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Cisco LAN Switching Fundamentals by Basir Sakandar - CCIE No. 6040, David Barnes - CCIE No. 6563

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Local Switched Port Analyzer

Switched Port Analyzer (SPAN) allows for a protocol analyzer such as a sniffer to passively inspect traffic generated by a VLAN(s) or specific source port(s). SPAN is flexible enough that the source can be a single port or multiple ports, or VLAN traffic copied to a user-defined SPAN destination port. For example, any traffic that is received or transmitted by ports 10/3-5 is also forwarded to port 10/1. (See Example 12-11.) The source and destination port must be on the same switch for SPAN, also known as Local SPAN.

Example 12-11. Monitoring Multiple Ports
Switch1 (enable) set span 10/3-5 10/1
Destination     : Port 10/1
Admin Source    : Port 10/3-5 
!List of all ports that are monitored
Oper Source     : Port 10/3 
!List ...

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