Internet DRAFT - draft-ietf-pppext-lapf
draft-ietf-pppext-lapf
Network Working Group W A Simpson
Internet Draft Daydreamer
expires in six months March 1993
PPP over Frame Relay
Status of this Memo
This memo is the product of the Point-to-Point Protocol Working Group
of the Internet Engineering Task Force (IETF). Comments on this memo
should be submitted to the ietf-ppp@ucdavis.edu mailing list.
Distribution of this memo is unlimited.
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Abstract
The Point-to-Point Protocol (PPP) [1] provides a standard method of
encapsulating Network Layer protocol information over point-to-point
links.
This document defines a method for using PPP to transport multi-
protocol datagrams over Frame Relay circuits.
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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.
PPP was designed as a standard method of communicating over point-
to-point links. Initial deployment has been over short local lines,
leased lines, and plain-old-telephone-service (POTS) using modems.
As new packet services and higher speed lines are introduced, PPP is
easily deployed in these environments as well.
One protocol to carry them all.
One protocol to mind them.
One protocol to link them all,
and in the network bind them.
Frame Relay is a relative newcomer to the serial link community. The
protocol was designed as a virtual circuit network. There has been
some interest in bringing the advantages of the PPP multi-protocol
datagram service to this venue. When Frame Relay emulates a point-
to-point circuit, PPP is well suited to use over Frame Relay.
2. Encapsulation
PPP provides an encapsulation protocol over both bit-oriented
synchronous links and asynchronous links with 8 bits of data and no
parity. These links MUST be full-duplex, but MAY be either dedicated
or circuit-switched. This fits the Frame Relay model.
PPP uses HDLC [2] as a basis for the default encapsulation. Frame
Relay is also in the family of HDLC derivatives, and the Frame Relay
header may be easily substituted for the smaller HDLC header.
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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
+-+-+-+-+-+-+-+-+
| Flag (0x7e) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Q.922 Address | Control | Pad (0) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PPP Protocol |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Unfortunately, the Frame Relay header is 3 octets in length.
Therefore, a single octet of zero padding is used to align the header
to a more convenient boundary. The use of this zero padding is
conformant with both the ISO Network Layer Protocol Identifier
(NLPID) Null Network layer, and the PPP protocol field extension
mechanism.
LCP negotiation MUST permit the Pad and Protocol fields to be
compressed to a single octet. This will bring the header to the same
size as the standard PPP HDLC header.
3. In-Band Protocol Detection
When Out-of-Band signaling is not used to configure call setup for
the circuit, or the Null encapsulation is indicated, the PPP Protocol
field may be easily distinguished from other NLPID values. Initial
LCP packets will contain the sequence 00-c0-21 following the header.
Older implementations [3] might contain the NLPID value CC hex.
Other ISO conformant implementations might contain other NLPID
values, such as 80 hex (SNAP), or 81 hex (CLNP). Such packets
indicate that the link is not properly configured for PPP operation,
and MUST generate a Protocol-Reject.
4. Out-of-Band signaling
There is no generally available method of out-of-band signalling.
5. Configuration Details
The standard LCP configuration defaults apply to Frame Relay links.
The following Configurations Options are recommended:
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Magic Number
Link Quality Monitoring
Address and Control Field Compression
Protocol Field Compression
Some early Frame Relay networks are only capable of 262 octet frames.
In order to operate PPP over a Frame Relay link, the minimum PPP MRU
of 1500 MUST be supported.
To detect these inoperable links, the LCP Configure-Request packet
MUST be padded to the full 1500 octet length. The padding MUST be a
sequence of octets beginning with 1, and ending with the number of
octets of padding.
XID negotiation is not supported for PPP links.
There is no need for Inverse ARP over PPP links.
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Security Considerations
Security issues are not discussed in this memo.
References
[1] Simpson, W. A., "The Point-to-Point Protocol", RFC 1331, May
1992.
[2] International Organization For Standardization, ISO Standard
3309-1979, "Data communication - High-level data link control
procedures - Frame structure", 1979.
[3] Bradley, T., Brown, C., and Malis, A., "Multiprotocol
Interconnect over Frame Relay", RFC 1294, January 1992.
Acknowledgments
Chair's Address
The working group can be contacted via the current chair:
Brian Lloyd
B.P. 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:
William Allen Simpson
Daydreamer
Computer Systems Consulting Services
P O Box 6205
East Lansing, MI 48826-6205
EMail: Bill.Simpson@um.cc.umich.edu
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Table of Contents
1. Introduction .......................................... 1
2. Encapsulation ......................................... 1
3. In-Band Protocol Detection ............................ 2
4. Out-of-Band signaling ................................. 2
5. Configuration Details ................................. 2
SECURITY CONSIDERATIONS ...................................... 4
REFERENCES ................................................... 4
ACKNOWLEDGEMENTS ............................................. 4
CHAIR'S ADDRESS .............................................. 4
AUTHOR'S ADDRESS ............................................. 4
Bill.Simpson@um.cc.umich.edu
