mirror of https://github.com/tLDP/LDP
246 lines
11 KiB
Plaintext
246 lines
11 KiB
Plaintext
<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook V4.1//EN">
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<article ID="IPaliasing">
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<articleinfo>
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<title>Setting up IP Aliasing on A Linux Machine Mini-HOWTO</title>
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<author>
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<firstname>Harish</firstname>
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<surname>Pillay</surname>
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<affiliation>
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<address> <email><ulink URL="mailto:h.pillay@ieee.org">h.pillay@ieee.org</ulink></email> </address>
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</affiliation>
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</author>
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<abstract>
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<para>This is a cookbook recipe on how to set up and run IP aliasing on a Linux
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box and how to set up the machine to receive e-mail
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on the aliased IP addresses.</para>
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</abstract>
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<pubdate>2001-01-23</pubdate>
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<revhistory>
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<revision>
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<revnumber>1.2</revnumber>
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<date>2001-01-26</date>
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<authorinitials>JEY</authorinitials>
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</revision>
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<revision>
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<revnumber>1.1</revnumber>
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<date>2001-01-24</date>
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<authorinitials>JEY</authorinitials>
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</revision>
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<revision>
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<revnumber>1.0</revnumber>
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<date>1997-01-13</date>
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<authorinitials>HP</authorinitials>
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</revision>
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</revhistory>
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<othercredit role="converter">
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<firstname>Joy</firstname>
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<surname>Yokley</surname>
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<contrib>Converted document from HTML to DocBook v4.1 (SGML)</contrib>
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</othercredit>
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</articleinfo>
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<sect1 ID="MySetup">
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<title>My Setup</title>
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<itemizedlist>
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<listitem><para>IP Alias is standard in kernels 2.0.x and 2.2.x, and available as a compile-time option in 2.4.x
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(IP Alias has been deprecated in 2.4.x and replaced by a more powerful firewalling mechanism.)
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</para></listitem>
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<listitem><para>IP Alias compiled as a loadable module. You would have indicated in
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the "make config" command to make your kernel, that you want the IP
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Masq to be compiled as a (M)odule. Check the Modules HOW-TO (if that
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exists) or check the info in <filename>/usr/src/linux/Documentation/modules.txt.</filename></para></listitem>
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<listitem><para>I have to support 2 additional IPs over and above the IP already
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allocated to me.</para></listitem>
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<listitem><para>A D-Link DE620 pocket adapter (not important, works with any Linux
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supported network adapter).</para></listitem>
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</itemizedlist>
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</sect1>
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<sect1 ID="Commands">
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<title>Commands</title>
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<orderedlist>
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<listitem><para>Load the IP Alias module (you can skip this step if you compiled
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the module into the kernel):</para>
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<screen>/sbin/insmod /lib/modules/`uname -r`/ipv4/ip_alias.o</screen>
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</listitem>
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<listitem><para>Setup the loopback, eth0, and all the IP addresses beginning with the
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main IP address for the eth0 interface:</para>
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<screen>
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/sbin/ifconfig lo 127.0.0.1
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/sbin/ifconfig eth0 up
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/sbin/ifconfig eth0 172.16.3.1
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/sbin/ifconfig eth0:0 172.16.3.10
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/sbin/ifconfig eth0:1 172.16.3.100</screen>
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<para>172.16.3.1 is the main IP address, while .10 and .100 are the aliases. The
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magic is the eth0:x where x=0,1,2,...n for the different IP addresses. The
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main IP address does not need to be aliased.</para></listitem>
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<listitem><para>Setup the routes. First route the loopback, then the net, and
