Network Engineer Interview Questions and How to Prepare for Them

I was a Network Engineer for 5 years before moving to Cyber Security. During this time, I personally did countless interviews for Jr and Associate Network Engineer candidates in 2 large fortune 500 companies. Because of this, I’ve picked up a wealth of information on what makes a good candidate, and the best ways to present your skills, knowledge and abilities when asked typical questions. Here are the some good Network Engineer Interview Questions and ways to prepare for them.

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Preface : What makes a good Network Engineer?

You should pick a career only if you have the motivation to do it day in and day out. A genuine Interest/Curiosity in Computers, Radio/Wireless, DataCom, TeleCom helps gives meaning and purpose to be a good Network Engineer.

A foundation in How Computers work and How to fix Basic Problems, Understanding of How a Business works, and Why a Network is needed there. A good candidate should be Skilled in Troubleshooting, Deductive and Investigating Thinking, CLI and Navigating and OS & GUI, Programming, Physical Cabling and Handling Network Equipment.

Finally, The ability to communicate, gather information from ambiguity, stay calm in stress, and find creative effective solutions to technical problems. Emphasis on this because these skills will be invaluable both in presenting yourself on an interview and in day-to-day work.

That being said, lets take a look at some Network Engineer Interview Questions!

Question : What is the OSI Model?

• Define it. Why is it used? Examples at each Level.
• Discuss the Layers in High Level if its HR or Deeper if its and IT person.
• Describe the Connection Flow for Interview Format (VOIP, Video etc)

For example if you are interviewing via video calls :

“Yes, Open Standards Interconnect is the framework for modern Data communication that lets different devices speak to another anywhere in the world. Such as this Interview Video call, Webex is the Application Layer which presents and encodes data with the Presentation Layer, which then is routes data between us via the Transport and Session Layers to keep the connection flow, below this the Network layer is handling TCP/IP chunking of the video into bits which finally travel via the DataLink and Physical layers between our Computers and Wires/Wifi to make this communication possible.”

• Try to be concise and infer the level of detail needed in your answer from the type of position and role of the interviewer. This is by far the most common Network Engineer Interview Questions.

Question : What is an APIPA Address?

• This is a Curve-ball question if you have not heard the term.
• Automatic Private IP Addressing = Placeholder address when no DHCP is set up on your LAN
• Typically reported if client DHCP is Reset

Topic : Physical Networking (Layer 1)

• What is a straight through, crossover, console, and aux cable in the context of a Switch on the LAN?
• What is single mode and multimode fiber?
• You have an AP that checks out fine, has unidirectional screw on antennas, but very poor signal broadcast, what is the first thing you would check?
• What is a loopback plug, what is it used to test? With Whom (typically)? (bonus : how do you make one yourself?)
• What is an out of band connection?
• What is the max transmission length of Cat6E?
• What is POE?
• An ethernet jack is solid yellow, what could this mean? (Cisco)

Topic:  Explain NATing

• Stands for Network Address Translation, helps hide private IP addresses by changing your IP address on a local network to one called a Public IP when you go across the internet.
Office Phone Line Analogy – Internal Phone Extensions are internal but when you call out the number uses the masked Main Phone Number. This is analogous to how NAT works. Analogies work great on HR Phone Screens that are high level.
• NAT Configuration on an Egress Router Interface (Technical Answer)
• Why is it used? (Common Followup Question) – to save IPv4 addresses

Topic :  Subnet Masks and Classes

Memorize the common ones and know where would you use them (VLAN vs P2P vs Core) Know the Classes of Addresses and ranges including the experimental and reserved. Also know why we use them, how a computer reads the Network/Host bits and why there’s a mathematical limit and how this was increased in IPv6.

Questions : Cisco Questions

• What is CDP?
• What is HDLC?
•What are the different kinds of passwords that are used to secure the Cisco router?
• What are the different levels in a CISCO router (User/ Privileged/ Config)? • What is Spanning Tree?
• Which version of OSPF supports IPv6?
• What is the process to recover an un-bootable router?

