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

The PPP SNA Control Protocol (SNACP

Status of this

This document specifies an Internet standards track protocol for
Internet community, and requests discussion and suggestions
improvements. Please refer to the current edition of the "
Official Protocol Standards" (STD 1) for the standardization
and status of this protocol. Distribution of this memo is unlimited

The Point-to-Point Protocol (PPP) [1] provides a standard method
transporting multi-protocol datagrams over point-to-point links.
defines an extensible Link Control Protocol, and proposes a family
Network Control Protocols for establishing and configuring
network-layer protocols

This document defines the Network Control Protocols for
and configuring Systems Network Architecture (SNA) over PPP and
over LLC 802.2 over PPP

Table of

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.

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
configuring different network-layer protocols

In order to establish communications over a point-to-point link,
end of the PPP link must first send LCP packets to configure and
the data link. After the link has been established and
facilities have been negotiated as needed by the LCP, PPP must
SNACP packets to choose and configure the SNA network-layer protocol
Once SNACP has reached the Opened state, SNA datagrams can be
over the link

The link will remain configured for communications until explicit
or SNACP packets close the link down, or until some external
occurs (an inactivity timer expires or network
intervention).

1.1. Specification of

In this document, several words are used to signify the
of the specification. These words are often capitalized

MUST This word, or the adjective "required", means that
definition is an absolute requirement of the specification

MUST NOT This phrase means that the definition is an
prohibition of the specification

SHOULD This word, or the adjective "recommended", means that
may exist valid reasons in particular circumstances
ignore this item, but the full implications must
understood and carefully weighed before choosing
different course

MAY This word, or the adjective "optional", means that
item is one of an allowed set of alternatives.
implementation which does not include this option MUST
prepared to interoperate with another implementation
does include the option

Fuqua Standards Track [Page 2]

RFC 2043 PPP SNACP October 1996

1.2.

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
passed to the data link layer

frame The unit of transmission at the data link layer. A
may include a header and/or a trailer, along with
number of units of data

packet The basic unit of encapsulation, which is passed across
interface between the network layer and the data
layer. A packet is usually mapped to a frame;
exceptions are when data link layer fragmentation is
performed, or when multiple packets are incorporated into
single frame

peer The other end of the point-to-point link

silently
This means the implementation discards the packet
further processing. The implementation SHOULD provide
capability of logging the error, including the contents
the silently discarded packet, and SHOULD record the
in a statistics counter

PIU Path information unit. A message unit consisting of
transmission header (TH) alone, or a TH followed by a
information unit (BIU) or a BIU segment. PIU is
to datagram

TH Transmission header. Control information,
followed by a basic information unit (BIU) or a
segment, that is created and used by path control to
message units and to control their flow within the network

BIU Basic information unit. In SNA, the unit of data
control information passed between half-sessions.
consists of a request/response header (RH) followed by
request/response unit (RU).

message
In SNA, the unit of data processed by any layer;
example, a basic information unit (BIU), a path
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

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
Protocol (LCP). SNACP packets may not be exchanged until PPP
reached the Network-Layer Protocol phase. SNACP packets
before this phase is reached should be silently discarded

Note that there are actually two SNA Network Control Protocols;
for SNA over LLC 802.2 and another for SNA without LLC 802.2.
SNA NCPs are negotiated separately and independently of each other

The SNA Control Protocol is exactly the same as the Link
Protocol [1] with the following exceptions

Frame

The packet may utilize any modifications to the basic frame
which have been negotiated during the Link Establishment phase

Data Link Layer Protocol

Exactly one SNACP packet is encapsulated in the PPP
field, where the PPP Protocol field indicates type hex 804B (
over LLC 802.2) or hex 804D (SNA).

Code

Only Codes 1 through 7 (Configure-Request, Configure-Ack
Configure-Nak, Configure-Reject, Terminate-Request, Terminate-
and Code-Reject) are used. Other Codes should be treated
unrecognized and should result in Code-Rejects

SNACP packets may not be exchanged until PPP has reached
Network-Layer Protocol phase. An implementation should be
to wait for Authentication and Link Quality Determination
finish before timing out waiting for a Configure-Ack or
response. It is suggested that an implementation give up
after user intervention or a configurable amount of time

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RFC 2043 PPP SNACP October 1996

Configuration Option

There are no Configuration Options for SNA or for SNA over
802.2.

3. Sending SNA PIUs and NLPs

Before any SNA packets may be communicated, PPP must reach
Network-Layer Protocol phase, and the appropriate SNA
Protocol must reach the Opened state

The maximum length of a SNA packet transmitted over a PPP link is
same as the maximum length of the Information field of a
encapsulated packet

The format of the PPP Information field itself is the same as
defined in [1]. Detailed information on SNA and APPN can be found
[3], [4], [5], [6], and [7].

3.1. Sending SNA XID or FID2 PIUs over

Exactly one SNA XID or FID2 PIU over LLC 802.2 is encapsulated in
PPP Information field, where the PPP Protocol field indicates
hex 004B (SNA over LLC 802.2).

A summary of this frame structure, beginning with the PPP
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)
included in this format for link-level error recovery.
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
Information field, where the PPP Protocol field indicates type
004D (SNA).

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RFC 2043 PPP SNACP October 1996

A summary of this frame structure, beginning with the PPP
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

It is architecturally possible to transport HPR NLPs over LLC
PPP using PPP Protocol field type hex 004B (SNA over LLC 802.2)
the optional HPR link-level error recover tower is included in
implementation

Security

Security issues are not discussed in this memo

[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,
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.

[7] "APPN High Performance Routing (HPR) Architecture",
ftp://networking.raleigh.ibm.com/pub/standards/aiw/appn/

IBM documents are orderable through 1-800-879-2755.

Fuqua Standards Track [Page 6]

RFC 2043 PPP SNACP October 1996

Some of the text in this document is taken from previous
produced by the Point-to-Point Protocol Working Group of the
Engineering Task Force (IETF).

Some of the text in this document is taken from miscellaneous
documents

Many people provided suggestions and portions of text for
document. Special thanks to Allen Carriker, Marcia Peters, and
G. Wasson

Chair's

The working group can be contacted via the current chair

Karl F.
Ascend
3518 Riverside Dr., Suite 101
Columbus, Ohio 4322

EMail: karl@ascend.

Author's

Questions about this memo can also be directed to

Andrew M.
International Business Machines
P. O. Box 12195
Research Triangle Park, NC 27709

EMail: fuqua@vnet.ibm.

Fuqua Standards Track [Page 7]

if you see any problems within the linking, don't worry be happy,
this is version 0.1 of the Relevance System and you gotta expect some crappy subroutines sometimes,
just be content we did not write this in Java, which would have made this "bigger and better" HAHAHHA.

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