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Versions: (draft-chown-homenet-arch) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 RFC 7368

Network Working Group                                      T. Chown, Ed.
Internet-Draft                                 University of Southampton
Intended status: Informational                                  J. Arkko
Expires: August 14, 2013                                        Ericsson
                                                               A. Brandt
                                                           Sigma Designs
                                                                O. Troan
                                                     Cisco Systems, Inc.
                                                                 J. Weil
                                                       Time Warner Cable
                                                       February 10, 2013


                 Home Networking Architecture for IPv6
                       draft-ietf-homenet-arch-07

Abstract

   This text describes evolving networking technology within
   increasingly large residential home networks.  The goal of this
   document is to define a general architecture for IPv6-based home
   networking, describing the associated principles, considerations and
   requirements.  The text briefly highlights specific implications of
   the introduction of IPv6 for home networking, discusses the elements
   of the architecture, and suggests how standard IPv6 mechanisms and
   addressing can be employed in home networking.  The architecture
   describes the need for specific protocol extensions for certain
   additional functionality.  It is assumed that the IPv6 home network
   is not actively managed, and runs as an IPv6-only or dual-stack
   network.  There are no recommendations in this text for the IPv4 part
   of the network.

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 http://datatracker.ietf.org/drafts/current/.

   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 August 14, 2013.



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Copyright Notice

   Copyright (c) 2013 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
   (http://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 . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  Terminology and Abbreviations  . . . . . . . . . . . . . .  5
   2.  Effects of IPv6 on Home Networking . . . . . . . . . . . . . .  6
     2.1.  Multiple subnets and routers . . . . . . . . . . . . . . .  6
     2.2.  Global addressability and elimination of NAT . . . . . . .  7
     2.3.  Multi-Addressing of devices  . . . . . . . . . . . . . . .  8
     2.4.  Unique Local Addresses (ULAs)  . . . . . . . . . . . . . .  8
     2.5.  Avoiding manual configuration of IP addresses  . . . . . .  9
     2.6.  IPv6-only operation  . . . . . . . . . . . . . . . . . . . 10
   3.  Homenet Architecture . . . . . . . . . . . . . . . . . . . . . 10
     3.1.  General Principles . . . . . . . . . . . . . . . . . . . . 11
       3.1.1.  Reuse existing protocols . . . . . . . . . . . . . . . 11
       3.1.2.  Minimise changes to hosts and routers  . . . . . . . . 12
     3.2.  Homenet Topology . . . . . . . . . . . . . . . . . . . . . 12
       3.2.1.  Supporting arbitrary topologies  . . . . . . . . . . . 12
       3.2.2.  Network topology models  . . . . . . . . . . . . . . . 12
       3.2.3.  Dual-stack topologies  . . . . . . . . . . . . . . . . 17
       3.2.4.  Multihoming  . . . . . . . . . . . . . . . . . . . . . 18
     3.3.  A Self-Organising Network  . . . . . . . . . . . . . . . . 19
       3.3.1.  Differentiating neighbouring homenets  . . . . . . . . 20
       3.3.2.  Largest practical subnets  . . . . . . . . . . . . . . 20
       3.3.3.  Homenet realms and borders . . . . . . . . . . . . . . 20
     3.4.  Homenet Addressing . . . . . . . . . . . . . . . . . . . . 21
       3.4.1.  Use of ISP-delegated IPv6 prefixes . . . . . . . . . . 22
       3.4.2.  Stable internal IP addresses . . . . . . . . . . . . . 23
       3.4.3.  Internal prefix delegation . . . . . . . . . . . . . . 24
       3.4.4.  Coordination of configuration information  . . . . . . 25
       3.4.5.  Privacy  . . . . . . . . . . . . . . . . . . . . . . . 26
     3.5.  Routing functionality  . . . . . . . . . . . . . . . . . . 26
       3.5.1.  Multicast support  . . . . . . . . . . . . . . . . . . 27



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     3.6.  Security . . . . . . . . . . . . . . . . . . . . . . . . . 28
       3.6.1.  Addressability vs reachability . . . . . . . . . . . . 28
       3.6.2.  Filtering at borders . . . . . . . . . . . . . . . . . 29
       3.6.3.  Marginal Effectiveness of NAT and Firewalls  . . . . . 29
       3.6.4.  Device capabilities  . . . . . . . . . . . . . . . . . 29
       3.6.5.  ULAs as a hint of connection origin  . . . . . . . . . 30
     3.7.  Naming and Service Discovery . . . . . . . . . . . . . . . 30
       3.7.1.  Discovering services . . . . . . . . . . . . . . . . . 30
       3.7.2.  Assigning names to devices . . . . . . . . . . . . . . 31
       3.7.3.  Name spaces  . . . . . . . . . . . . . . . . . . . . . 31
       3.7.4.  The homenet name service . . . . . . . . . . . . . . . 33
       3.7.5.  Independent operation  . . . . . . . . . . . . . . . . 34
       3.7.6.  Considerations for LLNs  . . . . . . . . . . . . . . . 35
       3.7.7.  DNS resolver discovery . . . . . . . . . . . . . . . . 35
     3.8.  Other Considerations . . . . . . . . . . . . . . . . . . . 35
       3.8.1.  Quality of Service . . . . . . . . . . . . . . . . . . 35
       3.8.2.  Operations and Management  . . . . . . . . . . . . . . 36
     3.9.  Implementing the Architecture on IPv6  . . . . . . . . . . 36
   4.  Conclusions  . . . . . . . . . . . . . . . . . . . . . . . . . 37
   5.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 37
     5.1.  Normative References . . . . . . . . . . . . . . . . . . . 37
     5.2.  Informative References . . . . . . . . . . . . . . . . . . 38
   Appendix A.  Acknowledgments . . . . . . . . . . . . . . . . . . . 41
   Appendix B.  Changes . . . . . . . . . . . . . . . . . . . . . . . 41
     B.1.  Version 07 . . . . . . . . . . . . . . . . . . . . . . . . 41
     B.2.  Version 06 . . . . . . . . . . . . . . . . . . . . . . . . 42
     B.3.  Version 05 . . . . . . . . . . . . . . . . . . . . . . . . 42
     B.4.  Version 04 . . . . . . . . . . . . . . . . . . . . . . . . 42
     B.5.  Version 03 . . . . . . . . . . . . . . . . . . . . . . . . 43
     B.6.  Version 02 . . . . . . . . . . . . . . . . . . . . . . . . 44
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 45




















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1.  Introduction

   This document focuses on evolving networking technology within
   increasingly large residential home networks and the associated
   challenges with their deployment and operation.  There is a growing
   trend in home networking for the proliferation of networking
   technology through an increasingly broad range of devices and media.
   This evolution in scale and diversity sets requirements on IETF
   protocols.  Some of these requirements relate to the introduction of
   IPv6, others to the introduction of specialised networks for home
   automation and sensors.

   While at the time of writing some complex home network topologies
   exist, but most are relatively simple single subnet networks, and
   ostensibly operate using just IPv4 (there may be IPv6 traffic within
   the network, e.g. for service discovery, but the homenet is
   provisioned by the ISP as an IPv4 network).  However, they also
   typically employ solutions that we would like to avoid such as
   private [RFC1918] addressing with (cascaded) network address
   translation (NAT)[RFC3022], or they may require expert assistance to
   set up.

   In contrast, emerging IPv6-capable home networks are very likely to
   have multiple internal subnets, e.g. to support private and guest
   networks, and have enough address space to allow every device to have
   a globally unique address.  Thus there are likely to be scenarios
   where internal routing is required, in which case such networks
   require methods for IPv6 prefixes to be delegated to those subnets.
   It is not practical to expect home users to configure such prefixes,
   thus the assumption of this document is that the homenet is as far as
   possible self-organising and self-configuring, i.e. it need not be
   pro-actively managed by the residential user.

   The architectural constructs in this document are focused on the
   problems to be solved when introducing IPv6 with an eye towards a
   better result than what we have today with IPv4, as well as a better
   result than if the IETF had not given this specific guidance.  The
   document aims to provide the basis and guiding principles for how
   standard IPv6 mechanisms and addressing [RFC2460] [RFC4291] can be
   employed in home networking, while coexisting with existing IPv4
   mechanisms.  In emerging dual-stack home networks it is vital that
   introducing IPv6 does not adversely affect IPv4 operation.  We assume
   that the IPv4 network architecture in home networks is what it is,
   and can not be affected by new recommendations.  It should not be
   assumed that any future new functionality created with IPv6 in mind
   will be backward-compatible to include IPv4 support.  Further, future
   deployments, or specific subnets within an otherwise dual-stack home
   network, may be IPv6-only, in which case considerations for IPv4



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   impact would not apply.

   This architecture document proposes a baseline homenet architecture,
   based on protocols and implementations that are as far as possible
   proven and robust.  The scope of the document is primarily the
   network layer technologies that provide the basic functionality to
   enable addressing, connectivity, routing, naming and service
   discovery.  While it may, for example, state that homenet components
   must be simple to deploy and use, it does not discuss specific user
   interfaces, nor does it discuss specific physical, wireless or data-
   link layer considerations.

   [RFC6204] defines basic requirements for customer edge routers
   (CERs).  The scope of this text is the internal homenet, and thus
   specific features on the CER are out of scope for this text.  While
   the network may be dual-stack or IPv6-only, the definition of
   specific transition tools on the CER, as introduced in RFC 6204-bis
   [I-D.ietf-v6ops-6204bis] with DS-Lite [RFC6333] and 6rd [RFC5969],
   are also considered out of scope of this text.

1.1.  Terminology and Abbreviations

   In this section we define terminology and abbreviations used
   throughout the text.

   o  ALQDN: Ambiguous Locally Qualified Domain Name.  An example would
      be .sitelocal.

   o  CER: Customer Edge Router.  A border router at the edge of the
      homenet.

   o  FQDN: Fully Qualified Domain Name.  A globally unique name space.

   o  LLN: Low-power and lossy network.

   o  LQDN: Locally Qualified Domain Name.  A name space local to the
      homenet.

   o  NAT: Network Address Translation.  Typically referring to IPv4
      Network Address and Port Translation (NAPT) [RFC3022].

   o  NPTv6: Network Prefix Translation for IPv6 [RFC6296].

   o  PCP: Port Control Protocol [I-D.ietf-pcp-base].

   o  'Simple Security'.  Defined in [RFC4864] and expanded further in
      [RFC6092]; describes recommended perimeter security capabilities
      for IPv6 networks.



