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Versions: (draft-arkko-townsley-homenet-arch) 00 01 draft-ietf-homenet-arch

Network Working Group                                           J. Arkko
Internet-Draft                                                  Ericsson
Intended status: Informational                                  T. Chown
Expires: March 24, 2012                        University of Southampton
                                                                 J. Weil
                                                       Time Warner Cable
                                                                O. Troan
                                                     Cisco Systems, Inc.
                                                      September 21, 2011


                 Home Networking Architecture for IPv6
                      draft-chown-homenet-arch-00

Abstract

   This text describes the evolving networking technology within small
   "residential home" networks.  The goal of this memo is to define the
   architecture for IPv6-based home networking.  The text highlights the
   impact of IPv6 on home networking, and illustrates some topology
   scenarios.  The architecture shows how standard IPv6 mechanisms and
   addressing can be employed in home networking, lists a number of
   principles that should apply, and outlines the need for specific
   protocol extensions for certain additional functionality.

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 March 24, 2012.

Copyright Notice

   Copyright (c) 2011 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



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   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 . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Effects of IPv6 on Home Networking . . . . . . . . . . . . . .  3
   3.  Architecture . . . . . . . . . . . . . . . . . . . . . . . . .  6
     3.1.  Network Models . . . . . . . . . . . . . . . . . . . . . .  7
     3.2.  Requirements . . . . . . . . . . . . . . . . . . . . . . . 11
     3.3.  Considerations . . . . . . . . . . . . . . . . . . . . . . 12
     3.4.  Principles . . . . . . . . . . . . . . . . . . . . . . . . 13
     3.5.  Implementing the Architecture on IPv6  . . . . . . . . . . 17
   4.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 18
     4.1.  Normative References . . . . . . . . . . . . . . . . . . . 18
     4.2.  Informative References . . . . . . . . . . . . . . . . . . 18
   Appendix A.  Acknowledgments . . . . . . . . . . . . . . . . . . . 19
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19


























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1.  Introduction

   This memo focuses on the evolving networking technology within small
   "residential home" networks and the associated challenges.  For
   example, a trend in home networking is 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 need for
   multiple subnets for private and guest networks, the introduction of
   IPv6, and the introduction of specialized networks for home
   automation and sensors.

   While advanced home networks have been built, most operate based on
   IPv4, employ solutions that we would like to avoid such as network
   address translation (NAT), or require expert assistance to set up.
   The architectural constructs in this document are focused on the
   problems to be solved when introducing IPv6 with a 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 for how standard
   IPv6 mechanisms and addressing [RFC2460] [RFC4291] can be employed in
   home networking, while coexisting with existing IPv4 mechanisms.
   Some general principles for the architecture are listed.  At this
   stage it is vital that introducing IPv6 does not adversely affect
   IPv4 operation.  Future deployments, or potentially specific subnets
   within an otherwise dual-stack home network, may be IPv6-only.

   Currently some parts of this text are somewhat "chatty", which is
   intended to solicit feedback on the issues presented.


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.  The following is an
   overview of some of the key areas impacted by the implementation of
   IPv6 into the home network that are both promising and problematic:

   Multiple segments

      While less complex layer 3 topologies involving as few subnets as
      possible are preferred in home networks for a variety of reasons
      including simpler management and service discovery, incorporation



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      of dedicated segments remains necessary for some cases.

      For instance, a common feature in modern home routers is the
      ability to support both guest and private network segments.  Also,
      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-powered
      sensor networks.  Similar needs for segmentation may occur in
      other cases, such as separating building control or corporate
      extensions from the Internet access network.  Also, different
      segments may be associated with subnets 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].

      In addition to routing, rather than NATing, between subnets, there
      are issues of when and how to extend mechanisms such as service
      discovery which currently rely on link-local addressing to limit
      scope.

      The presence of a multiple segment, multi-router network implies
      that there is some kind of automatic routing mechanism in place.
      In advanced configurations similar to those used in multihomed
      corporate networks, there may also be a need to discover border
      router(s) by an appropriate mechanism.

   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.  Thus it should be considered the norm for devices on
      IPv6 home networks to be multi-addressed, and to also have an IPv4
      address where the network is dual-stack.  Default address
      selection mechanisms [I-D.ietf-6man-rfc3484-revise] allow a node
      to select appropriate src/dst address pairs for communications,
      though such selection may face problems in the event of
      multihoming, where nodes may have multiple globally unique
      addresses and multiple exit routers associated with them.

