Networks (D325)

Correct Answer

A. 128, 192, or 256 bits

Explanation

The Advanced Encryption Standard (AES) supports key sizes of 128, 192, and 256 bits. AES is a symmetric encryption algorithm used to secure data, and the key size determines the strength of the encryption. AES with larger key sizes, such as 256 bits, provides stronger security compared to the smaller 128-bit key. AES is widely used because of its efficiency and strength in encrypting sensitive data.

Why other options are wrong

B. 112 or 168 bits

This key size corresponds to the older Data Encryption Standard (DES) and Triple DES (3DES) encryption standards, not AES. AES does not support key sizes of 112 or 168 bits.

C. 64 bits

AES does not support a 64-bit key size. A 64-bit key size is typically associated with older encryption algorithms like DES, which is no longer considered secure. AES uses 128, 192, or 256 bits for its key sizes.

D. 56 bits

A 56-bit key size is also associated with older encryption algorithms, specifically the DES standard. AES uses longer key sizes for better security, with no support for 56-bit keys.

Correct Answer

B. Segmentation and reassembly of packets

Explanation

The Transport layer (Layer 4 in the OSI model) in the TCP/IP stack is responsible for the segmentation and reassembly of data into smaller packets. This ensures that large messages are divided into manageable chunks for transmission over the network and then reassembled correctly at the destination. It also handles flow control and error detection, but segmentation and reassembly are its core responsibilities.

Why other options are wrong

A. Error control

While the Transport layer is involved in error detection and correction (especially through protocols like TCP), it is not its primary function. The main role is managing the data transfer process, including segmentation and reassembly. Error control is part of that but not the sole responsibility.

C. Identifying and locating the destination

Identifying and locating the destination is the responsibility of the Network layer (Layer 3). This layer uses IP addresses to route data to the appropriate destination.

D. Specifying end-user needs

Specifying end-user needs is more of an application-level concern, typically handled by the Application layer (Layer 7) in the OSI model. The Transport layer ensures reliable data transfer, but it does not deal with user-specific application logic or requirements directly.

Correct Answer

D. Denial-of-Service (DoS)

Explanation

A Denial-of-Service (DoS) attack aims to disrupt the availability of a service by overwhelming the target system with excessive traffic or resource requests. This prevents legitimate users from accessing the service. It typically involves sending massive volumes of data or requests, consuming network resources, and making the service or system unavailable.

Why other options are wrong

A. Buffer Overflow

A buffer overflow occurs when more data is written to a buffer than it can handle, potentially causing the system to crash or allowing for malicious code execution. While this is a security vulnerability, it is not related to overwhelming a service with traffic, which is the hallmark of a DoS attack.

B. Ping flood attack

A Ping flood attack is a type of DoS attack that involves sending large numbers of ICMP Echo Request (ping) packets to a target to exhaust network resources. While it is a specific type of DoS attack, it does not fully describe all types of DoS attacks, which can involve other kinds of traffic besides pings.

C. ARP poisoning

ARP poisoning, or ARP spoofing, is a technique where an attacker sends falsified ARP messages over a local network to associate their MAC address with the IP address of another device. This can result in man-in-the-middle attacks or network disruptions but does not fit the description of a DoS attack, which focuses on overwhelming the service with traffic.

Correct Answer

B. CSMA/CD

Explanation

Ethernet uses the Carrier Sense Multiple Access with Collision Detection (CSMA/CD) media access method. This method allows devices on the same network to detect if another device is transmitting before they begin sending data. If two devices transmit simultaneously, a collision is detected, and they wait a random amount of time before retransmitting. This helps manage data traffic efficiently on a shared medium.

Why other options are wrong

A. CSMA/CA

CSMA/CA stands for Carrier Sense Multiple Access with Collision Avoidance and is used in wireless networks, not Ethernet. It attempts to avoid collisions by waiting for a clear signal before transmitting, which is suitable for wireless environments where detecting collisions is more challenging. Therefore, it is not applicable to Ethernet's wired setup.

C. UTP

UTP (Unshielded Twisted Pair) is a type of physical cable used in networking, not a media access method. While Ethernet often runs over UTP cables, the cable type itself does not determine how devices share the communication medium. Thus, it does not fulfill the role that CSMA/CD does in Ethernet networking.

D. TCP/IP

TCP/IP is a suite of communication protocols used to interconnect network devices on the internet and local networks. It operates at a higher layer than the Ethernet access method. While Ethernet and TCP/IP are used together, TCP/IP is not the method by which media access is controlled on Ethernet networks.

