draft-ietf-ipv6-privacy-addrs-v2-04.txt   draft-ietf-ipv6-privacy-addrs-v2-05.txt 
IPv6 Working Group T. Narten IPv6 Working Group T. Narten
Internet-Draft IBM Corporation Internet-Draft IBM Corporation
Expires: November 25, 2005 R. Draves Obsoletes: 3041 (if approved) R. Draves
Microsoft Research Expires: February 2, 2007 Microsoft Research
S. Krishnan S. Krishnan
Ericsson Research Ericsson Research
May 24, 2005 August 2006
Privacy Extensions for Stateless Address Autoconfiguration in IPv6 Privacy Extensions for Stateless Address Autoconfiguration in IPv6
draft-ietf-ipv6-privacy-addrs-v2-04 draft-ietf-ipv6-privacy-addrs-v2-05
Status of this Memo Status of this Memo
By submitting this Internet-Draft, each author represents that any By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79. aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that Task Force (IETF), its areas, and its working groups. Note that
skipping to change at page 1, line 37 skipping to change at page 1, line 37
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt. http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html. http://www.ietf.org/shadow.html.
This Internet-Draft will expire on November 25, 2005. This Internet-Draft will expire on February 2, 2007.
Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2005). Copyright (C) The Internet Society (2006).
Abstract Abstract
Nodes use IPv6 stateless address autoconfiguration to generate Nodes use IPv6 stateless address autoconfiguration to generate
addresses using a combination of locally available information and addresses using a combination of locally available information and
information advertised by routers. Addresses are formed by combining information advertised by routers. Addresses are formed by combining
network prefixes with an interface identifier. On interfaces that network prefixes with an interface identifier. On interfaces that
contain embedded IEEE Identifiers, the interface identifier is contain embedded IEEE Identifiers, the interface identifier is
typically derived from it. On other interface types, the interface typically derived from it. On other interface types, the interface
identifier is generated through other means, for example, via random identifier is generated through other means, for example, via random
skipping to change at page 2, line 20 skipping to change at page 2, line 20
identifiers that change over time, even in cases where the interface identifiers that change over time, even in cases where the interface
contains an embedded IEEE identifier. Changing the interface contains an embedded IEEE identifier. Changing the interface
identifier (and the global scope addresses generated from it) over identifier (and the global scope addresses generated from it) over
time makes it more difficult for eavesdroppers and other information time makes it more difficult for eavesdroppers and other information
collectors to identify when different addresses used in different collectors to identify when different addresses used in different
transactions actually correspond to the same node. transactions actually correspond to the same node.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 Conventions used in this document . . . . . . . . . . . . 4 1.1. Conventions used in this document . . . . . . . . . . . . 4
1.2 Problem Statement . . . . . . . . . . . . . . . . . . . . 4 1.2. Problem Statement . . . . . . . . . . . . . . . . . . . . 4
2. Background . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2. Background . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1 Extended Use of the Same Identifier . . . . . . . . . . . 5 2.1. Extended Use of the Same Identifier . . . . . . . . . . . 5
2.2 Address Usage in IPv4 Today . . . . . . . . . . . . . . . 6 2.2. Address Usage in IPv4 Today . . . . . . . . . . . . . . . 6
2.3 The Concern With IPv6 Addresses . . . . . . . . . . . . . 7 2.3. The Concern With IPv6 Addresses . . . . . . . . . . . . . 7
2.4 Possible Approaches . . . . . . . . . . . . . . . . . . . 8 2.4. Possible Approaches . . . . . . . . . . . . . . . . . . . 8
3. Protocol Description . . . . . . . . . . . . . . . . . . . . . 10 3. Protocol Description . . . . . . . . . . . . . . . . . . . . . 10
3.1 Assumptions . . . . . . . . . . . . . . . . . . . . . . . 10 3.1. Assumptions . . . . . . . . . . . . . . . . . . . . . . . 10
3.2 Generation Of Randomized Interface Identifiers . . . . . . 12 3.2. Generation Of Randomized Interface Identifiers . . . . . . 12
3.2.1 When Stable Storage Is Present . . . . . . . . . . . . 12 3.2.1. When Stable Storage Is Present . . . . . . . . . . . . 12
3.2.2 In The Absence of Stable Storage . . . . . . . . . . . 13 3.2.2. In The Absence of Stable Storage . . . . . . . . . . . 13
3.2.3 Alternate approaches . . . . . . . . . . . . . . . . . 14 3.2.3. Alternate approaches . . . . . . . . . . . . . . . . . 14
3.3 Generating Temporary Addresses . . . . . . . . . . . . . . 14 3.3. Generating Temporary Addresses . . . . . . . . . . . . . . 14
3.4 Expiration of Temporary Addresses . . . . . . . . . . . . 15 3.4. Expiration of Temporary Addresses . . . . . . . . . . . . 15
3.5 Regeneration of Randomized Interface Identifiers . . . . . 16 3.5. Regeneration of Randomized Interface Identifiers . . . . . 16
3.6 Deployment Considerations . . . . . . . . . . . . . . . . 17 3.6. Deployment Considerations . . . . . . . . . . . . . . . . 17
4. Implications of Changing Interface Identifiers . . . . . . . . 19 4. Implications of Changing Interface Identifiers . . . . . . . . 19
5. Defined Constants . . . . . . . . . . . . . . . . . . . . . . 20 5. Defined Constants . . . . . . . . . . . . . . . . . . . . . . 20
6. Future Work . . . . . . . . . . . . . . . . . . . . . . . . . 21 6. Future Work . . . . . . . . . . . . . . . . . . . . . . . . . 21
7. Significant Changes from RFC 3041 . . . . . . . . . . . . . . 22 7. Security Considerations . . . . . . . . . . . . . . . . . . . 22
8. Changes from version 00 . . . . . . . . . . . . . . . . . . . 23 8. Significant Changes from RFC 3041 . . . . . . . . . . . . . . 23
9. Changes from version 01 . . . . . . . . . . . . . . . . . . . 24 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 24
10. Changes from version 02 . . . . . . . . . . . . . . . . . . 25 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 25
11. Changes from version 03 . . . . . . . . . . . . . . . . . . 26 10.1. Normative References . . . . . . . . . . . . . . . . . . . 25
12. Security Considerations . . . . . . . . . . . . . . . . . . 27 10.2. Informative References . . . . . . . . . . . . . . . . . . 25
