Sending 802.1Q-Marked and 802.1p-Marked Packets on an Offloaded TCP Connection

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[The TCP chimney offload feature is deprecated and should not be used.]

When processing a send packet on an offloaded TCP connection, an offload target uses the values of the VlanId and UserPriority members to determine whether an IEEE 802.3ac packet header, referred to as a tag header, should be included. The IEEE 802.3ac header contains a VLAN identifier value, a priority value, and a bit called CFI, which is always set to zero.

An offload target uses the following algorithm to determine whether to insert an 802.3ac header into a packet and what VLAN identifier and priority values to supply in the header:

  • If the neighbor VlanId is zero:
    • If the value of UserPriority for the TCP connection is zero, the offload target does not insert a tag header into the packet.
    • If the value of UserPriority for the TCP connection is nonzero, the offload target inserts a tag header into the packet. In this tag header, the offload target specifies a VLAN identifier of zero and a priority value that is equal to the value of UserPriority for the TCP connection.
  • If the neighbor VlanId is nonzero, the offload target inserts a tag header into the packet. In this tag header, the offload target specifies a VLAN identifier that is equal to the neighbor VlanId and a priority value that is equal to the value of UserPriority for the TCP connection.