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SLAP quadrant selection options for DHCPv6
draft-ietf-dhc-slap-quadrant-03

The information below is for an old version of the document.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 8948.
Authors Carlos J. Bernardos , Alain Mourad
Last updated 2020-02-27
Replaces draft-bernardos-dhc-slap-quadrant
RFC stream Internet Engineering Task Force (IETF)
Formats
Reviews
Additional resources Mailing list discussion
Stream WG state Waiting for WG Chair Go-Ahead
Revised I-D Needed - Issue raised by WGLC, Doc Shepherd Follow-up Underway
Associated WG milestone
Nov 2019
WGLC SLAP quadrant selection options for DHCPv6
Document shepherd Ian Farrer
IESG IESG state Became RFC 8948 (Proposed Standard)
Consensus boilerplate Yes
Telechat date (None)
Responsible AD (None)
Send notices to Tomek Mrugalski <tomasz.mrugalski@gmail.com>, Ian Farrer <ianfarrer@gmx.com>
draft-ietf-dhc-slap-quadrant-03
DHC WG                                                     CJ. Bernardos
Internet-Draft                                                      UC3M
Intended status: Standards Track                               A. Mourad
Expires: August 31, 2020                                    InterDigital
                                                       February 28, 2020

               SLAP quadrant selection options for DHCPv6
                    draft-ietf-dhc-slap-quadrant-03

Abstract

   The IEEE originally structured the 48-bit MAC address space in such a
   way that half of it was reserved for local use.  Recently, the IEEE
   has been working on a new specification (IEEE 802c) which defines a
   new "optional Structured Local Address Plan" (SLAP) that specifies
   different assignment approaches in four specified regions of the
   local MAC address space.

   The IEEE is working on mechanisms to allocate addresses in the one of
   these quadrants (IEEE 802.1CQ).  There is work also in the IETF on
   specifying a new mechanism that extends DHCPv6 operation to handle
   the local MAC address assignments.  In this document, we complement
   this ongoing IETF work by defining a mechanism to allow choosing the
   SLAP quadrant to use in the allocation of the MAC address to the
   requesting device/client.

   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 allocates the MAC address to the
   given client out of the quadrant requested by relay or client.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on August 31, 2020.

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Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Problem statement . . . . . . . . . . . . . . . . . . . .   4
       1.1.1.  WiFi devices  . . . . . . . . . . . . . . . . . . . .   4
       1.1.2.  Hypervisor: migratable vs non-migratable functions  .   5
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Quadrant Selection Mechanisms . . . . . . . . . . . . . . . .   6
   4.  DHCPv6 Extensions . . . . . . . . . . . . . . . . . . . . . .   9
     4.1.  Address Assignment from the Preferred SLAP Quadrant
           Indicated by the Client . . . . . . . . . . . . . . . . .   9
     4.2.  Address Assignment from the SLAP Quadrant Indicated by
           the Relay . . . . . . . . . . . . . . . . . . . . . . . .  11
   5.  DHCPv6 Options Definitions  . . . . . . . . . . . . . . . . .  13
     5.1.  Quad (IA-LL) option . . . . . . . . . . . . . . . . . . .  13
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  15
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  15
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  15
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  16
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  16
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  16
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  16

1.  Introduction

   The IEEE originally structured the 48-bit MAC address space in such a
   way that half of it was reserved for local use (where the U/L bit is
   set to 1).  Recently, the IEEE has been working on a new
   specification (IEEE 802c [IEEEStd802c-2017]) which 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 Figure 2 for details):

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   o  Quadrant "Extended Local Identifier" (ELI) MAC addresses are
      assigned based on a Company ID (CID), which takes 24-bits, leaving
      the remaining 24-bits for the locally assigned address for each
      CID for unicast (M-bit = 0) and also for multicast (M-bit = 1).
      The CID is assigned by the IEEE Registration Authority (RA).

   o  Quadrant "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.

   o  Quadrant "Administratively Assigned Identifier" (AAI) MAC
      addresses are assigned locally by an administrator.  Multicast
      IPv6 packets use a destination address starting in 33-33 and this
      falls within this space and therefore should not be used to avoid
      conflict with IPv6 multicast addresses.  For 48-bit MAC addresses,
      44 bits are available.

   o  Quadrant "Reserved for future use" where MAC addresses may be
      assigned using new methods yet to be defined, or by an
      administrator like in the AAI quadrant.

