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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: September 13, 2012                                     Ericsson
                                                               A. Brandt
                                                           Sigma Designs
                                                                O. Troan
                                                     Cisco Systems, Inc.
                                                                 J. Weil
                                                       Time Warner Cable
                                                          March 12, 2012


                 Home Networking Architecture for IPv6
                       draft-ietf-homenet-arch-02

Abstract

   This text describes evolving networking technology within small
   residential home networks.  The goal of this memo is to define the
   architecture for IPv6-based home networking and the associated
   principles, considerations and requirements.  The text briefly
   highlights the implications of the introduction of IPv6 for home
   networking, discusses topology scenarios, 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 September 13, 2012.




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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.





































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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  Terminology and Abbreviations  . . . . . . . . . . . . . .  5
   2.  Effects of IPv6 on Home Networking . . . . . . . . . . . . . .  5
     2.1.  Multiple subnets and routers . . . . . . . . . . . . . . .  5
     2.2.  Global addressability and elimination of NAT . . . . . . .  6
     2.3.  Multi-Addressing of devices  . . . . . . . . . . . . . . .  7
     2.4.  Unique Local Addresses (ULAs)  . . . . . . . . . . . . . .  7
     2.5.  Security and borders . . . . . . . . . . . . . . . . . . .  8
     2.6.  Naming, and manual configuration of IP addresses . . . . .  8
   3.  Architecture . . . . . . . . . . . . . . . . . . . . . . . . .  9
     3.1.  Network Models . . . . . . . . . . . . . . . . . . . . . .  9
       3.1.1.  A: Single ISP, Single CER, Internal routers  . . . . . 10
       3.1.2.  B: Two ISPs, Two CERs, Shared subnet . . . . . . . . . 12
       3.1.3.  C: Two ISPs, One CER, Shared subnet  . . . . . . . . . 13
     3.2.  Determining the Requirements . . . . . . . . . . . . . . . 13
     3.3.  Considerations . . . . . . . . . . . . . . . . . . . . . . 14
       3.3.1.  Multihoming  . . . . . . . . . . . . . . . . . . . . . 14
       3.3.2.  Quality of Service . . . . . . . . . . . . . . . . . . 16
       3.3.3.  Operations and Management  . . . . . . . . . . . . . . 16
       3.3.4.  Privacy considerations . . . . . . . . . . . . . . . . 16
     3.4.  Design Principles and Requirements . . . . . . . . . . . . 17
       3.4.1.  Reuse existing protocols . . . . . . . . . . . . . . . 17
       3.4.2.  Dual-stack Operation . . . . . . . . . . . . . . . . . 18
       3.4.3.  Largest Possible Subnets . . . . . . . . . . . . . . . 19
       3.4.4.  Security vs Transparent, End-to-End Communications . . 19
       3.4.5.  IP Connectivity between All Nodes  . . . . . . . . . . 20
       3.4.6.  Routing functionality  . . . . . . . . . . . . . . . . 21
       3.4.7.  Self-Organising  . . . . . . . . . . . . . . . . . . . 23
       3.4.8.  Fewest Topology Assumptions  . . . . . . . . . . . . . 26
       3.4.9.  Naming and Service Discovery . . . . . . . . . . . . . 26
       3.4.10. Proxy or Extend? . . . . . . . . . . . . . . . . . . . 27
       3.4.11. Adapt to ISP constraints . . . . . . . . . . . . . . . 27
     3.5.  Implementing the Architecture on IPv6  . . . . . . . . . . 29
   4.  Conclusions  . . . . . . . . . . . . . . . . . . . . . . . . . 29
   5.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 29
     5.1.  Normative References . . . . . . . . . . . . . . . . . . . 29
     5.2.  Informative References . . . . . . . . . . . . . . . . . . 31
   Appendix A.  Acknowledgments . . . . . . . . . . . . . . . . . . . 34
   Appendix B.  Changes . . . . . . . . . . . . . . . . . . . . . . . 34
     B.1.  Version 02 . . . . . . . . . . . . . . . . . . . . . . . . 34
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 35








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1.  Introduction

   This document focuses on evolving networking technology within small
   residential home networks and the associated challenges.  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.  There are also likely to be scenarios where internal
   routing is required, for example to support private and guest
   networks, in which case home networks will use multiple subnets.

