Network Working Group D. Haskin
Request for Comments: 2472 E. Allen
Obsoletes: 2023 Bay Networks, Inc.
Category: Standards Track December 1998
IP Version 6 over PPP
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.
Copyright Notice
Copyright (C) The Internet Society (1998). All Rights Reserved.
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 ................................ 2
3. A PPP Network Control Protocol for IPv6 ............... 3
4. IPV6CP Configuration Options .......................... 4
4.1. Interface-Identifier .............................. 4
4.2. IPv6-Compression-Protocol.......................... 9
5. Stateless Autoconfiguration and Link-Local Addresses .. 10
6 Security Considerations ............................... 11
7 Acknowledgments ....................................... 11
8 Changes from RFC-2023 ................................. 11
9 References ............................................ 12
10 Authors' Addresses .................................... 13
11 Full Copyright Statement .............................. 14
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.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [7].
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 the
information field at least as large as the minimum link MTU size
required for IPv6 [2].
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.
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.
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-Identifier
2 IPv6-Compression-Protocol
The only IPV6CP options defined in this document are Interface-
Identifier and IPv6-Compression-Protocol. Any other IPV6CP
configuration options that can be defined over time are to be defined
in separate documents.
4.1. Interface-Identifier
Description
This Configuration Option provides a way to negotiate a unique 64-
bit interface identifier to be used for the address
autoconfiguration [3] at the local end of the link (see section 5).
A Configure-Request MUST contain exactly one instance of the
Interface-Identifier option [1]. The interface identifier MUST be
unique within the PPP link; i.e. upon completion of the
negotiation different Interface-Identifier values are to be
selected for the ends of the PPP link. The interface identifier
MAY also be unique over a broader scope.
Before this Configuration Option is requested, an implementation
chooses its tentative Interface-Identifier. The non-zero value of
the tentative Interface-Identifier 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
interface identifier to a completely random interface identifier is
to provide stability to global scope addresses that can be formed
from the interface identifier.
Assuming that interface identifier bits are numbered from 0 to 63
in canonical bit order where the most significant bit is the bit
number 0, the bit number 6 is the "u" bit (universal/local bit
in IEEE EUI-64 [5] terminology) which indicates whether or not the
interface identifier is based on a globally unique IEEE identifier
(EUI-48 or EUI-64 [5]) (see the case 1 below). It is set to
one (1) if a globally unique IEEE identifier is used to derive
the interface identifier, and it is set to zero (0) otherwise.
The following are methods for choosing the tentative Interface
Identifier in the preference order:
1) If an IEEE global identifier (EUI-48 or EUI-64) is
available anywhere on the node, it should be used to construct
the tentative Interface-Identifier due to its uniqueness
properties. When extracting an IEEE global identifier from
another device on the node, care should be taken to that the
extracted identifier is presented in canonical ordering [8].
The only transformation from an EUI-64 identifier is to invert
the "u" bit (universal/local bit in IEEE EUI-64 terminology).
For example, for a globally unique EUI-64 identifier of the
form:
most-significant least-significant
bit bit
|0 1|1 3|3 4|4 6|
|0 5|6 1|2 7|8 3|
+----------------+----------------+----------------+----------------+
|cccccc0gcccccccc|cccccccceeeeeeee|eeeeeeeeeeeeeeee|eeeeeeeeeeeeeeee|
+----------------+----------------+----------------+----------------+
where "c" are the bits of the assigned company_id, "0" is the
value of the universal/local bit to indicate global scope, "g"
is group/individual bit, and "e" are the bits of the extension
identifier,
the IPv6 interface identifier would be of the form:
most-significant least-significant
bit bit
|0 1|1 3|3 4|4 6|
|0 5|6 1|2 7|8 3|
+----------------+----------------+----------------+----------------+
|cccccc1gcccccccc|cccccccceeeeeeee|eeeeeeeeeeeeeeee|eeeeeeeeeeeeeeee|
+----------------+----------------+----------------+----------------+
The only change is inverting the value of the universal/local
bit.
