I want to know how can i use VPN (Virtual Private Network)
in my application for connecting a remote LAN client.

i am explaning situation bt following figure:

---- ------ --- ---
|Machine A| --- >> |internet(WAN)| ---->> |Server|-- >|M/C B|
---- ------ --- ---
^--------^

(LAN)

machine A is not in a LAN, it is connected to internet with static IP. while B is in a LAN, behind a Server . and this server having public IP Address. B is not directly accessible , we can access it only through server. my one application is running on B and can connect to A when a connection request is made. My another apllication is running on A.

has a static IP, while machine B is not publicly visible outside world. but we know IP address of server,and of machine A and machine B. and also port no on B and A.

problem is that when i send a connect request to B from A, via Server
then connection is not established.

If we try to establish a connection from B to A then it succeded,
while from A to B it will not.

If somebody know then please reply.
Regards
Harish.