Network Working Group S. Senum
Request for Comments: 1376 Network Systems Corporation
November 1992

The PPP DECnet Phase IV Control Protocol (DNCP)

Status of this Memo

This RFCspecifies 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
Digital's DNA Phase IV Routing protocol (DECnet Phase IV) over PPP.
This document applies only to DNA Phase IV Routing messages (both
data and control), and not to other DNA Phase IV protocols (MOP, LAT,
etc.).

1. IntrodUCtion

There are two basic approaches to running the DNA Phase IV Routing
protocol over a serial line:

1. The approached that several router vendors have taken which is to
treat the serial link as an Ethernet, using the same data and
control messages an Ethernet would use.

2. The approach defined by Digital, which uses DDCMP and slightly
different control messages.

This document will define a method that uses the first approach.

2. Overview Of Phase IV DNA Protocols

The Phase IV DNA protocols which act as data link clients are:

o DNA Phase IV Routing
The Phase IV Digital Network Architecture (DNA) Routing
protocol is a network layer protocol providing services similar
to that of DoD IP. It routes messages in Phase IV DECnet
networks and manages the packet flow. The complete definition
of the DNA Phase IV Routing protocol can be found in [2].

o DNA System Console
The Digital Network Architecture (DNA) System Console protocol
is a maintenance protocol providing low level Access to a
system for the functions of:

. Identify processor
. Read data link counters
. Boot system
. Console carrier (a general purpose i/o channel)

The complete definition of the DNA System Console protocol can
be found in [3].

o Digital Customer Use
The Digital Customer Use protocol type is a value reserved for
use by Digital customers. It allocates a type for private use
which will not conflict with Digital or other vendor protocols.

o DNA Diagnostics
The Digital Network Architecture (DNA) Diagnostics protocol
type is reserved to allow diagnostic software communications in
parallel with other data link clients.

o DNA Naming Service (DNS)
The Digital Network Architecture Naming Service (DNS) provides
a distributed naming service. It allows clients to register
named objects and to bind a set of attributes to the objects in
a distributed database.

o DNA Time Service (DTS)
The Digital Network Architecture Time Service (DTS) is a
protocol providing global clock synchronization in a
distributed environment.

o DNA Load/Dump
The Digital Network Architecture (DNA) Load/Dump protocol is a
maintenance protocol for copying the contents of processor

memory to or from a remote system. For example, a system
manager can load an operating system into an unattended, remote
system. The complete definition of the Phase IV DNA Load/Dump
protocol can be found in [3].

o DNA EXPerimental Use
The Digital Network Architecture (DNA) Experimental Use
protocol type allows Digital experimental protocols to share a
data link with other data link clients. It is for use by
Digital Equipment Corporation only.

o DNA Communications Test
The Digital Network Architecture (DNA) Communications Test
protocol is a maintenance protocol for testing the data link
communications path. The complete definition of the DNA
Communications Test protocol can be found in [3].

o Digital Protocol X1
The Digital X1 protocol is a network layer protocol currently
private to Digital.

This document defines the NCP for establishing and configuring
Digital's DNA Phase IV Routing protocol (DECnet Phase IV) over PPP.
This document applies only to DNA Phase IV Routing messages (both
data and control), and not to other DNA Phase IV protocols (MOP, LAT,
etc.).

3. A PPP Network Control Protocol for DNA Phase IV Routing

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

The DNA Phase IV Routing 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 DNCP packet is encapsulated in the Information field

of a PPP Data Link Layer frame where the Protocol field indicates
type hex 8027 (DNA Phase IV 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

DNCP 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

DNCP has no Configuration Options.

4. Sending DNA Phase IV Routing Packets

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

Exactly one octet-count field and one DNA Phase IV Routing packet are
encapsulated in the information field of a PPP Data Link Layer frame
where the Protocol field indicates type hex 0027 (DNA Phase IV
Routing). The octet-count contains a count of the number of octets
in the DNA Phase IV Routing packet. It is two octets in length
itself, and is stored in VAX byte ordering, to be more consistent
with DNA Phase IV Routing over Ethernet (i.e. least significant byte
first). It is needed to disambiguate optional padding octets from
real information.

The maximum length of an DNA Phase IV Routing packet transmitted over
a PPP link is the same as the maximum length of the Information field
of a PPP data link layer frame minus 2 octets (for the Length field).

The format of the packets themselves is the same as the format used
over Ethernet, without the Ethernet header, Pad, and FCS fields.

A summary of the information field 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Length LSB Length MSB DATA ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Length LSB

Least significant byte of length field

Length MSG

Most significant byte of length field

DATA

DNA Phase IV Routing data, as specified in [2]

5. General Considerations

When a topology change in the network occurs, DNA Phase IV Routing
nodes immediately propagate changes via Level 1 and Level 2 Routing
messages, with a 1 second minimum delay between updates. DNA Phase
IV Routing nodes also periodically retransmit the complete Level 1
and Level 2 distance vectors to guard against data corruption in host
memory, and (in the case of Ethernet) loss of packets due to media
errors. Because Digital's serial links run a protocol that
guarantees delivery of packets (DDCMP), the recommended default
retransmit time is long (600 seconds), whereas for Ethernet, where
packet delivery is not guaranteed, the recommended default is short
(10 seconds), as documented in [2]. To achieve convergence of routes
within a satisfactory time, the interval between updates should be
based upon the error rate of underlying data link. As such, it is
recommended that the time between routing updates be user
configurable per PPP interface.

The Hello timer and Listen timer should be set according to the
recommendations for broadcast links (15 and 45 seconds,
respectively).

Routers are not required to send routing updates if the remote node
connected via the PPP link is an endnode. Endnodes are required to
discard all routing updates received over a PPP link. The type of a
node (endnode versus routing) can be determined from the hello
messages received from it.

References

[1] Simpson, W., "The Point-to-Point Protocol (PPP)", RFC1331,
Daydreamer, May 1992.

[2] Digital Equipment Corporation, "DNA Routing Layer Functional
Specification", Version 2.0.0, Order No. AA-X435A-TK.

[3] Digital Equipment Corporation, "DNA Maintenance Operations
Functional Specification", Version 3.0.0, Order No. AA-X436A-TK.

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).

The author wishes to thank Jim Muchow (Network Systems Corporation),
and Arthur Harvey (Digital Equipment Corporation) for their input to
this memo.

Security Considerations

Security issues are not discussed in this memo.

Chair's Address

The working group can be contacted via the current chair:

Brian Lloyd
Lloyd & Associates
3420 Sudbury Road
Cameron Park, California 95682

Phone: (916) 676-1147
EMail: brian@lloyd.com

Author's Address

Questions about this memo can also be directed to the author:

Steven J. Senum
Network Systems Corporation
7600 Boone Avenue North
Minneapolis, Minnesota 55428

Phone: (612) 424-4888
EMail: sjs@network.com