draft-ietf-6man-rfc4941bis-11.txt   draft-ietf-6man-rfc4941bis-12.txt 
IPv6 Maintenance (6man) Working Group F. Gont IPv6 Maintenance (6man) Working Group F. Gont
Internet-Draft SI6 Networks Internet-Draft SI6 Networks
Obsoletes: 4941 (if approved) S. Krishnan Obsoletes: 4941 (if approved) S. Krishnan
Intended status: Standards Track Kaloom Intended status: Standards Track Kaloom
Expires: April 3, 2021 T. Narten Expires: May 6, 2021 T. Narten
R. Draves R. Draves
Microsoft Research Microsoft Research
September 30, 2020 November 2, 2020
Temporary Address Extensions for Stateless Address Autoconfiguration in Temporary Address Extensions for Stateless Address Autoconfiguration in
IPv6 IPv6
draft-ietf-6man-rfc4941bis-11 draft-ietf-6man-rfc4941bis-12
Abstract Abstract
This document describes an extension to IPv6 Stateless Address This document describes an extension to IPv6 Stateless Address
Autoconfiguration that causes nodes to generate global scope Autoconfiguration that causes hosts to generate global scope
addresses with randomized interface identifiers that change over addresses with randomized interface identifiers that change over
time. Changing global scope addresses over time limits the window of time. Changing global scope addresses over time limits the window of
time during which eavesdroppers and other information collectors may time during which eavesdroppers and other information collectors may
trivially perform address-based network activity correlation when the trivially perform address-based network activity correlation when the
same address is employed for multiple transactions by the same node. same address is employed for multiple transactions by the same host.
Additionally, it reduces the window of exposure of a node via an Additionally, it reduces the window of exposure of a host as being
address that becomes revealed as a result of active communication. accessible via an address that becomes revealed as a result of active
This document obsoletes RFC4941. communication. This document obsoletes RFC4941.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
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."
This Internet-Draft will expire on April 3, 2021. This Internet-Draft will expire on May 6, 2021.
Copyright Notice Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of (https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
skipping to change at page 2, line 35 skipping to change at page 2, line 35
2. Background . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Background . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Extended Use of the Same Identifier . . . . . . . . . . . 4 2.1. Extended Use of the Same Identifier . . . . . . . . . . . 4
2.2. Possible Approaches . . . . . . . . . . . . . . . . . . . 6 2.2. Possible Approaches . . . . . . . . . . . . . . . . . . . 6
3. Protocol Description . . . . . . . . . . . . . . . . . . . . 6 3. Protocol Description . . . . . . . . . . . . . . . . . . . . 6
3.1. Design Guidelines . . . . . . . . . . . . . . . . . . . . 7 3.1. Design Guidelines . . . . . . . . . . . . . . . . . . . . 7
3.2. Assumptions . . . . . . . . . . . . . . . . . . . . . . . 7 3.2. Assumptions . . . . . . . . . . . . . . . . . . . . . . . 7
3.3. Generation of Randomized Interface Identifiers . . . . . 8 3.3. Generation of Randomized Interface Identifiers . . . . . 8
3.3.1. Simple Randomized Interface Identifiers . . . . . . . 8 3.3.1. Simple Randomized Interface Identifiers . . . . . . . 8
3.3.2. Hash-based Generation of Randomized Interface 3.3.2. Hash-based Generation of Randomized Interface
Identifiers . . . . . . . . . . . . . . . . . . . . . 9 Identifiers . . . . . . . . . . . . . . . . . . . . . 9
3.4. Generating Temporary Addresses . . . . . . . . . . . . . 10 3.4. Generating Temporary Addresses . . . . . . . . . . . . . 11
3.5. Expiration of Temporary Addresses . . . . . . . . . . . . 12 3.5. Expiration of Temporary Addresses . . . . . . . . . . . . 12
3.6. Regeneration of Temporary Addresses . . . . . . . . . . . 12 3.6. Regeneration of Temporary Addresses . . . . . . . . . . . 13
3.7. Implementation Considerations . . . . . . . . . . . . . . 14 3.7. Implementation Considerations . . . . . . . . . . . . . . 14
3.8. Defined Constants and Configuration Variables . . . . . . 14 3.8. Defined Constants and Configuration Variables . . . . . . 14
4. Implications of Changing Interface Identifiers . . . . . . . 15 4. Implications of Changing Interface Identifiers . . . . . . . 15
5. Significant Changes from RFC4941 . . . . . . . . . . . . . . 16 5. Significant Changes from RFC4941 . . . . . . . . . . . . . . 17
6. Future Work . . . . . . . . . . . . . . . . . . . . . . . . . 17 6. Future Work . . . . . . . . . . . . . . . . . . . . . . . . . 18
7. Implementation Status . . . . . . . . . . . . . . . . . . . . 17 7. Implementation Status . . . . . . . . . . . . . . . . . . . . 19
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
9. Security Considerations . . . . . . . . . . . . . . . . . . . 18 9. Security Considerations . . . . . . . . . . . . . . . . . . . 19
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 18 10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 20
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 19 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 21
11.1. Normative References . . . . . . . . . . . . . . . . . . 19 11.1. Normative References . . . . . . . . . . . . . . . . . . 21
11.2. Informative References . . . . . . . . . . . . . . . . . 20 11.2. Informative References . . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24
1. Introduction 1. Introduction
Stateless address autoconfiguration (SLAAC) [RFC4862] defines how an [RFC4862] specifies "Stateless Address Autoconfiguration (SLAAC) for
IPv6 node generates addresses without the need for a Dynamic Host IPv6", which typically results in hosts configuring one or more
Configuration Protocol for IPv6 (DHCPv6) server. The security and "stable" IPv6 addresses composed of a network prefix advertised by a
privacy implications of such addresses have been discussed in detail local router and a locally-generated Interface Identifier (IID). The
in [RFC7721],[RFC7217], and [RFC7707]. This document specifies an security and privacy implications of such addresses have been
extension for SLAAC to generate temporary addresses, that can help discussed in detail in [RFC7721], [RFC7217], and [RFC7707]. This
mitigate some of the aforementioned issues. This is a revision of document specifies an extension for SLAAC to generate temporary
RFC4941, and formally obsoletes RFC4941. Section 5 describes the addresses, that can help mitigate some of the aforementioned issues.
changes from [RFC4941]. This is a revision of RFC4941, and formally obsoletes RFC4941.
Section 5 describes the changes from [RFC4941].
The default address selection for IPv6 has been specified in The default address selection for IPv6 has been specified in
[RFC6724]. The determination as to whether to use stable versus [RFC6724]. The determination as to whether to use stable versus
temporary addresses can in some cases only be made by an application. temporary addresses can in some cases only be made by an application.
For example, some applications may always want to use temporary For 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. An Application Programming Interface circumstances or not at all. An Application Programming Interface
(API) such as that specified in [RFC5014] can enable individual (API) such as that specified in [RFC5014] can enable individual
applications to indicate a preference for the use of temporary applications to indicate a preference for the use of temporary
addresses. addresses.
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1.2. Problem Statement 1.2. Problem Statement
Addresses generated using stateless address autoconfiguration Addresses generated using stateless address autoconfiguration
[RFC4862] contain an embedded interface identifier, which may remain [RFC4862] contain an embedded interface identifier, which may remain
stable over time. Anytime a fixed identifier is used in multiple stable 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 host in question and
the peer(s) to which it is communicating, and who can view the the peer(s) to which it is communicating, and who can view the
IPv6 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 host has communicated.
Since the identifier is embedded within the IPv6 address, it cannot Since the identifier is embedded within the IPv6 address, it cannot
be hidden. This document proposes a solution to this issue by be hidden. This document proposes a solution to this issue by
generating interface identifiers that vary over time. generating 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 on unencrypted packets based on significant correlation based on:
o The payload contents of the packets on the wire o The payload contents of unencrypted 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 correlation, nor
correlation, which can only be addressed by widespread deployment of will it prevent an on-link observer (e.g. the host's default router)
encryption as discussed in [RFC7624]. Nor will it prevent an on-link from tracking all the host's addresses.
observer (e.g. the node's default router) to track all the node's
addresses.
