DHCP server is running on my DC (windows 2008 r2). It seems when I need to reboot my laptop or a VM, a new IP is set. The issue is with my DNS entries, I see a bunch of entries for the same host with some old IPs. Hence, when I go ping it may grab one of the older IPs and I would need to wait a few minutes before my laptop successfully resolves the correct IP.

For example, workstation1 has an IP of but when I reboot it, it comes up with In DNS, I'll have two entries for workstation. This also happens with any linux clients as well as MACs.


You need to use DHCP reservation. DHCP reservations provide a mechanism by which IP addresses may be permanently assigned to a specific client based on the MAC address of that client.

To configure reservation using the DHCP console, select Start -> All Programs -> Administration Tools -> DHCP and select the DHCP server and unfold the appropriate scope from the tree in the left panel. Within the scope sub-list, select Reservations.

Right click on Reservations and choose New Reservation... from the menu to launch the New Reservation dialog.

Begin by entering a name for the reservation followed by the IP address from the currently selected scope which is to be reserved for the client together with the MAC address of the client (or more specifically the network adapter of the client). Finally specify whether the reservation is to be made for BOOTP or DHCP clients, or both. Once the information has been entered click the Add button. When all reservations have been entered click Cancel to close the dialog.

  • I dont want to reserve any IPs. I want DNS to stop allocating A records. I think I need to look at scavenging options. (I'm not a windows admin).
    – sdot257
    Mar 2 '12 at 19:38
  • @luckytaxi - but then you'll be left with no name resolution (or netbios, which isnt accurate for long computer names)... Mar 2 '12 at 19:41
  • All i remember is at my previous job, I could reboot my laptop 5 times a day and I would get the same IP. It may change a week later but each reboot never yielded a new IP. At my new gig, for some reason, I keep getting new IPs. Hence, new DNS records are created.
    – sdot257
    Mar 2 '12 at 19:44
  • @luckytaxi The client is releasing its IP lease during the reboot. Maybe this didn't function correctly at your previous job? Should be able to get the DNS under control, though. How is the DHCP server configured regarding DNS updates? Mar 2 '12 at 21:18
  • That I'm not sure, like I said I'm not the windows admin. At my current job, there isnt a dedicated windows admin so I kind of got stuck with it. :-)
    – sdot257
    Mar 2 '12 at 21:22

Easy Solution is to extend the DHCP lease time (6-8 hours is good for keeping an address throughout a work day). Read some of the following article to help you determine a good timeframe.


If your lease time is already set to a sufficiently long duration, there's likely something a bit wrong with the DHCP server's setup with identifying MAC addresses that are still retaining a leased address.

  • Looks like lease time is set to 8hrs. I'm not a windows guy so I'm not sure where to look for some of these other options. I came across an option under DHCP where it can handle dynamic DNS updates. All of those are checked BTW.
    – sdot257
    Mar 2 '12 at 20:03
  • I'm not too much of a Windows guy anymore. Dynamic DNS updating from the DHCP server-side sounds like it should help with your immediate issue. The fact that your DHCP server isn't reissuing the same IP to the host within the lease time frame is still a bit of a concern though. You may find yourself running out of pool addresses on that Class C network.
    – NcA
    Mar 2 '12 at 20:29
  • I took a look, it looks like it "releases" the IP but there are at least 3-4 old DNS entries. I took a look and our DHCP pool looks fine. Roughly 15 addresses are handed out and that sounds right. I go look in the DNS console and for my laptop alone, I see 3-4 entries.
    – sdot257
    Mar 2 '12 at 21:21

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