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Unique IPv6 Prefix Per Host

The information below is for an old version of the document.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 8273.
Authors John Jason Brzozowski , Gunter Van de Velde
Last updated 2017-09-09 (Latest revision 2017-07-31)
Replaces draft-jjmb-v6ops-unique-ipv6-prefix-per-host
RFC stream Internet Engineering Task Force (IETF)
Additional resources Mailing list discussion
Stream WG state Submitted to IESG for Publication
Document shepherd Ron Bonica
Shepherd write-up Show Last changed 2017-05-09
IESG IESG state Became RFC 8273 (Informational)
Consensus boilerplate Yes
Telechat date (None)
Responsible AD Warren "Ace" Kumari
Send notices to, Ron Bonica <>
IANA IANA review state IANA OK - No Actions Needed
v6ops                                                      J. Brzozowski
Internet-Draft                                             Comcast Cable
Intended status: Best Current Practice                   G. Van De Velde
Expires: February 1, 2018                                          Nokia
                                                           July 31, 2017

                      Unique IPv6 Prefix Per Host


   In some IPv6 environments, the need has arisen for hosts to be able
   to utilize a unique IPv6 prefix, even though the link or media may be
   shared.  Typically hosts (subscribers) on a shared network, either
   wired or wireless, such as Ethernet, WiFi, etc., will acquire unique
   IPv6 addresses from a common IPv6 prefix that is allocated or
   assigned for use on a specific link.

   In most deployments today, IPv6 address assignment from a single IPv6
   prefix on a shared network is done by either using IPv6 stateless
   address auto-configuration (SLAAC) and/or stateful DHCPv6.  While
   this is still viable and operates as designed, there are some large
   scale environments where this concept introduces significant
   performance challenges and implications, specifically related to IPv6
   router and neighbor discovery.

   This document outlines an approach utilising existing IPv6 protocols
   to allow hosts to be assigned a unique IPv6 prefix (instead of a
   unique IPv6 address from a shared IPv6 prefix).  Benefits of unique
   IPv6 prefix over a unique IPv6 address from the service provider
   include improved subscriber isolation and enhanced subscriber

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

   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."

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   This Internet-Draft will expire on February 1, 2018.

Copyright Notice

   Copyright (c) 2017 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
   ( 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.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Motivation and Scope of Applicability . . . . . . . . . . . .   3
   3.  Design Principles . . . . . . . . . . . . . . . . . . . . . .   4
   4.  IPv6 Unique Prefix Assignment . . . . . . . . . . . . . . . .   4
   5.  IPv6 Neighbor Discovery Best Practices  . . . . . . . . . . .   6
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   9.  Normative References  . . . . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   The concepts in this document are originally developed as part of a
   large scale, production deployment of IPv6 support for a provider
   managed shared network service.  In this document IPv6 support does
   not preclude support for IPv4; however, the primary objectives for
   this work was to make it so that user equipment (UE) were capable of
   an IPv6 only experience from a network operators perspective.  In the
   context of this document, UE can be 'regular' end-user-equipment, as
   well as a server in a datacenter, assuming a shared network (wired or

   Details of IPv4 support are out of scope for this document.  This
   document will also, in general, outline the requirements that must be
   satisfied by UE to allow for an IPv6 only experience.

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   In most current deployments, User Equipment (UE) IPv6 address
   assignment is commonly done using either IPv6 SLAAC RFC4862 [RFC4862]
   and/or DHCP IA_NA RFC3315 [RFC3315].  During the time when this
   approach was developed and subsequently deployed, it has been
   observed that some operating systems do not support the use of DHCPv6
   for the acquisition of IA_NA per RFC7934 [RFC7934].  As such the use
   of IPv6 SLAAC based subscriber and address management for provider
   managed shared network services is the recommended technology of
   choice, as it does not exclude any known IPv6 implementation.  In
   addition an IA_NA-only network is not recommended per RFC 7934
   RFC7934 [RFC7934] section 8.  This document will detail the mechanics
   involved for IPv6 SLAAC based address and subscriber management
   coupled with stateless DHCPv6, where beneficial.

   This document will focus upon the process for UEs to obtain a unique
   IPv6 prefix.

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

2.  Motivation and Scope of Applicability

   The motivation for this work falls into the following categories:

   o  Deployment advice for IPv6 that will allow stable and secure IPv6
      only experience, even if IPv4 support is present

   o  Ensure support for IPv6 is efficient and does not impact the
      performance of the underlying network and in turn the customer

   o  Allow for the greatest flexibility across host implementation to
      allow for the widest range of addressing and configuration
      mechanisms to be employed.  The goal here is to ensure that the
      widest population of UE implementations can leverage the
      availability of IPv6

   o  Lay the technological foundation for future work related to the
      use of IPv6 over shared media requiring optimized subscriber

   o  Two devices (subscriber/hosts), both attached to the same provider
      managed shared network should only be able to communicate through
      the provider managed First Hop Router

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   o  Provide guidelines regarding best common practices around IPv6
      neighborship discovery RFC4861 [RFC4861] and IPv6 address managent
      settings between the First Hop router and directly connected

3.  Design Principles

   The First Hop router discussed in this document is the L3-Edge router
   responsible for the communication with the devices (hosts and
   subscribers) directly connected to a provider managed shared network,
   and to transport traffic between the directly connected devices and
   between directly connected devices and remote devices.