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   o  ULA: IPv6 Unique Local Addresses [RFC4193].

   o  ULQDN: Unique Locally Qualified Domain Name.  An example might be
      .<UniqueString>.sitelocal.

   o  UPnP: Universal Plug and Play.  Includes the Internet Gateway
      Device (IGD) function, which for IPv6 is UPnP IGD Version 2
      [IGD-2].

   o  VM: Virtual machine.

   o  WPA2: Wi-Fi Protected Access, as defined by the Wi-Fi Alliance.


2.  Effects of IPv6 on Home Networking

   While IPv6 resembles IPv4 in many ways, there are some notable
   differences in the way it may typically be deployed.  It changes
   address allocation principles, making multi-addressing the norm, and,
   through the vastly increased address space, allows globally unique IP
   addresses to be used for all devices in a home network.  This section
   presents an overview of some of the key implications of the
   introduction of IPv6 for home networking, that are simultaneously
   both promising and problematic.

2.1.  Multiple subnets and routers

   While simple layer 3 topologies involving as few subnets as possible
   are preferred in home networks, the incorporation of dedicated
   (routed) subnets remains necessary for a variety of reasons.  For
   instance, an increasingly common feature in modern home routers is
   the ability to support both guest and private network subnets.
   Likewise, there may be a need to separate building control or
   corporate extensions from the main Internet access network, or
   different subnets may in general be associated with parts of the
   homenet that have different routing and security policies.  Further,
   link layer networking technology is poised to become more
   heterogeneous, as networks begin to employ both traditional Ethernet
   technology and link layers designed for low-power and lossy networks
   (LLNs), such as those used for certain types of sensor devices.
   Constraining the flow of certain traffic from Ethernet links to much
   lower capacity links thus becomes an important topic.

   The introduction of IPv6 for home networking enables the potential
   for every home network to be delegated enough address space to
   provision globally unique prefixes for each such subnet in the home.
   As discussed later, this assumes the customer's ISP delegates enough
   address space to the home.  While the number of addresses in a



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   standard /64 IPv6 prefix is practically infinite, the number of
   prefixes available for assignment to the home network is not.  As a
   result the growth inhibitor for the home network shifts from the
   number of addresses to the number of prefixes offered by the
   provider.

   The addition of routing between subnets raises the issue of how to
   extend mechanisms such as service discovery which currently only
   operate within a single subnet using link-local traffic.  In a
   typical IPv4 home network, there is only one subnet, so such
   mechanisms would normally operate as expected.  For multi-subnet IPv6
   home networks there are two broad choices to enable such protocols to
   work across the scope of the entire homenet; extend existing
   protocols to work across that scope, or introduce proxies for
   existing link layer protocols.  This topic is discussed later in the
   document.

   There will also be the need to discover which routers in the homenet
   are the border router(s) by an appropriate mechanism.  Here, there
   are a number of choices, including the use of an appropriate service
   discovery protocol.  Whatever method is chosen would likely have to
   deal with handling more than one router responding in multihomed
   environments.

2.2.  Global addressability and elimination of NAT

   The end-to-end communication that is potentially enabled with IPv6 is
   on the one hand an incredible opportunity for innovation and simpler
   network operation, but it is also a concern as it exposes nodes in
   the internal networks to receipt of potentially unwanted traffic from
   the Internet.

   With devices and applications able to talk directly to each other
   when they have globally unique addresses, there may be an expectation
   of improved host security to compensate for this.  It should be noted
   that many devices may (for example) ship with default settings that
   make them readily vulnerable to compromise by external attackers if
   globally accessible, or may simply not have robustness designed-in
   because it was either assumed such devices would only be used on
   private networks or the device itself doesn't have the computing
   power to apply the necessary security methods.

   It is important to distinguish between addressability and
   reachability.  While IPv6 offers global addressability through use of
   globally unique addresses in the home, whether devices are globally
   reachable or not would depend on the firewall or filtering
   configuration, and not, as is commonly the case with IPv4, the
   presence or use of NAT.  In this respect, IPv6 networks may or may



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   not have filters applied at their borders to control such traffic,
   i.e. at the homenet CER.  [RFC4864] and [RFC6092] discuss such
   filtering, and the merits of 'default allow' against 'default deny'
   policies for external traffic initiated into a homenet.  This
   document takes no position on which mode is the default, but assumes
   the choice to use either would be made available.

2.3.  Multi-Addressing of devices

   In an IPv6 network, devices will often acquire multiple addresses,
   typically at least a link-local address and one or more globally
   unique addresses.  Where a homenet is multihomed, a device would
   typically receive a globally unique address from within the delegated
   prefix from each upstream ISP.  Devices may also have an IPv4 address
   if the network is dual-stack, an IPv6 Unique Local Address (ULA)
   [RFC4193] (see below), and one or more IPv6 Privacy Addresses
   [RFC4941].

   It should thus be considered the norm for devices on IPv6 home
   networks to be multi-addressed, and to need to make appropriate
   address selection decisions for the candidate source and destination
   address pairs for any given connection.  Default Address Selection
   for IPv6 [RFC6724] provides a solution for this, though it may face
   problems in the event of multihoming where, as described above, nodes
   will be configured with one address from each upstream ISP prefix.
   In such cases the presence of upstream BCP 38 [RFC2827] ingress
   filtering requires multi-addressed nodes to select the correct source
   address to be used for the corresponding uplink, but the node may not
   have the information it needs to make that decision based on
   addresses alone.  We discuss such challenges in the multihoming
   section later in this document.

2.4.  Unique Local Addresses (ULAs)

   [RFC4193] defines Unique Local Addresses (ULAs) for IPv6 that may be
   used to address devices within the scope of a single site.  Support
   for ULAs for IPv6 CERs is described in [RFC6204].  A home network
   running IPv6 should deploy ULAs alongside its globally unique
   prefix(es) to allow stable communication between devices (on
   different subnets) within the hoemnet where that externally allocated
   globally unique prefix may change over time (e.g. due to renumbering
   within the subscriber's ISP) or where external connectivity may be
   temporarily unavailable.  While setting up a network there may also
   be a period with no connectivity, in which case ULAs would be
   required for inter-subnet communication.  In the case where LLNs are
   being set up in a new home/deployment, individual LLNs may, at least
   initially, each use their own /48 ULA prefix.




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   While a homenet should operate correctly with two or more /48 ULAs
   enabled, a mechanism for the creation and use of a single /48 ULA
   prefix is desirable for addressing consistency and policy
   enforcement.  It may thus be expected that one router in the homenet
   be elected a 'master' to delegate ULA prefixes to subnets from a
   single /48 ULA prefix.

   Where both a ULA and a global prefix are in use, the default address
   selection mechanisms described above should ensure that a ULA source
   address is used to communicate with ULA destination addresses when
   appropriate, i.e. when the ULA destination lies within the /48 ULA
   prefix(es) known to be used within the same homenet.  Note that
   unlike private IPv4 RFC 1918 space, the use of ULAs does not imply
   use of host-based IPv6 NAT, or NPTv6 prefix-based NAT [RFC6296],
   rather that in an IPv6 homenet a node should use its ULA address
   internally, and its additional globally unique IPv6 address as the
   source address for external communications.  By using such globally
   unique addresses between networks, the architectural cost and
   complexity, particulrly to applications, of NAT or NPTv6 translation
   is avoided.  As such, neither IPv6 NAT or NPTv6 is recommended for
   use in the homenet architecture.

   A counter-argument to using ULAs is that it is undesirable to
   aggressively deprecate global prefixes for temporary loss of
   connectivity, so for a host to lose its global address there would
   have to be a connection breakage longer than the lease period, and
   even then, deprecating prefixes when there is no connectivity may not
   be advisable.  However, it is assumed in this architecture that
   homenets will need to support and use ULAs.

   As noted later in this text, if appropriate filtering is in place on
   the CER(s), a ULA source address may be taken as an indication of
   locally sourced traffic.

2.5.  Avoiding manual configuration of IP addresses

   Some IPv4 home networking devices expose IPv4 addresses to users,
   e.g. the IPv4 address of a home IPv4 CER that may be configured via a
   web interface.  In potentially complex future IPv6 homenets, users
   should not be expected to enter IPv6 literal addresses in devices or
   applications, given their much greater length and apparent randomness
   of such addresses to a typical home user.  Thus, even for the
   simplest of functions, simple naming and the associated (minimal, and
   ideally zero configuration) discovery of services is imperative for
   the easy deployment and use of homenet devices and applications.

   As mentioned previously, this means that zeroconf naming and service
   discovery protocols must be capable of operating across subnet



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   boundaries.

2.6.  IPv6-only operation

   It is likely that IPv6-only networking will be deployed first in
   'greenfield' homenet scenarios, or perhaps as one element of an
   otherwise dual-stack network.  Running IPv6-only adds additional
   requirements, e.g. for devices to get configuration information via
   IPv6 transport (not relying on an IPv4 protocol such as IPv4 DHCP),
   and for devices to be able to initiate communications to external
   devices that are IPv4-only.  Thus, for example, the following
   requirements are amongst those that should be considered in IPv6-only
   environments:

   o  Ensuring there is a way to access content in the IPv4 Internet.
      This can be arranged through appropriate use of NAT64 [RFC6144]
      and DNS64 [RFC6145], for example, or via a node-based DS-Lite
      [RFC6333] approach.

   o  DNS discovery mechanisms are enabled for IPv6.  Both stateless
      DHCPv6 [RFC3736] [RFC3646] and Router Advertisement options
      [RFC6106] may have to be supported and turned on by default to
      ensure maximum compatibility with all types of hosts in the
      network.  This requires, however, that a working DNS server is
      known and addressable via IPv6, and that the automatic discovery
      of such a server is possible through multiple routers in the
      homenet.

   o  All nodes in the home network support operations in IPv6-only
      mode.  Some current devices work well with dual-stack but fail to
      recognise connectivity when IPv4 DHCP fails, for instance.

   The widespread availability of robust solutions to these types of
   requirements will help accelerate the uptake of IPv6-only homenets.
   The specifics of these are however beyond the scope of this document,
   especially those functions that reside on the CER.


3.  Homenet Architecture

   The aim of this architecture text is to outline how to construct
   advanced IPv6-based home networks involving multiple routers and
   subnets using standard IPv6 protocols and addressing [RFC2460]
   [RFC4291].  In this section, we present the elements of such a home
   networking architecture, with discussion of the associated design
   principles.

   Existing IETF work [RFC6204] defines the 'basic' requirements for



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   CERs, while [I-D.ietf-v6ops-6204bis] updates the current requirements
   based on operator feedback and adds new requirements for IP
   transition technologies and transition technology coexistence.  This
   document describes a homenet architecture which is focused on the
   internal homenet, rather than the CER(s).

