DHCPv6 Prefix Delegating Relay Requirements
RFC 8987

Document Type RFC - Proposed Standard (February 2021; No errata)
Authors Ian Farrer  , Naveen Kottapalli  , Martin Hunek  , Richard Patterson 
Last updated 2021-02-28
Replaces draft-fkhp-dhc-dhcpv6-pd-relay-requirements
Stream Internent Engineering Task Force (IETF)
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Stream WG state Submitted to IESG for Publication (wg milestone: Apr 2020 - WGLC DHCPv6 Prefix D... )
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IESG IESG state RFC 8987 (Proposed Standard)
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Responsible AD Éric Vyncke
Send notices to Bernie Volz <volz@cisco.com>
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Internet Engineering Task Force (IETF)                         I. Farrer
Request for Comments: 8987                           Deutsche Telekom AG
Category: Standards Track                                  N. Kottapalli
ISSN: 2070-1721                                            Benu Networks
                                                                M. Hunek
                                         Technical University of Liberec
                                                            R. Patterson
                                                             Sky UK Ltd.
                                                           February 2021

              DHCPv6 Prefix Delegating Relay Requirements


   This document describes operational problems that are known to occur
   when using DHCPv6 relays with prefix delegation.  These problems can
   prevent successful delegation and result in routing failures.  To
   address these problems, this document provides necessary functional
   requirements for operating DHCPv6 relays with prefix delegation.

   It is recommended that any network operator using DHCPv6 prefix
   delegation with relays ensure that these requirements are followed on
   their networks.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at

Copyright Notice

   Copyright (c) 2021 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.  Terminology
     2.1.  General
     2.2.  Topology
     2.3.  Requirements Language
   3.  Problems Observed with Existing Delegating Relay
     3.1.  DHCP Messages Not Being Forwarded by the Delegating Relay
     3.2.  Delegating Relay Loss of State on Reboot
     3.3.  Multiple Delegated Prefixes for a Single Client
     3.4.  Dropping Messages from Devices with Duplicate MAC Addresses
           and DUIDs
     3.5.  Forwarding Loops between Client and Relay
   4.  Requirements for Delegating Relays
     4.1.  General Requirements
     4.2.  Routing Requirements
     4.3.  Service Continuity Requirements
     4.4.  Operational Requirements
   5.  IANA Considerations
   6.  Security Considerations
   7.  References
     7.1.  Normative References
     7.2.  Informative References
   Authors' Addresses

1.  Introduction

   For Internet service providers that offer native IPv6 access with
   prefix delegation to their customers, a common deployment
   architecture is to have a DHCPv6 relay agent function located in the
   ISP's Layer 3 customer edge device and a separate, centralized DHCPv6
   server infrastructure.  [RFC8415] describes the functionality of a
   DHCPv6 relay, and Section 19.1.3 of [RFC8415] mentions this
   deployment scenario, but it does not provide details for all of the
   functional requirements that the relay needs to fulfill to operate
   deterministically in this deployment scenario.

   A DHCPv6 relay agent for prefix delegation is a function commonly
   implemented in routing devices, but implementations vary in their
   functionality and client/server interworking.  This can result in
   operational problems such as messages not being forwarded by the
   relay or unreachability of the delegated prefixes.  This document
   provides a set of requirements for devices implementing a relay
   function for use with prefix delegation.

   The mechanisms for a relay to inject routes (including aggregated
   ones) on its network-facing interface based on prefixes learned from
   a server via DHCP prefix delegation (DHCP-PD) are out of scope of the

   Multi-hop DHCPv6 relaying is not affected.  The requirements in this
   document are solely applicable to the DHCP relay agent co-located
   with the first-hop router to which the DHCPv6 client requesting the
   prefix is connected, so no changes to any subsequent relays in the
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