Switch Stacking allows you to combine multiple ECS-S switches into a single logical switch, managed as one device in UniFi Network. The stacked switches are interconnected with stacking cables in a ring topology and share unified control and management planes, so the entire stack behaves like a single high-port-count switch.

Switch Stacking is a component of UniFi's full-stack high availability and redundancy solution. For more information, see our High Availability Overview.

Benefits

• Cross-stack link aggregation: Aggregated links (LAGs) can span ports on different stacked switches. An uplink or a client connection built this way keeps working even if an entire switch fails, not just a single port or cable.
• Resiliency against switch failure: If a switch in the stack goes offline, the remaining switches continue forwarding traffic and the stack remains fully manageable, with no action required.
• Unified management: The stack appears as a single device in UniFi Network. All ports across all stacked switches are shown in one port panel, and configuration changes are applied to the entire stack through the single stack entry. You never need to manage the switches individually.
• Grow as demand increases: A stack can be extended at any time by connecting an additional switch into the sacking ring. The new switch joins automatically, adding port capacity without reconfiguration or downtime for the rest of the stack.

Requirements

• Supported devices: ECS-48S-PoE, ECS-24S-PoE, ECS-48S, and ECS-24S.
• Matching port count: All switches in a stack must have the same port count. A 24-port switch cannot join a stack of 48-port switches.
• Stack size: Up to 4 switches per stack. This limit will be increased in a future release.
• Stacking cables: The switches must be interconnected with QSFP stacking cables, such as the UACC-DAC-QSFP28, in a ring topology, where the last switch connects back to the first. The ring is required because it provides two paths between any two switches; if a single cable or switch fails, traffic and stack management continue over the remaining path instead of splitting the stack.
• UniFi Network Application: Version 10.6 or later.

Common Stacking Operations

Creating a Stack

Switches can only join a stack in their factory default state. If a switch was previously adopted or configured, reset it to factory defaults using its pinhole reset button before connecting it to the stacking ring.

A stack can be created in two ways:

Adopting a New Stack

1. Connect the stacking ports of all switches with stacking cables, forming a complete ring (the last switch connects back to the first).
2. Connect the stack to your network and power on all switches.
3. In UniFi Network, adopt the stack. It appears and is adopted as a single device.

Adding a Switch to an Existing Stack

1. Connect the new switch into the stacking ring of an existing stack and close the ring.
2. The switch is automatically admitted into the stack. No manual configuration or separate adoption is needed.

Creating a Cross-Stack LAG

A cross-stack LAG can serve as an uplink for the stack or connect a downstream device, such as a server or another switch. Configure the downstream end of the aggregated link first:

• Uplink LAG: configure the cross-stack LAG on the stack first, then the matching LAG on the upstream switch.
• Downlink LAG: configure the matching LAG on the downstream device first, then the cross-stack LAG on the stack.

To configure the cross-stack LAG on the stack:

1. In UniFi Network, navigate to Settings > High Availability > Stacking.
2. Select your stack group.
3. Next to Cross-Stack LAG Membership, click Configure.
4. Select the ports to aggregate. For maximum redundancy, choose ports on at least two different switches in the stack.
5. Click Save.

Note: It is recommended to set the same fixed speed on all ports in the LAG.

Growing a Stack

1. Disconnect one stacking cable in the ring and connect the new switch in its place, then close the ring again with an additional stacking cable.
2. UniFi Network shows the new switch joining the stack and syncing its firmware.
3. Once the firmware sync completes, the new switch's ports appear in the stack's port panel and are ready to use.

Note: If the stack is already at its maximum size, the new switch will not join until another switch is removed.

Removing a Switch from a Stack

1. Disconnect the stacking cables from the switch you want to remove and reconnect the remaining switches to close the ring.
2. Reset the removed switch to factory defaults using its pinhole reset button.
3. Adopt the switch in UniFi Network as a standalone (non-stacked) switch.

Replacing a Failed Switch

1. Disconnect the failed switch and remove it from the rack.
2. Install the replacement switch in its place.
3. Reconnect the stacking cables to close the ring.

The replacement switch is automatically admitted into the stack, syncs its firmware, and receives the stack's configuration. The stack remains fully operational and manageable throughout the replacement.

Note: If the removed switch is reset to defaults and reconnected to the network as a standalone device before the replacement is added, the replacement will not inherit its configuration.