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Network Working Group                                           A. FuquaRequest for Comments: 2043                                           IBMCategory: Standards Track                                   October 1996The PPP SNA Control Protocol (SNACP)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 standard method for   transporting 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.   This document defines the Network Control Protocols for establishing   and configuring Systems Network Architecture (SNA) over PPP and SNA   over LLC 802.2 over PPP.Table of Contents1.     Introduction ..........................................21.1       Specification of Requirements ...................21.2       Terminology .....................................32.     A PPP Network Control Protocol for SNA ................43.     Sending SNA PIUs and NLPs. ............................53.1       Sending SNA XID or FID2 PIUs over LLC ...........53.2       Sending HPR Network Layer Packets (NLPs) ........53.3       Other Considerations ............................6   SECURITY CONSIDERATIONS ......................................6   REFERENCES ...................................................6   ACKNOWLEDGEMENTS... ..........................................7   CHAIR'S ADDRESS ..............................................7   AUTHOR'S ADDRESS .............................................7Fuqua                       Standards Track                     [Page 1]

RFC 2043                       PPP SNACP                    October 19961.  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   SNACP packets to choose and configure the SNA network-layer protocol.   Once SNACP has reached the Opened state, SNA datagrams can be sent   over the link.   The link will remain configured for communications until explicit LCP   or SNACP 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 must 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.Fuqua                       Standards Track                     [Page 2]

RFC 2043                       PPP SNACP                    October 19961.2.  Terminology   This document frequently uses the following terms:   datagram  The unit of transmission in the network layer (such as IP).             A datagram may be encapsulated in one or more packets             passed to the data link layer.   frame     The unit of transmission at the data link layer.  A frame             may include a header and/or a trailer, along with some             number of units of data.   packet    The basic unit of encapsulation, which is passed across the             interface between the network layer and the data link             layer.  A packet is usually mapped to a frame; the             exceptions are when data link layer fragmentation is being             performed, or when multiple packets are incorporated into a             single frame.   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.   PIU       Path information unit.  A message unit consisting of a             transmission header (TH) alone, or a TH followed by a basic             information unit (BIU) or a BIU segment.  PIU is analogous             to datagram.   TH        Transmission header.  Control information, optionally             followed by a basic information unit (BIU) or a BIU             segment, that is created and used by path control to route             message units and to control their flow within the network.   BIU       Basic information unit.  In SNA, the unit of data and             control information passed between half-sessions.  It             consists of a request/response header (RH) followed by a             request/response unit (RU).   message unit             In SNA, the unit of data processed by any layer; for             example, a basic information unit (BIU), a path information             unit (PIU), or a request/response unit (RU).Fuqua                       Standards Track                     [Page 3]

RFC 2043                       PPP SNACP                    October 1996   NLP       Network Layer Packet.  In High Performance Routing (HPR),             the message unit used to carry data over the route.             Network Layer Packet is analogous to datagram.2.  A PPP Network Control Protocol for SNA   The SNA Control Protocol (SNACP) is responsible for configuring,   enabling, and disabling SNA on both ends of the point-to-point link.   SNACP uses the same packet exchange mechanism as the Link Control   Protocol (LCP). SNACP packets may not be exchanged until PPP has   reached the Network-Layer Protocol phase.  SNACP packets received   before this phase is reached should be silently discarded.   Note that there are actually two SNA Network Control Protocols; one   for SNA over LLC 802.2 and another for SNA without LLC 802.2.  These   SNA NCPs are negotiated separately and independently of each other.   The SNA 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 SNACP packet is encapsulated in the PPP Information      field, where the PPP Protocol field indicates type hex 804B (SNA      over LLC 802.2) or hex 804D (SNA).   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      SNACP 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.Fuqua                       Standards Track                     [Page 4]

