Data Communication & Networking (QUESTION BANK)
(CSE) Question and answer
UNIT-3
LIST OF QUESTIONS:
1. Distinguish between the process of routing a packet from the source to the destination and the process of forwarding a packet at each router.
2. In classless addressing, can two different blocks have the same prefix length? Explain.
3. Why does the network-layer protocol need to provide packetizing service to the transport layer?
4. In classless addressing, we know the first and the last address in the block.
5. List four types of delays in a packet-switched network.
6. If a label in a connection-oriented service is 8 bits, how many virtual circuits can be established at the same time?
7. List the three phases in the virtual-circuit approach to switching.
8. In classless addressing, we know the first address and the number of addresses in the block. Can we find the prefix length? If the answer is yes, show the process.
9. If a label in a connection-oriented service is 8 bits, how many virtual circuits can be established at the same time?
10. Distinguish between the process of Packet Switching & Circuit Switching Network.
11. Draw & Explain DHCP Message Format.
12. Explain in brief FSM for DHCP Client.
13. Define IPV4 occupation of the address space in classful addressing.
14. Elaborate the terms Routing, Forwarding, and Packetizing.
15. List & explain other services expected from the Network layer.
16. Define the term Network Address Translation.
17. Each of the following addresses belongs to a block. Find the first and the last address in each block.
a. 14.12.72.8/24
b. 200.107.16.17/18
(NOTE: EXPLORE THIS QUESTIONS ACCORDING TO YOUR NEED)
1. Distinguish between the process of routing a packet from the source to the destination and the process of forwarding a packet at each router.
Routing a packet refers to the overall process of determining the path that a packet should take from its source to its destination across an internetwork. It involves making decisions at each router based on routing algorithms and network protocols. The routing process considers factors such as network topology, link costs, and routing table information to find the most suitable path for the packet.
Forwarding a packet, on the other hand, occurs at each individual router along the determined path. It is the act of sending the packet from an incoming interface to an outgoing interface according to the information in the router's forwarding table. Forwarding is a local decision made by each router based on the destination address of the packet. It does not involve the global network-wide decision-making process like routing does.
2. In classless addressing, can two different blocks have the same prefix length? Explain.
Yes, in classless addressing, two different blocks can have the same prefix length. Classless addressing, also known as Classless Inter-Domain Routing (CIDR), allows for flexible allocation of IP addresses by using variable-length subnet masks (VLSM). With VLSM, the prefix length can be adjusted to create subnets of different sizes.
The prefix length represents the number of bits in the network portion of the IP address. Two blocks with the same prefix length may have different network addresses but share the same number of significant bits in their subnet masks. This allows for finer granularity in dividing the IP address space and efficient utilization of available addresses.
3. Why does the network-layer protocol need to provide packetizing service to the transport layer?
The network-layer protocol provides packetizing service to the transport layer to enable the transmission of data across a network. The transport layer deals with data in terms of segments, while the network layer operates on packets. The packetizing service bridges this gap by encapsulating transport layer segments into network layer packets.
Packetizing involves breaking down the transport layer segments into smaller units suitable for transmission across the network. This process includes adding headers to the segments, which contain essential information such as source and destination IP addresses, protocol identifiers, and other control information. Packetizing also ensures that the data is properly formatted for reliable and efficient delivery over the network.
By providing packetizing service, the network-layer protocol allows the transport layer to focus on its core responsibilities, such as ensuring end-to-end data delivery, flow control, and error recovery, while leveraging the network layer for efficient packet transmission.
4. In classless addressing, we know the first and the last address in the block. Can we find the prefix length? If the answer is yes, show the process.
Yes, we can find the prefix length in classless addressing when we know the first and the last address in the block. The process involves comparing the binary representations of the first and last addresses to determine the common prefix.
Here's the process to find the prefix length:
1. Convert the first and last addresses from decimal to binary representation.
For example, let's consider a block with the first address 14.12.72.8 and the last address 14.12.72.15.
First address: 00001110.00001100.01001000.00001000
Last address: 00001110.00001100.01001000.00001111
2. Compare the binary representations bit by bit, starting from the leftmost bit.
Count the number of bits that are the same in both addresses until a bit that differs is encountered.
