When configuring network switches, especially in enterprise-grade environments like those using Aruba devices, understanding the difference between tagged and untagged ports is essential. This knowledge is particularly important when setting up VLANs (Virtual Local Area Networks), which allow you to segment traffic efficiently across your network. Knowing when to use tagged vs untagged on Aruba switches can help you avoid connectivity issues, maintain security, and ensure your network is functioning at its best.
Understanding VLAN Basics
A VLAN is a way to logically divide a physical network into separate broadcast domains. Each VLAN is assigned a unique VLAN ID, and traffic within that VLAN remains isolated from other VLANs unless routed intentionally. Aruba switches, like many other managed switches, use VLANs to handle network segmentation and improve both performance and security.
When it comes to VLANs, ports on a switch can be configured as either tagged or untagged. The terms refer to how VLAN information is handled on Ethernet frames that pass through those ports.
What is a Tagged Port?
A tagged port carries traffic for one or more VLANs and includes VLAN ID information in each Ethernet frame. These VLAN tags follow the IEEE 802.1Q standard, which adds a small header to each frame indicating which VLAN it belongs to.
- Used in trunk links between switches or between switches and routers.
- Can carry multiple VLANs simultaneously.
- The receiving device must understand VLAN tagging to process the frames correctly.
Tagged ports are essential when you want to connect different parts of the network that use multiple VLANs. Aruba switches let you specify which VLANs are allowed on each tagged port, ensuring controlled access.
What is an Untagged Port?
An untagged port, in contrast, is assigned to a single VLAN. When a frame is sent from the switch through an untagged port, the VLAN tag is removed. Similarly, when a frame arrives on an untagged port, the switch assumes it belongs to the untagged VLAN assigned to that port.
- Used to connect end devices like computers, printers, or IP phones.
- Traffic from these ports is only part of one VLAN.
- No VLAN tagging is visible to the end device.
On Aruba switches, you can designate one untagged VLAN per port. This simplifies connectivity for users and devices that don’t support VLAN tagging themselves.
Tagged vs Untagged in Real-World Aruba Configuration
Let’s take a practical example to show how tagged and untagged settings are used on Aruba switches. Suppose you have three VLANs: VLAN 10 for office computers, VLAN 20 for IP phones, and VLAN 30 for management. You may want to configure a trunk port (tagged) to connect to another switch, and access ports (untagged) for desktop computers.
Trunk Port Example (Tagged)
To create a trunk port on an Aruba switch that carries VLANs 10, 20, and 30, you would use commands or the web interface to assign the port as tagged for those VLANs:
- Port 1/1/1 is set as tagged for VLAN 10, 20, 30.
- Frames are sent with VLAN ID headers.
- The connected switch must be configured the same way.
This setup allows inter-switch communication for all defined VLANs.
Access Port Example (Untagged)
Now let’s say you have a desktop computer connected to port 1/1/2, and it should only access VLAN 10:
- Port 1/1/2 is set as untagged for VLAN 10.
- Frames are sent and received without VLAN tags.
- The switch internally maps all traffic from that port to VLAN 10.
This allows end devices to communicate on a VLAN without needing any knowledge of VLAN tagging.
How Aruba Switches Handle Tagged and Untagged VLANs
Aruba switches provide flexible VLAN configuration through their CLI (Command Line Interface) or web GUI. For each port, you can define:
- One untagged VLAN (also known as the native VLAN).
- Multiple tagged VLANs, depending on your network requirements.
The untagged VLAN typically handles default or native traffic, especially in cases where legacy devices are in use. Tagged VLANs are for traffic that must retain VLAN identification across multiple network segments.
Default Behavior
By default, Aruba switches assign all ports to VLAN 1 as untagged. This means that if you don’t configure anything, all ports belong to the same VLAN and will behave like a basic unmanaged switch. For effective VLAN segmentation, manual configuration is necessary.
Common Use Cases for Tagged and Untagged Ports
Tagged Port Use Cases
- Trunk links between switches
- Uplinks to routers or firewalls that support VLAN routing
- Connecting to wireless access points handling multiple SSIDs/VLANs
Untagged Port Use Cases
- Connecting to standard user devices (PCs, printers)
- Devices that do not support VLAN tagging
- Simplifying network access for guests or employees
Troubleshooting VLAN Configuration on Aruba
Misconfigured VLAN tagging often leads to connectivity issues. Here are a few common problems and solutions:
- Issue: Device cannot access the network.
- Cause: Port is tagged when it should be untagged.
- Fix: Change the port to untagged VLAN.
- Issue: VLAN traffic not passing between switches.
- Cause: VLAN is not tagged on trunk ports on both switches.
- Fix: Ensure matching VLAN tag settings on both sides.
- Issue: Network loops or broadcast storms.
- Cause: Improper VLAN tagging or trunk configuration.
- Fix: Double-check port roles and use Spanning Tree Protocol (STP).
Best Practices for VLAN Tagging on Aruba Switches
- Use descriptive VLAN names to avoid confusion during configuration.
- Document all VLAN IDs and port assignments for easier maintenance.
- Regularly audit switch configurations to ensure compliance with network policies.
- Apply access control where necessary to limit cross-VLAN traffic.
- Test new configurations during off-hours to avoid disrupting production traffic.
The difference between tagged and untagged ports is crucial in setting up Aruba switches correctly. Tagged ports are best suited for trunk links and multiple VLANs, while untagged ports are ideal for single VLAN access to end-user devices. Understanding when and how to apply these settings ensures a reliable and secure network infrastructure. With careful planning, consistent documentation, and adherence to best practices, configuring VLANs on Aruba devices becomes a manageable and essential part of network design.