One document matched: draft-ietf-homenet-arch-07.xml
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docName="draft-ietf-homenet-arch-07"
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<front>
<title abbrev="IPv6 Home Networking">Home Networking Architecture for IPv6</title>
<author fullname="Tim Chown" initials="T.J." surname="Chown" role="editor">
<organization> University of Southampton </organization>
<address>
<postal>
<street> Highfield </street>
<city> Southampton </city>
<code> SO17 1BJ </code>
<region> Hampshire </region>
<country> United Kingdom </country>
</postal>
<email> tjc@ecs.soton.ac.uk </email>
</address>
</author>
<author initials="J" surname="Arkko" fullname="Jari Arkko">
<organization>Ericsson</organization>
<address>
<postal>
<street/>
<city>Jorvas</city> <code>02420</code>
<country>Finland</country>
</postal>
<email>jari.arkko@piuha.net</email>
</address>
</author>
<author initials="A" surname="Brandt" fullname="Anders Brandt">
<organization>Sigma Designs</organization>
<address>
<postal>
<street>Emdrupvej 26A, 1</street>
<city>Copenhagen</city> <code>DK-2100</code>
<country>Denmark</country>
</postal>
<email>abr@sdesigns.dk</email>
</address>
</author>
<author initials="O" surname="Troan" fullname="Ole Troan">
<organization>Cisco Systems, Inc.</organization>
<address>
<postal>
<street>Drammensveien 145A</street>
<city>Oslo</city><code>N-0212</code>
<country>Norway</country>
</postal>
<email>ot@cisco.com</email>
</address>
</author>
<author initials="J" surname="Weil" fullname="Jason Weil">
<organization>Time Warner Cable</organization>
<address>
<postal>
<street>13820 Sunrise Valley Drive</street>
<city>Herndon, VA</city><code>20171</code>
<country>USA</country>
</postal>
<email>jason.weil@twcable.com</email>
</address>
</author>
<date month="February" year="2013" />
<keyword>IPv6</keyword>
<abstract>
<t>This text describes evolving networking technology within
increasingly large residential home networks. The goal of this
document is to define a general architecture for IPv6-based home
networking, describing the associated principles, considerations and
requirements. The text briefly highlights specific implications
of the introduction of IPv6 for home networking, discusses the
elements of the architecture, and suggests how standard IPv6 mechanisms
and addressing can be employed in home networking. The architecture
describes the need for specific protocol extensions for certain
additional functionality. It is assumed that the IPv6 home network
is not actively managed, and runs as an IPv6-only or dual-stack network.
There are no recommendations in this text for the IPv4 part of the network.
</t>
</abstract>
</front>
<middle>
<section anchor="intro" title="Introduction">
<t>This document focuses on evolving networking technology within
increasingly large residential home networks and the associated
challenges with their deployment and operation. There
is a growing trend in home networking for the proliferation of networking
technology through an increasingly broad range of devices and media. This
evolution in scale and diversity sets requirements on IETF protocols.
Some of these requirements relate to the introduction of IPv6, others
to the introduction of specialised networks for home automation and
sensors.</t>
<t>
While at the time of writing
some complex home network topologies exist, but most are relatively simple
single subnet networks, and ostensibly operate using just IPv4 (there may
be IPv6 traffic within the network, e.g. for service discovery, but the
homenet is provisioned by the ISP as an IPv4 network). However, they also
typically employ solutions that we would like to avoid such as
private <xref target="RFC1918"></xref> addressing with (cascaded)
network address translation (NAT)<xref target="RFC3022"></xref>,
or they may require expert assistance to set up.
</t>
<t>
In contrast, emerging IPv6-capable home networks are very likely to
have multiple internal subnets, e.g. to support private and guest networks,
and have enough address space to allow every device to have a globally
unique address. Thus there are likely to be scenarios where internal
routing is required, in which case such networks
require methods for IPv6 prefixes to be delegated to those subnets.
It is not practical to expect home users to configure such prefixes, thus
the assumption of this document is that the
homenet is as far as possible self-organising and self-configuring, i.e.
it need not be pro-actively managed by the residential user.
</t>
<t>The
architectural constructs in this document are focused on the problems
to be solved when introducing IPv6 with an eye towards a better result
than what we have today with IPv4, as well as a better result than if
the IETF had not given this specific guidance.
