20 VLAN Interview Questions and Answers

A virtual LAN (VLAN) is a logical group of network devices, such as computers, printers and servers, that share a common set of network parameters. VLANs are used to segment a network into smaller, more manageable groups. When applying for a position that involves working with VLANs, you can expect to be asked questions about your knowledge and experience. In this article, we will review some of the most common VLAN interview questions and provide some tips on how to answer them.

VLAN Interview Questions and Answers

Here are 20 commonly asked VLAN interview questions and answers to prepare you for your interview:

1. What is VLAN?

A VLAN is a virtual LAN. It is a logical grouping of devices on a network, usually based on function, department, or location. Devices in the same VLAN can communicate with each other as if they were on the same physical network. VLANs improve network security and performance by isolating traffic on the network.

2. Why do we need a VLAN?

A VLAN can be used to segment a network into smaller, more manageable pieces. This can be useful in a number of situations, such as isolating different departments within a company or creating a separate network for guest access. VLANs can also help improve security by making it more difficult for unauthorized users to access sensitive data.

3. How does a VLAN work?

A VLAN is a virtual LAN that is used to segment a network into smaller, more manageable pieces. VLANs are created by adding switches to a network and then assigning each switch to a different VLAN. This allows for each VLAN to be isolated from the others, which can help improve security and performance.

4. Can you explain how to configure multiple VLANS in the same switch?

In order to configure multiple VLANS in the same switch, you will need to create a separate VLAN for each network. You will then need to configure the switch so that it knows which VLAN each port is a part of. Finally, you will need to configure the switch so that it knows how to route traffic between the different VLANS.

5. Can you explain the difference between Layer 2 and Layer 3 VLANs?

Layer 2 VLANs are created by adding switch ports to a VLAN. This type of VLAN is used when devices need to communicate with each other on the same network. Layer 3 VLANs are created by adding router ports to a VLAN. This type of VLAN is used when devices need to communicate with each other on different networks.

6. What are some of the benefits of using a virtual LAN?

There are many benefits to using a virtual LAN, including increased security, improved performance, and easier management. A virtual LAN can help to isolate traffic on a network, which can improve security by making it more difficult for unauthorized users to access sensitive data. Additionally, a virtual LAN can help to improve network performance by reducing congestion and increasing bandwidth. Finally, a virtual LAN can make it easier to manage a network by simplifying the configuration of network devices.

7. Do VLANs improve security? If yes, then how?

VLANs can improve security by isolating traffic on a network. By keeping different types of traffic on separate VLANs, it becomes more difficult for unauthorized users to access sensitive data. Additionally, VLANs can be used to segment a network into different security zones, further increasing security.

8. What’s the best way to create a new VLAN on a Cisco switch?

The best way to create a new VLAN on a Cisco switch is to use the “vlan” command. This will create a new VLAN with the specified ID.

9. What’s the purpose of port-based VLANs?

Port-based VLANs are used to segment a network into different logical sub-networks. This allows for better security and organization of the network, as well as easier management.

10. Can you explain what trunking is?

Trunking is a method for consolidating multiple network links into a single link. This is often done to increase bandwidth or to provide redundancy. Trunking can be used with any type of network link, but is most commonly seen with Ethernet links.

11. What is the maximum number of VLANs allowed per switch?

The maximum number of VLANs allowed per switch is 4096.

12. Why do you think it’s not possible to have more than 4,000 VLANs configured on an interface?

The IEEE 802.1Q standard, which is the standard for VLANs, only allows for a maximum of 4,000 VLANs to be configured on an interface. This is because the VLAN ID is only 12 bits, so the maximum number of VLANs that can be represented is 2^12, or 4,096.

13. Why would you use a router on a stick for inter-VLAN routing?

A router on a stick is a common configuration for inter-VLAN routing, and it is used because it is a very simple and cost-effective way to set up this type of routing. With a router on a stick, you only need a single router and a single physical connection to the network in order to route traffic between multiple VLANs. This can be a very helpful solution if you have a limited budget or if you need to set up inter-VLAN routing quickly.

14. What happens if you try to connect two switches with a trunk link that doesn’t support any common VLANs?

If you try to connect two switches with a trunk link that doesn’t support any common VLANs, then the link will not work. All traffic on the link will be blocked.

15. Can you explain what native VLANs are?

A native VLAN is a VLAN that is configured on a switch port without any extra configuration. All untagged traffic that comes in on a port will be automatically placed into the native VLAN for that port.

16. What is double tagging?

Double tagging is the process of adding a second tag to a packet as it moves between different VLANs. This allows the packet to be identified as belonging to a specific VLAN, even as it travels through a network that contains multiple VLANs. Double tagging can be used to improve security and to help ensure that packets are routed correctly.

17. Are tagged frames processed by the native VLAN?

No, tagged frames are not processed by the native VLAN. The native VLAN is only for untagged frames.

18. Is it possible to send untagged traffic across a trunked link?

Yes, it is possible to send untagged traffic across a trunked link. This is often referred to as “native VLAN” traffic. Any traffic that is not explicitly tagged with a VLAN ID will be assumed to be part of the native VLAN and will be sent across the trunk link without being tagged.

19. What is the default priority level used by STP when assigning root bridges?

The default priority level used by STP when assigning root bridges is 0.

20. What information is exchanged when two switches are negotiating which one will become the root bridge in a network?

When two switches are negotiating which one will become the root bridge in a network, they exchange information about their bridge ID, which is a combination of their MAC address and a priority value. The switch with the lowest bridge ID will become the root bridge.