Internet Engineering Task Force J. Henry
Internet-Draft Cisco Systems
Intended status: Informational Y. Lee
Expires: 9 September 2021 Comcast
8 March 2021
Randomized and Changing MAC Address Framework
draft-henry-madinas-framework-00
Abstract
To limit the association between a device traffic and its user,
client vendors have started implementing MAC address rotation. When
such rotation happens, sessions may break, which may affect network
efficiency and the user experience. This document lists network
services that may be affected by such rotation, and examines
solutions to maintain user privacy while preserving user quality of
experience and network operation efficiency.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on 9 September 2021.
Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. MAC Adress As An Identity: User vs Device . . . . . . . . . . 3
3. The Actors: Network Functional Entities and Human Entities . 5
3.1. Network Functional Entities . . . . . . . . . . . . . . . 5
3.2. Human-related Entities . . . . . . . . . . . . . . . . . 7
3.3. The Trust and the Environments . . . . . . . . . . . . . 8
3.4. The Purpose of Identification and Associated Problems . . 10
3.5. Scenario Mapping Table . . . . . . . . . . . . . . . . . 12
3.6. Problem Statments . . . . . . . . . . . . . . . . . . . . 12
3.7. Existing Solutions Directions . . . . . . . . . . . . . . 13
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
5. Security Considerations . . . . . . . . . . . . . . . . . . . 15
6. Normative References . . . . . . . . . . . . . . . . . . . . 15
7. Informative References . . . . . . . . . . . . . . . . . . . 15
Appendix A. Additional Stuff . . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16
1. Introduction
It has become easier for attackers to observe the activity of a
personal device, particularly when traffic is sent over a wireless
link. Once the association between a device and its user is made,
identifying the device and its activity is sufficient to deduce
information about what the user is doing, without the user consent.
To reduce the risks of correlation between a device activity and its
owner, multiple vendors have started to implement Randomized and
Changing Mac address (RCM). With this scheme, and end-device
implements a different RCM over time when exchanging traffic over a
wireless network. By randomizing the change, the association between
a given traffic flow and a single device is made more difficult.
However, such address change may affect the user experience and the
efficiency of network operations. For many decades, the unicity of
the association between a device and a MAC address was assumed. When
this association is broken, sessions may also break, packets in
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translation may find themselves without clear source or destination,
network services may be over-solicited by a small number of stations
that appear as many clients.
There is a need to assess how this association is made, enumerate
services that may be affected by RCM, and evaluate possible solutions
to maintain the quality of user experience and network efficiency
while RCM happens and user privacy is reinforced. This document
presents such assessment and recommendations.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
2. MAC Adress As An Identity: User vs Device
Any device member of an IEEE 802 network [IEEE.802-1D.1993] includes
several operating layers. Among them, the Media Access Control (MAC)
layer defines rules to control how the device accesses the shared
medium. In a network where a machine can communicate with one or
more other machines, one such rule is that each machine needs to be
identified, either as the target destination of a message, or as the
source of a message (and thus the target destination of the answer).
Initially intended as a 48-bit (6 octets) value, later versions of
the Standard [IEEE.802.15.4P_2014] also allowed this address to take
an extended format of 64 bits (8 octets), thus enabling a larger
number of MAC addresses to coexist as the 802 technologies became
widely adopted.
Regardless of the address length, different networks have different
needs, and several bits of the first octet are reserved for specific
purposes. In particular, the first bit is used to identify the
destination address either as an individual (bit set to 0) or a group
address (bit set to 1). The second bit, called the Universally or
Locally Administered (U/L) Address Bit, indicates whether the address
has been assigned by a local or universal administrator. Universally
administered addresses have this bit set to 0. If this bit is set to
1, the entire address (i.e., 48 bits) has been locally administered
(802-1990 5.2.1).
The intent of this provision is important for the present document.
The 802 Standard recognized that some devices may never travel and
thus, always attaching to the same network, would not need a globally
unique MAC address. To accommodate for this relaxed requirement, the
second bit of the MAC address first octet the MAC address format was
designed to express whether the address was intended to be globally
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unique, or if significance was only local. The address allocation
method was not defined in the Standard in this later case, but the
mechanism was defined in the same clause that defined that an address
should be unique so as to avoid collision.
