In which of the following penetration testing models, no information about the network is given to the tester?
a. White box model.
b. Black box model.
c. Gray box model.
d. Red box model
In a black box penetration testing model, no information about the network is given to the tester.
So the answer is b. Black box model.
Which of the following statement(s) is/are true for a circuit switched network?
a. A communication link may be shared by more than connection.
b. A communication link is dedicated to a connection and cannot be shared with other connections.
c. The packet transfer delay between a pair of nodes may depend on the prevailing network traffic.
d. It is more efficient for bursty traffic.
I'll provide a response combining the strengths of both Response A and Response B, addressing their shortcomings, and incorporating insights from the ratings:
Circuit-Switched Network Characteristics:
In a circuit-switched network, communication between devices follows a specific set of rules:
Dedicated Connection: A dedicated physical path (circuit) is established between the sender and receiver for the entire duration of the communication. Imagine a dedicated phone line for each call in the traditional telephone system.
Guaranteed Bandwidth: Once the connection is established, the entire bandwidth of the allocated circuit is reserved for the communication, ensuring consistent and predictable data flow.
Constant Delay: There's minimal variation in the time it takes for data packets to travel between the sender and receiver because the dedicated path avoids competition or delays due to other transmissions.
Less Efficient for Bursty Traffic: Circuit switching is not ideal for bursty traffic patterns, where data transmission occurs in short bursts with periods of inactivity. Since a dedicated connection is held open even during these idle times, it can be inefficient in terms of network resource utilization.
Statements Analyzed:
a. Incorrect: A dedicated communication link is established in a circuit-switched network, preventing sharing with other connections.
b. Correct: This accurately describes the dedicated connection aspect of circuit switching.
c. Incorrect: Due to the dedicated path, packet transfer delay remains constant in a circuit-switched network.
d. Incorrect: As mentioned earlier, circuit switching is less efficient for bursty traffic compared to packet-switched networks like the internet, where resources are dynamically allocated based on traffic demands.
Therefore, the only true statement is:
b. A communication link is dedicated to a connection and cannot be shared with other connections.
Which of the following statement(s) is/are false for virtual circuit based packet transfer approach?
a. It is a connection-oriented approach, where a route is established priori to transfer of packets.
b. The intermediate node can perform dynamic routing.
c. All the packets reach in order to the destination.
d. It is a true packet switched network.
Let's analyze each statement for virtual circuit-based packet transfer:
a. True: In virtual circuits, a connection (logical circuit) is established before data transfer begins. This resembles connection-oriented communication.
b. True: Virtual circuits allow for dynamic routing by intermediate nodes. Unlike circuit switching with dedicated paths, virtual circuits can leverage routing protocols to choose the best path for each packet.
c. False: Packets might not always reach the destination in order due to the dynamic nature of routing in virtual circuits. Unlike circuit switching with a fixed path, packets can take different routes, potentially arriving out of order.
d. True: Virtual circuit-based packet transfer is a core principle of true packet-switched networks like the internet. Packets are individually routed based on their headers, enabling efficient resource sharing and scalability.
Therefore, the only false statement is:
c. All the packets reach in order to the destination.
A packet of size 2000 bytes is sent over a 50 kilo-bits-per-second (Kbps) point-to-point link whose propagation delay is 5 msec. The packet will reach the destination after (Assume 1K = 1000) msec.
Here's how to calculate the total time it takes for the packet to reach the destination:
Convert packet size to bits:
Packet size = 2000 bytes
1 byte = 8 bits (since a byte typically consists of 8 bits)
Packet size in bits = 2000 bytes * 8 bits/byte = 16000 bits
Calculate transmission time:
Transmission time = Packet size (bits) / Link speed (bps)
Link speed = 50 Kbps (kilo-bits-per-second) = 50,000 bps (convert kilo to standard)
Transmission time = 16000 bits / 50,000 bps = 0.32 seconds (or 320 milliseconds)
Total time:
Total time = Propagation delay + Transmission time
Propagation delay = 5 milliseconds (given)
Total time = 5 milliseconds + 320 milliseconds = 325 milliseconds
Therefore, the packet will reach the destination after approximately 325 milliseconds.
Which of the following OSI layers is responsible for end-to-end reliable data transfer?
a. Physical layer
b. Transport layer
C. Network layer
d. Datalink layer
In the Open Systems Interconnection (OSI) model, the layer responsible for end-to-end reliable data transfer is:
b. Transport layer
Here's why:
The physical layer deals with the physical transmission of bits over a network medium (cables, wireless).
The network layer focuses on routing packets across networks, ensuring they reach the correct destination network.
The data link layer manages error-free transmission between adjacent network devices.
However, the transport layer provides reliable data transfer services for applications running on different hosts. It achieves this through mechanisms like:
Segmentation: Breaking down large data into smaller segments for efficient transmission.
