Context :- For network monitoring/packet mirrioring techniques like SPAN and RSPAN.

Why is it mandatory to have a dedicated vlan for RSPAN ? why can't we mirror the packets received in a port and send it directly to a specific destination, why to forward it as vlan only ?

  • When you say send it directly to a destination, do you mean send it to a specific IP or send it to a specific interface? Commented Nov 6, 2014 at 12:00
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2 Answers 2


When performing RSPAN another tag (the RSPAN VLAN tag) is added to the packet. Please note that this is not an actual encapsulation. You just add a second tag to the packet. The RSPAN Vlan has learning disabled, therefore the packets are flooded inside RSPAN VLAN. At the destination, the RSPAN tag is removed and you have the packet sent by the source unmodified. This is what you want when you mirror a packet. If you would not use a VLAN then your packet would be discarded.


Because RSPAN is "Remote Span" right? SPAN is just local on the same switch. With RSAPN You need to configure a vlan because you are 'mirroring' a remote port on a remote switch. In order to pass this traffic to the destination port, on a remote switch, you need to configure a vlan for this purpose.

  • 2
    The RSPAN vlan ("outer tag") is to encapsulate the packets that might already be tagged ("inner tag"). Otherwise, tagged traffic would be acted upon like any other traffic at the next-hop switch.
    – Ricky
    Commented Nov 6, 2014 at 21:35

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