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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><?dbtimestamp format="Y/m/d"?></pubdate>
<copyright>
<year>2001-2009</year>
<holder>Thomas M. Eastep</holder>
</copyright>
<copyright>
<year>2005</year>
<holder>Arne Bernin &amp; Thomas M. Eastep</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>
<important>
<para>Traffic shaping is complex and the Shorewall community is not well
equipped to answer traffic shaping questions. So if you are the type of
person who needs "insert tab A into slot B" instructions for everything
that you do, then please don't try to implement traffic shaping using
Shorewall. You will just frustrate yourself and we won't be able to help
you.</para>
</important>
<warning>
<para>Said another way, reading just Shorewall documentation is not going
to give you enough background to use this material.</para>
<para>At a minimum, you will need to refer to at least the following
additional information:</para>
<itemizedlist>
<listitem>
<para><emphasis>The LARTC HOWTO</emphasis>: <ulink
url="http://www.lartc.org">http://www.lartc.org</ulink></para>
</listitem>
<listitem>
<para>T<emphasis>he HTB User's Guide</emphasis>: <ulink
url="http://luxik.cdi.cz/~devik/qos/htb/manual/userg.htm">http://luxik.cdi.cz/~devik/qos/htb/manual/userg.htm</ulink></para>
</listitem>
<listitem>
<para><emphasis>HFSC Scheduling with Linux</emphasis>: <ulink
url="http://linux-ip.net/articles/hfsc.en/">http://linux-ip.net/articles/hfsc.en/</ulink></para>
</listitem>
<listitem>
<para>Some of the documents listed at <ulink
url="http://www.netfilter.org/documentation/index.html#documentation-howto">http://www.netfilter.org/documentation/index.html#documentation-howto</ulink>.
The tutorial by Oskar Andreasson is particularly good.</para>
</listitem>
<listitem>
<para>The output of <command>man iptables</command></para>
</listitem>
</itemizedlist>
</warning>
<section id="Intro">
<title>Introduction</title>
<para>Shorewall has builtin support for traffic shaping and control. This
support does not cover all options available (and especially all
algorithms that can be used to queue traffic) in 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 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 id="LinuxTC">
<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, we strongly recommend that you
take a deeper look into the <ulink url="http://lartc.org/howto/">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 queuing algorithm will not stop it from doing
so.</para>
<para>For Shorewall traffic shaping we use three algorithms: HTB
(Hierarchical Token Bucket), HFSC (Hierarchical Fair Service Curves) 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 normally works well. HTB and HFSC allow you to define a
set of classes, and you can put the traffic you want into these classes.
You can define minimum and maximum bandwidth settings for those classes
and order them hierarchically (the less prioritized classes only get
bandwidth if the more important have what they need). Additionally, HFSC
allows you to specify the maximum queuing delay that a packet may
experience. Shorewall builtin traffic shaping allows you to define these
classes (and their bandwidth limits), and it uses SFQ inside these classes
to make sure, that different data streams are handled equally. If SFQ's
default notion of a 'stream' doesn't work well for you, you can change it
using the <emphasis role="bold">flow</emphasis> option described <link
linkend="tcclasses">below</link>.</para>
<para>You can shape incoming traffic through use of an
<firstterm>Intermediate Frame Block</firstterm> (IFB) device. <link
linkend="IFB">See below</link>. <emphasis role="bold">But beware: using an
IFB can result in queues building up both at your ISPs router and at your
own.</emphasis></para>
<para>If you wish to shape downloads, you can also configure traffic
shaping on your firewall's local interface. An example appears <link
linkend="Downloads">below</link>. Again, however, <emphasis
role="bold">this can result in queues building up both at your ISPs router
and at your own</emphasis>.</para>
<para>You shape and control outgoing traffic by assigning the traffic to
<firstterm>classes</firstterm>. Each class is associated with exactly one
network interface and has a number of attributes:</para>
<orderedlist>
<listitem>
<para>PRIORITY - Used to give preference to one class over another
when selecting a packet to send. The priority is a numeric value with
1 being the highest priority, 2 being the next highest, and so
on.</para>
</listitem>
<listitem>
<para>RATE - The minimum bandwidth this class should get, when the
traffic load rises. Classes with a higher priority (lower PRIORITY
value) are served even if there are others that have a guaranteed
bandwidth but have a lower priority (higher PRIORITY value).</para>
</listitem>
<listitem>
<para>CEIL - The maximum bandwidth the class is allowed to use when
the link is idle.</para>
</listitem>
<listitem>
<para>MARK - Netfilter has a facility for
<firstterm>marking</firstterm> packets. Packet marks have a numeric
value which is limited in Shorewall to the values 1-255 (1-16383 if
you set WIDE_TC_MARKS=Yes in <ulink
url="manpages/shorewall.conf.html">shorewall.conf</ulink> (5) ). You
assign packet marks to different types of traffic using entries in the
<filename>/etc/shorewall/tcrules</filename> file.</para>
</listitem>
</orderedlist>
<para>One class for each interface must be designated as the
<firstterm>default class</firstterm>. This is the class to which unmarked
traffic (packets to which you have not assigned a mark value in
<filename>/etc/shorewall/tcrules</filename>) is assigned.</para>
<para>Netfilter also supports a mark value on each connection. You can
assign connection mark values in
<filename>/etc/shorewall/tcrules</filename>, you can copy the current
packet's mark to the connection mark (SAVE), or you can copy the
connection mark value to the current packet's mark (RESTORE). For more
information, see<ulink url="PacketMarking.html"> this
article</ulink>.</para>
</section>
<section id="Kernel">
<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 Ingress scheduler, the
PRIO pseudoscheduler and SFQ queue. The other scheduler or queue
algorithms are not needed.</para>
<para>This screen shot shows how I configured QoS in a 2.6.16
Kernel:</para>
<graphic align="center" fileref="images/traffic_shaping2.6.png" />
<para>And here's my recommendation for a 2.6.21 kernel:<graphic
align="center" fileref="images/traffic_shaping2.6.21.png" /></para>
</section>
<section id="Shorewall">
<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 "<emphasis
role="bold">Internal</emphasis>" in /etc/shorewall/shorewall.conf.
Setting <emphasis role="bold">TC_ENABLED=Yes</emphasis> 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 <emphasis role="bold">Yes</emphasis>
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 id="Builtin">
<title>Using builtin traffic shaping/control</title>
<para>Shorewall's builtin traffic shaping feature provides a thin layer on
top of the ingress qdesc, HTB and SFQ. That translation layer allows you
to:</para>
<itemizedlist>
<listitem>
<para>Define HTB classes using Shorewall-style column-oriented
configuration files.</para>
</listitem>
<listitem>
<para>Integrate the reloading of your traffic shaping configuration
with the reloading of your packet-filtering and marking
configuration.</para>
</listitem>
<listitem>
<para>Assign traffic to HTB classes by TOS value.</para>
</listitem>
<listitem>
<para>Assign outgoing TCP ACK packets to an HTB class.</para>
</listitem>
<listitem>
<para>Assign traffic to HTB classes based on packet mark value.</para>
</listitem>
</itemizedlist>
<para>Those few features are really all that builtin traffic
shaping/control provides; consequently, you need to understand HTB and
Linux traffic shaping as well as Netfilter packet marking in order to use
the facility. Again, please see the links at top of this article.</para>
<para>For defining bandwidths (for either devices or classes) please use
kbit or kbps (for Kilobytes per second) and make sure there is <emphasis
role="bold">NO</emphasis> space between the number and the unit (it is
100kbit <emphasis role="bold">not</emphasis> 100 kbit). Using mbit, mbps
or a raw number (which means bytes) could be used, but note that only
integer numbers are supported (0.5 is <emphasis role="bold">not
valid</emphasis>).</para>
<para><emphasis role="bold">To properly configure the settings for your
devices you need to find out the real up- and downstream rates you
have</emphasis>. This is especially the case, if you are using a DSL
connection or one of another type that do not have a guaranteed bandwidth.
