Top 10 VLAN Interview Questions (With Example Answers)

By Indeed Editorial Team

Published 1 July 2022

The Indeed Editorial Team comprises a diverse and talented team of writers, researchers and subject matter experts equipped with Indeed's data and insights to deliver useful tips to help guide your career journey.

A virtual local area network or VLAN is a logical subnetwork that combines different devices from physical local area networks or LANs. Hiring managers can ask questions about VLAN when recruiting network engineers, network operators, network architects, IT security managers and system administrators. Preparing answers to common VLAN questions can help you make a positive impression on the interviewer. In this article, we outline 10 VLAN interview questions, discuss why interviewers ask those questions and share their sample answers to help you prepare for your next interview.

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10 Commonly Asked VLAN Interview Questions

Here are some commonly asked VLAN interview questions and their example answers:

1. What is a VLAN?

How you answer this question can tell the hiring manager about your fundamental knowledge of networking concepts such as VLAN. In your response, you can define VLAN and explain its significance.

Example: "A VLAN is a logical group of networking devices linked to administratively defined ports on a switch. It is important to note that only a catalyst switch can support a VLAN. The creation of LAN breaks a larger broadcast domain into a smaller, isolated one. So, no two VLANs can communicate with each other without a router."

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2. What are the advantages of VLAN?

This question allows the hiring manager to evaluate if you are aware of the advantages of VLAN and its uses. In your answer, you can list the major advantages of using VLAN.

Example: "VLAN provides a number of advantages such as reducing the broadcast traffic and providing an additional layer of security. It also enables easier management of devices and their logical grouping based on their functions, instead of relying on their locations.'

3. What are the different types of VLAN memberships?

This question can help the hiring manager assess your expertise and professional experience. It can be helpful to answer this question in detail and explain the two types of VLAN memberships.

Example: "There are two types of VLAN memberships, static VLAN and dynamic VLAN. Static VLAN, also known as port-based VLAN, is a type of VLAN membership in which the network administrator builds a VLAN and then allocates switch ports to it. In static VLAN, until the administrator changes the port assignment, the association with the VLAN remains the same. So, the physical switch port of the end-user devices determines their VLAN membership.

Dynamic VLAN dynamically assigns the port to the VLAN based on information from the end-user device, such as the IP address. When a device connects to the port, the switch queries a database to set up a VLAN membership. It is important for network administrators to establish the VLAN database of a VLAN Membership Policy Server (VMPS)."

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4. What is the range of VLAN?

The hiring manager wants to assess your practical knowledge through this interview question. You can respond by stating the range, explaining the different sub-ranges and discussing their allotment.

Example: "The range of VLAN is 0–4096, with 0 being the first VLAN and 4096 being the last VLAN. We cannot use both the first and the last VLANs. 1 is the default VLAN, or the management VLAN and 2 –1001 is the normal VLAN range. 1002–1005 is for the token ring and FDDI VLANs., whereas, 1006–4095 is the extended VLAN range. It is for service providers to allow the provisioning of new customers."

5. What is the difference between access and trunk ports?

The hiring manager wants to assess your understanding of ports and whether you know their different applications. To answer this question, briefly explain the differences between them and mention their usage in a VLAN.

Example: "At any given moment, an access port, sometimes referred to as an untagged port, belongs to and transmits the traffic of one VLAN. Any data frame received on an access port belongs to the VLAN established on that port. Access ports cannot connect with ports outside their VLAN unless the packet gets routed since VLANs cannot communicate directly with each other. Before an access port receives the packet, switches delete any VLAN information from it. As a result, every device connected to an access port is ignorant that it is a part of a VLAN.

A trunk port, sometimes referred to as a tagged port, does not belong to a specific VLAN. It can send traffic from several VLANs at the same time. So, trunk ports can simultaneously send tagged traffic to a defined VLAN and untagged traffic to a local VLAN."

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6. What do you mean by frame tagging?

This question helps the hiring manager test your understanding of the basic VLAN terminology. While answering this question, you can define the term and also mention the different types of frame tagging to highlight your knowledge.

Example: "Frame tagging is a method that assigns a distinctive VLAN ID to each frame transmitted out of the trunk link. This tagging is for identifying the VLAN that the frame belongs to when it travels between switches or between a switch and a router for routing. There are mainly two types of frame tagging methods, namely Inter-switch link (ISL) and 802.1Q, also known as Dot1q. They are also known as frame encapsulation protocols."

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7. What is the difference between ISL and 802.1Q?

This interview question enables the hiring manager to test your in-depth understanding of the different types of protocols. In your response, you can explain the two protocols and how they work.

Example: "802.1Q, also known as Dot1q, is an open standard protocol. It works with the switches of any vendor. To identify the VLAN to which a frame belongs, you can insert a field into the header of the frame. This light-weighted protocol works by adding only 4 bytes within the header of the frame. The greatest number of VLANs permitted in 802.1Q is 4094.

ISL is a Cisco proprietary protocol, which means that, unlike other protocols, it works between Cisco switches only. It works by adding a header of 26 bytes and a trailer of 4 bytes with the original Ethernet frame. The greatest number of VLANs permitted in ISL is 1000."

8. How do you delete VLAN information on a switch?

This VLAN interview question can help the hiring manager assess your coding knowledge. While answering this question, you can briefly describe where a switch saves the information and explain the required command to delete it.

Example: "The switch does not save the VLAN information either in its running configuration or start-up configuration. It saves it separately in a file known as "vlan.dat" in its flash memory. We can delete the VLAN information from the flash memory using the command delete flash:vlan.dat."

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9. What are the different modes of VTP?

The hiring manager can evaluate your in-depth understanding of VLAN concepts through this question. You can start your answer by describing VTP and then discuss its different modes.

Example: "VTP, or VLAN trunking protocol, is a Cisco proprietary protocol that replicates the definition of a VLAN on one switch onto the switches of the whole local network. VTP has three modes: server mode, client mode and transparent mode.

The server mode is the default VTP mode. You can create, delete or add VLANs on a switch in server mode. The switch advertises the changes to the entire VTP domain. You cannot create, add or delete VLANs in client mode on the switch. Switches in client mode respond to VTP advertising from other switches by changing their VLAN settings. In transparent mode, switches do not take part in the VTP domain, but they can receive and forward VTP advertising through the defined trunk links."

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10. What do you mean by inter-VLAN routing?

This question allows the interview to check whether you know how VLANs communicate. In your response, you can briefly explain what inter-VLAN routing is and mention the different methods available for it.

Example: "A VLAN divides a broadcast domain into several segments. Only the members of the same VLAN can communicate with each other. To communicate with the members of other VLANs, routing traffic between them is essential. The process of routing network traffic from one VLAN to another is known as inter-VLAN routing. We can route traffic using two methods, namely the router-on-stick and switched virtual interfaces (SVI) method."

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