Which two are IP-based overlay VPN technologies? (Choose two.)

A.
MPLS.

B.
Frame Relay

C.
IP Security (IPSec)

D.
Generic Route Encapsulation (GRE)

Explanation:

Two well-known tunneling technologies are IP Security (IPSec) and generic routing encapsulation (GRE). GRE is fast and simple to implement and supports multiple routed protocols, but it provides no security and is thus unsuitable for deployment over the Internet. An alternative tunneling technology is IPSec, which provides network-layer authentication and optional encryption to make data transfer over the Internet secure.
IPSec supports only the IP routed protocol.
Reference: Cisco Press – Implementing Cisco MPLS study guide p.4-19