Internet Engineering Task Force (IETF) T. WintersInternet-DraftRequest for Comments: 9818 QA Cafe Updates: 7084(if approved) 22 MayJuly 2025Intended status:Category: InformationalExpires: 23 November 2025ISSN: 2070-1721 IPv6CECustomer Edge (CE) Routers LAN DHCPv6 Prefix Delegationdraft-ietf-v6ops-cpe-lan-pd-09Abstract This document defines requirements for IPv6 Customer Edge (CE) routers to support DHCPv6 Prefix Delegation for distributing available prefixes that were delegated to a IPv6 CE router. This document updates RFC 7084. Status of This Memo ThisInternet-Draftdocument issubmitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documentsnot an Internet Standards Track specification; it is published for informational purposes. This document is a product of the Internet Engineering Task Force (IETF).Note that other groups may also distribute working documents as Internet-Drafts. The listIt represents the consensus ofcurrent Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draftthe IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Not all documentsvalidapproved by the IESG are candidates fora maximumany level ofsix monthsInternet Standard; see Section 2 of RFC 7841. Information about the current status of this document, any errata, and how to provide feedback on it may beupdated, replaced, or obsoleted by other documentsobtained atany 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 23 November 2025.https://www.rfc-editor.org/info/rfc9818. Copyright Notice Copyright (c) 2025 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)(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 Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. Table of Contents 1. Introduction. . . . . . . . . . . . . . . . . . . . . . . . 22. Requirements Language. . . . . . . . . . . . . . . . . . . . 33. Terminology. . . . . . . . . . . . . . . . . . . . . . . . . 34. IPv6 End-User Network Architecture. . . . . . . . . . . . . 35. Requirements. . . . . . . . . . . . . . . . . . . . . . . . 45.1. LAN Prefix Delegation Requirements (LPD). . . . . . . . 56. Security Considerations. . . . . . . . . . . . . . . . . . . 67. IANA Considerations. . . . . . . . . . . . . . . . . . . . . 68.Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6 9.References. . . . . . . . . . . . . . . . . . . . . . . . . 6 9.1.8.1. Normative References. . . . . . . . . . . . . . . . . . 6 9.2.8.2. Informative References. . . . . . . . . . . . . . . . . 7Acknowledgements Author's Address. . . . . . . . . . . . . . . . . . . . . . . . 81. Introduction This document describes guidelines for DHCPv6 Prefix Delegation in IPv6 Customer Edge (CE) routers([RFC7084])[RFC7084] in order to properly utilize the IPv6 prefixes delegated by service providers. Many service providers assign larger address blocks than /64 to CE routers, as recommended in [RFC6177]. If an IPv6 CE router does not support the Identity Association for Prefix Delegation (IA_PD) Prefix Option (Section 21.21 of [RFC8415]) on the LAN, it will not be able to assign any prefixes beyond its local interfaces, limiting the usefulness of assigning prefixes larger than /64 by the operator. Supporting IA_PD on the LAN interfaces of a CERouterrouter will allow those unused prefixes to be distributed into a network. Note that efforts such as those of the Stub Networking Auto Configuration (SNAC) Working Group depend on IPv6 prefixes being properly distributed in the LAN. Two models, hierarchical prefix and flat, were proposed in the past for prefix sub-delegation beyond an IPv6 CE router. Hierarchical prefix delegation requires an IPv6 CE router tosub delegatesub-delegate IPv6 prefixes based on a set of rules. If more than one router uses hierarchical prefix delegation, an IPv6 prefix tree is created. When no routing protocol is enabled to discover the network topology, it is possible to have an unbalanced prefix delegationtreetree, which leads to running out of prefixes. More information on hierarchical prefix