TNS-12543: TNS:destination host unreachable
There are multiple reasons for the error to occur due to unreachable host itself and there is nothing to do from database or listener.
[oracle@xhydra ~]$ tnsping xscalibal
Used TNSNAMES adapter to resolve the alias
Attempting to contact (DESCRIPTION = (ADDRESS_LIST = (ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.56.1)(PORT = 1521))) (CONNECT_DATA = (SERVICE_NAME = xscalibal)(UR = A)))
TNS-12543: TNS:destination host unreachable
One of the main reason is firewall service which does not allow the connections.
[oracle@DBZX21 ~]$ service firewalld status
Redirecting to /bin/systemctl status firewalld.service
● firewalld.service - firewalld - dynamic firewall daemon
Loaded: loaded (/usr/lib/systemd/system/firewalld.service; enabled; vendor preset: enabled)
Active: active (running) since Tue 2023-06-13 12:47:34 IST; 1h 59min ago
Docs: man:firewalld(1)
Main PID: 877 (firewalld)
Tasks: 2 (limit: 35835)
Memory: 30.1M
CGroup: /system.slice/firewalld.service
└─877 /usr/libexec/platform-python -s /usr/sbin/firewalld --nofork --nopid
[oracle@DBZX21 ~]$ service firewalld stop
Redirecting to /bin/systemctl stop firewalld.service
==== AUTHENTICATING FOR org.freedesktop.systemd1.manage-units ====
Authentication is required to stop 'firewalld.service'.
Authenticating as: kishan
Password:
polkit-agent-helper-1: pam_authenticate failed: Authentication failure
==== AUTHENTICATION FAILED ====
Failed to stop firewalld.service: Access denied
See system logs and 'systemctl status firewalld.service' for details.
[oracle@DBZX21 ~]$ su
Password:
[root@DBZX21 oracle]# service firewalld stop
Redirecting to /bin/systemctl stop firewalld.service
[root@DBZX21 oracle]# service firewalld disable
The service command supports only basic LSB actions (start, stop, restart, try-restart, reload, force-reload, status). For other actions, please try to use systemctl.
After disabling firewall, tnsping worked fine.
[oracle@xhydra ~]$ tnsping xscalibal
(SERVICE_NAME = xscalibal)(UR = A)))
OK (0 msec)