How to monitor windows client via VPN

Hi guys,

I’m really new in Nagios, and my boss is asking me whether Nagios could monitor a client via VPN.
Please tell me what information should I have first and then how to configure Nagios.

My boss also doesn’t know the VPN configuration and the others won’t give me explanation about it :x
They only do what i asked. For example, please open port 5666, then they will open that port.
And, ping is disabled through VPN :evil:

Please give some hints :?:

thank you,