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Disappearing Computers

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  • Disappearing Computers

    Small network, two 2008 R2 Servers with Active Directory. Several Win 7 Enterprise, one XP Pro SP 3. All updated as required.
    Two days ago, connectivity between the XP and a Win 7 computer suddenly ceased. Other Win 7 computers can see all others, and show them under Network in Explorer.
    All of the computers can be found, using Search Active Directory, from all Win 7 and 2008 R2 computers. However, both Domain Controllers and one Win 7 fail to show the same two particular computers (one Win 7, the main machine, and the XP).
    The XP machine will not show the network under Microsoft Windows Network (access is denied).
    However, I can access all machines from the Win 7 computer that is invisible! And, in fact, from another Win 7 computer that has not been rebooted lately.

    This was a problem in the past, that I could not cure, which disappeared. It is now back with a vengeance.

    Last edited by dickins_paul; 7th June 2011, 12:32. Reason: Content removed

  • #2
    Re: Disappearing Computers

    "Content unavailable or you do not have permission"
    You have plenty of posts so can add an image directly to this page
    Tom Jones
    MCT, MCSE (2000:Security & 2003), MCSA:Security & Messaging, MCDBA, MCDST, MCITP(EA, EMA, SA, EDA, ES, CS), MCTS, MCP, Sec+
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    Ossian Ltd

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    • #3
      Re: Disappearing Computers

      XP machine renamed with ease. Did not cure networking snafu. I think this image might help. If not, please advise.
      Attached Files


      • #4
        Re: Disappearing Computers

        The image shows Gallowglass Explorer on Network. Note the computers list to the bottom left shows Leicester (unavailable) and Lancaster, its new name. Note that Gallowglass is present.

        Looking at icons top right, Gallowglass is absent. Active Directory allows logging on, renaming, etc., but nothing helps to cure Explorer, which means that I cannot use Lancaster other than through Gallowglass. Copying, etc., is possible from Lancaster using Gallowglass Explorer, so what is going on here? Note that the old name, Leicester, is there, but not the new one. Doesn't stop me using Lancaster from Gallowglass.

        Truly weird!
        Attached Files
        Last edited by dickins_paul; 7th June 2011, 13:58. Reason: Image added and info.


        • #5
          Re: Disappearing Computers

          Here is Explorer on Lancaster, the XP Pro SP3 machine. Note that I can access a share on the Datacenter, Bucephalus. But, trying to open Windows Network gives the denial object! Using Gallowglass, any file on Lancaster can be copied, edited, etc., to any other machine on the network.
          The two DCs know that the computer was renamed, but won't show that or Gallowglass in Windows Explorer on their monitors.
          Attached Files


          • #6
            Re: Disappearing Computers

            Have you searched the eventviewer on the XP machine for "Service Control Manager" events concerning the "Computer Browser service".
            Is the windows firewall enabled on the client?
            Are all computers on the same subnet?


            related subject:
            - What’s the Microsoft Computer Browser Service?
            - Hide a Server from the Microsoft Computer Browser Service
            Last edited by Rems; 14th June 2011, 14:13. Reason: typo, also added the links

            This posting is provided "AS IS" with no warranties, and confers no rights.


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            • #7
              Re: Disappearing Computers

              I have installed Win 7 Ult SP1 on the XP box, and it is still invisible to Explorer on any machine, other than the single Win 7 Gallowglass: it does not matter what name it has, that machine sees it!

              There was some strange message from the DC, but I am in the middle of changing monitors, since the AGP card on the XP has no Win 7 drivers! I shall try again to add a computer, but the DC would not allow that and gave it its old name, which is really peculiar.

              Plus, everything was working until three or so days ago, with all machines on one internal subnet (as always, for over a decade!), and firewalls on Windows have no import, since some of the machines have different settings and still work together. Except for the two mentioned previously.


              The ex-XP machine has been removed, especially since it is a Dell Precision 650 and not worth the bother. Will cannibalise for drives, etc.