Don't trust the values your provider tells you for this; especially
measuring the real download speed is important! There are several online
tools that help you find out; search for "dsl speed test" on google (For
Germany you can use <ulink
url="http://www.speedcheck.arcor.de/cgi-bin/speedcheck.cgi">arcor speed
check</ulink>). Be sure to choose a test site located near you.</para>
<section id="tcdevices">
<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. For additional information, see <ulink
url="manpages/shorewall-tcdevices.html">shorewall-tcdevices</ulink>
(5).</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! Shorewall will
determine if the device exists and will only configure the device if
it does exist. If it doesn't exist, the following warning is
issued:</para>
<para><emphasis role="bold">WARNING: Device &lt;device name&gt; not
found -- traffic-shaping configuration skipped</emphasis></para>
<para>Shorewall assigns a sequential <firstterm>interface
number</firstterm> to each interface (the first entry in
<filename>/etc/shorewall/tcdevices</filename> is interface 1, the
second is interface 2 and so on) You can also explicitly specify the
interface number by prefixing the interface name with the number and
a colon (":"). Example: 1:eth0.</para>
</listitem>
<listitem>
<para>IN-BANDWIDTH - The incoming Bandwidth of that interface.
Please note that when you use this column, you are not traffic
shaping 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 excess 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 (or to 0
(zero).</para>
<para>To determine the optimum value for this setting, we recommend
that you start by setting it significantly below your measured
download bandwidth (20% or so). While downloading, measure the
<emphasis>ping</emphasis> response time from the firewall to the
upstream router as you gradually increase the setting.The optimal
setting is at the point beyond which the <emphasis>ping</emphasis>
time increases sharply as you increase the setting.</para>
</listitem>
<listitem>
<para>OUT-BANDWIDTH - Specify 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>
<listitem>
<para>OPTIONS — A comma-separated list of options from the following
list:</para>
<variablelist>
<varlistentry>
<term>classify</term>
<listitem>
<para>If specified, classification of traffic into the various
classes is done by CLASSIFY entries in
<filename>/etc/shorewall/tcrules</filename> or by entries in
<filename>/etc/shorewall/tcfilters</filename>. No MARK value
will be associated with classes on this interface.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>hfsc</term>
<listitem>
<para>Shorewall normally uses the <firstterm>Hierarchical
Token Bucket</firstterm> queuing discipline. When
<option>hfsc</option> is specified, the
<firstterm>Hierarchical Fair Service Curves</firstterm>
discipline is used instead.</para>
</listitem>
</varlistentry>
</variablelist>
</listitem>
<listitem>
<para>REDIRECTED INTERFACES — Entries are appropriate in this column
only if the device in the INTERFACE column names a <link
linkend="IFB">Intermediate Frame Block (IFB)</link>. It lists the
physical interfaces that will have their input shaped using classes
defined on the IFB. Neither the IFB nor any of the interfaces listed
in this column may have an IN-BANDWIDTH specified. You may specify
zero (0) or a dash ("-:) in the IN-BANDWIDTH column.</para>
<para>IFB devices automatically get the <emphasis
role="bold">classify</emphasis> option.</para>
</listitem>
</itemizedlist>
<example id="Example0">
<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 id="tcclasses">
<title>/etc/shorewall/tcclasses</title>
<para>This file allows you to define the actual classes that are used to
split the outgoing traffic. For additional information, see <ulink
url="manpages/shorewall-tcclasses.html">shorewall-tcclasses</ulink>
(5).</para>
<itemizedlist>
<listitem>
<para>INTERFACE - Name of interface. Users may also specify the
interface number. Must match the name (or number) of an interface
with an entry in <filename>/etc/shorewall/tcdevices</filename>. If
the interface has the <emphasis role="bold">classify</emphasis>
option in <filename>/etc/shorewall/tcdevices</filename>, then the
interface name or number must be followed by a colon and a
<firstterm>class number</firstterm>. Examples: eth0:1, 4:9. Class
numbers must be unique for a given interface. Normally, all classes
defined here are sub-classes of a root class that is implicitly
defined from the entry in <ulink
url="shorewall-tcdevices.html">shorewall-tcdevices</ulink>(5). You
can establish a class hierarchy by specifying a
<emphasis>parent</emphasis> class (e.g.,
<emphasis>interface</emphasis>:<emphasis>parent-class</emphasis>:<emphasis>class</emphasis>)
-- the number of a class that you have previously defined. The
sub-class may borrow unused bandwidth from its parent.</para>
</listitem>
<listitem>
<para>MARK - The mark value which is an integer in the range 1-255
(1-16383 if you set WIDE_TC_MARKS=Yes in <ulink
url="manpages/shorewall.conf.html">shorewall.conf</ulink> (5) ). You
define these marks in the tcrules file, marking the traffic you want
to go into the queuing classes defined in here. You can use the same
marks for different Interfaces. You must specify "-' in this column
if the device specified in the INTERFACE column has the <emphasis
role="bold">classify</emphasis> option in
<filename>/etc/shorewall/tcdevices</filename>.</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 bandwidth but a lower priority. <emphasis
role="bold">If the sum of the RATEs for all classes assigned to an
INTERFACE exceed that interfaces's OUT-BANDWIDTH, then the
OUT-BANDWIDTH limit will not be honored.</emphasis></para>
<para>When using HFSC, this column may contain 1, 2 or 3 pieces of
information separated by colons (":"). In addition to the minimum
bandwidth, leaf classes may specify realtime criteria: DMAX (maximum
delay in milliseconds) and optionally UMAX (the largest packet
expected in the class).</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 prioritized ones. 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
packets 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 packets 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>
<listitem>
<para>occurs=<emphasis>number</emphasis> - Typically used with
an IPMARK entry in tcrules. Causes the rule to be replicated for
a total of <emphasis>number</emphasis> rules. Each rule has a
successively class number and mark value.</para>
<para>When 'occurs' is used:</para>
<itemizedlist>
<listitem>
<para>The associated device may not have the 'classify'
option.</para>
</listitem>
<listitem>
<para>The class may not be the default class.</para>
</listitem>
<listitem>
<para>The class may not have any 'tos=' options (including
'tcp-ack').</para>
</listitem>
<listitem>
<para>The class should not specify a MARK value. If one is
specified, it will be ignored with a warning message.</para>
</listitem>
</itemizedlist>
<para>The 'RATE' and 'CEIL' parameters apply to each instance of
the class. So the total RATE represented by an entry with
'occurs' will be the listed RATE multiplied by
<emphasis>number</emphasis>. For additional information, see
<ulink url="manpages/shorewall-tcrules.html">tcrules</ulink>
(5).</para>
</listitem>
<listitem>
<para>flow=<emphasis>keys</emphasis> - Shorewall attaches an SFQ
queuing discipline to each leaf HTB class. SFQ ensures that each
<firstterm>flow</firstterm> gets equal access to the interface.
The default definition of a flow corresponds roughly to a
Netfilter connection. So if one internal system is running
BitTorrent, for example, it can have lots of 'flows' and can
thus take up a larger share of the bandwidth than a system
having only a single active connection. The
<option>flow</option> classifier (module cls_flow) works around
this by letting you define what a 'flow' is. The clasifier must
be used carefully or it can block off all traffic on an
interface! The flow option can be specified for an HTB leaf
class (one that has no sub-classes). We recommend that you use
the following:</para>
<simplelist>
<member>Shaping internet-bound traffic: flow=nfct-src</member>
<member>Shaping traffic bound for your local net:
flow=dst</member>
</simplelist>
<para>These will cause a 'flow' to consists of the traffic
to/from each internal system.</para>
<para>When more than one key is give, they must be enclosed in
parenthesis and separated by commas.</para>
<para>To see a list of the possible flow keys, run this
command:</para>
<blockquote>
<para><command>tc filter add flow help</command></para>
</blockquote>
<para>Those that begin with "nfct-" are Netfilter connection
tracking fields. As shown above, we recommend flow=nfct-src;
that means that we want to use the source IP address
<emphasis>before NAT</emphasis> as the key.</para>
</listitem>
</itemizedlist>
</listitem>
</itemizedlist>
</section>
<section id="tcrules">
<title>/etc/shorewall/tcrules</title>
<important>
<para>Unlike rules in the <ulink
url="manpages/shorewall-rules.html">shorewall-rules</ulink>(5) file,
evaluation of rules in this file will continue after a match. So the
final mark for each packet will be the one assigned by the LAST tcrule
that matches.</para>
<para>Also unlike rules in the <ulink
url="manpages/shorewall-rules.html">shorewall-rules</ulink>(5) file,
the tcrules file is not stateful. So every packet that goes into, out
of or through your firewall is subject to entries in the tcrules
file.</para>
<para>Because tcrules are not stateful, it is necessary to understand
basic IP socket operation. Here is an edited excerpt from a post on
the Shorewall Users list:<blockquote>
<para>For the purposes of this discussion, the world is separated
into clients and servers. Servers provide services to
clients.</para>
<para>When a server starts, it creates a socket and
<emphasis>binds</emphasis> the socket to an
<emphasis>address</emphasis>. For AF_INET (IPv4) and AF_INET6
(IPv6) sockets, that address is an ordered triple consisting of an
IPv4 or IPv6 address, a protocol, and possibly a port number. Port
numbers are only used when the protocol is TCP, UDP, SCTP or DCCP.
