DRAG DROP
Topology:
Drag the required troubleshooting steps on the left and drop them in the boxes on the right, with the lowest OSI layer as the topmost box.
Answer: 
Explanation:
Drag the required troubleshooting steps on the left and drop them in the boxes on the right…
DRAG DROP
Topology:
Drag the required troubleshooting steps on the left and drop them in the boxes on the right, with the lowest OSI layer as the topmost box.
From my perspective:
1. Check the router interface status to see if it is in the up/up state.
2. Check if the routers are learning the loopback interface of the other routers via the IGP. (If the loopback interface IP addresses are not in the routing table, then why try to ping them a this point?)
3. Check if each router can ping the loopback interface of all the other routers. (ICMP can be blocked inbound to the router for the interface you are trying to ping.)
4. Check the BGP configurations on all the routers.