              Now, going entry to entry through Services on two Win 7 machines, one (Gallowglass) that can see all the computers, and another that can see all, except Gallowglass, there is no difference whatsoever between them.

              What else controls Windows Explorer? Yes, it's an intrinsic part of the OS, but so what, since I can't have it working properly? The DC allows me to log on with Gallowglass, as it did with the XP box, and, it can list it in Computers, but it also fails to show it under Network with Explorer.
              Last edited by dickins_paul; 9th June 2011, 04:12. Reason: Additional info.


              • #8
                Re: Disappearing Computers

                Continuing problem:
                a) Removed the XPPro SP3 box.
                b) Brought home an HP XW4400: transferred some SATA drives to it, and others, U320 SCSI, went to one of the DCs (removed its SATA drives and added two SCSI).
                c) Installed Win7Ult SP1 on the XW4400, and added it to the network. Can log on, of course, but can see, in Explorer/Network, all the other computers, except Gallowglass and itself. It can access those computers it can see, thank goodness.
                d) Gallowglass cannot see the new computer, but does see all the others, as it could before.

                I also brought another XW4400, to remove the weak white box (a 32-bit mother board, with an X64 Athlon processor), Oxford, by transferring the drives to it, and hoping Win7 accepts the changes. Back up done, of course. Probably have to reactivate, but that's minimal. Then to see what happens with the Explorer/Network.

                Utter botheration, this problem, that had also occurred a few months past. I couldn't cure it, but one of the update Tuesdays did, but now its back.

                I fear no one has a cure!
                Last edited by dickins_paul; 11th June 2011, 14:03. Reason: Clarification


                • #9
                  Re: Disappearing Computers

                  Doing my normal stuff and suddenly notice that Gallowglass, the invisible one on my small network, has decided to add Cornwall, the new computer, that I added yesterday, to the Network and, of course, it is reachable.

                  Nothing on Cornwall, or the other computers has changed at all.
                  The attached files show Cornwall, and Gallowglass, with Cornwall's drives visible.

                  I had thought of changing the DC and starting a whole other private domain, but not just yet.

                  I am awaiting bits and pieces so that I can redo Oxford on the 'new' HP XW4400.

                  Now, on the old white box, because Win7 X64 is installed, even though the motherboard is 32-bit (see prior post), it won't install 32-bit files, for an Adaptec SCSI card, with an HP ScanJet IIc attached (an old scanner of excellent quality that I wish to keep working). Will try to install Win7 X86 on the white box.

                  I shall wait with bated breath to see if the network shows the 'new' Oxford and the renamed current machine.

                  There are posts about my overall problem on Microsoft's support pages, but there are no fixes, it would seem.
                  Attached Files
                  Last edited by dickins_paul; 12th June 2011, 03:48. Reason: Clarification


                  • #10
                    Re: Disappearing Computers

                    My 2 cents here:
                    - please check that the Network Discovery is ON on the Win7 machine that "disappeared";
                    - please check what kind of network is the Win7 computer attached to: is it Private, Domain, Public? Given the fact that is in a Domain, the answer should be obvious, but just to be sure ...
                    - one of the options you have in Network and Sharing Center is to draw a map of your entire network. In domain networks, this option is disabled by default. By any chance, is it enabled on yours? If the answer is Yes, I would let the computer draw the entire map.

                    Sorin Solomon

                    In order to succeed, your desire for success should be greater than your fear of failure.


                    • #11
                      Re: Disappearing Computers

                      Hi Sorinso,
                      a) Network Discovery is 'ON'
                      b) Domain (for ever!)
                      c) nowhere available

                      Plus, services identical for all Win 7 machines.
                      UAC turned off, too.

                      Since it's my private network, a single user for all computers.
                      Network Discovery is on for all computers.

