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rfc:rfc1069

Network Working Group R. Callon Request for Comments: 1069 DEC Obsoletes: RFC 986 H.W. Braun

                                                                 UMich
                                                         February 1989
       Guidelines for the use of Internet-IP addresses in the
              ISO Connectionless-Mode Network Protocol

Status of This Memo

 This RFC suggests an addressing scheme for use with the ISO
 Connectionless Network Protocol (CLNP) in the Internet.  This is a
 solution to one of the problems inherent in the use of "ISO-grams" in
 the Internet.  This RFC suggests a proposed protocol for the Internet
 community, and requests discussion and suggestions for improvements.
 Distribution of this memo is unlimited.
 This memo is a revision of RFC 986.  Changes were made in order to
 allow the addressing used in the CLNP in the Internet to be
 potentially useful for routing in the context of new inter- and
 intra-domain routing protocols, and in the context of large numbers
 of networks and routing domains.  The addressing scheme proposed in
 this RFC allows individual routing domains to make use of internal
 routing algorithms utilizing a variety of addressing formats, while
 still providing for a common addressing approach for use by inter-
 domain routing.  These features are important due to the rapid growth
 currently being experienced in the Internet.

1. Objectives

 The data communications protocols currently emerging out of the
 international standardization efforts warrant an early integration
 into the existing extensive Internet network infrastructure.  The two
 possible approaches are a top-down one, where ISO applications like
 FTAM, X.400 and VTP are integrated on top of the transport function
 of the IP protocol suite, or a bottom-up approach where the whole ISO
 tower gets integrated without merging the two suites.  The bottom-up
 approach may make use of the fact that the ISO-CLNP and the IP are
 very similar in function.  This implies that it is reasonable to
 implement a multiprotocol function in some or all of the Internet
 gateways (potentially including part or all of the Internet
 environment).  The result would be that at least large portions of
 the Internet, in particular the backbones, can become usable for full
 implementations of the ISO protocol stack.
 A major problem with this approach is that there are open issues with

Callon & Braun [Page 1] RFC 1069 IP ISO Addressing February 1989

 regard to the ISO addressing within the CLNP.  In particular, the ISO
 network layer addressing standard allows a great deal of flexibility
 in the assignment of addresses, and a particular address format must
 be chosen.  A further problem is the need for implementation and
 integration of routing facilities for the ISO-compatible subset of
 the Internet environment.
 This paper proposed to use addresses which are considerably more
 flexible than the addresses used in the current IP Internet
 environment.  This flexibility is necessary in order to allow some
 routing domains to base their internal routing protocol on addresses
 derived from the current IP addresses, to allow other routing domains
 to base routing on addresses in accordance to the intra-domain
 routing protocol being developed by ANSI and ISO [6], and to allow
 generality for a future inter-domain routing protocol.
 The addressing scheme proposed here makes use of the concept of
 "routing domains" as used in ANSI and ISO.  This concept is similar
 to, but not identical with, the concept of "Autonomous System" used
 in the Internet.  Routing domains include a combination of gateways,
 networks, and end systems (not just gateways), and routing domain
 boundaries may be used to define associated access control and policy
 routing constraints.  Like autonomous systems, routing domains may be
 assumed to be topologically contiguous.  There is no a priori reason
 why routing domains assigned for use with the ISO IP need to have any
 particular relation with existing autonomous systems which have been
 assigned for use with the IP.  The assignment of specific routing
 domain identifiers is an "assigned numbers" function which is
 necessary for use of the ISO IP in the Internet, but is beyond the
 scope of this document.
 It is expected that this addressing scheme will be appropriate for
 long term use with the ISO IP in the Internet.  However, it is also
 expected that in the long term, the Internet will be interconnected
 with other routing domains making use of other schemes, such as
 addresses assigned to commercial internets through ANSI, and
 addresses assigned by national standards organizations in other
 countries.  This implies that, in the long term, gateways in the
 Internet will need to be able to route datagrams to destinations in
 other routing domains not conforming to the addressing format
 proposed here.  This is discussed in greater detail in section 6.

2. 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.

