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shorewall_code/manpages/shorewall-masq.xml
Tom Eastep 2b7515f434 Refer manpage readers to the 'Pairs' information 
Signed-off-by: Tom Eastep <teastep@shorewall.net>
2011-09-26 10:16:52 -07:00

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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>shorewall-masq</refentrytitle>
<manvolnum>5</manvolnum>
</refmeta>
<refnamediv>
<refname>masq</refname>
<refpurpose>Shorewall Masquerade/SNAT definition file</refpurpose>
</refnamediv>
<refsynopsisdiv>
<cmdsynopsis>
<command>/etc/shorewall/masq</command>
</cmdsynopsis>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para>Use this file to define dynamic NAT (Masquerading) and to define
Source NAT (SNAT).</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="shorewall-route_rules.html">shorewall-route_rules</ulink>(5) or
PREROUTING entries in <ulink
url="shorewall-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">INTERFACE:DEST</emphasis> - {[<emphasis
role="bold">+</emphasis>]<emphasis>interfacelist</emphasis>[<emphasis
role="bold">:</emphasis>[<emphasis>digit</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>interfacelist</emphasis>. This may be a
comma-separated list of interface names. This is usually your
internet interface. If ADD_SNAT_ALIASES=Yes in <ulink
url="shorewall.conf.html">shorewall.conf</ulink>(5), you may add ":"
and a <emphasis>digit</emphasis> to indicate that you want the alias
added with that name (e.g., eth0:0). This will allow the alias to be
displayed with ifconfig. <emphasis role="bold">That is the only use
for the alias name; it may not appear in any other place in your
Shorewall configuratio</emphasis>n.</para>
<para>Each interface must match an entry in <ulink
url="shorewall-interfaces.html">shorewall-interfaces</ulink>(5).
Shorewall allows loose matches to wildcard entries in <ulink
url="shorewall-interfaces.html">shorewall-interfaces</ulink>(5). For
example, <filename class="devicefile">ppp0</filename> in this file
will match a <ulink
url="shorewall-interfaces.html">shorewall-interfaces</ulink>(5)
entry that defines <filename
class="devicefile">ppp+</filename>.</para>
<para>Where <ulink
url="http://www.shorewall.net/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 interfaces's
address for that provider in the ADDRESS column.</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="shorewall-exclusion.html">shorewall-exclusion</ulink>(5)).</para>
<para>If you wish to inhibit the action of ADD_SNAT_ALIASES for this
entry then include the ":" but omit the digit:</para>
<programlisting> eth0(Avvanta):
eth2::192.0.2.32/27</programlisting>
<para>Normally Masq/SNAT rules are evaluated after those for
one-to-one NAT (defined in <ulink
url="shorewall-nat.html">shorewall-nat</ulink>(5)). If you want the
rule to be applied before one-to-one NAT rules, prefix the interface
name with "+":</para>
<programlisting> +eth0
+eth0:192.0.2.32/27
+eth0:2</programlisting>
<para>This feature should only be required if you need to insert
rules in this file that preempt entries in <ulink
url="shorewall-nat.html">shorewall-nat</ulink>(5).</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 the word 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 with only the word
COMMENT.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">SOURCE</emphasis> (Formerly called SUBNET)
-
{<emphasis>interface</emphasis>[:<emphasis>exclusion</emphasis>]|<emphasis>address</emphasis>[<emphasis
role="bold">,</emphasis><emphasis>address</emphasis>][<emphasis>exclusion</emphasis>]}</term>
<listitem>
<para>Set of hosts that you wish to masquerade. You can specify this
as an <emphasis>address</emphasis> (net or host) or as an
<emphasis>interface</emphasis> (use of an
<emphasis>interface</emphasis> is deprecated). If you give the name
of an interface, the interface must be up before you start the
firewall and the Shorewall rules compiler will warn you of that
fact. (Shorewall will use your main routing table to determine the
appropriate addresses to masquerade).</para>
<para>In order to exclude a address of the specified SOURCE, you may
append an <emphasis>exclusion</emphasis> ("!" and a comma-separated
list of IP addresses (host or net) that you wish to exclude (see
<ulink
url="shorewall-exclusion.html">shorewall-exclusion</ulink>(5))).
