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Forward DNS updating and Scavenging

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  • Forward DNS updating and Scavenging

    Someone explain this to me. Ok two things. Using AD Integrated DNS on server 2008 R2 SP1. Domain currently has around 3700 computers. Computer A is on the network and stops working. Needs parts. Computer B is installed and given the same ip address. I look in forward DNS and both are still there. Two different names A and B and same address. I look in reverse and see the it updated. Computer A was removed and B was added.

    I am missing something with forwarding? Is it supposed to update and computer A's record removed and B only remain when using the same IP. At this time we pretty much use only static addressing here on each client.

    Is this what scavenging would normally clean up, and if so why does reverse update like its supposed to? When I get to a point and can turn scavenging on how does that affect all the clients like servers etc or non windows boxes that are added to DNS. Will it remove all of them and I need to add them all back manually. It's my understanding I will.


  • #2
    Re: Forward DNS updating and Scavenging

    IIRC scavenging only expunges stale Host (A) records after 7 days (by default), so when a new PC picks up the IP address from DHCP it will register it's new Host (A) record in DNS straight away. Even with static addressing a Windows PC will automatically register it's IP in DNS at assignment time.

    However, a reverse lookup zone works the other way. Multiple names can resolve to a single IP in a forward lookup zone, but a reverse lookup zone resolves an IP to a name so the new registration overwrites the old.

    E.g. on an SBS Network the server will register (amongst other things) Host (A) records for it's DNS name and also for companyweb and connect, but only the actual server name will have a PTR record in the reverse lookup zone.
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    • #3
      Re: Forward DNS updating and Scavenging

      Thanks for explaining that. So looks like it is working well. I just need to get scavenging setup for the duplicate host records to be taken care of.


      • #4
        Re: Forward DNS updating and Scavenging

        Actually, it's completely possible to have erroneous PTR records for the same IP point to different hosts.

        Aging and scavenging will only affect dynamically registered records. Static records will not be affected. Note that dynamic DNS records have nothing to do with DHCP, as Cruachan mentioned.

        When you configure aging and scavenging, be sure to configure it in the server properties and the zone properties. It needs to be enabled in both locations.

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