In this case, the first 28 bits are the same: 00001110.00001100.01001000.
3. Count the number of bits in the common prefix.
In this example, the common prefix has 28 bits.
4. The prefix length is the number of bits in the common prefix.
The prefix length for this block would be /28.
By analyzing the binary representations and identifying the common prefix, we can determine the prefix length for a given block in classless addressing.
5. List four types of delays in a packet-switched network.
In a packet-switched network, there are several types of delays that can occur during the transmission of packets. Four common types of delays are:
1. Transmission Delay: This delay occurs when a packet is being transmitted over a link. It is the time taken to push the entire packet onto the link and is influenced by factors such as the packet size and the link's data rate.
2. Propagation Delay: This delay is the time taken for a packet to travel from the source to the destination. It depends on the physical distance between the sender and receiver and the propagation speed of the medium through which the packet is traveling.
3. Processing Delay: This delay occurs when a router or network device processes a packet. It includes the time required for tasks such as examining the packet headers, making forwarding decisions, and performing any necessary packet modifications.
4. Queuing Delay: In a packet-switched network, packets may need to wait in queues at routers before they can be transmitted. Queuing delay is the time spent by a packet in a queue, waiting for its turn to be transmitted. It is influenced by factors such as the traffic load, the buffer size at the router, and the scheduling algorithm used.
These four types of delays collectively contribute to the overall end-to-end delay experienced by packets in a packet-switched network.
6. If a label in a connection-oriented service is 8 bits, how many virtual circuits can be established at the same time?
In a connection-oriented service, the label is used to identify and differentiate between different virtual circuits. If the label size is 8 bits, it means that there are 2^8 (256) possible unique label values.
Therefore, if the label size is 8 bits, it would be possible to establish a maximum of 256 virtual circuits at the same time.
7. List the three phases in the virtual-circuit approach to switching.
The virtual-circuit approach to switching, commonly used in connection-oriented networks, involves three phases:
1. Connection Establishment: In this phase, a path or route is established between the source and destination nodes before data transmission can occur. This involves setting up a virtual circuit, which includes reserving network resources and negotiating parameters between the nodes involved in the communication. This phase ensures that a logical connection is established along the desired path before data transfer can begin.
2. Data Transfer: Once the virtual circuit is established, the data transfer phase begins. Data packets are transmitted along the established virtual circuit from the source to the destination. The packets are forwarded through intermediate network nodes based on the information stored in the forwarding tables or routing tables.
3. Connection Termination: After the data transfer is complete, the connection termination phase takes place. This phase involves releasing the network resources allocated for the virtual circuit and freeing up any temporary state information associated with the connection. It ensures the graceful termination of the virtual circuit and allows the network resources to be utilized for other connections.
These three phases—connection establishment, data transfer, and connection termination—are integral to the virtual-circuit approach to switching, providing reliable and ordered delivery of data in connection-oriented networks.
8. In classless addressing, we know the first address and the number of addresses in the block. Can we find the prefix length? If the answer is yes, show the process.
Yes, we can find the prefix length in classless addressing when we know the first address and the number of addresses in the block. The process involves determining the number of host bits required to accommodate the given number of addresses.
Here's the process to find the prefix length:
1. Subtract 2 from the number of addresses in the block to account for the network address and the broadcast address. The result will give the number of usable addresses or host addresses in the block.
2. Take the logarithm base 2 of the number of usable addresses to find the number of host bits required. Round up the result to the next integer to ensure that the block can accommodate the given number of addresses.
3. Subtract the number of host bits from the total length of the IP address to obtain the prefix length. The prefix length represents the number of network bits or the number of bits used to identify the network in the block.
By applying this process, we can determine the prefix length for a given block in classless addressing when we know the first address and the number of addresses in the block.
9. If a label in a connection-oriented service is 8 bits, how many virtual circuits can be established at the same time?
If a label in a connection-oriented service is 8 bits, the number of virtual circuits that can be established at the same time depends on the specific implementation and protocol. In general, with an 8-bit label, there can be a maximum of 2^8 (256) unique label values.
