draft-ietf-dhc-dhcpv6-privacy-01.txt   draft-ietf-dhc-dhcpv6-privacy-02.txt 
dhc S. Krishnan dhc S. Krishnan
Internet-Draft Ericsson Internet-Draft Ericsson
Intended status: Informational T. Mrugalski Intended status: Informational T. Mrugalski
Expires: February 27, 2016 ISC Expires: June 29, 2016 ISC
S. Jiang S. Jiang
Huawei Technologies Co., Ltd Huawei Technologies Co., Ltd
August 26, 2015 December 27, 2015
Privacy considerations for DHCPv6 Privacy considerations for DHCPv6
draft-ietf-dhc-dhcpv6-privacy-01 draft-ietf-dhc-dhcpv6-privacy-02
Abstract Abstract
DHCPv6 is a protocol that is used to provide addressing and DHCPv6 is a protocol that is used to provide addressing and
configuration information to IPv6 hosts. This document described the configuration information to IPv6 hosts. This document described the
privacy issues associated with the use of DHCPv6 by the Internet privacy issues associated with the use of DHCPv6 by the Internet
users. It is intended to be an analysis of the present situation and users. It is intended to be an analysis of the present situation and
doe not propose any solutions. doe not propose any solutions.
Status of This Memo Status of This Memo
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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 http://datatracker.ietf.org/drafts/current/. Drafts is at http://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 February 27, 2016. This Internet-Draft will expire on June 29, 2016.
Copyright Notice Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Identifiers in DHCPv6 . . . . . . . . . . . . . . . . . . . . 4 3. DHCPv6 options carrying identifiers . . . . . . . . . . . . . 4
3.1. DUID . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3.1. DUID . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.2. Client ID Option . . . . . . . . . . . . . . . . . . . . 4 3.2. Client Identifier Option . . . . . . . . . . . . . . . . 4
3.3. IA_NA, IA_TA, IA_PD, IA Address and IA Prefix Options . . 4 3.3. IA_NA, IA_TA, IA_PD, IA Address and IA Prefix Options . . 4
3.4. Client FQDN Option . . . . . . . . . . . . . . . . . . . 5 3.4. Client FQDN Option . . . . . . . . . . . . . . . . . . . 5
3.5. Client Link-layer Address Option . . . . . . . . . . . . 5 3.5. Client Link-layer Address Option . . . . . . . . . . . . 5
3.6. Option Request Option . . . . . . . . . . . . . . . . . . 6 3.6. Option Request Option . . . . . . . . . . . . . . . . . . 6
3.7. Vendor Class and Vendor-specific Information Options . . 6 3.7. Vendor Class and Vendor-specific Information Options . . 6
3.8. Civic Location Option . . . . . . . . . . . . . . . . . . 6 3.8. Civic Location Option . . . . . . . . . . . . . . . . . . 6
3.9. Coordinate-Based Location Option . . . . . . . . . . . . 6 3.9. Coordinate-Based Location Option . . . . . . . . . . . . 6
3.10. Client System Architecture Type Option . . . . . . . . . 7 3.10. Client System Architecture Type Option . . . . . . . . . 7
3.11. Relay Agent Options . . . . . . . . . . . . . . . . . . . 7 3.11. Relay Agent Options . . . . . . . . . . . . . . . . . . . 7
3.11.1. Subscriber ID . . . . . . . . . . . . . . . . . . . 7 3.11.1. Subscriber ID Option . . . . . . . . . . . . . . . . 7
3.11.2. Interface ID . . . . . . . . . . . . . . . . . . . . 7 3.11.2. Interface ID Option . . . . . . . . . . . . . . . . 7
3.11.3. Remote ID . . . . . . . . . . . . . . . . . . . . . 8 3.11.3. Remote ID Option . . . . . . . . . . . . . . . . . . 8
3.11.4. Relay-ID Option . . . . . . . . . . . . . . . . . . 8 3.11.4. Relay-ID Option . . . . . . . . . . . . . . . . . . 8
4. Existing Mechanisms That Affect Privacy . . . . . . . . . . . 8 4. Existing Mechanisms That Affect Privacy . . . . . . . . . . . 8
4.1. Temporary addresses . . . . . . . . . . . . . . . . . . . 8 4.1. Temporary addresses . . . . . . . . . . . . . . . . . . . 8
4.2. DNS Updates . . . . . . . . . . . . . . . . . . . . . . . 9 4.2. DNS Updates . . . . . . . . . . . . . . . . . . . . . . . 9
4.3. Allocation strategies . . . . . . . . . . . . . . . . . . 9 4.3. Allocation strategies . . . . . . . . . . . . . . . . . . 9
5. Attacks . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 5. Attacks . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
5.1. Device type discovery (fingerprinting) . . . . . . . . . 10 5.1. Device type discovery (fingerprinting) . . . . . . . . . 10
