Networking Question #1

What is a Firewall?

A Firewall prevents connection between two or more sources. It basically blocks any incoming or outgoing traffic.

Firewalls come in two forms: software or hardware firewalls.

Networking Question #2

Can you explain the difference between HTTP and HTTPS protocols?

HTTP stands for HyperText Transfer Protocol and is used by the majority of websites as a means of transmitting website data, and it allows for the use of hyperlinks.

This Protocol uses TCP port 80. HTTPS is a secure version of the HTTP protocol that allows for identity verification and low level encryption using TCP port 443.

Networking Question #3

What is a VPN?

A VPN is a Virtual Private Network.  It allows users to create a secure connection over public networks such as the Internet.

VPN’s are commonly used by mobile workers in order to access their company’s network from remote locations.

Networking Question #4

What are two types of IP addresses and what are they used for?

All IPv4 IP addresses can be divided into two major groups: public and private IP addresses.

A public IP address is an IP address that is used to access the Internet. Public IP addresses are routed on the Internet.

Private internal IP addresses are not routed on the Internet and traffic cannot be sent to them from the Internet, they are only supposed to work within local networks.

Networking Question #5

What is DNS?

DNS stands for Domain Name System.  It is basically the phonebook of the Internet. DNS translates domain names, for example www.google.com or www.youtube.com, to IP addresses so browsers can load those Internet resources through the Internet protocol.

Networking Question #6

What is a default route?

A default route is a configuration of the Internet Protocol (IP) that establishes a forwarding rule for packets when no specific address of a next-hop host is available from the routing table or other routing mechanism.

Networking Question #7

What is DHCP and what is it used for?

DHCP stands for Dynamic Host Configuration Protocol and it automatically assigns IP addresses to network devices.

It completely removes the process of manual allocation of IP addresses and reduces the errors caused due to this.

Networking Question #8

What is DoS?

DoS, or Denial-of-Service attack, is an attempt to prevent users from being able to access the Internet or any other network services.

Such attacks may come in different forms and are commonly performed by hackers. One common method of doing this is to overload a web server so that it can no longer process legitimate traffic.  Any website on this web server then becomes inaccessible.

Networking Question #9

What is Network Topology?

Network topology is a physical layout of the computer network and it defines how the computers, devices, cables, etc. are connected to each other.

Networking Question #10

What is a Router?

A router is a device that manages the flow of data to multiple connected devices. It is a network device that connects two or more network segments. It is used to transfer information from the source to the destination.

In simple words, the cable coming from your ISP goes into a modem, which converts input signals into digital data useable by a computer.

A router connects your modem with other devices to allow communication between those devices and the Internet.

Routers send information in the form of data packets.  When a router receives a packet, it checks its routing table to determine if the destination address is for a system on one of its attached networks or if the message must be forwarded to another router.

When packets are forwarded from one router to another router, the receiving router reads the network address in the packets and identifies the destination network and repeats the process mentioned above.

Networking Question #11

What is the OSI reference model, and how many layers does it have?

The Open System Interconnection model is a conceptual reference model that defines how applications communicate with each other within a network.

It also helps you to understand the relationship between networks and defines the process of communication in a network. It has 7 layers.

Networking Question #12

Let’s say a company is expanding its business to other countries. It wants all of its branches to remain connected to its corporate headquarters 24/7. Which network technology do you think they should use?

They should use a WAN.

Networking Question #13

What is a Proxy Server and how do they protect the computer network?

All devices on a network have an IP address.  Knowing the exact IP address of a network device can leave that device exposed to an attack.

Proxy servers prevent unauthorized external users from accessing those internal IP addresses. It makes the computer network virtually invisible to external users.

Networking Question #14

What is meant by 127.0.0.1 and localhost?

Simply put, localhost is the default name used to establish a connection with your own computer using the loopback address network. Think of loopback as “looping back” to your own machine.

The loopback address network has a default IP address of 127.0.0.1. Localhost is used to test applications on a local computer. When you move to a production or remote server you will change the references from localhost to the domain name you are using.

The IP address 127.0.0.1, is reserved for loopback or localhost connections. These networks are usually reserved for the biggest customers or some of the original members of the Internet.

To identify a connection issue, the initial troubleshooting step is to ping the server and check if it is responding.

