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  • DNS Issue: "A" Record Keeps Changing

    Last night I updated several virtual machines that were running on VMware Server 1.02 to VMware ESXi 4.1. Everything seemed to work except for one hitch - every server that I migrated ended up loosing their original virtual network interface and had it replaced with a new one. The new network interface was configured for DHCP, and as such changed the DNS entrieswhen recieving their new IP information. I repaired this, restoring the original static IP addresses.

    (The VMware conversion process caused this problem, I followed these directions to fix it.)

    The problem is, every so often, the DHCP-based entries re-appear in DNS.

    As you can imagine, this is causing all kinds of connection issues with services today.

    It's acting like DNS replication is causing the problem, but I can't seem to track it down. It appears as though the change is occuring every hour at the top of the hour (I'm getting this from the timestamp value reported in the DNS console.)

    A bit of information about my DNS setup: I have 4 DNS servers - three running Windows Server 2003 R2, one running 2008 R2.

    Whenever I change the entry, I change it on the 2008 R2 server (because it's faster, no other reason).

    Has anyone else seen this problem? More importantly, anyone know how to cure it? Can someone tell me WHY it's happening?

    Thanks in advance,
    --

    ScatterBrain

    "I reject your reality and substitute my own!"
    -- The Mythbusters

  • #2
    Re: DNS Issue: "A" Record Keeps Changing

    Raise the serial number of the DNS zone on the 2008 system after the change.
    This makes sure it has the highest serial number, and for DNS he has the most recent updates.

    This should be done automatically though but sometimes it doesn't work well. Giving him a little can help.
    Also did you reboot the VM's after removing the ghosted NIC?
    Marcel
    Technical Consultant
    Netherlands
    http://www.phetios.com
    http://blog.nessus.nl

    MCITP(EA, SA), MCSA/E 2003:Security, CCNA, SNAF, DCUCI, CCSA/E/E+ (R60), VCP4/5, NCDA, NCIE - SAN, NCIE - BR, EMCPE
    "No matter how secure, there is always the human factor."

    "Enjoy life today, tomorrow may never come."
    "If you're going through hell, keep going. ~Winston Churchill"

    Comment


    • #3
      Re: DNS Issue: "A" Record Keeps Changing

      First, thanks for replying!


      Originally posted by Dumber View Post
      Raise the serial number of the DNS zone on the 2008 system after the change.
      This makes sure it has the highest serial number, and for DNS he has the most recent updates.

      This should be done automatically though but sometimes it doesn't work well. Giving him a little can help.
      I'll try the serial number trick in just a minute.


      Originally posted by Dumber View Post
      Also did you reboot the VM's after removing the ghosted NIC?
      As for the reboot, I honestly can't remember. But I will reboot them before I make the next DNS change.


      Will report back in a few minutes.
      --

      ScatterBrain

      "I reject your reality and substitute my own!"
      -- The Mythbusters

      Comment


      • #4
        Re: DNS Issue: "A" Record Keeps Changing

        OK, all three virtual machines that were converted, have been rebooted. Before I rebooted them, I confirmed that the "Ghosted" NIC was indeed gone, and it was. I also confirmed that the current NIC was set properly, and that was true as well.

        I have changed the DNS records to reflect the proper information and set the zone increment number to a random higher number on the 2008 Server. It's been about 15 minutes and things seem to be sticking. I'll wait for another hour or so before reporting back.


        Thanks again for the help.
        --

        ScatterBrain

        "I reject your reality and substitute my own!"
        -- The Mythbusters

        Comment


        • #5
          Re: DNS Issue: "A" Record Keeps Changing

          30 minutes and so far so good.
          --

          ScatterBrain

          "I reject your reality and substitute my own!"
          -- The Mythbusters

          Comment


          • #6
            Re: DNS Issue: "A" Record Keeps Changing

            Five minutes later and the bogus DNS records are back.

            So back to square one.
            --

            ScatterBrain

            "I reject your reality and substitute my own!"
            -- The Mythbusters

            Comment


            • #7
              Re: DNS Issue: "A" Record Keeps Changing

              Here's my suggestion:

              Remove the virtual NIC from the guest. Reboot the guest. Remove any "ghost" interfaces from the registry on the guest. Reboot the guest. Add virtual NIC to guest. Assign ip addressing information.

              Comment


              • #8
                Re: DNS Issue: "A" Record Keeps Changing

                What I think I have found is that my DHCP server (a Windows 2003 Server) still had entries for the virtual machines in the leased addresses. I've removed those leases and am hoping that they don't re-appear.

