There is a nifty tool that you'll want to know about: tnsping. It does what you'd expect, and is basically like testing DNS name resolution using ping instead of a more appropriate tool. When you can't find a database via TNS it's pretty handy for figuring out why.
bash-2.05$ tnsping testdb TNS Ping Utility for Solaris: Version 10.1.0.2.0 - Production on 11-OCT-2004 16:09:53 Copyright (c) 1997, 2003, Oracle. All rights reserved. Used parameter files: Used TNSNAMES adapter to resolve the alias Attempting to contact (description = (address_list = (address = (protocol = tcp) (host = 10.10.0.130) (port = 1521))) (connect_data = (sid = test))) OK (10 msec)