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<rfc xmlns:xi="http://www.w3.org/2001/XInclude" category="info" docName="draft-ietf-madinas-mac-address-randomization-15"
     ipr="trust200902"> ipr="trust200902" number="9724" consensus="true" obsoletes="" updates="" submissionType="IETF" xml:lang="en" tocInclude="true" tocDepth="3" symRefs="true" sortRefs="true" version="3">

  <front>
    <title abbrev="Randomized and Changing MAC Address"> abbrev="State of Affairs for Randomized and Changing MAC Address State Addresses">State of Affairs
      </title>

    <!-- AUTHORS --> for Randomized and Changing Media Access Control (MAC) Addresses</title>
    <seriesInfo name="RFC" value="9724"/>
    <author fullname="Juan Carlos Zúñiga" initials="JC." surname="Zúñiga">
      <organization abbrev="CISCO">
        CISCO
      </organization> abbrev="Cisco">Cisco</organization>
      <address>
        <postal>
          <street></street>
          <city>Montreal</city>
          <code> QC</code>
          <region>QC</region>
          <country>Canada</country>
        </postal>
        <email>juzuniga@cisco.com</email>
      </address>
    </author>
    <author fullname="Carlos J. Bernardos" initials="CJ." surname="Bernardos" role="editor">
      <organization abbrev="UC3M">
        Universidad abbrev="UC3M">Universidad Carlos III de Madrid
      </organization> Madrid</organization>
      <address>
        <postal>
          <street>Av. Universidad, 30</street>
          <city>Leganes, Madrid</city>
          <code>28911</code>
          <country>Spain</country>
        </postal>
        <phone>+34 91624 6236</phone>
        <email>cjbc@it.uc3m.es</email>
        <uri>http://www.it.uc3m.es/cjbc/</uri>
      </address>
    </author>
    <author fullname="Amelia Andersdotter" initials="A." surname="Andersdotter">
      <organization abbrev="Safespring AB">
        Safespring AB
      </organization> AB">Safespring AB</organization>
      <address>
        <email>amelia.ietf@andersdotter.cc</email>
      </address>
    </author>
    <date year="2024"/>

    <area>Internet</area>

    <workgroup>MADINAS</workgroup> year="2025" month="January"/>
    <area>INT</area>
    <workgroup>madinas</workgroup>

    <abstract>
      <t>
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 MAC
Media Access Control (MAC) addresses.
      </t>
      <t>
There have been several initiatives within the IETF and the IEEE 802 standards
committees to overcome address some of these the privacy issues. issues involved. This document provides an
overview of these activities to help coordinating coordinate standardization activities in these bodies.
      </t>
    </abstract>
  </front>
  <middle>

<!-- BEGIN Terminology -->

    <section anchor="sec:introduction" title="Introduction"> anchor="sec_introduction" numbered="true" toc="default">
      <name>Introduction</name>

      <t>
Privacy is becoming a huge concern, as more and more devices are
getting connecting to
the Internet either directly (e.g., via Wi-Fi) or indirectly (e.g., via a
smartphone using
Bluetooth) connected to the Internet. Bluetooth). This ubiquitous connectivity, together with the
lack of proper education about privacy make 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, for instance sharing 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/MAC) Layer 2
(L2) address (i.e., MAC address) or
Layer-3 Layer 3 (L3) address, web trackers, etc.; and/or the weak (or even null in some
cases) authentication and encryption mechanisms used to secure communications. etc.
      </t>
      <t>
This privacy concern affects
Privacy concerns affect all layers of the protocol stack, from the lower
layers involved in the access to the network (e.g., the MAC/Layer-2 MAC/L2 and Layer-3 L3
addresses can be used to obtain the location of a user) to higher layer higher-layer protocol
identifiers and user applications <xref target="CSCN2015" />. format="default"/>. In
particular, IEEE 802 MAC addresses have historically been an easy target for
tracking users <xref target="wifi_tracking" />. format="default"/>.

