Updated!, see below
: Network researchers at the University of Colorado have dug more deeply
into Comcast's new network management practices. Comcast continues to use
forged TCP RST packets (essentially faking communication from your PC saying you aren't there) to derail connections and disrupt upstream BitTorrent traffic
. Now, if this report is to be believed, Comcast is applying the same concept to all TCP traffic. From their research notes:
We have recently observed this shift in policy, and have collected network traffic traces to demonstrate the behavior of their traffic shaping. In particular, we are able (during peak usage times) to synthetically generate a relatively large number of TCP reset packets aimed at any new TCP connection regardless of the application-level protocol.
Researcher Kevin Bauer tells us that Comcast essentially just super-sized their previous traffic shaping practices. The researchers claim this broader approach now impacts far more than just BitTorrent traffic, and can now impact e-mail or web browsing:
Surprisingly, this traffic shaping even disrupts normal web browsing and e-mail applications...Users may find it extremely difficult to establish new TCP connections while using any application that has a relatively high rate of TCP connection establishment on a Comcast link.
Comcast, in contrast, tells us this is not
the new "protocol agnostic" approach discussed in their recent announcement
, and repeated to us that their new traffic shaping system would not be implemented until the end of the year. We're digging into the claims and are seeking additional comment from Comcast. Update
: Comcast spokesperson Charlie Douglas e-mails us this official response:
I can confirm that we have not made any shift in our network management policy yet and have not implemented the protocol agnostic approach that we announced two weeks ago. At that time, we said we would migrate to this new system before the end of the year. We are currently attempting to contact the PhD students and associate professors at the University of Colorado to better understand their analysis.
: Researchers at the University of Colorado have now retracted their findings after talking about the situation with several network engineers:
A note regarding our findings: Further experiments have led us to believe that our initial conclusions that indicated Comcast's responsibility for dropping TCP SYN packets and forging TCP SYN, ACK and RST (reset) packets was incorrect. Our experiments were conducted from behind a network address translator (NAT). The anomalous packets were generated when the outbound TCP SYN packets exceeded the NAT's resources available in it's state table. In this case, TCP SYN, ACK and RST packets were sent. We would like to thank Don Bowman, Robb Topolski, Neal Krawetz, and Comcast engineers for bringing this to our attention. We sincerely apologize for any inconvenience that this posting may have caused.