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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<article>
<!--$Id$-->
<articleinfo>
<title>Traffic Shaping/Control</title>
<authorgroup>
<author>
<firstname>Tom</firstname>
<surname>Eastep</surname>
</author>
<author>
<firstname>Arne</firstname>
<surname>Bernin</surname>
</author>
</authorgroup>
<pubdate>2005-10-08</pubdate>
<copyright>
<year>2001-2004</year>
<holder>Thomas M. Eastep</holder>
</copyright>
<copyright>
<year>2005</year>
<holder>Arne Bernin</holder>
</copyright>
<legalnotice>
<para>Permission is granted to copy, distribute and/or modify this
document under the terms of the GNU Free Documentation License, Version
1.2 or any later version published by the Free Software Foundation; with
no Invariant Sections, with no Front-Cover, and with no Back-Cover
Texts. A copy of the license is included in the section entitled
<quote><ulink url="GnuCopyright.htm">GNU Free Documentation
License</ulink></quote>.</para>
</legalnotice>
</articleinfo>
<section>
<title>Introduction</title>
<para>Starting with Version 2.5.5, Shorewall has builtin support for
traffic shaping and control. Before this version, the support was quite
limited. You were able to use your own tcstart script (and you still are),
but besides the tcrules file it was not possible to define classes or
queueing discplines inside the Shorewall config files.</para>
<para>The support for traffic shaping and control still does not cover all
options available (and especially all algorithms that can be used to queue
traffic) for the Linux kernel but it should fit most needs. If you are
using your own script for traffic control and you still want to use it
rather the builtin support in the future, you will find information on how
to do this, <link linkend="owntcstart">later in this document</link>. But
for this to work, you will also need to enable traffic shaping in the
kernel and Shorewall as covered by the next sections.</para>
</section>
<section>
<title>Linux traffic shaping and control</title>
<para>This section gives a brief introduction of how controlling traffic
with the linux kernel works. Although this might be enough for configuring
it in the Shorewall configuration files, it still might be a good idea to
take a deeper look into the <ulink url="http://ds9a.nl/lartc">Linux
Advanced Routing and Shaping HOWTO</ulink>. At the time of writing this,
the current version is 1.0.0.</para>
<para>Since kernel 2.2 Linux has extensive support for controlling
traffic. You can define different algorithms that are used to queue the
traffic before it leaves an interface. The standard one is called pfifo
and is (as the name suggests) of the type First In First out. This means,
that it does not shape anything, if you have a connection that eats up all
your bandwidth, this qeueing algorithm will not stop it from doing
so.</para>
<para>For Shorewall traffic shaping we use two algorithms, one is called
HTB (Hierarchical Token Bucket) and SFQ (Stochastic Fairness Queuing). SFQ
is easy to explain: it just tries to track your connections (tcp or udp
streams) and balances the traffic between them. This normaly works ok. HTB
allows you to define a set of classes, and you can put the traffic you
want into these classes. You can define minimum and maximum bandwitdh
settings for those classes and order the hierachically (the less priorized
classes only get bandwitdth if the more important have what they need).
