2.2.1 SMB2 Packet Header
The SMB2 Packet Header (also called the SMB2 header) is the header of all SMB 2.0 Protocol packets.
There are two variants of this header:
If the SMB2_FLAGS_ASYNC_COMMAND bit is set in Flags, the header takes the form: SMB2 Protocol Header - ASYNC (section 188.8.131.52). This header format is used for responses to requests processed asynchronously by SMB2 server. For more details refer to sections 184.108.40.206, 220.127.116.11.4 and 18.104.22.168. The SMB2_CANCEL_Request uses this format for canceling requests that are being processed asynchronously.
If the SMB2_FLAGS_ASYNC_COMMAND bit is not set in Flags, the header takes the form: SMB2 Protocol Header - SYNC (section 22.214.171.124). This format is used for all requests with the exception of the SMB2_CANCEL_Request to cancel a previously sent request being processed asynchronously.