Note that a colon (":") must appear between an
<replaceable>interface</replaceable> name and the
<replaceable>exclusion</replaceable>;</para>
<para>Example: eth1:!192.168.1.4,192.168.32.0/27</para>
<para>In that example traffic from eth1 would be masqueraded unless
it came from 192.168.1.4 or 196.168.32.0/27</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">ADDRESS</emphasis> (Optional) - [<emphasis
role="bold">-</emphasis>|<emphasis
role="bold">NONAT</emphasis>|[<emphasis>address-or-address-range</emphasis>[,<emphasis>address-or-address-range</emphasis>]...][:<emphasis>lowport</emphasis><emphasis
role="bold">-</emphasis><emphasis>highport</emphasis>][<emphasis
role="bold">:random</emphasis>][:persistent]|<emphasis
role="bold">detect</emphasis>|<emphasis
role="bold">random</emphasis>]</term>
<listitem>
<para>If you specify an address here, SNAT will be used and this
will be the source address. If ADD_SNAT_ALIASES is set to Yes or yes
in <ulink url="shorewall.conf.html">shorewall.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. Unlike <emphasis
role="bold">random</emphasis>, <emphasis
role="bold">persistent</emphasis> may not be used by itself.</para>
<para>You may also use the special value "detect" which causes
Shorewall to determine the IP addresses configured on the interface
named in the INTERFACES 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>This column may not contain DNS Names.</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" or "udp" in the PROTO column.</para>
<para>Examples:</para>
<programlisting> 192.0.2.4:5000-6000
:4000-5000</programlisting>
<para>If you simply place <emphasis role="bold">NONAT</emphasis> in
this column, no rewriting of the source IP address or port number
will be performed. This is useful if you want particular traffic to
be exempt from the entries that follow in the file.</para>
<para>If you want to leave this column empty but you need to specify
the next column then place a hyphen ("-") here.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">PROTO</emphasis> (Optional) - {<emphasis
role="bold">-</emphasis>|[!]<emphasis>protocol-name</emphasis>|[!]<emphasis>protocol-number</emphasis>}</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>
</listitem>
</varlistentry>
<varlistentry>
<term><emphasis role="bold">PORT(S)</emphasis> (Optional) -
[[!]<emphasis>port-name-or-number</emphasis>[,<emphasis>port-name-or-number</emphasis>]...]</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>
</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/GROUP</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>
</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 192.168.0.0/24.</para>
<para>Your entry in the file will be:</para>
<programlisting> #INTERFACE SOURCE
eth0 192.168.0.0/24</programlisting>
</listitem>
</varlistentry>
<varlistentry>
<term>Example 2:</term>
<listitem>
<para>You add a router to your local network to connect subnet
192.168.1.0/24 which you also want to masquerade. You then add a
second entry for eth0 to this file:</para>
<programlisting> #INTERFACE SOURCE
eth0 192.168.1.0/24</programlisting>
</listitem>
</varlistentry>
<varlistentry>
<term>Example 3:</term>
<listitem>
<para>You have an IPSEC tunnel through ipsec0 and you want to
masquerade packets coming from 192.168.1.0/24 but only if these
packets are destined for hosts in 10.1.1.0/24:</para>
<programlisting> #INTERFACE SOURCE
ipsec0:10.1.1.0/24 196.168.1.0/24</programlisting>
</listitem>
</varlistentry>
<varlistentry>
<term>Example 4:</term>
<listitem>
<para>You want all outgoing traffic from 192.168.1.0/24 through eth0
to use source address 206.124.146.176 which is NOT the primary
address of eth0. You want 206.124.146.176 to be added to eth0 with
name eth0:0.</para>
<programlisting> #INTERFACE SOURCE ADDRESS
eth0:0 192.168.1.0/24 206.124.146.176</programlisting>
</listitem>
</varlistentry>
<varlistentry>
<term>Example 5:</term>
<listitem>
<para>You want all outgoing SMTP traffic entering the firewall from
172.20.1.0/29 to be sent from eth0 with source IP address
206.124.146.177. You want all other outgoing traffic from
172.20.1.0/29 to be sent from eth0 with source IP address
206.124.146.176.</para>
<programlisting> #INTERFACE SOURCE ADDRESS PROTO PORT(S)
eth0 172.20.1.0/29 206.124.146.177 tcp smtp
eth0 172.20.1.0/29 206.124.146.176</programlisting>
<warning>
<para>The order of the above two rules is significant!</para>
</warning>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>FILES</title>
<para>/etc/shorewall/masq</para>
</refsect1>
<refsect1>
<title>See ALSO</title>
<para><ulink
url="http://shorewall.net/configuration_file_basics.htm#Pairs">http://shorewall.net/configuration_file_basics.htm#Pairs</ulink></para>
<para>shorewall(8), shorewall-accounting(5), shorewall-actions(5),
shorewall-blacklist(5), shorewall-exclusion(5), shorewall-hosts(5),
shorewall_interfaces(5), shorewall-ipsets(5), shorewall-maclist(5),
shorewall-nat(5), shorewall-netmap(5), shorewall-params(5),
shorewall-policy(5), shorewall-providers(5), shorewall-proxyarp(5),
shorewall-route_rules(5), shorewall-routestopped(5), shorewall-rules(5),
shorewall.conf(5), shorewall-secmarks(5), shorewall-tcclasses(5),
shorewall-tcdevices(5), shorewall-tcrules(5), shorewall-tos(5),
shorewall-tunnels(5), shorewall-zones(5)</para>
</refsect1>
</refentry>
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