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Catalyst 3750-X and 3560-X Switch Software Configuration Guide
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Chapter 32 Configuring SPAN and RSPAN Understanding SPAN and RSPAN
Source Ports
A source port (also called a monitored port) is a switched or routed port that you monitor for network
traffic analysis. In a local SPAN session or RSPAN source session, you can monitor source ports or
VLANs for traffic in one or both directions. The switch supports any number of source ports (up to the
maximum number of available ports on the switch) and any number of source VLANs (up to the
maximum number of VLANs supported). However, the switch supports a maximum of two sessions
(local or RSPAN) with source ports or VLANs. You cannot mix ports and VLANs in a single session.
A source port has these characteristics:
• It can be monitored in multiple SPAN sessions.
• Each source port can be configured with a direction (ingress, egress, or both) to monitor.
• It can be any port type (for example, EtherChannel, Gigabit Ethernet, and so forth).
• For EtherChannel sources, you can monitor traffic for the entire EtherChannel or individually on a
physical port as it participates in the port channel.
• It can be an access port, trunk port, routed port, or voice VLAN port.
• It cannot be a destination port.
• Source ports can be in the same or different VLANs.
• You can monitor multiple source ports in a single session.
Source VLANs
VLAN-based SPAN (VSPAN) is the monitoring of the network traffic in one or more VLANs. The SPAN
or RSPAN source interface in VSPAN is a VLAN ID, and traffic is monitored on all the ports for that
VLAN.
VSPAN has these characteristics:
• All active ports in the source VLAN are included as source ports and can be monitored in either or
both directions.
• On a given port, only traffic on the monitored VLAN is sent to the destination port.
• If a destination port belongs to a source VLAN, it is excluded from the source list and is not
monitored.
• If ports are added to or removed from the source VLANs, the traffic on the source VLAN received
by those ports is added to or removed from the sources being monitored.
• You cannot use filter VLANs in the same session with VLAN sources.
• You can monitor only Ethernet VLANs.
VLAN Filtering
When you monitor a trunk port as a source port, by default, all VLANs active on the trunk are monitored.
You can limit SPAN traffic monitoring on trunk source ports to specific VLANs by using VLAN
filtering.
• VLAN filtering applies only to trunk ports or to voice VLAN ports.
• VLAN filtering applies only to port-based sessions and is not allowed in sessions with VLAN
sources.