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gferg 2002-09-26 17:47:59 +00:00
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commit 85d6a99ee2
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94
LDP/howto/docbook/ADSL-Bandwidth-Management-HOWTO.sgml
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@ -15,10 +15,30 @@
<revhistory>
<revision>
<revnumber>1.0</revnumber>
<date>2002-08-21</date>
<authorinitials>ds</authorinitials>
<revremark>Better control over bandwidth, more theory, updated for 2.4 kernels</revremark>
<revnumber>1.2</revnumber>
<date>2002-09-26</date>
<authorinitials>ds</authorinitials>
<revremark>
Added <link linkend="emaillist">link</link> to new Email Discussion List.
Added small teaser to caveat section regarding new and improved
QoS for Linux designed specifically for ADSL to be released soon.
</revremark>
</revision>
<revision>
<revnumber>1.1</revnumber>
<date>2002-08-26</date>
<authorinitials>ds</authorinitials>
<revremark>
A few corrections (Thanks to the many that pointed
them out!). Added informational caveat to implementation
section.
</revremark>
</revision>
<revision>
<revnumber>1.0</revnumber>
<date>2002-08-21</date>
<authorinitials>ds</authorinitials>
<revremark>Better control over bandwidth, more theory, updated for 2.4 kernels</revremark>
</revision>
<revision>
<revnumber>0.1</revnumber>
@ -51,10 +71,20 @@
<title>New Versions of This Document</title>
<para>You can always view the latest version of this document on the World
Wide Web at the
URL <ulink url="http://www.linuxdoc.org">http://www.linuxdoc.org</ulink>.</para>
URL: <ulink url="http://www.tldp.org">http://www.tldp.org</ulink>.</para>
<para>New versions of this document will also be uploaded to various Linux
WWW and FTP sites, including the LDP home page at
<ulink url="http://www.linuxdoc.org">http://www.linuxdoc.org</ulink>.</para>
<ulink url="http://www.tldp.org">http://www.tldp.org</ulink>.</para>
</sect2>
<sect2 id="emaillist">
<title>Email Discussion List</title>
<para>
For questions and update information regarding ADSL Bandwidth Management
please subscribe to the ADSL Bandwidth Management email list at
<ulink
url="http://jared.sonicspike.net/mailman/listinfo/adsl-qos"
>http://jared.sonicspike.net/mailman/listinfo/adsl-qos</ulink>.
</para>
</sect2>
<sect2>
<title>Disclaimer</title>
@ -64,13 +94,14 @@
</sect2>
<sect2 id="copyright">
<title>Copyright and License</title>
<para>This document is copyright 2001 by Dan Singletary, and is
<para>This document is copyright 2002 by Dan Singletary, and is
released under the terms of the GNU Free Documentation License,
which is hereby incorporated by reference. </para>
</sect2>
<sect2>
<title>Feedback and corrections</title>
<para>If you have questions or comments about this document, please feel free
<para>If you have questions or comments about this document, please feel free to
contact the author at <ulink url="mailto:dvsing@sonicspike.net">dvsing@sonicspike.net</ulink>.
</para>
</sect2>
</sect1>
@ -91,6 +122,10 @@
<listitem>
<para>
HTB queue - <ulink url="http://luxik.cdi.cz/~devik/qos/htb/">http://luxik.cdi.cz/~devik/qos/htb/</ulink>
</para>
<para>
Note: it has been reported that kernels since version 2.4.18-3 shipped with Mandrake (8.1, 8.2)
have already been patched for HTB.
