Reducing the No Refresh and Refresh Interval in Windows 2003 DNS

Posted on 2011-05-09
Last Modified: 2012-05-11
What will happen if I reduce the No Refresh and Refresh Interval in DNS?  Our is currently set to 30.  I would like to set it back to the default of 7 but I'm afraid of what will happen.  We are getting some duplicate entries in DNS which is why I would like to adjust the interval.
Question by:Glitterati2006
    LVL 76

    Expert Comment

    30 what days? changing to 7 days? Where are you looking?
    There is no "no refresh" interval, there is the Refresh, retry, Minimum TTL and Expire.
    For refresh, this will mean that there will be more frequent check to see whether the record/zone changed increaseing DNS traffic.  If this is an expiry record change, this will mean if the zone can no be accessed from the upstream server and the period configured has been exceeded, the zone is seen as expired/Invlaid and this server will respond with a no-such zone error.
    LVL 21

    Expert Comment

    You want to set  your no-refresh and refresh intervals according to the length of your DHCP lease.

    The No-Refresh interval is the time between when the record was created and the time it can be renewed/refreshed.  Once the refresh interval expires you have the time of the Refresh interval to update your record before it becomes stale and is scavenged.

    If your DHCP lease time is set to the default of 8 days the recommended no-refresh interval would be 3 days with a refresh interval of 5 days.

    Also make sure you have DNS Aging turned on for both the zone and for the server (RC the Server name in DNS console and select "Set Aging/Scavenging for all Zones", then RC the Zone, Propoerties, Aging)

    You can also allow DHCP to release the DNS record when the lease is deleted.  RC the scope in DHCP console and select Properties, DNS Tab, Check "Disard A and PTR records when lease is deleted".

    Author Comment

    Our DHCP lease is set to 8 days and DNS aging has been turned on for the zone and the server just like it should but for some reason our refresh/no refresh intervals are set to 30 days.  I'm afraid if I change that to something much less (like the default of 7) it will scavenge records that it shouldn't. You're saying this is not the case?
    LVL 21

    Accepted Solution

    It will not scavenge valid records as the DHCP server refreshes the time stamp on the record when it renews the lease or for static clients the client refreshes the time stamp.

    The problem you have with 30 day scavenge cycle is the DHCP lease expires after 8 days (and the DHCP server must not be set to discard the DNS records when the lease expires) then it gives out the same IP to a new client and registers with DNS, however, DNS says this record must be at least 30 days old before I will delete it therefore you get duplicate records for the same IP address.

    If you want to look at records to see if they will be scavenged just click view, advanced in the dns console then look at a record's properties.  You will be able to see the record's time stamp there.

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