draft-ietf-dhc-anonymity-profile-07.txt		draft-ietf-dhc-anonymity-profile-08.txt
	Network Working Group C. Huitema		Network Working Group C. Huitema
	Internet-Draft Microsoft		Internet-Draft Microsoft
	Intended status: Standards Track T. Mrugalski		Intended status: Standards Track T. Mrugalski
	Expires: August 18, 2016 ISC		Expires: August 22, 2016 ISC
	S. Krishnan		S. Krishnan
	Ericsson		Ericsson
	February 15, 2016		February 19, 2016
	Anonymity profile for DHCP clients		Anonymity profile for DHCP clients
	draft-ietf-dhc-anonymity-profile-07.txt		draft-ietf-dhc-anonymity-profile-08.txt
	Abstract		Abstract
	Some DHCP options carry unique identifiers. These identifiers can		Some DHCP options carry unique identifiers. These identifiers can
	enable device tracking even if the device administrator takes care of		enable device tracking even if the device administrator takes care of
	randomizing other potential identifications like link-layer addresses		randomizing other potential identifications like link-layer addresses
	or IPv6 addresses. The anonymity profile is designed for clients		or IPv6 addresses. The anonymity profile is designed for clients
	that wish to remain anonymous to the visited network. The profile		that wish to remain anonymous to the visited network. The profile
	provides guidelines on the composition of DHCP or DHCPv6 requests,		provides guidelines on the composition of DHCP or DHCPv6 requests,
	designed to minimize disclosure of identifying information.		designed to minimize disclosure of identifying information.
	skipping to change at page 1, line 39		skipping to change at page 1, line 39
	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 August 18, 2016.		This Internet-Draft will expire on August 22, 2016.
	Copyright Notice		Copyright Notice
	Copyright (c) 2016 IETF Trust and the persons identified as the		Copyright (c) 2016 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
	(http://trustee.ietf.org/license-info) in effect on the date of		(http://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 3, line 4		skipping to change at page 3, line 4
	4.6. Option Request Option . . . . . . . . . . . . . . . . . . 19		4.6. Option Request Option . . . . . . . . . . . . . . . . . . 19
	4.6.1. Previous option values . . . . . . . . . . . . . . . 19		4.6.1. Previous option values . . . . . . . . . . . . . . . 19
	4.7. Authentication Option . . . . . . . . . . . . . . . . . . 19		4.7. Authentication Option . . . . . . . . . . . . . . . . . . 19
	4.8. User and Vendor Class DHCPv6 options . . . . . . . . . . 19		4.8. User and Vendor Class DHCPv6 options . . . . . . . . . . 19
	4.9. Client FQDN Option . . . . . . . . . . . . . . . . . . . 20		4.9. Client FQDN Option . . . . . . . . . . . . . . . . . . . 20
	5. Operational Considerations . . . . . . . . . . . . . . . . . 20		5. Operational Considerations . . . . . . . . . . . . . . . . . 20
	6. Security Considerations . . . . . . . . . . . . . . . . . . . 20		6. Security Considerations . . . . . . . . . . . . . . . . . . . 20
	7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20		7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
	8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 20		8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 20
	9. Changes from previous versions . . . . . . . . . . . . . . . 21		9. Changes from previous versions . . . . . . . . . . . . . . . 21
	10. References . . . . . . . . . . . . . . . . . . . . . . . . . 23		10. References . . . . . . . . . . . . . . . . . . . . . . . . . 24
	10.1. Normative References . . . . . . . . . . . . . . . . . . 23		10.1. Normative References . . . . . . . . . . . . . . . . . . 24
	10.2. Informative References . . . . . . . . . . . . . . . . . 24		10.2. Informative References . . . . . . . . . . . . . . . . . 25
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 26		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 27
	1. Introduction		1. Introduction
	Reports surfaced recently of systems that would monitor the wireless		There have been reports of systems that would monitor the wireless
	connections of passengers at Canadian airports [CNBC]. We can assume		connections of passengers at Canadian airports [CNBC]. We can assume
	that these are either fragments or trial runs of a wider system that		that these are either fragments or trial runs of a wider system that
	would attempt to monitor Internet users as they roam through wireless		would attempt to monitor Internet users as they roam through wireless
	access points and other temporary network attachments. We can also		access points and other temporary network attachments. We can also
	assume that privacy conscious users will attempt to evade this		assume that privacy conscious users will attempt to evade this
	monitoring, for example by ensuring that low level identifiers such		monitoring, for example by ensuring that low level identifiers such
	as link-layer addresses are "randomized," so that the devices do not		as link-layer addresses are "randomized," so that the devices do not
	broadcast a unique identifier in every location that they visit.		broadcast the same unique identifier in every location that they
			visit.