Callon & Braun [Page 2] RFC 1069 IP ISO Addressing February 1989

 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 Internet
 environment, consistent with the international standardized NSAP
 addresses.
                                           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

Callon & Braun [Page 3] RFC 1069 IP ISO Addressing February 1989

3. Addresses for Use in the Internet

 This section describes the addresses used to address NSAPs in the
 Internet.
 The appropriate Authority and Format Identifier (AFI) is one octet in
 length.  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.
 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 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.  Note that there is no particular
 relationship required between addressing domains and routing domains.
 In this case, although the Internet is considered to be a single
 addressing domain, it is expected that it will consist of multiple
 routing domains.
 The DSP of the address specifies a one octet version number, a two
 octet global area number, a two octet routing domain number, a
 variable length padding field, a variable length IGP specific part,
 and a one octet selector field.
 The version number is provided to allow for future extensions, and
 must contain the value "02".
 The global area number and routing domain number are provided to
 allow for inter-domain routing.  Initially, the global area number is
 reserved and must be set to zero.  The routing domain number may be
 set to the routing domain number of any gateway by which the
 associated host address is directly reachable.
 The IGP specific part of the address may contain whatever addressing
 format is used in the routing domain.  Two particular formats are
 expected to be used initially, and are presented in section 4.
 Padding is used so that the entire address will always be 20 octets
 in length.
 The selector field performs the same function as the user protocol

Callon & Braun [Page 4] RFC 1069 IP ISO Addressing February 1989

 field in the 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.
 The assignment of specific routing domain identifiers to defined
 routing domains, and the assignment of values for use in the selector
 field, are functions for the Assigned Numbers authority for the
 Internet [4].  The specific values to be used are outside of the
 scope of this document.
 In summary, a source or destination address within the ISO
 Connectionless Protocol, when used in the Internet, looks as follows:
                                                Octet
                     +------------------------+
                     |          AFI           |     1
                     +------------------------+
                     |       IDI / ICD        |     2
                     +--                    --+
                     |(specifies DoD Internet)|     3
                     +------------------------+
                     |     Version Number     |     4
                     +------------------------+
                     |      Global Area       |     5
                     +---                  ---+
                     |         Number         |     6
                     +------------------------+
                     |        Routing         |     7
                     +---                  ---+
                     |         Domain         |     8
                     +------------------------+
                     |                        |     9
                     :        Padding         :     :
                     :                        :     :
                     |                        |     n
                     +------------------------+
                     |          IGP           |   n+1
                     :                        :     :
                     :                        :     :
                     |        Specific        |    19
                     +------------------------+
                     |        Selector        |    20
                     +------------------------+
                  Figure 2: ISO IP address structure

Callon & Braun [Page 5] RFC 1069 IP ISO Addressing February 1989

 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 "02".  The Global Area
 Number must contains the value "00".  The Padding field is of
 variable length, but must contain the value zero.

4. Specific Values for use with the IGP specific field

 In general, a particular routing domain may specify any addressing
 scheme for use with the IGP specific part of the address, up to 11
 octets in length (consistent with the maximum address length of 20
 octets).  However, it is expected that initially addresses used in
 this field will consist of either the current IP addresses, or
 addresses conformant with those specified in the draft ANSI proposal
 for intra-domain routing.
 For end systems which are members of routing domains using the IP
 addresses for internal routing, the addresses will look as follows:

Callon & Braun [Page 6] RFC 1069 IP ISO Addressing February 1989

                                                Octet
                     +------------------------+
                     |          AFI           |     1
                     +------------------------+
                     |       IDI / ICD        |     2
                     +--                    --+
                     |(specifies DoD Internet)|     3
                     +------------------------+
                     |     Version Number     |     4
                     +------------------------+
                     |      Global Area       |     5
                     +---                  ---+
                     |         Number         |     6
                     +------------------------+
                     |        Routing         |     7
                     +---                  ---+
                     |         Domain         |     8
                     +------------------------+
                     |                        |     9
                     :        Padding         :     :
                     :                        :     :
                     |                        |    15
                     +------------------------+
                     |       Four Octet       |    16
                     +---                  ---+
                     |        Internet        |    17
                     +---                  ---+
                     |          DoD           |    18
                     +---                  ---+
                     |        Address         |    19
                     +------------------------+
                     |        Selector        |    20
                     +------------------------+
         Figure 3: ISO IP Address with Encoded DoD IP Address
 For end systems which are members of routing domains using the
 address format specified in the draft ANSI proposal for intra-domain
 routing [6], the addresses will look as follows:

Callon & Braun [Page 7] RFC 1069 IP ISO Addressing February 1989

                                                Octet
                     +------------------------+
                     |          AFI           |     1
                     +------------------------+
                     |       IDI / ICD        |     2
                     +--                    --+
                     |(specifies DOD Internet)|     3
                     +------------------------+
                     |     Version Number     |     4
                     +------------------------+
                     |      Global Area       |     5
                     +---                  ---+
                     |         Number         |     6
                     +------------------------+
                     |        Routing         |     7
                     +---                  ---+
                     |         Domain         |     8
                     +------------------------+
                     |                        |     9
                     +---                  ---+
                     |        Padding         |    10
                     +---                  ---+
                     |                        |    11
                     +------------------------+
                     |                        |    12
                     +---     LOC-AREA     ---+
                     |                        |    13
                     +------------------------+
                     |                        |    14
                     :           ID           :     :
                     :                        :     :
                     |                        |    19
                     +------------------------+
                     |        Selector        |    20
                     +------------------------+
       Figure 4: ISO IP Address with Encoded ANSI-format Address

5. 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, may make use of a
 separate address format based on their X.121 address.  Such addresses
 may, for example, use the ISO-X.121 address format discussed in [3].
 These addresses will need to be handled for routing purposes in much
 the same way as addresses in routing domains which have been

Callon & Braun [Page 8] RFC 1069 IP ISO Addressing February 1989

 interconnected to the Internet, but which use other address formats,
 such as those specified by national standards bodies.

6. Migration to Future Routing Protocols

 Initially, routing of ISO datagrams in the Internet may make use of
 the first 8 octets of the address (AFI, ICD, version, global area
 number, and routing domain number) as a flat field identifying the
 routing domain.  This implies that if EGP is initially used for
 routing between routing domains, a new version of EGP may be required
 to carry 8 octet routing domain numbers instead of 3 octet network
 numbers.
 There are currently several efforts underway to determine the
 requirements for inter-autonomous system routing, and to define a new
 protocol.  One of the requirements of inter-autonomous system routing
 is the need to be able to deal with a very large Internet.  It is
 anticipated that during the lifetime of the addressing scheme
 described in this RFC the number of networks in the Internet will
 grow to the point where it is no longer feasible for any gateway to
 maintain separate routes to every network in the Internet.  Allowing
 inter-domain routing to be done by routing domain number instead of
 network number is therefore a necessary step in the long term.
 It is difficult to anticipate the rate at which the number of routing
 domains may grow.  For example, during a period of time in which the
 number of networks grows by a factor of 100, it is not clear whether
 the number of routing domains may also be expected to grow by a
 factor of 100, or by some lesser amount.  It is possible that the
 number of routing domains will also grow to a point where it is not
 feasible for a single gateway to maintain separate routes to each.
 In order to prepare for this eventuality, we have provided for a
 "global area" field.
 In the long term, it will be necessary for gateways to route to
 destinations which are in routing domains utilizing other addressing
 formats, specified by other organizations such as ANSI, ECMA, etc.
 In this case, it will not be possible to ensure that the first 8
 octets of the address specifies the routing domain.  In the long
 term, it will therefore be necessary to route based on variable
 length routing domain identifiers.  It may be assumed that future
 inter-domain routing protocols will allow for specification of either
 (1) an address mask, specifying which part of an address is relevant
 for specifying those destinations which are reachable via a
 particular domain; or (2) a length field, specifying how many leading
 octets in a particular address are relevant.  Specification of the
 details of such a routing protocol is beyond the scope of this
 document.

Callon & Braun [Page 9] RFC 1069 IP ISO Addressing February 1989

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-1010,
      USC/Information Sciences Institute, May 1987.
 [5]  Callon, R. and H. W. Braun, "Working Draft -- Guidelines for the
      use of Internet-IP addresses in the ISO Connectionless-Mode
      Network Protocol," RFC-986, June 1986.
 [6]  ISO TC97/SC6/WG2 working document, "Intermediate System to
      Intermediate System Intra-Domain Routing Exchange Protocol".

Callon & Braun [Page 10]

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