I'm having a strange problem with DHCP on my network where a device keeps its IP address tied to its NIC, even when changing VLANs. This happens whether the connection is wired or wireless. For instance, when a device connects to our Guest Network, it still retains its Corporate network address on the NIC. I've done some troubleshooting, including checking IP helper addresses, firewall rules, and confirmed that various devices not on the Corporate network get DHCP just fine. Using 'ipconfig /release /renew' hasn't resolved the issue either. We're using Server 2022 and Server 2025 for DHCP, and I'm wondering if that matters. Any insights would be appreciated!
5 Answers
A few ideas come to mind! First, check if your DHCP servers for the Guest and Corporate networks share any common interface or if the Corporate network range is replicated for failover on the Guest DHCP server. Also, see if your network setup is doing DHCP snooping or relaying — this could lead the servers to see the same MAC address and mistakenly provide the old lease. To test, connect the device to the Corporate network, disconnect it, and check for an existing lease before moving it to the Guest network. That should help clarify things.
Thanks for the tips, Claude!
The fact that 'ipconfig /release /renew' isn't working is particularly informative. It likely means the VLAN switch isn’t occurring at the network layer, leaving the device still on the Corporate VLAN, which causes it to receive the same IP lease. Here are a few steps you can take: 1. Confirm that the VLAN assignment really changes. After moving the device, check the switch port or AP client table. 2. Look for MAC reservations on both DHCP servers. 3. If you have 802.1X/NAC, see if re-authentication is affecting this. 4. Instead of releasing/renewing, try disabling and re-enabling the NIC. 5. Conduct a Wireshark capture during the DHCP process to identify issues.
Make sure your subnet masks on both DHCP servers are configured correctly and don’t overlap. Using a traffic sniffer can also reveal what’s happening behind the scenes. Ideally, when the client switches networks, the server should send a NACK to force a full DORA sequence. If you see an ACK from the wrong server, it definitely indicates a configuration issue with the scope or subnet.
This situation often occurs due to MAC reservations. If the device already has an assigned address, it won't fetch a new lease until the previous one has been deleted or expired. Double-check if there's a reservation set for that MAC.
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