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Connections persist for days after removing/stopping a torrent


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Whenever I use uTorrent (or any BT client), which is rare now because of this problem, I get between several connections a second and a dozen connections a minute for roughly 2 days after stopping a torrent. The only reason I notice this is because I play online FPS's a lot, and can notice spikes in my ping in the netgraphs. Otherwise, I wouldn't even realize there was a problem. My download speed is not affected, nor is my upload speed. The only thing wrong is that I get LOTS of ping spikes. They're not severe, often only a 60ms spike for a few ms, but it's enough to make games unplayable. The problem is most severe roughly an hour after stopping the torrent, with 3-5 blocked connections a second. The hour before that my connection is close to normal, so my strategy now is to stop torrents right before I want to play a game. After about a day, the connections per second is down to a dozen a minute or so. About 2-3 days after stopping torrents, my connection is back to normal. This has been going on for well over a year, probably close to two. It's happened so many times that there is no doubt that it's uTorrent. That and my active sessions viewer on my router's control panel has hundreds of active sessions on my uTorrent port. After a day, it's down to 50-75 sessions. Normally, with nothing but my web browser running, it's less than 10.

I'm on a 10mbit down/1mbit up cable line. My ISP throttles torrents, but encryption takes care of that. I use a DLink DGL-4100 Gigabit router with QoS configured to have uTorrent as the lowest priority and games as the highest. It makes my connection more stable, but does nothing to fix this problem. I have onboard Gigabit by Realtek. I've also tried with onboard from nForce2 and onboard from a crap SiS chipset, and they both have the same problem, so it's not my NIC. I also doubt it's my router, since it's advertised as being capable of handling thousands of concurrent connections. For what it's worth, this seems to be true. I can have 4 or 5 torrents going with 1000 connections and it doesn't choke at all. I can fire up a game and play with only slightly increased ping. I have a newly purchased WRT54GL (Tomato firmware) acting as a WAP for my laptop and printer, so I could swap routers to test, if need be.

My uTorrent settings are as follows:

Max upload 80 kb/s

Max connections per torrent 200

Max upload slots 6

Max halfopen 8

Protocol encryption forced for outgoing

I've brought this up on numerous times and have been unable to fix the problem. I brought it up here a while ago but nothing anyone suggested fixed it.

Here's a sample of my log, roughly 24 hours after using BT to download 1 file for 2 hours:

[INFO] Tue Dec 02 19:04:47 2008 Blocked outgoing ICMP packet (ICMP type 3) from to
[INFO] Tue Dec 02 19:04:45 2008 Blocked outgoing ICMP packet (ICMP type 3) from to
[INFO] Tue Dec 02 19:04:33 2008 Blocked outgoing ICMP packet (ICMP type 3) from to
[INFO] Tue Dec 02 19:04:31 2008 Blocked outgoing ICMP packet (ICMP type 3) from to
[INFO] Tue Dec 02 19:03:57 2008 Blocked outgoing ICMP packet (ICMP type 3) from to
[INFO] Tue Dec 02 19:03:52 2008 Blocked outgoing ICMP packet (ICMP type 3) from to
[INFO] Tue Dec 02 19:03:48 2008 Blocked outgoing ICMP packet (ICMP type 3) from to
[INFO] Tue Dec 02 19:03:48 2008 Blocked outgoing ICMP packet (ICMP type 3) from to
[INFO] Tue Dec 02 19:03:45 2008 Blocked outgoing ICMP packet (ICMP type 3) from to
[INFO] Tue Dec 02 19:03:43 2008 Blocked outgoing ICMP packet (ICMP type 3) from to
[INFO] Tue Dec 02 19:03:42 2008 Blocked outgoing ICMP packet (ICMP type 3) from to
[INFO] Tue Dec 02 19:03:35 2008 Blocked outgoing ICMP packet (ICMP type 3) from to

I know someone's going to say my max connections is way too high. Yeah, maybe you're right, but let me say this:

why does it make no different if I have 1 torrent on or 5? That's a different of 800 connections, and there is no change in how many connections I get afterwards. I can also play games WHILE having ~1000 connections in BT and I don't lag any worse than I do a day after shutting BT down. If my router and connection were incapable of handling all these connections, why can I even play a game with BT on? Why will BT happily run with 1000 connections and keep speed stable? Why does my router barely break a sweat with all these connections, yet have a ping spike every time I get a blocked connection? Like I said, a day after shutting down BT, I have roughly 60 active sessions and maybe a dozen connection attempts from random IP's a minute. I'm playing a game that needs only a few connections, and maybe 5kb/s both ways, and one or two connection attempts in 5 seconds cause a ping spike? Something's not making sense.

Sorry, my post's all over the place, long, and probably a bit rantish. If anyone can help or has experienced the same problem, your input would be greatly appreciated.


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This is something kinda inherent in the way most clients are implemented. Because they cache peer IP:port combinations, they continue to attempt to connect to the peer for a period of time, even after the peer may have disconnected. "Good" clients would be smart about this and slow the connection attempt rate if it sees that it can't connect to the peer after several tries (which most, if not all, clients probably do already do, but who knows). There isn't anything you can do about this, as there is no provision for BitTorrent clients to tell other peers that it's leaving the swarm. Firstly, it could potentially be extremely bandwidth intense just to do that (if there are lots of peers in the swarm). Secondly, there is no guarantee that you know of all the peers in the swarm, so you'll almost never be able to tell all peers that you're disconnecting (and those that you don't know about may attempt a connection after you leave).

Then there's also the case of DHT and PEX, which propogate your IP outside of the normal tracker communication... They also cause similar behaviors, with DHT possibly aggrevating the situation the most.

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Oh, and as for allowing those ICMPs, it will let your machine tell the others to back off, eventually reducing how many connections you'll get.

For a hardware firewall, an enterprise-level router will do the job. :P Or build yourself a Linux firewall.

Truth be told, it's pretty unnecessary for home users to have anything beyond a simple firewall.

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I realize it's unnecessary. I'm just saying if I can ever get my hands on one cheap, I'd pick it up. I live in a big city, so there are lots of government surplus sales and the like.


Anyway, I enabled WAN ping respond, but outgoing ICMP packets were still being blocked.:/ I figured this was because incoming packets were directed to my BT port, so they were targeted at a computer behind the router. I "unforwarded" the BT port, and now I'm getting a bunch of blocked packets directed at said port. Redirecting traffic destined for that port to port 7 stops the messages. Maybe it's just a coincidence.

Edit: Well, it stops TCP connections obviously. UDP packets are still being blocked, and I don't think there's anything I can do about that. Hopefully the reduction in the amount of packets that need to be blocked will cut down on the lag.

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