[oracle@testdb2 ~]$ tnsping testdb1

TNS Ping Utility for Linux: Version 11.2.0.3.0 - Production on 18-APR-2017 21:47:19

Copyright (c) 1997, 2011, Oracle.  All rights reserved.

Used parameter files:

/opt/oracle/product/11.2.0.3/network/admin/sqlnet.ora

Used TNSNAMES adapter to resolve the alias

Attempting to contact (DESCRIPTION = (ADDRESS_LIST = (ADDRESS = (PROTOCOL = TCP)(HOST = 10.0.76.54)(PORT = 1521))) (CONNECT_DATA = (SERVICE_NAME = testdb1)))

TNS-12543: TNS:destination host unreachable

 

Solution:

Common causes for the ORA-12543 error include:

• Host name resolving problem. Check the hostname mentioned in tnsnames entry exist in /etc/hosts file and you can ping by hostname
• Network driver not working properly
• Network is down or experiencing other problems
• Firewall issues
• Database server is down

If this is due to firewall issue then follow the instruction to disable firewall:

[root@testdb1 ~]# service iptables save

Saving firewall rules to /etc/sysconfig/iptables:          [  OK  ]

[root@testdb1 ~]# service iptables stop

Flushing firewall rules:                                   [  OK  ]

Setting chains to policy ACCEPT: filter                    [  OK  ]

Unloading iptables modules:                                [  OK  ]

[root@testdb1 ~]# chkconfig iptables off

 

[oracle@testdb2 ~]$ tnsping testdb1

TNS Ping Utility for Linux: Version 11.2.0.3.0 - Production on 18-APR-2017 22:02:08

Copyright (c) 1997, 2011, Oracle.  All rights reserved.

 

Used parameter files:

/opt/oracle/product/11.2.0.3/network/admin/sqlnet.ora

Used TNSNAMES adapter to resolve the alias

Attempting to contact (DESCRIPTION = (ADDRESS_LIST = (ADDRESS = (PROTOCOL = TCP)(HOST = 10.0.76.54)(PORT = 1521))) (CONNECT_DATA = (SERVICE_NAME = testdb1)))

OK (0 msec)