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Unique IPv6 Prefix per Host

The information below is for an old version of the document that is already published as an RFC.
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 2017-12-04 (Latest revision 2017-10-16)
Replaces draft-jjmb-v6ops-unique-ipv6-prefix-per-host
RFC stream Internet Engineering Task Force (IETF)
Intended RFC status Best Current Practice
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)
Action Holders
Consensus boilerplate Yes
Telechat date (None)
Responsible AD Warren "Ace" Kumari
Send notices to, Ron Bonica <>
IANA IANA review state Version Changed - Review Needed
IANA action state No IANA Actions
v6ops                                                      J. Brzozowski
Internet-Draft                                             Comcast Cable
Intended status: Best Current Practice                   G. Van De Velde
Expires: April 19, 2018                                            Nokia
                                                        October 16, 2017

                      Unique IPv6 Prefix Per Host


   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 service provider IPv6 address include
   improved host isolation and enhanced subscriber management on shared
   network segments.

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."

   This Internet-Draft will expire on April 19, 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

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   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  . . . . . . . . . . . . . . . . . . . . . .   8
   9.  Normative References  . . . . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

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 access network service.

   A shared network service, is a service offering where a particular L2
   access network (e.g. wifi) is shared and used by multiple visiting
   devices (i.e. subscribers).  Many service providers offering shared
   access network services, have legal requirements, or find it good
   practice, to provide isolation between the connected visitor devices
   to control potential abuse of the shared access network.

   A network implementing a unique IPv6 prefix per host, can simply
   ensure that devices cannot send packets to each other except through
   the first-hop router.  This will automatically provide robust
   protection against attacks between devices that rely on link-local
   ICMPv6 packets, such as DAD reply spoofing, ND cache exhaustion,
   malicious redirects, and rogue RAs.  This form of protection is much
   more scalable and robust than alternative mechanisms such as DAD
   proxying, forced forwarding, or ND snooping.

   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 wireless).

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   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.

   In most current deployments, User Equipment (UE) IPv6 address
   assignment is commonly done using either IPv6 SLAAC RFC4862 [RFC4862]
   and/or DHCP IA_NA (Identity Association - Non-temporary Address)
   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].  To not exclude any known IPv6
   implementations, IPv6 SLAAC based subscriber and address management
   is the recommended technology to reach highest percentage of
   connected IPv6 devices on a provider managed shared network service.
   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 focuses 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

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   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.  Often service providers
      have legal requirements, or find it good practice, to provide
      isolation between the connected visitor devices to control
      potential abuse of the shared access network.

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

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.

   This document recommends providing a unique IPv6 prefix to devices
   connected to the managed shared network.  Each unique IPv6 prefix can
   function as control-plane anchor point to make sure that each device
   receives expected subscriber policy and service levels (throughput,
   QoS, security, parental-control, subscriber mobility management,

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 subscriber sends a RS (Router Solicitation) message.

   The First Hop Router receives this subscriber RS message and starts
   the process to compose the response to the subscriber originated RS
   message.  The First Hop Router will answer using a solicited RA
   (Router Advertisement) to the subscriber.

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   When the First Hop Router sends a solicited RA response, or
   periodically sends unsolicited RAs, the RA MUST be sent only to the
   subscriber that has been assigned the Unique IPv6 prefix contained in
   the RA.  This is achieved by sending a solicited RA response or
   unsolicited RAs to the all-nodes group, as detailed in RFC4861
   [RFC4861] section 6.2.4 and 6.2.6, but instead of using the link-
   layer multicast address associated with the all-nodes group, the
   link-layer unicast address of the subscriber that has been assigned
   the Unique IPv6 prefix contained in the RA MUST be used as the link-
   layer destination RFC6085 [RFC6085].  Or, optionally in some cases, a
   solicited RA response could be sent unicast to the link-local address
   of the subscriber as detailed in RFC4861 [RFC4861] section 6.2.6,
   nevertheless unsolicited RAs are always sent to the all-nodes group.

   This solicited RA contains two important parameters for the
   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 Router
   or from a centrally allocated pool.  The flags indicate to the
   subscriber to use SLAAC and/or DHCPv6 for address assignment; it 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 (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 subscriber can configure itself using SLAAC)

   o  L-flag = 0 (the prefix is not an on-link prefix, which means that
      the 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 subscriber adds an additional
   level of protection and efficiency.  The protection is driven because
   all external communication of a connected device is directed to the
   first hop router as required by RFC4861 [RFC4861].  Best efficiency
   is achieved because the recommended RA flags allow broadest support
   on connected devices to receive a valid IPv6 address (i.e. privacy
   addresses RFC4941 [RFC4941] or SLAAC RFC4862 [RFC4862]).

