Internet Engineering Task Force (IETF) P. Sangster
Request for Comments: 5792 Symantec Corporation
Category: Standards Track K. Narayan
ISSN: 2070-1721 Cisco Systems
March 2010
PA-TNC: A Posture Attribute (PA) Protocol Compatible
with Trusted Network Connect (TNC)
Abstract
This document specifies PA-TNC, a Posture Attribute protocol
identical to the Trusted Computing Group's IF-M 1.0 protocol. The
document then evaluates PA-TNC against the requirements defined in
the NEA Requirements specification.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc5792.
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
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include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Sangster & Narayan Standards Track [Page 1]RFC 5792 PA-TNC March 2010
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Table of Contents
1. Introduction ....................................................4
1.1. Prerequisites ..............................................4
1.2. Message Diagram Conventions ................................4
1.3. Conventions Used in This Document ..........................4
2. Design Considerations ...........................................4
2.1. Standard Attribute Namespace for Interoperability ..........4
2.2. Vendor-Defined Namespace for Differentiation and Agility ...5
2.3. Use of TLV-Based Encoding for Efficiency ...................6
3. PA-TNC Message Protocol .........................................7
3.1. PA-TNC Messaging Model .....................................7
3.2. PA-TNC Relationship to PB-TNC ..............................8
3.3. PB-PA Posture Collector and Posture Validator
Identifiers ...............................................10
3.4. PA-TNC Messages in PB-TNC .................................10
3.5. IETF Standard PA Subtypes .................................11
3.6. PA-TNC Message Header Format ..............................12
4. PA-TNC Attributes ..............................................13
4.1. PA-TNC Attribute Header ..................................13
4.2. IETF Standard PA-TNC Attribute Types .....................17
4.2.1. Attribute Request ..................................18
4.2.2. Product Information ................................20
4.2.3. Numeric Version ....................................22
4.2.4. String Version .....................................24
4.2.5. Operational Status .................................26
4.2.6. Port Filter ........................................29
4.2.7. Installed Packages .................................31
4.2.8. PA-TNC Error .......................................34
4.2.9. Assessment Result ..................................41
4.2.10. Remediation Instructions ..........................42
4.2.11. Forwarding Enabled ................................45
4.2.12. Factory Default Password Enabled ..................47
4.3. Vendor-Defined Attributes ................................48
5. Security Considerations ........................................48
5.1. Trust Relationships .......................................48
Sangster & Narayan Standards Track [Page 2]RFC 5792 PA-TNC March 2010
5.1.1. Posture Collector ..................................49
5.1.2. Posture Validator ..................................49
5.1.3. Posture Broker Client, Posture Broker Server .......49
5.2. Security Threats ..........................................50
5.2.1. Attribute Theft ....................................50
5.2.2. Message Fabrication ................................51
5.2.3. Attribute Modification .............................51
5.2.4. Attribute Replay ...................................52
5.2.5. Attribute Insertion ................................52
5.2.6. Denial of Service ..................................53
6. Privacy Considerations .........................................53
7. IANA Considerations ............................................54
7.1. Designated Expert Guidelines ..............................55
7.2. PA Subtypes ...............................................56
7.3. Registry for PA-TNC Attribute Types .......................56
7.4. Registry for PA-TNC Error Codes ...........................57
7.5. Registry for PA-TNC Remediation Parameters Types ..........58
8. Acknowledgments ................................................58
9. References .....................................................59
9.1. Normative References ......................................59
9.2. Informative References ....................................59
Appendix A. Use Cases .............................................60
A.1. Initial Client-Triggered Assessment .......................60
A.2. Server-Initiated Assessment with Remediation ..............64
A.3. Client-Triggered Reassessment .............................71
Appendix B. Evaluation against NEA Requirements ...................77
B.1. Evaluation against Requirements C-1 .......................77
B.2. Evaluation against Requirements C-2 .......................77
B.3. Evaluation against Requirements C-3 .......................77
B.4. Evaluation against Requirements C-4 .......................78
B.5. Evaluation against Requirements C-5 .......................78
B.6. Evaluation against Requirements C-6 .......................78
B.7. Evaluation against Requirements C-7 .......................79
B.8. Evaluation against Requirements C-8 .......................79
B.9. Evaluation against Requirements C-9 .......................79
B.10. Evaluation against Requirements C-10 .....................80
B.11. Evaluation against Requirements C-11 .....................80
B.12. Evaluation against Requirements PA-1 .....................81
B.13. Evaluation against Requirements PA-2 .....................81
B.14. Evaluation against Requirements PA-3 .....................81
B.15. Evaluation against Requirements PA-4 .....................82
B.16. Evaluation against Requirements PA-5 .....................82
B.17. Evaluation against Requirements PA-6 .....................83
Sangster & Narayan Standards Track [Page 3]RFC 5792 PA-TNC March 2010
1. Introduction
This document specifies PA-TNC, a Posture Attribute (PA) Protocol
identical to the Trusted Computing Group's IF-M 1.0 protocol [8].
The document then evaluates PA-TNC against the requirements defined
in the Network Endpoint Assessment (NEA) Requirements specification
[9].
1.1. Prerequisites
This document does not define an architecture or reference model.
Instead, it defines a protocol that works within the reference model
described in the NEA Overview and Requirements specification. The
reader is assumed to be thoroughly familiar with that document. No
familiarity with TCG specifications is assumed.
1.2. Message Diagram Conventions
This specification defines the syntax of PA-TNC messages using
diagrams. Each diagram depicts the format and size of each field in
bits. Implementations MUST send the bits in each diagram as they are
shown, traversing the diagram from top to bottom and then from left
to right within each line (which represents a 32-bit quantity).
Multi-byte fields representing numeric values must be sent in network
(big endian) byte order.
Descriptions of bit field (e.g., flag) values are described referring
to the position of the bit within the field. These bit positions are
numbered from the most significant bit through the least significant
bit, so a 1-octet field with only bit 0 set has the value 0x80.
1.3. Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [1].
2. Design Considerations
This section discusses some of the key design considerations for the
PA protocol.
2.1. Standard Attribute Namespace for Interoperability
The PA protocol requires the use of two categories of namespaces:
component types (AKA PA subtypes) and attributes. Each of these
namespace categories needs to contain well-known, interoperable names
with defined syntax and semantics co-existing with names for vendor-
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RFC 5792 PA-TNC March 2010
defined private extensions. Similarly, each namespace category needs
to be readily extensible without repeated coordination yet avoids
naming conflicts.
The PA-TNC and PB-TNC protocols provide for multiple orthogonal
namespaces for each category that exist without overlap by including
a Structure of Management Information (SMI) Private Enterprise Number
(PEN) field to identify the definer of namespace of the associated
field. This allows the IETF NEA WG to define a set of standard
component types and attribute types while allowing vendors to each
create additional names outside of the IETF standard namespace. Over
time, vendor-defined names might be proposed for standardization and
thus migration into the IETF namespace.
The PB-TNC protocol defines an IETF standard namespace (using
vendor-id=0) that allows for definition of standard component types
(e.g., Operating System, Firewall, Anti-Virus) using the PA Subtype
field (see section 3.2). Similarly, PA-TNC defines a set of standard
attributes in section 4.2 that represent the most common capabilities
(attributes) of these types of components across a variety of vendor
implementations. The standard namespace allows NEA deployments with
both open source and vendor-provided NEA implementations to support a
consistent set of policies across their environment based on these
standard attributes. The standard attributes can be used with a
variety of endpoints (hosts, printers, mobile devices) that are
running applications and operating systems (defined by the PA
subtypes) from a variety of vendors.
2.2. Vendor-Defined Namespace for Differentiation and Agility
The endpoint is a very dynamic environment in terms of rate of new
features being deployed and attacks that are crafted against existing
and new applications such as viruses, worms, malware, and spyware.
It is difficult to imagine the standard namespaces being able to keep
pace with this rapidly changing environment. Vendors typically
differentiate themselves by moving rapidly to provide unique
mechanisms to address such threats and their ability to deal with
changes in an agile manner. The PA-TNC and PB-TNC protocols allow
for creation of vendor-defined namespace(s) where each namespace
allows use of vendor-defined PA subtypes to identify non-standard
applications or operating system variants and vendor-defined
attributes describing new aspects of each type of component. The
vendor namespaces will allow NEA deployments to craft compliance
policies using a mixture of attributes from both the IETF standard
namespace and vendor-defined namespaces that may include multiple
vendors representing the various hardware and software components
present on the endpoints.
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The PA-TNC protocol's use of vendor-id to identify the namespace of
each attribute allows Posture Collectors to support some or all of
the IETF standard attributes plus optionally a set of vendor-defined
attributes (potentially from more than one vendor-id namespace). For
instance, an open source anti-virus Posture Collector might be
written that supports all of the IETF standard attributes used to
describe a local anti-virus component and a subset of multiple anti-
virus manufacturers' vendor-defined attributes. This Posture
Collector might therefore be able to interoperate with Posture
Validators from multiple vendors. Conversely, a simple Posture
Collector might be written to ignore any vendor-defined attributes
requested and only return standard attributes that it supports. If
the vendor-provided Posture Validator's policy allows for this subset
to be considered compliant, then these simple Posture Collectors can
be used to perform a successful assessment.
2.3. Use of TLV-Based Encoding for Efficiency
The PA-TNC protocol has chosen to employ a binary encoding using a
type-length-value (TLV) structure. TLV encoding was preferred over
the use of a textual encoding format such as XML to provide a more
efficient utilization of the potentially constrained bandwidth
available between the NEA Client and NEA Server (see NEA Overview and
Architecture [9]). Efficiency was a primary criterion for this
choice with consideration given to both:
1. Optimization of the bits-on-the-wire to accommodate NEA
requirements for assessment over low bandwidth or high latency
links (C-8) and allow for the Posture Transport (PT) protocol
to run over existing network access protocols (PT-4, C-11) that
are constrained by packet size.
2. Optimization of CPU utilization on the endpoint to accommodate
for low power endpoints such as mobile devices.
The choice of TLV encoding does not preclude the use of XML-based
attribute values within the vendor namespaces or future standard
attributes. It is conceivable that certain vendors may utilize XML
encoding for extensibility within their namespace when the above
considerations are less applicable to their technologies. Attributes
encoded within the vendor-defined namespace using alternate encoding
such as XML will be opaque to NEA software only supporting standard
attributes and will be processed primarily by the vendor-defined
components (collector/validator).
Sangster & Narayan Standards Track [Page 6]RFC 5792 PA-TNC March 2010
3. PA-TNC Message Protocol
This section discusses the use of the PA-TNC message and its
attributes, and specifies the syntax and semantics for the PA-TNC
message header. The details of each attribute included within the
PA-TNC payload are specified in section 4.2.
3.1. PA-TNC Messaging Model
PA-TNC messages are carried by the PB-TNC protocol [5], which
provides a multi-roundtrip reliable transport and end-to-end message
delivery to subscribed (interested) parties using a variety of
underlying network protocols. PA-TNC is unaware of these underlying
PT protocols being used below PB-TNC.
The interested parties consist of Posture Collectors on the NEA
Client and Posture Validators associated with the NEA Server that
have registered to receive messages about particular types of
components (e.g., anti-virus) during an assessment. The PA-TNC
messaging protocol operates synchronously within an assessment
session, with Posture Collectors and Posture Validators taking turns
sending one or more messages to each other. Each PA-TNC message may
contain one or more attributes associated with the functional
component identified in the component type (PA Subtype) of the
Posture Broker (PB) protocol.
Posture Collectors may only send PA-TNC messages to Posture
Validators and vice versa. No Posture Collector-to-Posture Collector
or Posture Validator-to-Posture Validator messaging is allowed to
occur. Each Posture Collector or Posture Validator may send several
PA-TNC messages in succession before indicating that it has completed
its batch of messages to the Posture Broker Client or Posture Broker
Server respectively. As necessary, the Posture Broker Client and
Posture Broker Server will batch these messages prior to sending them
over the network.
PB-TNC provides a publish/subscribe model of message exchange. This
means that, at any given point in time, zero or more subscribers for
a particular type of message may be present on a Posture Broker
Client or Posture Broker Server. This is beneficial, since it allows
one Posture Collector or Posture Validator to combine multiple
functions (like anti-virus and personal firewall) by subscribing to
both TNC standard component types. It also allows multiple Posture
Collectors or Posture Validators to support the same components, such
as two anti-virus Posture Validators that are each used to manage
their own respective anti-virus client software.
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However, this publish/subscribe model has some possible negative side
effects. When a Posture Collector or Posture Validator initially
sends a PA-TNC message, it does not know whether it will receive
many, one, or no PA-TNC messages from the other side. For many types
of assessments, this is acceptable, but in some cases a more direct
channel binding between a particular Posture Collector and Posture
Validator pair is necessary. For example, a Posture Validator may
wish to provide remediation instructions to a particular Posture
Collector that it knows is capable of remediating a non-compliant
component. This can be accomplished using the exclusive delivery PB-
TNC capability to limit distribution of a message to a single Posture
Collector by including the target Posture Collector Identifier in the
PB-PA header. For more information on the PB-PA header, see section
4.5 of the PB-TNC specification.
3.2. PA-TNC Relationship to PB-TNC
This section summarizes the major elements of a PA-TNC message as
they might appear inside of a PB-TNC message. The double line (===)
in the diagram below indicates the separation between the PB-TNC and
PA-TNC protocols. The PA-TNC portion of the message is delivered to
each Posture Collector or Posture Validator registered to receive
messages containing a particular message type. Note that PB-TNC is
capable of carrying multiple PB-TNC and PA-TNC messages in a single
PB-TNC batch. See the PB-TNC specification [5] for more information
on its capabilities.
One important linkage between the PA-TNC and PB-TNC protocols is the
PA message type (PA Message Vendor ID and PA Subtype) that is used by
the Posture Broker Client and Posture Broker Server to route messages
to interested Posture Collectors and Posture Validators. The message
type indicates the software component (component type) that is
associated with the attributes included inside the PA-TNC message.
Therefore, Posture Collectors and Posture Validators written to
support an assessment of a particular component can register to
receive messages about the component and thus participate in its
assessment. Each Posture Collector and Posture Validator MUST only
send PA-TNC messages containing attributes that pertain to the
software component defined in the message type of the message. This
ensures that only the appropriate Posture Collectors and Posture
Validators that support a particular type of component will receive
attributes related to that component. If a PA-TNC message contained
a mix of attributes about different components and a message type of
only one of those components, the message would only be delivered to
parties interested in the component type included in the message
type, so other interested recipients wouldn't see those attributes.
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RFC 5792 PA-TNC March 2010
The message type is composed of two fields: a PA Message Vendor ID
and a PA Subtype. The PA Message Vendor ID identifies the vendor or
other organization that defined this message type. The PA Subtype
identifies the message type more specifically within the set of
message types defined by that vendor. This specification defines
several IETF Standard PA Subtypes to be used with a PA Message Vendor
ID of zero (0). Within this specification, the PA Subtype field is
used to indicate the type of component (e.g., firewall) involved with
the message's attributes. Therefore, for clarity, the PA subtype
will be referred to as the "component type" in this specification.
Vendor-defined namespaces may use other semantics for the PA Subtype
field as this is outside the scope of this specification.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PB-TNC Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PB-TNC Message of type PB-PA-Message |
|(includes PA Message Vendor ID, PA Subtype, and other fields |
| used by Posture Broker Client and Posture Broker Server for |
| routing) |
===============================================================
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PA-TNC Message Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PA-TNC Attribute |
| (e.g., Product Information) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PA-TNC Attribute |
| (e.g., Operational Status) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1. Overview of a PB-TNC batch that contains a PA-TNC message
For example, if a Posture Broker Client sent a PB-TNC batch that
contained a PA-TNC message with a message type indicating firewall
component, this message would be routed by the Posture Broker Server
to Posture Validators registered to assess firewalls. Each
registered Posture Validator would receive a copy of the PA-TNC
message including the PA-TNC header and set of attributes. It is
important that each of the attributes included in the PA-TNC message
be associated with the firewall component because only the Posture
Collector and Posture Validator interested in firewalls will receive
such messages.
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RFC 5792 PA-TNC March 2010
If the above message contained both firewall and operating system
attributes inside a PA-TNC message with a component type of firewall,
then any Posture Collector and Posture Validator registered to
receive operating system messages would not receive those attributes,
as the messages would only be delivered to those registered for
firewall messages.
