Internet Engineering Task Force (IETF) JC. Zúñiga
Request for Comments: 9724 Cisco
Category: Informational CJ. Bernardos, Ed.
ISSN: 2070-1721 UC3M
A. Andersdotter
Safespring AB
January 2025
State of Affairs for Randomized and Changing Media Access Control (MAC) Address State of
Affairs
Addresses
Abstract
Internet users are becoming more aware that their activity over the
Internet leaves a vast digital footprint, that communications might
not always be properly secured, and that their location and actions
can be tracked. One of the main factors that eases tracking of
Internet users is the wide use of long-lasting, and sometimes
persistent, identifiers at various protocol layers. This document
focuses on Media Access Control (MAC) addresses.
There have been several initiatives within the IETF and the IEEE 802
standards committees to overcome address some of the privacy issues involved.
This document provides an overview of these activities to help
coordinate standardization activities in these bodies.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are candidates for any level of Internet
Standard; see Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9724.
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Table of Contents
1. Introduction
2. Background
2.1. MAC Address Usage
2.2. MAC Address Randomization
2.3. Privacy Workshop, Tutorial, and Experiments at IETF and
IEEE 802 Meetings
3. Activities Relating to Randomized and Changing MAC Addresses in
the IEEE 802
4. Recent Activities Related to MAC Address Randomization in the
WBA
5. IPv6 Address Randomization in the IETF
6. Taxonomy of MAC Address Selection Policies
6.1. Per-Vendor OUI MAC Address (PVOM) Address
6.2. Per-Device Generated MAC Address (PDGM) Address
6.3. Per-Boot Generated MAC Address (PBGM) Address
6.4. Per-Network Generated MAC Address (PNGM) Address
6.5. Per-Period Generated MAC Address (PPGM) Address
6.6. Per-Session Generated MAC Address (PSGM) Address
7. OS Current Practices
8. IANA Considerations
9. Security Considerations
10. Informative References
Acknowledgments
Authors' Addresses
1. Introduction
Privacy is becoming a huge concern, as more and more devices are
connecting to the Internet either directly (e.g., via Wi-Fi) or
indirectly (e.g., via a smartphone using Bluetooth). This ubiquitous
connectivity, together with the lack of proper education about
privacy, makes it very easy to track/monitor the location of users
and/or eavesdrop on their physical and online activities. This is
due to many factors, such as the vast digital footprint that users
leave on the Internet with or without their consent and the weak (or
even null) authentication and encryption mechanisms used to secure
communications. A digital footprint may include information shared
on social networks, cookies used by browsers and servers for various
reasons, connectivity logs that allow tracking of a user's Layer 2
(L2) address (i.e., MAC address) or Layer 3 (L3) address, web
trackers, etc.
Privacy concerns affect all layers of the protocol stack, from the
lower layers involved in the access to the network (e.g., MAC/L2 and
L3 addresses can be used to obtain the location of a user) to higher-
layer protocol identifiers and user applications [CSCN2015]. In
particular, IEEE 802 MAC addresses have historically been an easy
target for tracking users [wifi_tracking].
There have been several initiatives within the IETF and the IEEE 802
standards committees to overcome address some of these privacy issues. This
document provides an overview of these activities to help coordinate
standardization activities within these bodies.
2. Background
2.1. MAC Address Usage
Most mobile devices used today are WLAN enabled (i.e., they are
equipped with an IEEE 802.11 wireless local area network interface).
Like any other kind of network interface based on IEEE 802 such as
Ethernet (i.e., IEEE 802.3), Wi-Fi interfaces have an L2 address
(also referred to as a MAC address) that can be seen by anybody who
can receive the radio signal transmitted by the network interface.
The format of these addresses (for 48-bit MAC addresses) is shown in
Figure 1.
+--------+--------+---------+--------+--------+---------+
| Organizationally Unique | Network Interface |
| Identifier (OUI) | Controller (NIC) Specific |
+--------+--------+---------+--------+--------+---------+
/ \
/ \
/ \ b0 (I/G bit):
/ \ 0: unicast
/ \ 1: multicast
/ \
/ \ b1 (U/L bit):
+--+--+--+--+--+--+--+--+ 0: globally unique (OUI enforced)
|b7|b6|b5|b4|b3|b2|b1|b0| 1: locally administered
+--+--+--+--+--+--+--+--+
Figure 1: IEEE 802 MAC Address Format (for 48-Bit Addresses)
MAC addresses can be either universally or locally administered.
Universally and locally administered addresses are distinguished by
setting the second least significant bit of the most significant byte
of the address (the U/L bit).