However, it's important to note that not all 256 label values may be available for establishing virtual circuits simultaneously. Some labels may be reserved for special purposes or used for control and management functions within the connection-oriented service. The actual number of virtual circuits that can be established at the same time may be lower than the total number of possible label values.
The specific protocol or technology implementing the connection-oriented service will define how these label values are allocated, managed, and used to establish virtual circuits.
10. Distinguish between the process of Packet Switching & Circuit Switching Network.
Packet Switching and Circuit Switching are two different approaches to network communication:
Packet Switching:
- Packet switching breaks data into small units called packets and sends them individually over the network.
- Each packet is treated as an independent unit and can take different paths to reach the destination.
- Packets may arrive out of order at the destination and need to be reordered before reconstructing the original message.
- Packet switching networks dynamically allocate network resources only when packets are being transmitted.
- Examples of packet-switched networks include the Internet (based on TCP/IP) and X.25 networks.
Circuit Switching:
- Circuit switching establishes a dedicated communication path, known as a circuit, between the source and destination before data transmission.
- The circuit remains active throughout the communication, providing a continuous, fixed bandwidth connection.
- Data is transmitted in a sequential and ordered manner along the established circuit.
- Circuit switching guarantees a constant delay and bandwidth for the duration of the connection.
- Examples of circuit-switched networks include traditional telephone networks (PSTN) and Integrated Services Digital Network (ISDN).
In summary, packet switching breaks data into packets and sends them independently over the network, allowing for efficient use of network resources and better handling of varying traffic conditions. On the other hand, circuit switching establishes a dedicated path for communication, ensuring a constant bandwidth but requiring dedicated resources even when no data is being transmitted.
11. Draw & Explain DHCP Message Format.
The DHCP (Dynamic Host Configuration Protocol) is used to automatically assign IP addresses and other network configuration parameters to devices on a network. The DHCP message format consists of four types of messages: Discover, Offer, Request, and Acknowledge. Here is an explanation of the DHCP message format:
1. DHCP Discover Message:
- Sent by a client to discover DHCP servers available on the network.
- Broadcast message (destination IP address: 255.255.255.255).
- Contains the client's MAC address (hardware address) and other optional parameters.
Format:
2. DHCP Offer Message:
- Sent by a DHCP server in response to a Discover message from a client.
- Unicast message sent to the client's IP address (if known) or broadcast if the client's IP address is not yet assigned.
- Contains the IP address offered to the client, lease duration, subnet mask, DHCP server IP address, and other configuration parameters.
Format:
3. DHCP Request Message:
- Sent by the client to formally request the offered IP address from a specific DHCP server.
- Unicast message sent to the DHCP server's IP address.
- Contains the client's selected IP address, lease duration, and other configuration parameters.
Format:
4. DHCP Acknowledge Message:
- Sent by the DHCP server to confirm the assignment of the requested IP address to the client.
- Unicast message sent to the client's IP address.
- Contains the client's assigned IP address, lease duration, subnet mask, default gateway, DNS server addresses, and other configuration parameters.
Format:
These four DHCP message types facilitate the automatic configuration of network parameters for devices, making it easier to manage IP addresses and ensure efficient network communication.
12. Explain in brief FSM for DHCP Client.
FSM stands for Finite State Machine, and it is a model used to describe the behavior of a system with a finite number of states and transitions between those states. In the context of a DHCP client, the FSM represents the different states and transitions that occur during the DHCP process. Here is a brief explanation of the FSM for a DHCP client:
1. Initial State:
- The client starts in the initial state, where it has no IP address and configuration parameters.
2. DHCP Discover State:
- The client broadcasts a DHCP Discover message to discover available DHCP servers on the network.
- Transition: Upon sending the Discover message, the client moves to the DHCP Offer state.
3. DHCP Offer State:
- The client receives DHCP Offer messages from one or more DHCP servers.
- Transition: The client selects an offer and moves to the DHCP Request state.
4. DHCP Request State:
- The client sends a DHCP Request message to the chosen DHCP server, formally requesting the offered IP address and configuration parameters.
- Transition: The client moves to the DHCP Acknowledge state upon receiving a positive response from the server.
5. DHCP Acknowledge State:
- The client receives a DHCP Acknowledge message from the DHCP server, confirming the assignment of the requested IP address and providing additional configuration parameters.