It is also important to note that the purpose of the Universal
version of the address was also to avoid collisions and confusion, as
any machine could connect to any network, and each machine needs to
determine if it is the intended destination of a message or its
response. The same clause 5.2.1 reminds network designers and
operators that all potential members of a network need to have a
unique identifier (if they are going to coexist in the network). The
advantage of a universal address is that a node with such an address
can be attached to any LAN in the world with an assurance that its
address is unique.
With the rapid development of wireless technologies and mobile
devices, this scenario became very common. With more than 70% of 802
networks on the planet implementing radio technologies at the access,
the MAC address of a wireless device can appear anywhere on the
planet and collisions should still be avoided. However, the same
evolution brought the distinction between two types of devices that
the 802 Standard generally referred to as 'nodes in a network'.
Their definition is found in the 802E Recommended Practice (clause
6.2). One type is a shared service device, which functions are used
by a number of people large enough that the device itself, its
functions or its traffic cannot be associated with a single or small
group of people. Examples of such devices include switches in a
dense network, 802.11 (Wi-Fi) access points in a crowded airport,
task-specific (e.g. barcode scanners) devices, etc. Another type is
a personal device, which is a machine, a node, primarily used by a
single person or small group of people, and so that any
identification of the device or its traffic can also be associated to
the identification of the primary user or their traffic. Quite
naturally, the unique identification of the device is trivial if the
device expresses a universally unique MAC address. Then, the
detection of elements directly or indirectly identifying the user of
the device (Personally Identifiable Information, or PII) is
sufficient to tie the universal MAC address to a user. Then, any
detection of traffic that can be associated to the device becomes
also associated with the known user of that device (Personally
Correlated Information, or PCI).
This possible identification or association presents a serious
privacy issue, especially with wireless technologies. For most of
them, and in particular for 802.11, the source and destination MAC
addresses are not encrypted even in networks that implement
encryption (so that each machine can easily detect if it is the
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intended target of the message before attempting to decrypt its
content, and also identify the transmitter, so as to use the right
key when multiple unicast keys are in effect).
This unique identification of the user associated to a node was
clearly not the intent of the 802 MAC address. A logical solution to
remove this association is to use a locally administered address
instead, and change the address in a fashion that prevents a temporal
association between one MAC address and some PII to be maintained
fruitfully. However, other network devices on the same LAN
implementing a MAC layer also expect the unicity of the MAC address.
When a device changes its MAC address, other devices on the same LAN
may fail to recognize that the same machine is attempting to
communicate with them. Additionally, multiple layers implemented at
upper OSI layers have been designed with the assumption that each
node on the LAN, using these services, would have a unique MAC
address. This assumption sometimes adds to the PII confusion, for
example in the case of AAA services authenticating the user of a
machine and associating the authenticated user to the device MAC
address. Other services solely focus on the machine (e.g. DHCP),
but still expect each device to use a single MAC address. Changing
the MAC address may disrupt these services.
3. The Actors: Network Functional Entities and Human Entities
The risk of service disruption is thus weighted against the privacy
benefits. However, the plurality of actors involved in the exchanges
tends to blurry the boundaries of what privacy should be protected
against. It might therefore be useful to list the actors to the
network exchanges. Some actors are functional entities, some others
are humans (or related) entities.
3.1. Network Functional Entities
Wireless access network infrastructure devices (e.g. Wi-Fi access
points or controllers): these devices participate in 802 LAN
operations. As such, they need to uniquely identify machines as a
source or destination so as to successfully continue exchanging
frames. Part of the identification includes recording, and adapting
to, devices communication capabilities (e.g. support for specific
protocols). As a device changes its connection (roams) from one
access point to another, the access points can exchange contextual
information (e.g. device MAC, keying material) allowing the device
session to continue seamlessly. These access points can also inform
devices further in the wired network about the roam, to ensure that
OSI model Layer 2 frames are redirected to the new device access
point.
