Hello Intervals and Hold Times – EIGRP for IPv4
EIGRP uses the Hello protocol to establish and maintain the connection to its neighbor. Hello protocol also monitors the established connection. It is sending Hello packet periodically to its neighbor. The rate at which EIGRP sends Hello Packet known is as the hello interval.
The Hold timer is working just like the dead interval of OSPF. It is the maximum wait time that the router should wait to receive the next Hello packet before declaring that neighbor as inaccessible or dead.
Both Hello intervals and Hold times are configurable values on a per-interface basis. The range of Hello interval “second” value is range from “1 to 65535”. The command syntax to configure a Hello interval is:
Router(config-if)# ip hello-interval eigrp <as-number> <seconds>
It is important to change the Hello interval equal to the Hold time value, or greater than, the Hello interval. if not, then neighbor adjacency will go down after the Hold time expires and before the next Hello interval. The range of Hello interval “second” value is also range from “1 to 65535”. To configure the Hold time value use the following command to configure:
Router(config-if)# ip hold-time eigrp <as-number> <seconds>
Figure 1 illustrates the EIGRP topology. We can configure the Hello interval and Hold timer for this topology. We know that the Hello Interval and Hold timer in EIGRP is a per-interface base configurable value, therefore, the Hello interval time and Hold time do not need to match for two routers to form an EIGRP adjacency and we can configure the different values for different interfaces on the above topology.
For faster link, we can configure less timing (in seconds) and for the slower link, we can configure larger timing (in seconds) to reduce the extra overhead on the network.
The default Hello Interval for 1.544 Mbps or slower link is 60 seconds and for T1 link and Ethernet link is 5 seconds. The default hold down timer for 1.544 Mbps or slower link is 180 seconds and for T1 link and Ethernet links are 15 seconds. The configuration of Hello Interval and Hold timer on the link between R1 and R2 is the following:
R1(config)# interface gigabitEthernet 0/0
R1(config-if)# ip hello-interval eigrp 100 80
R1(config-if)# ip hold-time eigrp 100 240
R2(config)# interface gigabitEthernet 0/0
R2(config-if)# ip hello-interval eigrp 100 80
R2(config-if)# ip hold-time eigrp 100 240
This configuration will set the hello interval to 80 seconds and hold timer to 240 seconds between R1 and R2 link. We can reset the values to default using the “no” form of the above commands.
Hello Intervals and Hold Times – EIGRP for IPv6
EIGRP for IPv6 also uses the same Hello protocol, which includes the hello interval and Holds times. The command to configure the Hello interval and Hold timers is similar commands for IPv4 with little difference. The commands syntax are the following:
Router(config-if)# ipv6 hello-interval eigrp <as-number> <seconds>
Router(config-if)# ipv6 hold-time eigrp <as-number> <seconds>