My monthly data usage had always been under 300 GB. Then, suddenly Xfinity says my data usage for September is 1187 GB and counting, despite nothing changing on my end. So, I tried to look into it.
Here's my setup: I'm using an SBG6580 cable modem. There are only three devices that should ever be connected to it: two desktop computers connected via ethernet, and my smart phone over wi-fi. It shows that only one device has connected to the wi-fi recently, and it's the MAC address of my phone. Also, the wi-fi password is a randomly-generated 32-character hexadecimal string, which is not realistically crackable by brute force.
The phone's wi-fi data usage shows 0.98 GB used from August 31 through today, September 28. And only part of that is from my own wi-fi; part of that number comes from the wi-fi I used at work.
The two desktop computers are both Linux computers, and I'm extremely careful about what software I install on them. I'm also the only person living in the house, and the only person with access to the computers. One of them computers is my primary workstation, and the other is essentially a stand-by that I only use for nightly backups of my primary computer.
On my secondary computer, running uptime shows that it has been running for 58 days since the last reboot. Running ifconfig shows that, over those 58 days, it has received a total of 75.3 GB and transmitted a total of 889.7 MB. I happen to know that nearly all of that data was from nightly backups of my primary computer, which occurs directly within my local network (via rsync) and should never touch the Internet. The secondary computer also gets system updates, but little else.
On my primary computer, running uptime shows that it has been running for 110 days since the last reboot. Running ifconfig shows that, over those 110 days, it has received a total of 792.7 GB and transmitted a total of 105.6 GB. Again, it's likely that a majority of that transmitted data was from the nightly backups, which wouldn't have touched the Internet. So, realistically speaking, my data usage comes almost entirely from the amount that my primary computer received: around 800 GB. Over the course of 110 days. That averages at around 225 GB a month, which is about equal to what Xfinity shows as my average monthly usage up until September, when Xfinity suddenly shows that I used 1187 GB in a single month.
Simply put: Xfinity is incorrect. I didn't use anywhere near 1187 GB of data this month, unless nearly all of that data was transmitted to my home from Comcast's network unprompted and was blocked by my router. In other words, I'm being penalized for Comcast's own network problems that have nothing to do with my usage of their service.
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