Span Configuration Guidelines - Cisco Catalyst 3550 series Software Configuration Manual

Chapter 24 Configuring SPAN and RSPAN

SPAN Configuration Guidelines

Follow these guidelines when configuring SPAN:
•
•
•
•
•
•
•
•
•
•
•
•
•
78-11194-09
SPAN sessions can coexist with RSPAN sessions within the limits described in the
RSPAN Session Limits" section on page
The destination port cannot be a source port; a source port cannot be a destination port.
You can have only one destination port per SPAN session. You cannot have two SPAN sessions using
the same destination port.
An EtherChannel port can be a SPAN source port; it cannot be a SPAN destination port.
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.
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.
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.
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:
If you change the VLAN configuration of a destination port, the change is not effective until
–
SPAN is disabled.
– If you disable all source ports or the destination port, the SPAN function stops until both a
source and the destination port are enabled.
– 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.
24-8.
Catalyst 3550 Multilayer Switch Software Configuration Guide
Configuring SPAN
"SPAN and
24-9