In the case of a EUI-48 identifier, it is first converted to the
EUI-64 format by inserting two bytes, with hexadecimal values of
0xFF and 0xFE, in the middle of the 48 bit MAC (between the
company_id and extension-identifier portions of the EUI-48
value). For example, for a globally unique 48 bit EUI-48
identifier of the form:
most-significant least-significant
bit bit
|0 1|1 3|3 4|
|0 5|6 1|2 7|
+----------------+----------------+----------------+
|cccccc0gcccccccc|cccccccceeeeeeee|eeeeeeeeeeeeeeee|
+----------------+----------------+----------------+
where "c" are the bits of the assigned company_id, "0" is the
value of the universal/local bit to indicate global scope, "g"
is group/individual bit, and "e" are the bits of the extension
identifier, the IPv6 interface identifier would be of the form:
most-significant least-significant
bit bit
|0 1|1 3|3 4|4 6|
|0 5|6 1|2 7|8 3|
+----------------+----------------+----------------+----------------+
|cccccc1gcccccccc|cccccccc11111111|11111110eeeeeeee|eeeeeeeeeeeeeeee|
+----------------+----------------+----------------+----------------+
2) If an IEEE global identifier is not available a different source
of uniqueness should be used. Suggested sources of uniqueness
include link-layer addresses, machine serial numbers, et cetera.
In this case the "u" bit of the interface identifier MUST be set
to zero (0).
3) If a good source of uniqueness cannot be found, it is
recommended that a random number be generated. In this case the
"u" bit of the interface identifier MUST be set to zero (0).
Good sources [1] of uniqueness or randomness are required for the
Interface-Identifier 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-Identifier transmitted in the
Configure-Request. In this case the PPP peer may provide a valid
non-zero Interface-Identifier 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 identifier
negotiation will succeed.
When a Configure-Request is received with the Interface-Identifier
Configuration Option and the receiving peer implements this option,
the received Interface-Identifier is compared with the Interface-
Identifier 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-Identifiers are different but the received
Interface-Identifier is zero, a Configure-Nak is sent with a non-
zero Interface-Identifier value suggested for use by the remote
peer. Such a suggested Interface-Identifier MUST be different from
the Interface-Identifier 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). The "u"
universal/local) bit of the suggested identifier MUST be set to
zero (0) regardless of its source unless the globally unique EUI-
48/EUI-64 derived identifier is provided for the exclusive use by
the remote peer.
If the two Interface-Identifiers are different and the received
Interface-Identifier is not zero, the Interface-Identifier MUST be
acknowledged, i.e. a Configure-Ack is sent with the requested
Interface-Identifier, meaning that the responding peer agrees with
the Interface-Identifier requested.
If the two Interface-Identifiers are equal and are not zero, a
Configure-Nak MUST be sent specifying a different non-zero
Interface-Identifier value suggested for use by the remote 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). The "u"
universal/local) bit of the suggested identifier MUST be set to
zero (0) regardless of its source unless the globally unique EUI-
48/EUI-64 derived identifier is provided for the exclusive use by
the remote peer.
If the two Interface-Identifiers are equal to zero, the Interface-
Identifiers negotiation MUST be terminated by transmitting the
Configure-Reject with the Interface-Identifier value set to zero.
In this case a unique Interface-Identifier can not be negotiated.
If a Configure-Request is received with the Interface-Identifier
Configuration Option and the receiving peer does not implement this
option, Configure-Rej is sent.
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-Identifier
option if a valid Interface-Identifier Configure-Reject is
received.
Reception of a Configure-Nak with a suggested Interface-Identifier
different from that of the last Configure-Nak sent to the peer
indicates a unique Interface-Identifier. In this case a new
Configure-Request MUST be sent with the identifier value suggested
in the last Configure-Nak from the peer. But if the received
Interface-Identifier is equal to the one sent in the last
Configure-Nak, a new Interface-Identifier MUST be chosen. In this
case, a new Configure-Request SHOULD be sent with the new tentative
Interface-Identifier. 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-
Identifiers chosen at either end will quickly diverge, terminating
the sequence.