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Other network devices operating at the MAC layer: many wireless
network access devices (e.g. 802.11 access points) are conceived as
Layer 2 devices, and as such they bridge a frame from one medium
(e.g. 802.11 or Wi-Fi) to another (e.g. 802.3 or Ethernet). This
means that a wireless device MAC address often exists on the wire
beyond the wireless access device. Devices connected to this wire
also implement 802 technologies, and as such operate on the
expectation that each device is associated to a unique MAC address
for the duration of continuous exchanges. For example, switches and
bridges associate MAC addresses to individual ports (so as to know
which port to send a frame intended for a particular MAC address).
Similarly, authentication, authorization and accounting (AAA)
services can validate the identity of a device and use the device MAC
address as a first pointer to the device identity (before operating
further verification). 802.1X-enabled devices may also selectively
block the data portion of a port until a connecting device is
authenticated. These services then use the MAC address as a first
pointer to the device identity to allow or block data traffic. This
list is not exhaustive. Multiple services are defined for 802.3
networks, and multiple services defined by the IEEE 802.1 working
group are also applicable to 802.3 networks. Wireless access points
may also connect to other mediums than 802.3, which also implements
mechanism under the umbrella of the general 802 Standard, and
therefore expect the unique association of a MAC address to a device.
Network devices operating at upper layers: some network devices
provide functions and services above the MAC layer. Some of them
also operate a MAC layer function: for example, routers provide IP
routing services, but rely on the device MAC address to create the
appropriate frame structure. Other devices and services operate at
upper layers, but also rely on the 802 principle of unique MAC-to-
device mapping. For example, DHCPv4 services commonly provide a
single IP address per MAC address (they do not assign more than one
IPv4 address per MAC address, and assign a new IPv4 address to each
new requesting MAC address). ARP and reverse-ARP services commonly
expect that, once an IP-to-MAC mapping has been established, this
mapping is valid and unlikely to change for the cache lifetime.
DHCPv6 services commonly do not assign the same IPv6 address to two
different requesting MAC addresses. Hybrid services, such as EoIP,
also assume stability of the device-to-MAC-and-IP mapping for the
duration of a given session.
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3.2. Human-related Entities
Over the air (OTA) observers: as the transmitting or receiving MAC
address is usually not encrypted in wireless 802-technologies
exchanges, and as any protocol-compatible device in range of the
signal can read the frame header, OTA observers are able to read
individual transmissions MAC addresses. Some wireless technologies
also support techniques to establish distances or positions, allowing
the observer, in some cases, to uniquely associate the MAC address to
a physical device and it associated location. It can happen that an
OTA observer has a legitimate reason to monitor a particular device,
for example for IT support operations. However, it is difficult to
control if another actor also monitors the same station with the goal
of obtaining PII or PCI.
Wireless access network operators: some wireless access networks are
only offered to users or devices matching specific requirements, such
as device type (e.g. IoT-only networks, factory operational
networks, etc.) Therefore, operators can attempt to identify the
devices (or the users) connecting to the networks under their care.
They can use the MAC address to represent an identified device.
Network access providers: wireless access networks are often
considered beyond the first 2 Layers of the OSI model. For example,
several regulatory or legislative bodies can group all OSI layers
into their functional effect of allowing network communication
between machines. In this context, entities operating access
networks can see their liability associated to the activity of
devices communicating through the networks that these entities
operate. In other contexts, operators assign network resources based
on contractual conditions (e.g. fee, bandwidth fair share, etc.) In
these scenarios, these operators may attempt to identify the devices
and the users of their networks. They can use the MAC address to
represent an identified device.
Over the wire internal (OTWi) observers: because the device wireless
MAC address continues to be present over the wire if the
infrastructure connection device (e.g. access point) functions as a
Layer 2 bridge, observers may be positioned over the wire and read
transmission MAC addresses. Such capability supposes that the
observer has access to the wired segment of the broadcast domain
where the frames are exchanged. In most networks, such capability
requires physical access to an infrastructure wired device in the
broadcast domain (e.g. switch closet), and is therefore not
accessible to all.