3.3. PB-PA Posture Collector and Posture Validator Identifiers
The PB-PA header contains several fields important to the processing
of a received PA message. The PA Vendor ID and Subtype are described
in the PB-TNC specification and above in section 3.2. Also present
in the PB-PA header is a pair of fields that identify the Posture
Collector and/or Posture Validator involved in the exchange. These
fields are used for performing exclusive delivery of messages as
described in section 3.1 and as an indicator for correlation of
received attributes.
Correlation of attributes is necessary when the sending Posture
Collector provides posture for multiple implementations of a single
type of component during an assessment, so the recipient Posture
Validators need to know which attributes are describing the same
implementation.
For example, a single Posture Collector might report attributes on
two installed VPN implementations on the endpoint. Because the
individual attributes do not include an indication of which VPN
product they are describing, the recipient needs something to perform
this correlation. Therefore, for this example, the VPN Posture
Collector would need to obtain two Posture Collector Identifiers from
the Posture Broker Client and consistently use one with each of the
implementations during an assessment. The VPN Posture Collector
would group all the attributes associated with a particular VPN
implementation into a single PB-PA message and send the message using
the Posture Collector Identifier it designates as going with the
particular implementation. This approach allows the recipient to
recognize when attributes in future assessment messages also describe
the same component implementation.
3.4. PA-TNC Messages in PB-TNC
As depicted in section 3.2, a PA-TNC message consists of a PA-TNC
header followed by a sequence of one or more attributes. The PA-TNC
message header (described in section 3.6) and the header for each of
the PA-TNC attributes (specified in section 4.1) have a fixed type-
length-value (TLV) format. Each PA-TNC message MAY contain a mixture
of standards-based and vendor-defined attributes identifiable using
the type portion of the attribute header. All Posture Collectors and
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RFC 5792 PA-TNC March 2010
Posture Validators compliant with this specification MUST be capable
of processing multiple attributes in a received PA-TNC message. A
Posture Collector or Posture Validator that receives a PA-TNC message
can use the attribute header's length field to skip any attributes
that it does not understand, unless the attribute is marked as
mandatory to process.
3.5. IETF Standard PA Subtypes
This section defines several IETF Standard PA Subtypes. Each PA
subtype defined here identifies a specific component relevant to the
endpoint's posture. This allows a small set of generic PA-TNC
attributes (e.g., Product Information) to be used to describe a large
number of different components (e.g., operating system, anti-virus,
etc.). It also allows Posture Collectors and Posture Validators to
specialize in a particular component and only receive PA-TNC messages
relevant to that component.
Value Integer Definition
----- ------- ----------
0 Testing Reserved for use in specification
examples, experimentation and
testing.
1 Operating System Operating system running on the
endpoint
2 Anti-Virus Host-based anti-virus software
3 Anti-Spyware Host-based anti-spyware software
4 Anti-Malware Host-based anti-malware (e.g., anti-
bot) software not included within
anti-virus or anti-spyware components
5 Firewall Host-based firewall
6 IDPS Host-based Intrusion Detection and/or
Prevention Software (IDPS)
7 VPN Host-based Virtual Private Network
(VPN) software
8 NEA Client NEA client software
These PA subtypes must be used in a PB-PA message with a PA Message
Vendor ID of zero (0) indicating an IETF standard type of component
(as described in the PB-TNC specification [5]). If these PA subtype
Sangster & Narayan Standards Track [Page 11]RFC 5792 PA-TNC March 2010
values are used with a different PA Message Vendor ID, they have a
completely different meaning that is not defined in this
specification. Posture Collectors and Posture Validators 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).
3.6. PA-TNC Message Header Format
This section describes the format and semantics of the PA-TNC header.
Every PA-TNC message MUST start with a PA-TNC header. The PA-TNC
header provides a common context applying to all of the attributes
contained within the PA-TNC payload. The payload consists of a
sequence of assessment attributes described in section 4.2.
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 | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Version
This field indicates the version of the format for the PA-TNC
message. This version is intended to allow for evolution of the
PA-TNC message header and payload in a manner that can easily be
detected by message recipients.
PA-TNC message senders MUST set this field to 0x01 for all PA-TNC
messages that comply with this specification. Implementations
responding to a PA-TNC message containing a supported version MUST
use the same version number to minimize the risk of version
incompatibility. Message recipients MUST respond to a PA-TNC
message containing an unsupported version by sending a Version Not
Supported error in a PA-TNC Error attribute that is the only PA-
TNC attribute in a PA-TNC message with version number 1.
PA-TNC message initiators supporting multiple PA-TNC protocol
versions SHOULD be able to alter which version of PA-TNC message
they send based on prior message exchanges with a particular peer
Posture Collector or Posture Validator.
Sangster & Narayan Standards Track [Page 12]RFC 5792 PA-TNC March 2010
Reserved
Reserved for future use. This field MUST be set to 0 on
transmission and ignored upon reception.
Message Identifier
This field contains a value that uniquely identifies this message,
differentiating it from others sent by a particular PA-TNC message
sender within this assessment. This value can be included in the
payload of a response message to indicate which message was
received and caused the response. This value is included in the
payload of PA-TNC error messages so the party who receives the
error message can determine which of the messages they had sent
caused the error.
PA-TNC message senders MUST NOT send the same message identifier
more than once during an assessment. Message identifiers may be
randomly generated or sequenced as long as values are not repeated
during an assessment message exchange. PA-TNC message recipients
are not required to check for duplicate message identifiers.
4. PA-TNC Attributes
This section defines the PA-TNC attributes that can be carried within
a PA-TNC message. The initial section defines the standard attribute
header that appears at the start of each attribute in a PA-TNC
message. The second section defines each of the IETF Standard PA-TNC
Attributes and the final section discusses how vendor-defined PA-TNC
attributes can be used within a PA-TNC message. Vendor-defined PA-
TNC attributes use the vendor's SMI Private Enterprise Number in the
Attribute Type field.
A PA-TNC message MUST contain a PA-TNC header (defined in section
3.6. followed by a sequence of zero or more PA-TNC attributes. All
PA-TNC attributes MUST begin with a standard PA-TNC attribute header,
as defined in section 4.1. The contents of PA-TNC attributes vary
widely, depending on their attribute type. Section 4.2 defines the
IETF Standard PA-TNC Attributes. Section 4.3 discusses how vendor-
specific PA-TNC attributes can be defined.
4.1. PA-TNC Attribute Header
Following the PA-TNC message header is a sequence of zero or more
attributes. All PA-TNC attributes MUST begin with the standard PA-
TNC attribute header defined in this subsection. Each attribute
described in this specification is represented by a TLV tuple. The
TLV tuple includes an attribute identifier comprised of the Vendor ID
Sangster & Narayan Standards Track [Page 13]RFC 5792 PA-TNC March 2010
and Attribute Type (type), the TLV tuple's overall length, and
finally the attribute's value. The use of TLV representation was
chosen due to its flexibility and extensibility and use in other
standards. Recipients of an attribute can use the attribute type
fields to determine the precise syntax and semantics of the attribute
value field and the length to skip over an unrecognized attribute.
The length field is also beneficial when a variable-length attribute
value is provided.
The TLV format does not contain an explicit TLV format version
number, so every attribute included in a particular PA-TNC message
MUST use the same TLV format. Using the PA-TNC message version
number to indicate the format of all TLV attributes within a PA-TNC
message allows for future versioning of the TLV format in a manner
detectable by PA-TNC message recipients. Similarly, requiring all
TLV attribute formats to be the same within a PA-TNC message also
ensures that recipients compliant with a particular PA-TNC message
version can at least parse every attribute header and use the length
to skip over unrecognized attributes. Finally, all attribute TLVs
within a PA-TNC message MUST pertain to the same implementation of
the component. This restriction is relevant when a single Posture
Collector is reporting on multiple implementations of a component, so
must send multiple PA-TNC messages each including only the attributes
describing a single implementation. For more information on how
Posture Collectors should handle multiple implementations, see
section 3.3.
Every PA-TNC-compliant TLV attribute MUST use the following TLV
format:
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-TNC Attribute Vendor ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PA-TNC Attribute Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PA-TNC Attribute Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Attribute Value (Variable Length) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Flags
This field defines flags impacting the processing of the
associated attribute.
Sangster & Narayan Standards Track [Page 14]RFC 5792 PA-TNC March 2010
Bit 0 (0x80) is the NOSKIP flag. Any Posture Collector or Posture
Validator that receives an attribute with this flag set to 1 but
does not support this attribute MUST NOT process any part of the
PA-TNC message and SHOULD respond with an Attribute Type Not
Supported error in a PA-TNC error message.
In order to avoid taking action on a subset of the attributes only
to later find an unsupported attribute with the NOSKIP flag set,
recipients of a multi-attribute PA-TNC message might need to scan
all of the attributes prior to acting upon any attribute.
When the NOSKIP flag is set to 0, recipients SHOULD skip any
unsupported attributes and continue processing the next attribute.
Bit 1-7 are reserved for future use. These bits MUST be set to 0
on transmission and ignored upon reception.
PA-TNC Attribute Vendor ID
This field indicates the owner of the namespace associated with
the PA-TNC Attribute Type. This is accomplished by specifying the
24-bit SMI Private Enterprise Number Vendor ID of the party who
owns the Attribute Type namespace. IETF Standard PA-TNC Attribute
Types MUST use zero (0) in this field.
The PA-TNC Attribute Vendor ID 0xffffff is reserved. Posture
Collectors and Posture Validators MUST NOT send PA-TNC messages in
which the PA-TNC Attribute Vendor ID has this reserved value
(0xffffff). If a Posture Collector or Posture Validator receives
a message in which the PA-TNC Attribute Vendor ID has this
reserved value (0xffffff), it SHOULD respond with an Invalid
Parameter error code in a PA-TNC Error attribute.
PA-TNC Attribute Type
This field defines the type of the attribute included in the
Attribute Value field. This field is qualified by the PA-TNC
Attribute Vendor ID field so that a particular PA-TNC Attribute
Type value (e.g., 327) has a completely different meaning
depending on the value in the PA-TNC Attribute Vendor ID field.
Posture Collectors and Posture Validators MUST NOT require support
for particular vendor-specific PA-TNC Attribute Types and MUST
interoperate with other parties despite any differences in the set
of vendor-specific PA-TNC Attribute Types supported (although they
MAY permit administrators to configure them to require support for
specific PA-TNC attribute types).
Sangster & Narayan Standards Track [Page 15]RFC 5792 PA-TNC March 2010
If the PA-TNC Attribute Vendor ID field has the value zero (0),
then the PA-TNC Attribute Type field contains an IETF Standard PA-
TNC Attribute Type, as listed in the IANA registry. IANA
maintains a registry of PA-TNC Attribute Types. Entries in this
registry are added by Expert Review with Specification Required,
following the guidelines in section 7. Section 4.2 of this
specification defines the initial set of IETF Standard PA-TNC
Attribute Types.
The PA-TNC Attribute Type 0xffffffff is reserved. Posture
Collectors and Posture Validators MUST NOT send PA-TNC messages in
which the PA-TNC Attribute Type has this reserved value
(0xffffffff). If a Posture Collector or Posture Validator
receives a message in which the PA-TNC Attribute Type has this
reserved value (0xffffffff), it SHOULD respond with an Invalid
Parameter error code in a PA-TNC Error attribute.
PA-TNC Attribute Length
This field contains the length in octets of the entire PA-TNC
attribute including the PA-TNC Attribute Header (the fields Flags,
PA-TNC Attribute Vendor ID, PA-TNC Attribute Type, and PA-TNC
Attribute Length). Therefore, this value MUST always be at least
12. Any Posture Collector or Posture Validator that receives a
message with a PA-TNC Attribute Length field whose value is less
than 12 SHOULD respond with an Invalid Parameter PA-TNC error
code. Similarly, if a Posture Collector or Posture Validator
receives a PA-TNC message for an Attribute Type that has a well-
known Attribute Value length (e.g., fixed-length attribute value)
and the Attribute Length indicates a different value (greater or
less than the expected value), the recipient SHOULD respond with
an Invalid Parameter PA-TNC error code.
Implementations that do not support the specified PA-TNC Attribute
Type can use this length to skip over this attribute to the next
attribute. Note that while this field is 4 octets the maximum
usable attribute length is less than 2^32-1 due to limitations of
the underlying protocol stack. Specifically, PB-TNC TLV header's
Batch Length field is also 32 bits in length. Therefore, the
maximum batch that PB-TNC can carry is 2^32-1, so the largest PA-
TNC message carried by PB-TNC must be less than 2^32-1 - size of
the PB-TNC header (see section 4.1 of PB-TNC for more details).
Attribute Value
This field varies depending on the particular type of attribute
being expressed. The contents of this field for each of the IETF
Standard PA-TNC Attribute Types are defined in section 4.2.
Sangster & Narayan Standards Track [Page 16]RFC 5792 PA-TNC March 2010
4.2. IETF Standard PA-TNC Attribute Types
This section defines an initial set of IETF Standard PA-TNC Attribute
Types. These Attribute Types MUST always be used with a PA-TNC
Vendor ID of zero (0). If these PA-TNC Attribute Type values are
used with a different PA-TNC Vendor ID, they have a completely
different meaning that is not defined in this specification.
The following table briefly describes each attribute and defines the
numeric value to be used in the PA-TNC Attribute Type field of the
PA-TNC Attribute Header. Later subsections provide detailed
specifications for each PA-TNC Attribute Value.
Number Integer Description
------ ------- -----------
0 Testing Reserved for use in
specification examples,
experimentation, and testing.
1 Attribute Request Contains a list of attribute
type values defining the
attributes desired from the
Posture Collectors.
2 Product Information Manufacturer and product
information for the component.
3 Numeric Version Numeric version of the
component.
4 String Version String version of the
component.
5 Operational Status Describes whether the component
is running on the endpoint.
6 Port Filter Lists the set of ports (e.g.,
TCP port 80 for HTTP) that are
allowed or blocked on the
endpoint.
7 Installed Packages List of software packages
installed on endpoint that
provide the requested
component.
8 PA-TNC Error PA-TNC message or attribute
processing error.
Sangster & Narayan Standards Track [Page 17]RFC 5792 PA-TNC March 2010
9 Assessment Result Result of the assessment
performed by a Posture
Validator.
10 Remediation Instructions Instructions for remediation
generated by a Posture
Validator.
11 Forwarding Enabled Indicates whether packet
forwarding has been enabled
between different interfaces on
the endpoint.
12 Factory Default Password Indicates whether the endpoint
Enabled has a factory default password
enabled.
The following subsections discuss the usage, format, and semantics of
the Attribute Value field for each IETF Standard PA-TNC Attribute
Type.
4.2.1. Attribute Request
This PA-TNC Attribute Type allows a Posture Validator to request
certain attributes from the registered set of Posture Collectors.
All Posture Collectors that implement any of the IETF Standard PA
Subtypes defined in this specification SHOULD support receiving and
processing this attribute type for at least those PA subtypes. This
requirement is only a "should" because there are deployment scenarios
(e.g., see section A.1) where the Posture Collectors proactively send
a set of attributes at the start of an assessment (e.g., based upon
local policy), so does not need to support Posture Validator
requested attributes. Posture Collectors that receive but do not
support the Attribute Request attribute MUST respond with an
Attribute Type Not Supported PA-TNC error code. Posture Collectors
that receive and process this attribute MAY choose to send all, a
subset, or none of the requested attributes but MUST NOT send
attributes that were not requested (except Error attributes). All
Posture Validators that implement any of the IETF Standard PA
Subtypes defined in this specification SHOULD support sending this
attribute type for at least those PA subtypes.
Posture Validators MUST NOT include this attribute type in an
Attribute Request attribute. It does not make sense for a Posture
Validator to request that a Posture Collector send an Attribute
Request attribute.
Sangster & Narayan Standards Track [Page 18]RFC 5792 PA-TNC March 2010
For this attribute type, the PA-TNC Attribute Vendor ID field MUST be
set to zero (0) and the PA-TNC Attribute Type field MUST be set to 1.
The following diagram illustrates the format and contents of the
Attribute Value field for this attribute type. The text after this
diagram describes the fields shown here.
