rfc1038.txt

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      a.  Output.  The use of the option is mandatory.  The
      classification level of an IP datagram should be within the range
      of levels for which the host is accredited.  The protection
      authorities flags should be one for all authorities under whose
      rules the datagram should be protected.

      b.  Input.  In the specific case where a multi-level or controlled
      host is accredited to directly interface with an unclassified
      environment, the host may accept IP datagrams without a basic
      security option.  Such datagrams should be assumed to be
      implicitly labelled unclassified, GENSER, and should be so
      labelled explicitly if they are later output.  In all other cases,
      the IP datagrams should have the basic security option on input,
      and the out-of-range procedure should be followed if it is not.

   There are two cases to be considered where the option is present.
   The first case is where the system environment permits the values in
   the option to be trusted to be correct for some range of values; the
   second is where the values cannot be trusted to be correct.  For each
   multi-level or controlled host, every input channel for IP datagrams
   must be considered and classed appropriately.  If a channel does have
   a trusted range, then the values of both the classification level and
   the protection authorities are checked to insure that they fall
   within that range and the range of accredited values for the



St. Johns                                                       [Page 4]

RFC 1038            Draft Revised IP Security Option        January 1988


   receiving host.  If within both ranges, the IP datagram is accepted
   for further processing; otherwise the out-of-range procedure is
   followed.  If the label cannot be trusted, then the receiving host
   must possess some accredited means of knowing what the correct
   marking should be (e.g., a trusted channel to a system-high host at a
   known level).  On receipt of an IP datagram, the host compares the
   actual values in the option to the correct values.  If the values
   match, the datagram is accepted for further processing; otherwise,
   the out-of-range procedure is followed.

9.3.15.3.4.4  Out-Of-Range Procedure.

   If an IP datagram is received which does not meet the input
   requirements, then:

      a)  The data field should be overwritten with ones.

      b) If the problem is a missing required Basic or Extended security
      option, an ICMP "parameter problem" message is sent to the
      originating host with the code field set to 1 (one) to indicate
      "missing required option" and the pointer field set to the option
      type of the missing option.  Otherwise, an ICMP "parameter
      problem" message is sent to the originating host with code field
      set to 0 (zero) and with the pointer field pointing to the
      position of the out-of-range security option.

      c) If the receiving host has an interface to a local security
      officer or equivalent, the problem should be identified across
      that interface in an appropriate way.

9.3.15.3.4.5  Trusted Intermediary Procedure.

   Certain devices in the internet may act as intermediaries to validate
   that communications between two hosts are authorized, based on a
   combination of knowledge of the hosts and the values in the IP
   security option.  These devices may receive IP datagrams which are in
   range for the intermediate device, but are either not within the
   acceptable range for the sender, or for the ultimate receiver.  In
   the former case, the datagram should be treated as described above
   for an out-of-range option.  In the latter case, a "destination
   unreachable" ICMP message should be sent, with the code value of 10
   (ten), indicating "Communication with Destination Host
   Administratively Prohibited".








St. Johns                                                       [Page 5]

RFC 1038            Draft Revised IP Security Option        January 1988


9.3.15.4  DoD Extended Security Option

    Option type:  133          Option length:  variable

   This option permits additional security related information, beyond
   that present in the Basic Security Option, to be supplied in an IP
   datagram to meet the needs of registered authorities.  If this option
   is required by an authority for a specific system, it must be
   specified explicitly in any Request for Proposal.  It is not
   otherwise required.  This option must be copied on fragmentation.
   This option may appear multiple times within a datagram.

   The format for this option is as follows:

          +------------+-------------+-------------+--------//-------+
          | 10000101   |  000LLLLL   |  AAAAAAAA   |   add sec info  |
          +------------+-------------+-------------+--------//-------+
           type = 133    LENGTH = Var.   ADDITIONAL    ADDITIONAL
                                         SECURITY      SECURITY
                                         INFO          INFO
                                         AUTHORITY
                                         CODE

                               FIGURE 10-B.

9.3.15.4.1  Additional Security Info Authority Code.

   length = 8 bits

   The values of this field are assigned by DCA Code R130, Washington,
   D.C.  20305-2000.  Each value corresponds to a requestor who, once
   assigned, becomes the authority for the remainder of the option
   definition for that value.

9.3.15.4.2  Additional Security Information.

   length - variable

   This field contains any additional security information as specified
   by the authority.











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RFC 1038            Draft Revised IP Security Option        January 1988


      BIT
      NUMBER     AUTHORITY

        0        GENSER

        1        SIOP

        2        DSCCS-SPINTCOM

        3        DSCCS-CRITICOM

      4-7        Unassigned

   AUTHORITY                                 SOURCE OF ANNEX DESCRIBING
                                             CURRENT CODING OF ADDITIONAL
                                             SECURITY INFORMATION

   GENSER
   National Access Program, less SIOP        Defense Communications
                                             Agency
                                             ATTN:  Code R130
                                             Washington, DC  20305

   SIOP
   National Access Program                   Department of Defense
                                             Organization of the
                                             Joint Chiefs of Staff
                                             Attn: J6T
                                             Washington, DC

   DSCCS-SPINTCOM
   National Access Program                   Defense Intelligence Agency
                                             Attn: DSE4
                                             Bolling AFB, MD

   DSCCS-CRITICOM
   National Access Program                   National Security Agency
                                             9800 Savage Road
                                             Attn: T03
                                             Ft. Meade, MD 20755-6000











St. Johns                                                       [Page 7]