   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 CPEs is described in [RFC6204].





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      A home network running IPv6 may deploy ULAs for communication
      between devices within the network.  Address selection mechanisms
      should ensure a ULA source address is used to communicate with ULA
      destination address.  The use of ULAs does not imply IPv6 NAT,
      rather that external communications should use a node's global
      IPv6 source address.

   Security, Borders, and the elimination of NAT

      The end-to-end communication that is promised with IPv6 is both 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.  Firewalls that restrict incoming connections may be
      used to prevent exposure, however, this reduces the efficacy of
      end-to-end connectivity that IPv6 has the potential to restore.
      [RFC6092] provides recommendations for an IPv6 firewall that
      applies "limitations on end-to-end transparency where security
      considerations are deemed important to promote local and Internet
      security."  The firewall operation is "simple" in that there is an
      assumption that traffic which is to be blocked by default is
      defined in the RFC and not expected to be updated by the user or
      otherwise.  The RFC also discusses an option for CPEs to have an
      option to be put into a "transparent mode" of operation.

      It is important to distinguish between addressability and
      reachability; i.e.  IPv6 through use of globally unique addressing
      in the home makes all devices potentially reachable from anywhere.
      Whether they are or not should depend on firewall or filtering
      behaviour, and not the presence or use of NAT.

      Advanced Security for IPv6 CPE [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 polices must be
      updated by a trusted party which can provide intrusion signatures
      an other "active" information on security threats.  This is much
      like a virus-scanning tool which must receive updates in order to
      detect and/or neutralize the latest attacks as they arrive.  As
      the name implies "advanced" security requires significantly more
      resources and infrastructure (including a source for attack
      signatures) vs. "simple" security.

      In addition to the security mechanisms themselves, it is important
      to know where to enable them.  If there is some indication as to
      which router is connected to the "outside" of the home network,
      this is feasible.  Otherwise, it can be difficult to know which
      security policies to apply where.  Further, security policies may
      be different for various address ranges if ULA addressing is setup



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      to only operate within the homenet itself and not be routed to the
      Internet at large.  Finally, such 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.

      It may be useful to classify the 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.

   Naming, and manual configuration of IP addresses

      In IPv4, a single subnet NATed home network environment is
      currently the norm.  As a result, it is common practice to reach a
      router for configuration, DNS resolver functions, or otherwise via
      192.168.1.1 or some other commonly used RFC 1918 address.  In
      IPv6, while ULAs exist and could potentially be used to address
      internally-reachable services, little deployment experience exists
      to date.  In addition, generally IPv6 addresses are more
      cumbersome for humans to manually configure, with a true ULA
      prefix effectively being a random 48-bit prefix.  As such, even
      for the simplest of functions, naming and the associated discovery
      of services is imperative for an easy to administer homenet.

      Naming and service discovery are thus important, but they may also
      be expected to operate across the scope of the entire home
      network, despite crossing subnet boundaries.  It should be noted
      that in IPv4, these services do not generally function across home
      router NAT boundaries, so this would be one area where there is
      room for an improvement in IPv6.


3.  Architecture

   An architecture outlines how to construct home networks involving
   multiple routers and subnets.  In the next section this text presents
   a few typical home network topology models/scenarios, followed by a
   list of topics that may influence the architecture discussions.  This
   is followed by a set of architectural principles that govern how the
   various nodes should work together.  Finally, some guidelines are
   given for realizing the architecture with the IPv6 addressing
   architecture, prefix delegation, global and ULA addresses, source
   address selection rules and other existing components of the IPv6



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   architecture.  The architecture also drives what protocols extensions
   are necessary, as will be discussed in Section 3.5.

3.1.  Network Models

   Figure 1 shows the simplest possible home network topology, involving
   just one router, a local area network, and a set of hosts.  Setting
   up such networks is in principle well understood today [RFC6204].


