First of all, we must install IRIX subsystems (they are not installed by default). The ipv6 product includes these subsystems:

       eoe.sw.ipv6                   kernel resident IPv6 protocol
                                     stack, IPv6 specific user
                                     commands, system daemons and
                                     configuration files

       eoe.man.ipv6                  Irix man pages for IPv6
                                     specific commands

       eoe.man.ipv6_rn               Irix release notes for IPv6
                                     (this document)

Approximate sizes of these subsystems are as follows:

       Subsystem Name                Subsystem Size
                                     (512-byte blocks)

       eoe.sw.ipv6                           1306

       eoe.man.ipv6                            61

       eoe.man.ipv6_rn                         19

The IRIX release notes give some details for the installation.

       All of the subsystems for ipv6 can be installed using IRIX.
       You do not need to use the miniroot. Refer to the IRIS
       Software Installation Guide for complete installation
       instructions.

       If you are installing this product for the first time, the
       subsystems above are not marked for installation by default
       in the eoe base product. You must explicitly mark them for
       installation. If upgrading a system that already has the
       ipv6 subsystems installed, an "install upgrade" will pick
       them up along with any other subsystems that normally would
       be upgraded, provided the versions to be installed are
       newer.

The steps are basically : open IRIX overlays with inst and then install these packages.

You can also do this with the Software Manager. Just expand IRIX Execution Environment and select IP Version 6 Networking.

In order to activate basic IPv6 functionalities, you first have to enable it (disabled by default). The IRIX release notes says:

       A tunable flag is used to enable IPv6 on the system. This is
       set off by default when the product is initially installed.

       The value of the flag ip6_enable can be changed using the
       systune utility. Set this value to 1 to enable IPv6. No IPv6
       traffic will be passed by the kernel if this flag is set to
       0. A reboot is necessary for the tunable to take effect.

       Additional tunables for IPv6 forwarding and IPv6 automatic
       and configured tunnelling can be found in the
       /var/sysgen/mtune/bsd file. These features are turned off by
       default.

So let's enable it:

mattieu@IRIS: ~ $ sudo systune ip6_enable 1
        ip6_enable = 0 (0x0)
        Do you really want to change ip6_enable to 1 (0x1)? (y/n)  y
 
In order for the change in parameter ip6_enable to become effective,
reboot the system

Then you have to reboot the system as it was asked. After that, everything should work since stateless autoconfig is enabled by default with IPv6.