A Note About Windows XP
Now that all of your computers are plugged into the network and everything is powered and fine and dandy, you should probably start thinking about the software configuration of your LAN. Assumed in this tutorial is that you have Windows XP. Now, it is obvious that not every single PC user today uses Windows XP. However, the majority of users do, and for the purposes of this guide, I believe that instructions for XP will suffice because many of the instructions used in this configuration tutorial are extremely similar on both Windows 9x and NT/2000 operating systems.
Router Configuration
Now, load up your Windows XP installation. If everything is physically set up correctly, Windows should “automagically” detect and configure your network connection. That’s it, right? Of course not. Actually, more important than client configuration on any network is the much-feared router configuration process. The router configuration process utilizes the HTTP or Hyper Text Transfer Protocol as an interface to the router’s internetworking operating system. Basically, what that means is that you will interface and configure the router through a web browser. However, here is the fundamental paradox: how is it possible to interface with a router using HTTP when your network is not properly configured in the first place? Hopefully, Windows XP has correctly detected your network settings. Go to Start -> Run and then type in “cmd” to get the almighty command prompt. From the command prompt, type in “ipconfig /all.” If your default gateway is not 0.0.0.0, then type in that IP into your web browser preceded by the “http://” string. Most likely it will be 192.168.0.0, 192.168.0.1, 192.168.1.0, 192.168.1.1, or 192.168.254.254. Whatever the case, once it loads, it will most likely load an authentication applet. Refer to your router’s documentation for this default password. Once your credentials have been accepted by the router, you are ready for action.
Now, herein lies a complicated dilemma for this guide. On one hand, it would be easiest for the reader of this guide to read each individual router’s particular method of configuration and such. However, on the other, to cover each and every router would take years. So, refer to router’s documentation when you doubt a reference or in lack of knowledge of the meaning or location of a particular setting.
DHCP
One of the fundamental concepts of the LAN is the concept of IP addresses. Now arises the question: how exactly are they assigned? The answer is through DHCP. DHCP stands for Dynamic Host Configuration Protocol and basically is used to assign nodes on the network IP addresses automatically such that none conflict with each other (i.e. two nodes sharing the same IP), are legal (i.e. not 192.177.454.4), and are sometimes even in order (192.168.1.10-192.168.1.20). DHCP works on a client-server level, in that the client (a node on the network) requests a “lease” on an IP from a server (usually the router). The server grants the node a specific IP. Now, you may or may not want to employ DHCP in your LAN setup. There are numerous advantages to DHCP, the foremost being that there is a much lessened chance of two nodes identifying with the same IP address. It is also self/automatically configuring and a very reliable server. In the case that you choose to use DHCP, configure DHCP for which IP addresses you wish it to give leases to start upon and end upon.
DMZ and Port Forwarding
Now, after DHCP is configured, every member of your network can now be assigned a unique IP address internally. However, externally, the Internet still may need to contact a specific computer in your network for a specific purpose. These purposes include things from Counter-Strike and UT2004 to web servers and MySQL databases. So, how does a computer on the Internet know how to specifically contact a computer in your network (which, through a router, a million computers could potentially be hidden under one IP address)? The port system of TCP/IP provides this option.
TCP/IP works on a system of IP addresses and port numbers. Port numbers are specific “holes” or entries to a node on a network for a specific purpose. Ports are infamous for their reputation as “security holes” because it is often through useless open ports that worms spread so powerfully, dangerously, and easily.
Now, for example, let’s say you needed to host a file server through FTP. After setting up the file server on your desired node, you will need to find the IP address of that specific node. Then, go to the port forwarding section in your router’s configuration setup dialogue and fill in the port forwarding form accordingly. Remember that FTP operates on Port 21. There is, however, another option.
Suppose on your network there is one computer or server that is so important that you feel you cannot individually specify which ports to forward to this computer on, you can set it as the almighty DMZ host. The DMZ host takes all of the non-forwarded ports and sends them straight to the DMZ Host instead of the router itself. The DMZ host role can be fulfilled by anyone, but generally speaking, being the DMZ Host is an invitation to be paid a visit from Bubba the Hacker. It is a wide-open computer system.
Just for your information, another term for the “Port Forwarding” section of your configuration software is “Services Configuration.” Now that you have finished with the configuration of your router, you can move on to the configuration of your client.
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