Computer Networking Interview questions and answers

In this lecture, we are going to learn the Computer Networking Interview questions and answers which can be very beneficial for your exam preparation.

Computer Networking Interview questions and answers

Que.1 What is a Network?

Answer: Network is a set of devices interconnected by a communication system. Each device is referred as an entity, an entity can be a computer, mobile or any other device.

Que.2 How the networks are classified on the basis of Topology?

Answer: On the basis of Topology there are 6 types of networks:

• Mesh topology
• Star topology
• Bus topology
• Ring topology
• Point to point 
• Tree topology

Que.3 How will you define network topology?

Answer: Network topology defines the physical interconnection of its constituent element. The topology of a network refers to the way nodes are interconnected in a network, the interconnection may be either real or logical.

Que.4 Which network topology is the most widely used topology?

Answer: Start topology is the most widely used topology. In a star topology, all computers are connected to a central location where they are all connected by a device called a hub. Each node on a star network Communicates with a central hub that resends the message to all the computers in a broadcast star network or only to the destination computer in a switched star network.

Que.5 How the networks are classified on the basis of network extent?

Answer: On the basis of network extent, networks are classified as:

1.  Local area network(LAN):  A local area network is restricted to a small region. these are widely used in business enterprises to connect personal computers, network servers, printers, and other network entities. They are in the diameter of the order of a few kilometers.
2.  Wide area network (WAN):  A WAN covers a large geographical area as compared to land it is extended to multiple states and countries. Internet is an example of a wide area network. WAN works on store and forward subnet that is a packet from the transmitter is routed to the intermediate node which is stored and out it to the next node until it reaches the receiver.
3.  Metropolitan area network(MAN):  This network is limited to the city.

Que.6 What is Switching?  what are the different types of switching in communication?

Answer:

• Switching is a process to forward packets coming in from one port to a port leading towards the destination.

• Different switching methods that are used in communication are:

1. Packet switching:  It is used in computer networks where individual users have need of channel intermittently.  In packet switching, messages are broken into short blocks and interleaved with other messages. data is sent in individual packets and each packet is forwarded from switch to switch eventually reaching its destination.
2. Circuit switching: In circuit switching, a dedicated path is provided for the transfer of data. Before transmission of data, a path is established. Telephone networks are examples of circuit switching.

Que.7 What is Routing?

Answer: Routing is the act of moving information across an Internet work from a source to a destination.

Que.8 What is a routing table?

Answer: Routing table is used to store all the information about the routers and their respective distances or paths which the router follows. Routers communicate with one another and maintain their routing table through the transmission of variety of messages. Every router may or may not have the exact path to other routers in the network but at least they know the interface through which they have to be forwarded. Different types of routing algorithms are used to determine all the routers connected on a network.

Que.9 What is the OSI model? Application of each layer of the OSI model.

Answer:

• International organizations for standardization develop the open system interconnection OSI as a reference model to perform networking tasks and understand and design a network architecture.

• It has 7 layers for transmission and reception of data on a network.

1. Physical layer: The lowest layer that coordinate the functions required to transmit about a bit stream over a communication channel.
2. Data-link layer:  Responsible for transmitting frames from one node to the next.
3. Network layer: The network layer is responsible for the delivery of packets from source to destination. Routers are used in this layer.
4. Transport layer: transport layer is responsible for the delivery of segments from one process to another. This layer ensures the whole message arrives intact and in order with error control and process control.
5. Session layer:  It established and synchronizes the interaction between the communication system.  This layer decides the processes to take place either in half-duplex or full-duplex mode.
6. Presentation layer:  presentation layer deals with the syntax and semantics of the information being exchanged. This layer is responsible for the translation, encryption, and compression of data.
7. Application layer:  this layer is responsible for accessing the network by the user. It provides a user interface and other supporting services such as email remote file access file transfer etc.

Que.10 What is TCP/ IP reference model?

Answer:

• TCP/IP protocol is the name of the two most important protocols -transmission control protocol and Internet Protocol.

• The main goal of the TCP/IP model was to build an interconnection of networks that differed from the Internet.

• It has mainly 4 layers:

1. Application layer
2. Transport layer
3. Internet layer
4. Host to the network layer.

Que.11 What is Addressing?  what are the different classifications of addressing techniques?

Answer: 

• Addressing refers to the process of assigning a unique identifier to entities to achieve communication between them.

