Bandwidth Limiting – How to

Bandwidth Limiting HOWTO
Tomasz Chmielewski
tch@writemail.com

Revision History
Revision 0.2 2001-05-20 Revised by: tc
This document describes how to set up your Linux server to limit download bandwidth or incoming traffic and how to use your internet link more efficiently.

Table of Contents


1. Introduction
1.1. New versions of this document
1.2. Disclaimer
1.3. Copyright and License
1.4. Feedback and corrections
1.5. Thanks
2. Before We Start
2.1. What do we need
2.2. How does it work?
3. Installing and Configuring Necessary Software
3.1. Installing Squid with the delay pools feature
3.2. Configuring Squid to use the delay pools feature
3.3. Solving remaining problems
3.3.1. Linux 2.2.x kernels (ipchains)
3.3.2. Linux 2.4.x kernels (iptables)
4. Dealing with Other Bandwidth-consuming Protocols Using CBQ
4.1. FTP
4.2. Napster, Realaudio, Windows Media and other issues
5. Frequently Asked Questions
5.1. Is it possible to limit bandwidth on a per-user basis with delay pools?
5.2. Is it possible to limit bandwidth on a per-user basis with cbq.init script?
5.3. CBQ sometimes doesn’t work for no reason.
5.4. Delay pools are stupid; why can’t I download something at full speed when the network is used only by me?
5.5. CBQ is stupid; why can’t I download something at full speed when the network is used only be me?
6. Miscellaneous
6.1. Useful resources

1. Introduction


The purpose of this guide is to provide an easy solution for limiting incoming traffic, thus preventing our LAN users from consuming all the bandwidth of our internet link.

This is useful when our internet link is slow or our LAN users download tons of mp3s and the newest Linux distro’s *.iso files.

1.1. New versions of this document


You can always view the latest version of this document on the World Wide Web at the URL http://www.linuxdoc.org.

New versions of this document will also be uploaded to various Linux WWW and FTP sites, including the LDP home page at http://www.linuxdoc.org.

1.2. Disclaimer


Neither the author nor the distributors, or any other contributor of this HOWTO are in any way responsible for physical, financial, moral or any other type of damage incurred by following the suggestions in this text.

1.3. Copyright and License


This document is copyright 2001 by Tomasz Chmielewski, and is released under the terms of the GNU Free Documentation License, which is hereby incorporated by reference.

1.4. Feedback and corrections


If you have questions or comments about this document, please feel free to mail us. I welcome any suggestions or criticisms. If you find a mistake or a typo in this document (and you will find a lot of them, as English is not my native language), please let me know so I can correct it in the next version. Thanks.

1.5. Thanks


I would like to thank everyone who helped me to convert the HOWTO into SGML format and corrected some mistakes. 

 

2. Before We Start

Let’s imagine the following situation:

We have 115,2 kbits/s ppp (modem) internet link (115,2/10 = 11,5 kbytes/s); yes, there are such types of connection! With eth connections (network card) we would divide 115,2 by 8; with ppp we divide by 10, because of start/stop bits (8 + 1 + 1 = 10).

We have some LAN stations and their users are doing bulk downloads all the time.

We want web pages to open fast, no matter how many downloads are happening.

Our internet interface is ppp0.

Our LAN interface is eth0.

Our network is 192.168.1.0/24

2.1. What do we need


Believe it or not, shaping the incoming traffic is an easy task and you don’t have to read tons of books about routing or queuing algorithms.

To make it work, we need at least Squid proxy; if we want to fine tune it, we will have to get familiar with ipchains or iptables and CBQ.

To test our efforts, we can install IPTraf.

2.2. How does it work?
Squid is probably the most advanced HTTP proxy server available for Linux. It can help us save bandwidth in two ways:

The first is a main characteristic of proxy servers — they keep downloaded web pages, pictures, and other objects in memory or on a disk. So, if two people are requesting the same web page, it isn’t downloaded from the internet, but from the local proxy.

Apart from normal caching, Squid has a special feature called delay pools. Thanks to delay pools, it is possible to limit internet traffic in a reasonable way, depending on so-called ‘magic words’, existing in any given URL. For example, a magic word could be ‘.mp3’, ‘.exe’ or ‘.avi’, etc. Any distinct part of a URL (such as .avi) can be defined as a magic word.

