How do i know what port my vpn is using?

my company has a central server with a number of client computers that use a vpn to connect remotely. To use the vpn on another company's wireless network, they need to open the port that my vpn requires to work. How can i figure out what port this vpn is using?
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Check the VPN configuration settings on you VPN device or you can use the simple DOS command "netstat -a", without the quotes.
vpn ports :-
for SSL vpn
port 443(TCP)
IP Protocol=TCP, TCP Port number=1723  
IP Protocol=GRE (value 47)  
For L2TP:
IP Protocol Type=UDP, UDP Port Number=500  
IP Protocol Type=UDP, UDP Port Number=4500  
IP Protocol Type=ESP (value 50)  
IP Protocol=TCP, TCP Port number=443  
For IKEv2:
IP Protocol Type=UDP, UDP Port Number=500    
IP Protocol Type=UDP, UDP Port Number=4500  
IP Protocol Type=ESP (value 50)

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In l2tp example above tcp port 1721 needs to be include
The example referenced in the encompassing set of information deals with l2tp over IPSec.
Openvpn uses tcp port 1194 by default but can b configured to use any port.
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