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All questions of Network Layer for Computer Science Engineering (CSE) Exam

Which one of the following is not a function of network layer?
  • a)
    routing
  • b)
    inter-networking
  • c)
    congestion control
  • d)
    none of the mentioned
Correct answer is option 'D'. Can you explain this answer?

Avinash Mehta answered
Network Layer :-
The network layer is responsible for the source-to-destination delivery of a packet, possibly across multiple networks (links).
Other functions of the network layer include the following :-
Logical addressing :- In order to identify each device on internetwork uniquely, network layer defines an addressing scheme.
Routing :- The network layer protocols determine which route is suitable from source to destination.
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The network layer concerns with
  • a)
    bits
  • b)
    frames
  • c)
    packets
  • d)
    none of the mentioned
Correct answer is option 'C'. Can you explain this answer?

Bijoy Kapoor answered
The network layer is responsible for routing packets from the source to destination. The routing algorithm is the piece of software that decides where a packet goes next (e.g., which output line, or which node on a broadcast channel).

For connectionless networks, the routing decision is made for each datagram. For connection-oriented networks, the decision is made once, at circuit setup time.

RIP is
  • a)
    Protocol used for transmission of IP datagrams across a serial line
  • b)
    Resource information protocol
  • c)
    Protocol used to exchange information between the routers
  • d)
    Protocol used to exchanger information between the layers
Correct answer is option 'C'. Can you explain this answer?

Prisha Sharma answered
Routing Information Protocol (RIP) is a routing protocol based on the distance vector algorithm, In this each router periodically shares its knowledge about the entire network with its neighbours.

Who can send ICMP error-reporting messages?
  • a)
    Routers
  • b)
    Destination hosts
  • c)
    Source host
  • d)
    Both (a) and (b)
Correct answer is option 'D'. Can you explain this answer?

Krithika Kaur answered
Both router and destination host can send ICMP error-reporting message to inform the source host about any failure or error occurred in packet.

Distance vector protocols use the concept of split horizon, but link-state routing protocols, such as OSPF, do not. 
  • a)
    True
  • b)
    False
Correct answer is option 'B'. Can you explain this answer?

Shubham Ghoshal answered
Answer: b
Explanation: Distance vector protocols use the concept of split horizon, but link-state routing protocols, such as OSPF, do not use this.

In virtual circuit network each packet contains
  • a)
    full source and destination address
  • b)
    a short VC number
  • c)
    both (a) and (b)
  • d)
    none of the mentioned
Correct answer is option 'B'. Can you explain this answer?

Raghav Joshi answered
Explanation:

Virtual Circuit Network is a type of network in which a dedicated path is established between the source and destination before transmitting the data. In this network, each packet contains a short VC (Virtual Circuit) number instead of a full source and destination address.

Advantages of using VC number:
- It reduces the overhead of routing and forwarding packets by eliminating the need for address lookup in each router along the path.
- It provides faster and more efficient packet switching as the network can quickly route the packets based on the VC number.

Disadvantages of using VC number:
- It requires a lot of resources to establish and maintain the virtual circuit path, which can result in higher latency and delay in transmission.
- It can also lead to network congestion as multiple virtual circuits may share the same physical link.

Therefore, the correct answer to the question is option 'B', which states that each packet in a virtual circuit network contains a short VC number instead of a full source and destination address.

During normal IP packet forwarding by routers which of the following packet fields are updated?
  • a)
    IP header source address
  • b)
    IP header destination address
  • c)
    IP header TTL
  • d)
    IP header check sum
Correct answer is option 'C'. Can you explain this answer?

Nilesh Mukherjee answered
During forwarding of an IP packet by routers, the packet fields namely IP header source address and IP header destination address remains same whereas check own and TTL are updated.

The frame relay committed information rate represents
  • a)
    Maximum data rate on the network
  • b)
    Steady state data rate on the network
  • c)
    Minimum data rate on the network
  • d)
    Interface data rate
Correct answer is option 'C'. Can you explain this answer?

Mainak Kulkarni answered
Frame relay committed information rate represents minimum data rate on the network.

Here cumulative number of bits sent during the predefined period should not exceed Bc.

Multidestination routing
  • a)
    is same as broadcast routing
  • b)
    contains the list of all destinations
  • c)
    data is not sent by packets
  • d)
    none of the mentioned
Correct answer is option 'C'. Can you explain this answer?

Anirban Khanna answered
Algorithms for effectively routing messages from a source to multiple destination nodes in a store-and-forward computer network are studied. The focus is on minimizing the network cost (NC), which is the sum of weights of the links in the routing path.

