Network Working Group B. Parker

Network Working Group B. Parker
Request for Comments: 1378 Cayman Systems
November 1992

The 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
[email protected] mailing list.

Table of Contents

1. Introduction .......................................... 2
2. A PPP Network Control Protocol (NCP) for AppleTalk .... 2
2.1 Sending AppleTalk Datagrams ........................... 3
2.2 Half-Routers .......................................... 4
3. ATCP Configuration Options ............................ 4
3.1 AppleTalk-Address ..................................... 5
3.2 Routing-Protocol ...................................... 7
3.3 Suppress-Broadcasts ................................... 8
3.4 AT-Compression-Protocol ............................... 9
3.5 Server-information .................................... 10
3.6 Zone-Information ...................................... 12
3.7 Default-Router-Address ................................ 13
APPENDICES ................................................... 14
A. ATCP Recommended Options .............................. 14
REFERENCES ................................................... 15

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ACKNOWLEDGEMENTS ............................................. 15
SECURITY CONSIDERATIONS ...................................... 16
CHAIR'S ADDRESS .............................................. 16
AUTHOR'S ADDRESS ............................................. 16

1. 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.

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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 reassembling

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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-Address

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3.1. 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.

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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.

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3.2. 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.

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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.

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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

4

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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.

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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 router

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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.

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3.7. 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).

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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)

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Intermediate 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 ([email protected]), Network Systems Corporation
Jim Muchow ([email protected]), Network Systems Corporation
Frank Slaughter ([email protected]), Shiva Corporation

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RFC 1378 PPP ATCP November 1992

Security 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: [email protected]

John Veizades
Apple Computer, Inc.
20525 Mariani Avenue
Cupertino, CA 95014

Phone: (408) 996-1010
EMail: [email protected]

Author's Address

Questions about this memo can also be directed to:

Brad Parker
Cayman Systems, Inc.
26 Landsdowne Street
Cambridge, Ma 02139

EMail: [email protected]

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