Workshop

Suppose your IP connectivity is okay. However, although you can ping by IP addresses all day, the
second you bring a domain name into the picture, your browser barfs. No problem! Let’s take a look at
the types of DNS problems you’re likely to see:
• Inside-to-outside problems—You can’t see others’ DNS names.
• Outside-to-inside problems—Others can’t see your DNS names.
For either type of problem, the tool of choice is nslookup. The nslookup tool allows you to connect to a
given DNS server and find out what that DNS server thinks about things.
Using Windows 95 or 98? Bummer! Although Microsoft has an exact UNIX-like version of nslookup for
NT, for some reason, it doesn’t supply this program with Windows 95/98. Fret not. You can find
reasonable equivalents by searching your local shareware site (www.shareware.com, www.tucows.com,
and so on) for “nslookup.” I can’t find the exact equivalent out there, but several programs offer nslookuplike
functionality, including these:
• dns11.zip
• nsb32-5.zip
• lookup.zip
• setuptk.exe
In other words, when you ping, you’re forced to use the DNS server configured into your TCP/IP stack,
but nslookup allows you to bypass this and choose which server to talk to. You can specify servers by IP
address (when name resolution isn’t working at all) or by name (when you’re trying to track down a
strange problem) and tell nslookup what type of information to give back to you.
The DNS Hierarchy
To be able to use the nslookup tool effectively, you’ll need to know the basics of the DNS hierarchy.
Like your hard drive, the DNS has so many individual records that it’s separated into many different
levels (folders on your hard drive; zones in the DNS world). Take a look at Figure 19.6. It’s drawn as a
tree, and you read it from the top down (dots separate the zones). Not too bad, right? That’s the way the
entire DNS is organized.