EIGRP works perfectly fine with its stock settings. However, there comes a time when settings need to get tweaked for various reason. EIGRP by default sends Hello packets every 5 seconds and has a Hold timer of 15 seconds. This means, by default, a router will send a hello packet every 5 seconds, and wait 15 seconds to receive a hello packet from its neighbors before it drops that route.
Hello packet set by each neighbor every 5 seconds:
If a link was to drop or if a neighbor does not receive a hello packet from any a neighbor, that route will be held for 15 seconds by default before its taken out of the routing table:
Here is an example with Fa0/1.60 interface going down:
Looking at the timer in Router1:
Before Router3’s Fa 0/1.60 interfaces goes down:
After Router3’s Fa 0/0.60 interface goes down:
Now lets say, those timers are too slow and you need something that can converge quicker. You can configure the hello/hold timers at the interface level to adjust how quick or slow you need these packets to be sent out.
Enter configuration commands, one per line. End with CNTL/Z.
Router1(config)#int gig 0/0.60
Router1(config-subif)#ip hello-interval eigrp ?
<1-65535> AS number
Router1(config-subif)#ip hello-interval eigrp 1 ?
<1-65535> Seconds between hello transmissions
Router1(config-subif)#ip hello-interval eigrp 1 2
Router1(config-subif)#ip hold-time eigrp ?
<1-65535> AS number
Router1(config-subif)#ip hold-time eigrp 1 ?
<1-65535> Seconds before neighbor is considered down
Router1(config-subif)#ip hold-time eigrp 1 8
Now if you check the frequency of hello packets sent and the hold-timer countdown, you will see the change in effect. To check this you will need to go to Router 2 or 3 to see the change of the hold-timer and the frequency at which you are receiving the hello packets from Router 1:
One more way to verify that the config was changed is to run the EIGRP interface detail command:
Router1#show ip eigrp 1 interface detail gig 0/0.60