Geek Speak Series: IP Addresses

Your Digital Address

A Basic Overview

If you’ve ever gotten into why something on your computer network isn’t working, you don’t have to go to far before you hit the concept of network addresses or IP (Internet Protocol) addresses.  Once you have a basic understanding of IP addresses, there’s a lot of troubleshooting you can do on your own if something goes wrong.  You’ll also have a better understanding of how the Internet works as a whole.

The many thousands of network routers on the Internet are like post offices, sorting and directing the mail (in this case packets of data), to their intended destination.  Every time you send an email, request a web page, used instant messaging or use your cell phone, you’re depending on all those routers to deliver email, graphics or voice as quickly and efficiently as possible to your IP address.

You can think of IP addresses like physical street addresses.  When you connect to a network,  whether wired or wireless, you get an IP ip-address-envelopeaddress.  Unless you’re connected directly to the Internet, you get a local (or private) IP address – just like your house.  However, if I handed a letter to our postman and said, “Deliver this to 121 Main St.,” he’d look at me and go, “Which Main St?!”  You can’t just give the Internet your local IP, none of the other routers on the Internet will know where to find you.

Your router (or modem) has two IP addresses: one local and at least one public.  The local address will look similar to the one your computer has, but the public IP will look completely different.  The public IP is like your town on the Internet.  If I hand a letter to my postman and said, “Deliver this to 121 Main St., Evansville, IN,” he’d have no problem getting that to the right place.  Those are the two most basic pieces of information the Internet needs to get your data delivered to the right place – your public IP and your local IP.

Trouble in IP Land

Problems arise when two places on a network have the same IP address.  Imagine if you lived at 437 Charleston Place and across town was another 437 Charleston Place.  You’re both in the same town, to whom does the post office deliver the mail?  They either pick one and not the other or they pick neither.  When two devices on a network, say a printer and a smart TV end up with the same address, both will have problems.  Routers have features designed to prevent these kinds of conflicts – and they don’t happen very often – but when they do, it can seem like a real mystery.  Usually, it is because one device has been set to use a specific IP address, but the router doesn’t know that address is taken, so it tries to hand it out to another device.  Windows will usually tell you if there is an IP address conflict between its own address and another on the network, but most other network and “smart” devices won’t tell you of such a conflict.


Basic Steps

If there is an IP conflict on your network, they can be difficult to pin down, but there are a couple of ways to do it.  If you get a popup on a Windows machine about an IP conflict, you can:

  1. Restart the computer – this will force the computer and router to communicate and hopefully it will get a usable IP address.
  2. Open a command prompt (Start > Type CMD > Hit Enter) and type ipconfig /release and hit Enter, then type ipconfig /renew and hit Enter.
  3. Restart the router – this will force all the devices on the network to communicate with the router

Advanced Steps

If a conflict still exists, you can dig into the Windows logs: Start > Control Panel > Administrative Tools > Event Viewer and look for a DHCP error.  In the description of the error, it may list a MAC (hardware) address for the conflicting machine.  The quickest way to then find the offending device is to run a program called Advanced IP Scanner.  There are actually better tools out there, but this one is the best combination of usefulness and ease-of-use.  The scanner will give you the IP address and MAC address of all the devices on the network (although sometimes not devices with a static IP).  Then, you can match the MAC address to the offending device and remove it from the network or reset its network settings.

Still Stuck

If none of that fixes it, you’re going to need to contact a professional.

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