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Chapter 25
Configuring SPAN and RSPAN
Figure 25-1 Example SPAN Configuration
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For SPAN configuration, the source ports and the destination port must be on the same switch.
SPAN does not affect the switching of network traffic on source ports; copies of the packets received or
transmitted by the source ports are sent to the destination port.
SPAN Configuration Guidelines
Follow these guidelines when configuring SPAN:
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Incoming traffic on the SPAN destination port is disabled by default. You can enable it using the
inpkts enable keywords. However, while the port receives traffic for its assigned VLAN, it does not
participate in spanning tree for that VLAN. To avoid creating spanning tree loops with incoming
traffic enabled, assign the SPAN destination port to an unused VLAN.
In software release 5.2 and later, with the inpkts option enabled, you can prevent the switch from
learning source MAC addresses from traffic received on the SPAN destination port using the
learning disable keywords. If you want the switch to learn source MAC addresses from traffic
received on the SPAN destination port, use the learning enable keywords. By default, the switch
learns source MAC addresses from incoming traffic (learning enable) if the inpkts option is
enabled. The source MAC address learning options only affect traffic received from a device
attached to the SPAN destination port itself, not from traffic mirrored from the SPAN source.
When monitoring a VLAN on a switch, you must monitor both transmit and receive traffic (both).
You cannot monitor only transmit (tx) or only receive (rx) traffic.
If you specify a set of VLANs with the filter option, the traffic spanned by the session is limited to
the VLANs specified.
Any traffic between two network nodes on the same network segment attached to a switch port
configured as a SPAN source port is not mirrored to the SPAN destination port. You can SPAN local
traffic that passes through the switch.
You can have up to five SPAN sessions running at the same time with any combination of ingress
and egress sessions.
You cannot configure SPAN on sc0.
Software Configuration Guide—Catalyst 4000 Family, Catalyst 2948G, Catalyst 2980G, Releases 6.3 and 6.4
Port 5 traffic mirrored
on Port 10
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SwitchProbe
SPAN Configuration Guidelines
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