rfc:rfc8948
Internet Engineering Task Force (IETF) CJ. Bernardos Request for Comments: 8948 UC3M Category: Standards Track A. Mourad ISSN: 2070-1721 InterDigital
December 2020
Structured Local Address Plan (SLAP) Quadrant Selection Option for
DHCPv6
Abstract
The IEEE originally structured the 48-bit Media Access Control (MAC) address space in such a way that half of it was reserved for local use. In 2017, the IEEE published a new standard (IEEE Std 802c) with a new optional Structured Local Address Plan (SLAP). It specifies different assignment approaches in four specified regions of the local MAC address space.
The IEEE is developing protocols to assign addresses (IEEE P802.1CQ). There is also work in the IETF on specifying a new mechanism that extends DHCPv6 operation to handle the local MAC address assignments.
This document proposes extensions to DHCPv6 protocols to 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. A new DHCPv6 option (QUAD) is defined for this purpose.
Status of This Memo
This is an Internet Standards Track document.
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). Further information on Internet Standards is available in 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/rfc8948.
Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the document authors. All rights reserved.
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Table of Contents
1. Introduction
1.1. Problem Statement
1.1.1. Wi-Fi (IEEE 802.11) Devices
1.1.2. Hypervisor: Functions That Are and Are Not Migratable
2. Terminology
3. DHCPv6 Extensions
3.1. Address Assignment from the Preferred SLAP Quadrant
Indicated by the Client
3.2. Address Assignment from the Preferred SLAP Quadrant
Indicated by the Relay
4. DHCPv6 Option Definition
4.1. QUAD Option
5. IANA Considerations
6. Security Considerations
7. References
7.1. Normative References
7.2. Informative References
Appendix A. Example Uses of Quadrant Selection Mechanisms
Acknowledgments
Authors' Addresses
1. Introduction
The IEEE structures the 48-bit MAC address space in such a way that half of it is reserved for local use (where the Universal/Local (U/L) bit is set to 1). In 2017, the IEEE published a new standard [IEEEStd802c] that defines a new optional Structured Local Address Plan (SLAP) that specifies different assignment approaches in four specified regions of the local MAC address space. These four regions, called SLAP quadrants, are briefly described below (see Figure 1 and Table 1 for details):
- In SLAP Quadrant 01, Extended Local Identifier (ELI) MAC addresses
are assigned based on a 24-bit Company ID (CID), which is assigned
by the IEEE Registration Authority (RA). The remaining bits are
specified as an extension by the CID assignee or by a protocol
designated by the CID assignee.
- In SLAP Quadrant 11, Standard Assigned Identifier (SAI) MAC
addresses are assigned based on a protocol specified in an IEEE
802 standard. For 48-bit MAC addresses, 44 bits are available.
Multiple protocols for assigning SAIs may be specified in IEEE
standards. Coexistence of multiple protocols may be supported by
limiting the subspace available for assignment by each protocol.
- In SLAP Quadrant 00, Administratively Assigned Identifier (AAI)
MAC addresses are assigned locally by an administrator. Multicast
IPv6 packets use a destination address starting in 33-33, so AAI
addresses in that range should not be assigned. For 48-bit MAC
addresses, 44 bits are available.
- SLAP Quadrant 10 is "Reserved for future use" where MAC addresses
may be assigned using new methods yet to be defined or until then
by an administrator as in the AAI quadrant. For 48-bit MAC
addresses, 44 bits would be available.
