Your company has more offices and each of them has a separate internet connection. The default route for each office points towards the ISP. Also, within each office you run iBGP using private AS numbers.
In the below diagram, you have Office-1 running AS 65100 and Office-2 running AS 65200.
You have been asked to configure an eBGP peering between Office-1 and Office-2. You did that by establishing a BGP session, using each border routers' loopbacks (as shown below).
Soon, you notice that the new eBGP peering does not come up. You perform the following troubleshooting:
sh ip bgp summBGP router identifier 18.104.22.168, local AS number 65100 BGP table version is 1, main routing table version 1 Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd 22.214.171.124 4 65200 0 0 0 0 0 never ActiveOffice-1# Office-1# Office-1# ping 126.96.36.199 source lo0Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 188.8.131.52, timeout is 2 seconds: Packet sent with a source address of 184.108.40.206 !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 1/16/56 ms Office-1# Office-1# Office-1# Office-1# traceroute 220.127.116.11 source lo0Type escape sequence to abort. Tracing the route to 18.104.22.168 1 22.214.171.124 4 msec 4 msec 16 msec 2 126.96.36.199 32 msec * 52 msec Office-1# Office-1# Office-1# Office-1# sh ip cef 188.8.131.52.0.0.0/0, version 9, epoch 0, cached adjacency to Serial0/0 0 packets, 0 bytes via 184.108.40.206, 0 dependencies, recursive next hop 220.127.116.11, Serial0/0 via 18.104.22.168/30 valid cached adjacency
As you can see, you can ping each others' loopback, but the BGP does not come up.
Note that Office-2 Border Router displays similar output
What is the problem ?
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