shorewall_code/Shorewall6/manpages/shorewall6-snat.xml

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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.4//EN"
"http://www.oasis-open.org/docbook/xml/4.4/docbookx.dtd">
<refentry>
<refmeta>
<refentrytitle>shorewall6-masq</refentrytitle>
<manvolnum>5</manvolnum>
<refmiscinfo>Configuration Files</refmiscinfo>
</refmeta>
<refnamediv>
<refname>snat</refname>
<refpurpose>Shorewall6 SNAT/Masquerade definition file</refpurpose>
</refnamediv>
<refsynopsisdiv>
<cmdsynopsis>
<command>/etc/shorewall6/snat</command>
</cmdsynopsis>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para>This file is used to define dynamic NAT (Masquerading) and to define
Source NAT (SNAT). While still supported, its use is deprecated in favor
of <ulink url="shorewall6-snat.html">shorewall6-snat</ulink>(5) which was
introduced in Shorewall 5.0.14.</para>
<warning>
<para>The entries in this file are order-sensitive. The first entry that
matches a particular connection will be the one that is used.</para>
</warning>
<warning>
<para>If you have more than one ISP link, adding entries to this file
will <emphasis role="bold">not</emphasis> force connections to go out
through a particular link. You must use entries in <ulink
url="/manpages6/shorewall6-rtrules.html">shorewall6-rtrules</ulink>(5)
or PREROUTING entries in <ulink
url="/manpages6/shorewall6-tcrules.html">shorewall-tcrules</ulink>(5) to
do that.</para>
</warning>
<para>The columns in the file are as follows.</para>
<variablelist>
<varlistentry>
<term><emphasis role="bold">ACTION</emphasis></term>
<listitem>
<para>Defines the type of rule to generate. Choices are:</para>
<variablelist>
<varlistentry>
<term><emphasis
role="bold">MASQUERADE</emphasis>[+][([<replaceable>lowport</replaceable>-<replaceable>highport</replaceable>][<option>random</option>])]</term>
<listitem>
<para>Causes matching outgoing packages to have their source
IP address set to the primary IP address of the interface
specified in the DEST column. if
<replaceable>lowport</replaceable>-<replaceable>highport</replaceable>
is given, that port range will be used to assign a source
port. If option <option>random</option> is used then port
mapping will be randomized. MASQUERADE should only be used
when the DEST interface has a dynamic IP address. Otherwise,
SNAT should be used and should specify the interface's static
address.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis
role="bold">SNAT</emphasis>[+]([<emphasis>address-or-address-range</emphasis>][:<emphasis>lowport</emphasis><emphasis
role="bold">-</emphasis><emphasis>highport</emphasis>][<emphasis
role="bold">:random</emphasis>][:<option>persistent</option>]|<emphasis
role="bold">detect</emphasis>|</term>
<listitem>
<para>If you specify an address here, matching packets will
have their source address set to that address. If
ADD_SNAT_ALIASES is set to Yes or yes in <ulink
url="shorewall6.conf.html">shorewall6.conf</ulink>(5) then
Shorewall will automatically add this address to the INTERFACE
named in the first column.</para>
<para>You may also specify a range of up to 256 IP addresses
if you want the SNAT address to be assigned from that range in
a round-robin fashion by connection. The range is specified by
<emphasis>first.ip.in.range</emphasis>-<emphasis>last.ip.in.range</emphasis>.