LSB MSB
M X Y Z - - - -
| | | |
| | | +------------ SLAP Z-bit
| | +--------------- SLAP Y-bit
| +------------------ X-bit (U/L) = 1 for locally assigned
+--------------------- M-bit (I/G) (unicast/group)
Legend:
LSB: Least Significant Bit
MSB: Most Significant Bit
Figure 1: IEEE 48-Bit MAC Address Structure (in IEEE Representation)
+==========+=======+=======+=======================+============+ | Quadrant | Y-bit | Z-bit | Local Identifier Type | Local | | | | | | Identifier | +==========+=======+=======+=======================+============+ | 01 | 0 | 1 | Extended Local | ELI | +----------+-------+-------+-----------------------+------------+ | 11 | 1 | 1 | Standard Assigned | SAI | +----------+-------+-------+-----------------------+------------+ | 00 | 0 | 0 | Administratively | AAI | | | | | Assigned | | +----------+-------+-------+-----------------------+------------+ | 10 | 1 | 0 | Reserved | Reserved | +----------+-------+-------+-----------------------+------------+
Table 1: SLAP Quadrants
1.1. Problem Statement
The IEEE is developing mechanisms to assign addresses [IEEE-P802.1CQ-Project]. And [RFC8947] specifies a new mechanism that extends DHCPv6 operation to handle the local MAC address assignments. This document proposes extensions to DHCPv6 protocols to enable a DHCPv6 client or a DHCPv6 relay to indicate a preferred SLAP quadrant to the server so that the server may allocate the MAC addresses in the quadrant requested by the relay or client.
In the following, we describe two application scenarios in which a need arises to assign local MAC addresses according to preferred SLAP quadrants.
1.1.1. Wi-Fi (IEEE 802.11) Devices
Today, most Wi-Fi devices come with interfaces that have a "burned- in" MAC address, allocated from the universal address space using a 24-bit Organizationally Unique Identifier (OUI) (assigned to IEEE 802 interface vendors). However, recently, the need to assign local (instead of universal) MAC addresses has emerged particularly in the following two scenarios:
- IoT (Internet of Things): In general, composed of constrained
devices [RFC7228] with constraints such as available power and
energy, memory, and processing resources. Examples of this
include sensors and actuators for health or home automation
applications. Given the increasingly high number of these
devices, manufacturers might prefer to equip devices with
temporary MAC addresses used only at first boot. These temporary
MAC addresses would just be used to send initial DHCP packets to
available DHCP servers. IoT devices typically need a single MAC
address for each available network interface. Once the server
assigns a MAC address, the device would abandon its temporary MAC
address. Home automation IoT devices typically do not move
(however, note that there is an increase of mobile smart health
monitoring devices). For this type of device, in general, any
type of SLAP quadrant would be good for assigning addresses, but
ELI/SAI quadrants might be more suitable in some scenarios. For
example, the device might need to use an address from the CID
assigned to the IoT communication device vendor, thus preferring
the ELI quadrant.
- Privacy: Today, MAC addresses allow the exposure of user locations
making it relatively easy to track user movements. One of the
mechanisms considered to mitigate this problem is the use of local
random MAC addresses: changing them every time the user connects
to a different network. In this scenario, devices are typically
mobile. Here, AAI is probably the best SLAP quadrant from which
to assign addresses; it is the best fit for randomization of
addresses, and it is not required for the addresses to survive
when changing networks.
1.1.2. Hypervisor: Functions That Are and Are Not Migratable
In large-scale virtualization environments, thousands of virtual machines (VMs) are active. These VMs are typically managed by a hypervisor, which is in charge of spawning and stopping VMs as needed. The hypervisor is also typically in charge of assigning new MAC addresses to the VMs. If a DHCP solution is in place for that, the hypervisor acts as a DHCP client and requests that available DHCP servers assign one or more MAC addresses (an address block). The hypervisor does not use those addresses for itself, but rather it uses them to create new VMs with appropriate MAC addresses. If we assume very large data-center environments, such as the ones that are typically used nowadays, it is expected that the data center is divided in different network regions, each one managing its own local address space. In this scenario, there are two possible situations that need to be tackled:
- Migratable functions: If a VM (providing a given function) needs
to be migrated to another region of the data center (e.g., for
maintenance, resilience, end-user mobility, etc.), the VM's
networking context needs to migrate with the VM. This includes
the VM's MAC address(es). Since the assignments from the ELI/SAI
SLAP quadrants are governed by rules per IEEE Std 802c, they are
more appropriate for use to ensure MAC address uniqueness globally
in the data center.
- Functions that are not migratable: If a VM will not be migrated to
another region of the data center, there are no requirements
associated with its MAC address. In this case, it is simpler to
allocate it from the AAI SLAP quadrant, which does not need to be
unique across multiple data centers (i.e., each region can manage
its own MAC address assignment without checking for duplicates
globally).
