How to configure a automatically native IPv6 connection on FreeBSD

First you need to install a DHCP client

Setup config for dhcp6c

Add the following

Add the following to /etc/rc.conf

Run the IPv6 startup script.

Now startup the client

To test the connection you should be able to ping XS4ALL.

You also might want to check out these posts for some more information:
How to use a PPPoE or PPPoA connection of XS4ALL on FreeBSD

How to configure IPv6 DHCP client for XS4ALL on FreeBSD

How to configure a IPv6 gateway for XS4ALL on FreeBSD