The PPP AppleTalk Control Protocol (ATCP)

Network Working Group                                          B. Parker
Request for Comments: 1378                                Cayman Systems
                                                           November 1992


               The PPP AppleTalk Control Protocol (ATCP)

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
   AppleTalk Protocol [3] over PPP.

   This memo is a joint effort of the AppleTalk-IP Working Group and the
   Point-to-Point Protocol Working Group of the Internet Engineering
   Task Force (IETF).  Comments on this memo should be submitted to the
   ietf-ppp@ucdavis.edu mailing list.

Table of Contents

   1.     Introduction ..........................................    2
   2.     A PPP Network Control Protocol (NCP) for AppleTalk ....    2
   2.1    Sending AppleTalk Datagrams ...........................    3
   2.2    Half-Routers ..........................................    4
   3.     ATCP Configuration Options ............................    4
   3.1    AppleTalk-Address .....................................    5
   3.2    Routing-Protocol ......................................    7
   3.3    Suppress-Broadcasts ...................................    8
   3.4    AT-Compression-Protocol ...............................    9
   3.5    Server-information ....................................   10
   3.6    Zone-Information ......................................   12
   3.7    Default-Router-Address ................................   13
   APPENDICES ...................................................   14
   A.     ATCP Recommended Options ..............................   14
   REFERENCES ...................................................   15
   ACKNOWLEDGEMENTS .............................................   15
   SECURITY CONSIDERATIONS ......................................   16
   CHAIR'S ADDRESS ..............................................   16
   AUTHOR'S ADDRESS .............................................   16

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).

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

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

   The AppleTalk 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 ATCP packet is encapsulated in the Information field
      of a PPP Data Link Layer frame where the Protocol field indicates
      type hex 8029 (AppleTalk 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

      ATCP 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

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

2.1.  Sending AppleTalk Datagrams

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

   Unless otherwise negotiated (via option 4), exactly one AppleTalk
   packet is encapsulated in the Information field of a PPP Data Link
   Layer frame where the Protocol field indicates type hex 0029
   (AppleTalk).

   Note that the negotiation of compression may imply the use of
   different encapsulation and hence different protocol fields.  These
   different protocol fields imply packet types which are sub-protocols
   of the base AppleTalk NCP.

   An encapsulated AppleTalk packet begins with an extended DDP
   (Datagram Delivery Protocol) header -- also known as a Long DDP
   header.  The maximum length of a DDP datagram is 599 octets.

   Since there is no standard method for fragmenting and reassembling
   AppleTalk datagrams, it is required that PPP links supporting
   AppleTalk allow at least 599 octets in the information field of a
   data link layer frame.

2.2.  Half-Routers

   One model for routers in [3] is two remote AppleTalk routers linked
   as "half-routers" without a Node ID or Network number assigned to
   either side of the link.  When acting as half-routers, the only
   effect on transported packets is that the hop count is incremented
   when it is received over the link.  Routing updates received over a
   half-router link should also increment the hop count of routing table
   updates.

   As part of normal operation, AppleTalk will send RTMP Routing updates
   every 10 seconds.

3.  ATCP Configuration Options

   ATCP Configuration Options allow negotiation of desirable AppleTalk
   parameters.  ATCP uses the same Configuration Option format defined
   for LCP [1], with a separate set of Options.

   The most up-to-date values of the ATCP Option Type field are
   specified in the most recent "Assigned Numbers" RFC [2].  Current
   values are assigned as follows:

   1       AppleTalk-Address

   2       Routing-Protocol

   3       Suppress-Broadcasts

   4       AT-Compression-Protocol

   5       RESERVED

   6       Server-information

   7       Zone-information

   8       Default-Router-Address

3.1.  AppleTalk-Address

   Description

      This Configuration Option provides a way to negotiate the
      AppleTalk network and node number to be used on the local end of
      the link.  It allows the sender of the Configure-Request to state
      which AppleTalk-address is desired, or to request that the peer
      provide the information.  The peer can provide this information by
      NAKing the option, and returning a valid AppleTalk-address.

      If negotiation about the remote AppleTalk-address is required, and
      the peer did not provide the option in its Configure-Request, the
      option SHOULD be appended to a Configure-Nak.  The value of the
      AppleTalk-address given must be acceptable as the remote
      AppleTalk-address, or indicate a request that the peer provide the
      information.

      By default, no AppleTalk address is assigned.  A network or node
      number specified as zero in a Configure-Request shall be
      interpreted as requesting the remote end to specify a value via a
      Configure-Nak.  A network or node number specified as zero in a
      Configure-Ack shall be interpreted as agreement that no value
      exists.

      An implementation which requires that no AppleTalk addresses be
      assigned (such as a intermediate system to intermediate system
      "half-routing") MUST Configure-Reject all AppleTalk-Address
      Configuration Options.

      An implementation which requires that AppleTalk addresses be
      assigned to it (such as a end system) MUST fail configuration if
      the remote side Configure-Rejects all AppleTalk-Address requests,
      or fails to provide a valid value.

