Internet Draft S.Varada (TranSwitch)
Document: draft-ietf-ipv6-over-ppp-v2-00.txt D.Haskins
Expires: November 2004 Ed Allen
May 2004
IP Version 6 over PPP
<draft-ietf-ipv6-over-ppp-v2-00.txt>
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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.
This document is an update to RFC 2472 and, hence, obsoletes RFC
2472.
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-Identifier......................................4
4.2 IPv6-Compression-Protocol.................................9
5. Stateless Autoconfiguration and Link-Local Addresses.....10
6. Security Considerations..................................11
7. Acknowledgments..........................................11
8. References...............................................11
Appendix A:Global Scope Addresses........................12
Appendix B:Changes from RFC-2472.........................12
Authors' Addresses.......................................12
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 unique to the link and, preferably, 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 (see Appendix
A) 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 hexa-
decimal 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,
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
>=3D 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.
The negotiated Interface-Identifier is used by the local end of the
PPP link to autoconfigure IPv6 link-local unicast address for the
PPP interface. However, it cannot be assumed that the same
Interface-Identifier is used in configuring global unicast
addresses for the PPP interface using IPv6 stateless address
autoconfiguration [3]. The PPP peer MAY generate one or more
Interface Identifiers, for instance, using a method described
in[9], to autoconfigure one or more global unicast addresses.
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 (DAD) as a part of the IPv6 Stateless
Address Autoconfiguration protocol [3] on the IPv6 link-local
address generated by the PPP peer. It MAY also be redundant to
perform DAD on any global unicast addresses created (using an
Interface-Identifier that is either negotiated during IPV6CP or
generated, for instance, as per [9]) for the interface as part of
the IPv6 Stateless Address Autoconfiguration protocol [3] provided
that the following two conditions are met:
1) The prefixes advertised, through the Router Advertisement
messages, by the access router terminating the PPP link are
exclusive to the PPP link.
2) The access router terminating the PPP link does not
autoconfigure any IPv6 global unicast addresses from the
prefixes that it advertises.
Therefore, it is recommended that for PPP links with the IPV6CP
Interface-Identifier option enabled and that satisfy the
aforementioned two conditions, the default value of the
DupAddrDetectTransmits autoconfiguration variable [3] be zero.
3GPP2 networks are an example of a technology that uses PPP to
enable a host to obtain an IPv6 global unicast address and
satisfies the aforementioned two conditions [10]. 3GPP networks
are another example [11].
Link-local addresses
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.
The editor is grateful for the input provided by members of the
IPv6 community in the spirit of updating the RFC 2472. Thanks, in
particular, go to Pete Barany and Karim El-malki for their
contributions. Also, thanks to Alex Conta for a thorough reviewing.
8. 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 2460, December 1998.
[3] Thomson, S., and T. Narten, "IPv6 Stateless Address
Autoconfiguration", RFC 2462, December 1998.
[4] IANA, "Assigned Numbers", http://www.iana.org/numbers.html
[5] IEEE, "Guidelines for 64-bit Global Identifier (EUI-64)
Registration Authority", April 2004.
[6] Hinden, R., and S. Deering, "IP Version 6 Addressing
Architecture", RFC 3513, July 1998.
[7] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels," BCP 14, RFC 2119, March 1997.
[8] Narten T., and C. Burton, "A Caution On The Canonical
Ordering Of Link-Layer Addresses,=94 RFC 2469, December 1998.
[9] Narten T., and R. Draves, "Privacy Extensions for Stateless
Address Autoconfiguration in IPv6,=94 RFC 3041, January 2001.
[10] 3GPP2 X.S0011-002-C v1.0, "cdma2000 Wireless IP Network
Standard: Simple IP and Mobile IP Access Services,=94 September=
2003.
[11] 3GPP TS 29.061 V5.8.0, "Interworking between the Public Land
Mobile Network (PLMN) Supporting packet based services and
Packet Data Networks (PDN) (Release 5),=94 January 2004.
[12] Droms, E., et al., =93Dynamic Host Configuration Protocol for
IPv6 (DHCPv6),=94 RFC 3315, July 2003.
Appendix A: Global Scope Addresses
A node on the PPP link MUST create global unicast addresses either
through stateless or stateful Address Auto-configuration mechanisms
[3]&[12]. In stateless address auto-configuration, the node relies
on sub-net prefixes advertised by the router via the Router
Advertisement messages to obtain global unicast addresses from an
interface identifier. In stateful address auto-configuration, the
host MAY rely on Router Advertisement messages or a Stateful
Server, like, DHCPv6 [12], to obtain global unicast addresses.
Appendix B: Changes from RFC-2472
The following changes were made from RFC-2472 "IP Version 6 over
PPP":
- Updated the text in section 4.1 to include the reference to
Appendix A and minor text clarifications.
- Updated the text in Section 5 to: (a) option the use of one or
more Interface-Identifiers generated, other than the IPV6CP
negotiated, in the creation of global unicast addresses, and (b)
identify cases against the DAD of created non-link-local
addresses.
- Added new and updated references.
- Added the Appendix A
Authors' Addresses
Dimitry Haskin
Ed Allen
Srihari Varada (Editor)
TranSwitch Corporation
3 Enterprise Dr.
Shelton, CT 06484.
EMail: varada@txc.com