How to Configure an IP on a Cisco Router


Many broadband users draw Internet Protocol (IP) addresses from a common shared pool that is owned by the provider. These dynamic IP addresses are typically exchanged every 24 hours, meaning that over the course of a week your address may change several times. Occasionally, there will be a network error that will cause your router to draw a bad address that is not usable. In this case, you will need to clear your mask and draw a new address. This is also done the first time a router is set up on a network. Almost all Cisco routers are designed for dynamic IP addresses.

Things You'll Need

  • Internet access
  • Cisco router
  • Turn on your router if it is not currently in the "On" position. There will be at least three green lights on the router itself to indicate that it is active. If there are any yellow lights, check all your physical cable connections for the router and the modem to ensure it is setup correctly. This means making sure everything is plugged in.

  • Open the "Start" menu in Windows, located in the lower left-hand corner for most Windows installations. Windows Vista and 7 will have the Windows icon in the lower left-hand corner that accesses the Start menu instead of the word "Start."

  • Enter the command "cmd" without the quotes into the Search/Run text box. This opens a special System32 or command shell window for directly accessing the disk operating system (DOS).

  • At the DOS prompt, type "Ipconfig /release." This command will release your current, if any, IP addresses and subnets for your router. All computers that currently access the Internet through your router will be unable to connect. Some Windows machines may try to automatically draw a new address.

  • Enter the command "Ipconfig /renew" at the DOS prompt. This will finish the reset and allow your router to configure in the default settings and draw a new IP address.

Tips & Warnings

  • You can typically use the "Repair" command under Network Settings in Windows to accomplish this same task, but it takes considerably longer and is not always successful.
  • Be careful about running other commands from the DOS prompt as the computer will typically not ask you if you are sure. This means that a few errant keystrokes could significantly destabilize your environment including power settings, security and speed. Always double check your command arguments before entering them into the DOS prompt.

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