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.
Where relevant, the DHCPv6 terminology from [RFC8415] also applies here. Additionally, the following definitions are updated for this document.
address Unless specified otherwise, a link-layer (or MAC)
address, as specified in [IEEEStd802]. The address is
6 or 8 bytes long.
address block A number of consecutive link-layer addresses. An
address block is expressed as a first address plus a
number that designates the number of additional
(extra) addresses. A single address can be
represented by the address itself and zero extra
addresses.
client A node that is interested in obtaining link-layer
addresses. It implements the basic DHCP mechanisms
needed by a DHCP client, as described in [RFC8415],
and supports the options (IA_LL and LLADDR) specified
in [RFC8947] as well as the new option (QUAD)
specified in this document. The client may or may not
support IPv6 address assignment and prefix delegation,
as specified in [RFC8415].
IA_LL Identity Association for Link-Layer Address, an
identity association (IA) used to request or assign
link-layer addresses. Section 11.1 of [RFC8947]
provides details on the IA_LL option.
LLADDR Link-layer address option that is used to request or
assign a block of link-layer addresses. Section 11.2
of [RFC8947] provides details on the LLADDR option.
relay A node that acts as an intermediary to deliver DHCP
messages between clients and servers. A relay, based
on local knowledge and policies, may include the
preferred SLAP quadrant in a QUAD option sent to the
server. The relay implements basic DHCPv6 relay agent
functionality, as described in [RFC8415].
server A node that manages link-layer address allocation and
is able to respond to client queries. It implements
basic DHCP server functionality, as described in
[RFC8415], and supports the options (IA_LL and LLADDR)
specified in [RFC8947] as well as the new option
(QUAD) specified in this document. The server may or
may not support IPv6 address assignment and prefix
delegation, as specified in [RFC8415].
3. DHCPv6 Extensions
3.1. Address Assignment from the Preferred SLAP Quadrant Indicated by
the Client
Next, we describe the protocol operations for a client to select a preferred SLAP quadrant using the DHCPv6 signaling procedures described in [RFC8947]. The signaling flow is shown in Figure 2.
+--------+ +--------+
| DHCPv6 | | DHCPv6 |
| client | | server |
+--------+ +--------+
| |
+----1. Solicit(IA_LL(LLADDR,QUAD))--->|
| |
|<--2. Advertise(IA_LL(LLADDR,QUAD))---+
| |
+---3. Request(IA_LL(LLADDR,QUAD))---->|
| |
|<------4. Reply(IA_LL(LLADDR))--------+
| |
. .
. (timer expiring) .
. .
| |
+---5. Renew(IA_LL(LLADDR,QUAD))------>|
| |
|<-----6. Reply(IA_LL(LLADDR))---------+
| |
Figure 2: DHCPv6 Signaling Flow (Client-Server)
1. Link-layer addresses (i.e., MAC addresses) are assigned in
blocks. The smallest block is a single address. To request an
assignment, the client sends a Solicit message with an IA_LL
option in the message. The IA_LL option MUST contain an LLADDR
option. In order to indicate the preferred SLAP quadrant(s), the
IA_LL option includes the new OPTION_SLAP_QUAD option in the
IA_LL-option field (alongside the LLADDR option).
2. The server, upon receiving an IA_LL option in a Solicit message,
inspects its contents. For each of the entries in the
OPTION_SLAP_QUAD, in order of the preference field (highest to
lowest), the server checks if it has a configured MAC address
pool matching the requested quadrant identifier and an available
range of addresses of the requested size. If suitable addresses
are found, the server sends back an Advertise message with an
IA_LL option containing an LLADDR option that specifies the
addresses being offered. If the server manages a block of
addresses belonging to a requested quadrant, the addresses being
offered MUST belong to a requested quadrant. If the server does
not have a configured address pool matching the client's request,
it SHOULD return the IA_LL option with the addresses being
offered belonging to a quadrant managed by the server (following
a local policy to select from which of the available quadrants).
If the server has a configured address pool of the correct
quadrant but no available addresses, it MUST return the IA_LL
option containing a Status Code option with status set to
NoAddrsAvail.
