

Network Working Group                                  Ross Callon (BBN)
Request for Comments: 986                      Hans-Werner Braun (UMich)
                                                               June 1986

                             WORKING DRAFT

         Guidelines for the use of Internet-IP addresses in the
                ISO Connectionless-Mode Network Protocol


Status of This Memo

   This RFC suggests a method to allow the existing IP addressing,
   including the IP protocol field, to be used for the ISO
   Connectionless Network Protocol (CLNP).  This is a draft solution to
   one of the problems inherent in the use of "ISO-grams" in the DOD
   Internet.  Related issues will be discussed in subsequent RFCs.  This
   RFC suggests a proposed protocol for the ARPA-Internet community, and
   requests discussion and suggestions for improvements.  Distribution
   of this memo is unlimited.

1.  Introduction

   The CLNP is documented in [1], but for matters of completeness the
   following illustration of the CLNP header is included here as
   Figure 1.

   The addressing part of the header is the subject of this RFC, i.e.,
   the source and the destination address, respectively.  These
   addresses are generally discussed in [2] and [3], with this document
   presenting a specific method for addressing in the DOD Internetwork
   environment, consistent with the international standardized NSAP
   addresses.




















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RFC 986                                                        June 1986
DOD IP Addresses in ISO CLNP


                                            Octet                     
  +--------------------------------------+                   +--------
  |  Network Layer Protocol Identifier   |  1                :        
  |--------------------------------------|                   :        
  |           Length Indicator           |  2                :        
  |--------------------------------------|                   :        
  |   Version/Protocol Id Extension      |  3                :   Fixed
  |--------------------------------------|                   :        
  |              Lifetime                |  4                :    Part
  |--------------------------------------|                   :        
  |SP|MS|E/R|      Type                  |  5                :        
  |--------------------------------------|                   :        
  |           Segment Length             |  6,7              :        
  |--------------------------------------|                   :        
  |              Checksum                |  8,9              :        
  |--------------------------------------|                   +--------
  | Destination Address Length Indicator |  10               :        
  |--------------------------------------|                   :        
  |         Destination Address          |  11 through m-1   : Address
  |--------------------------------------|                   :        
  |    Source Address Length Indicator   |  m                :    Part
  |--------------------------------------|                   :        
  |            Source Address            |  m+1 through n-1  :        
  |--------------------------------------|                   +--------
  |         Data Unit Identifier         |  n,n+1            :        
  |--------------------------------------|                   : Segment
  |            Segment Offset            |  n+2,n+3          :   ation
  |--------------------------------------|                   :        
  |             Total Length             |  n+4,n+5          :    Part
  |--------------------------------------|                   +--------
  |                Options               |  n+6 through p    : Options
                                                                  Part
  |--------------------------------------|                   +--------
  |                 Data                 |  p+1 through z    :    Data
  +--------------------------------------+                   +--------

                     Figure 1:   PDU Header Format












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RFC 986                                                        June 1986
DOD IP Addresses in ISO CLNP


2.  Addresses for Use in the Internet

   This section describes the primary addresses used to address NSAPs in
   the Internet.  A later section will describe a separate address
   format for end systems and individual simple LANs that are attached
   to the Internet only through intervening Public Data Networks.

   The appropriate Authority and Format Identifier (AFI) is one octet in
   length.

      "The AFI consists of an integer with a value between 0 and 99 with
      an abstract syntax of two decimal digits" [3], that is, the AFI
      codes are binary coded decimal (BCD).

   It specifies an ISO-6523-ICD assignment, and also that the Domain
   Specific Part (DSP) of the address is based on binary.  The AFI octet
   uses the value "47".  The ISO-6523-ICD format is used to emphasize
   that this is an administrative assignment.  The usage of an ISO DCC
   (Data Country Code) would be possible, but could be misleading due to
   the fairly far spread geographical extent of the Internet-IP.

   As required by the ISO addressing standard, the next two octets of
   the address, in this case, specify the Initial Domain Identifier.
   This two octet value is the International Code Designator (ICD)
   assigned to the DOD Internet, "0006".

   The remainder of the NSAP address is the Domain Specific Part (DSP).
   This is assigned by the Internet administration, which is considered
   to be an addressing domain.  The remainder of the address specifies a
   one byte version number, the four byte Internet Protocol address and
   a one byte IP user protocol field. The version number allows for
   future extensions.  The IP address used is the same as the current
   four octet IP address.  The user protocol field is the same as the
   user protocol field in the current IP header.  This is necessary
   because the ISO protocol considers identification of the user
   protocol to be an addressing issue, and therefore does not allow for
   the user protocol to be specified in the protocol header
   independently from the address.











