Windows 7: IP Address Conflict: Event Viewer

As described in a previous post, I was trying to resolve an "IP address conflict" error message that would pop up when I connected more than one computer to the NetGear FS605 switch on my home network.  The message, in Windows 7, read like this:

Network Error

Windows has detected an IP address conflict.

Another computer on this network has the same IP address as this computer.

I had worked through a number of possible solutions that did not work for me.  Then one source suggested going into Control Panel > Administrative Tools > Event Viewer.  I had to wait a minute while it read its various events.  In its Summary of Administrative Events, I saw some events whose Source was Dhcp-Client.  This Summary seemed to indicate that details were contained in the Microsoft-Windows-DHCP Client Events/Admin log.  In the Log Summary panel at the bottom of the screen, I looked for a log with that name.  I found one and double-clicked on it.  It opened up a list of 343 events.  I sorted these by Event ID.  Event ID 1001 provided this General error message:

Your computer was not assigned an address from the network (by the DHCP Server) for the Network Card with network address 0x1C6F6541080C. The following error occurred: 0x79. Your computer will continue to try and obtain an address on its own from the network address (DHCP) server.

Event ID 1002 (which, like others below, occurred multiple times) provided this message on its General tab:

The IP address lease 192.168.1.64 for the Network Card with network address 0x1C6F6541080C has been denied by the DHCP server 192.168.1.254 (The DHCP Server sent a DHCPNACK message).

Event ID 1005 was a Warning rather than an Error.  Its General tab said:

Your computer has detected that the IP address 192.168.1.64 for the Network Card with network address 0x1C6F6541080C is already in use on the network. Your computer will automatically attempt to obtain a different address.

Event ID 50034, an Error message, said:

An error has occurred in initializing the adapter 11. Error Code is 0x1004

Chronologically, about half of the events listed on this log had occurred on this particular morning, though I had only been on the computer for about an hour.  Many of them seemed to be spaced about 10 or 11 seconds apart.  I assumed older items scrolled off.  Event 1001 had not occurred in the past several days.  Event 1002 had occurred only once this morning, first thing, when I started up the computer.  All of the events on this log occurred within the first 15 minutes after I restored the computer from sleep (or possibly hybrid sleep).  Maybe that was when this computer B stopped complaining about an IP address conflict.  An Event 1005 was the last one on the log.  Apparently the computer had succeeded, at that point, in finding a different address.

I looked at the Event Log on computer A.  It went back for weeks, so maybe I was wrong about older events scrolling off.  I had installed Win7 relatively recently on computer B.  The Event Log on computer A had the same Event ID numbers.  It also had some others.  On this particular day, it had Event ID 20, which was too long to reproduce here in full, but which started as follows:

The description for Event ID 20 from source Google Update cannot be found. Either the component that raises this event is not installed on your local computer or the installation is corrupted. You can install or repair the component on the local computer.

And it also had Event ID 134 on this day:

NtpClient was unable to set a manual peer to use as a time source because of DNS resolution error on ". NtpClinet will try again in 3473457 minutes and double the reattempt interval thereafter.  The error was: No such host is known. (0x80072AF9)

It also had Event ID 315, which said:

The print spooler failed to share printer Brother MFC-7340 with shared resource name Brother MFC-7340. Error 2114. The printer cannot be used by others on the network.

And it had Event ID 1014, which said this:

Name resolution for the name teredo.ipv6.microsoft.com timed out after none of the configured DNS servers responded.

It also had Event ID 4199:

The system detected an address conflict for IP address 192.168.1.64 with the system having network hardware address 1C-6F-65-41-08-0C.  Network operations on this sytem may be disrupted as a result.

There were some other errors that it had not yet had on this particular day.  There were also some that had occurred on this day, but that I have not reported here, at least not yet, because the ones listed above seemed to give me enough to think about for the time being.  These others were Event IDs 8021, 8032, 43029, and 52236.

