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207 lines
7.3 KiB
XML
207 lines
7.3 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.4//EN"
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"http://www.oasis-open.org/docbook/xml/4.4/docbookx.dtd">
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<article>
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<!--$Id$-->
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<articleinfo>
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<title>Simple way to set up Split DNS</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><?dbtimestamp format="Y/m/d"?></pubdate>
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<copyright>
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<year>2008</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
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<quote><ulink url="GnuCopyright.htm">GNU Free Documentation
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License</ulink></quote>.</para>
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</legalnotice>
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</articleinfo>
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<section>
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<title>What is Split DNS</title>
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<para><firstterm>Split DNS</firstterm> is simply a configuration in which
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the IP address to which a DNS name resolves is dependent on the location
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of the client. It is most often used in a NAT environment to insure that
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local clients resolve the DNS names of local servers to their RFC 1918
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addresses while external clients resolve the same server names to their
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public counterparts.</para>
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</section>
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<section>
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<title>Why would I want to use Split DNS?</title>
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<para>See <ulink url="FAQ.htm#faq2">Shorewall FAQ 2</ulink>.</para>
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</section>
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<section>
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<title>Setting up Split DNS</title>
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<para>Setting up Split DNS is extremely simple:</para>
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<orderedlist>
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<listitem>
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<para>Be sure that your firewall/router can resolve external DNS
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names.</para>
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</listitem>
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<listitem>
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<para>Install the <emphasis role="bold">dnsmasq</emphasis> package
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(<ulink
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url="http://www.thekelleys.org.uk/dnsmasq/doc.html">http://www.thekelleys.org.uk/dnsmasq/doc.htm</ulink>l)
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and arrange for it to start at boot time. There are many dnsmasq
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HOWTOs on the Internet.</para>
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</listitem>
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<listitem>
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<para>Add your local hosts to <filename>/etc/hosts</filename> on the
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firewall/router using their local RFC 1918 addresses. Here's an
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example:<programlisting>#
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# hosts This file describes a number of hostname-to-address
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# mappings for the TCP/IP subsystem. It is mostly
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# used at boot time, when no name servers are running.
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# On small systems, this file can be used instead of a
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# "named" name server.
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# Syntax:
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#
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# IP-Address Full-Qualified-Hostname Short-Hostname
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#
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127.0.0.1 localhost
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<emphasis role="bold">172.20.0.1 openvpn.shorewall.net openvpn
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172.20.0.2 vpn02.shorewall.net vpn02
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172.20.0.3 vpn03.shorewall.net vpn03
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172.20.0.4 vpn04.shorewall.net vpn04
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172.20.0.5 vpn05.shorewall.net vpn05
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172.20.0.6 vpn06.shorewall.net vpn06
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172.20.0.7 vpn07.shorewall.net vpn07
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172.20.0.8 vpn08.shorewall.net vpn08
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172.20.0.9 vpn09.shorewall.net vpn09
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172.20.0.10 vpn10.shorewall.net vpn10
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172.20.0.11 vpn11.shorewall.net vpn11
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172.20.0.12 vpn12.shorewall.net vpn12
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172.20.0.13 vpn13.shorewall.net vpn13
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172.20.0.14 vpn14.shorewall.net vpn14
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172.20.0.15 vpn15.shorewall.net vpn15
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172.20.0.16 vpn16.shorewall.net vpn16
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172.20.1.1 linksys.shorewall.net linksys
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172.20.1.100 hp8500.shorewall.net hp8500
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172.20.1.102 ursa.shorewall.net ursa
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172.20.1.105 tarry.shorewall.net tarry
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172.20.1.107 teastep.shorewall.net teastep
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172.20.1.109 hpmini.shorewall.net hpmini
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172.20.1.130 lanursa.shorewall.net lanursa
