Server 2012R2 - DHCP issuing new IP addresses despite existing leases present RRS feed

  • Question

  • We are experiencing issues where mobile clients obtain different IP addresses from the same scope. To trigger the behavior we have two wireless networks setup on different VLANs. Each VLAN has an ip helper-address pointing to the single DHCP server. We connect to 'Wireless 1' and DORA completes successfully. The client will get an address for example We then have the client connect to 'Wireless 2' and DORA completes successfully. The client now gets an address from that network scope We then bounce back and forth a few times between each network. Eventually the client will get a different address than it had previously. We enabled DHCP Audit logging and can confirm ASSIGNs occuring but no deletion,expiration, or release of the original lease that was ASSIGNed. We have a professional support case open with Microsoft but it is approaching 2 weeks and still no traction. They believe the DHCP server is issuing a new lease because the client is starting back at DISCOVER/OFFER instead of REQUEST/ACK. It is my understanding a lease is a lease and should be provided to the client if it exists whether that is DISCOVER/OFFER or REQUEST/ACK. I looked up RFC2131 4.3.1 and it shows the Discover message behavior and how the address should be chosen 1st looking for the current binding, 2nd a previous binding that may be expired/released but not allocated, 3rd the IP address requested if specified and unallocated, and 4th any unallocated in the pool. This appears to confirm my understanding that no matter what the client does - whether it does a DISCOVER or a REQUEST. As long as a lease exists the server should either OFFER or ACK that lease's IP. If this is confirmed then we appear to have a bug. We have dhcp audit logging enabled and nothing is logged showing something happened to the original lease - the server goes directly to ASSIGNing a new lease when the issue occurs. We performed a port mirror of the DHCP interface traffic and confirmed the DHCP is offering new IP addresses instead of the previously assigned. We already paid for professional support to review but after 2 weeks have no traction. I'm now posting in the DHCP forum on technet in hopes a member of the Microsoft DHCP team can assist us in understanding what may be happening. 
    • Edited by steve.wh Friday, May 18, 2018 8:07 PM incorrect rfc reference
    Friday, May 18, 2018 7:33 PM

All replies

  • Hi,

    I understand that your this issue is urgent and complex, I'll try to find something helpful for the resolution.

    Based on my research, it may be related to that clients connected to different vlans. The DHCP server recongnized that DHCP address request packets came from different VLAN because of they were tagged different VLAN labels through different Switches.

    I think we'll also need to configure swithes something with the DHCP server. We best involve your Swtich Vendor for the specific implementation.

    Here is a link regarding a similar situation, it may be helpful.

    Hope above information can help. I look forward hearing your good news. If you have any question, please feel free to let me know.

    Best regards,


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    Saturday, May 19, 2018 1:56 PM