The document aims to provide the basis and guiding principles for how
standard IPv6 mechanisms and addressing <xref target="RFC2460"/> <xref
target="RFC4291"/> can be employed in home networking, while
coexisting with existing IPv4 mechanisms. In emerging dual-stack
home networks it is vital that introducing IPv6 does not adversely
affect IPv4 operation. We assume that the IPv4 network
architecture in home networks is what it is, and can not be affected by
new recommendations.
It should not be assumed that any future new functionality created with
IPv6 in mind will be backward-compatible to include IPv4 support.
Further, future deployments, or specific subnets within
an otherwise dual-stack home network, may be IPv6-only, in which
case considerations for IPv4 impact would not apply.
</t>
<t>
This architecture document proposes a baseline homenet architecture, based
on protocols and implementations that are as far as possible proven and
robust.
The scope of the document is primarily the network layer technologies
that provide the basic functionality to enable addressing, connectivity,
routing, naming and service discovery. While it may, for example,
state that homenet components must be simple to deploy and use, it does
not discuss specific user interfaces, nor does it discuss specific
physical, wireless or data-link layer considerations.
</t>
<t>
<xref target="RFC6204"/> defines basic requirements for customer edge
routers (CERs). The scope of this text is the internal
homenet, and thus specific features on the CER are out of scope
for this text. While the network may be
dual-stack or IPv6-only, the definition of specific transition tools
on the CER, as introduced in RFC 6204-bis
<xref target="I-D.ietf-v6ops-6204bis"/> with DS-Lite
<xref target="RFC6333"/> and 6rd <xref target="RFC5969"/>, are also
considered out of scope of this text.
</t>
<section title="Terminology and Abbreviations">
<t>
In this section we define terminology and abbreviations used throughout the text.
</t>
<t>
<list style="symbols">
<t>ALQDN: Ambiguous Locally Qualified Domain Name. An example would be .sitelocal.</t>
<t>CER: Customer Edge Router. A border router at the edge of the homenet.</t>
<t>FQDN: Fully Qualified Domain Name. A globally unique name space.</t>
<t>LLN: Low-power and lossy network.</t>
<t>LQDN: Locally Qualified Domain Name. A name space local to the homenet.</t>
<t>NAT: Network Address Translation. Typically referring to IPv4
Network Address
and Port Translation (NAPT) <xref target="RFC3022"/>.</t>
<t>NPTv6: Network Prefix Translation for IPv6 <xref target="RFC6296"/>.</t>
<t>PCP: Port Control Protocol <xref target="I-D.ietf-pcp-base"></xref>. </t>
<t>'Simple Security'. Defined in <xref target="RFC4864"></xref> and
expanded further in <xref target="RFC6092"></xref>;
describes recommended perimeter security capabilities for IPv6 networks.</t>
<t>ULA: IPv6 Unique Local Addresses <xref target="RFC4193"></xref>.</t>
<t>ULQDN: Unique Locally Qualified Domain Name. An example might be .<UniqueString>.sitelocal.</t>
<t>UPnP: Universal Plug and Play. Includes the Internet Gateway Device (IGD)
function, which for IPv6 is UPnP IGD Version 2 <xref target="IGD-2"/>.</t>
<t>VM: Virtual machine.</t>
<t>WPA2: Wi-Fi Protected Access, as defined by the Wi-Fi Alliance.</t>
</list>
</t>
</section>
</section>
<section anchor="trends" title="Effects of IPv6 on Home Networking">
<t>
While IPv6 resembles IPv4 in many ways, there are some notable differences
in the way it may typically be deployed. It changes address allocation
principles,
making multi-addressing the norm, and, through the vastly increased address
space, allows globally unique IP addresses to be used for all devices
in a home network. This section presents an overview
of some of the key implications of the introduction of IPv6 for home
networking, that are simultaneously both promising and problematic.
</t>
<section title="Multiple subnets and routers">
<t>
While simple layer 3 topologies involving as few subnets as possible
are preferred in home networks, the incorporation of dedicated (routed)
subnets remains necessary for a variety of reasons.
For instance, an increasingly common feature in modern home routers
is the ability to support both guest and private network subnets.