	Of course, link layer "MAC" addresses are not the only way to		Of course, link layer "MAC" addresses are not the only way to
	identify a device. As soon as it connects to a remote network, the		identify a device. As soon as it connects to a remote network, the
	device may use DHCP and DHCPv6 to obtain network parameters. The		device may use DHCP and DHCPv6 to obtain network parameters. The
	analysis of DHCP and DHCPv6 options shows that parameters of these		analysis of DHCP and DHCPv6 options shows that parameters of these
	protocols can reveal identifiers of the device, negating the benefits		protocols can reveal identifiers of the device, negating the benefits
	of link-layer address randomization. This is documented in detail in		of link-layer address randomization. This is documented in detail in
	[I-D.ietf-dhc-dhcp-privacy] and [I-D.ietf-dhc-dhcpv6-privacy]. The		[I-D.ietf-dhc-dhcp-privacy] and [I-D.ietf-dhc-dhcpv6-privacy]. The
	natural reaction is to restrict the number and values of such		natural reaction is to restrict the number and values of such
	parameters in order to minimize disclosure.		parameters in order to minimize disclosure.
	skipping to change at page 4, line 23		skipping to change at page 4, line 24
	individual people, even when all application data sent from the		individual people, even when all application data sent from the
	devices is encrypted. link-layer addresses can also be correlated		devices is encrypted. link-layer addresses can also be correlated
	with IP addresses of devices, negating potential privacy benefits of		with IP addresses of devices, negating potential privacy benefits of
	IPv6 "privacy" addresses. Privacy advocates have reasons to be		IPv6 "privacy" addresses. Privacy advocates have reasons to be
	concerned.		concerned.
	The obvious solution is to "randomize" the MAC address. Before		The obvious solution is to "randomize" the MAC address. Before
	connecting to a particular network, the device replaces the MAC		connecting to a particular network, the device replaces the MAC
	address with a randomly drawn 48 bit value. Link-layer address		address with a randomly drawn 48 bit value. Link-layer address
	randomization was successfully tried at the IETF in Honolulu in		randomization was successfully tried at the IETF in Honolulu in
	November 2014 [IETFMACRandom]. However, we have to consider the		November 2014 [IETFMACRandom] and in following meetings
	linkage between link-layer addresses, DHCP identifiers and IP		[IETFTrialsAndMore]; it is studied in the IEEE 802 EC Privacy
	addresses.		Recommendation Study Group [IEEE802PRSG]. However, we have to
			consider the linkage between link-layer addresses, DHCP identifiers
			and IP addresses.
	2.1. MAC address Randomization hypotheses		2.1. MAC address Randomization hypotheses
	There is not yet an established standard for randomizing link-layer		There is not yet an established standard for randomizing link-layer
	addresses. Various prototypes have tried different strategies, such		addresses. Various prototypes have tried different strategies, such
	as:		as:
	Per connection: Configure a random link-layer address at the time of		Per connection: Configure a random link-layer address at the time of
	connecting to a network, e.g. to specific Wi-Fi SSID, and keep it		connecting to a network, e.g. to specific Wi-Fi SSID, and keep it
	for the duration of the connection.		for the duration of the connection.
	skipping to change at page 5, line 8		skipping to change at page 5, line 11
	connection" or "per network" variants. On Wi-Fi networks, changing		connection" or "per network" variants. On Wi-Fi networks, changing
	the link-layer address requires dropping the existing Wi-Fi		the link-layer address requires dropping the existing Wi-Fi
	connection and then re-establishing it, which implies repeating the		connection and then re-establishing it, which implies repeating the
	connection process and associated procedures. The IP addresses will		connection process and associated procedures. The IP addresses will
	change, which means that all required TCP connections will have to be		change, which means that all required TCP connections will have to be
	re-established. If the network access is provided through a NAT,		re-established. If the network access is provided through a NAT,
	changing IP address also means that the NAT traversal procedures will		changing IP address also means that the NAT traversal procedures will
	have to be restarted. This means a lot of disruption. At the same		have to be restarted. This means a lot of disruption. At the same
	time, an observer on the network will easily notice that a station		time, an observer on the network will easily notice that a station
	left, another came in just after that, and that the new one appears		left, another came in just after that, and that the new one appears
	to be communicating with pretty much the same set of IP addresses as		to be communicating with the same set of IP addresses as the old one.
	the old one. This provides for easy correlation.		This provides for easy correlation.
	The anonymity profile pretty much assumes that the link-layer address		The anonymity profile pretty much assumes that the link-layer address
	randomization follows the "per connection" or "per network"		randomization follows the "per connection" or "per network"
	strategies, or a variant of the "time interval" strategy in which the		strategies, or a variant of the "time interval" strategy in which the
	interval has about the same duration as the average connection.		interval has about the same duration as the average connection.
	2.2. MAC address Randomization and DHCP		2.2. MAC address Randomization and DHCP
	From a privacy point of view, it is clear that link-layer address, IP		From a privacy point of view, it is clear that link-layer address, IP
	address and DHCP identifier shall evolve in synchrony. For example,		address and DHCP identifier shall evolve in synchrony. For example,
	skipping to change at page 6, line 45		skipping to change at page 6, line 47
	anonymous, it would be good if the client told the server about that		anonymous, it would be good if the client told the server about that
	in case the server is willing to co-operate. Another possibility		in case the server is willing to co-operate. Another possibility
	would be to use specific privacy-oriented construct, such as for		would be to use specific privacy-oriented construct, such as for
	example a new type of DUID for a temporary DUID that would be		example a new type of DUID for a temporary DUID that would be
	changing over time.		changing over time.
