246 lines
13 KiB
Plaintext
246 lines
13 KiB
Plaintext
Setting up IP Aliasing on A Linux Machine Mini-HOWTO
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Harish Pillay
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h.pillay@ieee.org
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Joy Yokley - Converted document from HTML to DocBook v4.1 (SGML)
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2001-01-23
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Revision History
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Revision 1.2 2001-01-26 Revised by: JEY
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Revision 1.1 2001-01-24 Revised by: JEY
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Revision 1.0 1997-01-13 Revised by: HP
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This is a cookbook recipe on how to set up and run IP aliasing on a Linux box
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and how to set up the machine to receive e-mail on the aliased IP addresses.
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-----------------------------------------------------------------------------
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Table of Contents
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1. My Setup
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2. Commands
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3. Troubleshooting: Questions and Answers
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3.1. Question: How can I keep the settings through a reboot?
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3.2. Question: How do I set up the IP aliased machine to receive e-mail
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on the various aliased IP addresses (on a machine using sendmail)?
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4. Acknowledgements
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-----------------------------------------------------------------------------
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1. My Setup
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* IP Alias is standard in kernels 2.0.x and 2.2.x, and available as a
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compile-time option in 2.4.x (IP Alias has been deprecated in 2.4.x and
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replaced by a more powerful firewalling mechanism.)
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* IP Alias compiled as a loadable module. You would have indicated in the
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"make config" command to make your kernel, that you want the IP Masq to
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be compiled as a (M)odule. Check the Modules HOW-TO (if that exists) or
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check the info in /usr/src/linux/Documentation/modules.txt.
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* I have to support 2 additional IPs over and above the IP already
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allocated to me.
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* A D-Link DE620 pocket adapter (not important, works with any Linux
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supported network adapter).
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-----------------------------------------------------------------------------
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2. Commands
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1. Load the IP Alias module (you can skip this step if you compiled the
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module into the kernel):
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/sbin/insmod /lib/modules/`uname -r`/ipv4/ip_alias.o
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2. Setup the loopback, eth0, and all the IP addresses beginning with the
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main IP address for the eth0 interface:
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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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172.16.3.1 is the main IP address, while .10 and .100 are the aliases.
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The magic is the eth0:x where x=0,1,2,...n for the different IP
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addresses. The main IP address does not need to be aliased.
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3. Setup the routes. First route the loopback, then the net, and finally,
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the various IP addresses starting with the default (originally allocated)
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one:
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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
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That's it.
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In the example IP address above, I am using the Private IP addresses (RFC
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1918) for illustrative purposes. Substitute them with your own official or
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private IP addresses.
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The example shows only 3 IP addresses. The max is defined to be 256 in /usr/
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include/linux/net_alias.h. 256 IP addresses on ONE card is a lot :-)!
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Here's what my /sbin/ifconfig looks like:
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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
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And /proc/net/aliases:
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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
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And /proc/net/alias_types:
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type name n_attach
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2 ip 2
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Of course, the stuff in /proc/net was created by the ifconfig command and not
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by hand!
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-----------------------------------------------------------------------------
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3. Troubleshooting: Questions and Answers
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3.1. Question: How can I keep the settings through a reboot?
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Answer: Whether you are using BSD-style or SysV-style (Redhat?? for example)
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init, you can always include it in /etc/rc.d/rc.local. Here's what I have on
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my SysV init system (Redhat?? 3.0.3 and 4.0):
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My /etc/rc.d/rc.local: (edited to show the relevant portions)
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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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#
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-----------------------------------------------------------------------------
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3.2. Question: How do I set up the IP aliased machine to receive e-mail on
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the various aliased IP addresses (on a machine using sendmail)?
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Answer: Create (if it doesn't already exist) a file called, /etc/
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mynames.cw,for example. The file does not have to be this exact name nor in
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the /etc directory.
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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.
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The /etc/mynames.cw might look like this:
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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
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In your sendmail.cf file, where it defines a file class macro Fw, add the
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following:
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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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That should do it. Test out the new setting by invoking sendmail in test
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mode. The following is an example:
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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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>
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Notice when I tested me@4.5.6.7, it delivered the mail to the local machine,
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while me@4.5.6.8 was handed off to the smtp mailer. That is the correct
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response.
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You are all set now.
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-----------------------------------------------------------------------------
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4. Acknowledgements
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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.
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Kudos to the ace programmers!
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If you find this document useful or have suggestions on improvements, email
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me at <[mailto:h.pillay@ieee.org] h.pillay@ieee.org>.
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Enjoy.
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For additional information on networking, you may want to consult the [http:/
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/www.linuxdoc.org/HOWTO/Networking-Overview-HOWTO.html] The Linux Networking
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Overview HOWTO.
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