Likewise, there may be a need to
separate building control or corporate extensions from the main Internet
access network, or different subnets may in general
be associated with parts of the
homenet that have different routing and security policies. Further,
link layer networking technology is poised to become more heterogeneous,
as networks begin to employ both traditional Ethernet technology and link
layers designed for low-power and lossy networks (LLNs), such as those
used for certain types of sensor devices. Constraining the flow of
certain traffic from Ethernet links to much lower capacity links
thus becomes an important topic.
</t>
<t>
The introduction of IPv6 for home networking enables the potential for
every home network to be delegated enough address space to provision
globally unique prefixes for each such subnet in the home. As discussed
later, this assumes the customer's ISP delegates enough address space
to the home. While the number of addresses in a standard /64 IPv6 prefix
is practically infinite, the number of prefixes available for assignment
to the home network is not. As a result the growth inhibitor for the
home network shifts from the number of addresses to the number of prefixes
offered by the provider.
</t>
<t>The addition of routing between subnets raises the issue of
how to extend mechanisms such as service discovery which currently only
operate within a single subnet using link-local traffic. In a typical
IPv4 home network, there is only one subnet, so such mechanisms would
normally operate as expected. For multi-subnet IPv6 home networks
there are two broad choices to enable such protocols to work across
the scope of the entire homenet;
extend existing protocols to work across that scope, or
introduce proxies for existing link layer protocols. This topic is
discussed later in the document.
</t>
<t>
There will also be the need to discover which routers in the homenet
are the border router(s) by an appropriate mechanism.
Here, there are a number of choices, including the use of
an appropriate service discovery protocol.
Whatever method is chosen would likely have
to deal with handling more than one router responding
in multihomed environments.
</t>
</section>
<section title="Global addressability and elimination of NAT">
<t>
The end-to-end communication that is potentially enabled with IPv6 is
on the one hand an incredible
opportunity for innovation and simpler network operation,
but it is also a concern as it exposes nodes in the internal
networks to receipt of potentially unwanted traffic from the
Internet.
</t>
<t>
With devices and applications able to talk directly to
each other when they have globally unique addresses, there may
be an expectation of improved host security to compensate for this.
It should be noted that many devices may (for
example) ship with default settings that make them readily vulnerable
to compromise by external attackers if globally accessible, or may simply
not have robustness designed-in because it was either assumed such devices
would only be used on private networks or the device itself doesn't
have the computing power to apply the necessary security methods.
</t>
<t>
It is important to distinguish between addressability and reachability.
While IPv6 offers global addressability through use of globally
unique addresses in the home, whether devices are globally reachable or
not would depend on the firewall or filtering configuration, and not,
as is commonly the case with IPv4, the presence or use of NAT.
In this respect, IPv6 networks may or may not have filters applied at
their borders to control such traffic, i.e. at the homenet CER.
<xref target="RFC4864"></xref> and <xref target="RFC6092"></xref>
discuss such filtering, and the merits of 'default allow' against
'default deny' policies for external traffic initiated into a homenet.
This document takes no position on which mode is the default, but
assumes the choice to use either would be made available.
</t>
</section>
<section title="Multi-Addressing of devices">
<t>
In an IPv6 network, devices will often acquire multiple addresses, typically
at least a link-local address and one or more globally unique addresses.
Where a homenet is multihomed, a device would typically receive a globally
unique address from within the delegated prefix from each upstream ISP.
Devices may also have an IPv4 address if the network is dual-stack, an
IPv6 Unique Local Address (ULA) <xref target="RFC4193"></xref> (see below),
and one or more IPv6 Privacy Addresses <xref target="RFC4941"></xref>.
</t>
<t>
It should thus be considered the norm for devices on IPv6 home networks
to be multi-addressed, and to need to make appropriate address selection
decisions for the candidate source and destination address pairs for any
given connection. Default Address Selection for IPv6
<xref target="RFC6724"></xref>
provides a solution for this, though it may face problems in the event
of multihoming where, as described above, nodes
will be configured with one address from each upstream ISP prefix.
In such cases the presence of upstream BCP 38
<xref target="RFC2827"></xref>
ingress filtering requires
multi-addressed nodes to select the correct source address to be used
for the corresponding uplink, but the node may not have the information
it needs to make that decision based on addresses alone.
We discuss such challenges in the multihoming section
later in this document.
