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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: January 16, 2014                                       Ericsson
                                                               A. Brandt
                                                           Sigma Designs
                                                                O. Troan
                                                     Cisco Systems, Inc.
                                                                 J. Weil
                                                       Time Warner Cable
                                                           July 15, 2013


                 Home Networking Architecture for IPv6
                       draft-ietf-homenet-arch-09

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 January 16, 2014.



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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 . . . . . . . . . . . . . . .  7
     2.2.  Global addressability and elimination of NAT . . . . . . .  8
     2.3.  Multi-Addressing of devices  . . . . . . . . . . . . . . .  8
     2.4.  Unique Local Addresses (ULAs)  . . . . . . . . . . . . . .  9
     2.5.  Avoiding manual configuration of IP addresses  . . . . . . 10
     2.6.  IPv6-only operation  . . . . . . . . . . . . . . . . . . . 11
   3.  Homenet Architecture . . . . . . . . . . . . . . . . . . . . . 11
     3.1.  General Principles . . . . . . . . . . . . . . . . . . . . 12
       3.1.1.  Reuse existing protocols . . . . . . . . . . . . . . . 12
       3.1.2.  Minimise changes to hosts and routers  . . . . . . . . 13
     3.2.  Homenet Topology . . . . . . . . . . . . . . . . . . . . . 13
       3.2.1.  Supporting arbitrary topologies  . . . . . . . . . . . 13
       3.2.2.  Network topology models  . . . . . . . . . . . . . . . 13
       3.2.3.  Dual-stack topologies  . . . . . . . . . . . . . . . . 18
       3.2.4.  Multihoming  . . . . . . . . . . . . . . . . . . . . . 19
     3.3.  A Self-Organising Network  . . . . . . . . . . . . . . . . 20
       3.3.1.  Differentiating neighbouring homenets  . . . . . . . . 21
       3.3.2.  Largest practical subnets  . . . . . . . . . . . . . . 21
       3.3.3.  Handling varying link technologies . . . . . . . . . . 21
       3.3.4.  Homenet realms and borders . . . . . . . . . . . . . . 22
     3.4.  Homenet Addressing . . . . . . . . . . . . . . . . . . . . 23
       3.4.1.  Use of ISP-delegated IPv6 prefixes . . . . . . . . . . 23
       3.4.2.  Stable internal IP addresses . . . . . . . . . . . . . 25
       3.4.3.  Internal prefix delegation . . . . . . . . . . . . . . 26
       3.4.4.  Coordination of configuration information  . . . . . . 27
       3.4.5.  Privacy  . . . . . . . . . . . . . . . . . . . . . . . 28
     3.5.  Routing functionality  . . . . . . . . . . . . . . . . . . 28



