Cisco Systems DOC-7814982 Creating a SPAN Session and Specifying Ports to Monitor

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Catalyst 2950 Desktop Switch Software Configuration Guide
78-14982-01
Chapter 21 Configuring SPAN and RSPAN Configuring SPAN
•When you configure a switch port a s a SPAN destination port, it is no longer a normal switch port;
only m onitore d traffic passes thr oug h th e SPAN dest ina tion p ort.
•A trunk por t c an be a sour ce por t or a desti nat ion port . Ou tgoi ng pa cket s thr ough t he SPAN
destinat ion port carry th e configured e ncap sulation heade rs—either I nter-Switch L ink (I SL) or
IEEE 8 02. 1Q. If no e nca psula tio n t ype is d efined, t he pac kets ar e sen t i n na tive form.
•You can configure a disabled port to be a source or destination port, b ut 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 lim it SPA N traffic to specific VLAN s by using the filter vlan keyword. If a trunk p ort is
being monitored, only traffic on the VLANs specified with this keyword is monitored. By default,
all VL AN s a re m oni tor ed on a tr unk po rt.
•A SPAN destination port never participates in any VLAN spanning tree. SPAN does include BPDUs
in the mon itored tr affic, so any spanning- tree BPDU s received on the SPAN destin ation po rt for a
SPA N session were copie d 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 an d th e dest inat ion po rt are enab le d.
– If the sourc e is a VLA N, the nu mber of po rts b ein g m onit ored c hang es when y ou move a por t
in or out of the monitored V LAN.
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 globa l configurati on 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.