Untagged packet forwarding

If the only authorized, inbound VLAN traffic on a port arrives untagged, then the port must be an untagged member of that VLAN. This is the case where the port is connected to a non-802.1Q compliant device or is assigned to only one VLAN.

To enable an inbound port to forward an untagged packet, the port must be an untagged member of either a protocol VLAN matching the packet's protocol, or an untagged member of a port-based VLAN.

That is, when a port receives an incoming, untagged packet, it processes the packet according to the following ordered criteria:

  1. If the port has no untagged VLAN memberships, the switch drops the packet.

  2. If the port has an untagged VLAN membership in a protocol VLAN that matches the protocol type of the incoming packet, then the switch forwards the packet on that VLAN.

  3. If the port is a member of an untagged, port-based VLAN, the switch forwards the packet to that VLAN. Otherwise, the switch drops the packet.

Untagged VLAN operation