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How frequent DNS entries will be refreshed for Non-windows DHCP clients if option "Always dynamically update DNS records" option is enabled RRS feed

  • Question

  • I have DHCP scope for Unix machines and the lease period is 180 days. I have configured the DHCP to use service account to register internal DNS entries on behalf of DHCP clients of the specific scope. I have enabled the option "Enable DNS dynamic updates according to the settings below" and selected "Always dynamically update DNS records". I have seen that the DNS entries are registered for my DHCP clients (Unix machines) in AD. My question is how frequent these DNS update will be refreshed in AD? I would like to know because Scavenging period enabled in my DNS is 7 days. Please help me with an answer.
    Thursday, June 7, 2018 6:52 AM

All replies

  • Hello,

    As far as I know DNS updates can occurs when lease change or is renewed (At 50% of the lease period and after at 75%).

    So in your case if you configure a lease of 180 days with "Always dynamically update DNS records", the DNS update will occur at first at 90 days. If you add the fact that you have configured scavenging with the default parameters, 7 days no-refresh, 7 days refresh and 7 days for the frequency, your record will be deleted before the renewal of the lease

    Best Regards,

    Thursday, June 7, 2018 1:14 PM
  • Hi,

    Thanks for your question.

    Please try the following suggestions to see if it could be of help.

    DHCP renewals are half the lease interval right, if it doesn’t get renewed, then it waits until 87.5% of the lease time to renew. If it doesn’t get renewed, then the lease is lost, and the DHCP client will attempt to get a new lease. According to your configuration, the DNS entries will be refreshed at 90 days or 157.5 days.

    If you have enabled DNS aging and scavenging, I suggest that you set the refresh interval longer than half of the lease(90days) to prevent records from being cleared before the renewal of the lease. In other words, I suggest that you set DNS scavenging to match DHCP duration.

    Refer to the following link:

    How DNS Scavenging and the DHCP lease duration relate

    https://blogs.technet.microsoft.com/askpfe/2011/06/03/how-dns-scavenging-and-the-dhcp-lease-duration-relate/

    https://blogs.msmvps.com/acefekay/2009/08/20/dhcp-dynamic-dns-updates-scavenging-static-entries-amp-timestamps-and-the-dnsproxyupdate-group/

    Hope you have a nice day!

    Best regards,

    Travis


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    Friday, June 8, 2018 5:31 AM
    Moderator
  • Hi,

    Thanks for your reply.

    But the above scenario will be applicable only for option "Dynamically update DNS records only if requested by the DHCP clients"??????? and to avoid this we are selecting option "Always dynamically update DNS records" right????????

    please correct me if i am wrong

    Regards,

    Viki

    Monday, June 11, 2018 12:18 PM
  • Hi,

    Thanks for your reply.

    I am bit confused with option "Dynamically update DNS records only if requested by the DHCP clients" and  "Always dynamically update DNS records"

    My assumption,

    When "Dynamically update DNS records only if requested by the DHCP clients" is selected then during renewal and new IP assignments, DHCP will register or update DNS record in DNS server using service account configured in my scenario 

    and

    "Always dynamically update DNS records" will be used when we don't like to have dependency with DHCP client to contact DHCP server.. DHCP server to automatically update DNS records of the client irrespective of DHCP client requests.

    If above is true then what will be the frequency of DNS update, i have checked the DNS log and could that there were transactions happened like below,

    On 7th June 2018

    6/7/2018 7:50:16 AM 0EEC PACKET  0000004937474220 UDP Rcv 192.168.5.46    cdb5   Q [0001   D   NOERROR] SOA    (16)testvm1(5)ABC(4)TEST(0)

    6/7/2018 7:50:16 AM 0EEC PACKET  0000004937474220 UDP Snd 192.168.5.46    cdb5 R Q [8085 A DR  NOERROR] SOA    (16)testvm1(5)ABC(4)TEST(0)


    On 10th June 2018

    6/10/2018 4:52:34 PM 0EEC PACKET  00000049374F8220 UDP Rcv 192.168.5.46    e9bf   Q [0001   D   NOERROR] SOA    (16)testvm1(5)ABC(4)TEST(0)

    6/10/2018 4:52:34 PM 0EEC PACKET  00000049374F8220 UDP Snd 192.168.5.46    e9bf R Q [8085 A DR  NOERROR] SOA    (16)testvm1(5)ABC(4)TEST(0)

    A three day interval there is some transaction but in DNS the dynamic Host A record is still there with time stamp 6/7/2018 7:00:00 AM

    Not sure is it 3 days it will auto update DNS, if yes then why the Host A record time stamp is not updated. 

    Regards,

    Viki

    Monday, June 11, 2018 12:28 PM
  • Hi,

    Thanks for your reply.

    l  Enable Dynamically update DNS records only if requested by the DHCP clients

    By default, after the client obtains the IP allocated by DHCP, it will go to the DNS registration A record in person because the ipv4 attribute of the network card—Advanced—DNS—checks the option to “Register the address of this connection in DNS”.

    l  Enable always update DNS records:

    When the client obtains IP, the DHCP server will replace the client to DNS registration A record.

    Best regards,

    Travis



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    Tuesday, June 12, 2018 1:52 AM
    Moderator
  • Hi Travis,

    Thanks for your answer.

    But in this case the clients are Unix and Linux machines.

    So how will be the behavior here.

    Regards,

    Viki

    Wednesday, June 13, 2018 6:40 AM
  • Hi,

    Thanks for your reply.

    DHCP lease agreement also applies to Linux/Unix clients, and the DHCP server will replace the client to DNS registration A record if you enable always update DNS records. In theory, there is no essential difference between Linux client and Windows client requesting DHCP service.

    I am sorry I cannot confirm the actual performance. I suggest you ask for help on the Linux forum.

    Thank you for your understanding and support.

    Best regards,

    Travis


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    Friday, June 15, 2018 5:41 AM
    Moderator
  • Hi,

    Was your issue resolved?

    If you resolved it using our solution, please "mark it as answer" to help other community members find the helpful reply quickly.

    If you resolve it using your own solution, please share your experience and solution here. It will be very beneficial for other community members who have similar questions.

    If no, please reply and tell us the current situation in order to provide further help.

    Best Regards,

    Travis


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    Friday, June 22, 2018 9:43 AM
    Moderator
  • Hi,

    Thanks for your reply and follow up.

    We have tested with both options and we did not see clients updating their DNS records in AD.

    Either DHCP or Client machines. As mentioned earlier, since we have Linux clients, i am not sure what will be the frequency of DNS registration. Windows client will do once in 24 hours but not sure about Linux client.

    Regards,

    Viki

    Thursday, July 5, 2018 9:54 PM