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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 is also referened to as PVID. When an untagged
frame or a priority-tagged frame is received,
the PVID of that port will be inserted in
the VLAN tag field of the frame. This frame with VID assigned by a port is called
PVID. Each port can only be assigned one PVID. The default value for PVID is 1,
which is the same as VID.
Ingress filtering:
This is the process to check a received packet and compare its VID to the
VLAN membership of the ingress port. The ingress filtering can be set by per port.
When receiving a packet, the VLAN bridge will examine if the VID in the frame’s
header presents.
If the VID of the received packet presents, the VID of the packet is used. The
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 untagged or a null tag packet, the ingress port’s PVID is
applied to the packet. The VLAN bridge will then look up the MAC address table
and determine as which ports the packet should be forwarded to. 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.