Odd DNS problem

[gshaw]

Was just running Angry IP Scanner to grab the MAC addresses of some new PCs yesterday but started feeling rather when none of them showed up in the list. Did a quick ipconfig and the IP addresses were right but the name resolution completely wrong! In the end it was showing as if there were 2 computers with the same IP responding yet I could see that there weren't any conflicts.

 

Checked DHCP and leases were fine, went to DNS and then the problem showed!

 

Each IP had 2-3 A records associated with it! So basically I had...

 

10.x.x.145 - Room21 (A)

10.x.x.145 - Room14 (A)

 

And so on. Event Viewer has no errors since Jan (when I fixed a metadata cleanup from a dead DC)

 

It's AD integrated DNS, 2 DNS servers (1 on the DC, one on another server). That's been setup ages, maybe it's wrong?

[Diello]

Have you got DNS scavenging enabled?

[gshaw]

Doesn't seem like it, I'm guessing it therefore isn't removing old records once they're no longer valid?

[Geoff]

Yes. You can check if that's happening by looking in your rDNS zone and sorting the display by the hostname column.

[SpuffMonkey]

You can get this happening if you re-Ghost Pcs with a new SSID - they lose permissions on the existing DNS record and can't refresh it.

[bizzel]

To avoid duplication, take a look at my post here for checking and enabling scavenging.

 

http://www.edugeek.net/forums/146909-post7.html

[Geoff]

You can get this happening if you re-Ghost Pcs with a new SSID - they lose permissions on the existing DNS record and can't refresh it.

 

You can allow non-secure updates and get round this problem. You would want to do this anyway in a mixed environment otherwise non-windows machines will not be able to register themselves in dns.

[gshaw]

Thanks for the link Bizzel, never knew there were that many boxes to tick to enable it - will try that soon, leases are set at 8 days so will your settings from the linked post be OK?

[PiqueABoo]

> leases are set at 8 days so will your settings from the linked post be OK?

 

That relationship is quite complicated, but doesn't matter too much unless you're seriously bothered about replication traffic. IIRC 8 days is the default DHCP lease, so stick with the defaults for DNS scavenging.

 

Very key point: If you have any manually added DNS RR's then make sure scavenging is turned off on the properties of those particular records.

Edited May 1, 2008 by PiqueABoo
typos

[gshaw]

Dredging up an old thread but enabled scavenging today as per the instructions above but keeping getting a 2502 event "Event ID 2502 - "A scavenging cycle has just been completed however no nodes were visited".

 

Went through Google and found that I needed to check "The Zone can be Scavenged after" date, as sometimes you have to wait for that interval to pass before scavenging. However mine is set to 01\01\1601 00:00:00 )

 

The reverse zone is fine and has 3rd August as the date, which makes sense but why is the forward zone gone all weird

 

EDIT: just tried reloading the zone and that seems to have done it... very odd!

[Geoff]

DNS stores it's data in a Jet database. This isn't exactly the most reliable of database engines.