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311 lines
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311 lines
12 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE refentry 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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<refentry>
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<refmeta>
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<refentrytitle>shorewall-names</refentrytitle>
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<manvolnum>5</manvolnum>
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<refmiscinfo>Configuration Files</refmiscinfo>
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</refmeta>
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<refnamediv>
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<refname>Names</refname>
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<refpurpose>Shorewall object names</refpurpose>
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</refnamediv>
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<refsect1>
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<title>Description</title>
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<para>When you define an object in Shorewall (<ulink
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url="manpages/shorewall-zones.html">Zone</ulink>, <link
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linkend="Logical">Logical Interface</link>, <ulink
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url="ipsets.html">ipsets</ulink>, <ulink
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url="Actions.html">Actions</ulink>, etc., you give it a name. Shorewall
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names start with a letter and consist of letters, digits or underscores
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("_"). Except for Zone names, Shorewall does not impose a limit on name
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length.</para>
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<para>When an ipset is referenced, the name must be preceded by a plus
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sign ("+").</para>
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<para>The last character of an interface may also be a plus sign to
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indicate a wildcard name.</para>
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<para>Physical interface names match names shown by 'ip link ls'; if the
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name includes an at sign ("@"), do not include that character or any
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character that follows. For example, "sit1@NONE" is referred to as simply
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'sit1".</para>
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</refsect1>
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<refsect1>
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<title>Zone and Chain Names</title>
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<para>For a pair of zones, Shorewall creates two Netfilter chains; one for
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connections in each direction. The names of these chains are formed by
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separating the names of the two zones by either "2" or "-".</para>
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<para>Example: Traffic from zone A to zone B would go through chain A2B
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(think "A to B") or "A-B".</para>
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<para>In Shorewall 4.6, the default separator is "-" but you can override
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that by setting ZONE_SEPARATOR="2" in <ulink
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url="manpages/shorewall.conf.html">shorewall.conf</ulink> (5).</para>
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<note>
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<para>Prior to Shorewall 4.6, the default separator was "2".</para>
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</note>
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<para>Zones themselves have names that begin with a letter and are
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composed of letters, numerals, and "_". The maximum length of a name is
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dependent on the setting of LOGFORMAT in <ulink
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url="manpages/shorewall.conf.html">shorewall.conf</ulink> (5). See <ulink
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url="manpages/shorewall-zones.html">shorewall-zones</ulink> (5) for
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details.</para>
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</refsect1>
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<refsect1>
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<title>Using DNS Names</title>
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<caution>
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<para>I personally recommend strongly against using DNS names in
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Shorewall configuration files. If you use DNS names and you are called
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out of bed at 2:00AM because Shorewall won't start as a result of DNS
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problems then don't say that you were not forewarned.</para>
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</caution>
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<para>Host addresses in Shorewall configuration files may be specified as
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either IP addresses or DNS Names.</para>
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<para>DNS names in iptables rules aren't nearly as useful as they first
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appear. When a DNS name appears in a rule, the iptables utility resolves
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the name to one or more IP addresses and inserts those addresses into the
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rule. So changes in the DNS->IP address relationship that occur after
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the firewall has started have absolutely no effect on the firewall's rule
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set.</para>
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<para>For some sites, using DNS names is very risky. Here's an
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example:</para>
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<programlisting>teastep@ursa:~$ dig pop.gmail.com
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; <<>> DiG 9.4.2-P1 <<>> pop.gmail.com
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;; global options: printcmd
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;; Got answer:
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;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 1774
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;; flags: qr rd ra; QUERY: 1, ANSWER: 3, AUTHORITY: 7, ADDITIONAL: 0
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;; QUESTION SECTION:
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;pop.gmail.com. IN A
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;; ANSWER SECTION:
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pop.gmail.com. <emphasis role="bold">300</emphasis> IN CNAME gmail-pop.l.google.com.