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       3.5.1.  Multicast support  . . . . . . . . . . . . . . . . . . 29
       3.5.2.  Mobility support . . . . . . . . . . . . . . . . . . . 30
     3.6.  Security . . . . . . . . . . . . . . . . . . . . . . . . . 30
       3.6.1.  Addressability vs reachability . . . . . . . . . . . . 30
       3.6.2.  Filtering at borders . . . . . . . . . . . . . . . . . 31
       3.6.3.  Partial Effectiveness of NAT and Firewalls . . . . . . 31
       3.6.4.  Device capabilities  . . . . . . . . . . . . . . . . . 32
       3.6.5.  ULAs as a hint of connection origin  . . . . . . . . . 32
     3.7.  Naming and Service Discovery . . . . . . . . . . . . . . . 32
       3.7.1.  Discovering services . . . . . . . . . . . . . . . . . 33
       3.7.2.  Assigning names to devices . . . . . . . . . . . . . . 34
       3.7.3.  Name spaces  . . . . . . . . . . . . . . . . . . . . . 34
       3.7.4.  The homenet name service . . . . . . . . . . . . . . . 36
       3.7.5.  Independent operation  . . . . . . . . . . . . . . . . 37
       3.7.6.  Considerations for LLNs  . . . . . . . . . . . . . . . 37
       3.7.7.  DNS resolver discovery . . . . . . . . . . . . . . . . 37
       3.7.8.  Devices roaming from the homenet . . . . . . . . . . . 38
     3.8.  Other Considerations . . . . . . . . . . . . . . . . . . . 38
       3.8.1.  Quality of Service . . . . . . . . . . . . . . . . . . 38
       3.8.2.  Operations and Management  . . . . . . . . . . . . . . 38
     3.9.  Implementing the Architecture on IPv6  . . . . . . . . . . 39
   4.  Conclusions  . . . . . . . . . . . . . . . . . . . . . . . . . 39
   5.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 40
     5.1.  Normative References . . . . . . . . . . . . . . . . . . . 40
     5.2.  Informative References . . . . . . . . . . . . . . . . . . 40
   Appendix A.  Acknowledgments . . . . . . . . . . . . . . . . . . . 43
   Appendix B.  Changes . . . . . . . . . . . . . . . . . . . . . . . 43
     B.1.  Version 09 (after WGLC)  . . . . . . . . . . . . . . . . . 43
     B.2.  Version 08 . . . . . . . . . . . . . . . . . . . . . . . . 44
     B.3.  Version 07 . . . . . . . . . . . . . . . . . . . . . . . . 44
     B.4.  Version 06 . . . . . . . . . . . . . . . . . . . . . . . . 45
     B.5.  Version 05 . . . . . . . . . . . . . . . . . . . . . . . . 45
     B.6.  Version 04 . . . . . . . . . . . . . . . . . . . . . . . . 46
     B.7.  Version 03 . . . . . . . . . . . . . . . . . . . . . . . . 46
     B.8.  Version 02 . . . . . . . . . . . . . . . . . . . . . . . . 47
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 48















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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, most are relatively simple single subnet networks, and
   ostensibly operate using just IPv4.  While there may be IPv6 traffic
   within the network, e.g. for service discovery, the homenet is
   provisioned by the ISP as an IPv4 network.  Such networks 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 facilitate private and guest
   networks, heterogeneous link layers, and smart grid components, and
   have enough address space available to allow every device to have a
   globally unique address.  This implies that internal routing
   functionality is required, and that the homenet's ISP both provides a
   large enough prefix to allocate a prefix to each subnet, and that a
   method is supported for such prefixes to be delegated efficiently to
   those subnets.

   It is not practical to expect home users to configure their networks.
   Thus the assumption of this document is that the homenet is as far as
   possible self-organising and self-configuring, i.e. it should
   function without pro-active management 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 modified by new recommendations.  This document does



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   not discuss how IPv4 home networks provision or deliver support for
   multiple subnets.  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 impact would not apply.

   This document proposes a baseline homenet architecture, using
   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).  This document has recently been updated with the definition
   of requirements for specific transition tools on the CER in
   [I-D.ietf-v6ops-6204bis], specifically DS-Lite [RFC6333] and 6rd
   [RFC5969].  Such detailed specification of CER devices is considered
   out of scope of this architecture document, and we assume that any
   required update of the CER device specification as a result of
   adopting this architecture will be handled as separate and specific
   updates to these existing documents.  Further, the scope of this text
   is the internal homenet, and thus specific features on the WAN side
   of the CER are out of scope for 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  Border: a point, typically resident on a router, between two
      networks, e.g. between the main internal homenet and a guest
      network.  This defines point(s) at which filtering and forwarding
      policies for different types of traffic may be applied.

   o  CER: Customer Edge Router: A border router intended for use in a
      homenet, which connects the homenet to a service provider network.

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





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   o  Homenet: A home network, comprising host and router equipment,
      with one or more CERs providing connectivity to service provider
      network(s).

   o  Internet Service Provider (ISP): an entity that provides access to
      the Internet.  In this document, a service provider specifically
      offers Internet access using IPv6, and may also offer IPv4
      Internet access.  The service provider can provide such access
      over a variety of different transport methods such as DSL, cable,
      wireless, and others.