The protocol and port number used by a server are typically
well-known so that clients will be able to connect to it or send
datagrams to it. So SSH servers bind to TCP port 22, SMTP servers
bind to TCP port 25, etc. We will call this port the SERVER
PORT.</para>
<para>When a client want to use the service provided by a server,
it also creates a socket and, like the server's socket, the
client's socket must be bound to an address. But in the case of
the client, the socket is usually given an automatic address
binding. For AF_INET and AF_INET6 sockets. the IP address is the
IP address of the client system (loose generalization) and the
port number is selected from a <firstterm>local port
range</firstterm>. On Linux systems, the local port range can be
seen by <command>cat
/proc/sys/net/ipv4/ip_local_port_range</command>. So it is not
possible in advance to determine what port the client will be
using. Whatever it is, we'll call it the CLIENT PORT.</para>
<para>Now: <blockquote>
<para>Packets sent from the client to the server will
have:<blockquote>
<para>SOURCE PORT = CLIENT PORT</para>
<para>DEST PORT = SERVER PORT</para>
</blockquote></para>
<para>Packets sent from the server to the client will have:
<blockquote>
<para>SOURCE PORT = SERVER PORT</para>
<para>DEST PORT = CLIENT PORT</para>
</blockquote></para>
</blockquote></para>
<para>Since the SERVER PORT is generally the only port known ahead
of time, we must categorize traffic from the server to the client
using the SOURCE PORT.</para>
</blockquote></para>
</important>
<para>The fwmark classifier provides a convenient way to classify
packets for traffic shaping. The <quote>/etc/shorewall/tcrules</quote>
file is used for specifying these marks in a tabular fashion. For an
in-depth look at the packet marking facility in Netfilter/Shorewall,
please see <ulink url="PacketMarking.html">this article</ulink>.</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 or CLASSIFY - MARK specifies the mark value is to be
assigned in case of a match. This is an integer in the range 1-255
(1-16383 if you set WIDE_TC_MARKS=Yes in <ulink
url="manpages/shorewall.conf.html">shorewall.conf</ulink> (5) ).
This value may be optionally followed by <quote>:</quote> and either
<quote>F</quote>, <quote>P</quote> or "T" to designate that the
marking will occur in the FORWARD, PREROUTING or POSTROUTING chains
respectively. If this additional specification is omitted, the chain
used to mark packets will be determined as follows:</para>
<itemizedlist>
<listitem>
<para>If the SOURCE is
$FW[:&lt;<emphasis>address</emphasis>&gt;], then the rule is
inserted in the OUTPUT chain.</para>
</listitem>
<listitem>
<para>Otherwise, the chain is determined by the setting of the
MARK_IN_FORWARD_CHAIN option in shorewall.conf.</para>
</listitem>
</itemizedlist>
<note>
<para><emphasis role="bold">Use the 'T' qualifier if you want the
rule to apply equally to traffic being routed through the firewall
and to traffic originating on the firewall
itself.</emphasis></para>
</note>
<para>Normally, the mark is applied to the packet. If you follow the
mark value with ":" and "C", then the mark is applied to the
connection. "C" can be combined with "F", "P" or "T" to designate
that the connection should be marked in a particular chain (e.g.,
"CF", "CP", "CT").</para>
<para>There are additional special values available:</para>
<orderedlist numeration="loweralpha">
<listitem>
<para><emphasis
role="bold">RESTORE</emphasis>[/<emphasis>mask</emphasis>] --
restore the packet's mark from the connection's mark using the
supplied mask if any. Your kernel and iptables must include
CONNMARK support.</para>
<para>As above, may be followed by <emphasis
role="bold">:P</emphasis>, <emphasis role="bold">:F</emphasis>
or <emphasis role="bold">:T</emphasis>.</para>
</listitem>
<listitem>
<para><emphasis
role="bold">SAVE</emphasis>[/<emphasis>mask</emphasis>] -- save
the packet's mark to the connection's mark using the supplied
mask if any. Your kernel and iptables must include CONNMARK
support.</para>
<para>As above, may be followed by <emphasis
role="bold">:P</emphasis>, <emphasis role="bold">:F</emphasis>
or <emphasis role="bold">:T</emphasis>.</para>
</listitem>
<listitem>
<para><emphasis role="bold">CONTINUE</emphasis> Don't process
any more marking rules in the table.</para>
<para>As above, may be followed by <emphasis
role="bold">:P</emphasis>, <emphasis role="bold">:F</emphasis>
or <emphasis role="bold">:T</emphasis>.</para>
</listitem>
<listitem>
<para><emphasis role="bold">COMMENT</emphasis> -- the rest of
the line will be attached as a comment to the Netfilter rule(s)
generated by the following entries. The comment will appear
delimited by "/* ... */" in the output of <command>shorewall
show mangle</command></para>
<para>To stop the comment from being attached to further rules,
simply include COMMENT on a line by itself.</para>
</listitem>
</orderedlist>
<para>To use CLASSIFY, your kernel and iptables must include
CLASSIFY target support. In that case, this column contains a
classification (classid) of the form &lt;major&gt;:&lt;minor&gt;
where &lt;major&gt; and &lt;minor&gt; are integers. Corresponds to
the 'class' specification in these traffic shaping modules:</para>
<simplelist>
<member>atm</member>
<member>cbq</member>
<member>dsmark</member>
<member>pfifo_fast</member>
<member>htb</member>
<member>prio</member>
</simplelist>
<para>Classification occurs in the POSTROUTING chain <emphasis
role="bold">except</emphasis> when the SOURCE contains
$FW[:&lt;<emphasis>address</emphasis>&gt;] in which case, the
classify action takes place in the OUTPUT chain. When used with the
builtin traffic shaper, the &lt;major&gt; class is the interface
number and the &lt;minor&gt; class is either:</para>
<orderedlist>
<listitem>
<para>Constructed by Shorewall. The method of construction
depends on the setting of WIDE_TC_MARKS (<ulink
url="manpages/shorewall.conf.html">shorewall.conf</ulink>
(5)).</para>
<para>When WIDE_TC_MARKS=No (the default), the &lt;minor&gt;
class is:</para>
<itemizedlist>
<listitem>
<para>the MARK value of the class preceded by the number "1"
or "10" (MARK value 1 is &lt;minor&gt; class 11, MARK value
22 is &lt;minor&gt; class 122, and so on). "10" is used
where there are more than 10 devices defined in <link
linkend="tcdevices">/etc/shorewall/tcdevices</link>.</para>
</listitem>
</itemizedlist>
<para>When WIDE_TC_MARKS=Yes, the &lt;minor&gt; class is
assigned sequentially beginning with 2.</para>
</listitem>
<listitem>
<para>The class number, if specified.</para>
</listitem>
</orderedlist>
</listitem>
<listitem>
<para>SOURCE - Source of the packet.</para>
<para>May be:</para>
<orderedlist>
<listitem>
<para>An interface name - matches traffic entering the firewall
on the specified interface. May not be used in classify rules or
in rules using the :T chain qualifier.</para>
</listitem>
<listitem>
<para>A comma-separated list of host or network IP addresses or
MAC addresses. <emphasis role="bold">This form will not match
traffic that originates on the firewall itself unless either
&lt;major&gt;&lt;minor&gt; or the :T chain qualifier is used in
the MARK column.</emphasis></para>
<para>Examples:<simplelist>
<member>0.0.0.0/0</member>
</simplelist></para>
<para><simplelist>
<member>192.168.1.0/24, 172.20.4.0/24</member>
</simplelist></para>
</listitem>
<listitem>
<para>An interface name followed by a colon (":") followed by a
comma-separated list of host or network IP addresses or MAC
addresses. May not be used in classify rules or in rules using
the :T chain qualifier.</para>
</listitem>
<listitem>
<para>$FW optionally followed by a colon (":") and a
comma-separated list of host or network IP addresses. matches
packets originating on the firewall. May not be used with a
chain qualifier (:P, :F, etc.) in the MARK column.</para>
</listitem>
</orderedlist>
<para>MAC addresses must be prefixed with "~" and use "-" as a
separator.</para>
<para>Example: ~00-A0-C9-15-39-78</para>
<para>If your kernel includes iprange match support, then address
ranges may be included in the address lists.</para>
</listitem>
<listitem>
<para>DEST - Destination of the packet.</para>
<para>May be:</para>
<orderedlist>
<listitem>
<para>An interface name. May not be used in the PREROUTING chain
(:P in the mark column or no chain qualifier and
MARK_IN_FORWARD_CHAIN=No in <ulink
url="manpages/shorewall.conf">shorewall.conf</ulink> (5)). The
interface name may be optionally followed by a colon (":") and
an IP address list.</para>
</listitem>
<listitem>
<para>A comma-separated list of host or network IP addresses.
