draft-ietf-6man-ug-01.txt   rfc7136.txt 
6MAN B. E. Carpenter Internet Engineering Task Force (IETF) B. Carpenter
Internet-Draft Univ. of Auckland Request for Comments: 7136 Univ. of Auckland
Updates: 4291 (if approved) S. Jiang Updates: 4291 S. Jiang
Intended status: Standards Track Huawei Technologies Co., Ltd Category: Standards Track Huawei Technologies Co., Ltd
Expires: November 26, 2013 May 25, 2013 ISSN: 2070-1721 February 2014
Significance of IPv6 Interface Identifiers Significance of IPv6 Interface Identifiers
draft-ietf-6man-ug-01
Abstract Abstract
The IPv6 addressing architecture includes a unicast interface The IPv6 addressing architecture includes a unicast interface
identifier that is used in the creation of many IPv6 addresses. identifier that is used in the creation of many IPv6 addresses.
Interface identifiers are formed by a variety of methods. This Interface identifiers are formed by a variety of methods. This
document clarifies that the bits in an interface identifier have no document clarifies that the bits in an interface identifier have no
generic meaning and that the identifier should be treated as an meaning and that the entire identifier should be treated as an opaque
opaque value. In particular, RFC 4291 defines a method by which the value. In particular, RFC 4291 defines a method by which the
Universal and Group bits of an IEEE link-layer address are mapped Universal and Group bits of an IEEE link-layer address are mapped
into an IPv6 unicast interface identifier. This document clarifies into an IPv6 unicast interface identifier. This document clarifies
that those bits apply only to interface identifiers that are derived that those two bits are significant only in the process of deriving
from an IEEE link-layer address. It updates RFC 4291 accordingly. interface identifiers from an IEEE link-layer address, and it updates
RFC 4291 accordingly.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This is an Internet Standards Track document.
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months This document is a product of the Internet Engineering Task Force
and may be updated, replaced, or obsoleted by other documents at any (IETF). It represents the consensus of the IETF community. It has
time. It is inappropriate to use Internet-Drafts as reference received public review and has been approved for publication by the
material or to cite them other than as "work in progress." Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
This Internet-Draft will expire on November 26, 2013. Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7136.
Copyright Notice Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Problem statement . . . . . . . . . . . . . . . . . . . . . . 3 2. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 3
3. Usefulness of the U and G Bits . . . . . . . . . . . . . . . 5 3. Usefulness of the U and G Bits . . . . . . . . . . . . . . . 5
4. The Role of Duplicate Address Detection . . . . . . . . . . . 6 4. The Role of Duplicate Address Detection . . . . . . . . . . . 6
5. Clarification of Specifications . . . . . . . . . . . . . . . 6 5. Clarification of Specifications . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 7 6. Security Considerations . . . . . . . . . . . . . . . . . . . 7
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
9. Change log [RFC Editor: Please remove] . . . . . . . . . . . 8 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 9.1. Normative References . . . . . . . . . . . . . . . . . . 8
10.1. Normative References . . . . . . . . . . . . . . . . . . 9 9.2. Informative References . . . . . . . . . . . . . . . . . 8
10.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction 1. Introduction
IPv6 unicast addresses consist of a subnet prefix followed by an IPv6 unicast addresses consist of a prefix followed by an Interface
Interface Identifier (IID), the latter supposedly unique on the links Identifier (IID). The IID is supposed to be unique on the links
reached by routing to that prefix. According to the IPv6 addressing reached by routing to that prefix, giving an IPv6 address that is
architecture [RFC4291], when a 64-bit IPv6 unicast IID is formed on unique within the applicable scope (link local or global). According
the basis of an IEEE EUI-64 address, usually itself expanded from a to the IPv6 addressing architecture [RFC4291], when a 64-bit IPv6
48-bit MAC address, a particular format must be used: unicast IID is formed on the basis of an IEEE EUI-64 address, usually
itself expanded from a 48-bit MAC address, a particular format must
be used:
"For all unicast addresses, except those that start with the binary For all unicast addresses, except those that start with the binary
value 000, Interface IDs are required to be 64 bits long and to be value 000, Interface IDs are required to be 64 bits long and to be
constructed in Modified EUI-64 format." constructed in Modified EUI-64 format.
