mirror of
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129 lines
3.8 KiB
XML
129 lines
3.8 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.4//EN"
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"http://www.oasis-open.org/docbook/xml/4.4/docbookx.dtd">
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<article id="ECN">
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<!--$Id$-->
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<articleinfo>
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<title>ECN</title>
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<authorgroup>
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<author>
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<firstname>Tom</firstname>
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<surname>Eastep</surname>
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</author>
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</authorgroup>
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<pubdate><?dbtimestamp format="Y/m/d"?></pubdate>
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<copyright>
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<year>2001</year>
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<year>2002</year>
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<year>2003</year>
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<year>2005</year>
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<year>2016</year>
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<holder>Thomas M. Eastep</holder>
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</copyright>
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<legalnotice>
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<para>Permission is granted to copy, distribute and/or modify this
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document under the terms of the GNU Free Documentation License, Version
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1.2 or any later version published by the Free Software Foundation; with
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no Invariant Sections, with no Front-Cover, and with no Back-Cover
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Texts. A copy of the license is included in the section entitled
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<quote><ulink url="GnuCopyright.htm">GNU Free Documentation
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License</ulink></quote>.</para>
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</legalnotice>
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</articleinfo>
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<warning>
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<para>2006-01-17. The ECN Netfilter target in some 2.6 Linux Kernels is
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broken. Symptoms are that you will be unable to establish a TCP connection
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to hosts defined in the /etc/shorewall/ecn file.</para>
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</warning>
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<section id="ecn">
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<title>Explicit Congestion Notification (ECN)</title>
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<para>Explicit Congestion Notification (ECN) is described in RFC 3168 and
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is a proposed Internet standard. Unfortunately, not all sites support ECN
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and when a TCP connection offering ECN is sent to sites that don't support
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it, the result is often that the connection request is ignored.</para>
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<para>To allow ECN to be used, Shorewall allows you to enable ECN on your
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Linux systems then disable it in your firewall when the destination
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matches a list that you create (the /etc/shorewall/ecn file).</para>
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<para>You enable ECN by</para>
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<programlisting>echo 1 > /proc/sys/net/ipv4/tcp_ecn</programlisting>
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<para>You must arrange for that command to be executed at system boot.
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Most distributions have a method for doing that -- on RedHat, you make an
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entry in /etc/sysctl.conf.</para>
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<programlisting>net.ipv4.tcp_ecn = 1</programlisting>
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<para>Entries in /etc/shorewall/ecn have two columns as follows:</para>
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<variablelist>
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<varlistentry>
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<term>INTERFACE</term>
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<listitem>
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<para>The name of an interface on your system</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>HOST(S)</term>
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<listitem>
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<para>An address (host or subnet) of a system or group of systems
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accessed through the interface in the first column. You may include
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a comma-separated list of such addresses in this column.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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<example id="Example1">
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<title>Your external interface is eth0 and you want to disable ECN for
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tcp connections to 192.0.2.0/24:</title>
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<para><table id="Table1">
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<title>/etc/shorewall/ecn</title>
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<tgroup cols="2">
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<thead>
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<row>
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<entry align="center">INTERFACE</entry>
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<entry align="center">HOST(S)</entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry>eth0</entry>
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<entry>192.0.2.0/24</entry>
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</row>
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</tbody>
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</tgroup>
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</table></para>
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</example>
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<para>Beginning with Shorewall 5.0.6, you may also specify clearing of the
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ECN flags through use of the ECN action in <ulink
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url="manpages/shorewall-ecn.html">shorewall-mangle(8)</ulink>.</para>
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</section>
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<lot/>
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</article>
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