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Over the wired external (OTWe) observers: beyond the broadcast
domain, frames headers are removed by a routing device, and a new
Layer 2 header is added before the frame is transmitted to the next
segment. The personal device MAC address is not visible anymore,
unless a mechanism copies the MAC address into a field that can be
read while the packet travels onto the next segment (e.g. pre-
[RFC4941] and pre- [RFC7217] IPv6 addresses built from the MAC
address). Therefore, unless this last condition exists, OTWe
observers are not able to see the device MAC address.
3.3. The Trust and the Environments
The surface of PII exposures that can drive MAC address randomization
depends on the environment where the device operates. Therefore, a
device can express an identity (such as a MAC address) that can be
stable over time if trust is established, or that can be temporal if
an identity is required for a service in an environment where trust
has not been established. Trust is not a binary currency. Thus it
is useful to distinguish what trust a personal device may establish
with the different entities at play in a L2 domain:
* 1. Full trust: there are environments where a personal device
establishes a trust relationship and can share a stable device
identity with the access network devices (access point and WLC),
the services beyond the access point in the L2 broadcast domain
(e.g. DHCP, AAA). The personal device (or its user) has
confidence that its identity is not shared beyond the L2 broadcast
domain boundary.
* 2. Selective trust: in other environments, the device may not be
willing to share a stable identity with some elements of the Layer
2 broadcast domain, but may be willing to share a stable identity
with other elements. For example, a device may want to change the
MAC address it uses to communicate with the access point while
maintaining the same IP address across the MAC address rotation
(thus expressing a stable identity to the DHCP server). That
stable identity may or may not be the same for different services.
* 3. Zero trust: in other environments, the device may not be
willing to share any stable identity with any entity reachable
through the Layer 2 broadcast domain, and may express a temporal
identity to each of them. That temporal identity may or not be
the same for different services.
This trust relationship naturally depends on the relationship between
the user of the personal device and the operator of the service.
Thus, it is useful to observ the typical trust structure of common
environments:
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* A. Residential settings under the control of the user: this is
typical of a home with Wi-Fi and Internet connection. In this
environment, the MAC address activity may be detectable beyond the
home walls. However, if traffic is encrypted (e.g. WPA3), some
protection for OTA eavesdropping can be assumed. The wire segment
within the broadcast domain is under the control of the user, and
is therefore usually not at risk of hosting an eavesdropper. Full
trust is typically established at this level. The device trusts
the access point and all L2 domain entities beyond the access
point. Traffic over the Internet does not expose the MAC address
if it is not copied to another field before routing happens.
* B. Managed residential settings: examples of this type of
environment include shared living facilities and other collective
environments where an operator manages the network for the
residents. The OTA exposure is similar to that of a home. A
number of devices larger than in a standard home may be present,
and the operator may be requested to provide IT support to the
residents. Therefore, the operator may need to identify a device
activity in real time, but may also need to analyze logs so as to
understand a past reported issue. For both activities, a device
identification associated to the session is needed. Full trust is
often established in this environment, at the scale of a series of
a few sessions.
* C. Public guest networks: public hotspots, such as in shopping
malls, hotels, stores, trains stations and airports are typical of
this environment. The guest network operator may be legally
mandated to identify devices or users or may have the option to
leave all devices and users untracked. In this environment, trust
is commonly not established with any element of the L2 broadcast
domain (Zero trust model by default).
* D. Enterprises (with BYOD): in this environment, users may be
provided corporate devices or may bring their own devices. The
devices are not directly under the control of a corporate IT team.
Trust may be established as the device joins the network. Some
enterprise models will mandate Full trust, others, considering the
BYOD nature of the device, will allow selective trust.
* E. Managed enterprises: in this environment, users are typically
provided with corporate devices, and all connected devices are
managed, for example through a Mobile Device Management (MDM)
profile installed on the device. Full trust is created as the MDM
profile is installed.
