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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: May 3, 2012                           University of Southampton
                                                                 J. Weil
                                                       Time Warner Cable
                                                                O. Troan
                                                     Cisco Systems, Inc.
                                                        October 31, 2011

                 Home Networking Architecture for IPv6


   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 and considerations.  The text highlights the impact of
   IPv6 on home networking, illustrates topology scenarios, and shows
   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 runs as an IPv6-only or dual-stack
   network, but there are no recommendations in this memo 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 May 3, 2012.

Copyright Notice

   Copyright (c) 2011 IETF Trust and the persons identified as the

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   document authors.  All rights reserved.

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

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Effects of IPv6 on Home Networking . . . . . . . . . . . . . .  3
   3.  Architecture . . . . . . . . . . . . . . . . . . . . . . . . .  7
     3.1.  Network Models . . . . . . . . . . . . . . . . . . . . . .  8
     3.2.  Requirements . . . . . . . . . . . . . . . . . . . . . . . 12
     3.3.  Considerations . . . . . . . . . . . . . . . . . . . . . . 13
     3.4.  Principles . . . . . . . . . . . . . . . . . . . . . . . . 15
     3.5.  Summary of Homenet Architecture Recommendations  . . . . . 21
     3.6.  Implementing the Architecture on IPv6  . . . . . . . . . . 22
   4.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 22
     4.1.  Normative References . . . . . . . . . . . . . . . . . . . 22
     4.2.  Informative References . . . . . . . . . . . . . . . . . . 23
   Appendix A.  Acknowledgments . . . . . . . . . . . . . . . . . . . 25
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 26

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1.  Introduction

   This memo focuses on 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 example 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 (cascaded)
   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 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.

   [RFC6204] defines basic requirements for customer edge routers
   (CPEs).  The scope of this text is the homenet, and thus the internal
   facing interface described that RFC as well as other components
   within the home network.  While the network may be dual-stack or
   IPv6-only, specific transition tools on the CPE 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

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 areas impacted by the implementation of

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   IPv6 into the home network that are both promising and problematic:

   Multiple segments and routers

      Simple 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.  However, the
      incorporation of dedicated (routed) segments 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 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 and
      lossy networks (LLNs) such as those used for certain types of
      sensor devices.  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

      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

      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 will be configured with one address from

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      each upstream ISP prefix, and the presence of upstream ingress
      filtering thus requires multi-addressed nodes to select the right
      source address to be used for the corresponding uplink.

   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 CPEs is described in [RFC6204].  A home
      network running IPv6 may deploy ULAs for communication between
      devices within the network.  ULAs have the potential to be used
      for stable addressing in a home network where the externally
      allocated global prefix changes over time or where external
      connectivity is temporarily unavailable.  However, it is
      undesirable to aggressively deprecate global prefixes for
      temporary loss of connectivity, so for this to matter there would
      have to be a connection breakage longer than the lease period, and
      even then, deprecating prefixes when there is no connectivity may
      not be advisable.  However, while setting a network up there may
      be a period with no connectivity.

      Another possible reason for using ULAs would be to provide an
      indication to applications that the traffic is local.  This could
      then be used with security settings to designate where a
      particular application is allowed to connect to.

      Address selection mechanisms should ensure a ULA source address is
      used to communicate with ULA destination addresses.  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

      Current IPv4 home networks typically receive a single global IPv4
      address from their ISP and use NAT with private [RFC1918].
      addressing for devices within the network.  An IPv6 home network
      removes the need to use NAT given the ISP offers a sufficiently
      large 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 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.

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      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 then
      need to signal that desire through a protocol such as uPNP or PCP

      Such an approach would reduces the efficacy of end-to-end
      connectivity that IPv6 has the potential to restore, since the
      need for IPv4 NAT traversal is replaced by a need to use a
      signalling protocol to request a firewall hole be opened.
      [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 does however state that CPEs should 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
      configuration, 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
      and 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) in comparision to "simple" security.

      In addition to establishing 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 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.

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      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 for example common
      practice for users to be able to connect to a router for
      configuration via a literal address such as 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.  Given a
      true ULA prefix is effectively a random 48-bit prefix, it is not
      reasonable to expect users to manually enter such address literals
      for configuration or other purposes.  As such, even for the
      simplest of functions, naming and the associated discovery of
      services is imperative for an easy to administer homenet.

      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 realizing 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 3.6.