   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  Realm: a network delimited by a defined border.  A guest network
      within a homenet may form one realm.

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

   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



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   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 from its
   ISP to provision globally unique prefixes for each such subnet in the
   home.  While the number of addresses in a 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; this topic is discussed in
   [RFC6177] (BCP 157), which recommends that "end sites always be able
   to obtain a reasonable amount of address space for their actual and
   planned usage".

   The addition of routing between subnets raises a number of issues.
   One is a method by which prefixes can be efficiently allocated to
   each subnet, without user intervention.  Another is the issue of how
   to extend mechanisms such as zero configuration 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 in



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   Section 3.7.

2.2.  Global addressability and elimination of NAT

   The possibility for direct end-to-end communication on the Internet
   to be restored by the introduction of IPv6 is on the one hand an
   incredible opportunity for innovation and simpler network operation,
   but on the other hand it is also a concern as it potentially exposes
   nodes in the internal networks to receipt of 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.  In addition, the
   upgrade cycle for devices (or their firmware) may be slow, and/or
   lack auto-update mechanisms.

   It is thus 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 any 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
   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 for the homenet to use either mode would be 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 (GUA) 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



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   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.  A challenge here is
   that the node may not have the information it needs to make that
   decision based on addresses alone.  We discuss this challenge in
   Section 3.2.4.

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 homenet 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.  A homenet using provider-assigned global
   addresses is exposed to its ISP renumbering the network to a much
   larger degree than before whereas, for IPv4, NAT isolated the user
   against ISP renumbering to some extent.

   While setting up a network there may be a period where it has no
   external 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 (as early as during construction of the
   home), LLNs will likely need to use their own /48 ULA prefix.
   Depending upon circumstances beyond the scope of homenet, it may be
   impossible to renumber the ULA used by the LLN so routing between ULA
   /48s may be required.  Also, some devices, particularly constrained
   devices, may have only a ULA (in addition to a link-local), while
   others may have both a GUA and a ULA.

   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 a source address for external communications.  By using such
   globally unique addresses between hosts and devices in remote
   networks, the architectural cost and complexity, particularly to
   applications, of NAT or NPTv6 translation is avoided.  As such,
   neither IPv6 NAT or NPTv6 is recommended for use in the homenet



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   architecture.

   Devices in a homenet may be given only a ULA as a means to restrict
   reachability from outside the homenet.  ULAs can be used by default
   for devices that, without additional configuration (e.g. via a web
   interface), would only offer services to the internal network.  For
   example, a printer might only accept incoming connections on a ULA
   until configured to be globally reachable, at which point it acquires
   a global IPv6 address and may be advertised via a global name space.

   Where both a ULA and a global prefix are in use, the ULA source
   address is used to communicate with ULA destination addresses when
   appropriate, i.e. when the ULA source and destination lie within the
   /48 ULA prefix(es) known to be used within the same homenet.  In
   cases where multiple /48 ULA prefixes are in use within a single
   homenet (perhaps because multiple homenet routers each independently
   auto-generate a /48 ULA prefix and then share prefix/routing
   information), utilising a ULA source address and a ULA destination
   address from two disjoint internal ULA prefixes is preferable to
   using GUAs.

   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.

   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 should support and use ULAs.

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 the 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



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   discovery protocols must be capable of operating across subnet
   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  Ensuring DNS resolver 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  Ensuring 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 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 the proposed home networking
   architecture, with discussion of the associated design principles.

   In general, home network equipment needs to be able to operate in



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   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 the
   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 text discusses how such
   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 (and available) code, is preferable.  Where new
   protocols are 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.






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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 capability 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.

   The topology of the homenet may change over time, due to the addition
   or removal of equipment, but also due to temporary failures or
   connectivity problems.  In some cases this may lead to, for example,
   a multihomed homenet being split into two isolated homenets, or,
   after such a fault is remedied, two isolated parts reconfiguring back
   to a single network.

