What is VSPAN?

A VLAN SPAN (VSPAN) configuration is a monitor session whose source is a VLAN rather than specific interfaces. When a VLAN is the source of a monitor session, all physical interfaces that are members of the VLAN are also sources.

In a VSPAN configuration, the monitor session is still sourced from physical interfaces.

Advantages

VSPAN is easy to configure and does not require you to know the interfaces to which every server is connected.
You use one command to add a group of physical interfaces as sources.
If servers move ports within the switch or VLAN, the change is transparent, requiring no change to the SPAN session.

Disadvantages

VSPAN does not let you control which interfaces are the source of a monitor session. Instead, you collect traffic on every interface in the VLAN.
The destination SPAN port may not be able to handle the data it receives, which can result in congestion and discards at the outbound interface.
VSPAN can cause duplicates in many scenarios. VSPAN is best suited for use on Layer 2 devices where one VLAN is sourced, either ingress-only or egress-only. This configuration allows each packet to be captured only as it enters the switch, or only as it leaves the switch.