13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 28 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 27
14. References . . . . . . . . . . . . . . . . . . . . . . . . . 29 Intellectual Property and Copyright Statements . . . . . . . . . . 28
14.1 Normative References . . . . . . . . . . . . . . . . . . . 29
14.2 Informative References . . . . . . . . . . . . . . . . . . 29
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 30
Intellectual Property and Copyright Statements . . . . . . . . 32
1. Introduction 1. Introduction
Stateless address autoconfiguration [ADDRCONF] defines how an IPv6 Stateless address autoconfiguration [ADDRCONF] defines how an IPv6
node generates addresses without the need for a DHCPv6 server. Some node generates addresses without the need for a DHCPv6 server. Some
types of network interfaces come with an embedded IEEE Identifier types of network interfaces come with an embedded IEEE Identifier
(i.e., a link-layer MAC address), and in those cases stateless (i.e., a link-layer MAC address), and in those cases stateless
address autoconfiguration uses the IEEE identifier to generate a 64- address autoconfiguration uses the IEEE identifier to generate a 64-
bit interface identifier [ADDRARCH]. By design, the interface bit interface identifier [ADDRARCH]. By design, the interface
identifier is likely to be globally unique when generated in this identifier is likely to be globally unique when generated in this
skipping to change at page 4, line 5 skipping to change at page 4, line 5
help mitigate those concerns for individual users and in environments help mitigate those concerns for individual users and in environments
where such concerns are significant. Section 2 provides background where such concerns are significant. Section 2 provides background
information on the issue. Section 3 describes a procedure for information on the issue. Section 3 describes a procedure for
generating alternate interface identifiers and global scope generating alternate interface identifiers and global scope
addresses. Section 4 discusses implications of changing interface addresses. Section 4 discusses implications of changing interface
identifiers. The term "global scope addresses" is used in this identifiers. The term "global scope addresses" is used in this
document to collectively refer to "Global unicast addresses" as document to collectively refer to "Global unicast addresses" as
defined in [ADDRARCH] and "Unique local addresses" as defined in defined in [ADDRARCH] and "Unique local addresses" as defined in
[ULA] [ULA]
1.1 Conventions used in this document 1.1. Conventions used in this document
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].
1.2 Problem Statement 1.2. Problem Statement
Addresses generated using Stateless address autoconfiguration Addresses generated using Stateless address autoconfiguration
[ADDRCONF]contain an embedded interface identifier, which remains [ADDRCONF]contain an embedded interface identifier, which remains
constant over time. Anytime a fixed identifier is used in multiple constant over time. Anytime a fixed identifier is used in multiple
contexts, it becomes possible to correlate seemingly unrelated contexts, it becomes possible to correlate seemingly unrelated
activity using this identifier. activity using this identifier.
The correlation can be performed by The correlation can be performed by
o An attacker who is in the path between the node in question and o An attacker who is in the path between the node in question and
skipping to change at page 5, line 11 skipping to change at page 5, line 11
Use of temporary addresses will not prevent such payload based Use of temporary addresses will not prevent such payload based
correlation. correlation.
2. Background 2. Background
This section discusses the problem in more detail, provides context This section discusses the problem in more detail, provides context
for evaluating the significance of the concerns in specific for evaluating the significance of the concerns in specific
environments and makes comparisons with existing practices. environments and makes comparisons with existing practices.
2.1 Extended Use of the Same Identifier 2.1. Extended Use of the Same Identifier
The use of a non-changing interface identifier to form addresses is a The use of a non-changing interface identifier to form addresses is a
specific instance of the more general case where a constant specific instance of the more general case where a constant
identifier is reused over an extended period of time and in multiple identifier is reused over an extended period of time and in multiple
independent activities. Anytime the same identifier is used in independent activities. Anytime the same identifier is used in
multiple contexts, it becomes possible for that identifier to be used multiple contexts, it becomes possible for that identifier to be used
to correlate seemingly unrelated activity. For example, a network to correlate seemingly unrelated activity. For example, a network
sniffer placed strategically on a link across which all traffic to/ sniffer placed strategically on a link across which all traffic to/
from a particular host crosses could keep track of which destinations from a particular host crosses could keep track of which destinations
a node communicated with and at what times. Such information can in a node communicated with and at what times. Such information can in
skipping to change at page 6, line 18 skipping to change at page 6, line 18
The use of a constant identifier within an address is of special The use of a constant identifier within an address is of special
concern because addresses are a fundamental requirement of concern because addresses are a fundamental requirement of
communication and cannot easily be hidden from eavesdroppers and communication and cannot easily be hidden from eavesdroppers and
other parties. Even when higher layers encrypt their payloads, other parties. Even when higher layers encrypt their payloads,
addresses in packet headers appear in the clear. Consequently, if a addresses in packet headers appear in the clear. Consequently, if a
mobile host (e.g., laptop) accessed the network from several mobile host (e.g., laptop) accessed the network from several
different locations, an eavesdropper might be able to track the different locations, an eavesdropper might be able to track the
movement of that mobile host from place to place, even if the upper movement of that mobile host from place to place, even if the upper
layer payloads were encrypted. layer payloads were encrypted.