Thus the specification assumes that that the normal case is to Thus, the specification assumes that the normal case is to transform
transform an Ethernet-style address into an IID, but in practice, an Ethernet-style address into an IID, but, in practice, there are
there are various methods of forming such an interface identifier. various methods of forming such an IID.
The Modified EUI-64 format preserves the information provided by two The Modified EUI-64 format preserves the information provided by two
particular bits in the MAC address: particular bits in the MAC address:
o The "u" bit in an IEEE address is set to 0 to indicate universal o The "u/l" bit in a MAC address [IEEE802] is set to 0 to indicate
scope (implying uniqueness) or to 1 to indicate local scope universal scope (implying uniqueness) or to 1 to indicate local
(without implying uniqueness). In an IID this bit is inverted, scope (without implying uniqueness). In an IID formed from a MAC
i.e., 1 for universal scope and 0 for local scope. According to address, this bit is simply known as the "u" bit and its value is
RFC 4291 and [RFC5342], the reason for this was to make it easier inverted, i.e., 1 for universal scope and 0 for local scope.
for network operators to manually configure local-scope IIDs. According to [RFC4291] and [RFC7042], the reason for this was to
make it easier for network operators to manually configure
local-scope IIDs.
In an IID, this bit is in position 6, i.e., position 70 in the In an IID, this bit is in position 6, i.e., position 70 in the
complete IPv6 address. complete IPv6 address (when counting from 0).
o The "g" bit in an IEEE address is set to 1 to indicate group o The "i/g" bit in a MAC address is set to 1 to indicate group
addressing (link-layer multicast). The value of this bit is addressing (link-layer multicast). The value of this bit is
preserved in an IID. preserved in an IID, where it is known as the "g" bit.
In an IID, this bit is in position 7, i.e., position 71 in the In an IID, this bit is in position 7, i.e., position 71 in the
complete IPv6 address. complete IPv6 address (when counting from 0).
This document discusses problems observed with the "u" and "g" bits This document discusses problems observed with the "u" and "g" bits
as a result of the above requirements and the fact that various other as a result of the above requirements and the fact that various other
methods of forming an IID have been defined, quite independently of methods of forming an IID have been defined independently of the
the method described in Appendix A of RFC 4291. It then discusses method described in Appendix A of RFC 4291. It then discusses the
the usefulness of these two bits and the significance of the bits in usefulness of these two bits and the significance of the bits in an
an IID in general. Finally it updates RFC 4291 accordingly. IID in general. Finally, it updates RFC 4291 accordingly.
1.1. Terminology 1.1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
2. Problem statement 2. Problem Statement
In addition to IIDs formed from IEEE EUI-64 addresses, various new In addition to IIDs formed from IEEE EUI-64 addresses, various new
forms of IID have been defined or proposed, such as temporary forms of IIDs have been defined, including temporary addresses
addresses [RFC4941], Cryptographically Generated Addresses (CGAs) [RFC4941], Cryptographically Generated Addresses (CGAs) [RFC3972]
[RFC3972], Hash-Based Addresses (HBAs) [RFC5535], stable privacy [RFC4982], Hash-Based Addresses (HBAs) [RFC5535], and ISATAP
addresses [I-D.ietf-6man-stable-privacy-addresses], or mapped addresses [RFC5214]. Other methods have been proposed, such as
addresses for 4rd [I-D.ietf-softwire-4rd]. In each case, the stable privacy addresses [IID-SLAAC] and mapped addresses for 4rd
question of how to set the "u" and "g" bits has to be decided. For [SOFTWR-4RD]. In each case, the question of how to set the "u" and
example, RFC 3972 specifies that they are both zero in CGAs, and the "g" bits has to be decided. For example, RFC 3972 specifies that
same applies to HBAs. On the other hand, RFC 4941 specifies that "u" they are both zero in CGAs, and RFC 4982 describes them as if they
must be zero but leaves "g" variable. The NAT64 addressing format were reserved bits. The same applies to HBAs. On the other hand,
[RFC6052] sets the whole byte containing "u" and "g" to zero. RFC 4941 specifies that "u" must be zero but leaves "g" variable.
