RFC 5793
PB-TNC: A Posture Broker (PB) Protocol Compatible with Trusted Network Connect (TNC)
4. PB-TNC Protocol Specification
This section defines the syntax and semantics of the PB-TNC protocol fields. If a Posture Broker Client or Posture Broker Server receives a batch that violates the requirements of this specification, it MUST respond by sending a fatal Invalid Parameter error in a CLOSE batch unless this document specifies otherwise.4.1. PB-TNC Header
Every PB-TNC batch MUST start with the following header. A PB-TNC batch MUST contain only one instance of this header followed by zero or more PB-TNC messages. The PB-TNC messages are defined in subsequent sections of this specification. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Version |D| Reserved | B-Type| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Batch Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Version (8 bits) This field indicates the version of the format for the PB-TNC message. This version is intended to allow for evolution of the PB-TNC protocol in a manner that can easily be detected by message recipients. This field MUST be set to 2 when the batch conforms to this specification. Later versions of PB-TNC may define other values for this field. The values 0x00, 0x09, 0x0a, 0x0d, 0x20, and 0x3c are reserved and cannot be used for any version of PB-TNC to ensure that PB-TNC can be easily distinguished from earlier posture broker protocols already in use. If a Posture Broker Client or Posture Broker Server receives a Version value that it does not support, it MUST respond with a PB- TNC batch with batch type CLOSE that contains only a fatal Version Not Supported error code and whose Version header field has the value 2. Implementations responding to a PB-TNC message containing a supported version MUST use the same Version number to minimize the risk of version incompatibility. PB-TNC message initiators that support multiple PB-TNC protocol versions SHOULD be able to alter which version of PB-TNC message they send based on prior message exchanges with a particular peer Posture Broker Client or Posture Broker Server.
Directionality (D) (1 bit)
When a Posture Broker Client is sending this message, the
Directionality bit MUST be set to 0. When a Posture Broker Server
is sending this message, the Directionality bit MUST be set to 1.
This helps avoid any situation where two Posture Broker Clients or
two Posture Broker Servers engage in a dialog. It also helps with
debugging.
Reserved (19 bits)
This field is reserved. For this version of this specification,
it MUST be set to 0 on transmission and ignored on reception.
Future versions of this specification may allow senders to set
some of these bits and recipients to interpret them.
B-Type (Batch Type) (4 bits)
This field is used to drive the state machine described in section
3.2. This field MUST have one of the values from the following
table. If any other value is received, the recipient MUST ignore
the contents of the batch and send a fatal Invalid Parameter error
code in a CLOSE batch. If the value received is not permitted for
the current state, according to the state machine in section 3.2.,
the recipient MUST ignore the contents of the batch and send a
fatal Unexpected Batch Type error code in a CLOSE batch.
Number Name Definition
------ ---- ----------
1 CDATA The Posture Broker Client may send a batch with
this Batch Type to convey messages to the
Posture Broker Server. A Posture Broker Server
MUST NOT send this Batch Type. A CDATA batch
may be empty (contain no messages) if the
Posture Broker Client has nothing to send.
2 SDATA The Posture Broker Server may send a batch with
this Batch Type to convey messages to the
Posture Broker Client. A Posture Broker Client
MUST NOT send this Batch Type. An SDATA batch
may be empty (contain no messages) if the
Posture Broker Server has nothing to send.
3 RESULT The Posture Broker Server may send a batch with
this Batch Type to indicate that it has
completed its evaluation. The batch MUST
include a PB-Assessment-Result message and MAY
include a PB-Access-Recommendation message.
4 CRETRY The Posture Broker Client may send a batch with
this Batch Type to indicate that it wishes to
restart an exchange. A Posture Broker Server
MUST NOT send this Batch Type. A CRETRY batch
may be empty (contain no messages) if the
Posture Broker Client has nothing else to send.
5 SRETRY The Posture Broker Server may send a batch with
this Batch Type to indicate that it wishes to
restart the exchange. A Posture Broker Client
MUST NOT send this Batch Type. A SRETRY batch
may be empty (contain no messages) if the
Posture Broker Server has nothing else to send.
6 CLOSE The Posture Broker Server or Posture Broker
Client may send a batch with this Batch Type to
indicate that it is about to terminate the
underlying PT connection. A CLOSE batch may be
empty (contain no messages) if there is nothing
to send. However, if the termination is due to a
fatal error, then the CLOSE batch MUST contain a
PB-Error message.
Batch Length (32 bits)
This length field contains the size of the full PB-TNC batch in
octets. This length includes the PB-TNC header and all the PB-TNC
messages in the batch. In other words, it includes the entire
contents of the batch. This field MUST contain at least the value
8 for the fixed-length fields in this header. Any Posture Broker
Client or Posture Broker Server that receives a PB-TNC message
with a PB-TNC Message Length field whose value is less than 8 MUST
respond with a fatal Invalid Parameter error code in a CLOSE
batch.
4.2. PB-TNC Message
All PB-TNC messages have the same overall structure, which is
described in this section. Of course, the format and semantics of
the PB-TNC Message Value field will vary, depending on the values of
the PB-TNC Vendor ID and PB-TNC Message Type fields.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | PB-TNC Vendor ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PB-TNC Message Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PB-TNC Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PB-TNC Message Value (Variable Length) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Flags (8 bits)
This field defines flags impacting the processing of this message.
Bit 0 of this Flags field (the most significant bit) is known as
the NOSKIP flag. If this flag is cleared (value 0), then the
recipient (a Posture Broker Client or Posture Broker Server) may
skip (ignore) this message if the message type is not understood
or the recipient cannot or will not process the message as
required in the definition of that message. If this flag is set
(value 1), then recipients MUST NOT skip this attribute.
This flag does not mean that all recipients must support this
message. Instead, any recipient that receives a message with this
flag set to 1 but cannot or will not process it as required MUST
NOT act on any part of the PB-TNC batch. Instead, the recipient
MUST respond with a fatal Unsupported Mandatory Message error code
in a CLOSE batch. In order to avoid taking action on some
messages in a batch only to later find an unsupported NOSKIP
flagged message, recipients of a PB-TNC batch might choose to scan
all of the messages in the batch prior to acting upon any of the
messages, checking to determine whether one of them is an
unsupported message with the NOSKIP flag set.
The other bits in this Flags field are reserved. For this version
of PB-TNC, they MUST be set to 0 on transmission and ignored on
reception.
