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Network Working Group A. Fuqua Request for Comments: 2043 IBM Category: Standards Track October 1996

                The 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 Contents

 1.     Introduction ..........................................    2
    1.1       Specification of Requirements ...................    2
    1.2       Terminology .....................................    3
 2.     A PPP Network Control Protocol for SNA ................    4
 3.     Sending SNA PIUs and NLPs. ............................    5
    3.1       Sending SNA XID or FID2 PIUs over LLC ...........    5
    3.2       Sending HPR Network Layer Packets (NLPs) ........    5
    3.3       Other Considerations ............................    6
 SECURITY CONSIDERATIONS ......................................    6
 REFERENCES ...................................................    6
 ACKNOWLEDGEMENTS... ..........................................    7
 CHAIR'S ADDRESS ..............................................    7
 AUTHOR'S ADDRESS .............................................    7

Fuqua Standards Track [Page 1] RFC 2043 PPP SNACP October 1996

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
 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 1996

1.2. 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) ————-

| |

+———-+———-+———-+———-+——————-+-

  | 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) |

+———-+——–+——–+——————+-

     | 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, RFC
       1700, 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 1996

Acknowledgements

 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.com

Author'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.com

Fuqua Standards Track [Page 7]