Discovering and Maintaining Routes in EIGRP
EIGRP uses hello packets to discover new neighboring routes, and after it finds a neighbor, the Cisco routers advertise all IP network entries.
Figure 5-1. Two-Router EIGRP Network
To start EIGRP on a Cisco router, you must first enable EIGRP with the command router eigrp autonomous system while in global configuration mode.
For routers sharing the same IP domain, the AS needs to be the same. Example 5-1 displays the configuration of EIGRP on R1.