Unfortunately, these more aggressive throttling methods can’t be circumvented by simply enabling encryption in your BitTorrent client. It is reported that Comcast is using an application from Sandvine to throttle BitTorrent traffic. Sandvine breaks every (seed) connection with new peers after a few seconds if it’s not a Comcast user. This makes it virtually impossible to seed a file, especially in small swarms without any Comcast users. Some users report that they can still connect to a few peers, but most of the Comcast customers see a significant drop in their upload speed.

The throttling works like this: A few seconds after you connect to someone in the swarm the Sandvine application sends a peer reset message (RST flag) and the upload immediately stops. Most vulnerable are users in a relatively small swarm where you only have a couple of peers you can upload the file to. Only seeding seems to be prevented, most users are able to upload to others while the download is still going, but once the download is finished, the upload speed drops to 0. Some users also report a significant drop in their download speeds, but this seems to be less widespread. Worse on private trackers, likely that this is because of the smaller swarm size

Well, okay, reading further, you can apparently stop Comcast's reset packets at your (unix) firewall with

iptables -A INPUT -p tcp –dport $TORRENT_CLIENT_PORT –tcp-flags RST RST -j DROP

This should be getting a lot of attention because it goes to the heart of the net neutrality argument. What kind of rights do consumers have to shape their own entertainment world?
- tom moody 8-19-2007 2:54 am

From their agreement for residential service:

Prohibited Uses of HSI [High Speed Internet]. You agree not to use HSI for operation as an Internet service provider, a server site for ftp, telnet, rlogin, e-mail hosting, "Web hosting" or other similar applications, for any business enterprise, or as an end-point on a non-Comcast local area network or wide area network. You agree to indemnify, defend and hold harmless Comcast and its affiliates, suppliers, and agents against all claims and expenses (including reasonable attorney fees) arising out of any breach of this Section including, but not limited to, any claims based on or arising out of any material violation of any applicable law.

Prohibited uses include, but are not limited to, using the Service, Customer Equipment, or the Comcast Equipment to:

[...snip...]

xiv. run programs, equipment, or servers from the Premises that provide network content or any other services to anyone outside of your Premises LAN (Local Area Network), also commonly referred to as public services or servers. Examples of prohibited services and servers include, but are not limited to, e-mail, Web hosting, file sharing, and proxy services and servers;

letter to boxer

- mark 8-19-2007 8:23 am

Comcast denies throttling BitTorrent traffic.
- jim 8-22-2007 7:22 pm

I have noticed some disruption.
- jimlouis 8-23-2007 12:58 am