                +-------+-------+                      \
                |   Service     |                       \
                |   Provider    |                        | Service
                |    Router     |                        | Provider
                +-------+-------+                        | network
                        |                               /
                        | Customer                     /
                        | Internet connection         /
                        |
                 +------+--------+                    \
                 |     IPv6      |                     \
                 | Customer Edge |                      \
                 |    Router     |                      /
                 +------+--------+                     /
                        |                             | End-User
          Local Network |                             | network(s)
               ---+-----+-------+---                   \
                  |             |                       \
             +----+-----+ +-----+----+                   \
             |IPv6 Host | |IPv6 Host |                   /
             |          | |          |                  /
             +----------+ +-----+----+                 /

                                 Figure 1

   Figure 2 shows another network that now introduces multiple local
   area networks.  These may be needed for reasons relating to different
   link layer technology or for policy reasons.  Note that a common
   arrangement is to have different link types supported on the same
   router, bridged together.  For the purposes of this memo and IP layer
   operation this arrangement is considered equivalent to the topology
   in Figure 1.

   This topology is also relatively well understood today [RFC6204],
   though it certainly presents additional demands with regards suitable
   firewall policies and limits the operation of certain applications
   and discovery mechanisms (which may typically today only succeed
   within a single subnet).



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                      +-------+-------+                    \
                      |   Service     |                     \
                      |   Provider    |                      | Service
                      |    Router     |                      | Provider
                      +------+--------+                      | network
                             |                              /
                             | Customer                    /
                             | Internet connection        /
                             |
                      +------+--------+                     \
                      |     IPv6      |                      \
                      | Customer Edge |                       \
                      |    Router     |                       /
                      +----+-------+--+                      /
           Network A       |       |   Network B            | End-User
     ---+-------------+----+-    --+--+-------------+---    | network(s)
        |             |               |             |        \
   +----+-----+ +-----+----+     +----+-----+ +-----+----+    \
   |IPv6 Host | |IPv6 Host |     | IPv6 Host| |IPv6 Host |    /
   |          | |          |     |          | |          |   /
   +----------+ +-----+----+     +----------+ +----------+  /

                                 Figure 2

   Figure 3 shows a little bit more complex network with two routers and
   eight devices connected to one ISP.  This network is similar to the
   one discussed in [I-D.ietf-v6ops-ipv6-cpe-router-bis].  The main
   complication in this topology compared to the ones described earlier
   is that there is no longer a single router that a priori understands
   the entire topology.  The topology itself may also be complex.  It
   may not be possible to assume a pure tree form, for instance.  This
   would be a consideration if there was an assumption that home users
   may plug routers together to form arbitrary topologies.


















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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 3













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           +-------+-------+     +-------+-------+         \
           |   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 4

   Figure 4 illustrates a multihomed home network model, where the
   customer has connectivity via CPE1 to ISP A and via CPE2 to ISP B.
   This example shows one shared subnet where IPv6 nodes would
   potentially be multihomed and received multiple IPv6 global
   addresses, one per ISP.  This model may also be combined with that
   shown in Figure 3 for example to create a more complex scenario.




















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

                                 Figure 5

   Figure 5 illustrates a model where a home network may have multiple
   connections to multiple providers or multiple logical connections to
   the same provider, but the associated subnet(s) are isolated.  Some
   deployment scenarios may require this model.

3.2.  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 topologies discussed above.
   Manual configuration is rarely, if at all, possible, given the
   knowledge lying with typical home users.  The equipment needs to be
   prepared to handle at least

   o  Prefix configuration for routers

   o  Managing routing

   o  Name resolution

   o  Service discovery




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   o  Network security

3.3.  Considerations

   This section lists some considerations for home networking that may
   affect the architecture depending on how or if they are included.
   Comments are certainly required here.

   Multihoming

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

      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.  Many general solutions for IPv6 multihoming
      have been worked for years in the IETF and to date there is little
      deployment of these mechanisms.  An argument can be made that home
      networking standards should not make another attempt at this.  An
      obvious counter-argument is that multihoming support may be
      necessary for many deployment situations.

      In any case, if multihoming is supported, additional requirements
      are necessary as described in [I-D.baker-fun-multi-router].  In
      the case of multiple exit routers, either the use of NAT66
      [RFC6296] or an alternative approach may be needed, e.g.
      [I-D.v6ops-multihoming-without-ipv6nat].  One could also argue
      that a "happy eyeballs" viewpoint, not too dissimilar to that
      proposed for multiple interface (mif) scenarios is also
      acceptable.  The central part of the arguments about IPv6
      multihoming is whether all devices exist in the same multihomed
      network, and if they, do they have one or multiple IPv6 addresses.

