Sometimes You can get “ORA-12543: TNS:destination host unreachable ” error.
Details of error are as follows.
ORA-12543: TNS:destination host unreachable Cause: Contact can not be made with remote party. Action: Make sure the network driver is functioning and the network is up.
niqme: reporting NS-12543 error as ORA-12543 niotns: Couldn't connect, returning 12543
If the Network driver is broken and network is down, you can get this error. So you need to make sure network is up and enabled.
Sometimes you can get this error because of Firewall issues.
Or If database server is down, you can also get ORA-12543: TNS:destination host unreachable.
You should make sure you are trying the right Connection string ( IP or hostname, Port and Service name or SID ).