What Is a VLAN? The Key to Streamlined, Scalable, and Secure Networking

Whenever a LAN comes up in a conversation, the first image that comes to mind is the early 2000s gaming parties at a local club. A few years later, when I got my first proper job, I realized just how vital LANs are in modern office setups.

So what happens when you add a ‘V’ to this network of devices physically connected within a single location? You get a virtual local area network, or VLAN.

A VLAN, which stands for Virtual Local Area Network, divides your physical network into smaller, more manageable virtual segments.

VLAN logically groups devices together, thus keeping a network running like a well-oiled machine while being more secure at the same time.

In the next 10 to 15 minutes, I’ll do my best to explain the nuances of VLANs, from their configuration to best practices, so you can have all the facts when deciding if it’s the right fit for your business.

On a very basic level, VLANs transform a physical switch into smaller mini-switches that operate independently. Here’s how that happens.

Layer 2 Segmentation

First off, we need to take a look at the open systems interconnection (OSI) model, which establishes a standard for different systems to communicate with each other. It splits network communication into seven layers, each responsible for a specific task.

VLANs operate at Layer 2, the Data Link Layer, which handles the transmission of data between devices on the same network. A VLAN divides a physical LAN into multiple broadcast domains, which are groupings of network devices that receive traffic from one another.

This means that devices within the same VLAN can communicate as if they were on the same physical segment, even if they’re separated.

Broadcast Domains

You see, broadcast traffic isn’t all that efficient because everyone receives it, regardless if they need or want it (it’s a broadcast, after all). A switch will forward it to all its interfaces, meaning some of the bandwidth will go to waste, perhaps even affecting the CPU cycles of a receiving device or two.

If you’re thinking, “But hey, we have Gigabit interfaces and faster-than-ever CPUs now, so this shouldn’t be a problem,” you’re right for the most part.

Still, it’s a good idea to limit the size of your broadcast domains in case a certain device (or more of them) sends a considerable amount of broadcast traffic, which can impact your performance.

One of the ways to do this is to implement VLANs on switches. They allow you to break broadcast domains into isolated segments and limit the traffic to them.

This partition is important for optimal network traffic flow as it reduces network congestion, plus it boosts security protocols if the network is sizable (e.g., an enterprise-level one).

MAC Address Handling

Quick refresher: a Media Access Control, or MAC address, is a unique identifier representing each device connected to a network. Through it, various devices recognize each other and communicate, while a switch uses it to figure out the VLAN to which a device belongs.

For example, your computer and office printer on the same network have their own MAC addresses, which is how the network knows where to route data. Every data packet sent includes the source MAC address (your computer) and the destination MAC address (office printer).

Here, switches play a major role as they use these MAC addresses to forward the data to the correct device.

Oftentimes, switches are configured in a way that maps out MAC addresses (also known as MAC Address Table) connected to every switchport. So, when data comes in, the switch takes a quick look at this table to efficiently route the traffic.

VLAN Tagging

This is a method of identifying and differentiating VLAN traffic from other network traffic. It’s usually done by inserting bits/metadata into an Ethernet frame, which itself is the basic unit of data transmission over an Ethernet network.

802.1Q Standard

As modern networks grow more complex, it helps to label data packets with a distinct sequence of bits, which is what the 802.1Q standard does.

As the omnipresent method of VLAN tagging, it inserts additional information in the form of a 4-byte tag into the Ethernet frame to mark the VLAN of which the frame is a part.

As a result, the tag tells the network where the packet should go. When a switch receives a packet with a VLAN tag, it checks the tag to see which virtual network the packet should go to.

Once that’s done, it sends the packet to the devices in the same virtual network. This keeps the traffic separate, and it makes the network more secure and efficient.

Untagged vs Tagged Frames

As you can guess, untagged frames have no extra information added to them. Instead, they are based on the physical ports on a switch, called access ports, where each port is attributed to a specific VLAN. In this scenario, you end up with multiple logical switches stemming from a single physical switch.

