Some problems, unfortunately, aren’t as easy to identify as the ones we’ve listed. You’ll probably experience some misbehavior that you won’t be able to attribute directly to its cause, often because any of a number of problems may cause the symptoms you see. For cases like this, we’ll suggest some of the common causes of these symptoms and ways to isolate them.
The first thing to do when a program like telnet or ftp can’t look up a local name is to use nslookup to try to look up the same name. When we say “the same name,” we mean literally the same name—don’t add a domain name and a trailing dot if the user didn’t type either one. Don’t query a different name server than the user did.
As often as not, the user will have mistyped the name or misunderstood how the search list works and just needs direction. Occasionally, you’ll turn up real host configuration errors, such as a mistake in the resolver configuration (e.g., the wrong IP address for a name server). You can check for errors like this using nslookup’s set all command.
If nslookup points to a problem with the name server, rather than with the host configuration, check for the problems associated with the type of name server. If the name server is the primary master for the zone but it doesn’t respond with data you think it should:
Check that the zone or zone data file contains the data in question.
Ensure that the domain names in the records are correct (problem 6).
If the name ...