Normally when you configure IPsec you have to configure security parameters (ESP/AH, DH, encryption algorithm, etc.) on both endpoints. Easy VPN is useful for remote workers so you don’t have to configure all these parameters on the client side. These VPN connections are all point-to-point.
Now imagine you have a large company with a HQ and multiple branch offices. All branch offices should be connected to the HQ and there should be some direct branch-to-branch VPNs. In this case, you really don’t want to configure dozens of these point-to-point VPNs which is why we have technology like DMVPN which uses point-to-multipoint tunnels.
I would recommend to read up a bit on DMVPN if you haven’t seen this before:
Everything I described above has one thing in common…we use “tunnels” to “bridge” networks together. This allows connectivity between networks with private addresses.
Now let’s say we have that large company with its multiple branch offices and everything is connected the way it should. Branch offices can reach each other directly, they can all reach the HQ etc. For now it doesn’t matter what we used…it could be MPLS VPN or DMVPN and we are not using any IPsec at all.
We want to make sure that all our traffic is protected through IPsec and we want to centralize this…
GETVPN uses a key server (a central router) which takes care of all keys and it can distribute security policies. Other routers are called group members and once authenticated by the key server, they belong to the group and they can securely communicate with other group members.
The original IP header is used which is why you already need to have connectivity through a private network like MPLS VPN or DMVPN.
So the short version…with GETVPN we have a bunch of routers that are already connected somehow. We use a central key server and all other routers are group members. Group members authenticate to the key server which takes care of keying/policies. Once you belong to the group, traffic is protected with IPsec. It only takes care of “protecting” your traffic which is why you need a private network like MPLS VPN or DMVPN (or anything else).
I hope this helps, if not let me know.