How to interconnect two aggregation switches

To interconnect two aggregation switches, use link aggregation technologies like MLAG, MC-LAG, or EtherChannel to combine multiple physical links into a single logical connection for redundancy and increased bandwidth.Key ConceptsAggregation switches consolidate traffic from multiple access switches and forward it to core switches or routers. Interconnecting two aggregation switches ensures high availability, load balancing, and failover in case one switch or link fails . The main technologies used are:MLAG (Multi-Chassis Link Aggregation): Aggregates ports across two switches to appear as a single logical link to connected devices, providing active-active Layer 2 redundancy and efficient bandwidth utilization .MC-LAG (Multi-Chassis LAG in UniFi): Similar to MLAG, used in UniFi networks to connect two ECS-Aggregation switches, enabling seamless failover and load balancing .EtherChannel (Cisco): Combines multiple physical links into a single logical channel, which can be configured as static or dynamic (LACP) and supports trunking for multiple VLANs .Steps to Interconnect Two Aggregation SwitchesSelect Ports for Aggregation Choose multiple ports on each switch that will form the aggregated link. Ensure all ports have the same speed and use identical SFP modules or DAC cables for proper negotiation .Configure Link AggregationMLAG/MC-LAG: Configure one switch as the primary (Top Switch) and the other as secondary (Bottom Switch). Define the aggregated ports and assign them to the MLAG/MC-LAG group. Save the configuration on both switches .EtherChannel (Cisco): Create a port channel on each switch, add the selected ports, and configure LACP or static mode. Ensure the port channel is trunked if multiple VLANs are required .Connect the Switches Physically Use multiple cables to connect the selected ports between the two switches. For redundancy, run cables over separate physical paths to minimize simultaneous failures .Verify Configuration Check that the aggregated link is active and that all ports are participating. Test failover by disconnecting one link to ensure traffic continues over the remaining links.Consider Spanning Tree Protocol (STP) MLAG and MC-LAG allow active-active links while maintaining STP integrity. Ensure STP is properly configured to prevent loops, or rely on the MLAG/MC-LAG distributed port channel to handle Layer 2 multipathing .Best PracticesUse identical switch models and firmware versions for MLAG/MC-LAG to avoid compatibility issues .Aggregate at least two or more links to maximize bandwidth and redundancy.Label and document port assignments to simplify troubleshooting.Monitor link status and traffic to ensure optimal performance. By following these steps, you can interconnect two aggregation switches to achieve high availability, increased throughput, and seamless failover in your network infrastructure .