Generic Routing Encapsulation (GRE) Tunnel Defined

What is a GRE tunnel? Let's begin with a technical definition. Generic routing encapsulation (or GRE) is a communication protocol. You can use it to share data directly through network nodes, rather than over the public network. That communication happens through a GRE tunnel.

You might use a GRE tunnel to communicate with a device (like a router) that is incompatible with your computer. Or you might use a GRE tunnel to ensure that a message gets to a recipient despite any protocol challenges you think might exist, even if you're not sure. 

But hackers can also use GRE tunnels in sophisticated attacks that take down critical systems for days. If you choose to either use or accept tunnels, you should understand the risks.

GRE explained 

To break down what a GRE tunnel is and how it works, we'll need to define a few critical terms. 

Any GRE protocol involves:

• Nodes: A device that can accept or send information (like computers, routers, printers, and switches) is a node. 
• Packets: Information sent from one device to another is split into packets. 
• Headers: Each packet contains a header with information abou