Internet Key Exchange (IKE)

D.

The correct answer is A. IPSec.

IPSec (Internet Protocol Security) is a widely-used protocol for secure communication over the internet. It provides security services, including confidentiality, data integrity, and authentication, to protect communication between two or more endpoints. IPSec operates at the network layer of the OSI model, which means it can be used to secure any application that uses IP, including HTTP, FTP, and VoIP.

To set up a secure communication channel using IPSec, a security association (SA) needs to be established between the two endpoints. The SA defines the security parameters that will be used to protect the communication, such as encryption algorithm, authentication method, and key lifetime.

The Internet Key Exchange (IKE) protocol is used to establish and manage the SAs required by IPSec. IKE provides a secure method for exchanging the encryption keys and negotiating the parameters needed for IPSec to operate. IKE can operate in two modes: main mode and aggressive mode. Main mode is more secure and is commonly used in enterprise networks, while aggressive mode is faster but less secure and is typically used in small offices or home environments.

L2TP (Layer 2 Tunneling Protocol) is a protocol used for tunneling traffic between two endpoints. It is commonly used in VPNs (Virtual Private Networks) to provide secure access to a remote network. L2TP does not provide encryption or authentication, and it is typically used in combination with IPSec to provide a more secure communication channel.

LEAP (Lightweight Extensible Authentication Protocol) is an authentication protocol used in wireless networks. It is considered to be insecure and has been deprecated in favor of more secure authentication methods.

ISAKMP (Internet Security Association and Key Management Protocol) is a protocol used to establish SAs and exchange keys for IPsec. ISAKMP is a precursor to IKE and is rarely used in modern networks.