2.2 Address Usage in IPv4 Today 2.2. Address Usage in IPv4 Today
Addresses used in today's Internet are often non-changing in practice Addresses used in today's Internet are often non-changing in practice
for extended periods of time. In an increasing number of sites, for extended periods of time. In an increasing number of sites,
addresses are assigned statically and typically change infrequently. addresses are assigned statically and typically change infrequently.
Over the last few years, sites have begun moving away from static Over the last few years, sites have begun moving away from static
allocation to dynamic allocation via DHCP [DHCP]. In theory, the allocation to dynamic allocation via DHCP [DHCP]. In theory, the
address a client gets via DHCP can change over time, but in practice address a client gets via DHCP can change over time, but in practice
servers often return the same address to the same client (unless servers often return the same address to the same client (unless
addresses are in such short supply that they are reused immediately addresses are in such short supply that they are reused immediately
by a different node when they become free). Thus, even within sites by a different node when they become free). Thus, even within sites
skipping to change at page 7, line 12 skipping to change at page 7, line 12
used to update the DNS dynamically, it may not always be available used to update the DNS dynamically, it may not always be available
depending on the administrative policy. In addition, changing an depending on the administrative policy. In addition, changing an
address but keeping the same DNS name does not really address the address but keeping the same DNS name does not really address the
underlying concern, since the DNS name becomes a non-changing underlying concern, since the DNS name becomes a non-changing
identifier. Servers generally require a DNS name (so clients can identifier. Servers generally require a DNS name (so clients can
connect to them), and clients often do as well (e.g., some servers connect to them), and clients often do as well (e.g., some servers
refuse to speak to a client whose address cannot be mapped into a DNS refuse to speak to a client whose address cannot be mapped into a DNS
name that also maps back into the same address). Section 4 describes name that also maps back into the same address). Section 4 describes
one approach to this issue. one approach to this issue.
2.3 The Concern With IPv6 Addresses 2.3. The Concern With IPv6 Addresses
The division of IPv6 addresses into distinct topology and interface The division of IPv6 addresses into distinct topology and interface
identifier portions raises an issue new to IPv6 in that a fixed identifier portions raises an issue new to IPv6 in that a fixed
portion of an IPv6 address (i.e., the interface identifier) can portion of an IPv6 address (i.e., the interface identifier) can
contain an identifier that remains constant even when the topology contain an identifier that remains constant even when the topology
portion of an address changes (e.g., as the result of connecting to a portion of an address changes (e.g., as the result of connecting to a
different part of the Internet). In IPv4, when an address changes, different part of the Internet). In IPv4, when an address changes,
the entire address (including the local part of the address) usually the entire address (including the local part of the address) usually
changes. It is this new issue that this document addresses. changes. It is this new issue that this document addresses.
skipping to change at page 8, line 12 skipping to change at page 8, line 12
an address could be used to track activities of an individual, even an address could be used to track activities of an individual, even
as they move topologically within the internet. as they move topologically within the internet.
In summary, IPv6 addresses on a given interface generated via In summary, IPv6 addresses on a given interface generated via
Stateless Autoconfiguration contain the same interface identifier, Stateless Autoconfiguration contain the same interface identifier,
regardless of where within the Internet the device connects. This regardless of where within the Internet the device connects. This
facilitates the tracking of individual devices (and thus potentially facilitates the tracking of individual devices (and thus potentially
users). The purpose of this document is to define mechanisms that users). The purpose of this document is to define mechanisms that
eliminate this issue, in those situations where it is a concern. eliminate this issue, in those situations where it is a concern.
2.4 Possible Approaches 2.4. Possible Approaches
One way to avoid having a static non-changing address is to use One way to avoid having a static non-changing address is to use
DHCPv6 [DHCPV6] for obtaining addresses. The DHCPv6 server could be DHCPv6[DHCPV6] for obtaining addresses. Section 12 of [DHCPV6]
configured to hand out addresses that change over time. But DHCPv6 discusses the use of DHCPv6 for the assignment and management of
will solve the privacy issue only if it frequently handed out "temporary addresses", which are never renewed and provide the same
constantly changing addresses to the nodes or if the DHCPv6 client property of temporary addresses described in this document with
moves from links to links frequently, being allocated independent regards to the privacy concern.
addresses from different DHCPv6 servers. However, the former does
not happen automatically, and is difficult to configure manually; the
latter cannot be assumed for static (not frequently moving) hosts.
Thus, DHCPv6 is not a self contained alternative for solving the
privacy issues addressed by this document. However, in the absence
of stateless address autoconfiguration, DHCPv6 can be used for
distributing temporary addresses to clients.
Another approach, compatible with the stateless address Another approach, compatible with the stateless address
autoconfiguration architecture, would be to change the interface autoconfiguration architecture, would be to change the interface
identifier portion of an address over time and generate new addresses identifier portion of an address over time and generate new addresses
from the interface identifier for some address scopes. Changing the from the interface identifier for some address scopes. Changing the
interface identifier can make it more difficult to look at the IP interface identifier can make it more difficult to look at the IP
addresses in independent transactions and identify which ones addresses in independent transactions and identify which ones
actually correspond to the same node, both in the case where the actually correspond to the same node, both in the case where the
routing prefix portion of an address changes and when it does not. routing prefix portion of an address changes and when it does not.
skipping to change at page 10, line 49 skipping to change at page 10, line 49
multicast groups may be required to put its interface into multicast groups may be required to put its interface into
promiscuous mode, resulting in possible reduced performance. promiscuous mode, resulting in possible reduced performance.
