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Dual IP

    Question

  • I'm showing dual ip's for a single host in DNS, I have scavenging setup on one of my 2 DNS servers for the following

    At the server level I set "Enable automatic scavenging of stale records to 1 day

    At the server level "Server Aging/Scavenging Properties" is set to No-refresh=4 days, Refresh=5 days

    At the Zone level Zone Aging/Scavenging Properties is set to No-refresh=4 days, Refresh=5 days

    My DHCP lease is 2 days on wired scopes and 4 hours on wireless scopes

    one dupe IP is showing

    one created today at 9am

    one created on 12/16/2016 at 3 pm

    if the first one did not age out yet, why did a second host grab the same IP?

    Monday, December 19, 2016 6:52 PM

Answers

  • The best practices is to set dhcp lease = refresh time+ no-refresh time.
    You should set your DHCP lease time to 9 days, or you should reduce refresh\no-refresh time to match DHCP lease.

    You can read more about correlation between scavenging and dhcp here:
    https://blogs.technet.microsoft.com/askpfe/2011/06/03/how-dns-scavenging-and-the-dhcp-lease-duration-relate/
    • Marked as answer by PDunn001 Wednesday, December 21, 2016 2:16 PM
    Wednesday, December 21, 2016 5:21 AM

All replies

  • Hi,

    any record is examined on server during subsequent scavenging in following way:
    Sum = Record time stamp + No-refresh interval for zone + Refresh interval for zone

    • If the value of this sum is greater than current server time, no action is taken and the record continues to age in the zone.
    • If the value of this sum is less than current server time, the record is deleted both from any zone data currently loaded in server memory and also from the applicable DnsZone object store in Active Directory Domain Services (AD DS) for the directory-integrated "example.microsoft.com" zone.

    You should increase your DHCP leases, because currently new records registers before old one have been deleted.
    Also please check that DHCP server is allowed to update DNS zone after lease expires.

    You can read more about scavenging and aging here




    • Edited by BearEater Tuesday, December 20, 2016 6:15 AM
    Tuesday, December 20, 2016 6:13 AM
  • Dear,

    Please find the link to understand how dns scavenging exactly works.

    https://blogs.technet.microsoft.com/networking/2008/03/19/dont-be-afraid-of-dns-scavenging-just-be-patient/

    Thanks

    Syea.

    Tuesday, December 20, 2016 6:59 AM
  • if my no refresh is 4 and refresh is 5 days, can I have my DHCP lease set to 7 days?. I am allowing DHCP to update DNS zone after lease expires.
    Tuesday, December 20, 2016 12:22 PM
  • The best practices is to set dhcp lease = refresh time+ no-refresh time.
    You should set your DHCP lease time to 9 days, or you should reduce refresh\no-refresh time to match DHCP lease.

    You can read more about correlation between scavenging and dhcp here:
    https://blogs.technet.microsoft.com/askpfe/2011/06/03/how-dns-scavenging-and-the-dhcp-lease-duration-relate/
    • Marked as answer by PDunn001 Wednesday, December 21, 2016 2:16 PM
    Wednesday, December 21, 2016 5:21 AM