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Versions: 00 01 02 03 04 05 06 07 08 09 10 11 RFC 5570

Network Working Group                                         M. StJohns
Internet-Draft                             R. Atkinson, Extreme Networks
draft-stjohns-sipso-01.txt                 G. Thomas, US Dept of Defense
Expires: 10 Oct 2007                                       10 April 2007


                          Son of IPSO (SIPSO)
               A Simple IPv6 Sensitivity Labeling Option



Status of this Memo

   This is an Internet-Draft.

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
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ABSTRACT


     This document describes an optional method for encoding explicit packet
   sensitivity labels on IPv6 packets.  It is intended for use only within
   multi-level secure (MLS) networking environments that are both trusted
   and trustworthy.








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1.  INTRODUCTION


        The original IPv4 specification in RFC-791 includes an option for
   labeling the sensitivity of IP packets. That option was revised by
   RFC-1038 and later by RFC-1108. [RFC-791][RFC-1038][RFC-1108]

       One or another IP sensitivity label option has been in limited
   deployment for about two decades, most usually in governmental or military
   internal networks.  There are also some commercial sector deployments where
   corporate security policies require mandatory access controls be applied to
   sensitive data.  For example, some banks use MLS technology to compartment
   information known to their investment banking staff so that their trading
   staff is unaware of that information.  This document specifies the explicit
   packet labeling extensions for IPv6 packets.


1.1 History


        This document is a direct descendent of RFC-1038 and RFC-1108 and
   is a close cousin to the work done in the Commercial IP Security Option
   (CIPSO) Working Group of the Trusted Systems Interoperability Group (TSIG).
   [FIPS-188] The IP Security options defined by 1038 and 1108 were designed
   with one specific purpose in mind: to support the fielding of an IPv4
   packet encryption device called a BLACKER.  Because of this, the
   definitions and assumptions in those documents were necessarily focused on
   the US Department of Defense and the BLACKER device.  Today, packet
   sensitivity labeling is most commonly deployed within multi-level secure
   (MLS) environments, often composed of Compartmented Mode Workstations
   (CMWs) connected via a Local Area Network (LAN).  So the mechanism defined
   here is accordingly more general than RFC-1038 or RFC-1108 were.

         Also, the deployment of Compartmented Mode Workstations ran into
   operational constraints caused by the limited, and relatively small, space
   available for IPv4 options.  This caused one non-IETF specification for
   IPv4 packet labeling to have a large number of sub-options.  A very
   unfortunate side-effect of having sub-options within an IPv4 label option
   was that it became much more challenging to implement intermediate-system
   support for mandatory access controls (e.g. in a router or MLS guard
   system) and still be able to forward traffic at or near wire-speed.
   In the last decade, typical Ethernet link speeds have changed from
   10 Mbps half-duplex to 1 Gbps full-duplex.  A 10 Gbps full- duplex
   Ethernet standard is widely available today.  The IEEE is actively
   developing a standard for 100 Gbps Ethernet as of this writing.
   Forwarding at those speeds typically requires support from ASICs;
   supporting more complex packet formats usually require significantly
   more gates than simpler packet formats.  So the pressure to have a



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   simple option format has only increased in the past decade.

        When IPv6 was initially being developed, it was anticipated that
   the availability of IP Security, in particular the Encapsulating Security
   Payload (ESP) and the IP Authentication Header (AH), would obviate the need
   for explicit packet sensitivity labels with IPv6. [RFC-1825, IPSEC, AH,
   ESP] For MLS IPv6 deployments where the use of AH or ESP is practical, use
   of AH and/or ESP is recommended.  However, some application architectures,
   most often those not designed for use with Compartmented Mode Workstations
   or other Multi-Level Secure (MLS) computers, multiplex transactions at
   different sensitivity levels and/or with different privileges over a single
   transport-layer communications session. In order to maintain data
   sensitivity labeling for such applications, in order to be able to
   implement routing and mandatory access control decisions in routers and
   guards on a per-IP-packet basis, and for other reasons, there is a need to
   have a mechanism for explicitly labeling the sensitivity information for
   each IPv6 packet.


1.2.  Intent


        This document describes a generic way of labeling IPv6 datagrams
   to reflect their particular sensitivity.  Provision is made for
   separating data based on domain of interpretation, relative sensitivity
   (i.e.  sensitivity levels), need-to-know or formal access programs
   (i.e. compartments or categories), and releasabilities.

        In particular, the authors believe that this mechanism is
   suitable for deployment in UN peace-keeping operations, in NATO
   operations, in all current US Government MLS environments,
   and for deployment in other similar commercial or governmental
   environments.

        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.[RFC-2119]



2.  DEFINITIONS


        This section defines several terms that are important to understanding
   and correctly implementing this specification.  Because of historical
   variations in terminology in different communities, several terms have
   defined synonyms.



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2.1.  Domain of Interpretation


        A Domain of Interpretation (DOI) is a shorthand way of identifying
   the use of a particular labeling, classification and handling system with
   respect to data, the computers and people who process it, and the networks
   that carry it.  The DOI policies, combined with a particular Sensitivity
   Label (which is defined to have meaning within that DOI) applied to a datum
   or collection of data, dictates which systems, and ultimately which persons
   may receive that data.  In other words a label of "SECRET" by itself is
   not meaningful; you also have to know the document or data belongs
   to the US Department of Defense before you can decide on who is allowed
   to receive the data.

        An SIPSO DOI is an opaque identifier that is used as a pointer to a
   particular set of policies which define the Sensitivity Levels and
   Compartments present within the DOI, and by inference, to the "real world"
   (e.g. used on paper documents) equivalent labels (See "Sensitivity Label"
   below).  Registering or defining a set of real world security policies as
   an SIPSO DOI results in a standard way of labeling IP data originating from
   end-systems "accredited" or "approved" to operate within that DOI and the
   constraints of those security policies.  For example, if one did this for
   the US Department of Defense, you would list all the acceptable labels
   such as "Secret" and "Top Secret", and one would link the SIPSO DOI to the
   DOD 5200.28 and DOD 5200.1R documents which define how to mark and protect
   data with the US Department of Defense (DoD).[DoD 5200.28][DoD 5200.1-R]

        The scope of the DOI is dependent on the organization establishing
   it. For example, the US might establish a DOI with specific meanings
   which correspond to the normal way it labels classified documents and
   which would apply primarily to the DOD, but might also apply to other
   associated agencies.  A company or other organisation might establish
   a DOI which applies only to itself.

        Note well: A SIPSO Domain of Interpretation is different from,
   and disjoint from, an ISAKMP/IKE Domain of Interpretation.  It is
   important not to confuse the two terms.


