• United States

Address Resolution Protocol

Jan 15, 20032 mins
Enterprise Applications

* Dr. Internet Steve Blass offers advice on using Address Resolution Protocol to detect IP addresses

How can I use Address Resolution Protocol (or something else) to detect if the IP address I was assigned is unique without causing all other hosts to update their cache and lose communication with the original owner?

If you have access to a second computer on the network, use that to ping the IP address in question to see if it is currently active on the network before booting your system with that address. Typing ‘arp -a’ from the command line should display the local Address Resolution Protocol cache and reveal the media-access-control address of the active IP address if it is on the same network segment (even if that system doesn’t respond to pings). If you try to detect this after starting up your system on the network with the questionable IP address, you should see “duplicate IP address” errors on your screen. As an end user on the network, your options are limited, unless you have network sniffer software available that lists and reviews active IP addresses. If IP communications are slow, appeal to your local network administrator. If you are the local network administrator, turn off the questionable system, wait a bit, and ping the IP address of interest from another machine to see if you get an answer.

Blass is a network architect. He can be reached at