A universally administered address is uniquely assigned to a device
by its manufacturer. Most physical devices are provided with a
universally administered address, which is composed of two parts:
Organizationally Unique Identifier (OUI): The first three octets in
transmission order, which identify the organization that issued
the identifier.
Network Interface Controller (NIC) Specific: The following three
octets, which are assigned by the organization that manufactured
the NIC, in such a way that the resulting MAC address is globally
unique.
Locally administered addresses override the burned-in address, and
they can be set up by either the network administrator or the
Operating System (OS) of the device to which the address pertains.
However, as explained in later sections of this document, there are
new initiatives in the IEEE 802 and other organizations to specify
ways in which these locally administered addresses should be
assigned, depending on the use case.
2.2. MAC Address Randomization
Since universally administered MAC addresses are by definition
globally unique, when a device uses this MAC address over a shared
medium to transmit data -- especially over the air -- it is
relatively easy to track this device by simple medium observation.
Since a device is usually directly associated to an individual, this
poses a privacy concern [link_layer_privacy].
MAC addresses can be easily observed by a third party, such as a
passive device listening to communications in the same L2 network.
In an 802.11 network, a station (STA) exposes its MAC address in two
different situations:
* While actively scanning for available networks, the MAC address is
used in the Probe Request frames sent by the device (also known as
IEEE 802.11 STA). device.
* Once associated to a given Access Point (AP), the MAC address is
used in frame transmission and reception, as one of the addresses
used in the unicast address fields of an IEEE 802.11 frame.
One way to overcome address this privacy concern is by using randomly
generated MAC addresses. IEEE 802 addressing includes one bit to
specify if the hardware address is locally or globally administered.
This allows local addresses to be generated without the need for any
global coordination mechanism to ensure that the generated address is
still unique within the local network. This feature can be used to
generate random addresses, which decouple the globally unique
identifier from the device and therefore make it more difficult to
track a user device from its MAC/L2 address
[enhancing_location_privacy].
Note that there are reports [contact_tracing_paper] of some mobile
OSes reporting persistently (every 20 minutes or so) on MAC addresses
(as well as other information), which would defeat MAC address
randomization. While these practices might have changed by now, it
is important to highlight that privacy-preserving techniques should
be conducted while considering all layers of the protocol stack.
2.3. Privacy Workshop, Tutorial, and Experiments at IETF and IEEE 802
Meetings
As an outcome to the STRINT W3C/IAB Workshop [strint], a tutorial
titled "Pervasive Surveillance of the Internet - Designing Privacy
into Internet Protocols" [privacy_tutorial] was given at the IEEE 802
Plenary meeting in San Diego in July of 2014. The tutorial provided
an update on the recent developments regarding Internet privacy, the
actions undertaken by other Standards Development Organizations
(SDOs) like the IETF, and guidelines that were being followed when
developing new Internet protocol specifications (e.g., the
considerations described in [RFC6973]). The tutorial highlighted
some privacy concerns that apply specifically to link-layer
technologies and provided suggestions on how IEEE 802 could help
address them.
Following the discussions and interest within the IEEE 802 community,
on 18 July 2014, the IEEE 802 Executive Committee (EC) created the
IEEE 802 EC Privacy Recommendation Study Group (SG)
[ieee_privacy_ecsg]. The work and discussions from the group have
generated multiple outcomes, such as: 802E PAR (Project Authorization
Request, this is the means by which standards projects are started
within the IEEE. PARs define the scope, purpose, and contact points
for a new project): Recommended Practice for Privacy Considerations
for IEEE 802 Technologies [IEEE_802E], and the 802c PAR: Standard for
Local and Metropolitan Area Networks - Overview and Architecture -
Amendment 2: Local Medium Access Control (MAC) Address Usage
[IEEE_802c].
In order to test the effects of MAC address randomization, trials
experiments were conducted at the IETF and IEEE 802 meetings between
November 2014 and March 2015 -- IETF 91, IETF 92, and the IEEE 802
Plenary in Berlin. The purpose of the trials experiments was to evaluate
the use of MAC address randomization from two different perspectives:
(1) the effect on the connectivity experience of the end user, as
well as any effect on applications and OSes, and (2) the potential
impact on the network infrastructure itself. Some of the findings
were published in [CSCN2015].
During the trials, experiments, it was observed that the probability of
address duplication in a network is negligible. The trials experiments also
revealed that other protocol identifiers (e.g., the DHCP client
identifier) can be correlated and can therefore still be used to
track an individual. Hence, effective privacy tools should not work
in isolation at a single layer; instead; they should be coordinated
with other privacy features at higher layers.
Since then, MAC address randomization has been further implemented by
mobile OSes to provide better privacy for mobile phone users when
connecting to public wireless networks [privacy_ios]
[privacy_windows] [privacy_android].