2.2.  Sensitivity Level


        A Sensitivity Level represents a mandatory separation of data based on
   relative sensitivity.  Seensitivity Levels ALWAYS have a specific ordering
   within a DOI.  Clearance to access a specific level of data also implies
   access to all levels whose sensitivity is less than that level.  For
   example, if the A, B and C are levels, and A is more sensitive than B which
   is in turn more sensitive than C (A > B > C), access to data at the B level



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   implies access to C as well. As an example, common UK terms for a
   Sensitivity Level include (from low to high) "Unclassified", "Restricted",
   "Confidential", "Secret", and "Most Secret".

         Note well: A Sensitivity Level is only one component of a Sensitivity
   Label.  It is important not to confuse the two terms. The term "Sensitivity
   Level" has the same meaning as the term "Security Level".


2.3.  Compartment


        A Compartment represents a mandatory segregation of data based on
   formal information categories, formal information compartments, or formal
   access programs for specific types of data.  For example, a small startup
   company creates "Finance" and "R&D" compartments to protect data critical
   to its success -- only employees with a specific need to know (e.g. the
   accountants and controller for "Finance", specific engineers for "R&D") are
   given access to each compartment.  Each Compartment is separate and
   distinct.  Access to one Compartment does not imply access to any other
   Compartment.  Data may be protected in multiple compartments
   (e.g. "Finance" data about a new "R&D" project) at the same time, in which
   case access to ALL of those compartments is required to access the data.
   Employees only possessing clearance for a given sensitivity level
   (i.e. without having clearance for any specific compartments at that
   sensitivity level) do not have access to any data classified in any
   compartments (e.g. SECRET FINANCE dominates SECRET).

        Note Well: The term "category" has the same meaning as "compartment".


2.4   Releasability


         A Releasability represents a mandatory segregation of data based
   on a formal decision to release information to others.  Historically,
   some MLS deployments handled Releasability as if it were a Compartment,
   but this is problematic, because the semantics of a compartment are
   different from the semantics of a Releasability.

          For example, two companies (ACME and ACE) are engaging in a
   technical alliance.  ACME labels all information present within its
   enterprise that is to be shared as part of the alliance as REL ACE
   (e.g.COMPANY CONFIDENTIAL REL ACE).  However, unlike the category example
   above, COMPANY CONFIDENTIAL dominates COMPANY CONFIDENTIAL REL ACE.
   This means that ACE employees granted a COMPANY CONFIDENTIAL REL ACE
   clearance can only access releasable material, while ACME employees
   with a COMPANY CONFIDENTIAL clearance can access all information.



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   If REL ACE were managed as a compartment, then users granted a
   COMPANY CONFIDENTIAL REL ACE clearance would have access to all of
   ACME's COMPANY CONFIDENTIAL material, which is undesirable.
   Releasabilities can be combined (e.g. COMPANY CONFIDENTIAL REL ACE/ABLE).
   In this case, users possessing a clearance of either COMPANY CONFIDENTIAL,
   COMPANY CONFIDENTIAL REL ACE, COMPANY CONFIDENTIAL REL ABLE,
   or COMPANY CONFIDENTIAL REL ACE/ABLE can access this information.


2.5.  Sensitivity Label


        A Sensitivity Label is a quadruple consisting of a DOI, a Sensitivity
   Level, a Compartment Set, and a Releasability Set.  The Compartment Set
   may be the empty set if and only if no compartments apply.  A Releasability
   Set may be the empty set if only if no releasabilities apply.  A DOI
   used within a end system may be implicit or explicit depending on its use.
   SIPSO Sensitivity Labels always have an explicit DOI. A SIPSO Sensitivity
   Label consists of a Sensitivity Label of a particular format (defined
   below) and ALWAYS contains an explicit DOI.

          A system which does not store a DOI as part of its internal
   sensitivity labels must be considered to have an implicit DOI --
   usually that of its primary Accrediting Authority; all objects
   on such a system inherit this implicit DOI.

        Note Well: The term "Security Marking" has the same meaning as
   "Sensitivity Label".

2.5.1 Sensitivity Label Comparison

        Two Sensitivity Labels (A and B) can be compared. Indeed, the only
   real reason that sensitivity labels exist is so that they may be compared
   as part of an access control decision.  Comparison is critical to
   determining if a subject (a person, network, etc.) operating at one
   sensitivity label (A) should be allowed to access an object (file, packet,
   route, etc) classified at another sensitivity label (B).  The comparison
   of two labels (A and B) can return one (and only one) of the following
   results:

     1) A can dominate B (e.g. A=SECRET, B=UNCLASSIFIED); A can read B
     2) B can dominate A (e.g. A=UNCLASSIFIED, B=SECRET); A cannot access B
     3) A equals B (e.g. A=SECRET, B=SECRET); A can read/write B
     4) A is incomparable to B (e.g. A=SECRET R&D, B=SECRET FINANCE);
        A cannot access B


        By definition, if A and B are members of different DOIs, the result of



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   comparison is always incomparable.  It is possible to overcome this if and
   only if A and/or B can be promoted such that the labels are interpretable
   within a single DOI.

2.5.2  Range

        A range is a pair of Sensitivity Labels which indicate variously a
   minimum and maximum acceptable sensitivity label for objects compared
   against it.  A range is usually expressed as "<minimum> : <maximum>" and
   always has the property that the minimum Sensitivity Label is less than or
   equal to the maximum Sensivitity Label (e.g. Not incomparable).  A range
   where <minimum> equals <maximum> may be expressed simply as <minimum>; in
   this case, the only acceptable Sensitivity Label is <minimum>.

2.6.  Import

        The act of receiving a datagram and translating the SIPSO Sensitivity
   Labels into the appropriate internal (end-system specific) Sensitivity
   Label.

2.7.  Export

        The act of selecting an appropriate DOI for an outbound datagram,
   translating the internal (end-system specific) label into an SIPSO
   Sensitivity Label based on that DOI, and sending the datagram.  The
   selection of the appropriate DOI may be based on many factors including,
   but not necessarily limited to:

        Source Port
        Destination Port
        Transport Protocol
        Application Protocol
        Application Information
        End-system
        Subnetwork
        Network
        Sending Interface
        System Implicit/Default DOI

        Regardless of the DOI selected, the Sensitivity Label of the
   outbound datagram must be consistent with the security policy monitor of
   the originating system and also with the DOI definition used by all other
   devices cognisant of that DOI.

2.8.  End System

        An End System is a host or router from which a datagram originates
   or to which a datagram is ultimately delivered.  The IPv6 community



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   often uses the term Node for what is here called an End System.

2.9.  Intermediate System

        An Intermediate System (IS) is a node that receives and transmits a
   particular datagram without being either the source or destination of that
   datagram.  An IPv6 router is an example of an IS.  A firewall or security
   guard device that applies security policies and forwards packets that
   comply with those security policies is another example of an intermediate
   system.

        An intermediate system may handle ("forward") a datagram without
   necessarily importing or exporting the datagram to/from itself.

