Description:
You have completed the NPS configuration using Windows Server 2019. You have put the correct secrets at the VPN servers. You also have make sure there's no Network Firewall between the VPN server and NPS Server.
However client machine cannot connect to the VPN. And you cannot see the traffic reaching the NPS Server. There's nothing in the NPS Server event viewer.
Resolution:
At the NPS server, open command prompt with elevated permission and type:
sc sidtype IAS unrestricted
Restart the server after that.
Windows Defender Firewall on the NPS should be automatically configured with exceptions, during the installation of NPS, to allow this RADIUS traffic to be sent and received.
With Server 2019 this firewall exception requires a modification to the service account security identifier to effectively detect and allow RADIUS traffic. If this security identifier change is not executed, the firewall will drop RADIUS traffic. The above command changes the IAS (RADIUS) service to use a unique SID instead of sharing with other NETWORK SERVICE services.
