draft-ietf-ipv6-privacy-addrs-v2-05.txt   rfc4941.txt 
IPv6 Working Group T. Narten Network Working Group T. Narten
Internet-Draft IBM Corporation Request for Comments: 4941 IBM Corporation
Obsoletes: 3041 (if approved) R. Draves Obsoletes: 3041 R. Draves
Expires: February 2, 2007 Microsoft Research Category: Standards Track Microsoft Research
S. Krishnan S. Krishnan
Ericsson Research Ericsson Research
August 2006 September 2007
Privacy Extensions for Stateless Address Autoconfiguration in IPv6 Privacy Extensions for Stateless Address Autoconfiguration in IPv6
draft-ietf-ipv6-privacy-addrs-v2-05
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Copyright (C) The Internet Society (2006). This document specifies an Internet standards track protocol for the
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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 an interface that
contain embedded IEEE Identifiers, the interface identifier is contains an embedded IEEE Identifier, 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
number generation. This document describes an extension to IPv6 number generation. This document describes an extension to IPv6
stateless address autoconfiguration for interfaces whose interface stateless address autoconfiguration for interfaces whose interface
identifier is derived from an IEEE identifier. Use of the extension identifier is derived from an IEEE identifier. Use of the extension
causes nodes to generate global scope addresses from interface causes nodes to generate global scope addresses from interface
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 . . . . . . . . . . . . . . . . . . . . . 9
3.1. Assumptions . . . . . . . . . . . . . . . . . . . . . . . 10 3.1. Assumptions . . . . . . . . . . . . . . . . . . . . . . . 10
3.2. Generation Of Randomized Interface Identifiers . . . . . . 12 3.2. Generation of Randomized Interface Identifiers . . . . . . 10
3.2.1. When Stable Storage Is Present . . . . . . . . . . . . 12 3.2.1. When Stable Storage Is Present . . . . . . . . . . . . 11
3.2.2. In The Absence of Stable Storage . . . . . . . . . . . 13 3.2.2. In The Absence of Stable Storage . . . . . . . . . . . 12
3.2.3. Alternate approaches . . . . . . . . . . . . . . . . . 14 3.2.3. Alternate Approaches . . . . . . . . . . . . . . . . . 12
3.3. Generating Temporary Addresses . . . . . . . . . . . . . . 14 3.3. Generating Temporary Addresses . . . . . . . . . . . . . . 13
3.4. Expiration of Temporary Addresses . . . . . . . . . . . . 15 3.4. Expiration of Temporary Addresses . . . . . . . . . . . . 14
3.5. Regeneration of Randomized Interface Identifiers . . . . . 16 3.5. Regeneration of Randomized Interface Identifiers . . . . . 15
3.6. Deployment Considerations . . . . . . . . . . . . . . . . 17 3.6. Deployment Considerations . . . . . . . . . . . . . . . . 16
4. Implications of Changing Interface Identifiers . . . . . . . . 19 4. Implications of Changing Interface Identifiers . . . . . . . . 17
5. Defined Constants . . . . . . . . . . . . . . . . . . . . . . 20 5. Defined Constants . . . . . . . . . . . . . . . . . . . . . . 18
6. Future Work . . . . . . . . . . . . . . . . . . . . . . . . . 21 6. Future Work . . . . . . . . . . . . . . . . . . . . . . . . . 18
7. Security Considerations . . . . . . . . . . . . . . . . . . . 22 7. Security Considerations . . . . . . . . . . . . . . . . . . . 19
8. Significant Changes from RFC 3041 . . . . . . . . . . . . . . 23 8. Significant Changes from RFC 3041 . . . . . . . . . . . . . . 19
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 24 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 20
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 25 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 20
10.1. Normative References . . . . . . . . . . . . . . . . . . . 25 10.1. Normative References . . . . . . . . . . . . . . . . . . . 20
10.2. Informative References . . . . . . . . . . . . . . . . . . 25 10.2. Informative References . . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 27
Intellectual Property and Copyright Statements . . . . . . . . . . 28
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 Dynamic Host
types of network interfaces come with an embedded IEEE Identifier Configuration Protocol for IPv6 (DHCPv6) server. Some types of
(i.e., a link-layer MAC address), and in those cases stateless network interfaces come with an embedded IEEE Identifier (i.e., a
address autoconfiguration uses the IEEE identifier to generate a 64- link-layer MAC address), and in those cases, stateless address
bit interface identifier [ADDRARCH]. By design, the interface autoconfiguration uses the IEEE identifier to generate a 64-bit
identifier is likely to be globally unique when generated in this interface identifier [ADDRARCH]. By design, the interface identifier
fashion. The interface identifier is in turn appended to a prefix to is likely to be globally unique when generated in this fashion. The
form a 128-bit IPv6 address. Note that an IPv6 identifier does not interface identifier is in turn appended to a prefix to form a
128-bit IPv6 address. Note that an IPv6 identifier does not
necessarily have to be 64 bits in length, but the algorithm specified necessarily have to be 64 bits in length, but the algorithm specified
in this document is targeted towards 64-bit interface identifiers. in this document is targeted towards 64-bit interface identifiers.