        Note Well: Any given system can be both an end system and an
   intermediate system -- which role the system assumes at any given time
   depends on the address(es) of the datagram you are considering and the
   address(es) associated with that system.

2.10 System Security Policy

        A system security policy (SSP) consists of a Sensitivity Label
   and the organizational security policies associated with content labeled
   with a given security policy.  The SSP acts as a bridge between how
   the organization's Mandatory Access Control (MAC) policy is stated
   and managed and how the network implements that policy.

3.  ARCHITECTURE

        This document describes a convention for labeling an IPv6 datagram
   within a particular system security policy.  The labels are designed for
   use within a Mandatory Access Control (MAC) system.  A real world example
   is the security classification system in use within the US Government.
   Some data held by the government is "classified", and is therefore
   restricted by law to those people who have the appropriate "clearances".
   Commercial examples also exist.  For example, one global electrical
   equipment company has a formal security policy that defines 6 different
   Sensitivity Levels for its internal data, ranging from "Class 1" to "Class
   6" information.  Some financial institutions use multiple compartments to
   restrict access to certain information (e.g. "mergers & acquisitions",
   "trading") to those working directly on those projects and to deny access
   to other groups within the company (e.g. equity trading).  A SIPSO
   Sensitivity Label is the network instantiation of a particular information
   security policy, and its related labels, classifications, compartments,
   and releasabilities.

         Some years ago, the Mandatory Access Control (MAC) policy for US
   Government classified information was specified formally in mathematical



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   notation.[BL73] As it happens, many other organisations have the same basic
   Mandatory Access Control (MAC) policy for information with differing
   ("vertical") Sensitivity Levels.  This document builds upon the formal
   definitions of Bell-LaPadula.[BL73] There are two basic principles "no
   write down" and "no read up".  The first rule means that an entity having
   minimum Sensitivity Level X must not be able to write information that is
   marked with a Sensitivity Level below X.  The second rule means that an
   entity having maximum Sensitivity Level X must not be able to read
   information having a Sensitivity Level above X.  In a normal deployment,
   information downgrading ("write down") must not occur automatically and is
   permitted if and only if a person with appropriate "downgrade" privilege
   manually verifies the information is permitted to be downgraded before the
   s/he manually re-labels ("downgrades") the information.  Subsequent to the
   original work in this area, this formal model was extended to also support
   ("horizontal") Compartments of information.

         This document extends Bell-LaPadula to accommodate the notion
   of separate Domains of Interpretation (DOI).  Each DOI constitutes
   a single comparable domain of sensitivity labels as stated by Bell-LaPadula.
   Sensitivity labels from different domains cannot be directly compared
   using Bell-LaPadula semantics.

        This document is focused on providing standards for encoding
   sensitivity labels in packets, as well as certain standards for how
   these labels are to be interpreted and enforced at the IP layer.  This
   document recognizes that there are several kinds of application processing
   that occur above the IP layer that significantly impact end-to-end system
   security policy enforcement, but are out of scope for this document.
   In particular, how the network labeling policy is enforced within processing
   in an end system is critical, but beyond the scope of a network (IP) layer
   sensitivity label encoding standard.  Other specifications exist which
   discuss such details. [TCSEC] [CMW] [ISO-15408] [CC] [DoD MLOS PP]

         This standard does not preclude a end-system capable of providing
   labeled packets across some range of Sensitivity Labels.  A Compartmented
   Mode Workstation (CMW) is an example of such an end-system.[CMW]  This
   is useful if the end-system is capable of and accredited to separate
   processing across some range of Sensitivity Labels.  Such an node would
   have a range associated with it within the network interface connecting the
   node to the network.  As an example, an end-system has the range SECRET:TOP
   SECRET associated with it in the intermediate-system to which the node is
   attached.  SECRET processing on the node is allowed to traverse the
   network to other SECRET:SECRET segments of the network, ultimately to a
   SECRET:SECRET node.  Likewise, TOP SECRET processing on the node is allowed
   to traverse a network through TOP SECRET:TOP SECRET segments, ultimately
   to a TOP SECRET:TOP SECRET node.  The node in this case can allow a user on
   this node to access SECRET and TOP SECRET resources, provided the user
   holds the appropriate clearances and has been correctly configured.



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        With respect to a given network, each distinct Sensitivity Label
   represents a separate virtual network which shares the same physical
   network.  There are rules for moving information between the various
   virtual networks.  The model we use within this document is based on the
   Bell-LaPadula model, but is extended to cover the concept of differing
   Domains of Interpretation.  Nodes that implement this protocol must
   enforce this mandatory separation of data.

        The SIPSO provides for both horizontal ("Compartment") and
   vertical ("Sensitivity Level") separation of information, as well as
   separation based on DOI.  The basic rule is that data must not be
   delivered to a user or system that is not approved to receive it.

   Note well: wherever we say "not approved", we also mean "not cleared",
   "not certified", and/or "not accredited" as applicable in one's
   operational community.

        This specification does not enable AUTOMATIC relabeling of
   information, within a DOI or to a different DOI.  That is, neither
   automatic "upgrading" nor automatic "downgrading" of information are
   enabled by this specification.  Local security policies might allow some
   limited downgrading, but this normally requires the intervention of some
   human entity and is usually done within a end-system with respect to the
   internal sensitivity label, rather than on a network or in a
   intermediate-system (e.g. router, guard).  Automatic downgrading is not
   suggested operational practice; further discussion of downgrading is
   outside the scope of this protocol specification.

        Implementers of this specification MUST NOT permit automatic
   upgrading or downgrading of information in the default configuration of
   their implementation.  Implementers MAY add a configuration knowb that
   would permit a System Security Officer holding appropriate privilege to
   enable automatic upgrading or downgrading of information.  If an
   implementation supports such a knob, the existence of the configuration
   knob must be clearly documented and the default knob setting MUST be that
   automatic upgrading or downgrading is DISABLED.  Automatic information
   upgrading and downgrading is not recommended operational practice.

        This specification does not preclude a node that implements this
   specification from supporting multiple DOIs concurrently.  Indeed, use of
   multiple DOIs might be operationally useful in deployments having very
   large numbers of compartments.  For example, such a deployment might have
   one set of related compartments in one DOI and a different set of
   compartments in a different DOI.  While this might make some
   implementations more complex, it might also reduce the typical size
   of the IPv6 SIPSO option in data packets.

        Moving information between any two DOIs is permitted if and only if



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   the owners of the DOIs:
        1) Agree to the exchange,
        2) Publish a table of equivalencies which maps the SIPSO
           values of one DOI into the other and make that table
           available within the scope of those two DOIs


        The owners of two DOIs may choose to permit the exchange on or
   between any of their systems, or may restrict exchange to a small subset
   of the systems they own/accredit.  One way agreements are permissible,
   as are agreements which are a subset of the full table of equivalences.
   Actual administration of inter-DOI agreements is outside the scope of this
   document.

