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Catalyst 4500 Series, Catalyst 2948G, Catalyst 2948G-GE-TX, and Catalyst 2980G Switches Software Configuration Guide—Release 8.2GLX
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Chapter 26 Configuring SPAN and RSPAN
Understanding How SPAN and RSPAN Work
Reflector Port
The reflector port is the mechanism that you use to copy packets onto an RSPAN VLAN. The reflector
port forwards only the traffic from the RSPAN source session with which it is affiliated. Any device that
is connected to a port that is set as a reflector port loses connectivity until the RSPAN source session is
disabled.
If the bandwidth of the reflector port cannot handle the traffic from the corresponding source ports, the
excess packets are dropped. A 10/100 port reflects at 100 Mbps. A Gigabit port reflects at 1 Gbps. A
blocking gigabit port reflects at a slightly lower rate.
The reflector port cannot be an EtherChannel port. In addition, a reflector port does not trunk and cannot
do protocol filtering. A port that is used as a reflector port cannot be a SPAN source or destination port,
and it cannot be a reflector port for more than one session at a time. Spanning tree is automatically
disabled on a reflector port; the port remains in the forwarding state even though the port is in loopback
mode.
The following ports cannot be used as reflector ports:
•
Gigabit uplink ports on the WS-4013 Supervisor II
•
Gigabit uplink ports on the 2980G-A
•
Gigabit ports on the WS-4232-L3 module
The SPAN line in the output of the show port capabilities command indicates whether a port can be
used as a reflector port.
Ingress SPAN
Ingress SPAN copies network traffic that is received by the source ports for analysis at the destination
port.
Egress SPAN
Egress SPAN copies network traffic that is transmitted from the source ports for analysis at the
destination port.
VSPAN
You can use VLAN-based SPAN (VSPAN) to analyze the network traffic in one or more VLANs. You
can configure VSPAN in a bidirectional mode (ingress and egress). All the ports in the source VLANs
become operational source ports for the VSPAN session. The destination port or the reflector port, if they
belong to any of the administrative source VLANs, are excluded from the operational source. If you add
or remove ports from the administrative source VLANs, the operational sources modify accordingly.
Use the following guidelines for VSPAN sessions:
•
Trunk ports are included as source ports for VSPAN sessions. Only the VLANs that are in the Admin
source list are monitored, if these VLANs are active in the trunk.
•
An inband port is not included as Oper source for VSPAN sessions.
•
When you clear a VLAN, it is removed from the source list for VSPAN sessions.
•
A VSPAN session is disabled if the Admin source VLANs list is empty.