3. Activities Relating to Randomized and Changing MAC Addresses in the
IEEE 802
Practical experiences with Randomized and Changing MAC addresses (RCM)
addresses in devices (some of which are explained in Section 6)
helped researchers fine-tune their understanding of attacks against
randomization mechanisms [when_mac_randomization_fails]. Within the
IEEE 802.11 group, these research experiences eventually formed the
basis for a specified mechanism that randomizes MAC addresses, which
was introduced in IEEE Std 802.11aq [IEEE_802.11aq] in 2018.
More recent developments include turning on MAC address randomization
in mobile OSes by default, which has an impact on the ability of
network operators to customize services [rcm_user_experience_csd].
Therefore, follow-on work in the IEEE 802.11 mapped effects of a
potentially large uptake of randomized MAC identifiers on a number of
commonly offered operator services in 2019 [rcm_tig_final_report].
In the summer of 2020, this work emanated in two new standards
projects with the purpose of developing mechanisms that do not
decrease user privacy but enable an optimal user experience when the
MAC address of a device in an Extended Service Set (a group of
interconnected IEEE 802.11 wireless access points and stations that
form a single logical network) is randomized or changes
[rcm_user_experience_par] and user privacy solutions applicable to
IEEE Std 802.11 [rcm_privacy_par].
IEEE Std 802 [IEEE_802], as of the amendment IEEE 802c-2017
[IEEE_802c], specifies a local MAC address space structure known as
the Structured Local Address Plan (SLAP) [RFC8948]. The SLAP
designates a range of Extended Local Identifiers for subassignment
within a block of addresses assigned by the IEEE Registration
Authority via a Company ID. A range of local MAC addresses is
designated for Standard Assigned Identifiers to be specified by IEEE
802 standards. Another range of local MAC addresses is designated
for Administratively Assigned Identifiers, which are subject to
assignment by a network administrator.
IEEE Std 802E-2020 ("IEEE Recommended Practice for Privacy
Considerations for IEEE 802(R) Technologies") [IEEE_802E] recommends
the use of temporary and transient identifiers if there are no
compelling reasons for a newly introduced identifier to be permanent.
This recommendation is part of the basis for the review of user
privacy solutions for IEEE Std 802.11 devices (also known as Wi-Fi
devices) as part of the RCM efforts [rcm_privacy_csd]. Annex T of
IEEE Std 802.1AEdk-2023 ("MAC Privacy Protection") [IEEE_802.1AEdk]
discusses privacy considerations in bridged networks.
As of 2024, two task groups in IEEE 802.11 are dealing with issues
related to RCM: RCM addresses:
* The IEEE 802.11bh task group, which is looking at mitigating the
repercussions that RCM creates addresses create on 802.11 networks and
related services.
* The IEEE 802.11bi task group, which is chartered to define
modifications to the IEEE Std 802.11 MAC specification to specify
new mechanisms that address and improve user privacy.
4. Recent Activities Related to MAC Address Randomization in the WBA
In the Wireless Broadband Alliance (WBA), the Testing and
Interoperability Work Group has been looking at issues related to MAC
address randomization and has identified a list of potential impacts
of these changes to existing systems and solutions, mainly related to
Wi-Fi identification.
As part of this work, the WBA has documented a set of use cases that
a Wi-Fi Identification Standard should address in order to scale and
achieve longer-term sustainability of deployed services. A first
version of this document has been liaised with the IETF as part of
the MAC Address Device Identification for Network and Application
Services (MADINAS) activities through the that document, a paper titled "Wi-Fi Identification In a
post MAC Randomization Era v1.0" paper [wba_paper]. [wba_paper], was created while
liaising with the IETF MADINAS Working Group.
5. IPv6 Address Randomization in the IETF
[RFC4862] specifies Stateless Address Autoconfiguration (SLAAC) for
IPv6, which typically results in hosts configuring one or more
"stable" addresses composed of a network prefix advertised by a local
router and an Interface Identifier (IID). [RFC8064] formally updated
the original IPv6 IID selection mechanism to avoid generating the IID
from the MAC address of the interface (via EUI64), as this
potentially allowed for tracking of a device at L3. Additionally,
the prefix part of an IP address provides meaningful insights of the
physical location of the device in general, which together with the
IID based on the MAC address, made it easier to perform global device
tracking.
