DHC WG CJ. Bernardos Internet-Draft UC3M Intended status: Standards Track A. Mourad Expires: November 28, 2020 InterDigital May 27, 2020 SLAP quadrant selection options for DHCPv6 draft-ietf-dhc-slap-quadrant-09 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. We complement this 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 addresses to the given client out of the quadrant requested by relay or client. A new DHCPv6 option (OPTION_SLAP_QUAD, or 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." Bernardos & Mourad Expires November 28, 2020 [Page 1] Internet-Draft DHCPv6 SLAP quadrant selection May 2020 This Internet-Draft will expire on November 28, 2020. 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 devices . . . . . . . . . . . . . . . . . . . . 4 1.1.2. Hypervisor: migratable vs non-migratable functions . 5 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6 3. Quadrant Selection Mechanisms examples . . . . . . . . . . . 7 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 . . . . . . . . . . . . . . . . . 14 5.1. Quad (IA_LL) option . . . . . . . . . . . . . . . . . . . 14 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15 7. Security Considerations . . . . . . . . . . . . . . . . . . . 16 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 16 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 16 9.1. Normative References . . . . . . . . . . . . . . . . . . 16 9.2. Informative References . . . . . . . . . . . . . . . . . 17 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17 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 Universal/ Local -- 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 Bernardos & Mourad Expires November 28, 2020 [Page 2] Internet-Draft DHCPv6 SLAP quadrant selection May 2020 of the local MAC address space. These four regions, called SLAP quadrants, are briefly described below (see Figure 1 and Figure 2 for details): 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 the MAC addresses used for use 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. 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 Bernardos & Mourad Expires November 28, 2020 [Page 3] Internet-Draft DHCPv6 SLAP quadrant selection May 2020 +----------+-------+-------+-----------------------+----------------+ | 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 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. We complement this 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. 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 Bernardos & Mourad Expires November 28, 2020 [Page 4] Internet-Draft DHCPv6 SLAP quadrant selection May 2020 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 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). Bernardos & Mourad Expires November 28, 2020 [Page 5] Internet-Draft DHCPv6 SLAP quadrant selection May 2020 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. 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 [RFC8415]. 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. Bernardos & Mourad Expires November 28, 2020 [Page 6] Internet-Draft DHCPv6 SLAP quadrant selection May 2020 3. Quadrant Selection Mechanisms examples 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 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, if 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 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 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 Bernardos & Mourad Expires November 28, 2020 [Page 7] Internet-Draft DHCPv6 SLAP quadrant selection May 2020 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. 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 Bernardos & Mourad Expires November 28, 2020 [Page 8] Internet-Draft DHCPv6 SLAP quadrant selection May 2020 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. 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) Bernardos & Mourad Expires November 28, 2020 [Page 9] Internet-Draft DHCPv6 SLAP quadrant selection May 2020 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 (with the LLAADR option). 2. The server, upon receiving an IA_LL option, 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 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 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 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. 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). Bernardos & Mourad Expires November 28, 2020 [Page 10] Internet-Draft DHCPv6 SLAP quadrant selection May 2020 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]). 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" (i.e., different) 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. Otherwise, the client SHOULD NOT configure the obtained address. It MAY repeat the process selecting a different DHCP server. 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. Bernardos & Mourad Expires November 28, 2020 [Page 11] Internet-Draft DHCPv6 SLAP quadrant selection May 2020 +--------+ +--------+ +--------+ | 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 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 Bernardos & Mourad Expires November 28, 2020 [Page 12] Internet-Draft DHCPv6 SLAP quadrant selection May 2020 instances of the IA_LL option in the same message, the DHCP relay MUST 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(s) of the option to process is selected. 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 the requested quadrant(s), then the addresses being offered MUST belong to the requested quadrant(s). 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 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]). When the Bernardos & Mourad Expires November 28, 2020 [Page 13] Internet-Draft DHCPv6 SLAP quadrant selection May 2020 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. 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. 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: 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 Bernardos & Mourad Expires November 28, 2020 [Page 14] Internet-Draft DHCPv6 SLAP quadrant selection May 2020 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, 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 a quadrant - preference tuple is used in this option (instead of using a list of quadrants ordered by preference) to 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 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). 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: Bernardos & Mourad Expires November 28, 2020 [Page 15] Internet-Draft DHCPv6 SLAP quadrant selection May 2020 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, Tomek Mrugalski, Eric Vyncke, Tatuya Jinmei and Carl Wallace 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). 9. References 9.1. 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-06 (work in progress), May 2020. Bernardos & Mourad Expires November 28, 2020 [Page 16] Internet-Draft DHCPv6 SLAP quadrant selection May 2020 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", STD 86, RFC 8200, DOI 10.17487/RFC8200, July 2017, . [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, . 9.2. Informative References [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/ Alain Mourad InterDigital Europe Email: Alain.Mourad@InterDigital.com URI: http://www.InterDigital.com/ Bernardos & Mourad Expires November 28, 2020 [Page 17]