MongoDB Replication - “Failed with No route to host”
Firewall! Go to the command line of s1-b5 and give command mongo --host 's2-b6:26052' you should have a successful login to "second" node. I guess that these two nodes are actually one machine?!? And when you use "external IP address", traffic goes thru the firewall. So, iptables-save command should show that this port 26052 is open for traffic.