ADSL Modems and Torrents

My ZyXEL ADSL modem (some ancient Prestige model, too lazy to check now) was causing me a trouble since I remember: it frequently drops internet connection when I use uTorrent. It happens after a few minutes, and the only way to continue is to hard-reset the modem by powering it off-and-on, and then renew the IP address on the PC. Which is very-very annoying, as I use torrents for my work (we distribute software updates using torrents). Some other modems, as well as other torrent clients might have similar issue, I guess. So, today I decided to put an end to this crap and to find a solution.

The problem is very likely on the modem side – it seems to be not able to handle that high number of connections that torrent clients open. The solution is to get your torrent client “behaving nicely”. And here is what I did with my uTorrent:

  1. Disabled Resolve IPs in the Peers tab’s context menu (you must have at least one active torrent to be able to get this menu) – absolutely useless feature that allows you to see DNS names of peers.
  2. Set peer.resolve_country parameter in Preferences > Advanced to false. Same as above – totally useless feature that allows you to see countries of peers.
  3. Disabled DHT by clearing Enable DHT Network option in Preferences > BitTorrent. This step might not be needed, but I am not using DHT now, so it is not harming, but resources are freed.
  4. Disabed UPnP and NAT-PMP by clearing Enable UPnP port mapping and Enable NAT-PMP port mapping options in Preferences > Connection (of course, assuming you are not randomizing ports and using manual firewall configuration). This step might not be needed as well, but then again, that ZyXEL modem is not a UPnP/NAT device, so…
  5. Reduced Global maximum number of connections parameter to 50 in Preferences > Bandwidth. You can try higher values, but for me 50 works fine. In fact, torrents’ downloading speed increased by about 10% after I reduced this parameter from 200 to 50, while general web browsing performance improved a lot (before these changes it was really painful to browse internet while downloading torrents).
  6. Set net.max_halfopen parameter in Preferences > Advanced to 4. Many people say that they have problems after 5+, so the default 8 is definitely a problem.

The result – no more drops! :) To be honest, I think that the last two points should help on their own, but other points do not hurt either.

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