I'm running a Windows Server 2008 R2 domain. We outgrew our /24 DHCP scope, and I ended up needing to expand it. This was done by exporting the old scope, changing the txt config, deleting the original, and importing the new config. The change made was to alter the subnet mask from /24 to /23 and open the scope up from to

This change was fine, but the problem I am running into is that none of the addresses that are in the 101.0-255 portion are populating into the reverse lookup zone.

I'm not sure what info needs to be provided for this issue, so please feel free to ask for some.


If I go into a forward lookup zone record, uncheck the update PTR record setting, apply it, and then go back in and recheck it, the respective reverse record will be created. However, this has to be done individually so it is not a realistic fix. It does provide insight that there are no errors creating the new records, but something is still preventing it from doing this automatically.


I'm going to post this as an answer even though I can't test it at the moment to prove it out, but I'm fairly certain that I've seen this before. Try this and if it doesn't work then simply undo it. AD isn't dependent on rDNS zones so if this doesn't work it won't create any AD related problems.

IIRC, rDNS zones in Windows DNS are classful. You can create a classless rDNS zone but I'm not sure it's worth the effort.

From the perspective of Windows DNS, your /23 network is actually two /24 networks. 192.168.100.x and 192.168.101.x. If you have a rDNS zone for 192.168.100.x then only devices with an address in that range are going to register in that rDNS zone. You would need to create a rDNS zone for 192.168.101.x in order for devices with addresses in that range to register in that rDNS zone.

So here are two methods you can use to make this happen:

  1. create a rDNS zone for 192.168.101.x


  1. Create a rDNS zone for and let Windows create the appropriate zones for 192.168.100.x and 192.168.101.x. The advantage of this method is that if you ever change the subnet mask again, Windows will create the needed zones as needed.
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  • I actually already have the 101.x rDNS zone in place along with the associate name servers. At this point, address 101.0-11 have been leased out without any entries in this particular rDNS zone. – MooseBalm Nov 2 '15 at 19:07
  • After a couple of days, only 2 DNS records have populated into the reverse lookup zone out of the 18 that have been issued in that portion of the scope. Something seems to be working, but not entirely. – MooseBalm Nov 5 '15 at 17:02

Are you able to get correct leases on the machines that are using the IP's in the new scope? Can you hit the GW from there?

Also, check DHCP reservations, do you have any old ones that might be preventing that from taking place?

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  • Yes, leases are going out correctly and there are no issues with reaching the gateway, or anything beyond. As far as reservations go, there are only a handful of them, and none of them exists in the 101.* half of the scope. – MooseBalm Nov 2 '15 at 17:43
  • Manually add a DHCP lease and see if it pops up in the lookup zone. Couldn't hurt to run a dnsflush either :) – Jonas Lear Nov 2 '15 at 17:45

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