I am trying to write a freeware client/server program that needs to scan the server's ports for the server's open UDP port.
Before I get too deep into this, are there any problems that I need to know of if I send a probe UDP packet that looks for the server to all ports on at the server's target IP?
The reason I am asking is that some users of this freeware server will be behind NATs and I may have to probe for the external port assigned to the internal server by the NAT device. The client would send an encrypted string that the server would know how to respond to. If this encrypted value is not what the server expected, no communication would take place.
Any help you can give would be greatly appreciated.