   While some advanced home networks 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.  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.

   This architecture 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.
   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.

   [RFC6204] defines basic requirements for customer edge routers
   (CERs).  The scope of this text is the homenet, and thus the relevant
   part of RFC 6204 is the internal facing interface as well as any
   other components within the home network.  While the network may be
   dual-stack or IPv6-only, the definition of specific transition tools
   on the CER are out of scope of this text, as is any advice regarding
   architecture of the IPv4 part of the network.  We assume that IPv4
   network architecture in home networks is what it is, and can not be
   affected by new recommendations.

   This architecture document proposes a baseline homenet architecture,
   based on protocols and implementations that are as far as possible
   proven and robust, and as such is a "version 1" architecture.  A
   future architecture may incorporate more advanced elements at a later
   date.



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1.1.  Terminology and Abbreviations

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

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

   o  LLN: Low-power and lossy network.

   o  NAT: Network Address Translation.  Typically referring to 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  ULA: Unique Local Addresses [RFC4193].

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

   o  VM: Virtual machine.

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


2.  Effects of IPv6 on Home Networking

   Service providers are deploying IPv6, content is becoming available
   on IPv6, 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, makes multi-
   addressing the norm, and allows direct IP addressability and routing
   to devices in the home from the Internet.  This section presents an
   overview of some of the key implications of the introduction of IPv6
   for home networking, that are 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, a common feature in modern home routers is the ability
   to support both guest and private network subnets.  Also, link layer
   networking technology is poised to become more heterogeneous, as
   networks begin to employ both traditional Ethernet technology and



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   link layers designed for low-power and lossy networks (LLNs) such as
   those used for certain types of sensor devices.  There may also be a
   need to separate building control or corporate extensions from the
   main Internet access network.  Also, different subnets may be
   associated with parts of the homenet that have different routing and
   security policies.

   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 will also be the need to
   discover which are the border router(s) by an appropriate mechanism.

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.

   In IPv4 NAT networks, the NAT provides an implicit firewall function.
   [RFC4864] suggests that IPv6 networks with global addresses utilise
   "Simple Security" in border firewalls to restrict incoming
   connections through a default deny policy.  Applications or hosts
   wanting to accept inbound connections in networks that are compliant
   with the architecture presented in this document would then need to
   signal that desire through 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 both exit
   routers.

   The "Simple Security" default deny approach effectively replaces the
   need for IPv4 NAT traversal by a need to use a signalling protocol to
   request a firewall hole be opened.  [RFC6092] states that while the
   default should be default deny, CERs should also have an option to be
   put into a "transparent" mode of operation which enables a default
   allow model.



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   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 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].

   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, but 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 right source address to be used for the corresponding
   uplink, but the node may not have the information it needs to make
   that decision based on addresses alone.

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 externally allocated
   global prefix changes over time (either due to renumbering within the
   subscriber's ISP or a change of 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 are 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.



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   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.

   ULA addresses will allow constrained LLN devices to create permanent
   relations 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.

   Default address selection mechanisms should ensure a ULA source
   address is used to communicate with ULA destination addresses when
   appropriate.  Unlike the IPv4 RFC1918 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
   globally unique IPv6 source address.

2.5.  Security and borders

   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.  Such methods should be
   able to be automatically updating.

   In addition to establishing the security mechanisms themselves, it is
   important to know where the borders are at which they need to be
   enabled.  Any required policies must be able to be applied by typical
   home users, e.g. to give a visitor in a "guest" network access to
   media services in the home.  Thus simple "association" mechanisms
   will be required.

   It may be useful 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 is useful for
   describing edge operations and interface requirements across multiple
   functional areas including security, routing, service discovery, and
   router discovery.

2.6.  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



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   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, 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 discovery
   of services is imperative for easy use of homenet devices and
   applications.

   In a multi-subnet homenet, naming and service discovery should be
   expected to operate 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 scope for an
   improvement in IPv6.