   In general, home network equipment needs to be able to operate in
   networks with a range of different properties and topologies, where
   home users may plug components together in arbitrary ways and expect
   the resulting network to operate.  Significant manual configuration
   is rarely, if at all, possible, or even desirable given the knowledge
   level of typical home users.  Thus the network should, as far as
   possible, be self-configuring, though configuration by advanced users
   should not be precluded.

   The homenet needs to be able to handle or provision at least

   o  Routing

   o  Prefix configuration for routers

   o  Name resolution

   o  Service discovery

   o  Network security

   The remainder of this document describes the principles by which a
   homenet architecture may deliver these properties.

3.1.  General Principles

   There is little that the Internet standards community can do about
   the physical topologies or the need for some networks to be separated
   at the network layer for policy or link layer compatibility reasons.
   However, there is a lot of flexibility in using IP addressing and
   inter-networking mechanisms.  This architecture text discusses how
   this flexibility should be used to provide the best user experience
   and ensure that the network can evolve with new applications in the
   future.  The principles described in this text should be followed
   when designing homenet solutions.

3.1.1.  Reuse existing protocols

   It is desirable to reuse existing protocols where possible, but at
   the same time to avoid consciously precluding the introduction of new
   or emerging protocols.  A generally conservative approach, giving
   weight to running code, is preferable.  Where new protocols are



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   required, evidence of commitment to implementation by appropriate
   vendors or development communities is highly desirable.  Protocols
   used should be backwardly compatible, and forward compatible where
   changes are made.

3.1.2.  Minimise changes to hosts and routers

   Where possible, any requirement for changes to hosts and routers
   should be minimised, though solutions which, for example,
   incrementally improve with host or router changes may be acceptable.

3.2.  Homenet Topology

   This section considers homenet topologies, and the principles that
   may be applied in designing an architecture to support as wide a
   range of such topologies as possible.

3.2.1.  Supporting arbitrary topologies

   There should ideally be no built-in assumptions about the topology in
   home networks, as users are capable of connecting their devices in
   'ingenious' ways.  Thus arbitrary topologies and arbitrary routing
   will need to be supported, or at least the failure mode for when the
   user makes a mistake should be as robust as possible, e.g. de-
   activating a certain part of the infrastructure to allow the rest to
   operate.  In such cases, the user should ideally have some useful
   indication of the failure mode encountered.

   There should be no topology scenarios which cause loss of
   connectivity, except when the user creates a physical island within
   the topology.  Some potentially pathological cases that can be
   created include bridging ports of a router together, however this
   case can be detected and dealt with by the router.  Loops within a
   routed topology are in a sense good in that they offer redundancy.
   Bridging loops can be dangerous but are also detectable when a switch
   learns the MAC of one of its interfaces on another or runs a spanning
   tree or link state protocol.  It is only loops using simple repeaters
   that are truly pathological.

3.2.2.  Network topology models

   Most IPv4 home network models at the time of writing tend to be
   relatively simple, typically a single NAT router to the ISP and a
   single internal subnet but, as discussed earlier, evolution in
   network architectures is driving more complex topologies, such as the
   separation of guest and private networks.  There may also be some
   cascaded IPv4 NAT scenarios, which we mention in the next section.




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   In general, the models described in [RFC6204] and its successor RFC
   6204-bis [I-D.ietf-v6ops-6204bis] should be supported by the IPv6
   home networking architecture.  The functions resident on the CER
   itself are, as stated previously, out of scope of this text.

   There are a number of properties or attributes of a home network that
   we can use to describe its topology and operation.  The following
   properties apply to any IPv6 home network:

   o  Presence of internal routers.  The homenet may have one or more
      internal routers, or may only provide subnetting from interfaces
      on the CER.

   o  Presence of isolated internal subnets.  There may be isolated
      internal subnets, with no direct connectivity between them within
      the homenet (with each having its own external connectivity).
      Isolation may be physical, or implemented via IEEE 802.1q VLANs.
      The latter is however not something a typical user would be
      expected to configure.

   o  Demarcation of the CER.  The CER(s) may or may not be managed by
      the ISP.  If the demarcation point is such that the customer can
      provide or manage the CER, its configuration must be simple.  Both
      models must be supported.

   Various forms of multihoming are likely to become more prevalent with
   IPv6 home networks, as discussed further below.  Thus the following
   properties should also be considered for such networks:

   o  Number of upstream providers.  The majority of home networks today
      consist of a single upstream ISP, but it may become more common in
      the future for there to be multiple ISPs, whether for resilience
      or provision of additional services.  Each would offer its own
      prefix.  Some may or may not provide a default route to the public
      Internet.

   o  Number of CERs.  The homenet may have a single CER, which might be
      used for one or more providers, or multiple CERs.  The presence of
      multiple CERs adds additional complexity for multihoming
      scenarios, and protocols like PCP that need to manage connection-
      oriented state mappings.

   In the following sections we give some examples of the types of
   homenet topologies we may see in the future.  This is not intended to
   be an exhaustive or complete list, rather an indicative one to
   facilitate the discussion in this text.





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3.2.2.1.  A: Single ISP, Single CER, Internal routers

   Figure 1 shows a home network with multiple local area networks.
   These may be needed for reasons relating to different link layer
   technologies in use or for policy reasons, e.g. classic Ethernet in
   one subnet and a LLN link layer technology in another.  In this
   example there is no single router that a priori understands the
   entire topology.  The topology itself may also be complex, and it may
   not be possible to assume a pure tree form, for instance (because
   home users may plug routers together to form arbitrary topologies
   including loops).








































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                     +-------+-------+                     \
                     |   Service     |                      \
                     |   Provider    |                       | Service
                     |    Router     |                       | Provider
                     +-------+-------+                       | network
                             |                              /
                             | Customer                    /
                             | Internet connection
                             |
                      +------+--------+                    \
                      |     IPv6      |                     \
                      | Customer Edge |                      \
                      |    Router     |                      |
                      +----+-+---+----+                      |
          Network A        | |   |      Network B(E)         |
    ----+-------------+----+ |   +---+-------------+------+  |
        |             |      |       |             |      |  |
   +----+-----+ +-----+----+ |  +----+-----+ +-----+----+ |  |
   |IPv6 Host | |IPv6 Host | |  | IPv6 Host| |IPv6 Host | |  |
   |    H1    | |    H2    | |  |    H3    | |    H4    | |  |
   +----------+ +----------+ |  +----------+ +----------+ |  |
                             |        |             |     |  |
                      Link F |     ---+------+------+-----+  |
                             |               | Network E(B)  |
                      +------+--------+      |               | End-User
                      |     IPv6      |      |               | networks
                      |   Interior    +------+               |
                      |    Router     |                      |
                      +---+-------+-+-+                      |
          Network C       |       |   Network D              |
    ----+-------------+---+       +---+-------------+---     |
        |             |               |             |        |
   +----+-----+ +-----+----+     +----+-----+ +-----+----+   |
   |IPv6 Host | |IPv6 Host |     | IPv6 Host| |IPv6 Host |   |
   |   H5     | |   H6     |     |    H7    | |    H8    |   /
   +----------+ +----------+     +----------+ +----------+  /

                                 Figure 1

   In this diagram there is one CER.  It has a single uplink interface.
   It has three additional interfaces connected to Network A, Link F,
   and Network B. IPv6 Internal Router (IR) has four interfaces
   connected to Link F, Network C, Network D and Network E. Network B
   and Network E have been bridged, likely inadvertently.  This could be
   as a result of connecting a wire between a switch for Network B and a
   switch for Network E.

   Any of logical Networks A through F might be wired or wireless.



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   Where multiple hosts are shown, this might be through one or more
   physical ports on the CER or IPv6 (IR), wireless networks, or through
   one or more layer-2 only Ethernet switches.

3.2.2.2.  B: Two ISPs, Two CERs, Shared subnet


           +-------+-------+     +-------+-------+         \
           |   Service     |     |   Service     |          \
           |  Provider A   |     |  Provider B   |           | Service
           |    Router     |     |    Router     |           | Provider
           +------+--------+     +-------+-------+           | network
                  |                      |                   /
                  |      Customer        |                  /
                  | Internet connections |                 /
                  |                      |
           +------+--------+     +-------+-------+         \
           |     IPv6      |     |    IPv6       |          \
           | Customer Edge |     | Customer Edge |           \
           |   Router 1    |     |   Router 2    |           /
           +------+--------+     +-------+-------+          /
                  |                      |                 /
                  |                      |                | End-User
     ---+---------+---+---------------+--+----------+---  | network(s)
        |             |               |             |      \
   +----+-----+ +-----+----+     +----+-----+ +-----+----+  \
   |IPv6 Host | |IPv6 Host |     | IPv6 Host| |IPv6 Host |  /
   |   H1     | |   H2     |     |    H3    | |    H4    | /
   +----------+ +----------+     +----------+ +----------+

                                 Figure 2

   Figure 2 illustrates a multihomed homenet model, where the customer
   has connectivity via CER1 to ISP A and via CER2 to ISP B. This
   example shows one shared subnet where IPv6 nodes would potentially be
   multihomed and receive multiple IPv6 global addresses, one per ISP.
   This model may also be combined with that shown in Figure 1 to create
   a more complex scenario with multiple internal routers.  Or the above
   shared subnet may be split in two, such that each CER serves a
   separate isolated subnet, which is a scenario seen with some IPv4
   networks today.










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3.2.2.3.  C: Two ISPs, One CER, Shared subnet


           +-------+-------+     +-------+-------+         \
           |   Service     |     |   Service     |          \
           |  Provider A   |     |  Provider B   |           | Service
           |    Router     |     |    Router     |           | Provider
           +-------+-------+     +-------+-------+           | network
                    |                 |                     /
                    |    Customer     |                   /
                    |    Internet     |                  /
                    |   connections   |                 |
                   +---------+---------+                 \
                   |       IPv6        |                   \
                   |   Customer Edge   |                    \
                   |      Router       |                    /
                   +---------+---------+                   /
                             |                            /
                             |                            | End-User
     ---+------------+-------+--------+-------------+---  | network(s)
        |            |                |             |      \
   +----+-----+ +----+-----+     +----+-----+ +-----+----+  \
   |IPv6 Host | |IPv6 Host |     | IPv6 Host| |IPv6 Host |  /
   |   H1     | |   H2     |     |    H3    | |   H4     | /
   +----------+ +----------+     +----------+ +----------+

                                 Figure 3

   Figure 3 illustrates a model where a home network may have multiple
   connections to multiple providers or multiple logical connections to
   the same provider, with shared internal subnets.