          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)

                Figure 1: IEEE 48-bit MAC address structure

   +----------+-------+-------+-----------------------+----------------+
   | 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       |
   +----------+-------+-------+-----------------------+----------------+

                         Figure 2: SLAP quadrants

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1.1.  Problem statement

   The IEEE is working on mechanisms to allocate addresses in the SAI
   quadrant (IEEE 802.1CQ project).  There is also ongoing work in the
   IETF [I-D.ietf-dhc-mac-assign] specifying a new mechanism that
   extends DHCPv6 operation to handle the local MAC address assignments.
   In this document, we complement ongoing IETF work with mechanisms to
   allow choosing the SLAP quadrant to use in the allocation of the MAC
   address to the requesting device/client.  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 allocates the MAC address to the given client out of the
   quadrant requested by relay or client.

   In the following, we describe two application scenarios where a need
   arises to assign local MAC addresses according to preferred SLAP
   quadrants.

1.1.1.  WiFi devices

   Today, most WiFi 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 in particular in the
   following two scenarios:

   o  IoT (Internet of Things): where there are a lot of cheap,
      sometimes short lived and disposable devices.  Examples of this
      include: sensors and actuators for health or home automation
      applications.  In this scenario, it is common that upon a first
      boot, the device uses a temporary MAC address, to send initial
      DHCP packets to available DHCP servers.  IoT devices typically
      request a single MAC address for each available network interface.
      Once the server assigns a MAC address, the device abandons its
      temporary MAC address.  This type of device is typically not
      moving.  In general, any type of SLAP quadrant would be good for
      assigning addresses from, but ELI/SAI quadrants might be more
      suitable in some scenarios, such as if the addresses need to
      belong to the CID assigned to the IoT communication device vendor.

   o  Privacy: Today, MAC addresses allow the exposure of users'
      locations making it relatively easy to track users' movement.  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 to
      assign addresses from, as it is the best fit for randomization of

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      addresses, and it is not required for the addresses to survive
      when changing networks.

1.1.2.  Hypervisor: migratable vs non-migratable functions

   In large scale virtualization environments, thousands of virtual
   machines (VMs) are active.  These VMs are typically managed by a
   hypervisor, 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 available DHCP servers to assign
   one or more MAC addresses (an address block).  The hypervisor does
   not use those addresses for itself, but rather 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:

   o  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).  Therefore, for this case, it is better
      to allocate addresses from the ELI/SAI SLAP quadrant, which can be
      centrally allocated by the DHCP server.

   o  Non-migratable functions.  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 more
      efficient to allocate it from the AAI SLAP quadrant, that 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 the DHCPv6 Protocol
   [RFC8415] also applies here.  Additionally, the following definitions
   are updated for this document.

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   client        A device that is interested in obtaining link-layer
                 addresses.  It implements the basic DHCPv6 mechanisms
                 needed by a DHCPv6 client as described in [RFC8415] and
                 supports the new options (IA_LL and LLADDR) specified
                 in [I-D.ietf-dhc-mac-assign].  The client may or may
                 not support address assignment and prefix delegation as
                 specified in [RFC8415].

   server        Software that manages link-layer address allocation and
                 is able to respond to client queries.  It implements
                 basic DHCPv6 server functionality as described in
                 [RFC8415] and supports the new options (IA_LL and
                 LLADDR) specified in [I-D.ietf-dhc-mac-assign].  The
                 server may or may not support address assignment and
                 prefix delegation as specified in [RFC8415].

   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 in [RFC8415] and supports
                 the new options (IA_LL and LLADDR) specified in
                 [I-D.ietf-dhc-mac-assign].

   address       Unless specified otherwise, an address means a link-
                 layer (or MAC) address, as defined in IEEE802.  The
                 address is typically 6 bytes long, but some network
                 architectures may use different lengths.

   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.

3.  Quadrant Selection Mechanisms

   The following section describes some examples of how the quadrant
   preference mechanisms could be used.

   Let's take first 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 take the decision:

   o  Type of IoT deployment: e.g., industrial, domestic, rural, etc.
      For small deployments, such as domestic ones, the IoT itself can
      decide to use the AAI quadrant (this might not even involve the

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      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 co-
      exist, the IoT can decide to use the ELI or SAI quadrants.

   o  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.

   o  Managed/unmanaged: depending on whether the IoT device is managed
      during its lifetime or cannot be re-configured, the selected
      quadrant might be different.  For example, it can be managed, this
      means that network topology changes might occur during its
      lifetime (e.g., due to changes on the deployment, such as
      extensions involving additional devices), and this might have an
      impact on the preferred quadrant (e.g., to avoid potential
      collisions in the future).

   o  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 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 simple
   decision making process based on pre-configured preferences.