You may follow the port range with<emphasis role="bold">
:random</emphasis> in which case assignment of ports from the
list will be random. <emphasis role="bold">random</emphasis>
may also be specified by itself in this column in which case
random local port assignments are made for the outgoing
connections.</para>
<para>Example: 206.124.146.177-206.124.146.180</para>
<para>You may follow the port range (or <emphasis
role="bold">:random</emphasis>) with <emphasis
role="bold">:persistent</emphasis>. This is only useful when
an address range is specified and causes a client to be given
the same source/destination IP pair. This feature replaces the
SAME modifier which was removed from Shorewall in version
4.4.0.</para>
<para>You may also use the special value
<option>detect</option> which causes Shorewall to determine
the IP addresses configured on the interface named in the DEST
column and substitute them in this column.</para>
<para>Finally, you may also specify a comma-separated list of
ranges and/or addresses in this column.</para>
<para>DNS Names names are not allowed.</para>
<para>Normally, Netfilter will attempt to retain the source
port number. You may cause netfilter to remap the source port
by following an address or range (if any) by ":" and a port
range with the format
<emphasis>lowport</emphasis>-<emphasis>highport</emphasis>. If
this is done, you must specify "tcp", "udp", "dccp" or "stcp"
in the PROTO column.</para>
<para>Example:</para>
<programlisting> [2001:470:a:787::2]:5000-6000</programlisting>
</listitem>
</varlistentry>
<varlistentry>
<term>CONTINUE[+]</term>
<listitem>
<para>Causes matching packets to be exempted from any
following rules in the file.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis
role="bold"><replaceable>action</replaceable></emphasis>[+][(<replaceable>parameter</replaceable>,...)]</term>
<listitem>
<para>where <replaceable>action</replaceable> is an action
declared in <ulink
url="shorewall6-actions.html">shorewall6-actions(5)</ulink>
with the <option>nat</option> option. See <ulink
url="/Actions.html">www.shorewall.net/Actions.html</ulink> for
further information.</para>
</listitem>
</varlistentry>
</variablelist>
<para>Normally Masq/SNAT rules are evaluated after those for
one-to-one NAT (defined in <ulink
url="/manpages6/shorewall6-nat.html">shorewall6-nat</ulink>(5)). If
you want the rule to be applied before one-to-one NAT rules, follow
the action name with "+": This feature should only be required if
you need to insert rules in this file that preempt entries in <ulink
url="/manpages6/shorewall6-nat.html">shorewall6-nat</ulink>(5).</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">SOURCE</emphasis> (Optional) -
[<emphasis>interface</emphasis>|<emphasis>address</emphasis>[<emphasis
role="bold">,</emphasis><emphasis>address</emphasis>...][<emphasis>exclusion</emphasis>]]</term>
<listitem>
<para>Set of hosts that you wish to SNAT; one or more host or
network addresses separated by comma. You may use ipset names
preceded by a plus sign (+) to specify a set of hosts.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">DEST</emphasis> -
{<emphasis>interface</emphasis>|[<emphasis
role="bold">:</emphasis>[<emphasis>dest-address</emphasis>[<emphasis
role="bold">,</emphasis><emphasis>dest-address</emphasis>]...[<emphasis>exclusion</emphasis>]]|?COMMENT}</term>
<listitem>
<para>Outgoing <emphasis>interface</emphasis>. This is usually your
internet interface.</para>
<para>The <replaceable>interface</replaceable> must match an entry
in <ulink
url="/manpages6/shorewall6-interfaces.html">shorewall6-interfaces</ulink>(5).
Shorewall allows loose matches to wildcard entries in <ulink
url="/manpages6/shorewall6-interfaces.html">shorewall6-interfaces</ulink>(5).
For example, <filename class="devicefile">ppp0</filename> in this
file will match a <ulink
url="/manpages6/shorewall6-interfaces.html">shorewall6-interfaces</ulink>(5)
entry that defines <filename
class="devicefile">ppp+</filename>.</para>
<para>Where <ulink url="/4.4/MultiISP.html#Shared">more that one
internet provider share a single interface</ulink>, the provider is
specified by including the provider name or number in
parentheses:</para>
<programlisting> eth0(Avvanta)</programlisting>
<para>In that case, you will want to specify the interface's address
for that provider as the SNAT parameter.</para>
<para>The interface may be qualified by adding the character ":"
followed by a comma-separated list of destination host or subnet
addresses to indicate that you only want to change the source IP
address for packets being sent to those particular destinations.