3. The client waits for available servers to send Advertise
responses and picks one server, as defined in Section 18.2.9 of
[RFC8415]. The client SHOULD NOT pick a server that does not
advertise an address in the requested quadrant(s). The client
then sends a Request message that includes the IA_LL container
option with the LLADDR option copied from the Advertise message
sent by the chosen server. It includes the preferred SLAP
quadrant(s) in a new QUAD IA_LL option.
4. Upon reception of a Request message with an IA_LL container
option, the server assigns requested addresses. The server MAY
alter the allocation at this time (e.g., by reducing the address
block). It then generates and sends a Reply message back to the
client. Upon receiving a Reply message, the client parses the
IA_LL container option and may start using all provided
addresses. Note that a client that has included a Rapid Commit
option in the Solicit message may receive a Reply message in
response to the Solicit message and skip the Advertise and
Request message steps above (following standard DHCPv6
procedures).
5. The client is expected to periodically renew the link-layer
addresses, as governed by T1 and T2 timers. This mechanism can
be administratively disabled by the server sending "infinity" as
the T1 and T2 values (see Section 7.7 of [RFC8415]). The client
sends a Renew option after T1. It includes the preferred SLAP
quadrant(s) in the new QUAD IA_LL option, so in case the server
is unable to extend the lifetime on the existing address(es), the
preferred quadrants are known for the allocation of any "new"
(i.e., different) addresses.
6. The server responds with a Reply message with an IA_LL option
that includes an LLADDR option with extended lifetime.
The client SHOULD check if the received MAC address comes from one of the requested quadrants. It MAY repeat the process selecting a different DHCP server.
3.2. Address Assignment from the Preferred SLAP Quadrant Indicated by
the Relay
Next, we describe the protocol operations for a relay to select a preferred SLAP quadrant using the DHCPv6 signaling procedures described in [RFC8947]. This is useful when a DHCPv6 server is operating over a large infrastructure split in different network regions, where each region might have different requirements. The signaling flow is shown in Figure 3.
+--------+ +--------+ +--------+
| DHCPv6 | | DHCPv6 | | DHCPv6 |
| client | | relay | | server |
+--------+ +--------+ +--------+
| | |
+-----1. Solicit(IA_LL)----->| |
| +----2. Relay-forward |
| | (Solicit(IA_LL),QUAD)------>|
| | |
| |<---3. Relay-reply |
| | (Advertise(IA_LL(LLADDR)))--+
|<4. Advertise(IA_LL(LLADDR))+ |
|-5. Request(IA_LL(LLADDR))->| |
| +-6. Relay-forward |
| | (Request(IA_LL(LLADDR)),QUAD)->|
| | |
| |<--7. Relay-reply |
| | (Reply(IA_LL(LLADDR)))-------+
|<--8. Reply(IA_LL(LLADDR))--+ |
| | |
. . .
. (timer expiring) .
. . .
| | |
+--9. Renew(IA_LL(LLADDR))-->| |
| |--10. Relay-forward |
| | (Renew(IA_LL(LLADDR)),QUAD)-->|
| | |
| |<---11. Relay-reply |
| | (Reply(IA_LL(LLADDR)))-----+
|<--12. Reply(IA_LL(LLADDR))-+ |
| | |
Figure 3: DHCPv6 Signaling Flow (Client-Relay-Server)
1. Link-layer addresses (i.e., MAC addresses) are assigned in
blocks. The smallest block is a single address. To request an
assignment, the client sends a Solicit message with an IA_LL
option in the message. The IA_LL option MUST contain an LLADDR
option.
2. The DHCP relay receives the Solicit message and encapsulates it
in a Relay-forward message. The relay, based on local knowledge
and policies, includes in the Relay-forward message the QUAD
option with the preferred quadrant. The relay might know which
quadrant to request based on local configuration (e.g., the
served network contains IoT devices only, thus requiring ELI/
SAI) or other means. Note that if a client sends multiple
instances of the IA_LL option in the same message, the DHCP
relay MAY only add a single instance of the QUAD option.