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



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   separation of guest and private networks.  There may also be some
   cascaded IPv4 NAT scenarios, which we mention in the next section.
   For IPv6 homenets, the network models described in [RFC6204] and its
   successor RFC 6204-bis [I-D.ietf-v6ops-6204bis] should, as a minimum,
   be supported.

   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, where the homenet may have two or more external
   ISP connections, 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 networks, such as ad-
   hoc mobile networks.

   In some cases IPv4 home networks may feature cascaded NATs.  End
   users are frequently unaware that they have created such networks as
   'home routers' and 'home switches' are frequently confused.  In
   addition, there are cases where NAT routers are included within
   Virtual Machine Hypervisors, or where Internet connection sharing
   services have been enabled.  This document applies equally to such
   hidden NAT 'routers'.  IPv6 routed versions of such cases will be
   required.  We should thus also 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, multihomed 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 illustrated 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 if exiting through the
   wrong 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 architecture 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,



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   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.

   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 router and, most likely, host changes.
   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 but avoid host changes.

   As explained previously, while NPTv6 has been proposed for providing
   multi-homing support in networks, its use is not recommended in the
   homenet architecture.

   It should be noted that some multihoming scenarios may see one
   upstream being a "walled garden", and thus only appropriate 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], MPTCP [RFC6824] 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

   The 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



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   routing configuration.  It is highly desirable that the number of
   such configurations is minimised.

3.3.1.  Differentiating neighbouring homenets

   It is important that self-configuration with 'unintended' devices is
   avoided.  There should be a way for a user to administratively assert
   in a simple way whether or not a device belongs to a homenet.  The
   goal is to allow the establishment of borders, particularly between
   two adjacent homenets, and to avoid unauthorised devices from
   participating in the homenet.  Such an authorisation capability may
   need to operate through multiple hops in the homenet.

   The homenet should thus support a way for a homenet owner to claim
   ownership of their devices in a reasonably secure way.  This could be
   achieved by a pairing mechanism, by for example pressing buttons
   simultaneously on an authenticated and a new homenet device, or by an
   enrolment process as part of an autonomic networking environment.

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.  In such subdivisions the logical
   topology may not necessarily match the physical topology.  This text
   does not, however, make recommendations on how such subdivision
   should occur.  It is expected that subsequent documents will address
   this problem.

   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.  Handling varying link technologies

   Homenets tend to grow organically over many years, and a homenet will
   typically be built over link-layer technologies from different



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   generations.  Current homenets typically use links ranging from
   1Mbit/s up to 1Gbit/s, which is a three orders of magnitude
   throughput discrepancy.  We expect this discrepancy to widen further
   as both high-speed and low-power technologies are deployed.

   Homenet protocols should be designed to deal well with
   interconnecting links of very different throughputs.  In particular,
   flows local to a link should not be flooded throughout the homenet,
   even when sent over multicast, and, whenever possible, the homenet
   protocols should be able to choose the faster links and avoid the
   slower ones.

   Links (particularly wireless links) may also have limited numbers of
   transmit opportunities (txops), and there is a clear trend driven by
   both power and downward compatibility constraints toward aggregation
   of packets into these limited txops while increasing throughput.
   Transmit opportunities may be a system's scarcest resource and
   therefore also strongly limit actual throughput available.

   Therefore protocols that avoid being 'chatty', do not require
   flooding, and enable isolation of traffic between subnets are
   preferable to those which burn scarce resources.

3.3.4.  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
   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



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   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.

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.

