Irksome Nslookup Oddities

One of my favorite Windows NT 4.0 utilities is Nslookup. I've used this utility for years to troubleshoot a variety of DNS name-resolution problems. However, shortly after my company began upgrading its network workstations to Windows 2000 Professional, I started noticing strange behavior from Win2K Pro's Nslookup. DNS record lookup queries were failing, and Nslookup was using my secondary DNS server rather than my primary one. Before I go into detail about the Win2K Pro Nslookup quirks that have been bugging me, let's recall the good ol' days of the reliable and useful NT 4.0 Nslookup utility.

The DNS Swiss Army Knife
Nslookup lets you directly query DNS servers for information such as the IP address name assigned to a particular host and whether particular record types within a DNS zone file are present and operating properly. This information is useful for troubleshooting as well as setting up new DNS zone file data.

To perform a simple-name (i.e., name—to—IP address) or reverse-name (i.e., IP address—to—name) lookup, at a command prompt, you simply type the Nslookup command followed by a host's name or IP address. The utility returns the corresponding IP address or host name. Within domain files on DNS servers, Address (A) records assign name—to—IP address mappings. When you use Nslookup commands, you're querying the contents of these A records.

You can also use Nslookup to query DNS servers for other record-type data, such as Name Server (NS) records, which identify the DNS servers supporting a particular domain name; Canonical Name (CNAME) records, which define aliases for DNS hosts assigned through A records; and mail exchanger (MX) records, which identify which mail hosts handle mail for a particular domain. You can query for all record types or a particular record type.

Internet mail servers use DNS queries to discover MX record information such as the server address and record preference value. When troubleshooting problems such as message bounces or delivery to the wrong mail server, manually performing the DNS queries can provide useful information. Doing so lets you see what DNS information remote servers are seeing, which can provide clues about your problem's source. You can use Nslookup to manually perform DNS zone-file queries against the DNS server of your choice.

Another useful Nslookup function is to display all the mail servers for a particular domain. To do so, set Nslookup to query only for the MX record type and provide the domain name of the domain that you want information about. The following commands start an Nslookup session and query for the xcedia.com domain. First, at a command prompt, type

nslookup

Press Enter, then type

set type=mx
xcedia.com

This query produces the output that Figure 1, page 92, shows.

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