UniFi link aggregation: the ultimate guide

Published onby Iron

UniFi link aggregation is a game-changer for network performance. Imagine transforming multiple network cables into one giant, super-speed "data highway." That's exactly what link aggregation does. It combines multiple Ethernet connections into a single logical connection, boosting speed, enhancing redundancy, and keeping your network running even if a cable fails.

Let's dive in!

Table of Contents

Link aggregation, also called port trunking, is the process of combining multiple Ethernet connections into one logical link. It provides higher bandwidth, increased reliability, and load balancing. The idea is simple: instead of one 1Gbps connection, you can combine two 1Gbps ports to get 2Gbps.

This concept is widely used in larger network setups, data centers, and business environments where fast, uninterrupted traffic flow is essential. UniFi makes this easy using the Link Aggregation Control Protocol (LACP). LACP dynamically manages link aggregation without manual intervention.

If you’re still on the fence, here are the key benefits of link aggregation.

1. More Bandwidth

Instead of a single 1 Gbps Ethernet connection, link aggregation allows you to combine multiple Ethernet ports. For example:

  • 2 x 1Gbps ports = 2Gbps
  • 4 x 1Gbps ports = 4Gbps This is especially useful when connecting a UniFi switch to a NAS, a file server, or other switches where heavy data transfer happens.

2. Failover & Redundancy

If one port or cable fails, traffic automatically switches to the remaining links. This ensures zero downtime. Without link aggregation, one broken cable could mean network downtime.

3. Load Balancing

Instead of all the traffic flowing through one port, link aggregation spreads it across multiple ports. This prevents a single port from being overwhelmed with too much traffic, making your network more efficient.

4. Improved Performance for NAS and Servers

File servers, backup devices, and NAS systems experience high traffic. If you frequently move large files, enable link aggregation on your NAS to dramatically reduce transfer times.

5. Better Switch-to-Switch Connectivity

Link aggregation is essential for connecting switches together. It lets you create a bigger "data highway" between them, ensuring fast communication between different parts of the network.

When people talk about link aggregation, they often mention LACP (Link Aggregation Control Protocol). So, what's the difference?

  • Manual Link Aggregation: You create the logical link manually. It works but is inflexible, and you must manually configure all connected devices.
  • LACP: This is a protocol that automates the setup. It automatically negotiates and activates aggregated links, making it much easier to manage.

For most users, LACP is the better choice since it automatically detects and configures connections. UniFi switches support LACP, so you’re in good hands.

Not all UniFi devices support link aggregation. Here’s a list of compatible devices.

Supported UniFi Devices

  • UniFi Switches (USW Series)
    • UniFi Switch Pro 16 PoE, 24 PoE, 48 PoE
    • UniFi Switch Enterprise 8/24/48
    • UniFi Switch Aggregation (USW-Aggregation, USW-Aggregation Pro)
  • UniFi Consoles
    • UniFi Dream Machine Pro (UDM Pro)
    • UniFi Dream Machine SE (UDM SE)

Unsupported Devices

  • UniFi Dream Router (UDR)
  • UniFi APs (Access Points) — Wi-Fi devices don't use Ethernet link aggregation
  • UniFi Cloud Key G2 Plus

UniFi uses LACP to manage link aggregation. Here’s how it works step-by-step:

  1. Port Bundling: Two or more Ethernet ports are "bundled" into a single logical port.
  2. Load Sharing: Traffic is split between the bundled ports using load-balancing algorithms.
  3. Redundancy: If one link fails, traffic automatically switches to the other links in the bundle.
  4. Speed Boost: The bandwidth of each port is combined, increasing total throughput.

Here’s a simple, step-by-step guide to enable link aggregation on your UniFi devices.

Step 1: Check Your Hardware

Make sure your switches and devices support link aggregation. For UniFi, the best devices are the UDM Pro, UDM SE, and the UniFi Aggregation Switch. You'll also need devices that support link aggregation, like a NAS or file server.

Step 2: Connect the Ethernet Cables

  • Plug two (or more) Ethernet cables into the ports you plan to aggregate.
  • If you’re aggregating a NAS, ensure the NAS has support for link aggregation or LACP.

Step 3: Configure the UniFi Switch

  1. Access UniFi Controller: Log in to your UniFi Network Controller.
  2. Select Your Switch: Go to Devices and click on your switch.
  3. Go to Ports: Find the ports you want to aggregate (e.g., port 1 & port 2).
  4. Aggregate the Ports: Select the ports, click Edit, and enable LACP.
  5. Name the LAG (Link Aggregation Group): Give your aggregation group a friendly name, like "NAS-Agg".
  6. Apply Changes: Click Apply and wait for the controller to update.

Step 4: Configure the Connected Device

If you’re connecting to a NAS (like Synology), enable LACP in the NAS's network settings.

Step 5: Test & Monitor

Use UniFi's port statistics to ensure load balancing is working. If you see both ports handling traffic, it’s working!

  • Use high-quality Ethernet cables (CAT6 or better) to avoid bottlenecks.
  • Avoid mismatched ports. If you combine a 1Gbps port with a 10Gbps port, traffic won't balance properly.
  • Monitor port usage via UniFi Controller to verify link aggregation is working as expected.
  • Label the aggregated ports in the controller to avoid confusion later.

Link aggregation is simple, but you may run into a few issues. Here are the most common problems and solutions.

1. LACP Isn't Working

  • Make sure LACP is enabled on both UniFi and the connected device.
  • Verify that you’re using compatible hardware and ports.

2. Ports Are Offline

  • Check for broken Ethernet cables.
  • Confirm that the ports are assigned to the correct LAG (Link Aggregation Group).

3. Load Balancing Isn’t Happening

  • Load balancing isn’t 50/50. It depends on the hashing algorithm used by the switch.
  • The distribution of traffic can be uneven, but it should still use multiple links.

You should use link aggregation if you want to:

  • Connect switches for higher throughput.
  • Connect a NAS or file server for faster file transfers.
  • Ensure redundancy — No single point of failure.
  • Increase bandwidth — Get a 2Gbps (or higher) connection instead of 1Gbps.

If you don’t have any of these needs, you probably don’t need link aggregation.

Final Thoughts

Link aggregation is a powerful tool that brings faster speeds, redundancy, and load balancing to your network. If you’re using a NAS, file server, or multiple switches, it’s a must-have. With UniFi, setting up link aggregation is simple thanks to LACP. Whether you're using a UDM Pro, UDM SE, or UniFi Switch, you can easily boost performance.

Need help managing your UniFi Controller? We can help. At UniHosted, we offer cloud-hosted UniFi controllers, making it easy to set up link aggregation. If you would like me to personally walk you through UniHosted, you can schedule a call with me here.

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