Network Working Group W. Simpson

Network Working Group W. Simpson
Request for Comments: 1552 Daydreamer
Category: Standards Track December 1993

The PPP Internetwork Packet Exchange Control Protocol (IPXCP)

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 method for
transmitting 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.

The IPX protocol was originally used in Novell's NetWare products
[3], and is now supported by numerous other vendors. This document
defines the Network Control Protocol for establishing and configuring
the IPX protocol over PPP.

This memo is the product of the Point-to-Point Protocol Working Group
of the IETF. Comments should be submitted to the ietf-
[email protected] mailing list.

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Table of Contents

1. Introduction ...................................................2
1.1 Specification of Requirements ..................................3
1.2 Terminology ....................................................3
2. A PPP Network Control Protocol for IPX .........................4
2.1 Sending IPX Datagrams ..........................................5
2.2 IPX-WAN protocol ...............................................5
2.3 Desired Parameters .............................................5
2.4 Co-existence with IPX-WAN ......................................6
3. IPXCP Configuration Options ....................................6
3.1 IPX-Network-Number .............................................7
3.2 IPX-Node-Number ................................................8
3.3 IPX-Compression-Protocol .......................................9
3.4 IPX-Routing-Protocol ...........................................11
3.5 IPX-Router-Name ................................................12
3.6 IPX-Configuration-Complete .....................................13
APPENDIX A. Link Delay and Throughput ..............................14
SECURITY CONSIDERATIONS ............................................14
REFERENCES .........................................................15
ACKNOWLEDGEMENTS ...................................................15
CHAIR'S ADDRESS ....................................................15
AUTHOR'S ADDRESS ...................................................16

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
IPXCP packets to choose and configure the IPX network-layer protocol.
Once IPXCP has reached the Opened state, IPX datagrams can be sent
over the link.

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

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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 should 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.

1.2 Terminology

This document frequently uses the following terms:

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.

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end-system

A user's machine. It only sends packets to servers and other
end-systems. It doesn't pass any packets through itself.

router

Allows packets to pass through, usually from one ethernet segment
to another. Sometimes these are called "intermediate-systems".

half-router

Two normal routers, with an unnumbered link between them. Each
looks like a router to the local users, but Netware doesn't
understand unnumbered links, so each router is made to look like
they both are a single machine.

2. A PPP Network Control Protocol for IPX

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

The IPX 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 IPXCP packet is encapsulated in the Information field
of a PPP Data Link Layer frame where the Protocol field indicates
type hex 802B (IPX 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.

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Timeouts

IPXCP 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

IPXCP has a distinct set of Configuration Options.

2.1 Sending IPX Datagrams

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

Exactly one IPX packet is encapsulated in the Information field of a
PPP Data Link Layer frame where the Protocol field indicates type hex
002B (IPX datagram).

The maximum length of an IPX datagram transmitted over a PPP link is
the same as the maximum length of the Information field of a PPP data
link layer frame. Since there is no standard method for fragmenting
and reassembling IPX datagrams, PPP links supporting IPX MUST allow
at least 576 octets in the information field of a data link layer
frame.

2.2 IPX-WAN protocol

A Novell specification called IPX-WAN [4] is intended to provide
mechanisms similar to IPXCP negotiation over wide area links. As
viewed by PPP, IPX-WAN is a part of IPX, and IPX-WAN packets are
indistinguishable from other IPX packets.

Currently, Novell has implemented IPXCP without any Configuration
Options, and requires successful IPX-WAN completion, even when all
required parameters have been hand configured. This makes it
impossible for the current Novell products to interoperate with other
IPXCP implementations which do not already include support for IPX-
WAN.

2.3 Desired Parameters

To resolve the possible conflict between the two configuration
methods, this specification defines the concept of "Desired

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Parameters". Where applicable, each Configuration Option indicates
the environment where the parameter which is negotiated MAY be
required by the implementation for proper operation.

This determination is highly implementation dependent. For example,
a particular implementation might require that all links have
addresses, while another implementation might not need such
addresses. The configuration negotiation is intended to discover
that this pair of implementations will never converge.

2.4 Co-existence with IPX-WAN

An IPXCP implementation which includes support for IPX-WAN SHOULD
always reach Opened state, even when unable to negotiate some
"Desired Parameter", and when no Configuration Options are
successfully negotiated. This allows IPX-WAN the opportunity to
finish the negotiation.

If an implementation does not include support for IPX-WAN, it SHOULD
NOT reach Opened state when unable to negotiate some "Desired
Parameter".

IPX-WAN uses a "Timer Request" packet to set up the link. These MUST
NOT be sent until IPXCP has Opened the link.

An implementation which provides both IPX-WAN and IPXCP Configuration
Options capability SHOULD only send a Timer Request packet when a
Timer Request packet is received, or upon failure to successfully
negotiate a "Desired Parameter".

