The obvious use for the hold timer is to determine how long you will holdup a neighbor relationship without hearing any EIGRP hellos. Each time a router receives a hello packet from a neighbor, it resets the hold timer to the hold time contained in the hello packet and decrements it once for each second that passes.
Once the hold timer reaches zero, the neighbor is assumed dead. All paths through that neighbor are marked unusable (DUAL is run over these destinations to determine if the route needs to go active), and the neighbor is marked down.
But the hold timer is also used by the EIGRP's reliable transport mechanism as an outer bound on how long to wait for a neighbor to acknowledge the receipt of a packet. As mentioned in Appendix C, EIGRP will attempt to retransmit 16 times or until retransmission has been occurring for as long as the hold timer, whichever is longer.
So, in the network depicted in Figure 7-18, assume that Router D's hold timer is 240 seconds. (Ignore the Hello timer because these are separate timers).
Was this article helpful?