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gmail-pop.l.google.com. <emphasis role="bold">300</emphasis> IN A 209.85.201.109
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gmail-pop.l.google.com. <emphasis role="bold">300</emphasis> IN A 209.85.201.111</programlisting>
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<para>Note that the TTL is 300 -- 300 seconds is only 5 minutes. So five
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minutes later, the answer may change!</para>
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<para>So this rule may work for five minutes then suddently stop
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working:</para>
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<programlisting>#ACTION SOURCE DEST PROTO DPORT
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POP(ACCEPT) loc net:pop.gmail.com</programlisting>
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<para>There are two options in <ulink
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url="manpages/shorewall.conf.html">shorewall[6].conf(5)</ulink> that
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affect the use of DNS names in Shorewall[6] config files:</para>
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<itemizedlist>
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<listitem>
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<para>DEFER_DNS_RESOLUTION - When set to No, DNS names are resolved at
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compile time; when set to Yes, DNS Names are resolved at
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runtime.</para>
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</listitem>
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<listitem>
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<para>AUTOMAKE - When set to Yes, <command>start</command>,
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<command>restart</command> and <command>reload</command> only result
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in compilation if one of the files on the CONFIG_PATH has changed
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since the the last compilation.</para>
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</listitem>
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</itemizedlist>
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<para>So by setting AUTOMAKE=Yes, and DEFER_DNS_RESOLUTION=No, compilation
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will only take place at boot time if a change had been make to the config
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but no <command>restart</command> or <command>reload</command> had taken
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place. This is clearly spelled out in the shorewall.conf manpage. So with
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these settings, so long as a 'reload' or 'restart' takes place after the
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Shorewall configuration is changes, there should be no DNS-related
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problems at boot time.</para>
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<important>
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<para>When DEFER_DNS_RESOLUTION=No and AUTOMAKE=Yes and a DNS change
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makes it necessary to recompile an existing firewall script, the
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<option>-c</option> option must be used with the
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<command>reload</command> or <command>restart</command> command to force
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recompilation.</para>
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</important>
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<para>If your firewall rules include DNS names then, even if
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DEFER_DNS_RESOLUTION=No and AUTOMAKE=Yes:</para>
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<itemizedlist>
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<listitem>
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<para>If your <filename>/etc/resolv.conf </filename>is wrong then your
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firewall may not start.</para>
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</listitem>
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<listitem>
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<para>If your <filename>/etc/nsswitch.conf</filename> is wrong then
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your firewall may not start.</para>
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</listitem>
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<listitem>
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<para>If your Name Server(s) is(are) down then your firewall may not
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start.</para>
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</listitem>
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<listitem>
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<para>If your startup scripts try to start your firewall before
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starting your DNS server then your firewall may not start.</para>
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</listitem>
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<listitem>
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<para>Factors totally outside your control (your ISP's router is down
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for example), can prevent your firewall from starting.</para>
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</listitem>
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<listitem>
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<para>You must bring up your network interfaces prior to starting your
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firewall, or the firewall may not start.</para>
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</listitem>
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</itemizedlist>
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<para>Each DNS name must be fully qualified and include a minimum of two
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periods (although one may be trailing). This restriction is imposed by
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Shorewall to insure backward compatibility with existing configuration
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files.</para>
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<example id="validdns">
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<title>Valid DNS Names</title>
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<itemizedlist>
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<listitem>
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<para>mail.shorewall.net</para>
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</listitem>
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<listitem>
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<para>shorewall.net. (note the trailing period).</para>
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</listitem>
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</itemizedlist>
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</example>
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<example id="invaliddns">
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<title>Invalid DNS Names</title>