2. Background 2. Background
This section discusses the problem in more detail, and provides This section discusses the problem in more detail, provides context
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. Any time the same identifier is used in independent activities. Any time 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 host 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 hosts 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 hosts.
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 hosts
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 hosts, say, just one, changing just the interface identifier will
not enhance privacy, since the prefix serves as a constant not enhance privacy, 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. provide one obvious example, but there are more. For example,
Many nodes also have DNS names associated with their addresses, in o Many hosts also have DNS names associated with their addresses, in
which case the DNS name serves as a similar identifier. Although the which case the DNS name serves as a similar identifier. Although
DNS name associated with an address is more work to obtain (it may the DNS name associated with an address is more work to obtain (it
require a DNS query), the information is often readily available. In may require a DNS query), the information is often readily
such cases, changing the address on a machine over time would do available. In such cases, changing the address on a host over
little to address the concerns raised in this document, unless the time would do little to address the concerns raised in this
DNS name is changed as well (see Section 4). document, unless the DNS name is changed at the same time as well
(see Section 4).
Web browsers and servers typically exchange "cookies" with each other o Web browsers and servers typically exchange "cookies" with each
[RFC6265]. Cookies allow web servers to correlate a current activity other [RFC6265]. Cookies allow web servers to correlate a current
with a previous activity. One common usage is to send back targeted activity with a previous activity. One common usage is to send
advertising to a user by using the cookie supplied by the browser to back targeted advertising to a user by using the cookie supplied
identify what earlier queries had been made (e.g., for what type of by the browser to identify what earlier queries had been made
information). Based on the earlier queries, advertisements can be (e.g., for what type of information). Based on the earlier
targeted to match the (assumed) interests of the end-user. queries, advertisements can be 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.
Changing global scope addresses over time limits the time window over Changing global scope addresses over time limits the time window over
which eavesdroppers and other information collectors may trivially which eavesdroppers and other information collectors may trivially
correlate network activity when the same address is employed for correlate network activity when the same address is employed for
multiple transactions by the same node. Additionally, it reduces the multiple transactions by the same host. Additionally, it reduces the
window of exposure of a node via an address that gets revealed as a window of exposure of a host as being accessible via an address that
result of active communication. becomes revealed as a result of active communication.
The security and privacy implications of IPv6 addresses are discussed The security and privacy implications of IPv6 addresses are discussed
in detail in [RFC7721], [RFC7707], and [RFC7217]. in detail in [RFC7721], [RFC7707], and [RFC7217].
2.2. Possible Approaches 2.2. Possible Approaches
One approach, compatible with the stateless address autoconfiguration One approach, compatible with the stateless address autoconfiguration
architecture, would be to change the interface identifier portion of architecture, would be to change the interface identifier portion of
an address over time. Changing the interface identifier can make it an address over time. Changing the interface identifier can make it
more difficult to look at the IP addresses in independent more difficult to look at the IP addresses in independent
transactions and identify which ones actually correspond to the same transactions and identify which ones actually correspond to the same
node, both in the case where the routing prefix portion of an address host, both in the case where the routing prefix portion of an address
changes and when it does not. changes and when it does not.
Many machines function as both clients and servers. In such cases, Many hosts function as both clients and servers. In such cases, the
the machine would need a DNS name for its use as a server. Whether host would need a name (e.g. a DNS domain name) for its use as a
the address stays fixed or changes has little privacy implication server. Whether the address stays fixed or changes has little
since the DNS name remains constant and serves as a constant privacy implication since the name remains constant and serves as a
identifier. When acting as a client (e.g., initiating constant identifier. When acting as a client (e.g., initiating
communication), however, such a machine may want to vary the communication), however, such a host may want to vary the addresses
addresses it uses. In such environments, one may need multiple it uses. In such environments, one may need multiple addresses: a
addresses: a stable address registered in the DNS, that is used to stable address associated with the name, that is used to accept
accept incoming connection requests from other machines, and a incoming connection requests from other hosts, and a temporary
temporary address used to shield the identity of the client when it address used to shield the identity of the client when it initiates
initiates communication. communication.
On the other hand, a machine that functions only as a client may want On the other hand, a host that functions only as a client may want to
to employ only temporary addresses for public communication. employ only temporary addresses for public communication.
To make it difficult to make educated guesses as to whether two To make it difficult to make educated guesses as to whether two
different interface identifiers belong to the same node, the different interface identifiers belong to the same host, the
algorithm for generating alternate identifiers must include input algorithm for generating alternate identifiers must include input
that has an unpredictable component from the perspective of the that has an unpredictable component from the perspective of the
outside entities that are collecting information. outside entities that are collecting information.
3. Protocol Description 3. Protocol Description
The following subsections define the procedures for the generation of The following subsections define the procedures for the generation of
IPv6 temporary addresses. IPv6 temporary addresses.
3.1. Design Guidelines 3.1. Design Guidelines
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Temporary addresses observe the following properties: Temporary addresses observe the following properties:
1. Temporary addresses are typically employed for initiating 1. Temporary addresses are typically employed for initiating
outgoing sessions. outgoing sessions.
2. Temporary addresses are used for a short period of time 2. Temporary addresses are used for a short period of time
(typically hours to days) and are subsequently deprecated. (typically hours to days) and are subsequently deprecated.
Deprecated addresses can continue to be used for established Deprecated addresses can continue to be used for established
connections, but are not used to initiate new connections. connections, but are not used to initiate new connections.
3. New temporary addresses are generated periodically to replace 3. New temporary addresses are generated over time to replace
temporary addresses that expire. temporary addresses that expire.
4. Temporary addresses must have a limited lifetime (limited "valid 4. Temporary addresses must have a limited lifetime (limited "valid
lifetime" and "preferred lifetime" from [RFC4862]), that should lifetime" and "preferred lifetime" from [RFC4862]). The lifetime
be statistically different for different addresses. The lifetime
of an address should be further reduced when privacy-meaningful of an address should be further reduced when privacy-meaningful
events (such as a node attaching to a different network, or the events (such as a host attaching to a different network, or the
regeneration of a new randomized MAC address) takes place. regeneration of a new randomized MAC address) takes place. The
lifetime of temporary addresses must be statistically different
for different addresses, such that it is hard to predict or infer
when a new temporary address is generated, or correlate a newly-
generated address with an existing one.
5. By default, one address is generated for each prefix advertised 5. By default, one address is generated for each prefix advertised
by stateless address autoconfiguration. The resulting Interface by stateless address autoconfiguration. The resulting Interface
Identifiers must be statistically different when addresses are Identifiers must be statistically different when addresses are
configured for different prefixes. That is, when temporary configured for different prefixes or different network
addresses are generated for different autoconfiguration prefixes interfaces. This means that, given two addresses, it must be
for the same network interface, the resulting Interface difficult for an outside entity to infer whether the addresses
Identifiers must be statistically different. This means that, correspond to the same host or network interface.
given two addresses that employ different prefixes, it must be
difficult for an outside entity to tell whether the addresses
correspond to the same network interface or even whether they
have been generated by the same host.
6. It must be difficult for an outside entity to predict the 6. It must be difficult for an outside entity to predict the
Interface Identifiers that will be employed for temporary Interface Identifiers that will be employed for temporary
addresses, even with knowledge of the algorithm/method employed addresses, even with knowledge of the algorithm/method employed
to generate them and/or knowledge of the Interface Identifiers to generate them and/or knowledge of the Interface Identifiers
previously employed for other temporary addresses. These previously employed for other temporary addresses. These
Interface Identifiers must be semantically opaque [RFC7136] and Interface Identifiers must be semantically opaque [RFC7136] and
must not follow any specific patterns. must not follow any specific patterns.
