EIGRP

Enhanced Interior Gateway Routing Protocol (EIGRP) is an advanced that is used on a computer network for automating routing decisions and configuration. The protocol was designed by Cisco Systems as a proprietary protocol, available only on Cisco routers. Partial functionality of EIGRP was converted to an open standard in 2013 and was published with informational status as RFC 7868 in 2016.

EIGRP is used on a router to share routes with other routers within the same autonomous system. Unlike other well known routing protocols, such as , EIGRP only sends incremental updates, reducing the workload on the router and the amount of data that needs to be transmitted.

The Enhanced Interior Gateway Routing Protocol replaced the (IGRP) in 1993. One of the major reasons for this was the change to classless IPv4 addresses in the , which IGRP could not support.

Almost all routers contain a routing table that contains rules by which traffic is forwarded in a network. If the router does not contain a valid path to the destination, the traffic is discarded. EIGRP is a dynamic routing protocol by which routers automatically share route information. This eases the workload on a network administrator who does not have to configure changes to the routing table manually.

In addition to the routing table, EIGRP uses the following tables to store information:

Information in the topology table may be inserted into the router's routing table and can then be used to forward traffic. If the network changes, for example, a physical link fails or is disconnected, the path will become unavailable. EIGRP is designed to detect these changes and will attempt to find a new path to the destination. The old path that is no longer available is removed from the routing table. Unlike most distance vector routing protocols, EIGRP does not transmit all the data in the router's routing table when a change is made but will only transmit the changes that have been made since the routing table was last updated. EIGRP does not send its routing table periodically, but will only send routing table data when an actual change has occurred. This behavior is more inline with , thus EIGRP is mostly considered a hybrid protocol.

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