3. Upon receiving a relayed message containing an IA_LL option, the
server inspects the contents for instances of OPTION_SLAP_QUAD
in both the Relay-forward message and the client's message
payload. Depending on the server's policy, the instance of the
option to process is selected (see the end of this section).
For each of the entries in OPTION_SLAP_QUAD, in order of the
preference field (highest to lowest), the server checks if it
has a configured MAC address pool matching the requested
quadrant identifier and an available range of addresses of the
requested size. If suitable addresses are found, the server
sends back an Advertise message with an IA_LL option containing
an LLADDR option that specifies the addresses being offered.
This message is sent to the Relay in a Relay-reply message. If
the server supports the semantics of the preferred quadrant
included in the QUAD option and manages a block of addresses
belonging to a requested quadrant, then the addresses being
offered MUST belong to a requested quadrant. The server SHOULD
apply the contents of the relay's supplied QUAD option for all
of the client's IA_LLs, unless configured to do otherwise.
4. The relay sends the received Advertise message to the client.
5. The client waits for available servers to send Advertise
responses and picks one server, as defined in Section 18.2.9 of
[RFC8415]. The client then sends a Request message that
includes the IA_LL container option with the LLADDR option
copied from the Advertise message sent by the chosen server.
6. The relay forwards the received Request in a Relay-forward
message. It adds, in the Relay-forward, a QUAD IA_LL option
with the preferred quadrant.
7. Upon reception of the forwarded Request message with IA_LL
container option, the server assigns requested addresses. The
server MAY alter the allocation at this time. It then generates
and sends a Reply message in a Relay-reply message back to the
relay.
8. Upon receiving a Reply message, the client parses the IA_LL
container option and may start using all provided addresses.
9. The client is expected to periodically renew the link-layer
addresses, as governed by T1 and T2 timers. This mechanism can
be administratively disabled by the server sending "infinity" as
the T1 and T2 values (see Section 7.7 of [RFC8415]). The client
sends a Renew option after T1.
10. This message is forwarded by the relay in a Relay-forward
message, including a QUAD IA_LL option with the preferred
quadrant.
11. The server responds with a Reply message, including an LLADDR
option with extended lifetime. This message is sent in a Relay-
reply message.
12. The relay sends the Reply message back to the client.
The server SHOULD implement a configuration parameter to deal with the case where the client's DHCP message contains an instance of OPTION_SLAP_QUAD and the relay adds a second instance in its Relay- forward message. This parameter configures the server to process either the client's or the relay's instance of option QUAD. It is RECOMMENDED that the default for such a parameter is to process the client's instance of the option.
The client MAY check if the received MAC address belongs to a
quadrant it is willing to use/configure and MAY decide based on that
whether to use/configure the received address.
4. DHCPv6 Option Definition
4.1. QUAD Option
The QUAD option is used to specify the preferences for the selected quadrants within an IA_LL. The option MUST be encapsulated either in the IA_LL-options field of an IA_LL option or in a Relay-forward message.
The format of the QUAD option is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_SLAP_QUAD | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| quadrant-1 | pref-1 | quadrant-2 | pref-2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| quadrant-n-1 | pref-n-1 | quadrant-n | pref-n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: QUAD Option Format
option-code OPTION_SLAP_QUAD (140).
option-len 2 * number of included (quadrant, preference). This
is a 2-byte field containing the total length of all
(quadrant, preference) pairs included in the option.
quadrant-n Identifier of the quadrant (0: AAI, 1: ELI, 2:
Reserved by IEEE [IEEEStd802c], and 3: SAI). Each
quadrant MUST only appear once at most in the option.
This is a 1-byte field.
pref-n Preference associated to quadrant-n. A higher value
means a more preferred quadrant. This is a 1-byte
field.
A quadrant identifier value MUST only appear, at most, once in the option. If an option includes more than one occurrence of the same quadrant identifier, only the first occurrence is processed, and the rest MUST be ignored by the server.
If the same preference value is used for more than one quadrant, the server MAY select which quadrant should be preferred (if the server can assign addresses from all or some of the quadrants with the same assigned preference). Note that this is not a simple list of quadrants ordered by preference with no preference value, but a list of quadrants with explicit preference values. This way it can support the case whereby a client really has no preference between two or three quadrants, leaving the decision to the server.