3.2. Assumptions 3.2. Assumptions
The following algorithm assumes that for a given temporary address, The following algorithm assumes that for a given temporary address,
an implementation can determine the prefix from which it was an implementation can determine the prefix from which it was
generated. When a temporary address is deprecated, a new temporary generated. When a temporary address is deprecated, a new temporary
address is generated. The specific valid and preferred lifetimes for address is generated. The specific valid and preferred lifetimes for
the new address are dependent on the corresponding lifetime values the new address are dependent on the corresponding lifetime values
set for the prefix from which it was generated. set for the prefix from which it was generated.
Finally, this document assumes that when a node initiates outgoing Finally, this document assumes that when a host initiates outgoing
communication, temporary addresses can be given preference over communication, temporary addresses can be given preference over
stable addresses (if available), when the device is configured to do stable addresses (if available), when the device is configured to do
so. [RFC6724] mandates implementations to provide a mechanism, which so. [RFC6724] 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 stable addresses. It also allows for an addresses over stable 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 host 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 stable addresses and indicate whether they prefer to use temporary or stable addresses and
override the system defaults (see e.g. [RFC5014]). override the system defaults (see e.g. [RFC5014]).
3.3. Generation of Randomized Interface Identifiers 3.3. Generation of Randomized Interface Identifiers
The following subsections specify example algorithms for generating The following subsections specify example algorithms for generating
temporary interface identifiers that follow the guidelines in temporary interface identifiers that follow the guidelines in
Section 3.1 of this document. The algorithm specified in Section 3.1 of this document. The algorithm specified in
Section 3.3.1 benefits from a Pseudo-Random Number Generator (PRNG) Section 3.3.1 benefits from a Pseudo-Random Number Generator (PRNG)
available on the system. The algorithm specified in Section 3.3.2 available on the system. The algorithm specified in Section 3.3.2
allows for code reuse by nodes that implement [RFC7217]. allows for code reuse by hosts that implement [RFC7217].
3.3.1. Simple Randomized Interface Identifiers 3.3.1. Simple Randomized Interface Identifiers
One approach is to select a pseudorandom number of the appropriate One approach is to select a pseudorandom number of the appropriate
length. A node employing this algorithm should generate IIDs as length. A host employing this algorithm should generate IIDs as
follows: follows:
1. Obtain a random number (see [RFC4086] for randomness requirements 1. Obtain a random number from a pseudo-random number generator
for security). (PRNG) that can produce random numbers of at least as many bits
as required for the Interface Identifier (please see the next
step). [RFC4086] specifies randomness requirements for security.
2. The Interface Identifier is obtained by taking as many bits from 2. The Interface Identifier is obtained by taking as many bits from
the random number obtained in the previous step as necessary. the random number obtained in the previous step as necessary.
See [RFC7136] for the necessary number of bits, that is, the See [RFC7136] for the necessary number of bits, that is, the
length of the IID. See also [RFC7421] for a discussion of the length of the IID. See also [RFC7421] for a discussion of the
privacy implications of the IID length. Note: there are no privacy implications of the IID length. Note: there are no
special bits in an Interface Identifier [RFC7136]. special bits in an Interface Identifier [RFC7136].
3. The resulting Interface Identifier MUST be compared against the 3. The resulting Interface Identifier MUST be compared against the
reserved IPv6 Interface Identifiers [RFC5453] [IANA-RESERVED-IID] reserved IPv6 Interface Identifiers [RFC5453] [IANA-RESERVED-IID]
and against those Interface Identifiers already employed in an and against those Interface Identifiers already employed in an
address of the same network interface and the same network address of the same network interface and the same network
prefix. In the event that an unacceptable identifier has been prefix. In the event that an unacceptable identifier has been
generated, a new interface identifier should be generated, by generated, a new interface identifier should be generated, by
repeating the algorithm from the first step. repeating the algorithm from the first step.
3.3.2. Hash-based Generation of Randomized Interface Identifiers 3.3.2. Hash-based Generation of Randomized Interface Identifiers
The algorithm in [RFC7217] can be augmented for the generation of The algorithm in [RFC7217] can be augmented for the generation of
temporary addresses. The benefit of this would be that a node could temporary addresses. The benefit of this would be that a host could
employ a single algorithm for generating stable and temporary employ a single algorithm for generating stable and temporary
addresses, by employing appropriate parameters. addresses, by employing appropriate parameters.
Nodes would employ the following algorithm for generating the Hosts would employ the following algorithm for generating the
temporary IID: temporary IID:
1. Compute a random identifier with the expression: 1. Compute a random identifier with the expression:
RID = F(Prefix, Net_Iface, Network_ID, Time, DAD_Counter, RID = F(Prefix, Net_Iface, Network_ID, Time, DAD_Counter,
secret_key) secret_key)
Where: Where:
RID: RID:
Random Identifier Random Identifier
F(): F():
A pseudorandom function (PRF) that MUST NOT be computable from A pseudorandom function (PRF) that MUST NOT be computable from
the outside (without knowledge of the secret key). F() MUST the outside (without knowledge of the secret key). F() MUST
also be difficult to reverse, such that it resists attempts to also be difficult to reverse, such that it resists attempts to
obtain the secret_key, even when given samples of the output obtain the secret_key, even when given samples of the output
of F() and knowledge or control of the other input parameters. of F() and knowledge or control of the other input parameters.
F() SHOULD produce an output of at least 64 bits. F() could F() SHOULD produce an output of at least as many bits as
be implemented as a cryptographic hash of the concatenation of required for the Interface Identifier. F() could be the
each of the function parameters. SHA-256 [FIPS-SHS] is one result of applying a cryptographic hash over an encoded
possible option for F(). Note: MD5 [RFC1321] is considered version of the function parameters. While this document does
unacceptable for F() [RFC6151]. not recommend a specific mechanism for encoding the function
parameters (or a specific cryptographic hash function), a
cryptographically robust construction will ensure that the
mapping from parameters to the hash function input is an
injective map, as might be attained by using fixed-width
encodings and/or length-prefixing variable-length parameters.
SHA-256 [FIPS-SHS] is one possible option for F(). Note: MD5
[RFC1321] is considered unacceptable for F() [RFC6151].
Prefix: Prefix:
The prefix to be used for SLAAC, as learned from an ICMPv6 The prefix to be used for SLAAC, as learned from an ICMPv6
Router Advertisement message. Router Advertisement message.
Net_Iface: Net_Iface:
The MAC address corresponding to the underlying network The MAC address corresponding to the underlying network
interface card, in the case the link uses IEEE802 link-layer interface card, in the case the link uses IEEE802 link-layer
identifiers. Employing the MAC address for this parameter identifiers. Employing the MAC address for this parameter
(over the other suggested options in RFC7217) means that the (over the other suggested options in RFC7217) means that the
re-generation of a randomized MAC address will result in a re-generation of a randomized MAC address will result in a
different temporary address. different temporary address.
Network_ID: Network_ID:
Some network-specific data that identifies the subnet to which Some network-specific data that identifies the subnet to which
this interface is attached -- for example, the IEEE 802.11 this interface is attached -- for example, the IEEE 802.11
skipping to change at page 10, line 4 skipping to change at page 10, line 16
interface card, in the case the link uses IEEE802 link-layer interface card, in the case the link uses IEEE802 link-layer
identifiers. Employing the MAC address for this parameter identifiers. Employing the MAC address for this parameter
(over the other suggested options in RFC7217) means that the (over the other suggested options in RFC7217) means that the
re-generation of a randomized MAC address will result in a re-generation of a randomized MAC address will result in a
different temporary address. different temporary address.
