Enhanced Interior Gateway Routing Protocol (EIGRP) is a dynamic routing network layer Protocol which works on the protocol number 88. EIGRP supports classless routing, VLSM, route summarization, load balacing and many other useful features. It is a Cisco proprietary protocol, so all routers in a network that is running EIGRP must be Cisco routers but now EIGRP is moving towards becoming an open standard protocol.
Types of packets in EIGRP.
EIGRP sends out five different types of packets—
hello, update, query, reply, and acknowledge (ACK)—that are used to establish the initial adjacency between neighbors and to keep the topology and routing current tables.
- Hello—Hello packets are used for neighbor discovery. They are sent as multicasts and do not require an acknowledgment. (They carry an acknowledgment number of 0.)
- Update—Update packets contain route change information. An update is sent to communicate the routes that a particular router has used to converge; an update is sent only to affected routers. These updates are sent as multicasts when a new route is discovered, and when convergence is completed (when the route becomes passive). To synchronize topology tables, updates are sent as unicasts to neighbors during their EIGRP startup sequence. Updates are sent reliably.
- Query—When a router is performing route computation and does not have a feasible successor, it sends a query packet to its neighbors, asking if they have a successor to the destination. Queries are normally multicast but can be retransmitted as unicast packets in certain cases; they are sent reliably.
- Reply—A reply packet is sent in response to a query packet. Replies are unicast to the originator of the query and are sent reliably.
- ACK—The ACK is used to acknowledge updates, queries, and replies. ACK packets are unicast hello packets and contain a nonzero acknowledgment number. (Note that hello and ACK packets do not require acknowledgment.
Basic EIGRP configuration:-
GfGB(config)#router eigrp 1 GfGB(config-router)#network 10.10.10.0 GfGB(config-router)#network 10.10.11.0 GfGB(config-router)#network 172.16.10.0 GfGB(config-router)#network 172.16.10.4 GfGDelhi(config)#router eigrp 1 GfGDelhi(config-router)#network 172.16.10.4 GfGDelhi(config-router)#network 10.10.50.0 GfGDelhi(config-router)#network 10.10.40.0 GfGN(config)#router eigrp 1 GfGN(config-router)#network 172.16.10.0 GfGN(config-router)#network 10.10.20.0 GfGN(config-router)#network 10.10.30.0 #sh ip route Note:- its show all routing table . HOW many types of routing tables in EIGRP? Each EIGRP router uses three to store routing information: Neighbor table – stores information about EIGRP neighbors. Before exchanging routes, routers need to establish a neighbor relationship. Information such as the IP address of the neighbor, the local interface on which the Hellos were received, the holddown timer, and Smooth round-trip time are kept in this table. #sh ip eigrp neighbor Topology table – stores routing information learned from neighbor routing tables. This table stores every EIGRP route inside the autonomous system. The topology table also holds the metrics for each of the listed EIGRP routes, the feasible successor and the successors. #sh ip eigrp topology Routing table – stores only the best routes to reach a remote network. #sh ip route eigrp Redistribution To and From Other Protocols Redistribution between EIGRP and other protocols - RIP and OSPF, for example - works in the same way as all redistribution. It is always best to use the default metric when redistributing between protocols. You should be aware of the following two issues when redistributing between EIGRP and other protocols: 1.Routes redistributed into EIGRP are not always summarized - see the "Summarization" section for an explanation. 2. External EIGRP routes have an administrative distance of 170.