Most people have learned that the EIGRP hold timer is renewed when it receives a hello packet from a neighbor. This is correct however the hello packet is not the only packet that renewes it…all EIGRP packets do. In order to demonstrate this we’ll take a look at the following two routers:
First I will configure EIGRP on both routers, nothing special I just want to make sure we have a neighbor adjacency:
R1(config)#router eigrp 12
R1(config-router)#network 192.168.12.0
R2(config)#router eigrp 12
R2(config-router)#network 192.168.12.0
Now I will increase the hold time so it doesn’t drop the neighbor adjacency so quickly. I’ll set it to 1 hour:
R2(config-if)#ip hold-time eigrp 12 3600
When we take a look at R1 you’ll see that it uses 3600 seconds as the hold time for R2:
R1#show ip eigrp neighbors
IP-EIGRP neighbors for process 12
H Address Interface Hold Uptime SRTT RTO Q Seq
(sec) (ms) Cnt Num
0 192.168.12.2 Fa0/0 3597 00:00:51 3 200 0 21
We have 3597 seconds and counting…now I will set the hello timer to a low value so that we can find out if other EIGRP packets will renew the hold time. I’ll set it to 5 minutes:
R2(config)#interface fastEthernet 0/0
R2(config-if)#ip hello-interval eigrp 12 300
R1 will now only receive a hello packet from R2 every 5 minutes. To show that different EIGRP packets will renew the hold time I will enable a debug on R1 so that we can see what kind of packets it receives from R2:
R1#debug eigrp packets
EIGRP Packets debugging is on
(UPDATE, REQUEST, QUERY, REPLY, HELLO, IPXSAP, PROBE, ACK, STUB, SIAQUERY, SIAREPLY)
Now I will create a new loopback interface on R2 and advertise it in EIGRP. This will cause some traffic between R1 and R2. Before I do this, let’s take a quick look at the current state of the hold time again:
look again at table:
R1#show ip eigrp neighbors
IP-EIGRP neighbors for process 12
H Address Interface Hold Uptime SRTT RTO Q Seq
(sec) (ms) Cnt Num
0 192.168.12.2 Fa0/0 3504 00:04:23 3 200 0 21
Right now we are down to 3504 seconds…let’s advertise that loopback interface in EIGRP: