forked from extern/shorewall_code
580 lines
20 KiB
XML
580 lines
20 KiB
XML
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<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<article id="Shorewall_and_Aliased_Interfaces">
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<articleinfo>
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<title>Shorewall and Aliased Interfaces</title>
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<authorgroup>
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<author>
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<firstname>Tom</firstname>
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<surname>Eastep</surname>
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</author>
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</authorgroup>
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<pubdate>2003-11-13</pubdate>
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<copyright>
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<year>2001</year>
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<year>2002</year>
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<year>2003</year>
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<holder>Thomas M. Eastep</holder>
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</copyright>
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<legalnotice>
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<para>Permission is granted to copy, distribute and/or modify this
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document under the terms of the GNU Free Documentation License, Version
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1.2 or any later version published by the Free Software Foundation; with
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no Invariant Sections, with no Front-Cover, and with no Back-Cover
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Texts. A copy of the license is included in the section entitled "<ulink
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url="GnuCopyright.htm">GNU Free Documentation License</ulink>".</para>
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</legalnotice>
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</articleinfo>
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<section>
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<title>Background</title>
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<para>The traditional net-tools contain a program called
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<emphasis>ifconfig</emphasis> which is used to configure network devices.
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ifconfig introduced the concept of <emphasis>aliased</emphasis> or
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<emphasis>virtual</emphasis> interfaces. These virtual interfaces have
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names of the form <emphasis>interface:integer</emphasis> (e.g., eth0:0)
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and ifconfig treats them more or less like real interfaces.</para>
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<example>
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<title>ifconfig</title>
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<programlisting>[root@gateway root]# ifconfig eth0:0
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eth0:0 Link encap:Ethernet HWaddr 02:00:08:3:FA:55
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inet addr:206.124.146.178 Bcast:206.124.146.255 Mask:255.255.255.0
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UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
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Interrupt:11 Base address:0x2000
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[root@gateway root]# </programlisting>
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</example>
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<para>The ifconfig utility is being gradually phased out in favor of the
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ip utility which is part of the <emphasis>iproute</emphasis> package. The
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ip utility does not use the concept of aliases or virtual interfaces but
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rather treats additional addresses on an interface as objects in their own
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right. The ip utility does provide for interaction with ifconfig in that
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it allows addresses to be <emphasis>labeled</emphasis> where these labels
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take the form of ipconfig virtual interfaces.</para>
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<example>
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<title>ip</title>
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<programlisting>[root@gateway root]# ip addr show dev eth0
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2: eth0: <BROADCAST,MULTICAST,UP> mtu 1500 qdisc htb qlen 100
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link/ether 02:00:08:e3:fa:55 brd ff:ff:ff:ff:ff:ff
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inet 206.124.146.176/24 brd 206.124.146.255 scope global eth0
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inet 206.124.146.178/24 brd 206.124.146.255 scope global secondary eth0:0
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[root@gateway root]# </programlisting>
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<para><note><para>One <emphasis role="bold">cannot</emphasis> type
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"ip addr show dev eth0:0" because "eth0:0" is a label
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for a particular address rather than a device name.</para><programlisting>[root@gateway root]# ip addr show dev eth0:0
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Device "eth0:0" does not exist.
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[root@gateway root]#</programlisting></note></para>
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</example>
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<para>The iptables program doesn't support virtual interfaces in
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either it's "-i" or "-o" command options; as a
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consequence, Shorewall does not allow them to be used in the
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/etc/shorewall/interfaces file or anywhere else except as described in the
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discussion below.</para>
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</section>
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<section>
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<title>Adding Addresses to Interfaces</title>
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<para>Most distributions have a facility for adding additional addresses
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to interfaces. If you have already used your distribution's capability
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to add your required addresses, you can skip this section.</para>
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<para>Shorewall provides facilities for automatically adding addresses to
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interfaces as described in the following section. It is also easy to add
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them yourself using the <emphasis role="bold">ip</emphasis> utility. The
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above alias was added using:</para>
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<programlisting>ip addr add 206.124.146.178/24 brd 206.124.146.255 dev eth0 label eth0:0</programlisting>
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<para>You probably want to arrange to add these addresses when the device
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is started rather than placing commands like the above in one of the
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Shorewall extension scripts. For example, on RedHat systems, you can place
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the commands in /sbin/ifup-local:</para>
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<programlisting>#!/bin/sh
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case $1 in
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eth0)
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/sbin/ip addr add 206.124.146.177 dev eth0 label eth0:0
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;;
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esac</programlisting>
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<para>RedHat systems also allow adding such aliases from the network
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administration GUI (which only works well if you have a graphical
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environment on your firewall).</para>
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</section>
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<section>
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<title>So how do I handle more than one address on an interface?</title>
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<para>The answer depends on what you are trying to do with the interfaces.