Correct Answer

B. Is a network device used to connect many, sometimes disparate, network segments together combining them into what we call an internetwork

Explanation

A router is a network device that connects multiple networks, or segments of a network, and forwards data packets between them. Routers operate at the Network layer (Layer 3) of the OSI model, and they use IP addresses to route data between different network segments, allowing them to communicate with one another. This makes them essential in building an internetwork, which is a network of interconnected networks.

Why other options are wrong

A. Is a data link device used to connect many, sometimes disparate, data link segments together combining them into what we call an internetwork

A router operates at the Network layer, not the Data Link layer. The Data Link layer deals with communication between devices on the same network, while the router's role is to forward packets between different networks.

C. Is a physical device used to connect many, sometimes disparate, physical segments together combining them into what we call an internetwork

Routers are not simply physical devices used to connect physical segments. They operate at a higher layer, using logical IP addresses for routing, whereas physical devices like hubs and switches operate at lower layers (Physical and Data Link layers) to connect devices within a network.

Correct Answer

D. physical

Explanation

In the OSI model, Layer 1 is the Physical Layer. It is responsible for transmitting raw data bits over a physical medium such as cables, wireless signals, or other transmission methods. The Physical Layer deals with the hardware components involved in data transmission, including connectors, cables, and signaling protocols.

Why other options are wrong

A. application

The Application Layer is Layer 7 in the OSI model and is responsible for providing network services directly to end-users and applications, such as email or file transfer services. It is not related to physical transmission.

B. TCP

TCP is a transport layer protocol and is part of Layer 4 in the OSI model. It is used for managing data transmission between applications and ensures reliable delivery of data, but it does not handle the physical transmission of data.

C. session

The Session Layer is Layer 5 in the OSI model and is responsible for establishing, managing, and terminating communication sessions between applications. It does not deal with physical transmission.

Correct Answer

C. It provides a unique MAC address for device identification.

Explanation

The NIC operates at the data link layer and is responsible for providing a unique MAC address, which is used to identify devices on a local network. This address helps ensure that data is correctly directed to the appropriate hardware device on the same local network.

Why other options are wrong

A. It manages IP addressing for devices on the network.

Managing IP addressing is the role of the network layer, particularly through protocols like DHCP. The NIC does not manage IP addresses; it is responsible for the MAC address.

B. It translates data packets into signals for transmission.

This task is typically handled by the physical layer, which deals with signal transmission. The NIC prepares the data link layer frames but does not directly translate data packets into physical signals.

D. It encrypts data for secure transmission.

Encryption typically occurs at higher layers of the OSI model, such as the application layer or transport layer. The NIC does not handle encryption for secure data transmission; that responsibility lies elsewhere in the network stack.

Correct Answer

B. It provides error detection and correction for data frames.

Explanation

The Data Link layer in the TCP/IP model is responsible for ensuring reliable data transfer between devices on the same network. It performs error detection and correction by checking the integrity of data frames as they are transmitted. The layer is also responsible for framing data for transmission, managing access to the physical medium, and detecting physical layer issues.

Why other options are wrong

A. It is responsible for routing packets across multiple networks.

Routing packets across multiple networks is a function of the Network layer, not the Data Link layer. The Network layer is responsible for packet forwarding and routing between devices on different networks.

C. It establishes, manages, and terminates sessions between applications.

Session management is the responsibility of the Session layer in the OSI model, not the Data Link layer. The Session layer manages communication sessions between applications.

D. It encrypts data to ensure secure transmission over the network.

Encryption is typically handled by the Transport or Application layers, depending on the context. The Data Link layer is not responsible for encryption, as its primary role is to ensure data integrity and proper transmission on the same network segment.

Correct Answer

A. Incoming and outgoing data packets

Explanation

Packet filtering firewalls inspect both incoming and outgoing data packets to determine if they should be allowed or blocked based on predefined security rules. These rules typically include the source and destination IP addresses, ports, and protocols. The firewall performs this inspection at the network layer to ensure only authorized packets pass through.

Why other options are wrong

B. Outgoing data packets only

A packet filtering firewall examines both incoming and outgoing data packets, not just outgoing packets. Limiting analysis to outgoing packets would leave the network vulnerable to inbound threats.

C. Incoming data packets only

Packet filtering firewalls analyze both incoming and outgoing traffic. Limiting analysis to just incoming packets would fail to filter potentially dangerous outgoing traffic, leaving the network exposed.

D. User data packet

Packet filtering firewalls do not focus only on user data packets. They examine the header information of all packets, including the source and destination addresses, as well as port numbers, to enforce security policies across all types of traffic.