There are significant differences between GRE and IPSec though they are both frequently described as working with tunnels.
GRE is the more simple protocol. It is easier (less complex) to configure and imposes lower overhead on the router to run it. The basic concept of GRE is that you take some packet and you re-encapsulate it in a new IP packet. (Essentially the original packet is now the payload of the new packet.) The packet is transmitted to the other end of the tunnel and de-encapsulated and the original packet if forwarded to its destination. One of the original motivations behind GRE was the ability to transport non-IP protocols over an IP only backbone.
IPSec is more complex to configure and to operate. The basic concept of IPSec is that it will protect traffic between the end points. There are parts of IPSec that will authenticate (so we can be very sure that the device we are talking to really is who we think it is) and IPSec can encrypt the traffic so that no one can observe the traffic and read it. GRE does not provide any authentication or any encryption.
So that summarizes the differences. which one is best depends on how you measure: is best the simplest and lowest overhead or is best the most secure?
HTH
Rick
HTH
Rick
