates: Unlike other distance-vector protocols that periodically send complete routing tables, EIGRP sends partial updates only when there is a change in the network topology. This reduces unnecessary data traffic and optimizes bandwidth.
- Neighbor Discovery and Recovery: EIGRP routers discover each other through Hello packets. This process is used to establish and maintain neighbor relationships, ensuring that routers can efficiently recover from changes in the network topology.
Applications and Deployment:
EIGRP is commonly used in enterprise networks where there is a predominance of Cisco equipment. It is particularly favored for its fast convergence, scalability, and flexibility in handling different network protocols. EIGRP’s ability to efficiently manage bandwidth and support for variable-length subnet masking (VLSM) and route summarization makes it a versatile choice for complex network architectures.
Transition to Open Standard:
Although EIGRP was a Cisco proprietary protocol, in 2013, Cisco released the basic EIGRP as an open standard to help promote its wider adoption and interoperability with non-Cisco devices. This move allowed other vendors to implement EIGRP on their devices, potentially increasing the protocol’s usage in multi-vendor environments.