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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 17, 2013                                       Ericsson
                                                               A. Brandt
                                                           Sigma Designs
                                                                O. Troan
                                                     Cisco Systems, Inc.
                                                                 J. Weil
                                                       Time Warner Cable
                                                           July 16, 2012


                 Home Networking Architecture for IPv6
                       draft-ietf-homenet-arch-04

Abstract

   This text describes evolving networking technology within
   increasingly large residential home networks.  The goal of this
   document is to define an architecture for IPv6-based home networking,
   while describing the associated principles, considerations and
   requirements.  The text briefly highlights the 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 17, 2013.



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Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  Terminology and Abbreviations  . . . . . . . . . . . . . .  5
   2.  Effects of IPv6 on Home Networking . . . . . . . . . . . . . .  6
     2.1.  Multiple subnets and routers . . . . . . . . . . . . . . .  6
     2.2.  Global addressability and elimination of NAT . . . . . . .  7
     2.3.  Multi-Addressing of devices  . . . . . . . . . . . . . . .  7
     2.4.  Unique Local Addresses (ULAs)  . . . . . . . . . . . . . .  8
     2.5.  Naming, and manual configuration of IP addresses . . . . .  9
     2.6.  IPv6-only operation  . . . . . . . . . . . . . . . . . . .  9
   3.  Homenet Architecture . . . . . . . . . . . . . . . . . . . . . 10
     3.1.  General Principles . . . . . . . . . . . . . . . . . . . . 10
       3.1.1.  Reuse existing protocols . . . . . . . . . . . . . . . 11
       3.1.2.  Minimise changes to hosts and routers  . . . . . . . . 11
     3.2.  Homenet Topology . . . . . . . . . . . . . . . . . . . . . 11
       3.2.1.  Supporting arbitrary topologies  . . . . . . . . . . . 11
       3.2.2.  Network topology models  . . . . . . . . . . . . . . . 11
       3.2.3.  Dual-stack topologies  . . . . . . . . . . . . . . . . 16
       3.2.4.  Multihoming  . . . . . . . . . . . . . . . . . . . . . 17
     3.3.  A Self-Organising Network  . . . . . . . . . . . . . . . . 18
       3.3.1.  Homenet realms and borders . . . . . . . . . . . . . . 19
       3.3.2.  Largest possible subnets . . . . . . . . . . . . . . . 19
       3.3.3.  Handling multiple homenets . . . . . . . . . . . . . . 20
       3.3.4.  Coordination of configuration information  . . . . . . 20
     3.4.  Homenet Addressing . . . . . . . . . . . . . . . . . . . . 20
       3.4.1.  Use of ISP-delegated IPv6 prefixes . . . . . . . . . . 20
       3.4.2.  Stable internal IP addresses . . . . . . . . . . . . . 22
       3.4.3.  Internal prefix delegation . . . . . . . . . . . . . . 22
       3.4.4.  Privacy  . . . . . . . . . . . . . . . . . . . . . . . 24
     3.5.  Routing functionality  . . . . . . . . . . . . . . . . . . 24
     3.6.  Security . . . . . . . . . . . . . . . . . . . . . . . . . 25



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       3.6.1.  Addressability vs reachability . . . . . . . . . . . . 26
       3.6.2.  Filtering at borders . . . . . . . . . . . . . . . . . 27
       3.6.3.  Device capabilities  . . . . . . . . . . . . . . . . . 27
       3.6.4.  ULAs as a hint of connection origin  . . . . . . . . . 27
     3.7.  Naming and Service Discovery . . . . . . . . . . . . . . . 27
     3.8.  Other Considerations . . . . . . . . . . . . . . . . . . . 30
       3.8.1.  Proxy or Extend? . . . . . . . . . . . . . . . . . . . 30
       3.8.2.  Quality of Service . . . . . . . . . . . . . . . . . . 30
       3.8.3.  Operations and Management  . . . . . . . . . . . . . . 31
     3.9.  Implementing the Architecture on IPv6  . . . . . . . . . . 31
   4.  Conclusions  . . . . . . . . . . . . . . . . . . . . . . . . . 32
   5.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 32
     5.1.  Normative References . . . . . . . . . . . . . . . . . . . 32
     5.2.  Informative References . . . . . . . . . . . . . . . . . . 33
   Appendix A.  Acknowledgments . . . . . . . . . . . . . . . . . . . 36
   Appendix B.  Changes . . . . . . . . . . . . . . . . . . . . . . . 36
     B.1.  Version 04 . . . . . . . . . . . . . . . . . . . . . . . . 36
     B.2.  Version 03 . . . . . . . . . . . . . . . . . . . . . . . . 36
     B.3.  Version 02 . . . . . . . . . . . . . . . . . . . . . . . . 38
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 38































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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 in 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 operate based on IPv4, employ solutions that we would
   like to avoid such as (cascaded) network address translation (NAT),
   or require expert assistance to set up.  In IPv6 home networks, there
   are likely to be scenarios where internal routing is required, for
   example to support private and guest networks, in which case such
   networks may use increasing numbers of subnets, and require methods
   for IPv6 prefixes to be delegated to those subnets.  The assumption
   of this document is that the homenet is as far as possible self-
   organising and self-configuring, and is thus not pro-actively managed
   by the residential user.