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<itemizedlist>
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<listitem>
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<para>mail (not fully qualified)</para>
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</listitem>
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<listitem>
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<para>shorewall.net (only one period)</para>
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</listitem>
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</itemizedlist>
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</example>
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<para>DNS names may not be used as:</para>
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<itemizedlist>
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<listitem>
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<para>The server address in a DNAT rule (/etc/shorewall/rules
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file)</para>
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</listitem>
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<listitem>
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<para>In the ADDRESS column of an entry in /etc/shorewall/masq.</para>
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</listitem>
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<listitem>
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<para/>
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</listitem>
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<listitem>
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<para>In the <filename>/etc/shorewall/nat</filename> file.</para>
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</listitem>
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</itemizedlist>
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<para>These restrictions are imposed by Netfilter and not by
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Shorewall.</para>
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</refsect1>
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<refsect1>
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<title>Logical Interface Names</title>
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<para>When dealing with a complex configuration, it is often awkward to
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use physical interface names in the Shorewall configuration.</para>
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<itemizedlist>
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<listitem>
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<para>You need to remember which interface is which.</para>
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</listitem>
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<listitem>
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<para>If you move the configuration to another firewall, the interface
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names might not be the same.</para>
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</listitem>
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</itemizedlist>
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<para>Beginning with Shorewall 4.4.4, you can use logical interface names
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which are mapped to the actual interface using the
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<option>physical</option> option in <ulink
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url="manpages/shorewall-interfaces.html">shorewall-interfaces</ulink>
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(5).</para>
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<para>Here is an example:</para>
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<programlisting>#ZONE INTERFACE OPTIONS
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net <emphasis role="bold">COM_IF </emphasis> dhcp,blacklist,tcpflags,optional,upnp,routefilter=0,nosmurfs,logmartians=0,<emphasis
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role="bold">physical=eth0</emphasis>
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net <emphasis role="bold">EXT_IF</emphasis> dhcp,blacklist,tcpflags,optional,routefilter=0,nosmurfs,logmartians=0,proxyarp=1,<emphasis
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role="bold">physical=eth2</emphasis>
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loc <emphasis role="bold">INT_IF </emphasis> dhcp,logmartians=1,routefilter=1,tcpflags,nets=172.20.1.0/24,<emphasis
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role="bold">physical=eth1</emphasis>
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dmz <emphasis role="bold">VPS_IF </emphasis> logmartians=1,routefilter=0,routeback,<emphasis
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role="bold">physical=venet0</emphasis>
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loc <emphasis role="bold">TUN_IF</emphasis> <emphasis role="bold">physical=tun+</emphasis></programlisting>
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<para>In this example, COM_IF is a logical interface name that refers to
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Ethernet interface <filename class="devicefile">eth0</filename>, EXT_IF is
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a logical interface name that refers to Ethernet interface <filename
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class="devicefile">eth2</filename>, and so on.</para>
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<para>Here are a couple of more files from the same configuration:</para>
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<para><ulink url="manpages/shorewall-masq.html">shorewall-masq</ulink>
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(5):</para>
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<programlisting>#INTERFACE SOURCE ADDRESS
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COMMENT Masquerade Local Network
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<emphasis role="bold">COM_IF</emphasis> 0.0.0.0/0
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<emphasis role="bold">EXT_IF </emphasis> !206.124.146.0/24 206.124.146.179:persistent</programlisting>
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<para><ulink
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url="manpages/shorewall-providers.html">shorewall-providers</ulink>
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(5)</para>
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<programlisting>#NAME NUMBER MARK DUPLICATE INTERFACE GATEWAY OPTIONS COPY
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Avvanta 1 0x10000 main <emphasis role="bold">EXT_IF </emphasis> 206.124.146.254 loose,fallback <emphasis
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role="bold">INT_IF,VPS_IF,TUN_IF</emphasis>
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Comcast 2 0x20000 main <emphasis role="bold">COM_IF</emphasis> detect balance <emphasis
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role="bold">INT_IF,VPS_IF,TUN_IF</emphasis></programlisting>
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<para>Note in particular that Shorewall translates TUN_IF to <filename
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class="devicefile">tun*</filename> in the COPY column.</para>
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</refsect1>
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</refentry>
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