If the client or relay agent provides the OPTION_SLAP_QUAD, the server MUST use the quadrant-n/pref-n values to order the selection of the quadrants. If the server can provide an assignment from one of the specified quadrants, it SHOULD proceed with the assignment. If the server does not have a configured address pool matching any of the specified quadrant-n fields or if the server has a configured address pool of the correct quadrant but no available addresses, it MUST return the IA_LL option containing a status of NoAddrsAvail.
There is no requirement that the client or relay agent order the quadrant/pref values in any specific order; hence, servers MUST NOT assume that quadrant-1/pref-1 have the highest preference (except if there is only one set of values).
For cases where a server may not be configured to have pools for the client or relay quadrant preferences, clients and relays SHOULD specify all quadrants in the QUAD option to assure the client gets an address (or addresses) -- if any are available. Specifying all quadrants also results in a QUAD option supporting server responding like a non-QUAD option supporting server, i.e., an address (or addresses) from any available quadrants can be returned.
5. IANA Considerations
IANA has assigned the QUAD (140) option code from the "Option Codes" subregistry of the "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)" registry maintained at <http://www.iana.org/assignments/ dhcpv6-parameters>:
Value: 140 Description: OPTION_SLAP_QUAD Client ORO: No Singleton Option: Yes Reference: RFC 8948
6. Security Considerations
See [RFC8415] and [RFC7227] for the DHCPv6 security and privacy considerations. See [RFC8200] for the IPv6 security considerations.
Also, see [RFC8947] for security considerations regarding link-layer address assignments using DHCP.
7. References
7.1. 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>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A.,
Richardson, M., Jiang, S., Lemon, T., and T. Winters,
"Dynamic Host Configuration Protocol for IPv6 (DHCPv6)",
RFC 8415, DOI 10.17487/RFC8415, November 2018,
<https://www.rfc-editor.org/info/rfc8415>.
[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>.
7.2. Informative References
[IEEE-P802.1CQ-Project]
IEEE, "P802.1CQ - Standard for Local and Metropolitan Area
Networks: Multicast and Local Address Assignment",
<https://standards.ieee.org/project/802_1CQ.html>.
[IEEEStd802]
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>.
[IEEEStd802c]
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>.
[RFC7227] Hankins, D., Mrugalski, T., Siodelski, M., Jiang, S., and
S. Krishnan, "Guidelines for Creating New DHCPv6 Options",
BCP 187, RFC 7227, DOI 10.17487/RFC7227, May 2014,
<https://www.rfc-editor.org/info/rfc7227>.
[RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for
Constrained-Node Networks", RFC 7228,
DOI 10.17487/RFC7228, May 2014,
<https://www.rfc-editor.org/info/rfc7228>.
[RFC7548] Ersue, M., Ed., Romascanu, D., Schoenwaelder, J., and A.
Sehgal, "Management of Networks with Constrained Devices:
Use Cases", RFC 7548, DOI 10.17487/RFC7548, May 2015,
<https://www.rfc-editor.org/info/rfc7548>.
[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/info/rfc8200>.
Appendix A. Example Uses of Quadrant Selection Mechanisms
This appendix describes some examples of how the quadrant preference mechanisms could be used.
First, let's take an IoT scenario as an example. An IoT device might decide on its own the SLAP quadrant it wants to use to obtain a local MAC address, using the following information to make the decision:
- Type of IoT deployment: For example, industrial, domestic, rural,
etc. For small deployments, such as domestic ones, the IoT device
itself can decide to use the AAI quadrant (this might not even
involve the use of DHCP, by the device just configuring a random
address computed by the device itself). For large deployments,
such as industrial or rural ones, where thousands of devices might
coexist, the IoT can decide to use the ELI or SAI quadrants.
- Mobility: If the IoT device can move, then it might prefer to
select the SAI or AAI quadrants to minimize address collisions
when moving to another network. If the device is known to remain
fixed, then the ELI is probably the most suitable one to use.
- Managed/Unmanaged: Depending on whether the IoT device is managed
during its lifetime or cannot be reconfigured [RFC7548], the
decision of what quadrant is more appropriate might be different.