Moving back to tagged frames, the difference here is that multiple tagged VLANs can occupy the same port on a switch. It helps to know that every tag consists of two parts:

• Priority Code Point (PCP) that indicates the priority of the frame
• VLAN Identifier (VLAN ID or VID) that identifies the VLAN to which the frame belongs

When a switch receives a tagged frame, it examines the VLAN ID to determine the appropriate VLAN for the frame. The switch then splits the traffic and forwards frames to the correct destinations — the ports belonging to the same VLAN.

Trunking

Finally, we have trunk ports — switchports that carry traffic for multiple VLANs across a single link between switches. Each frame sent via a trunk port is tagged with a VLAN ID.

The switches on either end of the trunk link (remember, it’s a physical link) use the VLAN ID to forward the frame to the correct VLAN on the destination switch.

Trunking does the trick for connecting network devices such as switches and routers to communicate across different VLANs.

A good example is a multi-department company, where each department, like Sales or HR, has its own virtual network. So, if they wanted to use a printer, it would be connected through a trunk port to be accessible to every department while keeping their networks apart.

VLAN Membership

Much like a gym membership, you can look at VLAN membership as an authorization to be part of the VLAN. It determines which devices are assigned to which VLANs. In that regard, we have two membership methods:

• Static VLANs: The network admin manually assigns ports on a switch to a VLAN. This setup is also known as port-based VLANs since you can assign multiple VLANs to ports on a single switch. Once a device is connected through a physical switch port to a port assigned to a particular VLAN, it becomes a member of that VLAN — until the network administrator changes the port assignment.
• Dynamic VLANs: The switch automatically assigns a VLAN to a port based on information from the connected device, which ranges from MAC and IP addresses to the Ethernet protocol type, depending on the vendor. When a device is plugged into a switchport, the switch queries a central database, known as a VLAN Membership Policy Server (VMPS), to determine the appropriate VLAN assignment.

Dynamic VLANs are a more advanced concept, especially considering the network admin must configure the VMPS with the necessary VLAN membership rules, but it’s useful to be aware of what they can do.

It might come as a surprise, but VLAN comes in numerous forms based on varying traffic, use cases, and security.

Default VLAN

Refers to the OG network that exists on all managed switches and can’t be edited or deleted. Most vendors label it as VLAN 1, as all switchports are members by default (hence the name). This means that any device connected to any port can communicate with other devices connected to different ports on the same switch.

Unless reconfigured, the default VLAN handles untagged traffic, which makes it the VLAN foundation for all network connectivity — but not a good fit for regular data traffic due to security gaps. That said, it’s often used for devices that don’t require strict VLAN separation.

Data VLAN

Divides the network into two main categories — users and devices. Data VLAN is specifically designed for user data and doesn’t handle voice or management traffic (which I’ll get to next). This allows admins to bundle users together, even if they’re connected to different switches.

You’ll routinely find data VLAN in organizations due to its rather handy capability of segregating traffic between departments (e.g. Marketing and Sales), projects, or even specified user groups.

By organizing devices into logical groups, it simplifies network management but also enhances network security and optimizes bandwidth allocation.

Voice VLAN

If the name didn’t give it away, voice VLAN prioritizes VoIP (Voice over IP) traffic by differentiating voice data generated by IP phones or VoIP systems from other types of data.

The idea is to prevent any disruptions to voice packets moving through the network. This is achieved by assigning higher transmission priority to voice traffic compared to the rest of the network traffic (calling is still a thing, young peeps!).

The isolation ensures better call quality through minimal latency, echo, and jitter, enabling consistent and reliable voice communication. Because they’re designed with VoIP traffic in mind, voice VLANs are a staple in businesses where daily high-quality, real-time VoIP communication is high on the list of priorities.

Management VLAN

This is a single network shared by all switches that is reserved for management traffic. In other words, all the configuring, monitoring, and maintenance of network devices is performed unrelated to user data traffic so that critical management operations remain unaffected by whatever users do.

Apart from better network stability, management VLAN is used for security reasons. It’s like a protective shield since a specific port can be designated to limit access to authorized administrators only and thus reduce the risk of attacks.