Network_ID: Network_ID:
Some network-specific data that identifies the subnet to which Some network-specific data that identifies the subnet to which
this interface is attached -- for example, the IEEE 802.11 this interface is attached -- for example, the IEEE 802.11
Service Set Identifier (SSID) corresponding to the network to Service Set Identifier (SSID) corresponding to the network to
which this interface is associated. Additionally, Simple DNA which this interface is associated. Additionally, "Simple
[RFC6059] describes ideas that could be leveraged to generate Procedures for Detecting Network Attachment in IPv6" ("Simple
a Network_ID parameter. This parameter is SHOULD be employed DNA") [RFC6059] describes ideas that could be leveraged to
if some form of "Network_ID" is available. generate a Network_ID parameter. This parameter SHOULD be
employed if some form of "Network_ID" is available.
Time: Time:
An implementation-dependent representation of time. One An implementation-dependent representation of time. One
possible example is the representation in UNIX-like systems possible example is the representation in UNIX-like systems
[OPEN-GROUP], that measure time in terms of the number of [OPEN-GROUP], that measure time in terms of the number of
seconds elapsed since the Epoch (00:00:00 Coordinated seconds elapsed since the Epoch (00:00:00 Coordinated
Universal Time (UTC), 1 January 1970). The addition of the Universal Time (UTC), 1 January 1970). The addition of the
"Time" argument results in (statistically) different interface "Time" argument results in (statistically) different interface
identifiers over time. identifiers over time.
DAD_Counter: DAD_Counter:
A counter that is employed to resolve Duplicate Address A counter that is employed to resolve Duplicate Address
Detection (DAD) conflicts. Detection (DAD) conflicts.
secret_key: secret_key:
A secret key that is not known by the attacker. The secret A secret key that is not known by the attacker. The secret
key SHOULD be of at least 128 bits. It MUST be initialized to key SHOULD be of at least 128 bits. It MUST be initialized to
a pseudo-random number (see [RFC4086] for randomness a pseudo-random number (see [RFC4086] for randomness
requirements for security) when the operating system is requirements for security) when the operating system is
"bootstrapped". "bootstrapped". The secret_key MUST NOT be employed for any
other purpose than the one discussed in this section. For
example, implementations MUST NOT employ the same secret_key
for the generation of stable addresses [RFC7217] and the
generation of temporary addresses via this algorithm.
2. The Interface Identifier is finally obtained by taking as many 2. The Interface Identifier is finally obtained by taking as many
bits from the RID value (computed in the previous step) as bits from the RID value (computed in the previous step) as
necessary, starting from the least significant bit. See necessary, starting from the least significant bit. See
[RFC7136] for the necessary number of bits, that is, the length [RFC7136] for the necessary number of bits, that is, the length
of the IID. See also [RFC7421] for a discussion of the privacy of the IID. See also [RFC7421] for a discussion of the privacy
implications of the IID length. Note: there are no special bits implications of the IID length. Note: there are no special bits
in an Interface Identifier [RFC7136]. in an Interface Identifier [RFC7136].
3. The resulting Interface Identifier MUST be compared against the 3. The resulting Interface Identifier MUST be compared against the
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generated, the value DAD_Counter should be incremented by 1, and generated, the value DAD_Counter should be incremented by 1, and
the algorithm should be restarted from the first step. the algorithm should be restarted from the first step.
3.4. Generating Temporary Addresses 3.4. Generating Temporary Addresses
[RFC4862] describes the steps for generating a link-local address [RFC4862] 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 [RFC4862] as addresses for other scopes. This document extends [RFC4862] as
follows. When processing a Router Advertisement with a Prefix follows. When processing a Router Advertisement with a Prefix
Information option carrying a prefix for the purposes of address Information option carrying a prefix for the purposes of address
autoconfiguration (i.e., the A bit is set), the node MUST perform the autoconfiguration (i.e., the A bit is set), the host MUST perform the
following steps: following steps:
1. Process the Prefix Information Option as defined in [RFC4862], 1. Process the Prefix Information Option as defined in [RFC4862],
adjusting the lifetimes of existing temporary addresses, with the adjusting the lifetimes of existing temporary addresses, with the
overall constraint that no temporary addresses should ever remain overall constraint that no temporary addresses should ever remain
"valid" or "preferred" for a time longer than "valid" or "preferred" for a time longer than
(TEMP_VALID_LIFETIME) 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. maximum 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. If the node has not configured any temporary address for the 3. If the host has not configured any temporary address for the
corresponding prefix, the node SHOULD create a new temporary corresponding prefix, the host SHOULD create a new temporary
address for such prefix. address for such prefix.
Note: Note:
For example, a host might implement prefix-specific policies For example, a host might implement prefix-specific policies
such as not configuring temporary addresses for the Unique such as not configuring temporary addresses for the Unique
Local IPv6 Unicast Addresses (ULA) [RFC4193] prefix. Local IPv6 Unicast Addresses (ULA) [RFC4193] prefix.
4. When creating a temporary address, the lifetime values MUST be 4. When creating a temporary address, the DESYNC_FACTOR MUST be
derived from the corresponding prefix as follows: computed for this prefix, and the lifetime values MUST be 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
prefix and TEMP_VALID_LIFETIME prefix and 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 and TEMP_PREFERRED_LIFETIME - DESYNC_FACTOR. of the prefix and 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 a randomized 6. New temporary addresses MUST be created by appending a randomized
interface identifier (generated as described in Section 3.3 of interface identifier to the prefix that was received.
this document) to the prefix that was received. Section 3.3 of this document specifies some sample algorithms for
generating the randomized interface identifier.
7. The node MUST perform duplicate address detection (DAD) on the 7. The host 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 host MUST generate a new randomized interface
identifier, and repeat the previous steps as appropriate up to identifier, and repeat the previous steps as appropriate up to
TEMP_IDGEN_RETRIES times. If after TEMP_IDGEN_RETRIES TEMP_IDGEN_RETRIES times. If after TEMP_IDGEN_RETRIES
consecutive attempts no non-unique address was generated, the consecutive attempts no non-unique address was generated, the
node MUST log a system error and SHOULD NOT attempt to generate a host MUST log a system error and SHOULD NOT attempt to generate a
temporary address for the given prefix for the duration of the temporary address for the given prefix for the duration of the
node's attachment to the network via this interface. This allows host's attachment to the network via this interface. This allows
hosts to recover from occasional DAD failures, or otherwise log hosts to recover from occasional DAD failures, or otherwise log
the recurrent address collisions. the recurrent address collisions.
3.5. Expiration of Temporary Addresses 3.5. 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 3.4, starting at step 4). Note that, except for the Section 3.4, starting at step 4). 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
ensure that a preferred temporary address is always available, a new ensure that a preferred temporary address is always available, a new
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 host 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.
3.6. Regeneration of Temporary Addresses 3.6. Regeneration of Temporary Addresses
The frequency at which temporary addresses change depends on how a The frequency at which temporary addresses change depends on how a
skipping to change at page 13, line 8 skipping to change at page 13, line 25
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
contain non-changing identifiers to make it worthwhile. Thus, having contain non-changing identifiers to make it worthwhile. Thus, having
large numbers of clients change their address on a daily or weekly large numbers of clients change their address on a daily or weekly
basis is likely to be sufficient to alleviate most privacy concerns. basis is likely to be sufficient to alleviate most privacy concerns.
There are also client costs associated with having a large number of There are also client costs associated with having a large number of
addresses associated with a node (e.g., in doing address lookups, the addresses associated with a host (e.g., in doing address lookups, the
need to join many multicast groups, etc.). Thus, changing addresses need to join many multicast groups, etc.). Thus, changing addresses
frequently (e.g., every few minutes) may have performance frequently (e.g., every few minutes) may have performance
implications. implications.