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RFC 986                                                        June 1986
DOD IP Addresses in ISO CLNP


   Therefore a source or destination address within the ISO
   Connectionless Protocol, when used in the DOD Internet, looks as
   follows:

                                               Octet

                    +------------------------+      
                    |          AFI           |     1
                    +------------------------+      
                    |       IDI / ICD        |     2
                    +--                    --+      
                    |(specifies DOD Internet)|     3
                    +------------------------+      
                    |     Version Number     |     4
                    +------------------------+      
                    |                        |     5
                    +---   four  byte     ---+      
                    |                        |     6
                    +---    Internet      ---+      
                    |                        |     7
                    +---   Address (IP)   ---+      
                    |                        |     8
                    +------------------------+      
                    |  IP User Protocol ID   |     9
                    +------------------------+      

                   Figure 2: ISO IP address structure

   The Authority and Format Identifier (AFI) is "47" (BCD).  The Initial
   Domain Identifier (IDI) consists of the International Code Designator
   (ICD) assigned to the Internet, and must contain the value "0006".
   The Version Number must contain the value "01".  The Current IP
   addresses and IP user protocol numbers can be found in [4].

3.  Devices Attached to PDNs

   Otherwise isolated end systems, which are attached to the Internet
   only indirectly via public data networks, and simple LANs which are
   similarly attached only via Public Data Networks, will make use of a
   separate address format based on their X.121 address.

   Figure 3 specifies the address for use by end systems attached to
   PDNs. Here the AFI specifies an ISO-X.121 address format, with the
   DSP based on binary.  The AFI occupies a single octet, and must take
   the value "37" (hexadecimal).  The IDI contains the X.121 addresses




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RFC 986                                                        June 1986
DOD IP Addresses in ISO CLNP


   encoded in binary (using BCD), padded at the end if necessary with
   all ones (binary "1111") to make up 7 full octets.  Finally, the DSP
   contains a single octet, which specifies the user protocol.

                                               Octet

                    +------------------------+      
                    |          AFI           |     1
                    +------------------------+      
                    |          IDI           |     2
                    +--                    --+      
                    |    (specifies X.121    |     3
                    +--                    --+      
                    |   address, padded to   |     4
                    +--                    --+      
                    |        7 octets)       |     5
                    +--                    --+      
                    |                        |     6
                    +--                    --+      
                    |                        |     7
                    +--                    --+      
                    |                        |     8
                    +------------------------+      
                    |  IP User Protocol ID   |     9
                    +------------------------+      

      Figure 3: ISO IP address structure for isolated end systems

   Figure 4 specifies the address for use by simple LANs attached to
   PDNs. This address is the same as the address used for end systems
   directly attached to PDNs, except for the addition of the (variable
   length) local address as used on the LAN.  Whether the address is of
   the form shown in figure 3, or of the form shown in figure 4, is
   determined by looking at the length of the address.















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RFC 986                                                        June 1986
DOD IP Addresses in ISO CLNP


                                              Octet

                 +------------------------+           
                 |          AFI           |     1     
                 +------------------------+           
                 |          IDI           |     2     
                 +--                    --+           
                 |    (specifies X.121    |     3     
                 +--                    --+           
                 |   address, padded to   |     4     
                 +--                    --+           
                 |        7 octets)       |     5     
                 +--                    --+           
                 |                        |     6     
                 +--                    --+           
                 |                        |     7     
                 +--                    --+           
                 |                        |     8     
                 +------------------------+           
                 |                        |     9     
                 +--     local net      --+           
                 |                        |           
                 +--      address       --+           
                 |                        |           
                 +---                   --+ (variable 
                 |                        |     sized)
                 +------------------------+           
                 |  IP User Protocol ID   |           
                 +------------------------+           

          Figure 4: ISO IP address structure for isolated LANs


















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RFC 986                                                        June 1986
DOD IP Addresses in ISO CLNP


References

   [1]  ISO, "Protocol for Providing the Connectionless-Mode Network
        Services", RFC-926, ISO, December 1984.

   [2]  ANSI, "Guidelines for the Specification of the Structure of the
        Domain Specific Part (DSP) of the ISO Standard NSAP Address",
        RFC-982, ANSI Working Document X3S3.3/85-258, April 1986.

   [3]  ISO, Draft International Standard 8348/DAD2, "Information
        Processing Systems  --  Data Communications  --  Network Service
        Definition, Addendum 2 Covering Network Layer Addressing",
        RFC-941, April 1985.

   [4]  Reynolds, J. and J. Postel, "Assigned Numbers", RFC-960, USC
        Information Sciences Institute, December 1985.

































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