Or someone in range of your Comcast router is using your xfinitywifi network.

Edit: this is incorrect apparently.

Those people don't share your IP address. That traffic is separate from customer traffic and encapsulated into a GRE tunnel back to Comcast.

Ah, I didn't realize that. I've got my own modem + router, I've only ever used my neighbors' xfinitywifi when I ran through my own data cap (that's a useful trick if you've got a data cap).

A number one reason to always buy your own equipment, and not pay to rent the shit that Comcast provides.

You can't for AT&T U-Verse. They won't assign an IP address to a 3rd party device. I've been meaning to get some cards and do some raw frame dumps to try to figure out how their Fiber modems work and see if I could get it to assign my own device an IP address. It's on the long list of things to do.

I've read how all you need is put the AT&T router behind your firewall and proxy the 802.1x packets to/from the AT&T device, thus faking out the upstream gateway.

I don't have AT&T so I didn't pay much attention to the details. One possible approach: https://github.com/jaysoffian/eap_proxy

xfinity has no affect on your connection at all. It uses its own IP, and the bandwidth used is not included in your allocation.

It has the same affect on you as your neighbor does.

Sure, but it's going through your router, right? So if you were torrenting and someone else jumped on the xfinity wifi and started torrenting, it would affect your ability to use your bandwidth, right?

As another post said, only jitter (and only minorly).

Bandwidth would be unaffected. Or more exactly, on WiFi (but not Ethernet): as affected as if your close neighbor used that amount (since WiFi itself has limited bandwidth). The connection from the router to the cable modem has lots of headroom, so that would be unaffected, as would wired connections.

yea, xfinitywifi affected our jitter test. We called Comcast to disable it & our jitter went down.