Only devices with predefined MAC addresses are allowed to connect to this port, thus preventing unauthorized access to switches and routers.

Native VLAN

A crucial (and dare I say special) part of networks that use VLAN tagging, native VLAN carries untagged traffic between trunk ports.

If that sounds a bit confusing, think of it as a default setting for untagged traffic that travels between switches and often includes important control and management data. Do note that you need to configure it the same on all connected devices for it to work as advertised.

Native VLAN works on any trunk port, which makes it the go-to choice for backward compatibility with devices that don’t support VLAN tagging. In this instance, the network serves as a common identifier, and the native VLAN acts as a translator, allowing older devices to communicate with newer ones.

Private VLAN (PVLAN)

The cherry on the cake of sorts, a private VLAN segments a VLAN into more of its instances within it — a “VLAN in a VLAN” vibe, if you will.

It splits the primary VLAN into multiple isolated broadcast subdomains and makes the router (or some other Layer 3 device) the focal point of communication between partitioned subdomains.

What private VLAN does best is provide an additional layer of security. The communication within the same VLAN is restricted, which is why you’ll see this configuration when isolating virtual machines or servers in a cloud environment, like ISP co-location.

These devices often handle sensitive data, so via private VLANs, you can build a secure environment that meets compliance and security requirements.

VLANs bring a lot of good stuff to the table that make them a must-have component of modern network infrastructures. I’m talking about things like:

Enhanced Security

Since VLANs slice a network into different parts, they allow you to isolate sensitive data from the rest of the network. By placing users or devices with similar security requirements in separate VLANs, you can minimize unauthorized access and limit exposure to potential threats.

This isolation helps protect confidential information and restrict the spread of malware or internal attacks, making VLANs a vital part of improving overall network security.

Take guest users as an example. You can place them in a separate VLAN, limiting their access to crucial business information. The same goes for respective departments — accounting doesn’t need access to the whole network.

Additionally, you can tailor security policies for each VLAN, applying distinct rules and controls based on the sensitivity of the information being handled, thereby reducing the risk of breaches.

Improved Network Performance

Breaking up a network into smaller VLANs based on the traffic type of group can reduce congestion. Doing so boosts network performance as you can limit the amount of broadcast traffic that travels through the entire network.

This isolation minimizes collisions and reduces latency, especially in high-traffic environments. By differentiating traffic streams, VLANs allow for more productive use of available bandwidth because devices only receive relevant data, which ultimately boosts the overall speed and reliability of the network.

For instance, when a large department like HR generates a lot of network activity, it won’t impact other departments’ performance.

VLANs can also enable Quality of Service (QoS) configurations, prioritizing major applications such as VoIP or video conferencing, so that these services operate smoothly even during peak usage times.

Simplified Network Management

When you have a large network on your hands, VLANs make it significantly easier to manage it. Network administrators can logically group devices regardless of their physical location, allowing them to reconfigure the network (remotely too) just as they prefer without the need for hardware changes.

Not only that, but VLANs also make it simpler to implement policies, configure devices, and manage access rights.

Let’s say you have to move a user to a different department. You can do so by reassigning their VLAN membership. This flexibility allows businesses of all shapes and sizes to adapt quickly to changes in staffing, project requirements, or operational needs.

Furthermore, if you employ centralized management tools to do your bidding, you can gain visibility into VLAN performance and security, simplifying troubleshooting and maintenance.

Scalability

A big reason why network administrators (at least the select few I know) love VLANs is because they don’t call for major changes in the existing network infrastructure. As business needs evolve, VLANs provide easy addition of new devices and users regardless of where they reside, making the network more adaptable to changes in business requirements.

More to the point, they can scale the network without compromising security, performance, or manageability, ensuring that as the network grows, it remains efficient and secure.

This capability is particularly beneficial for companies with fluctuating needs, such as seasonal companies or those expanding into new markets. You can also design a scalable architecture that can band together users from different geographical regions under the same VLAN.