</t>
</section>
<section title="Unique Local Addresses (ULAs)">
<t>
<xref target="RFC4193"></xref> defines Unique Local Addresses (ULAs)
for IPv6 that may be used to address devices within the scope of a
single site. Support for ULAs for IPv6 CERs is described in <xref
target="RFC6204"></xref>. A home network running IPv6 should deploy ULAs
alongside its globally unique prefix(es) to allow stable communication
between devices (on different subnets) within the homenet
where that externally allocated globally unique prefix may change over
time (e.g. due to renumbering within the subscriber's ISP) or where
external connectivity may be temporarily unavailable. While setting
up a network there may also be a period with no connectivity, in which case
ULAs would be required for inter-subnet communication. In the case where
LLNs are being set up in a new home/deployment, individual LLNs may, at
least initially, each use their own /48 ULA prefix.
</t>
<t>
While a homenet should operate correctly with two or more /48 ULAs
enabled, a mechanism for the creation and use of a single /48
ULA prefix is desirable for addressing consistency and policy enforcement.
It may thus be expected that one router in the homenet be elected a 'master'
to delegate ULA prefixes to subnets from a single /48 ULA prefix.
</t>
<t>
Where both a ULA and a global prefix are in use, the
default address selection mechanisms described above should ensure that a
ULA source address is used to communicate with ULA destination addresses
when appropriate, i.e. when the ULA destination lies within
the /48 ULA prefix(es) known to be used within the same homenet.
Note that unlike private IPv4 RFC 1918 space, the use of ULAs does not
imply use of host-based IPv6 NAT, or NPTv6 prefix-based NAT
<xref target="RFC6296"/>, rather that in an IPv6 homenet a node should
use its ULA address internally, and its additional globally unique IPv6
address as the source address for external communications. By using
such globally unique addresses between networks, the architectural cost
and complexity, particularly to applications,
of NAT or NPTv6 translation is avoided. As such, neither
IPv6 NAT or NPTv6 is recommended for use in the homenet architecture.
</t>
<t>
A counter-argument to using ULAs is that it is undesirable to aggressively
deprecate global prefixes for temporary loss of connectivity, so for a
host to lose its global address there would have to be a connection
breakage longer than the lease period, and even then, deprecating prefixes
when there is no connectivity may not be advisable. However, it is
assumed in this architecture that homenets will need to support and use ULAs.
</t>
<t>
As noted later in this text, if appropriate filtering is in place on the
CER(s), a ULA source address may be taken as an indication of locally
sourced traffic.
</t>
</section>
<section title="Avoiding manual configuration of IP addresses">
<t>
Some IPv4 home networking devices expose IPv4 addresses to users, e.g.
the IPv4 address of a home IPv4 CER that may be configured via a web
interface. In potentially complex future IPv6 homenets, users should not
be expected to enter IPv6 literal addresses in devices or applications,
given their much greater length and apparent randomness of such addresses to
a typical home user. Thus, even for the simplest of functions, simple
naming and the associated (minimal, and ideally zero configuration)
discovery of services is imperative for the easy deployment and use of
homenet devices and applications.
</t>
<t>
As mentioned previously, this means that zeroconf naming and service
discovery protocols must be capable of operating across subnet boundaries.
</t>
</section>
<section title="IPv6-only operation">
<t>
It is likely that IPv6-only networking
will be deployed first in 'greenfield' homenet scenarios, or perhaps
as one element of an otherwise dual-stack network.
Running IPv6-only adds additional requirements, e.g. for devices to get
configuration information via IPv6 transport (not relying on an IPv4
protocol such as IPv4 DHCP), and for devices to be able to
initiate communications to external devices that are IPv4-only. Thus,
for example, the following requirements are amongst those that
should be considered in IPv6-only environments:
<list style="symbols">
<t>Ensuring there is a way to access content in the IPv4 Internet. This can
be arranged through appropriate use of <xref target="RFC6144">NAT64</xref>
and <xref target="RFC6145">DNS64</xref>, for example, or via
a node-based <xref target="RFC6333">DS-Lite</xref> approach.
