Network Working Group                                         D. Perkins
Request for Comments: 1134                                           CMU
                                                           November 1989


       The Point-to-Point Protocol: A Proposal for Multi-Protocol
          Transmission of Datagrams Over Point-to-Point Links


                           Table of Contents

   Status of this Memo ...................................    2
   Abstract ..............................................    2
   1. Introduction .......................................    2
   1.1 Motivation ........................................    2
   1.2 Overview of PPP ...................................    3
   1.3 Organization of the document ......................    4
   2. Physical Layer Requirements ........................    4
   3. The Data Link Layer ................................    4
   3.1 Frame Format ......................................    5
   4. The PPP Link Control Protocol (LCP) ................    8
   4.1 The LCP Automaton .................................    9
   4.1.1 Overview ........................................    9
   4.1.2 State Diagram ...................................   10
   4.1.3 State Transition Table ..........................   12
   4.1.4 Events ..........................................   12
   4.1.5 Actions .........................................   14
   4.1.6 States ..........................................   16
   4.2 Loop Avoidance ....................................   19
   4.3 Packet Format .....................................   19
   4.3.1 Configure-Request ...............................   21
   4.3.2 Configure-Ack ...................................   21
   4.3.3 Configure-Nak ...................................   22
   4.3.4 Configure-Reject ................................   24
   4.3.5 Terminate-Request and Terminate-Ack .............   25
   4.3.6 Code-Reject .....................................   26
   4.3.7 Protocol-Reject .................................   27
   4.3.8 Echo-Request and Echo-Reply .....................   28
   4.3.9 Discard-Request .................................   29
   4.4 Configuration Options .............................   30
   4.4.1 Format ..........................................   31
   5. A PPP Network Control Protocol (NCP) for IP ........   32
   5.1 Sending IP Datagrams ..............................   33
   APPENDICES ............................................   33
   A. Asynchronous HDLC ..................................   33
   B. Fast Frame Check Sequence (FCS) Implementation .....   35
   B.1 FCS Computation Method ............................   35
   B.2 Fast FCS table generator ..........................   36



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RFC 1134                          PPP                      November 1989


   REFERENCES ............................................   37
   AUTHOR'S ADDRESS ......................................   38

Status of this Memo

   This memo defines a proposed protocol for the Internet community.

   This proposal is the product of the Point-to-Point Protocol Working
   Group of the Internet Engineering Task Force (IETF).  Comments on this
   memo should be submitted to the IETF Point-to-Point Protocol Working
   Group chair by January 15, 1990.  Comments will be reviewed at the
   February 1990 IETF meeting, with the goal of advancing PPP to draft
   standard status.  Distribution of this memo is unlimited.

Abstract

   The Point-to-Point Protocol (PPP) provides a method for transmitting
   datagrams over serial point-to-point links.  PPP is composed of three
   parts:

      1. A method for encapsulating datagrams over serial links.

      2. An extensible Link Control Protocol (LCP).

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

   This document defines the encapsulation scheme, the basic LCP, and an
   NCP for establishing and configuring the Internet Protocol (IP)
   (called the IP Control Protocol, IPCP).

   The options and facilities used by the LCP and the IPCP are defined
   in separate documents.  Control protocols for configuring and
   utilizing other network-layer protocols besides IP (e.g., DECNET,
   OSI) are expected to be developed as needed.

.  Introduction

1.1.  Motivation

   In the last few years, the Internet has seen explosive growth in the
   number of hosts supporting TCP/IP.  The vast majority of these hosts
   are connected to Local Area Networks (LANs) of various types,
   Ethernet being the most common.  Most of the other hosts are
   connected through Wide Area Networks (WANs) such as X.25 style Public
   Data Networks (PDNs).  Relatively few of these hosts are connected
   with simple point-to-point (i.e., serial) links.  Yet, point-to-point
   links are among the oldest methods of data communications and almost



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RFC 1134                          PPP                      November 1989


   every host supports point-to-point connections.  For example,
   asynchronous RS-232-C [1] interfaces are essentially ubiquitous.

   One reason for the small number of point-to-point IP links is the
   lack of a standard encapsulation protocol.  There are plenty of non-
   standard (and at least one defacto standard) encapsulation protocols
   available, but there is not one which has been agreed upon as an
   Internet Standard.  By contrast, standard encapsulation schemes do
   exist for the transmission of datagrams over most popular LANs.

   One purpose of this memo is to remedy this problem.  But even more
   importantly, the Point-to-Point Protocol proposes more than just an
   encapsulation scheme.  Point-to-Point links tend to exacerbate many