No Oracle client installed ... network debug

Facing an interesting scenario:

2 servers: 1 test & 1 dev, both having some oracle rpm installed:

DEV:

[root@orcl1 client64]# rpm -qa | grep oracle

oracle-instantclient11.2-sqlplus-11.2.0.3.0-1.x86_64

oracle-instantclient11.2-basic-11.2.0.3.0-1.x86_64

TEST:

[root@orcl2 client64]# rpm -qa | grep oracle

oracle-instantclient11.2-sqlplus-11.2.0.3.0-1.x86_64

oracle-instantclient11.2-basic-11.2.0.3.0-1.x86_64

One is able to connect to the db server (TEST), but other one not (DEV), what is the issue and how to debug/troubleshoot?

Ports are open, telnet is working fine. Please assist/advise/guide

Thanks in advance.