   If we now take the WiFi 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:

   o  Type of network the device is connected: public, work, home.

   o  Trusted network?  Y/N.

   o  First time visited network?  Y/N.

   o  Network geographical location.

   o  Mobility?  Y/N.

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   o  Operating System (OS) network profile, including security/trust
      related parameters.  Most modern OSs keep metadata associated to
      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 to configure a
      local MAC address or not, from which SLAP quadrant and how often.

   o  Triggers coming from applications regarding location privacy.  An
      app might request to the OS to maximize location privacy (due to
      the nature of the application) and this might require that the OS
      forces the use of a local MAC address, or that the local MAC
      address is 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 point several times, and therefore it is best to
   minimize the chances of address collision, using the SAI or AAI
   quadrants.  If the device is not moving and attached to a trusted
   network (e.g. 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 used 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 to 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 (CMS) or virtualization infrastructure manager (VIM) running
   on top of the hypervisor.  This information might include, but is not
   limited to:

   o  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 some quadrants are
      better suited (e.g., ELI/SAI) for supporting migration in a large
      data center.

   o  VM connectivity characteristics , e.g.,: standalone, part of a
      pool, 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.

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4.  DHCPv6 Extensions

4.1.  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 [I-D.ietf-dhc-mac-assign].  The signaling flow is shown
   in Figure 3.

    +--------+                            +--------+
    | DHCPv6 |                            | DHCPv6 |
    | client |                            | server |
    +--------+                            +--------+
        |                                      |
        +-------1. Solicit(IA_LL(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 3: 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 a IA_LL
       option in the message.  The IA_LL option MUST contain a LLADDR
       option.  In order to indicate the preferred SLAP quadrant(s), the
       IA_LL option includes the new OPTION_SLAP_QUAD option(s) in the
       IA-LL-option field (with the LLAADR option).

   2.  The server, upon receiving a IA_LL option, inspects its content
       and may offer an address or addresses for each LLADDR option
       according to its policy.  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 supports
       the new QUAD IA-LL-option, and manages a block of addresses

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       belonging to the requested quadrant(s), the addresses being
       offered MUST belong to the requested quadrant(s).  If the server
       does not have a configured address pool matching the client's
       request, it MUST return the IA_LL option containing a Status Code
       option with status set to NoQuadAvail (IANA-2).  If the client
       specified more than one SLAP quadrant, the server MUST only
       return a NoQuadAvail status code if the address pool configured
       at the server does not match any of the specified SLAP 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 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 the new QUAD IA-LL-option.

   4.  Upon reception of a 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 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, may receive a Reply in response to
       the Solicit and skip the Advertise and Request steps above
       (following standard DHCPv6 procedures).

   5.  When the assigned addresses are about to expire, the client sends
       a Renew message.  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" addresses.

   6.  The server responds with a Reply message, including an LLADDR
       option with extended lifetime.

   The client SHOULD check if the received MAC address comes from one
   of the requested quadrants.  If not, SHOULD NOT configure the
   obtained address.  It MAY repeat the process selecting a different
   DHCP server.

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4.2.  Address Assignment from the 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 [I-D.ietf-dhc-mac-assign].  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 4.

   +--------+                  +--------+                     +--------+
   | 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 4: 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 a IA_LL

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        option in the message.  The IA_LL option MUST contain a 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_LLoption in the same message, the DHCP relay
        MUST ONLY add a singleinstance of the QUAD option.  The server
        SHOULD apply thecontents of the relay's supplied QUAD option for
        all of theclient's IA_LLs, unless configured to do otherwise.

   3.   The server, upon receiving the forwarded Solicit message
        including a IA_LL option, inspects its content and decide may
        offer an address or addresses for each LLADDR option according
        to its policy.  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 the requested quadrant(s),
        then the addresses being offered SHOULD belong to the requested
        quadrant(s).  Note that if the client is sending multiple
        instances of the IA_LL in the same message, a single QUAD option
        is supported, applying to all of the IA_LLs in the client's
        message.

   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 back to the relay.

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   8.   Upon receiving a Reply message, the client parses the IA_LL
        container option and may start using all provided addresses.

   9.   When the assigned addresses are about to expire, the client
        sends a Renew message.

   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.