5.2. Operating system discovery (fingerprinting) . . . . . . . 11 5.2. Operating system discovery (fingerprinting) . . . . . . . 11
5.3. Finding location information . . . . . . . . . . . . . . 11 5.3. Finding location information . . . . . . . . . . . . . . 11
5.4. Finding previously visited networks . . . . . . . . . . . 11 5.4. Finding previously visited networks . . . . . . . . . . . 11
5.5. Finding a stable identity . . . . . . . . . . . . . . . . 11 5.5. Finding a stable identity . . . . . . . . . . . . . . . . 11
5.6. Pervasive monitoring . . . . . . . . . . . . . . . . . . 11 5.6. Pervasive monitoring . . . . . . . . . . . . . . . . . . 12
5.7. Finding client's IP address or hostname . . . . . . . . . 12 5.7. Finding client's IP address or hostname . . . . . . . . . 12
5.8. Correlation of activities over time . . . . . . . . . . . 12 5.8. Correlation of activities over time . . . . . . . . . . . 12
5.9. Location tracking . . . . . . . . . . . . . . . . . . . . 12 5.9. Location tracking . . . . . . . . . . . . . . . . . . . . 12
5.10. Leasequery & bulk leasequery . . . . . . . . . . . . . . 12 5.10. Leasequery & bulk leasequery . . . . . . . . . . . . . . 13
6. Security Considerations . . . . . . . . . . . . . . . . . . . 13 6. Security Considerations . . . . . . . . . . . . . . . . . . . 13
7. Privacy Considerations . . . . . . . . . . . . . . . . . . . 13 7. Privacy Considerations . . . . . . . . . . . . . . . . . . . 13
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 13 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
10.1. Normative References . . . . . . . . . . . . . . . . . . 13 10.1. Normative References . . . . . . . . . . . . . . . . . . 14
10.2. Informative References . . . . . . . . . . . . . . . . . 14 10.2. Informative References . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16
1. Introduction 1. Introduction
DHCPv6 [RFC3315] is a protocol that is used to provide addressing and DHCPv6 [RFC3315] is a protocol that is used to provide addressing and
configuration information to IPv6 hosts. The DHCPv6 protocol uses configuration information to IPv6 hosts. The DHCPv6 protocol uses
several identifiers that could become a source for gleaning several identifiers that could become a source for gleaning
information about the IPv6 host. This information may include device information about the IPv6 host. This information may include device
type, operating system information, location(s) that the device may type, operating system information, location(s) that the device may
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identifiers used by DHCPv6 and the potential privacy issues identifiers used by DHCPv6 and the potential privacy issues
[RFC6973]. In particular, it also takes into consideration the [RFC6973]. In particular, it also takes into consideration the
problem of pervasive monitoring [RFC7258]. problem of pervasive monitoring [RFC7258].
Future works may propose protocol changes to fix the privacy issues Future works may propose protocol changes to fix the privacy issues
that have been analyzed in this document. Protocol changes are out that have been analyzed in this document. Protocol changes are out
of scope for this document. of scope for this document.
The primary focus of this document is around privacy considerations The primary focus of this document is around privacy considerations
for clients to support client mobility and connection to random for clients to support client mobility and connection to random
networks. The privacy or DHCP servers and relay agents are networks. The privacy of DHCP servers and relay agents are
considered less important as they are typically open for public considered less important as they are typically open for public
services. And, it is generally assumed that relay agent to server services. And, it is generally assumed that relay agent to server
communication is protected from casual snooping, as that communication is protected from casual snooping, as that
communication occurs in the provider's backbone. Nevertheless, the communication occurs in the provider's backbone. Nevertheless, the
topics involving relay agents and servers are explored to some topics involving relay agents and servers are explored to some
degree. However, future work may want to further explore privacy of degree. However, future work may want to further explore privacy of
DHCP servers and relay agents. DHCP servers and relay agents.
