Explanation/Reference:
The reference monitor refers to abstract machine that mediates all access to objects by subjects.
This question is asking for the concept that governs access by subjects to objects, thus the reference monitor is the best answer. While the security kernel is similar in nature, it is what actually enforces the concepts outlined in the reference monitor.
In operating systems architecture a reference monitor concept defines a set of design requirements on a reference validation mechanism, which enforces an access control policy over subjects' (e.g., processes and users) ability to perform operations (e.g., read and write) on objects (e.g., files and sockets) on a system. The properties of a reference monitor are:
The reference validation mechanism must always be invoked (complete mediation). Without this property, it is possible for an attacker to bypass the mechanism and violate the security policy.
The reference validation mechanism must be tamperproof (tamperproof). Without this property, an attacker can undermine the mechanism itself so that the security policy is not correctly enforced.
The reference validation mechanism must be small enough to be subject to analysis and tests, the completeness of which can be assured (verifiable). Without this property, the mechanism might be flawed in such a way that the policy is not enforced.
For example, Windows 3.x and 9x operating systems were not built with a reference monitor, whereas the Windows NT line, which also includes Windows 2000 and Windows XP, was designed to contain a reference monitor, although it is not clear that its properties (tamperproof, etc.) have ever been independently verified, or what level of computer security it was intended to provide.
The claim is that a reference validation mechanism that satisfies the reference monitor concept will correctly enforce a system's access control policy, as it must be invoked to mediate all security-sensitive operations, must not be tampered, and has undergone complete analysis and testing to verify correctness.
The abstract model of a reference monitor has been widely applied to any type of system that needs to enforce access control, and is considered to express the necessary and sufficient properties for any system making this security claim.
According to Ross Anderson, the reference monitor concept was introduced by James Anderson in an influential 1972 paper.
Systems evaluated at B3 and above by the Trusted Computer System Evaluation Criteria (TCSEC) must enforce the reference monitor concept.
The reference monitor, as defined in AIO V5 (Harris) is: "an access control concept that refers to an abstract machine that mediates all access to objects by subjects."
The security kernel, as defined in AIO V5 (Harris) is: "the hardware, firmware, and software elements of a trusted computing based (TCB) that implement the reference monitor concept. The kernel must mediate all access between subjects and objects, be protected from modification, and be verifiable as correct." The trusted computing based (TCB), as defined in AIO V5 (Harris) is: "all of the protection mechanisms within a computer system (software, hardware, and firmware) that are responsible for enforcing a security policy."
The security domain, "builds upon the definition of domain (a set of resources available to a subject) by adding the fact that resources withing this logical structure (domain) are working under the same security policy and managed by the same group."
The following answers are incorrect:
"The security kernel" is incorrect. One of the places a reference monitor could be implemented is in the security kernel but this is not the best answer.
"The trusted computing base" is incorrect. The reference monitor is an important concept in the TCB but this is not the best answer.
"The security domain is incorrect." The reference monitor is an important concept in the security domain but this is not the best answer.
Reference(s) used for this question:
Official ISC2 Guide to the CBK, page 324
AIO Version 3, pp. 272 - 274
AIOv4 Security Architecture and Design (pages 327 - 328)
AIOv5 Security Architecture and Design (pages 330 - 331)
Wikipedia article at https://en.wikipedia.org/wiki/Reference_monitor

