Cisco Catalyst 2950 Software Configuration Manual page 450

Understanding SPAN and RSPAN
Figure 24-1
2
1
Only traffic that enters or leaves source ports can be monitored by using SPAN.
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 24-2
Source switch
RSPAN
source port
SPAN and RSPAN do not affect the switching of network traffic on source ports; 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.
You can use the SPAN destination port to inject traffic from a network security device. For example, if
you connect a Cisco Intrusion Detection System (IDS) Sensor Appliance to a destination port, the IDS
device can send TCP Reset packets to close down the TCP session of a suspected attacker.
You cannot use the RSPAN destination port to inject traffic from a network security device. The switch
Note
does not support ingress forwarding on an RSPAN destination port.
Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide
24-2
Example SPAN Configuration
1 2 3 4 5 6 7 8 ...
4 5
3 6
7
Network analyzer
Example of RSPAN Configuration
RSPAN
VLAN
Reflector
port
Port 4 traffic mirrored
on Port 8
8
Intermediate switch
RSPAN
VLAN
Chapter 24 Configuring SPAN and RSPAN
Figure
Destination switch
RSPAN
destination port
78-11380-12
24-2.