The NAT64 addressing format [RFC6052] sets the whole byte containing
"u" and "g" to zero.
Another case where the "u" and "g" bits are specified is in the Another case where the "u" and "g" bits are specified is in the
Reserved IPv6 Subnet Anycast Address format [RFC2526], which states Reserved IPv6 Subnet Anycast Address format [RFC2526], which states
that "for interface identifiers in EUI-64 format, the universal/local that "for interface identifiers in EUI-64 format, the universal/local
bit in the interface identifier MUST be set to 0" (i.e., local) and bit in the interface identifier MUST be set to 0" (i.e., local) and
requires that "g" bit to be set to 1. However, the text neither the "g" bit is required to be set to 1. However, the text neither
states nor implies any semantics for these bits in anycast addresses. states nor implies any semantics for these bits in anycast addresses.
A common operational practice for well-known servers is to manually A common operational practice for well-known servers is to manually
assign a small number as the IID, in which case "u" and "g" are both assign a small number as the IID, in which case "u" and "g" are both
zero. zero.
These cases illustrate that the statement quoted above from RFC 4291 These cases illustrate that the statement quoted above from RFC 4291
requiring "Modified EUI-64 format" is rather meaningless when applied requiring "Modified EUI-64 format" is inapplicable when applied to
to forms of IID that are not in fact based on an underlying EUI-64 forms of IID that are not in fact based on an underlying EUI-64
address. In practice, the IETF has chosen to assign some 64-bit IIDs address. In practice, the IETF has chosen to assign some 64-bit IIDs
that have nothing to do with EUI-64. that have nothing to do with EUI-64.
A particular case is that of /127 prefixes for point-to-point links A particular case is that of /127 prefixes for point-to-point links
between routers, as standardised by [RFC6164]. The addresses on between routers, as standardised by [RFC6164]. The addresses on
these links are undoubtedly global unicast addresses, but they do not these links are undoubtedly global unicast addresses, but they do not
have a 64-bit IID. The bits in the positions named "u" and "g" in have a 64-bit IID. The bits in the positions named "u" and "g" in
such an IID have no special significance and their values are not such an IID have no special significance and their values are not
specified. specified.
Each time a new IID format is proposed, the question arises whether Each time a new IID format is proposed, the question arises whether
these bits have any meaning. Section 2.2.1 of RFC 5342 discusses the these bits have any meaning. Section 2.2.1 of [RFC7042] discusses
mechanics of the bit allocations but does not explain the purpose or the mechanics of the bit allocations but does not explain the purpose
usefulness of these bits in an IID. There is an IANA registry for or usefulness of these bits in an IID. There is an IANA registry for
reserved IID values [RFC5453] but again there is no explanation of reserved IID values [RFC5453], but again there is no explanation of
the purpose of the "u" and "g" bits. the purpose of the "u" and "g" bits.
There was a presumption when IPv6 was designed and the IID format was There was a presumption when IPv6 was designed and the IID format was
first specified that a universally unique IID might prove to be very first specified that a universally unique IID might prove to be very
useful, for example to contribute to solving the multihoming problem. useful, for example to contribute to solving the multihoming problem.
Indeed, the addressing architecture [RFC4291] states this explicitly: Indeed, the addressing architecture [RFC4291] states this explicitly:
"The use of the universal/local bit in the Modified EUI-64 format The use of the universal/local bit in the Modified EUI-64 format
identifier is to allow development of future technology that can take identifier is to allow development of future technology that can
advantage of interface identifiers with universal scope." take advantage of interface identifiers with universal scope.