2. Terminology 2. Terminology
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Stable identifier - Any property disclosed by a DHCP client that Stable identifier - Any property disclosed by a DHCP client that
does not change over time or changes very infrequently and is does not change over time or changes very infrequently and is
unique for said client in a given context. Examples may unique for said client in a given context. Examples may
include MAC address, client-id or a hostname. Some include MAC address, client-id or a hostname. Some
identifiers may be considered stable only under certain identifiers may be considered stable only under certain
conditions, for example one client implementation may keep conditions, for example one client implementation may keep
its client-id stored in stable storage while other may its client-id stored in stable storage while other may
generate it on the fly and use a different one after each generate it on the fly and use a different one after each
boot. Stable identifier may or may not be globally unique. boot. Stable identifier may or may not be globally unique.
3. Identifiers in DHCPv6 3. DHCPv6 options carrying identifiers
There are several identifiers used in DHCPv6. This section provides In DHCPv6, there are many options which include identification
an introduction to the various options that will be used further in information or can be used to extract the identification information
the document. about the client. This section enumerates various options and
identifiers conveyed in them, which can be used to disclose client
identification.
3.1. DUID 3.1. DUID
Each DHCPv6 client and server has a DHCPv6 Unique Identifier (DUID) Each DHCPv6 client and server has a DHCPv6 Unique Identifier (DUID)
[RFC3315]. The DUID is designed to be unique across all DHCPv6 [RFC3315]. The DUID is designed to be unique across all DHCPv6
clients and servers, and to remain stable after it has been initially clients and servers, and to remain stable after it has been initially
generated. The DUID can be of different forms. Commonly used forms generated. The DUID can be of different forms. Commonly used forms
are based on the link-layer address of one of the device's network are based on the link-layer address of one of the device's network
interfaces (with or without a timestamp), on the Universally Unique interfaces (with or without a timestamp), on the Universally Unique
IDentifier (UUID) [RFC6355]. The default type, defined in IDentifier (UUID) [RFC6355]. The default type, defined in
Section 9.2 of [RFC3315] is DUID-LLT that is based on link-layer Section 9.2 of [RFC3315] is DUID-LLT that is based on link-layer
address. It is commonly implemented in most popular clients. address. It is commonly implemented in most popular clients.
It is important to understand DUID lifecycle. Clients and servers It is important to understand DUID lifecycle. Clients and servers
are expected to generate their DUID once (during first operation) and are expected to generate their DUID once (during first operation) and
store it in a non-volatile storage or use the same deterministic store it in a non-volatile storage or use the same deterministic
algorithm to generate the same DUID value again. This means that algorithm to generate the same DUID value again. This means that
most implementations will use the available link-layer address during most implementations will use the available link-layer address during
its first boot. Even if the administrator enables privacy extensions its first boot. Even if the administrator enables link-layer address
(see [RFC4941]) and its equivalent for link-layer address randomization, it is likely that it was disabled during the first
randomization, it is likely that those privacy mechanisms were device boot. Hence the original, unobfuscated link-layer address
disabled during the first device boot. Hence the original, will likely end up being announced as client DUID, even if the link-
unobfuscated link-layer address will likely end up being announced as layer address has changed (or even if being changed on a periodic
client DUID, even if the link-layer address has changed (or even if basis). The exposure of the original link-layer address in DUID will
being changed on a periodic basis). also undermine other privacy extensions such as [RFC4941].
3.2. Client ID Option 3.2. Client Identifier Option
The Client Identifier Option (OPTION_CLIENTID) [RFC3315] is used to The Client Identifier Option (OPTION_CLIENTID) [RFC3315] is used to
carry the DUID of a DHCPv6 client between a client and a server. carry the DUID of a DHCPv6 client between a client and a server.
There is an analogous Server Identifier Option but it is not as There is an analogous Server Identifier Option but it is not as
interesting in the privacy context (unless a host can be convinced to interesting in the privacy context (unless a host can be convinced to
start acting as a server). Client ID is an example of DUID. See start acting as a server). See Section 3.1 for relevant discussion
Section 3.1 for relevant discussion about DUIDs. about DUIDs.
