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355
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4
Helpful
7
Replies

BGP Neighborhship Using Loopback

uni1389
Level 1
Level 1

‎07-04-2025 05:11 AM

 Hi All, 

am using the following topology for BGP testing , but am not able to establish bgp neighborships between R1/R3 and R2/R4. The  sample config/output is mentioned below:-

 

uni1389_0-1751630553518.png

******************************************************

R1#show ip bgp summary
BGP router identifier 192.168.1.1, local AS number 12
BGP table version is 25, main routing table version 25
8 network entries using 1152 bytes of memory
8 path entries using 672 bytes of memory
1/1 BGP path/bestpath attribute entries using 160 bytes of memory
0 BGP route-map cache entries using 0 bytes of memory
0 BGP filter-list cache entries using 0 bytes of memory
BGP using 1984 total bytes of memory
BGP activity 25/17 prefixes, 26/18 paths, scan interval 60 secs

Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
172.16.12.2 4 12 0 0 1 0 0 never Active
172.16.13.3 4 3 0 0 1 0 0 00:04:13 Idle
R1# ping 172.16.13.3
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.16.13.3, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/5/6 ms
R1#ping 192.168.3.3 sour 192.168.1.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.3.3, timeout is 2 seconds:
Packet sent with a source address of 192.168.1.1
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 3/4/7 ms
R1#show run | sec router bgp
router bgp 12
bgp router-id 192.168.1.1
bgp log-neighbor-changes
network 10.10.1.1 mask 255.255.255.255
network 10.10.1.2 mask 255.255.255.255
network 10.10.1.3 mask 255.255.255.255
network 10.10.1.4 mask 255.255.255.255
network 10.10.1.5 mask 255.255.255.255
network 10.10.12.0 mask 255.255.255.0
network 172.16.12.0 mask 255.255.255.0
network 172.16.13.0 mask 255.255.255.0
neighbor 172.16.12.2 remote-as 12
neighbor 172.16.12.2 update-source Loopback0
neighbor 172.16.13.3 remote-as 3
neighbor 172.16.13.3 update-source Loopback0
R1#show ip int br
Interface IP-Address OK? Method Status Protocol
GigabitEthernet0/0 172.16.13.1 YES NVRAM up up
GigabitEthernet0/1 172.16.12.1 YES NVRAM up up
GigabitEthernet0/2 10.10.12.1 YES NVRAM up up
GigabitEthernet0/3 unassigned YES NVRAM down down
GigabitEthernet0/4 unassigned YES NVRAM down down
GigabitEthernet0/5 unassigned YES NVRAM down down
GigabitEthernet0/6 unassigned YES NVRAM down down
GigabitEthernet0/7 unassigned YES NVRAM down down
Loopback0 192.168.1.1 YES NVRAM up up
Loopback1 10.10.1.1 YES NVRAM up up
Loopback2 10.10.1.2 YES NVRAM up up
Loopback3 10.10.1.3 YES NVRAM up up
Loopback4 10.10.1.4 YES NVRAM up up
Loopback5 10.10.1.5 YES NVRAM up up
**********************************************************************


