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I have the topology from the attached image with I-BGP neighborship between 192.168.21.1 and 192.168.21.2 and E-BGP neighborship between 192.168.6.1 and 192.168.6.2. I have advertised network 2.2.2.2/32 (loopback address) from R2 and configured next-hop-self on R4 for 192.168.21.1.

When I use show ip bgp command on R3, I can see that the path to 2.2.2.2 is valid and best. Also, the next hop is 192.168.21.2. The router also has this route in its routing table.

When I use show ip bgp command on R4, I can see that the path to 2.2.2.2 is valid and best. Also, the next hop is 192.168.6.1. The router also has this route in its routing table.

Both neighborships are functional, between R3 and R4 and between R4 and R2, but the ping from R3 to R2 does not work. I have also checked with a traceroute to 2.2.2.2, and the packet stops after entering through 192.168.21.2. Ping works from R3 to R4, and from R4 to R2, but it does not work from R3 to R2. What could be the cause?

There are the configurations on each router:

router bgp 100
 no synchronization
 bgp log-neighbor-changes
 network 2.2.2.2 mask 255.255.255.255
 network 192.168.6.0 mask 255.255.255.252
 network 192.168.7.0 mask 255.255.255.252
 network 192.168.8.0 mask 255.255.255.252
 neighbor 192.168.6.2 remote-as 200
 neighbor 192.168.7.2 remote-as 200
 neighbor 192.168.8.2 remote-as 200

R4:
router bgp 200
 no synchronization
 bgp log-neighbor-changes
 network 4.4.4.4 mask 255.255.255.255
 network 192.168.2.0 mask 255.255.255.252
 network 192.168.12.0 mask 255.255.255.252
 network 192.168.14.0 mask 255.255.255.252
 neighbor 192.168.6.2 remote-as 200
 neighbor 192.168.7.2 remote-as 200
 neighbor 192.168.8.2 remote-as 200
 neighbor 3.3.3.3 remote-as 200
 neighbor 192.168.6.1 remote-as 100
 neighbor 192.168.6.1 ebgp-multihop 2
 neighbor 192.168.21.1 remote-as 200
 neighbor 192.168.21.1 next-hop-self

R3:
router bgp 100
 no synchronization
 bgp log-neighbor-changes
 network 3.3.3.3 mask 255.255.255.255
 neighbor 4.4.4.4 remote-as 200
 neighbor 4.4.4.4 update-source Loopback1
 neighbor 192.168.21.2 remote-as 200

Thanks in advance!

topology image

R2 show ip route

R3 show ip route

R4 show ip route

Alex Dobre
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  • Please provide output of `show ip route` on the routers in question, if the table is large because of active eBGP, use the same command for iBGP/eBGP peer networks and advertised network. – Peter Zhabin Jun 13 '22 at 11:57
  • @PeterZhabin I have attached the routing tables for the 3 routers (cannot paste it as text because of a GNS3 problem) – Alex Dobre Jun 13 '22 at 12:46
  • Thanks. Your network diagram got lost, but this is not a problem. Please minimize your configuration by removing full-mesh connections unnecessary at this point, leaving R2-R3-R4 triangle with one pair of IPs per peer and see if it works. – Peter Zhabin Jun 13 '22 at 16:51

0 Answers0