Note that this diagram shows two attribute types. The actual number
of attribute types included in an Attribute Request attribute can
vary from one to a large number (limited only by the maximum message
and length supported by the underlying PT protocol). However, each
Attribute Request MUST contain at least one attribute type. Because
the length of a PA-TNC Attribute Vendor ID paired with a PA-TNC
Attribute Type and a 1-octet Reserved field is always 8 octets, the
number of requested attributes can be easily computed using the PA-
TNC Attribute Length field by subtracting the number of octets in the
PA-TNC Attribute Header and dividing by 8. If the PA-TNC Attribute
Length field is invalid, Posture Collectors SHOULD respond with an
Invalid Parameter PA-TNC error code.
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 | PA-TNC Attribute Vendor ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PA-TNC Attribute Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | PA-TNC Attribute Vendor ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PA-TNC Attribute Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Reserved
Reserved for future use. This field MUST be set to 0 on
transmission and ignored upon reception.
PA-TNC Attribute Vendor ID
This field contains the SMI Private Enterprise Number of the
organization that controls the namespace for the following PA-TNC
Attribute Type. This field enables IETF Standard PA-TNC
Attributes and vendor-defined PA-TNC attributes to be used without
potential collisions.
Sangster & Narayan Standards Track [Page 19]RFC 5792 PA-TNC March 2010
Any IETF Standard PA-TNC Attribute Types defined in section 4.2
MUST use zero (0) in this field. Vendor-defined attributes MUST
use the SMI Private Enterprise Number of the organization that
defined the attribute.
PA-TNC Attribute Type
The PA-TNC Attribute Type field (together with the PA-TNC Vendor
ID field) indicates the specific attribute requested. Some IETF
Standard PA-TNC Attribute Types MUST NOT be requested using this
field (e.g., requesting a PA-TNC Error attribute). This is
explicitly indicated in the description of those PA-TNC Attribute
Types. Any Posture Collector or Posture Validator that receives
an Attribute Request containing one of the prohibited Attribute
Types SHOULD respond with an Invalid Parameter error in a PA-TNC
error message.
4.2.2. Product Information
This PA-TNC Attribute Type contains identifying information about a
product that implements the component specified in the PA Subtype
field, as described in section 3.5. For example, if the PA Subtype
is Anti-Virus, this attribute would contain information identifying
an anti-virus product installed on the endpoint.
All Posture Collectors that implement any of the IETF Standard PA
Subtypes defined in this specification MUST support sending this
attribute type, at least for those PA subtypes. Whether a particular
Posture Collector actually sends this attribute type SHOULD still be
governed by local privacy and security policies. All Posture
Validators that implement any of the IETF Standard PA Subtypes
defined in this specification MUST support receiving this attribute
type, at least for those PA subtypes. Posture Validators MUST NOT
send this attribute type.
For this attribute type, the PA-TNC Attribute Vendor ID field MUST be
set to zero (0) and the PA-TNC Attribute Type field MUST be set to 2.
The value in the PA-TNC Attribute Length field will vary, depending
on the length of the Product Name field. However, the value in the
PA-TNC Attribute Length field MUST be at least 17 because this is the
length of the fixed-length fields in the PA-TNC Attribute Header and
the fixed-length fields in this attribute type. If the PA-TNC
Attribute Length field is less than the size of these fixed-length
fields, implementations SHOULD respond with an Invalid Parameter PA-
TNC error code.
Sangster & Narayan Standards Track [Page 20]RFC 5792 PA-TNC March 2010
This attribute type includes both numeric and textual identifiers for
the organization that created the product (the "product creator") and
for the product itself. For automated processing, numeric
identifiers are superior because they are less ambiguous and more
efficient. However, numeric identifiers are only available if the
product creator has assigned them. Therefore, a textual identifier
is also included. This textual identifier has the additional benefit
that it may be easier for humans to read (although this benefit is
minimal since the primary purpose of this attribute is automated
assessment).
The following diagram illustrates the format and contents of the
Attribute Value field for this attribute 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Product Vendor ID | Product ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Product ID | Product Name (Variable Length) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Product Vendor ID
This field contains the SMI Private Enterprise Number for the
product creator. If the SMI PEN for the product creator is
unknown or if the product creator does not have an SMI PEN, the
Product Vendor ID field MUST be set to 0 and the identity of the
product creator SHOULD be included in the Product Name along with
the name of the product.
Product ID
This field identifies the product using a numeric identifier
assigned by the product creator. If this Product ID value is
unknown or if the product creator has not assigned such a value,
this field MUST be set to 0. If the Product Vendor ID is 0, this
field MUST be set to 0. In any case, the name of the product
SHOULD be included in the Product Name field.
Note that a particular Product ID value (e.g., 635) will have
completely different meanings depending on the Product Vendor ID.
Each Product Vendor ID defines a different space of Product ID
values. Product creators are encouraged to publish lists of
Product ID values for their products.
Sangster & Narayan Standards Track [Page 21]RFC 5792 PA-TNC March 2010
Product Name
This variable-length field contains a UTF-8 [2] string identifying
the product (e.g., "Symantec Norton AntiVirus(TM) 2008") in enough
detail to unambiguously distinguish it from other products from
the product creator. Products whose creator is known, but does
not have a registered SMI Private Enterprise Number, SHOULD be
represented using a combination of the creator name and full
product name (e.g., "Ubuntu(R) IPtables" for the IPtables firewall
in the Ubuntu distribution of Linux). If the product creator's
SMI Private Enterprise Number is included in the Product Vendor ID
field, the product creator's name may be omitted from this field.
The length of this field can be determined by starting with the
value in the PA-TNC Attribute Length field in the PA-TNC Attribute
Header and subtracting the size of the fixed-length fields in that
header (12) and the size of the fixed-length fields in this
attribute (5). If the PA-TNC Attribute Length field is less than
the size of these fixed-length fields, implementations SHOULD
respond with an Invalid Parameter PA-TNC error code.
4.2.3. Numeric Version
This PA-TNC Attribute Type contains numeric version information for a
product on the endpoint that implements the component specified in
the PA Subtype field, as described in section 3.5. For example, if
the PA Subtype is Operating System, this attribute would contain
numeric version information for the operating system installed on the
endpoint. The version information in this attribute is associated
with a particular product, so Posture Validators are expected to also
possess the corresponding Product Information attribute when
interpreting this attribute.
All Posture Collectors that implement the IETF Standard PA Subtype
for Operating System SHOULD support sending this attribute type, at
least for the Operating System PA subtype. Other Posture Collectors
MAY support sending this attribute type. Whether a particular
Posture Collector actually sends this attribute type SHOULD still be
governed by local privacy and security policies. All Posture
Validators that implement the IETF Standard PA Subtype for Operating
System SHOULD support receiving this attribute type, at least for the
Operating System PA subtype. Other Posture Validators MAY support
receiving this attribute type. A Posture Validator that does not
support receiving this attribute type SHOULD simply ignore attributes
with this type. Posture Validators MUST NOT send this attribute
type.
Sangster & Narayan Standards Track [Page 22]RFC 5792 PA-TNC March 2010
For this attribute type, the PA-TNC Attribute Vendor ID field MUST be
set to zero (0) and the PA-TNC Attribute Type field MUST be set to 3.
The value in the PA-TNC Attribute Length field MUST be 28. If the
PA-TNC Attribute Length field is less than the size of these fixed-
length fields, implementations SHOULD respond with an Invalid
Parameter PA-TNC error code.
This attribute type includes numeric values for the product version
information, enabling Posture Validators to do comparative operations
on the version. Some Posture Collectors may not be able to determine
some or all of this information for a product. However, this
attribute can be especially useful for describing the version of the
operating system, where numeric version numbers are generally
available.
The following diagram illustrates the format and contents of the
Attribute Value field for this attribute 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Major Version Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Minor Version Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Build Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Service Pack Major | Service Pack Minor |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Major Version Number
This field contains the major version number for the product, if
applicable. If unused or unknown, this field SHOULD be set to 0.
Minor Version Number
This field contains the minor version number for the product, if
applicable. If unused or unknown, this field SHOULD be set to 0.
Sangster & Narayan Standards Track [Page 23]RFC 5792 PA-TNC March 2010
Build Number
This field contains the build number for the product, if
applicable. This may provide more granularity than the minor
version number, as many builds may occur leading up to an official
release, and all these builds may share a single major and minor
version number. If unused or unknown, this field SHOULD be set to
0.
Service Pack Major
This field contains the major version number of the service pack
for the product, if applicable. If unused or unknown, this field
SHOULD be set to 0.
Service Pack Minor
This field contains the minor version number of the service pack
for the product, if applicable. If unused or unknown, this field
SHOULD be set to 0.
4.2.4. String Version
This PA-TNC Attribute Type contains string version information for a
product on the endpoint that implements the component specified in
the PA Subtype field, as described in section 3.5. For example, if
the PA Subtype is Firewall, this attribute would contain string
version information for a host-based firewall product installed on
the endpoint (if any). The version information in this attribute is
associated with a particular product, so Posture Validators are
expected to also possess the corresponding Product Information
attribute when interpreting this attribute.
All Posture Collectors that implement any of the IETF Standard PA
Subtypes defined in this document MUST support sending this attribute
type, at least for those PA subtypes. Other Posture Collectors MAY
support sending this attribute type. Whether a particular Posture
Collector actually sends this attribute type SHOULD still be governed
by local privacy and security policies. All Posture Validators that
implement any of the IETF Standard PA Subtypes defined in this
document MUST support receiving this attribute type, at least for
those PA subtypes. Other Posture Validators MAY support receiving
this attribute type. Posture Validators MUST NOT send this attribute
type.
For this attribute type, the PA-TNC Attribute Vendor ID field MUST be
set to zero (0) and the PA-TNC Attribute Type field MUST be set to 4.
The value in the PA-TNC Attribute Length field will vary, depending
Sangster & Narayan Standards Track [Page 24]RFC 5792 PA-TNC March 2010
on the length of the Component Version Number, Internal Build Number,
and Configuration Version Number fields. However, the value in the
PA-TNC Attribute Length field MUST be at least 15 because this is the
length of the fixed-length fields in the PA-TNC Attribute Header and
the fixed-length fields in this attribute type. If the PA-TNC
Attribute Length field is less than the size of these fixed-length
fields or does not match the length indicated by the sum of the
fixed-length and variable-length fields, implementations SHOULD
respond with an Invalid Parameter PA-TNC error code.
The following diagram illustrates the format and contents of the
Attribute Value field for this attribute 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Version Len | Product Version Number (Variable Length) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Build Num Len | Internal Build Number (Variable Length) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Config. Len | Configuration Version Number (Variable Length)|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Version Len
This field defines the number of octets in the Product Version
Number field. If the product version number is unavailable or
unknown, this field MUST be set to 0 and the Product Version
Number field will be zero length (effectively not present).
Product Version Number
This field contains a UTF-8 string identifying the version of the
component (e.g., "1.12.23.114"). This field MUST be sized to fit
the version string and MUST NOT include extra octets for padding
or NUL character termination.
Various products use a wide range of different formats and
semantics for version strings. Some use alphabetic characters,
white space, and punctuation. Some consider version "1.21" to be
later than version "1.3" and some earlier. Therefore, the syntax
and semantics of this string are not defined.
Sangster & Narayan Standards Track [Page 25]RFC 5792 PA-TNC March 2010
Build Num Len
This field defines the number of octets in the Internal Build
Number field. For products where the internal build number is
unavailable or unknown, this field MUST be set to 0 and the
Internal Build Number field will be zero length (effectively not
present).
Internal Build Number
This field contains a UTF-8 string identifying the engineering
build number of the product. This field MUST be sized to fit the
build number string and MUST NOT include extra octets for padding
or NUL character termination. The syntax and semantics of this
string are not defined.
Config. Len
This field defines the number of octets in the Configuration
Version Number field. If the configuration version number is
unavailable or unknown, this field MUST be set to 0 and the
Configuration Version Number field will be zero length
(effectively not present).
Configuration Version Number
This field contains a UTF-8 string identifying the version of the
configuration used by the component. This version SHOULD
represent the overall configuration version even if several
configuration policy files or settings are used. Posture
Collectors MAY include multiple version numbers in this single
string if a single version is not practical. This field MUST be
sized to fit the version string and MUST NOT include extra octets
for padding or NUL character termination.
Various products use a wide range of different formats for version
strings. Some use alphabetic characters, white space, and
punctuation. Some consider version "1.21" to be later than
version "1.3" and some earlier. In addition, some Posture
Collectors may place multiple configuration version numbers in
this single string. Therefore, the syntax and semantics of this
string are not defined.
4.2.5. Operational Status
This PA-TNC Attribute Type describes the operational status of a
product that can implement the component specified in the PA Subtype
field, as described in section 3.5. For example, if the PA Subtype is
Sangster & Narayan Standards Track [Page 26]RFC 5792 PA-TNC March 2010
Anti-Spyware, this attribute would contain information about the
operational status of a host-based anti-spyware product that may or
may not be installed on the endpoint.
Posture Collectors that implement the IETF Standard PA Subtype for
Operating System or VPN MAY support sending this attribute type for
those PA subtypes. Posture Collectors that implement other IETF
Standard PA Subtypes defined in this specification SHOULD support
sending this attribute type for those PA subtypes. Other Posture
Collectors MAY support sending this attribute type. Whether a
particular Posture Collector actually sends this attribute type
SHOULD still be governed by local privacy and security policies.
Posture Validators that implement the IETF Standard PA Subtype for
Operating System or VPN MAY support receiving this attribute type, at
least for those PA subtypes. Posture Validators that implement other
IETF Standard PA Subtypes defined in this specification SHOULD
support receiving this attribute type, at least for those PA
subtypes. Other Posture Validators MAY support receiving this
attribute type. A Posture Validator that does not support receiving
this attribute type SHOULD simply ignore attributes with this type.
Posture Validators MUST NOT send this attribute type.
For this attribute type, the PA-TNC Attribute Vendor ID field MUST be
set to zero (0) and the PA-TNC Attribute Type field MUST be set to 5.
The value in the PA-TNC Attribute Length field MUST be 36. If the
PA-TNC Attribute Length field does not have this value,
implementations SHOULD respond with an Invalid Parameter PA-TNC error
code.
The following diagram illustrates the format and contents of the
Attribute Value field for this attribute 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Status | Result | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Last Use |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Last Use (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Last Use (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Last Use (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Last Use (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Sangster & Narayan Standards Track [Page 27]RFC 5792 PA-TNC March 2010
Status
This field gives the operational status of the product. The
following table lists the values currently defined for this field.
Value Description
----- -----------
0 Unknown or other
1 Not installed
2 Installed but not operational
3 Operational
If a Posture Validator receives a value for this field that it
does not recognize, it SHOULD treat this value as equivalent to
the value 0.
Result
This field contains the result of the last use of the product.
The following table lists the values currently defined for this
field.
Value Description
----- -----------
0 Unknown or other
1 Successful use with no errors detected
2 Successful use with one or more errors detected
3 Unsuccessful use (e.g., aborted)
Posture Collectors SHOULD set this field to 0 if the Status field
contains a value of 1 (Not installed) or 2 (Installed but not
operational). If a Posture Validator receives a value for this
field that it does not recognize, it SHOULD treat this value as
equivalent to the value 0.
Reserved
This field is reserved for future use. The field MUST be set to 0
on transmission and ignored upon reception.
Last Use
This field contains the date and time of the last use of the
component. The Last Use date and time MUST be represented as an
RFC 3339 [4] compliant ASCII string in Coordinated Universal Time
(UTC) time with the additional restrictions that the 't' delimiter
and the 'z' suffix MUST be capitalized and fractional seconds
(time-secfrac) MUST NOT be included.
Sangster & Narayan Standards Track [Page 28]RFC 5792 PA-TNC March 2010
This field conforms to the date-time ABNF production from section
5.6 of RFC 3339 with the above restrictions. Leap seconds are
permitted and Posture Validators MUST support them.
The last use string MUST NOT be NUL terminated or padded in any
way. If the last use time is not known, not applicable, or cannot
be represented in this format, the Posture Collector MUST set this
field to the value "0000-00-00T00:00:00Z" (allowing this field to
be fixed length). Note that this particular reserved value is NOT
a valid RFC 3339 date and time and MUST NOT be used for any other
purpose in this field.
This encoding produces a string that is easy to read, parse, and
interpret. The format (more precisely defined in RFC 3339) is
YYYY-MM-DDTHH:MM:SSZ, resulting in one and only one representation
for each second in UTC time from year 0000 to year 9999. For
example, 9:05:00AM EST (GMT-0500) on January 19, 1995 can be
represented as "1995-01-19T14:05:00Z". The length of this field
is always 20 octets.