   The architectural constructs in this document are focused on the
   problems to be solved when introducing IPv6 with an eye towards a
   better result than what we have today with IPv4, as well as a better
   result than if the IETF had not given this specific guidance.  The
   document aims to provide the basis and guiding principles for how
   standard IPv6 mechanisms and addressing [RFC2460] [RFC4291] can be
   employed in home networking, while coexisting with existing IPv4
   mechanisms.  In emerging dual-stack home networks it is vital that
   introducing IPv6 does not adversely affect IPv4 operation.  We assume
   that the IPv4 network architecture in home networks is what it is,
   and can not be affected by new recommendations.  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 architecture document proposes a baseline homenet architecture,
   based on protocols and implementations that are as far as possible
   proven and robust.  The scope of the document is primarily the
   network layer technologies that provide the basic functionality to
   enable addressing, connectivity, routing, naming and service
   discovery.  While it may, for example, state that homenet components
   must be simple to deploy and use, it does not discuss specific user
   interfaces, nor does it discuss specific physical, wireless or data-
   link layer considerations.



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

1.1.  Terminology and Abbreviations

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

   o  "Advanced Security".  Describes advanced security functions for a
      CER, as defined in [I-D.vyncke-advanced-ipv6-security], where the
      default inbound connection policy is generally "default allow".

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

   o  LLN: Low-power and lossy network.

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

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

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

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

   o  ULA: IPv6 Unique Local Addresses [RFC4193].

   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.








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2.  Effects of IPv6 on Home Networking

   Service providers are deploying IPv6, content is becoming available
   on IPv6 (accelerated recently by the World IPv6 Launch event) and
   support for IPv6 is increasingly available in devices and software
   used in the home.  While IPv6 resembles IPv4 in many ways, it changes
   address allocation principles, making multi-addressing the norm, and
   allowing direct IP addressability of home networking devices from the
   Internet.  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

   The introduction of IPv6 for home networking enables the potential
   for every home network to be delegated enough address space to
   provision globally unique prefixes for each subnet in the home.  Such
   subnetting is not common practice in existing IPv4 homenets, but is
   very likely to become increasingly standard in future IPv6 homenets.

   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.

   Documents that provide some more specific background and depth on
   this topic include: [I-D.herbst-v6ops-cpeenhancements],
   [I-D.baker-fun-multi-router], and [I-D.baker-fun-routing-class].

   The addition of routing between subnets raises the issue of how to
   extend mechanisms such as service discovery which currently rely on
   link-local addressing to limit scope.  There are two broad choices;
   extend existing protocols to work across the scope of the homenet, or
   introduce proxies for existing link-layer protocols.  This topic is
   discussed later in the document.

   There will also be the need to discover which routers in the homenet



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   are the border router(s) by an appropriate mechanism.  Here, there
   are a number of choices.  These include an appropriate service
   discovery protocol, or the use of a well-known name, resolved by some
   local name service.  Both might have to deal with handling more than
   one router responding in multihomed environments.

2.2.  Global addressability and elimination of NAT

   Current IPv4 home networks typically receive a single global IPv4
   address from their ISP and use NAT with private [RFC1918] addresses
   for devices within the network.  An IPv6 home network removes the
   need to use NAT given the ISP offers a sufficiently large globally
   unique IPv6 prefix to the homenet, allowing every device on every
   link to be assigned a globally unique IPv6 address.

   The end-to-end communication that is potentially enabled with IPv6 is
   on the one hand an incredible opportunity for innovation and simpler
   network operation, but it is also a concern as it exposes nodes in
   the internal networks to receipt of otherwise unwanted traffic from
   the Internet.  There may thus be an expectation of improved host
   security to compensate for this, at least in general networked
   devices, but it must be noted that many devices may also (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.

   IPv6 networks may or may not have filters applied at their borders,
   i.e. at the homenet CER.  [RFC4864], [RFC6092] and
   [I-D.vyncke-advanced-ipv6-security] discuss such filtering, and the
   merits of "default allow" against "default deny" policies for
   external traffic initiated into a homenet.  It is important to
   distinguish between addressability and reachability.  While IPv6
   offers global addressability through use of globally unique addresses
   in the home, whether they are globally reachable or not would depend
   on the firewall or filtering configuration, and not, as is commonly
   the case with IPv4, the presence or use of NAT.

2.3.  Multi-Addressing of devices

   In an IPv6 network, devices may acquire multiple addresses, typically
   at least a link-local address and a globally unique address.  They
   may also have an IPv4 address if the network is dual-stack, a Unique
   Local Address (ULA) [RFC4193] (see below), and one or more IPv6
   Privacy Addresses [RFC4941].