However, this has not so far proved to be the case. Also, there is However, so far, this has not proved to be the case. Also, there is
evidence from the field that IEEE MAC addresses with "u" = 0 are evidence from the field that MAC addresses with universal scope are
sometime incorrectly assigned to multiple MAC interfaces. Firstly, sometimes assigned to multiple MAC interfaces. There are recurrent
there are recurrent reports of manufacturers assigning the same MAC reports of manufacturers assigning the same MAC address to multiple
address to multiple devices. Secondly, significant re-use of the devices, and significant reuse of the same virtual MAC address is
same virtual MAC address is reported in virtual machine environments. reported in virtual machine environments. Once transformed into IID
Once transformed into IID format (with "u" = 1) these identifiers format (with "u" = 1), these identifiers would purport to be
would purport to be universally unique but would in fact be universally unique but would in fact be ambiguous. This has no known
ambiguous. This has no known harmful effect as long as the harmful effect as long as the replicated MAC addresses and IIDs are
replicated MAC addresses and IIDs are used on different layer 2 used on different layer 2 links. If they are used on the same link,
links. If they are used on the same link, of course there will be a of course there will be a problem, very likely interfering with
problem, to be detected by duplicate address detection [RFC4862], but link-layer transmission. If not, the problem will be detected by
such a problem can usually only be resolved by human intervention. duplicate address detection [RFC4862] [RFC6775], but such an error
can usually only be resolved by human intervention.
The conclusion from this is that the "u" bit is not a reliable The conclusion from this is that the "u" bit is not a reliable
indicator of universal uniqueness. indicator of universal uniqueness.
We note that Identifier-Locator Network Protocol (ILNP), a We note that Identifier-Locator Network Protocol (ILNP), a
multihoming solution that might be expected to benefit from multihoming solution that might be expected to benefit from
universally unique IIDs in modified EUI-64 format, does not in fact universally unique IIDs in modified EUI-64 format, does not in fact
rely on them. ILNP uses its own format, defined as a Node Identifier rely on them. ILNP uses its own format defined as a Node Identifier
[RFC6741]. ILNP has the constraint that a given Node Identifier must [RFC6741]. ILNP has the constraint that a given Node Identifier must
be unique within the context of a given Locator (i.e. within a be unique within the context of a given Locator (i.e., within a
single given IPv6 subnetwork). As we have just shown, the state of single given IPv6 subnetwork). As we have just shown, the state of
the "u" bit does not in any way guarantee such uniqueness, but the "u" bit does not in any way guarantee such uniqueness, but
duplicate address detection is available. duplicate address detection is available.
Thus, we can conclude that the value of the "u" bit in IIDs has no Thus, we can conclude that the value of the "u" bit in IIDs has no
particular meaning. In the case of an IID created from a MAC address particular meaning. In the case of an IID created from a MAC address
according to RFC 4291, its value is determined by the MAC address, according to RFC 4291, its value is determined by the MAC address,
but that is all. but that is all.
An IPv6 IID should not be created from a MAC group address, so the An IPv6 IID should not be created from a MAC group address, so the
"g" bit will normally be zero, but this value also has no particular "g" bit will normally be zero. But, this value also has no
meaning. Additionally, the "u" and the "g" bits are both meaningless particular meaning. Additionally, the "u" and the "g" bits are both
in the format of an IPv6 multicast group ID [RFC3306], [RFC3307]. meaningless in the format of an IPv6 multicast group ID [RFC3306]
[RFC3307].
None of the above implies that there is a problem with using the "u" None of the above implies that there is a problem with using the "u"
and "g" bits in MAC addresses as part of the process of generating and "g" bits in MAC addresses as part of the process of generating
IIDs from MAC addresses, or with specifying their values in other IIDs from MAC addresses, or with specifying their values in other
methods of generating IIDs. What it does imply is that, after an IID methods of generating IIDs. What it does imply is that after an IID
is generated by any method, no reliable deductions can be made from is generated by any method, no reliable deductions can be made from
the state of the "u" and "g" bits; in other words, these bits have no the state of the "u" and "g" bits; in other words, these bits have no
useful semantics in an IID. useful semantics in an IID.
Once this is recognised, we can avoid the problematic confusion Once this is recognised, we can avoid the problematic confusion
caused by these bits each time that a new form of IID is proposed. caused by these bits each time that a new form of IID is proposed.
3. Usefulness of the U and G Bits 3. Usefulness of the U and G Bits
Given that the "u" and "g" bits do not have a reliable meaning in an Given that the "u" and "g" bits do not have a reliable meaning in an
IID, it is relevant to consider what usefulness they do have. IID, it is relevant to consider what usefulness they do have.