Shorewall builtin traffic shaping allows you to define these classes (and
their bandwidth limits), and it uses SFW inside these classes to make
sure, that different data streams are handled equally.</para>
<para>You can only shape outgoing traffic. The reason for this is simple,
the packets were already received by your network card before you can
decide what to do with them. So the only choice would be to drop them
which does normally makes no sense (since you received the packet already,
it went through the possible bottleneck (the incoming connection). The
next possible bottleneck might come if the packet leaves on another
interface, so this will be the place where queuing might occur. So,
defining queues for incoming packages is not very useful, you just want to
have it forwarded to the outgoing interface as fast as possible.</para>
<para>There is one exception, though. Limiting incoming traffic to a value
a bit slower than your actual line speed will avoid queuing on the other
end of that connection. This is mostly useful if you don't have access to
traffic control on the other side and if this other side has a faster
network connection than you do (the line speed between the systems is the
bottleneck, e.g. a DSL connection to you providers router). So, if you
drop packages that are coming in too fast, the underlaying protocol might
recognize this and slow down the connection. TCP has a builtin mechanism
for this, UDP has not (but the protocol over UDP might recognize it , if
there is any).</para>
<para>The reason why qeueing is bad in these cases is, that you might have
packets which need to be priorized over others, e.g. VoIP or ssh. For this
type of connections it is important that packets arrive in a certain
amount of time. For others like http downloads, it does not really matter
if it takes a few seconds more.</para>
<para>If you have a large queue on the other side and the router there
does not care about QoS or the QoS bits are not set properly, your
important packets will go into the same queue as your less timecritical
download packets which will result in a large delay.</para>
</section>
<section>
<title>Linux Kernel Configuration</title>
<para>You will need at least kernel 2.4.18 for this to work, please take a
look at the following screenshot for what settings you need to enable. For
builtin support, you need the HTB scheduler, the PRIO pseudoscheduler and
SFQ queue. The other scheduler or queue algorithms are not needed.</para>
<para>This screen shot show how I've configured QoS in my Kernel:<graphic
align="center" fileref="images/QoS.png" /></para>
</section>
<section>
<title>Enable TC support in Shorewall</title>
<para>You need this support whether you use the builtin support or whether
you provide your own tcstart script.</para>
<para>To enable the builtin traffic shaping and control in Shorewall, you
have to do the following:</para>
<itemizedlist>
<listitem>
<para>Set <emphasis role="bold">TC_ENABLED</emphasis> to No in
/etc/shorewall/shorewall.conf. While that seems a bit illogical, it is
done for compatibility with previous releases where TC_ENABLED=Yes
causes Shorewall to look for an external tcstart file (See <link
linkend="tcstart">a later section</link> for details).</para>
</listitem>
<listitem>
<para>Setting <emphasis role="bold">CLEAR_TC</emphasis> parameter in
/etc/shorewall/shorewall.conf to Yes will clear the traffic shaping
configuration during Shorewall [re]start and Shorewall stop. This is
normally what you want when using the builtin support (and also if you
use your own tcstart script)</para>
</listitem>
<listitem>
<para>The other steps that follow depend on whether you use your own
script or the builtin solution. They will be explained in the
following sections.</para>
</listitem>
</itemizedlist>
</section>
<section>
<title>Using builtin traffic shaping/control</title>
<para>For defining bandwidths (for either devices or classes) please use
kbit or kbps(for Kilobytes per second) and make sure there is NO space
between the number and the unit (100kbit not 100 kbit). You generally
could use mbit or mbps or just Bytes, but i suggest to use kbit, as values
lether than 1 are not supported (NO 0.5mbit).</para>
<para>To properly configure the settings for your devices you might need
to find out, the real up- and downstream rates you have. This is
especially the case, if you are using a DSL connection or one of another
type that do not have a guaranteed bandwidth. There are several online
tools that help you find out, try ..... Don't trust the values your
provider tells you for this, especially measuring the real download speed
is important!</para>
<section>
<title>/etc/shorewall/tcrules</title>
<para>The fwmark classifier provides a convenient way to classify
packets for traffic shaping. The /etc/shorewall/tcrules file provides a
means for specifying these marks in a tabular fashion.</para>
<para>Normally, packet marking occurs in the PREROUTING chain before any
address rewriting takes place. This makes it impossible to mark inbound
packets based on their destination address when SNAT or Masquerading are
being used. You can cause packet marking to occur in the FORWARD chain
by using the MARK_IN_FORWARD_CHAIN option in shorewall.conf.</para>
<para>Columns in the file are as follows:</para>
<itemizedlist>
<listitem>
<para>MARK - Specifies the mark value is to be assigned in case of a
match. This is an integer in the range 1-255. This value may be
optionally followed by <quote>:</quote> and either <quote>F</quote>
or <quote>P</quote> to designate that the marking will occur in the
FORWARD or PREROUTING chains respectively. If this additional
specification is omitted, the chain used to mark packets will be
determined by the setting of the MARK_IN_FORWARD_CHAIN option in
shorewall.conf.</para>
</listitem>
<listitem>
<para>SOURCE - The source of the packet. If the packet originates on
the firewall, place <quote>fw</quote> in this column. Otherwise,
this is a comma-separated list of interface names, IP addresses, MAC
addresses in Shorewall Format and/or Subnets.</para>
<para>Examples <programlisting> eth0 192.168.2.4,192.168.1.0/24</programlisting></para>
</listitem>
<listitem>
<para>DEST -- Destination of the packet. Comma-separated list of IP
addresses and/or subnets.</para>
</listitem>
<listitem>
<para>PROTO - Protocol - Must be the name of a protocol from
/etc/protocol, a number or <quote>all</quote></para>
</listitem>
<listitem>
<para>PORT(S) - Destination Ports. A comma-separated list of Port
names (from /etc/services), port numbers or port ranges (e.g.,
21:22); if the protocol is <quote>icmp</quote>, this column is
interpreted as the destination icmp type(s).</para>
</listitem>
<listitem>
<para>CLIENT PORT(S) - (Optional) Port(s) used by the client. If
omitted, any source port is acceptable. Specified as a
comma-separate list of port names, port numbers or port
ranges.</para>
</listitem>
<listitem>
<para>USER (Added in Shorewall version 1.4.10) - (Optional) This
column may only be non-empty if the SOURCE is the firewall itself.