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172.20.1.131 wookie.shorewall.net wookie
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172.20.1.132 tipper.shorewall.net tipper
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172.20.1.133 nasty.shorewall.net nasty
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172.20.1.134 ursadog.shorewall.net ursadog
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172.20.1.135 opensuse.shorewall.net opensuse
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172.20.1.136 centos.shorewall.net centos
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172.20.1.137 fedora.shorewall.net fedora
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172.20.1.138 debian.shorewall.net debian
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172.20.1.139 archlinux.shorewall.net archlinux
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172.20.1.140 foobar.shorewall.net foobar
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172.20.1.141 deblap.shorewall.net deblap
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172.20.1.254 firewall.shorewall.net firewall
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206.124.146.254 blarg.shorewall.net blarg
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</emphasis>
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# special IPv6 addresses
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::1 localhost ipv6-localhost ipv6-loopback
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fe00::0 ipv6-localnet
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ff00::0 ipv6-mcastprefix
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ff02::1 ipv6-allnodes
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ff02::2 ipv6-allrouters
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ff02::3 ipv6-allhosts
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<emphasis role="bold">2002:ce7c:92b4::1 gateway6.shorewall.net gateway6
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2002:ce7c:92b4:1::2 mail6.shorewall.net mail6
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2002:ce7c:92b4:1::2 lists6.shorewall.net lists6
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2002:ce7c:92b4:2::2 server6.shorewall.net server6</emphasis>
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</programlisting></para>
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</listitem>
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<listitem>
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<para> If your local hosts are configured using DHCP, that is a simple
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one-line change to the DHCP configuration.</para>
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</listitem>
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</orderedlist>
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<para><emphasis role="bold">And that's it!</emphasis> Your local clients
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will resolve those names in the firewall/router's
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<filename>/etc/hosts</filename> file as defined in that file. All other
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names will be resolved using the firewall/router's Name Server as defined
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in <filename>/etc/resolv.conf</filename>.</para>
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<para>Example:</para>
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<para>From an Internet Host:<programlisting>gateway:~ # host linksys.shorewall.net
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linksys.shorewall.net has address 206.124.146.180
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gateway:~ # </programlisting></para>
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<para>From Tipper (192.168.1.132):<programlisting>teastep@tipper:~$ host linksys
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linksys.shorewall.net has address 172.20.1.1
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teastep@tipper:~$ </programlisting></para>
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<para>As a bonus, dnsmasq can also act as a DHCP server. Here are some
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excerpts from the corresponding /etc/dnsmasq.conf:</para>
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<programlisting>interface=eth1
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dhcp-range=172.20.1.210,172.20.1.219,24h
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dhcp-host=00:11:85:89:da:9b,172.20.1.220
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dhcp-host=00:1A:73:DB:8C:35,172.20.1.102
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dhcp-host=00:25:B3:9F:5B:FD,172.20.1.100
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dhcp-host=00:1F:E1:07:53:CA,172.20.1.105
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dhcp-host=00:1F:29:7B:04:04,172.20.1.107
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dhcp-host=00:24:2b:59:96:e2,172.20.1.109
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dhcp-host=00:1B:24:CB:2B:CC,172.20.1.130
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dhcp-host=00:21:5a:22:ac:e0,172.20.1.131
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dhcp-host=08:00:27:B1:46:a9,172.20.1.132
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dhcp-host=08:00:27:31:45:83,172.20.1.133
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dhcp-host=08:00:27:28:64:50,172.20.1.134
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dhcp-host=08:00:27:4b:38:88,172.20.1.135
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dhcp-host=08:00:27:f6:4d:65,172.20.1.136
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dhcp-host=08:00:27:dc:cd:94,172.20.1.137
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dhcp-host=08:00:27:0f:d3:8f,172.20.1.138
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dhcp-host=08:00:27:42:9c:01,172.20.1.139
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dhcp-host=08:00:27:5a:6c:d8,172.20.1.140
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dhcp-host=08:00:27:da:96:78,172.20.1.141
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dhcp-option=19,0 # option ip-forwarding off
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dhcp-option=44,0.0.0.0 # set netbios-over-TCP/IP nameserver(s) aka WINS server(s)
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dhcp-option=45,0.0.0.0 # netbios datagram distribution server
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dhcp-option=46,8 # netbios node type
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dhcp-option=47 # empty netbios scope.
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dhcp-option=option:domain-search,shorewall.net
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</programlisting>
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</section>
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</article>
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