3.3. IA_NA, IA_TA, IA_PD, IA Address and IA Prefix Options 3.3. IA_NA, IA_TA, IA_PD, IA Address and IA Prefix Options
The Identity Association for Non-temporary Addresses (IA_NA) option The Identity Association for Non-temporary Addresses (IA_NA) option
[RFC3315] is used to carry the parameters and any non-temporary [RFC3315] is used to carry the parameters and any non-temporary
addresses associated with the given IA_NA. The Identity Association addresses associated with the given IA_NA. The Identity Association
for Temporary Addresses (IA_TA) option [RFC3315] is analogous to the for Temporary Addresses (IA_TA) option [RFC3315] is analogous to the
IA_NA option but for temporary addresses. The IA Address option IA_NA option but for temporary addresses. The IA Address option
[RFC3315] is used to specify IPv6 addresses associated with an IA_NA [RFC3315] is used to specify IPv6 addresses associated with an IA_NA
or an IA_TA and is encapsulated within the Options field of such an or an IA_TA and is encapsulated within the Options field of such an
IA_NA or IA_TA option. The Identity Association for Prefix IA_NA or IA_TA option. The Identity Association for Prefix
Delegation (IA_PD) [RFC3633] option is used to carry the prefixes Delegation (IA_PD) [RFC3633] option is used to carry the prefixes
that are assigned to the requesting router. IA Prefix option that are assigned to the requesting router. IA Prefix option
[RFC3633] is used to specify IPv6 prefixes associated with an IA_PD [RFC3633] is used to specify IPv6 prefixes associated with an IA_PD
and is encapsulated within the Options field of such an IA_PD option. and is encapsulated within the Options field of such an IA_PD option.
To differentiate between instances of the same type of IA containers, To differentiate between instances of the same type of IA containers
each IA_NA, IA_TA and IA_PD options have an IAID field that is unique for a client, each IA_NA, IA_TA and IA_PD options have an IAID field
for each client/option type pair. It is up to the client to pick with a unique value for a given IA type. It is up to the client to
unique IAID values. At least one popular implementation uses last pick unique IAID values. At least one popular implementation uses
four octets of the link-layer address. In most cases, that means last four octets of the link-layer address. In most cases, that
that merely two bytes are missing for a full link-layer address means that merely two bytes are missing for a full link-layer address
reconstruction. However, the first three octets in a typical link- reconstruction. However, the first three octets in a typical link-
layer address are vendor identifier. That can be determined with layer address are vendor identifier. That can be determined with
high level of certainty using other means, thus allowing full link- high level of certainty using other means, thus allowing full link-
layer address discovery. layer address discovery.
3.4. Client FQDN Option 3.4. Client FQDN Option
The Client Fully Qualified Domain Name (FQDN) option [RFC4704] is The Client Fully Qualified Domain Name (FQDN) option [RFC4704] is
used by DHCPv6 clients and servers to exchange information about the used by DHCPv6 clients and servers to exchange information about the
client's fully qualified domain name and about who has the client's fully qualified domain name and about who has the
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and server to client communications. and server to client communications.
The information contained in the data area of this option is The information contained in the data area of this option is
contained in one or more opaque fields that identify details of the contained in one or more opaque fields that identify details of the
hardware configuration, for example, the version of the operating hardware configuration, for example, the version of the operating
system the client is running or the amount of memory installed on the system the client is running or the amount of memory installed on the
client. client.
3.8. Civic Location Option 3.8. Civic Location Option
DHCPv6 servers use the Civic Location option [RFC4776] to delivery of DHCPv6 servers use the Civic Location option [RFC4776] to deliver the
location information (the civic and postal addresses) from the DHCPv6 location information (the civic and postal addresses) from the DHCPv6
server to the DHCPv6 clients. It may refer to three locations: the server to the DHCPv6 clients. It may refer to three locations: the
location of the DHCPv6 server, the location of the network element location of the DHCPv6 server, the location of the network element
believed to be closest to the client, or the location of the client, believed to be closest to the client, or the location of the client,
identified by the "what" element within the option. identified by the "what" element within the option.
3.9. Coordinate-Based Location Option 3.9. Coordinate-Based Location Option
The GeoLoc options [RFC6225] is used by DHCPv6 server to provide the The GeoLoc options [RFC6225] is used by DHCPv6 server to provide the
coordinate- based geographic location information to the DHCPv6 coordinate- based geographic location information to the DHCPv6
clients. It enable a DHCPv6 client to obtain its location. clients. It enable a DHCPv6 client to obtain its location.
After the relevant DHCPv6 exchanges have taken place, the location
information is stored on the end device rather than somewhere else,
where retrieving it might be difficult in practice.
3.10. Client System Architecture Type Option 3.10. Client System Architecture Type Option
The Client System Architecture Type option [RFC5970] is used by The Client System Architecture Type option [RFC5970] is used by
DHCPv6 client to send a list of supported architecture types to the DHCPv6 client to send a list of supported architecture types to the
DHCPv6 server. It is used to provide configuration information for a DHCPv6 server. It is used by clients that must be booted using the
node that must be booted using the network rather than from local network rather than from local storage, so the server can decide
storage. which boot file should be provided to the client.