3.  Architecture

   An architecture outlines how to construct home networks involving
   multiple routers and subnets.  In this section, we present a set of
   typical home network topology models/scenarios, followed by a list of
   topics that may influence the architecture discussions, and a set of
   architectural principles that govern how the various nodes should
   work together.  Finally, some guidelines are given for realising the
   architecture with the IPv6 addressing, prefix delegation, global and
   ULA addresses, source address selection rules and other existing
   components of the IPv6 architecture.  The architecture also drives
   what protocol extensions are necessary, as will be discussed in
   Section 3.5.

3.1.  Network Models

   Most IPv4 home network models 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 architectures, such as separation of visitors and private
   networks.  These considerations apply to IPv6 networks as well.

   In general, the models described in [RFC6204] and
   [I-D.ietf-v6ops-ipv6-cpe-router-bis] should be supported by an IPv6
   home networking architecture.

   The following properties apply to any IPv6 home network:






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   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.

   It has also been suggested that various forms of multihoming are more
   prevalent with IPv6 home networks.  Thus the following properties may
   also apply to 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.  Multiple CERs
      adds additional complexity for multihoming scenarios, and
      protocols like PCP that need to manage connection-oriented state
      mappings.

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

   In the following sections we show some example homenet models.

3.1.1.  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.  This is a
   valid consideration as home users may plug routers together to form
   arbitrary topologies including loops (we discuss support for
   arbitrary topologies in layer sections).




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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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3.1.2.  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 home network 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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3.1.3.  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.

3.2.  Determining the Requirements

   [RFC6204] defines "basic" requirements for IPv6 Customer Edge
   Routers, while [I-D.ietf-v6ops-ipv6-cpe-router-bis] describes
   "advanced" features.  In general, home network equipment needs to
   cope with the different types of network properties and topologies
   discussed above.  Manual configuration is rarely, if at all,
   possible, given the knowledge level of typical home users.  The
   equipment needs to be prepared to handle at least

   o  Routing

   o  Prefix configuration for routers

   o  Name resolution




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   o  Service discovery

   o  Network security

   The remainder of the architecture document is presented as
   considerations and principles that lead to more specific requirements
   for the five general areas listed above.

3.3.  Considerations

   This section lists some considerations for home networking that may
   affect the architecture and associated requirements.

3.3.1.  Multihoming

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

   In an integrated network, specific appliances or applications may use
   their own external connectivity, or the entire network may change its
   connectivity based on the status of the different upstream
   connections.  The complexity of the multihoming solution required
   will depend on the Network Model deployed.  For example, Network
   Model C in the previous section has a single CER and thus could
   perform source routing at the single network exit point.

   The general approach for IPv6 multihoming is for a host to receive
   multiple addresses from multiple providers, and to select the
   appropriate source address to communicate via a given provider.  An
   alternative is to deploy ULAs with a site and then use NPTv6
   [RFC6296], a prefix translation-based mechanism, at the edge.  This
   obviously comes at some architectural cost, which is why approaches
   such as [I-D.v6ops-multihoming-without-ipv6nat] have been suggested.
   There has been much work on multihoming in the IETF, without (yet)
   widespread deployment of proposed solutions.

   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
   [I-D.ietf-v6ops-happy-eyeballs] exist; simplified versions of this
   are implemented in some commonly used web browsers for example.

   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,



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   e.g. a 6rd [RFC5969] sunset scenario.  Second, one upstream may be a
   "walled garden", and thus only appropriate to be used for
   connectivity to the services of that provider.

   If the homenet architecture supports multihoming, additional
   requirements apply.  The general multihoming problem is broad, and
   solutions may include complex architectures for monitoring
   connectivity, traffic engineering, identifier-locator separation,
   connection survivability across multihoming events, and so on.  This
   implies that if there is any support for multihoming defined in the
   homenet architecture it should be limited to a very small subset of
   the overall problem.

   The current set of assumptions and requirements proposed by the
   homenet architecture team is:

   MH1)  The homenet WG should not try to make another attempt at
         solving complex multihoming; we should prefer to support
         scenarios for which solutions exist today.