3.4.1.  Use of ISP-delegated IPv6 prefixes

   Discussion of IPv6 prefix allocation policies is included in
   [RFC6177].  In practice, 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; it is generally
   expected that ISPs will offer relatively stable prefixes to their
   residential customers.  Regardless, the home network needs to be
   adaptable as far as possible 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, for example, only a /64 is offered by the ISP, the
   homenet may be severely constrained or even unable to function.
   [RFC6177] (BCP 157) states that "a key principle for address
   management is that end sites always be able to obtain a reasonable



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   amount of address space for their actual and planned usage, and over
   time ranges specified in years rather than just months.  In practice,
   that means at least one /64, and in most cases significantly more.
   One particular situation that must be avoided is having an end site
   feel compelled to use IPv6-to-IPv6 Network Address Translation or
   other burdensome address conservation techniques because it could not
   get sufficient address space."  This architecture text assumes that
   this guidance is being followed by ISPs.

   There are many problems that would arise from a homenet not being
   offered a sufficient prefix size for its needs.  Rather than attempt
   to contrive a method for a homenet to operate in a constrained manner
   when faced with insufficient prefixes, such as the use of subnet
   prefixes longer than /64 (which would break SLAAC), use of NPTv6, or
   falling back to bridging across potentially very different media, it
   is recommended that the receiving router instead enters an error
   state and issues appropriate warnings.  Some consideration may need
   to be given to how such a warning or error state should best be
   presented to a typical home user.

   Thus a homenet CER should request, for example 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, even if 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 it is highly preferable that the ISP offers at least a
   /56.  It is expected that the allocated prefix to the homenet from
   any single ISP is a contiguous, aggregated one.  While it may be
   possible for a homenet CER to issue multiple prefix requests to
   attempt to obtain multiple delegations, such behaviour is out of
   scope of this document.

   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
   generally support Provider Independent (PI) addressing for
   residential homenets.

   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



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   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.  Similarly, if an ISP has a planned renumbering
   process, it may be able to adjust lease timers, etc appropriately.

   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.  The homenet may also be forced to renumber itself if
   significant internal 'replumbing' is undertaken by the user.
   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 stable
   routing and connectivity between subnets and hosts regardless of
   whether a globally unique ISP-provided prefix is available.  In the
   case of a prolonged external connectivity outage, ULAs allow internal
   operations across routed subnets to continue.  ULA addresses also
   allow constrained LLN devices to create permanent relationships
   between IPv6 addresses, e.g. from a wall controller to a lamp, where
   symbolic host names would require additional non-volatile memory and
   updating global prefixes in sleeping LLN devices might also be
   problematic.

   As discussed previously, it would be expected that ULAs would



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

   In cases where ULA prefixes are in use within a homenet but there is
   no external IPv6 connectivity (and thus no GUAs in use),
   recommendations ULA-5, L-3 and L-4 in RFC 6204 should be followed to
   ensure correct operation, in particular where the homenet may be
   dual-stack with IPv4 external connectivity.  The use of the Route
   Information Option described in [RFC4191] provides a mechanism to
   advertise such more-specific ULA routes.

   The use of ULAs should be restricted to the homenet scope through
   filtering at the border(s) of the homenet, as mandated by RFC 6024
   requirement S-2.

   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.  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 should be
   provisioned for stable internal communications or for use on
   constrained/LLN networks.

   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



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   gracefully as possible in the event of prefix exhaustion (though the
   options in such cases may be limited).

   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 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 result in each link being
   assigned a stable prefix that is persistent across reboots, power
   outages and similar short-term outages.  The availability of
   persistent prefixes should not depend on the router boot order.  The
   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.  However, delegated ULA
   prefixes within the homenet should remain persistent through an ISP-
   driven renumbering event.

   Provisioning 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).

   There are multiple potential solutions for prefix delegation within a
   homenet.  One solution could be based on DHCPv6 PD, as described in
   [RFC3315] and [RFC3633].  An alternative solution could be to convey
   prefixes within the chosen homenet routing protocol.  This document
   makes no specific recommendation, but notes that it is very likely
   that all routing devices participating in a homenet must use the same
   internal prefix delegation method.  This implies that only one
   delegation method should be in use.

