82598EB Datasheet, PDF (279/596 Pages) Intel Corporation – Intel® 82598EB 10 Gigabit Ethernet Controller Datasheet

Intel^® 82598EB 10 GbE Controller - 802.1q VLAN Support
3.5.5.1 802.1q VLAN Packet Format
The following table compares an untagged 802.3 Ethernet packet with an 802.1q VLAN tagged packet:
Table 3-78. Comparing Packets
802.3 Packet
DA
SA
Type/Length
Data
CRC
#Octets
6
6
2
46-1500
4
802.1q VLAN
Packet
DA
SA
802.1q Tag
Type/Length
Data
CRC*
#Octets
6
6
4
2
46-1500
4
Note:
The CRC for the 802.1q tagged frame is re-computed, so that it covers the entire tagged
frame including the 802.1q tag header. Also, max frame size for an 802.1q VLAN packet is
1522 octets as opposed to 1518 octets for a normal 802.3z Ethernet packet.
3.5.5.2 802.1q Tagged Frames
For 802.1q, the Tag Header field consists of four octets comprised of the Tag Protocol Identifier (TPID)
and Tag Control Information (TCI); each taking two octets. The first 16 bits of the tag header makes up
the TPID. It contains the protocol type that identifies the packet as a valid 802.1q tagged packet.
The two octets making up the TCI contain three fields:
• User Priority (UP)
• Canonical Form Indicator (CFI). Should be 0b for transmits. For receives, the device has the
capability to filter out packets that have this bit set. See the CFIEN and CFI bits in the VLNCTRL.
• VLAN Identifier (VID)
The bit ordering is as follows:
Octet 1
UP
Octet 2
VID
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