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router problem or self-DOSing with bittorrent?
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Senso
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Joined: 17 Jun 2003
Posts: 250
Location: Montreal, Quebec

PostPosted: Sun Jul 11, 2004 5:58 pm    Post subject: router problem or self-DOSing with bittorrent? Reply with quote

I've been having connection problems for a while now but I always assumed it was my ISP. I'm on DSL, behind a D-Link DI-704P router. Normally, I can see that my modem is connected (green lights) but I can't go outside my LAN. Usually rebooting the modem and router fixed the problem for a few hours.

Today I noticed the light on my router telling a computer is connected to it kept fading to black. Rebooting the router would work for about 2 minutes, enough time to ping google.com a few times to see that it works. Then the router light would go out, just like if I had unplugged the cat5 cable. I tried another cable, same problem.

Doing /etc/init.d/net.eth0 restart would simply timeout at "* Bringing eth0 up via DHCP... ".

dmesg shows:
Code:

NETDEV WATCHDOG: eth0: transmit timed out
eth0: Tx timed out, cable problem? TSR=0x16, ISR=0x0, t=24.


Even when not "connected" to the router, ifconfig shows:
Code:

eth0      Link encap:Ethernet  HWaddr 00:50:BA:CD:AD:92
          inet addr:192.168.0.5  Bcast:192.168.0.255  Mask:255.255.255.0
          UP BROADCAST NOTRAILERS RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:19279732 errors:14 dropped:13326 overruns:0 frame:1828
          TX packets:21311899 errors:11870 dropped:0 overruns:0 carrier:23606
          collisions:321677 txqueuelen:1000
          RX bytes:2626536677 (2504.8 Mb)  TX bytes:1425073799 (1359.0 Mb)
          Interrupt:5 Base address:0xd400
 
lo        Link encap:Local Loopback
          inet addr:127.0.0.1  Mask:255.0.0.0
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:7208 errors:0 dropped:0 overruns:0 frame:0
          TX packets:7208 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:633902 (619.0 Kb)  TX bytes:633902 (619.0 Kb)


11870 TX errors? I don't think it's normal. Anyway, I was using qtorrent at the time, downloading/seeding about 3-4 large files - meaning "netstat -tupan" showed dozens and dozens of connections. After the 16th "blackout" or so, I was thinking about switching the network card but then I stopped qtorrent and rebooted the router. Wow, it works.

I've been connected for about 15 minutes now without having problems, which leads me to think qtorrent was the problem somehow. Or maybe not qtorrent itself but maybe having 50 TCP connections kind of blew out the tcp stack or something. I'm using 2.4.25-gentoo but as far as I know, I had the same problem using 2.6.x. Is it possible to overflow the connections table or something like that? So overflowed that even connecting to 192.168.0.1 would be impossible? Did I DOSed myself? Weird. It could also be at the router or modem level, hard to say.
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bk0
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Joined: 04 Jan 2004
Posts: 266

PostPosted: Tue Jul 13, 2004 1:57 am    Post subject: Reply with quote

I've had similar problems with the Motorola NAT/router that Vonage supplies for VoIP service. Lots of simultaneous TCP connections would cause the box to simply stop passing traffic, after a reboot it would work again for a little while. I can't prove anything but I suspect I was overflowing the connection-tracking tables with BitTorrent traffic like you. It was a bit different though because it would pass UDP/ICMP packets fine, just TCP connections couldn't be established. I don't remember seeing tx errors but I didn't check either.

Unless the manufacturer supplies a firmware update that fixes it there's no real solution other than ditching the piece of crap router. I'm working on setting up a dedicated NAT box as a replacement.
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Senso
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Joined: 17 Jun 2003
Posts: 250
Location: Montreal, Quebec

PostPosted: Tue Jul 13, 2004 3:13 am    Post subject: Reply with quote

bk0 wrote:
I can't prove anything but I suspect I was overflowing the connection-tracking tables with BitTorrent traffic like you. It was a bit different though because it would pass UDP/ICMP packets fine, just TCP connections couldn't be established.


I'll have to check that. I wouldn't be surprised if UDP still passed, as it's stateless. Well, I guess I'll have to start downloading 4-5 movies again, just to test the idea. :?

bk0 wrote:
Unless the manufacturer supplies a firmware update that fixes it there's no real solution other than ditching the piece of crap router. I'm working on setting up a dedicated NAT box as a replacement.


I was thinking about the same thing - I've got 2-3 P200 lying around just waiting to get some hot routing action. May not be the best but I've heard you don't need a lot of CPU to do NAT stuff.
D-Link's last firmware update for this model is dated 2002 and I'm using it. Hell, we shouldn't even call these things "routers", they're more like "ethernet hubs" or maybe "PLASTIC BOXES FULL OF FLASHING LEDS!!1!".

I've started using bittorent again, but only 1-2 torrents at a time, and keeping a maximum of 5 uploads for each of them. That seems to work. Which makes me really think it's not my ISP/modem/network card but that damn Residential Gateway(tm)(r)(c) thing.
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