PB-TNC Vendor ID (24 bits)
The PB-TNC Vendor ID field identifies a vendor by using the SMI
Private Enterprise Number (PEN). Any organization can receive its
own unique PEN from IANA, the Internet Assigned Numbers Authority.
This Vendor ID qualifies the PB-TNC Message Type field so that
each vendor has 2^32-1 separate message types available for their
use.
Message types standardized by the IETF use zero (0) in this field.
The Vendor ID 0xffffff is reserved. Posture Broker Clients and
Posture Broker Servers MUST NOT send messages in which the Vendor
ID has this reserved value (0xffffff). If a Posture Broker Client
or Posture Broker Server receives a message in which the PB-TNC
Vendor ID has this reserved value (0xffffff), it MUST respond with
a fatal Invalid Parameter error code in a CLOSE batch.
PB-TNC Message Type (32 bits)
The PB-TNC Message Type field identifies the type of the PB-TNC
message contained in the PB-TNC Message Value field. The PB-TNC
message type 0xffffffff is reserved. Posture Broker Clients and
Posture Broker Servers MUST NOT send messages in which the PB-TNC
Message Type field has this reserved value (0xffffffff). If a
Posture Broker Client or Posture Broker Server receives a message
in which the PB-TNC Message Type field has this reserved value
(0xffffffff), it MUST respond with a fatal Invalid Parameter error
code in a CLOSE batch. Unless otherwise prohibited in the
definition of a particular PB-TNC message type (e.g., PB-Language-
Preference), a single PB-TNC batch may contain multiple messages
with the same message type and/or vendor ID.
The IETF and any other organization with a PEN can define 2^32-1
unique PB-TNC message types, as long as the organization's PEN is
placed in the PB-TNC Vendor ID field of the message. Since the
PB-TNC message type is qualified by the vendor ID, there is no
risk of conflicts as long as each organization uses its own PEN
for the vendor ID and manages its own set of 2^32-1 message type
values.
This document defines certain PB-TNC message types that, when used
with the IETF SMI PEN (0), have standard meanings. These are
known as IETF Standard PB-TNC Message Types. Some of these PB-TNC
message types are mandatory and therefore MUST be implemented by
all Posture Broker Client and Posture Broker Server
implementations that claim compliance with this specification.
For details on which PB-TNC message types are mandatory, see the
description of these message types later in section 4.
IANA maintains a registry of PB-TNC message types. Entries in
this registry are added by Expert Review with Specification
Required, following the guidelines in section 6.1.
New vendor-specific PB-TNC message types (those used with a non-
zero PB-TNC vendor ID) may be defined and employed by vendors
without IETF or IANA involvement. However, Posture Broker Clients
and Posture Broker Servers MUST NOT require support for particular
vendor-specific PB-TNC message types and MUST interoperate with
other parties despite any differences in the set of vendor-
specific PB-TNC message types supported (although they MAY permit
administrators to configure them to require support for specific
PB-TNC message types).
Note that the PB-TNC Message Type field is completely separate
from the PA Subtype field. The same value (e.g., 0) may have
different meanings as a PB-TNC message type and as a PA subtype.
PB-TNC Message Length (32 bits)
This field specifies the length of this PB-TNC message in octets.
It includes this header (the fields Flags, PB-TNC Vendor ID, PB-
TNC Message Type, and PB-TNC Message Length). Therefore, this
value MUST always be at least 12. Any Posture Broker Client or
Posture Broker Server that receives a message with a PB-TNC
Message Length field whose value is less than 12 MUST respond with
a fatal Invalid Parameter error code in a CLOSE batch.
PB-TNC Message Value (variable length)
The syntax and semantics of this field vary, depending on the
values in the PB-TNC Vendor ID and PB-TNC Message Type fields.
The syntax and semantics of several standard messages are defined
in subsequent sections of this specification.
4.3. IETF Standard PB-TNC Message Types
The following table provides a reference list with brief descriptions of the IETF Standard PB-TNC Message Types defined in this specification. These PB-TNC message types must be used with a PB-TNC vendor ID of zero (0). If these PB-TNC message type values are used with a different PB-TNC vendor ID, they have a completely different meaning that is not defined in this specification. For more details on these message types, see the remainder of section 4. For IETF Standard PA Subtypes (which are completely different from PB-TNC message types), please refer to the PA-TNC specification [10]. Message Type Definition ------------ ---------- 0 PB-Experimental - reserved for experimental use 1 PB-PA - contains a PA message 2 PB-Assessment-Result - the overall assessment result computed by the Posture Broker Server 3 PB-Access-Recommendation - includes Posture Broker Server access recommendation 4 PB-Remediation-Parameters - includes Posture Broker Server remediation parameters 5 PB-Error - error indicator 6 PB-Language-Preference - sender's preferred language(s) for human-readable strings 7 PB-Reason-String - string explaining reason for Posture Broker Server access recommendation4.4. PB-Experimental
The PB-Experimental PB-TNC message type is a PB-TNC message type (value 0) that has been set aside for experimental purposes. It may be used to test code or for other experimental purposes. It MUST NOT be used in a production environment or in a product. This meaning for this PB-TNC message type only applies if the PB-TNC Vendor ID field in the PB-TNC Message Header contains the value zero (0). If a different Vendor ID is contained in that field, the PB-TNC message type 0 has a completely different meaning not defined in this specification. The contents of the PB-TNC Message Length and PB-TNC Message Value fields for this PB-TNC message type are not specified. They may have almost any value, depending on what experiments are being conducted. Similarly, the Flags field for this message may have the NOSKIP bit set or cleared, depending on what experiments are being conducted. However, note that the PB-TNC Message Length field must have a value
of at least 12 since that is the total of the length of the fixed- length fields at the start of the PB-TNC message (the fields Flags, PB-TNC Vendor ID, PB-TNC Message Type, and PB-TNC Message Length). Any Posture Broker Client or Posture Broker Server that receives a message with a PB-TNC Message Length field whose value is invalid MUST respond with a fatal Invalid Parameter error code in a CLOSE batch. A Posture Broker Client or Posture Broker Server implementation intended for production use MUST NOT send a message with this Message Type with the value zero (0) as the vendor ID. If it receives a message with this message type and with the value zero (0) as the vendor ID, it MUST ignore the message unless the NOSKIP bit is set, in which case it MUST respond with a fatal Unsupported Mandatory Message error code in a CLOSE batch.4.5. PB-PA
The PB-TNC message type named PB-PA (value 1) contains one PA message. Many batches will contain several PB-PA messages, but some batches may not contain any messages of this type. All Posture Broker Client and Posture Broker Server implementations MUST implement support for this PB-TNC message type. Generally, this support will consist of forwarding the enclosed PA message to the appropriate Posture Collectors and Posture Validators. Specific requirements are contained later in the description of this message type. The type of the PA message contained in a PB-PA message is indicated by the PA Message Vendor ID and PA Subtype fields, as described later in this section. The PA-TNC specification [10] describes several standard PA message types that can be identified by the PA Message Vendor ID and PA Subtype values listed in the PA-TNC specification. Other PA message types may also be defined, as described in the description of the PA Subtype field later in this section. The NOSKIP flag in the PB-TNC Message Header MUST be set for this message type. Any Posture Broker Client or Posture Broker Server that receives a PB-PA message with the NOSKIP flag not set MUST ignore the message and MUST respond with a fatal Invalid Parameter error code in a CLOSE batch. For the PB-PA message type, the PB-TNC Vendor ID field MUST contain the value zero (0) and the PB-TNC Message Type field MUST contain 1. If a non-zero value is contained in the PB-TNC Vendor ID field, message type 1 has a completely different meaning not defined in this specification.