delegation can be found, e.g., in Section 8.5 of CableLabs IPv6 eRouterSpecifictionspecification [eRouter]. A flat prefix delegation requires the router to be provisioned with the initial prefix and to assign /64 prefixes to all other prefix requests from routers in the LAN- facing interface. The default configuration of CERouterrouter supporting prefix delegation is designed to be a flat model to supportzerozero- configuration networking. This document does not cover dealing with multi-provisioned networks with more than one provider. Due to the complexity of a solution that would require routing,provisioningprovisioning, and policy, this is out of scope of this document. 2. Requirements Language 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. This document uses these keywords not strictly for the purpose of interoperability, but rather for the purpose of establishing industry-common baseline functionality. As such, the document points to several other specifications(preferable in RFC or stable form)to provide additional guidance to implementers regarding any protocol implementation required to produce a successful CE router that interoperates successfully with a particular subset of currentlydeployingdeployed and planned common IPv6 access networks. 3. Terminology The document makes use of the followingtermsterms, some of which are from Section 2 of [RFC8200]*IPv6 node: A device that implements IPv6 protocol.*IPv6 router: An IPv6 node that forwards IPv6 packets not explicitly addressed to itself.*IPv6 host: An IPv6 node that is not a router.* ULA:UniqueULA: Unique Local Address, as defined in [RFC4193].* GUA:Global Unique Addresses,GUA: Global Unicast Address, as defined in [RFC4291]. 4. IPv6 End-User Network Architecture The end-user network for IPv6 that is a stub network. Figure 1 illustrates the model topology. +-----------+ | Service | | Provider | | Router | +-----+-----+ | | | Customer | Internet Connection | +-----v-----+ | IPv6 | | CE | | Router | +-----+-----+ | +------+-------+ | | | | +---+----+ +-----+-----+ | IPv6 | | | | Host | | Router | | | | | +--------+ +-----+-----+ | | +---+----+ | IPv6 | | Host | | | +--------+ Figure 1: Example IPv6End UserEnd-User Topology 5. Requirements IPv6 CE routers distribute configuration information obtained during WAN interface provisioning to LAN-facing IPv6 hosts and routers.An [RFC7084] compliantA CE router that is compliant with [RFC7084] would only provide IPv6 hosts with configuration information. This document allows for addressing and routing of IPv6 prefixes to both hosts and routers. These requirements are in addition to the ones in Section 4.3 of [RFC7084]. 5.1. LAN Prefix Delegation Requirements (LPD) LPD-1: Each IPv6 CEroutersrouter MUST support IPv6 prefix assignment according to Section 13.3 of [RFC8415] (Identity Association for Prefix Delegation (IA_PD) option) on its LAN interface(s). LPD-2: IPv6 CE routers MUST assign a prefix from the delegated prefix as specified by L-2 in Section 4.3 of [RFC7084]. If insufficient prefixes areavailableavailable, the IPv6 CERouterrouter MUST log a system management error. LPD-3: The prefix assigned to a link MUST NOT change in the absence of a local policy or a topology change. LPD-4: After LAN link prefix assignments, the IPv6 CE router MUST keep the remaining IPv6 prefixes available to other routers via Prefix Delegation. LPD-5: IPv6 CE routers MUST maintain a local routing table that is dynamically updated with leases and the associated next hops as they are delegated to clients. When a delegated prefix is released or expires, the associated route MUST be removed from the IPv6 CE router's routing table. A delegated prefix expires when the valid lifetime assigned in the IA_PD expires without being renewed. When a prefix is released orexpiresexpires, it MUST be returned the pool of available prefixes. LPD-6: By default, the IPv6 CE router filtering rules MUST allow forwarding of packets with an outer IPv6 header containing