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Intel
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82575EB Gigabit Ethernet Controller — Double VLAN Support
Intel
®
82575EB Gigabit Ethernet Controller 324632-003
Software Developer’s Manual and EEPROM Guide Revision: 2.1
262 January 2011
Table 84. Packet Reception Decision Table
10.4 Double VLAN Support
The 82575 supports a mode where all received and sent packet have at least one VLAN tag in addition
to the regular tagging which may optionally be added. This mode is used for systems where the
switches add an additional tag containing switching information.
When a port of the 82575 is working in this mode, the 82575 assumes that all packets received or sent
to this port have at least one VLAN, including packet received or sent on the NC-SI interface.
One exception to this rule are flow control PAUSE packets which are not expected to have any VLAN.
Insertion or stripping of VLAN is done on the second VLAN if it exists. All the filtering functions of the
82575 (Rx filtering) ignores the first VLAN in this mode.
This mode is activated by setting CTRL_EXT.EXTENDED_VLAN bit. The default of this bit is set according
to bit 1 in word 24h/14h of the EEPROM for ports 0 and 1, respectively.
The type of the VLAN tag used for the additional VLAN is defined in the VET.VET_EXT field.
The Rx filter detects the presence of this VLAN and indicates it in the RDESC.STATUS.VEXT bit.
§ §
Is packet
802.1q?
CTRL.
VME
RCTL.
VFE
Action
No X X Normal packet reception.
Yes 0 0 Receive a VLAN packet if it passes the standard filters (only). Leave the packet as
received in the data buffer. Clear the VP bit in the receive descriptor.
Yes 0 1 Receive a VLAN packet if it passes the standard filters and the VLAN filter table. Leave
the packet as received in the data buffer (the VLAN tag is not stripped). Clear the VP
bit in the receive descriptor.
Yes 1 0 Receive a VLAN packet if it passes the standard filters (only). Strip off the VLAN
information (four bytes) from the incoming packet and store in the descriptor. Set the
VP bit in the receive descriptor.
Yes 1 1 Receive a VLAN packet if it passes the standard filters and the VLAN filter table. Strip
off the VLAN information (four bytes) from the incoming packet and store in the
descriptor. Set the VP bit in the receive descriptor.