Exclusion is allowed (see <ulink
url="/manpages6/shorewall6-exclusion.html">shorewall6-exclusion</ulink>(5))
as are ipset names preceded by a plus sign '+'.</para>
<para>Comments may be attached to Netfilter rules generated from
entries in this file through the use of ?COMMENT lines. These lines
begin with ?COMMENT; the remainder of the line is treated as a
comment which is attached to subsequent rules until another ?COMMENT
line is found or until the end of the file is reached. To stop
adding comments to rules, use a line containing only
?COMMENT.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">PROTO</emphasis> (Optional) - {<emphasis
role="bold">-</emphasis>|[!]{<emphasis>protocol-name</emphasis>|<emphasis>protocol-number</emphasis>}[,...]|+<replaceable>ipset</replaceable>}</term>
<listitem>
<para>If you wish to restrict this entry to a particular protocol
then enter the protocol name (from protocols(5)) or number
here.</para>
<para>Beginning with Shorewall 4.5.12, this column can accept a
comma-separated list of protocols.</para>
<para>Beginning with Shorewall 4.6.0, an
<replaceable>ipset</replaceable> name can be specified in this
column. This is intended to be used with
<firstterm>bitmap:port</firstterm> ipsets.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">DPORT</emphasis> (Optional) -
{-|[!]<emphasis>port-name-or-number</emphasis>[,<emphasis>port-name-or-number</emphasis>]...|+<replaceable>ipset</replaceable>}</term>
<listitem>
<para>If the PROTO column specifies TCP (6), UDP (17), DCCP (33),
SCTP (132) or UDPLITE (136) then you may list one or more port
numbers (or names from services(5)) or port ranges separated by
commas.</para>
<para>Port ranges are of the form
<emphasis>lowport</emphasis>:<emphasis>highport</emphasis>.</para>
<para>Beginning with Shorewall 4.6.0, an
<replaceable>ipset</replaceable> name can be specified in this
column. This is intended to be used with
<firstterm>bitmap:port</firstterm> ipsets.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">IPSEC</emphasis> (Optional) -
[<emphasis>option</emphasis>[<emphasis
role="bold">,</emphasis><emphasis>option</emphasis>]...]</term>
<listitem>
<para>If you specify a value other than "-" in this column, you must
be running kernel 2.6 and your kernel and iptables must include
policy match support.</para>
<para>Comma-separated list of options from the following. Only
packets that will be encrypted via an SA that matches these options
will have their source address changed.</para>
<variablelist>
<varlistentry>
<term><emphasis
role="bold">reqid=</emphasis><emphasis>number</emphasis></term>
<listitem>
<para>where <emphasis>number</emphasis> is specified using
setkey(8) using the 'unique:<emphasis>number</emphasis> option
for the SPD level.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">spi=</emphasis>&lt;number&gt;</term>
<listitem>
<para>where <emphasis>number</emphasis> is the SPI of the SA
used to encrypt/decrypt packets.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">proto=</emphasis><emphasis
role="bold">ah</emphasis>|<emphasis
role="bold">esp</emphasis>|<emphasis
role="bold">ipcomp</emphasis></term>
<listitem>
<para>IPSEC Encapsulation Protocol</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis
role="bold">mss=</emphasis><emphasis>number</emphasis></term>
<listitem>
<para>sets the MSS field in TCP packets</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">mode=</emphasis><emphasis
role="bold">transport</emphasis>|<emphasis
role="bold">tunnel</emphasis></term>
<listitem>
<para>IPSEC mode</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis
role="bold">tunnel-src=</emphasis><emphasis>address</emphasis>[/<emphasis>mask</emphasis>]</term>
<listitem>
<para>only available with mode=tunnel</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis
role="bold">tunnel-dst=</emphasis><emphasis>address</emphasis>[/<emphasis>mask</emphasis>]</term>
<listitem>
<para>only available with mode=tunnel</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">strict</emphasis></term>
<listitem>
<para>Means that packets must match all rules.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">next</emphasis></term>
<listitem>
<para>Separates rules; can only be used with strict</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">yes</emphasis></term>
<listitem>
<para>When used by itself, causes all traffic that will be
encrypted/encapsulated to match the rule.</para>
</listitem>
</varlistentry>
</variablelist>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">MARK</emphasis> - [<emphasis
role="bold">!</emphasis>]<emphasis>value</emphasis>[/<emphasis>mask</emphasis>][<emphasis
role="bold">:C</emphasis>]</term>
<listitem>
<para>Defines a test on the existing packet or connection mark. The
rule will match only if the test returns true.</para>
<para>If you don't want to define a test but need to specify
anything in the following columns, place a "-" in this field.</para>
<variablelist>
<varlistentry>
<term>!</term>
<listitem>
<para>Inverts the test (not equal)</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis>value</emphasis></term>
<listitem>
<para>Value of the packet or connection mark.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis>mask</emphasis></term>
<listitem>
<para>A mask to be applied to the mark before testing.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">:C</emphasis></term>
<listitem>
<para>Designates a connection mark. If omitted, the packet
mark's value is tested.</para>
</listitem>
</varlistentry>
</variablelist>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">USER</emphasis> (Optional) - [<emphasis
role="bold">!</emphasis>][<emphasis>user-name-or-number</emphasis>][<emphasis
role="bold">:</emphasis><emphasis>group-name-or-number</emphasis>][<emphasis
role="bold">+</emphasis><emphasis>program-name</emphasis>]</term>
<listitem>
<para>Only locally-generated connections will match if this column
is non-empty.</para>
<para>When this column is non-empty, the rule matches only if the
program generating the output is running under the effective
<emphasis>user</emphasis> and/or <emphasis>group</emphasis>
specified (or is NOT running under that id if "!" is given).</para>
<para>Examples:</para>
<variablelist>
<varlistentry>
<term>joe</term>
<listitem>
<para>program must be run by joe</para>
</listitem>
</varlistentry>
<varlistentry>
<term>:kids</term>
<listitem>
<para>program must be run by a member of the 'kids'
group</para>
</listitem>
</varlistentry>
<varlistentry>
<term>!:kids</term>
<listitem>
<para>program must not be run by a member of the 'kids'
group</para>
</listitem>
</varlistentry>
<varlistentry>
<term>+upnpd</term>
<listitem>
<para>#program named upnpd</para>
<important>
<para>The ability to specify a program name was removed from
Netfilter in kernel version 2.6.14.</para>
</important>
</listitem>
</varlistentry>
</variablelist>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">SWITCH -
[!]<replaceable>switch-name</replaceable>[={0|1}]</emphasis></term>
<listitem>
<para>Added in Shorewall 4.5.1 and allows enabling and disabling the
rule without requiring <command>shorewall restart</command>.</para>
<para>The rule is enabled if the value stored in
<filename>/proc/net/nf_condition/<replaceable>switch-name</replaceable></filename>
is 1. The rule is disabled if that file contains 0 (the default). If
'!' is supplied, the test is inverted such that the rule is enabled
if the file contains 0.</para>
<para>Within the <replaceable>switch-name</replaceable>, '@0' and
'@{0}' are replaced by the name of the chain to which the rule is a
added. The <replaceable>switch-name</replaceable> (after '@...'
