How to check firewall log, a network application fails if client and server are on
 

How to check firewall log, a network application fails if client and server are on different machine are but works when the two application are on same the machine. I can ping between those two machine. I just wanted to ensure if the issue is because of firewall. I want to know what all connections were attempted recently and which were allowed and which weren't

You could use tcpdump or if you have a gui installed use wireshark.
If you're brave you could write some iptables rules and tail -f on /var/log/syslog

Also make sure that the services are listening on the outbound interface and not localhost. Use netstat -tulpn to see where and which process are listening.

Cheers Zhjim