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Catalyst 2940 Switch Software Configuration Guide
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Chapter20 Configuring SPAN
Configuring SPAN
Configuring SPAN
This section describes how to configure SPAN on your switch. It contains this configuration information:
•SPAN Configuration Guidelines, page 20-6
•Creating a SPAN Session and Specifying Ports to Monitor, page 20-6
•Creating a SPAN Session and Enabling Ingress Traffic, page 20-8
•Removing Ports from a SPAN Session, page 20-9

SPAN Configuration Guidelines

Follow these guidelines when configuring SPAN:
•The destination port cannot be a source port; a source port cannot be a destination port.
•You can have only one destination port.
•An EtherChannel port can be a SPAN source port; it cannot be a SPAN destination port.
•For SPAN source ports, you can monitor sent and received traffic for a single port or for a series or
range of ports.
•When you configure a switch port as a SPAN destination port, it is no longer a normal switch port;
only monitored traffic passes through the SPAN destination port.
•You can configure a disabled port to be a source or destination port, but the SPAN function does not
start until the destination port and at least one source port is enabled.
•A SPAN destination port never participates in any VLAN spanning tree. SPAN does include BPDUs
in the monitored traffic, so any spanning-tree BPDUs received on the SPAN destination port for a
SPAN session were copied from the SPAN source ports.
•When SPAN is enabled, configuration changes have these results:
–
If you change the VLAN configuration of a destination port, the change is not effective until
SPAN is disabled.
–
If you disable all source ports or the destination port, the SPAN function stops until both a
source and the destination port are enabled.

Creating a SPAN Session and Specifying Ports to Monitor

Beginning in privileged EXEC mode, follow these steps to create a SPAN session and specify the source
(monitored) and destination (monitoring) ports:
Command Purpose
Step1 configure terminal Enter global configuration mode.
Step2 no monitor session {session_number | all |
local | remote}Clear any existing SPAN configuration for the session.
For session_number, specify 1.
Specify all to remove all SPAN sessions, local to remove all local
sessions, or remote to remove all remote SPAN sessions.