R3#show ip int br
Interface IP-Address OK? Method Status Protocol
GigabitEthernet0/0 172.16.13.3 YES NVRAM up up
GigabitEthernet0/1 172.16.113.3 YES NVRAM up up
GigabitEthernet0/2 172.16.123.3 YES NVRAM up up
GigabitEthernet0/3 172.16.37.3 YES NVRAM up up
GigabitEthernet0/4 unassigned YES NVRAM down down
GigabitEthernet0/5 unassigned YES NVRAM down down
GigabitEthernet0/6 unassigned YES NVRAM down down
GigabitEthernet0/7 unassigned YES NVRAM down down
Loopback0 192.168.3.3 YES NVRAM up up
Loopback1 10.10.3.1 YES NVRAM up up
Loopback2 10.10.3.2 YES NVRAM up up
Loopback3 10.10.3.3 YES NVRAM up up
Loopback4 10.10.3.4 YES NVRAM up up
Loopback5 10.10.3.5 YES NVRAM up up
R3# show run
R3# show running-config | sec router bgp
router bgp 3
bgp router-id 192.168.3.3
bgp log-neighbor-changes
network 10.10.3.1 mask 255.255.255.255
network 10.10.3.2 mask 255.255.255.255
network 10.10.3.3 mask 255.255.255.255
network 10.10.3.4 mask 255.255.255.255
network 10.10.3.5 mask 255.255.255.255
network 172.16.13.0 mask 255.255.255.0
network 172.16.37.0 mask 255.255.255.0
network 172.16.113.0 mask 255.255.255.0
network 172.16.123.0 mask 255.255.255.0
neighbor 172.16.13.1 remote-as 12
neighbor 172.16.13.1 update-source Loopback0
neighbor 172.16.37.7 remote-as 7
neighbor 172.16.37.7 update-source Loopback0
neighbor 172.16.113.11 remote-as 11
neighbor 172.16.113.11 update-source Loopback0
neighbor 172.16.123.12 remote-as 22
neighbor 172.16.123.12 update-source Loopback0
R3#
R3#
R3#ping 192.168.1.1 sour 192.168.3.3
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.1.1, timeout is 2 seconds:
Packet sent with a source address of 192.168.3.3
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 3/6/12 ms
R3#show ip bgp sum
R3#show ip bgp summary
BGP router identifier 192.168.3.3, local AS number 3
BGP table version is 10, main routing table version 10
9 network entries using 1296 bytes of memory
9 path entries using 756 bytes of memory
1/1 BGP path/bestpath attribute entries using 160 bytes of memory
0 BGP route-map cache entries using 0 bytes of memory
0 BGP filter-list cache entries using 0 bytes of memory
BGP using 2212 total bytes of memory
BGP activity 25/16 prefixes, 26/17 paths, scan interval 60 secs

Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
172.16.13.1 4 12 0 0 1 0 0 00:08:32 Idle
172.16.37.7 4 7 0 0 1 0 0 never Active
172.16.113.11 4 11 0 0 1 0 0 never Active
172.16.123.12

*******************************************************************

R2#show ip int br
Interface IP-Address OK? Method Status Protocol
GigabitEthernet0/0 172.16.24.2 YES NVRAM up up
GigabitEthernet0/1 172.16.12.2 YES NVRAM up up
GigabitEthernet0/2 10.10.12.2 YES NVRAM up up
GigabitEthernet0/3 unassigned YES NVRAM down down
GigabitEthernet0/4 unassigned YES NVRAM down down
GigabitEthernet0/5 unassigned YES NVRAM down down
GigabitEthernet0/6 unassigned YES NVRAM down down
GigabitEthernet0/7 unassigned YES NVRAM down down
Loopback0 192.168.2.2 YES NVRAM up up
Loopback1 10.10.2.1 YES NVRAM up up
Loopback2 10.10.2.2 YES NVRAM up up
Loopback3 10.10.2.3 YES NVRAM up up
Loopback4 10.10.2.4 YES NVRAM up up
Loopback5 10.10.2.5 YES NVRAM up up
R2#ping 192.168.4.4 source 192.168.2.2
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.4.4, timeout is 2 seconds:
Packet sent with a source address of 192.168.2.2
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/5/10 ms
R2#
R2#
R2#show ip bgp sum
R2#show ip bgp summary
BGP router identifier 192.168.2.2, local AS number 12
BGP table version is 10, main routing table version 10
9 network entries using 1296 bytes of memory
9 path entries using 756 bytes of memory
1/1 BGP path/bestpath attribute entries using 160 bytes of memory
0 BGP route-map cache entries using 0 bytes of memory
0 BGP filter-list cache entries using 0 bytes of memory
BGP using 2212 total bytes of memory
BGP activity 18/9 prefixes, 18/9 paths, scan interval 60 secs

Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
172.16.12.1 4 12 0 0 1 0 0 never Active
172.16.24.4 4 4 0 0 1 0 0 never Idle
R2#show run
R2#show running-config | sec router bgp
router bgp 12
bgp router-id 192.168.2.2
bgp log-neighbor-changes
network 10.10.2.1 mask 255.255.255.255
network 10.10.2.2 mask 255.255.255.255
network 10.10.2.3 mask 255.255.255.255
network 10.10.2.4 mask 255.255.255.255
network 10.10.2.5 mask 255.255.255.255
network 10.10.12.0 mask 255.255.255.0
network 172.16.12.0 mask 255.255.255.0
network 172.16.24.0 mask 255.255.255.0
network 192.168.2.2 mask 255.255.255.255
neighbor 172.16.12.1 remote-as 12
neighbor 172.16.12.1 update-source Loopback0
neighbor 172.16.24.4 remote-as 4
neighbor 172.16.24.4 update-source Loopback0
R2#

*******************************************************************

R4#show ip int br
Interface IP-Address OK? Method Status Protocol
GigabitEthernet0/0 172.16.24.4 YES NVRAM up up
GigabitEthernet0/1 172.16.124.4 YES NVRAM up up
GigabitEthernet0/2 172.16.114.4 YES NVRAM up up
GigabitEthernet0/3 172.16.48.4 YES NVRAM up up
GigabitEthernet0/4 unassigned YES NVRAM administratively down down
GigabitEthernet0/5 unassigned YES NVRAM administratively down down
GigabitEthernet0/6 unassigned YES NVRAM administratively down down
GigabitEthernet0/7 unassigned YES NVRAM administratively down down
Loopback0 192.168.4.4 YES NVRAM up up
Loopback1 10.10.4.1 YES NVRAM up up
Loopback2 10.10.4.2 YES NVRAM up up
Loopback3 10.10.4.3 YES NVRAM up up
Loopback4 10.10.4.4 YES NVRAM up up
Loopback5 10.10.4.5 YES NVRAM up up
R4#ping 192.168.2.2 source 192.168.4.4
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.2.2, timeout is 2 seconds:
Packet sent with a source address of 192.168.4.4
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/6/8 ms
R4#show ip bgp sum
R4#show ip bgp summary
BGP router identifier 192.168.4.4, local AS number 4
BGP table version is 11, main routing table version 11
10 network entries using 1440 bytes of memory
10 path entries using 840 bytes of memory
1/1 BGP path/bestpath attribute entries using 160 bytes of memory
0 BGP route-map cache entries using 0 bytes of memory
0 BGP filter-list cache entries using 0 bytes of memory
BGP using 2440 total bytes of memory
BGP activity 10/0 prefixes, 10/0 paths, scan interval 60 secs

Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
172.16.24.2 4 12 0 0 1 0 0 never Idle
172.16.48.8 4 8 0 0 1 0 0 never Active
172.16.114.11 4 11 0 0 1 0 0 never Idle
172.16.124.12 4 22 0 0 1 0 0 never Active
R4#
R4#show run
R4#show running-config | sec router bgp
router bgp 4
bgp router-id 192.168.4.4
bgp log-neighbor-changes
network 10.10.4.1 mask 255.255.255.255
network 10.10.4.2 mask 255.255.255.255
network 10.10.4.3 mask 255.255.255.255
network 10.10.4.4 mask 255.255.255.255
network 10.10.4.5 mask 255.255.255.255
network 172.16.24.0 mask 255.255.255.0
network 172.16.48.0 mask 255.255.255.0
network 172.16.114.0 mask 255.255.255.0
network 172.16.124.0 mask 255.255.255.0
network 192.168.4.4 mask 255.255.255.255
neighbor 172.16.24.2 remote-as 12
neighbor 172.16.24.2 update-source Loopback0
neighbor 172.16.48.8 remote-as 8
neighbor 172.16.48.8 update-source Loopback0
neighbor 172.16.114.11 remote-as 11
neighbor 172.16.114.11 update-source Loopback0
neighbor 172.16.124.12 remote-as 22
neighbor 172.16.124.12 update-source Loopback0
R4#