127.0.0.1 and localhost are the same things in most of the computer network.

Networking Question #15

What is a MAC Address?

A MAC address is a unique device address given to every network connected hardware.

Unlike IP addresses, MAC addresses are permanent. Every network connected device has one and only one MAC address.

MAC stands for Media Access Control. It is a unique 48-bit serial number burned into the network circuitry of every Ethernet and Wi-Fi device.

Networking Question #16

What is Data Encapsulation?

In a computer network, to enable data transmission from one computer to another, the network devices send messages in the form of packets. These packets are then added with the IP header by the relevant OSI reference model layer.

The Data Link Layer encapsulates each packet in a frame that contains the hardware address of the source and destination computer.

If a destination computer is on a remote network then the frames are routed through a gateway or router to the destination computer.

Networking Question #17

What is Ipconfig and Ifconfig?

Ipconfig stands for Internet Protocol Configuration and is a command used on Microsoft Windows to view and configure the network interface.

The command Ipconfig is useful for displaying all TCP/IP network information currently available on a network.  It also helps to modify the DHCP protocol and DNS settings.

Ifconfig also known as Interface Configuration, is a command that is used on Linux, Mac, and UNIX operating systems. It is used to view and configure the TCP/IP network interface parameters from the Command Line.

Networking Question #18

What is SNMP?

SNMP stands for Simple Network Management Protocol. It is a protocol used for collecting, organizing, and exchanging information between network devices.

SNMP is widely used in network management for configuring network devices like switches, hubs, routers, printers, and servers.

Networking Question #19

Explain three types of networks based on their sizes?

The size of a network is defined by the geographic area it covers, and the number of computers or network devices within it.

Three types of networks based on their sizes are:

Local Area Network (LAN): A network with a minimum of two computers to a maximum of thousands of computers within an office or a building is known as a LAN. Generally, it works for a single site where people can share resources like printers, data storage, and more.

Metropolitan Area Network (MAN): It is larger than a LAN and used to connect various LANs across small regions, a city, campus of colleges or universities, and the like, which in turn forms a larger network.

Wide Area Network (WAN): Multiple LANs and MANs connected together form a WAN. It covers a wider area like a whole country or the world.

Networking Question #20

Define Round Trip Time?

The time taken for a signal to reach the destination and travel back to the sender with the acknowledgment is termed as Round Trip Time (RTT). It is also called Round Trip Delay (RTD).

Networking Question #21

What is encryption and decryption?

Encryption is the process of converting transmitted data into a form that cannot be read by any device other than the intended recipient.

Decryption is the process of converting back the encrypted data to its original form.

An algorithm called a cipher is used in the encryption and decryption process.

Networking Question #22

Mention two important actions performed by a Cisco switch?

It uses the source MAC addresses of frames to build and maintain a MAC address table. It also utilizes the MAC address table to forward frames via the destination MAC address.

Networking Question #23

What is a Link?

A link refers to the connectivity between two devices. It includes the type of cables and protocols used for one device to be able to communicate with the other.

Networking Question #24

Briefly describe NAT?

NAT stands for Network Address Translation. This is a protocol that provides a way for multiple computers on a common network to share a single connection to the Internet.

Networking Question #25

What is RIP?

RIP, short for Routing Information Protocol is used by routers to send data from one network to another. It efficiently manages routing data by broadcasting its routing table to all other routers within the network. It determines the network distance in units of hops.

Networking Question #26

You have one 48-port switch with 3 VLANs. How many collision domains and how many broadcast domains?

3 broadcast domains and 48 collision domains.

Networking Question #27

Draw a diagram of a network you’ve worked on, and please explain it to me.

This is one of the most common questions asked in network administrator interviews.

This question will test your problem-solving skills, confidence, and work experience. Check out Lucid Chart’s networking diagramming tips, and draw simple and complex networks for practice.

Networking Question #28

What’s the most important thing about the OSI Model?

The most important factor about the OSI model is that we can divide up the protocols into layers. Another key factor is that the layers of the OSI model provide encapsulation and abstraction.

Networking Question #29

Can you name the layers of the OSI Model?

Physical, Data Link, Network, Transport, Session, Presentation, and Application

Networking Question #30

Why can’t MAC addresses be used instead of IPv4 or IPv6 for networking?

