BGP Timers

When a neighbor crashes or a link dies silently, BGP doesn't receive a warning packet.
By default, that silence lasts up to three minutes before BGP tears down the session.

That's three minutes of sending production traffic straight into a black hole.

Two timers manage this detection process:

• Keepalive Interval (Default: 60s): How often the router sends a small "I'm still here" packet.

• Hold Time (Default: 180s): How long a router waits without hearing anything before declaring the neighbor dead and dropping its routes. Every received keepalive resets this timer back to 180 seconds.

Figure 1 – Default BGP timers: a keepalive every 60 seconds, a hold time of 180 seconds

Here is your topology: R1 in AS 65001 connected to R2 in AS 65002.

Figure 2 – The lab topology: R1 in AS 65001, R2 in AS 65002

Nothing to rebuild here, this is the exact session you brought up in the previous lesson, and the eBGP peering is still Established.

Go straight to the timers.

Read the Timers in Use

The session is up. Now read the timers this session is actually using:

R1# show bgp ipv4 unicast neighbors 10.0.12.2
BGP neighbor is 10.0.12.2,  remote AS 65002, external link
  BGP version 4, remote router ID 192.168.2.1
  BGP state = Established, up for 00:02:07
  Last read 00:00:16, last write 00:00:17, hold time is 180, keepalive interval is 60 seconds
<output omitted>

Both routers are running the defaults: a keepalive every 60 seconds and a hold time of 180 seconds.
Time to speed up the detection.

Change the timers on R1 only to a 10-second keepalive and a 40-second hold time (neighbor 10.0.12.2 timers 10 40). Leave R2 with its defaults.