3-17 bgp router-id ip-address

3-17 bgp router-id ip-address

Syntax Description:

• ip-address ” IP address to use for the BGP router ID.

Purpose: To explicitly set the BGP router ID. BGP normally uses the highest IP address assigned to an interface as the router ID. If loopback interfaces are used, the BGP router ID is the highest address assigned to a loopback interface, regardless of the IP addresses assigned to any physical interface.

Cisco IOS Software Release: 10.0

Configuration Example: BGP Router IDs

The scenario in Figure 3-12 is used to demonstrate the three possibilities for determining a BGP router ID. Initially, configure Router B without using loopback interfaces.

Figure 3-12. Scenario Used to Demonstrate BGP Router IDs

 Router A  router bgp 1   neighbor 10.1.1.2 remote-as 2   ___________________________________________________________________________  Router B  interface ethernet 0   ip address 150.150.1.1 255.255.255.0   !   interface serial 0   ip address 10.1.1.2   !   router bgp 2   neighbor 10.1.1.1 remote-as 1  

There are two physical interfaces on Router B ” Ethernet 0 and Serial 0. The BGP router ID is the highest assigned IP address, 150.150.1.1:

 rtrB#  show ip bgp summuary   BGP router identifier 150.150.1.1, local AS number 2  BGP table version is 1, main routing table version 1 Neighbor        V    AS MsgRcvd MsgSent   TblVer  InQ OutQ Up/Down  State/PfxRcd 10.1.1.1        4     2       0       0        0    0    0 never    Idle 

Now add a loopback interface on Router B:

 Router B  interface loopback 0   ip add 1.1.1.1 255.255.255.255  

The BGP router ID should now be 1.1.1.1 even though this is not the highest IP address assigned to Router B. The loopback address takes precedence over physical addresses when it comes to assigning the router ID:

 rtrB#  show ip bgp summary   BGP router identifier 1.1.1.1, local AS number 2  BGP table version is 1, main routing table version 1 Neighbor        V    AS MsgRcvd MsgSent   TblVer  InQ OutQ Up/Down  State/PfxRcd 10.1.1.1        4     2       1       2        0    0    0 never    OpenConfirm 

Now override the BGP route ID using the command bgp router-id ip-address:

 Router B  router bgp 2   bgp router-id 5.5.5.5   neighbor 10.1.1.1 remote-as 1  

Verification

Verify that the BGP router ID has been changed to 5.5.5.5:

 rtrB#  show ip bgp summuary   BGP router identifier 5.5.5.5, local AS number 2  BGP table version is 1, main routing table version 1 Neighbor        V    AS MsgRcvd MsgSent   TblVer  InQ OutQ Up/Down  State/PfxRcd 10.1.1.1        4     2       7       6        0    0    0 00:00:18 Active 

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 BGP router ID should be changed if you are using the bgp router-id ip-address command. Verify using the show ip bgp summary command