If unable to complete IPX-WAN setup when a "Desired Parameter" is
unknown, by default IPXCP SHOULD terminate the link.

However, some implementations might be capable of operating without
all indicated "Desired Parameters", in which case the termination
MUST be configurable.

3. IPXCP Configuration Options

IPXCP Configuration Options allow modifications to the standard
characteristics of the network-layer protocol to be negotiated. If a
Configuration Option is not included in a Configure-Request packet,
the default value for that Configuration Option is assumed.

IPXCP uses the same Configuration Option format defined for LCP [1],
with a separate set of Options.

Up-to-date values of the IPXCP Option Type field are specified in the

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most recent "Assigned Numbers" RFC [2]. Current values are assigned
as follows:

1 IPX-Network-Number
2 IPX-Node-Number
3 IPX-Compression-Protocol
4 IPX-Routing-Protocol
5 IPX-Router-Name
6 IPX-Configuration-Complete

3.1 IPX-Network-Number

Description

This Configuration Option provides a way to negotiate the IPX
network number to be used for the link. This allows an
implementation to learn the network number, or to ensure agreement
on the network number.

The network number MUST be unique within the routing domain, or
zero to indicate that it is not used for routing.

The sender of the Configure-Request states which network number is
desired. A network number specified as zero in a Configure-
Request shall be interpreted as requesting the peer to specify
another value in a Configure-Nak. A network number specified as
zero in a Configure-Ack shall be interpreted as agreement that no
value exists.

Both ends of the link MUST have the same network number. When a
Configure-Request is received which has a lower network number
than locally configured, a Configure-Nak MUST be returned with the
highest network number.

When the peer did not provide the option in its Configure-Request,
the option SHOULD NOT be appended to a Configure-Nak.

By default, no network number is assigned to the link (the network
number is zero). There is no need for a network number if the
interface is not used by a routing protocol.

This is a Desired Parameter when the implementation is operating
as a router. It MUST be negotiated if the network number is non-
zero, and has been derived from another interface.

Any IPX-WAN packets received MUST supercede information negotiated
in this option.

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A summary of the IPX-Network-Number 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 | IPX-Network-Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPX-Network-Number (cont.) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Type

1

Length

6

IPX-Network-Number

The four octet IPX-Network-Number is the desired local IPX network
number of the sender of the Configure-Request. This number may be
zero, which is interpreted as being a local network of unknown
number that is not used by the routing protocol.

3.2 IPX-Node-Number

Description

This Configuration Option provides a way to negotiate the IPX node
number to be used for the local end of the link. This allows an
implementation to learn its node number, or to inform the peer of
its node number.

The node number MUST be unique for the network number.

The sender of the Configure-Request states which node number is
desired. A node number specified as zero in a Configure-Request
shall be interpreted as requesting the peer to specify another
value in a Configure-Nak. A node number specified as zero in a
Configure-Ack shall be interpreted as agreement that no value
exists.

If negotiation about the peer node number is required, and the
peer did not provide the option in its Configure-Request, the
option can be appended to a Configure-Nak. The value of the node
number given MUST be acceptable as the peer IPX-Node-Number, or

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indicate with a zero value that the peer provide the information.

By default, no node number is assigned to the link (the node
number is zero). There is no need for a node number if the
interface is not used by a routing protocol.

This is a Desired Parameter when the implementation is operating
as an end-system. However, when the node number has been
statically configured, this option SHOULD NOT be negotiated unless
requested by the peer.

Any IPX-WAN packets received MUST supercede information negotiated
in this option.

A summary of the IPX-Node-Number 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 | IPX-Node-Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPX-Node-Number (cont.) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Type

2

Length

8

IPX-Node-Number

The six octet IPX-Node-Number is the desired local IPX node number
of the sender of the Configure-Request.

3.3 IPX-Compression-Protocol

Description

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

The sender of this Configuration Option indicates that it can
receive packets with the specified compression technique. A

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Configure-Ack MAY obligate the peer to send such packets,
depending on the protocol negotiated.

Information negotiated in this option MUST supercede any IPX-WAN
packets received, since IPX-WAN packets could be affected by the
compression technique.

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

Type

3

Length

>= 4

IPX-Compression-Protocol

The IPX-Compression-Protocol field is two octets and indicates the
compression protocol desired. Odd values for this field are always
the same as the PPP Data Link Layer Protocol field values for that
same compression protocol. Even values are used when the compression
protocol is interleaved with IPX packets.

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

Value (in hex) Protocol

0002 Telebit Compressed IPX
0235 Shiva Compressed NCP/IPX

Data

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

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3.4 IPX-Routing-Protocol

Description

This Configuration Option provides a way to negotiate the use of a
specific routing protocol (or no routing protocol, if desired).
The sender of this option is specifying that it wishes to receive
information of the specified routing protocol. Multiple protocols
MAY be requested by sending multiple IPX-Routing-Protocol
Configuration Options. The "no routing protocol required" value
is mutually exclusive with other values.

