Find out common questions IT managers ask network engineers in job interviews.
In November, we tend to reflect on what we did or didn't accomplish over the course of the year. Some conclude that it's time to make a change in their professional career, so they begin the process of refreshing resumes, scouring job boards, and preparing for job interviews. But for networking professionals, preparing for a job interview is much easier said than done because networking technologies span such a wide spectrum and blend into other infrastructure genres. What should you focus on to ensure you can ace the interview?
This slideshow lists 10 interview questions that you should be prepared to answer while interviewing for an entry- or mid-level network administrator or engineering role at an enterprise organization. These questions are based on my experience, both as a job candidate and as a hiring manager.
As you prepare for your next career move, keep in mind that not all enterprises are running bleeding-edge technologies. Even if they are, they don't necessarily expect prospective candidates to have mastered the latest and greatest. Instead, IT managers are far more likely to seek out individuals who can demonstrate they understand the basics. If someone has a sound grasp of core network technologies like subnetting, ACLs, and ARP, all new iterations can build on that foundation.
Still, there are some relatively new technologies that you should at least be able to discuss at a high level. For example, many companies are migrating applications, data, and services to the cloud for flexibility and scalability. Managing network operations in a cloud or hybrid environment requires special skills, so network admins must have a solid grasp of cloud technologies and their impact on the network.
If you’ve looked back at 2016 and decided it's time for something new in your networking career, continue on to find out how you can prepare to impress potential employers and get that next job.
What is the purpose of a subnet mask?
Without a doubt, the most important part of networking that an engineer must understand is how to break IPv4 space into multiple, smaller subnets. You need to know and be ready to explain that subnets are used on IP networks to break up broadcast domains. You may also be asked to demonstrate the fundamentals of subnetting such as: "What is the maximum number of hosts in a /25 network?"
How would you secure a router/switch?
Given the times that we live in, network engineers must broaden their knowledge of infrastructure security. The first step in that knowledge base is understanding how to secure a typical router or switch deployed on a production network. During your interview, expect questions on network security topics such as logging, routing protocol authentication/encryption, network time protocol (NTP), access control lists (ACLs), and management of authentication, authorization and accounting (AAA).
Can you read and explain this network diagram to me?
No two networks are designed and built the same. That’s why it’s so important to be able to quickly read and decipher critical information from a network diagram. While there is no true methodology when it comes to network diagrams, most adhere to similar design methodologies and include key information such as network device types, management IP addresses, and interconnection types. So, before you head to your next interview, make certain you brush up on your network diagram reading skills.
What is the purpose of NAT and how does it work?
Simply put, network address translation (NAT) is the process of using a network device to manage the translation of an IP address into another. The primary reason for NAT on enterprise networks is because an organization is using private, RFC 1918 IP space internally. These IP addresses are not routable on the internet. Instead, they must be translated from the internal IP space to an IP address that is usable on the internet.
Besides understanding why NAT is used, interviewees should also be able to describe the difference between a 1-to-1 and a 1-to-many NAT translation and situations when these are most commonly used. Also, note that while IPv6 supports NAT, IPv6 largely renders NAT unnecessary due to the sheer amount of publicly routable IPv6 addresses available.
What is the difference between a layer 2 and layer 3 switch?
While they may look the same from the outside, a layer 2 and layer 3 switch are vastly different. The primary differentiation between the two rests in the fact that a layer 3 switch can route packets based on either MAC address (layer 2) or by IP address (layer 3). A layer 2 switch simply keeps a table of MAC addresses to port mappings. At a minimum, a layer 3 switch can be configured with static routes, while in many cases, layer 3 switches can also run dynamic routing protocols.
Can you explain what an IP ARP table does?
ARP stands for address resolution protocol. This is essentially a table that maintains IP address to MAC address mappings for routing purposes. The table is required because packets are switched toward the next hop MAC address of the connected device where the IP address is known to reside on the network based on statically or dynamically learned routes. Most IP ARP entries are dynamically learned. Expect to be asked questions about IP ARP, and possibly how to track down devices on a network when only given an IP or MAC address.
At what layer of the OSI model do MAC addresses operate?
Network administrators must know the seven-layer OSI reference model. From a network perspective, the first four layers of the model are critical. In addition to being asked what layer of the OSI model MAC addresses come into play, be prepared for questions like "If I’m talking about TCP port 80, what layer of the OSI model am I referring to?"
What is the purpose of a dynamic routing protocol?
The responsibility of routing packets on an enterprise network largely rests with routers and layer 3 switches. While statically configured routes are technically possible, most use dynamic routing protocols instead. In your interview, you may be asked to explain the purpose and/or benefits of a routing protocol. Answers such as “allows for dynamic re-routing of packets when a failure occurs” and “eases management in a changing infrastructure environment” are valid.
What are the benefits/challenges associated with virtual network infrastructure?
One of the newer skillsets that network engineers must possess is the ability to move network devices and functions away from dedicated hardware and onto virtualized appliances. Benefits include increased deployment flexibility and improved scalability. Drawbacks can include things such as increased complexity and inability to troubleshoot using physical hardware and cabling since this has all become virtualized.
As a network engineer, what challenges do you face managing a hybrid environment?
If there’s one technology that has truly changed the responsibilities of your average network administrator's role, it's the cloud. Many organizations want networking pros who understand how to network external cloud resources with private data centers in a hybrid environment. You should be able to describe challenges associated with this, including security, QoS, and latency.