DHCP not handing out to VoIP Phones


  • Hello,

    We are having an issue where DHCP addresses are no longer being handed out and the DHCP error 20287 is logged. Here is the error we get:

    DHCP client request from 08000FB342BE was dropped since the applicable IP address ranges in scope/superscope SCOPENAME Scope are out of available IP addresses. This could be because of IP address ranges of a policy being out of available IP addresses.

    I expanded the scope (although it wasn't out at the time) and currently have about 60 addresses available.

    What is very strange is that the only devices not getting DHCP from this scope are VoIP phones. As in both MiTel and Yealink phones sit at "Waiting for IP address". All other devices (Apple, Linux, IPhones, Android devices) get a proper DHCP.

    I ran a wireshark from the DHCP server as well as the phone. I confirmed that the DHCP server gets the discovery packet, but as that 20287 states, it never sends ACK or an offer to the phones.

    I simplified the setup as much as possible so the server is directly plugged in to the same switch (unmanaged) as the phones. No VLANs are in place.

    I also tried deactivating the scope on one Server 2012R2 installation and installing a new role on another server as well as another scope, still the same result. 

    If I change the DHCP server to no longer be on the Windows server and instead be on my Router, it works fine. 

    Any clue as to why only my phones won't pull DHCP?


    Tuesday, July 10, 2018 8:33 PM

All replies

  • Hi,

    Thanks for your question.

    Event 20287 may be caused by VoIP Phones sending request packet in short interval time. Is it possible to modify some configurations on a VoIP phone? Or is it possible to configure specific DHCP options for VoIP phones on the DHCP server?

    Have you tried configuring address reservation for VoIP phones?

    Refer to the following links:

    Managing DHCP after adding IP phones

    Please Note: Since the web site is not hosted by Microsoft, the link may change without notice. Microsoft does not guarantee the accuracy of this information. 

    Best regards,


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    Wednesday, July 11, 2018 2:20 AM
  • Thank you for the response,

    I tried setting a reservation with the phones MAC address and still get the same issue. The phone does not pull the reserved address I set for it in the pool. However, that MAC address I tested with no longer shows in the DHCP event admin log with error 20287.

    I reviewed the documents you posted. The arstencia article is describing what I am trying to setup. However, without getting DHCP from the untagged network, I am unable to set the DHCP option to tag the phone on the VLAN network and complete the provisioning process.

    I am unsure how I would be able to reduce the frequency of DHCP requests from these phones. But I don't know that that would be helpful considering I get the same issue across multie VOiP brands (Cisco, MiTel, Yealink).


    Wednesday, July 11, 2018 4:00 PM
  • Hi,

    Thanks for your reply.

    Why not consult the phone manufacturer, maybe they know how to reduce the frequency of requests.

    Best regards,


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    Thursday, July 12, 2018 8:15 AM