Understanding VLANs with Unmanaged Switches: Insights into Building a Robust UniFi Network

Hi, I’m Juan David, Tech Lead Support at Flytec and a UniFi Certified Trainer. If you’re diving into networking, VLANs, and UniFi setups, welcome! Today, we’ll discuss a fascinating question I recently encountered online: can you configure VLANs on downlink ports connected to unmanaged switches and achieve the desired network behavior?

This blog is written to help tech-savvy enthusiasts, geeks, and network engineers like you understand the nuances of VLANs with unmanaged switches and avoid common pitfalls.

Scenario Overview: The Setup at Hand

Here’s the proposed setup we’ll analyze:

1. UniFi Cloud Gateway:
• Port 3: Downlink configured for VLAN 20 with a network of 10.0.20.0/24.
• Port 4: Downlink configured for VLAN 30 with a network of 10.0.30.0/24.
2. Unmanaged Switches:
• Port 3 connects to an unmanaged switch for VLAN 20 devices.
• Port 4 connects to another unmanaged switch for VLAN 30 devices.
3. Goal: Devices connected to each unmanaged switch should receive IPs in their respective VLAN networks (10.0.20.0/24 and 10.0.30.0/24).
4. Concern: Will unmanaged switches handle VLAN-tagged traffic properly, or will this setup fail?

The Basics: VLANs and Unmanaged Switches

VLANs (Virtual Local Area Networks) allow you to segment networks logically within a single physical network. Each VLAN operates as a separate broadcast domain, ensuring better organization and security.

However, unmanaged switches don’t inherently understand VLAN tags. They pass all traffic untagged, meaning they can’t differentiate between VLANs. This creates challenges, especially when VLAN-tagged traffic enters the unmanaged switch.

How This Setup Works

The setup described will work under specific conditions:

1. Downlink Ports on UniFi Cloud Gateway:
• When you configure a downlink port’s native VLAN (e.g., VLAN 20 for Port 3), any untagged traffic received will be assigned to that VLAN.
• Devices connected to the unmanaged switch will receive IP addresses in the 10.0.20.0/24 range via DHCP.
2. Traffic Flow:
• Since unmanaged switches strip VLAN tags, traffic is treated as untagged on these switches.
• This setup assumes end devices won’t send VLAN-tagged packets. The Cloud Gateway assigns tags to outbound traffic based on the native VLAN of the port.

Key Consideration:

This setup works because unmanaged switches don’t interact with VLAN tags. However, if VLAN-tagged traffic needs to traverse these switches, communication may break down.

Pitfalls and Common Mistakes

Let’s address some common pitfalls to ensure your network remains robust:

1. Adding a Managed Switch or Access Point

• If a managed switch or VLAN-aware AP connects to an unmanaged switch, the unmanaged switch might strip VLAN tags from frames. This disrupts communication.
• Example: If an AP broadcasts SSIDs on VLAN 30, but the upstream switch (unmanaged) strips tags, devices won’t get DHCP leases on VLAN 30. Instead, they’ll fall back to default IPs (e.g., 169.x.x.x).

Solution: Use managed switches that respect VLAN tagging in such scenarios.

2. Misconfiguring Native VLANs

• Setting a VLAN as the native (primary) network on a port where VLAN-aware devices are connected can cause issues.
• Example: If VLAN 30 is the native VLAN for Port 4 and an AP connects to this port, it can’t broadcast SSIDs on VLAN 30 effectively.

Solution: Avoid configuring SSIDs and APs on the same VLAN set as the native VLAN of their uplink ports. 

3. Untagged vs. Tagged Traffic

• Unmanaged switches handle only untagged traffic. If tagged traffic arrives at these switches, it might fall into the native VLAN or get dropped.

Solution: Ensure all traffic passing through unmanaged switches is untagged.

4. Scaling the Network

• If additional switches or APs are added downstream, unmanaged switches can become a bottleneck, preventing proper VLAN tagging.

Solution: Replace unmanaged switches with managed ones for scalability.

VLAN Troubleshooting Tips for UniFi Networks

If you run into issues, UniFi provides tools like the VLAN Viewer to identify and resolve problems. Here’s a quick troubleshooting guide:

1. Identify the Problematic VLAN:
• Use the VLAN Viewer in the UniFi Controller to pinpoint misconfigured ports.
2. Check Port Configurations:
• Ensure VLAN tagging is correctly configured along the path from the device to the gateway.
3. Avoid Common Mistakes:
• VLAN not tagged on upstream switch ports.
• Native VLAN misconfigured for APs or devices.
4. Validate Configuration:
• Confirm that devices on VLANs receive the correct IP range and can communicate with the gateway.

Recommendations for an Optimal Network

1. Plan for Scalability:
• Start with managed switches to future-proof your network for VLAN expansion and AP integrations.
2. Simplify Configurations:
• Use UniFi tools like VLAN Viewer to monitor and maintain network health.
3. Stay Updated:
• Regularly check UniFi’s user guides and forums for tips and best practices.

 Final Thoughts

VLANs are an excellent tool for organizing and securing your network. However, understanding their interaction with unmanaged switches is crucial. The setup we discussed works within specific parameters but can face challenges if scaled or altered.

 If you’re new to networking, don’t hesitate to experiment and learn. As always, Flytec is here to help! If you have any questions, feel free to contact us!