Explanation/Reference:
The question mentions clearly "operating together". Which means the BEST answer is Dual Control.
Two mechanisms necessary to implement high integrity environments where separation of duties is paramount are dual control or split knowledge.
Dual control enforces the concept of keeping a duo responsible for an activity. It requires more than one employee available to perform a task. It utilizes two or more separate entities (usually persons), operating together, to protect sensitive functions or information.
Whenever the dual control feature is limited to something you know., it is often called split knowledge (such as part of the password, cryptographic keys etc.) Split knowledge is the unique "what each must bring" and joined together when implementing dual control.
To illustrate, let say you have a box containing petty cash is secured by one combination lock and one keyed lock. One employee is given the combination to the combo lock and another employee has possession of the correct key to the keyed lock. In order to get the cash out of the box both employees must be present at the cash box at the same time. One cannot open the box without the other. This is the aspect of dual control.
On the other hand, split knowledge is exemplified here by the different objects (the combination to the combo lock and the correct physical key), both of which are unique and necessary, that each brings to the meeting.
This is typically used in high value transactions / activities (as per the organizations risk appetite) such as:
Approving a high value transaction using a special user account, where the password of this user account is split into two and managed by two different staff. Both staff should be present to enter the password for a high value transaction. This is often combined with the separation of duties principle. In this case, the posting of the transaction would have been performed by another staff. This leads to a situation where collusion of at least 3 people are required to make a fraud transaction which is of high value.
Payment Card and PIN printing is separated by SOD principles. Now the organization can even enhance the control mechanism by implementing dual control / split knowledge. The card printing activity can be modified to require two staff to key in the passwords for initiating the printing process. Similarly, PIN printing authentication can also be made to be implemented with dual control. Many Host Security modules (HSM) comes with built in controls for dual controls where physical keys are required to initiate the PIN printing process.
Managing encryption keys is another key area where dual control / split knowledge to be implemented.
PCI DSS defines Dual Control as below. This is more from a cryptographic perspective, still useful:
Dual Control: Process of using two or more separate entities (usually persons) operating in concert to protect sensitive functions or information. Both entities are equally responsible for the physical protection of materials involved in vulnerable transactions. No single person is permitted to access or use the materials (for example, the cryptographic key). For manual key generation, conveyance, loading, storage, and retrieval, dual control requires dividing knowledge of the key among the entities. (See also Split Knowledge).
Split knowledge: Condition in which two or more entities separately have key components that individually convey no knowledge of the resultant cryptographic key.
It is key for information security professionals to understand the differences between Dual Control and Separation of Duties. Both complement each other, but are not the same.
The following were incorrect answers:
Segregation of Duties address the splitting of various functions within a process to different users so that it will not create an opportunity for a single user to perform conflicting tasks.
For example, the participation of two or more persons in a transaction creates a system of checks and balances and reduces the possibility of fraud considerably. So it is important for an organization to ensure that all tasks within a process has adequate separation.
Let us look at some use cases of segregation of duties
A person handling cash should not post to the accounting records
A loan officer should not disburse loan proceeds for loans they approved Those who have authority to sign cheques should not reconcile the bank accounts The credit card printing personal should not print the credit card PINs Customer address changes must be verified by a second employee before the change can be activated.
In situations where the separation of duties are not possible, because of lack of staff, the senior management should set up additional measure to offset the lack of adequate controls.
To summarise, Segregation of Duties is about Separating the conflicting duties to reduce fraud in an end to end function.
Need To Know (NTK):
The term "need to know", when used by government and other organizations (particularly those related to the military), describes the restriction of data which is considered very sensitive. Under need-to-know restrictions, even if one has all the necessary official approvals (such as a security clearance) to access certain information, one would not be given access to such information, unless one has a specific need to know; that is, access to the information must be necessary for the conduct of one's official duties. As with most security mechanisms, the aim is to make it difficult for unauthorized access to occur, without inconveniencing legitimate access. Need-to-know also aims to discourage "browsing" of sensitive material by limiting access to the smallest possible number of people.
EXAM TIP: HOW TO DECIPHER THIS QUESTION
First, you probably nototiced that both Separation of Duties and Segregation of Duties are synonymous with each others. This means they are not the BEST answers for sure. That was an easy first step.
For the exam remember:
Separation of Duties is synonymous with Segregation of Duties
Dual Control is synonymous with Split Knowledge
Reference(s) used for this question:
Hernandez CISSP, Steven (2012-12-21). Official (ISC)2 Guide to the CISSP CBK, Third Edition ((ISC)2 Press) (Kindle Locations 16048-16078). Auerbach Publications. Kindle Edition.
and
http://www.ciso.in/dual-control-or-segregation-of-duties/

A hot site has the equipment, software and communications capabilities to facilitate a recovery within a few minutes or hours following the notification of a disaster to the organization's primary site. With the exception of providing your own hot site, commercial hot sites provide the greatest protection. Most will allow you up to six weeks to restore your sites if you declare a disaster. They also permit an annual amount of time to test the Disaster Plan.
The following answers are incorrect:
Cold sites. Cold sites are empty computer rooms consisting only of environmental systems, such as air conditioning and raised floors, etc. They do not meet the requirements of most regulators and boards of directors that the disaster plan be tested at least annually.
Reciprocal Agreement. Reciprocal agreements are not contracts and cannot be enforced. You cannot force someone you have such an agreement with to provide processing to you. Government regulators do not accept reciprocal agreements as valid disaster recovery backup sites.
Time Brokers. Time Brokers promise to deliver processing time on other systems. They charge a fee, but cannot guaranty that processing will always be available, especially in areas that experienced multiple disasters.
The following reference(s) were/was used to create this question:
ISC2 OIG, 2007 p368 Shon Harris AIO v3. p.710

Section: Analysis and Monitoring
Explanation/Reference:
A weakness of the signature-based (or knowledge-based) intrusion detection approach is that only attack signatures that are stored in a database are detected. Network-based intrusion detection can either be signature-based or statistical anomaly-based (also called behavior-based).
Source: KRUTZ, Ronald L. & VINES, Russel D., The CISSP Prep Guide: Mastering the Ten Domains of Computer Security, John Wiley & Sons, 2001, Chapter 2: Access control systems (page 49).

Explanation/Reference:
With a packet switched network, packets are difficult to monitor because they can be transmitted using different paths.
A packet-switched network is a digital communications network that groups all transmitted data, irrespective of content, type, or structure into suitably sized blocks, called packets. The network over which packets are transmitted is a shared network which routes each packet independently from all others and allocates transmission resources as needed.
The principal goals of packet switching are to optimize utilization of available link capacity, minimize response times and increase the robustness of communication. When traversing network adapters, switches and other network nodes, packets are buffered and queued, resulting in variable delay and throughput, depending on the traffic load in the network.
Most modern Wide Area Network (WAN) protocols, including TCP/IP, X.25, and Frame Relay, are based on packet-switching technologies. In contrast, normal telephone service is based on a circuit-switching technology, in which a dedicated line is allocated for transmission between two parties. Circuit-switching is ideal when data must be transmitted quickly and must arrive in the same order in which it's sent. This is the case with most real-time data, such as live audio and video. Packet switching is more efficient and robust for data that can withstand some delays in transmission, such as e-mail messages and Web pages.
All of the other answer are wrong
Reference(s) used for this question:
TIPTON, Hal, (ISC)2, Introduction to the CISSP Exam presentation.
and
https://en.wikipedia.org/wiki/Packet-switched_network
and
http://www.webopedia.com/TERM/P/packet_switching.html