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draft-ietf-ipngwg-ipv6-over-ppp-01.txt
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Internet Engineering Task Force
INTERNET-DRAFT Dimitry Haskin
Expires September 1997 Ed Allen
<draft-ietf-ipngwg-ipv6-over-ppp-01.txt> Bay Networks, Inc.
March 1997
IP Version 6 over PPP
Status of this Memo
This document is an Internet-Draft. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its
areas, and its working groups. Note that other groups may also
distribute working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six
months and may be updated, replaced, or obsoleted by other
documents at any time. It is inappropriate to use Internet-
Drafts as reference material or to cite them other than as
``work in progress.''
To learn the current status of any Internet-Draft, please check
the ``1id-abstracts.txt'' listing contained in the Internet-
Drafts Shadow Directories on ftp.is.co.za (Africa),
nic.nordu.net (Europe), munnari.oz.au (Pacific Rim),
ds.internic.net (US East Coast), or ftp.isi.edu (US West Coast).
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 method for transmission of IP Version 6 [2]
packets over PPP links as well as the Network Control Protocol (NCP)
for establishing and configuring the IPv6 over PPP. It also specifies
the method of forming IPv6 link-local addresses on PPP links.
Table of Contents
1. Introduction .......................................... 2
1.1. Specification of Requirements ...................... 2
2. Sending IPv6 Datagrams ................................ 3
3. A PPP Network Control Protocol for IPv6 ............... 3
4. IPV6CP Configuration Options .......................... 4
4.1. Interface-Token ................................... 4
4.2. IPv6-Compression-Protocol.......................... 7
5. Stateless Autoconfiguration and Link-Local Addresses .. 9
A. IPV6CP Recommended Options ............................. 9
Security Considerations ....................................... 10
References .................................................... 10
Acknowledgments ............................................... 10
Authors' Addresses ............................................ 10
Haskin & Allen [Page 1]
Draft IP Version 6 over PPP March 1997
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.
In this document, the NCP for establishing and configuring the IPv6
over PPP is referred as the IPv6 Control Protocol (IPV6CP).
The link will remain configured for communications until explicit LCP
or NCP packets close the link down, or until some external event
occurs (power failure at the other end, carrier drop, etc.).
1.1. Specification of Requirements
In this document, several words are used to signify the requirements
of the specification. These words are often capitalized.
MUST This word, or the adjective "required", means that the
definition is an absolute requirement of the specification.
MUST NOT This phrase means that the definition is an absolute
prohibition of the specification.
SHOULD This word, or the adjective "recommended", means that there
may exist valid reasons in particular circumstances to
ignore this item, but the full implications must be
understood and carefully weighed before choosing a
different course.
MAY This word, or the adjective "optional", means that this
item is one of an allowed set of alternatives. An
implementation which does not include this option MUST be
Haskin & Allen [Page 2]
Draft IP Version 6 over PPP March 1997
prepared to inter-operate with another implementation which
does include the option.
2. Sending IPv6 Datagrams
Before any IPv6 packets may be communicated, PPP must reach the
Network-Layer Protocol phase, and the IPv6 Control Protocol must
reach the Opened state.
Exactly one IPv6 packet is encapsulated in the Information field of
PPP Data Link Layer frames where the Protocol field indicates type
hex 0057 (Internet Protocol Version 6).
The maximum length of an IPv6 packet transmitted over a PPP link is
the same as the maximum length of the Information field of a PPP data
link layer frame. PPP links supporting IPv6 must allow at least 576
octets in the information field of a data link layer frame.
3. A PPP Network Control Protocol for IPv6
The IPv6 Control Protocol (IPV6CP) is responsible for configuring,
enabling, and disabling the IPv6 protocol modules on both ends of the
point-to-point link. IPV6CP uses the same packet exchange mechanism
as the Link Control Protocol (LCP). IPV6CP packets may not be
exchanged until PPP has reached the Network-Layer Protocol phase.
IPV6CP packets received before this phase is reached should be
silently discarded.
The IPv6 Control Protocol is exactly the same as the Link Control
Protocol [1] with the following exceptions:
Data Link Layer Protocol Field
Exactly one IPV6CP packet is encapsulated in the Information field
of PPP Data Link Layer frames where the Protocol field indicates
type hex 8057 (IPv6 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.
Haskin & Allen [Page 3]
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Timeouts
IPV6CP 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
IPV6CP has a distinct set of Configuration Options, which are
defined below.