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.  If
   ISPs offer relatively stable IPv6 prefixes to customers, the network
   prefix part of addresses associated with the homenet may not change
   over a reasonably long period of time.  This exposure is similar to
   IPv4 networks using 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.  Regardless of the solution method, the functionality
   discussed below should be met.

   The homenet unicast routing protocol should be a previously deployed
   protocol that has been shown to be reliable, robust, to allow
   lightweight implementations, and of which open source implementations
   are available.  It is desirable, but not absolutely required, that
   the routing protocol be able to give a complete view of the network,
   and that it be able to 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.

   The routing protocol should support the generic use of multiple
   customer Internet connections, and the concurrent use of multiple
   delegated prefixes.  A routing protocol that can make routing
   decisions based on source and destination addresses is thus
   desirable, to avoid upstream ISP BCP38 ingress filtering problems.
   Multihoming support should also 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



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   homenet.

   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.ietf-ospf-ospfv3-autoconfig].
   Minimising convergence time should be a goal in any routed
   environment, but as a guideline a maximum convergence time at most 30
   seconds should be the target.

   As per prefix delegation, it is assumed that a single routing
   solution is in use in the homenet architecture.  If there is an
   identified need to support multiple solutions, these must be
   interoperable.

   An appropriate mechanism is required to discover which router(s) in
   the homenet are providing the CER function.  Borders may include but
   are not limited to the interface to the upstream ISP, a gateway
   device to a separate home network such as a LLN network, or a gateway
   to a guest or private corporate extension 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 internal 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 homenet-wide service discovery should a site-
   scope multicast service discovery protocol be defined, 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



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   cannot reasonably support it.

   Multicast may also be received by or sourced from the homenet from/to
   external networks, e.g. where video applications use multicast to
   conserve the bandwidth they consume.  Such multicast traffic would be
   greater than site scope.

   The multicast environment should support the ability for applications
   to pick a unique multicast group to use.

3.5.2.  Mobility support

   Devices may be mobile within the homenet.  While resident on the same
   subnet, their address will remain persistent, but should devices move
   to a different (wireless) subnet, they will acquire a new address in
   that subnet.  It is desirable that the homenet supports internal
   device mobility.  To do so, the homenet may either extend the reach
   of specific wireless subnets to enable wireless roaming across the
   home (availability of a specific subnet across the home), or it may
   support mobility protocols to facilitate such roaming where multiple
   subnets are used.

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
   various 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.

   [RFC4864] describes a 'Simple Security' model for IPv6 networks,
   whereby stateful perimeter filtering can be applied to control the
   reachability of devices in a homenet.  RFC 4864 states in Section 4.2
   that "the use of firewalls ... is recommended for those that want



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   boundary protection in addition to host defences".  It should be
   noted that a 'default deny' filtering 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, e.g. a
   protocol such as UPnP or PCP [I-D.ietf-pcp-base].  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.

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.  Partial Effectiveness of NAT and Firewalls

   Security by way of obscurity (address translation) or through
   firewalls (filtering) is at best only partially effective.  The very
   poor security track record of home computer, home networking and



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   business PC computers and networking is testimony to this.  A
   security 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 current evidence of home network products with very
   poor default device security, putting a firewall in place does
   provide some level of protection.  The use of firewalls today,
   whether a good practice or not, is common practice and whatever
   protection afforded, even if marginally effective, should not be
   lost.  Thus, while it is highly desirable that all hosts in a homenet
   be adequately protected by built-in security functions, it should
   also be assumed that all CERs will continue to support appropriate
   perimeter defence functions, as per [I-D.ietf-v6ops-6204bis].

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 able to be initiated to them through security filters in the
   homenet, either for all ports or for specific services.  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

   As noted in Section 3.6, if appropriate filtering is in place on the
   CER(s), as mandated by RFC 6024 requirement S-2, a ULA source address
   may be taken as an indication of locally sourced traffic.  This
   indication 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

   The homenet requires devices to be able to determine and use unique
   names by which they can be accessed on the network.  Users and
   devices will need to be able to discover devices and services
   available on the network, e.g. media servers, printers, displays or
   specific home automation devices.  Thus naming and service discovery
   must be supported in the homenet, and, given the nature of typical
   home network users, 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,



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   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.  Remote access may be desired by
   the homenet residents while travelling, but also potentially by
   manufacturers or other 'benevolent' third parties.

