An Invaluable DNS-Troubleshooting Resource
A article about DNS troubleshooting would be incomplete without at least a mention of the incredible set of free, online DNS tools at DNSstuff.com (http://www.dnsstuff.com). Developed, maintained, and offered by R. Scott Perry, DNSstuff.com offers more than a dozen DNS, IP, domain, and other tools for easy, Web-based troubleshooting purposes. With tools that tackle such tasks as name-to-IP address resolution, reverse lookups, WHOIS lookups, and checking IP addresses against known blocks of IP addresses currently recognized as a source of spam, I've found DNSstuff.com to be an indispensable resource when I'm troubleshooting DNS problems for clients.
I particularly value the fact that their host lookup \will perform an entire iterative DNS query— starting at the root servers and working all the way through to the final host name—in a nice simple Web interface. This functionality saves me the trouble of performing this process manually through Nslookup, and it gives me a simple interface with which to show results to clients in a much more understandable format than Nslookup provides. Also, they provide an option to query the DNS servers of certain major ISPs to see whether they might be returning a separate cached answer for the same query.