Computer Networking Cheatsheet (Last Minute Notes)

Prasun Das| July 6, 2022 at 8:41 PM | 9 minutes Read

 Computer Networks is one of the most important computer fundamental subject when it come to placement below is a brief last minutes notes on Computer Network and Interview Question with them

Networking: Importance in real life!

Using a computer for work, as well as for personal use, has become a necessity in today's environment. Networking entered the scene as technologies advanced, and we gradually progressed from the original wired network technology to this wireless network technology. We can clearly see that networking affects everything if we think about it.

What is a network actually?

According to Merriam Webster, a network is a loosely knit group or association of various entities such as people, computers, radio stations, and so on. But that's the definition for the macroscopic world isn’t it? We want specifications in the field of software development. Let’s delve deep into it.

Computer Networks: What is it?

Computer networks connect computers together, or we may say that a computer network is a collection of connected computers that allow one computer to communicate with another computer. It serves as the foundation for communication in the field of information technology (IT). It is a network of interconnected computing devices that exchanges data and resources. The network's connected devices use wired and wireless communication links to exchange data through a data communication system.

Types of Computer Networks we use!

Computers have the ability to connect to the Network and communicate with one another through any medium. The three main types of networks for operating over the area they cover are LAN, MAN, and WAN. There are various similarities as well as differences between them. One of the biggest differences between them is the geographic region that each covers, with LAN covering the smallest, MAN covering an area greater than LAN, and WAN making up the largest of all.

Okay I know computer networks, now what?

Computer networks have become an integral element of our lives and technical interviews because of the Internet, which connects all various network-enabled devices and allows for data and information transfer between them. And that’s why companies nowadays are asking more of these networking questions in their interviews. 

Topics to study while appearing for interviews!

  1. OSI Model (Open System InterConnection)
  2. TCP/IP models
  3. ARQ (Automatic Repeat Request technique
  4. Most Asked protocols
  5. Hubs, Switches, Routers
  6. Routing protocols

Particulars on the aforementioned subjects!

                              Fig: 1.1 - Seven Layers of OSI Architecture.

OSI Model:

  1. Details to be studied about all the 7 layers in this model.
  2. Application Layer
  3. Presentation Layer
  4. Session Layer
  5. Transport Layer
  6. Network Layer
  7. DataLink Layer
  8. Physical Layer

Questions regarding to this segment: 

        i. What are the functions of transport, network and data link layer?

        ii. What are the various protocols used at each layer?

       iii. What is a port number and give us some examples?

TCP/IP model: TCP/IP model consists of 4 layers. It was developed before the OSI model and is more reliable than the OSI model.

Questions regarding to this segment:

     i. Explain the range of TCP/IP classes?

     ii. How is dependability provided by TCP protocol?

      . ARQ (Automatic Repeat Request Technique) - It is an error control method in which, when an error is detected in a signal, a request for information transfer of that signal is made.

Topics regarding to this segment:

i. STOP and WAIT ARQ: The sender receives a single packet and then waits for an affirmation (acknowledgment). If the sender receives an acknowledgement, the next packet is sent; otherwise, the previous packet is resent.

ii. GO Back-N ARQ:Before receiving any Acknowledgement, the sender sends N packets (N=window size). All subsequent packets will be retransmitted if an acknowledgment for any one packet is not received.

iii. Selective Repeat ARQ: Before any ACK, the sender sends N packets (N=window size). If no Ack is received for any packet, only those packets will be retransmitted for which no ACK is received (A buffer is created at the receiver side for this purpose).

Most Asked Protocols (in interviews): 

i. Point to Point Protocol(PPP) 

ii. High-Level Data Link Control(HDLC):

iii. Hypertext Transfer Protocol(HTTP): It is a request-response application-layer protocol used for communication between web browsers and web servers.

iv. Network Time Protocol(NTP): It is used to synchronise the clock of the computer system to one standard time source. It is useful for bank transactions.

v. Address Resolution Protocol(ARP): It is used for discovering the link-layer address, such as a MAC address with the help of the IP address of the device in a network.

vi. Reverse Address Resolution Protocol(RARP): It is used by the client computer to request its IP address in a network with the help of the MAC address of the device.

vii. Internet Control Message Protocol(ICMP): It is a network layer protocol used by devices in a network to diagnose network communication issues. It sends several control messages such as source route failed, destination network unreachable and source quench.

viii. Domain Name System(DNS): It is a directory service that provides a mapping between the name of a host on the network and its numerical address i.e. IP address.

ix. File Transfer Protocol(FTP): It is a standard network protocol used for the transfer of computer files between a client and a server on a computer network.

Simple Mail Transfer Protocol(SMTP): It is a push protocol and used to send the mail whereas Internet Message Access Protocol(IMAP) is used to retrieve those messages at the receiver side.

x. Dynamic Host Configuration Protocol(DHCP): It is a network management protocol whereby a DHCP server dynamically assigns an IP address and other network configuration parameters to each device on the network.


     Fig 1.2: A visual representation of Switches, Routers and Hubs.

HUB: It is a central device that has the power to split the network connection into multiple devices. Whenever a request is made, the hub is responsible for distributing this request to all the connected devices.


SWITCHES: It is similar to a hub that connects all the devices with the exception that it only sends the request to the device for which it belongs to.

ROUTER: A router is a networking device that forwards data packets between computer networks. The router inspects a given data packet’s destination IP address, then calculates the best way for it to reach its destination after which it forwards it accordingly.

