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User Manual
Publication date: January, 2005
Revision A1
42
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 Identi fier:
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 Identifi er:
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 be inserted 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. The ingress filtering can be set by per port. When
receiving a packet, VLAN bridge examines if the VID in the frame’s header presents.
If the VID of the received packet presents, 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.