Multihomed NICs under Linux

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From https://www.redhat.com/archives/redhat-install-list/2002-April/msg00578.html 

   * From: Rick Stevens <rstevens vitalstream com>
   * To: redhat-install-list redhat com
   * Subject: Re: Problems with having multiple IPs on Single NIC
   * Date: Tue, 23 Apr 2002 10:00:46 -0700

Kevin Bramblett wrote: 

   I appreciate the pointer, but it looks like I wasn't clear enough with my
   request.  My apologies.  I need Linux to multihome IPs, to have multiple IPs
   on a single IP, like IP Aliasing does.  My problem is my Linux box is
   replacing a W2K box that multihomed several IPs on a single NIC.  I've been
   able to duplicate all of the functions it did except this multihome deal.
   IP Masquerading for use on the Internet isn't quite what I need either.
   Supposedly IP Aliasing was replaced by a firewall item, but I cannot figure
   out what it is in order to research it.



   Again, I appreciate all pointers, no matter how insignificant they may seem!


Aliases for ethernet ports on Linux use a nomenclature like "eth0:x". The "eth0" is the primary interface, the ":x" part is the alias with 0 being the first alias, 1 the second, etc. You treat these aliases just like the primary.


One way to set them up is to add lines similar to: 

ifconfig eth0:0 first-alias-ip netmask netmask-you-want
ifconfig eth0:1 second-alias-ip netmask netmask-you-want


in the "/etc/rc.d/rc.local" file. For example: 

ifconfig eth0:0 192.168.3.4 netmask 255.255.255.0
ifconfig eth0:1 10.24.19.45 netmask 255.0.0.0


would add two aliases to the first ethernet card. The first alias would be 192.168.3.4 with a /24 netmask (class C), the second would be 10.24.19.45 with a /8 netmask (class A).


You can add aliases to each physical port you have such as "eth1:0" and so on. I'm not certain, but looking briefly at the startup scripts, you _should_ be able to create appropriately named files in "/etc/sysconfig/network-scripts", thereby thereby putting in the config stuff where Linux normally expects it to be and without adding the stuff to /etc/rc.d/rc.local. I haven't tried that, but it should work.

- Rick Stevens, SSE, VitalStream, Inc. rstevens vitalstream com - - 949-743-2010 (Voice) http://www.vitalstream.com - - - - BASIC is the Computer Science version of `Scientific Creationism' -

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