Vlan Filtering - Cisco Catalyst 2960 series Configuration Manual

Information About SPAN and RSPAN
• 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.
• When a VLAN filter list is specified, only those VLANs in the list are monitored on trunk ports or on
voice VLAN access ports.
• SPAN traffic coming from other port types is not affected by VLAN filtering; that is, all VLANs are
allowed on other ports.
• VLAN filtering affects only traffic forwarded to the destination SPAN port and does not affect the
switching of normal traffic.
Destination Port
Each local SPAN session or RSPAN destination session must have a destination port (also called a monitoring
port) that receives a copy of traffic from the source ports or VLANs and sends the SPAN packets to the user,
usually a network analyzer.
A destination port has these characteristics:
• For a local SPAN session, the destination port must reside on the same switch or switch stack as the
source port. For an RSPAN session, it is located on the switch containing the RSPAN destination session.
There is no destination port on a switch or switch stack running only an RSPAN source session.
• When a port is configured as a SPAN destination port, the configuration overwrites the original port
configuration. When the SPAN destination configuration is removed, the port reverts to its previous
configuration. If a configuration change is made to the port while it is acting as a SPAN destination port,
the change does not take effect until the SPAN destination configuration had been removed.
Note
• If the port was in an EtherChannel group, it is removed from the group while it is a destination port. If
it was a routed port, it is no longer a routed port.
• It can be any Ethernet physical port.
• It cannot be a secure port.
• It cannot be a source port.
• It can participate in only one SPAN session at a time (a destination port in one SPAN session cannot be
a destination port for a second SPAN session).
• When it is active, incoming traffic is disabled. The port does not transmit any traffic except that required
for the SPAN session. Incoming traffic is never learned or forwarded on a destination port.
• If ingress traffic forwarding is enabled for a network security device, the destination port forwards traffic
at Layer 2.
• It does not participate in any of the Layer 2 protocols (STP, VTP, CDP, DTP, PagP).
Consolidated Platform Configuration Guide, Cisco IOS Release 15.2(4)E (Catalyst 2960-X Switches)
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When QoS is configured on the SPAN destination port, QoS takes effect immediately.