   In general, while the architecture may focus on likely common
   topologies, it should not preclude any arbitrary topology from being
   constructed.

3.2.3.  Dual-stack topologies

   It is expected that most homenet deployments will for the immediate
   future be dual-stack IPv4/IPv6.  In such networks it is important not
   to introduce new IPv6 capabilities that would cause a failure if used
   alongside IPv4+NAT, given that such dual-stack homenets will be
   commonplace for some time.  That said, it is desirable that IPv6
   works better than IPv4 in as many scenarios as possible.  Further,
   the homenet architecture must operate in the absence of IPv4.

   A general recommendation is to follow the same topology for IPv6 as
   is used for IPv4, but not to use NAT.  Thus there should be routed



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   IPv6 where an IPv4 NAT is used and, where there is no NAT, routing or
   bridging may be used.  Routing may have advantages when compared to
   bridging together high speed and lower speed shared media, and in
   addition bridging may not be suitable for some media, such as ad-hoc
   mobile networks.

   In some cases IPv4 home networks may feature cascaded NATs, which
   could include cases where NAT routers are included within VMs, or
   where Internet connection sharing services are used.  IPv6 routed
   versions of such cases will be required.  We should thus note that
   routers in the homenet may not be separate physical devices; they may
   be embedded within other devices.

3.2.4.  Multihoming

   A homenet may be multihomed to multiple providers, as the network
   models above illustrate.  This may either take a form where there are
   multiple isolated networks within the home or a more integrated
   network where the connectivity selection needs to be dynamic.
   Current practice is typically of the former kind, but the latter is
   expected to become more commonplace.

   In the general homenet architecture, hosts should be multi-addressed
   with a global IPv6 address from the global prefix delegated from each
   ISP they communicate with or through.  When such multi-addressing is
   in use, hosts need some way to pick source and destination address
   pairs for connections.  A host may choose a source address to use by
   various methods, most commonly [RFC6724].  Applications may of course
   do different things, and this should not be precluded.

   For the single CER Network Model C illistrated above, multihoming may
   be offered by source routing at the CER.  With multiple exit routers,
   as in CER Network Model B, the complexity rises.  Given a packet with
   a source address on the home network, the packet must be routed to
   the proper egress to avoid BCP 38 filtering at an ISP.  It is highly
   desirable that the packet is routed in the most efficient manner to
   the correct exit, though as a minimum requirement the packet should
   not be dropped.

   The homenet archiecture should support both the above models, i.e.
   one or more CERs.  However, the general multihoming problem is broad,
   and solutions suggested to date within the IETF have included complex
   architectures for monitoring connectivity, traffic engineering,
   identifier-locator separation, connection survivability across
   multihoming events, and so on.  It is thus important that the homenet
   architecture should as far as possible minimise the complexity of any
   multihoming support.




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   An example of such a 'simpler' approach has been documented in
   [I-D.ietf-v6ops-ipv6-multihoming-without-ipv6nat].  Alternatively a
   flooding/routing protocol could potentially be used to pass
   information through the homenet, such that internal routers and
   ultimately end hosts could learn per-prefix configuration
   information, allowing better address selection decisions to be made.
   However, this would imply probably host and certainly router changes.
   Or another avenue is to introduce support for source routing
   throughout the homenet; while greatly improving the 'intelligence' of
   routing decisions within the homenet, such an approach would require
   relatively significant router changes.

   As explained previously, NPTv6 is not recommended in the homenet
   architecture.

   There are some other multihoming considerations for homenet
   scenarios.  First, it may be the case that multihoming applies due to
   an ISP migration from a transition method to a native deployment,
   e.g. a 6rd [RFC5969] sunsetting scenario.  Second, one upstream may
   be a "walled garden", and thus only appropriate to be used for
   connectivity to the services of that provider; an example may be a
   VPN service that only routes back to the enterprise business network
   of a user in the homenet.  While we should not specifically target
   walled garden multihoming as a principal goal, it should not be
   precluded.

   The homenet architecture should also not preclude use of host or
   application-oriented tools, e.g.  Shim6 [RFC5533] or Happy Eyeballs
   [RFC6555].  In general, any incremental improvements obtained by host
   changes should give benefit for the hosts introducing them, but not
   be required.

3.3.  A Self-Organising Network

   A home network architecture should be naturally self-organising and
   self-configuring under different circumstances relating to the
   connectivity status to the Internet, number of devices, and physical
   topology.  At the same time, it should be possible for advanced users
   to manually adjust (override) the current configuration.

   While a goal of the homenet architecture is for the network to be as
   self-organising as possible, there may be instances where some manual
   configuration is required, e.g. the entry of a cryptographic key to
   apply wireless security, or to configure a shared routing secret.
   The latter may be relevant when considering how to bootstrap a
   routing configuration.  It is highly desirable that the number of
   such configurations is minimised.




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3.3.1.  Differentiating neighbouring homenets

   It is important that self-configuration with 'unintended' devices is
   avoided.  Methods are needed for devices to know whether they are
   intended to be part of the same homenet site or not.  Thus methods to
   ensure separation between neighbouring homenets are required.  This
   may require use of some unique 'secret' for devices/protocols in each
   homenet.  Some existing mechanisms exist to assist home users to
   associate devices as simply as possible, e.g. 'connect' button
   support.

3.3.2.  Largest practical subnets

   Today's IPv4 home networks generally have a single subnet, and early
   dual-stack deployments have a single congruent IPv6 subnet, possibly
   with some bridging functionality.  More recently, some vendors have
   started to introduce 'home' and 'guest' functions, which in IPv6
   would be implemented as two subnets.

   Future home networks are highly likely to have one or more internal
   routers and thus need multiple subnets, for the reasons described
   earlier.  As part of the self-organisation of the network, the
   homenet should subdivide itself to the largest practical subnets that
   can be constructed within the constraints of link layer mechanisms,
   bridging, physical connectivity, and policy, and where applicable
   performance or other criteria.  For example, bridging a busy Gigabit
   Ethernet subnet and a wireless subnet together may impact wireless
   performance.

   While it may be desirable to maximise the chance of link-local
   protocols operating across a homenet by maximising the size of a
   subnet, multi-subnet home networks are inevitable, so their support
   must be included.

3.3.3.  Homenet realms and borders

   The homenet will need to be aware of the extent of its own 'site',
   which will, for example, define the borders for ULA and site scope
   multicast traffic, and may require specific security policies to be
   applied.  The homenet will have one or more such borders with
   external connectivity providers.

   A homenet will most likely also have internal borders between
   internal realms, e.g. a guest realm or a corporate network extension
   realm.  It should be possible to automatically discover these
   borders, which will determine, for example, the scope of where
   network prefixes, routing information, network traffic, service
   discovery and naming may be shared.  The default mode internally



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   should be to share everything.

   It is expected that a realm would span at least an entire subnet, and
   thus the borders lie at routers which receive delegated prefixes
   within the homenet.  It is also desirable for a richer security model
   that hosts, which may be running in a transparent communication mode,
   are able to make communication decisions based on available realm and
   associated prefix information in the same way that routers at realm
   borders can.

   A simple homenet model may just consider three types of realm and the
   borders between them, namely the internal homenet, the ISP and a
   guest network.  In this case the borders will include that from the
   homenet to the ISP, that from the guest network to the ISP, and that
   from the homenet to the guest network.  Regardless, it should be
   possible for additional types of realms and borders to be defined,
   e.g. for some specific Grid or LLN-based network, and for these to be
   detected automatically, and for an appropriate default policy to be
   applied as to what type of traffic/data can flow across such borders.

   It is desirable to classify the external border of the home network
   as a unique logical interface separating the home network from
   service provider network/s.  This border interface may be a single
   physical interface to a single service provider, multiple layer 2
   sub-interfaces to a single service provider, or multiple connections
   to a single or multiple providers.  This border makes it possible to
   describe edge operations and interface requirements across multiple
   functional areas including security, routing, service discovery, and
   router discovery.

   It should be possible for the homenet user to override any
   automatically determined borders and the default policies applied
   between them.

   Some initial proposals towards border discovery are presented in
   [I-D.kline-default-perimeter].

3.4.  Homenet Addressing

   The IPv6 addressing scheme used within a homenet must conform to the
   IPv6 addressing architecture [RFC4291].  In this section we discuss
   how the homenet needs to adapt to the prefixes made available to it
   by its upstream ISP, such that internal subnets, hosts and devices
   can obtain the and configure the necessary addressing information to
   operate.






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3.4.1.  Use of ISP-delegated IPv6 prefixes

   A homenet may receive an arbitrary length IPv6 prefix from its
   provider, e.g. /60, /56 or /48.  The offered prefix may be stable or
   change from time to time.  Some ISPs may offer relatively stable
   prefixes, while others may change the prefix whenever the CER is
   reset.  Some discussion of IPv6 prefix allocation policies is
   included in [RFC6177] which discusses why, for example, a one-size-
   fits-all /48 allocation is not desirable.

   The homenet architecture expects internal host subnets to be /64 in
   size.  While it may be possible to operate a DHCPv6-only network with
   prefixes longer than /64, doing so would break SLAAC, and is thus not
   recommended.

   The home network needs to be adaptable to ISP prefix allocation
   policies, and thus make no assumptions about the stability of the
   prefix received from an ISP, or the length of the prefix that may be
   offered.  However, if only a /64 is offered by the ISP, the homenet
   may be severely constrained or even unable to function.  As stated
   above, attempting to use internal subnet prefixes longer than /64
   would break SLAAC, and is thus not recommended.  Using ULA prefixes
   internally with NPTv6 at the boundary is not recommended for reasons
   given elsewhere.  Reverting to bridging would destroy subnetting,
   breaks multicast if bridged onto 802.11 wireless networks and has
   serious limitations with regard to heterogeneous link layer
   technologies and LLNs.  For those reasons it is recommended that
   DHCP-PD or OSPFv3 capable routers have the ability to issue a warning
   upon receipt of a /64 if required to assign further prefixes within
   the home network.  Though some consideration needs to be given to how
   that should be presented to a typical home user.

   Thus the border CER router should 'hint', most likely via DHCP-PD,
   that it would like a /48 prefix from its ISP, i.e. it asks the ISP
   for the maximum size prefix it might expect to be offered, but in
   practice it may only be offered a /56 or /60.  For a typical IPv6
   homenet, it is not recommended that an ISP offer less than a /60
   prefix, and should preferably offer at least a /56.

