13
3.4 VLAN
3.4.1 IEEE 802.1Q VLAN
Go to
VLAN > IEEE 802.1Q VLAN
IEEE 802.1Q is a protocol for Ethernet frame carrying VLAN tag. The traffic is encapsulated so that a
number of logically separate VLANs can be carried by the same physical LAN.
The VLAN ID associates a frame with specific VLAN and provides the information that switches need to
process the frame across the network. A tagged frame is four bytes longer than an untagged frame and
contains two bytes for the TPID (Tag protocol Identifier, residing within the type/length filed of the Ethernet
frame) and two bytes for the TCI (Tag Control Information, starting after the source address field of the
Ethernet frame).
The CFI (Canonical Format Indicator) is a single-bit flag, always set to zero for Ethernet switches. If a
frame received at an Ethernet port has a CFI set to 1, then that frame should not be forwarded as it is to
an untagged port. The remaining twelve bits define the VLAN ID are independent of each other. A frame
with VID (VLAN Identifier) of null (0) is called a priority frame, meaning that only the priority level is
significant and the default VID of the ingress priority frames and the value 4095 (FFF) is reserved, so the
maximum possible number of VLAN configurations is 4094.
TPID
User Priority
CFI
VLAN ID
2 Bytes
3 Bits
1 Bit
12 bits
Once the VLAN table is configured and maintained in GS-5008PL, frames will be handled by all
operations of VLAN configuration. These operations include the stripping or adding of the IEEE 802.1Q
tag.