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shorewall_code/docs/IPP2P.xml
Jeremy Sowden c93817f30b Correct GFDL text embedded in document sources 
The invariant sections clause doesn't quite match the official text.  It should
read:

  with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts

not:

  with no Invariant Sections, with no Front-Cover, and with no Back-Cover Texts

Signed-off-by: Jeremy Sowden <jeremy@azazel.net>
2023-01-31 22:50:37 +00:00

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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.4//EN"
"http://www.oasis-open.org/docbook/xml/4.4/docbookx.dtd">
<article>
<!--$Id$-->
<articleinfo>
<title>Shorewall and ipp2p</title>
<authorgroup>
<author>
<firstname>Tom</firstname>
<surname>Eastep</surname>
</author>
</authorgroup>
<pubdate><?dbtimestamp format="Y/m/d"?></pubdate>
<copyright>
<year>2004</year>
<year>2005</year>
<year>2006</year>
<year>2009</year>
<year>2016</year>
<holder>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, no Front-Cover Texts, and 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>
<caution>
<para><emphasis role="bold">This article applies to Shorewall 4.3 and
later. If you are running a version of Shorewall earlier than Shorewall
4.3.5 then please see the documentation for that
release.</emphasis></para>
</caution>
<section id="Intro">
<title>Introduction</title>
<para>Shorewall includes support for the ipp2p match facility. This is a
departure from my usual policy in that the ipp2p match facility is
included in xtables-addons and is unlikely to ever be included in the
kernel.org source tree. Questions about how to install xtables-addons or
how to build your kernel and/or iptables should not be posted on the
Shorewall mailing lists but should rather be referred to the Netfilter
Mailing List.</para>
</section>
<section id="Scope">
<title>Scope</title>
<para>In the following files, the "PROTO" or "PROTOCOL" column may contain
"ipp2p":</para>
<simplelist>
<member><ulink
url="traffic_shaping.htm">/etc/shorewall/tcrules</ulink></member>
<member><ulink
url="manpages/shorewall-mangle.html">/etc/shorewall/mangle</ulink></member>
<member><ulink
url="Accounting.html">/etc/shorewall/accounting</ulink></member>
<member><ulink
url="Shorewall_and_Routing.html">/etc/shorewall/rules</ulink> (Not
Recommend. But if you insist, then you should place the rules in the
ESTABLISHED section of that file).</member>
</simplelist>
<para>When the PROTO or PROTOCOL column contains "ipp2p" then the DEST
PORT(S) or PORT(S) column may contain a recognized ipp2p option
(Shorewall-perl 4.2.5 and later accepts a comma-separated list of
options); for a list of the options and their meaning, at a root prompt
type:</para>
<programlisting><command>iptables -m ipp2p --help</command></programlisting>
<para>You must not include the leading "--" on the option(s); Shorewall
will supply those characters for you. If you do not include an option then
Shorewall will assume "edk,kazaa,gnu,dc".</para>
<para>If 'ipp2p' is specified, Shorewall will substitute
"edk,kazaa,gnu,dc".</para>
</section>
<section id="Example">
<title>Example:</title>
<para>Example 2 in the ipp2p documentation recommends the following
iptables rules:</para>
<programlisting>01# iptables -t mangle -A PREROUTING -p tcp -j CONNMARK --restore-mark
02# iptables -t mangle -A PREROUTING -p tcp -m mark ! --mark 0 -j ACCEPT
03# iptables -t mangle -A PREROUTING -p tcp -m ipp2p --ipp2p -j MARK --set-mark 1
04# iptables -t mangle -A PREROUTING -p tcp -m mark --mark 1 -j CONNMARK --save-mark
05# iptables -t mangle -A POSTROUTING -o eth0 -m mark --mark 1 -j CLASSIFY --set-class 1:12
