shorewall_code/docs/configuration_file_basics.xml
2009-11-11 11:29:21 -08:00

1321 lines
50 KiB
XML
Raw Permalink Blame History

This file contains invisible Unicode characters

This file contains invisible Unicode characters that are indistinguishable to humans but may be processed differently by a computer. If you think that this is intentional, you can safely ignore this warning. Use the Escape button to reveal them.

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.4//EN"
"http://www.oasis-open.org/docbook/xml/4.4/docbookx.dtd">
<article>
<!--$Id$-->
<articleinfo>
<title>Configuration Files</title>
<authorgroup>
<author>
<firstname>Tom</firstname>
<surname>Eastep</surname>
</author>
</authorgroup>
<pubdate><?dbtimestamp format="Y/m/d"?></pubdate>
<copyright>
<year>2001-2008</year>
<holder>Thomas M. Eastep</holder>
</copyright>
<legalnotice>
<para>Permission is granted to copy, distribute and/or modify this
document under the terms of the GNU Free Documentation License, Version
1.2 or any later version published by the Free Software Foundation; with
no Invariant Sections, with no Front-Cover, and with no Back-Cover
Texts. A copy of the license is included in the section entitled
<quote><ulink url="GnuCopyright.htm">GNU Free Documentation
License</ulink></quote>.</para>
</legalnotice>
</articleinfo>
<caution>
<para><emphasis role="bold">This article applies to Shorewall 4.3 and
later. If you are running a version of Shorewall earlier than Shorewall
4.3.5 then please see the documentation for that
release.</emphasis></para>
</caution>
<caution>
<para>If you copy or edit your configuration files on a system running
Microsoft Windows, you must run them through <ulink
url="http://www.megaloman.com/~hany/software/hd2u/">dos2unix</ulink>
before you use them with Shorewall.</para>
</caution>
<section id="Files">
<title>Files</title>
<para><itemizedlist>
<listitem>
<para><filename>/etc/shorewall/shorewall.conf</filename> - used to
set global firewall parameters.</para>
</listitem>
<listitem>
<para><filename>/etc/shorewall/params</filename> - use this file to
set shell variables that you will expand in other files.</para>
</listitem>
<listitem>
<para><filename>/etc/shorewall/zones</filename> - partition the
firewall's view of the world into zones.</para>
</listitem>
<listitem>
<para><filename>/etc/shorewall/policy</filename> - establishes
firewall high-level policy.</para>
</listitem>
<listitem>
<para><filename>/etc/shorewall/interfaces</filename> - describes the
interfaces on the firewall system.</para>
</listitem>
<listitem>
<para><filename>/etc/shorewall/hosts</filename> - allows defining
zones in terms of individual hosts and subnetworks.</para>
</listitem>
<listitem>
<para><filename>/etc/shorewall/masq</filename> - directs the
firewall where to use many-to-one (dynamic) Network Address
Translation (a.k.a. Masquerading) and Source Network Address
Translation (SNAT).</para>
</listitem>
<listitem>
<para><filename>/etc/shorewall/rules</filename> - defines rules that
are exceptions to the overall policies established in
/etc/shorewall/policy.</para>
</listitem>
<listitem>
<para><filename>/etc/shorewall/nat</filename> - defines one-to-one
NAT rules.</para>
</listitem>
<listitem>
<para><filename>/etc/shorewall/proxyarp</filename> - defines use of
Proxy ARP.</para>
</listitem>
<listitem>
<para><filename>/etc/shorewall/routestopped</filename> - defines
hosts accessible when Shorewall is stopped.</para>
</listitem>
<listitem>
<para><filename>/etc/shorewall/tcrules </filename>- defines marking
of packets for later use by traffic control/shaping or policy
routing.</para>
</listitem>
<listitem>
<para><filename>/etc/shorewall/tos</filename> - defines rules for
setting the TOS field in packet headers.</para>
</listitem>
<listitem>
<para><filename>/etc/shorewall/tunnels</filename> - defines tunnels
(VPN) with end-points on the firewall system.</para>
</listitem>
<listitem>
<para><filename>/etc/shorewall/blacklist</filename> - lists
blacklisted IP/subnet/MAC addresses.</para>
</listitem>
<listitem>
<para><filename>/etc/shorewall/init</filename> - commands that you
wish to execute at the beginning of a <quote>shorewall start</quote>
or <quote>shorewall restart</quote>.</para>
</listitem>
<listitem>
<para><filename>/etc/shorewall/start</filename> - commands that you
wish to execute at the completion of a <quote>shorewall
start</quote> or <quote>shorewall restart</quote></para>
</listitem>
<listitem>
<para><filename>/etc/shorewall/stop </filename>- commands that you
wish to execute at the beginning of a <quote>shorewall
stop</quote>.</para>
</listitem>
<listitem>
<para><filename>/etc/shorewall/stopped</filename> - commands that
you wish to execute at the completion of a <quote>shorewall
stop</quote>.</para>
</listitem>
<listitem>
<para><filename>/etc/shorewall/ecn</filename> - disable Explicit
Congestion Notification (ECN - RFC 3168) to remote hosts or
networks.</para>
</listitem>
<listitem>
<para><filename>/etc/shorewall/accounting</filename> - define IP
traffic accounting rules</para>
</listitem>
<listitem>
<para><filename>/etc/shorewall/actions</filename> and
<filename>/usr/share/shorewall/action.template</filename> allow
user-defined actions.</para>
</listitem>
<listitem>
<para><filename>/etc/shorewall/providers</filename> - defines an
alternate routing table.</para>
</listitem>
<listitem>
<para><filename>/etc/shorewall/route_rules</filename> - Defines
routing rules to be used in conjunction with the routing tables
defined in <filename>/etc/shorewall/providers</filename>.</para>
</listitem>
<listitem>
<para><filename>/etc/shorewall/tcdevices</filename>,
<filename>/etc/shorewall/tcclasses</filename>,
<filename>/etc/shorewall/tcfilters</filename> - Define traffic
shaping.</para>
</listitem>
<listitem>
