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BitTorrent speed tip. - Adventures in Engineering — LiveJournal
The wanderings of a modern ronin.

Ben Cantrick
  Date: 2006-01-26 20:48
  Subject:   BitTorrent speed tip.
Public
  Music:"And knowing is half the battle! GEEEEE-EYEEEEEE-JJJOOOOOO!"
I just configured my BitTorrent client to not allow connections from people using the default 6880-6889 data ports... and I'm seeing about a 5x sustained improvement in transfer rates. (~20K/sec to ~100K/sec.) My guess is that this is related to the cable modem companies who either traffic shape or throttle BitTorrent traffic. They apparently haven't implemented stateful packet inspection yet, and are only shaping/throttling by port number. Hence, anyone who uses the default ports (or anyone who tries to transfer files with someone using the default ports) gets throttled. Anyone who doesn't, gets the kind of speeds that BitTorrent was designed to give. (I'm assuming, of course, that you've correctly configured your firewall for BT in the first place. Cuz you won't ever get above 10K/sec without doing that.)

Also, if you're using a LinkSys WRT-54 series router (and a lot of us are), their TCP/IP implementation sucks donkey balls. You can install an embedded version of Linux on it that will perform better. But this is recommended only for advanced users, since if you screw it up you can destroy the router.

So now you know.
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Ben Cantrick
  User: mackys
  Date: 2006-01-26 23:59 (UTC)
  Subject:   (no subject)
In general, it's a lot cheaper for ISP's to do traffic control based on ports. Nearly any router can do that. Not every router can do SPI, and it takes a lot of CPU to do it.

Odd to see you seemingly jump to the defense of the ISPs here. I didn't intend this post as a criticism of them.

Small ISP's could do it using a Linux box as their router, but might lack the expertise. I would bet that large ISP's have the expertise, but don't consider the problem to be big enough to be worth committing the time - so they just use quick and dirty port throttles.

And people are lazy. Most BT users don't bother changing the default ports, so the Q&D port throttling does work for the most part.

What's more, shaping by ports is less likely to kill something else as an unintended consequence.

Um no, absolutely wrong. Stateful Inspection implemented with even a modicum of competence is far LESS likely to cause unintended consequences than blind port filtering. It is, by design, a far more selective and careful method of deciding which packets to operate on.


-Ben
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  User: jigenm4c
  Date: 2006-01-28 00:59 (UTC)
  Subject:   Hmmm...
Maybe we should install that other firmware. I've been toying with that idea for a while now, anyway.
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