Basic Router ID in BGP

Hi all,

Having a router ID set is a good requirement for BGP not have this set the BGP process will select on for you the highest IP address of any loopback interface will be selected first and if none is found then the highest IP address of any physical interface.

R1
R1#sh ip bgp neighbors 
BGP neighbor is 10.1.1.2,  remote AS 200, external link
BGP version 4, remote router ID 172.17.0.1

R2
R2#sh ip bgp neighbors 
BGP neighbor is 10.1.1.1,  remote AS 100, external link
BGP version 4, remote router ID 10.1.0.1
BGP state = Established, up for 2d06h

We can control this selection with the “bgp router-id” command. Lets set our router id for R1 to 1.1.1.1 and R2 2.2.2.2.

R1
R1#config t
R1(config)#router bgp 100
R1(config-router)#bgp router-id 1.1.1.1
*Mar  8 02:54:27.985: %BGP-5-ADJCHANGE: neighbor 10.1.1.2 Down Router ID changed
*Mar  8 02:54:29.461: %BGP-5-ADJCHANGE: neighbor 10.1.1.2 Up 
R1(config-router)#

R2
R2#config t
R2(config)#router bgp 200
R2(config-router)#bgp router-id 2.2.2.2
*Mar 10 01:11:39.422: %BGP-5-ADJCHANGE: neighbor 10.1.1.1 Down Router ID changed
*Mar 10 01:11:42.178: %BGP-5-ADJCHANGE: neighbor 10.1.1.1 Up 
R2(config-router)#