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DHCP failover 2012-2016 problem

I.Kom 1 Reputation point
2020-07-30T09:06:01.567+00:00

I have already failover with 2012R2 and 2016 version.
Sometimes I get problem with it and don't know how it fix.

  1. win2016 dhcp server stop giving IP to clients. In log only this lines:

32,07/27/20,19:16:58,DNS Update Successful,10.80.0.179,main-61.domain.com,,,0,6,,,,,,,,,0
24,07/27/20,20:00:33,Database Cleanup Begin,,,,,0,6,,,,,,,,,0
25,07/27/20,20:00:33,0 leases expired and 0 leases deleted,,,,,0,6,,,,,,,,,0
25,07/27/20,20:00:33,0 leases expired and 0 leases deleted,,,,,0,6,,,,,,,,,0
24,07/27/20,21:00:35,Database Cleanup Begin,,,,,0,6,,,,,,,,,0
25,07/27/20,21:00:35,0 leases expired and 0 leases deleted,,,,,0,6,,,,,,,,,0
25,07/27/20,21:00:35,0 leases expired and 0 leases deleted,,,,,0,6,,,,,,,,,0
24,07/27/20,22:00:36,Database Cleanup Begin,,,,,0,6,,,,,,,,,0
25,07/27/20,22:00:36,0 leases expired and 0 leases deleted,,,,,0,6,,,,,,,,,0
25,07/27/20,22:00:36,0 leases expired and 0 leases deleted,,,,,0,6,,,,,,,,,0
24,07/27/20,23:00:38,Database Cleanup Begin,,,,,0,6,,,,,,,,,0
25,07/27/20,23:00:38,0 leases expired and 0 leases deleted,,,,,0,6,,,,,,,,,0
25,07/27/20,23:00:38,0 leases expired and 0 leases deleted,,,,,0,6,,,,,,,,,0

First line in example is "work" state of server. After that server stop giving IP, but dhcp service work, I can manage them through mmc.

  1. win2012 work fine, but some client can't get IP, if they ask "renew" from win2016 server.
  2. failover work fine after restart win2016 server (dhcp service restart freeze a long time at this situation. If I have not problem, it restart fine). How to debug this problem, or maybe anybody get this problem.
Windows DHCP
Windows DHCP
Windows: A family of Microsoft operating systems that run across personal computers, tablets, laptops, phones, internet of things devices, self-contained mixed reality headsets, large collaboration screens, and other devices.DHCP: Dynamic Host Configuration Protocol (DHCP). A communications protocol that lets network administrators manage centrally and automate the assignment of Internet Protocol (IP) addresses in an organization's network.
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  1. Sunny Qi 10,926 Reputation points Microsoft Vendor
    2020-07-31T06:59:28.21+00:00

    Hi,

    Welcome to our new Q&A platform.

    Before we go further, I would like to confirm the following questions:

    What's the mode of the DHCP failover relationship?

    When the server 2016 stopped to provide IP address, did the state of this server in failover relationship changed to partner down? Automatically or manually?

    Based on my understanding your issue is when server 2012 worked and server 2016 didn't work, the client who obtained IP address from server 2016 cannot renew its IP address lease. please feel free to let me know if my understanding is wrong.

    Best Regards,
    Sunny

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  2. I.Kom 1 Reputation point
    2020-08-06T10:21:03.467+00:00

    Good day.

    1. load balance
    2. No, it's up. For example, i can manually replicate existing or new scope.
    3. Yes, you're right. After reboot 2016 server, all work fine. Some clients update their IP from 2012, some clients renew IP from 2016.
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  3. Sunny Qi 10,926 Reputation points Microsoft Vendor
    2020-08-11T08:57:09.68+00:00

    Hi,

    Sorry for the delayed response and thanks for your update.

    May I know what's the value of lease duration and MCLT were configured on DHCP server?

    When the partner DHCP server offered IP addresses depends on the lease duration and MCLT.

    I have done a test in my environment and here is the result for your reference.

    Failover relationship was established between DC1/DHCP and DHCP1 with load balance mode.
    Lease duration: 16 minutes
    MCLT: 8 minutes

    1. Windows 10 client obtained IP from DC1/DHCP first, the lease duration was 8 minutes.
    2. At 50% of the lease time (MCLT/2=4minutes) , the client requests a renewal for its lease from DC1/DHCP. And now the lease duration changes to 16 minutes.
    3. Turn off DC1/DHCP and the State of the server on DHCP 1 changed to Lost contact with partner.
    4. At 50% of the lease time (Lease duration=8minutes), win 10 requests a renewal for its lease from DC1/DHCP, but DC1/DHCP was not available so the lease it not renewed.
    5. At 7/8 of the duration (14minutes), the client moves into a REBINDING state and broadcasts a lease renewal request.
    6. DHCP1 determined that the client belongs to DC1/DHCP, but since DHCP1 is in communications interrupted state, it offers a temporary lease to the client for the duration of the MCLT (8 minutes).

    I also found detailed steps regarding how DHCP load balance mode works for your reference.

    The following illustration and its corresponding steps provide a detailed description of the processes involved when a DHCP client acquires a DHCP lease from DHCP servers configured for DHCP failover in load balancing mode.

    16850-image-1.jpg
    16995-image-2.jpg

    Hope my answer will help you.

    ---Please Accept as answer if the reply is helpful---

    Best Regards,
    Sunny

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