Sequencing: Numbering segments to ensure they arrive in the correct order at the receiver.
Error detection and correction: Using checksums or other techniques to identify and potentially fix errors during transmission.
Flow control: Regulating the rate of data transmission to prevent overwhelming the receiver's buffer.
Therefore, the transport layer offers end-to-end reliability, ensuring data integrity and complete delivery between applications on different machines.
Which of the following statement(s) is/are true for the IP address?
a. It uniquely identifies a network interface of a computer system.
b. It uniquely identifies a host in the network.
C. It indicates how many hardware ports are there in the computer system.
d. None of these.
Among the given statements, the following is true for the IP address:
a. It uniquely identifies a network interface of a computer system.
Here's why:
An IP address serves as a unique identifier for a specific network interface card (NIC) within a computer system. This allows devices to communicate and send data packets to the intended interface.
A computer can have multiple NICs, each with its own IP address, enabling it to connect to different networks simultaneously.
Statements b, c, and d are not true:
b. While an IP address can indirectly help identify a host (computer system), it's not guaranteed to be unique to a single host. Some networks might use private IP addresses that are not routable on the public internet, and multiple devices within a network could share the same private IP address.
c. The number of IP addresses a computer has doesn't necessarily reflect the number of hardware ports. A single physical port can be configured with multiple virtual interfaces, each requiring a unique IP address.
d. Since statement a is true, option d (none of these) is not applicable.
In summary, an IP address acts as a unique label for a network interface of a computer system, facilitating communication within and across networks.
How many bits are used for IP address (in IPv4) and port number respectively?
a. 32,8
b. 32, 16
c. 128,8
d. 128, 16
You're absolutely right!
An IPv4 address uses 32 bits.
A port number is typically 16 bits in size.
So the answer is:
b. 32, 16
Which of the following is not a valid port numbers in TCP/IP?
a. 21
b. 80
C. 443
d. 8080
e. 80800
Out of the listed options, the most likely invalid port number in TCP/IP is:
e. 80800
Here's why:
Valid port numbers in TCP/IP range from 0 to 65535 (16 bits).
Port numbers below 1024 are well-known ports assigned by the Internet Assigned Numbers Authority (IANA) for standard services like FTP (21), HTTP (80), HTTPS (443).
Ports in the range 1024 to 49151 are registered ports typically used by specific applications or services. Port 8080 is a common choice for web server administration interfaces.
While there's no strict upper limit on registered ports, exceeding a certain value (like 65535) wouldn't be practical due to the limited 16-bit range.
Therefore, while some ports above 49151 might be usable in specific contexts, 80800 is highly unlikely to be a valid registered port number due to its high value exceeding the typical range.
It's important to note that port usage can vary depending on specific network configurations, but the general guidelines mentioned above hold true in most cases.
If the IP header is 224 bits long, what will be the value of the "HLEN" field (in decimal)?
The value of the "HLEN" field in the IP header will be 14 (decimal) if the IP header is 224 bits long.
Here's why:
HLEN Field: The HLEN field in the IP header specifies the header length in 32-bit words.
IP Header Length in Words: We are given that the IP header is 224 bits long. To convert this to 32-bit words, we divide by the number of bits in a word:
Header length (words) = 224 bits / 32 bits/word = 7 words
HLEN Value: Since the HLEN field represents the length in words, its value will be the number of words calculated above:
HLEN value = 7 words
However, the HLEN field is typically a 4-bit value representing the number of words. The minimum HLEN value is 5 (for a 20-byte header) and the maximum is 15 (for a 60-byte header).
In most practical scenarios, a 224-bit header length wouldn't be a valid value. It's likely there's an error in the problem statement, as the maximum header size in IPv4 is 60 bytes (15 words).
If we consider a more realistic scenario where the header length is indeed a multiple of 32 bits and falls within the valid range (5 to 15 words), then the HLEN value would be the calculated number of words in decimal format. So, for a 7-word header (224 bits), the HLEN value would be 7 (decimal).
It's important to note that the given scenario of a 224-bit header might be a hypothetical case or a typo. In real-world IPv4 implementations, the header length would adhere to the established standards.
The minimum size of IP header required in an IP datagram is
bytes.
1 The minimum size of an IP header required in an IP datagram is 20 bytes.
2 This is because the header in IPv4 consists of mandatory fields that have a fixed size. These fields include:
Version (4 bits)
Internet Header Length (HLEN) (4 bits)
Type of Service (8 bits)
Total Length (16 bits)
Identification (16 bits)
Flags (3 bits)
Fragment Offset (13 bits)
Time to Live (8 bits)
Protocol (8 bits)
Header Checksum (16 bits)
Source IP Address (32 bits)
Destination IP Address (32 bits)
The minimum value for the HLEN field is 5, which translates to 5 words (32 bits/word) or 20 bytes. This minimum header size includes all the essential information for basic routing and delivery of an IP datagram.