      </t>
      <t>
There have been several initiatives at 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 coordinating coordinate standardization activities
within these bodies.
      </t>
    </section>

<!-- BEGIN Problem statement -->

    <section anchor="sec:background" title="Background"> anchor="sec_background" numbered="true" toc="default">
      <name>Background</name>
      <section anchor="sec:mac_usage" title="MAC address usage"> anchor="sec_mac_usage" numbered="true" toc="default">
        <name>MAC Address Usage</name>
        <t>
Most mobile devices used today are WLAN enabled (i.e., they are equipped with
an IEEE 802.11 wireless local area network interface). Wi-Fi interfaces, as Like any other kind of IEEE 802-based
network interface, like interface based on IEEE 802 such as Ethernet (i.e., IEEE 802.3) 802.3), Wi-Fi
interfaces have a Layer-2 an L2 address also (also referred to as a MAC address, which 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 <xref target="fig:ieee802_mac_address_format" />. target="fig_ieee802_mac_address_format" format="default"/>.
        </t>

        <figure anchor="fig:ieee802_mac_address_format" title="IEEE anchor="fig_ieee802_mac_address_format">
          <name>IEEE 802 MAC Address Format (for 48-bit addresses)" >
<artwork><![CDATA[ 48-Bit Addresses)</name>
          <artwork name="" type="" align="left" alt=""><![CDATA[
        +--------+--------+---------+--------+--------+---------+
        |  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
+--+--+--+--+--+--+--+--+
]]></artwork>
        </figure>

        <t>
MAC addresses can either be either universally administered or locally administered.
Universally administered and locally administered addresses are distinguished by
setting the second-least-significant second least significant bit of the most significant byte of the
address (the U/L bit).
        </t>
        <t>
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: (i) the Organizationally parts:</t>

<dl newline="false" spacing="normal">
  <dt>Organizationally Unique
  Identifier (OUI), which are the (OUI):</dt><dd>The first three octets in transmission order and order, which identify the organization that issued the identifier, and (ii) Network identifier.</dd>
  <dt>Network Interface
Controller (NIC) Specific, which are the Specific:</dt><dd>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.
        </t> unique.</dd>
</dl>

        <t>
Locally administered addresses override the burned-in address, and they can
either be set-up
set up by either the network administrator, administrator or by the Operating System (OS) of the
device to which the address pertains. However, as explained in further later sections
of this document, there are new initiatives at in the IEEE 802 and other
organizations to specify ways in which these locally administered addresses
should be assigned, depending on the use case.
        </t>
      </section>
<!-- END Problem statement -->

<!-- BEGIN MAC address randomization -->

    <section anchor="sec:mac_addr_random" title="MAC address randomization"> anchor="sec_mac_addr_random" numbered="true" toc="default">
        <name>MAC Address Randomization</name>
        <t>
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 -- especially over the air- 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 <xref target="link_layer_privacy"/>. target="link_layer_privacy" format="default"/>.
        </t>

        <t>
MAC addresses can be easily observed by a third party, such as a passive device
listening to communications in the same layer-2 L2 network. In an 802.11 network, a station (STA)
exposes its MAC address in two different situations:
        </t>

<t><list style="symbols">
        <ul spacing="normal">
          <li>

            <t>
While actively scanning for available networks, the MAC address is used in the
Probe Request frames sent by the device (a.k.a. IEEE 802.11 STA). device.
            </t>
          </li>
          <li>
            <t>
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.
            </t>
</list></t>
          </li>
        </ul>
        <t>
One way to overcome address this privacy concern is by using randomly generated MAC
addresses. The IEEE 802 addressing includes one bit to specify if the hardware
address is locally or globally administered. This allows generating local
addresses to be generated without the need of 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 <xref target="enhancing_location_privacy" />. format="default"/>.
        </t>
        <t>
Note that there are reports <xref target="contact_tracing_paper" /> format="default"/> of some
mobile Operating Systems (OSes) OSes reporting persistently (every 20 minutes or so)
on MAC addresses (among (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 privacy-preserving techniques should be conducted while considering
all layers of the protocol stack.
        </t>
      </section>
      <section anchor="sec:mac_addr_experiments" title="Privacy anchor="sec_mac_addr_experiments" numbered="true" toc="default">
        <name>Privacy Workshop, Tutorial Tutorial, and Experiments at IETF and IEEE 802 meetings"> Meetings</name>
        <t>
As an outcome to the STRINT W3C/IAB Workshop <xref target="strint" />, format="default"/>, a
tutorial on titled "Pervasive Surveillance of the Internet - Designing Privacy into
Internet Protocols" <xref target="privacy_tutorial" format="default"/> was given at the IEEE 802 Plenary meeting in San Diego <xref
target="privacy_tutorial" /> in July of 2014. The tutorial provided an update on
the recent developments regarding Internet privacy, the actions undertaken by
other SDOs such as 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 <xref target="RFC6973" />). format="default"/>). The
tutorial highlighted some privacy concerns applicable that apply specifically to link-layer
technologies and provided suggestions on how IEEE 802 could help addressing address
them.
        </t>