3.11. Relay Agent Options 3.11. Relay Agent Options
A DHCPv6 relay agent may include a number of options. Those option A DHCPv6 relay agent may include a number of options. Those option
contain information that can be used to identify the client. Those contain information that can be used to identify the client. Those
options are almost exclusively exchanged between the relay agent and options are almost exclusively exchanged between the relay agent and
the server, thus never leaving the operators network. In particular, the server, thus never leaving the operators network. In particular,
they're almost never present in the last wireless hop in case of WiFi they're almost never present in the last wireless hop in case of WiFi
networks. The only exception to that rule is somewhat infrequently networks. The only exception to that rule is somewhat infrequently
used Relay Supplied Options option [RFC6422]. This fact implies that used Relay Supplied Options option [RFC6422]. This fact implies that
the threat model related relay options is slightly different. the threat model related relay options is slightly different.
Traffic sniffing at the last hop and related class of attacks Traffic sniffing at the last hop and related class of attacks
typically do not apply. On the other hand, all attacks that involve typically do not apply. On the other hand, all attacks that involve
operator's intfrastructure (either willing or coerced cooperation or operator's intfrastructure (either willing or coerced cooperation or
infrastructure being compromised) usually apply. infrastructure being compromised) usually apply.
The following subsections describe various options inserted by the The following subsections describe various options inserted by the
relay agents. relay agents.
3.11.1. Subscriber ID 3.11.1. Subscriber ID Option
A DHCPv6 relay may include a Subscriber ID option [RFC4580] to A DHCPv6 relay may include a Subscriber ID option [RFC4580] to
associate some provider-specific information with clients' DHCPv6 associate some provider-specific information with clients' DHCPv6
messages that is independent of the physical network configuration. messages that is independent of the physical network configuration.
In many deployments, the relay agent that inserts this option is In many deployments, the relay agent that inserts this option is
configured to use client's link-layer address as Subscriber ID. configured to use client's link-layer address as Subscriber ID.
3.11.2. Interface ID 3.11.2. Interface ID Option
A DHCPv6 relay includes the Interface ID [RFC3315] option to identify A DHCPv6 relay includes the Interface ID [RFC3315] option to identify
the interface on which it received the client message that is being the interface on which it received the client message that is being
relayed. relayed.
Although in principle Interface ID can be arbitrarily long with Although in principle Interface ID can be arbitrarily long with
completely random values, it is often a text string that includes the completely random values, it is sometimes a text string that includes
relay agent name followed by interface name. This can be used for the relay agent name followed by interface name. This can be used
fingerprinting the relay or determining client's point of attachment. for fingerprinting the relay or determining client's point of
attachment.
3.11.3. Remote ID 3.11.3. Remote ID Option
A DHCPv6 relay includes a Remote ID option [RFC4649] to identify the A DHCPv6 relay includes a Remote ID option [RFC4649] to identify the
remote host end of the circuit. remote host end of the circuit.
The remote-id is vendor specific, for which the vendor is indicated The remote-id is vendor specific, for which the vendor is indicated
in the enterprise-number field. The remote-id field may encode the in the enterprise-number field. The remote-id field may encode the
information that identified the DHCPv6 clients: information that identified the DHCPv6 clients:
o a "caller ID" telephone number for dial-up connection o a "caller ID" telephone number for dial-up connection
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3.11.4. Relay-ID Option 3.11.4. Relay-ID Option
Relay agent may include Relay-ID [RFC5460], which contains a unique Relay agent may include Relay-ID [RFC5460], which contains a unique
relay agent identifier. While its intended use is to provide relay agent identifier. While its intended use is to provide
additional information for the server, so it would be able to respond additional information for the server, so it would be able to respond
to leasequeries later, this information can be also used to identify to leasequeries later, this information can be also used to identify
client's location within the network. client's location within the network.
4. Existing Mechanisms That Affect Privacy 4. Existing Mechanisms That Affect Privacy
This section describes available DHCPv6 mechanisms that one can use This section describes deployed DHCPv6 mechanisms that can affect
to protect or enhance one's privacy. privacy.
4.1. Temporary addresses 4.1. Temporary addresses
[RFC3315] defines a mechanism for a client to request temporary [RFC3315] defines a mechanism for a client to request temporary
addresses. The idea behind temporary addresses is that a client can addresses. The idea behind temporary addresses is that a client can
request a temporary address for a specific purpose, use it, and then request a temporary address for a specific purpose, use it, and then
never renew it. i.e. let it expire. never renew it. i.e. let it expire.