A node highly concerned about privacy MAY use different interface A node highly concerned about privacy MAY use different interface
identifiers on different prefixes, resulting in a set of global identifiers on different prefixes, resulting in a set of global
addresses that cannot be easily tied to each other. For example addresses that cannot be easily tied to each other. For example
a node MAY create different interface identifiers I1,I2, and I3 a node MAY create different interface identifiers I1,I2, and I3
for use with different prefixes P1,P2, and P3 on the same for use with different prefixes P1,P2, and P3 on the same
interface. interface.
3.1 Assumptions 3.1. Assumptions
The following algorithm assumes that each interface maintains an The following algorithm assumes that each interface maintains an
associated randomized interface identifier. When temporary addresses associated randomized interface identifier. When temporary addresses
are generated, the current value of the associated randomized are generated, the current value of the associated randomized
interface identifier is used. While the same identifier can be used interface identifier is used. While the same identifier can be used
to create more than one temporary address, the value SHOULD change to create more than one temporary address, the value SHOULD change
over time as described in Section 3.5. over time as described in Section 3.5.
The algorithm also assumes that for a given temporary address, an The algorithm also assumes that for a given temporary address, an
implementation can determine the prefix from which it was generated. implementation can determine the prefix from which it was generated.
skipping to change at page 12, line 5 skipping to change at page 12, line 5
[ADDR_SELECT] mandates implementations to provide a mechanism, which [ADDR_SELECT] mandates implementations to provide a mechanism, which
allows an application to configure its preference for temporary allows an application to configure its preference for temporary
addresses over public addresses. It also allows for an addresses over public addresses. It also allows for an
implementation to prefer temporary addresses by default, so that the implementation to prefer temporary addresses by default, so that the
connections initiated by the node can use temporary addresses without connections initiated by the node can use temporary addresses without
requiring application-specific enablement. This document also requiring application-specific enablement. This document also
assumes that an API will exist that allows individual applications to assumes that an API will exist that allows individual applications to
indicate whether they prefer to use temporary or public addresses and indicate whether they prefer to use temporary or public addresses and
override the system defaults. override the system defaults.
3.2 Generation Of Randomized Interface Identifiers 3.2. Generation Of Randomized Interface Identifiers
We describe two approaches for the generation and maintenance of the We describe two approaches for the generation and maintenance of the
randomized interface identifier. The first assumes the presence of randomized interface identifier. The first assumes the presence of
stable storage that can be used to record state history for use as stable storage that can be used to record state history for use as
input into the next iteration of the algorithm across system input into the next iteration of the algorithm across system
restarts. A second approach addresses the case where stable storage restarts. A second approach addresses the case where stable storage
is unavailable and there is a need to generate randomized interface is unavailable and there is a need to generate randomized interface
identifiers without previous state. identifiers without previous state.
The random interface identifier generation algorithm, as described in The random interface identifier generation algorithm, as described in
this document, uses MD5 as the hash algorithm. The node MAY use this document, uses MD5 as the hash algorithm. The node MAY use
another algorithm instead of MD5 to produce the random interface another algorithm instead of MD5 to produce the random interface
identifier. identifier.
3.2.1 When Stable Storage Is Present 3.2.1. When Stable Storage Is Present
The following algorithm assumes the presence of a 64-bit "history The following algorithm assumes the presence of a 64-bit "history
value" that is used as input in generating a randomized interface value" that is used as input in generating a randomized interface
identifier. The very first time the system boots (i.e., out-of-the- identifier. The very first time the system boots (i.e., out-of-the-
box), a random value SHOULD be generated using techniques that help box), a random value SHOULD be generated using techniques that help
ensure the initial value is hard to guess [RANDOM]. Whenever a new ensure the initial value is hard to guess [RANDOM]. Whenever a new
interface identifier is generated, a value generated by the interface identifier is generated, a value generated by the
computation is saved in the history value for the next iteration of computation is saved in the history value for the next iteration of
the algorithm. the algorithm.
skipping to change at page 13, line 13 skipping to change at page 13, line 13
obtained in step 2 in place of the history value in step 1. obtained in step 2 in place of the history value in step 1.
5. Save the generated identifier as the associated randomized 5. Save the generated identifier as the associated randomized
interface identifier. interface identifier.
6. Take the rightmost 64-bits of the MD5 digest computed in step 2) 6. Take the rightmost 64-bits of the MD5 digest computed in step 2)
and save them in stable storage as the history value to be used and save them in stable storage as the history value to be used
in the next iteration of the algorithm. in the next iteration of the algorithm.
