A vulnerability is a weakness in a system that can be exploited by a threat.

Section: Risk, Response and Recovery
Explanation/Reference:
Many elements of a BCP will address senior management, such as the statement of importance and priorities, the statement of organizational responsibility, and the statement of urgency and timing. Executive management staff initiates the project, gives final approval and gives ongoing support. The BCP committee directs the planning, implementation, and tests processes whereas functional business units participate in implementation and testing.
Source: KRUTZ, Ronald L. & VINES, Russel D., The CISSP Prep Guide: Mastering the Ten Domains of Computer Security, John Wiley & Sons, 2001, Chapter 8: Business Continuity Planning and Disaster Recovery Planning (page 275).

Section: Access Control
Explanation/Reference:
A Network Access Server (NAS) operates as a client of RADIUS. The client is responsible for passing user information to designated RADIUS servers, and then acting on the response which is returned.
RADIUS servers are responsible for receiving user connection requests, authenticating the user, and then returning all configuration information necessary for the client to deliver service to the user.
RADIUS authentication is based on provisions of simple username/password credentials. These credentials are encrypted by the client using a shared secret between the client and the RADIUS server. OIG 2007, Page 513 RADIUS incorporates an authentication server and can make uses of both dynamic and static passwords.
Since it uses the PAP and CHAP protocols, it also incluses static passwords.
RADIUS is an Internet protocol. RADIUS carries authentication, authorization, and configuration information between a Network Access Server and a shared Authentication Server. RADIUS features and functions are described primarily in the IETF (International Engineering Task Force) document RFC2138.
The term " RADIUS" is an acronym which stands for Remote Authentication Dial In User Service.
The main advantage to using a RADIUS approach to authentication is that it can provide a stronger form of authentication. RADIUS is capable of using a strong, two-factor form of authentication, in which users need to possess both a user ID and a hardware or software token to gain access.
Token-based schemes use dynamic passwords. Every minute or so, the token generates a unique 4-, 6- or 8- digit access number that is synchronized with the security server. To gain entry into the system, the user must generate both this one-time number and provide his or her user ID and password.
Although protocols such as RADIUS cannot protect against theft of an authenticated session via some realtime attacks, such as wiretapping, using unique, unpredictable authentication requests can protect against a wide range of active attacks.
RADIUS: Key Features and Benefits
Features Benefits
RADIUS supports dynamic passwords and challenge/response passwords.
Improved system security due to the fact that passwords are not static.
It is much more difficult for a bogus host to spoof users into giving up their passwords or password-generation algorithms.
RADIUS allows the user to have a single user ID and password for all computers in a network.
Improved usability due to the fact that the user has to remember only one login combination.
RADIUS is able to:
Prevent RADIUS users from logging in via login (or ftp).
Require them to log in via login (or ftp)
Require them to login to a specific network access server (NAS);
Control access by time of day.
Provides very granular control over the types of logins allowed, on a per-user basis.
The time-out interval for failing over from an unresponsive primary RADIUS server to a backup RADIUS server is site-configurable.
RADIUS gives System Administrator more flexibility in managing which users can login from which hosts or devices.
Stratus Technology Product Brief
http://www.stratus.com/products/vos/openvos/radius.htm
Source: KRUTZ, Ronald L. & VINES, Russel D., The CISSP Prep Guide: Mastering the Ten Domains of Computer Security, 2001, John Wiley & Sons, Pages 43, 44.
Also check: MILLER, Lawrence & GREGORY, Peter, CISSP for Dummies, 2002, Wiley Publishing, Inc., pages
45-46.

Section: Network and Telecommunications
Explanation/Reference:
Bridges are simple, protocol-dependent networking devices that are used to connect two or more homogeneous LANs to form an extended LAN.
A bridge does not change the contents of the frame being transmitted but acts as a relay.
A gateway is designed to reduce the problems of interfacing any combination of local networks that employ different level protocols or local and long-haul networks.
A router connects two networks or network segments and may use IP to route messages.
Firewalls are methods of protecting a network against security threats from other systems or networks by centralizing and controlling access to the protected network segment.
Source: HARRIS, Shon, All-In-One CISSP Certification Exam Guide, McGraw-Hill/Osborne, 2002, chapter 7:
Telecommunications and Network Security (page 397).

Explanation/Reference:
DES works with 64 bit blocks of text using a 64 bit key (with 8 bits used for parity, so the effective key length is 56 bits).
Some people are getting the Key Size and the Block Size mixed up. The block size is usually a specific length. For example DES uses block size of 64 bits which results in 64 bits of encrypted data for each block. AES uses a block size of 128 bits, the block size on AES can only be 128 as per the published standard FIPS-197.
A DES key consists of 64 binary digits ("0"s or "1"s) of which 56 bits are randomly generated and used directly by the algorithm. The other 8 bits, which are not used by the algorithm, may be used for error detection. The 8 error detecting bits are set to make the parity of each 8-bit byte of the key odd, i.e., there is an odd number of "1"s in each 8-bit byte1. Authorized users of encrypted computer data must have the key that was used to encipher the data in order to decrypt it.
IN CONTRAST WITH AES
The input and output for the AES algorithm each consist of sequences of 128 bits (digits with values of 0 or
1). These sequences will sometimes be referred to as blocks and the number of bits they contain will be referred to as their length. The Cipher Key for the AES algorithm is a sequence of 128, 192 or 256 bits.
Other input, output and Cipher Key lengths are not permitted by this standard.
The Advanced Encryption Standard (AES) specifies the Rijndael algorithm, a symmetric block cipher that can process data blocks of 128 bits, using cipher keys with lengths of 128, 192, and 256 bits. Rijndael was designed to handle additional block sizes and key lengths, however they are not adopted in the AES standard.
The AES algorithm may be used with the three different key lengths indicated above, and therefore these different "flavors" may be referred to as "AES-128", "AES-192", and "AES-256".
The other answers are not correct because:
"64 bits of data input results in 56 bits of encrypted output" is incorrect because while DES does work with
64 bit block input, it results in 64 bit blocks of encrypted output.
"128 bit key with 8 bits used for parity" is incorrect because DES does not ever use a 128 bit key.
"56 bits of data input results in 56 bits of encrypted output" is incorrect because DES always works with 64 bit blocks of input/output, not 56 bits.
Reference(s) used for this question:
Official ISC2 Guide to the CISSP CBK, Second Edition, page: 336-343
http://csrc.nist.gov/publications/fips/fips197/fips-197.pdf
http://csrc.nist.gov/publications/fips/fips46-3/fips46-3.pdf