ICSI Netalyzr is a service maintained by the Networking Group at the International Computer Science Institute, an affiliate with the University of California, Berkeley and funded by the National Science Foundation. The service got some publicity and found importance after late 2007 when Comcast was sued for throttling Internet traffic which Comcast later admitted to be true.
[Editor’s note: this review was written by Freewaregenius contributor Jason H. Check out his tech blog: 404techsupport.com].
Netalyzr is not the traditional freeware covered here at Freewaregenius, but it is a free service that allows you to test and find out more information about the Internet connection you’re paying for. With no real established metrics for what an ISP must provide, Netalyzr gives you the inside scoop in a convenient report. By running the test, not only will you find out information about your connection and its capabilities, but you’ll also share information with researchers that may improve the Internet infrastructure and provide data to the Net Neutrality argument. From their Learn More page:
The Netalyzr analyzes various properties of your Internet connection that you should care about — including blocking of important services, HTTP caching behavior and proxy correctness, your DNS server’s resilience to abuse, NAT detection, as well as latency & bandwidth measurements — and reports its findings in a detailed report.
Netalyzr is a simple 3-step process and simply requires that you have Java installed and visit a site with your browser. From the ICSI Netalyzr home page, just click the Start analysis link. If you don’t see the text, Start analysis, it means you don’t have a compatible version of Java installed. After you start the test, you’ll be prompted to allow the Java Applet run from the International Computer Science Institute. Hit Run, if you want to take the test.
After the Applet begins running, you can watch the status to see all the different things that are tested. The test will take a few minutes to complete so you might want to let it run while you’re doing something else. Visiting other websites should not effect the final results, so maybe go play some Chibi Knight or go visit my website, 404 Tech Support. 
After the test completes, you’ll get a long list telling you the results of the tests in accurate, but not-too-technical terms. This can alert you to any problems with your connection, issues with your router, or limitations of your ISP. A small example of what the results can tell you include NAT detection, Access to remote ports: FTP, IMAP/SSL, BitTorrent, DNS, HTTP; Connection Latency; Upload and Download speeds; IPv6 compatibility, and many more. Netalyzr has a sample results page that you can view to see all of what gets tested.
One small note is that your antivirus might give you a notice (not an alert or a warning) because of some of the ports that Netalyzr tests, but everything is safe.
You can visit the site and take the test at ICSI Netalyzr’s page hosted by UC-Berkley. Be sure to check out their links to similar projects if this kind of thing interests you.
I dont think Netalyzr is a big fan of open dns
Agreed. It throws a flag but if you know you’re using OpenDNS, it should be safe to ignore.
Other things like NameBench are not fans of OpenDNS either.
@Jason H
Hm? I was testing DNS for recent post and namebench gave OpenDNS first place on my connection.
If you get bad results maybe it does perform poorly on yours.
I too have been investigating DNS for a post. Google Public DNS (though lacking many features) beat OpenDNS in 3 different environments where I tested it, but lacks any of the features beyond the infrastructure. I use OpenDNS and would recommend it.
Here’s my article on the service: http://www.404techsupport.com/2010/02/10/opendns-pt-1-a-solution-to-many-problems/
NameBench just seemed to provide a note for OpenDNS because it didn’t like the fact that you’re redirected to their “Couldn’t Find” page when you type in a non-existent URL.
This test must be done with your firewall OFF
I tried running it and it just crashed my firefox (3.6)