MD5 was chosen for convenience, and because its particular properties MD5 was chosen for convenience, and because its particular properties
were adequate to produce the desired level of randomization. IPv6 were adequate to produce the desired level of randomization.The node
nodes are already required to implement MD5 as part of IPsec [IPSEC], MAY use another algorithm instead of MD5 to produce the random
thus the code will already be present on IPv6 machines. interface identifier
In theory, generating successive randomized interface identifiers In theory, generating successive randomized interface identifiers
using a history scheme as above has no advantages over generating using a history scheme as above has no advantages over generating
them at random. In practice, however, generating truly random them at random. In practice, however, generating truly random
numbers can be tricky. Use of a history value is intended to avoid numbers can be tricky. Use of a history value is intended to avoid
the particular scenario where two nodes generate the same randomized the particular scenario where two nodes generate the same randomized
interface identifier, both detect the situation via DAD, but then interface identifier, both detect the situation via DAD, but then
proceed to generate identical randomized interface identifiers via proceed to generate identical randomized interface identifiers via
the same (flawed) random number generation algorithm. The above the same (flawed) random number generation algorithm. The above
algorithm avoids this problem by having the interface identifier algorithm avoids this problem by having the interface identifier
(which will often be globally unique) used in the calculation that (which will often be globally unique) used in the calculation that
generates subsequent randomized interface identifiers. Thus, if two generates subsequent randomized interface identifiers. Thus, if two
nodes happen to generate the same randomized interface identifier, nodes happen to generate the same randomized interface identifier,
they should generate different ones on the followup attempt. they should generate different ones on the followup attempt.
3.2.2 In The Absence of Stable Storage 3.2.2. In The Absence of Stable Storage
In the absence of stable storage, no history value will be available In the absence of stable storage, no history value will be available
across system restarts to generate a pseudo-random sequence of across system restarts to generate a pseudo-random sequence of
interface identifiers. Consequently, the initial history value used interface identifiers. Consequently, the initial history value used
above SHOULD be generated at random. A number of techniques might be above SHOULD be generated at random. A number of techniques might be
appropriate. Consult [RANDOM] for suggestions on good sources for appropriate. Consult [RANDOM] for suggestions on good sources for
obtaining random numbers. Note that even though machines may not obtaining random numbers. Note that even though machines may not
have stable storage for storing a history value, they will in many have stable storage for storing a history value, they will in many
cases have configuration information that differs from one machine to cases have configuration information that differs from one machine to
another (e.g., user identity, security keys, serial numbers, etc.). another (e.g., user identity, security keys, serial numbers, etc.).
One approach to generating a random initial history value in such One approach to generating a random initial history value in such
cases is to use the configuration information to generate some data cases is to use the configuration information to generate some data
bits (which may remain constant for the life of the machine, but will bits (which may remain constant for the life of the machine, but will
vary from one machine to another), append some random data and vary from one machine to another), append some random data and
compute the MD5 digest as before. compute the MD5 digest as before.
3.2.3 Alternate approaches 3.2.3. Alternate approaches
Note that there are other approaches to generate random interface Note that there are other approaches to generate random interface
identifiers, albeit with different goals and applicability. One such identifiers, albeit with different goals and applicability. One such
approach is CGA [CGA], which generates a random interface identifier approach is CGA [CGA], which generates a random interface identifier
based on the public key of the node. The goal of CGAs is to prove based on the public key of the node. The goal of CGAs is to prove
ownership of an address and to prevent spoofing and stealing of ownership of an address and to prevent spoofing and stealing of
existing IPv6 addresses. They are used for securing neighbor existing IPv6 addresses. They are used for securing neighbor
discovery using [SEND]. The CGA random interface identifier discovery using [SEND]. The CGA random interface identifier
generation algorithm may not be suitable for privacy addresses generation algorithm may not be suitable for privacy addresses
because of the following properties because of the following properties
o It requires the node to have a public key. This means that the o It requires the node to have a public key. This means that the
node can still be identified by its public key node can still be identified by its public key
o The random interface identifier process is computationally o The random interface identifier process is computationally
intensive and hence discourages frequent regeneration intensive and hence discourages frequent regeneration
3.3 Generating Temporary Addresses 3.3. Generating Temporary Addresses
[ADDRCONF] describes the steps for generating a link-local address [ADDRCONF] describes the steps for generating a link-local address
when an interface becomes enabled as well as the steps for generating when an interface becomes enabled as well as the steps for generating
addresses for other scopes. This document extends [ADDRCONF] as addresses for other scopes. This document extends [ADDRCONF] as
follows. When processing a Router Advertisement with a Prefix follows. When processing a Router Advertisement with a Prefix
Information option carrying a global scope prefix for the purposes of Information option carrying a global scope prefix for the purposes of
address autoconfiguration (i.e., the A bit is set), the node MUST address autoconfiguration (i.e., the A bit is set), the node MUST
perform the following steps: perform the following steps:
1. Process the Prefix Information Option as defined in [ADDRCONF], 1. Process the Prefix Information Option as defined in [ADDRCONF],
skipping to change at page 15, line 16 skipping to change at page 15, line 15
3. When a new public address is created as described in [ADDRCONF], 3. When a new public address is created as described in [ADDRCONF],
the node SHOULD also create a new temporary address. the node SHOULD also create a new temporary address.
4. When creating a temporary address, the lifetime values MUST be 4. When creating a temporary address, the lifetime values MUST be
derived from the corresponding prefix as follows: derived from the corresponding prefix as follows:
* Its Valid Lifetime is the lower of the Valid Lifetime of the * Its Valid Lifetime is the lower of the Valid Lifetime of the
public address or TEMP_VALID_LIFETIME public address or TEMP_VALID_LIFETIME
* Its Preferred Lifetime is the lower of the Preferred Lifetime * Its Preferred Lifetime is the lower of the Preferred Lifetime
of the prefix or TEMP_PREFERRED_LIFETIME - DESYNC_FACTOR. of the public address or TEMP_PREFERRED_LIFETIME -
DESYNC_FACTOR.
5. A temporary address is created only if this calculated Preferred 5. A temporary address is created only if this calculated Preferred
Lifetime is greater than REGEN_ADVANCE time units. In Lifetime is greater than REGEN_ADVANCE time units. In
particular, an implementation MUST NOT create a temporary address particular, an implementation MUST NOT create a temporary address
with a zero Preferred Lifetime. with a zero Preferred Lifetime.