• Classification of addresses:

1. Scope-wise classification:

• Local address:  private addresses used within an organization.
• Global address: these addresses are applicable throughout the globe. Example IP address

2.  Utility-wise classification: is based on the utility or the purpose that an address serves. These are

• Locator: help to locate the entity addressed by the locator. Example- URL.
• Identifier: The address does not provide any information about the location of the entity being addressed. For example Ethernet address.

3. Layer-wise classification:

• OSI model follows layer-wise classification.

4.  Functionality-wise classification:

• It is based on the number of entities being addressed and we can classify it as:
  • Unicast: it is used for point-to-point communication.
  • Multicast:  A multicast address refers to an address that identifies a group of unicast addresses. A packet sent on a multicast address is directed to all the entities part of the multicast group.
  • Broadcast:  This network is used to forward packets to all the entities residing on a network.
  • Anycast: this address is used when it is it is desired to reach any member of a group.

Que.12 What is IP version 4 of IP addressing?

Answer:

• This is the addressing technique that is uniquely used to determine or device on the Internet.

• The IP version 4 of IP addressing is a 32-bit address and it consists of 2 components:

1. Network component:  of address consisting of network bids which are in the left portion of the address.
2. The host portion of the address: consists of host bits which is the right portion of the network bits.

• The 32-bit address is divided into 4 groups of 8 bits. Each group of 8 bits is called an octet and it is written as a decimal number ranging from 0 to 255 separated by dots. The network bit remains fixed but the host bit may vary.

Que.13 What is Subnetting?

Answer: Subnet masks are used to make the classful networks more manageable and efficient by creating smaller subnets and reducing the number of host addresses per subnet.

Que.14 What is IPV 6? what features of IPV 6  are different from IPV 4?

Answer:

• IPV 6 is called Internet Protocol next generation. It is a new addressing protocol design to incorporate all the possible requirements of future Internet known to us it has ample features to address the shortcomings of IPV 4.

•  Features of IPV 6:

1. Larger address space: In contrast to IPV 4, IPV 6 uses 4 times more bits to address a device on the Internet.
2. End-to-end connectivity:  it does not require network address translation protocol or any other translating component for using the network unlike IPV 4. In IPV 6 addressing every host can directly reach other hosts on the Internet.
3. Auto-configuration:  IPV 6 supports both stateful and stateless auto-configuration mode of its host device so the absence of a DHCP server does not create any trouble.
4. Fast-forwarding:  the information contained in the first part of the header is adequate for a router to make routing decisions thus making routing decisions very fast.
5. Security: it has inbuilt security Which makes it more secure than IPV 4.
6. Mobility: IPV 6 was designed keeping mobility in mind.  this feature enables hosts to roam around in different geographical areas and remain connected with the same IP address.

Que.15 What is the Address resolution protocol? How do ARP works?

Answer:

• Address resolution protocol is a protocol for mapping an Internet Protocol address to a physical machine address that is recognized in the local network.

• When an incoming packet destined for a host machine on a particular local area network arrives at a gateway,  the gateway asks the ARP program to find the physical host or Mac address that matches the IP address. A table usually called ARP cache is used to maintain a correlation between each Mac address and its corresponding IP address. ARP provides protocol rules for making this correlation and providing address conversion in both directions. It is a protocol between the network layer and the data link layer.

Que.16 What is reverse ARP?

Answer:

• Reverse address resolution protocol (RARP):  is a protocol by which a physical machine in a local area network can request to learn its IP address from a gateway servers address resolution protocol table. Administrators create a table in the local area networks gateway router that maps the physical machine Mac address to the corresponding Internet Protocol address.

• When a new machine is set up its RARP client program request the ARP server on the router to send its IP address. RARP server will return the IP address to the machine which can store it for future use.

Que.17 What are the functions of the Application layer protocol?

Answer:

• Application layer protocols are used by both source and destination devices during a communication session. the protocol specifies how data inside the message is structured and the types of messages that are sent between source and destination. the protocols established consistent rules for exchanging data between the application and services loaded on the participating devices.

• Application and services may use multiple protocols in the course of a single conversation one protocol may specify how to establish the network connections another describes the process for data transfer when the message is passed to the next lower layer.

•  Application layer protocols define:

1. Types of messages
2. Types of messages syntax of messages.
3. Meaning of any informational fields.
4. How messages are sent and the expected response.

Que.18 What does the Port number specify?

