An Echo Function for CLNP (ISO 8473)
RFC 1575

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Network Working Group                                           S. Hares
Request for Comments: 1575                                  Merit/NSFNET
Obsoletes: 1139                                             C. Wittbrodt
Category: Standards Track                    Stanford University/BARRNet
                                                           February 1994

                  An Echo Function for CLNP (ISO 8473)

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Abstract

   This memo defines an echo function for the connection-less network
   layer protocol.  The mechanism that is mandated here is in the final
   process of being standardized by ISO as "Amendment X: Addition of an
   Echo function to ISO 8473" an integral part of Version 2 of ISO 8473.

Table of Contents

   Section 1. Conventions .................................    2
   Section 2. Introduction ................................    2
   Section 3. The Generic Echo Function ...................    3
   Section 3.1 The Echo-Request ...........................    3
   Section 3.2 The Echo-Response ..........................    3
   Section 4. The Implementation Mechanism ................    4
   Section 4.1 The Echo-Request ...........................    4
   Section 4.2 The Echo-Response ..........................    4
   Section 5. Implementation Notes ........................    4
   Section 5.1 Discarding Packets .........................    4
   Section 5.2 Error Report Flag ..........................    4
   Section 5.3 Use of the Lifetime Field ..................    5
   Section 5.4 Echo-request function ......................    5
   Section 5.5 Echo-response function .....................    6
   Section 5.6 Use of the Priority Option .................    8
   Section 5.7 Use of the Source Route Option .............    8
   Section 5.8 Transmission of Multiple Echo-Requests .....    9
   Section 6. Security Considerations .....................    9
   Section 7. Authors' Addresses ..........................    9
   Section 8. References ..................................    9

Hares & Wittbrodt                                               [Page 1]
RFC 1575          An Echo Function for CLNP (ISO 8473)     February 1994

1.  Conventions

   The following language conventions are used in the items of
   specification in this document:

      o MUST, SHALL, or MANDATORY -- the item is an absolute
        requirement of the specification.

      o SHOULD or RECOMMENDED -- the item should generally be followed
        for all but exceptional circumstances.

      o MAY or OPTIONAL -- the item is truly optional and may be
        followed or ignored according to the needs of the implementor.

2.  Introduction

   The OSI Connection-less network layer protocol (ISO 8473) defines a
   means for transmitting and relaying data and error protocol data
   units, (PDUs) or preferably, packets through an OSI internet.
   Unfortunately, the world that these packets travel through is
   imperfect.  Gateways and links may fail.  This memo defines an echo
   function to be used in the debugging and testing of the OSI network
   layer.  Hosts and routers which support the OSI network layer MUST be
   able to originate an echo packet as well as respond when an echo is
   received.

   Network management protocols can be used to determine the state of a
   gateway or link.  However, since these protocols themselves utilize a
   protocol that may experience packet loss, it cannot be guaranteed
   that the network management applications can be utilized.  A simple
   mechanism in the network layer is required so that systems can be
   probed to determine if the lowest levels of the networking software
   are operating correctly.  This mechanism is not intended to compete
   with or replace network management; rather it should be viewed as an
   addition to the facilities offered by network management.

   The code-path consideration requires that the echo path through a
   system be identical (or very close) to the path used by normal data.
   An echo path must succeed and fail in unison with the normal data
   path or else it will not provide a useful diagnostic tool.

   Previous drafts describing an echo function for CLNP offered two
   implementation alternatives (see RFC 1139).  Although backward
   compatibility is an important consideration whenever a change is made
   to a protocol, it is more important at this point that the echo
   mechanisms used on the Internet interoperate.  For this reason, this
   memo defines one implementation mechanism (consistent with one of the
   previous drafts).

Hares & Wittbrodt                                               [Page 2]