6. New temporary addresses MUST be created by appending the 6. New temporary addresses MUST be created by appending the
interface's current randomized interface identifier to the prefix interface's current randomized interface identifier to the prefix
that was received. that was received.
skipping to change at page 15, line 38 skipping to change at page 15, line 38
generated temporary address. If DAD indicates the address is generated temporary address. If DAD indicates the address is
already in use, the node MUST generate a new randomized interface already in use, the node MUST generate a new randomized interface
identifier as described in Section 3.2 above, and repeat the identifier as described in Section 3.2 above, and repeat the
previous steps as appropriate up to TEMP_IDGEN_RETRIES times. If previous steps as appropriate up to TEMP_IDGEN_RETRIES times. If
after TEMP_IDGEN_RETRIES consecutive attempts no non-unique after TEMP_IDGEN_RETRIES consecutive attempts no non-unique
address was generated, the node MUST log a system error and MUST address was generated, the node MUST log a system error and MUST
NOT attempt to generate temporary addresses for that interface. NOT attempt to generate temporary addresses for that interface.
Note that DAD MUST be performed on every unicast address Note that DAD MUST be performed on every unicast address
generated from this randomized interface identifier. generated from this randomized interface identifier.
3.4 Expiration of Temporary Addresses 3.4. Expiration of Temporary Addresses
When a temporary address becomes deprecated, a new one MUST be When a temporary address becomes deprecated, a new one MUST be
generated. This is done by repeating the actions described in generated. This is done by repeating the actions described in
Section 3.3, starting at step 3). Note that, except for the Section 3.3, starting at step 3). Note that, except for the
transient period when a temporary address is being regenerated, in transient period when a temporary address is being regenerated, in
normal operation at most one temporary address per prefix should be normal operation at most one temporary address per prefix should be
in a non-deprecated state at any given time on a given interface. in a non-deprecated state at any given time on a given interface.
Note that if a temporary address becomes deprecated as result of Note that if a temporary address becomes deprecated as result of
processing a Prefix Information Option with a zero Preferred processing a Prefix Information Option with a zero Preferred
Lifetime, then a new temporary address MUST NOT be generated. To Lifetime, then a new temporary address MUST NOT be generated. To
skipping to change at page 16, line 15 skipping to change at page 16, line 13
race conditions in the case where generating a new temporary address race conditions in the case where generating a new temporary address
is not instantaneous, such as when duplicate address detection must is not instantaneous, such as when duplicate address detection must
be run. The node SHOULD start the address regeneration process be run. The node SHOULD start the address regeneration process
REGEN_ADVANCE time units before a temporary address would actually be REGEN_ADVANCE time units before a temporary address would actually be
deprecated. deprecated.
As an optional optimization, an implementation MAY remove a As an optional optimization, an implementation MAY remove a
deprecated temporary address that is not in use by applications or deprecated temporary address that is not in use by applications or
upper-layers as detailed in Section 6. upper-layers as detailed in Section 6.
3.5 Regeneration of Randomized Interface Identifiers 3.5. Regeneration of Randomized Interface Identifiers
The frequency at which temporary addresses changes depends on how a The frequency at which temporary addresses changes depends on how a
device is being used (e.g., how frequently it initiates new device is being used (e.g., how frequently it initiates new
communication) and the concerns of the end user. The most egregious communication) and the concerns of the end user. The most egregious
privacy concerns appear to involve addresses used for long periods of privacy concerns appear to involve addresses used for long periods of
time (weeks to months to years). The more frequently an address time (weeks to months to years). The more frequently an address
changes, the less feasible collecting or coordinating information changes, the less feasible collecting or coordinating information
keyed on interface identifiers becomes. Moreover, the cost of keyed on interface identifiers becomes. Moreover, the cost of
collecting information and attempting to correlate it based on collecting information and attempting to correlate it based on
interface identifiers will only be justified if enough addresses interface identifiers will only be justified if enough addresses
skipping to change at page 17, line 25 skipping to change at page 17, line 23
new set of temporary addresses. If a device moves from one ethernet new set of temporary addresses. If a device moves from one ethernet
to another, generating a new set of temporary addresses from a to another, generating a new set of temporary addresses from a
different randomized interface identifier ensures that the device different randomized interface identifier ensures that the device
uses different randomized interface identifiers for the temporary uses different randomized interface identifiers for the temporary
addresses associated with the two links, making it more difficult to addresses associated with the two links, making it more difficult to
correlate addresses from the two different links as being from the correlate addresses from the two different links as being from the
same node. The node MAY follow any process available to it, to same node. The node MAY follow any process available to it, to
determine that the link change has occurred. One such process is determine that the link change has occurred. One such process is
described by Detecting Network Attachment [DNA]. described by Detecting Network Attachment [DNA].
3.6 Deployment Considerations 3.6. Deployment Considerations
Devices implementing this specification MUST provide a way for the Devices implementing this specification MUST provide a way for the
end user to explicitly enable or disable the use of temporary end user to explicitly enable or disable the use of temporary
addresses. In addition, a site might wish to disable the use of addresses. In addition, a site might wish to disable the use of
temporary addresses in order to simplify network debugging and temporary addresses in order to simplify network debugging and
operations. Consequently, implementations SHOULD provide a way for operations. Consequently, implementations SHOULD provide a way for
trusted system administrators to enable or disable the use of trusted system administrators to enable or disable the use of
temporary addresses. temporary addresses.
