Which of the following protocols is used by the Point-to-Point Protocol to validate users before allowing them access to server resources?

A.
PAP

B.
PPP

C.
IAPP

D.
SCP

Explanation:
A password authentication protocol (PAP) is an authentication protocol that uses a password. PAP is used by Point to Point Protocol to validate users before allowing them access to server resources. Almost all network operating system remote servers support PAP.
Working cycle:
Client sends username and password.
Server sends authentication-ack (if credentials are OK) or authentication-nak. Answer option B is incorrect. Point-to-Point Protocol (PPP) is a remote access protocol commonly used to connect to the Internet. PPP supports compression and encryption and can be used to connect to a variety of networks. It can connect to a network running on IPX, TCP/IP, or NetBEUI protocol. PPP supports multi-protocol and dynamic IP assignments. It is the default protocol for the Microsoft Dial-Up adapter.
Answer option C is incorrect. IEEE 802.11F or Inter-Access Point Protocol (IAPP) is a recommendation that describes an optional extension to IEEE 802.11 and provides wireless access-point communications among multivendor systems. IAPP is required in order to ensure that all relevant information is delivered to the correct access point to which the client station is associated.

Answer option D is incorrect. The SCP (secure copy) protocol is a network protocol that supports file transfers. The SCP protocol, which runs on port 22, is based on the BSD RCP protocol which is tunneled through the Secure Shell (SSH) protocol to provide encryption and authentication. SCP might not even be considered a protocol itself, but merely a combination of RCP and SSH. The RCP protocol performs the file transfer and the SSH protocol performs authentication and encryption. SCP protects the authenticity and confidentiality of the data in transit. It hinders the ability for packet sniffers to extract usable information from the data packets.