Probably there’s something wrong with the host (server) name or ip address you are connecting to.
First of all, open dos box or Unix shell script and execute:
to determine the host.
This is the output that will be returned (Oracle 9.2 style)
Used parameter files:c:\oracle\ora92\network\admin\sqlnet.ora Used TNSNAMES adapter to resolve the alias Attempting to contact (DESCRIPTION = (ADDRESS_LIST = (ADDRESS = (PROTOCOL = TCP)(HOST = unknown)(PORT = 1521))) (CONNECT_DATA = (SERVICE_NAME = ORA920.WORLD) (SERVER = DEDICATED))) TNS-12545: Connect failed because target host or object does not exist
Now, try to ping the hostname or ip address that was returned by the tnsping command:
If the ping command doesn’t succeed, there’s something wrong with the network or DNS setup.
Possibile causes are ip address conflicts, DNS outages, …Consult your network team to resolve the unknown host by either adding it to a DNS server, add it to the /etc/hosts or %windows home%\system32\drivers\etc\hosts file or other server name resolving technologies.