The list may include ip address ranges if your kernel and
iptables include iprange support.</para>
</listitem>
</orderedlist>
</listitem>
<listitem>
<para>PROTO - Protocol - Must be "tcp", "udp", "icmp", "ipp2p",
"ipp2p:udp", "ipp2p:all" a number, or "all". "ipp2p" requires ipp2p
match support in your kernel and iptables.</para>
</listitem>
<listitem>
<para>PORT(S) - Destination Ports. A comma-separated list of Port
names (from /etc/services), port numbers or port ranges; if the
protocol is "icmp", this column is interpreted as the destination
icmp-type(s).</para>
<para>If the protocol is ipp2p, this column is interpreted as an
ipp2p option without the leading "--" (example "bit" for
bit-torrent). If no PORT is given, "ipp2p" is assumed. Note that the
xtables-addons version of IPP2P does not support the "ipp2p" option;
if the column is empty or contains "ipp2p" when using that version
of IPP2P, Shorewall will substitute "edk,kazaa,gnu,dc".</para>
<para>This column is ignored if PROTOCOL = all but must be entered
if any of the following field is supplied. In that case, it is
suggested that this field contain "-"</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/GROUP (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;][+&lt;program name&gt;]</para>
<para>The colon is optional when specifying only a user.</para>
<para>Examples:</para>
<programlisting>joe #program must be run by joe
:kids #program must be run by a member of the 'kids' group
!:kids #program must not be run by a member of the 'kids' group
+upnpd #program named upnpd (This feature was removed from Netfilter in kernel version 2.6.14).</programlisting>
</listitem>
<listitem>
<para>TEST (Optional) Defines a test on the existing packet or
connection mark. The rule will match only if the test returns true.
Tests have the format [!]&lt;value&gt;[/&lt;mask&gt;][:C]</para>
<para>Where:</para>
<simplelist>
<member>! Inverts the test (not equal)</member>
<member>&lt;value&gt; Value of the packet or connection
mark.</member>
<member>&lt;mask&gt; A mask to be applied to the mark before
testing</member>
<member>:C Designates a connection mark. If omitted, the packet
mark's value is tested.</member>
</simplelist>
</listitem>
<listitem>
<para>LENGTH (Optional) This field, if present, allows you to match
the length of a packet against a specific value or range of values.
A range is specified in the form &lt;min&gt;:&lt;max&gt; where
either &lt;min&gt; or &lt;max&gt; (but not both) may be omitted. If
&lt;min&gt; is omitted, then 0 is assumed; if &lt;max&gt; is
omitted, than any packet that is &lt;min&gt; or longer will
match.</para>
<para>You must have iptables length support for this to work. If you
let it empty or place an "-" here, no length match will be
done.</para>
<para>Examples: 1024, 64:1500, :100</para>
</listitem>
<listitem>
<para>TOS (Optional) Type of Service. Either a standard name, or a
numeric value to match.</para>
<blockquote>
<simplelist>
<member>Minimize-Delay (16)</member>
<member>Maximize-Throughput (8)</member>
<member>Maximize-Reliability (4)</member>
<member>Minimize-Cost (2)</member>
<member>Normal-Service (0)</member>
</simplelist>
</blockquote>
</listitem>
<listitem>
<para>HELPER (Optional). Names one of the Netfilter protocol helper
modules such as <emphasis>ftp</emphasis>, <emphasis>sip</emphasis>,
<emphasis>amanda</emphasis>, etc.</para>
</listitem>
</itemizedlist>
<example id="Example1">
<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 PORT(S)
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 id="Example2">
<title></title>
<para>All GRE (protocol 47) packets destined for 155.186.235.151
should be marked with 12.</para>
<programlisting>#MARK SOURCE DESTINATION PROTOCOL PORT(S)
12:T 0.0.0.0/0 155.182.235.151 47</programlisting>
</example>
<example id="Example3">
<title></title>
<para>All SSH request 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 PORT(S)
22:T 192.168.1.0/24 155.182.235.151 tcp 22</programlisting>
</example>
<example id="Example4">
<title></title>
<para>All SSH packets packets going out of the first device in in
/etc/shorewall/tcdevices should be assigned to the class with mark
value 10.</para>
<programlisting>#MARK SOURCE DESTINATION PROTOCOL PORT(S) CLIENT
# PORT(S)
1:110 0.0.0.0/0 0.0.0.0/0 tcp 22
1:110 0.0.0.0/0 0.0.0.0/0 tcp - 22</programlisting>
</example>
<example id="Example5">
<title></title>
<para>Mark all ICMP echo traffic with packet mark 1. Mark all peer to
peer traffic with packet mark 4.</para>
<para>This is a little more complex than otherwise expected. Since the
ipp2p module is unable to determine all packets in a connection are
P2P packets, we mark the entire connection as P2P if any of the
packets are determined to match. We assume packet/connection mark 0 to
means unclassified. Traffic originating on the firewall is not covered
by this example.</para>
<programlisting>#MARK SOURCE DESTINATION PROTOCOL PORT(S) CLIENT USER/ TEST
# PORT(S) GROUP
1 0.0.0.0/0 0.0.0.0/0 icmp echo-request
1 0.0.0.0/0 0.0.0.0/0 icmp echo-reply
RESTORE 0.0.0.0/0 0.0.0.0/0 all - - - 0
CONTINUE 0.0.0.0/0 0.0.0.0/0 all - - - !0
4 0.0.0.0/0 0.0.0.0/0 ipp2p:all
SAVE 0.0.0.0/0 0.0.0.0/0 all - - - !0</programlisting>
<para>The last four rules can be translated as:</para>
<blockquote>
<para>"If a packet hasn't been classified (packet mark is 0), copy
the connection mark to the packet mark. If the packet mark is set,
we're done. If the packet is P2P, set the packet mark to 4. If the
packet mark has been set, save it to the connection mark."</para>
</blockquote>
</example>
<example>
<title></title>
<para>Mark all forwarded VOIP connections with connection mark 1 and
ensure that all VOIP packets also receive that mark (assumes that
nf_conntrack_sip is loaded).</para>
<programlisting>#MARK SOURCE DESTINATION PROTOCOL PORT(S) CLIENT USER/ TEST CONNBYTES TOS HELPER
# PORT(S) GROUP
RESTORE 0.0.0.0/0 0.0.0.0/0 all - - - 0
CONTINUE 0.0.0.0/0 0.0.0.0/0 all - - - !0
1 0.0.0.0/0 0.0.0.0/0 all - - - - - - sip
SAVE 0.0.0.0/0 0.0.0.0/0 all - - - !0</programlisting>
</example>
</section>
<section id="ppp">
<title>ppp devices</title>
<para>If you use ppp/pppoe/pppoa) to connect to your Internet provider
and you use traffic shaping you need to restart shorewall traffic
shaping. The reason for this is, that if the ppp connection gets
restarted (and it usually does this at least daily), all
<quote>tc</quote> filters/qdiscs related to that interface are
deleted.</para>
<para>The easiest way to achieve this, is just to restart shorewall once
the link is up. To achieve this add a small executable script
to<quote>/etc/ppp/ip-up.d</quote>.</para>
<programlisting>#! /bin/sh
