Your IP Address Can Change

Most home networks today will consist of a broadband modem, a router and one or more computers that share that Internet connection. The router has two IP addresses: An exterior IP address seen by the outside world and an interior IP address seen only by the computers on the local network. Your ISP assigns the router it's exterior address, which may be something like 69.x.x.x (where the Xs are numbers).

The router will then give each internal PC its own local address, usually something like 192.168.1.2. Other PCs will have an address similar to 192.168.1.3, etc. In this case the router is considered the DHCP server and the gateway to the Internet. When you boot your machine, the computer will broadcast a request for an IP address and the router will normally answer. If it does not see the DHCP server it will give up and make up an IP address for itself. This IP will often look something like 169.x.x.x. This is a local address that will not likely have any communication with other PCs on the network.

We mention the 169 IP address because people will suddenly lose Internet connectivity when it worked the previous day. An easy way to attempt to fix this is to just reboot everything—modem, router and PCs.

In XP you can check your IP address by going to the command line. Go to START>RUN and type cmd and hit Okay. Next, type ipconfig /all and hit Enter. You will be able to see a lot of information about the gateway and the IP address of the computer. The IP address should be similar to 192.168.1.2 with a subnet mask of 255.255.255.0. If you have the 169 IP address, we can try the reboot.

Follow these steps in sequence:

1. Shut all PCs down.

2. Unplug the router.

3. Unplug the modem. Wait a minute or two.

4. Plug the modem back in and wait until all lights are green.

5. Plug router back in. Wait a minute.

6. Reboot the PCs, one at a time.

Even if you have the correct IP addresses, it's not a bad idea to reboot everything occasionally. So if your Internet speeds are slow on all connections, or if you suffer from a loss of Internet connectivity, reboot the modem, router and PC for a quick fix.