New proposed Bittorrent enhancement to overcome ISP's traffic shaping / disconnection

From Torrent Freak...

BitTorrent Developers Introduce Comcast Busting Encryption

Written by Ernesto on February 15, 2008

Several BitTorrent developers have joined forces to propose a new protocol extension with the ability to bypass the BitTorrent interfering techniques used by Comcast and other ISPs. This new form of encryption will be implemented in BitTorrent clients including uTorrent, so Comcast subscribers are free to share again.

BitTorrent throttling is not a new phenomenon, ISPs have been doing it for years. When the first ISPs started to throttle BitTorrent traffic most BitTorrent clients introduced a countermeasure, namely, protocol header encryption. This was the beginning of an ongoing cat and mouse game between ISPs and BitTorrent client developers, which is about to enter new level.

Unfortunately, protocol header encryption doesn’t help against more aggressive forms of BitTorrent interference, like the Sandvine application used by Comcast. A new extension to the BitTorrent protocol is needed to stay ahead of the ISPs, and that is exactly what is happening right now.

Back in August we were the first to report that Comcast was actively disconnecting BitTorrent seeds. Comcast of course denied our allegations, and ever since there has been a lot of debate about the rights and wrongs of Comcast’s actions. On Wednesday, Comcast explained their BitTorrent interference to the FCC in a 57-page filing. Unfortunately they haven’t stopped lying yet, since they now argue that they only delay BitTorrent traffic, while in fact they disconnect people, making it impossible for them to share files with non-Comcast users.

In short, the Comcast interference works like this: A few seconds after you connect to someone in a BitTorrent swarm, a peer reset message (RST flag) is sent by Comcast 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.

For the networking savvy people among us, here’s an example of real RST interference (video) on a regular BitTorrent connection. In this case, the reset happens immediately after the bitfields are exchanged. Evil? Yes - but there is hope.

The goal of this new type of encryption (or obfuscation) is to prevent ISPs from blocking or disrupting BitTorrent traffic connections that span between the receiver of a tracker response and any peer IP-port appearing in that tracker response, according to the proposal.

“This extension directly addresses a known attack on the BitTorrent protocol performed by some deployed network hardware. By obscuring the ip-port pairs network hardware can no longer easily identify ip-port pairs that are running BitTorrent by observing peer-to-tracker communications. This deployed hardware under some conditions disrupts BitTorrent connections by injecting forged TCP reset packets. Once a BitTorrent connection has been identified, other attacks could be performed such as severely rate limiting or blocking these connections.”

So, the new tracker peer obfuscation technique is especially designed to be a workaround for throttling devices, such as the Sandvine application that Comcast uses. More details on the proposal can be found at BitTorrent.org, which aims to become a coordination platform for BitTorrent developers.