By default, Novell's combination of Routing Information Protocol
(RIP) and Server Advertising Protocol (SAP) is expected.

This is a Desired Parameter when the implementation is operating
as an end-system, to indicate that no routing protocol is
necessary.

Any IPX-WAN packets received MAY add to information negotiated in
this option.

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

Type

4

Length

>= 4

IPX-Routing-Protocol

The IPX-Routing-Protocol field is two octets and indicates the
type of Routing-Protocol desired. This two octet quantity is sent
most significant octet first.

Up-to-date values of the IPX-Routing-Protocol field are specified

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in the most recent "Assigned Numbers" RFC [2]. Current values are
assigned as follows:

Value Protocol

0 No routing protocol required
1 RESERVED
2 Novell RIP/SAP required
4 Novell NLSP required

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.

3.5 IPX-Router-Name

Description

This Configuration Option provides a way to convey information
about the IPX server name.

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. This option MUST NOT be included in a Configure-
Nak.

A summary of the IPX-Router-Name 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 | Name... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Type

5

Length

>= 3

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Name

This field contains the name of the IPX entity on this end of the
link. The symbolic name should be between 1 and 47 ASCII
characters in length, containing the characters 'A' through 'Z',
underscore (_), hyphen (-) and "at" sign (@). The length of the
name is bounded by the option length.

On reception, the name SHOULD be padded to 48 characters using the
NUL character. Those readers familiar with NetWare 3.x servers
will realize that this is equivalent to the file server name.

3.6 IPX-Configuration-Complete

Description

This Configuration Option provides a way to indicate that all
implementation-dependent Desired Parameters are satisfied. It is
provided as a means of detecting when convergence will occur in a
heterogeneous environment.

This option SHOULD be included in a Configure-Request when the
combination of statically configured parameters and offered
Configuration Options will result in successful configuration.

The nature of this option is advisory only. This option MUST NOT
be included in a Configure-Nak.

Implementation Note: An implementation which does not support
IPX-WAN can immediately detect that link setup will not be
successful when a Desired Parameter is unknown, if this option is
not present in the peer's Configure-Request or is Rejected by the
peer. This avoids timeout delays.

An implementation which supports IPX-WAN may improve link setup
time by skipping IPX-WAN entirely when this option has been Ack'd
in both directions.

However, it is perfectly acceptable to complete configuration
without including this option. An implementation which includes
the entire panoply of configuration options and IPX- WAN SHOULD
interoperate with an implementation which does not support IPX-WAN
nor any configuration options (including this one), as long as the
Desired Parameters are satisfied by default or hand configuration.

A summary of the IPX-Configuration-Complete Option format is shown
below. The fields are transmitted from left to right.

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0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Type

6

Length

2

APPENDIX A. Link Delay and Throughput

There has been some concern over correctly estimating the link delay
(in 55 millisecond ticks) used by Novell routing protocols.

IPX-WAN uses its Timer Request and Reply for this purpose. The
measured delay is multiplied by a factor of 6, because the
measurement is done during initialization of the link, and does not
reflect actual loading.

The delay is better measured using the PPP LCP Echo facility, by
inserting a timestamp in the data part of the Request, and comparing
it with the same timer when the reply returns. This method could be
used to periodically re-evaluate the actual round trip delay as link
and system loads change. The echo packet size SHOULD be 576, to
match the default IPX packet size.

In the absence of such dynamic measurements, empirical evidence has
shown the following to be sufficient:

2,400 bps 134 ticks
14,400 bps 21 ticks
57,600 bps 5 ticks
> 1 Mbps 1 tick

Security Considerations

Security issues are not discussed in this memo.

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References

[1] Simpson, W., "The Point-to-Point Protocol (PPP)", RFC 1548,
Daydreamer, December 1993.

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

[3] Novell Inc., "NetWare System Interface Technical Overview",
Novell Part Number 883-001143-001.

[4] Allen, M., "Novell IPX Over Various WAN Media", RFC 1551,
Novell Inc., December 1993.

[5] Mathu, S., and M. Lewis, "Compressing IPX Headers Over WAN
Media (CIPX)", RFC 1553, Telebit Corporation, December 1993.

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:

Michael Allen ([email protected])
Dave McCool ([email protected])
Robert D Vincent ([email protected])
Marty Del Vecchio ([email protected])

Chair's Address

The working group can be contacted via the current chair:

Fred Baker
Advanced Computer Communications
315 Bollay Drive
Santa Barbara, California, 93111

EMail: [email protected]

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Author's Address

Questions about this memo can also be directed to:

William Allen Simpson
Daydreamer
Computer Systems Consulting Services
P O Box 6205
East Lansing, MI 48826-6205

EMail: [email protected]

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