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Versions: (draft-bernardos-dhc-slap-quadrant) 00 01 02 03 04 05 06 07 08 09 10 11

DHC WG                                                     CJ. Bernardos
Internet-Draft                                                      UC3M
Intended status: Standards Track                               A. Mourad
Expires: February 4, 2021                                   InterDigital
                                                          August 3, 2020


               SLAP quadrant selection option for DHCPv6
                    draft-ietf-dhc-slap-quadrant-10

Abstract

   IEEE originally structured the 48-bit MAC address space in such a way
   that half of it was reserved for local use.  In 2017, 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.

   IEEE is developing protocols to assign addresses (IEEE P802.1CQ).
   There is work also 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 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 February 4, 2021.







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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
   to this document.  Code Components extracted from this document must
   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 (IEEE 802.11) devices  . . . . . . . . . . . . .   4
       1.1.2.  Hypervisor: migratable vs non-migratable functions  .   5
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  DHCPv6 Extensions . . . . . . . . . . . . . . . . . . . . . .   7
     3.1.  Address Assignment from the Preferred SLAP Quadrant
           Indicated by the Client . . . . . . . . . . . . . . . . .   7
     3.2.  Address Assignment from the SLAP Quadrant Indicated by
           the Relay . . . . . . . . . . . . . . . . . . . . . . . .   9
   4.  DHCPv6 Option Definition  . . . . . . . . . . . . . . . . . .  11
     4.1.  Quad option . . . . . . . . . . . . . . . . . . . . . . .  11
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  13
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  13
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  14
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  14
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  14
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  14
   Appendix A.  Quadrant Selection Mechanisms examples . . . . . . .  15
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  17

1.  Introduction

   IEEE structures the 48-bit MAC address space in such a way that half
   of it was reserved for local use (where the Universal/Local -- U/L --
   bit is set to 1).  In 2017, IEEE published a new standard (IEEE Std
   802c [IEEEStd802c]) 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  In SLAP Quadrant 01, "Extended Local Identifier" (ELI) MAC
      addresses are assigned based on a 24-bit Company ID (CID),
      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.

   o  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.

   o  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.

   o  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)

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

                         Figure 2: SLAP quadrants





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1.1.  Problem statement

   IEEE is developing mechanisms to assign addresses (IEEE P802.1CQ
   project) [IEEE-P802.1CQ-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.
   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.  WiFi (IEEE 802.11) 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): 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.  In this scenario, a reasonable behavior would be
      that, upon a first boot, the device uses a temporary MAC address
      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 abandons its temporary MAC address.  Home automation IoT
      devices typically do not move (however, not that there is an
      increase of smart health monitoring devices, which are mobile).
      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.

   o  Privacy: Today, MAC addresses allow the exposure of users'
      locations making it relatively easy to track users' 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



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      quadrant from which to assign addresses, as 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: 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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   IA_LL         Identity Association for Link-Layer Address: an
                 identity association (IA) used to request or assign
                 link-layer addresses.  Section 10.1 of
                 [I-D.ietf-dhc-mac-assign] 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 10.2
                 of [I-D.ietf-dhc-mac-assign] provides details on the
                 LLADDR option.

   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
                 [I-D.ietf-dhc-mac-assign], 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].

   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 [I-D.ietf-dhc-mac-assign], 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].

   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].

   address       Unless specified otherwise, an address means a link-
                 layer (or MAC) address, as specified in IEEE Std 802
                 [IEEEStd802].  The address is six or eight 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.






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

    +--------+                            +--------+
    | 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 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 an 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 in the
       IA_LL-option field (alongside the LLADDR option).

   2.  The server, upon receiving an IA_LL option in Solicit, inspects
       its contents.  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



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       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 supports the new QUAD IA_LL-option,
       and 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 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 no
       address pool(s) configured at the server 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 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 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, may receive a Reply in response to the Solicit and skip
       the Advertise and Request 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.



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   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 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)




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   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 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_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 also at 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.




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   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.

   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 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     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      .                                                               .
      .                                                               .
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  quadrant-n-1 |   pref-n-1    |   quadrant-n  |    pref-n     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                       Figure 5: Quad Option Format

   option-code     OPTION_SLAP_QUAD (IANA-1).

   option-len      2 * number of included (quadrant, preference).  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], 3: SAI).  Each
                   quadrant MUST only appear once at most in the option.
                   A 1-byte field.

   pref-n          Preference associated to quadrant-n.  A higher value
                   means a more preferred quadrant.  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 occurence 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 without 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 provide 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



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   specified quadrant-n fields, it MUST NOT assign any addresses and
   return a status of NoQuadAvail (IANA-2) in the IA_LL Option.  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
   statis 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 1 set of values).

5.  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


6.  Security Considerations

   See [RFC8415] and [RFC7227] for the DHCPv6 security and privacy
   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.







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7.  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, Eric 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 to Roger Marks and Antonio de la Oliva for
   comments related to IEEE work and references.

   The work in document draft has been supported by the H2020 5Growth
   (Grant 856709) and 5G-DIVE projects (Grant 859881).

8.  References

8.1.  Normative 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-08 (work in progress), July 2020.

   [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>.

8.2.  Informative References

   [IEEE-P802.1CQ-Project]
              IEEE, "IEEE P802.1CQ: Multicast and Local Address
              Assignment".

   [IEEEStd802]
              IEEE, "IEEE Standard for Local and Metropolitan Area
              Networks: Overview and Architecture, IEEE Std 802-2014",
              June 2014.




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   [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", June 2017.

   [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.  Quadrant Selection Mechanisms examples

   This appendix 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 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
      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.




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   o  Managed/unmanaged: depending on whether the IoT device is managed
      during its lifetime or cannot be re-configured [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).

   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 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 pre-
   configured preferences.

   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: Yes/No.

   o  First time visited network: Yes/No.

   o  Network geographical location.

   o  Mobility: Yes (the device might change its network attachment
      point)/No (the device is not going to change its network
      attachment point).

   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



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      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 expected to move and 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 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 or virtualization infrastructure manager 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 the ELI and SAI
      quadrants are better suited 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.

Authors' Addresses








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   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/


   Alain Mourad
   InterDigital Europe

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



































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