</t>
<t>DNS discovery mechanisms are enabled for IPv6. Both stateless
DHCPv6 <xref target="RFC3736"/> <xref
target="RFC3646"/> and Router Advertisement options <xref
target="RFC6106"/> may have to be supported and turned on by default
to ensure maximum compatibility with all types of hosts in the
network. This requires, however, that a working DNS server is known
and addressable via IPv6, and that the automatic discovery of such
a server is possible through multiple routers in the homenet.</t>
<t>All nodes in the home network support operations in IPv6-only
mode. Some current devices work well with dual-stack but fail to
recognise connectivity when IPv4 DHCP fails, for instance.</t>
</list>
</t>
<t>
The widespread availability of robust solutions to these types of
requirements will help accelerate the uptake of IPv6-only homenets.
The specifics of these are however beyond the scope of this document,
especially those functions that reside on the CER.
</t>
</section>
</section>
<section anchor="arch" title="Homenet Architecture">
<t>The aim of this architecture text is to
outline how to construct advanced IPv6-based home networks involving
multiple routers and subnets using
standard IPv6 protocols and addressing <xref target="RFC2460"/> <xref
target="RFC4291"/>.
In this section, we present the elements
of such a home networking architecture, with discussion of the
associated design principles.
</t>
<t>
Existing IETF work <xref target="RFC6204"/> defines the 'basic'
requirements for CERs,
while <xref target="I-D.ietf-v6ops-6204bis"></xref> updates the
current requirements based on operator feedback and adds new
requirements for IP transition technologies and transition technology
coexistence. This document describes a homenet architecture
which is focused on the internal homenet, rather than the CER(s).
</t>
<t>
In general, home network equipment needs to be able to operate in
networks with a range of different properties and topologies,
where home users may plug components together in arbitrary ways and
expect the resulting network to operate.
Significant manual configuration is rarely, if at all, possible, or
even desirable given the knowledge level of typical home users.
Thus the network should, as far as possible, be self-configuring, though
configuration by advanced users should not be precluded.
</t>
<t>
The homenet needs to be able to handle or provision at least
<list style="symbols">
<t>Routing</t>
<t>Prefix configuration for routers</t>
<t>Name resolution</t>
<t>Service discovery</t>
<t>Network security</t>
</list></t>
<t>
The remainder of this document describes the principles by which a
homenet architecture may deliver these properties.
</t>
<section title="General Principles">
<t>There is little that the Internet standards community can do about
the physical topologies or the need for some networks to be separated
at the network layer for policy or link layer compatibility reasons.
However, there is a lot of flexibility in using IP addressing and
inter-networking mechanisms. This architecture text discusses
how this flexibility should be used to provide the best
user experience and ensure that the network can evolve with new
applications in the future. The principles described in this text
should be followed when designing homenet
solutions. </t>
<section title="Reuse existing protocols">
<t>
It is desirable to reuse existing protocols where possible, but at
the same time to avoid consciously precluding the introduction of new or
emerging protocols.
A generally conservative approach, giving weight to running code, is
preferable. Where new protocols are required, evidence of commitment to
implementation by appropriate vendors or development communities is
highly desirable. Protocols used should be backwardly compatible,
and forward compatible where changes are made.
</t>
</section>
<section title="Minimise changes to hosts and routers">
<t>
Where possible, any requirement for changes to hosts and
routers should be minimised, though solutions which, for example,
incrementally improve with host or router changes may be acceptable.
</t>
</section>
</section>
<section title="Homenet Topology">
<t>
This section considers homenet topologies, and the principles
that may be applied in designing an architecture to support as wide a range
of such topologies as possible.
</t>
<section title="Supporting arbitrary topologies">
<t>
There should ideally be no built-in assumptions about the topology in home
networks, as users are capable of connecting their devices in
'ingenious' ways. Thus arbitrary topologies and arbitrary routing
will need to be supported,
or at least the failure mode for when the user makes a mistake should
be as robust as possible, e.g. de-activating a certain part of the
infrastructure to allow the rest to operate. In such cases,
the user should ideally have some useful
indication of the failure mode encountered.</t>
<t>There should be no topology scenarios which cause loss of
connectivity, except when the user
creates a physical island within the topology. Some potentially
pathological cases that can be created include bridging ports of a
router together, however this case can be detected and dealt with by
the router. Loops within a routed topology are in a sense good in
that they offer redundancy. Bridging loops can be dangerous but are
also detectable when a switch learns the MAC of one of its interfaces
on another or runs a spanning tree or link state protocol.