4.2.6. Port Filter
This PA-TNC Attribute Type provides the list of port numbers and
associated protocols (e.g., TCP and UDP) that are currently blocked
or allowed by a host-based firewall on the endpoint.
Posture Collectors that implement the IETF Standard PA Subtype for
Firewall or VPN SHOULD support sending this attribute type for those
PA subtypes. Posture Collectors that implement other IETF Standard
PA Subtypes defined in this specification MUST NOT support sending
this attribute type for those PA subtypes. Other Posture Collectors
MAY support sending this attribute type, if it is appropriate to
their PA subtype. Whether a particular Posture Collector actually
sends this attribute type SHOULD still be governed by local privacy
and security policies. Posture Validators that implement the IETF
Standard PA Subtype for Firewall or VPN SHOULD support receiving this
attribute type, at least for those PA subtypes. Posture Validators
that implement other IETF Standard PA Subtypes defined in this
specification MUST NOT support receiving this attribute type for
those PA subtypes. Other Posture Validators MAY support receiving
this attribute type. A Posture Validator that does not support
receiving this attribute type SHOULD simply ignore attributes with
this type. Posture Validators MUST NOT send this attribute type.
For this attribute type, the PA-TNC Attribute Vendor ID field MUST be
set to zero (0) and the PA-TNC Attribute Type field MUST be set to 6.
Sangster & Narayan Standards Track [Page 29]RFC 5792 PA-TNC March 2010
The following diagram illustrates the format and contents of the
Attribute Value field for this attribute type. The text after this
diagram describes the fields shown here.
Note that this diagram shows two Protocol/Port Number pairs. The
actual number of Protocol/Port Number pairs included in a Port Filter
attribute can vary from one to a large number (limited only by the
maximum message and length supported by the underlying PT protocol).
However, each Port Filter attribute MUST contain at least one
Protocol/Port Number pair. Because the length of a Protocol/Port
Number pair with the Reserved field and B flag is always 4 octets,
the number of Protocol/Port Number pairs can be easily computed using
the PA-TNC Attribute Length field by subtracting the number of octets
in the PA-TNC Attribute Header and dividing by 4. If the PA-TNC
Attribute Length field is invalid, Posture Validators SHOULD respond
with an Invalid Parameter PA-TNC error code.
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 |B| Protocol | Port Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |B| Protocol | Port Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Reserved
This field is reserved for future use. It MUST be set to 0 on
transmission and ignored upon reception.
B Flag (Blocked or Allowed Port)
This single-bit field indicates whether the following port is
blocked or allowed. This bit MUST be set to 1 if the protocol and
port combination is blocked. Otherwise, this field MUST be set to
0. This field was provided to allow for more abbreviated
reporting of the port filtering policy (e.g., when all ports are
blocked except a few, the Posture Collector can just list the few
that are allowed).
Posture Collectors MUST NOT provide a mixed list of blocked and
non-blocked ports for a particular protocol. To be more precise,
a Posture Collector MUST NOT include two Protocol/Port Number
pairs in a single Port Filter attribute where the protocol number
is the same but the B flag is different. Also, Posture Collectors
MUST NOT list the same Protocol and Port Number combination twice
in a Port List attribute.
Sangster & Narayan Standards Track [Page 30]RFC 5792 PA-TNC March 2010
Posture Collectors MAY list all blocked ports for one protocol and
all allowed ports for a different protocol in a single Port List
attribute, using the B flag to indicate whether each entry is
blocked. For example, a Posture Collector might list all the
blocked TCP ports but only list the allowed UDP ports. However,
it MUST NOT list some blocked TCP ports and some other allowed TCP
ports.
Protocol
This field contains the transport protocol number (e.g., tcp is 6)
being blocked or allowed. The values used in this field are the
same ones used in the IPv4 Protocol and IPv6 Next Header fields.
The IANA already maintains the Assigned Internet Protocol Numbers
registry of these values for use in this field.
Port Number
This field contains the transport protocol (e.g., tcp) port number
being blocked or allowed. The values used in this field are
specific to the protocol identified by the Protocol field. The
IANA maintains registries for well-known and user-requested TCP
and UDP port numbers for use in this field.
4.2.7. Installed Packages
This PA-TNC Attribute Type contains a list of the installed packages
that comprise a product on the endpoint that implements the component
specified in the PA Subtype field, as described in section 3.5. This
allows a Posture Validator to check which packages are installed for
a particular product and which versions of those packages are
installed.
Posture Collectors that implement any of the IETF Standard PA
Subtypes defined in this document SHOULD support sending this
attribute type for those PA subtypes. Other Posture Collectors MAY
support sending this attribute type, if it is appropriate to their PA
subtype. Whether a particular Posture Collector actually sends this
attribute type SHOULD still be governed by local privacy and security
policies. Posture Validators that implement any of the IETF Standard
PA Subtypes defined in this document SHOULD support receiving this
attribute type, at least for those PA subtypes. Other Posture
Validators MAY support receiving this attribute type. A Posture
Validator that does not support receiving this attribute type SHOULD
simply ignore attributes with this type. Posture Validators MUST NOT
send this attribute type.
Sangster & Narayan Standards Track [Page 31]RFC 5792 PA-TNC March 2010
This attribute type can be quite long, especially for the Operating
System PA subtype. This can cause problems, especially with 802.1X
and other limited transport protocols. Therefore, Posture Collectors
SHOULD NOT send this attribute unless specifically requested to do so
using the Attribute Request attribute or otherwise configured to do
so. Also, Posture Validators SHOULD NOT request this attribute
unless the transport protocol in use can support the large amount of
data that may be sent in response.
For this attribute type, the PA-TNC Attribute Vendor ID field MUST be
set to zero (0) and the PA-TNC Attribute Type field MUST be set to 7.
The value in the PA-TNC Attribute Length field will vary, depending
on the number of packages and the length of the Package Name and
Package Version Number fields for those packages. However, the value
in the PA-TNC Attribute Length field MUST be at least 16 because this
is the length of the fixed-length fields in the PA-TNC Attribute
Header and the fixed-length fields in this attribute type. If the
PA-TNC Attribute Length field is less than the size of these fixed-
length fields or does not match the length indicated by the sum of
the fixed-length and variable-length fields, implementations SHOULD
respond with an Invalid Parameter PA-TNC error code.
The following diagram illustrates the format and contents of the
Attribute Value field for this attribute type. The text after this
diagram describes the fields shown here.
Note that this diagram shows an attribute containing information on
one package. The actual number of package descriptions included in
an Installed Packages attribute is indicated by the Package Count
field. This value may vary from zero to a large number (up to 65535,
if the underlying PT protocol can support that many). If this number
is not sufficient, specialized patch management software should be
employed that can simply report compliance with a pre-established
patch policy.
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 | Package Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Pkg Name Len | Package Name (Variable Length) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Version Len | Package Version Number (Variable Length) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Sangster & Narayan Standards Track [Page 32]RFC 5792 PA-TNC March 2010
Reserved
This field is reserved for future use. The field MUST be set to 0
on transmission and ignored upon reception.
Package Count
This field is an unsigned 16-bit integer that indicates the number
of packages listed in this attribute. For each package so
indicated, a Pkg Name Len, Package Name, Version Len, and Package
Version Number field is included in the attribute.
Pkg Name Len
This field is an unsigned 8-bit integer that indicates the length
of the Package Name field in octets. This field may be zero if a
Package Name is not available.
Package Name
This field contains the name of the package associated with the
product. This field is a UTF-8 encoded character string whose
octet length is given by the Pkg Name Len field. This field MUST
NOT include extra octets for padding or NUL character termination.
The syntax and semantics of this name are not specified in this
document, since they may vary across products and/or operating
systems. Posture Collectors MAY list two packages with the same
name in a single Installed Packages attribute. The meaning of
doing so is not defined here.
Version Len
This field is an unsigned 8-bit integer that indicates the length
of the Package Version Number field in octets. This field may be
zero if a Package Version Number is not available.
Package Version Number
This field contains the version string for the package named in
the previous Package Name field. This field is a UTF-8 encoded
character string whose octet length is given by the Version Len
field. This field MUST NOT include extra octets for padding or
NUL character termination. The syntax and semantics of this
version string are not specified in this document, since they may
vary across products and/or operating systems. Posture Collectors
Sangster & Narayan Standards Track [Page 33]RFC 5792 PA-TNC March 2010
MAY list two packages with the same Package Version Number (and
even the same Package Name and Package Version Number) in a single
Installed Packages attribute. The meaning of doing so is not
defined here.
4.2.8. PA-TNC Error
This PA-TNC Attribute Type contains an error code and supplemental
information regarding an error pertaining to PA-TNC.
All Posture Collectors and Posture Validators that implement any of
the IETF Standard PA Subtypes defined in this specification MUST
support sending and receiving this attribute type, at least for those
PA subtypes.
For this attribute type, the PA-TNC Attribute Vendor ID field MUST be
set to zero (0) and the PA-TNC Attribute Type field MUST be set to 8.
The value in the PA-TNC Attribute Length field will vary, depending
on the length of the Error Information field. However, the value in
the PA-TNC Attribute Length field MUST be at least 20 because this is
the length of the fixed-length fields in the PA-TNC Attribute Header
and the fixed-length fields in this attribute type.
A PA-TNC error code SHOULD be sent with the same PA Message Vendor ID
and PA Subtype used by the PA-TNC message that caused the error so
that the error code is sent to the party who sent the offending PA-
TNC message. Other measures (such as setting PB-TNC's EXCL flag and
Posture Collector Identifier or Posture Validator Identifier fields)
SHOULD also be taken to attempt to ensure that only the party who
sent the offending message receives the error.
When a PA-TNC error code is received, the recipient MUST NOT respond
with a PA-TNC error code because this could result in an infinite
loop of errors. Instead, the recipient MAY log the error, modify its
behavior to attempt to avoid the error (attempting to avoid loops or
long strings of errors), ignore the error, terminate the assessment,
or take other action as appropriate (as long as it is consistent with
the requirements of this specification).
Posture Validators MUST NOT include this attribute type in an
Attribute Request attribute. It does not make sense for a Posture
Validator to request that a Posture Collector send a PA-TNC Error
attribute.
Sangster & Narayan Standards Track [Page 34]RFC 5792 PA-TNC March 2010
The following diagram illustrates the format and contents of the
Attribute Value field for this attribute 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | PA-TNC Error Code Vendor ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PA-TNC Error Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Error Information (Variable Length) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Reserved
This field is reserved for future use. This field MUST be set to
0 on transmission and ignored upon reception.
PA-TNC Error Code Vendor ID
This field contains the SMI Private Enterprise Number for the
organization that defined the PA-TNC Error Code that is being used
in the attribute. For IETF Standard PA-TNC Error Code values this
field MUST be set to zero (0).
PA-TNC Error Code
This field contains the PA-TNC Error Code being reported in this
attribute. Note that a particular PA-TNC Error Code value will
have completely different meanings depending on the PA-TNC Error
Code Vendor ID. Each PA-TNC Error Code Vendor ID defines a
different space of PA-TNC Error Code values. Posture Collectors
and Posture Validators MUST NOT require support for particular
vendor-specific PA-TNC Error Codes and MUST interoperate with
other parties despite any differences in the set of vendor-
specific PA-TNC Error Codes supported (although they MAY permit
administrators to configure them to require support for specific
PA-TNC Error Codes).
When the PA-TNC Error Code Vendor ID is set to zero (0), the PA-
TNC Error Code is an IETF Standard PA-TNC Error Code. IANA
maintains a registry of PA-TNC Error Codes. Entries in this
registry are added by Expert Review with Specification Required,
following the guidelines in section 7.
Sangster & Narayan Standards Track [Page 35]RFC 5792 PA-TNC March 2010
The following table lists the IETF Standard PA-TNC Error Codes
defined in this specification:
Integer Description
------- -----------
0 Reserved
1 Invalid Parameter
2 Version Not Supported
3 Attribute Type Not Supported
The next few subsections of this document provide detailed
definitions of these error codes.
Error Information
This field provides additional context for the error. The
contents of this field vary based on the PA-TNC Error Code Vendor
ID and PA-TNC Error Code. Therefore, whenever a PA-TNC Error Code
is defined, the format of this field for that error code must also
be defined. The definitions of IETF Standard PA-TNC Error Codes
on the next few pages provide good examples of such definitions.
The length of this field can be determined by the recipient using
the PA-TNC Attribute Length field by subtracting the length of the
fixed-length fields in the PA-TNC Attribute Header and the fixed-
length fields in this attribute.
4.2.8.1. Invalid Parameter Error Code
The Invalid Parameter error code is an IETF Standard PA-TNC Error
Code (value 1) that indicates that the sender of this error code has
detected an invalid value in a PA-TNC message sent by the recipient
of this error code in the current assessment.
For this error code, the Error Information field contains the first 8
octets of the PA-TNC message that contained the invalid parameter and
an offset indicating the position within that message of the invalid
parameter.
Sangster & Narayan Standards Track [Page 36]RFC 5792 PA-TNC March 2010
The following diagram illustrates the format and contents of the
Error Information field for this error code. 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Version | Copy of Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Offset |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Version
This field MUST contain an exact copy of the Version field in the
PA-TNC Message Header of the PA-TNC message that caused this
error.
Copy of Reserved
This field MUST contain an exact copy of the Reserved field in the
PA-TNC Message Header of the PA-TNC message that caused this
error.
Message Identifier
This field MUST contain an exact copy of the Message Identifier
field in the PA-TNC Message Header of the PA-TNC message that
caused this error.
Offset
This field MUST contain an octet offset from the start of the PA-
TNC Message Header of the PA-TNC message that caused this error to
the start of the value that caused this error. For instance, if
the first PA-TNC attribute in the message had an invalid PA-TNC
Attribute Length (e.g., 0), this value would be 16.
4.2.8.2. Version Not Supported Error Code
The Version Not Supported error code is an IETF Standard PA-TNC Error
Code (value 2) that indicates that the sender of this error code does
not support the PA-TNC version number included in the PA-TNC Message
Header of a PA-TNC message sent by the recipient of this error code
in the current assessment.
Sangster & Narayan Standards Track [Page 37]RFC 5792 PA-TNC March 2010
For this error code, the Error Information field contains the first 8
octets of the PA-TNC message that contained the unsupported version
as well as Max Version and Min Version fields that indicate which PA-
TNC version numbers are supported by the sender of the error code.
The sender MUST support all PA-TNC versions between the Min Version
and the Max Version, inclusive (i.e., including the Min Version and
the Max Version). When possible, recipients of this error code
SHOULD send future messages to the Posture Collector or Posture
Validator that originated this error message with a PA-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 PA-TNC attribute in a PA-TNC
message with version number 1. All parties that send PA-TNC messages
MUST be able to properly process a message that meets this
description, even if they cannot process any other aspect of PA-TNC
version 1. This ensures that a PA-TNC version exchange can proceed
properly, no matter what versions of PA-TNC the parties implement.
The following diagram illustrates the format and contents of the
Error Information field for this error code. 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Version | Copy of Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Max Version | Min Version | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Version
This field MUST contain an exact copy of the Version field in the
PA-TNC Message Header of the PA-TNC message that caused this
error.
Copy of Reserved
This field MUST contain an exact copy of the Reserved field in the
PA-TNC Message Header of the PA-TNC message that caused this
error.
Sangster & Narayan Standards Track [Page 38]RFC 5792 PA-TNC March 2010
Message Identifier
This field MUST contain an exact copy of the Message Identifier
field in the PA-TNC Message Header of the PA-TNC message that
caused this error.
Max Version
This field MUST contain the maximum PA-TNC version supported by
the sender of this error code.
Min Version
This field MUST contain the minimum PA-TNC version supported by
the sender of this error code.
Reserved
Reserved for future use. This field MUST be set to 0 on
transmission and ignored upon reception.
4.2.8.3. Attribute Type Not Supported Error Code
The Attribute Type Not Supported error code is an IETF Standard PA-
TNC Error Code (value 3) that indicates that the sender of this error
code does not support the PA-TNC Attribute Type included in the Error
Information field. This PA-TNC Attribute Type was included in a PA-
TNC message sent by the recipient of this error code in the current
assessment.
For this error code, the Error Information field contains the first 8
octets of the PA-TNC message that contained the unsupported attribute
type as well as a copy of the attribute type that caused the problem.