All nodes combine interface identifiers (whether derived from an IEEE All nodes combine interface identifiers (whether derived from an IEEE
identifier or generated through some other technique) with the identifier or generated through some other technique) with the
reserved link-local prefix to generate link-local addresses for their reserved link-local prefix to generate link-local addresses for their
attached interfaces. Additional addresses can then be created by attached interfaces. Additional addresses can then be created by
combining prefixes advertised in Router Advertisements via Neighbor combining prefixes advertised in Router Advertisements via Neighbor
Discovery [DISCOVERY] with the interface identifier. Discovery [DISCOVERY] with the interface identifier.
Not all nodes and interfaces contain IEEE identifiers. In such Not all nodes and interfaces contain IEEE identifiers. In such
cases, an interface identifier is generated through some other means cases, an interface identifier is generated through some other means
(e.g., at random), and the resultant interface identifier may not be (e.g., at random), and the resultant interface identifier may not be
globally unique and may also change over time. The focus of this globally unique and may also change over time. The focus of this
document is on addresses derived from IEEE identifiers, because document is on addresses derived from IEEE identifiers because
tracking of individual devices, the concern being addressed here, is tracking of individual devices, the concern being addressed here, is
possible only in those cases where the interface identifier is possible only in those cases where the interface identifier is
globally unique and non-changing. The rest of this document assumes globally unique and non-changing. The rest of this document assumes
that IEEE identifiers are being used, but the techniques described that IEEE identifiers are being used, but the techniques described
may also apply to interfaces with other types of globally unique may also apply to interfaces with other types of globally unique
and/or persistent identifiers. and/or persistent identifiers.
This document discusses concerns associated with the embedding of This document discusses concerns associated with the embedding of
non-changing interface identifiers within IPv6 addresses and non-changing interface identifiers within IPv6 addresses and
describes extensions to stateless address autoconfiguration that can describes extensions to stateless address autoconfiguration that can
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
the peer(s) it is communicating to, and can view the IPv6 the peer(s) to which it is communicating, and who can view the
addresses present in the datagrams. IPv6 addresses present in the datagrams.
o An attacker who can access the communication logs of the peers o An attacker who can access the communication logs of the peers
with which the node has communicated. with which the node has communicated.
Since the identifier is embedded within the IPv6 address, which is a Since the identifier is embedded within the IPv6 address, which is a
fundamental requirement of communication, it cannot be easily hidden. fundamental requirement of communication, it cannot be easily hidden.
This document proposes a solution to this issue by generating This document proposes a solution to this issue by generating
interface identifiers which vary over time. interface identifiers that vary over time.
Note that an attacker, who is on path, may be able to perform Note that an attacker, who is on path, may be able to perform
significant correlation based on significant correlation based on
o The payload contents of the packets on the wire o The payload contents of the packets on the wire
o The characteristics of the packets such as packet size and timing o The characteristics of the packets such as packet size and timing
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
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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
some cases be used to infer things, such as what hours an employee some cases be used to infer things, such as what hours an employee
was active, when someone is at home, etc. Although it might appear was active, when someone is at home, etc. Although it might appear
that changing an address regularly in such environments would be that changing an address regularly in such environments would be
desirable to lessen privacy concerns, it should be noted that the desirable to lessen privacy concerns, it should be noted that the
network prefix portion of an address also serves as a constant network prefix portion of an address also serves as a constant
identifier. All nodes at (say) a home, would have the same network identifier. All nodes at, say, a home, would have the same network
prefix, which identifies the topological location of those nodes. prefix, which identifies the topological location of those nodes.
This has implications for privacy, though not at the same granularity This has implications for privacy, though not at the same granularity
as the concern that this document addresses. Specifically, all nodes as the concern that this document addresses. Specifically, all nodes
within a home could be grouped together for the purposes of within a home could be grouped together for the purposes of
collecting information. If the network contains a very small number collecting information. If the network contains a very small number
of nodes, say just one, changing just the interface identifier will of nodes, say, just one, changing just the interface identifier will
not enhance privacy at all, since the prefix serves as a constant not enhance privacy at all, since the prefix serves as a constant
identifier. identifier.
