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Mirroring with Trunk Ports

When the source port of a SPAN or port mirror session is a trunk port, you can monitor specific VLANs on that port. Use the following command:

monitor session session-number filter vlan-list

You can configure an interface as a trunk port to filter the VLANs that leave a destination port. Use the following command:

switchport trunk allowed vlan vlan-list

This command lets you specify which VLANs the interface transmits. An interface configured as a destination interface filters out traffic. By filtering VLANs, you reduce contention for bandwidth and lower the probability of packet discards due to buffers filling.