Filter
Top Products
802.1q VLAN Support — Intel
®
82575EB Gigabit Ethernet Controller
324632-003 Intel
®
82575EB Gigabit Ethernet Controller
Revision: 2.1 Software Developer’s Manual and EEPROM Guide
January 2011 259
10.0 802.1q VLAN Support
The 82575 provides several specific mechanisms to support 802.1q VLANs:
• Optional adding (for transmits) and stripping (for receives) of IEEE 802.1q VLAN tags
• Optional ability to filter packets belonging to certain 802.1q VLANs
10.1 802.1q VLAN Packet Format
Table 81 compares an untagged 802.3 Ethernet packet with an 802.1q VLAN tagged packet.
Table 81. VLAN Packet Format Comparison
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.
10.1.1 802.1q 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 2 octets. The first 16 bits of the tag header make up the
TPID. It contains the “protocol type” which identifies the packet as a valid 802.1q tagged packet.
The two octets making up the TCI contain three fields (see Table 82 for details):
• User Priority (UP)
• Canonical Form Indicator (CFI). The CFI should be 0b for transmits. For receives, the 82575 has the
capability to filter out packets that have this bit set. See the CFIEN and CFI bits in the RCTL as
described in Section 14.3.47.
• VLAN Identifier (VID)
802.3 Packet #Octets 802.1q VLAN Packet #Octets
DA 6 DA 6
SA 6 SA 6
Type/Length 2 8021.q Tag 4
Data 46-1500 Type/Length 2
CRC 4 Data 46-1500
CRC* 4