If you take a router, your settings will be:
Public IP: IP address given to you by your ISP or Dynamic IP. The private side of the router's IP will be the IP address of the router and is the LAN's default gateway, usually something like 182.168.16.1. By default ALL traffic inside to outside is allowed. By default ALL traffic outside to inside is blocked. Using Access Lists, you allow traffic from the WAN to the LAN such as 80, 443, 987 (SharePoint), 3389 for RDP. These can then be forwarded to the IP address of your server if you are using DNS and your clients are pointing to that server.
Given that by default, all traffic from inside to outside is allowed, you can choose to deny traffic which you don't want used. But, you can never deny four things:
1. HTTP service from the LAN to the router is always allowed.
2. DHCP service from the LAN is always allowed.
3. DNS service from the LAN is always allowed.
4. Ping service from the LAN to the router is always allowed.
Do you have static IP addresses? What brand and model router do you have? Have you downloaded the complete guide of the router and gone through it step by step?
If you do not have a static IP, it would be much easier to set up a domain name and work with the router. You can use DynDNS, but static is still better in my opinion. While you can get by with one IP address, many ISPs provide seven the first and last which are not useable. I have to use three as I use one for my public IP, one for setting up wireless access for my patients and one for VoIP. Yes, I could have used the guest account and I could have used a VLAN, but I prefer it this way. And, if I want to run a web server...