        <t>
Following the discussions and interest within the IEEE 802 community, on 18 July
2014
2014, the IEEE 802 Executive Committee (EC) created an the IEEE 802 EC Privacy
Recommendation Study Group (SG) <xref target="ieee_privacy_ecsg" />. format="default"/>. 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
<xref target="IEEE_802E" />, format="default"/>, and the 802c PAR: Standard for Local and
Metropolitan Area Networks - Overview and Architecture Amendment - Amendment 2: Local Medium
Access Control (MAC) Address Usage <xref target="IEEE_802c" />. format="default"/>.
        </t>

        <t>
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 - IETF91,
IETF92 -- 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: (i) (1) the
effect on the connectivity experience of the end-user, also checking if end user, as well as any effect on
applications and OSes were affected; OSes, and (ii) (2) the potential impact on the
network infrastructure itself. Some of the findings were published in <xref target="CSCN2015" />. format="default"/>.
        </t>

        <t>
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 still track an individual. Hence, effective privacy tools should not
work in isolation at a single layer, but layer; instead; they should be coordinated with other
privacy features at higher layers.
        </t>
        <t>
Since then, MAC address randomization has further been further implemented by mobile OSes to
provide better privacy for mobile phone users when connecting to public wireless
networks <xref target="privacy_ios" />, format="default"/> <xref target="privacy_windows" />, format="default"/> <xref target="privacy_android" />. format="default"/>.
        </t>
      </section>
<!-- END L2 address randomization -->

    </section>

<!-- BEGIN Tools -->

    <section anchor="sec:mac_rnd_at_ieee802" title="Randomized anchor="sec_mac_rnd_at_ieee802" numbered="true" toc="default">
      <name>Activities Relating to Randomized and Changing MAC addresses activities at Addresses in the IEEE 802"> 802</name>
      <t>
Practical experiences of with Randomized and Changing MAC addresses (RCM) addresses in
devices (some of them which are explained in Section <xref target="rcm-types" />)
format="default"/>) helped researchers fine-tune their understanding of
attacks against randomization mechanisms <xref
target="when_mac_randomization_fails" />. At format="default"/>. Within the IEEE
802.11 group group, these research experiences eventually formed the basis for a
specified mechanism that randomizes MAC addresses, which was introduced in the
IEEE Std 802.11aq in 2018 which randomize MAC
addresses <xref target="IEEE_802_11_aq" />. target="IEEE_802.11aq" format="default"/> in 2018.
      </t>

      <t>
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 <xref target="rcm_user_experience_csd" />. format="default"/>. 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<xref 2019 <xref target="rcm_tig_final_report" />. format="default"/>. In the summer of 2020 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 <xref target="rcm_user_experience_par" /> format="default"/> and user privacy solutions applicable to
IEEE Std 802.11 <xref target="rcm_privacy_par" />. format="default"/>.
      </t>
      <t>
IEEE Std 802 <xref target="IEEE_802" />, format="default"/>, as of the amendment IEEE 802c-2017
<xref target="IEEE_802c" />, format="default"/>, specifies a local MAC address space structure known
as the Structured Local Address Plan (SLAP) <xref target="RFC8948" />. format="default"/>. 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 Identifiers, which are subject to assignment
by a network administrator.
      </t>