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In the sub-sections that follow, we'll take a look at common
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scenarios.</para>
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<section>
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<title>Separate Rules</title>
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<para>If you need to make a rule for traffic to/from the firewall itself
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that only applies to a particular IP address, simply qualify the $FW
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zone with the IP address.</para>
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<example>
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<title>allow SSH from net to eth0:0 above</title>
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<para><table><title>/etc/shorewall/rules</title><tgroup cols="7"><thead><row><entry
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align="center">ACTION</entry><entry align="center">SOURCE</entry><entry
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align="center">DESTINATION</entry><entry align="center">PROTOCOL</entry><entry
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align="center">PORT(S)</entry><entry align="center">SOURCE PORT(S)</entry><entry
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align="center">ORIGINAL DESTINATION</entry></row></thead><tbody><row><entry>ACCEPT</entry><entry>net</entry><entry>$FW:206.124.146.178</entry><entry>tcp</entry><entry>22</entry><entry></entry><entry></entry></row></tbody></tgroup></table></para>
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</example>
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</section>
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<section>
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<title>DNAT</title>
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<para>Suppose that I had set up eth0:0 as above and I wanted to port
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forward from that virtual interface to a web server running in my local
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zone at 192.168.1.3. That is accomplised by a single rule in the
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/etc/shorewall/rules file:</para>
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<table>
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<title>/etc/shorewall/rules</title>
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<tgroup cols="7">
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<thead>
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<row>
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<entry align="center">ACTION</entry>
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<entry align="center">SOURCE</entry>
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<entry align="center">DESTINATION</entry>
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<entry align="center">PROTOCOL</entry>
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<entry align="center">PORT(S)</entry>
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<entry align="center">SOURCE PORT(S)</entry>
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<entry align="center">ORIGINAL DESTINATION</entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry>DNAT</entry>
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<entry>net</entry>
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<entry>loc:192.168.1.3</entry>
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<entry>tcp</entry>
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<entry>80</entry>
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<entry>-</entry>
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<entry>206.124.146.178</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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</section>
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<section>
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<title>SNAT</title>
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<para>If you wanted to use eth0:0 as the IP address for outbound
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connections from your local zone (eth1), then in /etc/shorewall/masq:</para>
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<table>
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<title>/etc/shorewall/masq</title>
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<tgroup cols="3">
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<thead>
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<row>
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<entry align="center">INTERFACE</entry>
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<entry align="center">SUBNET</entry>
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<entry align="center">ADDRESS</entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry>eth0</entry>
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<entry>eth1</entry>
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<entry>206.124.146.178</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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<para>Shorewall can create the alias (additional address) for you if you
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set ADD_SNAT_ALIASES=Yes in /etc/shorewall/shorewall.conf. Beginning
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with Shorewall 1.3.14, Shorewall can actually create the "label"