When this column is non-empty, the rule applies only if the program
generating the output is running under the effective user and/or
group. It may contain :</para>
<para>[&lt;user name or number&gt;]:[&lt;group name or
number&gt;]</para>
<para>The colon is optionnal when specifying only a user.</para>
<para>Examples : john: / john / :users / john:users</para>
</listitem>
</itemizedlist>
<example>
<title></title>
<para>All packets arriving on eth1 should be marked with 1. All
packets arriving on eth2 and eth3 should be marked with 2. All packets
originating on the firewall itself should be marked with 3.</para>
<programlisting>#MARK SOURCE DESTINATION PROTOCOL USER/GROUP
1 eth1 0.0.0.0/0 all
2 eth2 0.0.0.0/0 all
2 eth3 0.0.0.0/0 all
3 fw 0.0.0.0/0 all</programlisting>
</example>
<example>
<title></title>
<para>All GRE (protocol 47) packets not originating on the firewall
and destined for 155.186.235.151 should be marked with 12.</para>
<programlisting>#MARK SOURCE DESTINATION PROTOCOL USER/GROUP
12 0.0.0.0/0 155.182.235.151 47</programlisting>
</example>
<example>
<title></title>
<para>All SSH packets originating in 192.168.1.0/24 and destined for
155.186.235.151 should be marked with 22.</para>
<programlisting>#MARK SOURCE DESTINATION PROTOCOL USER/GROUP
22 192.168.1.0/24 155.182.235.151 tcp 22</programlisting>
</example>
</section>
<section>
<title>/etc/shorewall/tcdevices</title>
<para>This file allows you to define the incoming and outgoing bandwidth
for the devices you want traffic shaping to be enabled. That means, if
you want to use traffic shaping for a device, you have to define it
here.</para>
<para>Columns in the file are as follows:</para>
<itemizedlist>
<listitem>
<para>INTERFACE - Name of interface. Each interface may be listed
only once in this file. You may NOT specify the name of an alias
(e.g., eth0:0) here; see <ulink url="FAQ.htm#faq18">FAQ #18</ulink>.
You man NOT specify wildcards here, e.g. if you have multiple ppp
interfaces, you need to put them all in here!</para>
</listitem>
<listitem>
<para>IN-BANDWIDTH - The incoming Bandwidth of that interface.
Please note that you are not able to do traffic shaping on incoming
traffic, as the traffic is already received before you could do so.
This Column allows you to define the maximum traffic allowed for
this interface in total, if the rate is exceeded, the packets are
dropped. You want this mainly if you have a DSL or Cable Connection
to avoid queuing at your providers side. If you don't want any
traffic to be dropped set this to a value faster than your interface
maximum rate.</para>
</listitem>
<listitem>
<para>OUT-BANDWIDTH - Specifiy the outgoing bandwidth of that
interface. This is the maximum speed your connection can handle. It
is also the speed you can refer as "full" if you define the tc
classes. Outgoing traffic above this rate will be dropped.</para>
</listitem>
</itemizedlist>
<example>
<title></title>
<para>Suppose you are using PPP over Ethernet (DSL) and ppp0 is the
interface for this. The device has an outgoing bandwidth of 500kbit
and an incoming bandwidth of 6000kbit</para>
<programlisting>#INTERFACE IN-BANDWITH OUT-BANDWIDTH
ppp0 6000kbit 500kbit</programlisting>
</example>
</section>
<section>
<title>/etc/shorewall/tcclasses</title>
<para>This file allows you to define the actual classes that are used to
split the outgoing traffic.</para>
<itemizedlist>
<listitem>
<para>INTERFACE - Name of interface. Each interface may be listed
only once in this file. You may NOT specify the name of an alias
(e.g., eth0:0) here; see <ulink url="FAQ.htm#faq18">FAQ #18</ulink>.