a source address belonging to Delegated Prefixes, along with reciprocal packets from the same flow, following the recommendations of [RFC6092]. This updates WPD-5 of [RFC7084] to not drop packets from prefixes that have been delegated. IPv6 CE routers MUST continue to drop packets including destination address that is not assigned to the LAN or delegated. LPD-7: The IPv6 CE routers MUST provision IA_PD prefixes with a prefix-length of 64 on the LAN-facing interface unless configured to use a different prefix-length by the CERouterrouter administrator. The prefix length of 64 is used as that is the current prefix length supported by SLAAC [RFC4862]. For hierarchical prefixdelegationdelegation, a prefix-length shorter than 64 may be configured. LPD-8: IPv6 CE routers configured to generate a ULA prefix as defined in ULA-1 of Section 4.3 of [RFC7084] MUST continue to provision available GUA IPv6 prefixes. LPD-9: If an IPv6 CE router is provisioning both ULA and GUA via prefix delegation, the GUA SHOULD appear first in the DHCPv6 packets. LPD-10: IPv6 CE routers MUST NOT delegate prefixes via DHCPv6 on the LAN using lifetimes that exceed the remaining lifetimes of the corresponding prefixes learned on the WAN. 6. Security Considerations This document does not add any new security considerations beyond those mentioned in Section 4 of [RFC8213], Section 22 of[RFC8415][RFC8415], and Section 6 of [RFC6092]. 7. IANA Considerations This documentmakeshas norequest of IANA.IANA actions. 8.Acknowledgements Thanks to the following people for their guidance and feedback: Marion Dillon, Erik Auerswald, Esko Dijk, Tim Carlin, Richard Patterson, Ted Lemon, Michael Richardson, Martin Huneki, Gabor Lencse, Ole Troan, Brian Carpenter, David Farmer, Kyle Rose, Mohamed Boucadair, Tim Chown, Ron Bonica, and Erica Johnson. 9.References9.1.8.1. 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>. [RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005, <https://www.rfc-editor.org/info/rfc4193>. [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing Architecture", RFC 4291, DOI 10.17487/RFC4291, February 2006, <https://www.rfc-editor.org/info/rfc4291>. [RFC7084] Singh, H., Beebee, W., Donley, C., and B. Stark, "Basic Requirements for IPv6 Customer Edge Routers", RFC 7084, DOI 10.17487/RFC7084, November 2013, <https://www.rfc-editor.org/info/rfc7084>. [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>. [RFC8213] Volz, B. and Y. Pal, "Security of Messages Exchanged between Servers and Relay Agents", RFC 8213, DOI 10.17487/RFC8213, August 2017, <https://www.rfc-editor.org/info/rfc8213>. [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>.9.2.8.2. Informative References [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless Address Autoconfiguration", RFC 4862, DOI 10.17487/RFC4862, September 2007, <https://www.rfc-editor.org/info/rfc4862>. [RFC6092] Woodyatt, J., Ed., "Recommended Simple Security Capabilities in Customer Premises Equipment (CPE) for Providing Residential IPv6 Internet Service", RFC 6092, DOI 10.17487/RFC6092, January 2011, <https://www.rfc-editor.org/info/rfc6092>. [RFC6177] Narten, T., Huston, G., and L. Roberts, "IPv6 Address Assignment to End Sites", BCP 157, RFC 6177, DOI 10.17487/RFC6177, March 2011, <https://www.rfc-editor.org/info/rfc6177>. [eRouter] CableLabs, "IPv4 and IPv6 eRouterSpecificationSpecification", Data- Over-Cable Service Interface Specifications, VersionI21", February 2022,I22, May 2024, <https://www.cablelabs.com/specifications/CM-SP-eRouter>. Acknowledgements Thanks to the following people for their guidance and feedback: Marion Dillon, Erik Auerswald, Esko Dijk, Tim Carlin, Richard Patterson, Ted Lemon, Michael Richardson, Martin Huneki, Gabor Lencse, Ole Troan, Brian Carpenter, David Farmer, Kyle Rose, Mohamed Boucadair, Tim Chown, Ron Bonica, and Erica Johnson. Author's Address Timothy Winters QA Cafe 100 Main Street, Suite #212 Dover, NH 03820 United States of America Email: tim@qacafe.com