My coworker was configuring a Windows Update server recently, and the domain was being blocked. We realized that there was a DNS entry that redirected Windows Update traffic to a local server. The way that we discovered this was with the Unix “dig” command.
You can use dig to look up any type of DNS record, including CNAME, A, and MX records.
The analogous command on Windows is:
NSLookup also works on Unix, but dig provides more information about a given domain.