EIGRP Neighbor Discovery

EIGRP relies on neighbor relationships to reliably propagate routing table changes throughout the network; two routers become neighbors when they see each other's hello packets on a common network.

Hello Packet

Hello packets are small packets that send between two neighbor to tell the other end that his neighbor is still alive.EIGRP sends hello packets every 5 seconds on high bandwidth links and every 60 seconds on low bandwidth multipoint links.

Hello interval

The rate at which EIGRP sends hello packets is called the hello interval
and you can adjust it per interface with the ip hello-interval eigrp command.

Hold Time

The hold time is the amount of time that a router will consider a neighbor alive without receiving a hello packet. The hold time is typically three times the hello interval, by default, 15 seconds and 180 seconds. You can adjust the hold time with the ip hold-time eigrp command.

Simulation

EIGRP simulation focus on neighbor discovery part of eigrp. Click on the routers to see the neighbor table.
For each router you can disable or enable one of the interfaces to see how the neighbor table is updated. You can also change the hold time and hello interval to see how eigrp animation effected from these parameters.