Scavenging and Dynamic Updates - General Question

Discussion in 'DNS Server' started by Microsoft, Aug 20, 2009.

  1. Microsoft

    Microsoft Guest

    I've noticed over the years that my Forward and Reverse Loopup zones carry a
    lot of old info. Many situations where the same IP shows up next to many
    hosts, and vice versa.
    My question is, can anyone explain the negative effects this would have?
    I'm assuming it could result in more network congestion and slower
    performance as packets go looking for the CORRECT host? Is that it, or does
    it go deeper.

    As the jack of all trades here, I've always shrugged my shoulders and spent
    my time elsewhere since it didn't seem to be hurting anything. I decided to
    look into it yesterday though. I've implemented scavenging, and set DHCP to
    own update and own the DNS records (hopefully correctly). Just wondering if
    I could get some general feedback on what this can mean for me.

    Microsoft, Aug 20, 2009
    1. Advertisements

  2. Microsoft

    Chris Dent Guest

    Hi Tim,

    It has more of an impact in Forward Lookup Zones. Perhaps most
    importantly because in general, computer don't look for the "correct"
    IP, if they get an answer from DNS for a name they take it as gospel. If
    it doesn't work the computer gives up. It can get quite messy if the
    situation applies to servers as well, connecting successfully becomes

    Reverse Lookup tends to be less of an issue, not as many things use it.
    Still, it's useful to be able to get to a name from an IP. Especially if
    whoever uses the IP is doing something wrong :)

    NetBIOS name resolution is the most likely thing to cause network issues
    if naming is not available, it will result in a lot of broadcasts for
    "Who Has ... ". That doesn't necessarily mean congestion, but it's not
    really a good thing (depending on the size of the environment in question).

    Still, you've configured Aging which is nice because it's all very low
    maintenance if it's correctly set :)

    Chris Dent, Aug 20, 2009
    1. Advertisements

  3. Microsoft

    Tim Guest

    Also, in my attempts to see that DHCP owns the DNS records, I came across
    this setting in DHCP:
    In Properties of the server, on DNS tab, under the option "Enable DNS
    dynamic updates according to the settings below"....
    I DID have "Dynamically update .... ONLY IF REQUESTED".
    I changed that to "Always Dynamically update...".

    None of the documentation I followed said to set it to "always"... it just
    said to set this so that DHCP does the dynamic updates.

    Tim, Aug 20, 2009

  4. Did you set credentials in DHCP properties, or did you add the DHCP server
    to the DnsUpdateProxy group?

    Chris gave you pretty much everything about the plusses and minuses. Read my
    following blog on DHCP and Scavenging. There's also a quoted section from
    Chris regarding short lease times. Chris, I hope you approve. If not, I will
    remove it.

    DHCP, Dynamic DNS Updates , Scavenging, static entries & timestamps, and the
    DnsProxyUpdate Group


    This posting is provided "AS-IS" with no warranties or guarantees and
    confers no rights.

    Please reply back to the newsgroup or forum to benefit from collaboration
    among responding engineers, and to help others benefit from your resolution.

    Ace Fekay, MCT, MCTS Exchange, MCSE, MCSA 2003 & 2000, MCSA Messaging
    Microsoft Certified Trainer

    For urgent issues, please contact Microsoft PSS directly. Please check for regional support phone numbers.
    Ace Fekay [MCT], Aug 21, 2009
  5. Microsoft

    Chris Dent Guest

    Chris, I hope you approve. If not, I will remove it.

    I have no problem with it :)

    Chris Dent, Aug 21, 2009

  6. Thanks!
    Ace Fekay [MCT], Aug 21, 2009
  7. Microsoft

    Tim Guest

    Did you set credentials in DHCP properties, or did you add the DHCP server
    I added credentials to DHCP properties. Sounded from everything I read that
    this was more secure and provided the same results.

    However, the setting I was questioning to is in the DNS tab of the servers
    DHCP properties. I was wondering if there was a right and wrong
    answer to whether I used "Always..." or not.

    So far it hasn't cleaned up anything... but I just set it yesterday. I
    tried running "Scavange stale resource records", but it didn't clean
    anything. I'm assuming that this is only because the "This zone can be
    scavanged after" date is not until 8/27 (since I set yesterday with default
    setting of 7 days). If you see a flaw in my understand, could you let me

    Thanks very much for the replies!
    Tim, Aug 21, 2009
  8. Microsoft

    Chris Dent Guest

    However, the setting I was questioning to is in the DNS tab of the servers
    "always" is normally used when clients aren't able to request updates or
    update themselves. Everything from Windows 2000 up can, so it tends not
    be necessary (not that it'll really cause you any problems).

    In fact, DHCP doesn't have to update for clients at all if you don't
    want it to, anything from Windows 2000 up can register directly without
    You're correct, nothing will be removed until then no matter how much
    you tell it to run :)

    Chris Dent, Aug 21, 2009
  9. As Chris said, the scavenging period is a patience thing. Wait.... Or if you
    know which ones to delete, you can give it a head start and delete them.

    As for that setting in DNS tab, I like to force DHCP to do it, this way it
    owns ALL the records and can update them as the DHCP clients are refreshed,
    just in case they get a new IP.

    Ace Fekay [MCT], Aug 21, 2009
    1. Advertisements

Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.