Cisco – Learned eBGP routes are advertised to iBGP neighbors but can’t ping the loopback who’s IP is configrued

bgpciscorouting

I have a setup in my GNS3 where I am trying to understand some basic iBGP and eBGP concepts.

Please refer to the diagram (I only took a screenshot of the part which is really required). I have advertised a loopback from R3 and I can see the route in the ip routing table of R10 but I can't ping it from R10.

enter image description here

R3 –> AS300
R8, R10 –> AS100

R3:

!
router ospf 1
 router-id 3.3.3.3
 network 3.3.3.3 0.0.0.0 area 0
!
router bgp 300
 no synchronization
 bgp log-neighbor-changes
 network 3.3.3.3 mask 255.255.255.255
 network 10.0.0.0 mask 255.255.255.252
 neighbor 192.168.0.14 remote-as 100 #eBGP tied on the physical interface.
 neighbor 192.168.0.14 update-source fastEthernet 3/0
 no auto-summary
 !

R8:

!
router ospf 1
router-id 8.8.8.8
network 8.8.8.8 0.0.0.0 area 0
network 192.168.0.28 0.0.0.3 area 0
!
router bgp 100
 no synchronization
 bgp log-neighbor-changes
 neighbor 10.10.10.10 remote-as 100
 neighbor 10.10.10.10 update-source Loopback0
 neighbor 10.10.10.10 next-hop-self
 neighbor 192.168.0.13 remote-as 300
 neighbor 192.168.0.13 update-source fastEthernet 3/0
 no auto-summary
 !

R10:

!
router ospf 1
 router-id 10.10.10.10
 network 10.10.10.10 0.0.0.0 area 0
 network 192.168.0.28 0.0.0.3 area 0
!
router bgp 100
 no synchronization
 bgp log-neighbor-changes
 neighbor 8.8.8.8 remote-as 100
 neighbor 8.8.8.8 update-source Loopback0
 no auto-summary
!

I can see the route to 3.3.3.3 in routing table of R10 and the next hop i.e. 8.8.8.8 is also reachable but a ping to 3.3.3.3 fails.

Any help is appreciated. Also, if there are some configurations (which would have been done in a better way, I would be happy to learn). Thanks in advance! 🙂

Best Answer

It is because R3 does not know how to return the traffic back to R10. In routing table of R3, it does not have any routes/prefixes located on R10.

R10 learned the prefix 3.3.3.3/32 from R3 via BGP (iBGP session with R8).

On R10, you need to advertise your local networks/prefixes into BGP, so that R3 can learn and know how to return the traffic back to R10.

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