   The work detailed in this document is focused on providing details
   regarding best common practices of the IPv6 neighbor discovery and
   related IPv6 address management settings between the First Hop router
   and directly connected hosts/subscribers.  The documented Best
   Current Practice helps a service provider to better manage the shared
   provider managed network on behalf of the connected devices.

   The Best Current Practice documented in this note is to provide a
   unique IPv6 prefix to hosts/subscribers devices connected to the
   provider managed shared network.  Each unique IPv6 prefix can
   function as control-plane anchor point to make sure that each
   subscriber is receiving expected subscriber policy and service levels
   (throughput, QoS, security, parental-control, subscriber mobility
   management, etc.).

4.  IPv6 Unique Prefix Assignment

   When a UE connects to the shared provider managed network and is
   attached, it will initiate IP configuration phase.  During this phase
   the UE will, from an IPv6 perspective, attempt to learn the default
   IPv6 gateway, the IPv6 prefix information, the DNS information
   RFC8106 [RFC8106], and the remaining information required to
   establish globally routable IPv6 connectivity.  For that purpose, the
   the UE/subscriber sends a RS (Router Solicitation) message.

   The First Hop Router receives this UE/subscriber RS message and
   starts the process to compose the response to the UE/subscriber
   originated RS message.  The First Hop Provider Router will answer
   using a unicast RA (Router Advertisement) to the UE/subscriber.  This
   RA contains two important parameters for the EU/subscriber to
   consume: a Unique IPv6 prefix (currently a /64 prefix) and some
   flags.  The Unique IPv6 prefix can be derived from a locally managed
   pool or aggregate IPv6 block assigned to the First Hop Provider
   Router or from a centrally allocated pool.  The flags indicate to the
   UE/subscriber to use SLAAC and/or DHCPv6 for address assignment; it

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   may indicate if the autoconfigured address is on/off-link and if
   'Other' information (e.g.  DNS server address) needs to be requested.

   The IPv6 RA flags used for best common practice in IPv6 SLAAC based
   Provider managed shared networks are:

   o  M-flag = 0 (UE/subscriber address is not managed through DHCPv6),
      this flag may be set to 1 in the future if/when DHCPv6 prefix
      delegation support is desired)

   o  O-flag = 1 (DHCPv6 is used to request configuration information
      i.e. DNS, NTP information, not for IPv6 addressing)

   o  A-flag = 1 (The UE/subscriber can configure itself using SLAAC)

   o  L-flag = 0 (the prefix is not an on-link prefix, which means that
      the UE/subscriber will NEVER assume destination addresses that
      match the prefix are on-link and will ALWAYS send packets to those
      addresses to the appropriate gateway according to route selection

   The use of a unique IPv6 prefix per UE adds an additional level of
   protection and efficiency as it relates to how IPv6 Neighbor
   Discovery and Router Discovery processing.  Since the UE has a unique
   IPv6 prefix all traffic by default will be directed to the First Hop
   provider router.  Further, the flag combinations documented above
   maximise the IPv6 configurations that are available by hosts
   including the use of privacy IPv6 addressing.

   The architected result of designing the RA as documented above is
   that each UE/subscriber gets its own unique IPv6 prefix for which it
   can use SLAAC or any other method to select its /128 unique address.
   In addition it will use stateless DHCPv6 to get the IPv6 address of
   the DNS server, however it SHOULD NOT use stateful DHCPv6 to receive
   a service provider managed IPv6 address.  If the UE/subscriber
   desires to send anything external including other UE/subscriber
   devices (assuming device to device communications is enabled and
   supported), then, due to the L-bit set, it SHOULD send this traffic
   to the First Hop Provider Router.

   After the UE/subscriber received the RA, and the associated flags, it
   will assign itself a 128 bit IPv6 address using SLAAC.  Since the
   address is composed by the UE/subscriber device itself, it will need
   to verify that the address is unique on the shared network.  The UE/
   subscriber will for that purpose, perform Duplicate Address Detection
   algorithm.  This will occur for each address the UE attempts to
   utilize on the shared provider managed network.

