How to aggregate dual uplinks on a switch

Dual uplinks can be aggregated using Link Aggregation (LAG) or LACP to increase bandwidth and provide redundancy between switches or to a firewall/server.

Understanding Link Aggregation

Link Aggregation allows multiple physical ports to act as a single logical connection. This provides:

• Increased throughput: Traffic is split across multiple links, improving total bandwidth when multiple clients or flows are active .
• Redundancy: If one link fails, traffic continues over the remaining link(s) without downtime .
• Simplified management: The aggregated ports appear as a single interface to the network . Two main types exist:
• Static LAG: Manually configured on both ends; does not provide automatic failover and is prone to misconfiguration .
• LACP (802.3ad): Industry-standard protocol that dynamically manages aggregation, ensures both ends agree on settings, and provides automatic failover .

Steps to Aggregate Dual Uplinks

1. Verify device support: Ensure both switches or the switch and firewall support LACP or port aggregation .
2. Select ports: Choose the physical ports to aggregate. Ports should ideally be sequential and of the same speed .
3. Configure the downstream device first: Apply aggregation settings on the device closer to the client or server, then move upstream to the core switch .
4. Enable LACP: On both ends, configure the selected ports as a LAG or aggregated interface and enable LACP .
5. Connect cables: Plug in the physical links. For best redundancy, run cables over separate paths to avoid simultaneous failure .
6. Verify aggregation: Check the status to ensure the LAG is active and both links are participating. Most switches provide a status page or CLI command to confirm this .

Best Practices

• Use matching port speeds: Aggregation works best when all ports have the same speed and duplex settings .
• Avoid mixing device types: Ensure both ends support the same aggregation protocol; mixing static LAG and LACP can cause issues .
• Consider redundancy: For critical uplinks, use multiple paths and consider MC-LAG if supported for higher resilience .
• Test failover: Disconnect one link to confirm traffic continues over the remaining link without interruption .

Example Use Cases

• Switch-to-switch aggregation: Increases bandwidth between two switches and provides redundancy for inter-switch traffic .
• Switch-to-client/server aggregation: Useful for high-performance servers requiring more bandwidth than a single port can provide . By following these steps and using LACP, dual uplinks can be effectively aggregated to improve network performance and reliability.