      <t>
"IEEE
IEEE Std 802E-2020: 802E-2020 ("IEEE Recommended Practice for Privacy Considerations for IEEE 802
Technologies" 802(R)
Technologies") <xref target="IEEE_802E" /> format="default"/> 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 (a.k.a. Wi-Fi) devices (also known as Wi-Fi devices) as
part of the RCM efforts <xref target="rcm_privacy_csd" /> efforts. format="default"/>. Annex T of IEEE Std
802.1AEdk-2023: MAC
802.1AEdk-2023 ("MAC Privacy Protection Protection") <xref target="IEEE802.1AEdk-2023" /> target="IEEE_802.1AEdk" format="default"/>
discusses privacy considerations in bridged networks.
</t>
      <t>
As per of 2024, two task groups in IEEE 802.11 are dealing with issues related to RCM:

  <list style="symbols"> RCM addresses:

      </t>
      <ul spacing="normal">
        <li>
          <t>
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, and services.
          </t>
        </li>
        <li>

          <t>
The IEEE 802.11bi task group, which is chartered to define modifications to the IEEE Std
802.11 medium access control (MAC) MAC specification to specify new mechanisms that
address and improve user privacy.
          </t>

  </list>

</t>
        </li>
      </ul>
    </section>
<!-- END Tools -->

    <section anchor="sec:wba" title="Recent anchor="sec_wba" numbered="true" toc="default">

      <name>Recent Activities Related to MAC randomization-related activities at Address Randomization in the WBA"> WBA</name>
      <t>
At
In the Wireless Broadband Alliance (WBA), the Testing and Interoperability Work
Group has been looking at the 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.
      </t>

      <t>
   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
   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 <xref target="wba_paper" />. format="default"/>, was created while
   liaising with the IETF MADINAS Working Group.
      </t>
    </section>

<!-- BEGIN Evaluation -->

    <section anchor="sec:mac_rnd_at_ietf" title="IPv6 address randomization at anchor="sec_mac_rnd_at_ietf" numbered="true" toc="default">
      <name>IPv6 Address Randomization in the IETF"> IETF</name>
      <t>
<xref target="RFC4862" /> format="default"/> 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, router and an
Interface Identifier (IID). <xref target="RFC8064" /> format="default"/> 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-based IID, address, made it easier to perform global device
tracking.
      </t>

      <t>
<xref target="RFC8981" /> format="default"/> identifies and describes the privacy
issues associated with embedding MAC stable addressing information into the IPv6
addresses (as part of the IID). It describes an extension to IPv6 SLAAC that
causes hosts to generate temporary addresses with randomized interface identifiers 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 would then be deprecated. Deprecated addresses can
continue to be used for already established
connections, 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 interface identifiers 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, 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 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, and this which might be an issue in certain
networks where addresses are used for operational purposes (e.g., filtering or
authentication). <xref target="RFC7217" />, format="default"/>, summarized next,
partially addresses the problems aforementioned.
      </t>
      <t>
<xref target="RFC7217" /> format="default"/> describes a method to generate Interface Identifiers IIDs
that are stable for each network interface within each subnet, subnet but that change
as a host moves from one network to another. This method enables keeping the
"stability" properties of the Interface Identifiers IIDs specified in <xref target="RFC4291" />, format="default"/> 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 which that takes the following as input input: information that is stable and associated to
the interface (e.g., a local interface identifier), IID), stable information
associated to the visited network (e.g., the IEEE 802.11 SSID), Service Set Identifier (SSID)), the IPv6 prefix, and
a secret key, plus and some other additional information. This basically ensures
that a different IID is generated when any one of the input fields changes (such as
the network or the prefix), prefix) but that the IID is the same within each subnet.
      </t>
      <t>
Currently,
To mitigate the privacy threats posed by the use of MAC-derived
IIDs, <xref target="RFC8064" /> format="default"/> recommends that nodes to implement <xref target="RFC7217" /> format="default"/> as the default scheme for generating stable IPv6 addresses
with SLAAC, to mitigate the privacy threats posed by the use of MAC-derived
IIDs. SLAAC.
      </t>

      <t>
In addition to the former documents, documents above, <xref target="RFC8947" /> format="default"/>
      proposes "an extension to a DHCPv6 that extension that:</t>
<blockquote>
      allows a scalable approach to link-layer
address assignments where preassigned link-layer address assignments (such as by
a manufacturer) are not possible or unnecessary". are unnecessary.
</blockquote>

<t>And <xref target="RFC8948" /> format="default"/> proposes "extensions to DHCPv6 protocols
to extensions that:</t>