The PB-TNC Message Length field MUST contain the length of the entire
PB-TNC message, including the fixed-length fields at the start of the
PB-TNC message (the fields Flags, PB-TNC Vendor ID, PB-TNC Message
Type, and PB-TNC Message Length), the fixed-length fields listed
below (Flags, PA Message Vendor ID, PA Subtype, Posture Collector
Identifier, and Posture Validator Identifier), and the PA Message
Body. Since the PA Message Body is variable length, the value in the
PB-TNC Message Length field will vary also. However, it MUST always
be at least 24 to cover the fixed-length fields listed in the
preceding sentences. Any Posture Broker Client or Posture Broker
Server that receives a PB-PA message with a PB-TNC Message Length
field that has an invalid value MUST respond with a fatal Invalid
Parameter error code in a CLOSE batch.
The following diagram illustrates the format and contents of the PB-
TNC Message Value field for this message type. The text after this
diagram describes the fields shown here.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | PA Message Vendor ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PA Subtype |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Posture Collector Identifier | Posture Validator Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PA Message Body (Variable Length) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Flags (8 bits)
This field contains flags relating to the PA message.
Bit 0 of this flags field (the most significant bit) is known as
the EXCL flag (for exclusive). If the EXCL bit is cleared (value
0), the Posture Broker Client or Posture Broker Server that
receives this PB-TNC message SHOULD deliver the PA message
contained in this PB-TNC message to all Posture Collectors or
Posture Validators that have expressed an interest in PA messages
with this PA Message Vendor ID and PA subtype. If a Posture
Broker Client receives a message with the EXCL flag set (value 1),
the Posture Broker Client SHOULD deliver the PA message contained
in this PB-TNC message only to the Posture Collector identified by
the Posture Collector Identifier field. However, if the
identified Posture Collector has not expressed an interest in PA
messages with this PA Message Vendor ID and PA subtype, the PA
message should be silently discarded. Analogous requirements
apply to a Posture Broker Server that receives a message with the
EXCL flag set.
The EXCL bit allows, for example, a Posture Validator to handle
the circumstance where there are two Posture Collectors on the
endpoint that are interested in a particular kind of PA messages
and the Posture Validator has remediation instructions that only
apply to one of those Posture Collectors.
The other bits in this Flags field are reserved. For this version
of PB-TNC, they MUST be set to 0 on transmission and ignored on
reception.
PA Message Vendor ID (24 bits)
The PA Message Vendor ID field identifies a vendor by using the
SMI Private Enterprise Number (PEN). Any organization can receive
its own unique PEN from IANA, the Internet Assigned Numbers
Authority. The PA Message Vendor ID qualifies the PA Subtype
field so that each vendor has 2^32-1 separate PA subtypes
available for its use. PA subtypes standardized by the IETF are
always used with a PA Message Vendor ID of the value zero (0) in
this field. The PA Message Vendor ID 0xffffff is reserved. A
Posture Broker Client or Posture Broker Server MUST NOT send
messages in which the PA Message Vendor ID field has this reserved
value (0xffffff). If a Posture Broker Client or Posture Broker
Server receives a message in which the PA Message Vendor ID has
this reserved value (0xffffff), it MUST respond with a fatal
Invalid Parameter error code in a CLOSE batch.
PA Subtype (32 bits)
The PA Subtype field identifies the type of the PA message
contained in the PA Message Body field. The PA subtype 0xffffffff
is reserved. A Posture Broker Client or Posture Broker Server
MUST NOT send messages in which the PA Subtype field has this
reserved value (0xffffffff). If a Posture Broker Client or
Posture Broker Server receives a message in which the PA Subtype
has this reserved value (0xffffffff), it MUST respond with a fatal
Invalid Parameter error code in a CLOSE batch. A Posture Broker
Client or Posture Broker Server MUST support having multiple PA
messages in a single PB-TNC batch that have the same PA subtype
and/or PA Message Vendor ID.
IANA maintains a registry of PA subtypes. Entries in this
registry are added by Expert Review with Specification Required,
following the guidelines in section 6.1. No PA subtypes are
defined in this specification. Definitions of IETF Standard PA
Subtypes are contained in the PA-TNC specification [10] and other
specifications. IETF Standard PA Subtypes are always used with a
PA Message Vendor ID of zero (0).
New vendor-specific PA subtypes (those used with a non-zero PA
Message Vendor ID) may be defined and employed by vendors without
IETF or IANA involvement. However, Posture Broker Clients and
Posture Broker Servers MUST NOT require support for particular
vendor-specific PA subtypes and MUST interoperate with other
parties despite any differences in the set of vendor-specific PA
subtypes supported (although they MAY permit administrators to
configure them to require support for specific PA subtypes).
Note that the PB-TNC Message Type field is completely separate
from the PA Subtype field. The same value (e.g., 0) may have
different meanings as a PB-TNC message type and as a PA subtype.
Posture Collector Identifier (16 bits)
The Posture Collector Identifier field contains the identifier of
the Posture Collector associated with this PA message.
