2.2.1 SMB2 Packet Header
The SMB2 Packet Header (also called the SMB2 header) is the header of all SMB 2 Protocol requests and responses.
There are two variants of this header:
If the SMB2_FLAGS_ASYNC_COMMAND bit is set in Flags, the header takes the form SMB2 Packet Header – ASYNC (section 126.96.36.199). This header format is used for responses to requests processed asynchronously by the server, as specified in sections 188.8.131.52, 184.108.40.206, 220.127.116.11, and 18.104.22.168.5. The SMB2 CANCEL Request MUST use this format for canceling requests that have received an interim response, as specified in sections 22.214.171.124 and 126.96.36.199.
If the SMB2_FLAGS_ASYNC_COMMAND bit is not set in Flags, the header takes the form SMB2 Packet Header – SYNC (section 188.8.131.52).