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VLAN-tagged frame:
An Ethernet frame, carrying VLAN tag field, contains VLAN identification without the value of 0 and
4095, and priority information.
Priority-tagged frame:
An Ethernet frame, carrying VLAN tag field, contains VLAN identification with the value of 0 and
priority information.
Untagged frame:
An Ethernet frame carries no VLAN tag information.
VLAN Identifier:
Also referred to as VID. It is used to identify a member whether it belongs to the VLAN group with
the VID. The assignable number is 1- 4094. If VID=0, the tagged frame is a priority packet. Both the value
of 0 and 4095 also cannot be assigned in VLAN management.
Port VLAN Identifier:
VLAN identifier of a port. It also can be referred to as PVID. When an untagged frame or a priority-
tagged frame is received, the frame will insert the PVID of that port in the VLAN tag field. The frame with
VID assigned by a port is called PVID. Each port can only be assigned a PVID. The default value for
PVID is 1, the same as VID.
Ingress filtering:
The process to check a received packet and compare its VID to the VLAN membership of the
ingress port is ingress filtering. The ingress filtering can be set per port. When receiving a packet, VLAN
bridge examines if the VID in the frame’s header is present.
If the VID of the received packet is present, the VID of the packet is used. And VLAN bridge will
check its MAC address table to see if the destination ports are members of the same VLAN. If both are
members of the tagged VLAN, then the packet will be forwarded.
If the packet is an untagged or a null tag packet, the ingress port’s PVID is applied to the packet.
VLAN bridge will then look up the MAC address table and determine to which ports the packet should be
forwarded. Next, it will check to see if the destination ports belong to the same VLAN with that PVID. If the
destination ports are members of the VLAN used by ingress port, the packet will be forwarded.
Note: VID can not be 0 or 4095.