**************************************************************

 

 

Labels:
0 Helpful
7 Replies 7

MHM Cisco World
VIP
VIP

‎07-04-2025 05:15 AM

You need 

Neighbor xxxx ebgp multihop 2

MHM

uni1389
Level 1
Level 1
In response to MHM Cisco World

‎07-04-2025 08:21 AM

R1

show ip bgp summary
BGP router identifier 192.168.1.1, local AS number 12
BGP table version is 10, main routing table version 10
9 network entries using 1296 bytes of memory
9 path entries using 756 bytes of memory
1/1 BGP path/bestpath attribute entries using 160 bytes of memory
0 BGP route-map cache entries using 0 bytes of memory
0 BGP filter-list cache entries using 0 bytes of memory
BGP using 2212 total bytes of memory
BGP activity 84/75 prefixes, 88/79 paths, scan interval 60 secs

Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
172.16.12.2 4 12 0 0 1 0 0 never Idle
172.16.13.3 4 3 0 0 1 0 0 02:56:47 Idle
R1# show running-config | sec router bgp
router bgp 12
bgp router-id 192.168.1.1
bgp log-neighbor-changes
network 10.10.1.1 mask 255.255.255.255
network 10.10.1.2 mask 255.255.255.255
network 10.10.1.3 mask 255.255.255.255
network 10.10.1.4 mask 255.255.255.255
network 10.10.1.5 mask 255.255.255.255
network 10.10.12.0 mask 255.255.255.0
network 172.16.12.0 mask 255.255.255.0
network 172.16.13.0 mask 255.255.255.0
network 192.168.1.1 mask 255.255.255.255
neighbor 172.16.12.2 remote-as 12
neighbor 172.16.13.3 remote-as 3
neighbor 172.16.13.3 ebgp-multihop 2
neighbor 172.16.13.3 update-source Loopback0
R1# show running-config | sec ip route
ip route 192.168.2.2 255.255.255.255 172.16.12.2
ip route 192.168.3.3 255.255.255.255 172.16.13.3
R1#


R2#show ip bgp summary
BGP router identifier 192.168.2.2, local AS number 12
BGP table version is 10, main routing table version 10
9 network entries using 1296 bytes of memory
9 path entries using 756 bytes of memory
1/1 BGP path/bestpath attribute entries using 160 bytes of memory
0 BGP route-map cache entries using 0 bytes of memory
0 BGP filter-list cache entries using 0 bytes of memory
BGP using 2212 total bytes of memory
BGP activity 77/68 prefixes, 80/71 paths, scan interval 60 secs

Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
172.16.12.1 4 12 0 0 1 0 0 02:57:13 Idle
172.16.24.4 4 4 0 0 1 0 0 02:57:13 Idle
R2# show running-config | sec router bgp

*Jul 4 15:18:04.294: %GRUB-5-CONFIG_WRITING: GRUB configuration is being updated on disk. Please wait...
*Jul 4 15:18:05.725: %GRUB-5-CONFIG_WRITTEN: GRUB configuration was written to disk successfully.router bgp 12
bgp router-id 192.168.2.2
bgp log-neighbor-changes
network 10.10.2.1 mask 255.255.255.255
network 10.10.2.2 mask 255.255.255.255
network 10.10.2.3 mask 255.255.255.255
network 10.10.2.4 mask 255.255.255.255
network 10.10.2.5 mask 255.255.255.255
network 10.10.12.0 mask 255.255.255.0
network 172.16.12.0 mask 255.255.255.0
network 172.16.24.0 mask 255.255.255.0
network 192.168.2.2 mask 255.255.255.255
neighbor 172.16.12.1 remote-as 12
neighbor 172.16.12.1 update-source Loopback0
neighbor 172.16.24.4 remote-as 4
neighbor 172.16.24.4 ebgp-multihop 2
neighbor 172.16.24.4 update-source Loopback0
R2# show running-config | sec ip route
ip route 192.168.1.1 255.255.255.255 172.16.12.1
ip route 192.168.4.4 255.255.255.255 172.16.24.4
R2#

