Slow download, fast net - Eliminated everything!

[Masterdog]

Help me with a differential diagnosis on this one:

For the last month or so, I've been getting download speeds of a maximum of around 50kb/s on a fully-seeded test torrent. Most torrents are coming in at around 5kb/s. My net connection maxes out at around 820kb/s (on a Usenet download for example). The problem affects my main PC as well as my laptop and torrent client on my phone. ONLY torrents are affected, and it happens regardless of torrent client (it's not a uTorrent problem). Upload speeds are not affected.

I've tried the following:

- Properly followed the port forwarding guide

- Put computers in a DMZ

- Replaced the router and done the two above things again

- Checked the speed issues thread and followed the advice (have now reset to default any changes I made)

- Used a Speedtouch USB modem directly from one of the laptops to the internet. This worked fine, so it's not the ISP throttling the connection.

Here's the state of things:

- The network status light in uTorrent is green.

- The port checker reports that the port is open

- My bandwidth configuration was automatically set as: Upload Limit 46kb/s, Upload slots 4, Connections per torrent 80, Global connections: 230, Max active torrents 3, Max active downloads 2. (I did have the Upload Limit set lower, to 30, and still had the problem).

- net.max.halfopen is set to 100 - was set to 4 as per the speed guide but didn't make a difference

- OS is Windows 7 - other OSes affected are Vista, MacOS (had to borrow a Mac for work) and Android 2.2

- I've disabled the Windows Firewall and the firewalls on both my routers

- The routers I've tried are a Belkin F5D7632 and a Linksys WAG-120N. The USB modem which worked was a Speedtouch 330

- My ISP is a small outfit called Vispa

- My line is an ADSL one. The speed guide reports 471.85kbit/s up and 6.73mbit/s down. Very occasionally I get Error 10053 on the speed guide though.

Thanks for reading all this...hope somebody can suggest something as I'm completely foxed.

Cheers,

MD

tl;dr - slow torrents, everything else fast. Not router, not ISP, not port forwarding, not uTorrent. Help!

[DreadWingKnight]

What kind of modem is the main modem you use?

[Masterdog]

I don't use a modem - both routers have ADSL modems built into them. Sorry, should have made that clear.

[DreadWingKnight]

Which may actually be part of the problem. Some Belkin devices are actually notorious for having HORRENDOUSLY low connection limits (to the tune of 64 global max across ALL connected devices). Additionally, some Linksys devices have problems with their firmware from official sources.

SPI firewalls need to be completely turned off in routers regardless. All they really do is tie up router resources for no security benefit.