   In practice, it is expected that ISPs will deliver a relatively
   stable home prefix to customers.  The norm for residential customers
   of large ISPs may be similar to their single IPv4 address provision;
   by default it is likely to remain persistent for some time, but
   changes in the ISP's own provisioning systems may lead to the
   customer's IP (and in the IPv6 case their prefix pool) changing.  It
   is not expected that ISPs will support Provider Independent (PI)
   addressing for general residential homenets.




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   When an ISP does need to restructure, and in doing so renumber its
   customer homenets, 'flash' renumbering is likely to be imposed.  This
   implies a need for the homenet to be able to handle a sudden
   renumbering event which, unlike the process described in [RFC4192],
   would be a 'flag day" event, which means that a graceful renumbering
   process moving through a state with two active prefixes in use would
   not be possible.  While renumbering can be viewed as an extended
   version of an initial numbering process, the difference between flash
   renumbering and an initial 'cold start' is the need to provide
   service continuity.

   There may be cases where local law means some ISPs are required to
   change IPv6 prefixes (current IPv4 addresses) for privacy reasons for
   their customers.  In such cases it may be possible to avoid an
   instant 'flash' renumbering and plan a non-flag day renumbering as
   per RFC 4192.

   The customer may of course also choose to move to a new ISP, and thus
   begin using a new prefix.  In such cases the customer should expect a
   discontinuity, and not only may the prefix change but potentially
   also the prefix length, if the new ISP offers a different default
   size prefix.  Regardless, it's desirable that homenet protocols
   support rapid renumbering and that operational processes don't add
   unnecessary complexity for the renumbering process.  Further, the
   introduction of any new homenet protocols should not make any form of
   renumbering any more complex than it already is.

   Finally, the internal operation of the home network should also not
   depend on the availability of the ISP network at any given time,
   other than of course for connectivity to services or systems off the
   home network.  This reinforces the use of ULAs for stable internal
   communication, and the need for a naming and service discovery
   mechanism that can operate independently within the homenet.

3.4.2.  Stable internal IP addresses

   The network should by default attempt to provide IP-layer
   connectivity between all internal parts of the homenet as well as to
   and from the external Internet, subject to the filtering policies or
   other policy constraints discussed later in the security section.

   ULAs should be used within the scope of a homenet to support routing
   between subnets regardless of whether a globally unique ISP-provided
   prefix is available.  As discussed previously, it would be expected
   that ULAs would be used alongside one or more such global prefixes in
   a homenet, such that hosts become multi-addressed with both globally
   unique and ULA prefixes.  ULAs should be used for all devices, not
   just those intended to only have internal connectivity.  Default



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   address selection would then enable ULAs to be preferred for internal
   communications between devices that are using ULA prefixes generated
   within the same homenet.

   ULA addresses will allow constrained LLN devices to create permanent
   relationships between IPv6 addresses, e.g. from a wall controller to
   a lamp.  Symbolic host names would require additional non-volatile
   memory.  Updating global prefixes in sleeping LLN devices might also
   be problematic.

   The use of ULAs should be restricted to the homenet scope through
   filtering at the border(s) of the homenet, as described in RFC 6092.

   Note that it is possible that in some cases multiple /48 ULA prefixes
   may be in use within the same homenet, e.g. when the network is being
   deployed, perhaps also without external connectivity.  It is expect
   that routers in the homenet would somehow elect a 'master' that would
   be responsible for delegating /64 prefixes to internal requesting
   routers, much as routers obtain /64 global prefixes from the prefix
   pool delegated by the ISP to the CER.  In cases where multiple ULA
   /48's are in use, hosts need to know that each /48 is local to the
   homenet, e.g. by inclusion in their local address selection policy
   table.

3.4.3.  Internal prefix delegation

   As mentioned above, there are various sources of prefixes.  From the
   homenet perspective, a single global prefix from each ISP should be
   received on the border CER [RFC3633].  Where multiple CERs exist with
   multiple ISP prefix pools, it is expected that routers within the
   homenet would assign themselves prefixes from each ISP they
   communicate with/through.  As discussed above, a ULA prefix can be
   made available for stable internal communications, or for use on
   constrained/LLN networks.  There may also be a prefix associated with
   NAT64, if in use in the homenet.

   The delegation or availability of a prefix pool to the homenet should
   allow subsequent internal autonomous delegation of prefixes for use
   within the homenet.  Such internal delegation should not assume a
   flat or hierarchical model, nor should it make an assumption about
   whether the delegation of internal prefixes is distributed or
   centralised.  The assignment mechanism should provide reasonable
   efficiency, so that typical home network prefix allocation sizes can
   accommodate all the necessary /64 allocations in most cases, and not
   waste prefixes.  Further, duplicate assignment of multiple /64s to
   the same network should be avoided, and the network should behave as
   gracefully as possible in the event of prefix exhaustion (though the
   options in such cases may be limited).



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   Where the home network has multiple CERs and these are delegated
   prefix pools from their attached ISPs, the internal prefix delegation
   would be expected to be served by each CER for each prefix associated
   with it.  However, where ULAs are used, most likely but not
   necessarily in parallel with global prefixes, one router should be
   elected as 'master' for delegation of ULA prefixes for the homenet,
   such that only one /48 ULA covers the whole homenet where possible.
   That router should generate a /48 ULA for the site, and then delegate
   /64's from that ULA prefix to subnets.  In cases where two /48 ULAs
   are generated within a homenet, the network should still continue to
   function, meaning that hosts will need to determine that each ULA is
   local to the homenet.

   Delegation within the homenet should give each subnet a prefix that
   is persistent across reboots, power outages and similar short-term
   outages.  Addition of a new routing device should not affect existing
   persistent prefixes, but persistence may not be expected in the face
   of significant 'replumbing' of the homenet.  Persistent prefixes
   should not depend on router boot order.  However, such persistent
   prefixes may imply the need for stable storage on routing devices,
   and also a method for a home user to 'reset' the stored prefix should
   a significant reconfiguration be required (though ideally the home
   user should not be involved at all).

   The delegation method should support renumbering, which would
   typically be 'flash' renumbering in that the homenet would not have
   advance notice of the event or thus be able to apply the types of
   approach described in [RFC4192].  As a minimum, delegated ULA
   prefixes within the homenet should remain persistent through an ISP-
   driven renumbering event.

   Several proposals have been made for prefix delegation within a
   homenet.  One group of proposals is based on DHCPv6 PD, as described
   in [I-D.baker-homenet-prefix-assignment], [RFC3315] and [RFC3633].
   The other uses OSPFv3, as described in
   [I-D.arkko-homenet-prefix-assignment].  More detailed analysis of
   these approaches needs to be made against the requirements/principles
   described above.

3.4.4.  Coordination of configuration information

   The network elements will need to be integrated in a way that takes
   account of the various lifetimes on timers that are used on different
   elements, e.g.  DHCPv6 PD, router, valid prefix and preferred prefix
   timers.






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3.4.5.  Privacy

   There are no specific privacy concerns discussed in this text.  It
   should be noted that, in general, ISPs are expected to offer
   relatively stable IPv6 prefixes to customers, and thus the network
   prefix associated with the host addresses they use may not change
   over a reasonably long period of time.  This exposure is similar to
   IPv4 networks that expose the same IPv4 global address via use of
   NAT, where the IPv4 address received from the ISP may change over
   time, but not necessarily that frequently.

   Hosts inside an IPv6 homenet may get new IPv6 addresses over time
   regardless, e.g. through Privacy Addresses [RFC4941].  This may
   benefit mutual privacy of users within a home network, but not mask
   which home network traffic is sourced from.

3.5.  Routing functionality

   Routing functionality is required when there are multiple routers
   deployed within the internal home network.  This functionality could
   be as simple as the current 'default route is up' model of IPv4 NAT,
   or, more likely, it would involve running an appropriate routing
   protocol.

   The homenet unicast routing protocol should preferably be an existing
   deployed protocol that has been shown to be reliable and robust, and
   it is preferable that the protocol is 'lightweight'.  It is desirable
   that the routing protocol has knowledge of the homenet topology,
   which implies a link-state protocol is preferable.  If so, it is also
   desirable that the announcements and use of LSAs and RAs are
   appropriately coordinated.  This would mean the routing protocol
   gives a consistent view of the network, and that it can pass around
   more than just routing information.

   Multiple interface PHYs must be accounted for in the homenet routed
   topology.  Technologies such as Ethernet, WiFi, MoCA, etc must be
   capable of coexisting in the same environment and should be treated
   as part of any routed deployment.  The inclusion of the PHY layer
   characteristics including bandwidth, loss, and latency in path
   computation should be considered for optimising communication in the
   homenet.  Multiple upstreams should be supported, as described in the
   multihoming section earlier.  This should include load-balancing to
   multiple providers, and failover from a primary to a backup link when
   available.  The protocol however should not require upstream ISP
   connectivity to be established to continue routing within the
   homenet.

   To support multihoming within a homenet, a routing protocol that can



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   make routing decisions based on source and destination addresses is
   desirable, to avoid upstream ISP ingress filtering problems.  In
   general the routing protocol should support multiple ISP uplinks and
   delegated prefixes in concurrent use.

   The routing environment should be self-configuring, as discussed
   previously.  An example of how OSPFv3 can be self-configuring in a
   homenet is described in [I-D.acee-ospf-ospfv3-autoconfig].
   Minimising convergence time should be a goal in any routed
   environment, but as a guideline a maximum convergence time of around
   30 seconds should be the target.

   Any routed solution will require a means for determining the
   boundaries of the homenet.  Borders may include but are not limited
   to the interface to the upstream ISP, or a gateway device to a
   separate home network such as a LLN network.  In some cases there may
   be no border present, which may for example occur before an upstream
   connection has been established.  The border discovery functionality
   may be integrated into the routing protocol itself, but may also be
   imported via a separate discovery mechanism.

   In general, LLN or other networks should be able to attach and
   participate the same way as the main homenet, or alternatively map/be
   gatewayed to the main homenet.  Current home deployments use largely
   different mechanisms in sensor and basic Internet connectivity
   networks.  IPv6 VM solutions may also add additional routing
   requirements.

3.5.1.  Multicast support

   It is desirable that, subject to the capacities of devices on certain
   media types, multicast routing is supported across the homenet.  The
   natural scopes for multicast would be link-local or site-local, with
   the latter constrained within the homenet, but other policy borders,
   e.g. to a guest subnet, or to certain media types, may also affect
   where specific multicast traffic is routed.