	This is not workable in a large number of cases as it is possible		This is not workable in a large number of cases as it is possible
	that the network operator (or other entities that have access to the		that the network operator (or other entities that have access to the
	operator's network) might be actively participating in surveillance		operator's network) might be actively participating in surveillance
	and anti-privacy, willingly or not. Declaring a preference for		and anti-privacy, willingly or not. Declaring a preference for
	anonymity is a bit like walking around with a Guy Fawkes mask. When		anonymity is a bit like walking around with a Guy Fawkes mask. (See
	anonymity is required, it is generally not a good idea to stick out		[GuyFawkesMask] for an explanation of this usage.) When anonymity is
	of the crowd. Simply revealing the desire for privacy, could cause		required, it is generally not a good idea to stick out of the crowd.
	the attacker to react by triggering additional surveillance or		Simply revealing the desire for privacy, could cause the attacker to
	monitoring mechanisms. Therefore we feel that it is preferable to		react by triggering additional surveillance or monitoring mechanisms.
	not disclose one's desire for privacy.
			Therefore we feel that it is preferable to not disclose one's desire
			for privacy.
	This preference leads to some important implications. In particular,		This preference leads to some important implications. In particular,
	we make an effort to make the mitigation techniques difficult to		we make an effort to make the mitigation techniques difficult to
	distinguish from regular client behaviors, if at all possible.		distinguish from regular client behaviors, if at all possible.
	2.6. Using the anonymity profiles		2.6. Using the anonymity profiles
	There are downsides to randomizing link-layer addresses and DHCP		There are downsides to randomizing link-layer addresses and DHCP
	identifiers. By definition, randomization will break management		identifiers. By definition, randomization will break management
	procedures that rely on tracking link-layer addresses. Even if this		procedures that rely on tracking link-layer addresses. Even if this
	skipping to change at page 7, line 26		skipping to change at page 7, line 29
	that many devices would get new random link-layer addresses at short		that many devices would get new random link-layer addresses at short
	intervals, maybe every few minutes. This would generate new DHCP		intervals, maybe every few minutes. This would generate new DHCP
	requests in rapid succession, with a high risk of exhausting DHCPv4		requests in rapid succession, with a high risk of exhausting DHCPv4
	address pools. Even with IPv6, there would still be a risk of		address pools. Even with IPv6, there would still be a risk of
	increased neighbor discovery traffic, and bloating of various address		increased neighbor discovery traffic, and bloating of various address
	tables. Implementers will have to be cautious when programming		tables. Implementers will have to be cautious when programming
	devices to use randomized MAC addresses. They will have to carefully		devices to use randomized MAC addresses. They will have to carefully
	chose the frequency with which such addresses will be renewed.		chose the frequency with which such addresses will be renewed.
	This document only provides guidelines for using DHCP when clients		This document only provides guidelines for using DHCP when clients
	care about privacy and servers do not object. We assume that the		care about privacy. We assume that the request for anonymity is
	request for anonymity is materialized by the assignment of a		materialized by the assignment of a randomized link-layer address to
	randomized link-layer address to the network interface. Once that		the network interface. Once that decision is made, the following
	decision is made, the following guidelines will avoid leakage of		guidelines will avoid leakage of identity in DHCP parameters or in
	identity in DHCP parameters or in assigned addresses.		assigned addresses.
	There may be rare situations where the clients want anonymity to		There may be rare situations where the clients want anonymity to
	attackers but not to their DHCP server. These clients should still		attackers but not to their DHCP server. These clients should still
	use link-layer address randomization to hide from observers, and some		use link-layer address randomization to hide from observers, and some
	form of encrypted communication to the DHCP server. This scenario is		form of encrypted communication to the DHCP server. This scenario is
	out of scope for this document.		out of scope for this document.
	To preserve anonymity, the clients need to not use stable values for		To preserve anonymity, the clients need to not use stable values for
	the client identifiers. This is clearly a tradeoff, because a stable		the client identifiers. This is clearly a tradeoff, because a stable
	client identifier guarantees that the client will receive consistent		client identifier guarantees that the client will receive consistent
	skipping to change at page 9, line 35		skipping to change at page 9, line 35
	encoding for these options, and transmit options in different orders.		encoding for these options, and transmit options in different orders.
	These choices can be use to fingerprint the client.		These choices can be use to fingerprint the client.
	The following sections provide guidance on the encoding of options		The following sections provide guidance on the encoding of options
	and fields within the packets. However, this guidance alone may not		and fields within the packets. However, this guidance alone may not
	be sufficient to prevent fingerprinting from revealing information,		be sufficient to prevent fingerprinting from revealing information,
	such as the device type, vendor type or OS type and in some cases		such as the device type, vendor type or OS type and in some cases
	specific version, or from revealing whether the client is using the		specific version, or from revealing whether the client is using the
	anonymity profile.		anonymity profile.
	The client willing to protect its privacy SHOULD limit the subset of		The client intending to protect its privacy SHOULD limit the subset
	options sent in messages to the subset listed in the following		of options sent in messages to the subset listed in the remaining
	sections.		subsections.