The Posture Broker Client is responsible for assigning one or more
Posture Collector Identifier values (but not 0xffff) to each
Posture Collector involved in a message exchange. Multiple
Posture Collector identifiers are required for appropriate
correlation in cases where there are multiple components of the
same type handled by a single Posture Collector, e.g., an endpoint
with two VPN client implementations handled by a single VPN
Posture Collector. Please refer to section 3.3 of the PA-TNC
specification for an example that illustrates the use of multiple
Posture Collector Identifiers. The Posture Collector Identifier
value(s) assigned to a Posture Collector by a Posture Broker
Client MUST NOT change during the course of a PT session. This
identifier is used to identify a unique Posture Collector
communicating with the Posture Broker Client on the endpoint
during a NEA exchange, and is used by the Posture Validator to
send response attributes to a specific Posture Collector component
if required.
When a Posture Broker Server sets the EXCL flag for a PA message,
the Posture Broker Server MUST set the Posture Collector
Identifier field to the identifier of the Posture Collector that
should receive the PA message. If the EXCL flag is not set, a
Posture Broker Server MAY still set the Posture Collector
Identifier value for PA messages that it sends to indicate that
the PA message is intended as a response to a message sent by the
Posture Collector associated with the specified Posture Collector
Identifier. If the Posture Broker Server does not wish to
indicate any Posture Collector in this manner, it SHOULD set this
field to the reserved value 0xffff.
Posture Validator Identifier (16 bits)
The Posture Validator Identifier field contains the identifier of
the Posture Validator associated with this PA message.
The Posture Broker Server MUST assign a unique Posture Validator
Identifier value (but not 0xffff) to each Posture Validator
involved in a message exchange and include this Posture Validator
identifier in this field for any PA messages sent by that Posture
Validator. The Posture Validator Identifier value assigned to a
Posture Validator by a Posture Broker Server MUST NOT change
during the course of a PT session. This identifier is used to
identify a unique Posture Validator communicating with the Posture
Broker Server endpoint during a NEA exchange, and is used by the
Posture Collector to send attributes to a specific Posture
Validator if required.
When a Posture Broker Client sets the EXCL flag for a PA message,
the Posture Broker Client MUST set the Posture Validator
Identifier field to the identifier of the Posture Validator that
should receive the PA message. If the EXCL flag is not set, a
Posture Broker Client MAY still set the Posture Validator
Identifier value for PA messages that it sends to indicate that
the PA message is intended as a response to a message sent by the
Posture Validator associated with the specified Posture Validator
Identifier. If the Posture Broker Client does not wish to
indicate any Posture Validator in this manner, it SHOULD set this
field to the reserved value 0xffff.
PA Message Body (variable length)
The PA Message Body field contains the body of the PA message that
is being carried in this PB-TNC message. The length of this field
can be determined by subtracting the length of the fixed-length
fields at the start of the PB-TNC message (the fields Flags, PB-
TNC Vendor ID, PB-TNC Message Type, and PB-TNC Message Length) and
the fixed-length fields at the start of the PB-PA message (Flags,
PA Message Vendor ID, PA Subtype, Posture Collector Identifier,
and Posture Validator Identifier) from the message length
contained in the PB-TNC Message Length field. The length of these
fixed-length fields is 24 octets. Therefore, any Posture Broker
Client or Posture Broker Server that receives a PB-PA message with
a PB-TNC Message Length field whose value is less than 24 MUST
respond with a fatal Invalid Parameter error code in a CLOSE
batch.
4.6. PB-Assessment-Result
The PB-TNC message type named PB-Assessment-Result (value 2) is used
by the Posture Broker Server to provide the assessment result after
the Posture Broker Server has completed the assessment of the
endpoint. The Posture Broker Server will typically compute the
assessment result as a cumulative of the individual assessment
results received from the various Posture Validators; the algorithm
for computation of assessment result at the Posture Broker layer is
implementation specific and can also change based on policies in a
specific deployment. The Posture Broker Server MUST include one
message of this type in any batch of type RESULT and MUST NOT include
a message of this type in any other type of batch. The Posture
Broker Client MUST NOT send a PB-TNC message with this message type.
If a Posture Broker Server receives a PB-TNC message with this
message type, it MUST respond with a fatal Invalid Parameter error in
a CLOSE batch. The Posture Broker Client MUST implement and process
this message and MUST ignore any message with this message type that
is not part of a batch of type RESULT.
The NOSKIP flag in the PB-TNC Message Header MUST be set for this
message type. The PB-TNC Vendor ID field MUST contain the value zero
(0) and the PB-TNC Message Type field MUST contain 2. If a non-zero
value is contained in the PB-TNC Vendor ID field, message type 2 has
a completely different meaning not defined in this specification.
The PB-TNC Message Length field MUST contain the value 16 since that
is the total of the length of the fixed-length fields at the start of
the PB-TNC message (the fields Flags, PB-TNC Vendor ID, PB-TNC
Message Type, and PB-TNC Message Length) along with the Assessment
Result field described below. Any Posture Broker Client or Posture
Broker Server that receives a PB-Assessment-Result message with a PB-
TNC Message Length field that does not have a value of 16 MUST
respond with a fatal Invalid Parameter error code in a CLOSE batch.
The following diagram illustrates the format and contents of the PB-
TNC Message Value field for this message type. The text after this
diagram describes the fields shown here.
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Assessment Result |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Assessment Result
This 32-bit field MUST contain one of the following values
Value Description
----- -----------
0 Posture Broker Server assessed the endpoint to be
compliant with policy.
1 Posture Broker Server assessed the endpoint to be non-
compliant with policy but the difference from compliance
was minor.
2 Posture Broker Server assessed the endpoint to be non-
compliant with policy and the assessed difference from
compliance was very significant.
3 Posture Broker Server was unable to determine policy
compliance due to an error.
4 Posture Broker Server was unable to determine whether the
assessed endpoint is compliant with policy based on the
attributes provided by endpoint.
If a Posture Broker Client receives an Assessment Result value
other than the five values described above, it MUST respond with a
fatal Invalid Parameter error in a CLOSE batch. Other values may
be defined in future versions of PB-TNC but only if the PB-TNC
version number is changed. Therefore, there is no need for an
IANA registry for Assessment Result values.