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   Thus it should be considered the norm for devices on IPv6 home
   networks to be multi-addressed, and to need to make appropriate
   address selection decisions for the candidate source and destination
   address pairs.  Default Address Selection for IPv6
   [I-D.ietf-6man-rfc3484bis] provides a solution for this, though it
   may face problems in the event of multihoming, where nodes will be
   configured with one address from each upstream ISP prefix.  In such
   cases the presence of upstream ingress filtering requires multi-
   addressed nodes to select the correct source address to be used for
   the corresponding uplink, to avoid ISP BCP 38 ingress filtering, but
   the node may not have the information it needs to make that decision
   based on addresses alone.  We discuss such challenges in the
   multihoming section later in this document.

2.4.  Unique Local Addresses (ULAs)

   [RFC4193] defines Unique Local Addresses (ULAs) for IPv6 that may be
   used to address devices within the scope of a single site.  Support
   for ULAs for IPv6 CERs is described in [RFC6204].  A home network
   running IPv6 may deploy ULAs for stable communication between devices
   (on different subnets) within the network where the externally
   allocated global prefix changes over time (e.g. due to renumbering
   within the subscriber's ISP) or where external connectivity is
   temporarily unavailable.

   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.  It should also be noted that there may be timers on
   the prefix lease to the homenet, on the internal prefix delegations,
   and on the Router Advertisements to the hosts.  Despite this counter-
   argument, while setting a network up there may be a period with no
   connectivity, in which case ULAs would be required for inter-subnet
   communication.  In the case where LLNs are being set up in a new
   home/deployment, individual LLNs may, at least initially, each use
   their own /48 ULA prefix.

   Default address selection mechanisms should ensure a ULA source
   address is used to communicate with ULA destination addresses when
   appropriate, in particular when the ULA destination lies within a /48
   ULA prefix known to be used within the same homenet.  Note that
   unlike the IPv4 private RFC 1918 space, the use of ULAs does not
   imply use of host-based IPv6 NAT, or NPTv6 prefix-based NAT
   [RFC6296], rather that external communications should use a node's
   additional globally unique IPv6 source address.




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2.5.  Naming, and 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.  Users should not be expected to enter IPv6 literal
   addresses in homenet devices or applications, given their much
   greater length and apparent randomness to a typical home user.  While
   shorter addresses, perhaps ones registered with IANA from ULA-C space
   [I-D.hain-ipv6-ulac], could be used for specific devices/services, in
   general it is better to not expose users to real IPv6 addresses.
   Thus, even for the simplest of functions, simple naming and the
   associated (ideally zero configuration) discovery of services is
   imperative for the easy deployment and use of homenet devices and
   applications.

   In a multi-subnet homenet, naming and service discovery should be
   expected to be capable of operating across the scope of the entire
   home network, and thus be able to cross subnet boundaries.  It should
   be noted that in IPv4, such services do not generally function across
   home router NAT boundaries, so this is one area where there is room
   for improvement in IPv6.

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 incorporating NAT64 [RFC6144] and
      DNS64 [RFC6145] functionality in the home gateway router, for
      instance.  Such features are outside the scope of this document
      however, being CER functions.

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




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

   The widespread availability of robust solutions to these types of
   requirements will help accelerate the uptake of IPv6-only homenets.


3.  Homenet Architecture

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

   Existing IETF work [RFC6204] defines the "basic" requirements for
   Customer Edge Routers, while [I-D.ietf-v6ops-6204bis] extends RFC
   6204 to describe additional features.  The homenet architecture is
   focused on the internal homenet, rather than the CER(s).  In general,
   home network equipment needs to be able to operate in networks with a
   range of different properties and topologies, where home users may
   plug components together in arbitrary ways and expect the resulting
   network to operate.  Significant manual configuration is rarely, if
   at all, possible, given the knowledge level of typical home users.
   Thus the network should, as far as possible, be self-configuring.

   The equipment also needs to be prepared to handle at least

   o  Routing

   o  Prefix configuration for routers

   o  Name resolution

   o  Service discovery

   o  Network security

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

3.1.  General Principles

   There is little that the Internet standards community can do about
   the physical topologies or the need for some networks to be separated
   at the network layer for policy or link layer compatibility reasons.



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   However, there is a lot of flexibility in using IP addressing and
   inter-networking mechanisms.  This architecture text discusses how
   this flexibility should be used to provide the best user experience
   and ensure that the network can evolve with new applications in the
   future.  The principles described in this text should be followed
   when designing homenet solutions.

3.1.1.  Reuse existing protocols

   It is desirable to reuse existing protocols where possible, but at
   the same time to avoid consciously precluding the introduction of new
   or emerging protocols.  A generally conservative approach, giving
   weight to running code, is preferable.  Where new protocols are
   required, evidence of commitment to implementation by appropriate
   vendors or development communities is highly desirable.  Protocols
   used should be backwardly compatible, and forward compatible where
   changes are made.

3.1.2.  Minimise changes to hosts and routers

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

3.2.  Homenet Topology

   In this section we consider homenet topologies, and the principles we
   may apply in designing an architecture to support as wide a range as
   possible of such topologies.

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.