<para><filename>/etc/shorewall/tcrules</filename> - Mark or classify
traffic for traffic shaping or multiple providers.</para>
</listitem>
<listitem>
<para><filename>/etc/shorewall/vardir</filename> - Determines the
directory where Shorewall maintains its state.</para>
</listitem>
<listitem>
<para><filename>/usr/share/shorewall/actions.std</filename> -
Actions defined by Shorewall.</para>
</listitem>
<listitem>
<para><filename>/usr/share/shorewall/action.*</filename> - Details
of actions defined by Shorewall.</para>
</listitem>
<listitem>
<para><filename>/usr/share/shorewall/macro.*</filename> - Details of
macros defined by Shorewall.</para>
</listitem>
<listitem>
<para><filename>/usr/share/shorewall/modules</filename> - directs
the firewall to load kernel modules.</para>
</listitem>
<listitem>
<para><filename>/usr/share/modules</filename> — Specifies the kernel
modules to be loaded during shorewall start/restart . .</para>
</listitem>
</itemizedlist></para>
<para><emphasis role="bold">If you need to change a file in
/usr/share/shorewall/, copy it to <filename>/etc/shorewall</filename> and
modify the copy</emphasis></para>
</section>
<section id="Manpages">
<title>Man Pages</title>
<para>Man pages are provided in section 5 for each of the Shorewall
configuration files. The name of the page is formed by prefixing the file
name with "shorewall-".</para>
<para>Example — To view the manual page for
<filename>/etc/shorewall/interfaces</filename>:</para>
<programlisting>man shorewall-interfaces</programlisting>
<para>The /etc/shorewall/shorewall.conf file is an exception -- the man
page for that file is 'shorewall.conf':</para>
<programlisting>man shorewall.conf</programlisting>
</section>
<section id="Comments">
<title>Comments</title>
<para>You may place comments in configuration files by making the first
non-whitespace character a pound sign (<quote>#</quote>). You may also
place comments at the end of any line, again by delimiting the comment
from the rest of the line with a pound sign.</para>
<example id="comment">
<title>Comments in a Configuration File</title>
<programlisting># This is a comment
ACCEPT net $FW tcp www #This is an end-of-line comment</programlisting>
</example>
</section>
<section id="COMMENT">
<title>Attach Comment to Netfilter Rules</title>
<para>If you kernel and iptables contain comment match support (see the
output of <command>shorewall show capabilities</command>), then you can
attach comments to Netfilter rules. This feature is available in the
following files:</para>
<itemizedlist>
<listitem>
<para><filename>/etc/shorewall/accounting</filename></para>
</listitem>
<listitem>
<para><filename>/etc/shorewall/masq</filename></para>
</listitem>
<listitem>
<para><filename>/etc/shorewall/nat</filename></para>
</listitem>
<listitem>
<para><filename>/etc/shorewall/notrack</filename></para>
</listitem>
<listitem>
<para><filename>/etc/shorewall/rules</filename></para>
</listitem>
<listitem>
<para><filename>/etc/shorewall/tcrules</filename></para>
</listitem>
<listitem>
<para><filename>/etc/shorewall/tunnels</filename></para>
</listitem>
<listitem>
<para>Action definition files
(<filename>/etc/shorewall/action.*</filename>)</para>
</listitem>
<listitem>
<para>Macro definition files (/etc/shorewall/macro.*)</para>
</listitem>
</itemizedlist>
<para>To attach a comment to one or more rules, insert a record above the
rules that begins with the word COMMENT (must be in all caps). The
remainder of the line is treated as a comment -- that comment will appear
delimited by "/* ... */" in the output of the <command>shorewall[-lite]
show</command> and <command>shorewall[-lite] dump</command> commands. The
comment will be attached to each generated rule until another COMMENT line
appears. To stop attaching comments to rules, simply insert a line that
contains the single word COMMENT.</para>
<para>Example (<filename>/etc/shorewall/rules</filename>):</para>
<programlisting>COMMENT Stop NETBIOS noise
REJECT loc net tcp 137,445
REJECT loc net udp 137:139
COMMENT Stop my idiotic work laptop from sending to the net with an HP source/dest IP address
DROP loc:!192.168.0.0/22 net
COMMENT</programlisting>
<para>Here's the corresponding output from
<filename>/sbin/shorewall-lite</filename>:</para>
<programlisting>gateway:~ # <command>shorewall-lite show loc2net</command>
Shorewall Lite 4.3.3 Chains loc2net at gateway - Mon Oct 16 15:04:52 PDT 2008
Counters reset Mon Oct 16 14:52:17 PDT 2006
Chain loc2net (1 references)
pkts bytes target prot opt in out source destination
0 0 LOG tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp dpt:25 LOG flags 0 level 6 prefix `FW:loc2net:REJECT:'
0 0 reject tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp dpt:25
0 0 LOG udp -- * * 0.0.0.0/0 0.0.0.0/0 udp dpts:1025:1031 LOG flags 0 level 6 prefix `FW:loc2net:REJECT:'
0 0 reject udp -- * * 0.0.0.0/0 0.0.0.0/0 udp dpts:1025:1031
0 0 reject tcp -- * * 0.0.0.0/0 0.0.0.0/0 multiport dports 137,445 <emphasis
role="bold">/* Stop NETBIOS noise */</emphasis>
0 0 reject udp -- * * 0.0.0.0/0 0.0.0.0/0 udp dpts:137:139 <emphasis
role="bold">/* Stop NETBIOS noise */</emphasis>
0 0 DROP all -- * * !192.168.0.0/22 0.0.0.0/0 <emphasis
role="bold">/* Stop my idiotic work laptop from sending to the net with an HP source/dest IP address */</emphasis>
5 316 ACCEPT all -- * * 0.0.0.0/0 0.0.0.0/0
gateway:~ #
</programlisting>
<para>COMMENT lines in macro files work somewhat differently from other
files. COMMENT lines in macros are ignored if COMMENT support is not
available or if there was a COMMENT in use when the top-level macro was
invoked. This allows the following:</para>
<para><filename>/usr/share/shorewall/macro.SSH</filename>:</para>
<para><programlisting>#ACTION SOURCE DEST PROTO DEST SOURCE RATE USER/
# PORT(S) PORT(S) LIMIT GROUP
COMMENT SSH
