2.2.3 SMB2 NEGOTIATE Request

The SMB2 NEGOTIATE Request packet is used by the client to notify the server what dialects of the SMB 2 Protocol the client understands. This request is composed of an SMB2 header, as specified in section 2.2.1, followed by this request structure.


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StructureSize

DialectCount

SecurityMode

Reserved

Capabilities

ClientGuid

...

...

...

(NegotiateContextOffset/NegotiateContextCount/Reserved2)/ClientStartTime

...

Dialects (variable)

...

Padding (variable)

...

NegotiateContextList (variable)

...

StructureSize (2 bytes): The client MUST set this field to 36, indicating the size of a NEGOTIATE request. This is not the size of the structure with a single dialect in the Dialects[] array. This value MUST be set regardless of the number of dialects or number of negotiate contexts sent.

DialectCount (2 bytes): The number of dialects that are contained in the Dialects[] array. This value MUST be greater than 0.<7>

SecurityMode (2 bytes): The security mode field specifies whether SMB signing is enabled or required at the client. This field MUST be constructed using the following values.

Value

Meaning

SMB2_NEGOTIATE_SIGNING_ENABLED

0x0001

When set, indicates that security signatures are enabled on the client. The client MUST set this bit if the SMB2_NEGOTIATE_SIGNING_REQUIRED bit is not set, and MUST NOT set this bit if the SMB2_NEGOTIATE_SIGNING_REQUIRED bit is set. The server MUST ignore this bit.

SMB2_NEGOTIATE_SIGNING_REQUIRED

0x0002

When set, indicates that security signatures are required by the client.

Reserved (2 bytes): The client MUST set this to 0, and the server SHOULD<8> ignore it on receipt.

Capabilities (4 bytes): If the client implements the SMB 3.x dialect family, the Capabilities field MUST be constructed using the following values. Otherwise, this field MUST be set to 0.

Value

Meaning

SMB2_GLOBAL_CAP_DFS

0x00000001

When set, indicates that the client supports the Distributed File System (DFS).

SMB2_GLOBAL_CAP_LEASING

0x00000002

When set, indicates that the client supports leasing.

SMB2_GLOBAL_CAP_LARGE_MTU

0x00000004

When set, indicates that the client supports multi-credit operations.

SMB2_GLOBAL_CAP_MULTI_CHANNEL

0x00000008

When set, indicates that the client supports establishing multiple channels for a single session.

SMB2_GLOBAL_CAP_PERSISTENT_HANDLES

0x00000010

When set, indicates that the client supports persistent handles.

SMB2_GLOBAL_CAP_DIRECTORY_LEASING

0x00000020

When set, indicates that the client supports directory leasing.

SMB2_GLOBAL_CAP_ENCRYPTION

0x00000040

When set, indicates that the client supports encryption.

ClientGuid (16 bytes): It MUST be a GUID (as specified in [MS-DTYP] section 2.3.4.2) generated by the client.

(NegotiateContextOffset/NegotiateContextCount/Reserved2)/ClientStartTime (8 bytes): This field is interpreted in different ways depending on the SMB2 Dialects field.

If the Dialects field contains 0x0311, this field is interpreted as the NegotiateContextOffset, NegotiateContextCount, and Reserved2 fields.

NegotiateContextOffset (4 bytes): The offset, in bytes, from the beginning of the SMB2 header to the first, 8-byte-aligned negotiate context in the NegotiateContextList.

NegotiateContextCount (2 bytes): The number of negotiate contexts in NegotiateContextList.

Reserved2 (2 bytes): The client MUST set this to 0, and the server MUST ignore it on receipt.

If the Dialects field doesn't contain 0x0311, this field is interpreted as the ClientStartTime field.

ClientStartTime (8 bytes):  This field MUST NOT be used and MUST be reserved. The client MUST set this to 0, and the server MUST ignore it on receipt.

Dialects (variable): An array of one or more 16-bit integers specifying the supported dialect revision numbers. The array MUST contain at least one of the following values.<9>

Value

Meaning

0x0202

SMB 2.0.2 dialect revision number.

0x0210

SMB 2.1 dialect revision number.<10>

0x0300

SMB 3.0 dialect revision number. <11>

0x0302

SMB 3.0.2 dialect revision number.<12>

0x0311

SMB 3.1.1 dialect revision number.<13>

Padding (variable): Optional padding between the end of the Dialects array and the first negotiate context in NegotiateContextList so that the first negotiate context is 8-byte aligned.

NegotiateContextList (variable): If the Dialects field contains 0x0311, then this field will contain an array of SMB2 NEGOTIATE_CONTEXTs. The first negotiate context in the list MUST appear at the byte offset indicated by the SMB2 NEGOTIATE request's NegotiateContextOffset field. Subsequent negotiate contexts MUST appear at the first 8-byte-aligned offset following the previous negotiate context.

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