How to use the aggregation and uplink mode of a switch

Switch aggregation combines multiple ports into a single logical link to increase bandwidth, provide redundancy, and optimize uplink connections.

What is Switch Aggregation

Switch aggregation, also called link aggregation or port trunking, allows multiple physical network ports to operate as a single logical connection. This increases total throughput, provides load balancing, and ensures redundancy if one link fails. Aggregation is commonly used in two scenarios: connecting multiple switches (switch-to-switch) or connecting high-performance devices like servers or NAS units (switch-to-client) to handle higher traffic loads .

Key Protocols

• LACP (Link Aggregation Control Protocol, 802.3ad): Dynamically manages aggregated links, ensures both ends agree on the configuration, and provides automatic failover .
• Static LAG: Requires manual configuration on both ends, prone to misconfiguration, and does not provide automatic failover .

Uplink Considerations

When connecting switches in a core-leaf topology:

• Use a high-capacity switch as the central hub.
• Connect peripheral switches to the core via dedicated uplinks.
• Aggregate two or more ports for each uplink to increase speed and resilience.
• Tag VLANs on the core switch to ensure proper traffic segmentation across leaf switches .

Step-by-Step Setup (UniFi Example)

1. Select Ports for Aggregation: Choose two or more sequential ports on the switch.
2. Enable LAG: In the UniFi Controller, select the ports → Edit → enable LACP.
3. Name the LAG: Assign a friendly name like "Core-Uplink" for easy management.
4. Apply VLANs: Tag all necessary VLANs (e.g., LAN, guest, IoT) on the aggregated ports.
5. Connect Devices: Plug the aggregated ports into the corresponding ports on the upstream switch or server.
6. Verify Traffic: Use port statistics to confirm load balancing and redundancy are active .

Best Practices

• Sequential Ports: Aggregated ports should be sequential in number.
• Limit Daisy-Chaining: Keep switch daisy-chain depth to 2 hops max to avoid latency and management complexity.
• Use SFP+ for High Throughput: For gateway-to-aggregation switch connections, SFP+ modules provide maximum bandwidth .
• Downstream First: Configure aggregation starting from the most downstream switch, then move upstream toward the core or controller .

Benefits

• Increased Bandwidth: Multiple ports combine to handle higher traffic.
• Redundancy: Traffic reroutes automatically if a link fails.
• Load Balancing: Distributes traffic evenly across aggregated links.
• Scalability: Additional links can be added without disrupting the network . By following these steps and best practices, you can effectively use a switch for aggregation and uplink, ensuring a high-performance, resilient network.