There are number of serious issues, both protocolar and There are a number of serious issues, both related to protocol and
implementational, that make them nearly useless for their original its implementations, that make temporary addresses nearly useless for
goal. First, [RFC3315] does not include T1 and T2 renewal timers in their original goal. First, [RFC3315] does not include T1 and T2
IA_TA (a container for temporary addresses). However, it mentions renewal timers in IA_TA (a container for temporary addresses).
that temporary addresses can be renewed. Many client implementations However, in section 18.1.3 it explicitly mentions that temporary
renew those addresses during a renewal procedure initiated by other addresses can be renewed. Client implementations may mistakenly
resources (non-temporary addresses or prefixes), thus forfeiting renew temporary addresses if they are not careful (i.e., by including
shortliveness. Second, [RFC4704] allows servers to update DNS for the IA_TA with the same IAID in Renew or Rebind requests, rather than
assigned temporary addresses. Publishing client's IPv6 address in a new IAID - see [RFC3315] Section 22.5), thus forfeiting short
DNS that is publicly available is a major privacy breach. liveness. [RFC4704] does not explicitly prohibit servers to update
DNS for assigned temporary addresses and there are implementations
that can be configured to do that. However, this is not advised as
publishing a client's IPv6 address in DNS that is publicly available
is a major privacy breach.
4.2. DNS Updates 4.2. DNS Updates
DNS Updates [RFC4704] defines a mechanism that allows both clients The Client FQDN Option[RFC4704] used along with DNS Update [RFC2136]
and server to insert into DNS domain information about clients. Both defines a mechanism that allows both clients and server to insert
forward (AAAA) and reverse (PTR) resource records can be updated. into the DNS domain information about clients. Both forward (AAAA)
This allows other nodes to conveniently refer to a host, despite the and reverse (PTR) resource records can be updated. This allows other
fact that its IPv6 address may be changing. nodes to conveniently refer to a host, despite the fact that its IPv6
address may be changing.
This mechanism exposes two important pieces of information: current This mechanism exposes two important pieces of information: current
address (which can be mapped to current location) and client's address (which can be mapped to current location) and client's
hostname. The stable hostname can then by used to correlate the hostname. The stable hostname can then by used to correlate the
client across different network attachments even when its IPv6 client across different network attachments even when its IPv6
address keeps changing. address keeps changing.
4.3. Allocation strategies 4.3. Allocation strategies
A DHCPv6 server running in typical, stateful mode is given a task of A DHCPv6 server running in typical, stateful mode is given a task of
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strategies are possible. Choices in this regard may have privacy strategies are possible. Choices in this regard may have privacy
implications. implications.
Iterative allocation - a server may choose to allocate addresses one Iterative allocation - a server may choose to allocate addresses one
by one. That strategy has the benefit of being very fast, thus can by one. That strategy has the benefit of being very fast, thus can
be favored in deployments that prefer performance. However, it makes be favored in deployments that prefer performance. However, it makes
the resources very predictable. Also, since the resources allocated the resources very predictable. Also, since the resources allocated
tend to be clustered at the beginning of available pool, it makes tend to be clustered at the beginning of available pool, it makes
scanning attacks much easier. scanning attacks much easier.
Identifier-based allocation - a server may choose to allocate an Identifier-based allocation - some server implementations use a fixed
address that is based on one of available identifiers, e.g. IID or identifier for a specific client, seemingly taken from the client's
MAC address. This has a property of being convenient for converting MAC address when available or some lower bits of client's source IPv6
IP address to/from other identifiers, especially if the identifier is address. This has a property of being convenient for converting IP
or contains MAC address. It is also convenient, as returning client address to/from other identifiers, especially if the identifier is or
is very likely to get the same address, even if the server does not contains MAC address. It is also convenient, as returning client is
store previous client's address. Those properties are convenient for very likely to get the same address, even if the server does not
system administrators, so DHCPv6 server implementors are sometimes retain previous client's address. Those properties are convenient
requested to implement it. There is at least one implementation that for system administrators, so DHCPv6 server implementors are
supports it. On the other hand, the downside of such allocation is sometimes requested to implement it. There is at least one
implementation that supports it. The downside of such allocation is
that the client now discloses its identifier in its IPv6 address to that the client now discloses its identifier in its IPv6 address to
all services it connects to. That means that correlation of all services it connects to. That means that correlation of
activities over time, location tracking, address scanning and OS/ activities over time, location tracking, address scanning and OS/
vendor discovery apply. vendor discovery apply.
