The reverse address resolution protocol (RARP) sends out a packet including a MAC address and a request to be informed of the IP address that should be assigned to that MAC.
Diskless workstations do not have a full operating system but have just enough code to know how to boot up and broadcast for an IP address, and they may have a pointer to the server that holds the operating system. The diskless workstation knows its hardware address, so it broadcasts this information so that a listening server can assign it the correct IP address.
As with ARP, Reverse Address Resolution Protocol (RARP) frames go to all systems on the subnet, but only the RARP server responds. Once the RARP server receives this request, it looks in its table to see which IP address matches the broadcast hardware address. The server then sends a message that contains its IP address back to the requesting computer. The system now has an IP address and can function on the network.
The Bootstrap Protocol (BOOTP) was created after RARP to enhance the functionality that RARP provides for diskless workstations. The diskless workstation can receive its IP address, the name server address for future name resolutions, and the default gateway address from the BOOTP server. BOOTP usually provides more functionality to diskless workstations than does RARP.
The evolution of this protocol has unfolded as follows: RARP evolved into BOOTP, which evolved into DHCP.
The following are incorrect answers:
NAT is a tool that is used for masking true IP addresses by employing internal addresses. ARP does the opposite of RARP, it finds the MAC address that maps with an existing IP address. Data Link layer The Data Link layer is not a protocol; it is represented at layer 2 of the OSI model. In the TCP/IP model, the Data Link and Physical layers are combined into the Network Access layer, which is sometimes called the Link layer or the Network Interface layer.
Reference(s) used for this question:
Harris, Shon (2012-10-25). CISSP All-in-One Exam Guide, 6th Edition, Telecommunications and Network Security, Page 584-585 and also 598. For Kindle users see Kindle Locations 12348-12357. McGraw-Hill. and KRUTZ, Ronald L. & VINES, Russel D., The CISSP Prep Guide: Mastering the Ten Domains of Computer Security, John Wiley & Sons, 2001, Chapter 3: Telecommunications and Network Security (page 87).

Section: Access Control
Explanation/Reference:
In order to protect the confidentiality of the data.
The following answers are incorrect because :
Install a firewall is incorrect as this would come after the information has been identified for sensitivity levels.
Implement encryption is also incorrect as this is one of the mechanisms to protect the data once it has been identified.
Review all user access rights is also incorrect as this is also a protection mechanism for the identified information.
Reference : Shon Harris AIO v3 , Chapter-4 : Access Control , Page : 126

Instead of using a Certificate Authority, PGP uses a "Web of Trust", where users can certify each other in a mesh model, which is best applied to smaller groups.
In cryptography, a web of trust is a concept used in PGP, GnuPG, and other OpenPGP compatible systems to establish the authenticity of the binding between a public key and its owner. Its decentralized trust model is an alternative to the centralized trust model of a public key infrastructure (PKI), which relies exclusively on a certificate authority (or a hierarchy of such). The web of trust concept was first put forth by PGP creator Phil Zimmermann in 1992 in the manual for PGP version 2.0.
Pretty Good Privacy (PGP) is a data encryption and decryption computer program that provides cryptographic privacy and authentication for data communication. PGP is often used for signing, encrypting and decrypting texts, E-mails, files, directories and whole disk partitions to increase the security of e-mail communications. It was created by Phil Zimmermann in 1991.
As per Shon Harris's book: Pretty Good Privacy (PGP) was designed by Phil Zimmerman as a freeware e-mail security program and was released in 1991. It was the first widespread public key encryption program. PGP is a complete cryptosystem that uses cryptographic protection to protect e-mail and files. It can use RSA public key encryption for key management and use IDEA symmetric cipher for bulk encryption of data, although the user has the option of picking different types of algorithms for these functions. PGP can provide confidentiality by using the IDEA encryption algorithm, integrity by using the MD5 hashing algorithm, authentication by using the public key certificates, and nonrepudiation by using cryptographically signed messages. PGP initially used its own type of digital certificates rather than what is used in PKI, but they both have similar purposes. Today PGP support X.509 V3 digital certificates.
Reference(s) used for this question:
KRUTZ, Ronald L. & VINES, Russel D., The CISSP Prep Guide: Mastering the Ten Domains of Computer Security, John Wiley & Sons, 2001, Chapter 4: Cryptography (page 169).
Shon Harris, CISSP All in One book https://en.wikipedia.org/wiki/Pretty_Good_Privacy TIPTON, Hal, (ISC)2, Introduction to the CISSP Exam presentation.

Explanation/Reference:
Source: TIPTON, Hal, (ISC)2, Introduction to the CISSP Exam presentation.

Section: Access Control
Explanation/Reference:
The Biba security model addresses the integrity of data being threatened when subjects at lower security levels are able to write to objects at higher security levels and when subjects can read data at lower levels.
Source: HARRIS, Shon, All-In-One CISSP Certification Exam Guide, McGraw-Hill/Osborne, 2002, Chapter 5:
Security Models and Architecture (Page 244).