NPS cannot connect to Domain Controller

Hi Everyone,

Mostly have Always ON VPN setup and configured, but we are getting an authentication error during trial connections.

Error: The NPS was unable to connect to a DC where the account is located, Because of this, authentication and Authorization for Radius request has failed.

Setup: VPN Server (windows 2019) (Physical server) connects and sends request to NPS
NPS Server (VM) (windows 2019) is supposed to authenticate.
DC (Physical Server) (Windows 2012)
(Added) We also have a Cert. Auth. (Windows 2019) (VM) though that seems to be working fine issuing certificates.

NPS can ping DC, it shows in the domain.

My thought is because it is 2012 server edition. Any thoughts or ideas?
Steve HarrisIT AnalystAsked:
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Cliff GaliherCommented:
Not likely because the DC is 2012. Mismatch security I settings generate different errors. And that wouldn't even be a mismatch with default out of box settings.

This sounds like an account/UPN suffix/domain suffix issue (loosely tied to DNS.)

Pinging a DC isn't much if the NPS server doesn't realize that DC can authenticate for that domain. It is going to rely on DC discovery methods to see who knows about a particular domain and then attempt to contact an appropriate DC.  That discovery process relies on DNS, global catalog servers, what AD knows about trusts etc.  

You'll need to review your event logs in that regard as well as verify your domains are healthy. Otherwise discovery attempts may fail and you get the types of errors you are seeing.
Steve HarrisIT AnalystAuthor Commented:
Ok, thank you for the input. Two errors generate on client side. linking me back to ports and routing as well. Sometimes the client can connect to the VPN server but fails authentication...other times it just fails to talk to the VPN server. (firewalls disabled for this)
Steve HarrisIT AnalystAuthor Commented:
Resolved via User groups. Failed to ensure the RAS, NPS, and DC were in a proper security group together.

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