/sbin/shorewall refresh</programlisting>
</section>
<section id="Real">
<title>Real life examples</title>
<section>
<title>A Shorewall User's Experience</title>
<para>Chuck Kollars has provided <ulink
url="http://www.ckollars.org/shaping.html">an excellent
writeup</ulink> about his traffic shaping experiences.</para>
</section>
<section id="Wondershaper">
<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 example it is assumed that your interface for
your 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 a 1:1 replacement doing exactly what wondershaper
should do. You are free to change it...</para>
<section id="realtcd">
<title>tcdevices file</title>
<programlisting>#INTERFACE IN-BANDWITH OUT-BANDWIDTH
ppp0 5000kbit 500kbit</programlisting>
</section>
<section id="realtcc">
<title>tcclasses file</title>
<programlisting>#INTERFACE MARK RATE CEIL PRIORITY OPTIONS
ppp0 1 5*full/10 full 1 tcp-ack,tos-minimize-delay
ppp0 2 3*full/10 9*full/10 2 default
ppp0 3 2*full/10 8*full/10 2</programlisting>
</section>
<section id="realtcr">
<title>tcrules file</title>
<programlisting>#MARK SOURCE DEST PROTO PORT(S) CLIENT USER
# PORT(S)
1:F 0.0.0.0/0 0.0.0.0/0 icmp echo-request
1:F 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>
</section>
<section id="lowpro">
<title>Setting hosts to low priority</title>
<para>lets assume the following settings from your 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 id="simiple">
<title>A simple setup</title>
<para>This is a simple setup for people sharing an Internet connection
and using different computers for this. It just basically shapes
between 2 hosts which have the ip addresses 192.168.2.23 and
192.168.2.42</para>
<section id="simpletcd">
<title>tcdevices file</title>
<programlisting>#INTERFACE IN-BANDWITH OUT-BANDWIDTH
ppp0 6000kbit 700kbit</programlisting>
<para>We have 6mbit down and 700kbit upstream.</para>
</section>
<section id="simpletcc">
<title>tcclasses file</title>
<programlisting>#INTERFACE MARK RATE CEIL PRIORITY OPTIONS
ppp0 1 10kbit 50kbit 1 tcp-ack,tos-minimize-delay
ppp0 2 300kbit full 2
ppp0 3 300kbit full 2
ppp0 4 90kbit 200kbit 3 default</programlisting>
<para>We add a class for tcp ack packets with highest priority, so
that downloads are fast. The following 2 classes share most of the
bandwidth between the 2 hosts, if the connection is idle, they may
use full speed. As the hosts should be treated equally they have the
same priority. The last class is for the remaining traffic.</para>
</section>
<section id="simpletcr">
<title>tcrules file</title>
<programlisting>#MARK SOURCE DEST PROTO PORT(S) CLIENT USER
# PORT(S)
1:F 0.0.0.0/0 0.0.0.0/0 icmp echo-request
1:F 0.0.0.0/0 0.0.0.0/0 icmp echo-reply
2:F 192.168.2.23 0.0.0.0/0 all
3:F 192.168.2.42 0.0.0.0/0 all</programlisting>
<para>We mark icmp ping and replies so they will go into the fast
interactive class and set a mark for each host.</para>
</section>
</section>
</section>
</section>
<section id="Xen">
<title>A Warning to Xen Users</title>
<para>If you are running traffic shaping in your dom0 and traffic shaping
doesn't seem to be limiting outgoing traffic properly, it may be due to
"checksum offloading" in your domU(s). Check the output of "shorewall show
tc". Here's an excerpt from the output of that command:</para>
<programlisting>class htb 1:130 parent 1:1 leaf 130: prio 3 quantum 1500 rate 76000bit <emphasis
role="bold">ceil 230000bit</emphasis> burst 1537b/8 mpu 0b overhead 0b cburst 1614b/8 mpu 0b overhead 0b level 0
Sent 559018700 bytes 75324 pkt (dropped 0, overlimits 0 requeues 0)
<emphasis role="bold">rate 299288bit</emphasis> 3pps backlog 0b 0p requeues 0
lended: 53963 borrowed: 21361 <emphasis role="bold">giants: 90174</emphasis>
tokens: -26688 ctokens: -14783</programlisting>
<para>There are two obvious problems in the above output:</para>
<orderedlist>
<listitem>
<para>The rate (299288) is considerably larger than the ceiling
(230000).</para>
</listitem>
<listitem>
<para>There are a large number (90174) of giants reported.</para>
</listitem>
</orderedlist>
<para>This problem will be corrected by disabling "checksum offloading" in
your domU(s) using the <command>ethtool</command> utility. See the <ulink
url="XenMyWay-Routed.html">one of the Xen articles</ulink> for
instructions.</para>
</section>
<section id="HFSC">
<title>An HFSC Example</title>
<para>As mentioned at the top of this article, there is an excellent
introduction to HFSC at <ulink
url="http://linux-ip.net/articles/hfsc.en/">http://linux-ip.net/articles/hfsc.en/</ulink>.
At the end of that article are 'tc' commands that implement the
configuration in the article. Those tc commands correspond to the
following Shorewall traffic shaping configuration.</para>
<para><filename>/etc/shorewall/tcdevices</filename>:</para>
<programlisting>#INTERFACE IN-BANDWITH OUT-BANDWIDTH OPTIONS
eth0 - 1000kbit hfsc</programlisting>
<para><filename>/etc/shorewall/tcclasses</filename>:</para>
<programlisting>#INTERFACE:CLASS MARK RATE: CEIL PRIORITY OPTIONS
# DMAX:UMAX
1:10 1 500kbit full 1
1:20 2 500kbit full 1
1:10:11 3 400kbit:53ms:1500b full 2
1:10:12 4 100kbit:30ms:1500b full 2</programlisting>
<para>The following sub-section offers some notes about the
article.</para>
<section id="MajicNumbers">
<title>Where Did all of those Magic Numbers come from?</title>
<para>As you read the article, numbers seem to be introduced out of thin
air. I'll try to shed some light on those.</para>
<para>There is very clear development of these numbers:</para>
<itemizedlist>
<listitem>
<para>12ms to transfer a 1500b packet at 1000kbits/second.</para>
</listitem>
<listitem>
<para>100kbits per second with 1500b packets, requires 8 packets per
second.</para>
</listitem>
<listitem>
<para>A packet from class 1:12 must be sent every 120ms.</para>
</listitem>
<listitem>
<para>Total transmit delay can be no more than 132ms (120 +
12).</para>
</listitem>
</itemizedlist>
<para>We then learn that the queuing latency can be reduced to 30ms if
we use a two-part service curve whose first part is 400kbits/second.
Where did those come from?</para>
<itemizedlist>
<listitem>
<para>The latency is calculated from the rate. If it takes 12ms to
transmit a 1500 byte packet at 1000kbits/second, it takes 30ms to
transmit a 1500b at 400kbits/second.</para>
</listitem>
<listitem>
<para>For the slope of the first part of the service curve, in
theory we can pick any number between 100 (the rate of class 1:12)
and 500 (the rate of the parent class) with higher numbers providing
lower latency.</para>
</listitem>
</itemizedlist>
<para>The final curious number is the latency for class 1:11 - 52.5ms.
