How to configure a IPv6 gateway for XS4ALL on FreeBSD

You might first need these two manuals.

How to use a PPPoE or PPPoA connection of XS4ALL on FreeBSD

How to configure IPv6 DHCP client for XS4ALL on FreeBSD

Configuring your server as a router is quite simple.

First edit /etc/rc.conf and add the following

This configures IPv6 for your interface and tells it to function as a gateway.

Now setup the config for rtadvd so it will give out the right IP range. Edit /etc/rtadvd.conf

Now fire up a client connected to the LAN side on em0 and visit the following page to check if you are using IPv6:

Another useful page with information how to configure IPv6 on your server is in the FreeBSD handbook.