Author: mark

Update: It seems I’ve created a monster. I’ve had my first two Google searchers arrive on this blog entry searching for “limit roomate downloading” and “netgear limit roomate”. Well after years of experimenting with QoS this is the best method I’ve found to do exactly that, so enjoy.

For part of the year I’m on a rural wifi network that, on a good day, gives me 3 megabits per second download speed and 700kbps upload speed. I’ve tried multiple rural providers, had them rip out their equipment because of the packet loss (that means you Skybeam), I’ve shouted at Qwest to upgrade the local exchange so we can get DSL, but for now I’m completely and utterly stuck on a 3 megabits downlink using Mile High Internet.

I have an occasional room-mate, my nephew, who downloads movies on iTunes and it uses about 1.5 to 3 megabits. I’ve tried configuring quality of service (QoS) on various routers including Netgear and Linksys/Cisco and the problem is that I need a zero latency connection for my SSH sessions to my servers. So while QoS might be great if everyone’s using non-realtime services like iTunes downloads and web browsing, when you are using SSH or a VoIP product like Skype, it really sucks when someone is hogging the bandwidth.

The problem arises because of the way most streaming movie players download movies. They don’t just do it using a smooth 1 megabit stream. They’ll suck down as much as your connection allows, buffer it and then use very little bandwidth for a few seconds, and then hog the entire connection again. If you are using SSH and you hit a key, it takes a while for the router to say: “Oh, you wanted some bandwidth, ok fine let me put this guy on hold. There. Now what did you want from me again? Hey you still there? Oh you just wanted one real-time keystroke. And now you’re gone. OK I guess I’ll let the other guy with a lower priority hog the bandwidth again until you hit another keystroke.”

So the trick, if you want to effectively deal with the movie downloading room-mate is to limit the amount of bandwidth they can use. That way netflix, iTunes, youtube, amazon unbox or any other streaming service has to use a constant 1 megabit rather than bursting to 3 megabits and then dropping to zero – and you always have some bandwidth available without having to wait for the router to do it’s QoS thing.

Here’s how you do it.

First install DD-WRT firmware on your router. I use a Netgear WNDR3300 router and after using various Linksys/Cisco routers I swear by this one. It has two built in radios so you can create two wireless networks, one on 2Ghz and one of 5Ghz. It’s also fast and works 100% reliably.

Then look up your router on dd-wrt’s site and download DD-WRT for your router and install it. I use version “DD-WRT v24-sp2 (10/10/09) std – build 13064”. There are newer builds available, but when I wrote this this was the recommended version.

Once you’re all set up and you have  your basic wireless network with DD-WRT, make sure you disable QoS (it’s disabled by default).

Then configure SSH on DD-WRT. It’s a two step process. First you have to click the “Services” tab and enable SSHd. Then you have to click the Administration tab and enable SSH remote management.

Only the paid version of DD-WRT supports per user bandwidth limits, but I’m going to show you how to do it free with a few shell commands. I actually tried to buy the paid version of DD-WRT to do this, but their site is confusing and I couldn’t get confirmation they actually support this feature. So perhaps the author can clarify in a comment.

Because you’re going to enter shell commands, I recommend adding a public key for password-less authentication when you log in to DD-WRT. It’s on the same DD-WRT page where you enabled  the SSHd.

Tip: Remember that with DD-WRT, you have to “Save” any config changes you make and then “Apply settings”. Also DD-WRT gets confused sometimes when you make a lot of changes, so just reboot after saving and it’ll unconfuse itself.

Now that you have SSHd set up, remote ssh login enabled and hopefully your public ssh keys all set up, here’s what you do.

SSH to your router IP address:

ssh root@192.168.1.1

Enter password.

Type “ifconfig” and check which interface your router has configured as your internal default gateway. The IP address is often 192.168.1.1. The interface is usually “br0”.

Lets assume it’s br0.

Enter the following command which clears all traffic control settings on interface br0:

tc qdisc del dev br0 root

Then enter the following:


tc qdisc add dev br0 root handle 1: cbq \
avpkt 1000 bandwidth 2mbit

tc class add dev br0 parent 1: classid 1:1 cbq \
rate 700kbit allot 1500 prio 5 bounded isolated

tc filter add dev br0 parent 1: protocol ip \
prio 16 u32 match ip dst 192.168.1.133 flowid 1:1

tc filter add dev br0 parent 1: protocol ip \
prio 16 u32 match ip src 192.168.1.133 flowid 1:1

These commands will rate limit the IP address 192.168.1.133 to 700 kilobits per second.

If you’ve set up automatic authentication and you’re running OS X, here’s a perl script that will do all this for you:

#!/usr/bin/perl

my $ip = $ARGV[0];
my $rate = $ARGV[1];

$ip =~ m/^\d+\.\d+\.\d+\.\d+$/ &&
$rate =~ m/^\d+$/ ||
die “Usage: ratelimit.pl\n”;

$rate = $rate . ‘kbit’;

print `ssh root\@192.168.1.1 “tc qdisc del dev br0 root”`;

print `ssh root\@192.168.1.1 “tc qdisc add dev br0 root handle 1: cbq avpkt 1000 bandwidth 2mbit ; tc class add dev br0 parent 1: classid 1:1 cbq rate $rate allot 1500 prio 5 bounded isolated ; tc filter add dev br0 parent 1: protocol ip prio 16 u32 match ip dst $ip flowid 1:1 ; tc filter add dev br0 parent 1: protocol ip prio 16 u32 match ip src $ip flowid 1:1″`;

You’ll see a few responses for DD-WRT when you run the script and might see an error about a file missing but that’s just because you tried to delete a rule on interface br0 that might not have existed when the script starts.

These rules put a hard limit on how  much bandwidth an IP address can use. What you’ll find is that even if you rate limit your room mate to 1 megabit, as long as you have 500 kbit all to yourself, your SSH sessions will have absolutely no latency, Skype will not stutter, and life will be good again. I’ve tried many different configurations with various QoS products and have not ever achieved results as good as I’ve gotten with these rules.

Notes: I’ve configured the rules on the internal interface even though most QoS rules are generally configured on an external interface because it’s the only thing that really really seems to work. The Cisco engineers among you may disagree, but go try it yourself before you comment. I’m using the Linux ‘tc’ command and the man page is here.

PS: If you are looking for a great router to install DD-WRT on, try the Cisco-Linksys E3200. It has a ton of RAM and the CPU is actually faster at 500 MHz than the E4200 which is more expensive and only has a 480 MHz CPU. It also is the cheapest Gigabit Ethernet E series router that Cisco-Linksys offers. Here is the Cisco-Linksys E3200’s full specs on DD-WRT’s site. The E3200 is fully DD-WRT compatible but if you are lazy and don’t want to mess with DD-WRT, check out the built in QoS (Quality of Service) that the E3200 has built in on this video.