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finally, the various IP addresses starting with the default (originally
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allocated) one:</para>
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<screen>
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/sbin/route add -net 127.0.0.0
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/sbin/route add -net 172.16.3.0 dev eth0
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/sbin/route add -host 172.16.3.1 dev eth0
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/sbin/route add -host 172.16.3.10 dev eth0:0
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/sbin/route add -host 172.16.3.100 dev eth0:1
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/sbin/route add default gw 172.16.3.200</screen>
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<para>That's it.</para></listitem>
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</orderedlist>
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<para>In the example IP address above, I am using the Private IP addresses (RFC 1918) for
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illustrative purposes. Substitute them with your own official or private IP
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addresses.</para>
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<para>The example shows only 3 IP addresses. The max is defined to be 256 in
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<filename>/usr/include/linux/net_alias.h.</filename> 256 IP addresses on ONE card is a lot :-)!</para>
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<para>Here's what my <filename>/sbin/ifconfig</filename> looks like:</para>
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<programlisting>
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lo Link encap:Local Loopback
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inet addr:127.0.0.1 Bcast:127.255.255.255 Mask:255.0.0.0
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UP BROADCAST LOOPBACK RUNNING MTU:3584 Metric:1
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RX packets:5088 errors:0 dropped:0 overruns:0
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TX packets:5088 errors:0 dropped:0 overruns:0
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eth0 Link encap:10Mbps Ethernet HWaddr 00:8E:B8:83:19:20
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inet addr:172.16.3.1 Bcast:172.16.3.255 Mask:255.255.255.0
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UP BROADCAST RUNNING PROMISC MULTICAST MTU:1500 Metric:1
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RX packets:334036 errors:0 dropped:0 overruns:0
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TX packets:11605 errors:0 dropped:0 overruns:0
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Interrupt:7 Base address:0x378
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eth0:0 Link encap:10Mbps Ethernet HWaddr 00:8E:B8:83:19:20
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inet addr:172.16.3.10 Bcast:172.16.3.255 Mask:255.255.255.0
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UP BROADCAST RUNNING MTU:1500 Metric:1
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RX packets:0 errors:0 dropped:0 overruns:0
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TX packets:0 errors:0 dropped:0 overruns:0
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eth0:1 Link encap:10Mbps Ethernet HWaddr 00:8E:B8:83:19:20
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inet addr:172.16.3.100 Bcast:172.16.3.255 Mask:255.255.255.0
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UP BROADCAST RUNNING MTU:1500 Metric:1
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RX packets:1 errors:0 dropped:0 overruns:0
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TX packets:0 errors:0 dropped:0 overruns:0</programlisting>
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<para>And <filename>/proc/net/aliases</filename>:</para>
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<screen>
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device family address
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eth0:0 2 172.16.3.10
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eth0:1 2 172.16.3.100</screen>
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<para>And <filename>/proc/net/alias_types</filename>: </para>
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<programlisting>
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type name n_attach
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2 ip 2</programlisting>
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<para>Of course, the stuff in <filename>/proc/net</filename> was created by the <command>ifconfig</command> command and
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not by hand!</para>
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</sect1>
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<sect1 ID="Troubleshooting">
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<title>Troubleshooting: Questions and Answers</title>
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<sect2 ID="KeepSettings">
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<title>Question: How can I keep the settings through a reboot?</title>
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<para>Answer: Whether you are using BSD-style or SysV-style (Redhat&trade for example)
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<command>init</command>, you can always include it in <filename>/etc/rc.d/rc.local</filename>. Here's what I have
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on my SysV init system (Redhat&trade 3.0.3 and 4.0):</para>
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<para>My <filename>/etc/rc.d/rc.local</filename>: (edited to show the relevant portions)</para>
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<screen>
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#setting up IP alias interfaces
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echo "Setting 172.16.3.1, 172.16.3.10, 172.16.3.100 IP Aliases ..."
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/sbin/ifconfig lo 127.0.0.1
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/sbin/ifconfig eth0 up
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/sbin/ifconfig eth0 172.16.3.1
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/sbin/ifconfig eth0:0 172.16.3.10
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/sbin/ifconfig eth0:1 172.16.3.100
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#setting up the routes
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echo "Setting IP routes ..."