 

 

R3#ping 192.168.1.1 source 192.168.3.3
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.1.1, timeout is 2 seconds:
Packet sent with a source address of 192.168.3.3
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/7/11 ms
R3#
R3#
R3#
R3#show ip bgp summary
BGP router identifier 192.168.3.3, local AS number 3
BGP table version is 11, main routing table version 11
10 network entries using 1440 bytes of memory
10 path entries using 840 bytes of memory
1/1 BGP path/bestpath attribute entries using 160 bytes of memory
0 BGP route-map cache entries using 0 bytes of memory
0 BGP filter-list cache entries using 0 bytes of memory
BGP using 2440 total bytes of memory
BGP activity 97/87 prefixes, 99/89 paths, scan interval 60 secs

Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
172.16.13.1 4 12 0 0 1 0 0 02:57:02 Idle
172.16.37.7 4 7 0 0 1 0 0 never Active
172.16.113.11 4 11 0 0 1 0 0 never Idle
172.16.123.12 4 22 0 0 1 0 0 never Active
R3# show running-config | sec router bgp
router bgp 3
bgp router-id 192.168.3.3
bgp log-neighbor-changes
network 10.10.3.1 mask 255.255.255.255
network 10.10.3.2 mask 255.255.255.255
network 10.10.3.3 mask 255.255.255.255
network 10.10.3.4 mask 255.255.255.255
network 10.10.3.5 mask 255.255.255.255
network 172.16.13.0 mask 255.255.255.0
network 172.16.37.0 mask 255.255.255.0
network 172.16.113.0 mask 255.255.255.0
network 172.16.123.0 mask 255.255.255.0
network 192.168.3.3 mask 255.255.255.255
neighbor 172.16.13.1 remote-as 12
neighbor 172.16.13.1 ebgp-multihop 2
neighbor 172.16.13.1 update-source Loopback0
neighbor 172.16.37.7 remote-as 7
neighbor 172.16.37.7 ebgp-multihop 2
neighbor 172.16.37.7 update-source Loopback0
neighbor 172.16.113.11 remote-as 11
neighbor 172.16.113.11 ebgp-multihop 2
neighbor 172.16.113.11 update-source Loopback0
neighbor 172.16.123.12 remote-as 22
neighbor 172.16.123.12 ebgp-multihop 2
neighbor 172.16.123.12 update-source Loopback0
R3# show running-config | sec ip route
ip route 192.168.1.1 255.255.255.255 172.16.13.1

 

 

 

 


R4#
R4#show ip bgp summary
BGP router identifier 192.168.4.4, local AS number 4
BGP table version is 11, main routing table version 11
10 network entries using 1440 bytes of memory
10 path entries using 840 bytes of memory
1/1 BGP path/bestpath attribute entries using 160 bytes of memory
0 BGP route-map cache entries using 0 bytes of memory
0 BGP filter-list cache entries using 0 bytes of memory
BGP using 2440 total bytes of memory
BGP activity 82/72 prefixes, 83/73 paths, scan interval 60 secs

Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
172.16.24.2 4 12 0 0 1 0 0 02:57:15 Idle
172.16.48.8 4 8 0 0 1 0 0 never Active
172.16.114.11 4 11 0 0 1 0 0 never Active
172.16.124.12 4 22 0 0 1 0 0 never Active
R4# show running-config | sec router bgp
router bgp 4
bgp router-id 192.168.4.4
bgp log-neighbor-changes
network 10.10.4.1 mask 255.255.255.255
network 10.10.4.2 mask 255.255.255.255
network 10.10.4.3 mask 255.255.255.255
network 10.10.4.4 mask 255.255.255.255
network 10.10.4.5 mask 255.255.255.255
network 172.16.24.0 mask 255.255.255.0
network 172.16.48.0 mask 255.255.255.0
network 172.16.114.0 mask 255.255.255.0
network 172.16.124.0 mask 255.255.255.0
network 192.168.4.4 mask 255.255.255.255
neighbor 172.16.24.2 remote-as 12
neighbor 172.16.24.2 ebgp-multihop 2
neighbor 172.16.24.2 update-source Loopback0
neighbor 172.16.48.8 remote-as 8
neighbor 172.16.48.8 ebgp-multihop 2
neighbor 172.16.48.8 update-source Loopback0
neighbor 172.16.114.11 remote-as 11
neighbor 172.16.114.11 ebgp-multihop 2
neighbor 172.16.114.11 update-source Loopback0
neighbor 172.16.124.12 remote-as 22
neighbor 172.16.124.12 ebgp-multihop 2
neighbor 172.16.124.12 update-source Loopback0
R4# show running-config | sec ip route
ip route 192.168.2.2 255.255.255.255 172.16.24.2
R4#
R4#
R4#
R4#ping 192.168.2.2 source 192.168.4.4
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.2.2, timeout is 2 seconds:
Packet sent with a source address of 192.168.4.4
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 3/6/11 ms
R4#

0 Helpful

MHM Cisco World
VIP
VIP
In response to uni1389

‎07-04-2025 08:28 AM

neighbor <LO of remote Peer> update-source <LO of Your Peer>
this how you config BGP using LO 
MHM

0 Helpful

MHM Cisco World
VIP
VIP
In response to MHM Cisco World

‎07-04-2025 08:31 AM

Also

neighbor <LO of remote Peer> as <remote Peer AS>

This need

MHM

0 Helpful

MHM Cisco World
VIP
VIP
In response to MHM Cisco World

‎07-04-2025 08:41 AM

neighbor <LO of remote Peer> as <remote Peer AS>

neighbor <LO of remote Peer> update-source <LO of Your Peer>

neighbor <LO of remote Peer> ebgp multihop 2

these how you config LO for BGP 
I put three commands in case you confuse

MHM

Harold Ritter
Spotlight
Spotlight
In response to uni1389

‎07-04-2025 08:42 AM - edited ‎07-04-2025 08:49 AM

Hi @uni1389 ,

If the goal is to use the loopback interface address for the eBGP session as well, you would need to do the following:

R1:

router bgp 12

neighbor 192.168.3.3 remote-as 3

neighbor 192.168.3.3 update-source lo0

neighbor 192.168.3.3 ebgp-multihop 2

ip route 192.168.3.3 255.255.255.255 172.16.13.3

R3:

router bgp 3

neighbor 192.168.1.1 remote-as 12

neighbor 192.168.1.1 update-source lo0

neighbor 192.168.1.1 ebgp-multihop 2

ip route 192.168.1.1 255.255.255.255 172.16.13.1

Regards,
Harold Ritter, CCIE #4168 (EI, SP)

Harold Ritter
Spotlight
Spotlight

‎07-04-2025 08:21 AM

Hi @uni1389 ,

R1 and R3 use the directly connected interface to establish the session. You should therefore remove the following command:

R1:

router bgp 12

no neighbor 172.16.13.3 update-source Loopback0

R3:

router bgp 3

no neighbor 172.16.13.1 update-source Loopback0

The same applies to the session between R2 and R4.

Regards,
Harold Ritter, CCIE #4168 (EI, SP)
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