rfc995.txt

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Network Working Group                                   ANSI X3S3.3 86-118
Request for Comments: 995                              ISO TC97/SC6/N 4053
                                                                April 1986





                                 I S O
             INTERNATIONAL ORGANIZATION FOR STANDARDIZATION
              ORGANISATION INTERNATIONALE DE NORMALISATION

     ______________________________________________________________________
    |                                                                     |
    |                            ISO/TC 97/SC 6                           |
    |                TELECOMMUNICATIONS AND INFORMATION                   |
    |                     EXCHANGE BETWEEN SYSTEMS                        |
    |                       Secretariat: USA (ANSI)                       |
    |                                                                     |
    |                                                                     |
    |_____________________________________________________________________|





  Title:    End System to Intermediate System Routing Exchange Protocol
            for use in conjunction with ISO 8473

  Source:   SC6/WG2
            Project 97.6.41




  ___________________________________________________________________________
 |This document is a progression of SC6/N3862, edited to incorporate member |
 |body comments and discussion at the Florence meeting of SC6/WG2. Pursuant |
 |to Recommendation 5 of that meeting, comments from member bodies on this  |
 |revision text are requested for discussion at the Tokyo meeting of SC6    |
 |and WGs.                                                                  |
 |__________________________________________________________________________|












ISO N4053                                                       [Page 1]

RFC 995                                                    December 1986


Contents

1   Introduction                                                           5

2   Scope and Field of Application                                         6

3   References                                                             7


SECTION ONE. GENERAL                                                       9

4   Definitions                                                            9
    4.1   Reference Model Definitions  . . . . . . . . . . . . . . . . .   9
    4.2   Network Layer Architecture Definitions   . . . . . . . . . . .   9
    4.3   Network Layer Addressing Definitions   . . . . . . . . . . . .   9
    4.4   Local Area Network Definitions   . . . . . . . . . . . . . . .  10
    4.5   Additional Definitions . . . . . . . . . . . . . . . . . . . .  10

5   Symbols and Abbreviations                                             10
    5.1   Data Units   . . . . . . . . . . . . . . . . . . . . . . . . .  10
    5.2   Protocol Data Units  . . . . . . . . . . . . . . . . . . . . .  10
    5.3   Protocol Data Unit Fields  . . . . . . . . . . . . . . . . . .  10
    5.4   Parameters . . . . . . . . . . . . . . . . . . . . . . . . . .  11
    5.5   Miscellaneous  . . . . . . . . . . . . . . . . . . . . . . . .  11

6   Overview of the Protocol                                              11
    6.1   Information Provided by the Protocol . . . . . . . . . . . . .  11
    6.2   Subsets of the Protocol. . . . . . . . . . . . . . . . . . . .  12
    6.3   Addressing   . . . . . . . . . . . . . . . . . . . . . . . . .  12
    6.4   Underlying Service Assumed by the Protocol   . . . . . . . . .  12
          6.4.1   Subnetwork Addresses . . . . . . . . . . . . . . . . .  12
          6.4.2   Subnetwork User Data . . . . . . . . . . . . . . . . .  13
    6.5   Service Assumed from Local Environment . . . . . . . . . . . .  13
    6.6   Subnetwork Types . . . . . . . . . . . . . . . . . . . . . . .  14
          6.6.1   Point-to-Point Subnetworks . . . . . . . . . . . . . .  15
          6.6.2   Broadcast Subnetworks  . . . . . . . . . . . . . . . .  15
          6.6.3   General Topology Subnetworks . . . . . . . . . . . . .  16


SECTION TWO. SPECIFICATION OF THE PROTOCOL                                18

7   Protocol Functions                                                    18
    7.1   Protocol Timers  . . . . . . . . . . . . . . . . . . . . . . .  18
          7.1.1   Configuration Timer  . . . . . . . . . . . . . . . . .  18
          7.1.2   Holding Timer  . . . . . . . . . . . . . . . . . . . .  18
    7.2   Report Configuration Function  . . . . . . . . . . . . . . . .  18
          7.2.1   Report Configuration by End Systems  . . . . . . . . .  19
          7.2.2   Report Configuration by Intermediate Systems . . . . .  19
    7.3   Record Configuration Function  . . . . . . . . . . . . . . . .  20
    7.4   Flush Old Configuration Function   . . . . . . . . . . . . . .  20
    7.5   Query Configuration Function . . . . . . . . . . . . . . . . .  20



ISO N4053                                                       [Page 2]

