BGP Router Identifier (BGP RID)-
It is the highest loopback IP address and in absence of loopback interface/s it will be the highest IP address of an active physical interface.
BGP Router must have BGP RID to establish BGP Peer session.
BGP router id can be also manually configured using bgp router-id command .
But once it is configured the bgp session will be reset.
R1#sh ip int brief
Interface IP-Address OK? Method Status Protocol
FastEthernet0 unassigned YES unset administratively down down
Serial0 12.1.1.1 YES manual up up
Serial1 unassigned YES unset administratively down down
Serial2 unassigned YES unset administratively down down
!! Currently BGP Router ID is 12.1.1.1
R1#sh ip bgp summary | i BGP router
BGP router identifier 12.1.1.1, local AS number 100
!! Configuration of loopback 0
R1(config)#int loopback 0
R1(config-if)#ip address 1.1.1.1 255.255.255.255
R1(config-if)#^Z
!! Change in BGP RID would need to reset the BGP sessions.HARD RESET IS REQUIRED .
Soft reset wont change the BGP RID .
R1#clear ip bgp *
R1#clear ip bgp all peer-group
Dec 11 11:11:39.911: %BGP-5-ADJCHANGE: neighbor 12.1.1.2 Down User reset
Dec 11 11:11:40.867: %BGP-5-ADJCHANGE: neighbor 12.1.1.2 Up
R1#sh ip bgp summary
BGP router identifier 1.1.1.1, local AS number 100
BGP table version is 1, main routing table version 1
Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
12.1.1.2 4 200 17 17 1 0 0 00:00:04 0
!! Configuration of loopback 1
R1(config)#int loopback 1
R1(config-if)#ip
Dec 11 11:17:25.827: %LINEPROTO-5-UPDOWN: Line protocol on Interface Loopback1, changed state to up
R1(config-if)#ip add
R1(config-if)#ip address 11.11.11.11 255.255.255.255
R1(config-if)#^Z
R1#clear ip bgp *
Dec 11 11:17:50.691: %BGP-5-ADJCHANGE: neighbor 12.1.1.2 Down User reset
Dec 11 11:17:51.323: %BGP-5-ADJCHANGE: neighbor 12.1.1.2 Up
R1#sh ip bgp summary
BGP router identifier 11.11.11.11, local AS number 100
BGP table version is 1, main routing table version 1
Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
12.1.1.2 4 200 27 27 1 0 0 00:00:02 0
R1(config)#no interface loopback 0
R1(config)#no interface loopback 1
R1(config)#int
Dec 11 11:19:42.095: %LINK-5-CHANGED: Interface Loopback0, changed state to administratively down
Dec 11 11:19:43.095: %LINEPROTO-5-UPDOWN: Line protocol on Interface Loopback0, changed state to down
R1(config)#int
Dec 11 11:19:43.623: %LINK-5-CHANGED: Interface Loopback1, changed state to administratively down
Dec 11 11:19:44.623: %LINEPROTO-5-UPDOWN: Line protocol on Interface Loopback1, changed state to down
R1(config)#^Z
R1#
Dec 11 11:19:47.491: %SYS-5-CONFIG_I: Configured from console by console
R1#clear ip bgp *
R1#config
Dec 11 11:19:52.691: %BGP-5-ADJCHANGE: neighbor 12.1.1.2 Down User reset
R1#sh ip bgp summary
Dec 11 11:19:53.771: %BGP-5-ADJCHANGE: neighbor 12.1.1.2 Up
R1#sh ip bgp summary
BGP router identifier 12.1.1.1, local AS number 100
BGP table version is 1, main routing table version 1
Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
12.1.1.2 4 200 33 33 1 0 0 00:00:01 0
R1#
!! Setting BGP RID Manually
R1(config)#
R1(config)#router bgp 100
R1(config-router)#bgp router-id 100.1.1.1
R1(config-router)#^Z
R1#
Dec 11 11:21:49.995: %BGP-5-ADJCHANGE: neighbor 12.1.1.2 Down Router ID changed
R1#
Dec 11 11:21:51.003: %SYS-5-CONFIG_I: Configured from console by console
Dec 11 11:21:51.267: %BGP-5-ADJCHANGE: neighbor 12.1.1.2 Up
R1#sh ip bgp sum
BGP router identifier 100.1.1.1, local AS number 100
BGP table version is 1, main routing table version 1
Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
12.1.1.2 4 200 38 38 1 0 0 00:00:12 0
Guys !!!! Please do remember once BGP RID is hard-cored the bgp session will be reset .
This may impact the production . So please be careful .
R2#sh ip bgp neighbors 12.1.1.1
BGP neighbor is 12.1.1.1, remote AS 100, external link
BGP version 4, remote router ID 100.1.1.1
BGP state = Established, up for 00:00:44
Last read 00:00:44, last write 00:00:44, hold time is 180, keepalive interval is 60 seconds
Neighbor capabilities:
Route refresh: advertised and received(old & new)
Address family IPv4 Unicast: advertised and received
Message statistics:
InQ depth is 0
OutQ depth is 0
Sent Rcvd
Opens: 6 6
Notifications: 0 0
Updates: 0 0
Keepalives: 41 41
Thanks for Reading !!!!!
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