Nodes following this specification SHOULD generate new temporary Hosts following this specification SHOULD generate new temporary
addresses on a periodic basis. This can be achieved by generating a addresses on a periodic basis. This can be achieved by generating a
new temporary address at least once every (TEMP_PREFERRED_LIFETIME - new temporary address at least once every (TEMP_PREFERRED_LIFETIME -
REGEN_ADVANCE - DESYNC_FACTOR) time units. As described above, REGEN_ADVANCE - DESYNC_FACTOR) time units. As described above,
generating a new temporary address REGEN_ADVANCE time units before a generating a new temporary address REGEN_ADVANCE time units before a
temporary address becomes deprecated produces addresses with a temporary address becomes deprecated produces addresses with a
preferred lifetime no larger than TEMP_PREFERRED_LIFETIME. The value preferred lifetime no larger than TEMP_PREFERRED_LIFETIME. The value
DESYNC_FACTOR is a random value (different for each client) that DESYNC_FACTOR is a random value computed for a prefix when a
ensures that clients don't synchronize with each other and generate temporary address is generated, that ensures that clients do not
new addresses at exactly the same time. When the preferred lifetime generate new addresses with a fixed frequency, and that clients do
expires, a new temporary address MUST be generated using the new not synchronize with each other and generate new addresses at exactly
randomized interface identifier. the same time. When the preferred lifetime expires, a new temporary
address MUST be generated using the algorithm specified in
Section 3.4.
Because the precise frequency at which it is appropriate to generate Because the precise frequency at which it is appropriate to generate
new addresses varies from one environment to another, implementations new addresses varies from one environment to another, implementations
SHOULD provide end users with the ability to change the frequency at SHOULD provide end users with the ability to change the frequency at
which addresses are regenerated. The default value is given in which addresses are regenerated. The default value is given in
TEMP_PREFERRED_LIFETIME and is one day. In addition, the exact time TEMP_PREFERRED_LIFETIME and is one day. In addition, the exact time
at which to invalidate a temporary address depends on how at which to invalidate a temporary address depends on how
applications are used by end users. Thus, the suggested default applications are used by end users. Thus, the suggested default
value of two days (TEMP_VALID_LIFETIME) may not be appropriate in all value of two days (TEMP_VALID_LIFETIME) may not be appropriate in all
environments. Implementations SHOULD provide end users with the environments. Implementations SHOULD provide end users with the
ability to override both of these default values. ability to override both of these default values.
Finally, when an interface connects to a new (different) link, a new Finally, when an interface connects to a new (different) link,
set of temporary addresses MUST be generated immediately for use on existing temporary addresses for the corresponding interface MUST be
the new link. If a device moves from one link to another, generating eliminated, and new temporary addresses MUST be generated immediately
a new set of temporary addresses ensures that the device uses for use on the new link. If a device moves from one link to another,
generating new temporary addresses ensures that the device uses
different randomized interface identifiers for the temporary 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 hosts. The host 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 "Simple Procedures for Detecting Network Attachment in described by Simple DNA [RFC6059]. Detecting link changes would
IPv6" [RFC6059]. Detecting link changes would prevent link down/up prevent link down/up events from causing temporary addresses to be
events from causing temporary addresses to be (unnecessarily) (unnecessarily) regenerated.
regenerated.
3.7. Implementation Considerations 3.7. Implementation 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.
skipping to change at page 14, line 25 skipping to change at page 14, line 41
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"
[RFC4193] prefixes while still generating temporary addresses for all [RFC4193] 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:db8:1::/48 and address generation only for the prefixes 2001:db8:1::/48 and
2001:db8:2::/48 while disabling it for all other prefixes. To 2001:db8:2::/48 while disabling it for all other prefixes. To
support this behavior, implementations SHOULD provide a way to enable support this behavior, implementations SHOULD provide a way to enable
and disable generation of temporary addresses for specific prefix and disable generation of temporary addresses for specific prefix
subranges. This per-prefix setting SHOULD override the global subranges. This per-prefix setting SHOULD override the global
settings on the node with respect to the specified prefix subranges. settings on the host with respect to the specified prefix subranges.
Note that the per-prefix setting can be applied at any granularity, Note that the per-prefix setting can be applied at any granularity,
and not necessarily on a per subnet basis. and not necessarily on a per subnet basis.
3.8. Defined Constants and Configuration Variables 3.8. Defined Constants and Configuration Variables
Constants and configuration variables defined in this document Constants and configuration variables defined in this document
include: include:
TEMP_VALID_LIFETIME -- Default value: 2 days. Users should be able TEMP_VALID_LIFETIME -- Default value: 2 days. Users should be able
to override the default value. to override the default value.
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Note: Note:
The TEMP_PREFERRED_LIFETIME value MUST be less than the The TEMP_PREFERRED_LIFETIME value MUST be less than the
TEMP_VALID_LIFETIME value, to avoid the pathological case where an TEMP_VALID_LIFETIME value, to avoid the pathological case where an
address is employed for new communications, but becomes invalid in address is employed for new communications, but becomes invalid in
less than 1 second, disrupting those communications less than 1 second, disrupting those communications
REGEN_ADVANCE -- 2 + (TEMP_IDGEN_RETRIES * DupAddrDetectTransmits * REGEN_ADVANCE -- 2 + (TEMP_IDGEN_RETRIES * DupAddrDetectTransmits *
RetransTimer / 1000) RetransTimer / 1000)
Note: Notes:
This parameter is specified as a function of other protocol This parameter is specified as a function of other protocol
parameters, to account for the time possibly spent in Duplicate parameters, to account for the time possibly spent in Duplicate
Address Detection (DAD) in the worst-case scenario of Address Detection (DAD) in the worst-case scenario of
TEMP_IDGEN_RETRIES. This prevents the pathological case where the TEMP_IDGEN_RETRIES. This prevents the pathological case where the
generation of a new temporary address is not started with enough generation of a new temporary address is not started with enough
anticipation such that a new preferred address is generated before anticipation such that a new preferred address is generated before
the currently-preferred temporary address becomes deprecated. the currently-preferred temporary address becomes deprecated.
DupAddrDetectTransmits and RetransTimer are specified in RetransTimer is specified in [RFC4861], while
[RFC4861]. DupAddrDetectTransmits is specified in [RFC4862]. Since
RetransTimer is specified in units of milliseconds, this
expression employs the constant "1000" such that REGEN_ADVANCE is
expressed in seconds.
MAX_DESYNC_FACTOR -- 10 minutes. Upper bound on DESYNC_FACTOR. MAX_DESYNC_FACTOR -- 0.4 * TEMP_PREFERRED_LIFETIME. Upper bound on
DESYNC_FACTOR.
Note:
Setting MAX_DESYNC_FACTOR to 0.4 TEMP_PREFERRED_LIFETIME results
in addresses that have statistically different lifetimes, and a
maximum of 3 concurrent temporary addresses when the default
parameters specified in this section are employed.
DESYNC_FACTOR -- A random value within the range 0 - DESYNC_FACTOR -- A random value within the range 0 -
MAX_DESYNC_FACTOR. It is computed once at system start (rather than MAX_DESYNC_FACTOR. It is computed for a prefix each time a temporary
each time it is used) and must never be greater than address is generated, and must be smaller than
(TEMP_PREFERRED_LIFETIME - REGEN_ADVANCE). (TEMP_PREFERRED_LIFETIME - REGEN_ADVANCE).
TEMP_IDGEN_RETRIES -- Default value: 3 TEMP_IDGEN_RETRIES -- Default value: 3
4. Implications of Changing Interface Identifiers 4. Implications of Changing Interface Identifiers
The desires of protecting individual privacy versus the desire to The desire to protect individual privacy can conflict with the desire
effectively maintain and debug a network can conflict with each % to effectively maintain and debug a network. Having clients use
other. Having clients use addresses that change over time will make addresses that change over time will make it more difficult to track
it more difficult to track down and isolate operational problems. down and isolate operational problems. For example, when looking at
For example, when looking at packet traces, it could become more packet traces, it could become more difficult to determine whether
difficult to determine whether one is seeing behavior caused by a one is seeing behavior caused by a single errant host, or by a number
single errant machine, or by a number of them. of them.
