VLAN Fundamentals in Junos OS


Virtual Local Area Networks (VLANs) play a pivotal role in segregating broadcast domains, enhancing network efficiency, and improving security. In Juniper's Junos OS, the configuration and management of VLANs are both intuitive and robust. This post introduces you to the fundamentals of VLANs in Junos OS and offers insights into their effective deployment.

1. What is a VLAN?

At its core, a VLAN is a logically segmented network within a physical network. Each VLAN is a distinct broadcast domain, ensuring data broadcasted within one VLAN isn't visible to devices outside it.


2. VLAN Types in Junos OS

Native VLAN:

Voice VLAN:

3. VLAN Configuration in Junos OS

Defining a VLAN:

user@switch# set vlans [vlan-name] vlan-id [vlan-id-number]

Assigning Ports to a VLAN:

user@switch# set interfaces [interface-name] unit 0 family ethernet-switching vlan members [vlan-name]

Configuring a Trunk Port:

user@switch# set interfaces [interface-name] unit 0 family ethernet-switching interface-mode trunk
user@switch# set interfaces [interface-name] unit 0 family ethernet-switching vlan members [vlan-list]

4. VLAN Interfaces (RVI) in Junos

VLANs primarily operate at Layer 2. However, for inter-VLAN routing, a Layer 3 construct, known as a Routed VLAN Interface (RVI), is used.

Configuring RVI:

user@switch# set interfaces vlan unit [vlan-id-number] family inet address [ip-address]

5. Monitoring and Troubleshooting VLANs

Display VLAN Information:

user@switch> show vlans

Display VLAN Assignments for an Interface:

user@switch> show ethernet-switching interfaces [interface-name]

Best Practices:

  1. Descriptive Naming: Always use descriptive VLAN names to simplify management.
  2. Consistent Native VLANs: Ensure the native VLAN is consistent across trunk links.
  3. Avoid VLAN 1: For security reasons, it's a good practice to avoid using the default VLAN (VLAN 1).


VLANs are instrumental in crafting efficient, secure, and organized networks. Junos OS offers a comprehensive set of tools and configurations to seamlessly integrate VLANs into your network architecture.

Dive deeper into the world of Junos OS with us as we unravel more concepts, configurations, and best practices. Happy networking, and stay connected for more insights into the dynamic world of Junos OS!

© Ben Jacobson.RSS