3.2.2.  Network topology models

   Most IPv4 home network models at the time of writing tend to be
   relatively simple, typically a single NAT router to the ISP and a
   single internal subnet but, as discussed earlier, evolution in
   network architectures is driving more complex topologies, such as the
   separation of visitor and private networks.



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

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

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

   o  Presence of isolated internal subnets.  There may be isolated
      internal subnets, with no direct connectivity between them within
      the homenet.  Isolation may be physical, or implemented via IEEE
      802.1q VLANs.

   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 be more prevalent with
   IPv6 home networks, as discussed further below.  Thus the following
   properties should also be considered for such networks:

   o  Number of upstream providers.  A typical homenet might just have a
      single upstream ISP, but it may become more common 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
      be walled gardens.

   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.

   A separate discussion of physical infrastructures for homenets is
   included in and [I-D.arkko-homenet-physical-standard].

   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 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 (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 | |  |
   |          | |          | |  |          | |          | |  |
   +----------+ +----------+ |  +----------+ +----------+ |  |
                             |        |             |     |  |
                             |     ---+------+------+-----+  |
                             |               | Network B/E   |
                      +------+--------+      |               | End-User
                      |     IPv6      |      |               | networks
                      |   Interior    +------+               |
                      |    Router     |                      |
                      +---+-------+-+-+                      |
          Network C       |       |   Network D              |
    ----+-------------+---+-    --+---+-------------+---     |
        |             |               |             |        |
   +----+-----+ +-----+----+     +----+-----+ +-----+----+   |
   |IPv6 Host | |IPv6 Host |     | IPv6 Host| |IPv6 Host |   |
   |          | |          |     |          | |          |   /
   +----------+ +----------+     +----------+ +----------+  /

                                 Figure 1













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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 |  /
   |          | |          |     |          | |          | /
   +----------+ +----------+     +----------+ +----------+

                                 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 |  /
   |          | |          |     |          | |          | /
   +----------+ +----------+     +----------+ +----------+

                                 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 there
   should be bridging if the link layer allows this.

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

3.2.4.  Multihoming

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

   The general multihoming problem is broad, and solutions suggested to
   date within the IETF may include complex architectures for monitoring
   connectivity, traffic engineering, identifier-locator separation,
   connection survivability across multihoming events, and so on.  It is
   thus important that the homenet architecture should as far as
   possible minimise the complexity of any multihoming support.  So we
   should limit the support to the smallest subset of the overall
   problem to meet the requirements of the topologies described above.
   This means that the homenet architecture should not try to make
   another attempt at solving complex multihoming, and we should prefer
   to support scenarios for which solutions exist today.

   In the general homenet architecture, hosts should be multi-addressed
   with globally unique prefixes from each ISP they may communicate with
   or through.  An alternative for a homenet would be to deploy NPTv6
   [RFC6296] at the CER, with ULAs then typically used internally, but
   this mode is not considered by this text.  If NPTv6 is used, the
   internal part of the homenet (which is the scope of this text) simply
   sees only the one (ULA) prefix in use.  It should be noted that
   running NPTv6 has an architectural cost, due to the prefix
   translation used.

   When 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, which would typically
   include [I-D.ietf-6man-rfc3484bis].  Applications may of course do
   different things, and this should not be precluded.

   For the single CER Network Model C, multihoming may be offered by



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   source routing at the CER.  With multiple exit routers, the
   complexity rises.  Given a packet with a source address on the
   network, the packet must be routed to the proper egress to avoid BCP
   38 filtering at an ISP that did not delegate the prefix the address
   is chosen from.  While the packet might not take an optimal path to
   the correct exit CER, the minimum requirement is that the packet is
   not dropped.  It is of course highly desirable that the packet is
   routed in the most efficient manner to the correct exit.

   There are various potential approaches to this problem, one example
   being described in [I-D.v6ops-multihoming-without-ipv6nat].  Another
   is discussed in [I-D.baker-fun-multi-router], which explores support
   for source routing throughout the homenet.  This approach would
   however likely require relatively significant routing changes to
   route the packet to the correct exit given the source address.  Such
   changes should preferably be minimised.

   There are some other multihoming considerations for homenet
   scenarios.  First, it may be the case that multihoming applies due to
   an ISP migration from a transition method to a native deployment,
   e.g. a 6rd [RFC5969] sunset scenario, as discussed in
   [I-D.townsley-troan-ipv6-ce-transitioning].  Second, one upstream may
   be a "walled garden", and thus only appropriate to be used for
   connectivity to the services of that provider; an example may be a
   VPN service that only routes back to the enterprise business network
   of a user in the homenet.  While we should not specifically target
   walled garden multihoming as a principal goal, it should not be
   precluded.

   Host-based methods such as Shim6 [RFC5533] have been defined, but of
   course require support in the hosts.  There are also application-
   oriented approaches such as Happy Eyeballs [RFC6555]; simplified
   versions of this are for example already implemented in some
   commonly-used web browsers.  The homenet architecture should not
   preclude use of such tools should hosts include their support.

