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Syntax Description:

• ip-address— Neighbor’s IP address.

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

• version-number— 2, 3, or 4.

Purpose: Currently, the default BGP version number is 4. Cisco’s implementation of BGP begins using version 4 and negotiates down to version 2. If you do not want to form a neighbor connection with a router that is not running version 4, you can lock down the version number using this command.

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

Configuration Example: Locking Down the Neighbor BGP Version

The following configuration locks down the version number with one neighbor to 4 and leaves the version number in auto-negotiate for the other neighbors:

Router A

router bgp 1

 neighbor 10.1.1.2 remote-as 2

 neighbor 10.1.1.2 version 4

 neighbor 10.2.1.2 remote-as 3

 neighbor 10.3.1.2 remote-as 4

Verification

Verify the version number by using the show ip bgp neighbors command:

rtrA#show ip bgp neighbors

BGP neighbor is 10.1.1.2,  remote AS 2, external link

 Index 1, Offset 0, Mask 0x2

  BGP version 4, remote router ID 10.1.1.2

  BGP state = Established, table version = 7, up for 00:53:07

  Last read 00:00:08, hold time is 180, keepalive interval is 60 seconds

  Minimum time between advertisement runs is 30 seconds

  Received 375 messages, 0 notifications, 0 in queue

  Sent 343 messages, 0 notifications, 0 in queue

  Prefix advertised 0, suppressed 0, withdrawn 0

 Connections established 20; dropped 19

  Last reset 00:53:28, due to User reset

  6 accepted prefixes consume 192 bytes, maximum limit 8

  Threshold for warning message 75%

  0 history paths consume 0 bytes

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

Local host: 10.1.1.1, Local port: 11015

Foreign host: 10.1.1.2, Foreign port: 179

Troubleshooting

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, check for a version number mismatch between neighbors.

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