EIGRP - Hello interval and Hold time
EIGRP uses two timers to establish and maintain neighbor relationships with neighboring routers. These are the Hello Interval and the Hold time.
The Hello interval tells the router how often to send hello packets to its neighbors.
The Hold time tells the router how long to wait without receiving a hello packet before it drops the neighbor adjacency and considers the EIGRP neighbor failed.
The hold time is reset every time it receives any type of packet from an EIGRP neighbor, not just hello packets.
By default, the values of these timers follow these guidelines:
- Hello Interval:
- On most networks, such as Ethernet networks, the default hello interval is 5 seconds.
- On multipoint non-broadcast networks, such as frame-relay, the default hello interval is 60 seconds.
- Hold Time:
- The default hold time, which is the period a router considers a neighbor as alive without receiving a hello packet, is typically three times the hello interval.
- This results in a default hold time of 15 seconds on most networks and 180 seconds on multipoint non-broadcast networks.
The rule of thumb to use when configuring the hold time and the hello interval is that typically, the hold time should be three times the hello interval. The default values adhere to this rule of thumb, but if you change the value of one timer, the other does not automatically change accordingly.
Note that the Hold time is often referred to as the holddown timer, or the hold down timer, or the hold-down timer. These terms, although often used in the context of EIGRP, are strictly incorrect. These terms are associated with RIP and BGP and should be carefully used.
Links:
https://forum.networklessons.com/t/eigrp-hold-time-and-hello-packets/1060/11?u=lagapidis
https://networklessons.com/eigrp/eigrp-hold-time-hello-packets