RFC 1570 (rfc1570) - Page 1 of 18
PPP LCP Extensions
Alternative Format: Original Text Document
Network Working Group W. Simpson, Editor
Request for Comments: 1570 Daydreamer
Updates: 1548 January 1994
Category: Standards Track
PPP LCP Extensions
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 standard method for
transporting multi-protocol datagrams over point-to-point links. PPP
defines an extensible Link Control Protocol (LCP) for establishing,
configuring, and testing the data-link connection. This document
defines several additional LCP features which have been suggested
over the past few years.
This document is the product of the Point-to-Point Protocol Working
Group of the Internet Engineering Task Force (IETF). Comments should
be submitted to the mailing list.
Table of Contents
1. Additional LCP Packets ................................ 1
1.1 Identification .................................. 1
1.2 Time-Remaining .................................. 3
2. Additional LCP Configuration Options .................. 6
2.1 FCS-Alternatives ................................ 6
2.1.1 LCP considerations .............................. 7
2.1.2 Null FCS ........................................ 8
2.2 Self-Describing-Padding ......................... 9
2.3 Callback ........................................ 11
2.4 Compound-Frames ................................. 12
2.4.1 LCP considerations .............................. 14
APPENDICES ................................................... 15
A. Fast Frame Check Sequence (FCS) Implementation ........ 15
A.1 32-bit FCS Computation Method ................... 15
SECURITY CONSIDERATIONS ...................................... 17
REFERENCES ................................................... 17
ACKNOWLEDGEMENTS ............................................. 18
CHAIR'S ADDRESS .............................................. 18
EDITOR'S ADDRESS ............................................. 18
Simpson [Page i]
RFC 1570 PPP LCP extensions January 1994
1. Additional LCP Packets
The Packet format and basic facilities are already defined for LCP
[1].
Up-to-date values of the LCP Code field are specified in the most
recent "Assigned Numbers" RFC [2]. This specification concerns the
following values:
12 Identification
13 Time-Remaining
1.1. Identification
Description
This Code provides a method for an implementation to identify
itself to its peer. This Code might be used for many diverse
purposes, such as link troubleshooting, license enforcement, etc.
Identification is a Link Maintenance packet. Identification
packets MAY be sent at any time, including before LCP has reached
the Opened state.
The sender transmits a LCP packet with the Code field set to 12
(Identification), the Identifier field set, the local Magic-Number
(if any) inserted, and the Message field filled with any desired
data, but not exceeding the default MRU minus eight.
Receipt of an Identification packet causes the RXR or RUC event.
There is no response to the Identification packet.
Receipt of a Code-Reject for the Identification packet SHOULD
generate the RXJ+ (permitted) event.
Rationale:
This feature is defined as part of LCP, rather than as a
separate PPP Protocol, in order that its benefits may be
available during the earliest possible stage of the Link
Establishment phase. It allows an operator to learn the
identification of the peer even when negotiation is not
converging. Non-LCP packets cannot be sent during the Link
Establishment phase.
Simpson