rfc9818v1.txt   rfc9818.txt 
Internet Engineering Task Force (IETF) T. Winters Internet Engineering Task Force (IETF) T. Winters
Request for Comments: 9818 QA Cafe Request for Comments: 9818 QA Cafe
Updates: 7084 July 2025 Updates: 7084 July 2025
Category: Informational Category: Informational
ISSN: 2070-1721 ISSN: 2070-1721
IPv6 Customer Edge (CE) Routers LAN DHCPv6 Prefix Delegation DHCPv6 Prefix Delegation on IPv6 Customer Edge (CE) Routers in LANs
Abstract Abstract
This document defines requirements for IPv6 Customer Edge (CE) This document defines requirements for IPv6 Customer Edge (CE)
routers to support DHCPv6 Prefix Delegation for distributing routers to support DHCPv6 Prefix Delegation for distributing
available prefixes that were delegated to a IPv6 CE router. This available prefixes to LAN devices that were delegated to a IPv6 CE
document updates RFC 7084. router. This document updates RFC 7084.
Status of This Memo Status of This Memo
This document is not an Internet Standards Track specification; it is This document is not an Internet Standards Track specification; it is
published for informational purposes. published for informational purposes.
This document is a product of the Internet Engineering Task Force This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has (IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents Internet Engineering Steering Group (IESG). Not all documents
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prefix delegation requires an IPv6 CE router to sub-delegate IPv6 prefix delegation requires an IPv6 CE router to sub-delegate IPv6
prefixes based on a set of rules. If more than one router uses prefixes based on a set of rules. If more than one router uses
hierarchical prefix delegation, an IPv6 prefix tree is created. When hierarchical prefix delegation, an IPv6 prefix tree is created. When
no routing protocol is enabled to discover the network topology, it no routing protocol is enabled to discover the network topology, it
is possible to have an unbalanced prefix delegation tree, which leads is possible to have an unbalanced prefix delegation tree, which leads
to running out of prefixes. More information on hierarchical prefix to running out of prefixes. More information on hierarchical prefix
delegation can be found, e.g., in Section 8.5 of CableLabs IPv6 delegation can be found, e.g., in Section 8.5 of CableLabs IPv6
eRouter specification [eRouter]. A flat prefix delegation requires eRouter specification [eRouter]. A flat prefix delegation requires
the router to be provisioned with the initial prefix and to assign the router to be provisioned with the initial prefix and to assign
/64 prefixes to all other prefix requests from routers in the LAN- /64 prefixes to all other prefix requests from routers in the LAN-
facing interface. The default configuration of CE router supporting facing interface. The default configuration of CE routers is
prefix delegation is designed to be a flat model to support zero- designed to be a flat model to support zero-configuration networking.
configuration networking.
This document does not cover dealing with multi-provisioned networks This document does not cover dealing with multi-prefix networks with
with more than one provider. Due to the complexity of a solution more than one provider. Due to the complexity of a solution that
that would require routing, provisioning, and policy, this is out of would require routing, provisioning, and policy, this is out of scope
scope of this document. of this document.
2. Requirements Language 2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in "OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
This document uses these keywords not strictly for the purpose of This document uses these keywords not strictly for the purpose of
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implementers regarding any protocol implementation required to implementers regarding any protocol implementation required to
produce a successful CE router that interoperates successfully with a produce a successful CE router that interoperates successfully with a
particular subset of currently deployed and planned common IPv6 particular subset of currently deployed and planned common IPv6
access networks. access networks.
3. Terminology 3. Terminology
The document makes use of the following terms, some of which are from The document makes use of the following terms, some of which are from
Section 2 of [RFC8200] Section 2 of [RFC8200]
IPv6 node: A device that implements IPv6 protocol. IPv6 node: A device that implements IPv6.
IPv6 router: An IPv6 node that forwards IPv6 packets not explicitly IPv6 router: An IPv6 node that forwards IPv6 packets not explicitly
addressed to itself. addressed to itself.
IPv6 host: An IPv6 node that is not a router. IPv6 host: An IPv6 node that is not a router.
ULA: Unique Local Address, as defined in [RFC4193]. ULA: Unique Local Address, as defined in [RFC4193].
GUA: Global Unicast Address, as defined in [RFC4291]. GUA: Global Unicast Address, as defined in [RFC4291].
4. IPv6 End-User Network Architecture 4. IPv6 End-User Network Architecture
The end-user network for IPv6 that is a stub network. Figure 1 The end-user network for IPv6 contains stub networks. Figure 1
illustrates the model topology. illustrates the model topology.
+-----------+ +-----------+
| Service | | Service |
| Provider | | Provider |
| Router | | Router |
+-----+-----+ +-----+-----+
| |
| |
| Customer | Customer
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These requirements are in addition to the ones in Section 4.3 of These requirements are in addition to the ones in Section 4.3 of
[RFC7084]. [RFC7084].
