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What Is Private VLAN and How It Works?

Updated on Feb 8, 2022 by
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What Is Private VLAN?

Private VLAN (PVLAN), also referred to as port isolation, is a layer 2 network segmentation technology. It allows for port isolation and traffic segmentation within the same IP segment. Implementing PVLAN in a shared network environment provides significant IP address savings and enhances switch port security at the layer 2 level.

Compared to VLAN, the private VLAN has multiple differences.

 Aspect  VLAN  Private VLAN
 Layer  VLAN operates at Layer 2 and Layer 3  PVLAN is a method of device segmentation that operates at Layer 2
 IP Subnet  Different VLANs belong to different IP subnets  PVLANs belong to the same IP subnet
 Spanning
 Can span multiple switches
 Can span only one switch
 Application  Vlan is the basic requirement environment for all local area networks.
PVLAN is necessary for specific requirements, where endpoints of the same VLAN should not communicate with each other. For example, mainly in ISP scenarios to prevent different customers from communicating with each other on the same LAN segment.

Port Types of PVLAN

Typically, there are three VLAN port types:

Promiscuous Port: This port type is able to send and receive frames from any other ports in the VLAN. It usually connects with a layer 3 switch, router, or other gateway devices.

Isolated Port: This type of port is located within a sub-VLAN and is dedicated to connecting with a host. It has limited communication capabilities and can only interact with promiscuous ports.

Community Port: Similar to isolated ports, community ports are also part of a sub-VLAN and connect with hosts. However, they can communicate with both promiscuous ports and other community ports within the same sub-VLAN.

VLAN Types of PVLAN

Within a private VLAN, VLANs are accessible in three types:

Primary VLAN: The primary VLAN, also known as the original VLAN, allows downstream frames to be transmitted from promiscuous ports to all host-connected ports within its sub-VLANs (secondary VLANs).

Isolated VLAN: As a secondary VLAN, the isolated VLAN restricts communication to only the switch ports (isolated ports) within the same isolated VLAN. Isolated ports can forward data to promiscuous ports in the primary VLAN but cannot communicate with each other, even within the same isolated VLAN.

Community VLAN: Another type of secondary VLAN is the community VLAN. Within the community VLAN, switch ports (community ports) can communicate with each other and with ports in the primary VLAN. But such a type of VLAN is also unable to communicate with other secondary VLANs, including other community VLANs.

How Does Private VLAN Work

How Does Private VLAN Work?

Generally, the private VLAN will go through the following stages :

1. The primary VLAN delivers frames downstream from the promiscuous port to all mapped hosts.

2. The isolated VLAN transports frames from the stub hosts upstream to the promiscuous port only.

3. Community VLANs allow bi-directional frame exchange within a single community group. Meanwhile, it will upstream data towards promiscuous ports.

4. Ethernet MAC address learning and forwarding procedures remain the same, as well as the broadcast/multicast flooding procedure within the boundaries of primary/secondary VLANs.

How to Set Up a Private VLAN on a Switch?

Here are general guidelines for the configuration process of private VLAN:

1. Log in to the switch: Use the appropriate management tool such as a command-line interface, web interface, or dedicated management software to log in to the switch's management interface.

2. Create a Primary VLAN: Create a Primary VLAN that will contain all the other secondary VLANs. Specify a VLAN ID and name to identify the Primary VLAN.

3. Create Secondary VLANs: Create a secondary VLAN for each device or group of devices that need to be isolated. Specify a unique VLAN ID and name to identify each secondary VLAN.

4. Configure Interfaces and Ports: Associate the interfaces or ports of the switch with the respective secondary VLANs or isolated ports. This controls communication and isolation between devices.

5. Configure Port Types: Based on requirements, configure the relevant ports as Promiscuous Ports, Community Ports, or Isolated Ports.

6. Configure Communication Permissions: Set which secondary VLANs can communicate with the Primary VLAN and which secondary VLANs can communicate with each other, based on your needs.

7. Apply the Configuration: Apply the configuration changes to make them take effect and ensure that the switch starts operating according to the new PVLAN settings.

Note: Setting up a private VLAN (PVLAN) on a switch may vary depending on the manufacturers and models of the switches. Please check the documentation or user guides provided by the switch manufacturer for detailed instructions. Taking the FS S5800-8TF12S switch as an example, you can follow the next steps to set PVLAN.

Step 1: Create primary and secondary VLANs and associate them.

Step 2: Configure isolated ports and community ports and bind them to the respective secondary VLANs.

Step 3: Configure interfaces as promiscuous ports, and map the promiscuous ports to the primary-secondary VLAN pair.

Step 4: If inter-VLAN routing is used, configure the primary switch virtual interface, and map secondary VLANs to the primary.

Step 5: Validate the private VLAN configuration.

The Benefits of Private VLAN

PVLAN provides a higher level of network isolation and access control, making it suitable for environments that require advanced levels of isolation and security.

  • Provide Security: PVLAN can restrict communication between devices and reduce potential attack surfaces. By placing devices in secondary VLANs or isolated ports, direct access between devices can be limited, thereby increasing network security. You can use a dedicated VLAN to separate the part of the organization that contains delicate data from the rest of the organization.

  • Provide Flexibility: PVLAN allows the creation of multiple secondary VLANs within a single VLAN and assigns different communication permissions to each secondary VLAN. This enables administrators to have granular access control over different devices or device groups as per their requirements, providing greater flexibility.

  • Simplified network configuration: PVLAN can simplify network configuration and reduce the number and complexity of VLANs. Compared to traditional VLANs, PVLANs can achieve more isolation and control within a single VLAN, eliminating the need for creating numerous VLANs to meet different isolation requirements.

  • IP address conservation: PVLAN can save IP address usage. Since secondary VLANs share the same IP subnet, fewer IP addresses can be used to fulfill the needs of multiple devices, reducing IP address wastage.

Benefits of PVLAN

Summary

Private VLAN is a network technology used to achieve fine-grained isolation and security. By utilizing primary VLANs, secondary VLANs, and isolated ports within a larger VLAN, private VLAN provides enhanced access control and device isolation, catering to specific security requirements while improving network reliability and security. FS, a global provider of communication and high-speed network system solutions, offers a variety of enterprise switches that support PVLAN for stable network configurations. Please visit FS.COM for more information.

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