	The client willing to protect its privacy SHOULD randomize options		The client intending to protect its privacy SHOULD randomize options
	order before sending any DHCPv4 message. If this random ordering		order before sending any DHCPv4 message. If this random ordering
	cannot be implemented, the client MAY arrange options by increasing		cannot be implemented, the client MAY arrange options by increasing
	order of option codes.		order of option codes.
	3.2. Client IP address field		3.2. Client IP address field
	Four bytes in the header of the DHCP messages carry the "Client IP		Four bytes in the header of the DHCP messages carry the "Client IP
	address" (ciaddr) as defined in [RFC2131]. In DHCP, this field is		address" (ciaddr) as defined in [RFC2131]. In DHCP, this field is
	used by the clients to indicate the address that they used		used by the clients to indicate the address that they used
	previously, so that as much as possible the server can allocate them		previously, so that as much as possible the server can allocate them
	the same address.		the same address.
	There is very little privacy implication of sending this address in		There is very little privacy implication of sending this address in
	the DHCP messages, except in one case, when connecting to a different		the DHCP messages, except in one case, when connecting to a different
	network than the last network connected. If the DHCP client somehow		network than the last network connected. If the DHCP client somehow
	repeated the address used in a previous network attachment,		repeated the address used in a previous network attachment,
	monitoring services might use the information to tie the two network		monitoring services might use the information to tie the two network
	locations. DHCP clients should ensure that the field is cleared when		locations. DHCP clients SHOULD ensure that the field is cleared when
	they know that the network attachment has changed, and in particular		they know that the network attachment has changed, and in particular
	if the link layer address is reset by the device's administrator.		if the link layer address is reset by the device's administrator.
	The clients using the anonymity profile MUST NOT include in the		The clients using the anonymity profile MUST NOT include in the
	message a Client IP Address that has been obtained with a different		message a Client IP Address that has been obtained with a different
	link-layer address.		link-layer address.
	3.3. Requested IP address option		3.3. Requested IP address option
	The Requested IP address option is defined in [RFC2132] with code 50.		The Requested IP address option is defined in [RFC2132] with code 50.
	skipping to change at page 11, line 14		skipping to change at page 11, line 14
	3.4. Client hardware address field		3.4. Client hardware address field
	Sixteen bytes in the header of the DHCP messages carry the "Client		Sixteen bytes in the header of the DHCP messages carry the "Client
	hardware address" (chaddr) as defined in [RFC2131]. The presence of		hardware address" (chaddr) as defined in [RFC2131]. The presence of
	this address is necessary for the proper operation of the DHCP		this address is necessary for the proper operation of the DHCP
	service.		service.
	Hardware addresses, called "link layer address" in many RFCs, can be		Hardware addresses, called "link layer address" in many RFCs, can be
	used to uniquely identify a device, especially if they follow the		used to uniquely identify a device, especially if they follow the
	IEEE 802 recommendations. These unique identifiers can be used by		IEEE 802 recommendations. If the hardware address is reset to a new
	monitoring services to track the location of the device and its user.		value, or randomized, the DHCP client SHOULD use the new randomized
	The only plausible defense is to somehow reset the hardware address		value in the DHCP messages.
	to a random value when visiting an untrusted location, before
	transmitting anything at that location with the hardware address. If
	the hardware address is reset to a new value, or randomized, the DHCP
	client SHOULD use the new randomized value in the DHCP messages.
	3.5. Client Identifier Option		3.5. Client Identifier Option
	The client identifier option is defined in [RFC2132] with option code		The client identifier option is defined in [RFC2132] with option code
	61. It is discussed in detail in [RFC4361]. The purpose of the		61. It is discussed in detail in [RFC4361]. The purpose of the
	client identifier option is to identify the client in a manner		client identifier option is to identify the client in a manner
	independent of the link layer address. This is particularly useful		independent of the link layer address. This is particularly useful
	if the DHCP server is expected to assign the same address to the		if the DHCP server is expected to assign the same address to the
	client after a network attachment is swapped and the link layer		client after a network attachment is swapped and the link layer
	address changes. It is also useful when the same node issues		address changes. It is also useful when the same node issues
	skipping to change at page 12, line 6		skipping to change at page 11, line 51
	(e.g., the Ethernet MAC address)." These strong recommendations are		(e.g., the Ethernet MAC address)." These strong recommendations are
	in fact a tradeoff between ease of management and privacy, and the		in fact a tradeoff between ease of management and privacy, and the
	tradeoff should depend on the circumstances.		tradeoff should depend on the circumstances.
	In contradiction to [RFC4361], when using the anonymity profile, DHCP		In contradiction to [RFC4361], when using the anonymity profile, DHCP
	clients MUST use client identifiers based solely on the link layer		clients MUST use client identifiers based solely on the link layer
	address that will be used in the underlying connection. This will		address that will be used in the underlying connection. This will
	ensure that the DHCP client identifier does not leak any information		ensure that the DHCP client identifier does not leak any information
	that is not already available to entities monitoring the network		that is not already available to entities monitoring the network
	connection. It will also ensure that a strategy of randomizing the		connection. It will also ensure that a strategy of randomizing the
	link layer address will not be nullified by DHCP options.		link layer address will not be nullified by the Client Identifier
			Option.