One of the requirements for correlating seemingly unrelated One of the requirements for correlating seemingly unrelated
activities is the use (and reuse) of an identifier that is activities is the use (and reuse) of an identifier that is
recognizable over time within different contexts. IP addresses recognizable over time within different contexts. IP addresses
provide one obvious example, but there are more. Many nodes also provide one obvious example, but there are more. Many nodes also
have DNS names associated with their addresses, in which case the DNS have DNS names associated with their addresses, in which case the DNS
name serves as a similar identifier. Although the DNS name name serves as a similar identifier. Although the DNS name
associated with an address is more work to obtain (it may require a associated with an address is more work to obtain (it may require a
DNS query) the information is often readily available. In such DNS query), the information is often readily available. In such
cases, changing the address on a machine over time would do little to cases, changing the address on a machine over time would do little to
address the concerns raised in this document, unless the DNS name is address the concerns raised in this document, unless the DNS name is
changed as well (see Section 4). changed as well (see Section 4).
Web browsers and servers typically exchange "cookies" with each other Web browsers and servers typically exchange "cookies" with each other
[COOKIES]. Cookies allow web servers to correlate a current activity [COOKIES]. Cookies allow Web servers to correlate a current activity
with a previous activity. One common usage is to send back targeted with a previous activity. One common usage is to send back targeted
advertising to a user by using the cookie supplied by the browser to advertising to a user by using the cookie supplied by the browser to
identify what earlier queries had been made (e.g., for what type of identify what earlier queries had been made (e.g., for what type of
information). Based on the earlier queries, advertisements can be information). Based on the earlier queries, advertisements can be
targeted to match the (assumed) interests of the end-user. targeted to match the (assumed) interests of the end user.
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.
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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
using DHCP, clients frequently end up using the same address for using DHCP, clients frequently end up using the same address for
weeks to months at a time. weeks to months at a time.
For home users accessing the Internet over dialup lines, the For home users accessing the Internet over dial-up lines, the
situation is generally different. Such users do not have permanent situation is generally different. Such users do not have permanent
connections and are often assigned temporary addresses each time they connections and are often assigned temporary addresses each time they
connect to their ISP. Consequently, the addresses they use change connect to their ISP. Consequently, the addresses they use change
frequently over time and are shared among a number of different frequently over time and are shared among a number of different
users. Thus, an address does not reliably identify a particular users. Thus, an address does not reliably identify a particular
device over time spans of more than a few minutes. device over time spans of more than a few minutes.
A more interesting case concerns always-on connections (e.g., cable A more interesting case concerns always-on connections (e.g., cable
modems, ISDN, DSL, etc.) that result in a home site using the same modems, ISDN, DSL, etc.) that result in a home site using the same
address for extended periods of time. This is a scenario that is address for extended periods of time. This is a scenario that is
just starting to become common in IPv4 and promises to become more of just starting to become common in IPv4 and promises to become more of
a concern as always-on internet connectivity becomes widely a concern as always-on Internet connectivity becomes widely
available. available.
Finally, it should be noted that nodes that need a (non-changing) DNS Finally, it should be noted that nodes that need a (non-changing) DNS
name generally have static addresses assigned to them to simplify the name generally have static addresses assigned to them to simplify the
configuration of DNS servers. Although Dynamic DNS [DDNS] can be configuration of DNS servers. Although Dynamic DNS [DDNS] can be
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.
If addresses are generated from an interface identifier, a home If addresses are generated from an interface identifier, a home
user's address could contain an interface identifier that remains the user's address could contain an interface identifier that remains the
same from one dialup session to the next, even if the rest of the same from one dial-up session to the next, even if the rest of the
address changes. The way PPP is used today, however, PPP servers address changes. The way PPP is used today, however, PPP servers
typically unilaterally inform the client what address they are to use typically unilaterally inform the client what address they are to use
(i.e., the client doesn't generate one on its own). This practice, (i.e., the client doesn't generate one on its own). This practice,
if continued in IPv6, would avoid the concerns that are the focus of if continued in IPv6, would avoid the concerns that are the focus of
this document. this document.
