Cisco 2950G 24 - Catalyst Switch Software Configuration Manual page 440

Understanding SPAN and RSPAN
Figure 21-1 Example SPAN Configuration
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1
Only traffic that enters or leaves source ports or traffic that enters source VLANs can be monitored by
using SPAN; traffic that gets routed to ingress source ports or source VLANs cannot be monitored. For
example, if incoming traffic is being monitored, traffic that gets routed from another VLAN to the source
VLAN is not monitored; however, traffic that is received on the source VLAN and routed to another
VLAN is monitored.
RSPAN extends SPAN by enabling remote monitoring of multiple switches across your network. The
traffic for each RSPAN session is carried over a user-specified RSPAN VLAN that is dedicated for that
RSPAN session in all participating switches. The SPAN traffic from the sources is copied onto the
RSPAN VLAN through a reflector port and then forwarded over trunk ports that are carrying the RSPAN
VLAN to any RSPAN destination sessions monitoring the RSPAN VLAN, as shown in
Figure 21-2 Example of RSPAN Configuration
Source switch
RSPAN
source port
SPAN and RSPAN do not affect the switching of network traffic on source ports or source VLANs; a
copy of the packets received or sent by the source interfaces are sent to the destination interface. Except
for traffic that is required for the SPAN or RSPAN session, reflector ports and destination ports do not
receive or forward traffic.
Catalyst 2950 Desktop Switch Software Configuration Guide
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5 8
4 9
3
10
Network analyzer
RSPAN
VLAN
Reflector
port
Port 5 traffic mirrored
on Port 10
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12
Intermediate switch
Chapter 21 Configuring SPAN and RSPAN
Destination switch
RSPAN
VLAN
RSPAN
destination port
Figure 21-2.
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