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Set up multi-homed hosts

How and why you should set up multi-homed hosts.

Any computer with two or more network interface cards is considered to be a router in Unix unless you specify that that host is multi-homed. A multi-homed system is one that doesn't use routing protocols or forward IP packets. There are several applications in which multi-homed hosts are either valuable or essential. For example, in firewalls, multi-homing provides protocol isolation. Database servers can use multiple interfaces to provide a larger throughput to connected clients; and NFS servers can attach to more than one network to provide file access to more users.

Here's how to create a multi-homed host in Solaris:

  1. Install two or more network cards in your host, if necessary.
  2. As a superuser on the host, create an /etc/hostname interface file for each network interface.
  3. Enter the following: % touch /etc/notrouter.
  4. Finally reboot the host so that the startup script can identify the /etc/notrouter file and so that script suppresses the in.routed –s or in.rdisc –r.

Once the startup script has run, IP forwarding is disabled by any interface that is recognized by ipconfig, regardless of whether or not the script detects an /etc/gateways file.

Barrie Sosinsky is president of consulting company Sosinsky and Associates (Medfield MA). He has written extensively on a variety of computer topics. His company specializes in custom software (database and Web related), training and technical documentation.

This was last published in May 2003

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