Unlike IP addresses, MAC addresses do not specify unique destinations for communication.

An IP scheme can be used for a group of computers to logically distinguish them as a group via routing tables.

These groups can be divided into multiple levels so that we don’t have to keep track of every single subnet.

For instance, 17.x.x.x is within the Apple network. Using an IP scheme helps Apple to keep track of where each of its thousands of subnets is located and how to get to them. That’s not possible with MAC addresses.

Networking Question #31

Explain the difference between a VLAN and a subnet? Do you need a VLAN to setup a subnet?

VLANs work at the Data Link layer. They refer to the 802.1Q standard. Using VLANs you can give ports a unique MAC address table, separating them from each other.

VLAN’s can transport one or more subnets. A VLAN is used for switch partitioning. For example, let’s assume that you have an 8-port switch. You can use VLANs and assign 4 ports to one VLAN (VLAN 1) and 4 ports to another VLAN (VLAN 2).

VLAN 1 is totally separated from VLAN 2 traffic and vice versa. On a logical basis you get two switches using this technique. Usually, if a switch hasn’t seen a MAC address it will “flood” the traffic to all other ports. VLANs prevent this.

A Subnet is a range of IP addresses determined by part of an address, often called network address and a subnet mask (netmask). In simple words, a subnet is a small network composed by a group of IP addresses. Subnets communicate with each other using routers.

Networking Question #32

Mention some common HTTP status codes

1xx – Informational responses – communicates transfer protocol-level information

2xx – Success – indicates that the client’s request was accepted successfully

3xx – Redirection – indicates that the client must take some additional action in order to complete their request

4xx – Client side error – this category of error status codes points the finger at clients

5xx – Server side error – the server takes responsibility for these error status codes

Networking Question #33

What is the smallest IPv4 subnet mask that can be applied to a network containing up to 30 devices?

If you have a standard /24 VLAN for users, a /30 for point-to-point links, and a network of up to 30 devices, the smallest IPV4 subnet mask would be a /27 – or a subnet mask of 255.255.255.224.

Networking Question #34

What is a packet filter and how does it work?

A packet filter is used as a firewall technique to control network access by monitoring outgoing and incoming packets.

Packets are checked based on their source and destination IP addresses, protocols, and ports.

Packet filtering is used for modest security requirements. It is used for providing isolation of one subnet from another.

Networking Question #35

What are the advantages of using a reverse proxy server?

A reverse proxy server will hide the topology and characteristics of your servers.

It also helps with load balancing because reverse proxy servers enforce algorithms like round robin, weighted round robin, and weighted least connections.

Some other advantages include SSL offloading and termination.

Networking Question #36

Can you explain the difference between a router and a gateway?

Gateways are used to regulate traffic between two dissimilar networks, while routers regulate traffic between similar networks.

Let’s say you have a Windows 2000 network which uses TCP/IP as its primary protocol. You can connect your network with the internet using a router because the internet also uses TCP/IP as its primary protocol.

On the other hand, you’d use a gateway to connect a PC network with a 3270 mainframe environment or to connect a Windows NT network with a NetWare network.

Networking Question #37

What is a default gateway?

A default gateway serves as an access point for outbound connections to other networks. It allows one computer to communicate with another computer on a different network.

Networking Question #38

Can you tell me how DNS records work?

DNS records tell the DNS server which IP address each domain is associated with.  It also tells how to handle requests sent to each domain. DNS records are basically mapping files.

DNS records use specific syntax for its configurations and functions. Some important DNS records are:

SOA – Start Of Authority records

A – Address Mapping records

AAAA – IP Version 6 Address records

CNAME – Canonical Name records

MX – Mail Exchanger records

NS – Name Server records

PTR – Reverse-lookup Pointer records

Networking Question #39

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

The number of Network ID bits in a Class C network is 24. The number of possible network IDs is 2 raised to 21 or 2,097,152. The number of host IDs per network ID is 2 raised to 8 minus 2, or 254.

Networking Question #40

A user in your company wants to connect two computers for file sharing. Is it possible to do this without using a hub or router?

Yes. You can use a crossover cable in this situation. The data transmit pin of one cable is connected to the data receive pin of the other cable, and vice versa.

Networking Question #41

Which connection provides a secure CLI session with encryption to a Cisco switch?

An SSH Connection.

