📄 rfc2472.txt
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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
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RFC 2472 IP Version 6 over PPP December 1998
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).
Haskin & Allen Standards Track [Page 2]
RFC 2472 IP Version 6 over PPP December 1998
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.
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RFC 2472 IP Version 6 over PPP December 1998
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
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RFC 2472 IP Version 6 over PPP December 1998
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.
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RFC 2472 IP Version 6 over PPP December 1998
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.
Haskin & Allen Standards Track [Page 6]
RFC 2472 IP Version 6 over PPP December 1998
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.
Haskin & Allen Standards Track [Page 7]
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