Workshop

Dialout DNS
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When you dial someone else’s IP network, you are using that person’s IP numbers on one of your
interfaces as well as relying on that person’s DNS servers to look up names. Because these DNS servers
(more than likely) do not hold the symbolic names of your servers, it’s likely that name resolution will
fail for local hosts. Because a DNS server will return a “no such host” message rather than failing with
no response, your computer will not go to the next DNS server in the list to try again—your request will
simply fail.
There’s one more thing that you should know about DNS and dialout. You can specify up to three DNS
entries in the Windows Control Panel. If you have a user who will be dialing out of your intranet, you
should not specify more than two in the normal Windows Control Panel. The reason for this is that if
three already exist, when the dialup adapter tries to add one more (for the remote network), it will fail
and the user won’t be able to resolve remote names.
Summary
Your intranet operates pretty much the same as the Internet at large—just on a smaller scale.
Accordingly, troubleshooting strategies that work on one will also work on the other.
Part of getting ready to troubleshoot your Internet connection is identifying what type of connection you
have. After you’ve done so, you’ll want to practice troubleshooting measures using nslookup, ping, and
traceroute to see if these tools will work through your firewall. To be able to rule out IP connectivity
issues versus DNS problems, you’ll want to keep a few IP numbers of reliable hosts on the Net handy.
If you have a DMZ (demilitarized zone) segment “in front” of your firewall, you can plug a laptop or
other workstation into it for the purposes of troubleshooting, even if the firewall will not allow diagnostic
tools to work through it.
A little DNS knowledge goes a long way when troubleshooting Internet problems—whether you’re
having trouble resolving a hostname or others are having trouble seeing your hosts. The nslookup tool
will give you a lot of help when troubleshooting DNS issues.
Routing problems may be addressed similarly to routing problems on your own network; the key lies in
finding out who is responsible for those routers and alerting them. Once again, nslookup to the rescue!
Problems with your Web server and intranet applications are typically either capacity related, reliability