In addition, VLANs facilitate the integration of new technologies and services, enabling you to innovate without disrupting existing operations.

If you know how to set up a physical network, you’ll feel right at home configuring VLANs. Here are the general steps to get the job done.

Creating a VLAN

You have two approaches to creating a VLAN on a managed switch. The first is CLI (command line interface), where you get to flex your coding muscles. In case command lines aren’t your thing, there’s always the option of using the switch’s web interface.

With CLI:

1. Log in to the switch’s CLI.
2. Use the configure terminal command to enter global configuration mode.
3. Use the vlan command, followed by the name command to assign a name (we’ll use HA as in HostingAdvice). For example:

switch# configure terminal

switch(config)# vlan 10

switch(config-vlan)# name HA_VLAN

4. Use the exit command to exit VLAN configuration mode.

With web interface:

1. Log in to your switch’s web interface using a web browser.
2. Navigate to the VLAN configuration section, something like ‘VLAN Management’ or ‘VLAN Settings’.
3. Look for the option to add or create a new VLAN.
4. You’ll need to specify the VLAN ID and name.
5. Apply the settings.

From here on, the switch will implement the VLAN configuration. Mind you, this is by no means a definitive guide as steps may vary depending on the specific switch model and its operating system.

Assigning Ports to a VLAN

When creating a VLAN, you’ll need to assign specific ports to VLANs, as well as specify whether they should be access or trunk ports. It’s worth repeating that the former works with a single VLAN, while the latter functions with multiple VLANs.

The default mode is different between switch models and vendors, so it’s best to consult your switch’s documentation.

In both scenarios, you first need to check out the port number on the switch where you want the connection to happen. Then, access the switch’s configuration mode using the CLI or web interface.

To assign a port to a VLAN as an access port, use these commands:

interface

switchport mode access

switchport access vlan

For a trunk post, commands are slightly different:

interface

switchport mode trunk

switchport trunk allowed vlan

Once again, you’ll need to follow vendor-specific guidelines and find the relevant section and settings in the web interface to specify either the specific port for access mode or allowed VLANs for the trunk mode.

VLAN Routing (Inter-VLAN Routing)

Any time devices in one VLAN need to communicate with their counterparts in another VLAN, the traffic must be routed through a routing device — a process known as inter-VLAN routing. To make it happen, you need a router or a Layer 3 switch.

If you recall (or simply scroll up), I briefly mentioned that setup when talking about private VLANs. That’s the router-on-a-stick (ROAS) network design, where you connect a router with a single physical link to a switch and do IP routing between VLANs.

The router’s smart software lets you configure a single interface to act like multiple interfaces, each representing a different VLAN.

You only need one physical connection between the router and switch to route traffic between different VLANs. The majority of today’s inter-VLAN routing implementations go the ROAS route, such as directing traffic between VLANs in a corporate network.

For network designs, it’s pretty undemanding as you require fewer physical interfaces on the routers, and you gain granular control over traffic between VLANs.

A good chunk of your VLAN-related responsibilities is to be aware of potential vulnerabilities and what you can do to mitigate or outright eliminate them. Here are the primary threats you’ll probably face and what you can do about them.