If an IID is known or guessed to have been created according to RFC If an IID is known or guessed to have been created according to
4291, it could be transformed back into a MAC address. This can be [RFC4291], it could be transformed back into a MAC address. This can
very helpful during operational fault diagnosis. For that reason, be very helpful during operational fault diagnosis. For that reason,
mapping the IEEE "u" and "g" bits into the IID has operational mapping the IEEE "u" and "g" bits into the IID has operational
usefulness. However, it should be stressed that "u" = "g" = 0 does usefulness. However, it should be stressed that an IID with "u" = 1
not prove that an IID was formed from a MAC address; on the contrary, and "g" = 0 might not be formed from a MAC address; on the contrary,
it might equally result from another method. With other methods, it might equally result from another method. With other methods,
there is no reverse transformation available. there is no reverse transformation available.
To the extent that each method of IID creation specifies the values Given that the values of the "u" and "g" bits in an IID have no
of the "u" and "g" bits, and that each new method is carefully particular meaning, new methods of IID formation are at liberty to
designed in the light of its predecessors, these bits tend to reduce use them as they wish, for example, as additional pseudo-random bits
the chances of duplicate IIDs. to reduce the chances of duplicate IIDs.
4. The Role of Duplicate Address Detection 4. The Role of Duplicate Address Detection
As mentioned above, Duplicate Address Detection (DAD) [RFC4862] is As mentioned above, Duplicate Address Detection (DAD) [RFC4862] is
able to detect any case where a collision of two IIDs on the same able to detect any case where a collision of two IIDs on the same
link leads to a duplicated IPv6 address. The scope of DAD may be link leads to a duplicated IPv6 address. The scope of DAD may be
extended to a set of links by a DAD proxy [I-D.ietf-6man-dad-proxy]. extended to a set of links by a DAD proxy [RFC6957] or by Neighbor
Since DAD is mandatory for all nodes, there will be no case in which Discovery Optimization [RFC6775]. Since DAD is mandatory for all
an IID collision, however unlikely it may be, is not detected. It is nodes, there will be almost no case in which an IID collision,
out of scope of most existing specifications to define the recovery however unlikely it may be, is not detected. It is out of scope of
action after a DAD failure, which is an implementation issue. The most existing specifications to define the recovery action after a
best procedure to follow will depend on the IID formation method in DAD failure, which is an implementation issue. If a manually created
use. For example, if an IID is formed by some pseudo-random process, IID, or an IID derived from a MAC address according to RFC 4291,
that process could simply be repeated. If a manually created IID, or leads to a DAD failure, human intervention will most likely be
an IID derived from a MAC address according to RFC 4291, leads to a required. However, as mentioned above, some methods of IID formation
DAD failure, human intervention will most likely be required. might produce IID values with "u" = 1 and "g" = 0 that are not based
on a MAC address. With very low probability, such a value might
collide with an IID based on a MAC address.
There is one case in RFC 4862 that requires additional consideration: As stated in RFC 4862:
"On the other hand, if the duplicate link-local address is not formed On the other hand, if the duplicate link-local address is not
from an interface identifier based on the hardware address, which is formed from an interface identifier based on the hardware address,
supposed to be uniquely assigned, IP operation on the interface MAY which is supposed to be uniquely assigned, IP operation on the
be continued." interface MAY be continued.
However, as mentioned above, some methods of IID formation might Continued operation is only possible if a new IID is created. The
produce IID values with "u" = "g" = 0 that are not based on a MAC best procedure to follow for this will depend on the IID formation
(hardware) address. With very low probability, such a value might method in use. For example, if an IID is formed by a pseudo-random
collide with an IID based on a MAC address. There is no algorithm process, that process could simply be repeated.
for determining whether this case has arisen, rather than a genuine
MAC address collision. Implementers should carefully consider the
consequences of continuing IPv6 operation on the interface in this
unlikely situation.
5. Clarification of Specifications 5. Clarification of Specifications
This section describes clarifications to the IPv6 specifications that This section describes clarifications to the IPv6 specifications that
result from the above discussion. Their aim is to reduce confusion result from the above discussion.
while retaining the useful aspects of the "u" and "g" bits in IIDs.
