AIX Tip of the Week

IP Aliasing

Audience: System Administration

Date: March 30, 2001

The following tip if from Bob Kelly, IBM Austin.

IP Aliasing allows a single network interface to have multiple IP addresses. One of the advantages of aliasing is the ability consolidate applications and web pages on one server without changing application code.

The commands to add/delete an IP alias are

To add an alias to your existing network adapter:
ifconfig en1 alias netmask

To delete an alias from your network adapter
ifconfig en1 delete

*For all you smitty folks, smitty inetalias will accomplish the same.

Important Notes: Sendmail can still be configured to receive mail to either address. It can be "told" to use the "firstwebsite" address, or you could use the "secondwebsite" address. To the outside world, it will appear that your network has two machines, "firstwebsite" and "secondwebsite", when actually they are one machine, with two TCP/IP addresses.

Be aware. There are known issues with AIX 4.3.3 gated and aliases. Gated was not designed to handle aliases implemented in the way AIX implement them. Gated will send a HELLO from each interface, which can confuse the routers.

Bruce Spencer,