Linux IPv6: Which One to Deploy?

If you are hesitant as to which IPv6 implementation to adopt for your Linux server, this article will help you decide.
Lessons Learned

Typically, working on such assignments, a lot of learning and competence building takes place. However, there are always some special lessons that you learn along the way, and they are worth mentioning.

It always pays to simplify problems. For instance, it was not obvious to know why a ping6 was able to crash the Linux kernel (v. 2.4.5) while we were running three web servers (Apache, Jigsaw and Tomcat) with patched code for IPv6 support in addition to an Alpha version of Java Merlin 1.4. Things got clearer when we disabled these servers and the Java Virtual Machine.

Also, adopting a complete implementation is much easier and more flexible than deploying patches. In some cases, we were faced with some bugs, and it was not easy to tell where they came from. Was it the application's IPv6 patches, the USAGI IPv6 kernel patches or the IPv6 patched binaries? Simplifying the problem helped a lot but proved that it may be easier to adopt the complete integrated implementation rather than patches that are downloaded and applied individually.

One important issue to mention is that our experience with the Open Source community has been a very positive one. People working with open-source software do their best to help you fix bugs and answers e-mails quickly. Since most of the software we use on our Linux clusters is based on open source, sometimes we go back to the community with questions, and we had no problems getting support from the developers—an important factor to acknowledge.


The Linux kernel IPv6 implementation has not undergone any major development since 2.4.0 was released. In many cases, we were able to crash the kernel with IPv6 traffic. On the other hand, USAGI provides an IPv6 implementation for Linux that is ported from the FreeBSD IPv6 stack, which is one of the best IPv6 implementations currently available. It also has proved to be more stable and reliable, and had better conformance test results than the Linux kernel implementation. The conclusion that can be drawn is that the USAGI stack is at least more mature than the kernel implementation and provides more functionalities and compliance with the specifications.

If you want to make a decision as to which IPv6 implementation to deploy on your Linux servers based on different factors, such as the development status, the number of people working on it, the support it's getting from industry and academia and its compliance with the latest RFCs, then it is most likely that you will choose the USAGI IPv6 implementation. Nevertheless, there is an important concern related to both implementations. Unfortunately, a complete “implementation” document describing all the supported RFCs and motivations behind different design decisions does not exist.

I hope that the Linux kernel community and the USAGI Project can work together more tightly and organize their efforts to bring to pass a very stable and efficient IPv6 implementation for Linux. I believe the result would be a Linux kernel with a stable and well-written IPv6 implementation—a needed success formula for the future IPv6 servers contributing to the making of the mobile internet.


Open Systems Lab at Ericsson Research Canada for approving the publication of this article; Marc Chatel, Bruno Hivert and David Gordon at Ericsson Research Canada for their help and support in the lab; and Conformance Lab at Ericsson Research Hungary for conducting the conformance tests.


Ibrahim Haddad (, currently is a researcher at the Ericsson Corporate Research Unit in Montréal, Canada. He is primarily involved in researching carrier-class server nodes for real-time all-IP networks.