IEEE 802.1Q Tag

 

 

 

 

Octets

 

 

 

 

0

1

2

3

4

Destination Address (6 Octets)

Source Address (6 Octets)

Ether Type = 0x8100

Tag Control Information

MAC Length/Type

Beginning of Data

 

 

 

Cyclic Redundancy Check (4 Octets)

 

 

 

 

 

 

 

 

 

 

 

 

User Priority

CFI

VLAN ID (VID)

 

 

 

 

 

 

 

3 bits

1 bit

12 bits

 

 

 

 

Figure 6- 38. IEEE 802.1Q Tag

 

The EtherType and VLAN ID are inserted after the MAC source address, but before the original EtherType/Length or Logical Link Control. Because the packet is now a bit longer than it was originally, the Cyclic Redundancy Check (CRC) must be recalculated.

Adding an IEEE 802.1 Tag

Dest.

Src.

Length/EType

Data

Old CRC

Original Ethernet Packet

Dest.

Src.

EType

Tag

Data

New CRC

New Tagged Packet

Priority

VLAN ID

Figure 6- 39.Adding an IEEE 802.1Q Tag

Allied Telesyn AT-9724TS High-Density Layer 3 Stackable Gigabit Ethernet Switch

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Allied Telesis AT-9724TS specifications Bits, Adding an Ieee 802.1Q Tag