4.7. PB-Access-Recommendation
The PB-TNC message type named PB-Access-Recommendation (value 3) is
used by the Posture Broker Server to provide an access recommendation
after the Posture Broker Server has completed some assessment of the
endpoint. The PB-Assessment-Result and the PB-Access-Recommendation
attribute together constitute the global assessment decision for an
endpoint. The PB-Access-Recommendation is not authoritative, and the
network and host-based access control systems would typically use
additional information to determine the network access that is
granted to the endpoint. The Posture Broker Server MAY include one
message of this type in any batch of type RESULT and MUST NOT include
a message of this type in any other type of batch. Posture Broker
Clients MUST NOT send a PB-TNC message with this message type. If a
Posture Broker Server receives a PB-TNC message with this message
type, it MUST respond with a fatal Invalid Parameter error in a CLOSE
batch. The Posture Broker Client MUST implement and process this
message and MUST ignore any message with this message type that is
not part of a batch of type RESULT.
The NOSKIP flag in the PB-TNC Message Header MUST NOT be set for this
message type. Any Posture Broker Client or Posture Broker Server
that receives a PB-Access-Recommendation message with the NOSKIP flag
set MUST ignore the message and MUST respond with a fatal Invalid
Parameter error code in a CLOSE batch. The PB-TNC Vendor ID field
MUST contain the value zero (0) and the PB-TNC Message Type field
MUST contain 3. If a non-zero value is contained in the PB-TNC
Vendor ID field, message type 3 has a completely different meaning
not defined in this specification. The PB-TNC Message Length field
MUST contain the value 16 since that is the total of the length of
the fixed-length fields at the start of the PB-TNC message (the
fields Flags, PB-TNC Vendor ID, PB-TNC Message Type, and PB-TNC
Message Length) along with the Access Recommendation field described
below. Any Posture Broker Client or Posture Broker Server that
receives a PB-Access-Recommendation message with a PB-TNC Message
Length field that does not have a value of 16 MUST respond with a
fatal Invalid Parameter error code in a CLOSE batch.
The following diagram illustrates the format and contents of the PB-
TNC Message Value field for this message type. The text after this
diagram describes the fields shown here.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Access Recommendation Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Reserved (16 bits)
These Reserved bits MUST be set to 0 on transmission and ignored
on reception.
Access Recommendation Code (16 bits)
The Access Recommendation Code field identifies the Access
Recommendation that the Posture Broker Server has made for this
Posture Broker Client at this time. This field MUST have one of
these three values: 1 for Access Allowed (full access), 2 for
Access Denied (no access), or 3 for Quarantined (partial access).
If a Posture Broker Client receives an Access Recommendation Code
value other than these three values, it MUST respond with a fatal
Invalid Parameter error code in a CLOSE batch. Other values may
be defined in future versions of PB-TNC but only if the PB-TNC
version number is changed. Therefore, there is no need for an
IANA registry for Access Recommendation Codes.
4.8. PB-Remediation-Parameters
The PB-TNC message type named PB-Remediation-Parameters (value 4) is
used by the Posture Broker Server to provide global (not Posture
Validator-specific) remediation parameters after the Posture Broker
Server has completed some assessment of the endpoint. The Posture
Broker Server MAY include one or more messages of this type in any
batch of any type, but this message type is most useful in batches of
type RESULT.
The Posture Broker Client MUST NOT send a PB-TNC message with this
message type. If a Posture Broker Server receives a PB-TNC message
with this message type, it MUST respond with a fatal Invalid
Parameter error in a CLOSE batch. The Posture Broker Client may
implement and process this message but is not required to do so. It
may skip this message. Even if the Posture Broker Client implements
this message type, it is not obligated to act on it.
The NOSKIP flag in the PB-TNC Message Header MUST NOT be set for this
message type. The PB-TNC Vendor ID field MUST contain the value zero
(0) and the PB-TNC Message Type field MUST contain 4. If a non-zero
value is contained in the PB-TNC Vendor ID field, message type 4 has
a completely different meaning not defined in this specification.
The PB-TNC Message Length field MUST contain the length of the entire
PB-TNC message, including the fixed-length fields at the start of the
PB-TNC message (the fields Flags, PB-TNC Vendor ID, PB-TNC Message
Type, and PB-TNC Message Length), the fixed-length fields listed
below (Reserved, Remediation Parameters Vendor ID, and Remediation
Parameters Type), and the Remediation Parameters. Since the
Remediation Parameters field is variable length, the value in the PB-
TNC Message Length field will vary also. However, it MUST always be
at least 20 to cover the fixed-length fields listed in the preceding
sentences. Any Posture Broker Client that receives a PB-Remediation-
Parameters message with a PB-TNC Message Length field that contains
an invalid value (e.g., less than 20) MUST respond with a fatal
Invalid Parameter error code in a CLOSE batch.
The following diagram illustrates the format and contents of the PB-
TNC Message Value field for this message type. The text after this
diagram describes the fields shown here.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Remediation Parameters Vendor ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remediation Parameters Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remediation Parameters (Variable Length) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Reserved (8 bits)
These Reserved bits MUST be set to 0 on transmission and ignored
on reception.
Remediation Parameters Vendor ID (24 bits)
The Remediation Parameters Vendor ID field identifies a vendor by
using the SMI Private Enterprise Number (PEN). Any organization
can receive its own unique PEN from IANA, the Internet Assigned
Numbers Authority. The Remediation Parameters Vendor ID qualifies
the Remediation Parameters Type field so that each vendor has 2^32
separate Remediation Parameters Types available for its use.
Remediation Parameters Types standardized by the IETF are always
used with the value zero (0) in this field.
Remediation Parameters Type (32 bits)
The Remediation Parameters Type field identifies the type of
remediation parameters contained in the Remediation Parameters
field. A Posture Broker Client or Posture Broker Server MUST
support having multiple Remediation Parameters messages contained
in a single PB-TNC batch that have the same Remediation Parameters
Type and/or Remediation Parameters Vendor ID.
IANA maintains a registry of PB-TNC Remediation Parameters Types.
Entries in this registry are added by Expert Review with
Specification Required, following the guidelines in section 6.1.
A list of IETF Standard PB-TNC Remediation Parameters Types
defined in this specification appears later in this section.
New vendor-specific Remediation Parameters Types (those used with
a non-zero Remediation Parameters vendor ID) may be defined and
employed by vendors without IETF or IANA involvement. However,
Posture Broker Clients and Posture Broker Servers MUST NOT require
support for particular vendor-specific Remediation Parameters
Types and MUST interoperate with other parties despite any
differences in the set of vendor-specific Remediation Parameters
Types supported (although they MAY permit administrators to
configure them to require support for specific Remediation
Parameters Types).
