Select two reasons to choose IPsec tunnels over GRE.

IPsec tunnels offer faster failure detection compared to GRE because IPsec includes built-in mechanisms like Dead Peer Detection (DPD) that actively monitor tunnel health and quickly identify when a peer is unreachable. GRE, by itself, does not have such integrated liveness checks and relies on routing protocols or higher-layer applications for failure detection, which can be slower. IPsec is also inherently more secure than GRE because it provides encryption, authentication, and integrity checking for the data transmitted within the tunnel. GRE, by contrast, is a tunneling protocol that encapsulates packets but does not provide any security features on its own; it typically requires IPsec to be layered on top for security. "Generally, they provide a higher bandwidth for tunnel connection" is incorrect; both GRE and IPsec introduce overhead, and neither inherently offers higher bandwidth than the other. "CFlowd is required" is incorrect; CFlowd is a Cisco feature for flow monitoring and is not a prerequisite for choosing IPsec over GRE. "A WAN Edge router is behind NAT" is incorrect; while IPsec can operate effectively behind NAT (using NAT-T), this is a capability, not a reason to choose it over GRE.