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utorrent 1.8.1 completely killing internal LAN speed o_O


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Hey All,

I've had this problem for quite a while and decided to do something about it today ;)

I have 2 computers on a LAN I set up.

Both PCs are connected to a switch and this switch is connected to an ADSL modem-router.

PC1 is,, (ip of modem-router)

PC2 is,, (ip of modem-router)

When utorrent is closed, everything is fine, copying files from a PC to the other uses around 75% of the LAN network speed (100Mbps).

If one PC is uploading to, for exemple, megaupload.com using 100% of the upload speed allowed by my internet connection (around 80ko up), I can still copy files from one PC to the other on the LAN at full speed (75% of network usage as seen in task manager).

However, as soon as I open utorrent on any of the PCs, even if i'm downloading at 5ko and uping at 2ko in uto, it completely kills file transfer on the LAN (!?).

If utorrent runs alone, network utlization in task manager shows less than 1% usage.

If I initiate a file transfer to the 2nd computer on the LAN, usage will show between 6-10% maximum as long as utorrent is opened. If I close utorrent, it jumps to 75%.

How does that make any sense?

How could the fact that utorrent is opened have any influence on the LAN speed AT ALL?

I just don't get; please enlighten me ;)

Again, If i maximize my internet upload speed, like uploading to megaupload or sending files via FTP, file transfer on the LAN is normal (75% usage).

So what exactly is utorrent doing?

Thanks for any help.



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Hi littlefire,

Yes, I tried the steps from the sticky, disables DHT, local peer echange, reduced max global number of connections and number of connections per torrent to respectively 200 & 50, also capped my upload to 50 out of 80 my internet connection can do... but it doesn't help.

In any case how do these utorrent settings have any effect on the internal LAN speed!

I'm nowhere near maxing the network usage when utorrent works, even when all the above is enabled; it reaches like 6% of network usage in task manager when I'm downloading fullspeed (700ko down in utorrent).

The LAN is 100Mbps, and I'm nowhere near maxing it's speed, yet file transfer between the 2 computers is insanely slow :/

Thanks for your support,


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I use Kaspersky anti-virus on both PCs. I've checked the LAN behavior when they're both totally disabled and the problem remains. I don't use a firewall. On both Network card settings, only "Microsoft client", "File sharing" and "TCP/IP" are enabled. I'm on XP SP3 with latest updates on both PCs.

See you,


edit: i also patched the TCPIP DLL to 50 instead of default 10 on both PCs, same results.

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Disable in uTorrent:

DHT, LPD, UPnP, NAT-PMP, and Resolve IPs.

Leave Peer Exchange enabled, as it reuses existing connections instead of making new ones like the above items do.

Try setting net.max_halfopen very low for testing -- like 1-4.

Also for testing, reduce global and per-torrent connection max to only 20 and 10.

Then see if LAN speeds are still killed. If so, you've probably got some serious issues with your computer's networking -- either drivers are corrupt or viruses/trojans/spyware is present or...well I haven't a clue except it's probably bad.

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