Sangster & Narayan Standards Track [Page 39]RFC 5792 PA-TNC March 2010
The following diagram illustrates the format and contents of the
Error Information field for this error code. 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Version | Copy of Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | PA-TNC Attribute Vendor ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PA-TNC Attribute Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Version
This field MUST contain an exact copy of the Version field in the
PA-TNC Message Header of the PA-TNC message that caused this
error.
Copy of Reserved
This field MUST contain an exact copy of the Reserved field in the
PA-TNC Message Header of the PA-TNC message that caused this
error.
Message Identifier
This field MUST contain an exact copy of the Message Identifier
field in the PA-TNC Message Header of the PA-TNC message that
caused this error.
Flags
This field MUST contain an exact copy of the Flags field in the
PA-TNC Attribute Header of the PA-TNC attribute that caused this
error.
PA-TNC Attribute Vendor ID
This field MUST contain an exact copy of the PA-TNC Attribute
Vendor ID field in the PA-TNC Attribute Header of the PA-TNC
attribute that caused this error.
Sangster & Narayan Standards Track [Page 40]RFC 5792 PA-TNC March 2010
PA-TNC Attribute Type
This field MUST contain an exact copy of the PA-TNC Attribute Type
field in the PA-TNC Attribute Header of the PA-TNC attribute that
caused this error.
4.2.9. Assessment Result
This PA-TNC attribute contains the final assessment result from a
particular Posture Validator. This attribute might be returned to a
Posture Collector for information purposes such as when an endpoint
is compliant. Similarly, the Assessment Result attribute could be
sent to indicate a non-compliant result where specific actions are
needed to bring an endpoint into compliance with the network's
policies. These actions could be defined in other PA-TNC attributes
such as Remediation Instructions sent to the Posture Collector.
All Posture Collectors that support an IETF Standard PA Subtype
defined in this specification SHOULD support receiving and processing
the Assessment Result attribute. All Posture Validators that
implement an IETF Standard PA Subtype defined in this specification
SHOULD support sending the Assessment Result attribute.
For this attribute type, the PA-TNC Attribute Vendor ID field MUST be
set to zero (0) and the PA-TNC Attribute Type field MUST be set to 9.
The following diagram illustrates the format and contents of the
Attribute Value field for this attribute 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 Validator assessed the endpoint component to
be compliant with policy.
1 Posture Validator assessed the endpoint component to
be non-compliant with policy but the difference from
compliant was minor.
Sangster & Narayan Standards Track [Page 41]RFC 5792 PA-TNC March 2010
2 Posture Validator assessed the endpoint component to
be non-compliant with policy and the assessed
difference was very significant.
3 Posture Validator was unable to determine policy
compliance of an endpoint component due to an error.
4 Posture Validator was unable to determine whether the
assessed endpoint component was compliant with policy
based on the attributes provided by the Posture
Collector.
4.2.10. Remediation Instructions
This PA-TNC attribute sent by the Posture Validator to the Posture
Collector contains remediation instructions for updating a particular
component to make the endpoint compliant with the assessment
policies. A Posture Validator might choose to send more than one
Remediation Instructions attribute in some circumstances (e.g., both
a URI and a human-readable message are necessary) to remediate one or
more components. This attribute supports the inclusion of either an
IETF standard or vendor-specific remediation instruction.
All Posture Collectors that implement an IETF Standard PA Subtype
defined in this specification SHOULD support receiving and processing
the Remediation Instructions attribute. All Posture Validators that
implement an IETF Standard PA Subtype defined in this specification
SHOULD support sending this attribute type. Posture Collectors and
Posture Validators supporting other non-IETF standard components MAY
support this attribute.
For this attribute type, the PA-TNC Attribute Vendor ID field MUST be
set to zero (0) and the PA-TNC Attribute Type field MUST be set to
10.
The following diagram illustrates the format and contents of the
Attribute Value field for this attribute 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Remediation Parameters Vendor ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remediation Parameters Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remediation Parameters (Variable Length) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Sangster & Narayan Standards Track [Page 42]RFC 5792 PA-TNC March 2010
Reserved (8 bits)
The 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 different
types of remediation instructions that can be contained in the
Remediation Parameters field. IANA maintains a registry of PA-TNC
Remediation Parameters Types. Entries in this registry are added
by Expert Review with Specification Required, following the
guidelines in section 7. A list of IETF Standard PA-TNC
Remediation Parameters Types defined in this specification appears
later in this section.
New vendor-specific remediation instructions can be created by
adding new Remediation Parameters Types (those used with a non-
zero Remediation Parameters vendor ID) without IETF or IANA
involvement. Posture Collectors and Posture Validators MUST NOT
require support for particular vendor-specific PA-TNC Remediation
Parameters Types and MUST interoperate with other parties despite
any differences in the set of vendor-specific PA-TNC Remediation
Parameters Types supported (although they MAY permit
administrators to configure them to require support for specific
PA-TNC remediation parameter types).
The following table lists the IETF Standard PA-TNC Remediation
Parameters Type values defined in this specification:
Integer Description
------- -----------
0 Reserved
1 Remediation URI
2 Remediation String
Sangster & Narayan Standards Track [Page 43]RFC 5792 PA-TNC March 2010
The next few subsections of this document provide detailed
definitions of the contents of the Remediation Parameters field
used with each Remediation Parameter Type.
Remediation Parameters (variable length)
The Remediation Parameters field contains the actual remediation
instructions for the Posture Collector.
4.2.10.1. Remediation URI Parameters Type
The Remediation URI Parameters Type is an IETF Standard Remediation
Parameters Type (value 1) that indicates that the sending Posture
Validator is providing a URI to instructions on how to remediate the
endpoint.
The following diagram illustrates the format and contents of the
Remediation Parameters field when carrying a Remediation URI
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 URI (Variable Length) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Remediation URI
The Remediation URI field MUST contain a URI, as described in RFC
3986 [7]. This URI SHOULD contain instructions to update a
particular component so that it might result in the component
being compliant with the policies in future assessments. Posture
Collectors should validate that the URI and instructions come from
a trustworthy source to avoid being tricked into performing
damaging actions (see security considerations).
4.2.10.2. Remediation String Parameters Type
The Remediation String Parameters Type is an IETF Standard
Remediation Parameters Type (value 2) that indicates that the sending
Posture Validator is providing a human-readable string containing
instructions on how to remediate the endpoint.
The following diagram illustrates the format and contents of the
Remediation Parameters field when the carrying a Remediation String
parameter. The text after this diagram describes the fields shown
here.
Sangster & Narayan Standards Track [Page 44]RFC 5792 PA-TNC March 2010
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
The Remediation String Length contains the length of the
Remediation String field in octets.
Remediation String
The Remediation String field MUST contain a UTF-8 encoded string.
This string contains human-readable instructions for remediation
that MAY be displayed to the user by the Posture Collector. NUL
termination MUST NOT be included. If a Posture Collector receives
a Remediation String that does contain a NUL termination, it
SHOULD send an Invalid Parameter error code.
Lang Code Len (Remediation String Language Code Length)
The Lang Code Len field contains the length of the Remediation
String Language Code field in octets.
Remediation String Lang Code
The Remediation String Lang(uage) Code field contains a US-ASCII
string composed of a well-formed RFC 4646 [6] 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 is not known.
4.2.11. Forwarding Enabled
This PA-TNC attribute indicates whether the endpoint is forwarding
traffic between interfaces. Endpoints that forward traffic between
networks connected to multiple network interfaces may be considered
non-compliant (and a security risk) in some enterprise network
deployments. For example, an endpoint with multiple connected
network interfaces might allow traffic from an interface connected to
a public network to be forwarded through another interface carrying a
VPN session to a protected enterprise network. This attribute is
Sangster & Narayan Standards Track [Page 45]RFC 5792 PA-TNC March 2010
currently envisioned to be specific to reporting posture for the
operating system component; however, could be useful for other future
types of components.
Posture Collectors that implement the IETF Standard PA Subtype for
Operating System SHOULD support sending the Forwarding Enabled
attribute. Posture Collectors that do not implement the Operating
System PA Subtype defined in this specification SHOULD NOT send the
Forwarding Enabled attribute unless it is appropriate to their PA
Subtype. Whether a particular Posture Collector actually sends this
attribute type SHOULD still be governed by local privacy and security
policies. Posture Validators that implement the IETF Standard PA
Subtype for Operating System SHOULD support receiving the Forwarding
Enabled attribute type. Posture Validators supporting components
other than Operating System MAY support receiving this attribute type
if it is appropriate to their PA Subtype. A Posture Validator that
does not support receiving this attribute type SHOULD simply ignore
attributes with this type. Posture Validators MUST NOT send this
attribute type.
For this attribute type, the PA-TNC Attribute Vendor ID field MUST be
set to zero (0) and the PA-TNC Attribute Type field MUST be set to
11.
The following diagram illustrates the format and contents of the
Attribute Value field for this attribute 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Forwarding Enabled |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Forwarding Enabled
This 32-bit field MUST contain one of the following values;
Value Description
----- -----------
0 Disabled - Endpoint is not forwarding traffic.
1 Enabled - Endpoint is forwarding traffic.
2 Unknown - Unable to determine whether endpoint is
forwarding traffic
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4.2.12. Factory Default Password Enabled
This PA-TNC attribute indicates whether the endpoint has a factory
default password enabled for use. Some types of endpoints include a
default static password for used to gain privileged access to the
endpoint. If this password is not changed or disabled before the
endpoint is accessible on the network, it's often easy to compromise
the endpoint.
Posture Collectors that implement the IETF Standard PA Subtype for
Operating System SHOULD support sending the Factory Default Password
Enabled attribute. Posture Collectors that implement other IETF
Standard PA Subtypes defined in this specification SHOULD NOT support
sending this attribute type for those PA subtypes. Other Posture
Collectors MAY support sending this attribute type, if it is
appropriate to their PA subtype. Whether a particular Posture
Collector actually sends this attribute type SHOULD still be governed
by local privacy and security policies. Posture Validators that
implement the IETF Standard PA Subtype for Operating System SHOULD
support receiving the Factory Default Password Enabled attribute.
Other Posture Validators MAY support receiving this attribute type.
A Posture Validator that does not support receiving this attribute
type SHOULD simply ignore attributes with this type. Posture
Validators MUST NOT send this attribute type.
For this attribute type, the PA-TNC Attribute Vendor ID field MUST be
set to zero (0) and the PA-TNC Attribute Type field MUST be set to
12.
The following diagram illustrates the format and contents of the
Attribute Value field for this attribute 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Factory Default Password Enabled |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Factory Default Password Enabled
This 32-bit field MUST contain one of the following values;
Value Description
----- -----------
0 Endpoint does not have factory default password enabled.
1 Endpoint has a factory default password enabled.
Sangster & Narayan Standards Track [Page 47]RFC 5792 PA-TNC March 2010
4.3. Vendor-Defined Attributes
This section discusses the use of vendor-defined attributes within
PA-TNC. The PA-TNC protocol was designed to allow for vendor-defined
attributes to be used as a replacement where a standard attribute
could be used. In some cases, even the standard attributes allow for
vendor-defined information to be included. It is envisioned that
over time as particular vendor-defined attributes become popular, an
equivalent standard attribute could be added allowing for broader
interoperability.
This specification does not define vendor-defined attributes, but
rather highlights how such attributes can be used with PA-TNC without
the potential for namespace collisions or misinterpretations. In
order to avoid collisions, PA-TNC uses the well-established SMI
Private Enterprise Numbers as vendor IDs to define separate
namespaces for important fields within a PA-TNC message. For
example, to ensure the uniqueness of attribute types while providing
for vendor extensions, vendor-defined attribute types include the
vendor's unique vendor ID, to indicate the intended namespace for the
attribute type, followed by the attribute type. IETF Standard PA-TNC
Attribute Types use a vendor ID of zero (0).
SMI Private Enterprise Numbers are used to provide a separate
identifier space for each vendor. The IANA provides a registry for
SMI Private Enterprise Numbers. Any organization (including non-
profit organizations, governmental bodies, etc.) can obtain one of
these numbers at no charge, and thousands of organizations have done
so. Within this document, SMI Private Enterprise Numbers are known
as "vendor IDs".
5. Security Considerations
This section discusses the major potential types of security threats
relevant to the PA-TNC message protocol. It is envisioned that
additional attribute types could be defined in the future to
facilitate the exchange of security capabilities, keys, and security
protected attributes if future use cases are adopted that require
such protections.
5.1. Trust Relationships
In order to understand where security countermeasures are necessary,
this section starts with a discussion of where the TNC architecture
envisions some trust relationships between the processing elements of
the PA-TNC protocol. The following subsections discuss the trust
properties associated with each portion of the NEA reference model
directly involved with the processing of the PA-TNC protocol.
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RFC 5792 PA-TNC March 2010
5.1.1. Posture Collector
The Posture Collectors are trusted by Posture Validators to:
o Collect valid information about the component type associated with
the Posture Collector
o Report upon collected information consistent with local security
and privacy policies
o Accurately report information associated with the type of
component for the PA-TNC message
o Not act maliciously to the Posture Broker Server and Posture
Validators, including attacks such as denial of service
5.1.2. Posture Validator
The Posture Validators are trusted by Posture Collectors to:
o Only request information necessary to assess the security state of
the endpoint
o Make assessment decisions based on deployer-defined policies
o Discard collected information consistent with data retention and
privacy policies
o Not act maliciously to the Posture Broker Server and Posture
Collectors, including attacks such as denial of service
o Not send malicious remediation instructions that do not fix or
that cause damage to the endpoint
5.1.3. Posture Broker Client, Posture Broker Server
The Posture Broker Client and Posture Broker Server are trusted by
the Posture Collector and Posture Validator to:
o Provide a reliable transport for PA-TNC messages
o Deliver messages for a particular PA Subtype only to those Posture
Collectors and Posture Validators that have registered for them
o Not disclose any provided attributes to unauthorized parties
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o Not act maliciously to drop messages, duplicate messages, or flood
Posture Collectors and Posture Validators with unnecessary
messages
o Not observe, fabricate, or alter the contents of a PA-TNC message
o Properly place Posture Collector and Posture Validator identifiers
into the PB-TNC protocol, deliver those identifiers to Posture
Collectors and Posture Validators as needed, and manage exclusive
delivery to a particular Posture Collector or Posture Validator
when requested
o Properly expose authentication information from PT security so
that Posture Collectors and Posture Validators can use the peer's
identity information to safely make policy decisions
5.2. Security Threats
Beyond the trusted relationships assumed in section 5.1, the PA-TNC
protocol faces a number of potential security attacks that could
require security countermeasures.
Generally, the PA-TNC protocol relies upon the underlying PT
protocol's security to protect the messages from attack when
traveling over the network. Once the message resides on the Posture
Broker Client or Posture Broker Server, the posture brokers are
trusted to properly and safely deliver the messages to the
appropriate Posture Collectors and Posture Validators.
5.2.1. Attribute Theft
When PA-TNC messages are sent over unprotected network links or
spanning local software stacks that are not trusted, the contents of
the PA-TNC messages may be subject to information theft by an
intermediary party. This theft could result in information being
recorded for future use or analysis by the adversary. Attributes
observed by eavesdroppers could contain information that exposes
potential weaknesses in the security of the endpoint, or system
fingerprinting information easing the ability of the attacker to
employ attacks more likely to be successful against the endpoint.
The eavesdropper might also learn information about the endpoint or
network policies that either singularly or collectively is considered
sensitive information (e.g., certain endpoints are lacking patches,
or particular sub-networks have more lenient policies).
PA-TNC attributes are not intended to carry privacy-sensitive
information, but should some exist in a message, the adversary could
come into possession of the information, which could be used for
Sangster & Narayan Standards Track [Page 50]RFC 5792 PA-TNC March 2010
financial gain. Therefore, it is important that PT provide strong
confidentiality protection to protect the message from eavesdroppers
when being sent between the Posture Transport Client and Posture
Transport Server.
5.2.2. Message Fabrication
Attackers on the network or present within the NEA system could
introduce fabricated PA-TNC messages intending to trick or create a
denial of service against aspects of an assessment. For example, an
adversary could attempt to send a falsified set of remediation
instructions using the Remediation URI support in hopes of the
Posture Collector automatically following the instructions. Posture
Collectors need to ensure that any requests to take actions on the
endpoint (such as remediation instructions) received from Posture
Validators are authentic and trustworthy using strong authentication
and integrity protections offered by PT. Posture Collectors should
not blindly follow remediation instructions received from a trusted
NEA Server. At least for patches and other potentially dangerous
actions, Posture Collectors should validate these actions (e.g., via
user confirmation) before proceeding.
