Encouraged by Matthias, I decided it was time to introduce my home network to IPv6. It turns out that this was a lot easier than I had expected it to be:

Client setup

For FreeBSD, adding ipv6_enable="YES" to /etc/rc.conf and rebooting was sufficient. Now all interfaces are able to communicate using IPv6.

Router setup

My Soekris router is currently running m0n0wall. With a halfway recent version (1.32), this was spectacularly easy: It boils down to enabling 6to4 on both WAN and LAN interfaces and adding an appropriate rule to the IPv6 part of the firewall. Here are some screenshots with the relevant parts highlighted (please click the images for larger versions):

m0n0wall LAN settings
IPv6 LAN settings
m0n0wall WAN settings
IPv6 WAN settings
m0n0wall firewall rules
IPv6 firewall rules

Caveat

The firewall rule is essential. m0n0wall will otherwise block any IPv6 traffic originating from your LAN.