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Chapter 25
Configuring SPAN and RSPAN
RSPAN has all the features of SPAN (see the
plus support for source ports and destination ports distributed across multiple switches, allowing 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 the reflector port and then forwarded over trunk ports carrying the RSPAN
VLAN to RSPAN destination ports monitoring the RSPAN VLAN.
Traffic sent out through the source port is also sent out on the reflector port. Because the reflector port
is an access (non-trunking) port in loopback mode, the traffic is switched out with no VLAN tag and is
immediately sent back to the switch. In the loopback, the traffic is encoded into the RSPAN VLAN. A
switch with an RSPAN destination session receives the traffic (see
The traffic type for sources (ingress, egress, or both) in an RSPAN session can be different for source
switches, but must be the same for all source ports on a given switch.
Do not configure any ports in an RSPAN VLAN except those selected to carry RSPAN traffic. Learning
is disabled on the RSPAN VLAN.
Figure 25-2 Flow of RSPAN Monitored Traffic
2/1
RSPAN
source port
(RX)
RSPAN Configuration Guidelines
Follow these guidelines when configuring RSPAN:
Tip
Because RSPAN VLANs have special properties, we recommend that you reserve a few VLANs across
your network for use as RSPAN VLANs; do not assign access ports to these VLANs.
•
•
•
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78-12647-02
Switch A (source)
VLAN 609
2/2
2/3
Reflector
port
RSPAN VLAN 609
All the items in the
"SPAN Configuration Guidelines" section on page 25-5
RSPAN sessions can coexist with SPAN sessions to a maximum of five sessions. The limit on the
number of sessions the Catalyst 4000 family switches can carry as an intermediate switch is the
maximum number of VLANs for the switch.
For RSPAN configuration, you can distribute the source ports and the destination port across
multiple switches.
A port cannot serve as an RSPAN source port or RSPAN destination port while designated as an
RSPAN reflector port.
Software Configuration Guide—Catalyst 4000 Family, Catalyst 2948G, Catalyst 2980G, Releases 6.3 and 6.4
" Understanding How SPAN Works" section on page
Switch B (intermediate)
1/1
Configuring RSPAN
Figure
25-2).
Switch C (destination)
VLAN 609
1/2
3/1
3/2
RSPAN
destination port
apply to RSPAN.
25-4),
25-9
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