This page has links to several web-based test resources that I have found to be quite useful over the years.

General Purpose

The first and most useful site that I use is Network Tools. This site provides many general purpose tools that allow you to discover information and to perform queries against your own sources.

I use this site often to find out what my Internet IP appears to be (it shows up in the input text box the first time you access the site). I also use it often when backtracing IP addresses to their owners or performing WHOIS queries. I also use their advanced DNS query tool to verify that my external zones are configured properly.

DNS

Obviously, for queries, I use Network Tools (see above).

For DNS health, I recommend IntoDNS.com. This will query the root servers for your nameservers and then verify that they are all online and configured similarly. It also performs a check for MX records (and common misconfigurations) as well as a default WWW record.

Another site with many tools is ViewDNS.info. This site has many “quick” tools to help you test various aspects of your DNS system (and backtrace any IPs you come across). Very useful.

There is also DNSStuff.com. This is a tool that is turning into a paid service, but it still has some query tools available for free.

SMTP

My standout favorite general purpose SMTP tool is MXToolbox.org. This tool will check your SMTP servers to ensure that they are running and receiving okay. It will show the SMTP conversation to you so you can troubleshoot any problems. It will also compare your server’s IP address against several blocklists to see if you have any problems there.

FTP

HTTP

OTHER