5.1. LAN Prefix Delegation Requirements (LPD) 5.1. LAN Prefix Delegation Requirements (LPD)
LPD-1: Each IPv6 CE router MUST support IPv6 prefix assignment LPD-1: Each IPv6 CE router MUST support IPv6 prefix assignment
according to Section 13.3 of [RFC8415] (Identity Association according to Section 13.3 of [RFC8415] (Identity Association
for Prefix Delegation (IA_PD) option) on its LAN for Prefix Delegation (IA_PD) option) on its LAN
interface(s). interface(s).
LPD-2: IPv6 CE routers MUST assign a prefix from the delegated LPD-2: Each IPv6 CE routers MUST assign a prefix from the delegated
prefix as specified by L-2 in Section 4.3 of [RFC7084]. If prefix as specified by L-2 in Section 4.3 of [RFC7084]. If
insufficient prefixes are available, the IPv6 CE router MUST insufficient prefixes are available, the IPv6 CE router MUST
log a system management error. log a system management error.
LPD-3: The prefix assigned to a link MUST NOT change in the absence LPD-3: The prefix assigned to a link MUST NOT change in the absence
of a local policy or a topology change. of a local policy or a topology change.
LPD-4: After LAN link prefix assignments, the IPv6 CE router MUST LPD-4: After LAN link prefix assignments, the IPv6 CE router MUST
keep the remaining IPv6 prefixes available to other routers keep the remaining IPv6 prefixes available to other routers
via Prefix Delegation. via Prefix Delegation.
LPD-5: IPv6 CE routers MUST maintain a local routing table that is LPD-5: IPv6 CE routers MUST maintain a local routing table that is
dynamically updated with leases and the associated next hops dynamically updated with leases and the associated next hops
as they are delegated to clients. When a delegated prefix as they are delegated to clients. Absent explicit
is released or expires, the associated route MUST be removed filtering, packets with destination addresses in a delegated
prefix MUST be forwarded to that prefix regardless of which
interface they are received on. 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 from the IPv6 CE router's routing table. A delegated prefix
expires when the valid lifetime assigned in the IA_PD expires when the valid lifetime assigned in the IA_PD
expires without being renewed. When a prefix is released or expires without being renewed. When a prefix is released or
expires, it MUST be returned the pool of available prefixes. expires, it MUST be returned the pool of available prefixes.
LPD-6: By default, the IPv6 CE router filtering rules MUST allow LPD-6: By default, the IPv6 CE router filtering rules MUST allow
forwarding of packets with an outer IPv6 header containing a forwarding of packets with an outer IPv6 header containing a
source address belonging to Delegated Prefixes, along with source address belonging to delegated prefixes, along with
reciprocal packets from the same flow, following the reciprocal packets from the same flow, following the
recommendations of [RFC6092]. This updates WPD-5 of recommendations of [RFC6092]. This updates WPD-5 of
[RFC7084] to not drop packets from prefixes that have been [RFC7084] to not drop packets from prefixes that have been
delegated. IPv6 CE routers MUST continue to drop packets delegated. IPv6 CE routers MUST continue to drop packets,
including destination address that is not assigned to the including destination address, that are not assigned to the
LAN or delegated. LAN or delegated.
LPD-7: The IPv6 CE routers MUST provision IA_PD prefixes with a LPD-7: The IPv6 CE routers MUST provision IA_PD prefixes with a
prefix-length of 64 on the LAN-facing interface unless prefix-length of 64 on the LAN-facing interface unless
configured to use a different prefix-length by the CE router configured to use a different prefix-length by the CE router
administrator. The prefix length of 64 is used as that is administrator. The prefix-length of 64 is used as that is
the current prefix length supported by SLAAC [RFC4862]. For the current prefix-length supported by SLAAC [RFC4862]. For
hierarchical prefix delegation, a prefix-length shorter than hierarchical prefix delegation, a prefix-length shorter than
64 may be configured. 64 may be configured.
LPD-8: IPv6 CE routers configured to generate a ULA prefix as LPD-8: IPv6 CE routers configured to generate a ULA prefix as
defined in ULA-1 of Section 4.3 of [RFC7084] MUST continue defined in ULA-1 of Section 4.3 of [RFC7084] MUST continue
to provision available GUA IPv6 prefixes. to provision available GUA IPv6 prefixes.
LPD-9: If an IPv6 CE router is provisioning both ULA and GUA via LPD-9: If an IPv6 CE router is provisioning both a ULA and GUA via
prefix delegation, the GUA SHOULD appear first in the DHCPv6 prefix delegation, the GUA SHOULD appear first in the DHCPv6
packets. packets.
LPD-10: IPv6 CE routers MUST NOT delegate prefixes via DHCPv6 on the LPD-10: IPv6 CE routers MUST NOT delegate prefixes via DHCPv6 on the
LAN using lifetimes that exceed the remaining lifetimes of LAN using lifetimes that exceed the remaining lifetimes of
the corresponding prefixes learned on the WAN. the corresponding prefixes learned on the WAN.
6. Security Considerations 6. Security Considerations
This document does not add any new security considerations beyond This document does not add any new security considerations beyond
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