Network deployments are currently recommended to provide multiple Network deployments are currently recommended to provide multiple
IPv6 addresses from each prefix to general-purpose hosts [RFC7934]. IPv6 addresses from each prefix to general-purpose hosts [RFC7934].
However, in some scenarios, use of a large number of IPv6 addresses However, in some scenarios, use of a large number of IPv6 addresses
may have negative implications on network devices that need to may have negative implications on network devices that need to
maintain entries for each IPv6 address in some data structures (e.g., maintain entries for each IPv6 address in some data structures (e.g.,
[RFC7039]). Additionally, concurrent active use of multiple IPv6 [RFC7039]). For example, concurrent active use of multiple IPv6
addresses will increase neighbour discovery traffic if Neighbour addresses will increase neighbor discovery traffic if Neighbor Caches
Caches in network devices are not large enough to store all addresses in network devices are not large enough to store all addresses on the
on the link. This can impact performance and energy efficiency on link. This can impact performance and energy efficiency on networks
networks on which multicast is expensive (e.g. on which multicast is expensive (e.g.
[I-D.ietf-mboned-ieee802-mcast-problems]). [I-D.ietf-mboned-ieee802-mcast-problems]). Additionally, some
network security devices might incorrectly infer IPv6 address forging
if temporary addresses are regenerated at a high rate.
The use of temporary addresses may cause unexpected difficulties with The use of temporary addresses may cause unexpected difficulties with
some applications. For example, some servers refuse to accept some applications. For example, 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. That is, they perform a DNS PTR query to determine into a DNS name. That is, they perform a DNS PTR query to determine
the DNS name, and may then also perform an AAAA query on the returned the DNS 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 name to verify that the returned DNS name maps back into the address
being used. Consequently, clients not properly registered in the DNS being used. Consequently, clients not properly registered in the DNS
may be unable to access some services. However, a node's DNS name may be unable to access some services. However, a host's DNS name
(if non-changing) would serve as a constant identifier. The wide (if non-changing) would serve as a constant identifier. The wide
deployment of the extension described in this document could deployment of the extension described in this document could
challenge the practice of inverse-DNS-based "validation", which has challenge the practice of inverse-DNS-based "validation", which has
little validity, though it is widely implemented. In order to meet little validity, though it is widely implemented. In order to meet
server challenges, nodes could register temporary addresses in the server challenges, hosts could register temporary addresses in the
DNS using random names (for example, a string version of the random DNS using random names (for example, a string version of the random
address itself), albeit at the expense of increased complexity. address itself), albeit at the expense of increased complexity.
In addition, some applications may not behave robustly if temporary In addition, some applications may not behave robustly if temporary
addresses are used and an address expires before the application has addresses are used and an address expires before the application has
terminated, or if it opens multiple sessions, but expects them to all terminated, or if it opens multiple sessions, but expects them to all
use the same addresses. use the same addresses.
[RFC4941] employed a randomized temporary Interface Identifier for
generating a set of temporary addresses, such that temporary
addresses configured at a given time for multiple SLAAC prefixes
would employ the same Interface Identifier. Sharing the same IID
among multiple address allowed host to join only one solicited-node
multicast group per temporary address set.
This document requires that the Interface Identifiers of all
temporary addresses on a host are statistically different from each
other. This means that when a network employs multiple prefixes,
each temporary address of a set will result in a different solicited-
node multicast address, and thus the number of multicast groups that
a host must join becomes a function of the number of SLAAC prefixes
employed for generating temporary addresses.
Thus, a network that employs multiple prefixes may require hosts to
join more multicast groups than for an RFC4941 implementation. If
the number of multicast groups were large enough, a node might need
to resort to setting the network interface card to promiscuous mode.
This could cause the node to process more packets than strictly
necessary, and might have a negative impact on battery-life, and on
system performance in general.
We note that since this document reduces the default
TEMP_VALID_LIFETIME from 7 days (in [RFC4941]) to 2 days, the number
of concurrent temporary addresses per SLAAC prefix will be smaller
than for RFC4941 implementations, and thus the number of multicast
groups for a network that employs, say, between 1 and three prefixes
will be similar than of RFC4941 implementations.
Implementations concerned with the maximum number of multicast groups
that would be required to join as a result of configured addresses,
or the overall number of configured addresses, should consider
enforcing implementation-specific limits on e.g. the maximum number
of configured addresses, the maximum number of SLAAC prefixes that
are employed for auto-configuration, and/or the maximum ratio for
TEMP_VALID_LIFETIME/TEMP_PREFERRED_LIFETIME (that ultimately controls
the approximate number of concurrent temporary addresses per SLAAC
prefix). Many of these configuration limits are readily available in
SLAAC and RFC4941 implementations. We note that these configurable
limits are meant to prevent pathological behaviors (as opposed to
simply limiting the usage of IPv6 addresses), since IPv6
implementations are expected to leverage the usage of multiple
addresses [RFC7934].
5. Significant Changes from RFC4941 5. Significant Changes from RFC4941
This section summarizes the changes in this document relative to RFC This section summarizes the substantive changes in this document
4941 that an implementer of RFC 4941 should be aware of. relative to RFC 4941.
Broadly speaking, this document introduces the following changes: Broadly speaking, this document introduces the following changes:
o Addresses a number of flaws in the algorithm for generating o Addresses a number of flaws in the algorithm for generating
temporary addresses: The aforementioned flaws include the use of temporary addresses: The aforementioned flaws include the use of
MD5 for computing the temporary IIDs, and reusing the same IID for MD5 for computing the temporary IIDs, and reusing the same IID for
multiple prefixes (see [RAID2015] and [RFC7721] for further multiple prefixes (see [RAID2015] and [RFC7721] for further
details). details).
o Allows hosts to employ only temporary addresses: o Allows hosts to employ only temporary addresses:
skipping to change at page 16, line 41 skipping to change at page 18, line 19
addition to stable addresses. This document does not imply or addition to stable addresses. This document does not imply or
require the configuration of stable addresses, and thus require the configuration of stable addresses, and thus
implementations can now configure both stable and temporary implementations can now configure both stable and temporary
addresses, or temporary addresses only. addresses, or temporary addresses only.
o Removes the recommendation that temporary addresses be disabled by o Removes the recommendation that temporary addresses be disabled by
default: default:
This is in line with BCP188 ([RFC7258]), and also with BCP204 This is in line with BCP188 ([RFC7258]), and also with BCP204
([RFC7934]). ([RFC7934]).
o Reduces the default Valid Lifetime for temporary addresses: o Reduces the default maximum Valid Lifetime for temporary
The default Valid Lifetime for temporary addresses has been addresses: The default Valid Lifetime for temporary addresses has
reduced from 1 week to 2 days, decreasing the typical number of been reduced from 1 week to 2 days, decreasing the typical number
concurrent temporary addresses from 7 to 2. This reduces the of concurrent temporary addresses from 7 to 3. This reduces the
possible stress on network elements (see Section 4 for further possible stress on network elements (see Section 4 for further
details). details).
o DESYNC_FACTOR is computed on a per-prefix basis each time a
temporary address is generated, such that each temporary address
has a statistically different preferred lifetime, and that
temporary addresses are not generated at a constant frequency.
o Changes the requirement to not try to regenerate temporary
addresses upon DAD failures from "MUST NOT" to "SHOULD NOT".
o The discussion about the security and privacy implications of
different address generation techniques has been replaced with
references to recent work in this area ([RFC7707], [RFC7721], and
[RFC7217]).
o Addresses all errata submitted for [RFC4941]. o Addresses all errata submitted for [RFC4941].