Hash allocation - it's an extension of identifier based allocation. Hash allocation - it's an extension of identifier based allocation.
Instead of using the identifier directly, it is being hashed first. Instead of using the identifier directly, it is being hashed first.
If the hash is implemented correctly, it removes the flaw of If the hash is implemented correctly, it removes the flaw of
disclosing the identifier, a property that eliminates susceptibility disclosing the identifier, a property that eliminates susceptibility
to address scanning and OS/vendor discovery. If the hash is poorly to address scanning and OS/vendor discovery. If the hash is poorly
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using the Remote ID Option, the Interface ID option (e.g. if an using the Remote ID Option, the Interface ID option (e.g. if an
access circuit on an Access Node corresponds to a civic location), or access circuit on an Access Node corresponds to a civic location), or
the Subscriber ID Option (if the attacker has access to subscriber the Subscriber ID Option (if the attacker has access to subscriber
info). info).
5.4. Finding previously visited networks 5.4. Finding previously visited networks
When DHCPv6 clients connect to a network, they attempt to obtain the When DHCPv6 clients connect to a network, they attempt to obtain the
same address they had used before they attached to the network. They same address they had used before they attached to the network. They
do this by putting the previously assigned address(es) in the IA do this by putting the previously assigned address(es) in the IA
Address Option(s) inside the IA_NA, IA_TA. By observing these Address Option(s). [RFC3315] does not exclude IA_TA in such a case,
so it is possible that a client implementation includes an address
contained in an IA_TA for the Confirm message. By observing these
addresses, an attacker can identify the network the client had addresses, an attacker can identify the network the client had
previously visited. previously visited.
5.5. Finding a stable identity 5.5. Finding a stable identity
An attacker might use a stable identity gleaned from DHCPv6 messages An attacker might use a stable identity gleaned from DHCPv6 messages
to correlate activities of a given client on unrelated networks. The to correlate activities of a given client on unrelated networks. The
Client FQDN option, the Subscriber ID Option and the Client ID Client FQDN option, the Subscriber ID Option and the Client ID
options can serve as long lived identifiers of DHCPv6 clients. The options can serve as long lived identifiers of DHCPv6 clients. The
Client FQDN option can also provide an identity that can easily be Client FQDN option can also provide an identity that can easily be
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Location information is information needed by the access concentrator Location information is information needed by the access concentrator
to forward traffic to a broadband-accessible host. This information to forward traffic to a broadband-accessible host. This information
includes knowledge of the host hardware address, the port or virtual includes knowledge of the host hardware address, the port or virtual
circuit that leads to the host, and/or the hardware address of the circuit that leads to the host, and/or the hardware address of the
intervening subscriber modem. intervening subscriber modem.
Furthermore, the attackers may use DHCPv6 bulk leasequery [RFC5460] Furthermore, the attackers may use DHCPv6 bulk leasequery [RFC5460]
mechanism to obtain bulk information about DHCPv6 bindings, even mechanism to obtain bulk information about DHCPv6 bindings, even
without knowing the target bindings. without knowing the target bindings.
Additionally, active leasequery Additionally, active leasequery [RFC7653] is a mechanism for
[I-D.ietf-dhc-dhcpv6-active-leasequery] is a mechanism for
subscribing to DHCPv6 lease update changes in near real-time. The subscribing to DHCPv6 lease update changes in near real-time. The
intent of this mechanism is to update operator's database, but if intent of this mechanism is to update operator's database, but if
misused, an attacker could defeat server's authentication mechanisms misused, an attacker could defeat server's authentication mechanisms
and subscribe to all updates. He then could continue receiving and subscribe to all updates. He then could continue receiving
updates, without any need for local presence. updates, without any need for local presence.
6. Security Considerations 6. Security Considerations
In current practice, the client privacy and the client authentication In current practice, the client privacy and the client authentication
are mutually exclusive. The client authentication procedure reveals are mutually exclusive. The client authentication procedure reveals
additional client information in their certificates/identifiers. additional client information in their certificates/identifiers.
Full privacy for the clients may mean the clients are also anonymous Full privacy for the clients may mean the clients are also anonymous
for the server and the network. for the server and the network.
7. Privacy Considerations 7. Privacy Considerations
This document at its entirety discusses privacy considerations in This document at its entirety discusses privacy considerations in
DHCPv6. As such, no dedicated section about this is needed. DHCPv6. As such, no dedicated discussion is needed.
8. IANA Considerations 8. IANA Considerations
This draft does not request any IANA action. This draft does not request any IANA action.