I looked at the first items of the day.  (These machines were not all set to hibernate or sleep in the same way, if at all.)  On computer A, the first event (other than 43029, "Display is not active") was an Event 4199.  On the Vista laptop, the first event of the day was a 1005, followed by a 4199.  On the WinXP machine, likewise, it was a 4199.  On computer B, by contrast, the first event was Event 1002, and there were no 4199s.  So Event 4199 seemed like it might describe the problem.  I verified that the IP address being referred to on all three machines reporting a 4199 was 192.168.1.64.  (The network hardware addresses reported by Event 4199 varied from one machine and from one Event 4199 message to another.)  That seemed to suggest that I should just reset the IP address on the other machines manually.  I went into IPv4 properties on computer A and changed it to 192.168.1.65.  But I was still unable to go online.  I went into the laptop and tried 192.168.1.66.  While I was there, I noticed that the option to "Obtain DNS server address automatically" was grayed out, and yet there was nothing typed in the manual alternative, so I referred back to my post about OpenDNS and added numbers there.  This did not make a difference on the laptop.  I rebooted and tried again, just in case it would make a difference.  It didn't.  Now I noticed the same thing about computer A, so I added Google's public DNS numbers there.  Somehow -- possibly because I checked the "Validate settings on exit" option -- I wound up in Windows Network Diagnostics on computer A.  It offered this:

Automatically update your network settings
Windows can detect the correct network settings for you.

I thought, why not? and selected "Apply this fix."  It came back with the announcement that troubleshooting had found that "DHCP is not enabled for 'Local Area Connection.'"  And maybe that was true.  But computer A was still not going online.  I went back and saw that it had wiped out what I had just entered.

I noticed, when I went through the troubleshooter on computer A just a moment earlier, that it had the temporary effect of making computer B unable to go online.  I just happened to be at this blog post, and perhaps Blogger was trying to save at that very moment or something.  Anyway, a moment later, Blogger was able to save again.  I was curious about this, so I went back into Event Viewer, sorted for date and time, and hit F5 to refresh.  But no, there were no more recent items, so apparently whatever had happened had been too brief a blip to register on the log.

I tried typing ipconfig in a command box (Start > type "cmd" > type "ipconfig"), on computer A, to see what IP address I had now.  My change to 192.168.1.65 had stuck.  And yet it could not go online.  How was the 65 address conflicting with the 64 address?  Didn't make sense.  I refreshed Event Viewer on computer A.  (I accidentally refreshed this post instead.  Thanks to Blogger, that scrambled what I had written here, so I had to go back and fix it.  That took maybe 20 minutes.)  The last events in Event Viewer on computer A included a 1005 reporting that 192.168.1.64 was already in use on the network.  But ipconfig on computer A reported an IPv4 Address of 192.168.1.65.  So, OK, maybe no more IP address conflicts?  But computer A was still unable to go online.  I rebooted it.  The situation was the same.  The IP address was definitely 192.168.1.65, and there were no new events in the log (from the past 25 minutes or so), and yet I couldn't browse online.  In the command box, I got results from "ping www.ehow.com" on computer B, but not computer A.

On computer B, I went into Control Panel > Network and Sharing Center > Troubleshoot problems > Internet Connections.  That troubleshooter again offered to change my settings.  Since it didn't work last time, I skipped it this time.  It reported the same "DHCP is not enabled" error as last time.  A search for that error led to comments about routers.  Suddenly it occurred to me:  was 192.168.1.64 the only address that the modem was making available -- was that how this worked?  (Note:  I had since discovered that my modem was actually a combination modem/router.)  Consulting my previous post on the modem's part in this drama, I logged into the modem's internal webpage and looked around.  It said that, on the local network, the modem's IP address was 192.168.1.254, but that wasn't what I wanted to know.  That was where I could log into the modem, as I had just done.  But going in the opposite direction, where would the modem find computer B?  There was a log here, too, and it had a bazillion entries saying things like this:

2011/01/15 8:25:35 GMT - L3 - DHCP: Address 192.168.1.64 declined

The date and time reported there were just a few hours earlier.  So it was listening to computer A; it just didn't like what it was hearing.  On the modem's Statistics tab, I found a section containing "LAN Information."  This section reported that the DHCP address was 192.168.1.64.  So maybe that was the address that the switch was supposed to be using?  And then the switch was supposed to generate new IP addresses that the computers could use?

