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################ End of IPFW rules file ###############################</programlisting>
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################ End of IPFW rules file ###############################</programlisting>
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      </sect3>
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      </sect3>
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    </sect2>
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    </sect2>
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	<sect2 id="firewalls-ipfw-dummynet">
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	  <title>Using Dummy</title>
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	  <para>Dummynet is a traffic shaper, bandwidth manager and delay emulator which may
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		be used to simulate different types of physical links. It can also be
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		&quot;misused&quot;	as a traffic shaper.</para>
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	  <para>Dummynet offers two objects. Pipes are an abstraction of a given link, having
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		a certain bandwidth, delay and loss. Queue are an abstraction used to implement
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		weighted fair queuing. In practice, pipes can be used to set hard limits to the
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		bandwidth that a flow can use, wheres queues can be used to determine how different
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		flows share that bandwidth.</para>
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	  <para>Please note that, in order for dummynet to work correctly, it is highly recommended to
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		increase the system clock tick. This can be accomplished by adding the following kernel option:</para>
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	  <programlisting>options	HZ=1000</programlisting>
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	  <para>Use the following command to configure a pipe which has 4Kbps
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		and a 100ms delay:</para>
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      <screen>&prompt.root; <userinput>ipfw pipe 10 config bw 4Kbit/s delay 100</userinput></screen>
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	  <para>To use this pipe, i.e. have some traffic go through it, use the following command:</para>
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      <screen>&prompt.root; <userinput>ipfw -q add pipe 10 all from 10.0.0.0/24 to any</userinput></screen>
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	  <para>Please note that to properly limit users, one should create separate pipes for download and upload.
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		</para>
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	  <para>Using the above pipe configuration, all LAN users compete for the
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		same bandwidth. If you would like to assign each of them 4Kbps
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		download and upload, you may create dynamic pipes based on the
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		source IP (for uplink) or destination IP (for downlink):</para>
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      <screen>&prompt.root; <userinput>ipfw pipe 10 config bw 4Kbit/s src-ip 0xffffffff</userinput>
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&prompt.root; <userinput>ipfw pipe 11 config bw 4Kbit/s dst-ip 0xffffffff</userinput>
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&prompt.root; <userinput>ipfw -q add pipe 10 all from any to any recv $if_lan</userinput>
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&prompt.root; <userinput>ipfw -q add pipe 11 all from any to any xmit $if_lan</userinput></screen>
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	</sect2>
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	<sect2 id="firewalls-ipfw-tables">
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	  <title>Using Tables</title>
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	  <para>Tables are a way of refering to multiple IP addresses
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		using a single identifier. They are useful in the following
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		situations:</para>
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	  <itemizedlist>
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		<listitem>
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	  <para>you must apply the same rule to a lot of IP addresses
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		(table lookups are fast)</para>
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		</listitem>
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		<listitem>
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	  <para>you must apply a lot of rules to some IP addresses
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		(use tables to add / remove IP addresses from a single location
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		in the ruleset)</para>
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		</listitem>
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	  </itemizedlist>
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	  <para>IP addresses contained in a table may also have an optional 32-bit unsigned value
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		assigned to it. A rule may be written in such a way that it will only match if the IP
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		found in a table has been assigned a specific value.</para>
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	  <para>These are the commands used to manipulate tables from the shell:</para>
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	  <para>Clear all IPs from a table:</para>
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      <screen>&prompt.root; <userinput>ipfw table 10 flush</userinput></screen>
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	  <para>Add a single IP address to a table:</para>
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      <screen>&prompt.root; <userinput>ipfw table 10 add 172.27.0.1</userinput></screen>
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	  <para>Add a CIDR network to a table:</para>
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      <screen>&prompt.root; <userinput>ipfw table 10 add 192.168.0.0/24</userinput></screen>
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	  <para>Add a CIDR network to a table and also assign a value to it:</para>
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      <screen>&prompt.root; <userinput>ipfw table 10 add 192.168.0.0/24 100</userinput></screen>	  
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	  <para>List the contents of a table:</para>
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      <screen>&prompt.root; <userinput>ipfw table 10 list</userinput></screen>
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	  <para>To use the table in a firewall rule, type something like this:</para>
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      <screen>&prompt.root; <userinput>ipfw -q add allow tcp from &quot;table(10)&quot; to any</userinput></screen>
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	  <para>Or, to use the table and the value in a firewall rule, type something like this:</para>
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      <screen>&prompt.root; <userinput>ipfw -q add allow tcp from &quot;table(10,100)&quot; to any</userinput></screen>
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	  <para>The following listing is an example of how one could use tables in a ruleset:</para>
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	  <programlisting>#!/bin/sh
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# Flush out the list before we begin.
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ipfw -q -f flush
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# Set rules command prefix
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cmd="ipfw -q add"
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table="ipfw -q table"
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# Create a table with all IPs allowed to connect to SSH
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$table 1 flush					# required
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$table 1 add 172.27.0.1			# single IP address
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$table 1 add 192.168.0.0/24		# CIDR network
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# Actual rule which allows SSH
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$cmd allow from "table(1)" to me 22 keep-state
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# Deny everything else
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$cmd deny from any to any</programlisting>
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	  <para>Here is another example, in which tables and values are used
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		to group clients into multiple bandwidth limitations
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		depending on their subscription:</para>
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	  <programlisting>#!/bin/sh
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# Flush out the list before we begin.
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ipfw -q -f flush
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# Set rules command prefix
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cmd="ipfw -q add"
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table="ipfw -q table"
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pipe="ipfw -q pipe"
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if_net="em0"
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#
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# Pipes
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#
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# Please note that dynamic pipes will be created for each client.
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# In other words, clients DO NOT compete for the bandwidth.
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# First subscription rate.
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$pipe 10 config queue 10 bw 512Kbit/s mask src-ip 0xffffffff	# uplink
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$pipe 11 config queue 10 bw 512Kbit/s mask dst-ip 0xffffffff	# downlink
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# Second subscription rate.
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$pipe 20 config queue 10 bw 768Kbit/s mask src-ip 0xffffffff	# uplink
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$pipe 21 config queue 10 bw 768Kbit/s mask dst-ip 0xffffffff	# downlink
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# Create a table with all IPs allowed to have Internet connection.
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# Note that although it is not required, values are the same
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# as the bandwidth which will be given to the client.
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$table 1 flush					# required
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$table 1 add 172.27.0.2	512		# 512Kbps client
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$table 1 add 172.27.0.3 768		# 768Kbps client
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$table 1 add 172.27.0.4 512		# 512Kbps client
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# Actual rules which classify the traffic
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$cmd pipe 10 all from "table(1,512)" to any xmit $if_net
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$cmd pipe 11 all from any to "table(1,512)" recv $if_net
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$cmd pipe 20 all from "table(1,768)" to any xmit $if_net
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$cmd pipe 21 all from any to "table(1,768)" recv $if_net
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# Deny everything else
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$cmd deny all from any to any</programlisting>
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	</sect2>
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  </sect1>
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  </sect1>
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</chapter>
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</chapter>
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