A more troubling case concerns mobile devices (e.g., laptops, PDAs, A more troubling case concerns mobile devices (e.g., laptops, PDAs,
etc.) that move topologically within the Internet. Whenever they etc.) that move topologically within the Internet. Whenever they
move they form new addresses for their current topological point of move, they form new addresses for their current topological point of
attachment. This is typified today by the "road warrior" who has attachment. This is typified today by the "road warrior" who has
Internet connectivity both at home and at the office. While the Internet connectivity both at home and at the office. While the
node's address changes as it moves, however, the interface identifier node's address changes as it moves, the interface identifier
contained within the address remains the same (when derived from an contained within the address remains the same (when derived from an
IEEE Identifier). In such cases, the interface identifier can be IEEE Identifier). In such cases, the interface identifier can be
used to track the movement and usage of a particular machine. For used to track the movement and usage of a particular machine. For
example, a server that logs usage information together with a source example, a server that logs usage information together with source
addresses, is also recording the interface identifier since it is addresses, is also recording the interface identifier since it is
embedded within an address. Consequently, any data-mining technique embedded within an address. Consequently, any data-mining technique
that correlates activity based on addresses could easily be extended that correlates activity based on addresses could easily be extended
to do the same using the interface identifier. This is of particular to do the same using the interface identifier. This is of particular
concern with the expected proliferation of next-generation network- concern with the expected proliferation of next-generation network-
connected devices (e.g., PDAs, cell phones, etc.) in which large connected devices (e.g., PDAs, cell phones, etc.) in which large
numbers of devices are in practice associated with individual users numbers of devices are, in practice, associated with individual users
(i.e., not shared). Thus, the interface identifier embedded within (i.e., not shared). Thus, the interface identifier embedded within
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,
users). The purpose of this document is to define mechanisms that potentially, users). The purpose of this document is to define
eliminate this issue, in those situations where it is a concern. mechanisms that 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. Section 12 of [DHCPV6] DHCPv6[DHCPV6] for obtaining addresses. Section 12 of [DHCPV6]
discusses the use of DHCPv6 for the assignment and management of discusses the use of DHCPv6 for the assignment and management of
"temporary addresses", which are never renewed and provide the same "temporary addresses", which are never renewed and provide the same
property of temporary addresses described in this document with property of temporary addresses described in this document with
regards to the privacy concern. regards to the privacy concern.
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different sequences. different sequences.
3. Protocol Description 3. Protocol Description
The goal of this section is to define procedures that: The goal of this section is to define procedures that:
1. Do not result in any changes to the basic behavior of addresses 1. Do not result in any changes to the basic behavior of addresses
generated via stateless address autoconfiguration [ADDRCONF]. generated via stateless address autoconfiguration [ADDRCONF].
2. Create additional addresses based on a random interface 2. Create additional addresses based on a random interface
identifier for the purpose of initiating outgoing sessions These identifier for the purpose of initiating outgoing sessions.
"random" or temporary addresses would be used for a short period These "random" or temporary addresses would be used for a short
of time (hours to days) and would then be deprecated. Deprecated period of time (hours to days) and would then be deprecated.
address can continue to be used for already established Deprecated address can continue to be used for already
connections, but are not used to initiate new connections. New established connections, but are not used to initiate new
temporary addresses are generated periodically to replace connections. New temporary addresses are generated periodically
temporary addresses that expire, with the exact time between to replace temporary addresses that expire, with the exact time
address generation a matter of local policy. between address generation a matter of local policy.
3. Produce a sequence of temporary global scope addresses from a 3. Produce a sequence of temporary global scope addresses from a
sequence of interface identifiers that appear to be random in the sequence of interface identifiers that appear to be random in the
sense that it is difficult for an outside observer to predict a sense that it is difficult for an outside observer to predict a
future address (or identifier) based on a current one and it is future address (or identifier) based on a current one, and it is
difficult to determine previous addresses (or identifiers) difficult to determine previous addresses (or identifiers)
knowing only the present one. knowing only the present one.
4. By default, generate a set of addresses from the same 4. By default, generate a set of addresses from the same
(randomized) interface identifier, one address for each prefix (randomized) interface identifier, one address for each prefix
for which a global address has been generated via stateless for which a global address has been generated via stateless
address autoconfiguration. Using the same interface identifier address autoconfiguration. Using the same interface identifier
to generate a set of temporary addresses reduces the number of IP to generate a set of temporary addresses reduces the number of IP
multicast groups a host must join. Nodes join the solicited-node multicast groups a host must join. Nodes join the solicited-node
multicast address for each unicast address they support, and multicast address for each unicast address they support, and
solicited-node addresses are dependent only on the low-order bits solicited-node addresses are dependent only on the low-order bits
of the corresponding address. This default behaviour was made to of the corresponding address. This default behavior was made to
address the concern that a node that joins a large number of address the concern that a node that joins a large number of
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.
When a temporary address is deprecated, a new temporary address is When a temporary address is deprecated, a new temporary address is
generated. The specific valid and preferred lifetimes for the new generated. The specific valid and preferred lifetimes for the new
address are dependent on the corresponding lifetime values set for address are dependent on the corresponding lifetime values set for
the prefix from which it was generated. the prefix from which it was generated.