PARAM - - tcp 22 </programlisting>
<filename>/etc/shorewall/rules</filename>:<programlisting>COMMENT Allow SSH from home
SSH/ALLOW net:$MYIP $FW
COMMENT</programlisting>The comment line in macro.SSH will not override the
COMMENT line in the rules file and the generated rule will show <emphasis
role="bold">/* Allow SSH from home */</emphasis> when displayed through
the Shorewall show and dump commands.</para>
</section>
<section id="BlankColumn">
<title>"Blank" Columns</title>
<para>If you don't want to supply a value in a column but want to supply a
value in a following column, simply enter '-' to make the column appear
empty.</para>
<para>Example:<programlisting>#INTERFACE BROADCAST OPTIONS
br0 - routeback</programlisting></para>
</section>
<section id="Continuation">
<title>Line Continuation</title>
<para>You may continue lines in the configuration files using the usual
backslash (<quote>\</quote>) followed immediately by a new line character
(Enter key).</para>
<example id="continuation">
<title>Line Continuation</title>
<programlisting>ACCEPT net $FW tcp \↵
smtp,www,pop3,imap #Services running on the firewall</programlisting>
<para>In certain cases, leading white space is ignored in continuation
lines:</para>
<itemizedlist>
<listitem>
<para>The continued line ends with a colon (":")</para>
</listitem>
<listitem>
<para>The continued line ends with a comma (",")</para>
</listitem>
</itemizedlist>
<para>Example (<filename>/etc/shorewall/rules</filename>):</para>
<programlisting>#ACTION SOURCE DEST PROTO DEST
# PORT(S)
ACCEPT net:\
206.124.146.177,\
206.124.146.178,\
206.124.146.180\
dmz tcp 873</programlisting>
<para>The leading white space on the first through third continuation
lines is ignored so the SOURCE column effectively contains
"net:206.124.146.177,206.124.147.178,206.124.146.180". Because the third
continuation line does not end with a comma or colon, the leading white
space in the last line is not ignored.</para>
</example>
</section>
<section id="SOURCE-DEST">
<title>Specifying SOURCE and DEST</title>
<para>Entries in Shorewall configuration files often deal with the source
(SOURCE) and destination (DEST) of connections and Shorewall implements a
uniform way for specifying them.</para>
<para>A SOURCE or DEST consists of one to three parts separated by colons
(":"):</para>
<orderedlist>
<listitem>
<para>ZONE — The name of a zone declared in
<filename>/etc/shorewall/zones</filename> or
<filename>/etc/shorewall6/zones</filename>. This part is only
available in the rules file (<filename>/etc/shorewall/rules</filename>
and <filename>/etc/shorewall6/rules</filename>).</para>
</listitem>
<listitem>
<para>INTERFACE — The name of an interface that matches an entry in
<filename>/etc/shorewall/interfaces</filename>
(<filename>/etc/shorewall6/interfaces</filename>).</para>
</listitem>
<listitem>
<para>ADDRESS LIST — A list of one or more addresses (host or network)
or address ranges, separated by commas. In an IPv6 configuration, this
list must be includes in angled brackets ("&lt;...&gt;"). The list may
have <link linkend="Exclusion">exclusion</link>.</para>
</listitem>
</orderedlist>
<para>Examples.</para>
<orderedlist>
<listitem>
<para>All hosts in the <emphasis role="bold">net</emphasis> zone —
<emphasis role="bold">net</emphasis></para>
</listitem>
<listitem>
<para>Subnet 192.168.1.0/29 in the <emphasis
role="bold">loc</emphasis> zone — <emphasis
role="bold">loc:192.168.1.0/29</emphasis></para>
</listitem>
<listitem>
<para>All hosts in the net zone connecting through <filename
class="devicefile">ppp0</filename><emphasis
role="bold">net:ppp0</emphasis></para>
</listitem>
<listitem>
<para>All hosts interfaced by <filename
class="devicefile">eth3</filename><emphasis
role="bold">eth3</emphasis></para>
</listitem>
<listitem>
<para>Subnet 10.0.1.0/24 interfacing through <filename><filename
class="devicefile">eth2</filename></filename><emphasis
role="bold">eth2:10.0.1.0/24</emphasis></para>
</listitem>
<listitem>
<para>Host 2002:ce7c:92b4:1:a00:27ff:feb1:46a9 in the <emphasis
role="bold">loc</emphasis> zone — <emphasis
role="bold">loc:&lt;2002:ce7c:92b4:1:a00:27ff:feb1:46a9&gt;</emphasis></para>
</listitem>
</orderedlist>
</section>
<section id="INCLUDE">
<title>INCLUDE Directive</title>
<para>Any configuration file may contain INCLUDE directives. An INCLUDE
directive consists of the word INCLUDE followed by a path name and causes
the contents of the named file to be logically included into the file
containing the INCLUDE. Relative path names given in an INCLUDE directive
are resolved using the current CONFIG_PATH setting (see <ulink
url="manpages/shorewall.conf.html">shorewall.conf</ulink>(5)).</para>
<para>INCLUDE's may be nested to a level of 3 -- further nested INCLUDE
directives are ignored with a warning message.</para>
<caution>
<para>If you are using <ulink
url="CompiledPrograms.html%23Lite">Shorewall Lite</ulink> , it is not
advisable to use INCLUDE in the <filename>params</filename> file in an
export directory. If you do that, you must ensure that the included file
is also present on the firewall system's <filename
class="directory">/etc/shorewall-lite/</filename> directory.</para>
<para>If you only need the <filename>params</filename> file at compile
time, you can set EXPORTPARAMS=No in
<filename>shorewall.conf</filename>. That prevents the
<filename>params</filename> file from being copied into the compiled
script. With EXPORTPARAMS=No, it is perfectly okay to use INCLUDE in the
<filename>params</filename> file.</para>
</caution>
<example id="include">
<title>Use of INCLUDE</title>
<programlisting> shorewall/params.mgmt:
   MGMT_SERVERS=1.1.1.1,2.2.2.2,3.3.3.3
   TIME_SERVERS=4.4.4.4
   BACKUP_SERVERS=5.5.5.5
   ----- end params.mgmt -----
   shorewall/params:
   # Shorewall 1.3 /etc/shorewall/params
   [..]
