Saturday, January 15, 2011

Windows 7: IP Address Conflict: What Could It Be?

I was continuing a long, long effort to resolve a home networking problem in Windows 7.  The problem was that, if I connected more than one computer to my Netgear FS605 network switch or my Linksys WRT54GL router, I would get an error message:  "Windows has detected an IP address conflict."  I had really tried a huge number of things -- many confusedly, redundantly, or otherwise chaotically, but nonetheless striving in some ill-formed sense to solve this problem.  The solutions I had tried had worked for others; they just weren't working for me.

At this pint, it occurred to me to take my laptop, router, and switch down the way, and try them on someone else's Internet connection.  But now it was late, so that would have to wait until the next day.  But I did not think that the hardware was the problem.  A router and a switch going bad at the same time, after both had served well?

I noticed, when I tried using Google Chrome to do a search during one of those IP conflict periods (i.e., when I had two computers connected to the switch), that Chrome gave me additional information.  Besides saying "This webpage is not available" and suggesting that I reload, their "More information on this error" link gave me an error message:

Error 105 (net::ERR_NAME_NOT_RESOLVED): The server could not be found.
I did a search on that.  It produced a variety of general and Chrome-specific possible solutions.  One ChromeBoard thread went through many of the issues I had examined here and in the previous post, including changing DNS server to OpenDNS or Google ( and  It seemed the change was supposed to be made in the router, though, not on the computer, and that was different from what I had tried before.  On the theory that my problem was one that a router could sort out, but a switch could not, I went back into my router (a Linksys WRT54GL), as described in that post.  I saw that the router was set to a PPPoE connection type, which was right for my modem but may have been wrong for the router.  I changed that to DHCP.  I saved and saw that this did not solve the problem.  My next step was to try the DNS advice, but it was not clear where in the router's page I should change those numbers.  The page had both "Router IP" and "Network Address Server Settings (DHCP)" sections with DNS options.  The latter seemed right.  But there were three "static DNS" spaces to fill.  I tried the Google numbers (above) for the first two of the three.  That wasn't the solution.  Pooofont recommended unplugging the computer from the wall power socket for a half-hour.  I tried for 15 minutes.  One thing that became clear, as I perused that long thread, was that there were many problems within this Error 105.  Continuing:  I checked Win7's Start > services.msc > DHCP Client and DNS Client; mine were already started and automatic.  Another new possibility:  flush DNS using "ipconfig /flushdns."  I tried it on two computers, and then connected them to the switch; no joy.

Another possibility occurred to me.  Perhaps I had a virus.  But a virus that would immediately affect WinXP, Vista, and multiple Win7 installations, without showing any other effects, and that was not picked up by Avast, AVG, or Windows Security Essentials, all of which had been running on one of these machines or another during this process?

Around this time, I noticed that something had changed.  I had noticed it before, but now it caught my full attention.  Computer B was no longer experiencing IP conflicts when I plugged the other computers into the switch.  They continued to report such conflicts, but now computer B was OK.  Not only was it not reporting IP address conflicts, but it was now able to go online, even through the switch, when all three other computers (one running Win7, one running Vista, one running Windows XP) were also plugged into the switch and were reporting IP address conflicts.

Somehow, computer B had reached a point of functionality.  What had I (or the computer) done to achieve this?  The solution was presumably not a matter of the router or the switch; it was seemingly something about computer B in particular.  But what?  I tried to trace back through the previous post, to see what I might have been doing when this change occurred.  I had noticed it while talking to the AT&T guy, so it was before that.  But then I had to call it a day.  The system went into hibernation overnight, and when I came back to it the next morning, computer B, too, was reporting an IP conflict and was unable to go online.  Maybe it had something to do with resetting the modem, though I didn't see how.  My thinking now was that the modem could not tell what lay on the other side of the switch.  As far as the modem was concerned, it was handing out just one Internet connection.  It was up to the switch or router to arbitrate among multiple computers.

Following advice, I opened a command window in each computer (Start > Run > cmd -- or, in Win7, Start > type "cmd") and typed "ipconfig" by itself.  This produced several different results.  In computer A (running Win7) and in the Vista laptop, it did not even try to report an IPv4 address.  In computer B, it reported an IPv4 address of  In the Windows XP machine, it reported as the only IP address.  This seemed to suggest computer B and the WinXP machine should not be in conflict.  I unplugged the two others from the switch.  But computer B and the WinXP machine were still unable to go online.  Only when I removed three of the four machines from the switch was the one remaining machine able to connect with the Internet.  This suggested that the IPv4 address was not the issue, or at least not the only issue.

Another possibility recommended in that same thread was to go into Device Manager (a Control Panel item in Vista and Win7; under Control Panel > System > Hardware in WinXP), look under Network Adapter, and uninstall the ethernet and wireless adapters, then scan for changes and let it reinstall them.  I wasn't using wireless, so I assumed that part would be irrelevant to my situation.  The wired part was a Realtek device on both computer B and the WinXP machine.  I made sure both computers were connected to the switch, and then uninstalled the Realtek adapter.  I did not opt to delete the driver software.  Then, in the Action menu item at the top of Control Panel, I ran "Scan for hardware changes" in both computers, one at a time.  The WinXP machine started its Found New Hardware Wizard.  I couldn't get the CD drive to read the motherboard manufacturer's installation CD at that point, so I rebooted the WinXP machine and it reinstalled its wired adapter automatically during reboot, and reported an IP address conflict when it came back up.  But now computer B was not reporting a conflict.  I tried the same approach with computer A. 
It still reported a conflict and was still unable to go online.

One thing that was different about computer B, in the networking department, was that I had installed VMware Workstation there.  This seemed potentially relevant because there were VMware Virtual Ethernet Adapter for VMnet1 and VMnet 8 listed in Device Manager on computer B.  But I had had the IP address conflict problem after installing VMware, so I didn't see how that could make a difference.

At this point, I came across a suggestion to use Win7's Event Viewer.  That discussion continues in a separate post.