6. Future Work 6. Future Work
An implementation might want to keep track of which addresses are An implementation might want to keep track of which addresses are
being used by upper layers so as to be able to remove a deprecated being used by upper layers so as to be able to remove a deprecated
temporary address from internal data structures once no upper layer temporary address from internal data structures once no upper layer
protocols are using it (but not before). This is in contrast to protocols are using it (but not before). This is in contrast to
current approaches where addresses are removed from an interface when current approaches where addresses are removed from an interface when
they become invalid [RFC4862], independent of whether or not upper they become invalid [RFC4862], independent of whether or not upper
skipping to change at page 18, line 13 skipping to change at page 19, line 45
found at: <https://github.com/openbsd/src/tree/master/sbin/slaacd> found at: <https://github.com/openbsd/src/tree/master/sbin/slaacd>
8. IANA Considerations 8. IANA Considerations
There are no IANA registries within this document. The RFC-Editor There are no IANA registries within this document. The RFC-Editor
can remove this section before publication of this document as an can remove this section before publication of this document as an
RFC. RFC.
9. Security Considerations 9. Security Considerations
If a very small number of nodes (say, only one) use a given prefix If a very small number of hosts (say, only one) use a given prefix
for extended periods of time, just changing the interface identifier for extended periods of time, just changing the interface identifier
part of the address may not be sufficient to mitigate address-based part of the address may not be sufficient to mitigate address-based
network activity correlation, since the prefix acts as a constant network activity correlation, since the prefix acts as a constant
identifier. The procedures described in this document are most identifier. The procedures described in this document are most
effective when the prefix is reasonably non static or is used by a effective when the prefix is reasonably non static or is used by a
fairly large number of nodes. Additionally, if a temporary address fairly large number of hosts. Additionally, if a temporary address
is used in a session where the user authenticates, any notion of is used in a session where the user authenticates, any notion of
"privacy" for that address is compromised. "privacy" for that address is compromised for the part(ies) that
receive the authentication information.
While this document discusses ways of obscuring a user's IP address, While this document discusses ways to limit the lifetime of Interface
the method described is believed to be ineffective against Identifiers to reduce the ability of attackers to perform address-
sophisticated forms of traffic analysis. To increase effectiveness, based network activity correlation, the method described is believed
one may need to consider the use of more advanced techniques, such as to be ineffective against sophisticated forms of traffic analysis.
Onion Routing [ONION]. To increase effectiveness, one may need to consider the use of more
advanced techniques, such as Onion Routing [ONION].
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 of Service (DDoS) attacks. In a network with a large number of
nodes, new temporary addresses are created at a fairly high rate. hosts, new temporary addresses are created at a fairly high rate.
This 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" (using 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, though as noted in Section 4 there
are corresponding costs for doing so.
10. Acknowledgments 10. Acknowledgments
The authors would like to thank (in alphabetical order) Fred Baker, The authors would like to thank (in alphabetical order) Fred Baker,
Brian Carpenter, Tim Chown, Lorenzo Colitti, David Farmer, Tom Brian Carpenter, Tim Chown, Lorenzo Colitti, Roman Danyliw, David
Herbert, Bob Hinden, Christian Huitema, Erik Kline, Gyan Mishra, Dave Farmer, Tom Herbert, Bob Hinden, Christian Huitema, Benjamin Kaduk,
Plonka, Michael Richardson, Mark Smith, Pascal Thubert, Ole Troan, Erik Kline, Gyan Mishra, Dave Plonka, Alvaro Retana, Michael
Johanna Ullrich, and Timothy Winters, for providing valuable comments Richardson, Mark Smith, Dave Thaler, Pascal Thubert, Ole Troan,
on earlier versions of this document. Johanna Ullrich, Eric Vyncke, and Timothy Winters, for providing
valuable comments on earlier versions of this document.
This document incorporates errata submitted for [RFC4941] by Jiri This document incorporates errata submitted for [RFC4941] by Jiri
Bohac and Alfred Hoenes. Bohac and Alfred Hoenes.
This document is based on [RFC4941] (a revision of RFC3041). Suresh This document is based on [RFC4941] (a revision of RFC3041). Suresh
Krishnan was the sole author of RFC4941. He would like to Krishnan was the sole author of RFC4941. He would like to
acknowledge the contributions of the IPv6 working group and, in acknowledge the contributions of the IPv6 working group and, in
particular, Jari Arkko, Pekka Nikander, Pekka Savola, Francis Dupont, particular, Jari Arkko, Pekka Nikander, Pekka Savola, Francis Dupont,
Brian Haberman, Tatuya Jinmei, and Margaret Wasserman for their Brian Haberman, Tatuya Jinmei, and Margaret Wasserman for their
detailed comments. detailed comments.
skipping to change at page 19, line 49 skipping to change at page 21, line 37
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
DOI 10.17487/RFC4861, September 2007, DOI 10.17487/RFC4861, September 2007,
<https://www.rfc-editor.org/info/rfc4861>. <https://www.rfc-editor.org/info/rfc4861>.
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862, Address Autoconfiguration", RFC 4862,
DOI 10.17487/RFC4862, September 2007, DOI 10.17487/RFC4862, September 2007,
<https://www.rfc-editor.org/info/rfc4862>. <https://www.rfc-editor.org/info/rfc4862>.
[RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy
Extensions for Stateless Address Autoconfiguration in
IPv6", RFC 4941, DOI 10.17487/RFC4941, September 2007,
<https://www.rfc-editor.org/info/rfc4941>.
[RFC5453] Krishnan, S., "Reserved IPv6 Interface Identifiers", [RFC5453] Krishnan, S., "Reserved IPv6 Interface Identifiers",
RFC 5453, DOI 10.17487/RFC5453, February 2009, RFC 5453, DOI 10.17487/RFC5453, February 2009,
<https://www.rfc-editor.org/info/rfc5453>. <https://www.rfc-editor.org/info/rfc5453>.
[RFC6724] Thaler, D., Ed., Draves, R., Matsumoto, A., and T. Chown, [RFC6724] Thaler, D., Ed., Draves, R., Matsumoto, A., and T. Chown,
"Default Address Selection for Internet Protocol Version 6 "Default Address Selection for Internet Protocol Version 6
(IPv6)", RFC 6724, DOI 10.17487/RFC6724, September 2012, (IPv6)", RFC 6724, DOI 10.17487/RFC6724, September 2012,
<https://www.rfc-editor.org/info/rfc6724>. <https://www.rfc-editor.org/info/rfc6724>.
[RFC7136] Carpenter, B. and S. Jiang, "Significance of IPv6 [RFC7136] Carpenter, B. and S. Jiang, "Significance of IPv6
Interface Identifiers", RFC 7136, DOI 10.17487/RFC7136, Interface Identifiers", RFC 7136, DOI 10.17487/RFC7136,
February 2014, <https://www.rfc-editor.org/info/rfc7136>. February 2014, <https://www.rfc-editor.org/info/rfc7136>.
[RFC7217] Gont, F., "A Method for Generating Semantically Opaque
Interface Identifiers with IPv6 Stateless Address
Autoconfiguration (SLAAC)", RFC 7217,
DOI 10.17487/RFC7217, April 2014,
<https://www.rfc-editor.org/info/rfc7217>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8190] Bonica, R., Cotton, M., Haberman, B., and L. Vegoda,
"Updates to the Special-Purpose IP Address Registries",
BCP 153, RFC 8190, DOI 10.17487/RFC8190, June 2017,
<https://www.rfc-editor.org/info/rfc8190>.
11.2. Informative References 11.2. Informative References
[FIPS-SHS] [FIPS-SHS]
NIST, "Secure Hash Standard (SHS)", FIPS NIST, "Secure Hash Standard (SHS)", FIPS
Publication 180-4, August 2015, Publication 180-4, August 2015,
<https://nvlpubs.nist.gov/nistpubs/FIPS/ <https://nvlpubs.nist.gov/nistpubs/FIPS/
NIST.FIPS.180-4.pdf>. NIST.FIPS.180-4.pdf>.