   #######################################
 
   INCLUDE params.mgmt   
 
   # params unique to this host here
   #LAST LINE - ADD YOUR ENTRIES ABOVE THIS ONE - DO NOT REMOVE
   ----- end params -----
   shorewall/rules.mgmt:
   ACCEPT net:$MGMT_SERVERS   $FW    tcp    22
   ACCEPT $FW          net:$TIME_SERVERS    udp    123
   ACCEPT $FW          net:$BACKUP_SERVERS  tcp    22
   ----- end rules.mgmt -----
   shorewall/rules:
   # Shorewall version 1.3 - Rules File
   [..]
   #######################################
 
   INCLUDE rules.mgmt    
 
   # rules unique to this host here
   #LAST LINE -- ADD YOUR ENTRIES BEFORE THIS ONE -- DO NOT REMOVE
   ----- end rules -----</programlisting>
<para>You may include multiple files in one command using an <link
linkend="Embedded">embedded shell command</link>.</para>
<para>Example (include all of the files ending in ".rules" in a
directory:):<programlisting>gateway:/etc/shorewall # ls rules.d
ALL.rules DNAT.rules FW.rules NET.rules REDIRECT.rules VPN.rules
gateway:/etc/shorewall # </programlisting></para>
<para>/etc/shorewall/rules:<programlisting>SECTION NEW
SHELL cat /etc/shorewall/rules.d/*.rules</programlisting></para>
</example>
</section>
<section id="Variables">
<title>Using Shell Variables</title>
<para>You may use the <filename>/etc/shorewall/params</filename> file to
set shell variables that you can then use in some of the other
configuration files.</para>
<para>It is suggested that variable names begin with an upper case letter
to distinguish them from variables used internally within the Shorewall
programs</para>
<para>Example:</para>
<blockquote>
<programlisting>    /etc/shorewall/params
NET_IF=eth0
NET_BCAST=130.252.100.255
NET_OPTIONS=routefilter,routefilter
    /etc/shorewall/interfaces record:
net $NET_IF $NET_BCAST $NET_OPTIONS
    The result will be the same as if the record had been written
net eth0 130.252.100.255 routefilter,routefilter
</programlisting>
</blockquote>
<para>Variables may be used anywhere in the other configuration
files.<note>
<para>If you use "$FW" on the right side of assignments in the
<filename>/etc/shorewall/params</filename> file, you must also set the
FW variable in that file.</para>
<para>Example:<programlisting>/etc/shorewall/zones:
#ZONE TYPE OPTIONS
<emphasis role="bold">fw</emphasis> firewall
/etc/shorewall/params:
FW=<emphasis role="bold">fw</emphasis>
BLARG=$FW:206.124.146.176</programlisting></para>
</note></para>
<para>Because the <filename>/etc/shorewall/params</filename> file is
simply sourced into the shell, you can place arbitrary shell code in the
file and it will be executed each time that the file is read. Any code
included should follow these guidelines:</para>
<orderedlist>
<listitem>
<para>The code should not have side effects, especially on other
shorewall configuration files.</para>
</listitem>
<listitem>
<para>The code should be safe to execute multiple times without
producing different results.</para>
</listitem>
<listitem>
<para>Should not depend on where the code is called from (the params
file is sourced by both /sbin/shorewall and
/usr/lib/shorewall/firewall).</para>
</listitem>
<listitem>
<para>Should not assume anything about the state of Shorewall.</para>
</listitem>
<listitem>
<para>The names of any functions or variables declared should begin
with an upper case letter.</para>
</listitem>
<listitem>
<para>The <filename>/etc/shorewall/params</filename> file is processed
by the compiler at compile-time and by the compiled script at
run-time. If you have set EXPORTPARAMS=No in
<filename>shorewall.conf</filename>, then the
<filename><filename>params</filename></filename> file is only
processed by the compiler; it is not run by the compiled
script.</para>
</listitem>
<listitem>
<para>If you are using <ulink
url="CompiledPrograms.html#Lite">Shorewall Lite</ulink> and if the
<filename>params</filename> script needs to set shell variables based
on the configuration of the firewall system, you can use this
trick:</para>
<programlisting>EXT_IP=$(ssh root@firewall "/sbin/shorewall-lite call find_first_interface_address eth0")</programlisting>
<para>The <command>shorewall-lite call</command> command allows you to
to call interactively any Shorewall function that you can call in an
extension script.</para>
</listitem>
</orderedlist>
<note>
<para>Only the $VAR and ${VAR} forms of variable expansion are
supported. You may not use the more exotic forms supported by the shell
($VAR, ${VAR}, ${VAR:=val}, ...)</para>
</note>
</section>
<section id="Embedded">
<title>Embedded Shell and Perl</title>
<para>Earlier versions of Shorewall offered <ulink