   If a client provides a QUAD IA-LL-option and the relay agent is still
   configured to add its preference value, the server SHOULD follow what
   is administratively configured in a QUAD_RELAY_PREF internal
   variable.  If the value is set to 1, then the realy provided
   preference overrides what the client has provided, while if the
   variable is set to 0, then the client's provided preference is
   considered.  It is RECOMMENDED that QUAD_RELAY_PREF is set to 1 at
   the server.

   The client SHOULD check if the received MAC address belongs to a
   quadrant it is willing to use/configure.  If not, SHOULD NOT
   configure the obtained address.

5.  DHCPv6 Options Definitions

5.1.  Quad (IA-LL) option

   The QUAD option is used to specify the preferences for the selected
   quadrants within an IA_LL.  The option must either be encapsulated in
   the IA-LL-options field of an IA_LL option or in a Relay-forward
   message.

   The format of the QUAD option is:

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       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     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      .                                                               .
      .                                                               .
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                       Figure 5: Quad Option Format

   option-code     OPTION_SLAP_QUAD (IANA-1).

   option-len      2 * number of included (quadrant, preference).

   quadrant-n      Identifier of the quadrant (0: AAI, 1: ELI, 2:
                   Reserved, 3: SAI).  Each quadrant MUST only appear
                   once at most in the option.

   pref-n          Preference associated to quadrant-n.  A higher value
                   means a more preferred quadrant.

   A quadrant value MUST only appear once at most in the option.  If an
   option includes more than one occurence of the same quadrant value,
   only the first occurence is processed and the rest MUST be ignored by
   the server.

   If a same preference value is used for more than one quadrant, it is
   left to the server implementation which quadrant should be preferred
   (if the server can assign addresses from all of some of the quadrants
   with the same assigned preference).

   If the client or relay agent provide the OPTION_SLAP_QUAD, the server
   uses 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 cannot provide an assignment from one of the specified
   quadrant-n fields, it MUST NOT assign any addresses and return a
   status of NoQuadAvail (IANA-2) in the IA_LL Option.

   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 1 set of values).

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   Client and relay agent MUST NOT place the same quadrant value into
   the option more than once; however servers should be capable of
   dealing with this by using the more preferred instance (as it
   requires no special handling).

6.  IANA Considerations

   IANA is requested to assign the QUAD (IANA-1) option code from the
   DHCPv6 "Option Codes" registry maintained at
   http://www.iana.org/assignments/dhcpv6-parameters and use the
   following data when adding the option to the registry:

       Value: IANA-1
       Description: OPTION_SLAP_QUAD
       Client ORO: No
       Singleton Option: No
       Reference: this document

   IANA is requested to assign the NoQuadAvail (IANA-2) code from the
   DHCPv6 "Status Codes" registry maintained
   athttp://www.iana.org/assignments/dhcpv6-parameters and use the
   following data when adding the option to the registry:

       Value: IANA-2
       Description: NoQuadAvail
       Reference: this document

7.  Security Considerations

   See [RFC8415] for the DHCPv6 security considerations.  See [RFC8200]
   for the IPv6 security considerations.

   See also [I-D.ietf-dhc-mac-assign] for security considerations
   regarding link-layer address assignments using DHCP.

8.  Acknowledgments

   The authors would like to thank Bernie Volz for his very valuable
   comments on this document.  We also want to thank Ian Farrer and
   Tomek Mrugalski for their very detailed and helpful reviews.

   The work in this draft will be further developed and explored under
   the framework of the H2020 5Growth (Grant 856709) and 5G-DIVE
   projects (Grant 859881).

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9.  References

9.1.  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>.

   [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>.

   [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>.

9.2.  Informative References

   [I-D.ietf-dhc-mac-assign]
              Volz, B., Mrugalski, T., and C. Bernardos, "Link-Layer
              Addresses Assignment Mechanism for DHCPv6", draft-ietf-
              dhc-mac-assign-03 (work in progress), January 2020.

   [IEEEStd802c-2017]
              IEEE Computer Society, "IEEE Standard for Local and
              Metropolitan Area Networks: Overview and Architecture,
              Amendment 2: Local Medium Access Control (MAC) Address
              Usage, IEEE Std 802c-2017".

Authors' Addresses

   Carlos J. Bernardos
   Universidad Carlos III de Madrid
   Av. Universidad, 30
   Leganes, Madrid  28911
   Spain

   Phone: +34 91624 6236
   Email: cjbc@it.uc3m.es
   URI:   http://www.it.uc3m.es/cjbc/

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   Alain Mourad
   InterDigital Europe

   Email: Alain.Mourad@InterDigital.com
   URI:   http://www.InterDigital.com/

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