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101 lines
3.5 KiB
XML
101 lines
3.5 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>
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<!--$Id$-->
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<articleinfo>
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<title>Connection Rate Limiting</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>2008</year>
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<year>2009</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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<section>
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<title>Introduction</title>
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<para>Shorewall supports several mechanisms for limiting connection rates.
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These are described in the following sections.</para>
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<para>Rates are expressed in terms of a <firstterm>connections per unit
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time</firstterm> and a <filename>burst</filename>. An
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<firstterm>interval</firstterm> is calculated by dividing the unit of time
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by the number of connections allowed in that unit of time
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(<replaceable>connections</replaceable>/{<option>sec</option>|<option>min</option>|<option>hour</option>|<option>day</option>|week|month}[:<replaceable>burst</replaceable>]</para>
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<para>Example: 4/min:5</para>
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<simplelist>
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<member>Connections = 4</member>
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<member>Unit of time = 1 minute</member>
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<member>Interval = 1 minute/4 = 15 seconds.</member>
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<member>Burst = 5</member>
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</simplelist>
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<para>As each connection arrives,if the burst count is > 0 the
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<firstterm>burst</firstterm> count is reduced by one and the connection is
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accepted. After each interval (15 seconds) that passes without a
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connection arriving, the <firstterm>burst</firstterm> count is incremented
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by 1 but is not allowed to exceed its initial setting (5).</para>
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<para>By default, the aggregate connection rate is limited. If the
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specification is preceded by "<option>s:</option>" or
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"<option>d:</option>", then the rate is limited per SOURCE or per
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DESTINATION IP address respectively.</para>
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<section>
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<title>Policy Rate Limiting</title>
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<para>The LIMIT column in the <filename>/etc/shorewall/policy</filename>
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file applies to TCP connections that are subject to the policy. The
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limiting is applied BEFORE the connection request is passed through the
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rules generated by entries in <filename>/etc/shorewall/rules</filename>.
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Those connections in excess of the limit are logged and dropped.</para>
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</section>
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<section>
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<title>Rules Rate Limiting</title>
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<para>The RATE LIMIT column in the
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<filename>/etc/shorewall/rules</filename> file allows limiting of
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ACCEPT, DNAT and Action rules.</para>
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</section>
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<section>
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<title>Limit Action</title>
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<para>The <ulink url="Actions.html#Limit">Limit Action</ulink> is a
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legacy mechanism that limits connections per source IP. It does not
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support the notion of a burst size.</para>
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</section>
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</section>
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</article>
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