	There are usages of DHCP where the underlying connection is a point		There are usages of DHCP where the underlying connection is a point
	to point link, in which case there is no link layer address available		to point link, in which case there is no link layer address available
	to construct a non-revealing identifier. If anonymity is desired in		to construct a non-revealing identifier. If anonymity is desired in
	such networks, the client SHOULD pick a random identifier that is		such networks, the client SHOULD pick a random identifier that is
	highly likely to be unique to the current link, using for example a		highly likely to be unique to the current link, using for example a
	combination of a local secret and an identifier of the connection.		combination of a local secret and an identifier of the connection.
	The algorithm for combining secret and identifiers described in		The algorithm for combining secret and identifiers described in
	section 5 of [RFC7217] solves a similar problem. The criteria for		section 5 of [RFC7217] solves a similar problem. The criteria for
	the generation of random numbers are stated in [RFC4086].		the generation of random numbers are stated in [RFC4086].
	skipping to change at page 13, line 17		skipping to change at page 13, line 13
	device. Monitoring services could use that information in		device. Monitoring services could use that information in
	conjunction with traffic analysis and quickly derive the identity of		conjunction with traffic analysis and quickly derive the identity of
	the device's owner.		the device's owner.
	When using the anonymity profile, DHCP clients SHOULD NOT send the		When using the anonymity profile, DHCP clients SHOULD NOT send the
	host name option. If they chose to send the option, DHCP clients		host name option. If they chose to send the option, DHCP clients
	MUST always send a non-qualified host name instead of a fully		MUST always send a non-qualified host name instead of a fully
	qualified domain name, and MUST obfuscate the host name value.		qualified domain name, and MUST obfuscate the host name value.
	There are many ways to obfuscate a host name. The construction rules		There are many ways to obfuscate a host name. The construction rules
	SOULD guarantee that a different host name is generated each time the		SHOULD guarantee that a different host name is generated each time
	link-layer address changes and that the obfuscated host name will not		the link-layer address changes and that the obfuscated host name will
	reveal the underlying link layer address. The construction SHOULD		not reveal the underlying link layer address. The construction
	generate names that are unique enough to minimize collisions in the		SHOULD generate names that are unique enough to minimize collisions
	local link. Clients MAY use the following algorithm: compute a		in the local link. Clients MAY use the following algorithm: compute
	secure hash of a local secret and of the link layer address that will		a secure hash of a local secret and of the link layer address that
	be used in the underlying connection, and then use the hexadecimal		will be used in the underlying connection, and then use the
	representation of the first 6 bytes of the hash as the obfuscated		hexadecimal representation of the first 6 bytes of the hash as the
	host name.		obfuscated host name.
	There is a potential downside to having a specific name pattern for		There is a potential downside to having a specific name pattern for
	hosts that require anonymity, as explained in Section 2.5. For this		hosts that require anonymity, as explained in Section 2.5. For this
	reason, the above algorithm is just a suggestion.		reason, the above algorithm is just a suggestion.
	3.8. Client FQDN Option		3.8. Client FQDN Option
	The Client FQDN option is defined in [RFC4702] with option code 81.		The Client FQDN option is defined in [RFC4702] with option code 81.
	The option allows the DHCP clients to advertise to the DHCP server		The option allows the DHCP clients to advertise to the DHCP server
	their fully qualified domain name (FQDN) such as		their fully qualified domain name (FQDN) such as
	skipping to change at page 14, line 25		skipping to change at page 14, line 23
	identifies the device.		identifies the device.
	The PXE system is clearly designed for devices operating in a		The PXE system is clearly designed for devices operating in a
	controlled environment. The main usage of the PXE system is to		controlled environment. The main usage of the PXE system is to
	install a new version of the operating system through a high speed		install a new version of the operating system through a high speed
	Ethernet connection. The process is typically controlled from the		Ethernet connection. The process is typically controlled from the
	user interface during the boot process. Common sense seems to		user interface during the boot process. Common sense seems to
	dictate that getting a new operating system from an unauthenticated		dictate that getting a new operating system from an unauthenticated
	server at an untrusted location is a really bad idea, and that even		server at an untrusted location is a really bad idea, and that even
	if the option was available users would not activate it. In any		if the option was available users would not activate it. In any
	case, the option is only used in the "pre boot" environment, and is		case, the option is only used in the "pre boot" environment, and
	there is no reason to use it once the system is up and running. If		there is no reason to use it once the system is up and running.
	only for privacy reasons, nodes visiting untrusted networks MUST NOT		Nodes visiting untrusted networks MUST NOT send or use the PXE
	send or use the PXE options.		options.
	3.10. User and Vendor Class DHCP options		3.10. User and Vendor Class DHCP options
	Vendor identifying options are defined in [RFC2132] and [RFC3925].		Vendor identifying options are defined in [RFC2132] and [RFC3925].