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3.4. The Purpose of Identification and Associated Problems
Most network functional devices offering a service to a personal
device use the device MAC address to maintain continuity of service.
Wireless access points and controllers use the MAC address to
validate the device connection context, including protocol
capabilities, confirmation that authentication was completed, QoS or
security profiles, encryption key material. Some advanced access
points and controllers also include upper layer functions which
purpose is covered below. A device changing its MAC address, without
another recorded device identity, would cause the access point and
the controller to lose these parameters. As such, the L2
infrastructure does not know that the device (with its new MAC
address) is authorized to communicate through the network. The
encryption keying material is not identified anymore (causing the
access point to fail decrypting the device traffic, and fail
selecting the right key to send encrypted traffic to the device). In
short, the entire context needs to be rebuilt, and a new session
restarted. The time consumed by this procedure breaks any flow that
needs continuity or short delay between packets on the device (e.g.
real-time audio, video, AR/VR etc.) The 802.11i Standard recognizes
that a device may leave the network and come back after a short time
window. As such, the standard suggests that the infrastructure
should keep the context for a device up to one hour after the device
was last seen. MAC address rotation in this context can cause
resource exhaustion on the wireless infrastructure and the flush of
contexts, including for devices that are simply in temporal sleep
mode.
Other devices in the Layer 2 broadcast domain also use the MAC
address to know when and where to forward frames. MAC rotation can
cause these devices to exhaust their resources, holding in memory
traffic for a device which port location can no longer be found. As
these infrastructure devices also implement a cache (to remember the
port position of each known device), frequent MAC rotation can cause
resources exhaustion and the flush of older MAC addresses, including
for devices that did not rotate their MAC. For the RCM device, these
effects translate into session discontinuity and return traffic
losses.
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In wireless contexts, 802.1X authenticators rely on the device and
user identity validation provided by a AAA server to open their port
to data transmission. The MAC address is used to verify that the
device is in the authorized list, and the associated key used to
decrypt the device traffic. A change in MAC address causes the port
to be closed to the device data traffic until the AAA server confirms
the validity of the new MAC address. Therefore, MAC rotation can
interrupt the device traffic, and cause a strain on the AAA server.
DHCP servers, without a unique identification of the device, lose
track of which IP address is validly assigned. Unless the RCM device
releases the IP address before the rotation occurs, DHCP servers are
at risk of scope exhaustion, causing new devices (and RCM devices) to
fail to obtain a new IP address. Even if the RCM device releases the
IP address before the rotation occurs, the DHCP server typically
holds the released IP address for a certain duration, in case the
leaving MAC would return. As the DHCP server cannot know if the
release is due to a temporal disconnection or a MAC rotation, the
risk of scope address exhaustion exists even in cases where the IP
address is released.
Routers keep track of which MAC address is on which interface. MAC
rotation can cause MAC address cache exhaustion, but also the need
for frequent ARP and inverse ARP exchanges.
In residential settings (environments type A), policies can be in
place to control the traffic of some devices (e.g. parental control).
These policies are often based on the device MAC address. Rotation
removes the possibility for such control.
In residential settings (environments type A) and in enterprises
(environments types D and E), device recognition and ranging may be
used for IoT-related functionalities (door unlock, preferred light
and temperature configuration, etc.) These functions often rely on
the detection of the device wireless MAC address. MAC address
rotation breaks the services based o such model.
In managed residential settings (environments types B) and in
enterprises (environments types D and E), the network operator is
often requested to provide IT support. With MAC address rotation,
real time support is only possible if the user is able to provide the
current MAC address. Service improvement support is not possible if
the MAC address that the device had at the (past) time of the
reported issue is not known at the time the issue is reported.