</para>
</listitem>
<listitem>
@ -334,6 +369,45 @@
<sect1 id="implementation">
<title>Implementation</title>
<para>Now with all of the explanation out of the way it's time to implement bandwidth management with Linux.</para>
<sect2>
<title>Caveats</title>
<para>
Limiting the actual rate of data sent to the DSL modem is not as simple as it may seem. Most DSL modems
are really just ethernet bridges that bridge data back and forth between your linux box and the gateway
at your ISP. Most DSL modems use ATM as a link layer to send data. ATM sends data in cells that are always
53 bytes long. 5 of these
bytes are header information, leaving 48 bytes available for data. Even if you are sending 1 byte of data,
an entire 53 bytes of bandwidth are consumed sent since ATM cells are always 53 bytes long. This means that
if you are
sending a typical TCP ACK packet which consists of 0 bytes data + 20 bytes TCP header + 20 bytes IP header
+ 18 bytes Ethernet header. In actuality, even though the ethernet packet you are sending has only 40 bytes of
payload (TCP and IP header), the minimum payload for an Ethernet packet is 46 bytes of data, so the remaining
6 bytes are padded with nulls. This means that the actual length of the Ethernet packet plus header is
18 + 46 = 64 bytes. In order to send 64 bytes over ATM, you have to send two ATM cells which consume 106
bytes of bandwidth. This means for every TCP ACK packet, you're wasting 42 bytes of bandwidth.
This would be okay if Linux accounted for the
encapsulation that the DSL modem uses, but instead, Linux only accounts the TCP header, IP header, and 14 bytes
of the MAC address (Linux doesn't count the 4 bytes CRC since this is handled at the hardware level). Linux
doesn't count the minimum Ethernet packet size of 46 bytes, nor does it take into account the fixed ATM cell
size.
</para>
<para>
What all of this means is that you'll have to limit your outbound bandwidth to somewhat less than your
true capacity (until we can figure out a packet scheduler that can account for the various types of
encapsulation being used). You may find that you've figured out a good number to limit your bandwidth to, but
then you download a big file and the latency starts to shoot up over 3 seconds. This is most likely
because the bandwidth those small ACK packets consume is being miscalculated by Linux.
</para>
<para>
I have been working on a solution to this problem for a few months and have almost settled on a solution
that I will soon release to the public for further testing. The solution involves using a user-space
queue instead of linux's QoS to rate-limit packets. I've basically implemented a simple HTB queue
using linux user-space queues. This solution (so far) has been able to regulate outbound traffic SO WELL
that even during a massive bulk download (several streams) and bulk upload (gnutella, several streams)
the latency PEAKS at 400ms over my nominal no-traffic latency of about 15ms. For more information on
this QoS method, subscribe to the email list for updates or check back on updates to this HOWTO.
</para>
</sect2>
<sect2>
<title>Script: myshaper</title>
<para>The following is a listing of the script which I use to control bandwidth on my Linux router. It uses
@ -518,7 +592,7 @@ tc filter add dev $DEV parent 1:0 prio 0 protocol ip handle 26 fw flowid 1:26
# add MYSHAPER-OUT chain to the mangle table in iptables - this sets up the table we'll use
# to filter and mark packets.
iptables -t mangle -N MYSHAPER-OUT
iptables -t mangle -I POSTROUTING -o eth0 -j MYSHAPER-OUT
iptables -t mangle -I POSTROUTING -o $DEV -j MYSHAPER-OUT
# add fwmark entries to classify different types of traffic - Set fwmark from 20-26 according to
# desired class. 20 is highest prio.
@ -585,7 +659,7 @@ tc filter add dev imq0 parent 1:0 prio 0 protocol ip handle 21 fw flowid 1:21
# add MYSHAPER-IN chain to the mangle table in iptables - this sets up the table we'll use
# to filter and mark packets.
iptables -t mangle -N MYSHAPER-IN
iptables -t mangle -I PREROUTING -i eth0 -j MYSHAPER-IN
iptables -t mangle -I PREROUTING -i $DEV -j MYSHAPER-IN
# add fwmark entries to classify different types of traffic - Set fwmark from 20-26 according to
# desired class. 20 is highest prio.

4
LDP/howto/docbook/HOWTO-INDEX/howtoChap.sgml
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@ -68,7 +68,7 @@ various issues related to this. </Para>
ADSL-Bandwidth-Management-HOWTO</ULink>,
<CiteTitle>ADSL Bandwidth Management HOWTO</CiteTitle>
</PARA> <Para>
<CiteTitle>Updated: August 2002</CiteTitle>.
