IPv6 over IPv4 (6in4) seems to be blocked
I've been using IPv6-over-IPv4 tunnel with Comcast Bussiness for a while without any problems.
Starting this Firday (Jul 24th, around 5am) all tunnel traffic (proto 41) seems to be blocked somewhere at Comcast or Comcast provided modem (CGA4131). Modem is in pass-thriough mode (all firewalling should be disabled according to the modem web UI). I suspect modem fw was updated and something got broken.