url="shorewall_extension_scripts.htm">extension scripts</ulink> to allow
users to extend Shorewall's functionality. Extension scripts were designed
to work under the limitations of the Bourne Shell. With the current
Perl-based compiler, <firstterm>Embedded scripts</firstterm> offer a
richer and more flexible extension capability.</para>
<para>While inline scripts may be written in either Shell or Perl, those
written in Perl have a lot more power.</para>
<para>Embedded scripts can be either single-line or multi-line. Single
line scripts take one of the following forms:</para>
<itemizedlist>
<listitem>
<para><emphasis role="bold">PERL</emphasis> &lt;<emphasis>perl
script</emphasis>&gt;</para>
</listitem>
<listitem>
<para><emphasis role="bold">SHELL</emphasis> &lt;<emphasis>shell
script</emphasis>&gt;</para>
</listitem>
</itemizedlist>
<para>Shell scripts run in a child shell process and their output is piped
back to the compiler which processes that output as if it were embedded at
the point of the script.</para>
<para>Example: The following entries in
<filename>/etc/shorewall/rules</filename> are equivalent:<programlisting>SHELL for z in net loc dmz; do echo "ACCEPT $z fw tcp 22"; done</programlisting><programlisting>ACCEPT net fw tcp 22
ACCEPT loc fw tcp 22
ACCEPT dmz fw tcp 22</programlisting></para>
<para>Perl scripts run in the context of of the compiler process using
Perl's eval() function. Perl scripts are implicitly prefixed by the
following:</para>
<programlisting>package Shorewall::User;
use Shorewall::Config qw/shorewall/;</programlisting>
<para>To produce output that will be processed by the compiler as if it
were embedded in the file at the point of the script, pass that output to
the Shorewall::Config::shorewall() function. The Perl equivalent of the
above SHELL script would be:<programlisting>PERL for ( qw/net loc dmz/ ) { shorewall "ACCEPT $_ fw tcp 22"; }</programlisting>A
couple of more points should be mentioned:</para>
<orderedlist>
<listitem>
<para>Compile-time extension scripts are also implicitly prefixed by
"package Shorewall::User;".</para>
</listitem>
<listitem>
<para>A <emphasis role="bold">compile</emphasis> extension script is
supported. That script is run early in the compilation process and
allows users to load additional modules and to define data and
functions for use in subsequent embedded scripts and extension
scripts.</para>
</listitem>
<listitem>
<para><ulink url="ManualChains.html">Manual Chains</ulink> may be
added in the <emphasis role="bold">compile</emphasis> extension
script..</para>
</listitem>
</orderedlist>
<para>Multi-line scripts use one of the following forms:<programlisting><emphasis
role="bold">BEGIN SHELL</emphasis>
&lt;<emphasis>shell script</emphasis>&gt;
<emphasis role="bold">END</emphasis> [ <emphasis role="bold">SHELL</emphasis> ]</programlisting><programlisting><emphasis
role="bold">BEGIN PERL</emphasis> [;]
&lt;<emphasis>perl script</emphasis>&gt;
<emphasis role="bold">END</emphasis> [ <emphasis role="bold">PERL</emphasis> ] [<emphasis
role="bold">;</emphasis>]</programlisting></para>
<para><emphasis role="bold">Note: </emphasis>The '[' and ']' above are
meta-characters which indicate that what they enclose is optional and may
be omitted. So you may follow PERL with a semicolon ( ':') or you may omit
the semicolon.</para>
</section>
<section id="dnsnames">
<title>Using DNS Names</title>
<caution>
<para>I personally recommend strongly against using DNS names in
Shorewall configuration files. If you use DNS names and you are called
out of bed at 2:00AM because Shorewall won't start as a result of DNS
problems then don't say that you were not forewarned.</para>
</caution>
<para>Host addresses in Shorewall configuration files may be specified as
either IP addresses or DNS Names.</para>
<para>DNS names in iptables rules aren't nearly as useful as they first
appear. When a DNS name appears in a rule, the iptables utility resolves
the name to one or more IP addresses and inserts those addresses into the
rule. So changes in the DNS-&gt;IP address relationship that occur after
the firewall has started have absolutely no effect on the firewall's rule
set.</para>
<para>For some sites, using DNS names is very risky. Here's an
example:</para>
<programlisting>teastep@ursa:~$ dig pop.gmail.com
; &lt;&lt;&gt;&gt; DiG 9.4.2-P1 &lt;&lt;&gt;&gt; pop.gmail.com
;; global options: printcmd
;; Got answer:
;; -&gt;&gt;HEADER&lt;&lt;- opcode: QUERY, status: NOERROR, id: 1774
;; flags: qr rd ra; QUERY: 1, ANSWER: 3, AUTHORITY: 7, ADDITIONAL: 0
;; QUESTION SECTION:
;pop.gmail.com. IN A
;; ANSWER SECTION:
pop.gmail.com. <emphasis role="bold">300</emphasis> IN CNAME gmail-pop.l.google.com.