For example, if the IoT device can be managed (e.g., configured)
and network topology changes might occur during its lifetime
(e.g., due to changes on the deployment, such as extensions
involving additional devices), this has an impact on the preferred
quadrant (e.g., to avoid potential collisions in the future).
- Operation / Battery Lifetime: Depending on the expected lifetime
of the device, a different quadrant might be preferred (as before,
to minimize potential address collisions in the future).
The previous parameters are considerations that the device vendor/
administrator may wish to use when defining the IoT device's
MAC address request policy (i.e., how to select a given SLAP
quadrant). IoT devices are typically very resource constrained, so
there may only be a simple decision-making process based on
preconfigured preferences.
We now take the Wi-Fi device scenario, considering, for example, that a laptop or smartphone connects to a network using its built-in MAC address. Due to privacy/security concerns, the device might want to configure a local MAC address. The device might use different parameters and context information to decide, not only which SLAP quadrant to use for the local MAC address configuration, but also when to perform a change of address (e.g., it might be needed to change address several times). This information includes, but it is not limited to:
- Type of network the device is connected: public, work, home.
- Trusted network: Yes/No.
- First time visited network: Yes/No.
- Network geographical location.
- Mobility: Yes (the device might change its network attachment
point) / No (the device is not going to change its network
attachment point).
- Operating System (OS) network profile, including security/trust-
related parameters: Most modern OSs keep metadata associated with
the networks they can attach to as, for example, the level of
trust the user or administrator assigns to the network. This
information is used to configure how the device behaves in terms
of advertising itself on the network, firewall settings, etc. But
this information can also be used to decide whether or not to
configure a local MAC address, from which SLAP quadrant it should
be assigned, and how often it may be assigned.
- Triggers coming from applications regarding location privacy: An
app might request that the OS maximize location privacy (due to
the nature of the application), and this might require the OS to
force the use of a local MAC address or the local MAC address to
be changed.
This information can be used by the device to select the SLAP quadrant. For example, if the device is moving around (e.g., while connected to a public network in an airport), it is likely that it might change access points several times; therefore, it is best to minimize the chances of address collision, using the SAI or AAI quadrants. If the device is not expected to move and is attached to a trusted network (e.g., in some scenarios at work), then it is probably best to select the ELI quadrant. These are just some examples of how to use this information to select the quadrant.
Additionally, the information can also be used to trigger subsequent changes of MAC address to enhance location privacy. Besides, changing the SLAP quadrant might also be used as an additional enhancement to make it harder to track the user location.
Last, if we consider the data-center scenario, a hypervisor might request local MAC addresses be assigned to virtual machines. As in the previous scenarios, the hypervisor might select the preferred SLAP quadrant using information provided by the cloud management system or virtualization infrastructure manager running on top of the hypervisor. This information might include, but is not limited to:
- Migratable VM: If the function implemented by the VM is subject to
be moved to another physical server or not, this has an impact on
the preference for the SLAP quadrant, as the ELI and SAI quadrants
are better suited for supporting migration in a large data center.
- VM connectivity characteristics: For example, standalone, part of
a pool, and part of a service graph/chain. If the connectivity
characteristics of the VM are known, this can be used by the
hypervisor to select the best SLAP quadrant.
Acknowledgments
The authors would like to thank Bernie Volz for his very valuable comments on this document. We also want to thank Ian Farrer, Tomek Mrugalski, Éric Vyncke, Tatuya Jinmei, Carl Wallace, Ines Robles, Ted Lemon, Jaime Jimenez, Robert Wilton, Benjamin Kaduk, Barry Leiba, Alvaro Retana, and Murray Kucherawy for their very detailed and helpful reviews. And thanks to Roger Marks and Antonio de la Oliva for comments related to IEEE work and references.
The work in this document has been supported by the H2020 5GROWTH (Grant 856709) and 5G-DIVE projects (Grant 859881).
Authors' Addresses
Carlos J. Bernardos 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/
Alain Mourad InterDigital Europe
Email: Alain.Mourad@InterDigital.com URI: http://www.InterDigital.com/
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