Let's assume your public ip is 1.2.3.4
First, you have your router at 192.168.1.1
Its admin panel is running at port 80, so you can access it with "192.168.1.1:80" using your browser, or just "192.168.1.1" (because the browser will visit port 80 by default).
From outside, you can access this by just doing "1.2.3.4(:80)".
Now you have your web service running at 192.168.1.2
Its service also uses port 80, so you can access it with "192.168.1.2:80"
From LAN, you can access both different services by doing "192.168.1.1" and "192.168.1.2".
Your router probably automatically forwarded its own port 80 to the outside, so you can access it from outside by going to 1.2.3.4 by default. But your router is also just a device in your network.
So when you entered a rule that says local ip = 192.168.1.2, local port = 80, port range = 80
This basically means 1.2.3.4:80 -> 192.168.1.2:80
Now you can enter a different rule local ip = 192.168.1.1, local port = 80, port range = 8080
This will make possible 1.2.3.4:8080 -> 192.168.1.1:80
Unless the router supports third-party firmware this won't be possible. – Ramhound – 2014-09-09T13:19:38.157
We had this configuration formerly with the default firmware, but we had to do a reset. – Jake – 2014-09-09T13:20:35.463
3Why would port 80 on IP 192.168.1.1 affect you having an internal web server being accessible on port 80... Your web server will either be accessed via a different internal IP 192.168.1.x or your external IP which should not be bringing up your router web interface? – CharlesH – 2014-09-09T13:22:09.353
Charles, we will also need to access the web server externally. I've edited the question to reflect this. – Jake – 2014-09-09T13:25:38.490
Ah sorry. Yep Ramhound would appear to be correct, couple of supported third party firmwares that enable this to be changed but with stock firmware it is not an option. – CharlesH – 2014-09-09T14:23:51.893
@JakeWasdin - Are you running the OEM firmware or a third-party firmware. – Ramhound – 2014-09-09T15:12:12.380
Ramhound, I am running OEM firmware. I'll add also that I don't know how it was configured before, but it was accessible at a port like 192.168.1:8443 and not port 80. – Jake – 2014-09-09T15:19:53.660