I have an L2TP server running on an EdgeRouter at a friend’s house. My iPhone and W10 Home laptop connect just fine from my office network. However my domain-controlled workstation at the office cannot connect the the server, neither can the guy next to me.
The only thing relevant I can find online is this KB. But that didn’t help me, and it’s old as hell anyway.
Also did all of this.
I think it’s pretty clear that this is a Windows issue. I suspect the domain controller is somehow interfering?