What is EIGRP Protocol (Enhanced Interior Gateway Routing)?

EIGRP (Enhanced Interior Gateway Routing Protocol) is an improved version of the original IGRP protocol developed by Cisco Systems. Cisco-specific EIGRP routing technology combines the advantages and benefits of link-state protocols and distance vector protocols.

EIGRP maintains the same distance vector algorithm and original IGRP matrix information; however, considerations regarding convergence time and expansion capacity have been significantly improved. EIGRP and IGRP use different matrix calculations. EIGRP multiplies the IGRP matrix by a factor of 256.

EIGRP uses a 32-bit metric, and IGRP uses a 24-bit matrix. EIGRP information can be duplicated or divided into 256 for easy exchange with IGRP. The maximum number of skips of the IGRP is 255. The maximum number of hops in the EIGRP is 224. This is more than enough to support large networks.

EIGRP provides features such as VLSM support and route summaries unavailable in IGRP. In addition, it offers features in protocols such as OSPF, such as partial incremental updates and reduced convergence time. As with the IGRP protocol, it only broadcasts routing table information to neighboring routers.

EIGRP contains the following three tables:

  • Neighbors Table
  • Topology Table
  • Routing Table

Neighbor routers are discovered through a simple Hello protocol for neighboring routers for the same physical network. Hello uses the multicast address to change greeting packets.

Once neighboring routers have been discovered, it uses a reliable transport protocol to ensure that information and routing table updates are transmitted accurately and regularly. A router follows its connected paths and all common routes of neighboring routers.

Based on this information, it can select the most cost-effective route to a destination efficiently and quickly and make sure that the way is not part of a regular cycle, which is chosen as the main route, called the successor. By storing the routing information of neighboring routers, the network is redesigned more quickly in case of a connection error or other topology modification.

In this case, the routing information is moved using the transport protocol. The EIGRP transmission defines a reliable protocol for broadcasting, validating, and requesting that reception and routing information be distributed appropriately to all neighboring routers.

When changes occur in topologies, it uses DUAL (standard update algorithm) to provide fast convergence between routers and distributes its routing tables to neighboring routers in alternative ways.

   Related Articles

1. What is VLAN
2. What is RIP
3. OSPF Routing

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