This white paper compares switch port mirroring with passive network TAPs for security, compliance, lawful interception, and performance analysis. SPAN ports are convenient and useful in low-throughput situations, but they are not truly passive and cannot guarantee complete data fidelity. Mirroring can alter packet timing, discard malformed or undersized frames, drop traffic during congestion, omit Layer 1 and Layer 2 details, and struggle with full-duplex links and VLAN environments. Because production traffic receives priority over mirrored traffic, packet loss may occur without warning, weakening troubleshooting results and the defensibility of forensic evidence. Passive TAPs provide a dedicated, non-intrusive copy of traffic at line rate, including errors and both directions. The paper

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