        When data leaves an end system it is "exported" to the network,
   and marked with a particular DOI, Sensitivity Level, Compartment Set,
   and Releasability Set (This quadruple is collectively termed a
   Sensitivity Label).  This Sensitivity Label is derived from the internal
   sensitivity label (the end-system specific implementation of a given
   sensitivity label), and the export DOI.  The export DOI is selected
   based on a range of parameters described in detail later in this document.

         When data arrives at an end system, it is "imported" from the network
   to the end-system.  The data from the datagram takes on an internal
   sensitivity label based on the Sensitivity Label contained in the datagram.
   This assumes the datagram is marked with a recognizable DOI, there is a
   corresponding internal sensitivity label equivalent to the SIPSO
   Sensitivity Label, and the datagram is "within range" for the receiving
   logical interface.

        An host or router has one or more physical interfaces.  Each
   physical interface is associated with a physical network segment used
   to connect the node, router, LAN, or WAN.  Each physical interface has
   one or more sensitivity label ranges associated with it.  Sensitivity
   Label ranges from multiple DOIs must be enumerated separately.  Multiple
   ranges from the same DOI are permissible.

        Each host or router also may have one or more logical interfaces.
   A given logical interface is associated with one and only one physical
   interface.  Each logical interface has one or more sensitivity label ranges
   associated with it.  Sensitivity label ranges from multiple DOIs must be
   enumerated separately.  Multiple ranges from the same DOI are permissible.
   Each range associated with a logical interface must fall within a range
   defined for the corresponding physical interface.

        In transit, a datagram is handled based on its SIPSO sensitivity
   label and is usually neither imported to or exported from the various
   intermediate systems it transits.  There also is the concept of "SIPSO



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   Gateways" which import data from one DOI and export it to another DOI
   such that the effective Sensitivity Label is NOT changed, it is merely
   represented using a different DOI.  In other words, such devices might
   be trustworthy, trusted, and authorised to provide on-the-fly re-labeling
   of packets at the boundaries between complete systems of hosts within a
   single DOI.  Typically, such systems require specific certification(s)
   and accreditation(s) before deployment or use.

4. DEFAULTS

        Each intermediate-system or end-system is responsible for
   properly interpreting and enforcing the mandatory access control policy.
   Practically, this means that each node must evaluate the label on the
   inbound packet, ensure that this sensitivity label is valid for the
   originating node, and at a minimum only route the packet to an interface
   and node where the sensitivity label of the packet falls within the
   assigned range of that node.  Packets arriving at an node with an invalid
   sensitivity label should be dropped.  A sensitivity label is valid
   if and only if the sensitivity label falls within the range assigned
   to the originating node.

        If a packet is received from an node which is not aware of SIPSO
   sensitivity labels (i.e. unaware to assign sensitivity labels itself)
   and the packet is destined for an node which is sensitivity label aware,
   the receiving node will insert a sensitivity label.  This sensitivity
   label will be equal to the maximum sensitivity label assigned to the
   originating node if that is known.  If the receiving node does not
   know which sensitivity label is assigned to the originating node,
   the maximum sensitivity label of the interface the packet was
   received upon will be inserted.

        If a packet is to be sent to an node which is defined to not be
   sensitivity label aware, from an node which is label aware, then the
   sensitivity label MAY be removed upon transmission if and only if local
   security policy explicitly permits this.  The originating node is still
   responsible for ensuring that the sensitivity label on the packet falls
   within the sensitivity label range associated with the receiving node.


5.  FORMAT

        This section describes the format of the SIPSO option for use
   with IPv6 datagrams.  SIPSO is an IPv6 hop-by-hop option to ensure
   that a security gateway or router could apply access controls to
   IPv6 packets based on the SIPSO label carried by the packet.  An IPv6
   datagram must not ever contain more than one SIPSO label.

        This option format is designed with intermediate systems in mind.



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   It is now common for a MLS network deployment to contain an intermediate
   systems acting as a guard (sometimes several acting as guards).  Such
   a guard device needs to be able to very rapidly parse the sensitivity
   label in each packet, apply ingress interface MAC policy, forward the
   packet while aware of the packet's sensitivity label, and then apply
   egress interface MAC policy.  At least one prior IP sensitivity labels
   option used a syntax that was unduly complex.

5.1.  Option Format

   ------------------------------------------------------------
   | Option Type | Option Length | Cmpt Length | Rel Length   |
   +-------------+---------------+-------------+--------------+
   |             SIPSO Domain of Interpretation               |
   +-------------+---------------+-------------+--------------+
   |  Sens Level |    RESERVED   |    CRC-16  Checksum        |
   ------------------------------------------------------------
   |      Compartment Bitmap (Optional; variable length)      |
   +-------------+---------------+-------------+--------------+
   |      Releasability Bitmap (Optional; variable length)    |
   +-------------+---------------+-------------+--------------+

5.1.1.  OPTION TYPE field

      This field contains an unsigned 8-bit value.  Its value is (to be
   assigned by IANA).  In the event the IPv6 packet is fragmented by the
   sending system, this option must be copied on fragmentation.

      The SIPSO option is an IPv6 Hop-by-Hop Option.  Following the
   nomenclature of RFC-2460, Section 4.2, the Option Data field of this
   option must have 4n+2 alignment.[RFC-2460] The Option Data MUST not
   change en-route. If the option type is not recognised by an intermediate
   system examining the packet, the option MAY be ignored.  If the option
   type is not recognised by an End System receiving the packet, then the
   packet MUST be dropped.

5.1.2.  OPTION LENGTH field

        This field contains an unsigned integer 1 octet in size.  It has
   minimum value is 10.  This field specifies the Length of the option data
   field of this option in octets.  The Option Type and Option Length fields
   are not included in the length calculation.

5.1.3   COMPARTMENT LENGTH field

        This field contains an unsigned 8-bit integer.  The field
   specifies the size of the COMPARTMENT BITMAP field in 64-bit words.
   The minimum value is zero, which is only when the information in



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   this packet is not in any compartment.

5.1.4   RELEASABILITY LENGTH field

        This field contains an unsigned 8-bit integer.  The field specifies
   the size of the RELEASABILITY BITMAP field in 64-bit words.  The minimum
   value is zero, which is used only when the information in this packet has
   no associated releasabilities.

5.1.5 DOMAIN OF INTERPRETATION field

        This field contains an unsigned 32-bit integer.  IANA maintains
   a registry with assignments of the DOI values used in this field.
   The DOI identifies the rules under which this datagram must be handled
   and protected.

   NOTE WELL: The DOMAIN OF INTERPRETATION where all 4 octets contain zero is
   defined to be the NULL DOI. The NULL DOI has no compartments and has a
   single level whose value and SIPSO representation are each zero. The NULL
   DOI MUST NOT ever appear on the wire.  If a packet is received containing
   the NULL DOI, that packet MUST be dropped and the event SHOULD be logged
   as a security fault.