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/sbin/route add -net 127.0.0.0
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/sbin/route add -net 172.16.3.0 dev eth0
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/sbin/route add -host 172.16.3.1 eth0
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/sbin/route add -host 172.16.3.10 eth0:0
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/sbin/route add -host 172.16.3.100 eth0:1
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/sbin/route add default gw 172.16.3.200
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# </screen>
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</sect2>
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<sect2 ID="SettingUpMail">
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<title>Question: How do I set up the IP aliased machine to receive e-mail on the
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various aliased IP addresses (on a machine using sendmail)?</title>
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<para>Answer: Create (if it doesn't already exist) a file called,
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<filename>/etc/mynames.cw</filename>,for example. The file does not have to be this exact name nor in the
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<filename>/etc directory</filename>.</para>
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<para>In that file, place the official domain names of the aliased IP addresses. If
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these aliased IP addresses do not have a domain name, then you can place the
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IP address itself.</para>
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<para> The <filename>/etc/mynames.cw</filename> might look like this:</para>
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<programlisting>
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# /etc/mynames.cw - include all aliases for your machine here; # is a comment
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domain.one.net
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domain.two.com
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domain.three.org
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4.5.6.7 </programlisting>
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<para>In your <filename>sendmail.cf</filename> file, where it defines a file class macro Fw, add
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the following:</para>
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<screen>
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##################
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# local info #
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##################
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# file containing names of hosts for which we receive email
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Fw/etc/mynames.cw
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</screen>
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<para>That should do it. Test out the new setting by invoking sendmail in
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test mode. The following is an example:</para>
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<screen>
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ganymede$ /usr/lib/sendmail -bt
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ADDRESS TEST MODE (ruleset 3 NOT automatically invoked)
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Enter < ruleset> < address>
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> 0 me@4.5.6.7
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rewrite: ruleset 0 input: me @ 4 . 5 . 6 . 7
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rewrite: ruleset 98 input: me @ 4 . 5 . 6 . 7
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rewrite: ruleset 98 returns: me @ 4 . 5 . 6 . 7
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rewrite: ruleset 97 input: me @ 4 . 5 . 6 . 7
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rewrite: ruleset 3 input: me @ 4 . 5 . 6 . 7
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rewrite: ruleset 96 input: me < @ 4 . 5 . 6 . 7 >
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rewrite: ruleset 96 returns: me < @ 4 . 5 . 6 . 7 . >
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rewrite: ruleset 3 returns: me < @ 4 . 5 . 6 . 7 . >
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rewrite: ruleset 0 input: me < @ 4 . 5 . 6 . 7 . >
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rewrite: ruleset 98 input: me < @ 4 . 5 . 6 . 7 . >
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rewrite: ruleset 98 returns: me < @ 4 . 5 . 6 . 7 . >
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rewrite: ruleset 0 returns: $# local $: me
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rewrite: ruleset 97 returns: $# local $: me
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rewrite: ruleset 0 returns: $# local $: me
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> 0 me@4.5.6.8
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rewrite: ruleset 0 input: me @ 4 . 5 . 6 . 8
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rewrite: ruleset 98 input: me @ 4 . 5 . 6 . 8
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rewrite: ruleset 98 returns: me @ 4 . 5 . 6 . 8
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rewrite: ruleset 97 input: me @ 4 . 5 . 6 . 8
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rewrite: ruleset 3 input: me @ 4 . 5 . 6 . 8
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rewrite: ruleset 96 input: me < @ 4 . 5 . 6 . 8 >
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rewrite: ruleset 96 returns: me < @ 4 . 5 . 6 . 8 >
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rewrite: ruleset 3 returns: me < @ 4 . 5 . 6 . 8 >
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rewrite: ruleset 0 input: me < @ 4 . 5 . 6 . 8 >
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rewrite: ruleset 98 input: me < @ 4 . 5 . 6 . 8 >
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rewrite: ruleset 98 returns: me < @ 4 . 5 . 6 . 8 >
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rewrite: ruleset 95 input: < > me < @ 4 . 5 . 6 . 8 >
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rewrite: ruleset 95 returns: me < @ 4 . 5 . 6 . 8 >
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rewrite: ruleset 0 returns: $# smtp $@ 4 . 5 . 6 . 8 $: me < @ 4 . 5 . 6 . 8 >
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rewrite: ruleset 97 returns: $# smtp $@ 4 . 5 . 6 . 8 $: me < @ 4 . 5 . 6 . 8 >
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rewrite: ruleset 0 returns: $# smtp $@ 4 . 5 . 6 . 8 $: me < @ 4 . 5 . 6 . 8 >
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></screen>
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<para>Notice when I tested me@4.5.6.7, it delivered the mail to the local
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machine, while me@4.5.6.8 was handed off to the smtp mailer.
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That is the correct response.</para>
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<para>You are all set now.</para>
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</sect2>
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</sect1>
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<sect1 ID="Acknowledgements">
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<title>Acknowledgements</title>
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<para>Thanks to all those who have done this great work on Linux and IP Aliasing.
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And especially to Juan Jose Ciarlante for clarifying my questions.</para>
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<para>Kudos to the ace programmers!</para>
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<para>If you find this document useful or have suggestions on improvements, email me at <email><ulink URL="mailto:h.pillay@ieee.org">h.pillay@ieee.org</ulink></email>.</para>
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<para>Enjoy.</para>
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<para>For additional information on networking, you may want to consult the <ulink URL="http://www.linuxdoc.org/HOWTO/Networking-Overview-HOWTO.html">The Linux Networking Overview HOWTO</ulink>.</para>
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</sect1>
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</article>
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