   MH2)  Single CER Network Model C is in scope, and may be solved by
         source routing at the CER.

   MH3)  The architecture does not support deployment of NPTv6 [RFC6296]
         at the CER.  Hosts should be multi-addressed with globally
         unique prefixes from each ISP they may communicate with or
         through.

   MH4)  Solutions that require host changes should be avoided, but
         solutions which incrementally improve with host changes may be
         acceptable.

   MH5)  Walled garden multihoming is in scope.

   MH6)  Transition method sunsetting is in scope.  The topic of
         multihoming with specific (6rd) transition coexistence is
         discussed in [I-D.townsley-troan-ipv6-ce-transitioning].

   MH7)  "Just" picking the right source address to use to fall foul of
         ingress filtering on upstream ISP connections (as per Network
         Model B) is not a trivial task.  A solution is highly
         desirable, but not required in the baseline homenet
         architecture.

   MH8)  A multihoming model for multiple CERs based on
         [I-D.baker-fun-multi-router] requires source routing throughout
         the homenet and thus relatively significant routing changes to
         "guarantee" routing the packet to the correct exit given the



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         source address.  Thus this approach is currently out of scope
         for homenet.

   Thus the homenet multihoming support is focused on the single CER
   model.

3.3.2.  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.

   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].

3.3.3.  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 detail in
   the 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.  The
   SNMPv3 family of protocols described in [RFC3411] and friends may be
   appropriate (previous versions are not deemed secure and have been
   marked as Historic by the IETF).

3.3.4.  Privacy considerations

   There are no specific privacy concerns discussed in this text.  It
   should be noted 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 would not generally
   change over a reasonable period of time.  This exposure is similar to
   IPv4 networks that expose the same IPv4 global address via use of



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   NAT, where the IPv4 address received from the ISP may change over
   time.

3.4.  Design Principles and Requirements

   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.  In this section we discuss 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 following principles should be followed when designing homenet
   solutions.  Where requirements are associated with those principles,
   they are listed here.  There is no implied priority by the order in
   which the principles themselves are listed.

3.4.1.  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.

   Where possible, changes to hosts should be minimised.  Some changes
   may be unavoidable however, e.g. signalling protocols to punch holes
   in firewalls where "Simple Security" is deployed in a CER.  Changes
   to routers should also be minimised, e.g.
   [I-D.baker-fun-routing-class] suggests introducing a routing protocol
   that may route on both source and destination addresses, which would
   be a significant change compared to current practices.

   Liaisons with other appropriate standards groups and related
   organisations is desirable, e.g. the IEEE and Wi-Fi Alliance.

   RE1)  Reuse existing protocols, giving weight to running code.

   RE2)  Minimise changes to hosts and routers.

   RE3)  Maintain backwards compatibility where possible.






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3.4.2.  Dual-stack Operation

   The homenet architecture targets both IPv6-only and dual-stack
   networks.  While the CER requirements in RFC 6204 are aimed at IPv6-
   only networks, it is likely that dual-stack homenets will be the norm
   for some period of time.  IPv6-only networking may first be deployed
   in home networks in "greenfield" scenarios, or perhaps as one element
   of an otherwise dual-stack network.  The homenet architecture must
   operate in the absence of IPv4, and IPv6 must work in the same
   scenarios as IPv4 today.

   Running IPv6-only may require documentation of additional
   considerations such as:

   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.

   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.

   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.

   In dual-stack networks, solutions for IPv6 should not adversely
   affect IPv4 operation.  It is likely that topologies of IPv4 and IPv6
   networks would be as congruent as possible.

   Note that specific transition tools, particularly those running on
   the border CER to support transition tools being used inside the
   homenet, are out of scope.  Use of tools, such as 6rd, on the border
   CER to support ISP access network transition are to be expected, but
   not within scope of homenet, which focuses on the internal
   networking.

   DS1)  The homenet must support IPv6-only or dual-stack operation; it
         must thus operate in the absence of IPv4 and IPv6 must work in
         the same scenarios as IPv4 today.







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   DS2)  IPv6 solutions should not adversely affect IPv4 operation.

3.4.3.  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.