The computation of the shortest path in OSPF is usually done by
  • a)
    Bellman-ford algorithm
  • b)
    Routing information protocol
  • c)
    Dijkstra’s algorithm
  • d)
    Distance vector routing
Correct answer is option 'C'. Can you explain this answer?

Jay Basu answered
Explanation:

Dijkstra's Algorithm:
- OSPF (Open Shortest Path First) uses Dijkstra's algorithm to compute the shortest path.
- Dijkstra's algorithm is a graph search algorithm that solves the single-source shortest path problem for a graph with non-negative edge weights.
- It starts at the source node and explores the neighboring nodes to find the shortest path to all other nodes in the graph.

Bellman-Ford Algorithm:
- The Bellman-Ford algorithm is another algorithm used for finding the shortest path in a network.
- It can handle graphs with negative edge weights but is not typically used in OSPF.

Routing Information Protocol (RIP):
- RIP is another routing protocol that uses distance vector routing, which is different from OSPF.
- It does not use Dijkstra's algorithm for computing the shortest path.

Distance Vector Routing:
- Distance vector routing, used by protocols like RIP, determines the best path based on the number of hops to a destination.
- OSPF, on the other hand, uses Dijkstra's algorithm which considers the actual cost or weight of the paths.
In conclusion, OSPF uses Dijkstra's algorithm for computing the shortest path because it is efficient and suitable for networks with non-negative edge weights.

Which of the following is not a type of OSPF packet?
  • a)
    Hello
  • b)
    Link-state request
  • c)
    Link-state response
  • d)
    Link-state ACK
Correct answer is option 'C'. Can you explain this answer?

Vaibhav Choudhary answered
Answer: c
Explanation: Five types of OSPF packets are: Hello, Database description, Link-state request, Link-state update, Link-state ACK

At which interval does OSPF refresh LSAs?
  • a)
    10 seconds
  • b)
    30 seconds
  • c)
    30 minutes
  • d)
    1 hour
Correct answer is option 'D'. Can you explain this answer?

Tanvi Datta answered
Understanding OSPF LSA Refresh Interval
Open Shortest Path First (OSPF) is a widely used routing protocol in large networks. One of the critical components of OSPF is the Link State Advertisement (LSA), which contains information about the network topology.
LSA Refresh Interval
- OSPF LSAs have a default refresh interval of 30 minutes.
- This means that an OSPF router will resend its LSAs to its neighbors every 30 minutes to ensure that all routers have the most current network information.
Why 30 Minutes?
- Stability: The 30-minute interval helps in maintaining stability in the network. Frequent updates may lead to unnecessary processing and bandwidth consumption.
- Network Changes: While LSAs are refreshed every 30 minutes, OSPF also has mechanisms to immediately propagate changes in the network topology through triggered updates. This ensures that routers can quickly adapt to changes without waiting for the next refresh.
- Age of LSAs: Each LSA has an age field that increments over time. If an LSA reaches an age of 60 minutes, it is considered stale and will be removed from the database, prompting a refresh.
Conclusion
- The correct answer to the interval at which OSPF refreshes LSAs is indeed 30 minutes (not 1 hour). It’s important to understand how this interval balances network efficiency with the need for up-to-date routing information.
By grasping the OSPF LSA refresh interval, network engineers can better manage and optimize their routing protocols for performance and reliability.

Which of the following is not a service primitive?
  • a)
    Connect
  • b)
    Listen
  • c)
    Send
  • d)
    Sound
Correct answer is option 'D'. Can you explain this answer?

Ujwal Nambiar answered
Service Primitives

Service primitives are the basic building blocks of communication protocols. They define the operations that can be performed on a communication service. There are typically four types of service primitives: connect, listen, send, and receive.

Connect
The connect primitive is used to establish a connection between two entities in a communication network. It allows the initiating entity to request a connection to a specific destination entity.

Listen
The listen primitive is used to wait for incoming connection requests. It allows an entity to passively listen for connection requests and accept them when they arrive.

Send
The send primitive is used to send data from one entity to another. It allows the sending entity to transmit data to the destination entity over an established connection.

Sound
The option 'D' in this question, "Sound," is not a service primitive. Sound refers to auditory perception resulting from vibrations that can be detected by the human ear. It is not a communication operation or a service provided by a communication protocol.

Explanation
In the given options, connect, listen, and send are all service primitives commonly used in communication protocols. These primitives are essential for establishing connections, listening for incoming requests, and transmitting data. However, sound is not a service primitive as it does not relate to communication protocols or network operations.

Sound is a sensory perception and not a service or operation that can be performed on a communication network. Therefore, the correct answer is option 'D' - Sound.

