Comcast turned IPv6 (through DHCPv6-PD) on by default on for all of their residential customers a little while ago, have had it on-by-default in many cities for

Comcast turned IPv6 (through DHCPv6-PD) on by default on for all of their residential customers a little while ago, have had it on-by-default in many cities for quite some time, and have had it opt-in for even longer. Additionally, their core infrastructure has been IPv6 only for a very long time.