rfc1069.txt

著名的RFC文档,其中有一些文档是已经翻译成中文的的.

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]