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3.5. Scenario Mapping Table
The previous section discusses different environements, different
settings and the expectations of users and network operators. The
following table summarizes the expected degree of Trust, Privacy and
Network Support
+==================+========+=========+==========+=================+
| Network Location | Trust | Privacy | Network | Network Support |
| | Degree | Need | Services | Expectation |
+==================+========+=========+==========+=================+
| Home | High | Low | Medium | Low |
+------------------+--------+---------+----------+-----------------+
| Campus (BYOD) | Medium | Medium | Complex | Medium |
+------------------+--------+---------+----------+-----------------+
| Enterprise (MDM) | High | Low | Complex | High |
+------------------+--------+---------+----------+-----------------+
| Hospitality | Low | High | Simple | Medium |
+------------------+--------+---------+----------+-----------------+
| Public WiFi | Low | Low | Simple | Low |
| Access Point | | | | |
+------------------+--------+---------+----------+-----------------+
Table 1: Scenario Mapping Table
For example: a Home network is considered to be trusted and safe.
Users expect a simple procedure to connect to their home newtork.
All devices in the home network trust each other. Privacy within the
L2 domain is not a major concern. The Home network can also include
many IoT devices, which need to be simple to onboard and manage. The
home user commonly expects the network operator to protect the home
entwork from external threats (attacks from the Internet). The home
user also commonly expects simple policy features (e.g., Parental
Control). Most home users do not expect to need networking skills to
manage their home network.
On the other end of the spectrum, Public WiFi is often considered to
be untrusted. Privacy is the number one concern for the user. Most
users connect to Public WiFi Access Point only require simple
Internet connectivity service, and expect only limited to no
techniqcal support.
3.6. Problem Statments
The section describes the Problem Statements for MAC-Address
Randomization <vspace>:
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PS1 Unless trust is established, the network must not make any
assumption about client MAC address continuity.
PS2 MAC address must happen while allowing for service continuity.
If a service is interrupted during the RCM process, there must
be a formal mechanism for the client and the service to exchange
about the interruption.
PS3 There must be a secure mechanism to inform the device about the
type of network the device is connecting to, allowing the user
to select the device identity (or identities) accordingly.
3.7. Existing Solutions Directions
Because the possible network disruptions related to RCM have been
envisioned in the past, several directions have been suggested to
alleviate these disruptions. None of them are formal enough to form
a complete solution set. However, it may be useful to list them to
provide a general suggested-solutions context.
In environments of type 1 (settings of type a, b, d and/or e), the
device or its user may have confidence that over the air
eavesdropping does not present a threat. In that case, usage of a
fixed MAC address per SSID is a possibility.
In other cases in the same environments, over the air eavesdropping
may be a concern. In that case, the device may be able to express,
in a protected frame, a stable identity to the wireless
infrastructure. The format of the container of this identity,
encapsulated into a Layer 2 element, is protocol-specific and can be
defined by the associated protocol standard designers. In that case,
the device expresses a randomized and changing MAC address (RCM) over
the air, but a stable identity to the wireless infrastructure.
In networks implementing 802.1X/EAP, a AAA server may be informed
that a device presenting a new MAC address expresses the same device
identity as the same device with a previous MAC address. That AAA
server may then inform the access network, for example with a RADIUS
[RFC5176] CoA message, of the unique identity of the device across
RCMs.
In the cases where the unicity of the station identity is expressed
through a protected mean to the trusted access infrastructure, the
infrastructure could also express a single MAC address for the device
toward the wired part of the network. In such setting, the device
first connects to the wireless infrastructure and expresses a stable
identity. The wireless infrastructure, acting as a proxy, generates
a locally-administered MAC address for the device. That MAC address
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is used to represent the device toward services in the other elements
of the wired network. Next, when the device rotates its over-the-air
MAC address and informs the wireless infrastructure of its stable
identity, the wireless infrastructure identifies that the new MAC
address matches the same device as the previous MAC address, and
continues using the previously generated locally-administered MAC
address to represent the device to wired infrastructure services.