   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
   network should subdivide itself to the largest possible subnets that
   can be constructed within the constraints of link layer mechanisms,
   bridging, physical connectivity, and policy.  For instance, separate
   subnetworks are necessary where two different link layers cannot be
   bridged, or when a policy requires the separation of private and
   visitor parts of the network.

   While it may be desirable to maximise the chance of link-local
   protocols operating across a homenet by maximising the size of a
   subnet across the homenet, multiple subnet home networks are
   inevitable, so their support must be included.  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 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, e.g.
   where NAT routers are included within VMs or Internet connection
   services are used.  IPv6 routed versions of such tools will be
   required.

   SN1)  The network should subdivide itself to the largest possible
         subnets that can be formed.

   SN2)  The IPv6 topology should follow the IPv4 topology, but not use
         NAT, thus there should be routed IPv6 where IPv4 NAT is used.

3.4.4.  Security vs Transparent, End-to-End Communications

   An IPv6-based home network architecture should 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 of course restrict the end-to-end
   communications, and thus while a host may be globally addressable it
   may not be globally reachable.  RFC 4864 sets a default deny "Simple
   Security" model, in which filtering is to be expected (while host-



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   based IPv6 NAT is not).  However, RFC 6092 states that while the
   default should be default deny, CERs should also have an option to be
   put into a "transparent" mode of operation which enables a default
   allow model (in which case home devices must be independently
   secure).  Such end-to-end communications are important for their
   robustness against failure of intermediate systems, where in contrast
   NAT is dependent on state machines which are not self-healing.

   In the presence of "Simple Security" the use of signalling protocols
   such as UPnP IGD (Version 2) or PCP may be expected to punch holes in
   the firewall (and be able to handle cases where there are multiple
   CERs/firewall(s).  When configuring holes in filters, protocols for
   securely associating devices are desirable.

   EE1)  The homenet should embrace transparent, end-to-end
         communications to, from and within the homenet.

   EE2)  The default security model at the homenet border is "Simple
         Security" (default deny).

   EE3)  Where "Simple Security" is applied, there must be support for
         an appropriate signalling protocol to open per-application
         holes for communications.

   EE4)  The homenet should also support a "transparent" mode of
         operation at its borders if configured to do so.

   EE5)  Users should have simple methods to associate devices to
         services that are expected to operate through borders at which
         "Simple Security" is applied.

3.4.5.  IP Connectivity between All Nodes

   A logical consequence of the end-to-end communications model is that
   the network should by default attempt to provide IP-layer
   connectivity between all internal parts as well as between the
   internal parts and the Internet.  This connectivity should be
   established at the link layer, if possible, and using routing at the
   IP layer otherwise.

   Local addressing (ULAs) may be used within the scope of a home
   network to provide a method to route between subnets.  It would be
   expected that ULAs may be used alongside one or more globally unique
   ISP-provided addresses/prefixes in a homenet.  ULAs may be used for
   all devices, not just those intended to have internal connectivity
   only.  ULAs may then be used for stable internal communications
   should the ISP-provided prefix (suddenly) change, or external
   connectivity be temporarily lost.  The use of ULAs should be



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   restricted to the homenet scope through filtering at the border(s) of
   the homenet; thus "end-to-end" for ULAs is limited to the homenet.

   In some cases 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).  Certain
   scenarios may require co-existence of ISP connectivity providing a
   general Internet service with provider connectivity to a private
   "walled garden" network.

   Some home networking scenarios/models may involve 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 example of where there may be secure perimeters
   inside the homenet.  Constrained LLN nodes may implement WPA-style
   network key security but may depend on access policies enforced by
   the LLN border router.

   CN1)  The homenet should utilise ULAs to provide stable addressing in
         the event of there being no global prefix available or changes
         in the global prefix.

   CN2)  ULAs must be filtered at the homenet site border(s).

   CN3)  Walled garden connectivity must be supported.

   CN4)  Isolated networks within the homenet must be supported.

3.4.6.  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 it could involve running an appropriate routing protocol.

