From the Oracle9i Net Services administrator's guide:
"In environments where simple connectivity is desired, host naming can eliminate the need for service name lookup in the tnsnames.ora files....
The service name must be resolved through an IP address translation mechanism, such as DNS, NIS, or a centrally-maintained TCP/IP host file, /etc/hosts. or example, if a service name of sales.us.acme.com for a database exists on a computer named sales-server, the entry in the /etc/hosts file would look like the following:
#IP address of server host name alias
144.25.219.146 sales-server sales.us.acme.com"