Questions

VPN's are implemented to provide a secure connection through public networks. A virtual private network extends a private network across a public network, and enables users to send and receive data across shared or public networks as if their computing devices were directly connected to the private network.

Glass Box (or white box) testing is the process of giving i/p to the system and checking how the system processes i/p to generate o/p

Black Box testing is the process of giving i/p to the system and checking if the system is giving correct o/p without bothering how the o/p is generated.

As we can see from the definitions, the role of black box testing is to ensure that the o/p generated is correct. And role of white box testing is to ensure that methods used to generate the o/p are correct.