I have a server with multiple IP addresses associated with it. I'm trying to run a node.js web server (which I do not want to run as root), using only one of those ip addresses (it would be very bad if the traffic from all the ip addresses were forwarded).

Through searching superuser, it looked like this could be possible with iptables:

How to setting up iptables for traffic fowarding on port 80 from specific sources

iptables -A PREROUTING -t nat -i eth0 -p tcp --dport 80 --source 212.333.111.222 -j REDIRECT --to-port 9020

However, I do not understand why eth0 is needed.

According to:

http://blog.softlayer.com/2011/iptables-tips-and-tricks-port-redirection/

this could be done with:

iptables -t nat -A PREROUTING -p tcp --dport 2525 -j REDIRECT --to-ports 25

What is the correct way of forwarding traffic from a single ip on port 80, lets say 111.111.111.111:80 to another port on the same server, lets say 111.111.111.111:8765?

thanks for your help!