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Networking Fundamentals · Intermediate

Port Mirroring (SPAN)

A switch feature that copies traffic from one or more ports or VLANs to a monitoring port for analysis.

Definition

Cisco calls it Switched Port Analyzer (SPAN), with RSPAN and ERSPAN variants that carry mirrored traffic across switches or over IP. Mirrored traffic can exceed the destination port's capacity, causing drops.

Example

monitor session 1 source interface g1/0/5 copies a server's traffic to a Wireshark laptop on g1/0/48.

Exam tip

To capture traffic on a switched network, you must use SPAN or a tap, because switches do not flood unicast.

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