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(virtual interface) so that you can see the created address using
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ifconfig. In addition to setting ADD_SNAT_ALIASES=Yes, you specify the
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virtual interface name in the INTERFACE column as follows:</para>
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<table>
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<title>/etc/shorewall/masq</title>
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<tgroup cols="3">
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<thead>
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<row>
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<entry align="center">INTERFACE</entry>
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<entry align="center">SUBNET</entry>
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<entry align="center">ADDRESS</entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry>eth0:0</entry>
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<entry>eth1</entry>
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<entry>206.124.146.178</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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<para>Shorewall can also set up SNAT to round-robin over a range of IP
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addresses. Do do that, you specify a range of IP addresses in the
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ADDRESS column. If you specify a label in the INTERFACE column,
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Shorewall will use that label for the first address of the range and
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will increment the label by one for each subsequent label.</para>
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<table>
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<title>/etc/shorewall/masq</title>
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<tgroup cols="3">
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<thead>
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<row>
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<entry align="center">INTERFACE</entry>
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<entry align="center">SUBNET</entry>
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<entry align="center">ADDRESS</entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry>eth0:0</entry>
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<entry>eth1</entry>
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<entry>206.124.146.178-206.124.146.180</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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<para>The above would create three IP addresses:</para>
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<programlisting>eth0:0 = 206.124.146.178
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eth0:1 = 206.124.146.179
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eth0:2 = 206.124.146.180</programlisting>
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</section>
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<section>
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<title>One-to-one NAT</title>
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<para>If you wanted to use one-to-one NAT to link eth0:0 with local
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address 192.168.1.3, you would have the following in /etc/shorewall/nat:<table><title>/etc/shorewall/nat</title><tgroup
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cols="5"><thead><row><entry align="center">EXTERNAL</entry><entry
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align="center">INTERFACE</entry><entry align="center">INTERNAL</entry><entry
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align="center">ALL INTERFACES</entry><entry align="center">LOCAL</entry></row></thead><tbody><row><entry>206.124.146.178</entry><entry>eth0</entry><entry>192.168.1.3</entry><entry>no</entry><entry>no</entry></row></tbody></tgroup></table></para>
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<para>Shorewall can create the alias (additional address) for you if you
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set ADD_IP_ALIASES=Yes in /etc/shorewall/shorewall.conf. Beginning with
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Shorewall 1.3.14, Shorewall can actually create the "label"
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(virtual interface) so that you can see the created address using
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ifconfig. In addition to setting ADD_IP_ALIASES=Yes, you specify the
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virtual interface name in the INTERFACE column as follows:</para>
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<table>
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<title>/etc/shorewall/nat</title>
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<tgroup cols="5">
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<thead>
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<row>
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<entry align="center">EXTERNAL</entry>
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<entry align="center">INTERFACE</entry>
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<entry align="center">INTERNAL</entry>
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<entry align="center">ALL INTERFACES</entry>
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<entry align="center">LOCAL</entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry>206.124.146.178</entry>
