Generic Routing Encapsulation - Definition from the Hotspot Shield Glossary
This is a protocol used to route packets over IP (Internet Protocol) Networks using encapsulation - This protocol is defined by IETF’s RFC 2784. GRE was originally created to carry Layer 3 protocols of the OSI reference model through a tunneling process - It effectively creates a P2P connection similar to the connection of a VPN network.
The mechanism of GRE involves encapsulating a packet within an outer IP packet so it can be transported to its intended network destination. Advantages of Generic Route Encapsulation include the ability to encase many protocols using a single protocol backbone, can bring together sub-networks that are not connected and can allow VPN’s over WAN’s. The only downside is that it is not considered a secure protocol as no encryption is used.