[I-D.ietf-mboned-ieee802-mcast-problems] [I-D.ietf-mboned-ieee802-mcast-problems]
Perkins, C., McBride, M., Stanley, D., Kumari, W., and J. Perkins, C., McBride, M., Stanley, D., Kumari, W., and J.
Zuniga, "Multicast Considerations over IEEE 802 Wireless Zuniga, "Multicast Considerations over IEEE 802 Wireless
Media", draft-ietf-mboned-ieee802-mcast-problems-11 (work Media", draft-ietf-mboned-ieee802-mcast-problems-12 (work
in progress), December 2019. in progress), October 2020.
[IANA-RESERVED-IID] [IANA-RESERVED-IID]
IANA, "Reserved IPv6 Interface Identifiers", IANA, "Reserved IPv6 Interface Identifiers",
<http://www.iana.org/assignments/ipv6-interface-ids>. <http://www.iana.org/assignments/ipv6-interface-ids>.
[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.
skipping to change at page 21, line 28 skipping to change at page 22, line 46
Ullrich, J. and E. Weippl, "Privacy is Not an Option: Ullrich, J. and E. Weippl, "Privacy is Not an Option:
Attacking the IPv6 Privacy Extension", International Attacking the IPv6 Privacy Extension", International
Symposium on Recent Advances in Intrusion Detection Symposium on Recent Advances in Intrusion Detection
(RAID), 2015, <https://www.sba-research.org/wp- (RAID), 2015, <https://www.sba-research.org/wp-
content/uploads/publications/Ullrich2015Privacy.pdf>. content/uploads/publications/Ullrich2015Privacy.pdf>.
[RFC1321] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321, [RFC1321] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
DOI 10.17487/RFC1321, April 1992, DOI 10.17487/RFC1321, April 1992,
<https://www.rfc-editor.org/info/rfc1321>. <https://www.rfc-editor.org/info/rfc1321>.
[RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy
Extensions for Stateless Address Autoconfiguration in
IPv6", RFC 4941, DOI 10.17487/RFC4941, September 2007,
<https://www.rfc-editor.org/info/rfc4941>.
[RFC5014] Nordmark, E., Chakrabarti, S., and J. Laganier, "IPv6 [RFC5014] Nordmark, E., Chakrabarti, S., and J. Laganier, "IPv6
Socket API for Source Address Selection", RFC 5014, Socket API for Source Address Selection", RFC 5014,
DOI 10.17487/RFC5014, September 2007, DOI 10.17487/RFC5014, September 2007,
<https://www.rfc-editor.org/info/rfc5014>. <https://www.rfc-editor.org/info/rfc5014>.
[RFC6059] Krishnan, S. and G. Daley, "Simple Procedures for [RFC6059] Krishnan, S. and G. Daley, "Simple Procedures for
Detecting Network Attachment in IPv6", RFC 6059, Detecting Network Attachment in IPv6", RFC 6059,
DOI 10.17487/RFC6059, November 2010, DOI 10.17487/RFC6059, November 2010,
<https://www.rfc-editor.org/info/rfc6059>. <https://www.rfc-editor.org/info/rfc6059>.
skipping to change at page 22, line 5 skipping to change at page 23, line 29
[RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265, [RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265,
DOI 10.17487/RFC6265, April 2011, DOI 10.17487/RFC6265, April 2011,
<https://www.rfc-editor.org/info/rfc6265>. <https://www.rfc-editor.org/info/rfc6265>.
[RFC7039] Wu, J., Bi, J., Bagnulo, M., Baker, F., and C. Vogt, Ed., [RFC7039] Wu, J., Bi, J., Bagnulo, M., Baker, F., and C. Vogt, Ed.,
"Source Address Validation Improvement (SAVI) Framework", "Source Address Validation Improvement (SAVI) Framework",
RFC 7039, DOI 10.17487/RFC7039, October 2013, RFC 7039, DOI 10.17487/RFC7039, October 2013,
<https://www.rfc-editor.org/info/rfc7039>. <https://www.rfc-editor.org/info/rfc7039>.
[RFC7217] Gont, F., "A Method for Generating Semantically Opaque
Interface Identifiers with IPv6 Stateless Address
Autoconfiguration (SLAAC)", RFC 7217,
DOI 10.17487/RFC7217, April 2014,
<https://www.rfc-editor.org/info/rfc7217>.
[RFC7258] Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an [RFC7258] Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an
Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May
2014, <https://www.rfc-editor.org/info/rfc7258>. 2014, <https://www.rfc-editor.org/info/rfc7258>.
[RFC7421] Carpenter, B., Ed., Chown, T., Gont, F., Jiang, S., [RFC7421] Carpenter, B., Ed., Chown, T., Gont, F., Jiang, S.,
Petrescu, A., and A. Yourtchenko, "Analysis of the 64-bit Petrescu, A., and A. Yourtchenko, "Analysis of the 64-bit
Boundary in IPv6 Addressing", RFC 7421, Boundary in IPv6 Addressing", RFC 7421,
DOI 10.17487/RFC7421, January 2015, DOI 10.17487/RFC7421, January 2015,
<https://www.rfc-editor.org/info/rfc7421>. <https://www.rfc-editor.org/info/rfc7421>.
[RFC7624] Barnes, R., Schneier, B., Jennings, C., Hardie, T.,
Trammell, B., Huitema, C., and D. Borkmann,
"Confidentiality in the Face of Pervasive Surveillance: A
Threat Model and Problem Statement", RFC 7624,
DOI 10.17487/RFC7624, August 2015,
<https://www.rfc-editor.org/info/rfc7624>.
[RFC7707] Gont, F. and T. Chown, "Network Reconnaissance in IPv6 [RFC7707] Gont, F. and T. Chown, "Network Reconnaissance in IPv6
Networks", RFC 7707, DOI 10.17487/RFC7707, March 2016, Networks", RFC 7707, DOI 10.17487/RFC7707, March 2016,
<https://www.rfc-editor.org/info/rfc7707>. <https://www.rfc-editor.org/info/rfc7707>.
[RFC7721] Cooper, A., Gont, F., and D. Thaler, "Security and Privacy [RFC7721] Cooper, A., Gont, F., and D. Thaler, "Security and Privacy
Considerations for IPv6 Address Generation Mechanisms", Considerations for IPv6 Address Generation Mechanisms",
RFC 7721, DOI 10.17487/RFC7721, March 2016, RFC 7721, DOI 10.17487/RFC7721, March 2016,
<https://www.rfc-editor.org/info/rfc7721>. <https://www.rfc-editor.org/info/rfc7721>.
[RFC7934] Colitti, L., Cerf, V., Cheshire, S., and D. Schinazi, [RFC7934] Colitti, L., Cerf, V., Cheshire, S., and D. Schinazi,
"Host Address Availability Recommendations", BCP 204, "Host Address Availability Recommendations", BCP 204,
RFC 7934, DOI 10.17487/RFC7934, July 2016, RFC 7934, DOI 10.17487/RFC7934, July 2016,
<https://www.rfc-editor.org/info/rfc7934>. <https://www.rfc-editor.org/info/rfc7934>.
[RFC8190] Bonica, R., Cotton, M., Haberman, B., and L. Vegoda,
"Updates to the Special-Purpose IP Address Registries",
BCP 153, RFC 8190, DOI 10.17487/RFC8190, June 2017,
<https://www.rfc-editor.org/info/rfc8190>.
Authors' Addresses Authors' Addresses
Fernando Gont Fernando Gont
SI6 Networks SI6 Networks
Evaristo Carriego 2644 Evaristo Carriego 2644
Haedo, Provincia de Buenos Aires 1706 Haedo, Provincia de Buenos Aires 1706
Argentina Argentina
Phone: +54 11 4650 8472 Phone: +54 11 4650 8472
Email: fgont@si6networks.com Email: fgont@si6networks.com
 End of changes. 88 change blocks. 
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