The error "ORA-12543: TNS: destination host unreachable" is most
commonly found when there is there is a problem with network
connectivity; however, there are a few other reasons for
encountering the error.
The Oracle docs note the following about ORA-12543:
Cause: Contact can not be made with remote
Action: Make sure the network driver is
functioning and the network is up.
Common causes for the ORA-12543 error include:
- Network driver not functioning
- There is a
problem resolving the host name given in the address
parameter of the tnsnames entry
- Network is down or experiencing other problems
- Firewall issues
- Database server is down
Also, see my notes on
troubleshooting network errors in Oracle.
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