   The homenet routing environment may include traditional IP networking
   where existing link-state or distance-vector protocols may be used,
   but also new LLN or other "constrained" networks where other
   protocols may be more appropriate.  IPv6 VM solutions may also add
   additional routing requirements.  Current home deployments use
   largely different mechanisms in sensor and basic Internet
   connectivity networks.

   In this section we list the assumptions and requirements for routing
   functionality within the homenet environment.




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   RT1)   The protocol should preferably be an existing deployed
          protocol that has been shown to be reliable and robust.

   RT2)   It is preferable that the protocol is "lightweight".

   RT3)   The protocol should be able to provide reachability between
          all nodes in the homenet.

   RT4)   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.

   RT5)   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.

   RT6)   Minimising convergence time should be a goal in any routed
          environment, but as a guideline a maximum convergence time of
          a couple of minutes should be the target.

   RT7)   It is desirable that the routing protocol has knowledge of the
          homenet topology, which implies a link-state protocol may be
          preferable.  If so, it is also desirable that the
          announcements and use of LSAs and RAs are appropriately
          coordinated.

   RT8)   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, 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 before
          an upstream connection has been established.  Devices in the
          homenet must be able to find the path to the Internet as well
          as other devices on the home intranet.  The border discovery
          functionality may be integrated into the routing protocol
          itself, but may also be imported via a separate discovery
          mechanism.

   RT9)   The routing environment should be self-configuring, as
          discussed in the next subsection.  An example of how OSPFv3
          can be self-configuring in a homenet is described in
          [I-D.acee-ospf-ospfv3-autoconfig].  An exception is
          configuration of a "secret" for authentication methods.




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   RT10)  The protocol should not require upstream ISP connectivity to
          be established to continue routing within the homenet.

   RT11)  Multiple upstreams should be supported, as described in the
          multihoming section earlier.  The primary target for
          multihoming support is the single CER case (where source
          routing may assist path selection).

   RT12)  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 general the routing protocol
          should support multiple ISP uplinks and delegated prefixes in
          concurrent use.

   RT13)  Load-balancing to multiple providers is not a requirement, but
          failover from a primary to a backup link when available must
          be a requirement.

   RT14)  It is assumed that the typical router designed for residential
          use does not contain the memory or CPU required to process a
          full Internet routing table this should not be a requirement
          for any homenet device.

   A new I-D has been published on homenet routing requirements, see
   [I-D.howard-homenet-routing-comparison] and evaluations of common
   routing protocols made against those requirements, see
   [I-D.howard-homenet-routing-requirements].  The requirements from the
   former document have been worked into this architecture text.

3.4.7.  Self-Organising

   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.

   The homenet will need to be aware of the extent of its own "site".
   The homenet will have one or more borders, with external connectivity
   providers and potentially parts of the internal network (e.g. for
   policy-based reasons).  It should be possible to automatically
   perform border discovery at least for the ISP borders.  Such borders
   determine for example the scope of ULAs, service discovery
   boundaries, site scope multicast boundaries and where firewall
   policies may be applied.

   The most important function in this respect is prefix delegation and



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   management.  The assumptions and requirements for the prefix
   delegation function are summarised as follows:

   PD1)   From the homenet perspective, a single prefix from each ISP
          should be received on the border CER [RFC3633].  The ISP
          should only see that aggregate, and not single /64 prefixes
          allocated within the homenet.

   PD2)   Each link in the homenet should receive a prefix from within
          the ISP-provided prefix(es).

   PD3)   Delegation should be autonomous, and not assume a flat or
          hierarchical model.

   PD4)   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.
          A currently typical /60 allocation gives 16 /64 subnets.

   PD5)   Duplicate assignment of multiple /64s to the same network
          should be avoided.

   PD6)   The network should behave as gracefully as possible in the
          event of prefix exhaustion.  The options in such cases may
          however be limited.

   PD7)   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.

   PD8)   Where ULAs are used, most likely but not necessarily in
          parallel with global prefixes, one router will need to 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.

   PD9)   Delegation within the homenet should give each link a prefix
          that is persistent across reboots, power outages and similar
          short-term outages.

   PD10)  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.







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   PD11)  Persistent prefixes should not depend on router boot order.

   PD12)  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).