The EUI-64 to IID transformation defined in the IPv6 addressing The EUI-64 to IID transformation defined in the IPv6 addressing
architecture [RFC4291] MUST be used for all cases where an IPv6 IID architecture [RFC4291] MUST be used for all cases where an IPv6 IID
is derived from an IEEE MAC or EUI-64 address. With any other form is derived from an IEEE MAC or EUI-64 address. With any other form
of link layer address, an equivalent transformation SHOULD be used. of link-layer address, an equivalent transformation SHOULD be used.
Specifications of other forms of 64-bit IID MUST specify how all 64 Specifications of other forms of 64-bit IIDs MUST specify how all 64
bits are set, but need not treat the "u" and "g" bits in any special bits are set, but a generic semantic meaning for the "u" and "g" bits
way. A general semantic meaning for these bits MUST NOT be defined. MUST NOT be defined. However, the method of generating IIDs for
However, the method of generating IIDs for specific link types MAY specific link types MAY define some local significance for certain
define some local significance for certain bits. bits.
In all cases, the bits in an IID have no general semantics; in other In all cases, the bits in an IID have no generic semantics; in other
words, they have opaque values. In fact, the whole IID value MUST be words, they have opaque values. In fact, the whole IID value MUST be
viewed as an opaque bit string by third parties, except possibly in viewed as an opaque bit string by third parties, except possibly in
the local context. the local context.
The following statement in section 2.5.1 of the IPv6 addressing The following statement in Section 2.5.1 of the IPv6 addressing
architecture [RFC4291]: architecture [RFC4291]:
"For all unicast addresses, except those that start with the binary For all unicast addresses, except those that start with the binary
value 000, Interface IDs are required to be 64 bits long and to be value 000, Interface IDs are required to be 64 bits long and to be
constructed in Modified EUI-64 format." constructed in Modified EUI-64 format.
is replaced by: is replaced by:
"For all unicast addresses, except those that start with the binary For all unicast addresses, except those that start with the binary
value 000, Interface IDs are required to be 64 bits long. If derived value 000, Interface IDs are required to be 64 bits long. If
from an IEEE MAC-layer address, they must be constructed in Modified derived from an IEEE MAC-layer address, they must be constructed
EUI-64 format." in Modified EUI-64 format.
The following statement in section 2.5.1 of the IPv6 addressing The following statement in Section 2.5.1 of the IPv6 addressing
architecture [RFC4291] is obsoleted: architecture [RFC4291] is obsoleted:
"The use of the universal/local bit in the Modified EUI-64 format The use of the universal/local bit in the Modified EUI-64 format
identifier is to allow development of future technology that can take identifier is to allow development of future technology that can
advantage of interface identifiers with universal scope." take advantage of interface identifiers with universal scope.
As far as is known, no existing implementation will be affected by As far as is known, no existing implementation will be affected by
these changes. The benefit is that future design discussions are these changes. The benefit is that future design discussions are
simplified. simplified.
6. Security Considerations 6. Security Considerations
No new security exposures or issues are raised by this document. No new security exposures or issues are raised by this document.
In some contexts, unpredictable IID values are considered beneficial
to enhance privacy and defeat scanning attacks. The recognition that
the IID value should be regarded as an opaque bit string is
consistent with methods of IID formation that result in
unpredictable, pseudo-random values.
7. IANA Considerations 7. IANA Considerations
This document requests no immediate action by IANA. However, the This document requests no immediate action by IANA. However, the
following should be noted when considering future proposed additions following should be noted when considering any future proposed
to the registry of reserved IID values, which requires Standards addition to the registry of reserved IID values, which requires
Action according to [RFC5453]. Standards Action [RFC5226] according to [RFC5453].
Full deployment of a new reserved IID value would require updates to Full deployment of a new reserved IID value would require updates to
IID generation code in every deployed IPv6 stack, so the technical IID generation code in every deployed IPv6 stack, so the technical
justification for such a Standards Action would need to be extremely justification for such a Standards Action would need to be extremely
strong. strong.