      If this option is negotiated, the two sides MUST negotiate a
      common AppleTalk network number and two unique Appletalk node
      numbers.  The network number MAY be zero but the Appletalk node
      numbers MUST be non-zero.  Values selected for network and node
      numbers must adhere to the ranges defined in [3].

      The AppleTalk protocol, phase 2, defines the concept of "extended"
      and "non-extended" networks.  Extended networks can support a
      large number (hundreds) of nodes, and requires multiple network
      numbers and multiple zone names to be managed effectively.  Non-
      extended networks can only support a small number of devices, and
      require only a single network number and zone name to be managed
      effectively.

      If a PPP link transporting AppleTalk is assigned an AppleTalk
      address, it must have the "non-extended" characteristics as
      defined in [3].

      The format of the network and node data is defined to be the same
      as the "AppleTalk address" in [3], chapter 3, "AppleTalk AARP
      packet formats on Ethernet and token ring".

   A summary of the AppleTalk-Address 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     |    Reserved   |     AT-Net    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     AT-Net    |    AT-Node    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   Type

      1

   Length

      6

   Reserved

      This octet is reserved and MUST be set to zero on transmission and
      ignored on reception.

   AT-Net

      The two octet AT-Net is the desired local AppleTalk network number
      of the sender of the Configure-Request.  This two octet quantity
      represents a 16 bit unsigned number sent "network byte order"
      (most significant octet first).

   AT-Node

      The one octet AT-Node is the desired local AppleTalk node ID of
      the sender of the Configure-Request.

3.2.  Routing-Protocol

   Description

      This Configuration Option provides a way to negotiate the use of a
      specific routing protocol.  In particular, "half-routers" may want
      to exchange routing information using a protocol optimized for the
      PPP connection.  By default, AppleTalk RTMP (Routing Table
      Maintenance Protocol) routing information is sent over the PPP
      connection.

      By default, AppleTalk RTMP routing information is sent over the
      PPP connection.

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


   Type

      2

   Length

      >= 4

   Routing-Protocol

      The Routing-Protocol field is two octets and indicates the type of
      Routing-Protocol desired.  This two octet quantity represents a 16
      bit number sent "network byte order" (most significant octet
      first).

      Negotiation of some routing protocols implies that you will
      receive packet types which transport these protocols.

      For example, negotiating AppleTalk AURP to exchange routing
      information implies both sides will accept EDDP type packets,
      since this is the transport type used by AURP.

      Initial values are assigned as follows:

      Value       Protocol

        0         No routing information exchange
        1         AppleTalk RTMP is used to exchange routing information
        2         AppleTalk AURP is used to exchange routing information
        3         AppleTalk ABGP is used to exchange routing information


   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.

      None of the Routing-Protocol options defined here require
      additional data.

3.3.  Suppress-Broadcasts

   Description

      This Configuration Option provides a way to negotiate the
      suppression of AppleTalk broadcast datagrams which might otherwise
      use up limitted PPP bandwidth.  This Configuration Option is used
      to inform the remote end that no AppleTalk broadcast datagrams of
      a given DDP type should be sent.

      This option is useful when negotiated by a single end system.  It
      allows the local end system to request that broadcast packets
      generated on a remote network not be propagated across the PPP
      link.  In the case of a single end system connected to a large
      network, this can be used to suppress regular NBP lookups
      generated by other end systems on the remote network.  This will
      mean that protocols such as NBP can no longer be used to find
      network entities on the local system, but since the option
      configuration is asymmetric, it does not inhibit the local
      system's ability to find network entities on the remote network.

      By default, no AppleTalk broadcast datagrams are suppressed.  Note
      that this option may conflict with other options (such as Routing
      Protocol).  If so, the Suppress-Broadcasts option takes
      precedence.

   A summary of the Suppress-Broadcasts 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     |  DDP-Type  1  |  DDP-Type  2  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | etc...
   +-+-+-+-+


   Type

      3

   Length

      >= 2

   DDP-Types

      A vector of one or more single octet DDP type values, each of
      which are to be suppressed if sent to the broadcast address.

      If no data is present (the length = 2), all broadcast packets are
      to be suppressed, regardless of DDP type.

3.4.  AT-Compression-Protocol

   Description

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

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


   Type

      4
   Length

      >= 4

   AT-Compression-Protocol

      The AT-Compression-Protocol field is two octets and indicates the
      compression protocol desired.  Values for this field are always
      the same as the PPP Data Link Layer Protocol field values for that
      same compression protocol.

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


         Value (in hex)          Protocol

                                 none defined


   Data

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

3.5.  Server-information

   Description

      This Configuration Option provides a way to obtain information
      about the communications server providing the remote side of the
      PPP connection.

      The nature of this option is advisory only.  It is provided as a
      means of improving an end system's ability to provide a simple
      user interface.

   A summary of the Server-Information 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     |          Server-class         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Server-implementation-id                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Server-name ...
   +-+-+-+-+-+-+-+-+-+-+-+-+


   Type

      6

   Length

      >= 8

   Server-class

      The Server-class field is two octets and indicates the class of
      the communication server providing the remote end of the PPP
      connection.