06# iptables -t mangle -A POSTROUTING -o eth1 -m mark --mark 1 -j CLASSIFY --set-class 2:12</programlisting>
<para>Let's examine the above rules more carefully.</para>
<para>The individual packets of a P2P data stream do not all carry
tell-tale signs that are identifiable as being a particular P2P
application. So simply asking the ipp2p match code to mark each individual
packet isn't enough because only those packets that carry these tell-tale
signs will be marked. Fortunately, Netfilter provides a different type of
mark -- the <firstterm>Connection Mark</firstterm> which is associated
with the entry in the conntrack table rather that with the individual
packet. You can see connection mark values with the <command>shorewall
show connections</command> command:</para>
<programlisting>gateway:/etc/test# shorewall show connections
Shorewall-2.5.6 Connections at gateway - Tue Oct 4 15:45:11 PDT 2005
tcp 6 269712 ESTABLISHED src=192.168.3.8 dst=206.124.146.177 sport=50584 dport=993 packets=4899
bytes=302282 src=206.124.146.177 dst=192.168.3.8 sport=993 dport=50584 packets=7760 bytes=10032928 [ASSURED] <emphasis
role="bold">mark=0</emphasis> use=1
...</programlisting>
<para>Connection marks are persistent -- that is, once a connection mark
is set it retains its value until the connection is terminated.</para>
<para>Netfilter provides features to:</para>
<orderedlist>
<listitem>
<para>Mark individual packets with a numeric value.</para>
</listitem>
<listitem>
<para>Save the current packet mark value in the connection
mark.</para>
</listitem>
<listitem>
<para>Restore the value in the connection mark to the current
packet.</para>
</listitem>
</orderedlist>
<para>The strategy employed in the above rules is to mark the connection
of each P2P session with a mark value of 1. That way, each packet that is
part of the session can be marked using the 'Restore' function and can be
classified accordingly.</para>
<orderedlist>
<listitem>
<para>Rule 01# restores the connection mark into the current
packet.</para>
</listitem>
<listitem>
<para>Rule 02# tests that restored mark and if it is not equal to
zero, the packet is ACCEPTed (no further processing).</para>
</listitem>
<listitem>
<para>Rule 03# asks the ipp2p match module to examine the packet and
if it is identifiable as part of a P2P session, mark the packet with
value 1.</para>
</listitem>
<listitem>
<para>Rule 04# saves the current packet mark in the conntrack table if
the current mark value is 1 (in other words, if it was marked by rule
03#).</para>
</listitem>
<listitem>
<para>Rule 05# classifies the packet to traffic shaping class 1:12 if
it is going out of eth0 and has mark value 1.</para>
</listitem>
<listitem>
<para>Rule 06# classifies the packet to traffic shaping class 2:12 if
it is going out of eth1 and has mark value 1.</para>
</listitem>
</orderedlist>
<para>These are implemented in the /etc/shorewall/tcrules and
/etc/shorewall/mangle files as follows:</para>
<programlisting>#ACTION SOURCE DEST PROTO DPORT SPORT USER TEST
RESTORE:P - - tcp
CONTINUE:P - - tcp - - - !0
1:P - - ipp2p ipp2p
SAVE:P - - tcp - - - 1
1:12 - eth0 - - - - 1
2:12 - eth1 - - - - 1</programlisting>
<para>These rules do exactly the same thing as their counterparts
described above.</para>
<para>One change that I recommend --do your marking in the FORWARD chain
rather than in the PREROUTING chain:</para>
<programlisting>#ACTION SOURCE DEST PROTO DPORT SPORT USER TEST
RESTORE:F - - tcp
CONTINUE:F - - tcp - - - !0
1:F - - ipp2p ipp2p
SAVE:F - - tcp - - - 1
1:12 - eth0 - - - - 1
2:12 - eth1 - - - - 1</programlisting>
<para>It will work the same and will work with a <ulink
url="MultiISP.html">Multi-ISP setup</ulink>.</para>
</section>
</article>
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