Topic : Troubleshooting

• How would you Troubleshoot XYZ (Slowness, Packet Loss, Timeouts)?
-Get Specifics, Reported Time, Scope (Communication Skills)
-Draw out the connection (Whiteboard if Possible)
-Isolate the Problem (Describe Tools and Process!)
-Consider recent Changes

• Common Scenarios :
-Slow Page/App
-Packet Loss
-Constantly Flapping Connection
-Slow transfer of high volume
-App Suddenly stopped processing connections
-VIP User is having Connection Issues

Topic : Effective Design

Problem : You have # number of users who need XZY , Whiteboard a network to solve their need or problems.
Ask clarifying Questions!
• Calculate Subnet, Interfaces, Protocols with Scalability and prudence in mind.
• Be vendor Agnostic, stick to fundamental concepts in design.
• Go Slowly, Think out loud as you layer the design.

Questions : Network Security

• How do you implement a secure DMZ? (Restrict Inbound, Allow Internal)
• What is a State-full and Stateless Firewall? (ACLs vs FW)
• What is AAA and whats an example of a poor AAA setup and a strong one?
• How would you mitigate a DDOS from 5 distinct IPs that have not changed?
• How would you block a SQL Injection attack on a public server?
• How would you implement Port Security? (Layer 1, 2 Protocols)
•How would you implement Network Monitoring? (SNMP, Netflow, Syslog)

Questions : Routing and Switching

• Which Numerical range of Administrative Distance is more preferred ?
• What is meant by a Link State and Distance Vector Routing Protocol ?
• What is a Trunk and Why is it used?
• How would you investigate and resolve WAN congestion on an MPLS link?
• What are the phases of a successful Site 2 Site VPN ? Whats needed to negotiate and get the tunnel up and running with another peer?
• What is a Gateway of Last Resort?
• What is Convergence?
• What is a CAM Table?
• What are JumboFrames?
• What is Spanning Tree Protocol and Why is it used?

Questions : Wireless

• What is DBi and give me two numbers, a strong and a weak value?
• What is a channel? What is Channel Overlap?
• Whats a Passive and Active Site Survey? What are general things to look for on a floorplan or site when planning to deploy wireless?
• What is a rouge AP?
• What is client disassociation? What can be a cause of it?
• What is AP Roaming?
• (Cisco specific) What is a blue/green/yellow light on a typical Cisco AP?

Questions : Network Services

• What is syslog and netflow? how would you configure it on a Cisco iOS Switch? What port is used in its operation?
• What is a SNMP OID and a SNMP MIB?
• What is TACACS+? What is RADIUS?
• What is 802.1X Authentication?
• What is a Proxy ? What are the benefits of using one ?
• You have to backup and manage the iOS config (in text) of 100 routers and switches, what are some effective ways we can do this?
• How would you implement a QoS Policy on a subnet to prioritize Video over other traffic to a specific IP?

Questions : Cloud and Automation/Scripting

• What is IaaS, PaaS, SaaS?
• What is the Shared Responsibility Model in an IaaS Provider?
• What is a region, availability zone, edge location? I explain this here.
• What is a VPC and What are 2 ways we can isolate and secure it on Layer 3?
• How would you connect to an public API and retrieve a specific Resource?
• What is a Class? Function? Module?
• What is IOT? What is a common Network Topology for them?
• What is a Boolean Variable?
• What is Serverless and whats an example of a use for it?
• How would you connect a physical Datacenter to the cloud?
• What is Iac?
• How would you design a WebApp archtecture that needs a backend DB and static storage as well as a distributed global presence? (think 2 tiered ALBs with NLBs and CDNs, with IaC for DR)
• What is Git? Why is it useful?
• What are some disadvantages of Cloud vs On-Prem?
• What is a Boolean Variable?
• Write out psudocode to read a text file line by line and return a data structure with 5 words of your choice. (Followup: Make it upper case words only) I wrote an example script and guide here to do a similar script

Conclusion :

This is just a small selection of questions, however the main points are to focus your strength’s as a candidate around the best attributes of a good Network Engineer. These being Communication, Technical Knowledge, Interest, Design, and Troubleshooting. Its impossible to predict all network engineer interview questions, however by building these foundations you can effectively answer them by just drawing from yourself and your own experience, which gives the interviewer an authentic answer and will land you the position.

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