With that, we can tell the Squid to download these kinds of files at a specified speed (in our example, it will be about 5 kbytes/s). If our LAN users download files at the same time, they will be downloaded at about 5 kbytes/s altogether, leaving remaining bandwidth for web pages, e-mail, news, irc, etc.

Of course, the Internet is not only used for downloading files via web pages (http or ftp). Later on, we will deal with limiting bandwidth for Napster, Realaudio, and other possibilities.

3. Installing and Configuring Necessary Software
Here, I will explain how to install the necessary software so that we can limit and test the bandwidth usage.

3.1. Installing Squid with the delay pools feature
As I mentioned before, Squid has a feature called delay pools, which allows us to control download bandwidth. Unfortunately, in most distributions, Squid is shipped without that feature.

So if you have Squid already installed, I must disappoint you — you need to uninstall it and do it once again with delay pools enabled in the way I explain below.

To get maximum performance from our Squid proxy, it’s best to create a separate partition for its cache, called /cache/. Its size should be about 300 megabytes, depending on our needs.

If you don’t know how to make a separate partition, you can create the /cache/ directory on a main partition, but Squid performance can suffer a bit.

We add a safe ‘squid’ user:

# useradd -d /cache/ -r -s /dev/null squid >/dev/null 2>&1

No one can log in as squid, including root.

We download Squid sources from http://www.squid-cache.org

When I was writing this HOWTO, the latest version was Squid 2.4 stable 1:

http://www.squid-cache.org/Versions/v2/2.4/squid-2.4.STABLE1-src.tar.gz

We unpack everything to /var/tmp:

# tar xzpf squid-2.4.STABLE1-src.tar.gz

We compile and install Squid (everthing is in one line):

# ./configure –prefix=/opt/squid –exec-prefix=/opt/squid –enable-delay-pools –enable-cache-digests –enable-poll –disable-ident-lookups –enable-truncate –enable-removal-policies

# make all

# make install

3.2. Configuring Squid to use the delay pools feature
Configure our squid.conf file (located under /opt/squid/etc/squid.conf):

#squid.conf
#Every option in this file is very well documented in the original squid.conf file
#and on http://www.visolve.com/squidman/Configuration%20Guide.html

#
#The ports our Squid will listen on
http_port 8080
icp_port 3130
#cgi-bins will not be cached
acl QUERY urlpath_regex cgi-bin \?
no_cache deny QUERY
#Memory the Squid will use. Well, Squid will use far more than that.
cache_mem 16 MB
#250 means that Squid will use 250 megabytes of disk space
cache_dir ufs /cache 250 16 256
redirect_rewrites_host_header off
cache_replacement_policy GDSF
acl localnet src 192.168.1.0/255.255.255.0
acl localhost src 127.0.0.1/255.255.255.255
acl Safe_ports port 80 443 210 119 70 20 21 1025-65535
acl CONNECT method CONNECT
acl all src 0.0.0.0/0.0.0.0
http_access allow localnet
http_access allow localhost
http_access deny !Safe_ports
http_access deny CONNECT
http_access deny all
maximum_object_size 3000 KB
store_avg_object_size 50 KB

#all our LAN users will be seen by external servers
#as if they all use Mozilla on Linux 🙂
anonymize_headers deny User-Agent
fake_user_agent Mozilla/5.0 (X11; U; Linux 2.4.4 i686)

#To make our connection even faster, we put a line similar
#to the one below. Don’t forget to change the server to your closest!
#Measure pings, traceroutes and so on.
#Make sure that http and icp ports are correct
#cache_peer w3cache.icm.edu.pl parent 8080 3130 no-digest default

#This is useful when we want to use the Cache Manager
#copy cachemgr.cgi to cgi-bin of your www server
cache_mgr your@email
cachemgr_passwd secret_password all

#This is a name of a user our Squid will work as
cache_effective_user squid
cache_effective_group squid

log_icp_queries off
buffered_logs on


#####DELAY POOLS
#This is the most important part for shaping incoming traffic with Squid
#For detailed description see squid.conf file or docs at http://www.squid-cache.org

#We don’t want to limit downloads on our local network
acl magic_words1 url_regex -i 192.168

#We want to limit downloads of these type of files
#Put this all in one line
acl magic_words2 url_regex -i ftp .exe .mp3 .vqf .tar.gz .gz .rpm .zip .rar .avi .mpeg .mpe .mpg .qt
.ram .rm .iso .raw .wav
#We don’t block .html, .gif, .jpg and similar files, because they
#generally don’t consume much bandwidth