gmail-pop.l.google.com. <emphasis role="bold">300</emphasis> IN A 209.85.201.109
gmail-pop.l.google.com. <emphasis role="bold">300</emphasis> IN A 209.85.201.111</programlisting>
<para>Note that the TTL is 300 -- 300 seconds is only 5 minutes. So five
minutes later, the answer may change!</para>
<para>So this rule may work for five minutes then suddently stop
working:</para>
<programlisting>#ACTION SOURCE DEST PROTO DEST
# PORT(S)
POP(ACCEPT) loc net:pop.gmail.com</programlisting>
<para>If your firewall rules include DNS names then:</para>
<itemizedlist>
<listitem>
<para>If your <filename>/etc/resolv.conf </filename>is wrong then your
firewall won't start.</para>
</listitem>
<listitem>
<para>If your <filename>/etc/nsswitch.conf</filename> is wrong then
your firewall won't start.</para>
</listitem>
<listitem>
<para>If your Name Server(s) is(are) down then your firewall won't
start.</para>
</listitem>
<listitem>
<para>If your startup scripts try to start your firewall before
starting your DNS server then your firewall won't start.</para>
</listitem>
<listitem>
<para>Factors totally outside your control (your ISP's router is down
for example), can prevent your firewall from starting.</para>
</listitem>
<listitem>
<para>You must bring up your network interfaces prior to starting your
firewall.</para>
</listitem>
</itemizedlist>
<para>Each DNS name must be fully qualified and include a minimum of two
periods (although one may be trailing). This restriction is imposed by
Shorewall to insure backward compatibility with existing configuration
files.</para>
<example id="validdns">
<title>Valid DNS Names</title>
<itemizedlist>
<listitem>
<para>mail.shorewall.net</para>
</listitem>
<listitem>
<para>shorewall.net. (note the trailing period).</para>
</listitem>
</itemizedlist>
</example>
<example id="invaliddns">
<title>Invalid DNS Names</title>
<itemizedlist>
<listitem>
<para>mail (not fully qualified)</para>
</listitem>
<listitem>
<para>shorewall.net (only one period)</para>
</listitem>
</itemizedlist>
</example>
<para>DNS names may not be used as:</para>
<itemizedlist>
<listitem>
<para>The server address in a DNAT rule (/etc/shorewall/rules
file)</para>
</listitem>
<listitem>
<para>In the ADDRESS column of an entry in /etc/shorewall/masq.</para>
</listitem>
<listitem>
<para>In the <filename>/etc/shorewall/nat</filename> file.</para>
</listitem>
</itemizedlist>
<para>These restrictions are imposed by Netfilter and not by
Shorewall.</para>
</section>
<section id="Lists">
<title>Comma-separated Lists</title>
<para>Comma-separated lists are allowed in a number of contexts within the
configuration files. A comma separated list:</para>
<itemizedlist>
<listitem>
<para>Must not have any embedded white space.<programlisting> Valid: routefilter,dhcp,arpfilter
Invalid: routefilter,     dhcp,     arpfilter</programlisting></para>
</listitem>
<listitem>
<para>If you use line continuation to break a comma-separated list,
the comma must be the last thing on the continued line before '\'
unless the continuation line has no leading white space.</para>
</listitem>
<listitem>
<para>Entries in a comma-separated list may appear in any
order.</para>
</listitem>
</itemizedlist>
</section>
<section id="Compliment">
<title>Complementing an Address or Subnet</title>
<para>Where specifying an IP address, a subnet or an interface, you can
precede the item with <quote>!</quote> to specify the complement of the
item. For example, !192.168.1.4 means <quote>any host but
192.168.1.4</quote>. There must be no white space following the
<quote>!</quote>.</para>
</section>
<section id="Exclusion">
<title>Exclusion Lists</title>
<para>Where a comma-separated list of addresses is accepted, an
<firstterm>exclusion list</firstterm> may also be included. An exclusion
list is a comma-separated list of addresses that begins with "!".</para>
<para>Example:</para>
<programlisting>!192.168.1.3,192.168.1.12,192.168.1.32/27</programlisting>
<para>The above list refers to "All addresses except 192.168.1.3,
192.168.1.12 and 192.168.1.32-192.168.1.63.</para>
<para>Exclusion lists can also be added after a network address.</para>
<para>Example:</para>
<programlisting>192.168.1.0/24!192.168.1.3,192.168.1.12,192.168.1.32/27</programlisting>
<para>The above list refers to "All addresses in 192.168.1.0-192.168.1.255
except 192.168.1.3, 192.168.1.12 and 192.168.1.32-192.168.1.63.</para>
</section>
<section id="IPRanges">
<title>IP Address Ranges</title>
<para>If you kernel and iptables have iprange match support, you may use
IP address ranges in Shorewall configuration file entries; IP address
ranges have the syntax &lt;<emphasis>low IP
address</emphasis>&gt;-&lt;<emphasis>high IP address</emphasis>&gt;.
Example: 192.168.1.5-192.168.1.12.</para>
<para>To see if your kernel and iptables have the required support, use
the <command>shorewall show capabilities</command> command:</para>
<programlisting>&gt;~ <command>shorewall show capabilities</command>
...