There was a "Routing Table" that seemed to say my ethernet network was connecting to the modem at 192.168.1.254.  That was the "Modem IP Address."  Further down, I saw a "Devices on LAN" section.  This listed two IP addresses as Active.  These were 192.168.1.64 and 192.168.1.65.  It listed two other addresses as Offline.  I hadn't seen those before.  I didn't know what those were for.  The 192.168.1.64 address looked like it was being associated with computer B -- the computer name it showed was partly familiar to me.

I wondered if this table would change if I changed things on the network.  So I unplugged the ethernet connections from the switch, for all computers except computer B.  Then I hit F5 to refresh the modem's webpage.  The name shown for computer B changed slightly, but otherwise these things seemed to be the same.  So the "Devices on LAN" section seemed to be listing all of the addresses from which computers had ever (or at least recently) tried to access the modem.  To test that, I unplugged computer B and plugged in computer A.  On computer A, I changed TCP/IPv4 Properties to specify an IP address of 192.168.1.66.  Sure enough, now the modem's "Devices on LAN" webpage was reporting a fifth entry, for that IP address.  The "MAC Address" reported for 192.168.1.65, on the modem's statistics page, was the same as reported for 192.168.1.66.  Apparently the MAC address was the "network hardware address" referred to in Event 4199 (above).

The modem's statistics page reported, as I say, a DHCP address of 192.168.1.64, and it reported a device on the LAN -- namely, computer B -- at that same address.  Did this mean that computer B was hogging the only available address of 192.168.1.64?  On computer A, I went back into TCP/IPv4 Properties and changed the IP address to 192.168.1.64.  With only computer A connected to the switch and therefore to the modem, I refreshed the modem's webpage.  Now it reported that 192.168.1.64 and 192.168.1.66 (but not 192.168.1.65) were Active, and the name of the computer at IP address 192.168.1.64 was simply "192.168.1.64."  Three of the five items in the Devices on LAN table had identical MAC addresses -- presumably that of computer A.  (The other two were 191.168.1.107 and 125.)

Unfortunately, computer A was not able to go online at this point, even with no other computers connected to the switch, or even with computer A connected directly to the modem.  I wondered if this was due to an internal conflict, in the sense that it now had these three identities.  I did a search for information related to my Motorola model 2210 modem and found a thread where someone said this:

Only one device can be set up as a dhcp client with the 2210.  All other devices will require a static private IP address.

Well, this was daylight.  Another person explained:

The DHCP server will assign only a single IP address, 192.168.1.64. It will be assigned to the first device which makes a DHCP request. Additional DHCP devices will be declined an IP address.

This raised the question of what would have happened if computer A had been the first one to contact the modem.  (For posterity, my search led to a manual for a Motorola 2220, which was apparently similar to the 2210 but had more features.)  To test that, I unplugged the modem and let it sit.  Meanwhile, I changed TCP/IPv4 properties in computer A to obtain and IP address and DNS server address automatically.  Then I powered up the modem, and after it was back online I viewed its webpage from computer A.  That did it.  Under Devices on LAN, it showed only 192.168.1.64.  And it appeared I was right about the internal conflict:  computer A was now able to go online.