Answer:

• The transport layer uses an addressing scheme called a port number. Port number identifies applications and application layer services that are the source and destination of data.

• For TCP/IP, Application layer protocols and services  TCP and UDP port numbers are normally used.  For Example- The domain Name System has TCP/UDP port 53.

Que.19 What is DNS? How does DNS work?

Answer: 

• DNS is a domain name service protocol used to resolve the Internet names to IP addresses.

• In data networks devices are leveled with numeric IP addresses so that they can participate in sending and receiving messages over the network., however, most people have a hard time remembering these numeric addresses hence domain names were created to convert the numeric IP address into a simple recognizable name.

• When a domain name is put in a browser, the computer searches it in its cache, if it is not available, then the request is transferred to the Internet service provider, If not available then the request is transferred to the root server check it in its cache, and if not available then at the last request is transferred to the Top-level DNS server. Once DNS gets the IP address then the same address is stored in the client PC cache.

Que.20 What is Cryptography?

Answer:

• Cryptography refers to the tools and techniques used to make messages secure for communication between participants and make messages immune to attacks by hackers.

Que.21 What are the different types of Cryptography techniques used for Network security?

Answer: 

• Types of cryptography techniques used for network security are :

1. Symmetric key cryptography: is also known as private key cryptography. In this type of same cryptography key is used for both encryption and decryption of data.
2. Public key cryptography:  Also known as symmetric cryptography. In this method, there are 2 keys- a private key and a public key.  The public key is announced to the public whereas the private keys are kept by the receiver. The sender uses the public key of the receiver for encryption and the receiver uses his private key for decryption.

Que.22 What are the types of Attacks on a communication network?

Answer: 

• The possible types of attack on a communication network are:

1. Interruption:  it is an attack on the availability of information by tapping wires, jamming wireless signals& dropping packets by the switch.
2. Interception:  as a message is communicated through a network, eavesdroppers can listen to it and use it for or their own benefit and tamper with it.
3. Modification: as a message is communicated to a network, eavesdroppers can intercept it and send a modified message in place of the original one.
4. Fabrication:  message may be sent by a stranger by posing as a friend.  This is also known as Impersonation.

Que.23 What are the services required to make Communication secure?

Answer: 

• Secured communication required the following 4 basic services:

1. Privacy:  a person should be able to send a message to another person privately. It implies that all the other messages should be unintelligible.
2. Authentication: After the message is received by the receiver he should be sure that the message has been sent by nobody else but the sender only.
3. Integrity:  receiver should be sure that message has not been tampered with in transit.
4. Non-repudiation:  receiver should be able to prove at a later stage that the message was indeed received from the sender.

Que.24 What is Firewall? what are the advantages of using a Firewall?

Answer:

• A firewall is an integrated collection of security measures designed to prevent unauthorized electronic access to a networked computer system.

•  Advantages of a Firewall are:

1. The firewall run much less code and hence has very few bugs.
2. A firewall can be professionally administered.
3. The firewall runs less software with more logging and monitoring.
4. They enforce the participation of a network into separate security domains.

Que.25 What are the different types of firewalls?

Answer:

• Stateless Firewall:   a stateless firewall does not maintain any remembered context with respect to the packets it is processing. Instead, it treats each packet attempting to travel through it in isolation without considering packets that it has processed previously.

• Stateful  Firewall:  it can tell when a packet is part of a legitimate session originating within a trusted network. Stateful firewalls maintain a table containing information on each active connection including the IP addresses, ports, and sequence number of the packets. Using these tables stateful firewalls can allow only inbound TCP packets that are in response to the connection initiated from within the internal network.

Que.26 What is Tunnelling?

Answer:

• Tunneling is used to prevent eavesdropping in network communication.

• The contents of TCP packets are not normally encrypted, so if someone is dropping on TCP connections, he can often see the complete contents of the payload in this session. the way to prevent such eavesdropping without changing the software performing the communication is to use a tunneling protocol.

• In such protocol communication between a client and server is automatically encrypted so that useful eavesdropping is infeasible.

Que.27 What is Pretty good privacy (PGP)?

Answer:

• PGP (pretty good privacy) is designed to provide all 4 aspects of security – privacy, integrity, authentication, and non-repudiation in the sending of email.

•  PGP uses a digital signature to provide integrity authentication and non-repudiation. It uses a combination of the secret key and public-key encryption to provide privacy.