4. IPV6CP Configuration Options
IPV6CP Configuration Options allow negotiation of desirable IPv6
parameters. IPV6CP uses the same Configuration Option format defined
for LCP [1], with a separate set of Options. If a Configuration
Option is not included in a Configure-Request packet, the default
value for that Configuration Option is assumed.
Up-to-date values of the IPV6CP Option Type field are specified in
the most recent "Assigned Numbers" RFC [4]. Current values are
assigned as follows:
1 Interface-Token
2 IPv6-Compression-Protocol
4.1. Interface-Token
Description
This Configuration Option provides a way to negotiate a unique
64-bit interface token to be used for the address
autoconfiguration [3] at the local end of the link (see section
5). The interface token MUST be unique within the PPP link; i.e.
upon completion of the negotiation different Interface-Token
values are to be selected for the ends of the PPP link.
Before this Configuration Option is requested, an implementation
chooses its tentative Interface-Token. The non-zero value of the
tentative Interface-Token SHOULD be chosen such that the value is
both unique to the link and, if possible, consistently
reproducible across initializations of the IPV6CP finite state
machine (administrative Close and reOpen, reboots, etc). The
rationale for preferring a consistently reproducible unique token
to a completely random token is to provide stability to global
scope addresses that can be formed from the interface token.
Suggested sources of uniqueness include machine serial numbers,
link-layer addresses, et cetera.
Haskin & Allen [Page 4]
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If a good source of uniqueness cannot be found, it is recommended
that a random number be generated. Good sources [1] of uniqueness
or randomness are required for the Interface-Token negotiation to
succeed. If neither a unique number or a random number can be
generated it is recommended that a zero value be used for the
Interface-Token transmitted in the Configure-Request. In this
case the PPP peer may provide a valid non-zero Interface-Token in
its response as described below. Note that if at least one of the
PPP peers is able to generate separate non-zero numbers for itself
and its peer, the token negotiation will succeed.
When a Configure-Request is received with the Interface-Token
Configuration Option and the receiving peer implements this
option, the received Interface-Token is compared with the
Interface-Token of the last Configure-Request sent to the peer.
Depending on the result of the comparison an implementation MUST
respond in one of the following ways:
If the two Interface-Tokens are different but the received
Interface-Token is zero, a Configure-Nak is sent with a non-zero
Interface-Token value suggested for use by the remote peer. Such
a suggested Interface-Token MUST be different from the Interface-
Token of the last Configure-Request sent to the peer. It is
recommended that the value suggested be consistently
reproducible across initializations of the IPV6CP finite state
machine (administrative Close and reOpen, reboots, etc).
If the two Interface-Tokens are different and the received
Interface-Token is not zero, the Interface-Token MUST be
acknowledged, i.e. a Configure-Ack is sent with the requested
Interface-Token, meaning that the responding peer agrees with the
Interface-Token requested.
If the two Interface-Tokens are equal and are not zero, a
Configure-Nak MUST be sent specifying a different non-zero
Interface-Token value suggested for use by the remote peer.
If the two Interface-Tokens are equal to zero, the Interface-
Tokens negotiation MUST be terminated by transmitting the
Configure-Reject with the Interface-Token value set to zero. In
this case a unique Interface-Token can not be negotiated.
If a Configure-Request is received with the Interface-Token
Configuration Option and the receiving peer does not implement
this option, Configure-Rej is sent.
Haskin & Allen [Page 5]
Draft IP Version 6 over PPP March 1997
A new Configure-Request SHOULD NOT be sent to the peer until
normal processing would cause it to be sent (that is, until a
Configure-Nak is received or the Restart timer runs out).
A new Configure-Request MUST NOT contain the Interface-Token
option if a valid Interface-Token Configure-Reject is received.
Reception of a Configure-Nak with a suggested Interface-Token
different from that of the last Configure-Nak sent to the peer
indicates a unique Interface-Token. In this case a new
Configure-Request MUST be sent with the token value suggested in
the last Configure-Nak from the peer. But if the received
Interface-Token is equal to the one sent in the last Configure-
Nak, a new Interface-Token MUST be chosen. In this case, a new
Configure-Request SHOULD be sent with the new tentative
Interface-Token. This sequence (transmit Configure-Request,
receive Configure-Request, transmit Configure-Nak, receive
Configure-Nak) might occur a few times, but it is extremely
unlikely to occur repeatedly. More likely, the Interface-Tokens
chosen at either end will quickly diverge, terminating the
sequence.