Finally, this document assumes that when a node initiates outgoing Finally, this document assumes that when a node initiates outgoing
communication, temporary addresses can be given preference over communication, temporary addresses can be given preference over
public addresses, when the device is configured to do so. public addresses when the device is configured to do so.
[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
skipping to change at page 12, line 41 skipping to change at page 11, line 31
A randomized interface identifier is created as follows: A randomized interface identifier is created as follows:
1. Take the history value from the previous iteration of this 1. Take the history value from the previous iteration of this
algorithm (or a random value if there is no previous value) and algorithm (or a random value if there is no previous value) and
append to it the interface identifier generated as described in append to it the interface identifier generated as described in
[ADDRARCH]. [ADDRARCH].
2. Compute the MD5 message digest [MD5] over the quantity created in 2. Compute the MD5 message digest [MD5] over the quantity created in
the previous step. the previous step.
3. Take the left-most 64-bits of the MD5 digest and set bit 6 (the 3. Take the leftmost 64-bits of the MD5 digest and set bit 6 (the
left-most bit is numbered 0) to zero. This creates an interface leftmost bit is numbered 0) to zero. This creates an interface
identifier with the universal/local bit indicating local identifier with the universal/local bit indicating local
significance only. significance only.
4. Compare the generated identifier against a list of reserved 4. Compare the generated identifier against a list of reserved
interface identifiers and to those already assigned to an address interface identifiers and to those already assigned to an address
on the local device. In the event that an unacceptable on the local device. In the event that an unacceptable
identifier has been generated, the node MUST restart the process identifier has been generated, the node MUST restart the process
at step 1 above, using the right-most 64 bits of the MD5 digest at step 1 above, using the rightmost 64 bits of the MD5 digest
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.The node were adequate to produce the desired level of randomization. The
MAY use another algorithm instead of MD5 to produce the random node MAY use another algorithm instead of MD5 to produce the random
interface identifier 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 follow-up 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 Cryptographically Generated Addresses (CGAs) [CGA], which
based on the public key of the node. The goal of CGAs is to prove generate a random interface identifier based on the public key of the
ownership of an address and to prevent spoofing and stealing of node. The goal of CGAs is to prove ownership of an address and to
existing IPv6 addresses. They are used for securing neighbor prevent spoofing and stealing of existing IPv6 addresses. They are
discovery using [SEND]. The CGA random interface identifier used for securing neighbor discovery using [SEND]. The CGA random
generation algorithm may not be suitable for privacy addresses interface identifier generation algorithm may not be suitable for
because of the following properties privacy addresses 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],
either creating a new public address or adjusting the lifetimes either creating a new public address or adjusting the lifetimes
of existing addresses, both public and temporary. If a received of existing addresses, both public and temporary. If a received
option will extend the lifetime of a public address, the option will extend the lifetime of a public address, the
lifetimes of temporary addresses should be extended, subject to lifetimes of temporary addresses should be extended, subject to
the overall constraint that no temporary addresses should ever the overall constraint that no temporary addresses should ever
remain "valid" or "preferred" for a time longer than remain "valid" or "preferred" for a time longer than
(TEMP_VALID_LIFETIME - DESYNC_FACTOR) or (TEMP_PREFERRED_LIFETIME (TEMP_VALID_LIFETIME) or (TEMP_PREFERRED_LIFETIME -
- DESYNC_FACTOR) respectively. The configuration variables DESYNC_FACTOR), respectively. The configuration variables
TEMP_VALID_LIFETIME and TEMP_PREFERRED_LIFETIME correspond to TEMP_VALID_LIFETIME and TEMP_PREFERRED_LIFETIME correspond to
approximate target lifetimes for temporary addresses. approximate target lifetimes for temporary addresses.
2. One way an implementation can satisfy the above constraints is to 2. One way an implementation can satisfy the above constraints is to
associate with each temporary address a creation time (called associate with each temporary address a creation time (called
CREATION_TIME) that indicates the time at which the address was CREATION_TIME) that indicates the time at which the address was
created. When updating the preferred lifetime of an existing created. When updating the preferred lifetime of an existing
temporary address, it would be set to expire at whichever time is temporary address, it would be set to expire at whichever time is
earlier: the time indicated by the received lifetime or earlier: the time indicated by the received lifetime or
(CREATION_TIME + TEMP_PREFERRED_LIFETIME - DESYNC_FACTOR). A (CREATION_TIME + TEMP_PREFERRED_LIFETIME - DESYNC_FACTOR). A
similar approach can be used with the valid lifetime. similar approach can be used with the valid lifetime.
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 public address or TEMP_PREFERRED_LIFETIME - of the public address or TEMP_PREFERRED_LIFETIME -
DESYNC_FACTOR. 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.
