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Network Working Group                                          B. ParkerRequest for Comments: 1378                                Cayman Systems                                                           November 1992The 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 Contents1.     Introduction ..........................................22.     A PPP Network Control Protocol (NCP) for AppleTalk ....22.1    Sending AppleTalk Datagrams ...........................32.2    Half-Routers ..........................................43.     ATCP Configuration Options ............................43.1    AppleTalk-Address .....................................53.2    Routing-Protocol ......................................73.3    Suppress-Broadcasts ...................................83.4    AT-Compression-Protocol ...............................93.5    Server-information ....................................103.6    Zone-Information ......................................123.7    Default-Router-Address ................................13   APPENDICES ...................................................14A.     ATCP Recommended Options ..............................14   REFERENCES ...................................................15Parker                                                          [Page 1]

RFC 1378                        PPP ATCP                   November 1992   ACKNOWLEDGEMENTS .............................................15   SECURITY CONSIDERATIONS ......................................16   CHAIR'S ADDRESS ..............................................16   AUTHOR'S ADDRESS .............................................161.  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.Parker                                                          [Page 2]

RFC 1378                        PPP ATCP                   November 1992   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 reassemblingParker                                                          [Page 3]

RFC 1378                        PPP ATCP                   November 1992   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-AddressParker                                                          [Page 4]

RFC 1378                        PPP ATCP                   November 19923.1.  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.Parker                                                          [Page 5]

RFC 1378                        PPP ATCP                   November 1992      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.Parker                                                          [Page 6]

RFC 1378                        PPP ATCP                   November 19923.2.  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.Parker                                                          [Page 7]

RFC 1378                        PPP ATCP                   November 1992      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.Parker                                                          [Page 8]

RFC 1378                        PPP ATCP                   November 1992    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      4Parker                                                          [Page 9]

RFC 1378                        PPP ATCP                   November 1992   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.Parker                                                         [Page 10]

RFC 1378                        PPP ATCP                   November 1992    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 routerParker                                                         [Page 11]

RFC 1378                        PPP ATCP                   November 1992   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.Parker                                                         [Page 12]

RFC 1378                        PPP ATCP                   November 19923.7.  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).Parker                                                         [Page 13]

RFC 1378                        PPP ATCP                   November 1992   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)Parker                                                         [Page 14]

RFC 1378                        PPP ATCP                   November 1992Intermediate 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 CorporationParker                                                         [Page 15]

RFC 1378                        PPP ATCP                   November 1992Security 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.comAuthor'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.comParker                                                         [Page 16]