When my Linux box has a lot of connections (eg when downloading an ISO via BitTorrent), the network connectivity gets very slow for other things.
Now this could be because the total bandwidth usage is high, but I'm seeing this even when the total bandwidth on my cable connection is say 50kbps down, 10kbps up.
As this is cable, I may be hitting Virgin bandwidth limits (I'm not sure how to tell), and this may sometimes be the case because if I test with another PC on my home network I sometimes find it is also slow. Other times the other PC is fine. In any case, killing the torrent download usually (not always) speeds everything up.
So, there seem to me to be several possible issues (any/all of which may be applying at different times), but I don't know how to diagnose it. For example, it may be the total number of connections at the router (a cheap Netgear wireless cable router supplied by Virgin), or maybe even at the virgin cable modem box? I try rebooting any of these and sometimes it works, sometimes it doesn't, but I am very aware that I'm just trying random things and not really getting anywhere!
On 7 Apr 2010, at 12:26, Mark Rogers wrote:
When my Linux box has a lot of connections (eg when downloading an ISO via BitTorrent), the network connectivity gets very slow for other things.
Now this could be because the total bandwidth usage is high, but I'm seeing this even when the total bandwidth on my cable connection is say 50kbps down, 10kbps up.
As this is cable, I may be hitting Virgin bandwidth limits (I'm not sure how to tell), and this may sometimes be the case because if I test with another PC on my home network I sometimes find it is also slow. Other times the other PC is fine. In any case, killing the torrent download usually (not always) speeds everything up.
So, there seem to me to be several possible issues (any/all of which may be applying at different times), but I don't know how to diagnose it. For example, it may be the total number of connections at the router (a cheap Netgear wireless cable router supplied by Virgin), or maybe even at the virgin cable modem box? I try rebooting any of these and sometimes it works, sometimes it doesn't, but I am very aware that I'm just trying random things and not really getting anywhere!
You might be hitting the bandwidth cap and hence be being throttled (see here http://allyours.virginmedia.com/html/internet/traffic.html) or there could be another possibility. I tend to find that uploading (which you tend to do a lot of with bittorrent) drastically reduces the download and upload connection speeds, so if you limit the upload speed of your torrent you may find this helps overall. There is probably a technical reason for why uploading limits the download speed too ... hopefully someone will come along and explain....
On 07/04/10 12:45, David Reynolds wrote:
You might be hitting the bandwidth cap and hence be being throttled (see here http://allyours.virginmedia.com/html/internet/traffic.html) or there could be another possibility. I tend to find that uploading (which you tend to do a lot of with bittorrent) drastically reduces the download and upload connection speeds, so if you limit the upload speed of your torrent you may find this helps overall.
If I understand the throttling correctly, if I'm getting throttled I should still have 75% of my bandwidth in each direction, so I should never go below 2Mb/128k. I'm seeing less than 20k up and not much more down.
There is probably a technical reason for why uploading limits the download speed too ... hopefully someone will come along and explain....
Well a typical download requires you to "upload" the request (eg for web browsing lots of separate HTTP requests), and also TCP will require a fair bit of handshaking (ie sending messages back), so when you run out of upstream bandwidth everything grinds to a halt. But according to the bittorrent software I'm not getting anywhere close to the limits, and it is often the case that another PC on the same LAN can access the internet fine even though I can't from my desktop, unless I kill the torrent software.
Mark Rogers wrote:
Well a typical download requires you to "upload" the request (eg for web browsing lots of separate HTTP requests), and also TCP will require a fair bit of handshaking (ie sending messages back), so when you run out of upstream bandwidth everything grinds to a halt. But according to the bittorrent software I'm not getting anywhere close to the limits, and it is often the case that another PC on the same LAN can access the internet fine even though I can't from my desktop, unless I kill the torrent software.
Out of interest, How do PC to PC transfers within your Lan perform when the network is in this state. So from your torrent machine to another box on your local subnet ?
Also is the PC with the torrents running on wlan or an ethernet connection ?. If it is on wlan do you have other machines on a wired connection to your router and are they unaffected when the rest of the network is in go-slow mode.
Finally you could use something like mtr, http://www.bitwizard.nl/mtr/ to trace to an external ip and give you a running average of the hops to your router and beyond and see if and where the latency increases when the network is in this state.
Answering those should at least allow you to eliminate your internal lan or the torrent machine itself, some cheap consumer grade routers do struggle with a high number of connections. But with something like mtr it should be possible to watch the hop across your local lan to the netgear, the hop from that to the virgin router and then the hop from the virgin router to its gateway and then possibly spot where the problem is.
On 08/04/10 10:48, Wayne Stallwood wrote:
Out of interest, How do PC to PC transfers within your Lan perform when the network is in this state. So from your torrent machine to another box on your local subnet ?
Good question, I haven't tried this.
Also is the PC with the torrents running on wlan or an ethernet connection ?. If it is on wlan do you have other machines on a wired connection to your router and are they unaffected when the rest of the network is in go-slow mode.
The "other" PC is an XP laptop on wireless, but the main machine is on a cabled connection.
Finally you could use something like mtr, http://www.bitwizard.nl/mtr/ to trace to an external ip and give you a running average of the hops to your router and beyond and see if and where the latency increases when the network is in this state.
Thanks for that one, I'll add that to the list to try.
Answering those should at least allow you to eliminate your internal lan or the torrent machine itself, some cheap consumer grade routers do struggle with a high number of connections. But with something like mtr it should be possible to watch the hop across your local lan to the netgear, the hop from that to the virgin router and then the hop from the virgin router to its gateway and then possibly spot where the problem is.
I'll try those tests and see where it gets me. eBuyer have a cheap wireless cable router for just over £10+VAT delivered that I'm going to try as well - for the sake of a tenner I figured it couldn't do any harm to compare notes!
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David Reynolds -
Mark Rogers -
Wayne Stallwood