- Transition: The client moves to the Bound state and configures its network settings with the received parameters.
6. Bound State:
- The client is now assigned an IP address and other network configuration parameters obtained from the DHCP server.
- The client can now communicate on the network using the assigned IP address.
- Transition: If the lease duration expires or the client releases the IP address, it moves back to the Initial state and restarts the DHCP process.
The FSM for a DHCP client represents the different states and transitions involved in obtaining an IP address and network configuration parameters from a DHCP server. By following this FSM, the DHCP client can successfully negotiate with the server and configure its network settings dynamically.
13. Define IPv4 occupation of the address space in classful addressing.
In IPv4, classful addressing is a method used to allocate IP addresses into different classes based on the network size. The address space in classful addressing is divided into five main classes: A, B, C, D, and E. Here is a definition of each class and their occupation of the address space:
1. Class A:
- Class A addresses have the first bit set to 0.
- The network portion is the first octet, while the host portion occupies the remaining three octets.
- The range of Class A addresses is from 0.0.0.0 to 127.255.255.255.
- The total number of Class A addresses is 2^7, which is approximately 128 million addresses.
- Class A addresses are primarily used for large networks.
2. Class B:
- Class B addresses have the first two bits set to 10.
- The network portion is the first two octets, while the host portion occupies the remaining two octets.
- The range of Class B addresses is from 128.0.0.0 to 191.255.255.255.
- The total number of Class B addresses is 2^14, which is approximately 16,384 addresses.
- Class B addresses are commonly used for medium-sized networks.
3. Class C:
- Class C addresses have the first three bits set to 110.
- The network portion is the first three octets, while the host portion is in the last octet.
- The range of Class C addresses is from 192.0.0.0 to 223.255.255.255.
- The total number of Class C addresses is 2^21, which is approximately 2 million addresses.
- Class C addresses are typically assigned to small networks.
4. Class D:
- Class D addresses have the first four bits set to 1110.
- They are used for multicast addresses, which are used for one-to-many or many-to-many communication.
- The range of Class D addresses is from 224.0.0.0 to 239.255.255.255.
- Class D addresses are not used for regular unicast communication.
5. Class E:
- Class E addresses have the first four bits set to 1111.
- They are reserved for experimental purposes and are not used for general addressing.
In classful addressing, the address space is primarily occupied by Class A, Class B, and Class C addresses, which cater to networks of different sizes. However, classful addressing has become less commonly used, and subnetting and classless addressing (CIDR) have replaced it to provide more efficient address allocation and flexibility.
14. Elaborate on the terms Routing, Forwarding, and Packetizing.
Routing:
Routing is the process of selecting the optimal path for data packets to travel from the source to the destination in a network. It involves determining the most efficient route based on various factors such as network topology, congestion, link quality, and routing protocols. The router, which operates at the network layer (Layer 3) of the OSI model, plays a key role in routing by examining the destination IP address in the packet header and making forwarding decisions to direct the packet towards its intended destination. Routing ensures that packets are delivered accurately and efficiently across interconnected networks.
Forwarding:
Forwarding is the process of transferring data packets from an incoming interface to the appropriate outgoing interface on a network device, such as a router or switch. It occurs at the data link layer (Layer 2) or network layer (Layer 3) of the OSI model. When a packet arrives at a network device, it examines the packet header to determine the destination address and uses the forwarding table or routing table to make the decision on where to send the packet next. Forwarding involves the actual transmission of the packet from one interface to another based on the forwarding decision made by the network device. It is a crucial operation in ensuring that packets reach their intended destinations efficiently.
Packetizing:
Packetizing refers to the process of breaking data into smaller units called packets for transmission over a network. In packet-switched networks, such as the Internet, data is divided into packets before transmission to facilitate efficient and reliable delivery. Each packet consists of a header, which contains control information like source and destination addresses, and a payload, which contains a portion of the original data. Packetizing allows for better utilization of network resources as packets can be transmitted independently and take different paths through the network. At the receiving end, the packets are reassembled in the correct order to reconstruct the original data. Packetizing is an essential aspect of packet-switched networks, enabling reliable and efficient data transmission.
