6.2 EIGRP Technology
6.2.2 Neighbor discovery and recovery
Unlike virtually every other distance-vector routing protocol, EIGRP does not rely exclusively and rigidly on the use of timers for maintaining its routing table. Instead, the basis for maintaining routing tables is a periodic communication between EIGRP routers. They use this process to:
  • Dynamically learn of new routers that join their network
  • Identify routers that become either unreachable or inoperable
  • Rediscover routers that had previously been unreachable
Lab Activity
  In this lab, you will learn how to enable EIGRP routing protocol with backup routes.

The basic neighbor discovery/recovery process consists of periodically transmitting a small hello packet to neighbors. The hello packet establishes the relationship between immediate neighbors (known as an adjacency). This relationship is used to exchange routing metrics supported and other information. -

An EIGRP router can safely assume that, as long as it is receiving hello packets from known neighbors, those neighbors (and their routes) remain viable. If an EIGRP router ceases to receive such greetings from a neighbor, however, it can assume that something is amiss. That router will enter the DUAL process for those routes. These processes are examined in more detail in the section titled "Hello Packets."