It is a consequence of everything that has gone before.</para>
<para>To acheive 400kbits/second with 1500-byte packets, 33.33 packets
per second are required. So a packet from class 1:11 must be sent every
30 ms. As the article says, "...the maximum transmission delay of this
class increases from 30ms to a total of 52.5 ms.". So we are looking for
an additional 22.5 ms.</para>
<para>Assume that both class 1:11 and 1:12 transmit for 30 ms at
400kbits/second. That is a total of 800kbits/second for 30ms. So Class
1:11 is punished for the excess. How long is the punishment? The two
classes sent 24,000 bits in 30ms; they are only allowed 0.030 * 500,000
= 15,000. So they are 9,000 bits over their quota. The amount of time
required to transmit 9,000 bits at 400,000 bits/second is
22.5ms!.</para>
</section>
</section>
<section id="Downloads">
<title>Shaping Download Traffic</title>
<para>As stated at the outset, traffic shaping works on traffic being sent
by the firewall. Download traffic from the Internet to local hosts is sent
by the firewall over a local interface. So it follows that if you want to
shape such traffic, you must configure shaping on the local
interface.</para>
<para>Shaping of download traffic is most straightforward when there are
only two interface. That way, traffic leaving the local interface falls
into only two broad categories:</para>
<itemizedlist>
<listitem>
<para>Traffic being forwarded from the Internet</para>
</listitem>
<listitem>
<para>Traffic that originated on the firewall itself</para>
</listitem>
</itemizedlist>
<para>In general, you will want to shape the forwarded traffic and leave
the local traffic unrestricted.</para>
<para>Extending the <link linkend="simiple">simple example</link>
above:</para>
<para><filename>/etc/shorewall/tcdevices</filename>:<programlisting>#INTERFACE IN-BANDWITH OUT-BANDWIDTH
ppp0 6000kbit 700kbit
eth1 - 100mbit</programlisting></para>
<para>/etc/shorewall/tcclasses:<programlisting>#INTERFACE MARK RATE CEIL PRIORITY OPTIONS
ppp0 1 10kbit 50kbit 1 tcp-ack,tos-minimize-delay
ppp0 2 300kbit full 2
ppp0 3 300kbit full 2
ppp0 4 90kbit 200kbit 3 default
eth0 1 100kbit 500kbit 1 tcp-ack
eth0 2 3mbit 6mbit 2
eth0 3 3mbit 6mbit 3
eth0 4 94mbit full default #for local traffic</programlisting></para>
<para>/etc/shorewall/tcrules:<programlisting>#MARK SOURCE DEST PROTO PORT(S) CLIENT USER
# PORT(S)
1:F 0.0.0.0/0 0.0.0.0/0 icmp echo-request
1:F 0.0.0.0/0 0.0.0.0/0 icmp echo-reply
2:F 192.168.2.23 0.0.0.0/0 all
3:F 192.168.2.42 0.0.0.0/0 all
2:F ppp0 192.168.2.23 all
3:F ppp0 192.168.2.42 all</programlisting></para>
</section>
<section id="IFB">
<title>Intermediate Frame Block (IFB) Devices</title>
<para>The principles behind an IFB is fairly simple:</para>
<itemizedlist>
<listitem>
<para>It looks like a network interface although it is never given an
IPv4 configuration.</para>
</listitem>
<listitem>
<para>Because it is a network interface, queuing disciplines can be
associated with an IFB.</para>
</listitem>
</itemizedlist>
<para>The magic of an IFB comes in the fact that a filter may be defined
on a real network interface such that each packet that arrives on that
interface is queued for the IFB! In that way, the IFB provides a means for
shaping input traffic.</para>
<para>To use an IFB, you must have IFB support in your kernel
(configuration option CONFIG_IFB). Assuming that you have a modular
kernel, the name of the IFB module is 'ifb' and may be loaded using the
command <command>modprobe ifb</command> (if you have modprobe installed)
or <command>insmod /path/to/module/ifb</command>.</para>
<para>By default, two IFB devices (ifb0 and ifb1) are created. You can
control that using the numifbs option (e.g., <command>modprobe ifb
numifbs=1</command>).</para>
<para>To create a single IFB when Shorewall starts, place the following
two commands in <filename>/etc/shorewall/init</filename>:</para>
<programlisting><command>modprobe ifb numifbs=1
ip link set ifb0 up</command></programlisting>
<para>Entries in <filename>/etc/shorewall/tcrules</filename> have no
effect on shaping traffic through an IFB. To allow classification of such
traffic, the /etc/shorewall/tcfilters file has been added. Entries in that
file create <ulink url="http://b42.cz/notes/u32_classifier/">u32
classification rules</ulink>.</para>
<section id="tcfilters">
<title>/etc/shorewall/tcfilters</title>
<para>While this file was created to allow shaping of traffic through an
IFB, the file may be used for general traffic classification as well.
The file is similar to <ulink
url="shorewall-tcrules.html">shorewall-tcrules</ulink>(5) with the
following key exceptions:</para>
<itemizedlist>
<listitem>
<para>The first match determines the classification, whereas in the
tcrules file, the last match determines the classification.</para>
</listitem>
<listitem>
<para>ipsets are not supported</para>
</listitem>
<listitem>
<para>DNS Names are not supported</para>
</listitem>
<listitem>
<para>filters are applied to packets as they <emphasis>appear on the
wire</emphasis>. So incoming packets will not have DNAT applied yet
(the destination IP address will be the external address) and
outgoing packets will have had SNAT applied.</para>
</listitem>
</itemizedlist>
<para>The last point warrants elaboration. When looking at traffic being
shaped by an IFB, there are two cases to consider:</para>
<orderedlist>
<listitem>
<para>Requests — packets being sent from remote clients to local
servers. These packets may undergo subsequent DNAT, either as a
result of entries in <filename>/etc/shorewall/nat</filename> or as a
result of DNAT or REDIRECT rules.</para>
<para>Example: <filename>/etc/shorewall/rules</filename>:</para>
<programlisting>#ACTION SOURCE DEST PROTO DEST SOURCE ORIGINAL
# PORT(S) PORT(S) DEST
DNAT net dmz:192.168.4.5 tcp 80 - 206.124.146.177</programlisting>
<para>Requests redirected by this rule will have destination IP
address 206.124.146.177 and destination port 80.</para>
</listitem>
<listitem>
<para>Responses — packets being sent from remote servers to local
clients. These packets may undergo subsequent DNAT as a result of
entries in <filename>/etc/shorewall/nat</filename> or in
<filename>/etc/shorewall/masq</filename>. The packet's destination
IP address will be the external address specified in the
entry.</para>
<para>Example:
<filename>/etc/shorewall/masq</filename>:<programlisting>#INTERFACE SOURCE ADDRESS
eth0 192.168.1.0/24 206.124.146.179</programlisting></para>
<para>HTTP response packets corresponding to requests that fall
under that rule will have destination IP address 206.124.146.179 and
<emphasis role="bold">source</emphasis> port 80.</para>
</listitem>
</orderedlist>
<para>Columns in the file are as follow. As in all Shorewall
configuration files, a hyphen ("-") may be used to indicate that no
value is supplied in the column.</para>
<variablelist>
<varlistentry>
<term>CLASS</term>
<listitem>
<para>The interface name or number followed by a colon (":") and
the class number.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>SOURCE</term>
<listitem>
<para>SOURCE IP address (host or network). DNS names are not
allowed.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>DEST</term>
<listitem>
<para>DESTINATION IP address (host or network). DNS names are not
allowed.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>PROTO</term>
<listitem>
<para>Protocol name or number.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>DEST PORT(S)</term>
<listitem>
<para>Comma-separated list of destination port names or numbers.
May only be specified if the protocol is TCP, UDP, SCTP or ICMP.