<CiteTitle>Updated: September 2002</CiteTitle>.
Describes how to configure a linux router to more
effectively manage outbound traffic on an ADSL modem. </Para>
</ListItem>
@ -515,7 +515,7 @@ partition images to and from a TFTP server. </Para>
Cluster-HOWTO</ULink>,
<CiteTitle>Linux Cluster HOWTO</CiteTitle>
</Para><Para>
<CiteTitle>Updated: May 2002</CiteTitle>.
<CiteTitle>Updated: September 2002</CiteTitle>.
How to set up high-performance Linux computing clusters. </Para>
</ListItem>

25
LDP/howto/docbook/HOWTO-INDEX/hwSect.sgml
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@ -100,7 +100,7 @@ various issues related to this. </Para>
Cluster-HOWTO</ULink>,
<CiteTitle>Linux Cluster HOWTO</CiteTitle>
</Para><Para>
<CiteTitle>Updated: May 2002</CiteTitle>.
<CiteTitle>Updated: September 2002</CiteTitle>.
How to set up high-performance Linux computing clusters. </Para>
</ListItem>
@ -191,6 +191,29 @@ Provides a guide for setting up a WWW-based kiosk using Linux, X11R6,
FVWM2, Netscape Navigator 4.X, and a customized trackball. </Para>
</ListItem>
<ListItem>
<Para>
<ULINK URL="../mini/KDE-Kiosk-Mode/index.html">
KDE-Kiosk-Mode</ULink>,
<citetitle>KDE-Kiosk-Mode HOWTO</CiteTitle>
</Para><Para>
<inlinemediaobject>
<imageobject>
<imagedata fileref="../images/archived.gif">
</imageobject>
<textobject>
<phrase>&lsqb; Archived &rsqb;</phrase>
</textobject>
</inlinemediaobject>
<CiteTitle>
Updated: September 2002</CiteTitle>.
Describes how to invoke the kiosk mode of KDE. </Para>
<Para>
<EMPHASIS>Further information can be found at:
<ULINK URL="http://www.brigadoon.de/peter/kde/">
http://www.brigadoon.de/peter/kde/</ULink>. </EMPHASIS> </Para>
</ListItem>
<ListItem>
<Para>
<ULINK URL="../Laptop-HOWTO.html">

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LDP/howto/docbook/HOWTO-INDEX/miniChap.sgml
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@ -694,6 +694,29 @@ get a permanent IP (if available), get a domain name, and have a
bona fide system running in a little over thirty minutes. </Para>
</ListItem>
<ListItem>
<Para>
<ULINK URL="../mini/KDE-Kiosk-Mode/index.html">
KDE-Kiosk-Mode</ULink>,
<citetitle>KDE-Kiosk-Mode HOWTO</CiteTitle>
</Para><Para>
<inlinemediaobject>
<imageobject>
<imagedata fileref="../images/archived.gif">
</imageobject>
<textobject>
<phrase>&lsqb; Archived &rsqb;</phrase>
</textobject>
</inlinemediaobject>
<CiteTitle>
Updated: September 2002</CiteTitle>.
Describes how to invoke the kiosk mode of KDE. </Para>
<Para>
<EMPHASIS>Further information can be found at:
<ULINK URL="http://www.brigadoon.de/peter/kde/">
http://www.brigadoon.de/peter/kde/</ULink>. </EMPHASIS> </Para>
</ListItem>
<ListItem>
<Para>
<ULINK URL="../mini/Kerneld/index.html">

2
LDP/howto/docbook/HOWTO-INDEX/networkingSect.sgml
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@ -54,7 +54,7 @@ the Linux Networking Kernel or more specifically kernel releases
ADSL-Bandwidth-Management-HOWTO</ULink>,
<CiteTitle>ADSL Bandwidth Management HOWTO</CiteTitle>
</PARA> <Para>
<CiteTitle>Updated: August 2002</CiteTitle>.
<CiteTitle>Updated: September 2002</CiteTitle>.
Describes how to configure a linux router to more
effectively manage outbound traffic on an ADSL modem. </Para>
</ListItem>