Telenet is an ISP in Belgium that provides its customers with IPv6. Everywhere I looked on the net I read that you should configure your firewall with a /56 IPv6 prefix, but I could not get it to work with my modem in bridging mode. I got it working after changing it to /57. Read along for the full explanation

I do not know if this is required, but I specifically requested a modem only installation by the technician. I got a DOCSIS 3.1 E-ROUTER, Compal CV8560E HGW3.1, a.k.a. Marakele.

The first step is enabling bridge mode on the Mijn Telenet customer portal:

1. Internet > Je thuisnetwerk > Modem details > Geavanceerde instellingen
2. You are now on the Telenet-modem – Geavanceerde instellingen page. Enter the MAC-address of the WAN interface of your pfSense in the MAC-adres field and click on Wijzigingen opslaan

Then on your pfSense firewall:

1. Interfaces > WAN
   • IPv6 Configuration Type: DHCP6
   • DHCPv6 Prefix Delegation size: 57
   • Enable Send IPv6 prefix hint
   • Disable Block bogon networks
2. Interfaces > LAN
   • IPv6 Configuration Type: Track Interface
   • Track IPv6 Interface: WAN
   • Track IPv6 Previx ID: 0

That should be it!

Thank you Wim van Eupen for updating the change form prefix 56 to 57.