expansion) must begin with a letter and be composed of letters,
decimal digits, underscores or hyphens. Switch names must be 30
characters or less in length.</para>
<para>Switches are normally <emphasis role="bold">off</emphasis>. To
turn a switch <emphasis role="bold">on</emphasis>:</para>
<simplelist>
<member><command>echo 1 &gt;
/proc/net/nf_condition/<replaceable>switch-name</replaceable></command></member>
</simplelist>
<para>To turn it <emphasis role="bold">off</emphasis> again:</para>
<simplelist>
<member><command>echo 0 &gt;
/proc/net/nf_condition/<replaceable>switch-name</replaceable></command></member>
</simplelist>
<para>Switch settings are retained over <command>shorewall
restart</command>.</para>
<para>Beginning with Shorewall 4.5.10, when the
<replaceable>switch-name</replaceable> is followed by
<option>=0</option> or <option>=1</option>, then the switch is
initialized to off or on respectively by the
<command>start</command> command. Other commands do not affect the
switch setting.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">ORIGDEST</emphasis> - [<emphasis
role="bold">-</emphasis>|<emphasis>address</emphasis>[,<emphasis>address</emphasis>]...[<emphasis>exclusion</emphasis>]|<emphasis>exclusion</emphasis>]</term>
<listitem>
<para>(Optional) This column may be included and may contain one or
more addresses (host or network) separated by commas. Address ranges
are not allowed. When this column is supplied, rules are generated
that require that the original destination address matches one of
the listed addresses. It is useful for specifying that SNAT should
occur only for connections that were acted on by a DNAT when they
entered the firewall.</para>
<para>This column was formerly labelled ORIGINAL DEST.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">PROBABILITY</emphasis> -
[<replaceable>probability</replaceable>]</term>
<listitem>
<para>Added in Shorewall 5.0.0. When non-empty, requires the
<firstterm>Statistics Match</firstterm> capability in your kernel
and ip6tables and causes the rule to match randomly but with the
given <replaceable>probability</replaceable>. The
<replaceable>probability</replaceable> is a number 0 &lt;
<replaceable>probability</replaceable> &lt;= 1 and may be expressed
at up to 8 decimal points of precision.</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Examples</title>
<variablelist>
<varlistentry>
<term>Example 1:</term>
<listitem>
<para>You have a simple 'masquerading' setup where eth0 connects to
a DSL or cable modem and eth1 connects to your local network with
subnet 2001:470:b:787::0/64</para>
<para>Your entry in the file will be:</para>
<programlisting> #ACTION SOURCE DEST
MASQUERADE 2001:470:b:787::0/64 eth0</programlisting>
</listitem>
</varlistentry>
<varlistentry>
<term>Example 2:</term>
<listitem>
<para>Your sit1 interface has two public IP addresses:
2001:470:a:227::1 and 2001:470:b:227::1. You want to use the
iptables statistics match to masquerade outgoing connections evenly
between these two addresses.</para>
<programlisting>/etc/shorewall/snat:
#ACTION SOURCE DEST
SNAT(2001:470:a:227::1) ::/0 sit1 { probability=0.50 }
SNAT(2001:470:a:227::2) ::/0 sit</programlisting>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>FILES</title>
<para>/etc/shorewall6/snat</para>
</refsect1>
</refentry>