5.1.6.  SENSITIVITY LEVEL field

        This contains an unsigned 8-bit value.  This field contains an
   opaque octet whose value indicates the relative sensitivity of the data
   contained in this datagram in the context of the indicated DOI.  The
   values of this field MUST be ordered, with 00000000 being the lowest
   sensitivity level and 11111111 being the highest sensitivity level.

        However, in a typical deployment, not all 256 sensitivity levels
   will be in use.  So the set of valid Sensitivity Level values depends
   upon the SIPSO DOI in use. This sensitivity ordering rule is necessary
   so that intermediate systems (e.g. routers or MLS guards) will be able
   to apply MAC policy with minimal per-packet computation and minimal
   configuration.

5.1.7   RESERVED field

        This field is reserved.  It MUST be set to all zeros by the
   originating node.  Receiving systems MUST zero this field upon receipt
   in order to reduce the potential bandwidth of network-derived covert
   channels.







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5.1.8.  CRC-16 Checksum Field

        This field contains an unsigned 16-bit integer containing the
   CRC-16 checksum calculated over the entire SIPSO option in this packet.
   The checksum algorithm is the 16 bit CRC defined by ITU. [ITU-T V.42]
   XXX

5.1.9.  Compartment Bitmap

        This contains a variable number of 64-bit words.  Each bit
   represents one compartment within the DOI.  Each "1" bit within an octet
   in the "Compartment Bitmap" field represents a separate compartment
   under whose rules the data in this packet must be protected.  Hence,
   each "0" bit indicates that the compartment corresponding with that bit
   is not applicable to the data in this packet.  The assignment of identity
   to individual bits within a Compartment Bitmap for a given DOI is left
   to the owner of that DOI.

5.1.10.  Releasability Bitmap

        This contains a variable number of 64-bit words.  Each bit
   represents one releasability within the DOI.  Each "1" bit within
   an octet in the Releasability Bitmap" field indicates that the release
   of this packet's data is permitted to the Release Category corresponding
   to that particular bit.  Hence, each "0" bit indicates that the release
   of this packet's data is NOT permitted to the Release Category
   corresponding with that bit.  The semantics of the Releasability
   Bitmap are always interpreted in the context of the DOI specified
   in the same SIPSO option.  The specification leaves the assignment
   of identity to individual bits within a Releasability Bitmap
   for a given DOI to the owner of that DOI.

       By way of example, each bit in the Releasability Bitmap might
   correspond with a distinct foreign country ("foreign" being relative
   to the owner of the DOI in use).  In such a case, then if all bits
   in the Releasability Bitmap were set to 0, the packet's data
   would not be releasable to any other country than the one indicated
   by the Domain of Interpretation (DOI).

5.2.  Packet Word Alignment considerations

       The basic option is variable length, due to two variable length
   fields (Compartment Bitmap and Releasability Bitmap).

        Intermediate Systems and most End Systems perform best when
   processing fixed length, fixed location items.  So the IPv6 base
   specification levies certain requirements on IPv6 optional headers.
   So the compartment bitmap fields must have length in quanta of



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   64-bit words (e.g. 0 bits, 64 bits, 128 bits)

6.  USAGE

        This section describes specific protocol processing steps
   required for systems that claim to implement or conform with this
   specification.

6.1.  Sensitivity label Comparisons

        This section describes how comparisons are made between two
   sensitivity labels.  Implementing this comparison correctly is critical
   to the MLS system providing the intended Mandatory Access Controls (MAC)
   to network traffic entering or leaving the system.

        A sensitivity label consists of a DOI, a sensitivity label,
   zero or more compartments, and zero or more releasabilities.  The
   following notation will be used:

     A.DOI   = the DOI portion of sensitivity label A
     A.LEV   = the sensitivity portion of sensitivity label A
     A.COMP  = the compartments portion of sensitivity label A
     A.REL   = the releasabilities portion of sensitivity label A
     A:IGNOR      = A, less the compartment bits represented in IGNOR

6.1.1.  "Within Range"

        A sensitivity label, "M", is "within range" for a particular range
   "A:B:IGNOR" if and only if:

        1.  M, A, and B are members of the same DOI.

            (M.DOI == A. DOI == B.DOI)

        2.  The range is a valid range.  A given range A:B:IGNOR is
              valid if and only if B:IGNOR is greater than A:IGNOR.

            (A.LEV < B.LEV) &&
            ((A.COMP & ^IGNOR) <= (B.COMP & ^IGNOR)) &&
            (A.REL >= B.REL)

        3.  The sensitivity label M has a Sensitivity Level which is greater
            than or equal to the Sensitivity Level contained in the low-end
            sensitivity label from the range and which is less than or equal
            to the Sensitivity Level contained in the high-end sensitivity
            label from the range and,

            (A.LEV <= M.LEV <= B.LEV)



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        4.  The sensitivity label M has a Compartment set which is a superset
            (proper or otherwise) of the compartment set contained in the
            sensitivity label from the low-end range and which is a subset
            (proper or otherwise) of the compartment set contained in the
            high end sensitivity label from the range.

            ((A.COMP & ^IGNOR) <= (M.COMP & ^IGNOR) <= (B.COMP & ^IGNOR))

        5.  The sensitivity label M has a Releasability set which is a subset
              (proper or otherwise) of the releasability set contained in the
              low end sensitivity label from the range and which is a superset
              (proper or otherwise) of the releasability set contained in the
              high end sensitivity label from the range.

            (A.REL >= M.REL >= B.REL)


6.1.2.  "Less Than" or "Below Range"

        A sensitivity label "M" is "less than" a sensitivity label "A"
   while considering a set of ignorable compartments IGNOR, if and only if:

        1.   The DOI for the sensitivity label M is identical to the
             DOI for both the low-end and high-end of the range.

             (M.DOI == A.DOI == B.DOI)

        2.   The sensitivity level of M is less than the sensitivity
             level of A.

             (M.LEV < A.LEV)

        3.   M.COMP is a subset (proper or otherwise) of A.COMP,
             excluding compartments specified in IGNOR.

             (M.COMP & ^IGNOR) <= (A.COMP & ^IGNOR)

        4.   M.REL is a superset (proper or otherwise) of A.REL.

             (M.REL >= A.REL)

   A sensitivity label "M" is "below range" for a sensitivity label
   "A:B:IGNOR", if M is less than A.

6.1.3.  "Greater Than" or "Above Range"

        A sensitivity label, "M" is "greater than" a sensitivity label "B"
   while considering a set of ignorable compartments IGNOR if and only if:



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        1.   Their DOI's are identical.