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<entry>eth0:0</entry>
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<entry>192.168.1.3</entry>
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<entry>no</entry>
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<entry>no</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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<para>In either case, to create rules that pertain only to this NAT
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pair, you simply qualify the local zone with the internal IP address.</para>
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<example>
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<title>You want to allow SSH from the net to 206.124.146.178 a.k.a.
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192.168.1.3.</title>
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<para><table><title>/etc/shorewall/rules</title><tgroup cols="7"><thead><row><entry
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align="center">ACTION</entry><entry align="center">SOURCE</entry><entry
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align="center">DESTINATION</entry><entry align="center">PROTOCOL</entry><entry
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align="center">PORT(S)</entry><entry align="center">SOURCE PORT(S)</entry><entry
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align="center">ORIGINAL DESTINATION</entry></row></thead><tbody><row><entry>ACCEPT</entry><entry>net</entry><entry>loc:192.168.1.3</entry><entry>tcp</entry><entry>22</entry><entry></entry><entry></entry></row></tbody></tgroup></table></para>
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</example>
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</section>
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<section>
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<title>MULTIPLE SUBNETS</title>
|
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<para>Sometimes multiple IP addresses are used because there are
|
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multiple subnetworks configured on a LAN segment. This technique does
|
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|
not provide for any security between the subnetworks if the users of the
|
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|
|
systems have administrative privileges because in that case, the users
|
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|
can simply manipulate their system's routing table to bypass your
|
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|
firewall/router. Nevertheless, there are cases where you simply want to
|
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consider the LAN segment itself as a zone and allow your firewall/router
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to route between the two subnetworks.</para>
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<example>
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<title>Local interface eth1 interfaces to 192.168.1.0/24 and
|
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192.168.20.0/24. The primary IP address of eth1 is 192.168.1.254 and
|
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eth1:0 is 192.168.20.254. You want to simply route all requests
|
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|
between the two subnetworks.</title>
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<variablelist>
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<varlistentry>
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<term>If you are running Shorewall 1.4.1 or Later</term>
|
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|
||
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<listitem>
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<para>In /etc/shorewall/interfaces:</para>
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|
||
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<table>
|
||
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<title>/etc/shorewall/interfaces</title>
|
||
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||
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<tgroup cols="4">
|
||
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<thead>
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||
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<row>
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<entry align="center">ZONE</entry>
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||
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<entry align="center">INTERFACE</entry>
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<entry align="center">BROADCAST</entry>
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||
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<entry align="center">OPTIONS</entry>
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||
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</row>
|
||
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</thead>
|
||
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|
||
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<tbody>
|
||
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|
<row>
|
||
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<entry>-</entry>
|
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<entry>eth1</entry>
|
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<entry>192.168.1.255,192.168.20.255</entry>
|
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|
