The PPP Internetworking Packet Exchange Control Protocol (IPXCP)

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-
   ppp@ucdavis.edu mailing list.

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).

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.

    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.

    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
   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
   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.

    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
      indicate with a zero value that the peer provide the information.

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

      This is a Desired Parameter when the implementation is operating
      as an end-system.  However, when the node number has been
      statically configured, this option SHOULD NOT be negotiated unless
      requested by the peer.

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

    A summary of the IPX-Node-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-Node-Number         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     IPX-Node-Number (cont.)                   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Type

         2

      Length

         8

      IPX-Node-Number

      The six octet IPX-Node-Number is the desired local IPX node number
      of the sender of the Configure-Request.

3.3 IPX-Compression-Protocol

   Description

      This Configuration Option provides a way to negotiate the use of a
      specific compression protocol.  By default, compression is not
      enabled.

      The sender of this Configuration Option indicates that it can
      receive packets with the specified compression technique.  A
      Configure-Ack MAY obligate the peer to send such packets,
      depending on the protocol negotiated.

      Information negotiated in this option MUST supercede any IPX-WAN
      packets received, since IPX-WAN packets could be affected by the
      compression technique.

    A summary of the IPX-Compression-Protocol 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-Compression-Protocol    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     Data ...
      +-+-+-+-+

      Type

         3

      Length

         >= 4

      IPX-Compression-Protocol

   The IPX-Compression-Protocol field is two octets and indicates the
   compression protocol desired.  Odd values for this field are always
   the same as the PPP Data Link Layer Protocol field values for that
   same compression protocol.  Even values are used when the compression
   protocol is interleaved with IPX packets.

   Up-to-date values of the IPX-Compression-Protocol field are specified
   in the most recent "Assigned Numbers" RFC [2].  Current values are
   assigned as follows:

            Value (in hex)  Protocol

            0002            Telebit Compressed IPX
            0235            Shiva Compressed NCP/IPX

    Data

      The Data field is zero or more octets and contains additional data
      as determined by the particular compression protocol.

3.4 IPX-Routing-Protocol

   Description

      This Configuration Option provides a way to negotiate the use of a
      specific routing protocol (or no routing protocol, if desired).
      The sender of this option is specifying that it wishes to receive
      information of the specified routing protocol.  Multiple protocols
      MAY be requested by sending multiple IPX-Routing-Protocol
      Configuration Options.  The "no routing protocol required" value
      is mutually exclusive with other values.

      By default, Novell's combination of Routing Information Protocol
      (RIP) and Server Advertising Protocol (SAP) is expected.

      This is a Desired Parameter when the implementation is operating
      as an end-system, to indicate that no routing protocol is
      necessary.

      Any IPX-WAN packets received MAY add to information negotiated in
      this option.

    A summary of the IPX-Routing-Protocol 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-Routing-Protocol      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     Data ...
      +-+-+-+-+

      Type

         4

      Length

         >= 4

      IPX-Routing-Protocol

      The IPX-Routing-Protocol field is two octets and indicates the
      type of Routing-Protocol desired.  This two octet quantity is sent
      most significant octet first.

      Up-to-date values of the IPX-Routing-Protocol field are specified
      in the most recent "Assigned Numbers" RFC [2].  Current values are
      assigned as follows:

      Value           Protocol

        0             No routing protocol required
        1             RESERVED
        2             Novell RIP/SAP required
        4             Novell NLSP required


    Data

      The Data field is zero or more octets and contains additional data
      as determined by the routing protocol indicated in the Routing-
      Protocol field.

3.5 IPX-Router-Name

   Description

      This Configuration Option provides a way to convey information
      about the IPX server name.

      The nature of this option is advisory only.  It is provided as a
      means of improving the end system's ability to provide a simple
      user interface.  This option MUST NOT be included in a Configure-
      Nak.

    A summary of the IPX-Router-Name 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     |           Name...             |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       Type

          5

       Length

          >= 3

    Name

      This field contains the name of the IPX entity on this end of the
      link.  The symbolic name should be between 1 and 47 ASCII
      characters in length, containing the characters 'A' through 'Z',
      underscore (_), hyphen (-) and "at" sign (@).  The length of the
      name is bounded by the option length.