             (M.DOI == B.DOI)

        2A.  The sensitivity label M's sensitivity level is greater than
             B's level while M's compartment set is a superset (proper or
             otherwise) of B's compartment set

             (M.LEV > B.LEV) && ((M.COMP & ^IGNOR) >= (B.COMP & ^IGNOR))

        2B.  XOR  M's level is greater than or equal to A's level,
             while M's compartment set is a proper superset of A's
             compartment set.

             (M.LEV >= A.LEV) && ((M.COMP & ^IGNOR) >= (A.COMP & ^IGNOR))

        4.   M.REL is a subset (proper or otherwise) of A.REL

             (M.REL <= A.REL) )

   A sensitivity label, "M", is "above range" for a sensitivity label,
   "A:B:IGNOR", if M is greater than B.

6.1.4.  "Equal To"

        A sensitivity label "A" is "equal to" another sensitivity label "B"
   while considering a set of ignorable compartments IGNOR if and only if:

        1.  They have the exact same DOI.

            (A.DOI == B.DOI)

        2.  They have identical sensitivity levels.

            (A.LEV == B.LEV)

        3.  Their compartment sets are identical.

            ((A.COMP & ^IGNOR) == (B.COMP & ^IGNOR))

        4.  Their Releasability sets are identical.

            (A.REL == B.REL)

6.1.5.  "Disjoint" or "Incomparable"

        A sensitivity label "A" is disjoint from another sensitivity label "B"
   while considering a set of ignorable compartments IGNOR if any of these



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   conditions are true:

        1.   Their DOI's differ.

             (A.DOI <> B.DOI)

        2.   They are neither less than, nor greater than,
             nor equal to each other.

             (^((A < B) | (A > B) | (A == B)))

        3.   Their compartment sets are disjoint from each
             other

             (^( ((A.COMP & ^IGNOR) <= (B.COMP & ^IGNOR))  |
                 ((A.COMP & ^IGNOR) => (B.COMP & ^IGNOR))  ))


        4.   The releasability sets are disjoint from each other

             (A.REL <> B.REL)

   XXX is the equation below (4) correct ??

6.2.  End System Processing

        This section describes SIPSO-related processing for IPv6 packets
   imported or exported from an End System claiming to implement or
   conform with this specification.  Nothing in this document applies
   to an IPv6 End System that does not claim to implement or conform
   with this specification.

6.2.1  Export

        An end system which sends data to the network is said to "export"
   it to the network.  Before a datagram can leave an end system and be
   transmitted over a network the following ordered steps must occur:

        1. Selection of the export DOI:

        a)     If the system implements or permits only one
               DOI, that DOI is the export DOI.
        b) elseIf the Upper Level Protocol selects a DOI, that
               DOI is the one used.  Note that a TCP connection
               must have the same DOI and Sensitivity Label
               for the life of the connection - the DOI is
               selected at connection initiation and may not change.




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        c) elseIf there are tables defining a specific default
               DOI for the specific destination end-system address or
               for the network address, then that DOI is
               selected.
        d) elseIf there is a specific DOI associated with the
           sending logical interface (i.e. IP address),
               then that DOI is selected.
        e)     Else the default DOI for the system is selected.

   Note Well: In the event the end-system selects and uses a specific
   DOI and that DOI is not recognised by the originating end-system's
   first-hop router, the packet MUST be dropped by the first-hop router.
   In such a case, the networking API should indicate the connection
   failure (e.g. with some appropriate error, such as ENOTREACH).  This
   represents either incorrect configuration of either the intermediate-
   system or of the end-system -- xor correct operation for a node
   that is not permitted to send IPv6 packets with that DOI through
   that intermediate-system.  When an MLS end-system is connected
   to an MLS LAN, it is possible that there would be more than one
   first-hop intermediate-system concurrently, with different
   intermediate-systems having different valid sensitivity-label
   ranges.  Thoughtful use of the IEEE 802 Virtual LAN standard
   might ease proper system configuration in this respect.


        2.  Export Labeling:
             Once the DOI is selected, the SIPSO sensitivity label
        and values are determined based on the internal sensitivity
        label and the DOI.  In the event the internal sensitivity
        level does not map to a valid SIPSO Sensitivity Label, then
        an error SHOULD be returned to the upper level protocol and
        MAY be logged.  No further attempt to send this datagram
        should be made.


        3.  Access Control:
             Once the datagram is marked and the sending logical
        interface is selected (by the routing code), the datagram's
        sensitivity label is compared against the sensitivity
        label range(s) associated with that logical interface.
        For the datagram to be sent, the interface must list the
        DOI of the datagram sensitivity label as one of the
        permissible DOI's and the datagram sensitivity label
        must be within range for the range associated with that DOI.
        If the datagram fails this access test an error SHOULD be
        returned to the upper level protocol and MAY be logged.
        No further attempt to send this datagram should be made.




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6.2.2.  Import

        When a datagram arrives at an interface on an end system,
   the end system MUST:

        1.   Verify the SIPSO checksum.  Datagrams with invalid
             checksums MUST be silently dropped.  Such a drop
             event SHOULD be logged as a security fault.
        2.   Verify the SIPSO has a known and valid DOI.
             Datagrams with unrecognized or illegal DOIs MUST
             be silently dropped.  Such an event SHOULD be
             logged as a security fault.
        3.   Verify the DOI is a permitted one for the receiving
             interface.  Datagrams with prohibited or unknown DOIs
             MUST be silently dropped.  Such an event SHOULD
             be logged as a security fault.
        4.   Verify the SIPSO Sensitivity Label is within the
             permitted range for the receiving interface.  N.B.
             EACH permitted DOI on an interface has a separate
             table describing the permitted range for that DOI:

             A datagram which has a sensitivity label within the
             permitted range is accepted for further processing.

             A datagram which has a sensitivity label disjoint
             with the permitted range MUST be silently dropped.
             Such an event SHOULD be logged as a security fault,
             with an indication that the packet was dropped
             because of a disjoint sensitivity label.  An ICMP
             error message MUST NOT be sent in this case.

             A datagram which has a sensitivity label below the
             permitted range MUST be dropped.  This event SHOULD be
             logged as a security fault.  An ICMP error message
             MUST NOT be sent in this case.

             A datagram with a sensitivity label above the permitted
             range MUST be dropped.  This event SHOULD be logged.
             An ICMP error message MUST NOT be sent in this case.

        5.   Once the datagram has been accepted, the import
             sensitivity label and DOI are used to associate the
             appropriate internal sensitivity label with the data
             contained in the datagram.  This information MUST be
             carried as part of the information returned to the
             upper-layer protocol.





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6.3.  Intermediate System Rules

        This section describes SIPSO-related processing for IPv6 packets
   transiting an IPv6 intermediate-system that claims to implement and
   comply with this specification.  Nothing in this document applies
   to an IPv6 intermediate-system that does not claim to comply
   with this specification.

