An Empirical Study on Port Mirroring and SPAN Performance in Enterprise Switches

Abstract

Port mirroring, also known as Switched Port Analyzer (SPAN), is a common method used in enterprise
networks to duplicate packet flows for analysis, intrusion detection, and troubleshooting. Despite its popularity,
concerns remain about the performance reliability of SPAN under high network loads—specifically regarding
dropped packets, buffer overflows, and latency in the mirrored traffic. This paper presents an empirical
benchmarking study of SPAN functionality across Cisco Catalyst and HP ProCurve switches. Using controlled
traffic generation and packet capture tools, we evaluate mirroring accuracy, CPU load, and loss rates under
incremental load conditions ranging from 10% to 100% link utilization. Our results indicate that while both
platforms perform reliably below 70% utilization, mirrored traffic suffers increasing packet loss and timing
inaccuracies as throughput rises, particularly under bursty traffic scenarios. We also compare SPAN
performance with that of dedicated hardware-based TAP (Test Access Point) devices and find that TAPs offer
superior fidelity at the cost of flexibility. Based on our analysis, we propose a dynamic, load-aware SPAN
configuration model and present best practices for deploying and scaling switch-level monitoring
infrastructure in high-throughput environments.