[RFC8981] identifies and describes the privacy issues associated with
embedding MAC stable addressing information into IPv6 addresses (as
part of the IID). It describes an extension to IPv6 SLAAC that
causes hosts to generate temporary addresses with randomized IIDs for
each prefix advertised with autoconfiguration enabled. Changing
addresses over time limits the window of time during which
eavesdroppers and other information collectors may trivially perform
address-based network-activity correlation when the same address is
employed for multiple transactions by the same host. Additionally,
it reduces the window of exposure of a host as being accessible via
an address that becomes revealed as a result of active communication.
These temporary addresses are meant to be used for a short period of
time (hours to days) and then deprecated. Deprecated addresses can
continue to be used for already-established connections but are not
used to initiate new connections. New temporary addresses are
generated periodically to replace temporary addresses that expire.
In order to do so,
To generate temporary addresses, a node produces a sequence of
temporary global scope addresses from a sequence of IIDs that appear
to be random in the sense that (1) it is difficult for an outside
observer to predict a future address (or identifier) based on a
current one and (2) it is difficult to determine previous addresses
(or identifiers) knowing only the present one. Temporary addresses
should not be used by applications that listen for incoming
connections (as these are supposed to be waiting on permanent/well-known permanent/well-
known identifiers). If a node changes network and comes back to a
previously visited one, the temporary addresses that the node would
use will be different, which might be an issue in certain networks
where addresses are used for operational purposes (e.g., filtering or
authentication). [RFC7217], summarized next, partially addresses the
problems aforementioned.
[RFC7217] describes a method to generate IIDs that are stable for
each network interface within each subnet but change as a host moves
from one network to another. This method enables the "stability"
properties of the IIDs specified in [RFC4291] to be kept, while still
mitigating address-scanning attacks and preventing correlation of the
activities of a host as it moves from one network to another. The
method defined to generate the IPv6 IID is based on computing a hash
function that takes the following as input: information that is
stable and associated to the interface (e.g., a local IID), stable
information associated to the visited network (e.g., the IEEE 802.11
SSID),
Service Set Identifier (SSID)), the IPv6 prefix, a secret key, and
some other additional information. This basically ensures that a
different IID is generated when one of the input fields changes (such
as the network or the prefix) but that the IID is the same within
each subnet.
To mitigate the privacy threats posed by the use of MAC-derived IIDs,
[RFC8064] recommends that nodes implement [RFC7217] as the default
scheme for generating stable IPv6 addresses with SLAAC.
In addition to the documents above, [RFC8947] proposes a DHCPv6
extension that:
| allows a scalable approach to link-layer address assignments where
| preassigned link-layer address assignments (such as by a
| manufacturer) are not possible or are unnecessary.
And [RFC8948] proposes DHCPv6 extensions that:
| enable a DHCPv6 client or a DHCPv6 relay to indicate a preferred
| SLAP quadrant to the server so that the server may allocate MAC
| addresses in the quadrant requested by the relay or client.
In addition to MAC and IP addresses, some DHCP options that carry
unique identifiers can also be used for tracking purposes. These
identifiers can enable device tracking even if the device
administrator takes care of randomizing other potential
identifications like link-layer addresses or IPv6 addresses.
[RFC7844] introduces anonymity profiles that are:
| designed for clients that wish to remain anonymous to the visited
| network
and that:
| provide guidelines on the composition of DHCP or DHCPv6 messages,
| designed to minimize disclosure of identifying information.
[RFC7844] also indicates that the link-layer address, IP address, and
DHCP identifier shall evolve in synchrony.
6. Taxonomy of MAC Address Selection Policies
This section documents different policies for MAC address selection.
Some OSes might use a combination of multiple policies.
| Note about the naming convention used: The "M" in "MAC" is
| included in the acronym but not the "A" from "Address". This
| allows one to talk about a PVOM Address "PVOM address" or PNGM Address. "PNGM address".
6.1. Per-Vendor OUI MAC Address (PVOM) Address
This form of MAC address selection is the historical default.
The vendor obtains an OUI from the IEEE. This is a 24-bit prefix
(including two upper bits that are set specifically) that is assigned
to the vendor. The vendor generates a unique 24-bit value for the
lower 24 bits, forming the 48-bit MAC address. It is not unusual for
the 24-bit value to be taken used as an incrementing counter, counter that was
assigned at the factory, factory and burnt into non-volatile storage.
Note that IEEE Std 802.15.4 [IEEE_802.15.4] uses 64-bit MAC
addresses, and the IEEE assigns 32-bit prefixes. The IEEE has
indicated that there may be a future Ethernet specification that uses
64-bit MAC addresses.
6.2. Per-Device Generated MAC Address (PDGM) Address
This form of MAC address is randomly generated by the device, usually
upon first boot. The resulting MAC address is stored in non-volatile
storage and is used for the rest of the device lifetime.