3.3.  A Self-Organising Network

   A home network architecture should be naturally self-organising and
   self-configuring under different circumstances relating to the
   connectivity status to the Internet, number of devices, and physical
   topology.  While the homenet should be self-organising, it should be
   possible 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 WPA2 key to apply
   wireless security, or to configure a shared routing secret.  The



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   latter may be relevant when considering how to bootstrap a routing
   configuration.  It is highly desirable that only one such key is
   needed for any set of functions, to increase usability for the
   homenet user.

3.3.1.  Homenet realms and borders

   The homenet will need to be aware of the extent of its own "site",
   which will define the borders for ULAs, site scope multicast, service
   discovery and security policies.  The homenet will have one or more
   borders with external connectivity providers and potentially also
   have borders within the internal network (e.g. for policy-based
   reasons).  It should be possible to automatically perform border
   discovery for the different borders.  Such borders determine for
   example the scope of where prefixes, routing information, network
   traffic, service discovery and naming may be shared.  The default
   internally should be to share everything.

   A simple homenet model may just consider three types of realm and the
   borders between them.  For example if the realms are the homenet, the
   ISP and the visitor network, then the borders will include that from
   the homenet to the ISP, and that from the homenet to a 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.

3.3.2.  Largest possible 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



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   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 possible subnets that
   can be constructed within the constraints of link layer mechanisms,
   bridging, physical connectivity, and policy.

   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 multiple homenets

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

3.3.4.  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.

3.4.  Homenet Addressing

   The IPv6 addressing scheme used within a homenet must conform to the
   IPv6 addressing architecture [RFC4291].  The homenet will need to
   adapt to the prefixes made available to it through the prefix
   delegation method used by its upstream ISP.

3.4.1.  Use of ISP-delegated IPv6 prefixes

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



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   be adaptable to such ISP policies, and thus make no assumptions about
   the stability of the prefix received from an ISP, or the length of
   the prefix that may be offered.  However, if only a /64 is offered by
   the ISP, the homenet may be severely constrained, or even unable to
   function.

   The internal operation of the home network should also not depend on
   the availability of the ISP network at any given time, other than for
   connectivity to services or systems off the home network.  This
   implies the use of ULAs for stable internal communication, as
   described in the next section.

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

   When an ISP needs 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 is an extended version of an
   initial numbering process, the difference between flash renumbering
   and an initial "cold start" is the need to provide service
   continuity.

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

   The customer may of course also choose to move to a new ISP, and thus
   begin using a new prefix.  In such cases the customer should expect a
   discontinuity, and not only may the prefix change, but potentially
   also the prefix length, if the new ISP offers a different default
   size prefix, e.g. a /60 rather than a /56.  Regardless, it's
   desirable that homenet protocols support rapid renumbering and that
   operational processes don't add unnecessary complexity for the
   renumbering process.

   The 6renum WG is studying IPv6 renumbering for enterprise networks.



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   It is not currently targetting homenets, but may produce outputs that
   are relevant.  The introduction of any new homenet protocols should
   not make any form of renumbering any more complex than it already is.

3.4.2.  Stable internal IP addresses

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

   ULAs should be used within the scope of a homenet to support routing
   between subnets regardless of whether a globally unique ISP-provided
   prefix is available.  It would be expected that ULAs would be used
   alongside one or more such global prefixes in a homenet, such that
   hosts become multi-addressed with both globally unique and ULA
   prefixes.  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.

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

   ULAs may be used for all devices, not just those intended to only
   have internal connectivity.  ULAs used in this way provide stable
   internal communications should the ISP-provided prefix (suddenly)
   change, or external connectivity be temporarily lost.  The use of
   ULAs should be restricted to the homenet scope through filtering at
   the border(s) of the homenet, as described in RFC 6092.

3.4.3.  Internal prefix delegation

   As mentioned above, there are various sources of prefixes, e.g. they
   may be globally unique prefixes originating from ISP(s), they may be
   globally unique or ULA prefixes allocated by "master" router(s) in
   the homenet, or they may be ULAs allocated by LLN gateways.  There
   may also be a prefix associated with NAT64, if in use in the homenet.

   From the homenet perspective, a single prefix from each ISP should be
   received on the border CER [RFC3633].  Then each subnet in the
   homenet should receive a prefix from within the ISP-provided
   prefix(es).  The ISP should only see the aggregate from the homenet,
   and not single /64 prefixes allocated within the homenet.

   Delegation should be autonomous, and not assume a flat or



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   hierarchical model.  This text makes no assumption about whether the
   delegation of 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.  A currently
   typical /60 allocation gives 16 /64 subnets.  Duplicate assignment of
   multiple /64s to the same network should be avoided.  The network
   should behave as gracefully as possible in the event of prefix
   exhaustion, though the options in such cases may be limited.

   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.

   Where ULAs are used, most likely but not necessarily in parallel with
   global prefixes, one router should be elected to offer ULA prefixes
   for the homenet.  The router should generate a /48 ULA for the site,
   and then delegate /64's from that ULA prefix to subnets.  In the
   normal state, a single /48 ULA should be used within the homenet.  In
   cases where two /48 ULAs are generated within a homenet, the network
   should still continue to function.