#We have two different delay_pools
delay_pools 2

#First delay pool
#W don’t want to delay our local traffic
#There are three pool classes; here we will deal only with the second
delay_class 1 2

#-1/-1 mean that there are no limits
delay_parameters 1 -1/-1 -1/-1

#magic_words1: 192.168
delay_access 1 allow magic_words1

#Second delay pool
#we want to delay downloading files mentioned in magic_words2
delay_class 2 2

#The numbers here are values in bytes;
#we must remember that Squid doesn’t consider start/stop bits
#5000/150000 are values for the whole network
#5000/120000 are values for the single IP
#after downloaded files exceed about 150000 bytes,
#(or even twice or three times as much)
#they will continue to download at about 5000 bytes/s

delay_parameters 2 5000/150000 5000/120000
delay_access 2 allow magic_words2

#EOF
OK, when we have configured everything, we must make sure everything under /opt/squid and /cache directories belongs to user ‘squid’.

# chown -R squid:squid /opt/squid/

# chown -R squid:squid /cache/

or

# chown -R squid.squid /opt/squid/

# chown -R squid.squid /cache/

Now everything is ready to run Squid. When we do it for the first time, we have to create its cache directories:

# /opt/squid/usr/bin/squid -z

We run Squid and check if everything is working. A good tool to do that is IPTraf; you can find it on http://freshmeat.net. Make sure you have set the appropriate proxy in your web browsers (192.168.1.1, port 8080 in our example):

# /opt/squid/usr/bin/squid

If everything is working, we add /opt/squid/usr/bin/squid line to the end of our initializing scripts. Usually, it can be /etc/rc.d/rc.local.

Other helpful options in Squid may be:

# /opt/squid/usr/bin/squid -k reconfigure (it reconfigures Squid if we made any changes in its squid.conf file)

# /opt/squid/usr/bin/squid -help 🙂 self-explanatory

You can also copy cachemgr.cgi to the cgi-bin directory of your WWW server.

3.3. Solving remaining problems
OK, we have installed Squid and configured it to use delay pools. I bet nobody wants to be restricted, especially our clever LAN users. They will likely try to avoid our limitations, just to download their favourite mp3s a little faster (and thus causing your headache).

I assume that you use IP-masquerade on your LAN so that your users can use IRC, ICQ, e-mail, etc. That’s OK, but we must make sure that our LAN users will use our delay pooled Squid to access web pages and use ftp.

We can solve most of these problems by using ipchains (Linux 2.2.x kernels) or iptables (Linux 2.4.x kernels).

3.3.1. Linux 2.2.x kernels (ipchains)
We must make sure that nobody will try to cheat and use a proxy server other than ours. Public proxies usually run on 3128 and 8080 ports:

/sbin/ipchains -A input -s ! 192.168.1.1 -d ! 192.168.1.1 3128 -p TCP -j REJECT

/sbin/ipchains -A input -s ! 192.168.1.1 -d ! 192.168.1.1 8080 -p TCP -j REJECT

We must also make sure that nobody will try to cheat and connect to the internet directly (IP-masquerade) to download web pages:

/sbin/ipchains -A input -s ! 192.168.1.1 -d ! 192.168.1.1 http -p TCP -j REDIRECT 8080

/sbin/ipchains -A input -s ! 192.168.1.1 -d ! 192.168.1.1 https -p TCP -j REDIRECT 8080

If everything is working, we add these lines to the end of our initializing scripts. Usually, it can be /etc/rc.d/rc.local.

We might think to block ftp traffic (ports 20 and 21) to force our LAN users to use Squid, but it’s not a good idea for at least two reasons:

Squid is a http proxy with ftp support, not a real ftp proxy. It can download from ftp, it can also upload to some ftp, but it can’t delete/change name of files on remote ftp servers.

When we block ports 20 and 21, we won’t be able to delete/change name of files on remote ftp servers.

IE5.5 has a bug — it doesn’t use a proxy to retrieve the ftp directory. Instead it connects directly via IP-masquerade.

When we block ports 20 and 21, we won’t be able to browse through ftp directories, using IE5.5.

So, we will block excessive ftp downloads using other methods. We will deal with it in chapter 4.

