If you are going to forward ports, you're going to have to deal with the DHCP issue. Otherwise you'll run into intermittent problems with DCC or any other application (such as games and p2p programs) that requires port forwarding. If you have installed a router, you have in effect setup a LAN (Local Area Network - a home network). It doesn't matter if there's just one computer or a hundred computers behind the router, it's a LAN.

I Am My IP Address
When you forward ports, you want specific ports to open on a specific computer. The router is going to forward the ports, so you want the router to forward the ports to the right computer. Computers are identified by an IP address, so the router actually forwards the ports to a specific IP address.

DHCP Server - Get Your IP Here!
Your computer, or computers in the case of a LAN (local area network-your home network), obtain their IP address in one of two ways. The usual way is for the router to assign IP addresses to the computers using its built-in DHCP server. DHCP stands for Dynamic Host Computer Protocol. When you boot your computer, the router sees a client (your computer) come alive and hears it calling out, "Hey! Mr. Router! I need an IP address so I can talk to my neighbors on the LAN and access the internet!" The router says "O.K. Let me check my address book and see what IP address is available."

The router "address book" has a fixed number of available IP addresses. This number varies depending on the addressing range used by the router, but there are usually around 254 addresses available. The router will assign the requesting computer (the one that's yelling "I need an IP address!") the lowest available number from its address book. That's all well and fine as long as there is only one computer behind the router. The computer will always be assigned the first available IP address and therefore the same IP address every time. However, if there is another computer already on the LAN, it will have gotten the first available IP address and your computer will get the next available address.

Same IP Address Needed All the Time - Why?
Why is it important to have the same IP address every time? When forwarded ports are setup, they are forwarded to a specific IP address. If your computers' IP address assigned by the router is different from the IP address associated with the forwarded ports, port forwarding will not work. Computers are assigned their IP address based on the order in which each computer requests an IP address. If the computers request their IP addresses in a different order each time, they will not be the same IP addresses that were assigned last time the computers logged on to the LAN. That's what the "Dynamic" in DHCP means. The addresses are assigned on a "first come first serve" basis. Consequently the IP addresses associated with the forwarded ports as initially set up will not be the same if the DHCP server is assigning the IP addresses dynamically. Bad result. Port forwarding won't work.

Ahhh… So We Need Static IP Addresses!
So now you can see the problem. For port forwarding to work, a computer needs to have the same IP address all the time. This leads us to the second way a computer obtains an IP address. You, the user, not the router, assign the computer a fixed IP address. The fixed IP address is called a static IP address. You assign the address by modifying your computers LAN configuration settings.

Why Configure the Router's DHCP Server?
Most routers these days are very configurable with respect to the DHCP server. The DHCP server's assignable IP range can be limited to a range of addresses rather than having the entire range available. You can also turn off the DHCP server so the router doesn't assign IP addresses.

The choice in configuring the router's DHCP server depends on how many computers are on your LAN and what programs the users on your LAN run. If you have only one computer on your LAN, it's easy to simply turn off the DHCP server. If you have 2 or more computers on your LAN, then defining the range of assignable addresses by the router may be easier. Both methods will require assigning static IP addresses to the computers that will use port forwarding.

Kill the DHCP Server
Simply turning off the DHCP server is easy. It requires opening the router interface (by typing the routers internal IP address into your web browser) and checking or unchecking the box that turns off the router's DHCP server. Next you open your computers LAN Connections Properties window and assign a static IP address. Now you can go back to the router interface and set up port forwarding. As you can see, it's simple to.

Restrict the DHCP Server's Address Book
Limiting the range of assignable IP addresses for the router will save you having to reconfigure the LAN connection properties of computers on your network that do not need port forwarding. Instead of turning off the DHCP server of the router, you find the configuration section that allows you to tell the router what IP addresses, or range of IP addresses, you want to allow it to assign. For example, your router may be able to assign IP addresses in the range from 192.168.1.2 up to 192.168.1.254. That is 252 addresses. You can tell your router you only want it to be able to assign a portion of those addresses, say 50 of them (from 192.168.1.2 up to 192.168.1.52). Those 50 IP addresses will then be assigned by the router to computers that don't require port forwarding. The other 202 IP addresses that the router does not have in its address book can then be used as static IP addresses on computers that need port forwarding. It saves you time because you only have to configure the computers that need port forwarding.

So Now You're an Expert!
So that's basically what DHCP and static addresses are all about. You now know the options and have the knowledge to decide how to configure your router for port forwarding.