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Catalyst 3750 Switch Software Configuration Guide
OL-8550-02
Chapter 28 Configuring SPAN and RSPAN
Configuring SPAN and RSPAN
• 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.
• 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.
• You cannot mix source VLANs and filter VLANs within a single SPAN session.
• Catalyst 3750-24PS, 3750-48PS, 3750-24TS, 3750-48TS, 3750G-12S, 3750G-24T, 3750G-24TS
and 3750G-16TD switches have hardware limitations related to SPAN. An egress SPAN copy of
routed unicast traffic might show an incorrect destination MAC address on both local and remote
SPAN sessions. This limitation does not apply to bridged packets. The workaround for local SPAN
is to use the replicate option.
• On Catalyst 3750-24PS, 3750-48PS, 3750-24TS, 3750-48TS, 3750G-12S, 3750G-24T,
3750G-24TS and 3750G-16TD switches, egress SPAN routed packets (both unicast and multicast)
show the incorrect source MAC address. For local SPAN packets with native encapsulation on the
destination port, the packet shows the MAC address of VLAN 1. This problem does not appear with
local SPAN when the encapsulation replicate option is used. This limitation does not apply to
bridged packets. The workaround is to use the encapsulate replicate keywords in the monitor
session global configuration command.
Creating a Local SPAN Session
Beginning in privileged EXEC mode, follow these steps to create a SPAN session and specify the source
(monitored) ports or VLANs and the destination (monitoring) ports:
Command Purpose
Step 1
configure terminal Enter global configuration mode.
Step 2
no monitor session {session_number | all |
local | remote}
Remove any existing SPAN configuration for the session.
For session_number, the range is 1 to 66.
Specify all to remove all SPAN sessions, local to remove all local
sessions, or remote to remove all remote SPAN sessions.
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