3.2.4.1 Sending Any Outgoing Message
Unless specifically noted in a subsequent section, the following logic MUST be applied to any request message being sent from the client to the server. After sending the request to the server, if the client generates a CancelId for the request as specified in section 3.2.4.1.3, it is returned to the calling application.
If Connection.Dialect belongs to the SMB 3.x dialect family and if Connection.SupportsMultiChannel or Connection.SupportsPersistentHandles is TRUE, the client MUST set ChannelSequence in the SMB2 header to Session.ChannelSequence.
If the Connection is over Direct TCP and the length of the message is greater than 16777215, the Client MUST NOT send the message and an implementation-specific local error MUST be returned to the caller.
If the Connection is over NetBIOS over TCP and the length of the message is greater than 131071, the Client MUST NOT send the message and an implementation-specific local error MUST be returned to the caller.