Here is my setup at home 1 ADSL Router D-Link ethernet My ISP has staticly assigned me an IP so when my router connects to ADSL it gets assigned its real IP as example: 12.12.12.12 also a reverse lookup IP aswell pointing to it of example home.myisp.com Then my two machines I assign them each an ip address of 192.168.0.2 and 192.168.0.3 (192.168.0.1 is the routers local IP(gateway) Now if for instance I have a FTP server running on my computer, then I also have a port forward in the router to forward the request for port 21 to 192.168.0.2 which is the computer running the ftp server. OK now when im at work I can ftp to example: 12.12.12.12 or home.myisp.com and gain access just fine cause my router takes the request and forwards it on right. BUT when im on my home machine why can I not ftp into it using 12.12.12.12 or home.myisp.com? I have to ftp in using the internal IP as 192.168.0.2 but I want to be able to type on my other machines in the house on the 192.168.0.X network home.myisp.com or 12.12.12.12 to connect to the server. I would have thought that by typing home.myisp.com in my machine that it would go to my ISP which then would tell it its pointing to 12.12.12.12 then come back to my router and see that its pointing at 192.168.0.2 ? Is this not the case? If anyone can shed any light on this topic id be gratefull

your isp dns server does not know about your internal ip addresses. How could it? They would have to charge you for your internal ip addresses if they could :-0 It works from outside since anything sent to 12.x.x.x goes to the router which takes it from there.

But wouldn't the isp see a request from my IP 12.x.x.x wanting 12.x.x.x and redirect it back down the line to the router to take it from there?

The request is not going to your ISP and is likely not leaving your router. You are trying to access the IP of your router so there is no reason for the packet to go past the destination IP (your router), to your ISP and back again. When you send to home.myisp.com (assuming it is a valid DNS entry), a DNS query to your ISP returns the 12.x.x.x address and your data packet goes to 12.x.x.x (your router). Not all reverse lookup names will resolve back to the original IP.