EIGRP Neighbor Relationship or Discovery and Route Exchange
The process of neighbor relationship or discovery and route exchange between two EIGRP routers is as follows:
- First it send hellos to build a neighbor table.
- The other router sends back a hello and an update(routing information)
- First router acknowledges the update and sens its update
- The other router acknowledges it
Hello packets are use as keepalives between the routers. Additional route information is sent only if a route is lost or a new route is discovered.
A neighbor is removed from the routing table if no hello is received within three hello periods (called the hold time). The default hello/hold timers are as follows:
■ 5 seconds/15 seconds for multipoint circuits with bandwidth greater than T1 and for point-to-point media
■ 60 seconds/180 seconds for multipoint circuits with bandwidth less than or equal to T1
Useful commands
- debug ip eigrp
- debug ip eigrp.
- show ip eigrp neighbors.
- ip hello-interval eigrp autonomous-system-number second
- ip hold-time eigrp autonomous-system-number seconds
Glossary:
Neighbor:
Neighbors are directly attached routers that have a the following properties
- Matching AS number
- K values (the timers don’t have to agree).
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