RFC 2043                       PPP SNACP                    October 1996   Configuration Option Types      There are no Configuration Options for SNA or for SNA over LLC      802.2.3.  Sending SNA PIUs and NLPs.   Before any SNA packets may be communicated, PPP must reach the   Network-Layer Protocol phase, and the appropriate SNA Control   Protocol must reach the Opened state.   The maximum length of a SNA packet transmitted over a PPP link is the   same as the maximum length of the Information field of a PPP   encapsulated packet.   The format of the PPP Information field itself is the same as that   defined in [1].  Detailed information on SNA and APPN can be found in   [3], [4], [5], [6], and [7].3.1.  Sending SNA XID or FID2 PIUs over LLC   Exactly one SNA XID or FID2 PIU over LLC 802.2 is encapsulated in the   PPP Information field, where the PPP Protocol field indicates type   hex 004B (SNA over LLC 802.2).   A summary of this frame structure, beginning with the PPP Protocol   field, is shown below. The fields are transmitted from left to right.                -- LLC portion (PPP Information Field) -------------               |                                                    |   -+----------+----------+----------+----------+-------------------+-    | Protocol | DSAP     | SSAP     | Control  | LLC Information   |    | 0x004B   | Address  | Address  | Field    | Field             |   -+----------+----------+----------+----------+-------------------+-   The LLC information field contains the XID or FID2 PIU. LLC(2) is   included in this format for link-level error recovery.  Error   recovery is done by the routers at each end of the PPP link.3.2.  Sending HPR Network Layer Packets (NLPs)   Exactly one HPR Network Layer Packet (NLP) is encapsulated in the PPP   Information field, where the PPP Protocol field indicates type hex   004D (SNA).Fuqua                       Standards Track                     [Page 5]

RFC 2043                       PPP SNACP                    October 1996   A summary of this frame structure, beginning with the PPP Protocol   field, is shown below. The fields are transmitted from left to right.                -- HPR Network Layer Packet (NLP) --                  |   (PPP Information Field)          |      -+----------+--------+--------+------------------+-       | Protocol | NHDR   | THDR   | data             |       | 0x004D   |        |        |                  |      -+----------+--------+--------+------------------+-3.3.  Other Considerations   It is architecturally possible to transport HPR NLPs over LLC over   PPP using PPP Protocol field type hex 004B (SNA over LLC 802.2) if   the optional HPR link-level error recover tower is included in the   implementation.Security Considerations   Security issues are not discussed in this memo.References   [1]   Simpson, W., "The Point-to-Point Protocol (PPP)", STD 51,RFC 1661, Daydreamer, July 1994.   [2]   Reynolds, J., and J. Postel, "Assigned Numbers", STD 2,RFC1700, USC/Information Sciences Institute, October 1994.   [3]   "SNA Formats", GA27-3136, IBM.   [4]   "SNA APPN Architecture Reference", SC30-3422, IBM.   [5]   "APPN Architecture and Product Implementations Tutorial",          GG24-3669-02, IBM.   [6]   APPN Implementers Workshop homepage,http://www.raleigh.ibm.com/app/aiwhome.htm   [7]   "APPN High Performance Routing (HPR) Architecture",ftp://networking.raleigh.ibm.com/pub/standards/aiw/appn/hpr   IBM documents are orderable through 1-800-879-2755.Fuqua                       Standards Track                     [Page 6]

RFC 2043                       PPP SNACP                    October 1996Acknowledgements   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).   Some of the text in this document is taken from miscellaneous IBM   documents.   Many people provided suggestions and portions of text for this   document.  Special thanks to Allen Carriker, Marcia Peters, and Scott   G. Wasson.Chair's Address   The working group can be contacted via the current chair:   Karl F. Fox   Ascend Communications   3518 Riverside Dr., Suite 101   Columbus, Ohio  4322   EMail: karl@ascend.comAuthor's Address   Questions about this memo can also be directed to:   Andrew M. Fuqua   International Business Machines Corporation   P. O. Box 12195   Research Triangle Park, NC  27709   EMail: fuqua@vnet.ibm.comFuqua                       Standards Track                     [Page 7]