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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                     /
         demarc #1 -->  | Internet connection         /
                 +------+--------+                    \
                 |     IPv6      |                     \
                 | Customer Edge |                      \
                 |    Router     |                      /
                 +------+--------+                     /
                        |                             |
         demarc #2 -->  |                             | End-User
                        |   Local network             | network(s)
               ---+-----+-------+---                   \
                  |             |                       \
             +----+-----+ +-----+----+                   \
             |IPv6 Host | |IPv6 Host |                   /
             |          | |          |                  /
             +----------+ +-----+----+                 /

                                 Figure 1

   Two possible demarcation points are illustrated in Figure 1, which
   indicate which party is responsible for configuration or
   autoconfiguration.  Demarcation #1 makes the Customer Edge Router the
   responsibility of the customer.  This is only practical if the
   Customer Edge Router can function with factory defaults installed.
   The Customer Edge Router may be pre-configured by the ISP, or by some
   suitably simple method by the home customer.  Demarcation #2 makes
   the Customer Edge Router the responsibility of the provider.  Both
   models of operation must be supported in the homenet architecture,
   including the scenarios below with multiple ISPs and demarcation

   Figure 2 shows another network that now introduces multiple local
   area networks.  These may be needed for reasons relating to different
   link layer technologies in use or for policy reasons.  Note that a

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   common arrangement is to have different link types supported on the
   same router, bridged together.

   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).

                      +-------+-------+                    \
                      |   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 receive 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 and associated requirements.


      A homenet 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, but the latter is expected to become more

      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 on for years in the IETF, though to date there is
      little deployment of these mechanisms.  While an argument can be
      made that home networking standards should not make another
      attempt at this, the obvious counter-argument is that multihoming
      support will be necessary for many deployment situations.

      One such approach is the use of NPTv6 [RFC6296], which is a prefix
      translation-based mechanism.  An alternative is presented in
      [I-D.v6ops-multihoming-without-ipv6nat].  Host-based methods such
      as Shim6 [RFC5533] have also been defined.

      In any case, if multihoming is supported additional requirements
      are necessary.  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.
      However, there is a general agreement that for the home case, if
      there is any support for multihoming it should be limited to a
      very small subset of the overall problem.  Specifically, multi-
      addressed hosts selecting the right source address to avoid
      falling foul of ingress filtering on upstream ISP connections
      [I-D.baker-fun-multi-router].  A solution to this particular
      problem is desirable.

      Some similar multihoming issues have already been teased out in
      the work described in [I-D.ietf-mif-dns-server-selection], which
      has led to the definition of a DHCPv6 route option

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      One could also argue that a "happy eyeballs" approach, not too
      dissimilar to that proposed for multiple interface (mif)
      scenarios, is also acceptable if such support becomes commonplace
      in hosts and applications.

      A further consideration and complexity here is that at least one
      upstream may be a "walled garden", and thus only appropriate to be
      used for connectivity to the services of that provider.

   Quality of Service in multi-service home networks

      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 QoS 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 in the homenet domain, such as ensuring proper
      buffering algorithms are used as described in [Gettys11].

   DNS services

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

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   Privacy considerations

      There are no specific privacy concerns for this text.  It should
      be noted that most ISPs are expected to offer static IPv6 prefixes
      to customers, and thus the addresses they use would not generally
      change over time.

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.  In this section we 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 following principles should be used as a guide 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

      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

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

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   Dual-stack Operation

      The homenet architecture targets both IPv6-only and dual-stack
      networks.  While the CPE requirements in RFC 6204 are targeted 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:

         Ensuring there is a way to access content in the IPv4 Internet.
         This can be arranged through incorporating NAT64 [RFC6144]
         functionality in the home gateway router, for instance.

         DNS discovery mechanisms are enabled even 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.

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

      In dual-stack networks, solutions for IPv6 must 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 CPE, are out of scope.  The homenet architecture
      focuses on the internal home network.

   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 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 links cannot be bridged, or when a

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      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.

      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.

   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 simpler
      given the availability of globally unique addresses to block
      certain nodes from communicating by use of an appropriate
      filtering device than to configure the address translation device
      to enable appropriate address/port forwarding in the presence of a

      As discussed previously, it is important to note the difference
      between hosts being addressable and reachable.  Thus filtering is
      to be expected, while IPv6 NAT is not.  End-to-end communications
      are important for their robustness to failure of intermediate
      systems, where in contrast NAT is dependent on state machines
      which are not self-healing.

      When configuring filters, protocols for securely associating
      devices are desirable.  In the presence of "Simple Security" the
      use of signalling protocols such as uPnP or PCP may be expected to
      punch holes in the firewall.  Alternatively, RFC 6092 supports the
      option for a border CPE to run in "transparent mode", in which
      case a protocol like PCP is not required, but the security model
      is more open.

   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

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      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.  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 change, or external connectivity be temporarily lost.  The
      use of ULAs should be restricted to the homenet scope through
      filtering at the border(s) of the homenet; 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).
      Note that 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 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 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 general, LLN or other networks
      should be able to attach and participate the same way or map/be
      gatewayed to the main homenet.

      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.

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      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].  It is important that self-
      configuration with "unintended" devices is avoided.

      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 prefixes in concurrent use.


      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.