<blockquote>
enable a DHCPv6 client or a DHCPv6 relay to indicate a preferred SLAP
quadrant to the server, server so that the server may allocate MAC addresses in the
quadrant requested by the relay or client".
      </t> client.
</blockquote>

<t>
Not only
     In addition to MAC and IP addresses addresses, some DHCP options that carry unique
     identifiers can also be used for tracking purposes. Some DHCP
options carry unique identifiers.  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. <xref target="RFC7844" /> format="default"/> introduces
     anonymity profiles, "designed profiles that are:</t>

<blockquote>
designed for clients that
wish to remain anonymous to the visited network. The profiles network
</blockquote>
<t>and that:</t>
<blockquote>
provide guidelines
on the composition of DHCP or DHCPv6 messages, designed to minimize disclosure
of identifying information". <xref information.
</blockquote>

<t><xref target="RFC7844" /> format="default"/> also indicates that the
link-layer address, IP address, and DHCP identifier shall evolve in synchrony.
      </t>

<!--
      <t>
Lately, the MAC Address Device Identification for Network and Application Services (MADINAS) IETF BoF
has discussed the need to examine the effect of RCM schemes on network and application services in several
scenarios identified as relevant.
      </t>
-->

    </section>
<!-- END Evaluation -->

    <section anchor="rcm-types" title="A taxonomy numbered="true" toc="default">
      <name>Taxonomy of MAC address selection
                                       policies"> Address Selection Policies</name>
      <t>
This section documents different policies for MAC address selection. Some OSes
might use a combination of multiple of these policies.
      </t>

      <t>
      <aside><t>
        Note about the used naming convention: the convention used: The "M" in MAC "MAC" is included in the
acronym,
acronym but not the "A" from address. "Address". This allows one to talk about a PVOM
Address, "PVOM
address" or PNGM Address.
      </t> "PNGM address".
      </t></aside>
      <t>
       <!-- The names are all in the form for per-period-of-time-selection. -->

      </t>
      <section anchor="policy-pvom" title="Per-Vendor numbered="true" toc="default">
        <name>Per-Vendor OUI MAC address (PVOM)"> (PVOM) Address</name>
        <t>
          This form of MAC address selection is the historical default.
        </t>

	<t>
          The vendor obtains an Organizationally Unique Identifier (OUI) OUI from the IEEE.
          This has been is a 24-bit prefix (including two upper bits which that are
          set specifically) that is assigned to the vendor.
          The vendor generates a unique 24-bit value for the lower 24-bits, 24 bits,
          forming the 48-bit MAC address.
   It has is not been 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.
        </t>
        <t>
          Note that IEEE Std 802.15.4 use <xref target="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 using that uses 64-bit MAC addresses.
        </t>
      </section>
      <section anchor="policy-pdgm" title="Per-Device numbered="true" toc="default">
        <name>Per-Device Generated MAC address (PDGM)"> (PDGM) Address</name>
        <t>
          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.
        </t>
      </section>
      <section anchor="policy-pbgm" title="Per-Boot numbered="true" toc="default">
        <name>Per-Boot Generated MAC address (PBGM)"> (PBGM) Address</name>

        <t>
          This form of MAC address is randomly generated by the device, device each
          time the device is booted.

          The resulting MAC address is *not* <strong>not</strong> 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).
        </t>
      </section>
      <section anchor="policy-pngm" title="Per-Network numbered="true" toc="default">
        <name>Per-Network Generated MAC address (PNGM)"> (PNGM) Address</name>
        <t>
          This form of MAC address is generated each time a new network
          attachment is created.
        </t>

        <t>
          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 on 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.
        </t>

        <t>
          It is possible to use a PNGM address for wired Ethernet connections through
          some passive observation of network traffic, such traffic (such as STP the Spanning Tree Protocol (SPT) <xref target="IEEE802.1D-2004" />, LLDP target="IEEE_802.1D" format="default"/>, the Link Layer Discovery Protocol (LLDP) <xref target="IEEE802.1AB-2016" />,
          DHCP target="IEEE_802.1AB" format="default"/>,
          DHCP, or Router Advertisements Advertisements) to determine which network has been
          attached.
        </t>
      </section>
      <section anchor="policy-ppgm" title="Per-Period numbered="true" toc="default">
        <name>Per-Period Generated MAC address (PPGM)"> (PPGM) Address</name>
        <t>
          This form of MAC address is generated periodically.
          Typical numbers are periodically,
          typically around every twelve hours.
          Like PNGM, PNGM addresses, it is used primarily with Wi-Fi.
        </t>

        <t>
          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 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).

