Understanding and Resolving IP Address Conflicts
June 18, 2007
IP address conflicts are usually temporary, but you can't count on them to always fix themselves.
Picture the following: You're sitting at the computer minding your own business. Then, all of a sudden, Windows presents you with a warning: "There is an IP address
This probably happens to many of us every so often, and as is typical, the cryptic Windows error message doesn't give you much to go on to help identify and fix the problem. Fortunately, IP address conflicts are usually temporary and often eventually resolve themselves. But you can't count that to always happen. Even when it does, the resolution is not always immediate, causing many to resort to time-consuming reboots that may or may not remedy the problem. This week, we'll examine likely causes of IP address conflicts and some ways to address them (forgive the pun).
So what are some possible causes of IP address conflicts? A classic one is when two systems are given an identical static (manually assigned) address. This scenario isn't as common as it once was, however, because on a typical home or small business network DHCP
DHCP servers which are built into most routers
But even avoiding the use of static addresses and relying entirely on DHCP doesn't eliminate the potential for address conflicts. For example, in some cases you may (often unknowingly) have more than one similarly configured DHCP server handing out overlapping addresses, especially if you have multiple wireless access points or other network devices with an embedded DHCP server (which is usually turned on by default). In this case, too many cooks spoil the broth, so you should only have one DHCP server running and make sure all others are turned off.
Another common cause of address conflicts is when a system comes back online after an extended period in stand-by or hibernate mode, especially if the system was previously part of another network (say, a work notebook brought home). A conflict will promptly occur if the address the system was previously configured with is the same as one that's already in use on the network.
Absent any of the above causes, conflicts can also be caused by internal DHCP server malfunctions, which cause them to lose track of which systems are using which addresses. This can be surprisingly common with some routers.
Finding and Fixing the Culprit
As we mentioned above, IP conflicts tend to eventually work themselves out in DHCP environments because systems issue repeated requests for valid addresses. But since the process can take a while and doesn't always work as planned, one way to hasten a fix is by manually entering IPCONFIG /RELEASE and IPCONFIG /RENEW from a command prompt (restarting a system accomplishes the same thing but takes a lot longer).
If the conflict persists even after renewing the IP address, it may be because your system's been re-issued the same address it already had and another system on your network is the source of the problem. You can get a clue about the offender by checking the System Log within the Windows Event Viewer (which you can get to via Start|Control Panel| Administrative Tools|Event Viewer) and looking for a DHCP error entry. The entry will list a network address (actually a MAC address) which you can use to identify the conflicting device, either by running IPCONFIG / ALL
If you experience chronic IP conflicts with no apparent cause, you may want to consider updating your router with its most recent firmware. If you're already running the latest firmware
Story courtesy of PracticallyNetworked.