Note that the Remediation Parameters Type is completely separate
from the PB-TNC Message Type and the PA Subtype fields. The same
value (e.g., 0) may have different meanings in each of these
fields.
Remediation Parameters (variable length)
The Remediation Parameters field contains the actual remediation
parameters carried in this PB-TNC message. The length of this
field can be determined by subtracting the length of the fixed-
length fields at the start of the PB-TNC message (the fields
Flags, PB-TNC Vendor ID, PB-TNC Message Type, and PB-TNC Message
Length) and the fixed-length fields at the start of the PB-
Remediation-Parameters message (Reserved, Remediation Parameters
Vendor ID, and Remediation Parameters Type) from the message
length contained in the PB-TNC Message Length field. The length
of these fixed-length fields is 20 octets. Therefore, any Posture
Broker Client that receives a PB-Remediation-Parameters message
with a PB-TNC Message Length field whose value is less than 20
MUST consider this a malformed message. The Posture Broker Client
MUST respond with a fatal Invalid Parameter error code in a CLOSE
batch.
4.8.1. IETF Standard PB-TNC Remediation Parameters Types
This subsection defines several Remediation Parameters Types that
have been standardized by the IETF.
Remediation-URI
This Remediation Parameters Type is employed by creating a PB-
Remediation-Parameters message with a Remediation Parameters
Vendor ID equal to the value zero (0) and a Remediation Parameters
Type of 1. The Remediation Parameters field in the PB-
Remediation-Parameters message MUST contain a URI, as described in
RFC 3986 [2]. This URI contains instructions and resources for
remediation. The Posture Broker Client MAY load the URI and
display the resulting web page to the user. The Posture Broker
Client MAY also ignore the URI or take another action with it.
The Posture Broker Server and any other parties involved in
configuring this remediation URI should consider the likely
capabilities of the Posture Broker Client when creating the URI
and the content referenced by the URI. For example, they should
consider the Posture Broker Client's language preferences as
expressed in the PB-Language-Preference message.
Remediation-String
This Remediation Parameters Type is employed by creating a PB-
Remediation-Parameters message with a Remediation Parameters
Vendor ID equal to the value zero (0) and a Remediation Parameters
Type of 2. The Remediation Parameters field in the PB-
Remediation-Parameters message MUST contain the structure defined
below, which contains human-readable instructions for remediation.
The Posture Broker Client MAY display the instructions to the
user. The Posture Broker Client MAY also ignore the instructions
or take another action with them. The Posture Broker Server and
any other parties involved in configuring these instructions
should consider the likely capabilities of the Posture Broker
Client when creating the instructions. For example, they should
consider the Posture Broker Client's language preferences as
expressed in the PB-Language-Preference message.
The following diagram illustrates the format and contents of the
Remediation Parameters field when carrying a Remediation-String
parameter. The text after this diagram describes the fields shown
here.
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remediation String Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remediation String (Variable Length) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Lang Code Len | Remediation String Lang Code (Variable Len) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Remediation String Length (32 bits)
The Remediation String Length contains the length of the
Remediation String field in octets.
Remediation String (variable length)
The Remediation String field MUST contain a UTF-8 [6] encoded
string. This string contains human-readable instructions for
remediation that MAY be displayed to the user by the Posture
Broker Client. NUL termination MUST NOT be included. If a
Posture Broker Client receives a Reason String that does contain a
NUL termination, it MUST respond with a fatal Invalid Parameter
error in a CLOSE batch.
Lang Code Len (8 bits)
The Lang Code Len field contains the length of the Remediation
String Lang Code field in octets. This value may be set to zero
to indicate that the language code for the Remediation String
field is not known.
Remediation String Lang Code (variable length)
The Remediation String Lang Code field contains a US-ASCII string
composed of a well-formed RFC 4646 [3] language tag that indicates
the language(s) used in the Remediation String in the Remediation
Parameters field. A zero-length string may be sent for this field
(essentially omitting this field) to indicate that the language
code for the Remediation String field is not known.
4.9. PB-Error
The PB-TNC message type named PB-Error (value 5) is used by the
Posture Broker Client or Posture Broker Server to indicate that an
error has occurred. The Posture Broker Client or Posture Broker
Server MAY include one or more messages of this type in any batch of
any type. Other messages may also be included in the same batch.
The party that receives a PB-Error message MAY log it or take other
action as deemed appropriate. If the FATAL flag is set (value 1),
the recipient MUST terminate the PB-TNC session after processing the
batch without sending any messages in response. Every Posture Broker
Client and Posture Broker Server MUST implement this message type.
The NOSKIP flag in the PB-TNC Message Header MUST be set for this
message type. The PB-TNC Vendor ID field MUST contain the value zero
(0) and the PB-TNC Message Type field MUST contain 5. If a non-zero
value is contained in the PB-TNC Vendor ID field, message type 5 has
a completely different meaning not defined in this specification.
The PB-TNC Message Length field MUST contain the length of the entire
PB-TNC message, including the fixed-length fields at the start of the
PB-TNC message (the fields Flags, PB-TNC Vendor ID, PB-TNC Message
Type, and PB-TNC Message Length), the fixed-length fields listed
below (Flags, Error Code Vendor ID, Error Code, and Reserved), and
the Error Parameters. Since the Error Parameters field is variable
length, the value in the PB-TNC Message Length field will vary also.
However, it MUST always be at least 20 to cover the fixed-length
fields listed in the preceding sentences. Any Posture Broker Client
or Posture Broker Server that receives a PB-Error message with a PB-
TNC Message Length field that contains an invalid value (e.g., less
than 20) MUST respond with a fatal Invalid Parameter error code in a
CLOSE batch. Any PB-Error message generated while processing a PB-
Error message MUST be a fatal error to avoid the chance of generating
an infinite loop of errors.
The following diagram illustrates the format and contents of the PB-
TNC Message Value field for this message type. The text after this
diagram describes the fields shown here.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | Error Code Vendor ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Error Code | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Error Parameters (Variable Length) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Flags (8 bits)
This field defines flags relating to the error.