      The most important function in this respect is prefix delegation
      and management.  Delegation should be autonomous, and not assume a
      flat or hierarchical model.  From the homenet perspective, a
      single prefix should be received on the border CPE from the
      upstream ISP, via [RFC3363].  The ISP should only see that
      aggregate, and not single /64 prefixes allocated within the

      Each link in the homenet should receive a prefix from within the
      ISP-provided prefix.  Delegation within the homenet should give
      each link a prefix that is persistent across reboots, power
      outages and similar short-term outages.  Addition of a new routing
      device should not affect existing persistent prefixes, but
      persistence may not be expected in the face of significant
      "replumbing" of the homenet.  Persistence should not depend on
      router boot order.  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.

      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.  For instance,
      duplicate assignment of multiple /64s to the same network should
      be avoided.

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      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 [RFC3363].
      The other uses OSPFv3, as described in

      While the homenet should be self-organising, it should be possible
      to manually adjust (override) the current configuration.  The
      network should also cope gracefully in the event of prefix

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

      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,
      site scope multicast boundaries and where firewall policies may be

      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

   Fewest 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

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

   Naming and Service 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

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

      Homenet naming systems will be required that work internally or
      externally, though the domains used may be different in each case.

   Proxy or Extend?

      Related to the above, we believe that general existing discovery
      protocols that are designed to only work within a subnet are
      modified/extended to work across subnets, rather than defining
      proxy capabilities for those functions.

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

   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

      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.
      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 static home prefix to
      customers.  However, it is possible, however unlikely, that an ISP
      may need to restructure and in doing so renumber its customer
      homenets.  In such cases "flash" renumbering may be imposed.  Thus
      it's desirable that homenet protocols or operational processes
      don't add unnecessary complexity for renumbering.

3.5.  Summary of Homenet Architecture Recommendations

   In this section we present a summary of the homenet architecture
   recommendations that were discussed in more detail in the previous

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   (Bullet points to be added in next version)

3.6.  Implementing the Architecture on IPv6

   The necessary mechanisms are largely already part of the IPv6
   protocol set and common implementations, though there are some
   exceptions.  For automatic routing, it is expected that existing
   routing protocols can be used as is.  However, a new mechanism may be
   needed in order to turn a selected protocol on by default.  Support
   for multiple exit routers and multi-homing would also require
   extensions, even if focused on the problem of multi-addressed hosts
   selecting the right source address to avoid falling foul of ingress
   filtering on upstream ISP connections.

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

4.  References

4.1.  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.

   [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.

   [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.

   [RFC3363]  Bush, R., Durand, A., Fink, B., Gudmundsson, O., and T.
              Hain, "Representing Internet Protocol version 6 (IPv6)

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              Addresses in the Domain Name System (DNS)", RFC 3363,
              August 2002.

   [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.

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

   [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

   [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.

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

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

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

              Vyncke, E., Yourtchenko, A., and M. Townsley, "Advanced
              Security for IPv6 CPE",
              draft-vyncke-advanced-ipv6-security-02 (work in progress),
              July 2011.

              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.

              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.

              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.

              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.

              Savolainen, T., Kato, J., and T. Lemon, "Improved DNS
              Server Selection for Multi-Interfaced Nodes",
              draft-ietf-mif-dns-server-selection-07 (work in progress),
              October 2011.

              Dec, W., Mrugalski, T., Sun, T., and B. Sarikaya, "DHCPv6

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              Route Options", draft-ietf-mif-dhcpv6-route-option-03
              (work in progress), September 2011.

              Baker, F. and R. Droms, "IPv6 Prefix Assignment in Small
              Networks", draft-baker-homenet-prefix-assignment-00 (work
              in progress), October 2011.

              Arkko, J. and A. Lindem, "Prefix Assignment in a Home
              Network", draft-arkko-homenet-prefix-assignment-00 (work
              in progress), October 2011.

              Lindem, A. and J. Arkko, "OSPFv3 Auto-Configuration",
              draft-acee-ospf-ospfv3-autoconfig-00 (work in progress),
              October 2011.

              Wing, D., Cheshire, S., Boucadair, M., Penno, R., and P.
              Selkirk, "Port Control Protocol (PCP)",
              draft-ietf-pcp-base-16 (work in progress), October 2011.

              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.

              Gettys, J., "Bufferbloat: Dark Buffers in the Internet",
              March 2011,

Appendix A.  Acknowledgments

   The authors would like to thank Brian Carpenter, Mark Andrews, Fred
   Baker, Ray Bellis, Cameron Byrne, 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, Erik Nordmark, Michael Richardson, Barbara Stark,
   Sander Steffann, Dave Thaler, JP Vasseur, Curtis Villamizar, 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

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Authors' Addresses

   Jari Arkko
   Jorvas  02420

   Email: jari.arkko@piuha.net

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

   Email: tjc@ecs.soton.ac.uk

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

   Email: jason.weil@twcable.com

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

   Email: ot@cisco.com

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