said by electroglyph:It's bridged.
My router clones the modem MAC and handles all DHCP.
That makes no sense at all, and it has nothing to do with whether or not your SBG6580 is in bridge mode.
Look at your router's WAN interface status. If it is getting a Comcast public IPv4 address from the Comcast DHCP server, then your SBG6580 is in bridge mode. If the router's WAN IPv4 address is in the 10/8 subnet, or the 172.16/12 subnet, or the 192.168/16 subnet, (see »
en.wikipedia.org/wiki/Pr ··· s_spaces ) then your SBG6580 is not in bridge mode.