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Making your Computer Accessible from the Public Internet

Address and Connect to Your PC

Below is a text transcription of the "IP Addesses" video that is part of the Making your Computer Accessible from the Public Internet tutorial series for troubleshooting remote access to server-based applications.

Handling static and dynamic IPs, and domain names

The most important thing to understand about IP addresses when getting your server–based application up and running is that you don't want it to change. In this tutorial we'll cover why a changing IP address is terrible for your server, and how you can ensure it won't change again. Once you understand these concepts, other issues such as port forwarding will also make more sense to you.

Public IP Addresses

An IP address, on a basic level, is similar to a telephone number. If someone wants to talk to you, they call you on your telephone number. In computer terms, if one computer wants to talk to another, they call each other using IP addresses. Like your telephone number, an IP address is a unique number.

However, unlike a telephone number, the IP address of a computer can change without notice. This type of address is called a dynamic IP. Dynamic IP addresses are assigned by Internet Service Providers, or ISPs, mostly on an as–needed basis. When your computer tries to connect to the internet, it requests an IP address to use during the session. If the computer doesn't use the IP address for a certain amount of time determined by the individual ISP, or sometimes even if the computer simply reboots, that IP address can be reassigned to another computer. When your computer connects to the Internet again and requests an IP address, it's not guaranteed that it will be reassigned the same IP address.

Keeping with the telephone analogy, imagine how difficult it would be for people to call you if your phone number changed all the time, like a dynamic IP address can. You would constantly have to give out your new number. People would try to call you, never knowing if they had the right number, or worse, they could assume you were out of business. The same thing can happen if your IP address changes all the time and clients or users are unable to reach your application.

That's the worst–case scenario. Many broadband ISPs offer a "sticky" dynamic IP address, in which an IP address is leased to the computer for a certain amount of time. Once the lease is up, the same IP address is usually reassigned to the computer, so the computer can function with a relatively stable IP address. Contact your ISP to find out how your public IP addresses are assigned, and how often you can expect the address to change.

Acquiring a Static IP or dynamic DNS for your Network

If dealing with dynamic IP addresses sounds like one big headache, there's another type of address: the static IP. A static IP does not change. You can request a static IP address from your ISP, usually for an additional fee, and only if the ISP offers static IPs to its customers. Another option is to use a dynamic DNS service. DNS stands for domain name system, and a dynamic DNS gives a permanent domain name to a computer, such as, and automatically keeps track of that computer's IP address, even if it changes. Therefore, when someone on the outside internet wants to contact your computer, they can contact, and the dynamic DNS service will know how to contact your computer. It's like having a personal assistant whose job it is to know how to reach you at all times.

IP Addresses on a Local Area Network (LAN)

In this tutorial, we've been discussing IP addresses as though computers connect directly to the internet. Most often, this is not the case. Many homes and businesses connect to the internet through a router. When the connection to the Internet is made, it is the router, not the computer, asking the ISP for the IP address. Through the router, a network of computers can share the same public IP address for outbound connections to the Internet.

However, this doesn't mean that your computer won't still have an IP address. When you turn your networked computer on, the computer asks the router for an IP address. The router assigns a dynamic IP address to your computer to use while it's on; for connecting to the internet, and for talking to other computers and devices within the network.

When the time comes that you want to allow the outside Internet to connect to your application, the router needs to know which computer the application resides on in order to forward the connection to the correct computer. To ensure this happens smoothly each time, you need to assign a static IP address to this computer, and configure your router to forward outside requests for the application to the correct computer with the static IP address.

There are two steps involved here. The first is to assign a static IP to your computer. We'll talk about that in just a moment. The second is to configure the router to forward outside connections to that static IP. This topic is covered in detail in our tutorial on port forwarding.

Assigning a Static IP to your Computer

Configuring a static IP is different on every operating system. You can find some resources under the IP address section at the address shown on your screen.

When you choose the static IP address for your computer, it's important to keep a few things in mind. You'll keep most of the IP address the same as the address assigned dynamically by the router; you'll only be changing the last set of numbers. You want to avoid assigning an IP address to your computer that the router could potentially assign to another computer or device on your network. Doing so will result in no Internet connection for either device. Also make sure you don't assign the router's IP address to your computer.


Now that your IP addresses are in order, there's still another element to consider before requests from the outside internet can be forwarded to your computer. Let's go back to the telephone analogy. Imagine you call a company, and the automated answering service prompts you to enter an extension. You've already called the correct phone number, but in order to access the correct person or service, your information needs to be more specific. You need to know which extension they work at. This is similar to someone from the outside internet accessing your computer, and your computer asking which port they need before they can be connected to the correct application.

You can usually find the port number the application runs on in the application documentation, or through the settings. Then, use the port number when you go on to forward ports in the router, or create rules and exceptions in firewalls for the application.

Hopefully this tutorial has helped shed some light on which components you need to configure to successfully make your computer accessible to the outside internet. Having a static IP address is extremely important, and works hand in hand with the other tutorials we have put together on this subject. You can view our other tutorials in this series, covering topics like port forwarding, setting rules in firewalls, STUN, and DMZ at the address shown on your screen.

Server-based Software Topics

IP Addresses
Router Issues & Port Forwarding
Firewall Configuration
Glossary of Terms

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