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

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

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



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3.4.4.  Privacy

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

   Hosts inside an IPv6 homenet may get new IPv6 addresses over time
   regardless, e.g. through Privacy Addresses [RFC4941].

3.5.  Routing functionality

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

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

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

   To support multihoming within a homenet, a routing protocol that can
   make routing decisions based on source and destination addresses is
   desirable, to avoid upstream ISP ingress filtering problems.  In



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   general the routing protocol should support multiple ISP uplinks and
   delegated prefixes in concurrent use.

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

   Any routed solution will require a means for determining the
   boundaries of the homenet.  Borders may include but are not limited
   to the interface to the upstream ISP, or a gateway device to a
   separate home network such as a SmartGrid or similar LLN network.  In
   some cases there may be no border such as occurs 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.

   [I-D.howard-homenet-routing-comparison] contains evaluations of
   common routing protocols made against the type of requirements
   described above.

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.  However, there are other challenges introduced, e.g.
   default filtering policies at the borders between other homenet
   realms.

   There is no defined "threat model" as such for the type of IPv6
   homenet described in this text.  Such a document may be very useful.
   It may include a variety of perspectives, from probing for specific
   types of home appliance being present, to potential denial of service
   attacks.  Hosts need to be able to operate securely, end-to-end where
   required, but also be robust against malicious traffic direct towards
   them.  We simply note at this point that software on home devices
   will have an increase in security if it allows its software to be



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   updated regularly.

3.6.1.  Addressability vs reachability

   An IPv6-based home network architecture should embrace and naturally
   offer a transparent end-to-end communications model as described in
   [RFC2775].  Each device should be addressable by a globally unique
   address, and those addresses must not be altered in transit.
   Security perimeters can (via policy) restrict end-to-end
   communications, and thus while a host may be globally addressable it
   may not be globally reachable.

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

   [RFC6092] expands on RFC 4864, giving a more detailed discussion of
   IPv6 perimeter security recommendations, without mandating a "default
   deny" approach.  Indeed, RFC 6092 does not proscribe a particular
   mode of operation, instead stating that CERs must provide an easily
   selected configuration option that permits a "transparent" mode of
   operation, 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, which in turn simply
   states that a CER should provide functionality sufficient to support
   the recommendations in that RFC.

   Advanced Security for IPv6 CPEs [I-D.vyncke-advanced-ipv6-security]
   takes the approach that in order to provide the greatest end-to-end
   transparency as well as security, security policies must be updated
   by a trusted party which can provide intrusion signatures and other
   "active" information on security threats.  This might for example
   allow different malware detection profiles to be configured on a CER.
   Such methods should be able to be automatically updating.





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3.6.2.  Filtering at borders

   It is desirable that there are mechanisms to detect different types
   of borders within the homenet, as discussed previously, and then the
   means to 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 visitor in a "guest" network
   access to media services in the home, or access to a printer in the
   residence.  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
   WPA2-style network key security but may depend on access policies
   enforced by the LLN border router.

3.6.3.  Device capabilities

   In terms of the devices, homenet hosts should implement their own
   security policies in accordance to their computing capabilities.
   They should have the means to request transparent communications to
   be initiated to them, either for all ports or for specific services.
   Users should have simple methods to associate devices to services
   that they wish to operate transparently through (CER) borders.

3.6.4.  ULAs as a hint of connection origin

   It has been suggested that using ULAs would provide an indication to
   applications that received traffic is locally sourced.  This could
   then be used with security settings to designate where a particular
   application is allowed to connect to or receive traffic from.

3.7.  Naming and Service Discovery

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

   The most natural way to think about such naming and service discovery
   is to enable it to work across the entire homenet residence (site),



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   disregarding technical borders such as subnets but potentially
   respecting policy borders such as those between visitor and internal
   network realms.

   Users will want simple ways to name devices, or be provided with
   appropriate ways for devices to generate unique names within the
   homenet.  Users may typically perform device (re)naming and discovery
   through GUI interfaces that hide the local domain name element from
   them.  Users may also wish to associated named devices to Internet
   domains, so that devices in their homenet can be accessed remotely.
   Thus from the user's perspective a device is given a name; the user
   may expect that same unqualified name toy be valid within the local
   name service or through an Internet name service.  Thus implies
   relative name resolution should be supported, i.e. there is some
   naming convention that allows name resolution while mitigating the
   need for the user to know an absolute location in the Internet name
   space.  Or that there is some means to discover the domain
   transparently to the user.

   Homenet devices may thus appear in one or more local homenet name
   spaces and also in one or more Internet name spaces.  While typically
   there would be only one local name space, there may be scenarios
   where segmentation of that name space may be desirable.  The naming
   system will be required to work internally or externally, be the user
   within the homenet or outside it, and there may be multiple naming
   domains used for any given device, e.g.  Internet, home or guest
   domains.  It is likely that a home user will want access to many of
   the devices and services in their home while "roaming" elsewhere.
   However, 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.

   The homenet name service must therefore at the very least co-exist
   with Internet name services.  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.  Consideration should be
   made for how these interact with each other in a homenet scenario.