15. List and explain other services expected from the Network layer.
In addition to routing, forwarding, and packetizing, the Network layer provides various other services that contribute to efficient and reliable network communication. Here are some of the key services expected from the Network layer:
1. Addressing: The Network layer assigns unique addresses (such as IP addresses in the case of IPv4 or IPv6) to each device on the network. These addresses enable identification and communication between devices.
2. Fragmentation and Reassembly: The Network layer handles fragmentation and reassembly of data packets when the maximum transmission unit (MTU) size of a network link is smaller than the packet size. It breaks larger packets into smaller fragments for transmission and reassembles them at the destination.
3. Logical Network Design: The Network layer allows for the creation of logical network designs that abstract the physical network infrastructure. This enables efficient routing and scalability by organizing devices into logical networks or subnets.
4. Quality of Service (QoS): The Network layer may implement QoS mechanisms to prioritize specific types of traffic, such as voice or video, over others. QoS ensures that critical or time-sensitive data receives appropriate bandwidth, latency, and reliability guarantees.
5. Network Address Translation (NAT): NAT is a Network layer service that translates private IP addresses used within a local network to a single public IP address when communicating with external networks. NAT helps conserve public IP addresses and provides a form of security by hiding internal network structure.
6. Network Layer Security: The Network layer can provide security mechanisms such as IPsec (IP security) to encrypt and authenticate network traffic, ensuring confidentiality, integrity, and authenticity of data transmitted over the network.
7. Congestion Control: The Network layer implements congestion control mechanisms to prevent network congestion and ensure fair allocation of network resources. This involves monitoring network conditions, detecting congestion, and adjusting transmission rates or routing paths accordingly.
8. Error Handling and Packet Loss Recovery: The Network layer may include error detection and error recovery mechanisms to detect and handle errors or lost packets during transmission. This helps maintain data integrity and reliability.
These additional services provided by the Network layer contribute to efficient, secure, and reliable network communication, supporting various applications and ensuring effective utilization of network resources.
16. Define the term Network Address Translation (NAT).
Network Address Translation (NAT) is a technique used in computer networking to translate IP addresses between different network domains. It is primarily used to conserve public IP addresses and enable communication between private IP addresses within a local network and the public Internet.
NAT operates at the Network layer (Layer 3) of the OSI model and works by modifying the IP addresses and port numbers in the packet headers. Here's a brief explanation of how NAT works:
1. Private IP Addresses: In a local network, devices are typically assigned private IP addresses that are not routable on the public Internet. Private IP address ranges include:
- Class A: 10.0.0.0 to 10.255.255.255
- Class B: 172.16.0.0 to 172.31.255.255
- Class C: 192.168.0.0 to 192.168.255.255
2. NAT Translation Table: A NAT-enabled device, such as a router or firewall, maintains a translation table that maps private IP addresses to public IP addresses. The translation table keeps track of the source and destination IP addresses and port numbers.
3. Outgoing Traffic: When a device with a private IP address sends a packet to the Internet, NAT modifies the packet's source IP address and port number with a public IP address and a unique port number from the available pool. This process is called "source NAT" or "SNAT."
4. Incoming Traffic: When a response packet arrives from the Internet, NAT examines the destination IP address and port number in the packet header. It then refers to the translation table to determine the private IP address and port number to which the packet should be forwarded. NAT modifies the packet accordingly and delivers it to the appropriate device in the local network. This process is known as "destination NAT" or "DNAT."
By translating IP addresses between private and public domains, NAT allows multiple devices in a local network to share a single public IP address. This helps conserve public IP address space and provides a basic level of security by hiding the internal network structure. NAT has become a standard feature in many home and small office networks, enabling them to connect to the Internet using a single public IP address.
17. Each of the following addresses belongs to a block. Find the first and last address in each block:
a. 14.12.72.8/24
- Block: Class C
- First Address: 14.12.72.0
- Last Address: 14.12.72.255
b. 200.107.16.17/18
- Block: Class C
- First Address: 200.107.16.0
- Last Address: 200.107.31.255
In both cases, the prefix length (/24 for a and /18 for b) indicates the number of bits in the network portion of the IP address. The remaining bits in the host portion can vary, resulting in a range of possible addresses within the block.
