Networking interview questions and answers – 2019

1. What is POP3 – “Post Office Protocol”?

the Post Office Protocol is an application-layer Internet standard protocol used by e-mail clients (mobile apps, gmail client, hotmail client) to retrieve e-mail from a mail server. POP version 3 is the version in common use.

POP is a very simple protocol that allows only few functionalities like downloading mails from mail server to mail client.

2. What do you mean by Bandwidth?

In computing, bandwidth is the maximum rate of data transfer across a given path. For digital devices, the bandwidth is usually expressed in bits per second(bps) or bytes per second.

3. What do you mean by MAC address?

A “Media Access Control address” is a unique identifier assigned to a network interface controller. For communications within a network segment, it is used as a network address for most IEEE 802 network technologies

Enter ipconfig command in windows command prompt to see MAC address as shown below.

4. What is LAN – “Local Area Network”?

A “local area network” is a computer network that interconnects computers within a limited area like home, school, University etc.

To give a simple example, If you have a home router and your electronic devices like mobile, TV, and PC are connected to your home router then you can say all those devices are connected in LAN.

5. What is WAN – “Wide Area Network”?

A wide area network is a telecommunications network that extends over a large geographical area for the primary purpose of computer networking. 

A WAN connects different smaller networks, including local area networks (LANs) and metro area networks (MANs). This ensures that computers and users in one location can communicate with computers and users in other locations.

6. What are IPv4 and IPv6? Who manages these?

IP stands for “Internet Protocol”, and the numbers 4 & 6 indicates different versions of the protocol.

When an electronic device connected to the internet, it is assigned with a unique address. which makes the communication between two remote computers/devices possible. Otherwise communication between two devices across the network is not possible since there are billions of devices connected to internet today and they can’t figure out which remote computer you are sending the information.

Due to huge growth in the internet connected devices in recent years the number of addresses IPv4 (32 bit address) has to offer going to be exhausted in near future, So the IETF started developing IPv6 which is 128 bit address and it can accommodate more and more new devices in the upcoming future.

IPv4 address is 32 bit number represented in 4 groups. for example76.45.234.12

IPv6 addresses are represented as eight groups, separated by colons, of four hexadecimal digits. The full representation may be simplified by several methods of notation; for example, 2001:0db8:0000:0000:0000:8a2e:0370:7334 becomes 2001:db8::8a2e:370:7334.

7. What is DNS – Domain Name System?

DNS is like a telephone registry for websites. A typical telephone registry will have users and their phone numbers, whereas a “Domain Name System/Service” will store domain name of a website and it’s IP address.

When a person wants to visit a website then the browser will do this DNS lookup internally on behalf of the user. It’ll contact Domain Name Servers to get the IP address of the website. Once it gets hold of the actual IP address then it’ll try to establish a TCP connection to the remote computer which assigned with the above IP address.

8. What is Internet Protocol or IP?

“Internet Protocol” – is a lower level protocol in network interface. It is one of the very important protocols to make the internet work. IP helps routing and navigation of the data packets across the network.

The routers in the internet decode the IP protocol header part and finds the source and destination IP addresses. Usually an IP packet will have source and destination IP addresses. The destination address will tell the router where the data packet is destined. The source address becomes destination address when the remote system sends response back to the source system.

9. What is IP address?

An Internet Protocol address is a 32 bit unique address assigned to each device connected to a computer network that uses the Internet Protocol for communication.

Routers use this address to relay the packets to the destination address. Without IP address computers cannot communicate with each other effectively.

Now a days an IP address is being used for tracking user location to target geographic specific content and locating cyber criminals etc.

10. Classification of IP addresses?

IPv4 addresses are classified into 5 categories, i.e Class A – Class E

ClassStart AddressEnd AddressSubnet MaskNumber of
per network
Class A1.0.0.0126.255.255.255255.0.0.012716Mil
Class B128.0.0.0191.255.255.255255.255.0.01600065000
Class C192.0.0.0223.255.255.255255.255.255.02Mil254
Class D224.0.0.0239.255.255.255*RM*RM*RM
Class E240.0.0.0254.255.255.255*R-R&D*R-R&D*R-R&D

*RM – Reserved for multi-casting
*R-R&D – Reserved for Research & Development

11. What is a Load balancer?

In Computer networking a “Load Balancer” is a load distributor. There are two types of Load Balancers exist, hardware load balancer and software load balancer.

