Sharing internet connection by using a wireless modem

Question

I have one Ethernet cable and one IP address for per PC at work. I need to use only this IP address and DNS to connect internet. Now I have bought a new laptop and I want to connect it to the internet too, but as I said the connection is wired and only one PC can connect with one IP address.

I had an old wireless modem and I want to turn it into an AP. I disabled my old modem's DHPC, changed WAN mode to routing, connected my eEhernet cable to old modem instead of computer and using this modem as an AP, it works well.

Now I have a wireless internet but the problem is that I still have only one IP address. Thus I can not use internet at the same on both computers.

Is there a way to avoid IP address conflicts issues?
Can I give this IP to the modem instead of computers and modem behaves like computer or something like this?

p.s: sharing internet with ICS is not solution. I need a long term solution. Sorry about my English.

Answer 1

I'm no expert, but shouldn't you have DHCP enabled on your old modem so your desktop and laptop receive IP addresses from it? Think about it like your home:

Cable Modem (only assigns one IP) --> Router (which assigns IP's to devices connected to it - Cable Modem can't see any devices past your router)

Work network (only assigns one IP) --> old modem (which assigns IP's to devices connected to it - Work network can't see any devices past your old modem)

Answer 2

There are at least two ways to make this work:

1. Ask for a second IP. That way your original computer and the laptop can get their own proper IP and have full access to the Internet.
2. Or use NAT. NAT is a somewhat ugly kludge where you give the externally routable IP to the router/modem and where you use a set of different IPs internally. This breaks quite a few features which normally work. E.g. you no longer can reach your computers from the outside. But it will work.