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<entry></entry>
|
||
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</row>
|
||
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|
</tbody>
|
||
|
|
</tgroup>
|
||
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|
</table>
|
||
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|
|
||
|
|
<para>In /etc/shorewall/hosts:</para>
|
||
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|
|
||
|
|
<table>
|
||
|
|
<title>/etc/shorewall/hosts</title>
|
||
|
|
|
||
|
|
<tgroup cols="3">
|
||
|
|
<thead>
|
||
|
|
<row>
|
||
|
|
<entry align="center">ZONE</entry>
|
||
|
|
|
||
|
|
<entry align="center">HOSTS</entry>
|
||
|
|
|
||
|
|
<entry align="center">OPTIONS</entry>
|
||
|
|
</row>
|
||
|
|
</thead>
|
||
|
|
|
||
|
|
<tbody>
|
||
|
|
<row>
|
||
|
|
<entry>loc</entry>
|
||
|
|
|
||
|
|
<entry>eth1:192.168.1.0/24</entry>
|
||
|
|
|
||
|
|
<entry></entry>
|
||
|
|
</row>
|
||
|
|
|
||
|
|
<row>
|
||
|
|
<entry>loc</entry>
|
||
|
|
|
||
|
|
<entry>eth1:192.168.20.0/24</entry>
|
||
|
|
|
||
|
|
<entry></entry>
|
||
|
|
</row>
|
||
|
|
</tbody>
|
||
|
|
</tgroup>
|
||
|
|
</table>
|
||
|
|
|
||
|
|
<note>
|
||
|
|
<para>You do NOT need any entry in /etc/shorewall/policy as
|
||
|
|
Shorewall 1.4.1 and later releases default to allowing
|
||
|
|
intra-zone traffic.</para>
|
||
|
|
</note>
|
||
|
|
</listitem>
|
||
|
|
</varlistentry>
|
||
|
|
|
||
|
|
<varlistentry>
|
||
|
|
<term>If you are running Shorewall 1.4.0 or earlier</term>
|
||
|
|
|
||
|
|
<listitem>
|
||
|
|
<para>In /etc/shorewall/interfaces:</para>
|
||
|
|
|
||
|
|
<table>
|
||
|
|
<title>/etc/shorewall/interfaces</title>
|
||
|
|
|
||
|
|
<tgroup cols="4">
|
||
|
|
<thead>
|
||
|
|
<row>
|
||
|
|
<entry align="center">ZONE</entry>
|
||
|
|
|
||
|
|
<entry align="center">INTERFACE</entry>
|
||
|
|
|
||
|
|
<entry align="center">BROADCAST</entry>
|
||
|
|
|
||
|
|
<entry align="center">OPTIONS</entry>
|
||
|
|
</row>
|
||
|
|
</thead>
|
||
|
|
|
||
|
|
<tbody>
|
||
|
|
<row>
|
||
|
|
<entry>-</entry>
|
||
|
|
|
||
|
|
<entry>eth1</entry>
|
||
|
|
|
||
|
|
<entry>192.168.1.255,192.168.20.255</entry>
|
||
|
|
|
||
|
|
<entry><xref linkend="multiple_subnets-ex1-n1" /></entry>
|
||
|
|
</row>
|
||
|
|
</tbody>
|
||
|
|
</tgroup>
|
||
|
|
</table>
|
||
|
|
|
||
|
|
<note id="multiple_subnets-ex1-n1">
|
||
|
|
<para> If you are running Shorewall 1.3.10 or earlier then you
|
||
|
|
must specify the <emphasis role="bold">multi</emphasis>
|
||
|
|
option.</para>
|
||
|
|
</note>
|
||
|
|
|
||
|
|
<para>In /etc/shorewall/policy:</para>
|
||
|
|
|
||
|
|
<table>
|
||
|
|
<title>/etc/shorewall/policy</title>
|
||
|
|
|
||
|
|
<tgroup cols="5">
|
||
|
|
<thead>
|
||
|
|
<row>
|
||
|
|
<entry align="center">SOURCE</entry>
|
||
|
|
|
||
|
|
<entry align="center">DESTINATION</entry>
|
||
|
|
|
||
|
|
<entry align="center">POLICY</entry>
|
||
|
|
|
||
|
|
<entry align="center">LOG LEVEL</entry>
|
||
|
|
|
||
|
|
<entry align="center">BURST:LIMIT</entry>
|
||
|
|
</row>
|
||
|
|
</thead>
|
||
|
|
|
||
|
|
<tbody>
|
||
|
|
<row>
|
||
|
|
<entry>loc</entry>
|
||
|
|
|
||
|
|
<entry>loc</entry>
|
||
|
|
|
||
|
|
<entry>ACCEPT</entry>
|
||
|
|
|
||
|
|
<entry></entry>
|
||
|
|
|
||
|
|
<entry></entry>
|
||
|
|
</row>
|
||
|
|
</tbody>
|
||
|
|
</tgroup>
|
||
|
|
</table>
|
||
|
|
</listitem>
|
||
|
|
</varlistentry>
|
||
|
|
</variablelist>
|
||
|
|
</example>
|
||
|
|
|
||
|
|
<example>
|
||
|
|
<title>Local interface eth1 interfaces to 192.168.1.0/24 and
|
||
|
|
192.168.20.0/24. The primary IP address of eth1 is 192.168.1.254 and
|
||
|
|
eth1:0 is 192.168.20.254. You want to make these subnetworks into
|
||
|
|
separate zones and control the access between them (the users of the
|
||
|
|
systems do not have administrative privileges).</title>
|
||
|
|
|
||
|
|
<para>In /etc/shorewall/zones:<table><title>etc/shorewall/zones</title><tgroup
|
||
|
|
cols="3"><thead><row><entry align="center">ZONE</entry><entry
|
||
|
|
align="center">DISPLAY</entry><entry align="center">DESCRIPTION</entry></row></thead><tbody><row><entry>loc</entry><entry>Local</entry><entry>Local
|
||
|
|
Zone 1</entry></row><row><entry>loc2</entry><entry>Local2</entry><entry>Local
|
||
|
|
Zone 2</entry></row></tbody></tgroup></table></para>
|
||
|
|
|
||
|
|
<para>In /etc/shorewall/interfaces:<table><title>/etc/shorewall/interfaces</title><tgroup
|
||
|
|
cols="4"><thead><row><entry align="center">ZONE</entry><entry
|
||
|
|
align="center">INTERFACE</entry><entry align="center">BROADCAST</entry><entry
|
||
|
|
align="center">OPTIONS</entry></row></thead><tbody><row><entry>-</entry><entry>eth1</entry><entry>192.168.1.255,192.168.20.255</entry><entry><xref
|
||
|
|
linkend="multiple_subnets-ex2-n1" /></entry></row></tbody></tgroup></table><note
|
||
|
|
id="multiple_subnets-ex2-n1"><para> If you are running Shorewall
|
||
|
|
1.3.10 or earlier then you must specify the <emphasis role="bold">multi</emphasis>
|
||
|
|
option.</para></note></para>
|
||
|
|
|
||
|
|
<para>In /etc/shorewall/hosts:<table><title>/etc/shorewall/hosts</title><tgroup
|
||
|
|
cols="3"><thead><row><entry align="center">ZONE</entry><entry
|
||
|
|
align="center">HOSTS</entry><entry align="center">OPTIONS</entry></row></thead><tbody><row><entry>loc</entry><entry>eth1:192.168.1.0/24</entry><entry></entry></row><row><entry>loc2</entry><entry>eth1:192.168.20.0/24</entry><entry></entry></row></tbody></tgroup></table></para>
|
||
|
|
|
||
|
|
<para>In /etc/shorewall/rules, simply specify ACCEPT rules for the
|
||
|
|
traffic that you want to permit.</para>
|
||
|
|
</example>
|
||
|
|
</section>
|
||
|
|
</section>
|
||
|
|
</article>
|