TNS-12543: TNS:destination host unreachable

[oracle@testdb2 ~]$ tnsping testdb1

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

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

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)