7. The node MUST Perform duplicate address detection (DAD) on the 7. The node MUST perform duplicate address detection (DAD) on the
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.
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temporary address SHOULD be regenerated slightly before its temporary address SHOULD be regenerated slightly before its
predecessor is deprecated. This is to allow sufficient time to avoid predecessor is deprecated. This is to allow sufficient time to avoid
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
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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
use of temporary addresses for some prefixes. For example, a site use of temporary addresses for some prefixes. For example, a site
might wish to disable temporary address generation for "Unique local" might wish to disable temporary address generation for "Unique local"
[ULA] prefixes while still generating temporary addresses for all [ULA] prefixes while still generating temporary addresses for all
other global prefixes. Another site might wish to enable temporary other global prefixes. Another site might wish to enable temporary
address generation only for the prefixes 2001::/16 and 2002::/16 address generation only for the prefixes 2001::/16 and 2002::/16,
while disabling it for all other prefixes. To support this behavior, while disabling it for all other prefixes. To support this behavior,
implementations SHOULD provide a way to enable and disable generation implementations SHOULD provide a way to enable and disable generation
of temporary addresses for specific prefix subranges. This per- of temporary addresses for specific prefix subranges. This per-
prefix setting SHOULD override the global settings on the node with prefix setting SHOULD override the global settings on the node with
respect to the specified prefix subranges. Note that the pre-prefix respect to the specified prefix subranges. Note that the pre-prefix
setting can be applied at any granularity, and not necessarily on a setting can be applied at any granularity, and not necessarily on a
per subnet basis. per-subnet basis.
The use of temporary addresses may cause unexpected difficulties with The use of temporary addresses may cause unexpected difficulties with
some applications. As described below, some servers refuse to accept some applications. As described below, some servers refuse to accept
communications from clients for which they cannot map the IP address communications from clients for which they cannot map the IP address
into a DNS name. In addition, some applications may not behave into a DNS name. In addition, some applications may not behave
robustly if temporary addresses are used and an address expires robustly if temporary addresses are used and an address expires
before the application has terminated, or if it opens multiple before the application has terminated, or if it opens multiple
sessions, but expects them to all use the same addresses. sessions, but expects them to all use the same addresses.
Consequently, the use of temporary addresses SHOULD be disabled by Consequently, the use of temporary addresses SHOULD be disabled by
default in order to minimize potential disruptions. Individual default in order to minimize potential disruptions. Individual
applications, which have specific knowledge about the normal duration applications, which have specific knowledge about the normal duration
of connections, MAY override this as appropriate. of connections, MAY override this as appropriate.
If a very small number of nodes (say only one) use a given prefix for If a very small number of nodes (say, only one) use a given prefix
extended periods of time, just changing the interface identifier part for extended periods of time, just changing the interface identifier
of the address may not be sufficient to ensure privacy, since the part of the address may not be sufficient to ensure privacy, since
prefix acts as a constant identifier. The procedures described in the prefix acts as a constant identifier. The procedures described
this document are most effective when the prefix is reasonably non in this document are most effective when the prefix is reasonably non
static or is used by a fairly large number of nodes. static or is used by a fairly large number of nodes.
4. Implications of Changing Interface Identifiers 4. Implications of Changing Interface Identifiers
The IPv6 addressing architecture goes to some lengths to ensure that The IPv6 addressing architecture goes to some lengths to ensure that
interface identifiers are likely to be globally unique where easy to interface identifiers are likely to be globally unique where easy to
do so. The widespread use of temporary addresses may result in a do so. The widespread use of temporary addresses may result in a
significant fraction of Internet traffic not using addresses in which significant fraction of Internet traffic not using addresses in which
the interface identifier portion is globally unique. Consequently, the interface identifier portion is globally unique. Consequently,
usage of the algorithms in this document may complicate providing usage of the algorithms in this document may complicate providing
skipping to change at page 19, line 34 skipping to change at page 17, line 41
exists. That is, they perform a DNS PTR query to determine the DNS exists. That is, they perform a DNS PTR query to determine the DNS
name, and may then also perform an AAAA query on the returned name to name, and may then also perform an AAAA query on the returned name to
verify that the returned DNS name maps back into the address being verify that the returned DNS name maps back into the address being
used. Consequently, clients not properly registered in the DNS may used. Consequently, clients not properly registered in the DNS may
be unable to access some services. As noted earlier, however, a be unable to access some services. As noted earlier, however, a
node's DNS name (if non-changing) serves as a constant identifier. node's DNS name (if non-changing) serves as a constant identifier.