Bit 0 of this flags field (the most significant bit) is known as
the FATAL flag. If the FATAL bit is cleared (value 0), the
Posture Broker Client or Posture Broker Server that receives this
PB-TNC message SHOULD process this error and then continue with
the exchange. If the FATAL flag is set (value 1), the Posture
Broker Client or Posture Broker Server that receives this PB-TNC
message MUST terminate the exchange after processing the error.
In addition, any Posture Broker Client or Posture Broker Server
that sends a fatal error MUST NOT process the batch that caused
the error and MUST terminate the exchange after sending the batch
containing the error report. A PB-Error message with the FATAL
flag set MUST always be sent in a CLOSE batch since the sender
will be terminating the exchange immediately after sending the
batch.
The FATAL bit allows a Posture Broker Client or Posture Broker
Server to signal a fatal error (like an invalid batch type) and/or
a non-fatal error (like an invalid language tag for a preferred
language).
The other bits in this Flags field are reserved. For this version
of PB-TNC, they MUST be set to 0 on transmission and ignored on
reception.
Error Code Vendor ID (24 bits)
The Error Code Vendor ID field identifies a vendor by using the
SMI Private Enterprise Number (PEN). Any organization can receive
its own unique PEN from IANA, the Internet Assigned Numbers
Authority. The Error Code Vendor ID qualifies the Error Code
field so that each vendor has 2^16 separate Error Codes available
for its use. Error codes standardized by the IETF are always used
with the value zero (0) in this field. For detailed descriptions
of those messages, see the next few subsections.
Error Code (16 bits)
The Error Code field identifies the type of error being signaled
with this message. The format of the Error Parameters field
depends on the value of the Error Code Vendor ID and the Error
Code. However, any recipient that does not understand a
particular error code can process the error fairly well by using
the FATAL flag to determine whether the error is fatal and the PB-
TNC Message Length to skip over the Error Parameters field (or log
it).
IANA maintains a registry of PB-TNC Error Codes. Entries in this
registry are added by Expert Review with Specification Required,
following the guidelines in section 6.1. A list of IETF Standard
PB-TNC Error Codes defined in this specification appears later in
section 4.9.1.
New vendor-specific error codes (those used with a non-zero error
code vendor ID) may be defined and employed by vendors without
IETF or IANA involvement. Posture Broker Clients and Posture
Broker Servers that receive an unknown error code MUST process
this error code gracefully by ignoring or logging it if it is not
marked as fatal and terminating the exchange if it is marked as
fatal.
Reserved (16 bits)
The Reserved bits MUST be set to 0 on transmission and ignored on
reception.
4.9.1. IETF Standard PB-TNC Error Codes
The following error codes are IETF Standard PB-TNC Error Codes, hence the Error Code Vendor ID MUST be the value zero (0). The following table defines the 16-bit error code. Vendor-specific error codes may be defined by setting the Error Code Vendor ID to the defining vendor's SMI PEN and setting the Error Code field to whatever error code(s) that vendor has defined. The format, length, and meaning of the Error Parameters field varies, based on the Error Code Vendor ID and Error Code. Subsequent sections of this document define the format, length, and meaning of the Error Parameters for the IETF Standard PB-TNC Error Codes defined in this section. Error Code Definition ---------- ---------- 0 Unexpected Batch Type. Error Parameters are empty. 1 Invalid Parameter. Error Parameters has offset where invalid value was found. 2 Local Error. Error Parameters are empty. 3 Unsupported Mandatory Message. Error Parameters has offset of offending PB-TNC Message 4 Version Not Supported. Error Parameters has information about which versions are supported.4.9.2. Error Parameters Structures for IETF Standard PB-TNC Error Codes
This section defines the format, length, and meaning of the Error Parameters field for the IETF Standard PB-TNC Error Codes defined in this specification. The Error Parameters field is zero length for the IETF Standard PB- TNC Error Code 0. The FATAL flag MUST be set for this error code. The Error Parameters field has the following structure for the IETF Standard PB-TNC Error Code 1. The Offset field is the offset in octets from the start of the PB-TNC batch to the invalid value. The FATAL flag may be either set or cleared for this error code. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Offset | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Error Parameters field is zero length for the IETF Standard PB-
TNC Error Code 2. The FATAL flag MUST be set for this error code.
The Error Parameters field has the following structure for the IETF
Standard PB-TNC Error Code 3. The Offset field is the offset in
octets from the start of the PB-TNC batch to the PB-TNC message whose
message type was not recognized (and where the NOSKIP flag was set).
The FATAL flag MUST be set for this error code.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Offset |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Error Parameters field has the following structure for the IETF
Standard PB-TNC Error Code 4. The FATAL flag MUST be set for this
error code.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Bad Version | Max Version | Min Version | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Bad Version field is the version number that was received and is
not supported. The Max Version and Min Version fields indicate which
PB-TNC version numbers are supported by the sender of the error code.
The sender MUST support all PB-TNC versions between the Min Version
and the Max Version, inclusive (i.e., including the Min Version and
the Max Version) but excluding the reserved versions listed in
section 4.1. The Reserved field MUST be set to 0 on transmission and
ignored upon reception. When possible, recipients of this error code
SHOULD send future messages to the Posture Broker Server or Posture
Broker Client that originated this error message with a PB-TNC
version number within the stated range.
Any party that is sending the Version Not Supported error code MUST
include that error code as the only PB-TNC message in a PB-TNC CLOSE
batch with version number 2. All parties that send PB-TNC batches
SHOULD be able to properly process a batch that meets this
description, even if they cannot process any other aspect of PB-TNC
version 2. This ensures that a PB-TNC version exchange can proceed
properly, no matter what versions of PB-TNC the parties implement.
