RFC 1764

Network Working Group                                           S. Senum
Request for Comments: 1764                                     DigiBoard
Category: Standards Track                                     March 1995

                The PPP XNS IDP Control Protocol (XNSCP)

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.


   The Point-to-Point Protocol (PPP) [1] provides a standard method for
   transporting multi-protocol datagrams over point-to-point links.  PPP
   defines an extensible Link Control Protocol, and proposes a family of
   Network Control Protocols for establishing and configuring different
   network-layer protocols.

   This document defines the Network Control Protocol for establishing
   and configuring the Xerox Network Systems (XNS) Internet Datagram
   Protocol (IDP) over PPP.

Table of Contents

   1.     Introduction ..........................................    2
      1.1       Specification of Requirements ...................    2
      1.2       Terminology .....................................    3
   2.     A PPP Network Control Protocol for XNS IDP ............    3
      2.1       Sending XNS IDP Datagrams .......................    4
   SECURITY CONSIDERATIONS ......................................    5
   REFERENCES ...................................................    5
      ACKNOWLEDGEMENTS ..........................................    5
   CHAIR'S ADDRESS ..............................................    5
   AUTHOR'S ADDRESS .............................................    5

Senum                                                           [Page 1]

RFC 1764                       PPP XNSCP                      March 1995

1.  Introduction

   PPP has three main components:

      1. A method for encapsulating multi-protocol datagrams.

      2. A Link Control Protocol (LCP) for establishing, configuring,
         and testing the data-link connection.

      3. A family of Network Control Protocols for establishing and
         configuring different network-layer protocols.

   In order to establish communications over a point-to-point link, each
   end of the PPP link must first send LCP packets to configure and test
   the data link.  After the link has been established and optional
   facilities have been negotiated as needed by the LCP, PPP must send
   XNSCP packets to choose and configure the XNS IDP network-layer
   protocol.  Once XNSCP has reached the Opened state, XNS IDP datagrams
   can be sent over the link.

   The link will remain configured for communications until explicit LCP
   or XNSCP packets close the link down, or until some external event
   occurs (an inactivity timer expires or network administrator

1.1.  Specification of Requirements

   In this document, several words are used to signify the requirements
   of the specification.  These words are often capitalized.

   MUST      This word, or the adjective "required", means that the
             definition is an absolute requirement of the specification.

   MUST NOT  This phrase means that the definition is an absolute
             prohibition of the specification.

   SHOULD    This word, or the adjective "recommended", means that there
             may exist valid reasons in particular circumstances to
             ignore this item, but the full implications must be
             understood and carefully weighed before choosing a
             different course.

   MAY       This word, or the adjective "optional", means that this
             item is one of an allowed set of alternatives.  An
             implementation which does not include this option MUST be
             prepared to interoperate with another implementation which
             does include the option.

Senum                                                           [Page 2]

RFC 1764                       PPP XNSCP                      March 1995

1.2.  Terminology

   This document frequently uses the following terms:

   datagram  The unit of transmission in the network layer (such as IP).
             A datagram may be encapsulated in one or more packets
             passed to the data link layer.

   frame     The unit of transmission at the data link layer.  A frame
             may include a header and/or a trailer, along with some
             number of units of data.

   packet    The basic unit of encapsulation, which is passed across the
             interface between the network layer and the data link
             layer.  A packet is usually mapped to a frame; the
             exceptions are when data link layer fragmentation is being
             performed, or when multiple packets are incorporated into a
             single frame.

   peer      The other end of the point-to-point link.

   silently discard
             This means the implementation discards the packet without
             further processing.  The implementation SHOULD provide the
             capability of logging the error, including the contents of
             the silently discarded packet, and SHOULD record the event
             in a statistics counter.

2.  A PPP Network Control Protocol for XNS IDP

   The XNS IDP Control Protocol (XNSCP) is responsible for configuring,
   enabling, and disabling the XNS IDP protocol modules on both ends of
   the point-to-point link.  XNSCP uses the same packet exchange
   mechanism as the Link Control Protocol (LCP).  XNSCP packets may not
   be exchanged until PPP has reached the Network-Layer Protocol phase.
   XNSCP packets received before this phase is reached should be
   silently discarded.

   The XNS IDP Control Protocol is exactly the same as the Link Control
   Protocol [1] with the following exceptions:

   Frame Modifications

      The packet may utilize any modifications to the basic frame format
      which have been negotiated during the Link Establishment phase.

Senum                                                           [Page 3]

RFC 1764                       PPP XNSCP                      March 1995

   Data Link Layer Protocol Field

      Exactly one XNSCP packet is encapsulated in the Information field
      of a PPP Data Link Layer frame, where the PPP Protocol field
      indicates type hex 8025 (XNS IDP Control Protocol).

   Code field

      Only Codes 1 through 7 (Configure-Request, Configure-Ack,
      Configure-Nak, Configure-Reject, Terminate-Request, Terminate-Ack
      and Code-Reject) are used.  Other Codes should be treated as
      unrecognized and should result in Code-Rejects.


      XNSCP packets may not be exchanged until PPP has reached the
      Network-Layer Protocol phase.  An implementation should be
      prepared to wait for Authentication and Link Quality Determination
      to finish before timing out waiting for a Configure-Ack or other
      response.  It is suggested that an implementation give up only
      after user intervention or a configurable amount of time.

   Configuration Option Types

      XNSCP has no Configuration Options.

2.1.  Sending XNS IDP Datagrams

   Before any XNS IDP packets may be communicated, PPP must reach the
   Network-Layer Protocol phase, and the XNS IDP Control Protocol must
   reach the Opened state.

   Exactly one XNS IDP packet is encapsulated in the Information field
   of a PPP Data Link Layer frame where the Protocol field indicates
   type hex 0025 (XNS IDP datagram).

   The maximum length of a XNS IDP datagram transmitted over a PPP link
   is the same as the maximum length of the Information field of a PPP
   data link layer frame.  Since there is no standard method for
   fragmenting and reassembling XNS IDP datagrams, PPP links supporting
   XNS IDP MUST allow at least 576 octets in the information field of a
   data link layer frame.

   The format of the Information field itself is the same as that
   defined in [2].

Senum                                                           [Page 4]

RFC 1764                       PPP XNSCP                      March 1995

Security Considerations

   Security issues are not discussed in this memo.


   [1] Simpson, W., "The Point-to-Point Protocol (PPP)", STD 51, RFC
       1661, Daydreamer, July 1994.

   [2] Xerox, "Internet Transport Protocols", January 1991, Order No.
       XNSS 029101.


   Some of the text in this document is taken from previous documents
   produced by the Point-to-Point Protocol Working Group of the Internet
   Engineering Task Force (IETF).

   In particular, Bill Simpson provided the boiler-plate used to create
   this document.

Chair's Address

   The working group can be contacted via the current chair:

   Fred Baker
   Cisco Systems
   519 Lado Drive
   Santa Barbara, California 93111

   Phone: (805) 681-0115
   EMail: fred@cisco.com

Author's Address

   Questions about this memo can also be directed to:

   Steven J. Senum
   6400 Flying Cloud Drive
   Eden Prairie, Minnesota 55344

   Phone: (612) 943-9020
   EMail: sjs@digibd.com

Senum                                                           [Page 5]