It felt, at this point, like the Event Viewer had introduced me to something resembling an intelligent way to resolve networking problems.  I had miles to go.  But this was starting to make sense.  So now, what would happen if I connected computer B to the switch?  I did that.  Now computer B was reporting an IP address conflict.  Computer A wasn't, at least not yet, and ipconfig there continued to report an IP address of 192.168.1.64, but now computer A was not able to go online in the web browser, though it did successfully ping http://www.ehow.com/.  The modem's webpage, duly refreshed, oddly still reported only one Devices on LAN:  192.168.1.64.  I was not presently clear on the name of the computer it was associating with that IP address, but tentatively it appeared that the computer that first approached the modem after a reset would be the one whose real name (i.e., the name I had assigned to it during Windows installation) would appear in the modem's Devices on LAN list.  (The modem's log, which I had erased with the reset, now reported a bunch of new "DHCP: Address 192.168.1.64 declined" errors.)

I still didn't understand why computer B would still gain dominance in terms of Internet access, when both were connected, even if computer A was the one associated with 192.168.1.64.  Life wasn't as easy for computer B this way -- when it wasn't first to the modem, it seemed to struggle more to get online when both were connected to the switch, but ultimately it was able to do so, displaying webpages after one or two refreshes if not right away.

The modem's webpage, viewed on computer B, was hung at this point -- it wasn't reporting statistics, just sitting there with that Win7 spinning hourglass, telling me that it was thinking about it -- so I ran troubleshooting on computer A.  It said, "'Local Area Connection' doesn't have a valid IP configuration," and it said it had fixed that.  Then I was able to see that computer A remained the only item listed in Devices on LAN.  But computer A (and not computer B) was still reporting an IP address conflict, and still couldn't view webpages.

Following another thread, I checked the modem's webpage for information on its range of available addresses.  But there didn't seem to be one.  Even if I found one, it would presumably make no difference.  The modem was going to work only with 192.168.1.64.  Assigning other static IP addresses would apparently not help.  But why would it be better to let computers acquire their own IP addresses, if 192.168.1.64 was the only one available?

I did a revised search.  This led to a webpage with several suggested steps to resolve DHCP problems.  The webpage said that an IP address conflict was one kind of DHCP problem.  It suggested typing (in a command window) "show ip dhcp conflict:".  I tried that.  The reply was, "'show' is not recognized as an internal or external command, operable program or batch file."  An old thread offered this interesting theory, about a system having a modem like mine:

The modem will only hand out one LAN IP address on the network. So the first device to request an IP will be the one to get it. If another device makes a request for an IP it will be denied and that computer will not have internet access.

Another poster in that thread revised that:

Slight correction, the last device to request an address is the one that gets it. So if you have two devices active at once you will get address stealing from each device as the DHCP leases are renewed.

Neither of these seemed to explain what was actually happening on my system.  Any way I sliced it, computer A was the junior partner.  I tried a revised search and then turned to a missing piece of the puzzle:  how did the switch work?  That was a matter for another post.

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 (8.8.8.8 and 8.8.4.4).  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 192.168.131.1.  In the Windows XP machine, it reported 192.168.1.64 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.

Windows 7: IP Address Conflict: Maybe It's the Modem!

I had been wrestling for days with a home networking problem.  The problem was that either of my two computers could go online, by itself, when I would connect it to the DSL modem directly or through a network switch; but when I would plug them both into a network switch or router, neither would go online or connect with each other.  Plugging both in at the same time would quickly produce an error message:

Network Error

Windows has detected an IP address conflict

Another computer on this network has the same IP address as this computer.

Most recently, I had explored the possibility that the problem was with a corrupted Windows 7 installation on computer A.  I had reinstalled Win7 on computer A with a brand-new installation; but as soon as I connected it to the switch, both computers were once again unable to go online.

I didn't want to go through the Win7 setup process again, so I replaced that new installation with one that I had made a day or two after the initial installation.  Eventually, computer A, with this day-old installation, did give me the Network Error message.  Interestingly, though, computer B did not.  It was now able to stay connected, through the switch, while computer A was failing to connect.