   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 (as per mDNS and DNS-SD) or a
   service where applications register in order to be found.

   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



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   implies the local network should also be able to perform a complete
   restart in the absence of external connectivity, and have local
   naming and discovery operate correctly.  This might be achieved via a
   local cache and an authoritative local name service.  Also, a change
   in ISP should also not affect local naming and service discovery.

   There should be consideration of the security of any local name
   space.  A typical problem here may be that many homenets may use a
   common "well-known" local domain suffix, e.g. .local, and this may be
   ambiguous to a device that could attach to multiple homenets that use
   that name, but this is also part of the "avoid joining unintended
   networks" problem.  A method to utilise a local trust anchor is
   desirable.

   With the introduction of new "dotless" top level domains, there is
   potential for ambiguity between for example a local host called
   "computer" and (if it is registered) a .computer gTLD.  This suggests
   some implicit local name space is probably required.  Such a name
   space should also be configurable to something else by the user.
   Discovery of a name service for access to external Internet resources
   is also a fundamental requirement in a multi-subnet homenet; the
   problem is not just name and service discovery within the homenet
   itself.

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

   A desirable target may be a fully functional, self-configuring secure
   local name service so that all devices can be referred to by name,
   and these FQDNs are resolved locally.  This could make clean use of
   ULAs and multiple ISP-provided prefixes much easier.  Such a local
   name service should be (by default) authoritative for the local name
   space in both IPv4 and IPv6.  A dual-stack residential gateway should
   include a dual-stack DNS server.

   Current service discovery protocols are generally aimed at single
   subnets.  If service discovery is to operate across the an entire
   homenet, by adopting an approach like that proposed as Extended mDNS
   (xmDNS) [I-D.lynn-homenet-site-mdns], then support may be required
   for IPv6 multicast across the scope of the whole homenet.






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3.8.  Other Considerations

   This section discusses some other considerations for home networking
   that may affect the architecture.

3.8.1.  Proxy or Extend?

   There are two broad choices for allowing services that would
   otherwise be link-local to work across a homenet site.  In the
   example of service discovery, one is to take protocols like mDNS and
   have them run over site multicast within the homenet.  This is fine
   if all hosts support the extension, and the scope within any internal
   borders is well-understood.  But it's not backwards-compatible with
   existing link-local protocols.  The alternative is to proxy service
   discovery across each link, to propagate it.  This is more complex,
   but is backwards-compatible.  It would need to work with IPv6, and
   dual-stack.

   The homenet architecture proposes that any existing protocols that
   are designed to only work within a subnet should be extended to work
   across subnets, rather than defining proxy capabilities for each of
   those functions.  However, while it is desirable to extend protocols
   to site scope operation rather than providing proxy functions on
   subnet boundaries, the reality is that until all hosts can use site-
   scope discovery protocols, existing link-local protocols would need
   to be proxied anyway.

   Some protocols already have proxy functions defined and in use, e.g.
   DHCPv6 relays, in which case those protocols would be expected to
   continue to operate that way.

3.8.2.  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 should 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).



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   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].

3.8.3.  Operations and Management

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

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

3.9.  Implementing the Architecture on IPv6

   This architecture text encourages re-use of existing protocols.  Thus
   the necessary mechanisms are largely already part of the IPv6
   protocol set and common implementations.  There are though some
   exceptions.  For automatic routing, it is expected that existing
   routing protocols can be used as is.  However, a new mechanism may be
   needed in order to turn a selected protocol on by default.

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

   Some protocol changes are however required in the architecture, e.g.
   for name resolution and service discovery, extensions to existing
   multicast-based name resolution protocols are needed to enable them
   to work across subnets, within the scope of the home network site.

   Some of the hardest problems in developing solutions for home
   networking IPv6 architectures include discovering the right borders
   where the domain "home" 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.




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4.  Conclusions

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


5.  References

5.1.  Normative References

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

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

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

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

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

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

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

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

   [RFC6092]  Woodyatt, J., "Recommended Simple Security Capabilities in
              Customer Premises Equipment (CPE) for Providing
              Residential IPv6 Internet Service", RFC 6092,
              January 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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   [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-09 (work in progress), May 2012.

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.

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

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

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

   [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.

   [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



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              Assignment to End Sites", BCP 157, RFC 6177, March 2011.

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

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

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

   [I-D.baker-fun-multi-router]
              Baker, F., "Exploring the multi-router SOHO network",
              draft-baker-fun-multi-router-00 (work in progress),
              July 2011.

   [I-D.lynn-homenet-site-mdns]
              Lynn, K. and D. Sturek, "Extended Multicast DNS",
              draft-lynn-homenet-site-mdns-00 (work in progress),
              March 2012.

   [I-D.townsley-troan-ipv6-ce-transitioning]
              Townsley, M. and O. Troan, "Basic Requirements for
              Customer Edge Routers - multihoming and transition",
              draft-townsley-troan-ipv6-ce-transitioning-02 (work in
              progress), December 2011.

