rfc1552.txt

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Network Working Group                                         W. Simpson
Request for Comments: 1552                                    Daydreamer
Category: Standards Track                                  December 1993


     The PPP Internetwork Packet Exchange Control Protocol (IPXCP)


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 method for
   transmitting 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.

   The IPX protocol was originally used in Novell's NetWare products
   [3], and is now supported by numerous other vendors.  This document
   defines the Network Control Protocol for establishing and configuring
   the IPX protocol over PPP.

   This memo is the product of the Point-to-Point Protocol Working Group
   of the IETF.  Comments should be submitted to the ietf-
   [e-mail] mailing list.



















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RFC 1552                       PPP IPXCP                   December 1993


Table of Contents

   1.  Introduction ...................................................2
   1.1 Specification of Requirements ..................................3
   1.2 Terminology ....................................................3
   2.  A PPP Network Control Protocol for IPX .........................4
   2.1 Sending IPX Datagrams ..........................................5
   2.2 IPX-WAN protocol ...............................................5
   2.3 Desired Parameters .............................................5
   2.4 Co-existence with IPX-WAN ......................................6
   3.  IPXCP Configuration Options ....................................6
   3.1 IPX-Network-Number .............................................7
   3.2 IPX-Node-Number ................................................8
   3.3 IPX-Compression-Protocol .......................................9
   3.4 IPX-Routing-Protocol ...........................................11
   3.5 IPX-Router-Name ................................................12
   3.6 IPX-Configuration-Complete .....................................13
   APPENDIX A. Link Delay and Throughput ..............................14
   SECURITY CONSIDERATIONS ............................................14
   REFERENCES .........................................................15
   ACKNOWLEDGEMENTS ...................................................15
   CHAIR'S ADDRESS ....................................................15
   AUTHOR'S ADDRESS ...................................................16

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
   IPXCP packets to choose and configure the IPX network-layer protocol.
   Once IPXCP has reached the Opened state, IPX datagrams can be sent
   over the link.

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



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RFC 1552                       PPP IPXCP                   December 1993


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 should 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.


1.2 Terminology

   This document frequently uses the following terms:

    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.






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RFC 1552                       PPP IPXCP                   December 1993


    end-system

      A user's machine.  It only sends packets to servers and other
      end-systems.  It doesn't pass any packets through itself.

    router

      Allows packets to pass through, usually from one ethernet segment
      to another.  Sometimes these are called "intermediate-systems".

    half-router

      Two normal routers, with an unnumbered link between them.  Each
      looks like a router to the local users, but Netware doesn't
      understand unnumbered links, so each router is made to look like
      they both are a single machine.

2. A PPP Network Control Protocol for IPX

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

   The IPX 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.

    Data Link Layer Protocol Field

      Exactly one IPXCP packet is encapsulated in the Information field
      of a PPP Data Link Layer frame where the Protocol field indicates
      type hex 802B (IPX 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.




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RFC 1552                       PPP IPXCP                   December 1993


    Timeouts

      IPXCP 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

      IPXCP has a distinct set of Configuration Options.

2.1 Sending IPX Datagrams

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

   Exactly one IPX packet is encapsulated in the Information field of a
   PPP Data Link Layer frame where the Protocol field indicates type hex
   002B (IPX datagram).

   The maximum length of an IPX 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 IPX datagrams, PPP links supporting IPX MUST allow
   at least 576 octets in the information field of a data link layer
   frame.

2.2 IPX-WAN protocol

   A Novell specification called IPX-WAN [4] is intended to provide
   mechanisms similar to IPXCP negotiation over wide area links.  As
   viewed by PPP, IPX-WAN is a part of IPX, and IPX-WAN packets are
   indistinguishable from other IPX packets.

   Currently, Novell has implemented IPXCP without any Configuration
   Options, and requires successful IPX-WAN completion, even when all
   required parameters have been hand configured.  This makes it
   impossible for the current Novell products to interoperate with other
   IPXCP implementations which do not already include support for IPX-
   WAN.

2.3 Desired Parameters

   To resolve the possible conflict between the two configuration
   methods, this specification defines the concept of "Desired



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RFC 1552                       PPP IPXCP                   December 1993


   Parameters".  Where applicable, each Configuration Option indicates
   the environment where the parameter which is negotiated MAY be
   required by the implementation for proper operation.

   This determination is highly implementation dependent.  For example,
   a particular implementation might require that all links have
   addresses, while another implementation might not need such
   addresses.  The configuration negotiation is intended to discover
   that this pair of implementations will never converge.