I had a laptop, running Vista.  It had been a while since I had tried to connect it to this wired network.  I connected it directly to the modem.  It was able to go online that way.  I connected it to the switch while computer B (but not computer A) was connected.  The laptop reported an IP address conflict.  This suggested that the problem was with computer B.  To test that, I removed computer B from the switch and plugged in computer A and the laptop.  But no, those two had a conflict as well.  Finally, I plugged in the laptop and a Windows XP computer.  Those two had an IP address conflict as well.  So it was not some kind of flaw with Win7.

This brought me back to a problem that I had considered previously.  I had seen, somewhere, an indication that the DSL modem was responsible for assigning IP addresses.  I had followed up on this partway:  I had called AT&T, and they had told me that, as long as a direct connection between the computer and the modem was successful, they could not provide me with any further free assistance.  I had had the option of paying for assistance, and at this point it seemed I should have taken that option, because now I was thinking that the modem was failing to assign IP addresses.  Well, but OK, now that it was diagnosed, I wondered if I could fix it myself.

I had bought this modem from AT&T about two and a half years earlier.  My previous notes on it did not detail the setup process.  I think maybe AT&T took care of that for me.  I had moved to another place; the modem had spent some time on a shelf.  But now it was back.  I looked on the bottom.  Nothing there specified a model number, but I guessed that's what the number 2210-02-1022 was.  It said it was "Style MSTATEA."  Motorola didn't seem to know anything about it.  At first, there didn't seem to be a user's guide, but then I figured out a search that got me somewhere.  The manual that I found said there was a web-based configuration page, which I could find at http://192.168.1.254/.  I went there.  It showed me a basic Connection Information and Modem Information and Local Network screen.  Here, I saw that the modem's model number was 2210-02 and I was using software version 7.7.5r8.

At the left side of that screen, I clicked on Login.  It said, "You are currently connected to the Internet."  I went into Advanced > Connection Configuration.  It asked for the Modem Access Code printed on the bottom of the modem.  Apparently this was secret information, so I decided not to type it in this post.  I entered the code.  Evidently I didn't need the login information I had gotten from the manual.  The manual said the default username was "admin" and the password was something that I created on the spot.  It already had the login information for my AT&T account there.  I remembered that a tech support guy had instructed me to set PPPoE as the protocol; that was still there.  The manual (page 9) said,

Your Modem serves Dynamically-assigned IP addresses by default.  Be sure to configure each computer connected to your Modem to accept a Dynamically-assigned IP address, commonly referred to as DHCP.

The instructions, translated into Win7 terms, essentially had me go into Control Panel > Network and Sharing Center > Change adapter properties > Local Area Connection > Properties > TCP/IPv4 > Properties > Advanced.  There, it looked like DHCP was set already, as the manual said.  Trying something else, I went into the router's Advanced > PPP Location option.  It said, "PPP is on the modem."  I had an alternative:

PPP is on the computer, gateway or router. This should only be used if you need to run a PPPoE client on your PC or you use another device (e.g., gateway or router) to initiate a PPPoE session. This is often referred to as "Bridged" mode.

I tried that.  The router's internal webpage gave me these further instructions:

PPP Location Warning

PRINT OR RECORD THIS INFORMATION NOW

When using Bridged mode, your access to the modem becomes limited. To return to the DSL modem user interface after this change you need to directly connect your PC to the modem without any gateway or router between the modem and the PC, and configure your computer appropriately.

Configure the IP address of your computer to be on the same network as the modem by using an IP address of the form 192.168.1.x (except 192.168.1.254) and a network mask of 255.255.255.0.

You may also return to the DSL modem user interface by resetting the modem back to its initial defaults. All configuration changes and other settings will no longer be available if this is done. To reset the modem press the "Reset" button located on the back of the modem.

Modem Restarting

The modem can be used after the power light has been steady green for at least 15 seconds.