The wide deployment of the extension described in this document could The wide deployment of the extension described in this document could
challenge the practice of inverse-DNS-based "authentication," which challenge the practice of inverse-DNS-based "authentication," which
has little validity, though it is widely implemented. In order to has little validity, though it is widely implemented. In order to
meet server challenges, nodes could register temporary addresses in meet server challenges, nodes could register temporary addresses in
the DNS using random names (for example a string version of the the DNS using random names (for example, a string version of the
random address itself). random address itself).
Use of the extensions defined in this document may complicate Use of the extensions defined in this document may complicate
debugging and other operational troubleshooting activities. debugging and other operational troubleshooting activities.
Consequently, it may be site policy that temporary addresses should Consequently, it may be site policy that temporary addresses should
not be used. Consequently, implementations MUST provide a method for not be used. Consequently, implementations MUST provide a method for
the end user or trusted administrator to override the use of the end user or trusted administrator to override the use of
temporary addresses. temporary addresses.
5. Defined Constants 5. Defined Constants
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The determination as to whether to use public versus temporary The determination as to whether to use public versus temporary
addresses can in some cases only be made by an application. For addresses can in some cases only be made by an application. For
example, some applications may always want to use temporary example, some applications may always want to use temporary
addresses, while others may want to use them only in some addresses, while others may want to use them only in some
circumstances or not at all. Suitable API extensions will likely circumstances or not at all. Suitable API extensions will likely
need to be developed to enable individual applications to indicate need to be developed to enable individual applications to indicate
with sufficient granularity their needs with regards to the use of with sufficient granularity their needs with regards to the use of
temporary addresses. Recommendations on DNS practices to avoid the temporary addresses. Recommendations on DNS practices to avoid the
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].
7. Security Considerations 7. Security Considerations
Ingress filtering has been and is being deployed as a means of Ingress filtering has been and is being deployed as a means of
preventing the use of spoofed source addresses in Distributed Denial preventing the use of spoofed source addresses in Distributed Denial
of Service(DDoS) attacks. In a network with a large number of nodes, of Service (DDoS) attacks. In a network with a large number of
new temporary addresses are created at a fairly high rate. This nodes, new temporary addresses are created at a fairly high rate.
might make it difficult for ingress filtering mechanisms to This might make it difficult for ingress filtering mechanisms to
distinguish between legitimately changing temporary addresses and distinguish between legitimately changing temporary addresses and
spoofed source addresses, which are "in-prefix"(They use a spoofed source addresses, which are "in-prefix" (using a
topologically correct prefix and non-existent interface ID). This topologically correct prefix and non-existent interface ID). This
can be addressed by using access control mechanisms on a per address can be addressed by using access control mechanisms on a per-address
basis on the network egress point. basis on the network egress point.
8. 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. Excluded certain interface identifiers from the range of 1. Excluded certain interface identifiers from the range of
acceptable interface identifiers. Interface IDs such as those acceptable interface identifiers. Interface IDs such as those
for reserved anycast addresses [RFC], etc. for reserved anycast addresses [RFC2526], 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 on a per- to enable or disable the use of temporary addresses on a per-
prefix basis. prefix basis.
3. Added a check for denial of service attacks using low valid 3. Added a check for denial of service attacks using low valid
lifetimes in router advertisements lifetimes in router advertisements.
4. DAD is now run on all temporary addresses, not just the first one 4. DAD is now run on all temporary addresses, not just the first 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. The node is now allowed to generate different interface 6. 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.
7. The algorithm used for generating random interface identifiers is 7. The algorithm used for generating random interface identifiers is
no longer restricted to just MD5 no longer restricted to just MD5.
8. Reduced default number of retries to from and added a 8. Reduced default number of retries to 3 and added a configuration
configuration variable variable.
9. RA processing algorithm is no longer included in the document, 9. Router advertisement (RA) processing algorithm is no longer
and is replaced by a reference to [ADDRCONF]. included in the document, and is replaced by a reference to
[ADDRCONF].
9. Acknowledgements 9. Acknowledgments
The authors would like to acknowledge the contributions of the ipv6 Rich Draves and Thomas Narten were the authors of RFC 3041. They
working group and, in particular, Ran Atkinson, Matt Crawford, Steve would like to acknowledge the contributions of the ipv6 working group
Deering, Allison Mankin, Peter Bieringer, Jari Arkko, Pekka Nikander, and, in particular, Ran Atkinson, Matt Crawford, Steve Deering,
Pekka Savola, Francis Dupont, Brian Haberman, Tatuya Jinmei and Allison Mankin, and Peter Bieringer.
Margaret Wasserman for their detailed comments.
Suresh Krishnan was the sole author of this version of the document.
