Controlling IPv6 or IPv4 Preference
By default, the firewall itself will prefer IPv6 if is is configured and has a default route. It is possible to control whether services on the firewall itself will prefer IPv4 over IPv6. This may need to be changed in order to run a firmware upgrade or manage packages if for some reason the IPv6 routing is not functional but the system believes it is up and working.
In pfSense 2.2 this is controlled under System > Advanced on the Networking tab. Check Prefer IPv4 over IPv6, then click Save.
On pfSense 2.1.x, there is no option in the GUI. It can still be changed at the shell (or with a shellcmd tag.)
To prefer IPv4:
env ip6addrctl_enable="yes" ip6addrctl_policy="prefer_ipv4" /etc/rc.d/ip6addrctl start
To prefer IPv6 again: