Windows 7 Screws Up the Network?

I had endured one of those fortunately infrequent but nonetheless time-consuming and frustrating network problems.  The basic idea was that my computers could not even stand to be on the network together at the same time.  I had been troubleshooting with a Netgear model of network switch that I had lying around.  That had worked better than my router.  So I concluded I needed a new router.

But then a new day dawned.  A bit of experimentation posed a new thought:  maybe the problem was not in the hardware, or not *only* in the hardware.  Maybe it was in Windows 7.  When I went online with my other computer (referred to here as "computer B"), booting from an Ubuntu live CD, I was able to surf the Web -- and then, suddenly, not.  It depended on whether the Windows 7 computer ("computer A") was connected to the switch.  For example, at the moment I was writing these words, I was connected to Blogger without a problem.  Then I plugged in computer A.  Within a minute, my connection was down; I was no longer able to save these words or surf to other webpages on the Ubuntu computer.  Disconnecting computer A and powering down the switch for a couple of minutes solved the problem.

This conclusion was subject to one amendment.  The switch was working reliably, but the router was not.  Even without plugging in computer A, an attempt to use the router again failed within a few minutes.  I was connected to its own internal webpage, and then I wasn't.  I wanted to try this again when my WinXP system (computer B) was back up.  But at the moment, I wondered if possibly Win7 had screwed up the router too.

When I did a search for the possibility that Win7 could be messing up my network, I found a thread in which someone said this:

I think he has a bad route that was left over from when the wireless AP was in the mix, or the AP was in 'more than AP mode' before it was removed.  If the AP was handing out IP addresses rather than the wired router handling DHCP, when it was removed, the unexpired lease could leave the box in limbo.  It 'grew up' knowing itself to be on a specific network, and needs all those entries removed from the registry.  Good luck with that...

I wasn't sure what this was about, but one possibility was that the router was decaying and it had messed up the Win7 installation, which was now reciprocally messing up the switch or, perhaps, any other network device I might connect to it.  I wasn't sure if this theory made sense, but it was better than the complete lack of any explanation that I had struggled with during the preceding day.  The hypothesis would then be that Windows 7 was only temporarily able to mess up the switch.  According to this theory, I should unbrick or replace the router and simultaneously reinstall Windows 7 (which, with the installation as it had progressed so far, would probably be faster than troubleshooting its network settings), and see if that fixed the situation.

I was interested in seeing what would happen when computer B (temporarily running Ubuntu live) booted back into Windows XP.  Would it have problems too?  But however that would turn out, the hypothesis raised a question about Windows 7:  was it fragile?  It seemed more than coincidental that this problem had emerged during the first few days of installing Windows 7, after having used Ubuntu and WinXP with that router for months.  Was Win7 going to convert other routers into bricks?

Well, at any rate, Windows 7 was networkingly nonfunctional, and after days of troubleshooting, I was sick of its built-in troubleshooters.  So I reinstalled it.  I tried first from an image that I had made after the first day's installation efforts.  I did not connect the router.  This was able to go online through the switch.  But now, surprisingly, WinXP was not able to connect.  Did I have a virus?  Its troubleshooter thought that I might have a problem with my modem and/or router.  It told me to shut the modem or router off for three minutes and then retry.  I was using the switch, not the router, but I did this anyway.  When I powered the switch back up, the situation did not change:  WinXP was still not able to connect, but the revitalized Win7 was still doing fine.  I ran the WinXP troubleshooter again, just in case.  No change.  I right-clicked on the network connection icon in the system tray and selected Repair, but got an error message indicating that this was not something that Windows cared to do for me at that moment.

I went away from this investigation for several days to pursue other topics, including virtual hard disks (VHDs).  By the time I returned, I had replaced WinXP on computer B with Win7.  Having Win7 running on both machines did not resolve the networking problems, unfortunately.  My efforts to grapple with that are described in a separate post.

At this point, I had just restored an Acronis image of Win7 on computer A.  That image had been made within 24 hours after first installing Win7 on computer A.  Now I was going to test it.  I started by connecting each computer, individually, directly to the DSL modem. That worked. Then I connected each computer individually to the network switch.  That worked.  I tried connecting each computer individually to the router.  That did not work.  I concluded that the router (having been debricked) was nonfunctioning.  So now a replacement router was on the way.  So apparently the router had been part of my problem, though confirmation of that would await the new replacement.

Next, I connected both computers to the switch simultaneously. That did not work. I got the same old "Windows has detected an IP address conflict" error that I had been getting previously.  So now I reinstalled Win7 from scratch on computer A.  As before, computer A was able to go online when it was the only computer connected to the switch.  But the IP address conflict reappeared when both computers were connected to the switch.  It appeared then, that the conflict was not generated by some kind of flaw that had developed in the installation of Win7 on computer A.  Regardless of whether I was using an old or a new installation, the problem persisted.  It did not appear to be a flawed Win7 installation that was screwing up the network.  I restored a more recent Win7 image to computer A, and tried to think of other possibilities.