        The SIPSO packet format has been designed so that one can
   configure an intermediate system with the minimum sensitivity level,
   maximum sensitivity level, minimum compartment bitmap, maximum
   compartment bitmap, minimum releasability, and maximum releasability
   -- and then deploy that system without forcing it to know the detailed
   meaning of each sensitivity level, compartment bit, or releasability bit.
   Instead, once the minimum and maximum labels have been configured,
   the intermediate system can apply a simple algorithm to determine
   whether or not a packet is within range for a given interface.

6.3.1.  Input

        Intermediate Systems have slightly different rules for processing
   marked datagrams than do end systems.  Primarily, Intermediate Systems
   do not IMPORT or EXPORT transit datagrams, they just route them.  Also,
   in most deployments intermediate systems are used to provide Mandatory
   Access Controls to packets traversing more than one subnetwork.

        The following checks MUST occur before any other processing.
   Upon receiving a SIPSO-labeled packet, an intermediate system must:

        1.   Determine whether or not this datagram is destined
             for (addressed to) this IS.  If so, the IS becomes
             an end-system for the purposes of receiving this
             datagram and the rules for IMPORTing described above
             are followed.

        2.   Verify the SIPSO checksum.  Datagrams with invalid
             checksums MUST be silently dropped.  The drop event
             SHOULD be logged as a network fault.

        3.   Verify the SIPSO has a known and valid DOI.
             Datagrams with unrecognized or illegal DOIs MUST
             be silently dropped.  Such an event SHOULD be logged
             as a security fault.

        4.   Verify the DOI is a permitted one for the receiving
             interface.  Datagrams with prohibited DOIs MUST be
             silently dropped.  Such a drop SHOULD be logged as
             a security fault.



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        5.   Verify the sensitivity label within the SIPSO is
             within the permitted range for the receiving interface.

             Note Well:  EACH permitted DOI on an interface has a
             separate table describing the permitted range for that DOI:

             A rejected datagram which has a sensitivity label below
             or disjoint with the permitted range MUST be silently
             dropped.  Such an event SHOULD be logged as a security
             fault, including details about the fault.  An ICMP
             error message MUST NOT be sent in this case.

             A rejected datagram with a sensitivity label above the
             permitted range MUST be dropped.  The drop event
             SHOULD be logged as a security fault.  An ICMP
             error message MUST NOT be sent in this case.


        If and only if all the above conditions are met is the datagram
   accepted by the IPv6 intermediate-system for further processing and
   forwarding.

        At this point, the datagram is within the permitted range
   for the IS, so appropriate ICMP error messages MAY be created
   by the IP module back to the originating end-system regarding the
   forwarding of the datagram.  These ICMP messages MUST be created
   with the exact same sensitivity label as the datagram causing
   the error.  Standard rules about generating ICMP error messages
   (e.g. never generate an ICMP error message in response to a
   received ICMP error message) continue to apply.  Note that these
   locally-generated ICMP messages must go through the same outbound
   checks (including MAC checks) as any other forwarded datagram
   as described in the following paragraphs.

6.3.2.  Translation

        It is at this point that TRANSLATION of the SIPSO takes place
   if at all.  Please see Section 6.4 for a discussion of the appropriate
   processing for Translation.

6.3.3.  Output

        Once the forwarding code has selected the interface through
   which the datagram will be transmitted the following takes place:

        1.  Verify the DOI is a permitted one for the sending
            interface and that the datagram is within the
            permitted range for the DOI and for the interface.



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        2.  Datagrams with prohibited DOIs or with out of range
            values MUST be dropped.  Any drop event SHOULD be
            logged as a security fault, including appropriate details.

        3.  Datagrams with prohibited DOIs or out of range values
            MAY result in an appropriate ICMP error message,
            depending upon the security configuration of the system.
            If an ICMP Error Message is sent, it must be sent with
            the same Sensitivity Label as the rejected datagram.
            The choice of whether or not to send an ICMP message,
            if implemented, MUST be configurable, and SHOULD default
            to OFF.  Standard conditions about generating ICMP error
            messages (e.g. never send an error message about a
            received error message) apply.

6.4.  Translation

        A system which provides on-the-fly re-labeling is said to
   "translate" from one DOI to another.  There are basically two ways
   a datagram can be relabeled; either the sensitivity label can be
   converted from an external (SIPSO) sensitivity label, to an internal
   sensitivity label and then back to a new external sensitivity label,
   or an external sensitivity label can be directly remapped into
   another external sensitivity label.

        The first of these methods is the functional equivalent of
   "importing" the datagram then "exporting" it and is covered in detail
   in the "Import" and "Export" sections above.  This section describes
   direct relabeling.  The choice of which method to use for relabeling
   is an implementation decision outside the scope of this document.

        A system which provides on-the-fly relabeling without
   importing or exporting is basically a special case of the Intermediate
   System rules listed above.  Translation or relabeling takes place
   AFTER all input checks take place, but before any output checks
   are done.

        Once a datagram has been accepted (passing all the
   appropriate checks described in section 5.3), it may be relabeled.
   To determine the new sensitivity label, first determine the new DOI.
   The selection of the new DOI may be based on any of DESTINATION
   END-SYSTEM, DESTINATION NETWORK, DESTINATION SUBNET, SENDING INTERFACE,
   or RECEIVING INTERFACE or combinations thereof.  Exact details on
   how the output DOI is selected are implementation dependent,
   with the caveat that it should be consistent and reversible.
   If a datagram from end-system A to end-system B with DOI X maps
   into DOI Y, then a datagram from B to A with DOI Y should map
   into DOI X.



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        Once the output DOI is selected, the output sensitivity label
   is determined based on (1) the input DOI and input sensitivity label
   and (2) the output DOI.  In the event the input sensitivity label
   does not map to a valid output sensitivity label for the output DOI,
   then the datagram MUST be silently dropped and the drop event
   SHOULD be logged as a security fault.

        Once the datagram is re-labeled, the output procedures under
   Section 5.3 "Intermediate Systems" are followed, with the exception
   that any error that would cause a ICMP error message to be generated
   back to the originating end-system instead MUST drop the datagram.
   Such a drop SHOULD be logged as a security fault.

7.  IMPLEMENTATION ISSUES AND HINTS

        The following are "hints" not "requirements".  Implementation
   experience could eventually turn some of them into implementation
   requirements.

7.1.  Intermediate Systems

        Performance is optimised if there is hardware support
   for applying the mandatory access controls based on this label option.

7.2.  End Systems

        It is possible to create two DOIs with different overlapping
   compartment ranges.  This can be used to reduce the size of the IPv6
   sensitivity label option in some deployments.

7.3.  Upper-Level Protocols

7.3.1.  TCP-related issues

        With respect to a network, each distinct sensitivity label
   represents a separate virtual network which shares the same physical
   network.