Port ranges are supported except for ICMP.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>SOURCE PORT</term>
<listitem>
<para>Comma-separated list of source port names or numbers. May
only be specified if the protocol is TCP, UDP or SCTP. Port ranges
are supported.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>TOS</term>
<listitem>
<para>Specifies the value of the TOS field. The value can be any
of the following:</para>
<itemizedlist>
<listitem>
<para><option>tos-minimize-delay</option></para>
</listitem>
<listitem>
<para><option>tos-maximuze-throughput</option></para>
</listitem>
<listitem>
<para><option>tos-maximize-reliability</option></para>
</listitem>
<listitem>
<para><option>tos-minimize-cost</option></para>
</listitem>
<listitem>
<para><option>tos-normal-service</option></para>
</listitem>
<listitem>
<para><replaceable>hex-number</replaceable></para>
</listitem>
<listitem>
<para><replaceable>hex-number</replaceable>/<replaceable>hex-number</replaceable></para>
</listitem>
</itemizedlist>
<para>The <replaceable>hex-number</replaceable>s must be exactly
two digits (e.g., 0x04).</para>
</listitem>
</varlistentry>
<varlistentry>
<term>LENGTH</term>
<listitem>
<para>Must be a power of 2 between 32 and 8192 inclusive. Packets
with a total length that is strictly less than the specified value
will match the rule.</para>
</listitem>
</varlistentry>
</variablelist>
<para>Example:</para>
<para>I've used this configuration on my own firewall. The IFB portion
is more for test purposes rather than to serve any well-reasoned QOS
strategy.</para>
<para><filename>/etc/shorewall/init</filename>:<programlisting>qt modprobe ifb numifbs=1
qt ip link set dev ifb0 up</programlisting></para>
<para><filename>/etc/shorewall/tcdevices</filename>:<programlisting>#INTERFACE IN-BANDWITH OUT-BANDWIDTH OPTIONS REDIRECTED
# INTERFACES
1:eth0 - 384kbit classify
2:ifb0 - 1300kbit - eth0</programlisting>
<filename>/etc/shorewall/tcclasses</filename>:<programlisting>#INTERFACE MARK RATE CEIL PRIORITY OPTIONS
1:110 - 5*full/10 full 1 tcp-ack,tos-minimize-delay
1:120 - 2*full/10 6*full/10 2 default
1:130 - 2*full/10 6*full/10 3
2:110 - 5*full/10 full 1 tcp-ack,tos-minimize-delay
2:120 - 2*full/10 6*full/10 2 default
2:130 - 2*full/10 6*full/10 3</programlisting><filename>/etc/shorewall/tcfilters</filename>:<programlisting>#INTERFACE: SOURCE DEST PROTO DEST SOURCE
#CLASS PORT(S) PORT(S)
#
# OUTGOING TRAFFIC
#
1:130 206.124.146.178 - tcp - 49441,49442 #BITTORRENT on wookie
1:110 206.124.146.178 #wookie
1:110 206.124.146.179 #SNAT of internal systems
1:110 206.124.146.180 #Work Laptop
1:110 - - icmp echo-request,echo-reply
1:110 - - icmp echo-reply
1:130 206.124.146.177 - tcp - 873,25 #Bulk Traffic
#
# INCOMING TRAFFIC
#
2:110 - 206.124.146.178 #Wookie
2:110 - 206.124.146.179 #SNAT Responses
2:110 - 206.124.146.180 #Work Laptop
2:130 - 206.124.146.177 tcp 25 #Incoming Email.</programlisting></para>
<para>You can examine the installed filters with the <command>shorewall
show filters</command> command. What follows shows the output for
<filename class="devicefile">eth0</filename> with the filters shown
above. <emphasis role="bold">Bold font</emphasis> are comments
explaining the rules.<programlisting>gateway:~ # shorewall-lite show filters
Shorewall Lite 4.1.6 Classifiers at gateway - Fri Mar 21 08:06:47 PDT 2008
Device eth1:
Device eth2:
Device eth0:
filter parent 1: protocol ip pref 10 u32
filter parent 1: protocol ip pref 10 u32 <emphasis role="bold">fh 3:</emphasis> ht divisor 1 <emphasis
role="bold"> &lt;========= Start of table 3. parses TCP header</emphasis>
filter parent 1: protocol ip pref 10 u32 <emphasis role="bold">fh 3</emphasis>::800 order 2048 key ht 3 bkt 0 <emphasis
role="bold">flowid 1:130</emphasis> (rule hit 102 success 0)
match 03690000/ffff0000 at nexthdr+0 (success 0 ) <emphasis
role="bold"> &lt;========= SOURCE PORT 873 goes to class 1:130</emphasis>
filter parent 1: protocol ip pref 10 u32 <emphasis role="bold">fh 2:</emphasis> ht divisor 1 <emphasis
role="bold"> &lt;========= Start of table 2. parses ICMP header</emphasis>
filter parent 1: protocol ip pref 10 u32 <emphasis role="bold">fh 2</emphasis>::800 order 2048 key ht 2 bkt 0 <emphasis
role="bold">flowid 1:110</emphasis> (rule hit 0 success 0)
match 08000000/ff000000 at nexthdr+0 (success 0 ) <emphasis
role="bold"> &lt;========= ICMP Type 8 goes to class 1:110</emphasis>
filter parent 1: protocol ip pref 10 u32 <emphasis role="bold">fh 2</emphasis>::801 order 2049 key ht 2 bkt 0 <emphasis
role="bold">flowid 1:110</emphasis> (rule hit 0 success 0)
match 00000000/ff000000 at nexthdr+0 (success 0 ) <emphasis
role="bold"> &lt;========= ICMP Type 0 goes to class 1:110</emphasis>
filter parent 1: protocol ip pref 10 u32 <emphasis role="bold">fh 1:</emphasis> ht divisor 1 <emphasis
role="bold"> &lt;========= Start of table 1. parses TCP header</emphasis>
filter parent 1: protocol ip pref 10 u32 <emphasis role="bold">fh 1:</emphasis>:800 order 2048 key ht 1 bkt 0 <emphasis
role="bold">flowid 1:130</emphasis> (rule hit 0 success 0)
match c1210000/ffff0000 at nexthdr+0 (success 0 ) <emphasis
role="bold"> &lt;========= SOURCE PORT 49441 goes to class 1:130</emphasis>
filter parent 1: protocol ip pref 10 u32 <emphasis role="bold">fh 1</emphasis>::801 order 2049 key ht 1 bkt 0 <emphasis
role="bold">flowid 1:130</emphasis> (rule hit 0 success 0)
match c1220000/ffff0000 at nexthdr+0 (success 0 ) <emphasis
role="bold"> &lt;========= SOURCE PORT 49442 goes to class 1:130</emphasis>
filter parent 1: protocol ip pref 10 u32 <emphasis role="bold">fh 800:</emphasis> ht divisor 1 <emphasis
role="bold">&lt;========= Start of Table 800. Packets start here!</emphasis>
<emphasis role="bold">=============== The following 2 rules are generated by the class definition in /etc/shorewall/classes ==================</emphasis>
filter parent 1: protocol ip pref 10 u32 <emphasis role="bold">fh 800:</emphasis>:800 order 2048 key ht 800 bkt 0 <emphasis
role="bold">flowid 1:110</emphasis> (rule hit 2204 success 138)
match 00060000/00ff0000 at 8 (success 396 ) <emphasis
role="bold">&lt;========= TCP </emphasis>
match 05000000/0f00ffc0 at 0 (success 250 ) <emphasis
role="bold">&lt;========= Header length 20 and Packet Length &lt; 64</emphasis>
match 00100000/00ff0000 at 32 (success 138 ) <emphasis
role="bold">&lt;========= ACK</emphasis>
filter parent 1: protocol ip pref 10 u32 <emphasis role="bold">fh 800:</emphasis>:801 order 2049 key ht 800 bkt 0 <emphasis
role="bold">flowid 1:110</emphasis> (rule hit 2066 success 0)
match 00100000/00100000 at 0 (success 0 ) <emphasis
role="bold">&lt;========= Minimize-delay</emphasis><emphasis
role="bold"> goes to class 1:110</emphasis>
<emphasis role="bold"> =============== Jump to Table 1 if the matches are met ==================</emphasis>
filter parent 1: protocol ip pref 10 u32 <emphasis role="bold">fh 800:</emphasis>:802 order 2050 key ht 800 bkt 0 <emphasis
role="bold">link 1:</emphasis> (rule hit 2066 success 0)
match ce7c92b2/ffffffff at 12 (success 1039 ) <emphasis
role="bold">&lt;========= SOURCE 206.124.146.178 </emphasis>
match 00060000/00ff0000 at 8 (success 0 ) <emphasis
role="bold">&lt;========= PROTO TCP</emphasis>
offset 0f00&gt;&gt;6 at 0 eat