4.10. PB-Language-Preference
The PB-TNC message type named PB-Language-Parameters (value 6) is used by the Posture Broker Client to indicate which language or languages it would prefer for any human-readable strings that might be sent to it. This allows the Posture Broker Server and Posture Validators to adapt any messages they may send to the Posture Broker Client's preferences (probably determined by the language preferences of the endpoint's users). The Posture Broker Server may also send this message type to the Posture Broker Client to indicate the Posture Broker Server's language preferences, but this is not very useful since the Posture Broker Client rarely sends human-readable strings to the Posture Broker Server and, if it does, rarely can adapt those strings to the preferences of the Posture Broker Server. No Posture Broker Client or Posture Broker Server is required to send or implement this message type. However, a Posture Broker Server SHOULD attempt to adapt to user language preferences by implementing this message type, passing the language preference information to Posture Validators, and allowing administrators to configure human- readable languages in whatever languages are preferred by their users. A Posture Broker Client or Posture Broker Server may include a message of this type in any batch of any type. However, it is suggested that this message be included in the first batch sent by the Posture Broker Client or Posture Broker Server in a PB-TNC session so that the recipient can start adapting its human-readable messages as soon as possible. If one PB-Language-Parameters message is received and then another one is received in a later batch for the same PB-TNC session, the value included in the later message should be considered to replace the value in the earlier message. A Posture Broker Client or Posture Broker Server MUST NOT include more than one message of this type in a single batch. If a Posture Broker Client or Posture Broker Server receives more than one message of this type in a single batch, it should ignore all but the last one. The NOSKIP flag in the PB-TNC Message Header MUST NOT be set for this message type. The PB-TNC Vendor ID field MUST contain the value zero (0) and the PB-TNC Message Type field MUST contain 6. If a non-zero value is contained in the PB-TNC Vendor ID field, message type 6 has a completely different meaning not defined in this specification.
The PB-TNC Message Length field MUST contain the length of the entire
PB-TNC message, including the fixed-length fields at the start of the
PB-TNC message (the fields Flags, PB-TNC Vendor ID, PB-TNC Message
Type, and PB-TNC Message Length) and the Language Preference field.
Since the Language Preference field is variable length, the value in
the PB-TNC Message Length field will vary also. However, it MUST
always be at least 12 to cover the fixed-length fields listed in the
preceding sentences.
The following diagram illustrates the format and contents of the PB-
TNC Message Value field for this message type. The text after this
diagram describes the fields shown here.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Language Preference (Variable Length) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Language Preference (variable length)
The Language Preference field contains an Accept-Language header,
as described in RFC 3282 [4] (using the RFC 2234 ABNF definition
of Accept-Language included in that RFC, US-ASCII only, no control
characters allowed, no comments, no NUL termination). Any Posture
Broker Client or Posture Broker Server that sends a PB-Language-
Preference message MUST ensure that the Language Preference field
conforms to this format. For example, one acceptable value would
be "Accept-Language: fr, en" (without the quote marks).
A zero-length Language Preference field indicates that no language
preference information is available. Generally, there's no need
to send a PB-Language-Preference message with a zero-length
Language Preference field since this is equivalent to sending no
PB-Language-Preference message at all, but it may be useful to
send a zero-length Language Preference field if a PB-Language-
Preference message with a non-zero-length Language Preference
field was sent in an earlier batch but these preferences no longer
apply.
4.11. PB-Reason-String
The PB-TNC message type named PB-Reason-String (value 7) is used by
the Posture Broker Server to provide a human-readable explanation for
the global assessment decision conveyed in the PB-Assessment-Result &
PB-Access-Recommendation messages. Therefore, a PB-Reason-String
message SHOULD only be included in the same batch as the PB- Assessment-Result and PB-Access-Recommendation message. The Posture Broker Client MUST NOT ever send a PB-Reason-String message. The Posture Broker Client is not required to implement this message type and the Posture Broker Server is not required to send it. However, there is some benefit to doing so since users are often curious about why the endpoint was considered non-compliant. The manner in which a Posture Broker Client uses this field is up to the implementer and not specified here. The Posture Broker Client MAY display the message to the user, log it, ignore it, or take any other action that is not inconsistent with the requirements of this specification. Since the strings contained in this message are human-readable, the Posture Broker Server SHOULD adapt them to the Posture Broker Client's language preferences as expressed in any PB- Language-Preference message sent by the Posture Broker Client in this PB-TNC session. A Posture Broker Server MAY include more than one message of this type in any batch of any type. However, it is suggested that this message be included in the same batch as the PB-Assessment-Result and PB-Access-Recommendation message. If more than one PB-Reason-String message is included in a single batch, the Posture Broker Client SHOULD consider the strings included in these messages to be equivalent in meaning. This allows the Posture Broker Server to return multiple equivalent reason strings in different languages, which may help if the Posture Broker Server is not able to accommodate the Posture Broker Client's language preferences. The NOSKIP flag in the PB-TNC Message Header MUST NOT be set for this message type. The PB-TNC Vendor ID field MUST contain the value zero (0) and the PB-TNC Message Type field MUST contain 7. If a non-zero value is contained in the PB-TNC Vendor ID field, message type 7 has a completely different meaning not defined in this specification. The PB-TNC Message Length field MUST contain the length of the entire PB-TNC message, including the fixed-length fields at the start of the PB-TNC message (the fields Flags, PB-TNC Vendor ID, PB-TNC Message Type, and PB-TNC Message Length), the fixed-length fields listed below (Reason String Length and Lang Code Len), and the Reason String and Reason String Language Code fields. Since the Reason String and Reason String Language Code fields are variable length, the value in the PB-TNC Message Length field will vary also. However, it MUST always be at least 17 to cover the fixed-length fields listed in the preceding sentences. In fact, the PB-TNC Message Length field MUST be exactly the sum of 17 (for the fixed-length fields) and the values
of the Reason String Length and Lang Code Len fields. If this is not
the case, the recipient MUST respond with a fatal Invalid Parameter
error code in a CLOSE batch.
The following diagram illustrates the format and contents of the PB-
TNC Message Value field for this message type. The text after this
diagram describes the fields shown here.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reason String Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reason String (Variable Length) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Lang Code Len | Reason String Language Code (Variable Length) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Reason String Length (32 bits)
The Reason String Length field contains the length of the Reason
String field in octets.
Reason String (variable length)
The Reason String field contains a UTF-8 encoded string that
provides a human-readable reason for the Posture Broker Server's
assessment decision. NUL termination MUST NOT be included. If a
Posture Broker Client receives a Reason String that does contain a
NUL termination, it MUST respond with a fatal Invalid Parameter
error code in a CLOSE batch. A zero-length string MUST NOT be
sent since this is the same as sending no reason string at all,
leaving the reason unspecified.
Lang Code Len (8 bits)
The Lang Code Len field contains the length of the Reason String
Language Code field in octets.
Reason String Language Code (variable length)
The Reason String Language Code field contains a US-ASCII string
containing a well-formed RFC 4646 [3] language tag that indicates
the language(s) used in the Reason String in this message. NUL
termination MUST NOT be included in this field. A zero-length
string MAY be sent for this field (essentially omitting this
field) to indicate that the language code for the reason string is
not known.
(next page on part 3)