Both does same job – i.e Both acts as a reverse proxy and distributes network or application traffic across a number of servers. Load balancers are used to increase server capacity thus the ability to handle more traffic without compromising application performance.

A hardware loadbalancer is a device that can be plugged into the network, whereas software loadbalancer is a software that runs on a computer and distributes the application layer protocols. For ex. apache reverse proxy, haproxy etc

12. What is backbone network?

A backbone is a part of computer network that interconnects various pieces of network, providing a path for the exchange of information between different LANs or subnetworks. A backbone can tie together diverse networks in the same building, in different buildings in a campus environment, or over wide areas. Normally, the backbone’s capacity is greater than the networks connected to it.

Below is the Internet connectivity across the world. It consists of several backbone networks, WANs, private networks etc.

For an interactive map click here:

13. What is a Router?

As the name suggests a router generally routes data packets between networks based on the IP address in the incoming data packet. When a router is connected to network it’ll obtain necessary information on various routes dynamically so that when it receives data packet it’ll know which direction to forward them.

It may also be used to convert the packets to another network interface, drop them, and perform other actions relating to a network.

Routers are categorized based on the network location it is placed in. For ex. a home router (WI-FI) router just forwards data from your PC to Internet Service Provider and back to your PC.

A Brouter is used to connect networks as it is used as Router and Bridge.

An Edge Router usually located at the end of a private/public network.

A Core Router routes traffic within the network – ex a company network

14. What is an “edge router”?

An edge router is a specialized router residing at the edge or boundary of a network. This router ensures the connectivity of its network with external networks. Instead of providing communication with an internal network, which the core router already does, an edge router may provide communication with different networks and autonomous systems.

Edge router uses an External Border Gateway Protocol, which is used extensively over the Internet to provide connectivity with remote networks.

15. What is “subnet mask”?

A subnetwork or subnet is a logical subdivision of an IP network into multiple, smaller network segments. It is typically used to subdivide large networks into smaller, more efficient subnetworks.

Image Source : wikipedia

16. What is UDP – “User Datagram Protocol”?

UDP – User Datagram Protocol is a another important protocol in IP protocol suite and is stateless protocol used in less critical applications. The primary uses for UDP include service advertisements, such as routing protocol updates and server availability, one-to-many multicast applications, and streaming applications, such as voice and video, where a lost datagram is far less important than an out-of-order datagram.

17. What is TCP – “Transmission Control Protocol”?

Transmission control protocol is one of the very important protocols in IP protocol suite. Most of the internet runs on TCP protocol due to its reliability. This means that TCP tracks all data sent, requiring an acknowledgment for each octet (generally).

If acknowledgment is not received for the packets being sent, the source will try to send those packets again until it gets the acknowledgment that the destination received the data packets..

18. What is the number of network IDs in a Class C network?

Class C gives 2 million network addresses, but each can have only 254 nodes. So class C is better suited for LANs.

19. What is ICMP?

ICMP – Internet Control Message Protocol is used to check whether the remote computer is up or shutdown.

20. What is Ping? and is it protocol or command?

Ping is a command, which uses ICMP protocol to check whether a remote computer is responding or not.

21. What is peer to peer?

A peer to peer networking can also be called – P2P, In a P2P network, the “peers” are computer systems which are connected to each other via the Internet.

P2P network allows two devices connect directly without a server between them. This type of networking used in most of the consumer applications like file-sharing, chat-applications etc.

22. What advantages does fiber optics have over other medium?

Fiber optics cable uses light pulses to transmit data across the geographical areas. Since the light is the fastest mode of transmission, data transmission over fiber optics cables is super fast.

Fiber optic cables have a much greater bandwidth than metal cables due to the speed. Fiber optic cables offer low power loss than any copper wire or other transmission modes. So low power loss means it can cover more distance without boosting the signals.