Such an attack could occur if an active attacker launches a man-in-
the-middle (MitM) attack by proxying the PA-TNC messages and was able
to replace undesired messages with ones easing future attack upon the
endpoint. Consider a scenario where PT security protection is not
used and the Posture Broker Server proxies all assessment traffic to
a remote Posture Broker Server. The proxy could eavesdrop and
replace assessment results attributes, tricking the endpoint into
thinking it has passed an assessment, when in fact it has not and
requires remediation. Because the Posture Collector has no way to
verify that attributes were actually created by an authentic Posture
Validator, it is unable to detect the falsified attribute or message.
Therefore, it is important that PT provides strong authentication and
integrity protection.
5.2.3. Attribute Modification
This attack could allow an active attacker capable of intercepting a
message to modify a PA-TNC message attribute to a desired value to
ease the compromise of an endpoint. Without the ability for message
recipients to detect whether a received message contains the same
content as what was originally sent, active attackers can stealthily
modify the attribute exchange.
For example, an attacker might wish to change the contents of the
firewall component's version string attribute to disguise the fact
that the firewall is running an old, vulnerable version. The
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RFC 5792 PA-TNC March 2010
attacker would change the version string sent by the firewall Posture
Collector to the current version number, so the Posture Validator's
assessment passes while leaving the endpoint vulnerable to attack.
Similarly, an attacker could achieve widespread denial of service by
altering large numbers of assessments' version string attributes to
an old value so they repeatedly fail assessments even after a
successful remediation. Upon receiving the lower value, the Posture
Validator would continue to believe that the endpoint is running old,
potentially vulnerable versions of the firewall that does not meet
network compliance policy, so therefore the endpoint would not be
allowed to join the network. Use of a PT protocol providing strong
integrity protection and authentication is essential as
countermeasures to these attacks.
5.2.4. Attribute Replay
Another potential attack against an unprotected PA-TNC message
attribute exchange is to exploit the lack of a strong binding between
the attributes sent during an assessment to the specific endpoint.
Without a strong binding of the endpoint to the posture information,
an attacker could record the attributes sent during an assessment of
a compliant endpoint and later replay those attributes so that a non-
compliant endpoint can now gain access to the network or protected
resource. This attack could be employed by a network MitM that is
able to eavesdrop and proxy message exchanges, or by using local
rogue agents on the endpoints. Assessments lacking some form of
freshness exchange could be subject to replay of prior assessment
data, even if it no longer reflects the current state of the
endpoint. Use of a PT protocol providing strong integrity protection
and authentication including a freshness exchange is necessary
countermeasure to these attacks.
5.2.5. Attribute Insertion
Similar to the attribute modification attacks, an adversary wishing
to include one or more attributes or PA-TNC messages inside a valid
assessment may be able to insert the attributes or messages without
detection by the recipient. For example, an attacker could add
attributes to the front of a PA-TNC message to cause an assessment to
succeed even for a non-compliant endpoint, particularly if it knew
that the recipient ignored repeated attributes within a message.
Similarly, if a Posture Collector or Posture Validator always
generated an error if it saw unexpected attributes, the attacker
could cause failures and denial of service by adding attributes or
messages to an exchange. Use of a PT protocol providing strong
authentication and integrity protection could prevent the adversary
from inserting attributes into the assessment.
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5.2.6. Denial of Service
A variety of types of denial-of-service attacks are possible against
the PA-TNC message exchange if left unprotected from untrusted
parties along the communication path between the Posture Collector
and Posture Validator. Normally, the PT exchange is bidirectionally
authenticated, which helps to prevent a MitM on the network from
becoming an active proxy, but transparent message routing gateways
may still exist on the communication path and can modify the
integrity of the message exchange unless adequate integrity
protection is provided. If the MitM or other entities on the network
can send messages to the Posture Broker Client or Posture Broker
Server that appear to be part of an assessment, these messages could
confuse the Posture Collector and Posture Validator or cause them to
perform unnecessary work or take incorrect action. Several example
denial-of-service situations are described in sections 5.2.3 and
5.2.5. Many potential denial-of-service examples exist, including
flooding messages to the Posture Collector or Posture Validator,
sending very large messages containing many attributes, and
repeatedly asking for resource-intensive operations.
6. Privacy Considerations
The PA-TNC protocol is designed to allow for controlled disclosure of
security-relevant information about an endpoint, specifically for the
purpose of enabling an assessment of the endpoint's compliance with
network policy. The purpose of this protocol is to provide
visibility into the state of the protective mechanisms on the
endpoint, in order for the Posture Validators and Posture Broker
Server to determine whether the endpoint is up to date and thus has
the best chance of being resilient in the face of malware threats.
One risk associated with providing visibility into the contents of an
endpoint is the increased chance for exposure of privacy-sensitive
information without the consent of the user.
While this protocol does provide the Posture Validator the ability to
request specific information about the endpoint, the protocol is not
open ended, bounding the Posture Validator to only query specific
information (attributes) about specific security features (component
types) of the endpoint. Each PA-TNC message is explicitly about a
single component from the list of components in section 3.5. These
components include a list of security-related aspects of the endpoint
that affect the ability of the endpoint to resist attacks and thus
are of interest during an assessment. Discretionary components used
by the user to create or view content are not on the list, as they
are more likely to have access to privacy-sensitive information.
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RFC 5792 PA-TNC March 2010
Similarly, PA-TNC messages contain a set of attributes that describe
the particular component. Each attribute contains generic
information (e.g., product information or versions) about the
component, so it is unlikely to include any user-specific or
identifying information. This combination of a limited set of
security-related components with non-user-specific attributes greatly
reduces the risk of exposure of privacy-sensitive information.
Vendors that choose to define additional component types and/or
attributes within their namespace are encouraged to provide similar
constraints.
Even with the bounding of standard attribute information to specific
components, it is possible that individuals might wish to share less
information with different networks they wish to access. For
example, a user may wish to share more information when connecting to
or being reassessed by the user's employer network than what would be
made available to the local coffee shop wireless network. While
these situations do not impact the protocol itself, they do suggest
that Posture Collector implementations should consider supporting a
privacy filter allowing the user and/or system owner to restrict
access to certain attributes based upon the target network.
The underlying PT protocol authenticates the network's Posture Broker
Server at the start of an assessment, so identity can be made
available to the Posture Collector and per-network privacy filtering
is possible. Network owners should make available a list of the
attributes they require to perform an assessment and any privacy
policy they enforce when handling the data. Users wishing to use a
more restricted privacy filter on the endpoint may risk not being
able to pass an assessment and thus not gain access to the requested
network or resource.
7. IANA Considerations
This section defines the contents of three new IANA registries: PA-
TNC Attribute Types, PA-TNC Error Codes, and PA-TNC Remediation
Parameters Types. This section explains how these registries work.
Also, this specification defines several new PA Subtypes for use with
PA-TNC.
All of the registries defined in this document support IETF standard
values and vendor-defined values. To explain this phenomenon, we
will use the PA-TNC Attribute Type as an example, but the other three
registries work the same way. Whenever a PA-TNC Attribute Type
appears on a network, it is always accompanied by an SMI Private
Enterprise Number (PEN), also known as a vendor ID. If this vendor
ID is zero, the accompanying PA-TNC Attribute Type is an IETF
standard value listed in the IANA registry for PA-TNC Attribute
Sangster & Narayan Standards Track [Page 54]
RFC 5792 PA-TNC March 2010
Types, and its meaning is defined in the specification listed for
that PA-TNC Attribute Type in that registry. If the vendor ID is not
zero, the meaning of the PA-TNC Attribute Type is defined by the
vendor identified by the vendor ID (as listed in the IANA registry
for SMI PENs). The identified vendor is encouraged but not required
to register with IANA some or all of the PA-TNC Attribute Types used
with their vendor ID and publish a specification for each of these
values.
This delegation of namespace is analogous to the technique used for
OIDs. It can result in interoperability problems if vendors require
support for particular vendor-specific values. However, such
behavior is explicitly prohibited by this specification (in section
4.1), which dictates that "Posture Collectors and Posture Validators
MUST NOT require support for particular vendor-specific PA-TNC
Attribute Types and MUST interoperate with other parties despite any
differences in the set of vendor-specific PA-TNC Attribute Types
supported (although they MAY permit administrators to configure them
to require support for specific PA-TNC Attribute Types)". Similar
requirements are included for PA Subtypes, Remediation Parameters
Types, and PA-TNC Error Codes.
7.1. Designated Expert Guidelines
For all of the IANA registries defined by this specification, new
values are added to the registry by Expert Review with Specification
Required, using the Designated Expert process defined in RFC 5226
[3].
This section provides guidance to designated experts so that they may
make decisions using a philosophy appropriate for these registries.
The registries defined in this document have plenty of values. In
most cases, the IETF has approximately 2^32 values available for it
to define and each vendor the same number of values for its use.
Because there are so many values available, designated experts should
not be terribly concerned about exhausting the set of values.
Instead, designated experts should focus on the following
requirements. All values in these IANA registries MUST be documented
in a specification that is permanently and publicly available. IETF
standard values MUST also be useful, not harmful to the Internet, and
defined in a manner that is clear and likely to ensure
interoperability.
Designated experts should encourage vendors to avoid defining similar
but incompatible values and instead agree on a single IETF standard
value. However, it is beneficial to document existing practice.
Sangster & Narayan Standards Track [Page 55]
RFC 5792 PA-TNC March 2010
There are several ways to ensure that a specification is permanently
and publicly available. It may be published as an RFC.
Alternatively, it may be published in another manner that makes it
freely available to anyone. However, in this latter case, the vendor
MUST supply a copy to the IANA and authorize the IANA to archive this
copy and make it freely available to all if at some point the
document becomes no longer freely available to all through other
channels.
Section 7.2 defines the new PA Subtypes. The following three
sections provide guidance to the IANA in creating and managing the
new IANA registries defined by this specification.
7.2. PA Subtypes
Section 3.5 of this specification defines several new PA Subtypes
that have been added to the PA Subtypes registry defined in the PB-
TNC specification. Here is a list of these assignments:
PEN Integer Name Defining Specification
--- ------- ---- ----------------------
0 0 Testing RFC 5792
0 1 Operating System RFC 5792
0 2 Anti-Virus RFC 5792
0 3 Anti-Spyware RFC 5792
0 4 Anti-Malware RFC 5792
0 5 Firewall RFC 5792
0 6 IDPS RFC 5792
0 7 VPN RFC 5792
0 8 NEA Client RFC 5792
These PA Subtypes have been added to the registry for PA Subtypes
defined in the PB-TNC specification, with this RFC as the reference.
7.3. Registry for PA-TNC Attribute Types
The name for this registry is "PA-TNC Attribute Types". Each entry
in this registry should include a human-readable name, an SMI Private
Enterprise Number, a decimal integer value between 0 and 2^32-1, and
a reference to the specification where the contents of this attribute
type are defined. This specification must define the meaning of this
PA-TNC attribute type and the format and semantics of the PA-TNC
Attribute Value field for PA-TNC attributes that include the
designated Private Enterprise Number in the PA-TNC Attribute Vendor
ID field and the designated numeric value in the PA-TNC Attribute
Type field.
Sangster & Narayan Standards Track [Page 56]RFC 5792 PA-TNC March 2010
The following entries for this registry are defined in this document.
They are the initial entries in the registry for PA-TNC Attribute
Types. Additional entries to this registry are added by Expert
Review with Specification Required, following the guidelines in
section 7.1.
PEN Integer Name Defining Specification
--- ------- ---- ----------------------
0 0 Testing RFC 5792
0 1 Attribute Request RFC 5792
0 2 Product Information RFC 5792
0 3 Numeric Version RFC 5792
0 4 String Version RFC 5792
0 5 Operational Status RFC 5792
0 6 Port Filter RFC 5792
0 7 Installed Packages RFC 5792
0 8 PA-TNC Error RFC 5792
0 9 Assessment Result RFC 5792
0 10 Remediation Instructions RFC 5792
0 11 Forwarding Enabled RFC 5792
0 12 Factory Default Password RFC 5792
Enabled
0 0xffffffff Reserved RFC 5792
7.4. Registry for PA-TNC Error Codes
The name for this registry is "PA-TNC Error Codes". Each entry in
this registry should include a human-readable name, an SMI Private
Enterprise Number, a decimal integer value between 0 and 2^32-1, and
a reference to the specification where this error code is defined.
This specification must define the meaning of this error code and the
format and semantics of the Error Information field for PA-TNC
attributes that have a PA-TNC vendor ID of 0, a PA-TNC Attribute Type
of PA-TNC Error, the designated Private Enterprise Number in the PA-
TNC Error Code Vendor ID field, and the designated numeric value in
the PA-TNC Error Code field.
The following entries for this registry are defined in this document.
They are the initial entries in the registry for PA-TNC Error Codes.
Additional entries to this registry are added by Expert Review with
Specification Required, following the guidelines in section 7.1.
Sangster & Narayan Standards Track [Page 57]RFC 5792 PA-TNC March 2010
PEN Integer Name Defining Specification
--- ------- ---- ----------------------
0 0 Reserved RFC 5792
0 1 Invalid Parameter RFC 5792
0 2 Version Not Supported RFC 5792
0 3 Attribute Type Not Supported RFC 5792
7.5. Registry for PA-TNC Remediation Parameters Types
The name for this registry is "PA-TNC Remediation Parameters Types".
Each entry in this registry should include a human-readable name, an
SMI Private Enterprise Number, a decimal integer value between 1 and
2^32-1, and a reference to the specification where the contents of
this remediation parameters type are defined. This specification
must define the meaning of this PA-TNC Remediation Parameters Type
and the format and semantics of the Remediation Parameters field for
PA-TNC attributes that include the designated Private Enterprise
Number in the Remediation Parameters Vendor ID field and the
designated numeric value in the Remediation Parameters Type field.
The following entries for this registry are defined in this document.
They are the initial entries in the registry for PA-TNC Remediation
Parameters Types. Additional entries to this registry are added by
Expert Review with Specification Required, following the guidelines
in section 7.1.
PEN Integer Name Defining Specification
--- ------- ---- ----------------------
0 0 Reserved RFC 5792
0 1 URI RFC 5792
0 2 Remediation String RFC 5792
8. Acknowledgments
Thanks to the Trusted Computing Group for contributing the initial
text [8] upon which this document was based. The authors would also
like to acknowledge the following people who have contributed to or
provided substantial input on the preparation of this document or
predecessors to it: Stuart Bailey, Roger Chickering, Lauren Giroux,
Charles Goldberg, Steve Hanna, Ryan Hurst, Meenakshi Kaushik, Greg
Kazmierczak, Scott Kelly, PJ Kirner, Houcheng Lee, Lisa Lorenzin,
Mahalingam Mani, Sung Lee, Ravi Sahita, Mauricio Sanchez, Brad Upson,
and Han Yin.
Sangster & Narayan Standards Track [Page 58]RFC 5792 PA-TNC March 2010
9. References
9.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Yergeau, F., "UTF-8, a transformation format of ISO 10646", STD
63, RFC 3629, November 2003.
[3] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", BCP 26, RFC 5226, May 2008.
[4] Klyne, G. and C. Newman, "Date and Time on the Internet:
Timestamps", RFC 3339, July 2002.
[5] Sahita, R., Hanna, S., Hurst, R., and K. Narayan, "PB-TNC: A
Posture Broker (PB) Protocol Compatible with Trusted Network
Connect (TNC)", RFC 5793, March 2010.
[6] Phillips, A., Ed., and M. Davis, Ed., "Tags for Identifying
Languages", BCP 47, RFC 5646, September 2009.
[7] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986,
January 2005.
9.2. Informative References
[8] Trusted Computing Group, "IF-M: TLV Binding",
http://www.trustedcomputinggroup.org/resources/
tnc_ifm_tlv_binding_specification, February 2010.
[9] Sangster, P., Khosravi, H., Mani, M., Narayan, K., and J.
Tardo, "Network Endpoint Assessment (NEA): Overview and
Requirements", RFC 5209, June 2008.