   PD13)  The delegation method should support "flash" renumbering.  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/
   assumptions listed above.

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

   The network cannot be expected to be completely self-organising, e.g.
   some security parameters are likely to need manual configuration,
   e.g.  WPA2 configuration for wireless access control.  Some existing
   mechanisms exist to assist home users to associate devices as simply
   as possible, e.g. "connect" button support.

   ZC1)  The homenet must as far as possible be self-organising and
         self-configuring.

   ZC2)  Manual override of the configuration should be possible.

   ZC3)  The homenet must be able to determine where its own borders
         lie.

   ZC4)  The homenet "site" defines the borders for ULAs, site scope
         multicast, service discovery and security policies.

   ZC5)  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.



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3.4.8.  Fewest Topology Assumptions

   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 will need to be supported.

   It is important not to introduce new IPv6 scenarios that would break
   with IPv4+NAT, given that dual-stack homenets will be commonplace for
   some time.  There may be IPv6-only topologies that work where IPv4 is
   not used or required.

   ZC1)  Arbitrary topologies should be supported.

3.4.9.  Naming and Service Discovery

   The most natural way to think about naming and service discovery
   within a homenet is to enable it to work across the entire residence
   (site), disregarding technical borders such as subnets but respecting
   policy borders such as those between visitor and internal networks.

   Homenet naming systems will be required that work internally or
   externally, be the user within the homenet or outside it, though the
   domains used may be different from those different perspectives.  It
   is possible that not all internal devices should be reflected by name
   in an external-facing domain.

   A desirable target may be a fully functional self-configuring secure
   local DNS service so that all devices can be referred to by name, and
   these FQDNs are resolved locally.  This would make clean use of ULAs
   and multiple ISP-provided prefixes much easier.  Such a local DNS
   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.

   Consideration will also need to be given for existing protocols that
   may be used within a network, e.g. mDNS, and how these interact with
   unicast-based DNS services.

   With the introduction of new "dotless" top level domains, there is
   potential for ambiguity between for example a local host called apple
   and (if it is registered) an apple gTLD, so some local name space is
   probably required, which should also be configurable to something
   else by a home user, e.g. ".home", if desired.  There is also
   potential ambiguity if, for example, a mobile device should move
   between two local name spaces called ".home".

   For service discovery, support may be required for IPv6 multicast
   across the scope of the home network.  This would be the case if an



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   approach to create Extended mDNS (xmDNS) is followed as described in
   [I-D.lynn-homenet-site-mdns].

   SD1)  The homenet must support naming and service discovery
         functions.

   SD2)  All naming and service discovery functions should be able to
         function across the entire homenet site if required.

   SD3)  Disconnected operation ("fate sharing"): name resolution for
         reachable devices continues if the local network is
         disconnected from the global Internet.

   SD4)  Message utilisation should be efficient considering the network
         technologies the service may need to operate over.

   SD5)  Devices represented in the homenet name space may also be
         represented in the global DNS namespace.

   SD6)  Site scope IPv6 multicast should be supported across the
         homenet.

3.4.10.  Proxy or Extend?

   Related to the above, the architecture proposes that any existing
   protocols (e.g. service discovery) that are designed to only work
   within a subnet should be modified/extended to work across subnets,
   rather than defining proxy capabilities for each of those functions.

   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.

   Feedback is desirable on which other functions/protocols assume
   subnet-only operation, in the context of existing home networks.
   Some experience from enterprises may be relevant here.

   SD1)  Prefer to extend protocols to site scope operation rather than
         providing proxy functions on subnet boundaries.

3.4.11.  Adapt to ISP constraints

   Different homenets may be subject to different behaviour by its
   ISP(s).  The home network may receive an arbitrary length IPv6 prefix
   from its provider, e.g. /60 or /56.  The offered prefix may be stable
   over time 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



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   policies is included in [RFC6177], which discusses why, for example,
   a one-size-fits-all /48 allocation is not appropriate.  The home
   network needs to be adaptable to such ISP policies.

   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 as supported in RFC6204.  If used, ULA
   addresses should be stable so that they can always be used
   internally, independent of the link to the ISP.