   There may be different drivers for multicast to be supported across
   the homenet, e.g. for service discovery should a proposal such as
   xmDNS [I-D.lynn-homenet-site-mdns] be deployed, or potentially for
   novel streaming or filesharing applications.  Where multicast is
   routed across a homenet an appropriate multicast routing protocol is
   required, one that as per the unicast routing protocol should be
   self-configuring.  It must be possible to scope or filter multicast
   traffic to avoid it being flooded to network media where devices
   cannot reasonably support it.

   The multicast environment should support the ability for applications



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   to pick a unique multicast group to use.

3.6.  Security

   The security of an IPv6 homenet is an important consideration.  The
   most notable difference to the IPv4 operational model is the removal
   of NAT, the introduction of global addressability of devices, and
   thus a need to consider whether devices should have global
   reachability.  Regardless, hosts need to be able to operate securely,
   end-to-end where required, and also be robust against malicious
   traffic direct towards them.  However, there are other challenges
   introduced, e.g. default filtering policies at the borders between
   other homenet realms.

3.6.1.  Addressability vs reachability

   An IPv6-based home network architecture should embrace the
   transparent end-to-end communications model as described in
   [RFC2775].  Each device should be globally addressable, and those
   addresses must not be altered in transit.  However, security
   perimeters can be applied to restrict end-to-end communications, and
   thus while a host may be globally addressable it may not be globally
   reachable.

   In IPv4 NAT networks, the NAT provides an implicit firewall function.
   [RFC4864] describes a 'Simple Security' model for IPv6 networks,
   whereby stateful perimeter filtering can be applied instead where
   global addresses are used.  RFC 4864 implies an IPv6 'default deny'
   policy for inbound connections be used for similar functionality to
   IPv4 NAT.  It should be noted that such a 'default deny' approach
   would effectively replace the need for IPv4 NAT traversal protocols
   with a need to use a signalling protocol to request a firewall hole
   be opened.  Thus to support applications wanting to accept
   connections initiated into home networks where a 'default deny'
   policy is in place support for a signalling protocol such as UPnP or
   PCP [I-D.ietf-pcp-base] is required.  In networks with multiple CERs,
   the signalling would need to handle the cases of flows that may use
   one or more exit routers.  CERs would need to be able to advertise
   their existence for such protocols.

   [RFC6092] expands on RFC 4864, giving a more detailed discussion of
   IPv6 perimeter security recommendations, without mandating a 'default
   deny' approach.  Indeed, RFC 6092 does not enforce a particular mode
   of operation, instead stating that CERs must provide an easily
   selected configuration option that permits a 'transparent' mode, thus
   ensuring a 'default allow' model is available.  The homenet
   architecture text makes no recommendation on the default setting, and
   refers the reader to RFC 6092.



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3.6.2.  Filtering at borders

   It is desirable that there are mechanisms to detect different types
   of borders within the homenet, as discussed previously, and further
   mechanisms to then apply different types of filtering policies at
   those borders, e.g. whether naming and service discovery should pass
   a given border.  Any such policies should be able to be easily
   applied by typical home users, e.g. to give a user in a guest network
   access to media services in the home, or access to a printer.  Simple
   mechanisms to apply policy changes, or associations between devices,
   will be required.

   There are cases where full internal connectivity may not be
   desirable, e.g. in certain utility networking scenarios, or where
   filtering is required for policy reasons against guest network
   subnet(s).  Some scenarios/models may as a result involve running
   isolated subnet(s) with their own CERs.  In such cases connectivity
   would only be expected within each isolated network (though traffic
   may potentially pass between them via external providers).

   LLNs provide an another example of where there may be secure
   perimeters inside the homenet.  Constrained LLN nodes may implement
   network key security but may depend on access policies enforced by
   the LLN border router.

3.6.3.  Marginal Effectiveness of NAT and Firewalls

   Security by way of obscurity (address translation) or through
   firewalls (filtering) is at best marginally effective.  The very poor
   security track record of home computer, home networking and business
   PC computers and networking is testimony to its ineffectiveness.  A
   compromise behind the firewall of any device exposes all others,
   making an entire network that relies on obscurity or a firewall as
   vulnerable as the most insecure device on the private side of the
   network.

   However, given home network products with very poor security, putting
   a firewall in place does provide some protection, even if only
   marginally effective.  The use of firewalls today, whether a good
   practice or not, is common practice and whatever protection afforded,
   even if marginally effective, must not be lost.

3.6.4.  Device capabilities

   In terms of the devices, homenet hosts should implement their own
   security policies in accordance to their computing capabilities.
   They should have the means to request transparent communications to
   be initiated to them, either for all ports or for specific services.



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   Users should have simple methods to associate devices to services
   that they wish to operate transparently through (CER) borders.

3.6.5.  ULAs as a hint of connection origin

   It has been suggested that using ULAs would provide an indication to
   applications that received traffic is locally sourced.  This could
   then be used with security settings to designate between which nodes
   a particular application is allowed to communicate, provided ULA
   address space is filtered appropriately at the boundary of the realm.

3.7.  Naming and Service Discovery

   Naming and service discovery must be supported in the homenet, and
   the service(s) providing this function must as far as possible
   support unmanaged operation.

   The naming system will be required to work internally or externally,
   be the user within the homenet or outside it, i.e. the user should be
   able to refer to devices by name, and potentially connect to them,
   wherever they may be.  The most natural way to think about such
   naming and service discovery is to enable it to work across the
   entire homenet residence (site), disregarding technical borders such
   as subnets but respecting policy borders such as those between guest
   and other internal network realms.

3.7.1.  Discovering services

   Users will typically perform service discovery through GUI interfaces
   that allow them to browse services on their network in an appropriate
   and intuitive way.  Such interfaces are beyond the scope of this
   document, but the interface should have an appropriate API for the
   discovery to be performed.

   Such interfaces may also typically hide the local domain name element
   from users, especially where only one name space is available.
   However, as we discuss below, in some cases the ability to discover
   available domains may be useful.

   We note that current service discovery protocols are generally aimed
   at single subnets.  There is thus a choice to make for multi-subnet
   homenets as to whether such protocols should be proxied or extended
   to operate across a whole homenet.  In this context, that may mean
   bridging a link-local method, taking care to avoid loops, or
   extending the scope of multicast traffic used for the purpose.  This
   document does not mandate either solution, rather it expresses the
   principles that should be used for a homenet naming and service
   discovery environment.  Or it may be that a new approach is



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   preferable, e.g. flooding information around the homenet as
   attributes within the routing protocol (which could allow per-prefix
   configuration).  In general we should prefer approaches that are
   backwardly compatible, and allow current implementations to continue
   to be used.

   One of the primary challenges facing service discovery today is lack
   of interoperability due to the ever increasing number of service
   discovery protocols available.  While it is conceivable for consumer
   devices to support multiple discovery protocols, this is clearly not
   the most efficient use of network and computational resources.  One
   goal of the homenet architecture should be a path to service
   discovery protocol interoperability either through a standards based
   translation scheme, hooks into current protocols to allow some for of
   communication among discovery protocols, extensions to support a
   central service repository in the homenet, or simply convergence
   towards a unified protocol suite.

3.7.2.  Assigning names to devices

   Given the large number of devices that may be networked in the
   future, devices should have a means to generate their own unique
   names within a homenet, and to detect clashes should they arise, e.g.
   where a second device of the same type/vendor as an existing device
   with the same default name is deployed, or where two running network
   elements with such devices are suddenly joined.  For example, mDNS
   [I-D.cheshire-dnsext-multicastdns] section 8 describes such a
   mechanism for a single subnetwork and the '.local' zone.  Before
   assigning a name to the device and the .local naming space, the
   device checks whether the name already belongs to another device by
   sending a multicast DNS query.

   Users will also want simple ways to (re)name devices, again most
   likely through an appropriate and intuitive interface that is beyond
   the scope of this document.  Note the name a user assigns to a device
   may be a label that is stored on the device as an attribute of the
   device, and may be distinct from the name used in a name service,
   e.g.  'Study Laser Printer' as opposed to printer2.<somedomain>.

3.7.3.  Name spaces

   It is desirable that only one name space is in use in the homenet,
   and that this name space is served authoritatively by a server in the
   homenet, most likely resident on the CER.

   If a user wishes to access their home devices remotely from elsewhere
   on the Internet a globally unique name space is required.  This may
   be acquired by the user or provided/generated by their ISP.  It is



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   expected that the default case is that a homenet will use a global
   domain provided by the ISP, but advanced users wishing to use a name
   space that is independent of their provider in the longer term should
   be able to acquire and use their own domain name.  Examples of
   provider name space delegation approaches are described in
   [I-D.mglt-homenet-naming-delegation] and
   [I-D.mglt-homenet-front-end-naming-delegation].  For users wanting to
   use their own independent domain names, such services are already
   available.

   If however a global name space is not available, the homenet will
   need to pick and use a local name space which would only have meaning
   within the local homenet (i.e. it would not be used for remote access
   to the homenet).  The .local name space currently has a special
   meaning for certain existing protocols which have link-local scope,
   and is thus not appropriate for multi-subnet home networks.  A
   different name space is thus required for the homenet.

   One approach for picking a local name space is to use an Ambiguous
   Local Qualified Domain Name (ALQDN) space, such as .sitelocal (or an
   appropriate name reserved for the purpose).  While this is a simple
   approach, there is the potential in principle for devices that are
   bookmarked somehow by an application in one homenet to be confused
   with a device with the same name in another homenet.

   An alternative approach for a local name space would be to use a
   Unique Locally Qualified Domain Name (ULQDN) space such as
   .<UniqueString>.sitelocal.  The <UniqueString> could be generated in
   a variety of ways, one potentially being based on the local /48 ULA
   prefix being used across the homenet.  Such a <UniqueString> should
   survive a cold restart, i.e. be consistent after a network power-
   down, or, if a value is not set on startup, the CER or device running
   the name service should generate a default value.  It could be
   desirable for the homenet user to be able to override the
   <UniqueString> with a value of their choice, but that would increase
   the likelihood of a name conflict.

   Whichever approach is used, the intent of using a ULQDN is to
   disambiguate the name space across different homenets, not to create
   a new IANA name space for such networks.  However, in practice an
   ALQDN may typically suffice, because the underlying service discovery
   protocols should be capable of handling moving to a network where a
   new device is using the same name as a device used previously in
   another homenet.  And regardless, if remote access to a homenet is
   required, a global domain is required, which implictly disambiguates
   devices.

