hello,
1)If an organization has got real IP address then does that IP address is
assigned to Computer Host or Hw Router?
2)If that organiztion want to connect 5 LANs to that Real IP address Then what are possible ways to that?
3)Also Does that organization needs Hardware Router or Linux made as Router is working?
4) then where to install FTP server,Web server MAIL server that can be access from Outside world? Can they be installed in any Internal host behind Router?
Then how can Router map to that internal FTP server host as outside world only knows that real IP address?
regards,
rahul

This is the standard way - you enable "NAT" (Network Address Translation) and Port Forwarding on the router.

- There must be a router to connect your networks to the Internet.
- Your one public IP address is assigned to the router.
- Enable NAT on your router to enable systems on your networks to access the Internet.
- Enable port forwarding on the router so that outside systems that connect to specific ports on your router are redirected to servers on your network.

The router can be either a Linux system or a hardware router. You can port forward from a port on your router to any other system on your network.