A VPN is a secure connection between two locations on the internet.
Ideally, no one can look at or interfere with the traffic between the two locations.
The traffic cannot be looked at because it is encrypted and cannot be interfered with
because authentication makes sure that each packet is...authentic.
If you'd like further reading for the layman on Authentication,
this 1988 dramatic play by Bill Bryant is both educational and entertaining.
If you'd like to learn more about encryption start with the tactics of the Roman Empire, watch that World War II movie with Benedict Cumberbatch (not the one with Hedy Lamarr) and be prepared to fall down the rabbit hole.
There are, of course, a few types of VPN.
- One type is through the browser when connecting to, for example, a bank account.
- Another type of VPN is 'always on'. It connects two offices.
- Another type of VPN is a temporary connection. A client connects to the host--but only for a session.
Unlike browsing various open and public internet websites, a secure connection is encrypted and protected from any kind of trickery.
(This is what the "https" part of the address is all about. It is called SSL)
It is setup in the routers that access the internet and is part of your IT infrastructure.
With this type of VPN you can easily access the printers and files on the company's network from a home or remote office. (This is called Site-to-Site)
You then disconnect. Clients are a vendor specific application that you run to make the connection.
If your offices have an existing VPN connection between them, a remote Avaya IP phone will not need the VPN client enabled to communicate with the IP Office.
Otherwise, the VPN client of the Avaya IP phone will need to be configured to communicate with the main office's VPN device.