	When using the anonymity profile, DHCP clients SHOULD NOT use the		When using the anonymity profile, DHCP clients SHOULD NOT use the
	Vendor Specific Information option (code 43), the Vendor Class		Vendor Specific Information option (code 43), the Vendor Class
	Identifier Option (60), the Vendor Class option (code 124), or the		Identifier Option (60), the Vendor Class option (code 124), or the
	Vendor Specific Information option (code 125) as these options		Vendor Specific Information option (code 125) as these options
	potentially reveal identifying information.		potentially reveal identifying information.
	skipping to change at page 15, line 11		skipping to change at page 15, line 9
	constructing these prefixes have different implications on privacy,		constructing these prefixes have different implications on privacy,
	which are discussed in [I-D.ietf-6man-default-iids] and		which are discussed in [I-D.ietf-6man-default-iids] and
	[I-D.ietf-6man-ipv6-address-generation-privacy]. In the stateless		[I-D.ietf-6man-ipv6-address-generation-privacy]. In the stateless
	scenario, clients use DHCPv6 to obtain network configuration		scenario, clients use DHCPv6 to obtain network configuration
	parameters, through the INFORMATION-REQUEST message.		parameters, through the INFORMATION-REQUEST message.
	The choice between the stateful and stateless scenarios depends on		The choice between the stateful and stateless scenarios depends on
	flag and prefix options published by the "Router Advertisement"		flag and prefix options published by the "Router Advertisement"
	messages of local routers, as specified in [RFC4861]. When these		messages of local routers, as specified in [RFC4861]. When these
	options enable stateless address configuration hosts using the		options enable stateless address configuration hosts using the
	anonymity profile SHOULD choose it over stateful address		anonymity profile SHOULD use stateless address configuration instead
	configuration, because stateless configuration requires fewer		of stateful address configuration, because stateless configuration
	information disclosures than stateful configuration.		requires fewer information disclosures than stateful configuration.
	When using the anonymity profile, DHCPv6 clients carefully select		When using the anonymity profile, DHCPv6 clients carefully select
	DHCPv6 options used in the various messages that they send. The list		DHCPv6 options used in the various messages that they send. The list
	of options that are mandatory or optional for each message is		of options that are mandatory or optional for each message is
	specified in [RFC3315]. Some of these options have specific		specified in [RFC3315]. Some of these options have specific
	implications on anonymity. The following sections provide guidance		implications on anonymity. The following sections provide guidance
	on the choice of option values when using the anonymity profile.		on the choice of option values when using the anonymity profile.
	4.1. Avoiding fingerprinting		4.1. Avoiding fingerprinting
	There are many choices for implementing DHCPv6 messages. As		There are many choices for implementing DHCPv6 messages. As
	explained in Section 3.1, these choices can be use to fingerprint the		explained in Section 3.1, these choices can be use to fingerprint the
	client.		client.
	The following sections provide guidance on the encoding of options.		The following sections provide guidance on the encoding of options.
	However, this guidance alone may not be sufficient to prevent		However, this guidance alone may not be sufficient to prevent
	fingerprinting from revealing information, such as the device type,		fingerprinting from revealing information, such as the device type,
	vendor type or OS type and in some cases specific version, or from		vendor type or OS type and in some cases specific version, or from
	revealing whether the client is using the anonymity profile.		revealing whether the client is using the anonymity profile.
	The client willing to protect its privacy SHOULD limit the subset of		The client intending to protect its privacy SHOULD limit the subset
	options sent in messages to the subset listed in the following		of options sent in messages to the subset listed in the following
	sections.		sections.
	The client willing to protect its privacy SHOULD randomize options		The client intending to protect its privacy SHOULD randomize options
	order before sending any DHCPv6 message. If this random ordering		order before sending any DHCPv6 message. If this random ordering
	cannot be implemented, the client MAY arrange options by increasing		cannot be implemented, the client MAY arrange options by increasing
	order of option codes.		order of option codes.
	4.2. Do not send Confirm messages, unless really sure where		4.2. Do not send Confirm messages, unless really sure where
	[RFC3315] requires clients to send a Confirm message when they attach		[RFC3315] requires clients to send a Confirm message when they attach
	to a new link to verify whether the addressing and configuration		to a new link to verify whether the addressing and configuration
	information they previously received is still valid. This		information they previously received is still valid. This
	requirement was relaxed in [I-D.ietf-dhc-rfc3315bis]. When these		requirement was relaxed in [I-D.ietf-dhc-rfc3315bis]. When these
	skipping to change at page 17, line 7		skipping to change at page 17, line 7
	set to 1 (DUID-LLT). Hardware type SHOULD be set appropriately to		set to 1 (DUID-LLT). Hardware type SHOULD be set appropriately to
	the hardware type. The link address embedded in the LLT SHOULD be		the hardware type. The link address embedded in the LLT SHOULD be
	set to a randomized value. Time SHOULD be set to a random timestamp		set to a randomized value. Time SHOULD be set to a random timestamp
	from the previous year. Time MAY be set to current time, but this		from the previous year. Time MAY be set to current time, but this
	will reveal the fact that the DUID is newly generated, and could		will reveal the fact that the DUID is newly generated, and could
	provide information for device fingerprinting. The criteria for		provide information for device fingerprinting. The criteria for
	generating highly unique random numbers are listed in [RFC4086].		generating highly unique random numbers are listed in [RFC4086].
	4.3.1. Anonymous Information-Request		4.3.1. Anonymous Information-Request
	According to [RFC3315], a DHCPv6 client typically includes its client		According to [RFC3315], a DHCPv6 client includes its client
	identifier in most of the messages it sends. There is one exception,		identifier in most of the messages it sends. There is one exception,
	however. Client is allowed to omit its client identifier when		however. Client is allowed to omit its client identifier when
	sending Information-Request.		sending Information-Request.
