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Catalyst 3550 Multilayer Switch Software Configuration Guide
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Chapter 24 Configuring SPAN and RSPAN
Configuring SPAN
SPAN Configuration Guidelines
Follow these guidelines when configuring SPAN:
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SPAN sessions can coexist with RSPAN sessions within the limits described in the
RSPAN Session Limits” section on page 24-8
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The destination port cannot be a source port; a source port cannot be a destination port.
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You can have only one destination port per SPAN session. You cannot have two SPAN sessions using
the same destination port.
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An EtherChannel port can be a SPAN source port; it cannot be a SPAN destination port.
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An 802.1X port can be a SPAN source port. You can enable 802.1X on a port that is a SPAN
destination or reflector port; however, 802.1X is disabled until the port is removed as a SPAN
destination or reflector port.
•
For SPAN source ports, you can monitor transmitted traffic for a single port and received traffic for
a series or range of ports or VLANs.
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When you configure a switch port as a SPAN destination port, it is no longer a normal switch port;
only monitored traffic passes through the SPAN destination port.
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A trunk port can be a source port or a destination port. Outgoing packets through the SPAN
destination port carry the configured encapsulation headers—either Inter-Switch Link (ISL) or IEEE
802.1Q. If no encapsulation type is defined, the packets are sent in native form.
•
You can configure a disabled port to be a source or destination port, but the SPAN function does not
start until the destination port and at least one source port or source VLAN are enabled.
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For received traffic, you can mix multiple source port and source VLANs within a single SPAN
session. You cannot mix source VLANs and filter VLANs within a SPAN session; you can have
source VLANs or filter VLANs, but not both at the same time.
•
You can limit SPAN traffic to specific VLANs by using the filter vlan keyword. If a trunk port is
being monitored, only traffic on the VLANs specified with this keyword is monitored. By default,
all VLANs are monitored on a trunk port.
•
A SPAN destination port never participates in any VLAN spanning tree. SPAN does include BPDUs
in the monitored traffic, so any spanning-tree BPDUs received on the SPAN destination port for a
SPAN session were copied from the SPAN source ports.
•
When SPAN is enabled, configuration changes have these results:
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If you change the VLAN configuration of a destination port, the change is not effective until
SPAN is disabled.
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If you disable all source ports or the destination port, the SPAN function stops until both a
source and the destination port are enabled.
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If the source is a VLAN, the number of ports being monitored changes when you move a port
in or out of the monitored VLAN.