        </t>
        <t>
          If DHCP is used, then a new DUID DHCP Unique Identifier (DUID) is generated so as to not link to
          the previous connection, and the result is connection; this usually results in the allocation of new IP addresses
          allocated. addresses.
        </t>
      </section>
      <section anchor="policy-psgm" title="Per-Session numbered="true" toc="default">
        <name>Per-Session Generated MAC address (PSGM)"> (PSGM) Address</name>

        <t>
          This form of MAC address is generated on a per session per-session basis. How a session is defined is implementation-dependant, implementation-dependent, for example, a session might be defined by logging in to a portal, VPN, etc. Like PNGM, PNGM and PPGM addresses, it is used primarily with Wi-Fi.
        </t>
        <t>
          Since the address changes only changes when a new session is established, there is no disconnection/reconnection involved.
        </t>
      </section>
    </section>

<!-- BEGIN OSes current practices -->

      <section anchor="sec:os_current_practices" title="OS current practices">

<!-- anchor="sec_os_current_practices" numbered="true" toc="default">
      <name>OS Current Practices</name>

        <t>
Since this content can evolve with time, it is now hosted at <eref target="https://github.com/ietf-wg-madinas/draft-ietf-madinas-mac-address-randomization/blob/main/OS-current-practices.md" />
        </t>
-->

        <t>
Most
By default, most modern OSes (especially mobile ones) do implement by default some MAC
address randomization policy. policies. Since the mechanism and policies that OSes implement can evolve with time, the content is now hosted at <eref target="https://github.com/ietf-wg-madinas/draft-ietf-madinas-mac-address-randomization/blob/main/OS-current-practices.md" />. <xref target="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.
      </t>
      <t>

<xref target="tab:current_practices" /> target="tab_current_practices" format="default"/> summarizes current
practices for Android and iOS, as iOS at the time of writing this document
(original (the original source posted at: https://www.fing.com/news/private-mac-address-on-ios-14, latest wayback machine's
snapshot is available here: https://web.archive.org/web/20230905111429/https://www.fing.com/news/private-mac-address-on-ios-14,
updated
at <xref target="private_mac"/>) and also includes
updates based on findings from the authors). authors.
      </t>

        <texttable anchor="tab:current_practices"
                   title="Android
      <table anchor="tab_current_practices" align="center">
        <name>Android and iOS MAC address randomization practices">
          <ttcol width="50%" Address Randomization Practices</name>
        <thead>
          <tr>
            <th align="left">Android 10+</ttcol>
          <ttcol width="50%" 10+</th>
            <th align="left">iOS 14+</ttcol>
            <c>The 14+</th>
          </tr>
        </thead>
        <tbody>
          <tr>
            <td align="left">The randomized MAC address is bound to the SSID</c>
            <c>The SSID.</td>
            <td align="left">The randomized MAC address is bound to the Basic SSID</c>
            <c></c>
            <c></c>
            <c>The SSID.</td>
          </tr>
          <tr>
            <td align="left">The randomized MAC address is stable across reconnections for the same network</c>
            <c>The network.</td>
            <td align="left">The randomized MAC address is stable across reconnections for the same network</c>
            <c></c>
            <c></c>
            <c>The network.</td>
          </tr>
          <tr>
            <td align="left">The randomized MAC address does not get re-randomized when the device forgets a WiFI network</c>
            <c>The Wi-Fi network.</td>
            <td align="left">The randomized MAC address is reset when the device forgets a WiFI network</c>
            <c></c>
            <c></c>
            <c>MAC Wi-Fi network.</td>
          </tr>
          <tr>
            <td align="left">MAC address randomization is enabled by default for all the new Wi-Fi networks. But if the device previously connected to a Wi-Fi network identifying itself with the real MAC address, no randomized MAC address will be used (unless manually enabled)</c>
            <c>MAC enabled).</td>
            <td align="left">MAC address randomization is enabled by default for all the new Wi-Fi networks</c>
        </texttable> networks.</td>
          </tr>
        </tbody>
      </table>
      <t>
In September 2021, we have performed some additional tests to evaluate how most OSes
that are widely used OSes behave regarding MAC address randomization. <xref
target="tab:experiments-2021" />
target="tab_experiments-2021" format="default"/> summarizes our findings, where show on
different findings;
the rows in the table show whether the OS performs address randomization per
network (PNGM according to the taxonomy introduced in <xref target="rcm-types" />),
format="default"/>), performs address randomization per new connection (PSGM), performs address randomization daily (PPGM with a period of 24h),
24 hours), supports configuration per SSID, supports address randomization for
scanning, and whether it does that supports address randomization for scanning by default.
      </t>