You man NOT specify wildcards here, e.g. if you have multiple ppp
interfaces, you need to put them all in here!</para>
</listitem>
<listitem>
<para>MARK - The mark value which is an integer in the range 1-255.
You define these marks in the tcrules file, marking the traffic you
want to go into the queueing classes defined in here. You can use
the same marks for different Interfaces.</para>
</listitem>
<listitem>
<para>RATE - The minimum bandwidth this class should get, when the
traffic load rises. Please note that first the classes which equal
or a lesser priority value are served even if there are others that
have a guaranteed bandwith but a lower priority.</para>
</listitem>
<listitem>
<para>CEIL - The maximum bandwidth this class is allowed to use when
the link is idle. Useful if you have traffic which can get full
speed when more important services (e.g. interactive like ssh) are
not used. You can use the value "full" in here for setting the
maximum bandwidth to the defined output bandwidth of that
interface.</para>
</listitem>
<listitem>
<para>PRIORITY - you have to define a priority for the class.
packets in a class with a higher priority (=lesser value) are
handled before less priorized onces. You can just define the mark
value here also, if you are increasing the mark values with lesser
priority.</para>
</listitem>
<listitem>
<para>OPTIONS - A comma-separated list of options including the
following:</para>
<itemizedlist>
<listitem>
<para>default - this is the default class for that interface
where all traffic should go, that is not classified
otherwise.</para>
<note>
<para>defining default for exactly <emphasis
role="bold">one</emphasis> class per interface is
mandatory!</para>
</note>
</listitem>
<listitem>
<para>tos-&lt;tosname&gt; - this lets you define a filter for
the given &lt;tosname&gt; which lets you define a value of the
Type Of Service bits in the ip package which causes the package
to go in this class. Please note, that this filter overrides all
mark settings, so if you define a tos filter for a class all
traffic having that mark will go in it regardless of the mark on
the package. You can use the following for this option:
tos-minimize-delay (16) tos-maximize-throughput (8)
tos-maximize-reliability (4) tos-minimize-cost (2)
tos-normal-service (0)</para>
<note>
<para>Each of this options is only valid for <emphasis
role="bold">one</emphasis> class per interface.</para>
</note>
</listitem>
<listitem>
<para>tcp-ack - if defined causes an tc filter to be created
that puts all tcp ack packets on that interface that have an
size of &lt;=64 Bytes to go in this class. This is useful for
speeding up downloads. Please note that the size of the ack
packages is limited to 64 bytes as some applications (p2p for
example) use to make every package an ack package which would
cause them all into here. We want only packages WITHOUT payload
to match, so the size limit. Bigger packets just take their
normal way into the classes.</para>
<note>
<para>This option is only valid for <emphasis
role="bold">class</emphasis> per interface.</para>
</note>
</listitem>
</itemizedlist>
</listitem>
</itemizedlist>
</section>
<section>
<title>Real life examples</title>
<section>
<title>Configuration to replace Wondershaper</title>
<para>You are able to fully replace the wondershaper script by using
the buitin traffic control.You can find example configuration files at
<ulink
url="http://www1.shorewall.net/pub/shorewall/Samples/tc4shorewall/">"http://www1.shorewall.net/pub/shorewall/Samples/tc4shorewall/</ulink>.
