Generic Routing Encapsulation
GRE mainly perform ‘tunneling’.
Does not provide a means to securely encrypt its payload
Often relies on application layer to provide encryption
May be used together with a network layer encryption (such as IPsec)
Example 1: use GRE to encapsulate non-IP traffic and then encrypt the GRE packet using IPsec
Example 2: use GRE to encapsulate multicast traffic, and then encrypt the GRE packet using IPsec
Question: Why not simply use IPsec?