If negotiation of the Interface-Token is required, and the peer
did not provide the option in its Configure-Request, the option
SHOULD be appended to a Configure-Nak. The tentative value of the
Interface-Token given must be acceptable as the remote Interface-
Token; i.e. should be different from the token value selected for
the local end of the PPP link. The next Configure-Request from
the peer may include this option. If the next Configure-Request
does not include this option the peer MUST NOT send another
Configure-Nak with this option included. It should assume that the
peer's implementation does not support this option.
By default, an implementation SHOULD attempt to negotiate the
Interface-Token for its end of the PPP connection.
Haskin & Allen [Page 6]
Draft IP Version 6 over PPP March 1997
A summary of the Interface-Token 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 | Interface-Token (MS Byte)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Interface-Token (cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Interface-Token (LS Byte) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
1
Length
10
Interface-Token
The 64-bit Interface-Token which is very likely to be unique on
the link or zero if a good source of uniqueness can not be found.
Default Token Value
If no valid interface token can be successfully negotiated, no
default Interface-Token value should be assumed. The procedures
for recovering from such a case are unspecified. One approach is
to manually configure the interface token of the interface.
4.2. IPv6-Compression-Protocol
Description
This Configuration Option provides a way to negotiate the use of a
specific IPv6 packet compression protocol. The IPv6-Compression-
Protocol Configuration Option is used to indicate the ability to
receive compressed packets. Each end of the link must separately
request this option if bi-directional compression is desired. By
default, compression is not enabled.
IPv6 compression negotiated with this option is specific to IPv6
datagrams and is not to be confused with compression resulting
from negotiations via Compression Control Protocol (CCP), which
potentially effect all datagrams.
Haskin & Allen [Page 7]
Draft IP Version 6 over PPP March 1997
A summary of the IPv6-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 | IPv6-Compression-Protocol |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Data ...
+-+-+-+-+
Type
2
Length
>= 4
IPv6-Compression-Protocol
The IPv6-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.
Up-to-date values of the IPv6-Compression-Protocol field are
specified in the most recent "Assigned Numbers" RFC [4].
Current values are assigned as follows:
Value (in hex) Protocol
004f IPv6 Header Compression
Data
The Data field is zero or more octets and contains additional data
as determined by the particular compression protocol.
Default
No IPv6 compression protocol enabled.
Haskin & Allen [Page 8]
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5. Stateless Autoconfiguration and Link-Local Addresses
The interface token, which is used for forming IPv6 addresses of a
PPP interface, SHOULD be negotiated in the IPV6CP phase of the PPP
connection setup (see section 4.1). If no valid interface token has
been successfully negotiated, procedures for recovering from such a
case are unspecified. One approach is to manually configure the
interface token of the interface.
As long as the interface token is negotiated in the IPV6CP phase of
the PPP connection setup, it is redundant to perform duplicate
address detection as a part of the IPv6 Stateless Autoconfiguration
protocol [3]. Therefore it is recommended that for PPP links with
the IPV6CP Interface-Token option enabled the default value of the
DupAddrDetectTransmits autoconfiguration variable [3] be zero.
Link-local addresses of PPP interfaces have the following format:
| 10 bits | 54 bits | 64 bits |
+----------+------------------------+-----------------------------+
|1111111010| 0 | Interface Token |
+----------+------------------------+-----------------------------+
The most significant 10 bits of the address is the Link-Local prefix
FE80::. 54 zero bits pad out the address between the Link-Local
prefix and the Interface Token fields.
A. IPV6CP Recommended Options
The following Configurations Options are recommended:
Interface-Token
IPv6-Compression-Protocol
Haskin & Allen [Page 9]
Draft IP Version 6 over PPP March 1997
Security Considerations
The IPv6 Control Protocol extension to PPP can be used
with all defined PPP authentication and encryption mechanisms.
References
[1] Simpson, W., "The Point-to-Point Protocol", STD 51, RFC 1661,
July 1994.
[2] Deering, S., and R. Hinden, Editors, "Internet Protocol,
Version 6 (IPv6) Specification", RFC 1883, December 1995.
[3] Thomson, S., and T. Narten, "IPv6 Stateless Address
Autoconfiguration", RFC 1971, August 1996.
[4] Reynolds, J., and J. Postel, "Assigned Numbers", STD 2, RFC
1700, October 1994.
Acknowledgments
This document borrows from the Magic-Number LCP option and as such is
partially based on previous work done by the PPP working group.
Authors' Addresses
Dimitry Haskin
Bay Networks, Inc.
2 Federal Street
Billerica, MA 01821
email: dhaskin@baynetworks.com
Ed Allen
Bay Networks, Inc.
2 Federal Street
Billerica, MA 01821
email: eallen@baynetworks.com
Haskin & Allen [Page 10]