Splitting Frames at the TCP Payload

NDIS miniport adapters that support header-data split must support splitting frames at the upper-layer-protocol header for TCP frames. However, if the TCP header does not contain any TCP options, the NIC should split the frame at the beginning of the TCP payload.

The NIC might not be able to split a TCP frame if the resulting header buffer has a greater length than the maximum header size. For more information about splitting frames when the maximum header size is exceeded, see Allocating the Header Buffer.

NICs must also support splitting TCP headers with only the timestamp option. That is, the timestamp option is the only TCP option that is mandatory. Otherwise, support for TCP headers with TCP options is optional. If the TCP header of a frame contains an unrecognized TCP option, the NIC must either split the frame at the beginning of TCP header (that is, at the upper-layer-protocol header) or not split the frame.

Note Supporting an IPv4 option, an IPv6 extension header or a TCP option, for the purposes of header-data requirements, implies the ability of the NIC to recognize the element, determine its length, include it in the header MDL and locate its end and the beginning of the next element in the frame.

For more information about splitting frames at the beginning of the upper-layer-protocol header, see Splitting Frames at the Beginning of the Upper-Layer-Protocol Headers.

If the header-data split provider splits the frame at the TCP payload, the indicated NET_BUFFER_LIST structures must have the NDIS_NBL_FLAGS_IS_TCP and NDIS_NBL_FLAGS_SPLIT_AT_UPPER_LAYER_PROTOCOL_PAYLOAD flags set in the NblFlags member. For more information about setting header-data split NET_BUFFER_LIST flags, see Setting NET_BUFFER_LIST Information.