IEEE 802.1Q Tag |
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Octets |
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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
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| Cyclic Redundancy Check (4 Octets) |
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| User Priority | CFI | VLAN ID (VID) |
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| 3 bits | 1 bit | 12 bits |
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| Figure 6- 38. IEEE 802.1Q Tag |
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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 | 56 |