                      Given that this has been current practice for years, why has this come up this year? Must be something with Win7 but what?????? Of course, I know that 2008 R2 is Win 7 hardened; after all, the Explorer is identical in style! Even if it doesn't show what I would like it to! How is it that the DCs show all computers, enable logging on, but explorer.exe in the \Windows directory provides inaccurate information?
                      Last edited by dickins_paul; 12th June 2011, 12:39. Reason: Spelling!


                      • #12
                        Re: Disappearing Computers

                        It has not much to do with updates. What is shown in 'Network' is a "browse list", any computer than can collect the list will also be in the list.
                        If there are different lists there could be multiple master browsers on the segment causing the problem.

                        The Computer Browser Service is a networking technology used by Windows-based computers to collect, distribute, and obtain browse lists, which are collections of information about workgroups, domains, and the computers within them. On a network there are different types of browse servers and browse clients together are called the browser system.

                        The Computer Browser service operates by exchanging a set of NetBIOS over TCP/IP (NetBT) broadcast and unicast messages. There is no support for computer browsing over IPv6. If NetBT is disabled, the Computer Browser service can no longer operate. This means that for a network that has NetBT disabled and is just using the Domain Name System (DNS) and Active Directory, you cannot view any LAN groups or servers using the Entire Network window. You must use find computers using Active Directory.
                        (more, TCP/IP Fundamentals for Microsoft Windows -> See "Appendix C Computer Browser Service", Page 518 )

                        When computers are no longer connected to the network it can take longer to disapear from the browse list than appearing on it. To allow for messages that might be lost during transmission, the master browse server does not remove a server from its list until three Host announcement periods (36 minutes) have passed. Host Announcement message to announce its presence to the master browse server are transmitted every 12 minutes.

                        Actually, as the "browser service" is a legacy service, if it is not really needed to browse to computers by using "Network", then you can savely ignore whether the list is complete or not you can simply hide 'Network' from start menu and explorer on all clients and member servers, so there is less to worrie about. And simply ignore any warning events concerning the "Computer Browser service" on the computers.

                        If you have to troubleshoot the Microsoft Computer Browser Service, start with finding the master browser on the segment on which the server is located. Run this command on the segment on which the missing computer resides: browstat status
                        Note! Windows Server 2008 sets the startup state of the Computer Browser service to disabled by default.


                        This posting is provided "AS IS" with no warranties, and confers no rights.


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                        • #13
                          Re: Disappearing Computers

                          Thank you Rems, although I did not understand everything you wrote!

                          I enabled the Computer Browser Service on both DCs.
                          Then, little by little, all the computers began to see each other, except Gallowglass, the only one that can see them and itself, too.

                          It might well have been to do with one update: after all, when I had the problem previously, it only went away at the time of an Update Tuesday.

                          It's nice that it's almost cured! At least, using Gallowglass, I can access every computer, and the others can _almost_ do the same: without having to use shares, which, to me, are an unnecessary chore!


                          • #14
                            Re: Disappearing Computers

                            Are the clients, servers and DC(s) all on the same subnet?
                            Here's a script that determine the master browser(s), run this script on few of the computers.

                            There should only be one master Browser on each segment! Additionally, The browser service is bound by broadcast segments and each master browser on the network maintains its own separate list. On a TCP/IP network the PDC for the domain is the domain master browser it merges these lists into a single domain-wide list.

                            Make sure that on all computers IPv4 is used, NetBT is enabeled and the browser service is started automatically (and UDP Ports 137 & 138, TCP Port 139 are not being blocked). Then search the eventviewer on several systems for Browser and MRxSmb events or Service Control Manager events that have "Browser" in its description.


                            This posting is provided "AS IS" with no warranties, and confers no rights.


                            ** Remember to give credit where credit's due **
                            and leave Reputation Points for meaningful posts


                            • #15
                              Re: Disappearing Computers

                              Rems: thank you, and I went through the whole lot to discover everything is as it should be.

                              What has happened so far is that all computers but the main DC, Bogtrotter in the images, see all other computers. Yes, the other DC sees Gallowglass!

                              The situation is acceptable, assuming it stays that way. Thank you, everyone that has added comments.