3.3.2. Linux 2.4.x kernels (iptables)
We must make sure that nobody will try to cheat and use a proxy server other than ours. Public proxies usually run on 3128 and 8080 ports:

/sbin/iptables -A FORWARD -s ! 192.168.1.1 -d ! 192.168.1.1 –dport 3128 -p TCP -j DROP

/sbin/iptables -A FORWARD -s ! 192.168.1.1 -d ! 192.168.1.1 –dport 8080 -p TCP -j DROP

We must also make sure that nobody will try to cheat and connect to the internet directly (IP-masquerade) to download web pages:

/sbin/iptables -A FORWARD -s ! 192.168.1.1 -d ! 192.168.1.1 –dport 80 -p TCP -j DROP

/sbin/iptables -A FORWARD -s ! 192.168.1.1 -d ! 192.168.1.1 –dport 443 -p TCP -j DROP

If everything is working, we add these lines to the end of our initializing scripts. Usually, it can be /etc/rc.d/rc.local.

We might think to block ftp traffic (ports 20 and 21) to force our LAN users to use Squid, but it’s not a good idea for at least two reasons:

Squid is a http proxy with ftp support, not a real ftp proxy. It can download from ftp, it can also upload to some ftp, but it can’t delete/change name of files on remote ftp servers.

When we block ports 20 and 21, we won’t be able to delete/change name of files on remote ftp servers.

IE5.5 has a bug — it doesn’t use a proxy to retrieve the ftp directory. Instead it connects directly via IP-masquerade.

When we block ports 20 and 21, our LAN users won’t be able to browse through ftp directories, using IE5.5.

So, we will block excessive ftp downloads using other methods. We will deal with it in chapter 4.

4. Dealing with Other Bandwidth-consuming Protocols Using CBQ
We must remember that our LAN users can spoil our efforts from chapter 3, if they use Napster or Realaudio. We must also remember that we didn’t block ftp traffic in section 3.3.

We will achieve it in a different way — not by limiting downloading directly, but rather, indirectly. If our internet device is ppp0 and LAN device is eth0, we will limit outgoing traffic on interface eth0, and thus, limit incoming traffic to ppp0.

To do it, we will get familiar with CBQ and cbq.init script. You can obtain it from ftp://ftp.equinox.gu.net/pub/linux/cbq/. Download cbq.init-v0.6.2 and put it in /etc/rc.d/.

You will also need iproute2 installed. It comes with every Linux distribution.

Now look in your /etc/sysconfig/cbq/ directory. There, you should have an example file, which should work with cbq.init. If it isn’t there, you probably don’t have it compiled in your kernel.

4.1. FTP
In chapter 3, we didn’t block ftp for two reasons — so that we could do uploads, and so that users with buggy IE5.5 could browse through ftp directories. In all, our web browsers and ftp programs should make downloads via our Squid proxy and ftp uploads/renaming/deleting should be made via IP-masquerade.

We create a file called cbq-10.ftp-network in the /etc/sysconfig/cbq/ directory:

# touch /etc/sysconfig/cbq/cbq-10.ftp-network

We insert the following lines into it:

DEVICE=eth0,10Mbit,1Mbit
RATE=10Kbit
WEIGHT=1Kbit
PRIO=5
RULE=:20,192.168.1.0/24
RULE=:21,192.168.1.0/24
You will find the description of thses lines in cbq.init-v0.6.2 file.

When you start /etc/rc.d/cbq.init-v.0.6.2 script, it will read your configuration, which is in /etc/sysconfig/cbq/:

# /etc/rc.d/cbq.init-v.0.6.2 start

If everything is working, we add /etc/rc.d/cbq.init-v.0.6.2 start to the end of your initializing scripts. Usually, it can be /etc/rc.d/rc.local.

Thanks to this command, your server will not send ftp data through eth0 faster than 10kbits/s, and thus will not download ftp data faster than 10kbits/s. Your LAN users will see that it’s more efficient to use Squid proxy for doing ftp downloads. They will be also able to browse ftp directories using their buggy IE5.5.

There is also another bug in IE5.5 – when you right click on a file in a ftp directory then select ‘Copy To Folder’, the file is downloaded not through proxy, but directly through IP-masquerade, thus omitting Squid with delay pools.

4.2. Napster, Realaudio, Windows Media and other issues
Here, the idea is the same as with ftp; we just add another port and set a different speed.