filter parent 1: protocol ip pref 10 u32 <emphasis role="bold">fh 800:</emphasis>:803 order 2051 key ht 800 bkt 0 <emphasis
role="bold">flowid 1:110</emphasis> (rule hit 2066 success 1039)
match ce7c92b2/ffffffff at 12 (success 1039 ) <emphasis
role="bold">&lt;========= SOURCE 206.124.146.178 goes to class 1:110</emphasis>
filter parent 1: protocol ip pref 10 u32 <emphasis role="bold">fh 800:</emphasis>:804 order 2052 key ht 800 bkt 0 <emphasis
role="bold">flowid 1:110</emphasis> (rule hit 1027 success 132)
match ce7c92b3/ffffffff at 12 (success 132 ) <emphasis
role="bold"> &lt;========= SOURCE 206.124.146.179 goes to class 1:110</emphasis>
filter parent 1: protocol ip pref 10 u32 <emphasis role="bold">fh 800:</emphasis>:805 order 2053 key ht 800 bkt 0 <emphasis
role="bold">flowid 1:110</emphasis> (rule hit 895 success 603)
match ce7c92b4/ffffffff at 12 (success 603 ) <emphasis
role="bold">&lt;========= SOURCE 206.124.146.180 goes to class 1:110</emphasis>
<emphasis role="bold"> =============== Jump to Table 2 if the matches are met ==================</emphasis>
filter parent 1: protocol ip pref 10 u32 <emphasis role="bold">fh 800:</emphasis>:806 order 2054 key ht 800 bkt 0 <emphasis
role="bold">link 2:</emphasis> (rule hit 292 success 0)
match 00010000/00ff0000 at 8 (success 0 ) <emphasis
role="bold">&lt;========= PROTO ICMP</emphasis>
offset 0f00&gt;&gt;6 at 0 eat
<emphasis role="bold"> =============== Jump to Table 3 if the matches are met ==================</emphasis>
filter parent 1: protocol ip pref 10 u32 <emphasis role="bold">fh 800:</emphasis>:807 order 2055 key ht 800 bkt 0 <emphasis
role="bold">link 3:</emphasis> (rule hit 292 success 0)
match ce7c92b1/ffffffff at 12 (success 265 ) <emphasis
role="bold">&lt;========= SOURCE 206.124.146.177</emphasis>
match 00060000/00ff0000 at 8 (success 102 ) <emphasis
role="bold">&lt;========= PROTO TCP</emphasis>
offset 0f00&gt;&gt;6 at 0 eat </programlisting></para>
</section>
</section>
<section id="show">
<title>Understanding the output of 'shorewall show tc'</title>
<para>The <command>shorewall show tc</command> (<command>shorewall-lite
show tc</command>) command displays information about the current state of
traffic shaping. For each device, it executes the following
commands:</para>
<programlisting> echo Device $device:
tc -s -d qdisc show dev $device
echo
tc -s -d class show dev $device
echo </programlisting>
<para>So, the traffic-shaping output is generated entirely by the
<command>tc</command> utility.</para>
<para>Here's the output of for eth0. The configuration is the one shown in
the preceding section (the output was obtained almost 24 hours later than
the <command>shorewall show filters</command> output shown above).</para>
<programlisting>Device eth0:
<emphasis role="bold"> ============== The primary queuing discipline is HTB (Hierarchical Token Bucket) ==================== </emphasis>
qdisc htb 1: r2q 10 default 120 direct_packets_stat 9 ver 3.17
Sent 2133336743 bytes 4484781 pkt (dropped 198, overlimits 4911403 requeues 21) <emphasis
role="bold">&lt;=========== Note the overlimits and dropped counts</emphasis>
rate 0bit 0pps backlog 0b 8p requeues 21
<emphasis role="bold">============== The ingress filter. If you specify IN-BANDWIDTH, you can see the 'dropped' count here. =========</emphasis>
<emphasis role="bold">In this case, the packets are being sent to the IFB for shaping</emphasis>
qdisc ingress ffff: ----------------
Sent 4069015112 bytes 4997252 pkt (dropped 0, overlimits 0 requeues 0)
rate 0bit 0pps backlog 0b 0p requeues 0
<emphasis role="bold">============ Each of the leaf HTB classes has an SFQ qdisc to ensure that each flow gets its turn ============</emphasis>
qdisc sfq 110: parent 1:110 limit 128p quantum 1514b flows 128/1024 perturb 10sec
Sent 613372519 bytes 2870225 pkt (dropped 0, overlimits 0 requeues 6)
rate 0bit 0pps backlog 0b 0p requeues 6
qdisc sfq 120: parent 1:120 limit 128p quantum 1514b flows 128/1024 perturb 10sec
Sent 18434920 bytes 60961 pkt (dropped 0, overlimits 0 requeues 0)
rate 0bit 0pps backlog 0b 0p requeues 0
qdisc sfq 130: parent 1:130 limit 128p quantum 1514b flows 128/1024 perturb 10sec
Sent 1501528722 bytes 1553586 pkt (dropped 198, overlimits 0 requeues 15)
rate 0bit 0pps backlog 11706b 8p requeues 15
<emphasis role="bold">============= Class 1:110 -- the high-priority class ===========
Note the rate and ceiling calculated from 'full'</emphasis>
class htb <emphasis role="bold">1:110</emphasis> parent 1:1 leaf 110: prio 1 quantum 4800 <emphasis
role="bold">rate 192000bit ceil 384000bit</emphasis> burst 1695b/8 mpu 0b overhead 0b cburst 1791b/8 mpu 0b overhead 0b level 0
Sent 613372519 bytes 2870225 pkt (dropped 0, overlimits 0 requeues 0)
<emphasis role="bold">rate 195672bit 28pps backlog 0b 0p</emphasis> requeues 0 <emphasis
role="bold">&lt;=========== Note the current rate of traffic. There is no queuing (no packet backlog)</emphasis>
lended: 2758458 borrowed: 111773 giants:
tokens: 46263 ctokens: 35157
<emphasis role="bold">============== The root class ============</emphasis>
class htb <emphasis role="bold">1:1 root</emphasis> rate 384000bit ceil 384000bit burst 1791b/8 mpu 0b overhead 0b cburst 1791b/8 mpu 0b overhead 0b level 7
<emphasis role="bold">Sent 2133276316 bytes 4484785 pkt</emphasis> (dropped 0, overlimits 0 requeues 0) <emphasis
role="bold">&lt;==== Total output traffic since last 'restart'</emphasis>
rate 363240bit 45pps backlog 0b 0p requeues 0
lended: 1081936 borrowed: 0 giants: 0
tokens: -52226 ctokens: -52226
<emphasis role="bold">============= Bulk Class (outgoing rsync, email and bittorrent) ============</emphasis>
class htb 1:130 parent 1:1 leaf 130: prio 3 quantum 1900 rate 76000bit ceil 230000bit burst 1637b/8 mpu 0b overhead 0b cburst 1714b/8 mpu 0b overhead 0b level 0
Sent 1501528722 bytes 1553586 pkt (dropped 198, overlimits 0 requeues 0)
<emphasis role="bold">rate 162528bit 14pps backlog 0b 8p</emphasis> requeues 0 <emphasis
role="bold">&lt;======== Queuing is occurring (8 packet backlog). The rate is still below the ceiling.</emphasis>
lended: 587134 borrowed: 966459 giants: 0 <emphasis role="bold">During peak activity, the rate tops out at around 231000 (just above ceiling).</emphasis>
tokens: -30919 ctokens: -97657
<emphasis role="bold">================= Default class (mostly serving web pages) ===============</emphasis>
class htb 1:120 parent 1:1 leaf 120: prio 2 quantum 1900 rate 76000bit ceil 230000bit burst 1637b/8 mpu 0b overhead 0b cburst 1714b/8 mpu 0b overhead 0b level 0
Sent 18434920 bytes 60961 pkt (dropped 0, overlimits 0 requeues 0)
rate 2240bit 2pps backlog 0b 0p requeues 0
lended: 57257 borrowed: 3704 giants: 0
tokens: 156045 ctokens: 54178
</programlisting>
</section>
<section id="External">
<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 id="Start">
<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>
<section id="Testing">
<title>Testing Tools</title>
<para>At least one Shorewall user has found this tool helpful: <ulink
url="http://e2epi.internet2.edu/network-performance-toolkit.html">http://e2epi.internet2.edu/network-performance-toolkit.html</ulink></para>
</section>
</article>
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