If negotiation of the Interface-Identifier 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-Identifier given must be acceptable as the remote
Interface-Identifier; i.e. it should be different from the
identifier 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-Identifier for its end of the PPP connection.
A summary of the Interface-Identifier 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-Identifier (MS Bytes)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Interface-Identifier (cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Interface-Identifier (LS Bytes) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
1
Length
10
Interface-Identifier
The 64-bit Interface-Identifier which is very likely to be unique on
the link or zero if a good source of uniqueness can not be found.
Default
If no valid interface identifier can be successfully negotiated, no
default Interface-Identifier value should be assumed. The procedures
for recovering from such a case are unspecified. One approach is to
manually configure the interface identifier 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.
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.
No IPv6-Compression-Protocol field values are currently assigned.
Specific assignments will be made in documents that define
specific compression algorithms.
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.
5. Stateless Autoconfiguration and Link-Local Addresses
The Interface Identifier of IPv6 unicast addresses [6] of a PPP
interface, SHOULD be negotiated in the IPV6CP phase of the PPP
connection setup (see section 4.1). If no valid Interface Identifier
has been successfully negotiated, procedures for recovering from such
a case are unspecified. One approach is to manually configure the
Interface Identifier of the interface.
As long as the Interface Identifier 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-Identifier 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 Identifier |
+----------+------------------------+-----------------------------+
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 Identifier fields.
6. Security Considerations
The IPv6 Control Protocol extension to PPP can be used with all
defined PPP authentication and encryption mechanisms.
7. 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.
8. Changes from RFC-2023
The following changes were made from RFC-2023 "IP Version 6 over
PPP":
- Changed to use "Interface Identifier" instead of the "Interface
Token" term according to the terminology adopted in [6].
- Increased the size of Interface Identifier to 64 bits according to
the newly adopted IPv6 addressing architecture [6].
- Added methods for selection of an interface identifier that is
consistently reproducible across initializations of the IPV6CP
finite state machine.
- Added the interface identifier selection methods for generating
globally unique interface identifier from an unique an IEEE global
identifier when it is available anywhere on the node.
- Changed to send a Configure-Nak instead a Configure-Ack in response
to receiving a Configure-Request with a zero Interface-Identifier
value.
- Replaced the value assignment of the IPv6-Compression-Protocol
field of the IPv6-Compression-Protocol Configuration option with
the text stating that no IPv6-Compression-Protocol field values are
currently assigned and that specific assignments will be made in
documents that define specific compression algorithms.
- Added new and updated references.
- Minor text clarifications and improvements.
9. 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", RFC2460, December 1998.
[3] Thomson, S., and T. Narten, "IPv6 Stateless Address
Autoconfiguration", RFC2462, December 1998.
[4] Reynolds, J., and J. Postel, "Assigned Numbers", STD 2, RFC
1700, October 1994. See also: http://www.iana.org/numbers.html
[5] IEEE, "Guidelines for 64-bit Global Identifier (EUI-64)
Registration Authority",
http://standards.ieee.org/db/oui/tutorials/EUI64.html, March
1997.
[6] Hinden, R., and S. Deering, "IP Version 6 Addressing
Architecture", RFC2373, July 1998.
[7] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels," BCP 14, RFC2119, March 1997.
[8] Narten T., and C. Burton, "A Caution On The Canonical Ordering
Of Link-Layer Addresses", RFC2469, December 1998.
10. Authors' Addresses
Dimitry Haskin
Bay Networks, Inc.
600 Technology Park
Billerica, MA 01821
EMail: dhaskin@baynetworks.com
Ed Allen
Bay Networks, Inc.
600 Technology Park
Billerica, MA 01821
EMail: eallen@baynetworks.com
11. Full Copyright Statement
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