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.  Devices may also need to discover other devices,
   without any user intervention or choice.  Either 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 zero-configuration 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.  It may mean that some proxy or hybrid service is utilised,
   perhaps co-resident on the CER.  Or it may be that a new approach is
   preferable, e.g. flooding information around the homenet as
   attributes within the routing protocol (which could allow per-prefix
   configuration).  However, we should prefer approaches that are
   backwardly compatible, and allow current implementations to continue
   to be used.  Note that this document does not mandate a particular
   solution, rather it expresses the principles that should be used for
   a homenet naming and service discovery environment.

   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



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   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.  It is expected that
   a device should have a fixed name while within the scope of the
   homenet.

   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

   If access to homenet devices is required remotely from anywhere on
   the Internet, then at least one globally unique name space is
   required, though the use of multiple name spaces should not be
   precluded.  The name space(s) should be served authoritatively by the
   homenet, most likely by a server resident on the CER.  Such name
   spaces may be acquired by the user or provided/generated by their ISP
   or an alternative cloud-based service.  It is likely 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.  For users wanting to use their own
   independent domain names, such services are already available.

   Devices may also be assigned different names in different name
   spaces, e.g. by third parties who may manage systems or devices in
   the homenet on behalf of the resident(s).  Remote management of the
   homenet is out of scope of this document.

   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



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   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 name by an application in one homenet to be
   confused with a device with the same name in another homenet.  In
   practice however 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.

   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 would 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.

   In the (likely) event that the homenet is accessible from outside the
   homenet (using the global name space), it is vital that the homenet
   name space follow the rules and conventions of the global name space.
   In this mode of operation, names in the homenet (including those
   automatically generated by devices) must be usable as labels in the
   global name space.  [RFC5890] describes considerations for
   Internationalizing Domain Names in Applications (IDNA).

   Also, with the introduction of new 'dotless' top level domains, there
   is 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 either different name spaces may be
   desired for different realms in the homenet, or for segmentation of a
   single name space within the homenet.  Thus hierarchical name space
   management is likely to be required.  There should also be nothing to
   prevent individual device(s) being independently registered in
   external name spaces.

   Where a user is 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 multiple associated name spaces exist.



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   This also 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
   [RFC6762].

   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.  One approach when
   provisioning such a name service, which is designed to facilitate
   name resolution from the global Internet, is to run an authoritative
   name service on the CER and a secondary resolving name service
   provided by the ISP or perhaps a cloud-based third party.

   Where zeroconf name services are used, it is desirable that these can
   also coexist with the Internet name service.  In particular, where
   the homenet is using a global name space, it is desirable that
   devices have the ability, where desired, to add entries to that name
   space.  There should also be a mechanism for such entries to be
   removed or expired from the global name space.

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

   Finally, the impact of a change in CER must be considered.  It would
   be desirable to retain any relevant state (configuration) that was



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   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 cloud-based 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.

   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 or any devices where
   battery power is used, 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 devices or 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
   and constrained devices that 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.



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3.7.8.  Devices roaming from the homenet

   It is likely that some devices which have registered names within the
   homenet Internet name space and that are mobile will attach to the
   Internet at other locations and acquire an IP address at those
   locations.  In such cases it is desirable that devices may be
   accessed by the same name as is used in the home network.

   Solutions to this problem are not discussed in this document.  They
   may include use of Mobile IPv6 or Dynamic DNS, either of which would
   put additional requirements on to the homenet, or establishment of a
   (VPN) tunnel to a server in the home network.

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
   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.