6.3. Per-Boot Generated MAC Address (PBGM) Address
This form of MAC address is randomly generated by the device each
time the device is booted. The resulting MAC address is *not* stored
in non-volatile storage. It does not persist across power cycles.
This case may sometimes be a PDGM address where the non-volatile
storage is no longer functional (or has failed).
6.4. Per-Network Generated MAC Address (PNGM) Address
This form of MAC address is generated each time a new network
attachment is created.
This is typically used with Wi-Fi (802.11) networks (i.e., 802.11 networks)
where the network is identified by an SSID Name. The generated
address is stored in non-volatile storage, indexed by the SSID. Each
time the device returns to a network with the same SSID, the device
uses the saved MAC address.
It is possible to use a PNGM address for wired Ethernet connections
through some passive observation of network traffic (such as STP the
Spanning Tree Protocol (SPT) [IEEE_802.1D], the Link Layer Discovery
Protocol (LLDP) [IEEE_802.1AB], DHCP, or Router Advertisements) to
determine which network has been attached.
6.5. Per-Period Generated MAC Address (PPGM) Address
This form of MAC address is generated periodically, typically around
every twelve hours. Like PNGM, PNGM addresses, it is used primarily with
Wi-Fi.
When the MAC address changes, the station disconnects from the
current session and reconnects using the new MAC address. This will
involve a new WPA/802.1x session: new Extensible Authentication
Protocol (EAP), TLS, etc. negotiations. A session, as well as obtaining (or
refreshing) a new DHCP, SLAAC will be
done. IP address (e.g., using DHCP or SLAAC).
If DHCP is used, then a new DHCP Unique Identifier (DUID) is
generated so as to not link to the previous connection; this usually
results in the allocation of new IP addresses.
6.6. Per-Session Generated MAC Address (PSGM) Address
This form of MAC address is generated on a per-session basis. How a
session is defined is implementation-dependent, for example, a
session might be defined by logging in to a portal, VPN, etc. Like
PNGM, PSGM
PNGM and PPGM addresses, it is used primarily with Wi-Fi.
Since the address only changes when a new session is established,
there is no disconnection/reconnection involved.
7. OS Current Practices
By default, most modern OSes (especially mobile ones) do implement
some MAC address randomization policies. Since the mechanism and
policies that OSes implement can evolve with time, the content is now
hosted at [OS_current_practices]. For completeness, a snapshot of
the content at the time of publication of this document is included
below. Note that the extensive testing reported in this document was
conducted in 2021, but no significant changes have been detected at
the time of publication of this document.
Table 1 summarizes current practices for Android and iOS at the time
of writing this document (the original source is available at
[private_mac]) and also includes updates based on findings from the
authors.
+=============================================+===================+
| Android 10+ | iOS 14+ |
+=============================================+===================+
| The randomized MAC address is bound to the | The randomized |
| SSID. | MAC address is |
| | bound to the |
| | Basic SSID. |
+---------------------------------------------+-------------------+
| The randomized MAC address is stable across | The randomized |
| reconnections for the same network. | MAC address is |
| | stable across |
| | reconnections for |
| | the same network. |
+---------------------------------------------+-------------------+
| The randomized MAC address does not get re- | The randomized |
| randomized when the device forgets a Wi-Fi | MAC address is |
| network. | reset when the |
| | device forgets a |
| | Wi-Fi network. |
+---------------------------------------------+-------------------+
| MAC address randomization is enabled by | MAC address |
| default for all the new Wi-Fi networks. | randomization is |
| But if the device previously connected to a | enabled by |
| Wi-Fi network identifying itself with the | default for all |
| real MAC address, no randomized MAC address | the new Wi-Fi |
| will be used (unless manually enabled). | networks. |
+---------------------------------------------+-------------------+
Table 1: Android and iOS MAC Address Randomization Practices
In September 2021, we performed some additional tests to evaluate how
OSes that are widely used behave regarding MAC address randomization.
Table 2 summarizes our findings; the rows in the table show whether
the OS performs address randomization per network (PNGM according to
the taxonomy introduced in Section 6), performs address randomization
per new connection (PSGM), performs address randomization daily (PPGM
with a period of 24 hours), supports configuration per SSID, supports
address randomization for scanning, and supports address
randomization for scanning by default.