Sangster & Narayan Standards Track [Page 59]RFC 5792 PA-TNC March 2010
Appendix A. Use Cases
A.1. Initial Client-Triggered Assessment
This scenario involves the assessment of an endpoint initiated during
network join. The assessment is triggered by the Posture Broker
Client (PBC) and involves collection of patch information from both
Standard Operating System (OS) Posture Collector and vendor-specific
Patch Posture Collector (PC). The assessment by both the vendor-
specific Patch Posture Validator (PV) and Standard OS Posture
Validator result in a compliant assessment decision that results in a
compliant System Assessment Decision to be returned by the Posture
Broker Server (PBS).
+--------+ +-------+ +---------+ +--------+ +-------++--------+
| Vndr. X| | Std. | | Std. | | Std. | | Std. || Vndr. X|
|Patch PC| | OS PC | | PBC | | PBS | | OS PV ||Patch PV|
+--+-----+ +-+-----+ +---+-----+ +-+------+ +-+------+--+-----+
| | N/W Join| | | |
| | ----->| | | |
| | Req Post. | | | |
| |<----------| | | |
| | Req Post. | | | |
|<--------------------| | | |
|Vndr X Patch Posture | | | |
|-------------------->| | | |
| |OS Posture | | | |
| |---------->| | | |
| | | Posture | | |
| | | Report | | |
| | |-------->| | |
| | | | Verify | |
| | | | Posture | |
| | | |---------> |
| | | | | Verify |
| | | | | Posture |
| | | |------------------->|
| | | | OS Reslt | |
| | | |<---------| |
| | | | VndrX Patch Result |
| | | Assess |<-------------------|
| | | Result | |
| | |<--------| | |
| | OS Reslt | | | |
| |<----------| | | |
| VndrX Patch Result | | | |
|<--------------------| | | |
Sangster & Narayan Standards Track [Page 60]RFC 5792 PA-TNC March 2010
A.1.1. Message Contents
This section shows the contents of the key fields in each of the PA
messages exchanged in this use case. When necessary, additional
commentary is provided to explain why certain fields contain the
shown values. Note that many of the flows shown are between
components on the same system so no message contents are shown.
A.1.1.1. N/W Join
This flow represents the event that causes the PBC to decide to start
an assessment of the endpoint in order to gain access to the network.
This is merely an event and does not include a message being sent.
A.1.1.2. Request Posture (Req Post.)
This flow illustrates an invocation of the OS and patch posture
collectors requesting particular posture attributes to be sent.
Because this use case is triggered locally, the contents of this flow
aren't specified by NEA.
A.1.1.3. Vendor X Patch Posture (VndrX Patch Posture)
This flow contains the PA message from the Patch Posture Collector:
Vendor X Patch Posture PA Message {
Attribute HDR {Message ID}
Attribute 1 {
vendor-id=1 (vendor X)
type=1 (Vendor X namespace attribute)
length
Value = {
VendorXAttribute1=123
}
}
Attribute 2 {
vendor-id=1 (vendor X)
type=2 (Vendor X namespace attribute)
length
Value = {
VendorXAttribute2=456
}
}
}
Sangster & Narayan Standards Track [Page 61]RFC 5792 PA-TNC March 2010
A.1.1.4. OS Posture
This flow contains the PA message from the OS Posture Collector:
OS Posture PA Message {
Attribute HDR {Message ID}
Attribute 1 {
vendor-id=0
type=2 (product information)
length
Value = {
Product-vendor-id=311 -- Microsoft's PEN
Product-name="Windows Vista"
}
}
Attribute 2 {
vendor-id=0
type=3 (numeric version)
length
Value = {
major-version=6 -- Vista is version 6.0
minor-version=0
build-number=456789
service-pack-major=0 -- No service packs
service-pack-minor=0
}
}
}
A.1.1.5. Posture Report
This flow contains the PB message containing the PA messages from the
Patch and OS Posture Collectors; the message content is described in
the PB-TNC specification.
A.1.1.6. Verify Posture
This flow illustrates an invocation of the OS and patch Posture
Validators requesting verification of the posture attributes
received. Because this flow happens locally within the NEA server,
NEA does not specify the message contents.
Sangster & Narayan Standards Track [Page 62]RFC 5792 PA-TNC March 2010
A.1.1.7. OS Posture Result (OS Reslt)
This flow contains the PA message (Posture Assessment Result) from
the OS Posture Validator
OS Posture Result PA Message {
Attribute HDR {Message ID}
Attribute 1 {
vendor-id=0
type=9 (assessment-result)
length
Value = {
assessment-result=0 (compliant)
}
}
}
A.1.1.8. Vendor X Patch Result (VndrX Patch Result)
This flow contains the PA message (Posture Assessment Result) from
the Vendor X Patch Posture Validator
Patch Vendor X Posture Result PA Message {
Attribute HDR {Message ID}
Attribute 1 {
vendor-id=0
type=9 (assessment-result)
length
Value = {
assessment-result=0 (compliant)
}
}
}
A.1.1.9. Assessment Result (Assess Result)
This flow contains the PB message containing the system assessment
result computed by the Posture Broker Server and the PA messages from
the Patch and OS Posture Validators; the message content is described
in the PB-TNC specification.
A.1.1.10. Posture Result (OS PRslt & Vndr X Post PResult)
These flows illustrate an invocation of the OS and Vendor X Patch
Posture Collectors to receive the posture assessment results.
Because this flow is triggered locally, NEA does not specify the
contents of this flow.
Sangster & Narayan Standards Track [Page 63]RFC 5792 PA-TNC March 2010
A.2. Server-Initiated Assessment with Remediation
This scenario involves the assessment of an endpoint initiated by the
NEA Server. The assessment is triggered by the Posture Broker Server
and involves collection of Anti-Virus attributes for two Anti-Virus
components running on the endpoint. The endpoint is assessed to be
compliant by one of the vendor (Vendor X) anti-virus Posture
Validators and non-compliant by the other vendor (Vendor Y) anti-
virus Posture Validator. Based upon the Posture Broker Server's
policy, this results in a non-compliant system assessment decision to
be returned by the Posture Broker Server. The Posture Broker Server
also returns remediation instructions for the endpoint as part of the
response.
Sangster & Narayan Standards Track [Page 64]
RFC 5792 PA-TNC March 2010
+--------+ +-------+ +---------+ +--------+ +-------+ +--------+
| Vndr Y | | Vndr X| | Std. | | Std. | | Vndr X| | Vndr Y |
| AV PC | | AV PC | | PBC | | PBS | | AV PV | | AV PV |
+----+---+ +---+---+ +-----+---+ +---+----+ +---+---+ +----+---+
| | | N/W Join| | |
| | | ------->| | |
| | | | Create | |
| | | |Post. Req | |
| | | |--------->| |
| | | |Create Posture Req |
| | | |----------+--------->|
| | | | Vndr Y AV Post Req |
| | | |<---------+----------|
| | | |Vndr X AV | |
| | | |Post. Req | |
| | | Posture |<---------| |
| | | Request | | |
| | Vndr X AV |<--------| | |
| | Post. Req | | | |
| |<----------| | | |
| Vndr Y AV | | | |
| Posture Req | | | |
+<---------+-----------| | | |
| Vndr Y AV Posture | | | |
+----------+---------->| | | |
| | Vndr X AV | | | |
| | Posture | | | |
| |---------->| Posture | | |
| | |Response | | |
| | |-------->| | |
| | | | Verify | |
| | | | Posture | |
| | | |--------->| |
| | | | Verify Posture |
| | | |----------+--------->|
| | | |Vndr Y AV Post Result|
| | | |<---------+----------|
| | | |Vndr X AV | |
| | | |Post Reslt| |
| | | Assess |<---------| |
| | | Result | | |
| | Vndr X AV |<--------| | |
| |Post Reslt |<--------| | |
| |<----------| | | |
| Vndr Y AV Post Reslt | | | |
+<---------+-----------| | | |
Sangster & Narayan Standards Track [Page 65]RFC 5792 PA-TNC March 2010
A.2.1. Message Contents
This section shows the contents of the key fields in each of the PA
messages exchanged in this use case. When necessary, additional
commentary is provided to explain why certain fields contain the
shown values. Note that many of the flows shown are between
components on the same system so no message contents are shown.
A.2.1.1. N/W Join
This flow represents the event that causes the PBS to decide to start
an assessment of the endpoint in order to gain access to the network.
This is merely an event and does not include a message being sent.
A.2.1.2. Create Posture Request (Create Posture Req)
This flow illustrates an invocation of the Vendor X and Vendor Y
Anti-Virus Posture Validators enabling posture request attributes to
be created. Because this use case is triggered locally, NEA does not
specify the contents of this flow.
A.2.1.3. Vendor Y AV Posture Request (Vndr Y AV Posture Req)
This flow contains the PA message (Posture Request) from the Vendor Y
Anti-Virus Posture Validator
Vendor Y AV Posture Request PA Message {
Attribute HDR {Message ID}
Attribute 1 {
vendor-id=0
type=1 (Attribute Request)
length
Value = {
Vendor-id=0 (IETF Standard)
Type=2 (Standard attribute, Product-Information)
Vendor-id=1 (Vendor Y)
Type=2 (Vendor Y attribute, Extended-Dat-Version)
}
}
}
Sangster & Narayan Standards Track [Page 66]RFC 5792 PA-TNC March 2010
A.2.1.4. Vendor X AV Posture Request (Vndr X AV Post. Req)
This flow contains the PA message (Posture Request) from the Vendor X
Anti-Virus Posture Validator
Vendor X AV Posture Request PA Message {
Attribute HDR {Message ID}
Attribute 1 {
vendor-id=0
type=1 (Attribute Request)
length
Value = {
Vendor-id=1 (Vendor X)
Type=1 (Vendor X attribute, Scan-Engine-Version)
Vendor-id=0 (IETF Standard)
Type=5 (Standard, Operational-Status)
}
}
}
A.2.1.5. Posture Request
This flow contains the PB message containing the PA messages from the
Vendor X and Vendor Y Anti-Virus Posture Validators; the message
content is described in the PB-TNC specification.
A.2.1.6. Posture Request (Vndr X AV Post Req & Vndr Y AV Post Req)
These flows illustrate an invocation of the Vendor X and Vendor Y
Anti-Virus Posture Collectors to process the Posture Request and
return the particular posture attributes requested. Because this
flow is triggered locally, NEA does not specify the contents of this
flow.
Sangster & Narayan Standards Track [Page 67]RFC 5792 PA-TNC March 2010
A.2.1.7. Vendor Y AV Posture (Vndr Y AV Posture)
This flow contains the PA message (response to the Posture Request)
from the Vendor Y Anti-Virus Posture Collector.
Vendor Y AV Posture PA Message {
Attribute HDR {Message ID}
Attribute 1 {
vendor-id=0 (IETF Standard)
Type=2 (Standard attribute, Product-Information)
length
Value = {
product-vendor-id=12345 (vendor Y)
product-id=987 (AV product id from vendor Y)
product-name="Vendor Y Anti-Virus"
}
}
Attribute 2 {
vendor-id=2 (vendor Y)
type=2 (vendor Y attribute, DAT-Version)
length
Value = {
DAT-version=5678
}
}
}
Sangster & Narayan Standards Track [Page 68]RFC 5792 PA-TNC March 2010
A.2.1.8. Vendor X AV Posture (Vndr X AV Posture)
This flow contains the PA message (response to the Posture Request)
from the Vendor X Anti-Virus Posture Collector.
Vendor X AV Posture PA Message {
Attribute HDR {Message ID}
Attribute 1 {
vendor-id=1
type=1 (vendor X attribute, Scan-Engine-Version)
length
Value = {
scan-engine-version=1234
}
}
Attribute 2 {
vendor-id=0 (IETF Standard)
type=5 (Standard, Operational-Status)
length
Value = {
status=2 (installed but non-operational)
result=0 (unknown)
last use="" (never used)
}
}
}
A.2.1.9. Posture Response
This flow contains the PB message containing the PA messages from the
Vendor X and Vendor Y Anti-Virus Posture Collectors; the message
content is described in the PB-TNC specification.
A.2.1.10. Verify Posture
This flow illustrates an invocation of the Vendor X and Vendor Y
Anti-Virus Posture Validators requesting verification of the posture
attributes received. Because this flow happens locally within the
NEA server, NEA does not specify the message contents.
Sangster & Narayan Standards Track [Page 69]RFC 5792 PA-TNC March 2010
A.2.1.11. Vendor Y AV Posture Result (Vndr Y AV Post Result)
This flow contains the PA message (Posture Assessment Result) from
the Vendor Y Anti-Virus Posture Validator
Vendor Y AV Posture Result PA Message {
Attribute HDR {Message ID}
Attribute 1 {
vendor-id=0
type=9 (assessment-result)
length
Value = {
assessment-result=0 (compliant)
}
}
}
A.2.1.12. Vendor X AV Posture Result (Vndr X AV Post Reslt)
This flow contains the PA message (Posture Assessment Result) from
the Vendor X Anti-Virus Posture Validator
Vendor X AV Posture Result PA Message {
Attribute HDR {Message ID}
Attribute 1 {
vendor-id=0
type=9 (assessment-result)
length
Value = {
assessment-result=1 (non-compliant)
}
}
}
A.2.1.13. Assessment Result (Assess Result)
This flow contains the PB message containing the system assessment
result computed by the Posture Broker Server and the PA messages from
the Vendor X and Vendor Y Anti-Virus Posture Validators; the message
content is described in the PB-TNC specification.
A.2.1.14. Posture Result (Vndr X AV Post Reslt & Vndr Y AV Post Reslt)
These flows illustrate an invocation of the Vendor X and Vendor Y
Anti-Virus Posture Collectors to receive the posture assessment
results. Because this flow is triggered locally, NEA does not
specify the contents of this flow.
Sangster & Narayan Standards Track [Page 70]RFC 5792 PA-TNC March 2010
A.3. Client-Triggered Reassessment
This scenario involves the reassessment of an endpoint as a result of
enabling a software component on the endpoint. The endpoint has two
VPN client software components, one from vendor X for the user's home
network and other from vendor Y for the network that the endpoint is
currently accessing. The assessment is triggered when the user tries
to use the Vendor X VPN client; this is a violation of the assessment
policy. The Posture Broker Client triggers the posture assessment
when it receives a notification from the VPN Posture Collector about
the change to the operational state of the VPN component on the
endpoint. Note that the VPN Posture Collector may support standard
attributes and some vendor-defined attributes from vendor X's and
vendor Y's namespaces. This use case does not leverage vendor-
defined attributes. The assessment involves verification of the
standard VPN posture attributes by the standard VPN Posture Validator
that results in a non-compliant assessment result.
This use case relies on the use of multiple Posture Collector IDs for
a single Posture Collector as described in section 3.3 of the PA-TNC
specification. In this example, the Posture Collector will obtain
two Posture Collector IDs to a single Posture Collector (Standard VPN
PC) and the Posture Collector will generate two separate PA messages
each using a different ID to report the posture for Vendor X and
Vendor Y VPN Clients. The Posture Broker Client will associate the
assigned IDs in the PB message sent to the NEA Server. This entire
behavior will be completely opaque to the NEA Server, which will
handle the PB message as if there were two VPN Posture Collectors on
the NEA Client.
Sangster & Narayan Standards Track [Page 71]
RFC 5792 PA-TNC March 2010
+--------+ +-------+ +---------+ +--------+ +--------+ +--------+
|Vndr X | |Vndr Y | |Standard | |Standard| |Standard| |Standard|
|VPNClnt | |VPNClnt| | VPN PC | | PBC | | PBS | | VPN PV |
+----+---+ +---+---+ +-----+---+ +---+----+ +---+----+ +----+---+
Enble| | | | | |
---->| | | | | |
| VPN Status Change | | | |
|--------------------->| Posture | | |
| | | Change | | |
| | |-------->| | |
| | |Req. Post| | |
| | |<--------| | |
| |Ins/Rq Info| | | |
| |<----------| | | |
| Inspect/Request Info | | | |
|<---------+-----------|VPNX Post| | |
| | |-------->| | |
| | |VPNY Post| | |
| | |-------->| | |
| | | | Posture | |
| | | | Report | |
| | | |--------->| |
| | | | |Vrfy Post. |
| | | | |---------->|
| | | | |VPN PRslt |
| | | | Assess |<----------|
| | | | Result | |
| | | |<---------| |
| | |VPN PRslt| | |
| | |<--------| | |
A.3.1. Message Contents
This section shows the contents of the key fields in each of the PA
messages exchanged in this use case. When necessary, additional
commentary is provided to explain why certain fields contain the
shown values. Note that many of the flows shown are between
components on the same system so no message contents are shown.
