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Syntax Description:

• peer-group-name— Name of the peer group to create or the name of the peer group to which the neighbor will be added.

• ip-address— IP address of the neighbor to be placed in the peer group with the name peer-group-name.

Purpose: Use the neighbor peer-group-name peer-group command to create a BGP peer group. The neighbor ip-address peer-group peer-group-name command adds a neighbor to an existing peer group. Assume that a router has multiple BGP neighbors and that it has identical update policies with those neighbors. The update policy could be configured for each neighbor. In this case, BGP would calculate a separate update for each neighbor even though the updates are identical. If the update policy is applied to a peer group and the neighbors are members of the peer group, the update is calculated once and then sent to all the neighbors in the peer group.

Cisco IOS Software Release: 11.0

Configuration Example: Creating Peer Groups

Router A in Figure 8-19 has two IBGP peers and two EBGP peers. Assume that Router A has the same update policy for the IBGP peers and the EBGP peers. The IBGP peers could be configured in one peer group and the EBGP peers in another. The first configuration is without using peer groups. The second configuration uses peer groups so that you can compare the syntax.

Figure 8-19. BGP Peer Groups

Router A (without using peer groups)

router bgp 1

 neighbor 10.1.1.2 remote-as 1

 neighbor 10.1.1.2 distribute-list 1 out

 neighbor 10.1.2.2 remote-as 1

 neighbor 10.1.2.2 distribute-list 1 out

 neighbor 172.16.1.2 remote-as 2

 neighbor 172.16.1.2 distribute-list 2 out

 neighbor 172.16.2.2 remote-as 3

 neighbor 172.16.2.2 distribute-list 2 out

___________________________________________________________________________

Router A (Using peer groups)

router bgp 1

 neighbor local peer-group

 neighbor local remote-as 1

 neighbor 10.1.1.2 peer-group local

 neighbor 10.1.2.2 peer-group local

 neighbor local distribute-list 1 out

 neighbor 10.1.2.2 peer-group local

 neighbor external peer-group

 neighbor 172.16.1.2 remote-as 2

 neighbor 172.16.2.2 remote-as 3

 neighbor 172.16.1.2 peer-group external

 neighbor 172.16.2.2 peer-group external

 neighbor external distribute-list 2 out

The sequence of events in configuring peer groups is as follows:

Step 1. Create the peer group.

Step 2. Assign neighbors to the peer group.

Step 3. If all members of a peer group are in the same AS, assign the peer group to the AS.

Step 4. Assign update policies to the peer group.

The commands neighbor local peer-group and neighbor external peer-group create the peer groups local and external. Routers B and C are in the same AS, so we can place the peer group local in AS 1 using neighbor local remote-as 1. Routers D and E are in different autonomous systems, so the peer group external cannot be put in an AS. In this case, the individual neighbors are placed in their respective autonomous systems.

The update policy for neighbors B and C uses distribute list 1 out. Applying distribute list to the peer group applies the policy to each member of the peer group. The same is true for the external peer group. Incoming policies can also be assigned to a peer group. For example, we can apply an incoming filter list to peer group local:

neighbor local filter-list 1 in

If another incoming policy is applied to a specific neighbor, this policy overrides the peer group policy:

neighbor local filter-list 1 in

neighbor 10.1.1.2 filter-list 2 in

Filter list 2 is applied to neighbor 10.1.1.2 instead of filter list 1. You can override only incoming policies.

Verification

Verify that a neighbor is a member of the peer group. For example, check the status of the relationship between Routers A and B:

rtrA#show ip bgp neighbors

BGP neighbor is 10.1.1.2,  remote AS 1, internal link

 Index 1, Offset 0, Mask 0x2

  local peer-group member

  BGP version 4, remote router ID 10.1.1.2

  BGP state = Established, table version = 41, up for 00:00:08

  Last read 00:00:07, hold time is 180, keepalive interval is 60 seconds

  Minimum time between advertisement runs is 5 seconds

  Received 14126 messages, 0 notifications, 0 in queue

  Sent 14138 messages, 0 notifications, 0 in queue

  Prefix advertised 15, suppressed 0, withdrawn 12

  Outgoing update network filter list is 1

  Connections established 5; dropped 3

  Last reset 00:00:17, due to Member added to peergroup

  2 accepted prefixes consume 64 bytes

  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: 11010

Foreign host: 10.1.1.2, Foreign port: 179

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. If the neighbors are in the Established state, check the following:

   • The spelling of the peer group name in the neighbor peer-group-name peer-group command.

   • The spelling of the peer group name in the neighbor ip-address peer-group peer-group-name command.

   • The IP address of the neighbor in the neighbor ip-address peer-group peer-group-name command.

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