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   The architected result of designing the RA as documented above is
   that each subscriber gets its own unique IPv6 prefix.  Each host can
   consequently use SLAAC or any other method of choice to select its
   /128 unique address.  Either stateless DHCPv6 RFC3736 [RFC3736] or
   IPv6 Router Advertisement Options for DNS Configuration RFC8106
   [RFC8106] can be used to get the IPv6 address of the DNS server.  If
   the subscriber desires to send anything external including towards
   other subscriber devices (assuming device to device communications is
   enabled and supported), then, due to the L-bit being unset, then
   RFC4861 [RFC4861] requires that this traffic is sent to the First Hop

   After the 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 subscriber device itself, it will need to
   verify that the address is unique on the shared network.  The
   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.

5.  IPv6 Neighbor Discovery Best Practices

   An operational consideration when using IPv6 address assignment using
   IPv6 SLAAC is that after the onboarding procedure, the subscriber
   will have a prefix with certain preferred and valid lifetimes.  The
   First Hop 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
   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 subscriber
   address assignment, this uncertainty on the First Hop Router is not
   of impact due to the stateful nature of DHCPv6 IA_NA address

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

   o  Maximum IPv6 Router Advertisement Interval (MaxRtrAdvInterval) =
      300s (or when battery consumption is a concern 686s, see Note

   o  IIPv6 Router LifeTime = 3600s (see Note below)

   o  Reachable time = 30s

   o  IPv6 Valid Lifetime = 3600s

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   o  IPv6 Preferred Lifetime = 1800s

   o  Retransmit timer = 0s

   Note: When servicing large numbers of battery powered devices,
   RFC7772 [RFC7772] suggests a maximum of 7 RAs per hour and a 45-90
   minute IPv6 Router Lifetime.  To achieve a maximum of 7 RAs per hour,
   the Minimum IPv6 Router Advertisement Interval (MinRtrAdvInterval) is
   the important parameter, and MUST be greater than or equal to 514
   seconds (1/7 of an hour).  Further as discussed in RFC4861 [RFC4861]
   section 6.2.1, MinRtrAdvInterval <=0.75 * MaxRtrAdvInterval,
   therefore MaxRtrAdvInterval MUST additionally be greater than or
   equal to 686 seconds.  As for the recommended IPv6 Router Lifetime,
   since this technique requires that RAs are sent using the link-layer
   unicast address of the subscriber, the concerns over multicast
   delivery discussed in RFC7772 [RFC7772] are already mitigated,
   therefore the above suggestion of 3600 seconds (an hour) seems
   sufficient for this use case.

   IPv6 SLAAC requires the router to maintain neighbor state, which
   implies costs in terms of memory, power, message exchanges, and
   message processing.  Stale entries can prove an unnecessary burden,
   especially on WiFi interfaces.  It is RECOMMENDED that stale neighbor
   state be removed quickly.

   When employing stateless IPv6 address assignment, a number of widely
   deployed operating systems will attempt to utilise 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.
   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 Router MUST be able to handle the presence and use of
   multiple globally routable IPv6 addresses.

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 a unique IPv6 Prefix per Host.
   However, when combining both IPv6 privacy extensions and a unique
   IPv6 Prefix per Host a reduced privacy experience for the subscriber
   is introduced, because a prefix may be associated with a subscriber,

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   even when the subscriber implemented IPv6 privacy extensions RFC4941
   [RFC4941].  If the operator assigns the same unique prefix to the
   same link-layer address every time a host connects, any remote party
   who is aware of this fact can easily track a host simply by tracking
   its assigned prefix.  This nullifies the benefit provided by privacy
   addresses RFC4941 [RFC4941].  If a host wishes to maintain privacy on
   such networks, it SHOULD ensure that its link-layer address is
   periodically changed or randomized.

   No other additional security considerations are made in this

8.  Acknowledgements

   The authors would like to explicit thank David Farmer and Lorenzo
   Colitti for their extended contributions and suggested text.

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

   Fred Baker, Ben Campbell, Brian Carpenter, Tim Chown, Killian
   Desmedt, Brad Hilgenfeld, Wim Henderickx, Erik Kline, Suresh
   Krishnan, 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, <>.

   [RFC3736]  Droms, R., "Stateless Dynamic Host Configuration Protocol
              (DHCP) Service for IPv6", RFC 3736, DOI 10.17487/RFC3736,
              April 2004, <>.

   [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,

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   [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,

   [RFC6085]  Gundavelli, S., Townsley, M., Troan, O., and W. Dec,
              "Address Mapping of IPv6 Multicast Packets on Ethernet",
              RFC 6085, DOI 10.17487/RFC6085, January 2011,

   [RFC7772]  Yourtchenko, A. and L. Colitti, "Reducing Energy
              Consumption of Router Advertisements", BCP 202, RFC 7772,
              DOI 10.17487/RFC7772, February 2016,

   [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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