Additionally, sites might wish to selectively enable or disable the Additionally, sites might wish to selectively enable or disable the
skipping to change at page 21, line 38 skipping to change at page 22, line 5
problem described in Section 4 when reverse DNS lookups fail may be problem described in Section 4 when reverse DNS lookups fail may be
needed. [DNSOP] contains a more detailed discussion of the DNS needed. [DNSOP] contains a more detailed discussion of the DNS
related issues. related issues.
While this document discusses ways of obscuring a user's permanent IP While this document discusses ways of obscuring a user's permanent IP
address, the method described is believed to be ineffective against address, the method described is believed to be ineffective against
sophisticated forms of traffic analysis. To increase effectiveness, sophisticated forms of traffic analysis. To increase effectiveness,
one may need to consider use of more advanced techniques, such as one may need to consider use of more advanced techniques, such as
Onion Routing [ONION]. Onion Routing [ONION].
Open Issues 7. Security Considerations
1) Implementations should allow system administrators to configure Ingress filtering has been and is being deployed as a means of
the use of temporary addresses. We've considered the possibility of preventing the use of spoofed source addresses in Distributed Denial
using Router Advertisements to configure a host's use of temporary of Service(DDoS) attacks. In a network with a large number of nodes,
addresses, but that has a major drawback: in some situations (for new temporary addresses are created at a fairly high rate. This
example a home user receiving RAs from an ISP's router), the might make it difficult for ingress filtering mechanisms to
administrator of the host and the administrator of the router may distinguish between legitimately changing temporary addresses and
have different opinions about the use of temporary addresses. Any spoofed source addresses, which are "in-prefix"(They use a
configuration mechanism that disables the use of temporary addresses topologically correct prefix and non-existent interface ID). This
without input from the user MUST ensure that the host's administrator can be addressed by using access control mechanisms on a per address
has authorized the disabling. basis on the network egress point.
7. Significant Changes from RFC 3041 8. Significant Changes from RFC 3041
This section summarizes the changes in this document relative to RFC This section summarizes the changes in this document relative to RFC
3041 that an implementer of RFC 3041 should be aware of. 3041 that an implementer of RFC 3041 should be aware of.
1. Added wording to exclude certain interface identifiers from the 1. Excluded certain interface identifiers from the range of
range of acceptable interface identifiers. Interface IDs such acceptable interface identifiers. Interface IDs such as those
as 0, those for reserved anycast addresses [RFC2526], etc. for reserved anycast addresses [RFC], etc.
2. Added a configuration knob that provides the end user with a way 2. Added a configuration knob that provides the end user with a way
to enable or disable the use of temporary addresses. to enable or disable the use of temporary addresses on a per-
prefix basis.
3. Under RFC 3041, RAs with short lifetimes (e.g., 1 hour) that 3. Added a check for denial of service attacks using low valid
always send the same lifetime for long periods of time (e.g., lifetimes in router advertisements
days to weeks) resulted in temporary addresses being created
with lifetimes of only 1 hour. Additional rules were added to
increase the Lifetime of temporary addresses when the advertised
lifetimes were short.
4. DAD is now run on all temporary addresses, not just the first 4. DAD is now run on all temporary addresses, not just the first one
one generated from an interface identifier. generated from an interface identifier.
5. Changed the default setting for usage of temporary addresses to 5. Changed the default setting for usage of temporary addresses to
be disabled. be disabled.
6. Added a security considerations section to highlight the ingress 6. The node is now allowed to generate different interface
filtering issues which can be caused by the use of temporary
addresses as described in this document
7. Removed references to site-local addresses
8. Added a check for denial of service attacks using low valid
lifetimes in router advertisements
9. Changed the document to use RFC2119 language
10. The node is now allowed to generate different interface
identifiers for different prefixes, if it so desires. identifiers for different prefixes, if it so desires.
8. Changes from version 00 7. The algorithm used for generating random interface identifiers is
no longer restricted to just MD5
This section summarizes the changes from version 00 of this draft
1. The algorithm used for generating random interface identifiers
is no longer restricted to just MD5
2. Added a problem statement
3. Classified the references into normative and informative
4. Reduced default number of retries to 3 from 5 and added a 8. Reduced default number of retries to from and added a
configuration variable configuration variable
5. Removed text about RA processing which is duplicated from 9. RA processing algorithm is no longer included in the document,
[ADDRCONF] and is replaced by a reference to [ADDRCONF].
6. Added text about the privacy implications of a non-changing
prefix
7. Added a per-prefix enable/disable setting
8. Added text about the means of correlation
9. Clarified text about DHCPv6
10. Added reference to dnsop issues draft
9. Changes from version 01
This section summarizes the changes from version 01 of this draft
1. Clarifiying the length of interface identifier
2. Added a per-prefix enable/disable knob as a SHOULD to retain
backward compatibility
3. Removed normative reference to ISATAP to avoid downref problem
4. Added text for per-prefix knobs to be applied at any granularity
5. Moved RFC2526 to informative reference
10. Changes from version 02
This section summarizes the changes from version 02 of this draft
1. Explained briefly the concern that is being addressed in the
introduction
2. Removed reference to 64 bit identifiers in the ADDRCONF context
3. Added clarifying text for the usage of DHCPv6 as an alternate
approach
4. Moved RFC3484 to informative reference
5. Updated references for SEND, and CGA as they became RFCs
6. Updated draft versions for ULA, DNSOP issues, 2461bis, 2462bis
and DNA goals
11. Changes from version 03
This section summarizes the changes from version 03 of this draft
1. Added additional clarifying text regarding regeneration of
identifiers as proposed in the AD(Margaret Wasserman) review
comments.
