FreeBSD is a 4.4BSD-Lite2 based operating system. It is free for all, and licensed under the BSD license. It contains a mature IPv6 stack. The first version to contain IPv6 support was FreeBSD 4, which included the KAME stack.
Several ports to support IPv6 users are included in the FreeBSD ports collection, which includes a variety of free and open-source software. These include net/sixxs-aiccu, net/ipv6calc, net/ipv6gen, net/radvd, net/gateway6, net/openvpn, and more.
Several types of tunnels are supported. Generally, these use the gif or tun devices, depending on the type of tunnel used.
IPv6 is supported in the GENERIC kernel which is installed when you install FreeBSD from release media. In order to explicitly compile IPv6 support into your kernel, the configuration must include the INET6 option directive. You may also wish to include support for the gif or faith devices.
Building ports and/or world
The following line can be added to your /etc/make.conf to enable IPv6 by default when building ports or world: