I'm troubleshooting an inconsistent IPv4/DHCP problem on a Windows 11 PC connected to a FRITZ!Box 7530 AX. Windows Settings sometimes shows no IPv4 address, while ipconfig reports 192.168.178.128 with a duplicate-address warning. The router's device list associates the same MAC address with 192.168.178.158. Before rebooting, the results were reversed: Windows showed the router's address, while ipconfig showed no usable IPv4 address.
The original problem was that Windows received APIPA addresses even though the router appeared to show a valid lease. I also had no outbound IPv4 traffic, although I could ping the gateway after manually configuring a static address. The same static configuration worked on another Windows device. DHCP is currently enabled, and I'm trying to determine whether the inconsistent addresses and duplicate warning point to a DHCP, adapter, ARP, or Windows networking problem.
3 Answers
A duplicate warning can be caused by another device answering for the address, but it can also come from a stale address on the local network or a second Windows interface. After obtaining a fresh DHCP lease, test with `ping ` and then `ping 1.1.1.1`. If the gateway works but the public IP does not, inspect the router’s IPv4 connection and firewall settings. If Windows immediately reports a duplicate again, disconnect every other network device temporarily and use `arp -a` to see which MAC Windows associates with the conflicting address.
The router’s device list is not always the same thing as the address currently configured on Windows. It may be displaying a remembered lease, a stale ARP entry, or a different interface that happens to have the same reported hardware address. Remove the old lease/device entry from the router, reboot the router, and then reconnect only the affected adapter. Check the router’s DHCP lease table again after the new lease is obtained.
Also confirm that the manually configured address is outside the DHCP pool, or create a DHCP reservation instead. A static address inside the active pool can eventually collide with another client even if it works during a quick test.
First make sure you’re troubleshooting the same physical adapter throughout. Disable Wi-Fi, Ethernet, VPN adapters, Hyper-V/VirtualBox adapters, and other unused interfaces temporarily. Also check whether Windows is using a randomized hardware address for Wi-Fi; that can make the router list the device differently. Compare the adapter’s MAC from `getmac /v` or `ipconfig /all` with the MAC shown by the router.
With the adapter set to obtain an address automatically, run `ipconfig /release`, `ipconfig /flushdns`, `ipconfig /renew`, then restart the PC. Check the full output of `ipconfig /all`, including the DHCP server, lease times, gateway, and whether more than one adapter has an address. A 169.254.x.x address means Windows did not complete DHCP; it does not necessarily mean the router has no lease recorded.
I had enabled a static address earlier only as a test; DHCP is enabled now. The confusing part is that the address reported as duplicated does not appear to be assigned to another client in the router interface, which is why I’m checking adapter identity and stale lease/ARP information rather than assuming two devices are using it.