Episode 33: Port Mirroring and SPAN — Monitoring Network Traffic
When you need to monitor what’s actually happening inside your network, port mirroring is the go-to technique. This episode focuses on SPAN (Switched Port Analyzer) and its role in duplicating network traffic from one port or VLAN to another. You’ll learn how port mirroring enables real-time packet capture for diagnostic tools like Wireshark and how it supports security monitoring, troubleshooting, and compliance auditing. We explain the difference between local SPAN and RSPAN, how to configure mirrored sessions on different platforms, and why understanding traffic direction (ingress, egress, or both) matters.
We also discuss the limitations of SPAN, including oversubscription of monitoring ports, performance impacts, and what traffic may be filtered out by hardware constraints. Knowing how to set up SPAN properly—and how to interpret what you see—is critical for incident response, forensic analysis, and baseline reviews. Whether you're troubleshooting an issue with dropped packets or analyzing suspicious behavior, port mirroring provides direct insight into the flow of information across your switches. This is a must-know feature for network technicians, analysts, and exam takers alike.