A.3.1.1. Enable VPN Client (Enble)
This flow represents the end user triggered event of starting the VPN
Client software from Vendor X. This is merely an event and does not
include a message being sent.
Sangster & Narayan Standards Track [Page 72]RFC 5792 PA-TNC March 2010
A.3.1.2. Notify Status Change (VPN Status Change)
This flow represents the detection of the active state of the Vendor
X VPN Client software by the VPN Posture Collector. This is merely
an event and does not include a message being sent.
A.3.1.3. Notify Posture Change (Posture Change)
This flow represents the notification of the VPN posture change sent
from the VPN Posture Collector to the Standard Posture Broker Client.
This is merely an event and does not include a message being sent.
A.3.1.4. Request Posture (Req. Post)
This flow illustrates an invocation of the VPN Posture Collector
requesting particular posture attributes to be sent. Because this
use case is triggered locally, NEA does not specify the contents of
this flow.
A.3.1.5. Inspect/Request Info (Ins/Rq Info)
This flow illustrates the acquisition of the posture information by
the VPN Posture Collector from the Vendor X and Vendor Y VPN Client
components. Because this flow is triggered locally, NEA does not
specify the message contents.
Sangster & Narayan Standards Track [Page 73]
RFC 5792 PA-TNC March 2010
A.3.1.6. Vendor X VPN Posture (VPNX Post)
This flow contains the PA message from the VPN Posture Collector
describing the Vendor X VPN Client's posture:
Vendor X VPN Posture PA Message{
Attribute HDR {Message ID}
Attribute 1 {
vendor-id=0
type=2 (product information)
length
Value = {
product-vendor-id=9876 (vendor X)
product-id=567 (VPN client identifier for Vndr X)
product-name="Vendor X VPN Client"
}
}
Attribute 2 {
vendor-id=0
type=5 (operational status)
length
Value = {
Status=3 (Operational)
Result=1 (Successful use with no errors detected)
last Use="2008-07-07T12:00:00Z"
}
}
Sangster & Narayan Standards Track [Page 74]RFC 5792 PA-TNC March 2010
A.3.1.7. Vendor Y VPN Posture (VPNY Post)
This flow contains the PA message from the VPN Posture Collector
including the Vendor Y VPN Client's posture:
Vendor Y VPN Posture PA Message{
Attribute HDR {Message ID}
Attribute 1 {
vendor-id=0
type=2 (product information)
length
Value = {
product-vendor-id=Vendor Y
product-id=234 (VPN client identifier for Vndr Y)
product-name="Vendor Y VPN Client"
}
}
Attribute 2 {
vendor-id=0
type=5 (operational status)
length
Value = {
Status=3 (Operational)
Result=1 (Successful use with no errors detected)
last Use="2008-07-07T14:05:00Z"
}
}
}
A.3.1.8. Posture Report
This flow contains the PB message containing the PA message from the
VPN Posture Collector; the message content is described in the PB-TNC
specification.
A.3.1.9. Verify Posture (Vrfy Post.)
This flow illustrates an invocation of the VPN Posture Validator
requesting verification of the posture attributes received. Because
this flow happens locally within the NEA Server, NEA does not specify
the message contents.
Sangster & Narayan Standards Track [Page 75]RFC 5792 PA-TNC March 2010
A.3.1.10. VPN Posture Result (VPN PRslt)
This flow contains the PA message (Posture Assessment Result) from
the VPN Posture Validator
VPN Posture Result PA Message {
Attribute HDR {Message ID}
Attribute 1 {
vendor-id=0
type=9 (assessment-result)
length
Value = {
assessment-result=1 (non-compliant)
}
}
}
A.3.1.11. Assessment Result (Assess Result)
This flow contains the PB message containing the system assessment
result computed by the Posture Broker Server and the PA messages from
the VPN Posture Validator; the message content is described in the
PB-TNC specification.
A.3.1.12. Posture Result (VPN PRslt)
This flow illustrates an invocation of the VPN Posture Collector to
receive the posture assessment result. Because this flow is
triggered locally, NEA does not specify the contents of this flow.
Sangster & Narayan Standards Track [Page 76]RFC 5792 PA-TNC March 2010
Appendix B. Evaluation against NEA Requirements
This section evaluates the PA-TNC protocol against the requirements
defined in the NEA Requirements document. Each subsection considers
a separate requirement from the NEA Requirements document. Only
common requirements (C-1 through C-10) and PA requirements (PA-1
through PA-6) are considered, since these are the only ones that
apply to PA.
B.1. Evaluation against Requirement C-1
Requirement C-1 says:
C-1 NEA protocols MUST support multiple round trips between the NEA
Client and NEA Server in a single assessment.
PA-TNC meets this requirement. It allows an unlimited number of
round trips between the NEA Client and NEA Server.
B.2. Evaluation against Requirement C-2
Requirement C-2 says:
C-2 NEA protocols SHOULD provide a way for both the NEA Client and
the NEA Server to initiate a posture assessment or reassessment as
needed.
PA-TNC meets this requirement. PA-TNC is designed to work whether
the NEA Client or the NEA Server initiates a posture assessment or
reassessment.
B.3. Evaluation against Requirement C-3
Requirement C-3 says:
C-3 NEA protocols including security capabilities MUST be capable
of protecting against active and passive attacks by intermediaries
and endpoints including prevention from replay-based attacks.
Security for PA-TNC messages being sent over the network is provided
through PT protocol security. Therefore, PA-TNC does not include any
security capabilities. Since this requirement only applies to NEA
protocols "including security capabilities", this specification is
not subject to this requirement (see section 5.2).
Sangster & Narayan Standards Track [Page 77]
RFC 5792 PA-TNC March 2010
B.4. Evaluation against Requirement C-4
Requirement C-4 says:
C-4 The PA and PB protocols MUST be capable of operating over any
PT protocol. For example, the PB protocol must provide a transport-
independent interface allowing the PA protocol to operate without
change across a variety of network protocol environments (e.g.,
EAP/802.1X, PANA, TLS and IKE/IPsec).
PA-TNC meets this requirement. PA-TNC can operate over any PT
protocol that meets the requirements for PT stated in the NEA
Requirements document. PA-TNC does not have any dependencies on
specific details of the underlying PT protocol.
B.5. Evaluation against Requirement C-5
Requirement C-5 says:
C-5 The selection process for NEA protocols MUST evaluate and
prefer the reuse of existing open standards that meet the
requirements before defining new ones. The goal of NEA is not to
create additional alternative protocols where acceptable solutions
already exist.
Based on this requirement, PA-TNC should receive a strong preference.
PA-TNC is equivalent with IF-M 1.0, an open TCG specification. Other
specifications from TCG and other groups are also under development
based on the IF-M 1.0 specification. Selecting PA-TNC as the basis
for the PA protocol will ensure compatibility with IF-M 1.0, with
these other specifications, and with their implementations.
B.6. Evaluation against Requirement C-6
Requirement C-6 says:
C-6 NEA protocols MUST be highly scalable; the protocols MUST
support many Posture Collectors on a large number of NEA Clients to
be assessed by numerous Posture Validators residing on multiple NEA
Servers.
PA-TNC meets this requirement. PA-TNC supports an unlimited number
of Posture Collectors, Posture Validators, NEA Clients, and NEA
Servers. It also is quite scalable in many other aspects as well. A
PA-TNC message can contain up to 2^32-1 octets and about 2^28 PA-TNC
attributes. Each organization with an SMI Private Enterprise Number
is entitled to define up to 2^32 vendor-specific PA-TNC Attribute
Types, 2^16 vendor-specific PA-TNC Product IDs, and 2^32 vendor-
Sangster & Narayan Standards Track [Page 78]
RFC 5792 PA-TNC March 2010
specific PA-TNC Error Codes. Each attribute can contain almost 2^32
octets. It is generally not advisable or necessary to send this much
data in a NEA assessment, but still PA-TNC is highly scalable and
meets requirement C-6 easily.
B.7. Evaluation against Requirement C-7
Requirement C-7 says:
C-7 The protocols MUST support efficient transport of a large
number of attribute messages between the NEA Client and the NEA
Server.
PA-TNC meets this requirement. Each PA-TNC message can contain about
2^28 PA-TNC attributes. PA-TNC supports up to 2^32 round trips in a
session so the maximum number of attribute messages that can be sent
in a single session is actually about 2^50. However, it is generally
inadvisable and unnecessary to send a large number of messages in a
NEA assessment. As for efficiency, PA-TNC adds only 12 octets of
overhead per attribute and 8 octets per message (which is negligible
on a per-attribute basis).
B.8. Evaluation against Requirement C-8
Requirement C-8 says:
C-8 NEA protocols MUST operate efficiently over low bandwidth or
high latency links.
PA-TNC meets this requirement. A PA-TNC exchange is envisioned
(based on current deployment experience) to involve one or two round
trips with less than 500 octets of PA-TNC messages. Of course, use
of vendor-specific PA-TNC attribute types could expand the
assessment. However, PA-TNC itself imposes an overhead of only 8
octets per PA-TNC message and 12 octets per attribute.
B.9. Evaluation against Requirement C-9
Requirement C-9 says:
C-9 For any strings intended for display to a user, the protocols
MUST support adapting these strings to the user's language
preferences.
PA-TNC meets this requirement. The only field included in a PB-TNC
attribute for display to the user includes a language tag that could
be selected based upon the user's PB-TNC negotiated preferred
language for the assessment (see section 4.10 of the PB-TNC
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RFC 5792 PA-TNC March 2010
specification). With this exception, all of the strings in the
standard PA-TNC attributes are intended for logging and programmatic
comparisons.
If any vendor-specific PA-TNC attribute types or future IETF Standard
PA-TNC Attribute Types include strings that are intended for display
to a user, they should be translated to the user's preferred
language. The Posture Broker Server will need to expose the user's
preferences to the Posture Validators through whatever API or
protocol is used to connect those components. However, that is all
out of scope for this specification.
B.10. Evaluation against Requirement C-10
Requirement C-10 says:
C-10 NEA protocols MUST support encoding of strings in UTF-8 format.
PA-TNC meets this requirement. All strings in the PA-TNC protocol
are encoded in UTF-8 format. This allows the protocol to support a
wide range of languages efficiently.
B.11. Evaluation against Requirement C-11
Requirement C-11 says:
C-11 Due to the potentially different transport characteristics
provided by the underlying candidate PT protocols, the NEA Client and
NEA Server MUST be capable of becoming aware of and adapting to the
limitations of the available PT protocol. For example, some PT
protocol characteristics that might impact the operation of PA and PB
include restrictions on which end can initiate a NEA connection,
maximum data size in a message or full assessment, upper bound on
number of round trips, and ordering (duplex) of messages exchanged.
The selection process for the PT protocols MUST consider the
limitations the candidate PT protocol would impose upon the PA and PB
protocols.
PA-TNC meets this requirement. The design of the PA-TNC protocol
emphasizes efficient transport of information in order to maximize
its usability in constrained PT environments. Local APIs could allow
Posture Collectors and Posture Validators to discover when they are
operating in a less constrained deployment and then make use of more
verbose attributes. Similarly, Posture Collectors could choose not
to send or use smaller attributes (including assertions from previous
assessments) when faced with a very constrained network connection.
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RFC 5792 PA-TNC March 2010
B.12. Evaluation against Requirement PA-1
Requirement PA-1 says:
PA-1 The PA protocol MUST support communication of an extensible set
of NEA standards-defined attributes. These attributes will be
uniquely identifiable from non-standard attributes.
PA-TNC meets this requirement. Each attribute is identified with a
PA-TNC Attribute Vendor ID and a PA-TNC Attribute Type. IETF
Standard PA-TNC Attribute Types use a vendor ID of zero (0), in
contrast with vendor-specific PA-TNC Attribute Types, which will use
the vendor's SMI Private Enterprise Number as the vendor ID. The
IANA will maintain a registry of PA-TNC Attribute Types with new
values added by Expert Review with Specification Required, as
described in the IANA Considerations section of this specification.
Thus, the set of standard attribute types is extensible, but all
standard attribute types are uniquely identifiable.
B.13. Evaluation against Requirement PA-2
Requirement PA-2 says:
PA-2 The PA protocol MUST support communication of an extensible set
of vendor-specific attributes. These attributes will be segmented
into uniquely identifiable vendor-specific namespaces.
PA-TNC meets this requirement. Each attribute is identified with a
PA-TNC Attribute Vendor ID and a PA-TNC Attribute Type. Vendor-
defined PA-TNC Attribute Types use the vendor's SMI Private
Enterprise Number as the PA-TNC Attribute Vendor ID. Each vendor can
define up to 2^32 PA-TNC Attribute Types, using its own internal
processes to manage its set of attribute types.
The IANA is not involved, other than the initial assignment of the
vendor's SMI Private Enterprise Number. Thus, the set of vendor-
specific attributes is segmented into uniquely identifiable vendor-
specific namespaces.
B.14. Evaluation against Requirement PA-3
Requirement PA-3 says:
PA-3 The PA protocol MUST enable a Posture Validator to make one or
more requests for attributes from a Posture Collector within a single
assessment. This enables the Posture Validator to reassess the
posture of a particular endpoint feature or to request additional
posture including from other parts of the endpoint.
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RFC 5792 PA-TNC March 2010
PA-TNC meets this requirement. The Attribute Request attribute type
is an IETF Standard PA-TNC Attribute Type that permits a Posture
Validator to send to one or more Posture Collectors a request for one
or more attributes. This attribute may be sent at any point in the
posture assessment process and may in fact be sent more than once if
the Posture Validator needs to first determine the type of operating
system and then request certain attributes specific to that operating
system, for example.
B.15. Evaluation against Requirement PA-4
Requirement PA-4 says:
PA-4 The PA protocol MUST be capable of returning attributes from a
Posture Validator to a Posture Collector. For example, this might
enable the Posture Collector to learn the specific reason for a
failed assessment and to aid in remediation and notification of the
system owner.
PA-TNC meets this requirement. A Posture Validator can easily send
attributes to one or more Posture Collectors.
B.16. Evaluation against Requirement PA-5
Requirement PA-5 says:
PA-5 The PA protocol SHOULD provide authentication, integrity, and
confidentiality of attributes communicated between a Posture
Collector and Posture Validator. This enables end-to-end security
across a NEA deployment that might involve traversal of several
systems or trust boundaries.
PA-TNC does not include an explicit PA-level security mechanism but
does lay a foundation allowing attribute-level security protections
to be added later. As an existence proof, the NEA working group
considered an Internet-Draft proposal capable of encapsulating PA
attributes within a Cryptographic Message Syntax (CMS) security
wrapper in a new attribute type. This proposal offered the
protections described in this requirement. However, the NEA WG
decided that the use cases in scope for the working group did not
require PA-level security. The use cases involving PA message
traversal of multiple systems or trust boundaries were considered out
of scope; therefore, a Posture Validator to Posture Collector end-to-
end security protection was considered not to be required.
Instead, PA-TNC attributes are protected by the PT layer
authentication, integrity, and confidentiality support. This
protects the attributes communicated between the Posture Transport
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RFC 5792 PA-TNC March 2010
Client and Posture Transport Server. Because the Posture Collector
is in the same address space as the Posture Broker Client and Posture
Transport Client and the Posture Validator is in the same address
space as the Posture Broker Server and Posture Transport Server, the
underlying broker and transport components are deemed trusted with
respect to not tampering with the PA messages (see trust model in
section 5.1 for details). Encrypting the PA-TNC messages would not
prevent a hostile broker or transport component from attacking the
messages.
B.17. Evaluation against Requirement PA-6
Requirement PA-6 says:
PA-6 The PA protocol MUST be capable of carrying attributes that
contain non-binary and binary data including encrypted content.
PA-TNC meets this requirement. PA-TNC attributes can contain non-
binary and binary data including encrypted content. For examples,
see the attribute type definitions contained in this specification.
Authors' Addresses
Paul Sangster
Symantec Corporation
6825 Citrine Drive
Carlsbad, CA 92009
USA
EMail: Paul_Sangster@symantec.com
Kaushik Narayan
Cisco Systems Inc.
10 West Tasman Drive
San Jose, CA 95134
USA
EMail: kaushik@cisco.com
Sangster & Narayan Standards Track [Page 83]
