I have a situation where I have a Windows 10 PC that is acting as a DHCP server on a private network with no internet connection. The PC has a second ethernet adapter that is connected to the internet through a router on a different network.
When I try to set up the PC with a static ip via Settings->Ethernet->Edit->IP settings, I select Manual and then turn IP4 ON and enter IP address: 192.168.123.150 Subnet prefix length: 24 Gateway: 192.168.123.150 and no DNS entries. When I press Enter it says that one or more of the settings is incorrect but not which ones. It will accept the settings if I set the Gateway to 192.168.123.1 but that address does not exist and the PC will begin ARPing for it. So, instead, I cancel and go to the adapter settings and am able to set those as I want and the PC appears as 192.168.123.150 and the DHCP server serves the other devices on the network. However, the Settings->Ethernet screen still shows DHCP as being set and the PC will start an ARP storm on that adapter asking for a lot of addresses that I do not recognize. There are multiple ARPs per second and communicating on the other adapter grounds to a halt.
I have had this happen on 2 different PCs, one running Windows 10 Home and the other Windows 10 Pro.
I have found on one of the PCs that if after I set the settings thru the adapter and then go back to Settings->Ethernet->Edit->IP settings and try to set to the same manual settings as I set on the adapter, it still won't let me change the settings to what I want but if I cancel out of that the ARP storm stops. But Settings->Ethernet stills shows as Automatic (DHCP).
So, I am at a loss as to how to properly setup the PC as a static IP to prevent the ARP storm.
I found this question, Can I configure my Windows 10 PC as a DHCP server on a local switch?, from a year or so ago but I didn't see an answer to my situation.
Updated 2/22/22 08:36: The DHCP server software is DHCPLite from github that has been modified for our specific purpose. The excessive ARPing occurs whether the server is running or not. Further, after running one of the PCs with the DHCP server running and Wireshark monitoring, the ARPing appears to eventually subside when left running. Looking at the Wireshark report I am not certain how long that period is because I was trying different things to get the ARPing to subside including unplugging the private network connection.
I will perform some more testing to see what the duration of the ARPing is and update with that information here.