Shorewall has detected the following iptables/netfilter capabilities:
NAT: Available
Packet Mangling: Available
Multi-port Match: Available
Connection Tracking Match: Available
Packet Type Match: Not available
Policy Match: Available
Physdev Match: Available
<emphasis role="bold">IP range Match: Available &lt;--------------</emphasis></programlisting>
</section>
<section id="Ports">
<title>Protocol Number/Names and Port Numbers/Service Names</title>
<para>Unless otherwise specified, when giving a protocol number you can
use either an integer or a protocol name from
<filename>/etc/protocols</filename>. Similarly, when giving a port number
you can use either an integer or a service name from
<filename>/etc/services</filename>.<note>
<para>The rules compiler translates protocol names to protocol numbers
and service names to port numbers itself.</para>
</note></para>
<para>Also, unless otherwise documented, a protocol number/name can be
preceded by '!' to specify "All protocols except this one" (e.g.,
"!tcp").</para>
</section>
<section id="ICMP">
<title>ICMP and ICMP6 Types and Codes</title>
<para>When dealing with ICMP, the DEST PORT specifies the type or type and
code. You may specify the numeric type, the numeric type and code
separated by a slash (e.g., 3/4) or you may use a type name.</para>
<para>Type names for IPv4 and their corresponding type or type/code
are:</para>
<programlisting>echo-reply' =&gt; 0
destination-unreachable =&gt; 3
network-unreachable =&gt; 3/0
host-unreachable =&gt; 3/1
protocol-unreachable =&gt; 3/2
port-unreachable =&gt; 3/3
fragmentation-needed =&gt; 3/4
source-route-failed =&gt; 3/5
network-unknown =&gt; 3/6
host-unknown =&gt; 3/7
network-prohibited =&gt; 3/9
host-prohibited =&gt; 3/10
TOS-network-unreachable =&gt; 3/11
TOS-host-unreachable =&gt; 3/12
communication-prohibited =&gt; 3/13
host-precedence-violation =&gt; 3/14
precedence-cutoff =&gt; 3/15
source-quench =&gt; 4
redirect =&gt; 5
network-redirect =&gt; 5/0
host-redirect =&gt; 5/1
TOS-network-redirect =&gt; 5/2
TOS-host-redirect =&gt; 5/3
echo-request =&gt; 8
router-advertisement =&gt; 9
router-solicitation =&gt; 10
time-exceeded =&gt; 11
ttl-zero-during-transit =&gt; 11/0
ttl-zero-during-reassembly=&gt; 11/1
parameter-problem =&gt; 12
ip-header-bad =&gt; 12/0
required-option-missing =&gt; 12/1
timestamp-request =&gt; 13
timestamp-reply =&gt; 14
address-mask-request =&gt; 17
address-mask-reply =&gt; 18</programlisting>
<para>Type names for IPv6 and their corresponding type or type/code
are:</para>
<programlisting>destination-unreachable =&gt; 1
no-route' =&gt; 1/0
communication-prohibited =&gt; 1/1
address-unreachable' =&gt; 1/2
port-unreachable' =&gt; 1/3
packet-too-big =&gt; 2
time-exceeded' =&gt; 3
ttl-exceeded' =&gt; 3
ttl-zero-during-transit =&gt; 3/0
ttl-zero-during-reassembly =&gt; 3/1
parameter-problem =&gt; 4
bad-header =&gt; 4/0
unknown-header-type =&gt; 4/1
unknown-option =&gt; 4/2
echo-request =&gt; 128
echo-reply =&gt; 129
router-solicitation =&gt; 133
router-advertisement =&gt; 134
neighbour-solicitation =&gt; 135
neighbour-advertisement =&gt; 136
redirect =&gt; 137</programlisting>
</section>
<section id="Ranges">
<title>Port Ranges</title>
<para>If you need to specify a range of ports, the proper syntax is
&lt;low port number&gt;:&lt;high port number&gt;. For example, if you want
to forward the range of tcp ports 4000 through 4100 to local host
192.168.1.3, the entry in /etc/shorewall/rules is:</para>
<programlisting>#ACTION SOURCE DESTINATION PROTO DEST PORTS(S)
DNAT net loc:192.168.1.3 tcp 4000:4100</programlisting>
<para>If you omit the low port number, a value of zero is assumed; if you
omit the high port number, a value of 65535 is assumed.</para>
<para>Also, unless otherwise documented, a port range can be preceded by
'!' to specify "All ports except those in this range" (e.g.,
"!4000:4100").</para>
</section>
<section id="Portlists">
<title>Port Lists</title>
<para>In most cases where a port or port range may appear, a
comma-separated list of ports or port ranges may also be entered.
Shorewall requires the Netfilter <emphasis
role="bold">multiport</emphasis> match capability if ports lists are used
(see the output of "<emphasis role="bold">shorewall show
capabilities</emphasis>").</para>
<para>Also, unless otherwise documented, a port list can be preceded by
'!' to specify "All ports except these" (e.g., "!80,443").</para>
<para>Prior to Shorewall 4.4.4, port lists appearing in the <ulink
url="manpages/shorewall-routestopped.html">/etc/shorewall/routestopped</ulink>
file may specify no more than 15 ports; port ranges appearing in a list
count as two ports each.</para>
</section>
<section id="MAC">
<title>Using MAC Addresses</title>
<para>Media Access Control (MAC) addresses can be used to specify packet
source in several of the configuration files. In order to control traffic
to/from a host by its MAC address, the host must be on the same network as
the firewall.</para>
<para>To use this feature, your kernel must have MAC Address Match support
(CONFIG_IP_NF_MATCH_MAC) included.</para>
<para>MAC addresses are 48 bits wide and each Ethernet Controller has a
unique MAC address.</para>
<para>In GNU/Linux, MAC addresses are usually written as a series of 6 hex
numbers separated by colons.</para>
<example id="mac">
<title>MAC Address of an Ethernet Controller</title>
<programlisting> gateway:~ # <command>ip link ls dev eth0</command>
4: eth0: &lt;BROADCAST,MULTICAST,UP,LOWER_UP&gt; mtu 1500 qdisc htb qlen 1000
link/ether <emphasis role="bold">02:00:08:E3:FA:55</emphasis> brd ff:ff:ff:ff:ff:ff
gateway:~ #</programlisting>
</example>
<para>Because Shorewall uses colons as a separator for address fields,
Shorewall requires MAC addresses to be written in another way. In
Shorewall, MAC addresses begin with a tilde (<quote>~</quote>) and consist
of 6 hex numbers separated by hyphens. In Shorewall, the MAC address in
the example above would be written <emphasis