2.4 Co-existence with IPX-WAN

   An IPXCP implementation which includes support for IPX-WAN SHOULD
   always reach Opened state, even when unable to negotiate some
   "Desired Parameter", and when no Configuration Options are
   successfully negotiated.  This allows IPX-WAN the opportunity to
   finish the negotiation.

   If an implementation does not include support for IPX-WAN, it SHOULD
   NOT reach Opened state when unable to negotiate some "Desired
   Parameter".

   IPX-WAN uses a "Timer Request" packet to set up the link.  These MUST
   NOT be sent until IPXCP has Opened the link.

   An implementation which provides both IPX-WAN and IPXCP Configuration
   Options capability SHOULD only send a Timer Request packet when a
   Timer Request packet is received, or upon failure to successfully
   negotiate a "Desired Parameter".

   If unable to complete IPX-WAN setup when a "Desired Parameter" is
   unknown, by default IPXCP SHOULD terminate the link.

   However, some implementations might be capable of operating without
   all indicated "Desired Parameters", in which case the termination
   MUST be configurable.

3. IPXCP Configuration Options

   IPXCP Configuration Options allow modifications to the standard
   characteristics of the network-layer protocol to be negotiated.  If a
   Configuration Option is not included in a Configure-Request packet,
   the default value for that Configuration Option is assumed.

   IPXCP uses the same Configuration Option format defined for LCP [1],
   with a separate set of Options.

   Up-to-date values of the IPXCP Option Type field are specified in the



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RFC 1552                       PPP IPXCP                   December 1993


   most recent "Assigned Numbers" RFC [2].  Current values are assigned
   as follows:

      1       IPX-Network-Number
      2       IPX-Node-Number
      3       IPX-Compression-Protocol
      4       IPX-Routing-Protocol
      5       IPX-Router-Name
      6       IPX-Configuration-Complete

3.1 IPX-Network-Number

   Description

      This Configuration Option provides a way to negotiate the IPX
      network number to be used for the link.  This allows an
      implementation to learn the network number, or to ensure agreement
      on the network number.

      The network number MUST be unique within the routing domain, or
      zero to indicate that it is not used for routing.

      The sender of the Configure-Request states which network number is
      desired.  A network number specified as zero in a Configure-
      Request shall be interpreted as requesting the peer to specify
      another value in a Configure-Nak.  A network number specified as
      zero in a Configure-Ack shall be interpreted as agreement that no
      value exists.

      Both ends of the link MUST have the same network number.  When a
      Configure-Request is received which has a lower network number
      than locally configured, a Configure-Nak MUST be returned with the
      highest network number.

      When the peer did not provide the option in its Configure-Request,
      the option SHOULD NOT be appended to a Configure-Nak.

      By default, no network number is assigned to the link (the network
      number is zero).  There is no need for a network number if the
      interface is not used by a routing protocol.

      This is a Desired Parameter when the implementation is operating
      as a router.  It MUST be negotiated if the network number is non-
      zero, and has been derived from another interface.

      Any IPX-WAN packets received MUST supercede information negotiated
      in this option.




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RFC 1552                       PPP IPXCP                   December 1993


    A summary of the IPX-Network-Number Configuration Option format is
    shown below.  The fields are transmitted from left to right.

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |     Type      |    Length     |       IPX-Network-Number      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |  IPX-Network-Number (cont.)   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       Type

          1

       Length

          6

       IPX-Network-Number

      The four octet IPX-Network-Number is the desired local IPX network
      number of the sender of the Configure-Request.  This number may be
      zero, which is interpreted as being a local network of unknown
      number that is not used by the routing protocol.

3.2 IPX-Node-Number

   Description

      This Configuration Option provides a way to negotiate the IPX node
      number to be used for the local end of the link.  This allows an
      implementation to learn its node number, or to inform the peer of
      its node number.

      The node number MUST be unique for the network number.

      The sender of the Configure-Request states which node number is
      desired.  A node number specified as zero in a Configure-Request
      shall be interpreted as requesting the peer to specify another
      value in a Configure-Nak.  A node number specified as zero in a
      Configure-Ack shall be interpreted as agreement that no value
      exists.

      If negotiation about the peer node number is required, and the
      peer did not provide the option in its Configure-Request, the
      option can be appended to a Configure-Nak.  The value of the node
      number given MUST be acceptable as the peer IPX-Node-Number, or



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