           6. ROUTING PROTOCOLS: Routing techniques are classified into two types:

i. Intradomain Routing (Within Autonomous System): Distance Vector Routing: In this type of routing, a router sends its distance vector to each of its neighbours in a routing packet, and each router recalculates its distance vector table. In distance vector routing, the Routing Information Protocol (RIP) is used, and the Bellman-Ford algorithm is used to calculate the shortest path.

ii. Link State Routing: In this protocol, each network node maintains the network's entire topology. For finding the shortest path through a network, Dijkstra Algorithm is employed. Open Shortest Path First (OSPF) is a Link State Routing Protocol implementation.

Bonus Section - For those who have read this far!

All readers of this blog may have left reading at some point or another, but those who are really watching this, should know what they are getting here at this point. You guys deserve something special. 

Here are some questions which have come from different Product Based Companies time and time again. Let’s have a look at some of these questions and become pro at cracking Networking Interviews!

1. What is a Link in Network?


A network can be as simple as two or more computers connected by a physical medium such as optical fibre or a coaxial cable. Such a physical medium is known as a Link.

2. What is Multiple Access?


When the physical links are shared by more than two nodes, it is known as Multiple Access.

3. What is a node?


A network can be as simple as two or more computers connected by a physical medium such as optical fibre or a coaxial cable. The physical medium is known as a Link, whereas the connected computers are known as the Nodes.

4. What is Routing?


The process of determining systematically how to forward messages toward the destination nodes based on their address is called routing.

5. What is a gateway or a Router?


A node that is connected to two or more networks is simply referred to as a Gateway or Router. Its purpose is to forward messages from one network to another network.

6. What are the advantages of Distributed Processing?



Distributed database

Faster Problem solving

Security through redundancy

Collaborative Processing

7. Define Bandwidth and Latency?


Network performance is measured in bandwidth (also known as throughput) and latency (also called delay).

  1. → A network's bandwidth is defined as the number of bits that may be transferred through the network in a specified amount of time.|
  2. → Latency is the amount of time the network takes for a message to move from one end of a network to the other end. It is measured exclusively in terms of time.

8. What is a peer-peer process?


The processes on each computer that communicate at a given layer are known as peer-peer process. In (P2P) peer-to-peer networking, a group of computers are linked with equal permissions and responsibilities for the purpose of processing data. Unlike traditional client-server networking, no devices in a peer-to-peer network are designated solely to serve or to receive data. 

9. What is HSRP (Hot Standby router Protocol)?


HSRP is a redundant protocol developed by Cisco to provide gateway level redundancy without performing any additional configuration on end devices in the network. HSRP Active and Standby routers send hello packets for communication over the UDP protocol. These hello messages are forwarded to multicast address to communicate between routers in HSRP, HSRP provides backup to a router in the event of failure.

10. What is Data Encapsulation & De-Encapsulation?


As the data is passed from the user application down the virtual layers of the OSI model, each layer adds a header containing the protocol information specific to that particular layer. These headers are called PDUs (Protocol Data Units), and the process of adding these headers is called encapsulation. 

 For example Transport layer protocol (TCP) will add a header containing flow control, port numbers & sequencing. 

The Network layer header contains logical addressing information. 

- On the receiving device, that Data-link header is processed and stripped away (De-encapsulation) before being sent up to Network and other upper layers. 

The process by which a receiving device removes one or more protocol headers is called de-encapsulation. As the data goes up the stack toward the end-user application, it gets de-encapsulated.

11. What exactly is Ethernet? Explain the various Cabling Types


Ethernet is a technology suite that includes data-link and physical specifications for controlling access to a shared network medium.

Ethernet can be installed using one of three types of cabling:

Fig 1.3: Types of cables.

Coaxial cabling is almost completely obsolete in Ethernet networking.

ThickNet ThinNet

Twisted-pair wiring

Three twists per inch for Cat3.

Cat5 is defined as five twists per inch.

5 twists per inch; pairs are twisted around each other.

Six twists per inch, Cat6

Fibre optic cable

SMF (single-mode fibre)

Fibre with multiple modes

12. Why is it vital for the network administrator to understand the OSI model's layers?

Ans - The layers of the OSI Model are crucial for the network administrator since they enable them to diagnose network issues by confirming each layer's operation.

ii. In many instances, the network administrator must determine at which layer the network issue manifests itself.

13. What are the different protocols which work at each of the layers of the OSI model?


  1. Physical Layer
  2. ISDN (Integrated Services Digital Network), ADSL (Asymmetric Digital       Subscriber Line), Universal Serial Bus, Bluetooth, Controller Area Network, Ethernet.

2. Data Link layer

  1. Spanning Tree Protocol, VLan Trunking Protocol, Dynamic Trunking Protocol, HDLC, PPP, Frame Relay, Token Ring.

3. Network Layer

                -  ICMP, IGMP, IPV4, IPV6, IPSEC, OSPF, EIGRP, RIP, BGP.

4. Transport Layer

                - TCP, UDP, GRE.

5. Session Layer

                 - NFS (Network File System).

6. Presentation Layer

                    - Data encryption/decryption, Data compression.

7. Application Layer

                   - DNS, DHCP, FTP, HTTP, NTP, SNMP, SMP, TELNET, TFTP, SSH.

16. What is the Range Of Port Numbers?


Well Known Ports  - 0 to 1023

Registered Ports - 1024 to 49151

Open Ports - 49152 to 65535

Coming Up Next: More Osi model Questions! 

That’s it? Will I be able to crack interviews?

To be honest, with these questions, you will get a decent knowledge about how things pan out in networking interviews.

But if you want more in depth insights about how interviewing questions pan out, then make sure to follow our blogs in future. We will be uploading more of these blogs once you guys show us love!

Till then, adios!

After this you should have a clear understanding on some important concepts on Computer Networks from interview perspective. Last not the least thanking Shambashib Majumdar for contributing to this blog.

#computer networks#cheatsheet#last minute notes#fundamentals to learn
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