Which one of the following routing algorithm can be used for network layer design?
  • a)
    shortest path algorithm
  • b)
    distance vector routing
  • c)
    link state routing
  • d)
    all of the mentioned
Correct answer is option 'D'. Can you explain this answer?

Rajeev Menon answered
The routing algorithm is what decides where a packet should go next. There are several routing techniques like shortest path algorithm, static and dynamic routing, decentralized routing, distance vector routing, link state routing, Hierarchical routing etc.

Which protocol use link state routing?
  • a)
    BGP
  • b)
    OSPF
  • c)
    RIP
  • d)
    None of these
Correct answer is option 'B'. Can you explain this answer?

Nandini Joshi answered
Link state routing is a type of routing protocol that is used to determine the best path for data packets to travel through a network. It is based on the concept of each router having a complete map of the network, including the status and cost of each link. This allows the routers to make informed decisions about the best path to forward packets.

The correct answer to the question is option 'B', which states that OSPF (Open Shortest Path First) uses link state routing. OSPF is a widely used routing protocol that is used in IP networks, particularly in large enterprise networks. It is designed to be scalable and efficient, and it uses link state routing to determine the shortest path between routers.

Here is a detailed explanation of why OSPF uses link state routing:

1. Link State Database:
- In OSPF, each router maintains a Link State Database (LSDB) that contains information about the network topology.
- The LSDB is built by exchanging Link State Advertisements (LSAs) between routers.
- LSAs contain information about the router's neighbors, the links it is connected to, and the cost of those links.
- By exchanging LSAs, routers can build a complete map of the network and have the same information about the network topology.

2. SPF Algorithm:
- OSPF uses a Shortest Path First (SPF) algorithm to calculate the best path for packets to travel.
- The SPF algorithm takes into account the cost of each link, which is determined by the administrator.
- It calculates the shortest path by summing up the costs of the links along a path.
- The path with the lowest total cost is considered the best path, and packets are forwarded along that path.

3. Dynamic Updates:
- OSPF supports dynamic updates, which means that routers can exchange LSAs to keep the LSDB up to date.
- When a link goes down or a new link is added to the network, routers exchange LSAs to inform each other about the changes.
- This allows OSPF to adapt to changes in the network and recalculate the best path if necessary.

In conclusion, OSPF is an example of a routing protocol that uses link state routing. It maintains a Link State Database and uses the SPF algorithm to calculate the best path for packets to travel through the network. OSPF is widely used in large networks because of its scalability and efficiency.

What is the IP protocol number for OSPF packets?
  • a)
    89
  • b)
    86
  • c)
    20
  • d)
    76
Correct answer is option 'A'. Can you explain this answer?

Rashi Banerjee answered
Explanation:

OSPF Protocol Number:
- The IP protocol number for OSPF (Open Shortest Path First) packets is 89.
- OSPF is a routing protocol that uses a link-state algorithm to determine the best path to a destination network.

Understanding Protocol Numbers:
- In networking, protocol numbers are used to identify different network protocols at the IP layer.
- These numbers are included in the IP header to indicate the specific protocol being used.

Significance of Protocol Number 89:
- OSPF uses protocol number 89 to differentiate its packets from other types of network traffic.
- This allows routers to identify OSPF packets and process them according to the OSPF protocol rules.

Conclusion:
- In summary, the protocol number for OSPF packets is 89, which is crucial for routers to correctly identify and handle OSPF traffic in a network environment.

Packets of the same session may be routed through different paths in​
  • a)
    TCP, but not UDP
  • b)
    TCP and UDP
  • c)
    UDP, but not TCP
  • d)
    Neither TCP nor UDP
Correct answer is option 'B'. Can you explain this answer?

Moumita Yadav answered
Explanation:
In computer networking, packets are the basic units of data that are transmitted over a network. They contain the payload (data) as well as the necessary information for routing and delivering the data to the intended destination.

Routing in TCP:
TCP (Transmission Control Protocol) is a reliable and connection-oriented protocol. It establishes a connection between two endpoints before transmitting data. The packets in a TCP session are sent in a sequential order and they are received at the destination in the same order. TCP ensures that the packets are delivered reliably and in order by using mechanisms like acknowledgment, retransmission, and flow control.

When it comes to routing, TCP packets are routed based on the IP addresses and port numbers of the source and destination. Once the connection is established, the routing path remains fixed for the duration of the session. This means that all the packets of a TCP session will follow the same path from the source to the destination. Therefore, packets of the same TCP session will be routed through the same path.

