A switch can aggregate multiple links into a single logical connection and then mirror traffic from that aggregated group to another port for monitoring or analysis.

Aggregation Overview

Aggregation, often implemented via Link Aggregation Control Protocol (LACP) or static link aggregation, combines multiple physical links into a single logical link. This increases bandwidth, provides redundancy, and reduces bottlenecks between access and core layers in a network . Aggregation switches consolidate traffic from multiple access switches or devices and forward it efficiently to core switches or routers .

Port Mirroring Overview

Port mirroring copies traffic from one or more source ports to a designated destination port for monitoring, analysis, or troubleshooting . It allows network administrators to inspect live traffic without interrupting normal operations. A switch can mirror multiple ports simultaneously, but there are limits depending on the switch model (e.g., up to eight source ports per mirror session on some Datto switches), .

Aggregation and Mirroring Together

When a switch performs aggregation first, the mirrored traffic can include all packets traversing the aggregated link. Key points include:

• Mirroring an aggregated group: You can mirror traffic from a Link Aggregation Group (LAG) to a monitoring port, capturing all combined traffic from the member links .
• Limitations: Individual ports within a LAG cannot be mirrored separately if they are part of the aggregation. The mirror must target the entire aggregated group .
• Use cases: This setup is useful for monitoring high-bandwidth connections, such as uplinks from access switches to aggregation switches, or for analyzing traffic from multiple servers connected via aggregated links .

Best Practices

• Ensure the destination port for mirroring is not part of the aggregated group.
• Monitor the bandwidth of the mirrored traffic to avoid overloading the monitoring port.
• Use aggregation for redundancy and performance, and mirroring for analysis and troubleshooting, keeping in mind that mirroring does not affect the aggregated link's performance directly . By combining aggregation and mirroring, network administrators can maximize throughput while maintaining visibility into network traffic for diagnostics, security, or performance monitoring.