rfc1332.txt

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Network Working Group                                        G. McGregor
Request for Comments: 1332                                         Merit
Obsoletes: RFC 1172                                             May 1992



           The PPP Internet Protocol Control Protocol (IPCP)



Status of this Memo

   This RFC specifies an IAB standards track protocol for the Internet
   community, and requests discussion and suggestions for improvements.
   Please refer to the current edition of the "IAB Official Protocol
   Standards" 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 of
   encapsulating Network Layer protocol information over point-to-point
   links.  PPP also defines an extensible Link Control Protocol, and
   proposes a family of Network Control Protocols (NCPs) for
   establishing and configuring different network-layer protocols.

   This document defines the NCP for establishing and configuring the
   Internet Protocol [2] over PPP, and a method to negotiate and use Van
   Jacobson TCP/IP header compression [3] with PPP.

   This RFC is a product of the Point-to-Point Protocol Working Group of
   the Internet Engineering Task Force (IETF).



















McGregor                                                        [Page i]

RFC 1332                        PPP IPCP                        May 1992


Table of Contents


     1.     Introduction ..........................................    1

     2.     A PPP Network Control Protocol (NCP) for IP ...........    2
        2.1       Sending IP Datagrams ............................    2

     3.     IPCP Configuration Options ............................    4
        3.1       IP-Addresses ....................................    5
        3.2       IP-Compression-Protocol .........................    6
        3.3       IP-Address ......................................    8

     4.     Van Jacobson TCP/IP header compression ................    9
        4.1       Configuration Option Format .....................    9

     APPENDICES ...................................................   11

     A.     IPCP Recommended Options ..............................   11

     SECURITY CONSIDERATIONS ......................................   11

     REFERENCES ...................................................   11

     ACKNOWLEDGEMENTS .............................................   11

     CHAIR'S ADDRESS ..............................................   12

     AUTHOR'S ADDRESS .............................................   12






















McGregor                                                       [Page ii]

RFC 1332                        PPP IPCP                        May 1992


1.  Introduction

   PPP has three main components:

      1. A method for encapsulating datagrams over serial links.

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

      3. A family of Network Control Protocols (NCPs) 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
   NCP packets to choose and configure one or more network-layer
   protocols.  Once each of the chosen network-layer protocols has been
   configured, datagrams from each network-layer protocol can be sent
   over the link.

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


























McGregor                                                        [Page 1]

RFC 1332                        PPP IPCP                        May 1992


2.  A PPP Network Control Protocol (NCP) for IP

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

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

   Data Link Layer Protocol Field

      Exactly one IPCP packet is encapsulated in the Information field
      of PPP Data Link Layer frames where the Protocol field indicates
      type hex 8021 (IP 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.

   Timeouts

      IPCP 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

      IPCP has a distinct set of Configuration Options, which are
      defined below.

2.1.  Sending IP Datagrams

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

   Exactly one IP packet is encapsulated in the Information field of PPP
   Data Link Layer frames where the Protocol field indicates type hex
   0021 (Internet Protocol).



McGregor                                                        [Page 2]

RFC 1332                        PPP IPCP                        May 1992


   The maximum length of an IP packet transmitted over a PPP link is the
   same as the maximum length of the Information field of a PPP data
   link layer frame.  Larger IP datagrams must be fragmented as
   necessary.  If a system wishes to avoid fragmentation and reassembly,
   it should use the TCP Maximum Segment Size option [4], and MTU
   discovery [5].













































McGregor                                                        [Page 3]

RFC 1332                        PPP IPCP                        May 1992


3.  IPCP Configuration Options

IPCP Configuration Options allow negotiatiation of desirable Internet
Protocol parameters.  IPCP uses the same Configuration Option format
defined for LCP [1], with a separate set of Options.

The most up-to-date values of the IPCP Option Type field are specified
in the most recent "Assigned Numbers" RFC [6].  Current values are
assigned as follows:

   1       IP-Addresses
   2       IP-Compression-Protocol
   3       IP-Address






































McGregor                                                        [Page 4]

RFC 1332                        PPP IPCP                        May 1992


3.1.  IP-Addresses

   Description

      The use of the Configuration Option IP-Addresses has been
      deprecated.  It has been determined through implementation
      experience that it is difficult to ensure negotiation convergence
      in all cases using this option.  RFC 1172 [7] provides information
      for implementations requiring backwards compatability.  The IP-
      Address Configuration Option replaces this option, and its use is
      preferred.

      This option SHOULD NOT be sent in a Configure-Request if a
      Configure-Request has been received which includes either an IP-
      Addresses or IP-Address option.  This option MAY be sent if a
      Configure-Reject is received for the IP-Address option, or a
      Configure-Nak is received with an IP-Addresses option as an
      appended option.

      Support for this option MAY be removed after the IPCP protocol
      status advances to Internet Draft Standard.






























McGregor                                                        [Page 5]