      Initial values are assigned as follows:

      Value        Class

        1          AppleTalk PPP Dial-in server.

                   The server-implementation-id is a four byte version
                   id, with the first byte defined as the major
                   version number (1-255) and the second byte defined
                   as the minor version number (1-255).

                   The third and fourth bytes are undefined and should
                   be zero.

        2          Generic AppleTalk PPP implementation.

                   The server-implementation-id is undefined and
                   vendor specific.

        3          Both dial-in server and router

   Server-implementation-id

      The Server-implementation-id field is four octets and indicates
      the version of the communication server providing the remote end
      of the PPP connection.

   Server-name

      This optional field contains the "AppleTalk ASCII" name of the
      server.  The character codes used in "AppleTalk ASCII" are defined
      in [3], appendix D, "Character codes".  The length of the name is
      bounded by the option length.

3.6.  Zone-Information

   Description

      This Configuration Option provides a way to obtain information
      about the AppleTalk zone used for the PPP connection.

      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.

   A summary of the Zone-Information 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     |           Zone-name...        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   Type

      7

   Length

      >= 3

   Zone-name

      This field contains the "AppleTalk ASCII" zone name in which the
      server resides.  The character codes used in "AppleTalk ASCII" are
      defined in [3], appendix D, "Character codes".  The length of the
      name is bounded by the option length.

3.7.  Default-Router-Address

   Description


      This Configuration Option provides a way to obtain information
      about a "default" Appletalk router which may be used to obtain
      network information such as zone names.  It is provided as a means
      of obtaining the address of a router in the case both sides of the
      link are end systems.

      Any AppleTalk RTMP packets received should supercede information
      negotiated in this option.

      By default, no default router is present.

   A summary of the Default-Router-Address 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     |    Reserved   |     AT-Net    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     AT-Net    |    AT-Node    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   Type

      8

   Length

      6

   Reserved

      This octet is reserved and MUST be set to zero on transmission and
      ignored on reception.

   AT-Net

      The two octet AT-Net is the AppleTalk network number of the
      default router.  This two octet quantity represents a 16 bit
      unsigned number sent in "network byte order" (most significant
      octet first).

   AT-Node

      The one octet AT-Node is the AppleTalk node ID of the default
      router.

A.  ATCP Recommended Options

   The ATCP is designed to support three different modes of operation.
   Each mode places constraints on the configuration options used and
   the values negotiated.

   The options for server information, zone information and default
   router address are "informational" options provided by one end of the
   connection and are not intended to be negotiated.  These options are
   provided to support a higher level of service to dial-in end systems.

   The options which SHOULD be negotiated in each case are outlined
   below.  Any option not listed may be rejected.

End System to Intermediate System - "dial-in"

   This mode of operation is intended to support end system dial-in.

         1       AppleTalk-Address (required)
         2       Routing-Protocol (required, no routing protocol)
         3       Suppress-Broadcasts (optional)
         4       AT-Compression-Protocol (optional)
         6       Server-information (optional, request from end system)

Intermediate system to Intermediate system - with network number

   This mode of operation is intended to support WAN-to-WAN, i.e.,
   router to router, connections where the link is configured with a
   network number.

         1      AppleTalk-Address (required, nets must be zero or equal)
         2      Routing-Protocol (optional)
         3      Suppress-Broadcasts (optional)

Intermediate system to Intermediate system - without network number

   This mode of operation is intended to support WAN-to-WAN, i.e.,
   router to router, connections where the link is not configured with a
   network number.  Routers in this mode are referred to as "half-
   routers" in [3].

         1      AppleTalk-Address (optional, nets & nodes MUST be zero)
         2      Routing-Protocol (optional)
         3      Suppress-Broadcasts (optional, suppress all broadcasts)

References

   [1] Simpson, W., "The Point-to-Point Protocol (PPP)", RFC 1331,
       Daydreamer, May 1992.

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

   [3] Sidhu G., Andrews, R., and A. Oppenheimer, "Inside AppleTalk,
       Second Edition", Addison-Wesley Publishing Company, Inc., May
       1990.

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:

   Steve Senum (sjs@network.com), Network Systems Corporation
   Jim Muchow (muchow@anubis.network.com), Network Systems Corporation
   Frank Slaughter (fgs@Shiva.COM), Shiva Corporation

Security Considerations

   Security issues are not discussed in this memo.

Chair's Address

   The working groups can be contacted via the current chairs:

   Brian Lloyd
   Lloyd & Associates
   3420 Sudbury Road
   Cameron Park, California 95682

   Phone: (916) 676-1147
   EMail: brian@lloyd.com


   John Veizades
   Apple Computer, Inc.
   20525 Mariani Avenue
   Cupertino, CA 95014

   Phone: (408) 996-1010
   EMail: veizades@apple.com

Author's Address

   Questions about this memo can also be directed to:

   Brad Parker
   Cayman Systems, Inc.
   26 Landsdowne Street
   Cambridge, Ma 02139

   EMail: brad@cayman.com