Networking Question #42

Let’s say a user opens three browsers on his PC to access www.cisco.com to search for CCNA information. The Cisco web server sends a datagram as a reply to the request from one of the web browsers. Can you tell which information is used by the TCP/IP protocol stack on the user machine to identify which of the three web browsers should receive the reply?

Yes, you can use the destination port number.

Networking Question #43

Where are Cisco IOS debug output messages sent by default?

They are sent to the Console Line.

Networking Question #44

Let’s say a network administrator issues a ‘copy running-config startup-config’ command after making configuration changes on a Cisco switch. What would be the impact of these commands?

The new configuration will be loaded if the switch is restarted.

Networking Question #45

Do you contribute to any open source projects?

Contributing to open source projects will help you expand your network and pass a lot of interviews.

Always say yes (if it’s true) when asked this question, because the employer would feel that you are enthusiastic about network administration and also willing to share your knowledge.

Contributing to open source projects could be very impactful for your career. Here are two examples from Reddit users to prove that.  These examples aren’t directly related to network administration but they are meant to prove a point.

“Even contributing to unknown OSS projects has gotten me through the door at several companies. Two companies specifically during my last job search even waived their take-home assignments and brought me in straight to the interview phase.

 Project “prestige” isn’t as important as solving real-life problems. Nobody at these companies had heard of the libraries I published, but they certainly listened when I started explaining why I published them in the first place.

 My projects were GraphQL libraries. It is such an immature ecosystem that there’s plenty of pain points still yet to be solved. I talked to several companies who attempted to solve the very same problems with GraphQL that I encountered… but with much bigger teams involved and more wasted salary hours.

 It impacted my career in that I now get invited to speak at local events about GraphQL…. even though, technically, my projects were all side projects and I’ve never actually used it in production.

 I also have a much easier time getting past the first-round, and sometimes second-round interview phases………. assuming, of course, that I can pivot the conversation to talking about my libraries.

 My advice to people who are looking to build up their portfolios: Ignore the standard “junior” apps.

 Don’t bother with Tic Tac Toe, REST APIs, or chat apps.

 Do a hacker news search on a popular buzzword, look for the biggest complaints about it, and then attempt to make a solution for just one of these problems.

 It doesn’t even have to fully work; the experience alone can help sell you for teams that suffered the same pain point.

 That’s how you make OSS projects work for you if all you’re looking for is a career boost.”

 Comment by Existential Own

 “I think it helped me get my most recent job.

 I had contributed to a well known library (don’t want to say which) that the team was about to implement in one of their projects. Nobody on the team had used it.

I actually didn’t need to do any technical challenge in my interview because they said my PRs for the library were complex enough.

 Skipping the technical was actually a red flag for me but I took the job anyway and I’m glad I did, it’s a great company with really good coding practices and talented engineers.”

 Comment by Pyjava

 Networking Question #46

Tell me about the biggest mistake you’ve made.

The interviewer wants to see if you are willing to embrace the fact that we’re all fallible. Be very open and say that you have made mistakes but they have helped you learn a lot and progress in life.

Try to mention a technical mistake in your career instead of a behavioral mistake.

For example, you can say that my biggest mistake was to un-plug a server that was running DHCP. Because of this mistake hundreds of people were not able to access the network for almost 50 minutes.

Networking Question #47

What technical news sources do you check daily?

The interviewer wants to gauge your passion for networking.

Just mention your favorite sources.  A good example could the Cisco Networking blog.

Networking Question #48

Tell me about an instance where your team, client, or boss disagreed with you. How did you resolve this situation?

This is a very common question asked to check your attitude towards disagreement. Every company wants a person who is open to disagreements and debate.

This question could be approached in a variety of ways. You can talk about a specific instance from your career or life or make up a situation (if you have no experience at all) to prove that you are a good listener, open communicator, and know how to analyze a situation.

Networking Question #49

A network administrator is measuring the transfer of bits across the company backbone for a very important application. The administrator notices that the network throughput is lower than the bandwidth expected. Can you tell which factors could influence the differences in throughput?

Some factors responsible could be the amount of traffic that is currently crossing the network, the type of traffic that is crossing the network, and the latency that is created by the number of network devices that the data is crossing.

Networking Question #50

How many hosts are addressable on a network that has a mask of 255.255.255.248?

6