Which feature would meet the design requirements?

You are asked to design a solution to verify IPsec peer reachability with data path forwarding.
Which feature would meet the design requirements?

A.
DPD over Phase 1 SA

B.
DPD over Phase 2 SA

C.
VPN monitoring over Phase 1 SA

D.
VPN monitoring over Phase 2 SA

Explanation:

Reference :http://forums.juniper.net/t5/SRX-Services-Gateway/dead-peer-detection-VS-VPNmonitor-in-IPSEC/td-p/176671