RFC 995                                                    December 1986


    7.6   Configuration Response Function  . . . . . . . . . . . . . . .  21
    7.7   Request Redirect Function. . . . . . . . . . . . . . . . . . .  22
    7.8   Record Redirect Function . . . . . . . . . . . . . . . . . . .  23
    7.9   Refresh Redirect Function  . . . . . . . . . . . . . . . . . .  23
    7.10  Flush Old Redirect Function  . . . . . . . . . . . . . . . . .  24
    7.11  PDU Header Error Detection   . . . . . . . . . . . . . . . . .  24
    7.12  Classification of Functions  . . . . . . . . . . . . . . . . .  25

8   Structure and Encoding of PDUs                                        25
    8.1   Structure  . . . . . . . . . . . . . . . . . . . . . . . . . .  26
    8.2   Fixed Part . . . . . . . . . . . . . . . . . . . . . . . . . .  26
          8.2.1   General  . . . . . . . . . . . . . . . . . . . . . . .  26
          8.2.2   Network Layer Protocol Identifier  . . . . . . . . . .  27
          8.2.3   Length Indicator . . . . . . . . . . . . . . . . . . .  27
          8.2.4   Version/Protocol Identifier Extension  . . . . . . . .  27
          8.2.5   Type Code  . . . . . . . . . . . . . . . . . . . . . .  28
          8.2.6   Holding Time . . . . . . . . . . . . . . . . . . . . .  28
          8.2.7   PDU Checksum . . . . . . . . . . . . . . . . . . . . .  28
    8.3   Network Address Part . . . . . . . . . . . . . . . . . . . . .  28
          8.3.1   General  . . . . . . . . . . . . . . . . . . . . . . .  28
          8.3.2   NPAI (Network Protocol Address Information) En-
                  coding . . . . . . . . . . . . . . . . . . . . . . . .  28
          8.3.3   Source Address Parameter for ESH PDU   . . . . . . . .  29
          8.3.4   Network Entity Title Parameter for ISH PDU . . . . . .  29
          8.3.5   Destination Address Parameter for RD PDU . . . . . . .  30
    8.4   Subnetwork Address Part  . . . . . . . . . . . . . . . . . . .  30
          8.4.1   Subnetwork Address Parameter for RD PDU  . . . . . . .  31
    8.5   Options Part . . . . . . . . . . . . . . . . . . . . . . . . .  31
          8.5.1   General  . . . . . . . . . . . . . . . . . . . . . . .  31
          8.5.2   Security . . . . . . . . . . . . . . . . . . . . . . .  32
          8.5.3   Quality of Service Maintenance . . . . . . . . . . . .  33
          8.5.4   Priority . . . . . . . . . . . . . . . . . . . . . . .  33
    8.6   End System Hello (ESH) PDU . . . . . . . . . . . . . . . . . .  34
          8.6.1   Structure  . . . . . . . . . . . . . . . . . . . . . .  34
    8.7   Intermediate System Hello (ISH) PDU  . . . . . . . . . . . . .  35
          8.7.1   Structure  . . . . . . . . . . . . . . . . . . . . . .  35
    8.8   Redirect (RD) PDU. . . . . . . . . . . . . . . . . . . . . . .  36
          8.8.1   Structure  . . . . . . . . . . . . . . . . . . . . . .  36

9   Formal Description                                                    37

10  Conformance                                                           37

ANNEX A. SUPPORTING TECHNICAL MATERIAL                                    38
    A.1   Use of Timers  . . . . . . . . . . . . . . . . . . . . . . . .  38
          A.1.1   Example of Holding Time for Route Redirection  . . . .  38
          A.1.2   Example of Holding Timer for Configuration Informa-
                  tion . . . . . . . . . . . . . . . . . . . . . . . . .  39
    A.2   Refresh and timeout of Redirection information . . . . . . . .  39
    A.3   System Initialization Considerations . . . . . . . . . . . . .  40
    A.4   Optimizations for Flushing Redirects   . . . . . . . . . . . .  41



ISO N4053                                                       [Page 3]

RFC 995                                                    December 1986


List of Tables

    1     Service Primitives for Underlying Service  . . . . . . . . . .  12
    2     Timer Primitives . . . . . . . . . . . . . . . . . . . . . . .  14
    3     Categories of Protocol Functions . . . . . . . . . . . . . . .  25
    4     Valid PDU Types  . . . . . . . . . . . . . . . . . . . . . . .  28


