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Catalyst 3550 Multilayer Switch Software Configuration Guide
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Chapter15 Configuring SPAN Configuring SPAN
Default SPAN Configuration
Table15-1 shows the default SPAN configuration.
This release supports only local SPAN; remote SPAN (RSPAN) is not supported.
SPAN Configuration Guidelines
Follow these guidelines when configuring SPAN:
•Use a network analyzer to monitor ports.
•Only two SPAN sessions can be active on a switch at the same time.
•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.
•For a SPAN source port, you can monitor transmitted traffic for a single port or 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. When a destination port is a trunk port,
outgoing packets through the SPAN port carry the encapsulation headers configured by the
user—either Inter-Switch Link (ISL) or IEEE 802.1Q. If no enc aps ulat ion typ e is defi ned, th e
packets are sent in native form.
•When you specify a single source port and do not specify a tr affic type (Tx, R x, or bot h), bot h is
used as the default.
•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.
Table15-1 Default SPAN Configuration
Feature Default Setting
SPAN state Disabled
Source port traffic to monitor Both received and sent traffic (both)
Note Only received traffic can be monitored on source
VLANs or multiple source ports
Encapsulation type (destination port) Native form (no encapsulation type header)