FYI: Comcast + SMC D3GCCR or Cisco DPC3939B

[MrMoo]

This is important information that should be in this forum for a bit, Comcast business connections can give any of three different devices,

SMC D3GCCR - modem doesn't route the sub-prefix delegation correctly breaking ipv6 connectivity
Cisco DPC3939B - ipv6 works properly for directly attached computers but the sub-prefix delegation isn't working
Netgear CG3000CDR - ipv6 for directly attached computers and sub-prefix delegation for router/firewall work correctly

http://forums.businesshelp.comcast.com/t5/IPV6/Dual-Stack-on-SMC-D3GCCR-and-Cisco-DPC3939B/td-p/20504

Comcast is working with the vendor(s) to get new firmware that fixes these issues, so don't go crazy thinking your pfSense configuration is wrong.