      On reception, the name SHOULD be padded to 48 characters using the
      NUL character.  Those readers familiar with NetWare 3.x servers
      will realize that this is equivalent to the file server name.

3.6 IPX-Configuration-Complete

   Description

      This Configuration Option provides a way to indicate that all
      implementation-dependent Desired Parameters are satisfied.  It is
      provided as a means of detecting when convergence will occur in a
      heterogeneous environment.

      This option SHOULD be included in a Configure-Request when the
      combination of statically configured parameters and offered
      Configuration Options will result in successful configuration.

      The nature of this option is advisory only.  This option MUST NOT
      be included in a Configure-Nak.

      Implementation Note: An implementation which does not support
      IPX-WAN can immediately detect that link setup will not be
      successful when a Desired Parameter is unknown, if this option is
      not present in the peer's Configure-Request or is Rejected by the
      peer.  This avoids timeout delays.

      An implementation which supports IPX-WAN may improve link setup
      time by skipping IPX-WAN entirely when this option has been Ack'd
      in both directions.

      However, it is perfectly acceptable to complete configuration
      without including this option.  An implementation which includes
      the entire panoply of configuration options and IPX- WAN SHOULD
      interoperate with an implementation which does not support IPX-WAN
      nor any configuration options (including this one), as long as the
      Desired Parameters are satisfied by default or hand configuration.

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

        0                   1
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |     Type      |    Length     |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       Type

          6

       Length

          2

APPENDIX A. Link Delay and Throughput

   There has been some concern over correctly estimating the link delay
   (in 55 millisecond ticks) used by Novell routing protocols.

   IPX-WAN uses its Timer Request and Reply for this purpose.  The
   measured delay is multiplied by a factor of 6, because the
   measurement is done during initialization of the link, and does not
   reflect actual loading.

   The delay is better measured using the PPP LCP Echo facility, by
   inserting a timestamp in the data part of the Request, and comparing
   it with the same timer when the reply returns.  This method could be
   used to periodically re-evaluate the actual round trip delay as link
   and system loads change.  The echo packet size SHOULD be 576, to
   match the default IPX packet size.

   In the absence of such dynamic measurements, empirical evidence has
   shown the following to be sufficient:

                2,400 bps    134 ticks
               14,400 bps     21 ticks
               57,600 bps      5 ticks
                 >  1 Mbps     1 tick

Security Considerations

   Security issues are not discussed in this memo.

References

   [1] Simpson, W., "The Point-to-Point Protocol (PPP)", RFC 1548,
       Daydreamer, December 1993.

   [2] Reynolds, J., and J. Postel, "Assigned Numbers", STD 2, RFC 1340,
       USC/Information Sciences Institute, July 1992.

   [3] Novell Inc., "NetWare System Interface Technical Overview",
       Novell Part Number 883-001143-001.

   [4] Allen, M., "Novell IPX Over Various WAN Media", RFC 1551,
       Novell Inc., December 1993.

   [5] Mathu, S., and M. Lewis, "Compressing IPX Headers Over WAN
       Media (CIPX)", RFC 1553, Telebit Corporation, December 1993.

Acknowledgments

   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).

   This document is derivative of drafts written by the following
   people.  Many thanks for their work, and for taking an initial stab
   at the protocol:

         Michael Allen (mallen@novell.com)
         Dave McCool (dave@shiva.com)
         Robert D Vincent (bert@shiva.com)
         Marty Del Vecchio (marty@shiva.com)

Chair's Address

   The working group can be contacted via the current chair:

      Fred Baker
      Advanced Computer Communications
      315 Bollay Drive
      Santa Barbara, California, 93111

      EMail: fbaker@acc.com

Author's Address

   Questions about this memo can also be directed to:

      William Allen Simpson
      Daydreamer
      Computer Systems Consulting Services
      P O Box 6205
      East Lansing, MI  48826-6205

      EMail: Bill.Simpson@um.cc.umich.edu