	When using stateless DHCPv6, clients wanting to protect their privacy		When using stateless DHCPv6, clients wanting to protect their privacy
	SHOULD NOT include client identifiers in their Information-Request		SHOULD NOT include client identifiers in their Information-Request
	messages. This will prevent the server from specifying client-		messages. This will prevent the server from specifying client-
	specific options if it is configured to do so, but the need for		specific options if it is configured to do so, but the need for
	anonymity precludes such options anyway.		anonymity precludes such options anyway.
	skipping to change at page 17, line 31		skipping to change at page 17, line 31
	Server Identifier Option (code 2) as specified in [RFC3315]. Clients		Server Identifier Option (code 2) as specified in [RFC3315]. Clients
	MUST only include server identifier values that were received with		MUST only include server identifier values that were received with
	the current link-layer address, because reuse of old values discloses		the current link-layer address, because reuse of old values discloses
	information that can be used to identify the client.		information that can be used to identify the client.
	4.5. Address assignment options		4.5. Address assignment options
	When using the anonymity profile, DHCPv6 clients might have to use		When using the anonymity profile, DHCPv6 clients might have to use
	SOLICIT or REQUEST messages to obtain IPv6 addresses through the DHCP		SOLICIT or REQUEST messages to obtain IPv6 addresses through the DHCP
	server. In DHCPv6, the collection of addresses assigned to a client		server. In DHCPv6, the collection of addresses assigned to a client
	is indemtified by an Identity Association (IA).Clients interested in		is identified by an Identity Association (IA).Clients interested in
	privacy SHOULD request addresses using the Identity Association for		privacy SHOULD request addresses using the Identity Association for
	Non-temporary Addresses Option (IA_NA, code 3).		Non-temporary Addresses Option (IA_NA, code 3).
	The IA_NA option includes an IAID parameter that identifies a unique		The IA_NA option includes an IAID parameter that identifies a unique
	identity association for the interface for which the Address is		identity association for the interface for which the Address is
	requested. Clients interested in protecting their privacy MUST		requested. Clients interested in protecting their privacy MUST
	ensure that the IAID does not enable client identification. They		ensure that the IAID does not enable client identification. They
	also need to conform to the requirement of [RFC3315] that the IAID		also need to conform to the requirement of [RFC3315] that the IAID
	for that IA MUST be consistent across restarts of the DHCP client.		for that IA MUST be consistent across restarts of the DHCP client.
	We interpret that as requiring that the IAID MUST be constant for the		We interpret that as requiring that the IAID MUST be constant for the
	skipping to change at page 23, line 41		skipping to change at page 23, line 41
	2. In Section 4.3, added precision that the generated DUID-LLT are		2. In Section 4.3, added precision that the generated DUID-LLT are
	meaningless, and added an informative reference to [RFC4086].		meaningless, and added an informative reference to [RFC4086].
	3. In Section 4.5.2, reworked the text to reflect the consensus from		3. In Section 4.5.2, reworked the text to reflect the consensus from
	IPv6 experts and provide informed guidance on the use of the		IPv6 experts and provide informed guidance on the use of the
	option if prefix delegation is required.		option if prefix delegation is required.
	4. In Section 5, noticed servers that might mandate link layer		4. In Section 5, noticed servers that might mandate link layer
	address registration.		address registration.
			Changes from draft-07 to draft-08 address comments received during
			IESG review
			1. Corrected a number of typos and applied several minor editing
			suggestions.
			2. Added reference to IEEE study group and other IETF experiments in
			Section 2.
			3. Added reference to journal paper on Guy Fawkes mask in
			Section 2.5.
			4. Removed "if servers do not object" from appliction scope in
			Section 2.6.
			5. Removed redondant text from Section 3.4.
			6. In Section 3.5, say "will not be nullified by the Client
			Identifier Option" instead of "will not be nullified by DHCP
			options."
			7. In Section 3.9, remove the qualification "if only for privacy
			reasons."
			8. Clarified the preference for stateless address configuration in
			Section 4.
	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,
	<http://www.rfc-editor.org/info/rfc2119>.		<http://www.rfc-editor.org/info/rfc2119>.
	[RFC2131] Droms, R., "Dynamic Host Configuration Protocol",		[RFC2131] Droms, R., "Dynamic Host Configuration Protocol",
	skipping to change at page 24, line 39		skipping to change at page 25, line 18
	<http://www.rfc-editor.org/info/rfc4941>.		<http://www.rfc-editor.org/info/rfc4941>.
	10.2. Informative References		10.2. Informative References
	[CNBC] Weston, G., Greenwald, G., and R. Gallagher, "CBC News:		[CNBC] Weston, G., Greenwald, G., and R. Gallagher, "CBC News:
	CSEC used airport Wi-Fi to track Canadian travellers", Jan		CSEC used airport Wi-Fi to track Canadian travellers", Jan
	2014, <http://www.cbc.ca/news/politics/csec-used-airport-		2014, <http://www.cbc.ca/news/politics/csec-used-airport-
	wi-fi-to-track-canadian-travellers-edward-snowden-		wi-fi-to-track-canadian-travellers-edward-snowden-
	documents-1.2517881>.		documents-1.2517881>.