        <texttable anchor="tab:experiments-2021"
                   title="Observed behavior from different OS
      <table anchor="tab_experiments-2021" align="center">
        <name>Observed Behavior in Different OSes (as of September 2021)">
          <ttcol width="35%" align="left">OS</ttcol>
          <ttcol width="15%" 2021)</name>
        <thead>
          <tr>
            <th align="left">OS</th>
            <th align="center">Linux (Debian "bookworm")</ttcol>
          <ttcol width="20%" "bookworm")</th>
            <th align="center">Android 10</ttcol>
          <ttcol width="20%" 10</th>
            <th align="center">Windows 10</ttcol>
          <ttcol width="10%" 10</th>
            <th align="center">iOS 14+</ttcol>
            <c>Random 14+</th>
          </tr>
        </thead>
        <tbody>
          <tr>
            <td align="left">Random. per net. (PNGM)</c><c>Y</c><c>Y</c><c>Y</c><c>Y</c>
            <c></c><c></c><c></c><c></c><c></c>
            <c>Random (PNGM)</td>
            <td align="center">Y</td>
            <td align="center">Y</td>
            <td align="center">Y</td>
            <td align="center">Y</td>
          </tr>
          <tr>
            <td align="left">Random. per connec. (PSGM)</c><c>Y</c><c>N</c><c>N</c><c>N</c>
            <c></c><c></c><c></c><c></c><c></c>
            <c>Random (PSGM)</td>
            <td align="center">Y</td>
            <td align="center">N</td>
            <td align="center">N</td>
            <td align="center">N</td>
          </tr>
          <tr>
            <td align="left">Random. daily (PPGM)</c><c>N</c><c>N</c><c>Y</c><c>N</c>
            <c></c><c></c><c></c><c></c><c></c>
            <c>SSID config.</c><c>Y</c><c>N</c><c>N</c><c>N</c>
            <c></c><c></c><c></c><c></c><c></c>
            <c>Random. for scan</c><c>Y</c><c>Y</c><c>Y</c><c>Y</c>
            <c></c><c></c><c></c><c></c><c></c>
            <c>Random. (PPGM)</td>
            <td align="center">N</td>
            <td align="center">N</td>
            <td align="center">Y</td>
            <td align="center">N</td>
          </tr>
          <tr>
            <td align="left">SSID config.</td>
            <td align="center">Y</td>
            <td align="center">N</td>
            <td align="center">N</td>
            <td align="center">N</td>
          </tr>
          <tr>
            <td align="left">Random. for scan</td>
            <td align="center">Y</td>
            <td align="center">Y</td>
            <td align="center">Y</td>
            <td align="center">Y</td>
          </tr>
          <tr>
            <td align="left">Random. for scan by default</c><c>N</c><c>Y</c><c>N</c><c>Y</c>
        </texttable> default</td>
            <td align="center">N</td>
            <td align="center">Y</td>
            <td align="center">N</td>
            <td align="center">Y</td>
          </tr>
        </tbody>
      </table>
      <t>
According to <xref target="privacy_android"/>, target="privacy_android" format="default"/>, starting in with Android 12, Android
      uses non-persistent randomization in the following situations: (i) a </t>
<ul spacing="normal">
      <li>A network
suggestion app application specifies that non-persistant non-persistent randomization be used for the
      network (through an API); or (ii) the API).</li>
      <li>The network is an open network that hasn't
encountered a captive portal portal, and an internal config option is set to do so (by
default
default, it is not).
      </t> not).</li>
      </ul>
    </section>
<!-- END OSes current practices -->