He would like to acknowledge the contributions of the ipv6 working
group and, in particular, Jari Arkko, Pekka Nikander, Pekka Savola,
Francis Dupont, Brian Haberman, Tatuya Jinmei, and Margaret Wasserman
for their detailed comments.
10. References 10. References
10.1. Normative References 10.1. Normative References
[ADDRARCH] [ADDRARCH] Hinden, R. and S. Deering, "IP Version 6 Addressing
Hinden, R. and S. Deering, "Internet Protocol Version 6 Architecture", RFC 4291, February 2006.
(IPv6) Addressing Architecture", RFC 3513, April 2003.
[ADDRCONF] [ADDRCONF] Thomson, S., Narten, T., and T. Jinmei, "IPv6
Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless Stateless Address Autoconfiguration", RFC 4862,
Address Autoconfiguration", draft-ietf-ipv6-rfc2462bis-07 September 2007.
(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), RFC 4861, September 2007.
February 2005.
[MD5] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321, [MD5] Rivest, R., "The MD5 Message-Digest Algorithm",
April 1992. RFC 1321, 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.
10.2. 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
RFC 3972, March 2005. (CGA)", 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.
[DDNS] Vixie, P., Thomson, S., Rekhter, Y., and J. Bound, [DDNS] Vixie, P., Thomson, S., Rekhter, Y., and J. Bound,
"Dynamic Updates in the Domain Name System (DNS UPDATE)", "Dynamic Updates in the Domain Name System (DNS
RFC 2136, April 1997. UPDATE)", RFC 2136, April 1997.
[DHCP] Droms, R., "Dynamic Host Configuration Protocol", [DHCP] Droms, R., "Dynamic Host Configuration Protocol",
RFC 2131, March 1997. RFC 2131, March 1997.
[DHCPV6] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., [DHCPV6] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins,
and M. Carney, "Dynamic Host Configuration Protocol for C., and M. Carney, "Dynamic Host Configuration
IPv6 (DHCPv6)", RFC 3315, July 2003. Protocol for IPv6 (DHCPv6)", RFC 3315, July 2003.
[DNA] Choi, J. and G. Daley, "Detecting Network Attachment in [DNA] Choi, JH. and G. Daley, "Goals of Detecting Network
IPv6 Goals", draft-ietf-dna-goals-04 (work in progress), Attachment in IPv6", RFC 4135, August 2005.
December 2004.
[DNSOP] Durand, A., Ihren, J., and P. Savola, "Operational [DNSOP] Durand, A., Ihren, J., and P. Savola, "Operational
Considerations and Issues with IPv6 DNS", Considerations and Issues with IPv6 DNS", RFC 4472,
draft-ietf-dnsop-ipv6-dns-issues-10 (work in progress), April 2006.
October 2004.
[ONION] Reed, MGR., Syverson, PFS., and DMG. Goldschlag, "Proxies [ONION] Reed, MGR., Syverson, PFS., and DMG. Goldschlag,
for Anonymous Routing", Proceedings of the 12th Annual "Proxies for Anonymous Routing", Proceedings of the
Computer Security Applications Conference, San Diego, CA, 12th Annual Computer Security Applications Conference,
December 1996. San Diego, CA, December 1996.
[RANDOM] Eastlake, D., Crocker, S., and J. Schiller, "Randomness [RANDOM] Eastlake, D., Schiller, J., and S. Crocker,
Recommendations for Security", RFC 1750, December 1994. "Randomness Requirements for Security", BCP 106,
RFC 4086, June 2005.
[SEND] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure [RFC2526] Johnson, D. and S. Deering, "Reserved IPv6 Subnet
Neighbor Discovery (SEND)", RFC 3971, March 2005. Anycast Addresses", RFC 2526, March 1999.
[SEND] Arkko, J., Kempf, J., Zill, B., and P. Nikander,
"SEcure 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", RFC 4193, October 2005.
progress), January 2005.
Authors' Addresses Authors' Addresses
Thomas Narten Thomas Narten
IBM Corporation IBM Corporation
P.O. Box 12195 P.O. Box 12195
Research Triangle Park, NC Research Triangle Park, NC
USA USA
Email: narten@raleigh.ibm.com EMail: narten@us.ibm.com
Richard Draves Richard Draves
Microsoft Research Microsoft Research
One Microsoft Way One Microsoft Way
Redmond, WA Redmond, WA
USA USA
Email: richdr@microsoft.com EMail: richdr@microsoft.com
Suresh Krishnan Suresh Krishnan
Ericsson Research Ericsson Research
8400 Decarie Blvd. 8400 Decarie Blvd.
Town of Mount Royal, QC Town of Mount Royal, QC
Canada Canada
Email: suresh.krishnan@ericsson.com EMail: suresh.krishnan@ericsson.com
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