• VLAN Hopping Attacks: Occurs when an attacker sends traffic to a different VLAN than intended by exploiting misconfigured trunk ports. They fool a network device into sending traffic to a VLAN it shouldn’t be on, which provides the attacker with unauthorized yet very real access to sensitive data or resources.
  • Prevention: For starters, disable unused ports on your switches either physically or logically. It’s also a good idea to use specific VLANs for trunking and specific purposes, as well as set a native VLAN different from the default VLAN to avoid accidental VLAN hopping (sadly, it happens).
• Double-Tagging Attacks: A sneaky trick where attackers add fake tags to network packets by exploiting the 802.1Q tagging system. This lets them sneak these packets into different VLANs, even if they’re not supposed to be there. Many switches are tricked by these fake tags and forward the packets to the wrong place.
  • Prevention: The good news is that this attack only works if the attacker is already part of the native VLAN on the network. The solution is to disable VLAN 1 (often used as a default VLAN) on trunk ports and configure switchport modes properly as either access or trunk ports.
• Securing VLAN Trunks: One key security measure is to prune the VLANs allowed on each trunk port so that they are only allowed to carry traffic for necessary VLANs. What does that mean, exactly? Well, VLAN pruning limits the number of VLANs that can be carried on a trunk port. As a result of this selective removal, you minimize the attack surface and make it harder for attackers to exploit chinks in VLANs armor.
  • Example: On a switch, restrict a trunk to only carry VLANs 10, 20, and 30 using the switchport trunk allowed vlan 10,20,30 command.
• VLAN Access Control: The idea is to control and filter network traffic within a VLAN. To that extent, you should use Access Control Lists (ACLs) to enforce specific traffic policies between VLANs and block unauthorized access. You can define VLAN maps and attach them to VLANs so you can apply a single access policy across the VLAN or have different policies across different VLANs.

Hopefully, you now have a better understanding of the dangers lurking out there and how to reduce the risk of attacks in the first place. Prevention before protection, I say.

It’s time to show you where VLANs are particularly valuable, demonstrating their versatility in diverse network environments.

Corporate Networks

In corporate settings, VLANs are widely used to take network organization and security to another level by segmenting users into different logical networks based on their roles or departments.

This prevents unauthorized access to important information, as users can only access the resources relevant to their role.

That way, HR can be isolated from Finance and IT, reducing the risk of data breaches and making sure that compliance with data protection regulations is in order.

Bottom line: isolating confidential data and limiting broadcast domains makes corporate networks more secure and better organized.

Data Centers

This one is kind of obvious. VLANs enable data centers to segment traffic between different customers or applications, optimizing resource allocation and boosting data flow control across virtualized environments.

Such a setup also supports multi-tenant architectures, allowing different customers to operate in the same physical environment while maintaining network security and performance.

To put it simply, VLANs facilitate efficient resource management and traffic optimization. By creating separate instances for different applications or client needs, data centers can better manage bandwidth and control network traffic, particularly since VLANs can simplify load balancing.

All in all, a win-win for both sides.

Educational Institutions

Schools and universities benefit from VLANs by creating dedicated networks for students, faculty, and administration. This slicing and dicing allows these educational institutions to manage bandwidth effectively and restrict access to sensitive data, such as student records or financial information.

VLANs are also used to prioritize academic applications or online learning tools, seeing to it that students have access to the resources they need without interference from unrelated network traffic.

This structure bolsters network security, enabling the seamless distribution of educational resources across departments without any butting in.

VoIP Networks

VLANs are often used to prioritize voice traffic in VoIP systems. Moving voice traffic away from regular data traffic and getting it its own space leads to low latency and high-quality calls, thereby improving call performance.

By dedicating a specific VLAN for voice services, you can ensure that VoIP calls receive the necessary bandwidth and priority, reducing issues like dropped calls, choppy audio, delays, and/or distortions of any kind. Plus, it’s much simpler to manage and troubleshoot voice services.

Guest Networks

As effective solutions for managing guest access in offices or public spaces go, VLANs are among the very top.

Simply put, they provide internet access to visitors without giving them access to the main network and by proxy, compromising the security of your internal networks.

This isolation protects classified data and resources from potential threats posed by unauthorized devices while still providing a convenient service for visitors.

You can also limit bandwidth usage (ideally on a sliding scale to align with utilization), preventing guest activities from disrupting critical business operations. So, next time you’re in a hotel, remember that VLAN is likely the one to “blame” for the slow guest WiFi.

There’s always room to step up your VLAN game — or at the very least, set up everything right from the start. Here are some useful and, more importantly, proven tips.

In the pantheon of tech acronyms, VLAN perhaps isn’t all that well-known, but it’s certainly well-equipped to deal with whatever you throw at it when organizing your network.

Remember, successful implementation begins with careful planning and configuration and continues with regular monitoring. Those are the ingredients for a more secure, efficient, and manageable network.