sub interfaces

[imported_RedHat]

Hi,

What would be the purpose of having multiple sub interfaces on an ethernet adapter? For instance, eth0:1, eth0:2, etc

I'm thinking this is if you own multiple IP addresses, you can assign an IP to a virtual device such as eth0:1. Am I right?

[gorn]

yeah you can do more than one ip. so let's say I'm running a webserver on 192.168.1.1 and a mail server on 192.168.1.2 and i need to take the webserver down for a little while. i could have the mail server take 192.168.1.1 but keep it's 192.168.1.2 and just have a dummy webpage that explains it being down. this way i don't need another nic.

or it can be used to sniff someone elses traffic through a switch, but arpspoof is a cleaner method of doing this.

[edit:moving to networking]

[imported_RedHat]

Don't most shell companies have a sub interface for each public ip address they have when setting up vhosts? BTW, sorry for posting this in the wrong forum.

[gorn]

no problem for posting in the wrong forum.

i'm not sure what you are asking. you mean when a web hosting company offers a bunch of different sites on one computer? this is done not by ip but by apache. (if i go to www.foo.com first i resolve to ip and that's 1.2.3.4 then i connect and send my request but also a Host: www.foo.com. then it knows foo.com is what i want. then I go to www.bar.com with ip 1.2.3.4 and i send Host: www.bar.com and it knows i want bar.com)