I spoke with a VERY knowledgable tech at Comcast who cut me off as soon as I said "VPN" and said he knows exactly what the problem is. He told me to check the brand of my modem and when I said Technicolor he said "there's your problem". He spent some time connected to my laptop (and onward to my modem admin page) trying to change the modem settings to get it to work, but eventually he told me to return the modem to the Comcast office and get a Cisco replacement. I did that and the VPN worked fine, with no changes in settings.
... View more