Talks to our forum user who first discovered practice...
A few months ago, an astute user in our forums started noticing that Comcast (in addition to their invisible download limits
) was using Sandvine traffic-shaping hardware, installed at the CMTSs, to limit the effectiveness
of BitTorrent seeding. The goal is to manage BitTorrent traffic without tipping off mainstream users that it's being done. Here's how it works, according to resident user Robb Topolski
, who has been dissecting the practice for months:
"The Sandvine application reads packets that are traversing the network boundary. If the application senses that outbound P2P traffic is higher than a threshold determined by Comcast, Sandvine begins to interrupt P2P protocol sequences that would initiate a new transfer from within the Comcast network to a peer outside of the Comcast network. The interruption is accomplished by sending a perfectly forged TCP packet (correct peer, port, and sequence numbering) with the RST (reset) flag set. This packet is obeyed by the network stack or operating system which drops the connection."
When asked about the practice, Comcast consistently denies any application blocking, but chooses their words carefully
. Ultimately, our users found they could get around the practice by enabling forced encryption
on many BitTorrent clients. So far, the game of cat and mouse had been ignored by major outlets, given that the sanctity of TCP/IP doesn't make compelling mainstream news fodder.
The Associated Press
changed that today by testing and confirming the practice using a copy of the Bible
. The AP reporter gets the stock response from Comcast about the use of Sandvine gear, but also speaks to Topolski and BitTorrent companies (some of them obviously video competitors) impacted by the practice. It didn't take long for network neutrality supporters to lambast Comcast