+=================+===============+=========+=========+=====+
| OS | Linux (Debian | Android | Windows | iOS |
| | "bookworm") | 10 | 10 | 14+ |
+=================+===============+=========+=========+=====+
| Random Random. per net. | Y | Y | Y | Y |
| net. (PNGM) | | | | |
+-----------------+---------------+---------+---------+-----+
| Random Random. per | Y | N | N | N |
| connec. (PSGM) | | | | |
+-----------------+---------------+---------+---------+-----+
| Random Random. daily | N | N | Y | N |
| (PPGM) | | | | |
+-----------------+---------------+---------+---------+-----+
| SSID config. | Y | N | N | N |
+-----------------+---------------+---------+---------+-----+
| Random. for | Y | Y | Y | Y |
| scan | | | | |
+-----------------+---------------+---------+---------+-----+
| Random. for | N | Y | N | Y |
| scan by default | | | | |
+-----------------+---------------+---------+---------+-----+
Table 2: Observed Behavior in Different OSes (as of
September 2021)
According to [privacy_android], starting with Android 12, Android
uses non-persistent randomization in the following situations:
* A network suggestion application specifies that non-persistent
randomization be used for the network (through an API).
* The network is an open network that hasn't encountered a captive
portal, and an internal config option is set to do so (by default,
it is not).
8. IANA Considerations
This document has no IANA actions.
9. Security Considerations
Privacy considerations regarding tracking the location of a user
through the MAC address of a device are discussed throughout this
document. Given the informational nature of this document, no
protocols/solutions are specified, but the current state of affairs
is documented.
Any future specification in this area would need to look into
security and privacy aspects, such as (but not limited to) the
following:
* Mitigating the problem of location privacy while minimizing the
impact on upper layers of the protocol stack
* Providing the means for network operators to authenticate devices
and authorize network access, despite the MAC addresses changing
according some pattern
* Providing the means for the device not to use MAC addresses that
it is not authorized to use or that are currently in use
A major conclusion of the work in IEEE Std 802E [IEEE_802E] concerned
the difficulty of defending privacy against adversaries of any
sophistication. Individuals can be successfully tracked by
fingerprinting, using aspects of their communication other than MAC
addresses or other permanent identifiers.
10. Informative References
[contact_tracing_paper]
Leith, D. J. and S. Farrell, "Contact Tracing App Privacy:
What Data Is Shared By Europe's GAEN Contact Tracing
Apps", IEEE INFOCOM 2021 - IEEE Conference on Computer
Communications, DOI 10.1109/INFOCOM42981.2021.9488728, May
2021, <https://ieeexplore.ieee.org/document/9488728>.
[CSCN2015] Bernardos, CJ., Zúñiga, JC., and P. O'Hanlon, "Wi-Fi
Internet Connectivity and Privacy: Hiding your tracks on
the wireless Internet", 2015 IEEE Conference on Standards
for Communications and Networking (CSCN),
DOI 10.1109/CSCN.2015.7390443, October 2015,
<https://doi.org/10.1109/CSCN.2015.7390443>.
[enhancing_location_privacy]
Gruteser, M. and D. Grunwald, "Enhancing Location Privacy
in Wireless LAN Through Disposable Interface Identifiers:
A Quantitative Analysis", Mobile Networks and
Applications, vol. 10, no. 3, pp. 315-325,
DOI 10.1007/s11036-005-6425-1, June 2005,
<https://doi.org/10.1007/s11036-005-6425-1>.
[IEEE_802] IEEE, "IEEE Standard for Local and Metropolitan Area
Networks: Overview and Architecture", IEEE Std 802-2014,
DOI 10.1109/IEEESTD.2014.6847097, June 2014,
<https://doi.org/10.1109/IEEESTD.2014.6847097>.
[IEEE_802.11aq]
IEEE, "IEEE Standard for Information technology--
Telecommunications and information exchange between
systems Local and metropolitan area network--Specific
requirements Part 11: Wireless LAN Medium Access Control
(MAC) and Physical Layer (PHY) Specifications Amendment 5:
Preassociation Discovery", IEEE Std 802.11aq-2018,
DOI 10.1109/IEEESTD.2018.8457463, August 2018,
<https://doi.org/10.1109/IEEESTD.2018.8457463>.
[IEEE_802.15.4]
IEEE, "IEEE Standard for Low‐Rate Wireless Networks", IEEE
Std 802.15.4-2024, DOI 10.1109/IEEESTD.2024.10794632,
December 2024,
<https://doi.org/10.1109/IEEESTD.2024.10794632>.
[IEEE_802.1AB]
IEEE, "IEEE Standard for Local and metropolitan area
networks - Station and Media Access Control Connectivity
Discovery", IEEE Std 802.1AB-2016,
DOI 10.1109/IEEESTD.2016.7433915, March 2016,
<https://doi.org/10.1109/IEEESTD.2016.7433915>.
