Static IP with airport/cable modem

Since you connect to your ISP using DHCP, you don't (by definition) have a static IP. Your ISP needs to assign you a static IP (they might charge extra for this).

 

I think the OP is asking how to setup a static IP on their local network so they can use port forwarding.

In the network settings on your Mac, change it from DHCP to manual configuration. Enter the static IP address you want based on IP the address of your Airport Extreme. I don't know what IP the Airport Extreme uses but for example my Linksys router is 192.168.1.1, so for a static IP I've entered 192.168.1.20 (this is outside the dynamic IP range of the router, which starts at .100). "Subnet mask" should be 255.255.255.0. For "Router", "DNS Servers", and "Search Domains", enter the IP of your Airport Extreme (again in my case is 192.168.1.1).

 

It sounds that way.

As for LAN, the default configuration would be for it to distribute addresses. If so, you probably want to reserve (or set a static) IP locally. That's where the port mapping comes in. You tell the router to pass specific traffic on that port to/from the local IP. Those outside will get to that machine throug the static IP your ISP gives you.

Example: ISP static 69.xxx.xxx.xxx:6112 <> 192.168.x.x for your local LAN machine.

 

I thought that right after hitting submit (of course). But, I think the OP's covered either way now.

 

Okay there are 2 kinds of IPs: internal and external; internal is within your network; your ISP gives you the external on (the one computers will use to connect to your network (and server). Most ISPs either charge a premium for a static IP or require you to have a business account (which is usually twice or thrice as expensive as a residential plan).