A single fast connection blocks almost all other network activities

Hi!
If I have a single fast up/download (or enough smaller/slower ones), it is able blocks almost all other network activities:
Torrent without up/down limit => everything else is "timing out" (or something. P.e. load a single page in firefox or ping my router - doing nothing).
Pacman is fetching a package from a fast server => the same.
Pages in firefox don't load if I just stop the fast traffic - it keeps doing nothing until I hit [reload].
Tested a few other network applications (java stuff, wget, curl, whatever pacman uses), it all looks the same.
This hasn't been like this up until a while ago (1-2 weeks?)... during that time, I changed nothing in the whole network except for
1) the arch updates (normal mirrors, no testing)
2) added a debian machine to the network (problem persists if I shut it down though)
Now I don't know where to start searching. Any hints?
Thanks!

As I understand things you are saying one fast connection is blocking out all other connections right?
If so we need some more information.
1. Your basic setup, like are you using a cable modem and what router. wireless?
2. The result of speed tests on your connection both upload and download (e.g. testmy.net)
3. What is the "one" fast connection and how much bandwidth is it taking (bittorrent?)
One thing to look for is that certain routers cannot handle many connections. A few of my old WRT54G routers with stock firmware could only handle 200 connections or so before crashing. So now I use dd-wrt on a WRT54GL.
Some more info on what might be happening:
1. The torrent client is using all the connections so the router cannot handle more connections.
2. The torrent client is taking all the upload bandwidth so the behaviour you describe occurs.
3. The torrent client is taking up all the download bandwidth.
[less likely]
4. Some complex ISP shaping and/or bandwidth limiting?
5. Malfunctioning network hardware locally (i.e. router, NIC, etc.)
6. Wireless router encountering interference thus limiting bandwidth severely?
Some Possible solutions (assuming the common stuff is the case):
1. Get a Better router/firmware.
2. Configure the torrent client to limit connections/upload/download.
3. Setup complex limiting on the local box using iptables.
4. Ties in with #1. Configure router to implement QoS and/or bandwidth limiting based on Application layer protocol/port/Ip address/mac etc. dfepending on situation.
Last edited by davidm (2010-02-07 19:40:38)

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A single fast connection blocks almost all other network activities

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