State of IPv6: Web Sites Now Offer Easy IPv6 Connectivity Tests

April 14, 2014 Bill Cerveny

There is a certain level of skill to creating an IPv6-capable network. There is even more skill to creating an IPv6-capable network correctly. To help confirm an IPv6-capable network has been configured correctly and that “upstream” IPv6 connectivity is correct, there are several Web sites which offer basic insights into the quality of IPv6 connectivity.

Such sites have been around in one form or another since at least 2000. The most famous early “test” Web site was perhaps “” – if the turtle (“kame” in Japanese) moved, the site was being reached via IPv6. The openly available “ipv6calc” software included a CGI that allowed one to confirm not only what IP version one was reaching the Web site with, but also information about the address.

To verify basic IPv6 functionality, a good starting point is the Web site “”.  This Web site provides an IPv6 readiness score from 0 to 10 and measures both client and network IPv6 readiness. In addition to testing for basic IPv6 capabilities, it reports on a sampling of IPv6-enabled destinations that can be reached, as well as IPv6 DNS and large packet support. The site is based on open-source software and source code can be found at There are also numerous mirrors around the world.

Another IPv6 test Web site is, not to be confused with mentioned above. This site offers Path MTU tests. is a bit less specific than about exactly which tests it performs and does not appear to provide source code or mirrors, as far as I can tell.

A site which offers more comprehensive testing of both IPv4 and IPv6 connectivity is the ICSI “Netalyzer.” This site was funded via a grant from the National Science Foundation and operated by the International Computer Science Institute at University of California -Berkeley. It performs a variety of IPv4 and IPv6 tests, including checks for open network ports, fragmentation functionality, path MTU discovery, general DNS functionality and DNSSec. Netalyzer information is accessible via a Web browser or by running a Java application on the command line. On initial inspection and after an unsuccessful attempt to reach the creators of the site, it appears source code is not available.

Certainly, these Web sites only provide a small amount of data in the quest to fully understand the network that one is connected to and there are other diagnostic tools one should seek to obtain a more comprehensive understanding of characteristics, connectivity and performance of a network.  However, these tools provide an excellent overview of basic IPv6 connectivity and network capabilities.

According to Jason Fesler, developer and maintainer of the Web site and the source code, the goal of test-ipv6 was not only to provide basic IP address information, but to help visitors identify certain failure conditions. Said Fesler, “Having no IPv6 is one thing; but having misconfigured IPv6 is a very different problem with very negative user experience issues.  Today, the browsers mostly work around those user experience issues; which create a different headache for system administrators — hiding the problems.”



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