PPP LCP Extensions
RFC 1570

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Network Working Group                                 W. Simpson, Editor
Request for Comments: 1570                                    Daydreamer
Updates: 1548                                               January 1994
Category: Standards Track

                           PPP LCP Extensions

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

   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 (LCP) for establishing,
   configuring, and testing the data-link connection.  This document
   defines several additional LCP features which have been suggested
   over the past few years.

   This document is the product of the Point-to-Point Protocol Working
   Group of the Internet Engineering Task Force (IETF).  Comments should
   be submitted to the ietf-ppp@ucdavis.edu mailing list.

Table of Contents

     1.     Additional LCP Packets ................................    1
        1.1       Identification ..................................    1
        1.2       Time-Remaining ..................................    3
     2.     Additional LCP Configuration Options ..................    6
        2.1       FCS-Alternatives ................................    6
           2.1.1  LCP considerations ..............................    7
           2.1.2  Null FCS ........................................    8
        2.2       Self-Describing-Padding .........................    9
        2.3       Callback ........................................   11
        2.4       Compound-Frames .................................   12
           2.4.1  LCP considerations ..............................   14
     APPENDICES ...................................................   15
     A.     Fast Frame Check Sequence (FCS) Implementation ........   15
        A.1       32-bit FCS Computation Method ...................   15
     SECURITY CONSIDERATIONS ......................................   17
     REFERENCES ...................................................   17
     ACKNOWLEDGEMENTS .............................................   18
     CHAIR'S ADDRESS ..............................................   18
     EDITOR'S ADDRESS .............................................   18

Simpson                                                         [Page i]

RFC 1570                   PPP LCP extensions               January 1994

1.  Additional LCP Packets

   The Packet format and basic facilities are already defined for LCP
   [1].

   Up-to-date values of the LCP Code field are specified in the most
   recent "Assigned Numbers" RFC [2].  This specification concerns the
   following values:

      12      Identification
      13      Time-Remaining

1.1.  Identification

   Description

      This Code provides a method for an implementation to identify
      itself to its peer.  This Code might be used for many diverse
      purposes, such as link troubleshooting, license enforcement, etc.

      Identification is a Link Maintenance packet.  Identification
      packets MAY be sent at any time, including before LCP has reached
      the Opened state.

      The sender transmits a LCP packet with the Code field set to 12
      (Identification), the Identifier field set, the local Magic-Number
      (if any) inserted, and the Message field filled with any desired
      data, but not exceeding the default MRU minus eight.

      Receipt of an Identification packet causes the RXR or RUC event.
      There is no response to the Identification packet.

      Receipt of a Code-Reject for the Identification packet SHOULD
      generate the RXJ+ (permitted) event.

      Rationale:

         This feature is defined as part of LCP, rather than as a
         separate PPP Protocol, in order that its benefits may be
         available during the earliest possible stage of the Link
         Establishment phase.  It allows an operator to learn the
         identification of the peer even when negotiation is not
         converging.  Non-LCP packets cannot be sent during the Link
         Establishment phase.

Simpson                                                         [Page 1]

RFC 1570                   PPP LCP extensions               January 1994

         This feature is defined as a separate LCP Code, rather than a
         Configuration-Option, so that the peer need not include it with
         other items in configuration packet exchanges, and handle
         "corrected" values or "rejection", since its generation is both
         rare and in one direction.  It is recommended that