< Free Open Study >

Syntax Description:

• ip-address— Neighbor’s IP address.

• peer-group-name— Name of the peer group. See section 8-19.

• seconds— 0 to 600.

Defaults: IBGP 5 seconds. EBGP 30 seconds.

Purpose: To set the minimum interval between the sending of Border Gateway Protocol (BGP) routing updates. To restore the default setting, use the no form of this command. When a route that is being advertised by BGP changes, BGP sends either an UPDATE or WITHDRAWN message. If an advertised route is flapping, usually caused when an interface is unstable, a flood of UPDATE and WITHDRAWN messages occurs. One method to control the flooding of BGP messages is to set a minimum advertisement interval. With the default value of 30 seconds for EBGP neighbors, BGP routing updates are sent only every 30 seconds, even if a route is flapping many times during this 30-second interval. BGP dampening can also be used to control the effects of flapping routes (see sections 3-7, 3-8, and 3-9).

Cisco IOS Software Release: 10.0. Peer group support was added in Release 11.0.

Configuration Example 1: Default Advertisement Interval

Figure 8-2 illustrates the default advertisement interval for IBGP and EBGP connections. The default advertisement interval is automatically set when the initial neighbor relationship is established.

Figure 8-2. Default BGP Advertisement Intervals for IBGP and EBGP

Router A

router bgp 1

 neighbor 10.1.1.2 remote-as 1

___________________________________________________________________________

Router B

router bgp 1

 neighbor 10.1.1.1 remote-as 1

 neighbor 10.2.1.2 remote-as 2

___________________________________________________________________________

Router C

router bgp 2

 neighbor 10.2.1.1 remote-as 1

Verification

The default advertisement value can be verified by examining the BGP neighbor information. Using the show ip bgp neighbors command on Router B, you can see the default advertisement interval for both the IBGP and EBGP neighbors, as shown in the following output:

RtrB#show ip bgp neighbors

BGP neighbor is 10.1.1.1,  remote AS 1, internal link

 Index 0, Offset 0, Mask 0x0

  BGP version 4, remote router ID 10.1.1.1

  BGP state = Established, table version = 2, up for 00:10:19

  Last read 00:00:20, hold time is 180, keepalive interval is 60 seconds

  Minimum time between advertisement runs is 5 seconds

  Received 331 messages, 0 notifications, 0 in queue

  Sent 331 messages, 0 notifications, 0 in queue

  Connections established 2; dropped 1

Connection state is ESTAB, I/O status: 1, unread input bytes: 0

Local host: 10.1.1.2, Local port: 179

Foreign host: 10.1.1.1, Foreign port: 11013



BGP neighbor is 10.2.1.2,  remote AS 2, external link

 Index 0, Offset 0, Mask 0x0

  BGP version 4, remote router ID 10.2.1.2

  BGP state = Established, table version = 2, up for 00:10:19

  Last read 00:00:15, hold time is 180, keepalive interval is 60 seconds

  Minimum time between advertisement runs is 30 seconds

  Received 229 messages, 0 notifications, 0 in queue

  Sent 229 messages, 0 notifications, 0 in queue

  Connections established 2; dropped 1

Connection state is ESTAB, I/O status: 1, unread input bytes: 0

Local host: 10.1.1.2, Local port: 179

Foreign host: 10.2.1.2, Foreign port: 11013

Configuration Example 2: Modifying the Advertisement Interval

In this example, we will change the advertisement interval on Router B for the IBGP neighbor to 15 seconds and for the EBGP neighbor to 45 seconds. The advertisement intervals on Routers A and C will remain set to the default values, as shown in Figure 8-3.

Figure 8-3. Configuring BGP Advertisement Intervals for IBGP and EBGP

Router A

router bgp 1

 neighbor 10.1.1.2 remote-as 1

___________________________________________________________________________

Router B

router bgp 1

 neighbor 10.1.1.1 remote-as 1

 neighbor 10.2.1.2 remote-as 2

 neighbor 10.1.1.1 advertisement-interval 15

 neighbor 10.2.1.2 advertisement-interval 45

___________________________________________________________________________

Router C

router bgp 2

 neighbor 10.2.1.1 remote-as 1

Verification

The preceding configuration of the advertisement intervals on Router B can be verified by using the show ip bgp neighbors command:

RtrB#show ip bgp neighbors

BGP neighbor is 10.1.1.1,  remote AS 1, internal link

 Index 0, Offset 0, Mask 0x0

  BGP version 4, remote router ID 10.1.1.1

  BGP state = Established, table version = 2, up for 00:10:19

  Last read 00:00:20, hold time is 180, keepalive interval is 60 seconds

  Minimum time between advertisement runs is 15 seconds

  Received 331 messages, 0 notifications, 0 in queue

  Sent 331 messages, 0 notifications, 0 in queue

  Connections established 2; dropped 1

Connection state is ESTAB, I/O status: 1, unread input bytes: 0

Local host: 10.1.1.2, Local port: 179

Foreign host: 10.1.1.1, Foreign port: 11013



BGP neighbor is 10.2.1.2,  remote AS 2, external link

 Index 0, Offset 0, Mask 0x0

  BGP version 4, remote router ID 10.2.1.2

  BGP state = Established, table version = 2, up for 00:10:19

  Last read 00:00:15, hold time is 180, keepalive interval is 60 seconds

  Minimum time between advertisement runs is 45 seconds

  Received 229 messages, 0 notifications, 0 in queue

  Sent 229 messages, 0 notifications, 0 in queue

  Connections established 2; dropped 1

Connection state is ESTAB, I/O status: 1, unread input bytes: 0

Local host: 10.1.1.2, Local port: 179

Foreign host: 10.2.1.2, Foreign port: 11013

Troubleshooting

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.

2. Verify that you have used the correct IP address for the neighbor or the correct name for the peer group.

3. Verify the default or configured advertisement interval using the show ip bgp neighbors command.

< Free Open Study >