OPEN ISSUE: Alternatively, we could decide to close the reserved IID The preceding sentence and a reference to this document have been
registry completely (which would also mean formally updating RFC added to the "Reserved IPv6 Interface Identifiers" registry.
5453). If we choose this approach, the following point can be
deleted. Comments welcome.
A reserved IID, or a range of reserved IIDs, will most likely specify
values for both "u" and "g", since they are among the high-order
bits. At the present time, none of the known methods of generating
IIDs will generate "u" = "g" = 1. Reserved IIDs with "u" = "g" = 1
are therefore unlikely to collide with automatically generated IIDs.
8. Acknowledgements 8. Acknowledgements
Valuable comments were received from Ran Atkinson, Remi Despres, Valuable comments were received from Ran Atkinson, Remi Despres,
Fernando Gont, Brian Haberman, Joel Halpern, Bob Hinden, Christian Ralph Droms, Fernando Gont, Eric Gray, Brian Haberman, Joel Halpern,
Huitema, Ray Hunter, Mark Smith, and other participants in the 6MAN Bob Hinden, Christian Huitema, Ray Hunter, Tatuya Jinmei, Roger
working group. Jorgensen, Mark Smith, Bernie Volz, and other participants in the
6MAN working group.
Brian Carpenter was a visitor at the Computer Laboratory, Cambridge Brian Carpenter was a visitor at the Computer Laboratory, Cambridge
University during part of this work. University during part of this work.
This document was produced using the xml2rfc tool [RFC2629]. 9. References
9. Change log [RFC Editor: Please remove]
draft-ietf-6man-ug-01: emphasised "opaque" nature of IID, added text
about DAD failures, expanded IANA considerations, 2013-05-25.
draft-ietf-6man-ug-00: first WG version, text clarified, added
possibility of link-local significance, 2013-03-28.
draft-carpenter-6man-ug-01: numerous clarifications following WG
comments, discussed DAD, added new section on the usefulness of the u
/g bits, expanded IANA considerations, set intended status,
2013-02-21.
draft-carpenter-6man-ug-00: original version, 2013-01-31.
10. References
10.1. Normative References 9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, February 2006. Architecture", RFC 4291, February 2006.
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862, September 2007. Address Autoconfiguration", RFC 4862, September 2007.
[RFC5342] Eastlake, D., "IANA Considerations and IETF Protocol Usage
for IEEE 802 Parameters", BCP 141, RFC 5342, September
2008.
[RFC5453] Krishnan, S., "Reserved IPv6 Interface Identifiers", RFC [RFC5453] Krishnan, S., "Reserved IPv6 Interface Identifiers", RFC
5453, February 2009. 5453, February 2009.
10.2. Informative References [RFC7042] Eastlake, D. and J. Abley, "IANA Considerations and IETF
Protocol and Documentation Usage for IEEE 802 Parameters",
BCP 141, RFC 7042, October 2013.
[I-D.ietf-6man-dad-proxy] 9.2. Informative References
Costa, F., Combes, J., Pougnard, X., and L. Hongyu,
"Duplicate Address Detection Proxy", draft-ietf-6man-dad-
proxy-07 (work in progress), April 2013.
[I-D.ietf-6man-stable-privacy-addresses] [IEEE802] "IEEE Standard for Local and Metropolitan Area Networks:
Overview and Architecture", IEEE Std 802-2001 (R2007),
2007.
[IID-SLAAC]
Gont, F., "A method for Generating Stable Privacy-Enhanced Gont, F., "A method for Generating Stable Privacy-Enhanced
Addresses with IPv6 Stateless Address Autoconfiguration Addresses with IPv6 Stateless Address Autoconfiguration
(SLAAC)", draft-ietf-6man-stable-privacy-addresses-07 (SLAAC)", Work in Progress, March 2012.
(work in progress), May 2013.
[I-D.ietf-softwire-4rd]
Despres, R., Jiang, S., Penno, R., Lee, Y., Chen, G., and
M. Chen, "IPv4 Residual Deployment via IPv6 - a Stateless
Solution (4rd)", draft-ietf-softwire-4rd-05 (work in
progress), April 2013.
