Computer Networks – Most frequently asked questions

In this article we have listed questions/topics from computer networks. We have provided short answers to questions wherever possible. We suggest that you refer standard book like Computer Networks by  Tanenbaum or Data Communication and Networking by Forouzan for more detailed answers.

Questions and answers :

Q: What is the difference between the Internet, Intranet and Extranet?
A: Intranet is shared content accessed by members within a single organization.
Extranet is shared content accessed by groups through cross enterprise boundaries.
Internet is global communication accessed through the Web.
This image below may help you understand this concept more clearly.

Computer Networks
The Internet, Intranet and Extranet

Q: How many layers OSI model have? What are their names?
A: OSI model have 7 layers. Their names are listed below :-
Physical Layer
Data Link Layer
Network Layer
Transport Layer
Session Layer
Presentation Layer
Application Layer

Q: What is the difference between Hub, Switch and Router? In which layer each device operates?
A: Watch this awesome video.

Q: What is piggy backing?
A: Piggy backing is the process to improve efficiency of bidirectional communication. When data packet from point A travels to point B , it also carries with it the information of last packed (received or failed) which was sent from point B to point A.

Q: What type of mode of communications are there?
A: Simplex :- In this mode of communication between two devices, flow of data is unidirectional. One can transmit the data and other can only receive the data. For example keyboard and CPU. Keyboard sends the data and CPU receives it.
Half-Duplex :- Data can be send and received by both the devices but only one can send at a time. Example is walkie talkie.
Full-Duplex :- Data can be send and received by both the devices at the same time. Example mobile phone calls.

Q: What is hamming code?
A: Hamming code is an error correction method. How does hamming code works?

Q: What is an IP address? How many bits are the in IP address?
A: IP address is a unique string of numbers separated by full stops that identifies each computer using the Internet Protocol to communicate over a network. IP addresses are made of 32 and 64 bits.

Q: What is localhost?
A: In computer networks localhost means this computer. Localhost have IP address – . This is used to access the network services running on this system.

Q: What are repeaters and bridges?
A: Repeaters receives the signal before it becomes too weak or corrupted and regenerates the original bit patter and put it back into the link. They are operated in physical layer of OSI mode.
Bridges connects two or more LANs. They provide security by partitioning the traffic. They operates on DLL and physical layer.

Q: What is the difference between error correction and error detection?
A: Error detection is the process of knowing is there is error in data received or not. It is relatively easy process than error correction. In error correction you must know how many bits are corrupted and algorithm have to correct the bits.

Topologies in computer networks:

Different topologies are shown in the diagram below.

Image source - Wikipedia
Image source – Wikipedia

Since this is a bit lengthy topic I suggest you to follow this Wikipedia article to read about topologies in detail.

Finding IP address and MAC address of you system:

Because practical knowledge is more important than theoretical knowledge.
Follow steps given in this short video to know your IP and MAC address on Linux system.

– Open Terminal and type the command ‘ifconfig’.


I have list some commonly used abbreviations in computer networks. In addition to knowing the full form of the abbreviations, you should also know what they are. Refer any book listed above or leave a comment.

URL – Uniform resource locator
DHCP – Dynamic host configuration protocol
TCP – Transmission control protocol
LAN – Local area network
MAC – Media access control
RTT – Round trip time
OSI – Open system interconnection
ICMP – Internet control message protocol
WWW – World wide web
ARP – Address resolution protocol
RARP – Reverse address resolution protocol

Protocol and port they run on:

FTP – File Transfer Protocol – 21
SSH – Secure Shell – 22
Telnet – Terminal Network – 23
SMTP – Simple Mail Transfer Protocol – 25
DNS – Domain Naming System – 53
HTTP – Hyper Text Transfer Protocol – 80
POP3 – Post Office Protocol  – 110
IMAP – Internet Message Access Protocol – 143
HTTPS – HTTP Secure – 443
RDP – Remote Desktop Protocol – 3389

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