                Does this make any sense to anyone? First, why would DHCP still have the leases listed? Second, why would DHCP be re-adding the entries?

                I do have DHCP setup to dynamically add DNS entries, but I've never seen it add an entry like this - when a machine didn't ask for a DHCP address. Maybe I'm missing something - it has been a long day.
                --

                ScatterBrain

                "I reject your reality and substitute my own!"
                -- The Mythbusters

                Comment


                • #9
                  Re: DNS Issue: "A" Record Keeps Changing

                  Were the MAC addresses for those ip address leases different? A DHCP assigned ip address is assigned based on the MAC address of a host so if the MAC addresses for the 'ghost" virtual NIC's were different then that would explain having multiple address leases per host. If your DHCP server is configured to update DNS that would explain why you have the DNS server A record issue.

                  Comment


                  • #10
                    Re: DNS Issue: "A" Record Keeps Changing

                    DHCP seemed to be the cause. Once I removed the leases bound to the bogus IPs assigned to each server, the DNS entries have stabilized (tested overnight) with the proper static IP information.

                    I'm still unsure as to WHY it was happening, but I can at least move on now.
                    --

                    ScatterBrain

                    "I reject your reality and substitute my own!"
                    -- The Mythbusters

                    Comment


                    • #11
                      Re: DNS Issue: "A" Record Keeps Changing

                      Originally posted by joeqwerty View Post
                      Were the MAC addresses for those ip address leases different? A DHCP assigned ip address is assigned based on the MAC address of a host so if the MAC addresses for the 'ghost" virtual NIC's were different then that would explain having multiple address leases per host. If your DHCP server is configured to update DNS that would explain why you have the DNS server A record issue.

                      The leases were pointing to the MAC address of the new (non-ghosted) network interface in the converted virtual machines. Since I moved the virtual machines to a new host, the new MAC addresses make sense.

                      What doesn't make sense is that AFTER I switched the virtual machined from DHCP to STATIC, DHCP kept re-adding the bogus information. I can see, and desire, DHCP to do this when a client asks for it. But there is no need to do this again and again, the first time is all that is needed.

                      This repeating is what I need to get to the bottom of. I need to prevent this from happening in the future.
                      --

                      ScatterBrain

                      "I reject your reality and substitute my own!"
                      -- The Mythbusters

                      Comment


                      • #12
                        Re: DNS Issue: "A" Record Keeps Changing

                        Before changing from DHCP to a static IP address I would make sure you run an IPconfig /release.
                        This releases the DHCP address information from the DHCP database.

                        Is DNS scavaging configured?
                        How are the DNS settings configured in the properties of the DHCP server?
                        Marcel
                        Technical Consultant
                        Netherlands
                        http://www.phetios.com
                        http://blog.nessus.nl

                        MCITP(EA, SA), MCSA/E 2003:Security, CCNA, SNAF, DCUCI, CCSA/E/E+ (R60), VCP4/5, NCDA, NCIE - SAN, NCIE - BR, EMCPE
                        "No matter how secure, there is always the human factor."

                        "Enjoy life today, tomorrow may never come."
                        "If you're going through hell, keep going. ~Winston Churchill"

                        Comment


                        • #13
                          Re: DNS Issue: "A" Record Keeps Changing

                          Sorry been a bit busy the last couple of days. Thanks again for responding.

                          Originally posted by Dumber View Post
                          Before changing from DHCP to a static IP address I would make sure you run an IPconfig /release.
                          This releases the DHCP address information from the DHCP database.
                          Yeah, I should have tried that.


                          Originally posted by Dumber View Post
                          Is DNS scavaging configured?
                          Yes. Set for 7 days, I have the 2008 server set to do the scavaging.


                          Originally posted by Dumber View Post
                          How are the DNS settings configured in the properties of the DHCP server?
                          I have it setup like this:

                          [x] Enable DNS dynamic updates.
                          [x] Always dynamically update DNS A and PTR records.
                          [x] Discard A and PTR records when the lease is deleted.
                          [x] Dynamically update A and PTR records for DHCP clients that do not request updates.
                          Last edited by ScatterBrain; 9th September 2011, 13:52. Reason: Fixed a typo
                          --

                          ScatterBrain

                          "I reject your reality and substitute my own!"
                          -- The Mythbusters

                          Comment

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