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   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 solutions can be found
   based on existing protocols.  Some relatively smaller updates are
   likely to be required, e.g. a new mechanism may be needed in order to
   turn a selected protocol on by default, a mechanism may be required
   to automatically assign prefixes to links within the homenet.

   Some functionality, if required by the architecture, may need more
   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
   zeroconf link-local 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.



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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.

   [RFC5890]  Klensin, J., "Internationalized Domain Names for
              Applications (IDNA): Definitions and Document Framework",
              RFC 5890, August 2010.

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.



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   [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.

   [RFC4191]  Draves, R. and D. Thaler, "Default Router Preferences and
              More-Specific Routes", RFC 4191, November 2005.

   [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.

   [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.




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   [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.

   [RFC6762]  Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
              February 2013.

   [RFC6824]  Ford, A., Raiciu, C., Handley, M., and O. Bonaventure,
              "TCP Extensions for Multipath Operation with Multiple
              Addresses", RFC 6824, January 2013.

   [I-D.ietf-v6ops-ipv6-multihoming-without-ipv6nat]
              Troan, O., Miles, D., Matsushima, S., Okimoto, T., and D.
              Wing, "IPv6 Multihoming without Network Address
              Translation",
              draft-ietf-v6ops-ipv6-multihoming-without-ipv6nat-05 (work
              in progress), March 2013.

   [I-D.ietf-ospf-ospfv3-autoconfig]
              Lindem, A. and J. Arkko, "OSPFv3 Auto-Configuration",
              draft-ietf-ospf-ospfv3-autoconfig-02 (work in progress),
              April 2013.

   [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.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>.



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   [IGD-2]    UPnP Gateway Committee, "Internet Gateway Device (IGD) V
              2.0", September 2010, <http://upnp.org/specs/gw/
              UPnP-gw-WANIPConnection-v2-Service.pdf>.


Appendix A.  Acknowledgments

   The authors would like to thank Aamer Akhter, Mikael Abrahamsson,
   Mark Andrews, Dmitry Anipko, Ran Atkinson, Fred Baker, Ray Bellis,
   Teco Boot, John Brzozowski, Cameron Byrne, Brian Carpenter, Stuart
   Cheshire, Julius Chroboczek, 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, Markus Stenberg, Sander Steffann, Don Sturek, Andrew Sullivan,
   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.  It does not imply that each
   controbutor agrees with every point in the document.


Appendix B.  Changes

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

B.1.  Version 09 (after WGLC)

   Changes made include:

   o  Added note about multicast into or out of site

   o  Removed further personal draft references, replaced with covering
      text

   o  Routing functionality text updated to avoid ambiguity

   o  Added note that devices away from homenet may tunnel home (via
      VPN)

   o  Added note that homenets more exposed to provider renumbering than
      with IPv4 and NAT

   o  Added note about devices that may be ULA-only until configured to
      be globally addressable



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   o  Removed paragraph about broken CERs that do not work with prefixes
      other than /64

   o  Noted no recommendation on methods to convey prefix information is
      made in this text

   o  Stated that this text does not recommend how to form largest
      possible subnets

   o  Added text about homenet evolution and handling disparate media
      types

   o  Rephrased NAT/firewall text on marginal effectiveness

   o  Emphasised that multihoming may be to any number of ISPs

B.2.  Version 08

   Changes made include:

   o  Various clarifications made in response to list comments

   o  Added note on ULAs with IPv4, where no GUAs in use

   o  Added note on naming and internationalisation (IDNA)

   o  Added note on trust relationships when adding devices

   o  Added note for MPTCP

   o  Added various naming and SD notes

   o  Added various notes on delegated ISP prefixes

B.3.  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.




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   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.

   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.4.  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.5.  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.




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

   o  Added text about multicast routing.

B.6.  Version 04

   Changes made include:

   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.7.  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.





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   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.

   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.8.  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.




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   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.

   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








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

   Email: ot@cisco.com


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

   Email: jason.weil@twcable.com



































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