   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 in 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.  The customer may of course also choose to move to a new
   ISP, and thus begin using a new prefix, though in such cases the
   customer may expect a discontinuity.  Regardless, it's desirable that
   homenet protocols support rapid renumbering and operational processes
   don't add unnecessary complexity for the renumbering process.

   The 6renum WG is studying IPv6 renumbering for enterprise networks.
   It is not currently targetting homenets, but may produce outputs that
   are relevant.

   AD1)  The homenet should make no assumptions about the stability of
         the prefix received from an ISP, or the length of the prefix
         that may be offered.

   AD2)  The operation of the homenet must not depend on the
         availability of the ISP connection.






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   AD3)  The homenet should support "flash" renumbering.  Applications
         and services operating within or to/from the homenet should be
         as resilient as possible to an external change of delegated
         prefix(es).

3.5.  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 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.


4.  Conclusions

   This text defines principles and requirements for a homenet
   architecture.  (More to be added.)


5.  References

5.1.  Normative References

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




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

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

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

   [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.

   [RFC3411]  Harrington, D., Presuhn, R., and B. Wijnen, "An
              Architecture for Describing Simple Network Management
              Protocol (SNMP) Management Frameworks", STD 62, RFC 3411,
              December 2002.

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

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

   [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.

   [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.



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   [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.

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

5.2.  Informative References

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

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

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

   [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.

   [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]



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              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.howard-homenet-routing-requirements]
              Howard, L., "Homenet Routing Requirements",
              draft-howard-homenet-routing-requirements-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.

   [I-D.ietf-v6ops-ipv6-cpe-router-bis]
              Singh, H., Beebee, W., Donley, C., Stark, B., and O.
              Troan, "Advanced Requirements for IPv6 Customer Edge
              Routers", draft-ietf-v6ops-ipv6-cpe-router-bis-01 (work in
              progress), July 2011.

   [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-01 (work in progress),
              March 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.



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   [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. and A. Lindem, "Prefix Assignment in a Home
              Network", draft-arkko-homenet-prefix-assignment-01 (work
              in progress), October 2011.

   [I-D.acee-ospf-ospfv3-autoconfig]
              Lindem, A. and J. Arkko, "OSPFv3 Auto-Configuration",
              draft-acee-ospf-ospfv3-autoconfig-01 (work in progress),
              March 2012.

   [I-D.ietf-pcp-base]
              Cheshire, S., Boucadair, M., Selkirk, P., Wing, D., and R.
              Penno, "Port Control Protocol (PCP)",
              draft-ietf-pcp-base-23 (work in progress), February 2012.

   [I-D.ietf-v6ops-happy-eyeballs]
              Wing, D. and A. Yourtchenko, "Happy Eyeballs: Success with
              Dual-Stack Hosts", draft-ietf-v6ops-happy-eyeballs-07
              (work in progress), December 2011.

   [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
              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>.






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Appendix A.  Acknowledgments

   The authors would like to thank Brian Carpenter, Mark Andrews, Fred
   Baker, Ray Bellis, Cameron Byrne, Brian Carpenter, Stuart Cheshire,
   Lorenzo Colitti, Ralph Droms, Lars Eggert, Jim Gettys, 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 Thaler, JP
   Vasseur, Curtis Villamizar, Dan Wing, Russ White, and James Woodyatt
   for their contributions within homenet WG meetings and the mailing
   list, and Mark Townsley for being an initial editor/author of this
   text before taking his position as homenet WG co-chair.


Appendix B.  Changes

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

B.1.  Version 02

   Changes made include:

   o  Made the IPv6 implications section briefer.

   o  Changed Network Models section to describe properties of the
      homent 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.





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   o  Added reference to the new xmDNS draft.

   o  Added naming/SD requirements from Ralph Droms.


Authors' Addresses

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

   Email: tjc@ecs.soton.ac.uk


   Jari Arkko
   Ericsson
   Jorvas  02420
   Finland

   Email: jari.arkko@piuha.net


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

   Email: abr@sdesigns.dk


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

   Email: ot@cisco.com











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

   Email: jason.weil@twcable.com












































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