2. Clarified confusing text which seemed to imply that the randomnly
generated identigiers could only be used with global scope
addresses.
3. Switched to the new IPR boilerplate
12. Security Considerations
Ingress filtering has been and is being deployed as a means of
preventing the use of spoofed source addresses in Distributed Denial
of Service(DDoS) attacks. In a network with a large number of nodes,
new temporary addresses are created at a fairly high rate. This
might make it difficult for ingress filtering mechanisms to
distinguish between legitimately changing temporary addresses and
spoofed source addresses, which are "in-prefix"(They use a
topologically correct prefix and non-existent interface ID). This
can be addressed by using access control mechanisms on a per address
basis on the network egress point.
13. Acknowledgements 9. Acknowledgements
The authors would like to acknowledge the contributions of the ipv6 The authors would like to acknowledge the contributions of the ipv6
working group and, in particular, Ran Atkinson, Matt Crawford, Steve working group and, in particular, Ran Atkinson, Matt Crawford, Steve
Deering, Allison Mankin, Peter Bieringer, Jari Arkko, Pekka Nikander, Deering, Allison Mankin, Peter Bieringer, Jari Arkko, Pekka Nikander,
Pekka Savola, Francis Dupont, Brian Haberman, Tatuya Jinmei and Pekka Savola, Francis Dupont, Brian Haberman, Tatuya Jinmei and
Margaret Wasserman for their detailed comments. Margaret Wasserman for their detailed comments.
14. References 10. References
14.1 Normative References 10.1. Normative References
[ADDRARCH] [ADDRARCH]
Hinden, R. and S. Deering, "Internet Protocol Version 6 Hinden, R. and S. Deering, "Internet Protocol Version 6
(IPv6) Addressing Architecture", RFC 3513, April 2003. (IPv6) Addressing Architecture", RFC 3513, April 2003.
[ADDRCONF] [ADDRCONF]
Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", draft-ietf-ipv6-rfc2462bis-07 Address Autoconfiguration", draft-ietf-ipv6-rfc2462bis-07
(work in progress), December 2004. (work in progress), December 2004.
[DISCOVERY] [DISCOVERY]
Narten, T., Nordmark, E., Simpson, W., and H. Soliman, Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", "Neighbor Discovery for IP version 6 (IPv6)",
draft-ietf-ipv6-2461bis-02 (work in progress), draft-ietf-ipv6-2461bis-02 (work in progress),
February 2005. February 2005.
[IPSEC] Kent, S. and R. Atkinson, "Security Architecture for the
Internet Protocol", RFC 2401, November 1998.
[MD5] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321, [MD5] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
April 1992. April 1992.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, March 1997. Requirement Levels", RFC 2119, March 1997.
14.2 Informative References 10.2. Informative References
[ADDR_SELECT] [ADDR_SELECT]
Draves, R., "Default Address Selection for Internet Draves, R., "Default Address Selection for Internet
Protocol version 6 (IPv6)", RFC 3484, February 2003. Protocol version 6 (IPv6)", RFC 3484, February 2003.
[CGA] Aura, T., "Cryptographically Generated Addresses (CGA)", [CGA] Aura, T., "Cryptographically Generated Addresses (CGA)",
RFC 3972, March 2005. RFC 3972, March 2005.
[COOKIES] Kristol, D. and L. Montulli, "HTTP State Management [COOKIES] Kristol, D. and L. Montulli, "HTTP State Management
Mechanism", RFC 2965, October 2000. Mechanism", RFC 2965, October 2000.
skipping to change at page 30, line 24 skipping to change at page 26, line 22
October 2004. October 2004.
[ONION] Reed, MGR., Syverson, PFS., and DMG. Goldschlag, "Proxies [ONION] Reed, MGR., Syverson, PFS., and DMG. Goldschlag, "Proxies
for Anonymous Routing", Proceedings of the 12th Annual for Anonymous Routing", Proceedings of the 12th Annual
Computer Security Applications Conference, San Diego, CA, Computer Security Applications Conference, San Diego, CA,
December 1996. December 1996.
[RANDOM] Eastlake, D., Crocker, S., and J. Schiller, "Randomness [RANDOM] Eastlake, D., Crocker, S., and J. Schiller, "Randomness
Recommendations for Security", RFC 1750, December 1994. Recommendations for Security", RFC 1750, December 1994.
[RFC2526] Johnson, D. and S. Deering, "Reserved IPv6 Subnet Anycast
Addresses", RFC 2526, March 1999.
[SEND] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure [SEND] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure
Neighbor Discovery (SEND)", RFC 3971, March 2005. Neighbor Discovery (SEND)", RFC 3971, March 2005.
[ULA] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast [ULA] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
Addresses", draft-ietf-ipv6-unique-local-addr-09 (work in Addresses", draft-ietf-ipv6-unique-local-addr-09 (work in
progress), January 2005. progress), January 2005.
Authors' Addresses Authors' Addresses
Thomas Narten Thomas Narten
skipping to change at page 32, line 41 skipping to change at page 28, line 41
This document and the information contained herein are provided on an This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Copyright Statement Copyright Statement
Copyright (C) The Internet Society (2005). This document is subject Copyright (C) The Internet Society (2006). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights. except as set forth therein, the authors retain all their rights.
Acknowledgment Acknowledgment
Funding for the RFC Editor function is currently provided by the Funding for the RFC Editor function is currently provided by the
Internet Society. Internet Society.
 End of changes. 45 change blocks. 
196 lines changed or deleted 86 lines changed or added

This html diff was produced by rfcdiff 1.33. The latest version is available from http://tools.ietf.org/tools/rfcdiff/