role="bold">~02-00-08-E3-FA-55</emphasis>.</para>
<note>
<para>It is not necessary to use the special Shorewall notation in the
<filename><ulink
url="MAC_Validation.html">/etc/shorewall/maclist</ulink></filename>
file.</para>
</note>
</section>
<section id="Logical">
<title>Logical Interface Names</title>
<para>When dealing with a complex configuration, it is often awkward to
use physical interface names in the Shorewall configuration.</para>
<itemizedlist>
<listitem>
<para>You need to remember which interface is which.</para>
</listitem>
<listitem>
<para>If you move the configuration to another firewall, the interface
names might not be the same.</para>
</listitem>
</itemizedlist>
<para>Beginning with Shorewall 4.4.4, you can use logical interface names
which are mapped to the actual interface using the
<option>physical</option> option in <ulink
url="manpages/shorewall-interfaces.html">shorewall-interfraces</ulink>
(5).</para>
<para>Here is an example:</para>
<programlisting>#ZONE INTERFACE BROADCAST OPTIONS
net COM_IF detect dhcp,blacklist,tcpflags,optional,upnp,routefilter=0,nosmurfs,logmartians=0,physical=eth0
net EXT_IF detect dhcp,blacklist,tcpflags,optional,routefilter=0,nosmurfs,logmartians=0,proxyarp=1,physical=eth2
loc INT_IF detect dhcp,logmartians=1,routefilter=1,tcpflags,nets=172.20.1.0/24,physical=eth1
dmz VPS_IF detect logmartians=1,routefilter=0,routeback,physical=venet0
loc TUN_IF detect physical=tun+</programlisting>
<para>In this example, COM_IF is a logical interface name that refers to
Ethernet interface <filename class="devicefile">eth0</filename>, EXT_IF is
a logical interface name that refers to Ethernet interface <filename
class="devicefile">eth2</filename>, and so on.</para>
<para>Here are a couple of more files from the same configuration:</para>
<para><ulink url="manpages/shorewall-masq.html">shorewall-masq</ulink>
(5):</para>
<programlisting>#INTERFACE SOURCE ADDRESS
COMMENT Masquerade Local Network
COM_IF 0.0.0.0/0
EXT_IF !206.124.146.0/24 206.124.146.179:persistent</programlisting>
<para><ulink
url="manpages/shorewall-providers.html">shorewall-providers</ulink>
(5)</para>
<programlisting>#NAME NUMBER MARK DUPLICATE INTERFACE GATEWAY OPTIONS COPY
Avvanta 1 0x10000 main EXT_IF 206.124.146.254 loose,fallback INT_IF,VPS_IF,TUN_IF
Comcast 2 0x20000 main COM_IF detect balance INT_IF,VPS_IF,TUN_IF</programlisting>
<para>Note in particular that Shorewall translates TUN_IF to <filename
class="devicefile">tun*</filename> in the COPY column.</para>
</section>
<section id="Levels">
<title>Shorewall Configurations</title>
<para>Shorewall allows you to have configuration directories other than
<filename class="directory">/etc/shorewall</filename>. The shorewall
check, start and restart commands allow you to specify an alternate
configuration directory and Shorewall will use the files in the alternate
directory rather than the corresponding files in /etc/shorewall. The
alternate directory need not contain a complete configuration; those files
not in the alternate directory will be read from <filename
class="directory">/etc/shorewall</filename>.<important>
<para>Shorewall requires that the file
<filename>/etc/shorewall/shorewall.conf</filename> to always exist.
Certain global settings are always obtained from that file. If you
create alternative configuration directories, do not remove
/etc/shorewall/shorewall.conf.</para>
</important></para>
<para>This facility permits you to easily create a test or temporary
configuration by</para>
<orderedlist>
<listitem>
<para>copying the files that need modification from /etc/shorewall to
a separate directory;</para>
</listitem>
<listitem>
<para>modify those files in the separate directory; and</para>
</listitem>
<listitem>
<para>specifying the separate directory in a <command>shorewall
start</command> or <command>shorewall restart</command> command (e.g.,
<command>shorewall restart /etc/testconfig</command> )</para>
</listitem>
</orderedlist>
</section>
<section id="Save">
<title>Saved Configurations</title>
<para>Shorewall allows you to <firstterm>save</firstterm> the
currently-running configuration in a form that permits it to be
re-installed quickly. When you save the configuration using the
<command>shorewall save</command> command, the running configuration is
saved in a file in the <filename
class="directory">/var/lib/shorewall</filename> directory. The default
name of that file is <filename>/var/lib/shorewall/restore</filename> but
you can specify a different name as part of the command. For example, the
command <command>shorewall save standard</command> will save the running
configuration in <filename>/var/lib/shorewall/standard</filename>. A saved
configuration is re-installed using the <command>shorewall
restore</command> command. Again, that command normally will restore the
configuration saved in <filename>/var/lib/shorewall/restore</filename> but
as with the <command>save</command> command, you can specify a different
file name in the command. For example, <command>shorewall restore
standard</command> will re-install the configuration saved in
<filename>/var/lib/shorewall/standard</filename>. By permitting you to
save different configurations under different names, Shorewall provides a
means for quickly switching between these different saved
configurations.</para>
<para>As mentioned above, the default configuration is called 'restore'
but like most things in Shorewall, that default can be changed. The
default name is specified using the <emphasis
role="bold">RESTOREFILE</emphasis> option in
<filename>/etc/shorewall/shorewall.conf</filename>.</para>
<warning>
<para>The default saved configuration is used by Shorewall in a number
of ways besides in the <command>restore</command> command; to avoid
surprises, I recommend that you read the <ulink
url="starting_and_stopping_shorewall.htm#Saved">Shorewall Operations
documentation section about saved configurations</ulink> before creating
one.</para>
</warning>
</section>
</article>