13-1 timers bgp keepalive holdtime

13-1 timers bgp keepalive holdtime

Syntax Description:

• keepalive ” 1 to 4294967295 seconds.

• holdtime ” 1 to 4294967295 seconds.

Purpose: To globally set the keepalive and holdtime values for all neighbors. Keepalive and holdtime are common among IP routing protocols. The keepalive time indicates how often a router sends a keepalive message to a neighbor to inform the neighbor that the router is still alive and well. The holdtime is used as a deathwatch. If a keepalive message is not received within the holdtime, the neighbor is declared dead, and the session is terminated . The default value for the keepalive time is 60 seconds. The holdtime is three times the keepalive time, or 180 seconds. Generally, these values do not need to be changed. If you do change them, it is a good rule to make the holdtime equal to three times whatever keepalive value you use. Of course, the holdtime should always be greater than the keepalive time. When two BGP speakers establish a connection, the smaller of the advertised keepalive and holdtime values will be used. For example, if one neighbor advertises a keepalive value of 70 and a holdtime of 210 and the other neighbor advertises a keepalive value of 72 and a holdtime of 205, the keepalive value will be 70 and the holdtime will be 205. If the timer values are set using the neighbor timers command (see section 8-31), these values will override the global values only for that neighbor.

IOS Release: 10.0

Configuration Example: BGP Timers

In this example, we will examine the result of various settings of keepalive and holdtimers. Figure 13-1 illustrates the basic setup for these examples.

Figure 13-1. Network Setup for BGP Timer Examples

 Router A  router bgp 1   neighbor 172.17.1.2 remote-as 2   ___________________________________________________________________________  Router B  router bgp 2   neighbor 172.17.1.1 remote-as 1  

The default values for the timers can be examined using the show ip bgp neighbors command:

 rtrA#  show ip bgp neighbors  BGP neighbor is 172.17.1.2,  remote AS 2, external link   BGP version 4, remote router ID 172.17.1.2   BGP state = Established, up for 00:01:50  Last read 00:00:50, hold time is 180, keepalive interval is 60 seconds  

Change the BGP timer values on Router A to 70 and 210:

 Router A  router bgp 1    timers bgp 70 210    neighbor 172.17.1.2 remote-as 2  

Clear the connection to force the timer values to take effect, and then inspect the new values:

 rtrA#  show ip bgp neighbors  BGP neighbor is 172.17.1.2,  remote AS 2, external link   BGP version 4, remote router ID 172.17.1.2   BGP state = Established, up for 00:00:14  Last read 00:00:14, hold time is 180, keepalive interval is 60 seconds  

The timer values did not change. Router B is advertising the defaults of 60 and 180. These values are smaller than the values configured on Router A, so the smaller values are used. Configure Router B with the same timer values as Router A:

 Router B  router bgp 2    timers bgp 70 210    neighbor 172.17.1.1 remote-as 1  

Clear the connection and view the timer values:

 rtrA#  show ip bgp neighbors  BGP neighbor is 172.17.1.2,  remote AS 2, external link   BGP version 4, remote router ID 172.17.1.2   BGP state = Established, up for 00:01:04  Last read 00:01:03, hold time is 210, keepalive interval is 70 seconds  

Finally, configure the timers and Routers A and B using the neighbor timers command, using values larger than 70 and 210.

 Router A  router bgp 1    timers bgp 70 210     neighbor 172.17.1.2 timers 80 240    neighbor 172.17.1.2 remote-as 2   ___________________________________________________________________________  Router B  router bgp 2    timers bgp 70 210     neighbor 172.17.1.1 timers 80 240    neighbor 172.17.1.1 remote-as 1  

Clear the connection and view the timers:

 rtrA#  show ip bgp neighbors  BGP neighbor is 172.17.1.2,  remote AS 2, external link   BGP version 4, remote router ID 172.17.1.2   BGP state = Established, up for 00:01:04  Last read 00:01:04, hold time is 240, keepalive interval is 80 seconds  Configured hold time is 240, keepalive interval is 80 seconds 

The timer values used with the neighbor command override the values used with the timers bgp command, regardless of their value.

Verification

Use the show ip bgp neighbors command to verify timer values.

Troubleshooting

Step 1. Verify that the BGP neighbors are in the Established state using the show ip bgp neighbors command.

If the neighbor relationship is not in the Established state, see section 8-23.

Step 2. The holdtime should be three times the keepalive value. If neighbors are using different keepalive and holdtime values, the smaller value is used.

Step 3. Timer values set using the neighbor command override values set using the timers bgp command, but only for that neighbor.