Network Working Group W. Simpson, Editor
Internet Draft DayDreamer
expires in six months July 1997
PPP LCP Extensions
draft-ietf-pppext-lcpext-ds-02.txt |
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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 additional LCP features that have been suggested over the
past few years.
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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" [2]. This document 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 pur-
poses, such as link troubleshooting, license enforcement, etc.
Identification is a Link Maintenance packet. Identification pack-
ets 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 gen-
erate 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.
This feature is defined as a separate LCP Code, rather than a Con-
figuration-Option, so that the peer need not include it with other
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items in configuration packet exchanges, and handle "corrected"
values or "rejection", since its generation is both rare and in
one direction. It is recommended that Identification packets be
sent whenever a Configure-Reject is sent or received, as a final
message when negotiation fails to converge, and when LCP reaches
the Opened state.
A summary of the Identification packet 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Code | Identifier | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Magic-Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ...
+-+-+-+-+-+-+-+-+
Code
12 for Identification
Identifier
The Identifier field MUST be changed for each Identification sent.
Length
>= 8
Magic-Number
The Magic-Number field is four octets and aids in detecting links
which are in the looped-back condition. Until the Magic-Number
Configuration Option has been successfully negotiated, the Magic-
Number MUST be transmitted as zero. See the Magic-Number Configu-
ration Option for further explanation.
Message
The Message field is zero or more octets, and its contents are
implementation dependent. It is intended to be human readable,
and MUST NOT affect operation of the protocol. It is recommended
that the message contain displayable ASCII characters 32 through
126 decimal. Mechanisms for extension to other character sets are
the topic of future research. The size is determined from the
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Length field.
Implementation Note:
The Message will usually contain such things as the sender's
hardware type, PPP software revision level, and PPP product
serial number, MIB information such as link speed and interface
name, and any other information that the sender thinks might be
useful in debugging connections. The format is likely to be
different for each implementor, so that those doing serial num-
ber tracking can validate their numbers. A robust implementa-
tion SHOULD treat the Message as displayable text, and SHOULD |
be able to receive and display a full MRU length Message.
1.2. Time-Remaining
Description
This Code provides a mechanism for notifying the peer of the time
remaining in this session.
The nature of this information is advisory only. It is intended
that only one side of the connection will send this packet (gener-
ally a "network access server"). The session is actually con-
cluded by the Terminate-Request packet.
Time-Remaining is a Link Maintenance packet. Time-Remaining pack-
ets may only be sent in the LCP Opened state.
The sender transmits a LCP packet with the Code field set to 13
(Time-Remaining), the Identifier field set, the local Magic-Number
(if any) inserted, and the Message field filled with any desired
data, but not exceeding the peer's established MRU minus twelve.
Receipt of an Time-Remaining packet causes the RXR or RUC event.
There is no response to the Time-Remaining packet.
Receipt of a Code-Reject for the Time-Remaining packet SHOULD gen-
erate the RXJ+ (permitted) event.
Rationale:
This notification is defined as a separate LCP Code, rather than a
Configuration-Option, in order that changes and warning messages
may occur dynamically during the session, and that the information
might be determined after Authentication has occurred. Typically,
this packet is sent when the link enters Network-Layer Protocol
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phase, and at regular intervals throughout the session, particu-
larly near the end of the session.
A summary of the Time-Remaining packet 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Code | Identifier | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Magic-Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Seconds-Remaining |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ...
+-+-+-+-+-+-+-+-+
Code
13 for Time-Remaining
Identifier
The Identifier field MUST be changed for each Time-Remaining sent.
Length
>= 12
Magic-Number
The Magic-Number field is four octets and aids in detecting links
which are in the looped-back condition. Until the Magic-Number
Configuration Option has been successfully negotiated, the Magic-
Number MUST be transmitted as zero. See the Magic-Number Configu-
ration Option for further explanation.
Seconds-Remaining
The Seconds-Remaining field is four octets and indicates the num-
ber of integral seconds remaining in this session. This 32 bit
unsigned value is sent most significant octet first. A value of
0xffffffff (all ones) represents no timeout, or "forever".
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Message
The Message field is zero or more octets, and its contents are
implementation dependent. It is intended to be human readable,
and MUST NOT affect operation of the protocol. It is recommended
that the message contain displayable ASCII characters 32 through
126 decimal. Mechanisms for extension to other character sets are
the topic of future research. The size is determined from the
Length field.
Security Considerations -
There are no known security vulnerabilities. |
Acknowledgements
The Identification feature was suggested by Bob Sutterfield. |
The Time-Remaining feature was suggested by Brad Parker. |
Special thanks to Ascend Communications for providing computing |
resources and network access support for writing this specification.
References
[1] Simpson, W., Editor, "The Point-to-Point Protocol (PPP)", |
STD-51, RFC-1661, December 1993.
[2] Reynolds, J.K., Postel, J.B., "Assigned Numbers", RFC-1700,
July 1992. -
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Contacts
Comments about this document should be discussed on the
ietf-ppp@merit.edu mailing list.
This document is a submission to the Point-to-Point Protocol Working
Group of the Internet Engineering Task Force (IETF). The working
group can be contacted via the current chair:
Karl Fox
Ascend Communications
3518 Riverside Drive Suite 101
Columbus, Ohio 43221
karl@MorningStar.com
karl@Ascend.com
Questions about this document can also be directed to:
William Allen Simpson
DayDreamer
Computer Systems Consulting Services
1384 Fontaine
Madison Heights, Michigan 48071
wsimpson@UMich.edu
wsimpson@GreenDragon.com (preferred)
bsimpson@MorningStar.com
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