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Catalyst 2950 Desktop Switch Software Configuration Guide
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Chapter 21 Configuring SPAN and RSPAN
Configuring SPAN
• 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.
• A trunk port can be a source port or a destination port. Outgoing packets through the SPAN
destination port carry the configured encapsulation headers—either Inter-Switch Link (ISL) or
IEEE 802.1Q. If no encapsulation type is defined, the packets are sent in native form.
• 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 or source VLAN are enabled.
• For received traffic, you can mix multiple source port and source VLANs within a single SPAN
session. You cannot mix source VLANs and filter VLANs within a SPAN session; you can have
source VLANs or filter VLANs, but not both at the same time.
• You can limit SPAN traffic to specific VLANs by using the filter vlan keyword. If a trunk port is
being monitored, only traffic on the VLANs specified with this keyword is monitored. By default,
all VLANs are monitored on a trunk port.
• 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.
–
If the source is a VLAN, the number of ports being monitored changes when you move a port
in or out of the monitored VLAN.
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
Step 1
configure terminal Enter global configuration mode.
Step 2
no monitor session {session_number | all |
local | remote}
Clear any existing SPAN configuration for the session.
For session_number, specify 1 or 2.
Specify all to remove all SPAN sessions, local to remove all local
sessions, or remote to remove all remote SPAN sessions.
