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RFC2472 - IP Version 6 over PPP

王朝other·作者佚名  2008-05-31
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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

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 11 33 44 6

0 56 12 78 3

+----------------+----------------+----------------+----------------+

cccccc0gcccccccccccccccceeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee

+----------------+----------------+----------------+----------------+

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 11 33 44 6

0 56 12 78 3

+----------------+----------------+----------------+----------------+

cccccc1gcccccccccccccccceeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee

+----------------+----------------+----------------+----------------+

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 11 33 4

0 56 12 7

+----------------+----------------+----------------+

cccccc0gcccccccccccccccceeeeeeeeeeeeeeeeeeeeeeee

+----------------+----------------+----------------+

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 11 33 44 6

0 56 12 78 3

+----------------+----------------+----------------+----------------+

cccccc1gcccccccccccccccc1111111111111110eeeeeeeeeeeeeeeeeeeeeeee

+----------------+----------------+----------------+----------------+

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

Copyright (C) The Internet Society (1998). All Rights Reserved.

This document and translations of it may be copied and furnished to

others, and derivative works that comment on or otherwise explain it

or assist in its implementation may be prepared, copied, published

and distributed, in whole or in part, without restriction of any

kind, provided that the above copyright notice and this paragraph are

included on all such copies and derivative works. However, this

document itself may not be modified in any way, such as by removing

the copyright notice or references to the Internet Society or other

Internet organizations, except as needed for the purpose of

developing Internet standards in which case the procedures for

copyrights defined in the Internet Standards process must be

followed, or as required to translate it into languages other than

English.

The limited permissions granted above are perpetual and will not be

revoked by the Internet Society or its successors or assigns.

This document and the information contained herein is provided on an

"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING

TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING

BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION

HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF

MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

 
 
 
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