[RFC2526] Johnson, D. and S. Deering, "Reserved IPv6 Subnet Anycast [RFC2526] Johnson, D. and S. Deering, "Reserved IPv6 Subnet Anycast
Addresses", RFC 2526, March 1999. Addresses", RFC 2526, March 1999.
[RFC2629] Rose, M.T., "Writing I-Ds and RFCs using XML", RFC 2629,
June 1999.
[RFC3306] Haberman, B. and D. Thaler, "Unicast-Prefix-based IPv6 [RFC3306] Haberman, B. and D. Thaler, "Unicast-Prefix-based IPv6
Multicast Addresses", RFC 3306, August 2002. Multicast Addresses", RFC 3306, August 2002.
[RFC3307] Haberman, B., "Allocation Guidelines for IPv6 Multicast [RFC3307] Haberman, B., "Allocation Guidelines for IPv6 Multicast
Addresses", RFC 3307, August 2002. Addresses", RFC 3307, August 2002.
[RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)", [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)",
RFC 3972, March 2005. RFC 3972, March 2005.
[RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy [RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy
Extensions for Stateless Address Autoconfiguration in Extensions for Stateless Address Autoconfiguration in
IPv6", RFC 4941, September 2007. IPv6", RFC 4941, September 2007.
[RFC4982] Bagnulo, M. and J. Arkko, "Support for Multiple Hash
Algorithms in Cryptographically Generated Addresses
(CGAs)", RFC 4982, July 2007.
[RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site
Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214,
March 2008.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[RFC5535] Bagnulo, M., "Hash-Based Addresses (HBA)", RFC 5535, June [RFC5535] Bagnulo, M., "Hash-Based Addresses (HBA)", RFC 5535, June
2009. 2009.
[RFC6052] Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X. [RFC6052] Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X.
Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052, Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052,
October 2010. October 2010.
[RFC6164] Kohno, M., Nitzan, B., Bush, R., Matsuzaki, Y., Colitti, [RFC6164] Kohno, M., Nitzan, B., Bush, R., Matsuzaki, Y., Colitti,
L., and T. Narten, "Using 127-Bit IPv6 Prefixes on Inter- L., and T. Narten, "Using 127-Bit IPv6 Prefixes on Inter-
Router Links", RFC 6164, April 2011. Router Links", RFC 6164, April 2011.
[RFC6741] Atkinson,, RJ., "Identifier-Locator Network Protocol [RFC6741] Atkinson,, RJ., "Identifier-Locator Network Protocol
(ILNP) Engineering Considerations", RFC 6741, November (ILNP) Engineering Considerations", RFC 6741, November
2012. 2012.
[RFC6775] Shelby, Z., Chakrabarti, S., Nordmark, E., and C. Bormann,
"Neighbor Discovery Optimization for IPv6 over Low-Power
Wireless Personal Area Networks (6LoWPANs)", RFC 6775,
November 2012.
[RFC6957] Costa, F., Combes, J-M., Pougnard, X., and H. Li,
"Duplicate Address Detection Proxy", RFC 6957, June 2013.
[SOFTWR-4RD]
Despres, R., Jiang, S., Penno, R., Lee, Y., Chen, G., and
M. Chen, "IPv4 Residual Deployment via IPv6 - a Stateless
Solution (4rd)", Work in Progress, October 2013.
Authors' Addresses Authors' Addresses
Brian Carpenter Brian Carpenter
Department of Computer Science Department of Computer Science
University of Auckland University of Auckland
PB 92019 PB 92019
Auckland 1142 Auckland 1142
New Zealand New Zealand
Email: brian.e.carpenter@gmail.com EMail: brian.e.carpenter@gmail.com
Sheng Jiang Sheng Jiang
Huawei Technologies Co., Ltd Huawei Technologies Co., Ltd
Q14, Huawei Campus Q14, Huawei Campus
No.156 Beiqing Road No.156 Beiqing Road
Hai-Dian District, Beijing 100095 Hai-Dian District, Beijing 100095
P.R. China P.R. China
Email: jiangsheng@huawei.com EMail: jiangsheng@huawei.com
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