9. Acknowledgements 9. Acknowledgements
The authors would like to thanks the valuable comments made by The authors would like to thank Stephen Farrell, Ted Lemon, Ines
Stephen Farrell, Ted Lemon, Ines Robles, Russ White, Christian Robles, Russ White, Christian Schaefer, Jinmei Tatuya, Bernie Volz,
Schaefer and other members of DHC WG. Marcin Siodelski, Christian Huitema and other members of DHC WG for
their valuable comments.
This document was produced using the xml2rfc tool [RFC2629]. This document was produced using the xml2rfc tool [RFC2629].
10. References 10. References
10.1. Normative References 10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
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[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, <http://www.rfc-editor.org/info/rfc7258>. 2014, <http://www.rfc-editor.org/info/rfc7258>.
10.2. Informative References 10.2. Informative References
[I-D.ietf-6man-ipv6-address-generation-privacy] [I-D.ietf-6man-ipv6-address-generation-privacy]
Cooper, A., Gont, F., and D. Thaler, "Privacy Cooper, A., Gont, F., and D. Thaler, "Privacy
Considerations for IPv6 Address Generation Mechanisms", Considerations for IPv6 Address Generation Mechanisms",
draft-ietf-6man-ipv6-address-generation-privacy-07 (work draft-ietf-6man-ipv6-address-generation-privacy-08 (work
in progress), June 2015. in progress), September 2015.
[I-D.ietf-dhc-dhcpv6-active-leasequery] [RFC2136] Vixie, P., Ed., Thomson, S., Rekhter, Y., and J. Bound,
Dushyant, D., Kinnear, K., and D. Kukrety, "DHCPv6 Active "Dynamic Updates in the Domain Name System (DNS UPDATE)",
Leasequery", draft-ietf-dhc-dhcpv6-active-leasequery-04 RFC 2136, DOI 10.17487/RFC2136, April 1997,
(work in progress), July 2015. <http://www.rfc-editor.org/info/rfc2136>.
[RFC2629] Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629, [RFC2629] Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629,
DOI 10.17487/RFC2629, June 1999, DOI 10.17487/RFC2629, June 1999,
<http://www.rfc-editor.org/info/rfc2629>. <http://www.rfc-editor.org/info/rfc2629>.
[RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic [RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
Host Configuration Protocol (DHCP) version 6", RFC 3633, Host Configuration Protocol (DHCP) version 6", RFC 3633,
DOI 10.17487/RFC3633, December 2003, DOI 10.17487/RFC3633, December 2003,
<http://www.rfc-editor.org/info/rfc3633>. <http://www.rfc-editor.org/info/rfc3633>.
skipping to change at page 16, line 9 skipping to change at page 16, line 13
<http://www.rfc-editor.org/info/rfc6355>. <http://www.rfc-editor.org/info/rfc6355>.
[RFC6422] Lemon, T. and Q. Wu, "Relay-Supplied DHCP Options", [RFC6422] Lemon, T. and Q. Wu, "Relay-Supplied DHCP Options",
RFC 6422, DOI 10.17487/RFC6422, December 2011, RFC 6422, DOI 10.17487/RFC6422, December 2011,
<http://www.rfc-editor.org/info/rfc6422>. <http://www.rfc-editor.org/info/rfc6422>.
[RFC6939] Halwasia, G., Bhandari, S., and W. Dec, "Client Link-Layer [RFC6939] Halwasia, G., Bhandari, S., and W. Dec, "Client Link-Layer
Address Option in DHCPv6", RFC 6939, DOI 10.17487/RFC6939, Address Option in DHCPv6", RFC 6939, DOI 10.17487/RFC6939,
May 2013, <http://www.rfc-editor.org/info/rfc6939>. May 2013, <http://www.rfc-editor.org/info/rfc6939>.
[RFC7653] Raghuvanshi, D., Kinnear, K., and D. Kukrety, "DHCPv6
Active Leasequery", RFC 7653, DOI 10.17487/RFC7653,
October 2015, <http://www.rfc-editor.org/info/rfc7653>.
Authors' Addresses Authors' Addresses
Suresh Krishnan Suresh Krishnan
Ericsson Ericsson
8400 Decarie Blvd. 8400 Decarie Blvd.
Town of Mount Royal, QC Town of Mount Royal, QC
Canada Canada
Phone: +1 514 345 7900 x42871 Phone: +1 514 345 7900 x42871
Email: suresh.krishnan@ericsson.com Email: suresh.krishnan@ericsson.com
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