IPv6 router behind AT&T U-Verse Motorola NVG510

I've tried for a long time to use IPv6 on a PfSense router behind the modem. The closet tutorial I found was this one on PfSense forum but I could not make it work the way I wanted. So I'll explain here how I managed to finally route my given IPv6 subnet.

AT&T Provide a /60 subnet which could easily be 'cut' into 8 pieces of /64. Only the first /64 is used by the modem for connected users so we'll play with the 7 other pieces of the cake. This should give us enough space for 129 127 208 515 967 000 000 machines.

Let's explain this with a simple table:

First, let's connect the WAN Interface of our router to any port of the modem and activate DHCPv6 client:

I could not make the subnet delegation options work properly so let's simply disable it:

By default every IPv6 compatible machine will have at least two addresses:

• the public one
• the link local one which is used for communications within the LAN.

Now I'm gonna grab the Link Local address of my PFSense WAN Interface

And we gonna tell the modem to send the /64 subnet to this address. To do that, let's open a console on the modem itself. I used that trick to get a CLI access on the modem:
http://earlz.net/view/2012/06/07/0026/rooting-the-nvg510-from-the-webui

After that, I just had to fire a shell by pressing ! and add these ipv6 routes :

ip -6 route add 2602:301:xxxx:xx1::/64 via fe80::215:60ff:fe0e:xxxx dev br1

ip -6 route add 2602:301:xxxx:xx2::/64 via fe80::215:60ff:fe0e:xxxx dev br1

ip -6 route add 2602:301:xxxx:xx3::/64 via fe80::215:60ff:fe0e:xxxx dev br1

That's it ! Of course the routes will be lost at the next reboot. I'm still trying to find a way to make these changes permanent without breaking the modem


Now let's use our available IPv6 subnet on the LAN side of our Router :

I'm assigning the IPv6 manually, taking the first available IP of the first subnet. Due to AT&T IPv6 in IPv4 encapsulation we should decrease the MTU to 1472 and the MSS to 1412.

Now let's setup the DHCP Server and Router advertisement on the LAN side :

Here is the result :