Chapter 21 Configuring Span And Rspan; Understanding Span And Rspan - Cisco Catalyst 3750 Software Configuration Manual

Metro switch

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Configuring SPAN and RSPAN

This chapter describes how to configure Switched Port Analyzer (SPAN) and Remote SPAN (RSPAN)

on the Catalyst 3750 Metro switch.

For complete syntax and usage information for the commands used in this chapter, refer to the command

reference for this release.

This chapter consists of these sections:

You can analyze network traffic passing through ports or VLANs by using SPAN or RSPAN to send a

copy of the traffic to another port on the switch or on another switch that has been connected to a network

analyzer or other monitoring or security device. SPAN copies (or mirrors) traffic received or sent (or

both) on source ports or source VLANs to a destination port for analysis. SPAN does not affect the

switching of network traffic on the source ports or VLANs. You must dedicate the destination port for

SPAN use. Except for traffic that is required for the SPAN or RSPAN session, destination ports do not

receive or forward traffic.

Only traffic that enters or leaves source ports or traffic that enters or leaves source VLANs can be

monitored by using SPAN; traffic routed to a source VLAN cannot be monitored. For example, if

incoming traffic is being monitored, traffic that gets routed from another VLAN to the source VLAN

cannot be monitored; however, traffic that is received on the source VLAN and routed to another VLAN

can be monitored.

Enhanced-services (ES) ports cannot be SPAN or RSPAN source ports.

You can use the SPAN or RSPAN destination port to inject traffic from a network security device. For

example, if you connect a Cisco Intrusion Detection System (IDS) sensor appliance to a destination port,

the IDS device can send TCP reset packets to close down the TCP session of a suspected attacker.

Understanding SPAN and RSPAN, page 21-1

Configuring SPAN and RSPAN, page 21-9

Displaying SPAN and RSPAN Status, page 21-23

C H A P T E R

Catalyst 3750 Metro Switch Software Configuration Guide

Troubleshooting