   With the introduction of new "dotless" top level domains, there is



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   also potential for ambiguity between, for example, a local host
   called 'computer' and (if it is registered) a .computer gTLD.  Thus
   qualified names should always be used, whether these are exposed to
   the user or not.

   There may be use cases where segmentation of the name space is
   desirable, e.g. for use in different realms within the homenet.  Thus
   hierarchical name space management is likely to be required.

   Where a user may be in a remote network wishing to access devices in
   their home network, there may be a requirement to consider the domain
   search order presented where two accompanying name spaces exist.  In
   such cases, a GUI may present the user a choice of domains to use,
   where the name of their devices is thus relative to that domain.
   This implies that a domain discovery function is desirable.

   It may be the case that not all devices in the homenet are made
   available by name via an Internet name space, and that a 'split view'
   is preferred for certain devices.

   This document makes no assumption about the presence or omission of a
   reverse lookup service.  There is an argument that it may be useful
   for presenting logging information to users with meaningful device
   names rather than literal addresses.

3.7.4.  The homenet name service

   The homenet name service should support both lookups and discovery.
   A lookup would operate via a direct query to a known service, while
   discovery may use multicast messages or a service where applications
   register in order to be found.

   It is highly desirable that the homenet name service must at the very
   least co-exist with the Internet name service.  There should also be
   a bias towards proven, existing solutions.  The strong implication is
   thus that the homenet service is DNS-based, or DNS-compatible.  There
   are naming protocols that are designed to be configured and operate
   Internet-wide, like unicast-based DNS, but also protocols that are
   designed for zero-configuration local environments, like mDNS
   [I-D.cheshire-dnsext-multicastdns].  Note that when DNS is used as
   the homenet name service, it includes both a resolving service and an
   authoritative service.  The authoritative service hosts the homenet
   related zone, that may be requested by the resolving service.

   As described in [I-D.mglt-homenet-naming-delegation], one approach is
   to run an authoritative name service in the homenet as well as a
   resolving name service, most likely on the CER.  The homenet
   resolving name service relies both on the homenet authoritative



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   service as well as on a secondary resolving name service provided by
   the ISP, for global Internet naming resolution.

   For a service such as mDNS to coexist with an Internet name service,
   where the homenet is preferably using a global domain name, it is
   desirable that the zeroconf devices have a way to add their names to
   the global name space in use.  One solution could be for zeroconf
   protocols to be used to indicate global FQDNs, e.g. an mDNS service
   could return a FQDN in a SRV record.

   Regardless, a method for local name service entries to be populated
   automatically by devices is desirable.  Interfaces to devices might
   choose to give users the option as to whether the device should
   register itself in the global name space.  There should also be a
   defined mechanism for device entries to be removed or expired from
   the global name space.

   It has been suggested that Dynamic DNS could be made to operate in a
   zero-configuration mode using a locally significant root domain and
   with minimal configuration or, using a DHCPv6 based means of
   automated delegation, populate a global DNS zone.

   To protect against attacks such as cache poisoning, it is desirable
   to support appropriate name service security methods, including
   DNSSEC.

   The CER is an appropriate location to host the naming service.
   However, it introduces an additional load due to the name service
   management, e.g. signing the zone, or resolving naming queries.  This
   additional load must be balanced with the CER capabilities, else the
   function(s) may need to be offloaded elsewhere, e.g. with the ISP,
   though this may impact on the independent operation principle.

   Finally, the impact of a change in CER must be considered.  It would
   be desirable to retain any relevant state (configuration) that was
   held in the old CER.  This might imply that state information should
   be distributed in the homenet, to be recoverable by/to the new CER,
   or to the homenet's ISP or a third party service by some means.

3.7.5.  Independent operation

   Name resolution and service discovery for reachable devices must
   continue to function if the local network is disconnected from the
   global Internet, e.g. a local media server should still be available
   even if the Internet link is down for an extended period.  This
   implies the local network should also be able to perform a complete
   restart in the absence of external connectivity, and have local
   naming and service discovery operate correctly.



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   The approach described above of a local authoritative name service
   with a cache would allow local operation for sustained ISP outages.

   Having an independent local trust anchor is desirable, to support
   secure exchanges should external connectivity be unavailable.

   A change in ISP should not affect local naming and service discovery.
   However, if the homenet uses a global name space provided by the ISP,
   then this will obviously have an impact if the user changes their
   network provider.

3.7.6.  Considerations for LLNs

   In some parts of the homenet, in particular LLNs, devices may be
   sleeping, in which case a proxy for such nodes may be required, that
   could respond (for example) to multicast service discovery requests.
   Those same parts of the network may have less capacity for multicast
   traffic that may be flooded from other parts of the network.  In
   general, message utilisation should be efficient considering the
   network technologies the service may need to operate over.

   There are efforts underway to determine naming and discovery
   solutions for use by the Constrained Application Protocol (CoAP) in
   LLN networks.  These are outside the scope of this document.

3.7.7.  DNS resolver discovery

   Automatic discovery of a name service to allow client devices in the
   homenet to resolve external domains on the Internet is required, and
   such discovery must support clients that may be a number of router
   hops away from the name service.  Similarly the search domains for
   local FQDN-derived zones should be included.

3.8.  Other Considerations

   This section discusses two other considerations for home networking
   that the architecture should not preclude, but that this text is
   neutral towards.

3.8.1.  Quality of Service

   Support for QoS in a multi-service homenet may be a requirement, e.g.
   for a critical system (perhaps healthcare related), or for
   differentiation between different types of traffic (file sharing,
   cloud storage, live streaming, VoIP, etc).  Different media types may
   have different such properties or capabilities.

   However, homenet scenarios should require no new QoS protocols.  A



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   DiffServ [RFC2475] approach with a small number of predefined traffic
   classes may generally be sufficient, though at present there is
   little experience of QoS deployment in home networks.  It is likely
   that QoS, or traffic prioritisation, methods will be required at the
   CER, and potentially around boundaries between different media types
   (where for example some traffic may simply not be appropriate for
   some media, and need to be dropped to avoid drowning the constrained
   media).

   There may also be complementary mechanisms that could be beneficial
   to application performance and behaviour in the homenet domain, such
   as ensuring proper buffering algorithms are used as described in
   [Gettys11].

3.8.2.  Operations and Management

   The homenet should be self-organising and configuring as far as
   possible, and thus not be pro-actively managed by the home user.
   Thus protocols to manage the network are not discussed in this
   architecture text.

   However, users may be interested in the status of their networks and
   devices on the network, in which case simplified monitoring
   mechanisms may be desirable.  It may also be the case that an ISP, or
   a third party, might offer management of the homenet on behalf of a
   user, in which case management protocols would be required.  How such
   management is done is out of scope of this document; many solutions
   exist.

3.9.  Implementing the Architecture on IPv6

   This architecture text encourages re-use of existing protocols.  Thus
   the necessary mechanisms are largely already part of the IPv6
   protocol set and common implementations, though there are some
   exceptions.

   For automatic routing, it is expected that existing routing protocols
   can be used as is.  However, a new mechanism may be needed in order
   to turn a selected protocol on by default.

   Some functionality, if required by the architecture, would add
   significant changes or require development of new protocols, e.g.
   support for multihoming with multiple exit routers would likely
   require extensions to support source and destination address based
   routing within the homenet.

   Some protocol changes are however required in the architecture, e.g.
   for name resolution and service discovery, extensions to existing



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   multicast-based name resolution protocols are needed to enable them
   to work across subnets, within the scope of the home network site.

   Some of the hardest problems in developing solutions for home
   networking IPv6 architectures include discovering the right borders
   where the 'home' domain ends and the service provider domain begins,
   deciding whether some of the necessary discovery mechanism extensions
   should affect only the network infrastructure or also hosts, and the
   ability to turn on routing, prefix delegation and other functions in
   a backwards compatible manner.


4.  Conclusions

   This text defines principles and requirements for a homenet
   architecture.  The principles and requirements documented here should
   be observed by any future texts describing homenet protocols for
   routing, prefix management, security, naming or service discovery.


5.  References

5.1.  Normative References

   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, December 1998.

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

   [RFC3633]  Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
              Host Configuration Protocol (DHCP) version 6", RFC 3633,
              December 2003.

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

   [RFC4193]  Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
              Addresses", RFC 4193, October 2005.

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, February 2006.

   [RFC4864]  Van de Velde, G., Hain, T., Droms, R., Carpenter, B., and
              E. Klein, "Local Network Protection for IPv6", RFC 4864,
              May 2007.




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5.2.  Informative References

   [RFC1918]  Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
              E. Lear, "Address Allocation for Private Internets",
              BCP 5, RFC 1918, February 1996.

   [RFC2475]  Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.,
              and W. Weiss, "An Architecture for Differentiated
              Services", RFC 2475, December 1998.

   [RFC2775]  Carpenter, B., "Internet Transparency", RFC 2775,
              February 2000.

   [RFC2827]  Ferguson, P. and D. Senie, "Network Ingress Filtering:
              Defeating Denial of Service Attacks which employ IP Source
              Address Spoofing", BCP 38, RFC 2827, May 2000.

   [RFC3022]  Srisuresh, P. and K. Egevang, "Traditional IP Network
              Address Translator (Traditional NAT)", RFC 3022,
              January 2001.

   [RFC3646]  Droms, R., "DNS Configuration options for Dynamic Host
              Configuration Protocol for IPv6 (DHCPv6)", RFC 3646,
              December 2003.

   [RFC4192]  Baker, F., Lear, E., and R. Droms, "Procedures for
              Renumbering an IPv6 Network without a Flag Day", RFC 4192,
              September 2005.

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

   [RFC5533]  Nordmark, E. and M. Bagnulo, "Shim6: Level 3 Multihoming
              Shim Protocol for IPv6", RFC 5533, June 2009.

   [RFC5969]  Townsley, W. and O. Troan, "IPv6 Rapid Deployment on IPv4
              Infrastructures (6rd) -- Protocol Specification",
              RFC 5969, August 2010.

   [RFC6092]  Woodyatt, J., "Recommended Simple Security Capabilities in
              Customer Premises Equipment (CPE) for Providing
              Residential IPv6 Internet Service", RFC 6092,
              January 2011.

   [RFC6106]  Jeong, J., Park, S., Beloeil, L., and S. Madanapalli,
              "IPv6 Router Advertisement Options for DNS Configuration",
              RFC 6106, November 2010.



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   [RFC6144]  Baker, F., Li, X., Bao, C., and K. Yin, "Framework for
              IPv4/IPv6 Translation", RFC 6144, April 2011.

   [RFC6145]  Li, X., Bao, C., and F. Baker, "IP/ICMP Translation
              Algorithm", RFC 6145, April 2011.