In environments of type 2, the device may share different identities
with different services. For example, the device may express an
over-the-air RCM, a stable encapsulated identity to the wireless
infrastructure, a device identity to a AAA server, and a different
client identity to a DHCP server. In a multi-link scenario, it may
also happen that the device expresses more than one identity to the
DHCP server, with connections going through the same wireless
infrastructure. Because the device may express a stable identity to
one or more network services, because this identity may be shareable
with the wireless infrastructure, the wireless infrastructure may use
a single MAC to represent the device, using one of the stable
identities expressed by that device. Because different identities
can be expressed, and because the role of the wireless infrastructure
is not to monitor closely all activities from the device, the
wireless infrastructure could use, as the device stable identity, the
stable identity expressed to the wireless infrastructure, if it is
available. If such identity is not available, the infrastructure
could use the stable identity expressed to the AAA server, if it is
available and shared back with the wireless infrastructure. If such
identity is not available, the wireless infrastructure could use a
stable identity expressed to the DHCP server, if such identity is
available and visible to the wireless infrastructure. These
possibilities recognize the fact that the wireless infrastructure has
visibility into all traversing non-protected traffic. As such, the
wireless infrastructure may be able to read identifiers sent in
unprotected DHCP requests. Additionally, the wireless infrastructure
would also see, for example, a device with a new MAC address
expressing the same DHCP identity, or requesting the same IP address,
as another device previously connected through the same wireless
system. Therefore, the device may not be able to obfuscate its DHCP
identity from the wireless infrastructure if DHCP exchanges are not
encrypted. Additionally, and because the wireless infrastructure may
not be able to distinguish a device rotating its MAC and attempting
to obtain the same DHCP address as with its previous MAC address,
from a malicious device attempting to steal the DHCP identity from
another device, mechanisms on the infrastructure may prevent such
requests for already assigned resources from being forwarded
successfully.
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In all environments where a device uses a rotating and changing
locally-administered MAC address, rotation from one address to the
next could be preceded by a release of network resources, such as
open connections closure and DHCP address releases.
4. IANA Considerations
This memo includes no request to IANA.
All drafts are required to have an IANA considerations section (see
Guidelines for Writing an IANA Considerations Section in RFCs
[RFC5226] for a guide). If the draft does not require IANA to do
anything, the section contains an explicit statement that this is the
case (as above). If there are no requirements for IANA, the section
will be removed during conversion into an RFC by the RFC Editor.
5. Security Considerations
All drafts are required to have a security considerations section.
See RFC 3552 [RFC3552] for a guide.
6. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC
Text on Security Considerations", BCP 72, RFC 3552,
DOI 10.17487/RFC3552, July 2003,
<https://www.rfc-editor.org/info/rfc3552>.
7. Informative References
[IEEE.802-1D.1993]
Institute of Electrical and Electronics Engineers,
"Information technology - Telecommunications and
information exchange between systems - Local area networks
- Media access control (MAC) bridges", IEEE Standard
802.1D, July 1993.
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[IEEE.802.15.4P_2014]
IEEE, "IEEE Standard for local and metropolitan area
networks - Part 15.4: Low-Rate Wireless Personal Area
Networks (LR-WPANs) - Amendment 7: Physical Layer for Rail
Communications and Control (RCC)", IEEE 802.15.4p-2014,
DOI 10.1109/ieeestd.2014.6809836, 2 May 2014,
<http://ieeexplore.ieee.org/servlet/
opac?punumber=6809834>.
[RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy
Extensions for Stateless Address Autoconfiguration in
IPv6", RFC 4941, DOI 10.17487/RFC4941, September 2007,
<https://www.rfc-editor.org/info/rfc4941>.
[RFC5176] Chiba, M., Dommety, G., Eklund, M., Mitton, D., and B.
Aboba, "Dynamic Authorization Extensions to Remote
Authentication Dial In User Service (RADIUS)", RFC 5176,
DOI 10.17487/RFC5176, January 2008,
<https://www.rfc-editor.org/info/rfc5176>.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", RFC 5226,
DOI 10.17487/RFC5226, May 2008,
<https://www.rfc-editor.org/info/rfc5226>.
[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>.
Appendix A. Additional Stuff
This becomes an Appendix.
Authors' Addresses
Jerome Henry
Cisco Systems
United States of America
Email: jerhenry@cisco.com
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Yiu L. Lee
Comcast
1800 Arch Street
Philadelphia, PA 19103
United States of America
Email: yiu_lee@comcast.com
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