GRE

A tunneling protocol that encapsulates many network layer protocols.

GRE is a tunneling protocol that encapsulates a wide variety of network layer protocols inside point to point links, allowing otherwise unsupported or private traffic to traverse an intermediate network. It is flexible and can carry multicast and non IP traffic, which plain IPSec tunnels cannot natively handle. The critical security caveat for the exam is that GRE provides no encryption or authentication on its own, so it is commonly paired with IPSec to add confidentiality and integrity. Used alone, GRE traffic is exposed to interception.