   [RFC6177]  Narten, T., Huston, G., and L. Roberts, "IPv6 Address
              Assignment to End Sites", BCP 157, RFC 6177, March 2011.

   [RFC6204]  Singh, H., Beebee, W., Donley, C., Stark, B., and O.
              Troan, "Basic Requirements for IPv6 Customer Edge
              Routers", RFC 6204, April 2011.

   [RFC6296]  Wasserman, M. and F. Baker, "IPv6-to-IPv6 Network Prefix
              Translation", RFC 6296, June 2011.

   [RFC6333]  Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual-
              Stack Lite Broadband Deployments Following IPv4
              Exhaustion", RFC 6333, August 2011.

   [RFC6555]  Wing, D. and A. Yourtchenko, "Happy Eyeballs: Success with
              Dual-Stack Hosts", RFC 6555, April 2012.

   [RFC6724]  Thaler, D., Draves, R., Matsumoto, A., and T. Chown,
              "Default Address Selection for Internet Protocol Version 6
              (IPv6)", RFC 6724, September 2012.

   [I-D.mglt-homenet-front-end-naming-delegation]
              Migault, D., Cloetens, W., Lemordant, P., and C.
              Griffiths, "IPv6 Home Network Front End Naming
              Delegation",
              draft-mglt-homenet-front-end-naming-delegation-01 (work in
              progress), November 2012.

   [I-D.mglt-homenet-naming-delegation]
              Cloetens, W., Lemordant, P., and D. Migault, "IPv6 Home
              Network Naming Delegation Architecture",
              draft-mglt-homenet-naming-delegation-00 (work in
              progress), July 2012.

   [I-D.lynn-homenet-site-mdns]
              Lynn, K. and D. Sturek, "Extended Multicast DNS",
              draft-lynn-homenet-site-mdns-01 (work in progress),
              September 2012.

   [I-D.ietf-v6ops-ipv6-multihoming-without-ipv6nat]
              Matsushima, S., Okimoto, T., Troan, O., Miles, D., and D.
              Wing, "IPv6 Multihoming without Network Address



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              Translation",
              draft-ietf-v6ops-ipv6-multihoming-without-ipv6nat-04 (work
              in progress), February 2012.

   [I-D.baker-homenet-prefix-assignment]
              Baker, F. and R. Droms, "IPv6 Prefix Assignment in Small
              Networks", draft-baker-homenet-prefix-assignment-01 (work
              in progress), March 2012.

   [I-D.arkko-homenet-prefix-assignment]
              Arkko, J., Lindem, A., and B. Paterson, "Prefix Assignment
              in a Home Network",
              draft-arkko-homenet-prefix-assignment-03 (work in
              progress), October 2012.

   [I-D.acee-ospf-ospfv3-autoconfig]
              Lindem, A. and J. Arkko, "OSPFv3 Auto-Configuration",
              draft-acee-ospf-ospfv3-autoconfig-03 (work in progress),
              July 2012.

   [I-D.cheshire-dnsext-multicastdns]
              Cheshire, S. and M. Krochmal, "Multicast DNS",
              draft-cheshire-dnsext-multicastdns-15 (work in progress),
              December 2011.

   [I-D.ietf-pcp-base]
              Wing, D., Cheshire, S., Boucadair, M., Penno, R., and P.
              Selkirk, "Port Control Protocol (PCP)",
              draft-ietf-pcp-base-29 (work in progress), November 2012.

   [I-D.kline-default-perimeter]
              Kline, E., "Default Border Definition",
              draft-kline-default-perimeter-01 (work in progress),
              November 2012.

   [I-D.ietf-v6ops-6204bis]
              Singh, H., Beebee, W., Donley, C., and B. Stark, "Basic
              Requirements for IPv6 Customer Edge Routers",
              draft-ietf-v6ops-6204bis-12 (work in progress),
              October 2012.

   [Gettys11]
              Gettys, J., "Bufferbloat: Dark Buffers in the Internet",
              March 2011,
              <http://www.ietf.org/proceedings/80/slides/tsvarea-1.pdf>.

   [IGD-2]    UPnP Gateway Committee, "Internet Gateway Device (IGD) V
              2.0", September 2010, <http://upnp.org/specs/gw/



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              UPnP-gw-WANIPConnection-v2-Service.pdf>.


Appendix A.  Acknowledgments

   The authors would like to thank Aamer Akhter, Mark Andrews, Dmitry
   Anipko, Ran Atkinson, Fred Baker, Ray Bellis, Cameron Byrne, Brian
   Carpenter, Stuart Cheshire, Lorenzo Colitti, Robert Cragie, Ralph
   Droms, Lars Eggert, Jim Gettys, Olafur Gudmundsson, Wassim Haddad,
   Joel M. Halpern, David Harrington, Lee Howard, Ray Hunter, Joel
   Jaeggli, Heather Kirksey, Ted Lemon, Acee Lindem, Kerry Lynn, Daniel
   Migault, Erik Nordmark, Michael Richardson, Mattia Rossi, Barbara
   Stark, Sander Steffann, Don Sturek, Dave Taht, Dave Thaler, Michael
   Thomas, Mark Townsley, JP Vasseur, Curtis Villamizar, Dan Wing, Russ
   White, and James Woodyatt for their comments and contributions within
   homenet WG meetings and on the WG mailing list.  An acknowledgement
   generally means that person's text made it in to the document, or was
   helpful in clarifying or reinforcing an aspect of the document.


Appendix B.  Changes

   This section will be removed in the final version of the text.

B.1.  Version 07

   Changes made include:

   o  Removed reference to NPTv6 in section 3.2.4.  Instead now say it
      has an architectural cost to use in the earlier section, and thus
      it is not recommended for use in the homenet architecture.

   o  Removed 'proxy or extend?' section.  Included shorter text in main
      body, without mandating either approach for service discovery.

   o  Made it clearer that ULAs are expected to be used alongside
      globals.

   o  Removed reference to 'advanced security' as described in
      draft-vyncke-advanced-ipv6-security.

   o  Balanced the text between ULQDN and ALQDN.

   o  Clarify text does not assume default deny or allow on CER, but
      that either mode may be enabled.

   o  Removed ULA-C reference for 'simple' addresses.  Instead only
      suggested service discovery to find such devices.



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   o  Reiterated that single/multiple CER models to be supported for
      multihoming.

   o  Reordered section 3.3 to improve flow.

   o  Added recommendation that homenet is not allocated less than /60,
      and a /56 is preferable.

   o  Tidied up first few intro sections.

   o  Other minor edits from list feedback.

B.2.  Version 06

   Changes made include:

   o  Stated that unmanaged goal is 'as far as possible'.

   o  Added note about multiple /48 ULAs potentially being in use.

   o  Minor edits from list feedback.

B.3.  Version 05

   Changes made include:

   o  Some significant changes to naming and SD section.

   o  Removed some expired drafts.

   o  Added notes about issues caused by ISP only delegating a /64.

   o  Recommended against using prefixes longer than /64.

   o  Suggested CER asks for /48 by DHCP-PD, even if it only receives
      less.

   o  Added note about DS-Lite but emphasised transition is out of
      scope.

   o  Added text about multicast routing.

B.4.  Version 04

   Changes made include:






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   o  Moved border section from IPv6 differences to principles section.

   o  Restructured principles into areas.

   o  Added summary of naming and service discovery discussion from WG
      list.

B.5.  Version 03

   Changes made include:

   o  Various improvements to the readability.

   o  Removed bullet lists of requirements, as requested by chair.

   o  Noted 6204bis has replaced advanced-cpe draft.

   o  Clarified the topology examples are just that.

   o  Emphasised we are not targetting walled gardens, but they should
      not be precluded.

   o  Also changed text about requiring support for walled gardens.

   o  Noted that avoiding falling foul of ingress filtering when
      multihomed is desirable.

   o  Improved text about realms, detecting borders and policies at
      borders.

   o  Stated this text makes no recommendation about default security
      model.

   o  Added some text about failure modes for users plugging things
      arbitrarily.

   o  Expanded naming and service discovery text.

   o  Added more text about ULAs.

   o  Removed reference to version 1 on chair feedback.

   o  Stated that NPTv6 adds architectural cost but is not a homenet
      matter if deployed at the CER.  This text only considers the
      internal homenet.

   o  Noted multihoming is supported.




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   o  Noted routers may not by separate devices, they may be embedded in
      devices.

   o  Clarified simple and advanced security some more, and RFC 4864 and
      6092.

   o  Stated that there should be just one secret key, if any are used
      at all.

   o  For multihoming, support multiple CERs but note that routing to
      the correct CER to avoid ISP filtering may not be optimal within
      the homenet.

   o  Added some ISPs renumber due to privacy laws.

   o  Removed extra repeated references to Simple Security.

   o  Removed some solution creep on RIOs/RAs.

   o  Load-balancing scenario added as to be supported.

B.6.  Version 02

   Changes made include:

   o  Made the IPv6 implications section briefer.

   o  Changed Network Models section to describe properties of the
      homenet with illustrative examples, rather than implying the
      number of models was fixed to the six shown in 01.

   o  Text to state multihoming support focused on single CER model.
      Multiple CER support is desirable, but not required.

   o  Stated that NPTv6 not supported.

   o  Added considerations section for operations and management.

   o  Added bullet point principles/requirements to Section 3.4.

   o  Changed IPv6 solutions must not adversely affect IPv4 to should
      not.

   o  End-to-end section expanded to talk about "Simple Security" and
      borders.

   o  Extended text on naming and service discovery.




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   o  Added reference to RFC 2775, RFC 6177.

   o  Added reference to the new xmDNS draft.

   o  Added naming/SD requirements from Ralph Droms.


Authors' Addresses

   Tim Chown (editor)
   University of Southampton
   Highfield
   Southampton, Hampshire  SO17 1BJ
   United Kingdom

   Email: tjc@ecs.soton.ac.uk


   Jari Arkko
   Ericsson
   Jorvas  02420
   Finland

   Email: jari.arkko@piuha.net


   Anders Brandt
   Sigma Designs
   Emdrupvej 26A, 1
   Copenhagen  DK-2100
   Denmark

   Email: abr@sdesigns.dk


   Ole Troan
   Cisco Systems, Inc.
   Drammensveien 145A
   Oslo  N-0212
   Norway

   Email: ot@cisco.com









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   Jason Weil
   Time Warner Cable
   13820 Sunrise Valley Drive
   Herndon, VA  20171
   USA

   Email: jason.weil@twcable.com












































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