That approach might have worked if I had still been using my router, but I wasn't.  I was using a network switch, and it wasn't playing ball.  Apparently switches weren't capable of doing the bridge thing.  I reset the modem (didn't have to connect directly; a switch was apparently like a straightpipe for that purpose).  Now, in the modem's Connection Information screen, I got back an Internet IP Address and Internet Gateway Address after a few seconds.  Now that I had gotten over my panic and saw that I could rescue the situation, I actually read the instructions and saw that I hadn't tried the part about configuring the computer's IP address to be 192.168.1.x.  So I went back and did it all again, and this time I did that part too, back in the same location as above ( Control Panel > Network and Sharing Center > Change adapter properties > Local Area Connection > Properties > TCP/IPv4 > Properties.  There, I replaced the automatic settings with the numbers shown above.  Still didn't work.  Windows Network Diagnostics started up automatically.  After a minute or two, it said it couldn't identify the problem.  So I guessed that maybe I had it right the first time, that I needed a router instead of a switch.  But that didn't make any sense.  I had used this switch with this modem before.

So, alright, the joke was on me.  I had to pay AT&T to make the same switch work with the same modem, where they had worked without a problem before.  In the meantime, while I was on hold, I tried to set the modem back the way I found it, but now I wasn't able to connect.  So that was good.  AT&T would have to help me with that.  I could get some more free service out of them before I had to pay them.  And I did.  The guy was very helpful at getting me back to where I started.  It took an hour.  Then he passed me on to AT&T's paid service (877-831-2880).  The phone there rang and rang.  Evidently AT&T wasn't so eager to take my money.  No canned voice giving me information on what number I had reached, or anything.  But at least no hold while listening to godawful music specially selected to discourage people from calling AT&T free tech support.  After ringing for several minutes, I hung up and tried that number again.  This time I did get a canned voice.  So apparently he put me through to the wrong number.  This, he said, was ConnectCheck.  It allowed me to choose tech support.  It rang and rang.  So maybe he was right after all.  He said they would be there until, oops, maybe the wrong time zone.  Friday night, too late, probably would have to wait until Monday.  AT&T, I love you!

So let us review.  How did the guy get me back to working order?  I think we mostly just did ordinary things.  He had me reboot into Win7's Safe Mode with Networking and see if I could browse.  I could.  So he thought maybe the problem there was with antivirus software.  We didn't pursue that back in Normal Mode, though.  He had me do hard reset on the modem, and then log into the modem's webpage, but I think we just looked at information there.  He really had no idea what a switch was; it took him a while to wrap his head around the concept.  Ultimately, he and his managers concluded that the IP Address Conflict error had to be coming either from a bad switch or from bad drivers.  Did I need drivers for the switch?  It was a Netgear FS605 v3.  Well, there was an installation guide.  A manual!  RTFM!  Fortunateliy, there was no installation process or software.  Just plug it in, which I had done.  So how about his other theory:  a bad switch?  Anything was possible, but what had happened on my system -- recurrently, it would seem -- that would have wiped out, first, my router, and then my switch?  Was AT&T sending out electromagnetic pulses to drum up customers for its paid support line?  I could get a replacement for $25 including tax at Sears, or a few bucks cheaper online if I didn't need it right away.

While I was talking to the guy, I plugged in my Vista laptop again.  It came up with a different error message than before.  In addition to the one about an IP conflict, it gave me an option to "Automatically get new IP settings for the network adapter "Local Area Connection."  It also advised turning off the modem or router and unplugging its power cord and then replugging after 10 seconds.  I tried the automatic solution first.  That immediately disappeared after I tried it.  It offered an option to "Reset the network adapter "Local Area Connection,'" so I tried that next.  That failed too, so I went on to unplug the modem, and simultaneously did likewise with the switch, and then replugged them sequentially, waiting for the modem to show solid green on four out of five lights before replugging the switch.  Most of these were steps that I had tried many times before at this point.  They didn't make any difference.

At this point in the game, pending paid support from AT&T which wouldn't materialize until Monday (this was Friday night), I decided that the modem was not the problem.  But what was?  That question called for a new post in this continuing saga.

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.