21-2
Catalyst 2950 Desktop Switch Software Configuration Guide
78-14982-01
Chapter 21 Configuring SPAN and RSPAN
Understan din g SPAN and RSPAN
Figure 21-1 Example SPAN Configuration
Only traffic that e nte rs or l eaves sourc e por ts or t raffic that e nte rs sour ce V LA Ns can be mon ito re d by
using SPAN; traffic that gets routed to ingress source ports or source VLA Ns cannot be monitored. For
exa mple, if incoming traff ic is being monitored, traf f ic that gets ro uted from anothe r VLAN to the so urce
VLAN is not mon itore d; however, traffic tha t is received on the source VLA N and route d to anoth er
VLAN is monitored.
RSPA N extends SPAN by enabling remote monitori ng of multip le switches across you r 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 ove r trunk ports that are carrying the RSPAN
VLAN to any RSPAN destination sessions monitoring the RSPAN VLAN, as shown in Figure 21-2.
Figure 21-2 Example of RSPAN Configuration
SPA N and RSPAN do not affect the swi tching of networ k traffic on source ports or source VLAN s; a
cop y of the packe ts rece i v ed or sent b y the sou rce inter fac es are sent to the d estinati on int erf ace. Exce pt
for tr affic t hat is requi r ed fo r the SPAN o r RSPAN se ssion, ref lec tor po rts a nd de sti nat ion ports do no t
receive or forward traffic.
1 2 3 4 5 6 7 8 9 10 11 12 Port 5 traffic mirrored
on Port 10
3
2
1
4567
8911 12
10
Network analyzer
43580
Source switch Intermediate switch Destination switch
74727
RSPAN
source port RSPAN
destination port
Reflector
port
RSPAN
VLAN RSPAN
VLAN