We create file called cbq-50.napster-network in the /etc/sysconfig/cbq/ directory:

# touch /etc/sysconfig/cbq/cbq-50.napsterandlive

Put these lines into that file:

DEVICE=eth0,10Mbit,1Mbit
RATE=50Kbit
WEIGHT=5Kbit
PRIO=5
#Windows Media Player
RULE=:1755,192.168.1.0/24
#Real Player uses TCP port 554, for UDP it uses different ports,
#but generally RealAudio in UDP doesn’t consume much bandwidth
RULE=:554,192.168.1.0/24
RULE=:7070,192.169.1.0/24
#Napster uses ports 6699 and 6700, maybe some other?
RULE=:6699,192.168.1.0/24
RULE=:6700,192.168.1.0/24
#Audiogalaxy uses ports around 41000, thera are many of them,
#so keep in mind I didn’t list all of them here
RULE=:41060,192.168.1.0/24
RULE=:41133,192.168.1.0/24
#Some clever users can connect to SOCKS servers when using Napster,
#Audiogalaxy etc.; it’s also a good idea to do so
#when you run your own SOCKS proxy
RULE=:1080,192.168.1.0/24
#Add any other ports you want; you can easily check
#ports that programs use with IPTraf
#RULE=:port,192.168.1.0/24
5. Frequently Asked Questions
5.1. Is it possible to limit bandwidth on a per-user basis with delay pools?
Yes. Look inside the original squid.conf file and check the Squid documentation on http://www.squid-cache.org

5.2. Is it possible to limit bandwidth on a per-user basis with cbq.init script?
Yes. Look inside this script; there are some examples.

5.3. CBQ sometimes doesn’t work for no reason.
Generally it shouldn’t occur. Sometimes, you can observe mass downloads, though you think you have blocked all ports Napster or Audiogalaxy uses. Well, there is always one more port open for mass downloads. To find it, you can use IPTraf. As there can be possibly thousands of such ports, it can be really hard task for you. To make it easier, you can consider running your own SOCKS proxy – Napster, Audiogalaxy and many programs can use SOCKS proxies, so it’s much easier to deal with just one port (1080), than to do so with thousands of possibilites. Don’t forget to close all ports for traffic, and leave open ports like 25 and 119 (SMTP and POP3), and other you think might be useful. You will find a link to NEC SOCKS proxy at the end of this HOWTO. If you intend to use it: don’t forget to apply a patch that can be found on their page.

5.4. Delay pools are stupid; why can’t I download something at full speed when the network is used only by me?
Unfortunately, you can’t do much about it.

The only thing you can do is to use cron and reconfigure it, for example, at 1.00 am, so that Squid won’t use delay pools, then reconfigure it again, let’s say at 7.30 am, to use delay pools.

5.5. CBQ is stupid; why can’t I download something at full speed when the network is used only be me?
Lucky you, it’s possible!

There are to ways to achieve it.

The first is the easy one, similar to the solution we’ve made with Squid. Insert a line similar to the one below to your CBQ config files placed in /etc/sysconfig/cbq/:

TIME=15:00-16:00;110Kbit/11Kbit
TIME=00:00-08:00;110Kbit/11Kbit
You can have multiple TIME parameters in your CBQ config files.

The second way is harder, but more intelligent. You can read about it in the Linux 2.4 Advanced Routing HOWTO.

6. Miscellaneous
6.1. Useful resources
Squid Web Proxy Cache

http://www.squid-cache.org

Squid 2.4 Stable 1 Configuration manual

http://www.visolve.com/squidman/Configuration%20Guide.html

http://www.visolve.com/squidman/Delaypool%20parameters.htm

Squid FAQ

http://www.squid-cache.org/Doc/FAQ/FAQ-19.html#ss19.8

cbq-init script

ftp://ftp.equinox.gu.net/pub/linux/cbq/

Linux 2.4 Advanced Routing HOWTO

http://www.linuxdoc.org/HOWTO/Adv-Routing-HOWTO.html

Traffic control (in Polish)

http://ceti.pl/~kravietz/cbq/

Securing and Optimizing Linux Red Hat Edition – A Hands on Guide

http://www.linuxdoc.org/guides.html

IPTraf

http://cebu.mozcom.com/riker/iptraf/

IPCHAINS

http://www.linuxdoc.org/HOWTO/IPCHAINS-HOWTO.html

NEC SOCKS proxy server

http://www.socks.nec.com/cgi-bin/download.pl

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