   Quality of Service in multi-service home networks

      Support for QoS between multiple services 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 QoS properties or capabilities.







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      A counter-argument for adding any specific support for home
      networking related standards is that again, there is little
      practical deployment of QoS mechanism even in the general
      networking world, let alone home networks.  It could also be
      argued that simpler mechanisms are more cost-effective, such as
      ensuring proper buffering algorithms to avoid the bufferbloat
      problem as described in [Gettys11].

   DNS services

      Consideration will need to be given for existing protocols that
      may be used within a network, e.g. mDNS.  With the introduction of
      new 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, and one
      that may be configurable by a home user.  It is probably desirable
      to have DNS treated the same within a home network for IPv4 and
      IPv6.  This will fall under the naming and service discovery
      requirements.  More input needed here.

   Privacy considerations

      There has been some suggestion to include privacy consideration in
      homenet.  What do we want to say about that here?

3.4.  Principles

   There is little that the Internet standards community can do about
   the physical topologies or the need for some networks to be separated
   at the network layer for policy or link layer compatibility reasons.
   However, there is a lot of flexibility in using IP addressing and
   inter-networking mechanisms.  It would be desirable to provide some
   guidance on 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 authors believe that the following principles guide us in
   designing these networks in the correct manner.  There is no implied
   priority by the order in which the principles are listed.

   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.  For example,
      [I-D.baker-fun-routing-class] suggests introducing a routing
      protocol that may may route on both source and destination
      addresses.  Protocols used should be backwardly compatible.



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      Do we wish to say anything about other home networking related
      standards or groups, e.g.  DLNA?

   Dual-stack Operation

      Any solutions for IPv6 must not adversely affect IPv4 operation.
      While RFC 6204 is targeted at IPv6-only networks, it is likely
      that dual-stack home networks will be the norm for some period of
      time, but IPv6-only home networks will be deployed in due course,
      perhaps first in "greenfield" scenarios, or may appear as one
      element of an otherwise dual-stack network.  It is likely that
      topologies of IPv4 and IPv6 networks would be as congruent as
      possible.

      Should the text say anything to say about transition tool use?
      Some discussion has also happened on mapping of external IPv6
      addresses to internal IPv4 ones.

   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 need multiple subnets, for reasons described
      earlier.  As part of the self-organization of the network, the
      network should subdivide itself to the largest possible subnets
      that can be constructed with the constraints of link layer
      mechanisms, bridging, physical connectivity, and policy.  For
      instance, separate subnetworks are necessary where two different
      links cannot be bridged, or when a policy requires the separation
      of a private and visitor parts of the network.

      While it may be desirable to maximise the chance of link-local
      protocols succeeding, 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.

      ** Perhaps add a Figure here to illustrate the principle.

   Transparent End-to-End Communications

      An IPv6-based home network architecture should naturally offer a
      transparent end-to-end communications model.  Each device should
      be addressable by a unique address.  Security perimeters can of
      course restrict the end-to-end communications, but it is much



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      easier to block certain nodes from communicating than it is to re-
      enable nodes to communicate if they have been hidden behind
      address translation devices.

      As discussed previously, it is important to note the difference
      between addressable and reachable.  So filtering is to be
      expected, but NAT is not.  For configuring filters, protocols for
      securely associating devices would be desirable.  The use of
      protocols including uPnP or PCP may be expected.  A default
      'transparent mode' (as per RFC6092) may be used.

      Local addressing (ULAs) may be used within the scope of a home
      network.  Should ULAs be encouraged for all devices or only those
      intended to have internal connectivity only?  IPv4 "thinking"
      would incorrectly associate ULAs with use of NAT.

   IP Connectivity between All Nodes

      A logical consequence of the end-to-end communications model is
      that the network should 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.

      Some home networking scenarios/models may involve isolated
      subnet(s) with their own CPEs.  In such cases connectivity would
      only be expected within each isolated network (though traffic may
      potentially pass between them via external providers).

   Routing functionality

      Routing functionality is required when multiple subnets are in
      use.  This functionality could be as simple as the current
      "default route is up" model of IPv4 NAT, or it could be running an
      actual routing protocol.

      The requirements for solutions in this area are unclear, but it
      seems likely that a solution is required and that it should be
      something that can work across different types of devices in the
      same home network.

