What are the default EIGRP hello and hold timers, and how does the hold time really work?
Show the answer
Say this first
Hello every 5 seconds and hold time 15 seconds on LAN and point-to-point links. On multipoint NBMA interfaces at T1 speed or slower, hello every 60 seconds and hold time 180 seconds. The hold time is carried in my hellos: it tells my neighbor how long to wait for me. Changing the hello interval does not change the hold time, so I always change both.
Go deeper
Reading it live
R1# show ip eigrp neighbors
EIGRP-IPv4 Neighbors for AS(100)
H Address Interface Hold Uptime SRTT RTO Q Seq
(sec) (ms) Cnt Num
0 10.0.12.2 Gi0/0/0 13 01:02:33 1 100 0 27The Hold column counts down from 15 and jumps back up each time a hello arrives, so values from about 10 to 14 are normal. If it keeps falling toward 0, hellos are being lost.
Changing them
Classic mode, per interface:
interface GigabitEthernet0/0/0
ip hello-interval eigrp 100 2
ip hold-time eigrp 100 6Named mode, under the af-interface:
router eigrp CAMPUS
address-family ipv4 unicast autonomous-system 100
af-interface GigabitEthernet0/0/0
hello-interval 2
hold-time 6For fast failure detection I prefer BFD over aggressive hellos: bfd all-interfaces under classic
router eigrp, or bfd under the af-interface in named mode. BFD detects a dead path in well under a
second without loading the EIGRP process.
They will ask next
Do the hold times have to match between neighbors?
No. R1 might wait 15 seconds for R2 while R2 waits 30 seconds for R1. Each side uses the value the other side advertised.
What happens to routes when the hold time expires?
The neighbor is declared down and every route learned from it is removed. Where a feasible successor exists the router switches at once; otherwise it goes active and queries for those prefixes.
Traps
- Changing only the hello interval and assuming the hold time scales with it like OSPF's dead interval.