    <section anchor="IANA" title="IANA Considerations"> numbered="true" toc="default">
      <name>IANA Considerations</name>
      <t>
This document has no IANA actions.
      </t>
    </section>
    <section anchor="Security" title="Security Considerations"> numbered="true" toc="default">
      <name>Security Considerations</name>
      <t>
Privacy considerations regarding tracking the location of a user through the MAC
address of this 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.
      </t>

      <t>
Any future specification in this area would have need to look into security and
privacy aspects, such as, but as (but not limited to: i) mitigating to) the following:</t>
<ul spacing="normal">
<li>Mitigating the problem of
location privacy while minimizing the impact on upper layers of the protocol
stack; ii) providing
stack</li>
<li>Providing the means to for network operators to authenticate devices
and authorize network access access, despite the MAC addresses changing following according
some
pattern; and, iii) provide pattern</li>
<li>Providing the means for the device not to use MAC
addresses that it is not authorized to use or that are currently in use.
      </t> use</li>
      </ul>

      <t>
A major conclusion of the work in IEEE Std 802E <xref target="IEEE_802E" format="default"/> concerned the difficulty of
defending privacy against adversaries of any sophistication. Individuals can be successfully tracked by fingerprinting fingerprinting,
using aspects of their communication other than MAC Addresses addresses or other permanent
identifiers.
      </t>
    </section>

    <section anchor="Acknowledgments" title="Acknowledgments">

      <t>
Authors would like to thank Guillermo Sanchez Illan for the extensive tests
performed on different OSes to analyze their behavior regarding address
randomization.
      </t>

      <t>
Authors would like to thank Jerome Henry, Hai Shalom, Stephen Farrel, Alan
DeKok, Mathieu Cunche, Johanna Ansohn McDougall, Peter Yee, Bob Hinden, Behcet
Sarikaya, David Farmer, Mohamed Boucadair, Éric Vyncke, Christian Amsüss, Roma Danyliw, Murray Kucherawy and Paul Wouters for their reviews and comments on
previous versions of this document. Authors would also like to thank Michael
Richardson for his contributions on the taxonomy section. Finally, authors would
also 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/).
      </t>

    </section>
  </middle>
  <back>

<!--    <references title="Normative References">
      &rfc2119;
    </references> -->

    <references title="Informative References">

      &rfc4862;
      &rfc6973;
      &rfc7217;
      &rfc8947;
      &rfc8948;
      &rfc7844;
      &rfc8981;
      &rfc4291;
      &rfc8064;

    <references>
      <name>Informative References</name>
      <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.4862.xml"/>
      <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.6973.xml"/>
      <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.7217.xml"/>
      <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8947.xml"/>
      <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8948.xml"/>
      <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.7844.xml"/>
      <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8981.xml"/>
      <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.4291.xml"/>
      <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8064.xml"/>

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    <section anchor="Acknowledgments" numbered="false" toc="default">
      <name>Acknowledgments</name>
      <t>
The authors would like to thank <contact fullname="Guillermo Sanchez Illan"/> for the extensive tests
performed on different OSes to analyze their behavior regarding address
randomization.
      </t>

      <t>
The authors would also like to thank <contact fullname="Jerome Henry"/>, <contact fullname="Hai Shalom"/>, <contact fullname="Stephen Farrell"/>, <contact fullname="Alan
DeKok"/>, <contact fullname="Mathieu Cunche"/>, <contact fullname="Johanna Ansohn McDougall"/>, <contact fullname="Peter Yee"/>, <contact fullname="Bob Hinden"/>, <contact fullname="Behcet
Sarikaya"/>, <contact fullname="David Farmer"/>, <contact fullname="Mohamed Boucadair"/>, <contact fullname="Éric Vyncke"/>, <contact fullname="Christian Amsüss"/>, <contact fullname="Roman Danyliw"/>, <contact fullname="Murray Kucherawy"/>, and <contact fullname="Paul Wouters"/> for their reviews and comments on
previous draft versions of this document. In addition, the authors would like to thank <contact fullname="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 (see <eref target="https://datatracker.ietf.org/liaison/1884/"/>).
      </t>
    </section>

  </back>

</rfc>