List of Figures

    1     PDU Header -- Fixed Part . . . . . . . . . . . . . . . . . . .  27
    2      Address Parameters  . . . . . . . . . . . . . . . . . . . . .  29
    3     ESH PDU - Network Address Part   . . . . . . . . . . . . . . .  29
    4     ISH PDU - Network Address Part . . . . . . . . . . . . . . . .  30
    5     RD PDU - Network Address Part  . . . . . . . . . . . . . . . .  30
    6     ESH PDU - Address Part   . . . . . . . . . . . . . . . . . . .  31
    7     All PDUs - Options Part  . . . . . . . . . . . . . . . . . . .  31
    8     Encoding of Option Parameters  . . . . . . . . . . . . . . . .  32
    9     ESH PDU Format . . . . . . . . . . . . . . . . . . . . . . . .  34
    10    ISH PDU Format . . . . . . . . . . . . . . . . . . . . . . . .  35
    11    RD PDU Format when Redirect is to an IS  . . . . . . . . . . .  36
    12    RD PDU Format when Redirect is to an ES  . . . . . . . . . . .  37
































ISO N4053                                                       [Page 4]

RFC 995                                                    December 1986


1     Introduction

   This Protocol is one of a set of International Standards produced to
   facilitate the interconnection of open systems. The set of standards
   covers the services and protocols required to achieve such intercon-
   nection.

   This Protocol is positioned with respect to other related standards
   by the layers defined in the Reference Model for Open System Inter-
   connection (ISO 7498) and by the structure defined in the Internal
   Organization of the Network Layer (DIS 8648).  In particular, it is a
   protocol of the Network Layer.  This protocol permits End Systems and
   Intermediate Systems to exchange configuration and routing informa-
   tion to facilitate the operation of the routing and relaying func-
   tions of the Network Layer.

   The aspects of Network Layer routing that are concerned with communi-
   cation between end systems and intermediate systems on the same sub-
   network are to a great extent separable from the aspects that are
   concerned with communication among the intermediate systems that con-
   nect multiple subnetworks. This protocol addresses only the former
   aspects. It will be significantly enhanced by the cooperative opera-
   tion of an additional protocol that provides for the exchange of
   routing information among intermediate systems, but is useful whether
   or not such an additional protocol is available.

      This protocol provides solutions for the following practical problems:

      1.  How do end systems discover the existence and reachability of
          intermediate systems that can route NPDUs to destinations on
          subnetworks other than the one(s) to which the end system is
          directly connected?

      2.  How do end systems discover the existence and reachability of
          other end systems on the same subnetwork (when direct
          examination of the destination NSAP address does not provide
          information about the destination subnetwork)?

      3.  How do intermediate systems discover the existence and
          reachability of end systems on each of the subnetworks to
          which they are directly connected?

      4.  How do end systems decide which intermediate system to use
          to forward NPDUs to a particular destination when more than one
          intermediate system is accessible?

      The protocol assumes that:

      1.  Routing to a specified subnetwork point of attachment address
          (SNPA) on the same subnetwork is carried out satisfactorily by
          the subnetwork itself.



ISO N4053                                                       [Page 5]

RFC 995                                                    December 1986


      2.  The subnetwork is not, however, capable of routing on a global
          basis using the NSAP address alone to achieve communication
          with a requested destination.

                                      Note:
          Consequently, it is not possible to use Application Layer
          communication to carry out the functions of this protocol.

      The protocol is connectionless, and is designed to:

      1.  minimize the amount of a priori state information needed by
          end systems before they can begin to communicate with other
          end systems;

      2.  minimize the amount of memory needed to store routing
          information in end systems; and

      3.  minimize the computational complexity of end system routing
          algorithms.


   The protocol is also designed to operate in close conjunction with
   the Protocol for the Provision of the Connectionless-mode Network
   Service (ISO 8473).  Since routing styles are usually closely related
   to communication styles, the information that this protocol provides
   to end systems and intermediate systems may or may not be appropriate
   information for supporting routing functions when a Network Layer
   protocol other than ISO 8473 is used.

2     Scope and Field of Application

   This International Standard specifies a protocol which is used by
   Network Layer entities operating ISO 8473 in End Systems and Inter-
   mediate Systems (referred to herein as ES and IS respectively) to
   maintain routing information.  The Protocol herein described relies
   upon the provision of a connectionless-mode underlying service.

     This Standard specifies:

     a)  procedures for the transmission of configuration and routing
         information between network entities residing in End Systems
         and network entities residing in Intermediate Systems;

     b)  the encoding of the protocol data units used for the transmission