Routing in UDP:
UDP (User Datagram Protocol) is a connectionless and unreliable protocol. It does not establish a connection before transmitting data and does not guarantee delivery or order of packets. Each UDP packet is independent and can take a different path to reach the destination. UDP does not have any built-in mechanisms for acknowledgment, retransmission, or flow control.

Since UDP does not maintain any connection state, the packets of a UDP session can be routed through different paths. The routing decisions are made by the routers based on factors like network congestion, availability of routes, and load balancing. Therefore, it is possible for packets of the same UDP session to take different paths.

Conclusion:
In conclusion, packets of the same session may be routed through different paths in both TCP and UDP. However, TCP ensures that the packets are delivered reliably and in order, while UDP does not provide such guarantees.

In ______ , data are sent or processed at a very inefficient rate, such as 1 byte at a time.
  • a)
    Nagle’s syndrome
  • b)
    Silly window syndrome
  • c)
    Sliding window syndrome
  • d)
    Delayed acknowledgment
Correct answer is option 'B'. Can you explain this answer?

Surbhi Kaur answered
Silly window syndrome problem can degrade TCP performance. This problem occurs when data are passed to the sending TCP entity in large blocks, but interactive application on the receiving side reads data T byte at a time.

Brouter
  • a)
    Is a type of bridge
  • b)
    Works at all the layers Of OS I model
  • c)
    Is able to bridge those protocols that are not routable
  • d)
    None of these
Correct answer is option 'C'. Can you explain this answer?

Arka Shah answered
Brouter is a device, which is combination of functionality of bridge and router. So, it works till network layer and is able to bridge those protocol that are not routable.

At which layer of the OSI model the router configuration problem reside
  • a)
    Transport
  • b)
    Network
  • c)
    Logical Link
  • d)
    Physical
Correct answer is option 'B'. Can you explain this answer?

Jatin Joshi answered
Routers are the networking devices that operate on network layer. Hence at network layer, the router configuration problem reside.

The 4 byte IP address consists of
  • a)
    network address
  • b)
    host address
  • c)
    both (a) and (b)
  • d)
    none of the mentioned
Correct answer is option 'C'. Can you explain this answer?

Preethi Basu answered
Explanation:

  • The 4 byte IP address consists of both network address and host address.

  • The IP address is divided into two parts, the network address and the host address.

  • The network address is used to identify the network, while the host address is used to identify the specific device on that network.

  • The network address is determined by the class of IP address, which can be Class A, B, or C.

  • The host address is determined by the subnet mask, which is used to divide the network into smaller subnetworks.

  • Together, the network address and the host address make up the complete IP address, which is used to route data between devices on different networks.

A TCP message consisting of 2100 bytes is passed to IP for delivery across two networks. The first network can carry a maximum payload of 1200 bytes per frame and the second network can carry a maximum payload of 400 bytes per frame, excluding network overhead. Assume that IP overhead per packet is 20 bytes. What is the total IP overhead in the second network for this transmission?
  • a)
    40 bytes
  • b)
    80 bytes
  • c)
    120 bytes
  • d)
    160 bytes
Correct answer is option 'C'. Can you explain this answer?

Shivam Dasgupta answered
In the question they have directly given the payload so 2100 will be divided into 1200 and 904 (900 is not a multiple of 8 so we have to pad 4 bits in order to make it a multiple of 8).
Now in second network payload is 400 B.
So 1200 bytes packet will be divided in 400,400, 400 with each having 20 B header, and 900 will be divided into 400,400 and 104 (4 bits padded) each having 20 B header.
So total overhead is 20 x 6 = 120 B.

ICMP is primarily used for
  • a)
    error and diagnostic functions
  • b)
    addressing
  • c)
    forwarding
  • d)
    none of the mentioned
Correct answer is option 'A'. Can you explain this answer?

Bijoy Kapoor answered
The Internet Control Message Protocol (ICMP) is primarily used for error and diagnostic functions.

Here are the details of ICMP: 

- ICMP is mainly used to determine whether or not data is reaching its intended destination in a timely manner. 

- Commonly, the ICMP protocol is used on network devices, such as routers. 

- ICMP is crucial for error reporting and testing, but it can also be used in distributed denial-of-service (DDoS) attacks.

Hence Option (A) is correct

For short notes on the chapter Network Layer click on the link given below:

How many digits of the network user Address are known as the DNIC (Data Network Identification Code)?
  • a)
    First three
  • b)
    First four
  • c)
    First five
  • d)
    First seven
Correct answer is option 'B'. Can you explain this answer?

Athul Pillai answered
As per the format, the first 4 digits of the international data number, the three digits that may represent the counter code one 1-digit network code i.e. the network digit.

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