Showing posts with label Packet Shaping. Show all posts
Showing posts with label Packet Shaping. Show all posts

Tuesday, August 21, 2007

Bit Torrent and Comcast

According to the latest reports, Comcast is hindering Bit Torrent traffic and doing packet shaping. Their method of "throttling" torrent traffic is sending RST packets.

These are the ports that will be affected: (Brian's BitTorrent FAQ and Guide)
Prior to version 3.2, BitTorrent by default uses ports in the range of 6881-6889. As of 3.2 and later, the range has been extended to 6881-6999. (These are all TCP ports, BitTorrent does not use UDP.)

Intrusion detection
"A standard transmission control protocol (TCP) connection is established by sending a SYN packet to the destination computer. If the destination is waiting for a connection on the specified port, it responds with a SYN/ACK packet. The initial sender replies with an ACK packet, and the connection is established. If the destination computer is not waiting for a connection on the specified port, it responds with an RST packet.
Most system logs do not log completed connections until the final ACK packet is received from the source. Sending an RST(Reset) packet instead of the final ACK results in the connection never actually being established."


INFO: Winsock TCP Connection Performance to Unused Ports
"Upon receiving the ACK/RST client from the target host, the client determines that there is indeed no service listening there. In the Microsoft Winsock implementation of TCP, a pending connection will keep attempting to issue SYN packets until a maximum retry value is reached (set in the registry, this value defaults to 3 extra times).

Since an ACK/RST was received from the target host, the TCP layer knows that the target host is indeed reachable and will not double the time-out value in the packet's IP header, as is standard during connection attempts with unacknowledged SYNs. Instead, the pending connection will wait for the base connection's time-out value and reissue another SYN packet to initiate a connection. As long as an ACK/RST packet from an unused port is received, the time-out value will not increase and the process will repeat until the maximum retry value is reached."

So perhaps a way around this is to not use the normal ports that are associated with regular Bit Torrent Protocols as I am sure that they are being monitored. If this is done to all ports then people will start to complain about their service being disrupted on a wide range scale.


What is your opinion?

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