Intel Intel Gigabit Ethernet Controllers, PCI-X manual Packet Reception Decision Table, Vfe

802.1q VLAN Support

In summary, the 4096 bit vector is composed of 128 32-bit registers. Matching to this bit vector follows the same algorithm as indicated in Section 13.5.1 for Multicast Address filtering. The VLAN Identifier (VID) field consists of 12 bits. The upper 7 bits of this field are decoded to determine the 32-bit register in the VLAN Filter Table Array to address and the lower 5 bits determine which of the 32 bits in the register to evaluate for matching.

Two other bits in the Receive Control register (see Section 13.4.22), CFIEN and CFI, are also used in conjunction with 802.1q VLAN filtering operations. CFIEN enables the comparison of the value of the CFI bit in the 802.1q packet to the Receive Control register CFI bit as an acceptance criteria for the packet.

Note: The VFE bit does not affect whether the VLAN tag is stripped. It only affects whether the VLAN packet passes the receive filter.

Table 9-3lists reception actions according to control bit settings.

Table 9-3. Packet Reception Decision Table

Is	CTRL.	RCTL.
packet			ACTION
	VME	VFE
802.1q?
No	X	X	Normal packet reception.
			Receive a VLAN packet if it passes the standard filters (only). Leave the
Yes	0	0	packet as received in the data buffer. Clear the VP bit in the receive
			descriptor.
			Receive a VLAN packet if it passes the standard filters and the VLAN
Yes	0	1	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.
			Receive a VLAN packet if it passes the standard filters (only). Strip off
Yes	1	0	the VLAN information (four bytes) from the incoming packet and store in
			the descriptor. Set the VP bit in the receive descriptor.
			Receive a VLAN packet if it passes the standard filters and the VLAN
Yes	1	1	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.

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