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Anecdote: back in 2009, I had a Comcast account in a metered market and didn't need cable service for a bit, so I tried an experiment. I plugged my cable modem

Anecdote: back in 2009, I had a Comcast account in a metered market and didn't need cable service for a bit, so I tried an experiment. I plugged my cable modem into a dumb switch. It had a link, but there was nothing else attached; there was no router to act as a DHCP client, no frames being sent to the cable modem at all. In six days, my usage meter incremented by 0.5 GB. Plugging in a protocol analyzer revealed a constant stream of ARP requests for other subscribers' IPs. These were apparently counted against my cap, and presumably they were counted against everyone's caps, making 250 GB/month 1% smaller than advertised. Comcast sent me to a document describing their metering methodology: http://www.netforecast.com/documents/NFR5101_Comcast_Usage_Meter_Accuracy.pdf http://www.netforecast.com/documents/NFR5101_Comcast_Usage_M... Their reps defended the practice of counting Comcast-generated broadcast traffic against everyone, even though there's no way for subscribers to prevent it.

brodie78382 11y ago
This is a fantastic point that I don't see brought up enough. I have some anecdotal experience of my own to help illustrate what an issue this really is. Our ISP has recently enacted data caps. The first time they threatened to disable our account for going over, I pointed out to them that: - My firewall has logged tens of gigabytes of dropped/rejected traffic. - That if I ran a TCPDump on our WAN interface, could see management and broadcast traffic for neighboring CPEs (modem). - That I know for a fact (I used to work for them in a previous iteration) that their network isn't built in a way that would allow them differentiate their management and monitoring traffic from individual customer traffic. - And finally, that the Layer 2 & 3 statistics of that WAN interface were nowhere close to their own statistics for the account. They have yet to respond to that complaint, despite going to the FCC. I really wonder what would happen if one were to take their ISP to court with the proper documentation.

brodie78382 11y ago

This is a fantastic point that I don't see brought up enough. I have some anecdotal experience of my own to help illustrate what an issue this really is. Our ISP has recently enacted data caps. The first time they threatened to disable our account for going over, I pointed out to them that: - My firewall has logged tens of gigabytes of dropped/rejected traffic. - That if I ran a TCPDump on our WAN interface, could see management and broadcast traffic for neighboring CPEs (modem). - That I know for a fact (I used to work for them in a previous iteration) that their network isn't built in a way that would allow them differentiate their management and monitoring traffic from individual customer traffic. - And finally, that the Layer 2 & 3 statistics of that WAN interface were nowhere close to their own statistics for the account. They have yet to respond to that complaint, despite going to the FCC. I really wonder what would happen if one were to take their ISP to court with the proper documentation.