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5.  IPv6 Neighbor Discovery Best Practices

   An operational consideration when using IPv6 address assignment using
   IPv6 SLAAC is that after the onboarding procedure, the UE/subscriber
   will have a prefix with certain preferred and valid lifetimes.  The
   First Hop Provider Router extends these lifetimes by sending an
   unsolicited RA, the applicable MaxRtrAdvInterval on the first hop
   router MUST therefore be lower than the preferred lifetime.  One
   consequence of this process is that the First Hop Router never knows
   when a UE/subscriber stops using addresses from a prefix and
   additional procedures are required to help the First Hop Router to
   gain this information.  When using stateful DHCPv6 IA_NA for IPv6 UE/
   subscriber address assignment, this uncertainty on the First Hop
   Router is not of impact due to the stateful nature of DHCPv6 IA_NA
   address assignment.

   Following is a reference table of the key IPv6 router discovery and
   neighbor discovery timers for provider managed shared networks:

   o  IPv6 Router Advertisement Interval = 300s

   o  IPv6 Router LifeTime = 3600s

   o  Reachable time = 30s

   o  IPv6 Valid Lifetime = 3600s

   o  IPv6 Preferred Lifetime = 1800s

   o  Retransmit timer = 0s

   The stateless nature of the UE/subscriber IPv6 SLAAC connectivity
   model provides a consideration to make regarding resource consumption
   (i.e. memory, neighbor state) on the First Hop Router.  To reduce
   undesired resource consumption on the First Hop Router the desire is
   to remove UE/subscriber context in the case of non-permanent UE, such
   as in the case of WiFi hotspots as quickly as possible.  A possible
   solution is to use a subscriber inactivity timer which, after
   tracking a pre-defined (currently unspecified) number of minutes,
   deletes the subscriber context on the First Hop Router.

   When employing stateless IPv6 address assignment, a number of widely
   deployed operating systems will attempt to utilise RFC 4941 RFC4941
   [RFC4941] temporary 'private' addresses.

   Similarly, when using this technology in a datacenter, the UE server
   may need to use several addresses from the same Unique IPv6 Prefix,
   for example because is using multiple virtual hosts, containers, etc.

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   in the bridged virtual switch.  This can lead to the consequence that
   a UE has multiple /128 addresses from the same IPv6 prefix.  The
   First Hop Provider Router MUST be able to handle the presence and use
   of multiple globally routable IPv6 addresses.

   For accounting purposes, the First Hop Provider Router must be able
   to send usage statistics per UE/subscriber using Radius attributes.

6.  IANA Considerations

   No IANA considerations are defined at this time.

7.  Security Considerations

   The mechanics of IPv6 privacy extensions RFC4941 [RFC4941] is
   compatible with assignment of an Unique IPv6 Prefix per Host.  The
   combination of both IPv6 privacy extensions and operator based
   assignment of a Unique IPv6 Prefix per Host provides each
   implementing operator a tool to manage and provide subscriber
   services and hence reduces the experienced privacy within each
   operator controlled domain.  However, beyond the operator controlled
   domain, IPv6 privacy extensions provide the desired privacy as
   documented in RFC4941 [RFC4941].

   No other additional security considerations are made in this

8.  Acknowledgements

   The authors would like to thank the following, in alphabetical order,
   for their contributions:

   Brian Carpenter, Tim Chown, Lorenzo Colitti, Killian Desmedt, Brad
   Hilgenfeld, Wim Henderickx, Erik Kline, Warren Kumari, Thomas Lynn,
   Jordi Palet, Phil Sanderson, Colleen Szymanik, Jinmei Tatuya, Eric
   Vyncke, Sanjay Wadhwa

9.  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,

   [RFC3315]  Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins,
              C., and M. Carney, "Dynamic Host Configuration Protocol
              for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July
              2003, <>.

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   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
              "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
              DOI 10.17487/RFC4861, September 2007,

   [RFC4862]  Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
              Address Autoconfiguration", RFC 4862,
              DOI 10.17487/RFC4862, September 2007,

   [RFC4941]  Narten, T., Draves, R., and S. Krishnan, "Privacy
              Extensions for Stateless Address Autoconfiguration in
              IPv6", RFC 4941, DOI 10.17487/RFC4941, September 2007,

   [RFC7934]  Colitti, L., Cerf, V., Cheshire, S., and D. Schinazi,
              "Host Address Availability Recommendations", BCP 204,
              RFC 7934, DOI 10.17487/RFC7934, July 2016,

   [RFC8106]  Jeong, J., Park, S., Beloeil, L., and S. Madanapalli,
              "IPv6 Router Advertisement Options for DNS Configuration",
              RFC 8106, DOI 10.17487/RFC8106, March 2017,

Authors' Addresses

   John Jason Brzozowski
   Comcast Cable
   1701 John F. Kennedy Blvd.
   Philadelphia, PA


   Gunter Van De Velde


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