[IEEE_802.1AEdk]
IEEE, "IEEE Standard for Local and metropolitan area
networks-Media Access Control (MAC) Security - Amendment
4: MAC Privacy protection", IEEE Std 802.1AEdk-2023,
DOI 10.1109/IEEESTD.2023.10225636, August 2023,
<https://doi.org/10.1109/IEEESTD.2023.10225636>.
[IEEE_802.1D]
IEEE, "IEEE Standard for Local and metropolitan area
networks: Media Access Control (MAC) Bridges", IEEE Std
802.1D-2004, DOI 10.1109/IEEESTD.2004.94569, June 2004,
<https://ieeexplore.ieee.org/document/1309630>.
<https://doi.org/10.1109/IEEESTD.2004.94569>.
[IEEE_802c]
IEEE, "IEEE Standard for Local and Metropolitan Area
Networks:Overview and Architecture--Amendment 2: Local
Medium Access Control (MAC) Address Usage", IEEE Std 802c-
2017, DOI 10.1109/IEEESTD.2017.8016709, August 2017,
<https://doi.org/10.1109/IEEESTD.2017.8016709>.
[IEEE_802E]
IEEE, "IEEE Recommended Practice for Privacy
Considerations for IEEE 802(R) Technologies", IEEE Std
802E-2020, DOI 10.1109/IEEESTD.2020.9257130, November
2020, <https://doi.org/10.1109/IEEESTD.2020.9257130>.
[ieee_privacy_ecsg]
IEEE 802 LAN/MAN Standards Committee, "IEEE 802 EC Privacy
Recommendation Study Group",
<http://www.ieee802.org/PrivRecsg/>.
[link_layer_privacy]
O'Hanlon, P., Wright, J., and I. Brown, "Privacy at the
link-layer", W3C/IAB workshop on Strengthening the
Internet Against Pervasive Monitoring (STRINT), February
2014.
[OS_current_practices]
"OS current practices", commit 795739b, July 2024,
<https://github.com/ietf-wg-madinas/draft-ietf-madinas-
mac-address-randomization/blob/main/OS-current-
practices.md>.
[privacy_android]
Android Open Source Project, "MAC randomization behavior",
Android OS Documentation,
<https://source.android.com/devices/tech/connect/wifi-mac-
randomization-behavior>.
[privacy_ios]
Apple Inc., "Use private Wi-Fi addresses on Apple
Devices", Apple Support,
<https://support.apple.com/en-us/102509>.
[privacy_tutorial]
Cooper, A., Hardie, T., Zuniga, JC., Chen, L., and P.
O'Hanlon, "Pervasive Surveillance of the Internet -
Designing Privacy into Internet Protocols", IEEE 802
Tutorial, 14 July 2014, <https://mentor.ieee.org/802-
ec/dcn/14/ec-14-0043-01-00EC-internet-privacy-
tutorial.pdf>.
[privacy_windows]
Microsoft Corporation, "How to use random hardware
addresses in Windows", Microsoft Support,
<https://support.microsoft.com/en-us/windows/how-to-use-
random-hardware-addresses-ac58de34-35fc-31ff-
c650-823fc48eb1bc>.
[private_mac]
Pantaleone, D., "Private MAC address on iOS 14", Wayback
Machine archive, September 2020,
<https://web.archive.org/web/20230905111429/
https://www.fing.com/news/private-mac-address-on-ios-14>.
[rcm_privacy_csd]
IEEE 802.11 WG RCM SG, "IEEE 802.11 Randomized And
Changing MAC Addresses Study Group CSD on user experience
mechanisms", doc.:IEEE 802.11-20/1346r1, 2020.
[rcm_privacy_par]
IEEE 802.11 WG RCM SG, "IEEE 802.11 Randomized And
Changing MAC Addresses Study Group PAR on privacy
mechanisms", doc.:IEEE 802.11-19/854r7, 2020.
[rcm_tig_final_report]
IEEE 802.11 WG RCM TIG, "IEEE 802.11 Randomized And
Changing MAC Addresses Topic Interest Group Report",
doc.:IEEE 802.11-19/1442r9, 2019.
[rcm_user_experience_csd]
IEEE 802.11 WG RCM SG, "IEEE 802.11 Randomized And
Changing MAC Addresses Study Group CSD on user experience
mechanisms", doc.:IEEE 802.11-20/1117r3, 2020.
[rcm_user_experience_par]
IEEE 802.11 WG RCM SG, "IEEE 802.11 Randomized And
Changing MAC Addresses Study Group PAR on user experience
mechanisms", doc.:IEEE 802.11-20/742r5, 2020.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, DOI 10.17487/RFC4291, February
2006, <https://www.rfc-editor.org/info/rfc4291>.
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862,
DOI 10.17487/RFC4862, September 2007,
<https://www.rfc-editor.org/info/rfc4862>.
[RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J.,
Morris, J., Hansen, M., and R. Smith, "Privacy
Considerations for Internet Protocols", RFC 6973,
DOI 10.17487/RFC6973, July 2013,
<https://www.rfc-editor.org/info/rfc6973>.
[RFC7217] Gont, F., "A Method for Generating Semantically Opaque
Interface Identifiers with IPv6 Stateless Address
Autoconfiguration (SLAAC)", RFC 7217,
DOI 10.17487/RFC7217, April 2014,
<https://www.rfc-editor.org/info/rfc7217>.
[RFC7844] Huitema, C., Mrugalski, T., and S. Krishnan, "Anonymity
Profiles for DHCP Clients", RFC 7844,
DOI 10.17487/RFC7844, May 2016,
<https://www.rfc-editor.org/info/rfc7844>.
[RFC8064] Gont, F., Cooper, A., Thaler, D., and W. Liu,
"Recommendation on Stable IPv6 Interface Identifiers",
RFC 8064, DOI 10.17487/RFC8064, February 2017,
<https://www.rfc-editor.org/info/rfc8064>.
[RFC8947] Volz, B., Mrugalski, T., and CJ. Bernardos, "Link-Layer
Address Assignment Mechanism for DHCPv6", RFC 8947,
DOI 10.17487/RFC8947, December 2020,
<https://www.rfc-editor.org/info/rfc8947>.
[RFC8948] Bernardos, CJ. and A. Mourad, "Structured Local Address
Plan (SLAP) Quadrant Selection Option for DHCPv6",
RFC 8948, DOI 10.17487/RFC8948, December 2020,
<https://www.rfc-editor.org/info/rfc8948>.
[RFC8981] Gont, F., Krishnan, S., Narten, T., and R. Draves,
"Temporary Address Extensions for Stateless Address
Autoconfiguration in IPv6", RFC 8981,
DOI 10.17487/RFC8981, February 2021,
<https://www.rfc-editor.org/info/rfc8981>.
[strint] W3C/IAB, "STRINT Workshop: A W3C/IAB workshop on
Strengthening the Internet Against Pervasive Monitoring
(STRINT)", <https://www.w3.org/2014/strint/>.
[wba_paper]
Wireless Broadband Alliance, "Wi-Fi Identification Scope
for Liasing - In a post MAC Randomization Era", doc.:WBA
Wi-Fi ID Intro: Post MAC Randomization Era v1.0 - IETF
liaison, March 2020.
[when_mac_randomization_fails]
Martin, J., Mayberry, T., Donahue, C., Foppe, L., Brown,
L., Riggins, C., Rye, E., and D. Brown, "A Study of MAC
Address Randomization in Mobile Devices and When it
Fails", arXiv:1703.02874v2, DOI 10.48550/arXiv.1703.02874,
March 2017, <https://doi.org/10.48550/arXiv.1703.02874>.
[wifi_tracking]
Vincent, J., "London's bins are tracking your smartphone",
The Independent, 9 August 2013,
<https://www.independent.co.uk/life-style/gadgets-and-
tech/news/updated-london-s-bins-are-tracking-your-
smartphone-8754924.html>.
Acknowledgments
The authors would like to thank Guillermo Sanchez Illan for the
extensive tests performed on different OSes to analyze their behavior
regarding address randomization.
The authors would also like to thank Jerome Henry, Hai Shalom,
Stephen Farrell, Alan DeKok, Mathieu Cunche, Johanna Ansohn
McDougall, Peter Yee, Bob Hinden, Behcet Sarikaya, David Farmer,
Mohamed Boucadair, Éric Vyncke, Christian Amsüss, Roman Danyliw,
Murray Kucherawy, and Paul Wouters for their reviews and comments on
previous draft versions of this document. In addition, the authors
would like to thank Michael Richardson for his contributions on the
taxonomy section. Finally, the authors would like to thank the IEEE
802.1 Working Group for its review and comments, performed as part of
the "Liaison statement on Randomized and Changing MAC Address"
(https://datatracker.ietf.org/liaison/1884/). comments (see
https://datatracker.ietf.org/liaison/1884/).
Authors' Addresses
Juan Carlos Zúñiga
Cisco
Montreal QC
Canada
Email: juzuniga@cisco.com
Carlos J. Bernardos (editor)
Universidad Carlos III de Madrid
Av. Universidad, 30
28911 Leganes, Madrid
Spain
Phone: +34 91624 6236
Email: cjbc@it.uc3m.es
URI: http://www.it.uc3m.es/cjbc/
Amelia Andersdotter
Safespring AB
Email: amelia.ietf@andersdotter.cc