What are the protocols used by VPN?

I found some information on the following site that might be helpful to you. I hope that it is. VPN Protocols (http://www.vpnc.org/vpn-standards.html)

What VPN are you using? Microsoft? Cisco? Are you using IPSec or PPtP? On some VPN clients such as Cisco, you can specify the high port. The VPN tunnel starts with port 500 and then uses IPSec over TCP (default) 1000 or you can use IPSec over UDP using NAT.

If you are using Windows VPN (PPTP) the port number is 1723. This VPN protocol also requires GRE (43) to be opened.