Allied Telesis AT-9724TS - Manual (Page 57)

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.
Figure 6- 39.Adding an IEEE 802.1Q Tag
56 Allied Telesyn AT-9724TS High-Density Layer 3 Stackable Gigabit Ethernet Switch
Octets
0
1 2 3
IEEE 802.1Q Tag
Destination Address (6 Octets)
Cyclic Redundancy Check (4 Octets)
VLAN ID (VID)
Source Address (6 Octets)
Ether Type = 0x8100 Tag Control Information
MAC Length/Type Beginning of Data
CFI User Priority
3 bits 1 bit 12 bits
4
Adding an IEEE 802.1 Tag
Length/EType Dest. Src. Data Old CRC
EType Dest. Src. Data New CRC Tag
Priority VLAN ID
Original Ethernet Packet
New Tagged Packet