Please note that they are just examples and need to be adjusted to
work for you. In this examples it is assumed that your interface for
you internet connection is ppp0 (for DSL) , if you use another
connection type, you have to change it. You also need to change the
settings in the tcdevices.wondershaper file to reflect your line
speed. The relevant lines of the config files follow here. Please note
that this is just an 1:1 replacement doing exactly what wondershaper
should do. You are free to change it...</para>
<para>tcclasses file</para>
<programlisting>#INTERFACE MARK RATE CEIL PRIORITY OPTIONS
ppp0 1 full full 1 tcp-ack,tos-minimize-delay
ppp0 2 9*full/10 9*full/10 2 default
ppp0 3 8*full/10 8*full/10 2</programlisting>
<para>tcdevices file</para>
<programlisting>#INTERFACE IN-BANDWITH OUT-BANDWIDTH
ppp0 5000kbit 500kbit</programlisting>
<para>tcrules file</para>
<programlisting>#MARK SOURCE DEST PROTO PORT(S) CLIENT USER
# PORT(S)
1:P 0.0.0.0/0 0.0.0.0/0 icmp echo-request
1:P 0.0.0.0/0 0.0.0.0/0 icmp echo-reply
# mark traffic which should have a lower priority with a 3:
# mldonkey
3 0.0.0.0/0 0.0.0.0/0 udp - 4666</programlisting>
<para>Wondershaper allows you to define a set of hosts and/or ports
you want to classify as low priority. To achieve this , you have to
add these hosts to tcrules and set the mark to 3 (true if you use the
example configuration files).</para>
<para>Setting hosts to low priority</para>
<para>lets assume the following settings from you old wondershaper
script (don't assume these example values are really useful, they are
only used for demonstrating):</para>
<programlisting>
# low priority OUTGOING traffic - you can leave this blank if you want
# low priority source netmasks
NOPRIOHOSTSRC="192.168.1.128/25 192.168.3.28"
# low priority destination netmasks
NOPRIOHOSTDST=60.0.0.0/24
# low priority source ports
NOPRIOPORTSRC="6662 6663"
# low priority destination ports
NOPRIOPORTDST="6662 6663"
</programlisting>
<para>This would result in the following additional settings to the
tcrules file:</para>
<programlisting>
3 192.168.1.128/25 0.0.0.0/0 all
3 192.168.3.28 0.0.0.0/0 all
3 0.0.0.0/0 60.0.0.0/24 all
3 0.0.0.0/0 0.0.0.0/0 udp 6662,6663
3 0.0.0.0/0 0.0.0.0/0 udp - 6662,6663
3 0.0.0.0/0 0.0.0.0/0 tcp 6662,6663
3 0.0.0.0/0 0.0.0.0/0 tcp - 6662,6663</programlisting>
</section>
</section>
</section>
<section>
<title id="tcstart">Using your own tc script</title>
<section id="owntcstart">
<title>Replacing builtin tcstart file</title>
<para>If you prefer your own tcstart file, just install it in
/etc/shorewall/tcstart.</para>
<para>In your tcstart script, when you want to run the <quote>tc</quote>
utility, use the run_tc function supplied by Shorewall if you want tc
errors to stop the firewall.</para>
<orderedlist>
<listitem>
<para>Set TC_ENABLED=Yes and CLEAR_TC=Yes</para>
</listitem>
<listitem>
<para>Supply an /etc/shorewall/tcstart script to configure your
traffic shaping rules.</para>
</listitem>
<listitem>
<para>Optionally supply an /etc/shorewall/tcclear script to stop
traffic shaping. That is usually unnecessary.</para>
</listitem>
<listitem>
<para>If your tcstart script uses the <quote>fwmark</quote>
classifier, you can mark packets using entries in
/etc/shorewall/tcrules.</para>
</listitem>
</orderedlist>
</section>
<section>
<title>Traffic control outside Shorewall</title>
<para>To start traffic shaping when you bring up your network
interfaces, you will have to arrange for your traffic shaping
configuration script to be run at that time. How you do that is
distribution dependent and will not be covered here. You then
should:</para>
<orderedlist>
<listitem>
<para>Set TC_ENABLED=No and CLEAR_TC=No</para>
</listitem>
<listitem>
<para>If your script uses the <quote>fwmark</quote> classifier, you
can mark packets using entries in /etc/shorewall/tcrules.</para>
</listitem>
</orderedlist>
</section>
</section>
</article>
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