			[GuyFawkesMask]
			Nickelsburg, M., "A brief history of the Guy Fawkes mask",
			July 2013, <http://theweek.com/articles/463151/
			brief-history-guy-fawkes-mask>.
	[I-D.ietf-6man-default-iids]		[I-D.ietf-6man-default-iids]
	Gont, F., Cooper, A., Thaler, D., and S. LIU,		Gont, F., Cooper, A., Thaler, D., and S. LIU,
	"Recommendation on Stable IPv6 Interface Identifiers",		"Recommendation on Stable IPv6 Interface Identifiers",
	draft-ietf-6man-default-iids-09 (work in progress),		draft-ietf-6man-default-iids-10 (work in progress),
	January 2016.		February 2016.
	[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-08 (work		draft-ietf-6man-ipv6-address-generation-privacy-08 (work
	in progress), September 2015.		in progress), September 2015.
	[I-D.ietf-dhc-dhcp-privacy]		[I-D.ietf-dhc-dhcp-privacy]
	Jiang, S., Krishnan, S., and T. Mrugalski, "Privacy		Jiang, S., Krishnan, S., and T. Mrugalski, "Privacy
	considerations for DHCPv4", draft-ietf-dhc-dhcp-privacy-03		considerations for DHCP", draft-ietf-dhc-dhcp-privacy-04
	(work in progress), January 2016.		(work in progress), February 2016.
	[I-D.ietf-dhc-dhcpv6-privacy]		[I-D.ietf-dhc-dhcpv6-privacy]
	Krishnan, S., Mrugalski, T., and S. Jiang, "Privacy		Krishnan, S., Mrugalski, T., and S. Jiang, "Privacy
	considerations for DHCPv6", draft-ietf-dhc-		considerations for DHCPv6", draft-ietf-dhc-
	dhcpv6-privacy-03 (work in progress), January 2016.		dhcpv6-privacy-04 (work in progress), February 2016.
	[I-D.ietf-dhc-rfc3315bis]		[I-D.ietf-dhc-rfc3315bis]
	Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A.,		Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A.,
	Richardson, M., Jiang, S., and T. Lemon, "Dynamic Host		Richardson, M., Jiang, S., and T. Lemon, "Dynamic Host
	Configuration Protocol for IPv6 (DHCPv6) bis", draft-ietf-		Configuration Protocol for IPv6 (DHCPv6) bis", draft-ietf-
	dhc-rfc3315bis-03 (work in progress), February 2016.		dhc-rfc3315bis-03 (work in progress), February 2016.
	[IEEE8021X]		[IEEE8021X]
	IEEE Std 802.1X-2010, "IEEE Standards for Local and		IEEE Std 802.1X-2010, "IEEE Standards for Local and
	Metropolitan Area Networks: Port based Network Access		Metropolitan Area Networks: Port based Network Access
	Control", Feb 2010, <http://standards.ieee.org/getieee802/		Control", Feb 2010, <http://standards.ieee.org/getieee802/
	download/802.1X-2010.pdf>.		download/802.1X-2010.pdf>.
			[IEEE802PRSG]
			IEEE 802 EC PRSG, "IEEE 802 EC Privacy Recommendation
			Study Group", Dec 2015,
			<http://www.ieee802.org/PrivRecsg/>.
	[IETFMACRandom]		[IETFMACRandom]
	Zuniga, JC., "MAC Privacy", November 2014,		Zuniga, JC., "MAC Privacy", November 2014,
	<http://www.ietf.org/blog/2014/11/mac-privacy/>.		<http://www.ietf.org/blog/2014/11/mac-privacy/>.
			[IETFTrialsAndMore]
			Bernardos, CJ., Zuniga, JC., and P. O'Hanlon, "Wi-Fi
			Internet connectivity and privacy: hiding your tracks on
			the wireless Internet", October 2015,
			<http://www.it.uc3m.es/cjbc/papers/
			pdf/2015_bernardos_cscn_privacy.pdf>.
	[RFC2132] Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor		[RFC2132] Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
	Extensions", RFC 2132, DOI 10.17487/RFC2132, March 1997,		Extensions", RFC 2132, DOI 10.17487/RFC2132, March 1997,
	<http://www.rfc-editor.org/info/rfc2132>.		<http://www.rfc-editor.org/info/rfc2132>.
	[RFC3925] Littlefield, J., "Vendor-Identifying Vendor Options for		[RFC3925] Littlefield, J., "Vendor-Identifying Vendor Options for
	Dynamic Host Configuration Protocol version 4 (DHCPv4)",		Dynamic Host Configuration Protocol version 4 (DHCPv4)",
	RFC 3925, DOI 10.17487/RFC3925, October 2004,		RFC 3925, DOI 10.17487/RFC3925, October 2004,
	<http://www.rfc-editor.org/info/rfc3925>.		<http://www.rfc-editor.org/info/rfc3925>.
	[RFC4086] Eastlake 3rd, D., Schiller, J., and S. Crocker,		[RFC4086] Eastlake 3rd, D., Schiller, J., and S. Crocker,
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