Setting Up SPAN on a Switch | Performance and Fault Management: A Practical Guide to Effectively Managing Cisco Network Devices (Cisco Press Core Series)

On the Catalyst Series switches, there is a feature called SPAN, which is basically a way to monitor transmitted and received traffic on different ports or VLANs on the local switch. (SPAN stands for Switched Port Analyzer.)

TIP

When doing capacity planning, it is recommended to physically allocate one 10 Megabit or 100 Megabit Ethernet port on the switch specifically for the use of the SPAN feature. Doing so eases the pain of troubleshooting traffic through a switch by giving one dedicated port for a network analyzer or RMON probe.

The SPAN feature allows network troubleshooters to have one physical network analyzer or probe per switch and to locate it on only one port instead of having to physically move the analyzer from one segment to another to monitor the network. SPAN is definitely a fault management tool like CDP.

To set up SPAN on the switch use the following CLI set command:

 set span {src_mod/src_vlan} [rx|tx|both] enable

For more information on configuring the SPAN feature, refer to the documentation on CCO. (See the references at the end of this chapter for specific URLs.)