        The above statement taken from section 3 has a non-obvious,
   but critical, corollary.  If there are separate virtual networks
   then it is possible for a system which exists in multiple virtual
   networks to have identical TCP connections, each one existing
   in a different virtual network.

        TCP connections are normally identified by source and
   destination port, and source and destination address.  If a system
   labels datagrams (which it must do if it exists in multiple virtual
   networks - e.g. a "multi-level secure" system), then TCP connections



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   are identified by source and destination port, source and destination
   address and SIPSO Security Sensitivity Label.

7.3.2.  UDP-related Issues

        Datagrams addressed to a UDP port should be delivered to all
   listeners whose equivalent sensitivity label is greater than or equal
   to the security sensitivity label of the UDP datagram.

7.3.3.  SCTP-related Issues

        Although a node might be multi-homed, it is entirely possible
   that only one of those interfaces is reachable for a given sensitivity
   label value.  For example, one interface on a node might have a
   sensitivity label range of Secret:Top Secret while a different interface
   might have a sensitivity label range of Unclassified:Unclassified.

SECURITY CONSIDERATIONS

        This document describes a mechanism for adding explicit
   sensitivity labels to IPv6 datagrams.  The primary purpose of these
   labels is to facilitate application of Mandatory Access Controls (MAC)
   in end-systems or intermediate-systems that implement this specification.
   As such, the implementation of this mechanism is very critical
   to the overall security of the systems and networks where this
   mechanisms is deployed.  Use of high-assurance development techniques
   is encouraged.

        A concern is that since this label is used for mandatory
   access controls, some method of binding the sensitivity label
   option to the rest of the packet is needed.  Without such binding,
   malicious modification of the sensitivity label in a packet
   would go undetected.  So, implementations of this sensitivity label
   option MUST also implement support for the IP Authentication Header.
   Implementations MUST permit the system administrator to configure
   whether AH is used or not.

        This mechanism is only intended for deployment in very
   limited circumstances where a set of systems and networks are in
   a well-protected operating environment and the threat of external
   or internal attack on this mechanism is considered acceptable
   to the accreditor of those systems and networks.  Accreditors
   of a given deployment should consider not only personnel clearances
   and physical security issues, but also electronic security
   (e.g. TEMPEST), network security (NETSEC), and communications
   security (COMSEC) issues.





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IANA CONSIDERATIONS

        IANA is requested to assign an IPv6 Hop-by-Hop option number
   to the SIPSO option described in this specification.  This option is
   immutable during transit.

        Also, IANA is requested to create a registry for SIPSO DOI
   values.  The initial values for this registry, shown in dotted-quad
   format, are as follows:

      DOI Value                  Organisation or Use
      0.0.0.0                    Null DOI; must not be used on the network
      0.0.0.1 to 0.255.255.255   For private use among consenting parties


        For the SIPSO DOI values registry, IANA is requested to issue
   a new DOI value to any organisation that requests it.  Assignment
   information normally should be made available on the IANA website.
   A commercial organisation will normally only be assigned one or two
   DOI values.  A national government or multi-national treaty organisation
   may be assigned a range of values if that is requested.  Different
   departments within a given national government each may independently
   request a range of values.

ACKNOWLEDGEMENTS

        This document is directly derived from an Internet-Draft by
   the first author written circa 1992.  Packet format changes have been
   made since that draft, primarily to comply with IPv6 syntax rules.
   Steve Brenneman, L.C. Bruzenak, and Paul Moore (in alphabetical order)
   provided feedback on earlier versions of this document.

INFORMATIVE REFERENCES
      [BL73]         Bell, D.E. & LaPadula, L.J., "Secure Computer Systems:
                     Mathematical Foundations and Model", Technical Report
                     M74-244, The MITRE Corporation, Bedford, MA, May 1973.

      [CMW]          US Defense Intelligence Agency, "Compartmented Mode
                     Workstation Evaluation Criteria", Technical Report
                     DDS-2600-6243-91, Washington, DC.

      [DOD 5200.1]   US Department of Defense, "DoD Information Security
                     Program", Directive 5200.1, 13 December 1996.

      [DOD 5200.1-R] US Department of Defense, "Information Security Program
                     Regulation", DoD 5200.1-R, 17 January 1997.

      [DoD 5200.28]  US Department of Defense, "Security Requirements



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                     for Automated Information Systems," Directive 5200.28,
                     21 March 1988.

      [DoD MLOS PP]  US Department of Defense, "Protection Profile
                     for Multi-level Operating Systems in Environments
                     requiring Medium Robustness, Version 1.22, 23 May
                     2001

      [ISO-15408]    International Stanards Organisation, "Evaluation
                     Criteria for IT Security", ISO/IEC 15408, 2005.

      [CC]           "Common Criteria for Information Technology Security
                     Evaluation", Version 3.1, Revision 1, CCMB-2006-09-001,
                     September 2006.

      [TCSEC]        US Department of Defense, "Trusted Computer System
                     Evaluation Criteria", DoD 5200.28-STD, 26 December 1985.

      [DoD 8500.1]   US Department of Defense, "Information Assurance",
                     Directive 8500.1, 24 October 2002.

      [FIPS-188]     US National Institute of Standards & Technology,
                     "Standard Security Labels for Information Transfer",
                     Federal Information Processing Standard (FIPS) 188,
                     September 1994.

      [RFC-791]      J. Postel, Internet Protocol, RFC-791, September 1981.

      [RFC-1038]     M. StJohns, Draft Revised IP Security Option, RFC-1038,
                     January 1988.

      [RFC-1108]     S. Kent, US DoD Security Options for the Internet
                     Protocol, RFC-1108, November 1991.

      [RFC-1825]     R. Atkinson, Security Architecture for the Internet
                     Protocol, RFC-1825, August 1995.

      [RFC-2119]    S. Bradner, "Key words for use in RFCs to Indicate
                    Requirement Levels", RFC-2119, March 1997.

      [IPSEC]       S. Kent, "Security Architecture for the Internet
                    Protocol", RFC-4301, December 2005.

      [AH]          S. Kent, "IP Authentication Header", RFC-4302,
                    December 2005.

      [ESP]         S. Kent, "IP Encapsulating Security Payload", RFC-4303,
                    December 2005.



StJohns & others                                               [Page 28]

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NORMATIVE REFERENCES

      [RFC-2460]     S. Deering & R. Hinden, Internet Protocol Version 6
                     Specification, RFC-2460, December 1998.

      [ITU-T V.42]   ITU-T, modem standard V.42 (for CRC-16 definition)
                     XXX [Is this the correct reference ?]


AUTHORS:

   M. StJohns
   Germantown, MD

   R. Atkinson
   Extreme Networks
   3585 Monroe Street
   Santa Clara, CA
   USA 95051

   rja@extremenetworks.com
   +1 (408)579-2800

   G. Thomas
   US Department of Defense
   Washington, DC
   USA

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StJohns & others                                               [Page 29]

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