      If an actual routing protocol is needed, is it necessary to pick
      one?  If there are multiple protocols, will some kind of
      negotation be needed?






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      If one routing protocol is recommended, which one should it be?
      Should the selection of the solution be guided by what already
      exists in most devices (the running code approach) or what
      satisfies the full requirements (the design principle)?

      Should sensor and machine-to-machine communication networks be
      dealt with as separate networks, or as a part of the routing
      mechanisms that handle the entire home network?  Or are the
      requirements and mechamisms for home networks too different from
      these specialized, low-power networks that attempting to use one
      solution would merely cause harm?  Current home deployments use
      largely different mechanisms in sensor and basic Internet
      connectivity networks.

   Self-Organization

      A home network architecture should be naturally self-organizing
      and self-configuring under different circumstances relating to
      connectivity status to the Internet, number of devices, and
      physical topology.

   Least Topology Assumptions

      There should be ideally 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.

   Discovery

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

      This implies support for IPv6 multicast across the scope of the
      home network, and thus at least all routing devices in the
      network.

   Proxy or Extend?

      Related to the above, it would be desirable to decide whether in
      general existing protocols that are designed to only work within a
      subnet are modified/extended to work across subnets, or whether
      proxy capabilities are defined for those functions.





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      We may need to do more analysis (a survey?) on which functions/
      protocols assume subnet-only operation, in the context of existing
      home networks (which today are most commonly a single subnet).
      Some experience from enterprises may be relevant here.

   Adapt to ISP constraints

      The home network may receive an arbitrary length IPv6 prefix from
      its provider, e.g. /60 or /56.  The offered prefix may be static
      or dynamic.  The home network needs to be adaptable to such ISP
      policies, e.g. on constraints placed by the size of prefix offered
      by the ISP.  The ISP may use [I-D.ietf-dhc-pd-exclude] for
      example.

      The internal operation of the home network should not also depend
      on the availability of the ISP network at any given time, other
      than for connectivity to services or systems off the home network.

   Intelligent Policy

      As the Internet continues to evolve, no part of the architecture
      or security design should depend on hard coding acceptable or
      unacceptable traffic patterns into the devices.  Rather, these
      traffic patterns should be driven off up-to-date databases in the
      Internet.

      This principle should also cover consideration to avoid hard
      coding IP literals or taking other actions that unnecessarily
      complicate any required home network renumbering operation.

3.5.  Implementing the Architecture on IPv6

   The necessary mechanisms are largely already part of the IPv6
   protocol set and common implementations.  The few known counter-
   examples are discussed in the following section.  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.  Support for multiple exit routers
   and multi-homing would also require extensions.  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.

   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 necessary discovery mechanism extensions should affect only
   the network infrastructure or also hosts, and the ability to turn on



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   routing, prefix delegation and other functions in a backwards
   compatible manner.


4.  References

4.1.  Normative References

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

   [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.

   [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.

4.2.  Informative References

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



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              Security for IPv6 CPE",
              draft-vyncke-advanced-ipv6-security-02 (work in progress),
              July 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-rfc3484-revise]
              Matsumoto, A., Kato, J., Fujisaki, T., and T. Chown,
              "Update to RFC 3484 Default Address Selection for IPv6",
              draft-ietf-6man-rfc3484-revise-04 (work in progress),
              July 2011.

   [I-D.ietf-dhc-pd-exclude]
              Korhonen, J., Savolainen, T., Krishnan, S., and O. Troan,
              "Prefix Exclude Option for DHCPv6-based Prefix
              Delegation", draft-ietf-dhc-pd-exclude-03 (work in
              progress), August 2011.

   [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.

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


Appendix A.  Acknowledgments

   The authors would like to thank to Stuart Cheshire, James Woodyatt,
   Lars Eggert, Ray Bellis, David Harrington, Wassim Haddad, Heather
   Kirksey, Dave Thaler, Fred Baker, and Ralph Droms for interesting
   discussions in this problem space, and Mark Townsley for being an
   initial editor/author of this text before taking his position as
   homenet WG co-chair.

   ** Additional acknowledgements TBA.







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Authors' Addresses

   Jari Arkko
   Ericsson
   Jorvas  02420
   Finland

   Email: jari.arkko@piuha.net


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

   Email: tjc@ecs.soton.ac.uk


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

   Email: jason.weil@twcable.com


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

   Email: ot@cisco.com
















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