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)