   [I-D.baker-fun-routing-class]
              Baker, F., "Routing a Traffic Class",
              draft-baker-fun-routing-class-00 (work in progress),
              July 2011.

   [I-D.howard-homenet-routing-comparison]
              Howard, L., "Evaluation of Proposed Homenet Routing
              Solutions", draft-howard-homenet-routing-comparison-00
              (work in progress), December 2011.

   [I-D.herbst-v6ops-cpeenhancements]
              Herbst, T. and D. Sturek, "CPE Considerations in IPv6
              Deployments", draft-herbst-v6ops-cpeenhancements-00 (work
              in progress), October 2010.

   [I-D.vyncke-advanced-ipv6-security]
              Vyncke, E., Yourtchenko, A., and M. Townsley, "Advanced
              Security for IPv6 CPE",
              draft-vyncke-advanced-ipv6-security-03 (work in progress),
              October 2011.



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   [I-D.ietf-6man-rfc3484bis]
              Thaler, D., Draves, R., Matsumoto, A., and T. Chown,
              "Default Address Selection for Internet Protocol version 6
              (IPv6)", draft-ietf-6man-rfc3484bis-06 (work in progress),
              June 2012.

   [I-D.v6ops-multihoming-without-ipv6nat]
              Troan, O., Miles, D., Matsushima, S., Okimoto, T., and D.
              Wing, "IPv6 Multihoming without Network Address
              Translation", draft-v6ops-multihoming-without-ipv6nat-00
              (work in progress), March 2011.

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

   [I-D.arkko-homenet-prefix-assignment]
              Arkko, J., Lindem, A., and B. Paterson, "Prefix Assignment
              in a Home Network",
              draft-arkko-homenet-prefix-assignment-02 (work in
              progress), July 2012.

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

   [I-D.ietf-pcp-base]
              Wing, D., Cheshire, S., Boucadair, M., Penno, R., and P.
              Selkirk, "Port Control Protocol (PCP)",
              draft-ietf-pcp-base-26 (work in progress), June 2012.

   [I-D.hain-ipv6-ulac]
              Hain, T., Hinden, R., and G. Huston, "Centrally Assigned
              IPv6 Unicast Unique Local Address Prefixes",
              draft-hain-ipv6-ulac-02 (work in progress), July 2010.

   [I-D.chakrabarti-homenet-prefix-alloc]
              Nordmark, E., Chakrabarti, S., Krishnan, S., and W.
              Haddad, "Simple Approach to Prefix Distribution in Basic
              Home Networks", draft-chakrabarti-homenet-prefix-alloc-01
              (work in progress), October 2011.

   [I-D.arkko-homenet-physical-standard]
              Arkko, J. and A. Keranen, "Minimum Requirements for
              Physical Layout of Home Networks",
              draft-arkko-homenet-physical-standard-00 (work in



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              progress), March 2012.

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

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


Appendix A.  Acknowledgments

   The authors would like to thank Aamer Akhter, Mark Andrews, Dmitry
   Anipko, Fred Baker, Ray Bellis, Cameron Byrne, Brian Carpenter,
   Stuart Cheshire, Lorenzo Colitti, Robert Cragie, Ralph Droms, Lars
   Eggert, Jim Gettys, olafur Gudmundsson, Wassim Haddad, Joel M.
   Halpern, David Harrington, Lee Howard, Ray Hunter, Joel Jaeggli,
   Heather Kirksey, Ted Lemon, Kerry Lynn, Erik Nordmark, Michael
   Richardson, Barbara Stark, Sander Steffann, Dave Taht, Dave Thaler,
   Mark Townsley, JP Vasseur, Curtis Villamizar, Dan Wing, Russ White,
   and James Woodyatt for their contributions within homenet WG meetings
   and on the WG mailing list.


Appendix B.  Changes

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

B.1.  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.2.  Version 03

   Changes made include:

   o  Various improvements to the readability.





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

   o  Noted 6204bis has replaced advanced-cpe draft.

   o  Clarified the topology examples are just that.

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

   o  Also changed text about requiring support for walled gardens.

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

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

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

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

   o  Expanded naming and service discovery text.

   o  Added more text about ULAs.

   o  Removed reference to version 1 on chair feedback.

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

   o  Noted multihoming is supported.

   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.




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   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.3.  Version 02

   Changes made include:

   o  Made the IPv6 implications section briefer.

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

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

   o  Stated that NPTv6 not supported.

   o  Added considerations section for operations and management.

   o  Added bullet point principles/requirements to Section 3.4.

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

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

   o  Extended text on naming and service discovery.

   o  Added reference to RFC 2775, RFC 6177.

   o  Added reference to the new xmDNS draft.

   o  Added naming/SD requirements from Ralph Droms.











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Authors' Addresses

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

   Email: tjc@ecs.soton.ac.uk


   Jari Arkko
   Ericsson
   Jorvas  02420
   Finland

   Email: jari.arkko@piuha.net


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

   Email: abr@sdesigns.dk


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

   Email: ot@cisco.com


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

   Email: jason.weil@twcable.com







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