It is only loops using simple repeaters that are truly pathological.</t>
</section>
<section title="Network topology models">
<t>
Most IPv4 home network models at the time of writing tend
to be relatively simple,
typically a single NAT router to the ISP and a single internal
subnet but, as discussed earlier, evolution in network architectures
is driving more complex topologies, such as the separation of guest
and private networks. There may also be some cascaded IPv4 NAT
scenarios, which we mention in the next section.
</t>
<t>
In general, the models described in
<xref target="RFC6204"/>
and its successor RFC 6204-bis <xref target="I-D.ietf-v6ops-6204bis"/>
should be supported by the IPv6 home networking architecture. The
functions resident on the CER itself are, as stated previously, out of
scope of this text.
</t>
<t>
There are a number of properties or attributes of a home network that
we can use to describe its topology and operation.
The following properties apply to any IPv6 home network:
</t>
<t>
<list style="symbols">
<t>Presence of internal routers. The homenet may have one or more internal
routers, or may only provide subnetting from interfaces on the CER.</t>
<t>Presence of isolated internal subnets. There may be isolated internal
subnets, with no direct connectivity between them within the homenet
(with each having its own external connectivity). Isolation may
be physical, or implemented via IEEE 802.1q VLANs. The latter is however
not something a typical user would be expected to configure.</t>
<t>Demarcation of the CER. The CER(s) may or may not be managed by
the ISP. If the demarcation point is such that the customer
can provide or manage the CER, its configuration must be simple. Both
models must be supported.</t>
</list>
</t>
<t>
Various forms of multihoming are likely to become more prevalent with
IPv6 home networks, as discussed further below.
Thus the following properties should also be considered for such networks:
</t>
<t>
<list style="symbols">
<t>Number of upstream providers. The majority of home networks today
consist of a single upstream ISP, but it may become more common
in the future for there to be multiple ISPs, whether for resilience
or provision of additional services.
Each would offer its own prefix. Some may or may not provide
a default route to the public Internet. </t>
<t>Number of CERs. The homenet may have a single CER, which might be
used for one or more providers, or multiple CERs. The presence
of multiple CERs adds
additional complexity for multihoming scenarios, and protocols like
PCP that need to manage connection-oriented state mappings.</t>
</list>
</t>
<t>
In the following sections we give some examples of the types of
homenet topologies we may see in the future. This is not
intended to be
an exhaustive or complete list, rather an indicative one to
facilitate the discussion in this text.
</t>
<section title="A: Single ISP, Single CER, Internal routers">
<t>Figure 1 shows a home network with multiple local area networks. These
may be needed for reasons relating to different link layer technologies
in use or for policy reasons, e.g. classic Ethernet in one subnet and
a LLN link layer technology in another. In this example there is no
single router that a priori understands the entire topology. The
topology itself may also be complex, and it may not be possible to
assume a pure tree form, for instance (because home
users may plug routers together to form arbitrary topologies
including loops).</t>
<figure align="left" anchor="Figure.1 ">
<preamble></preamble>
<artwork align="left">
+-------+-------+ \
| Service | \
| Provider | | Service
| Router | | Provider
+-------+-------+ | network
| /
| Customer /
| Internet connection
|
+------+--------+ \
| IPv6 | \
| Customer Edge | \
| Router | |
+----+-+---+----+ |
Network A | | | Network B(E) |
----+-------------+----+ | +---+-------------+------+ |
| | | | | | |
+----+-----+ +-----+----+ | +----+-----+ +-----+----+ | |
|IPv6 Host | |IPv6 Host | | | IPv6 Host| |IPv6 Host | | |
| H1 | | H2 | | | H3 | | H4 | | |
+----------+ +----------+ | +----------+ +----------+ | |
| | | | |
Link F | ---+------+------+-----+ |
| | Network E(B) |
+------+--------+ | | End-User
| IPv6 | | | networks
| Interior +------+ |
| Router | |
+---+-------+-+-+ |
Network C | | Network D |
----+-------------+---+ +---+-------------+--- |
| | | | |
+----+-----+ +-----+----+ +----+-----+ +-----+----+ |
|IPv6 Host | |IPv6 Host | | IPv6 Host| |IPv6 Host | |
| H5 | | H6 | | H7 | | H8 | /
+----------+ +----------+ +----------+ +----------+ /
</artwork>
<postamble></postamble>
</figure>
<t>
In this diagram there is one CER. It has a single uplink interface.
It has three additional interfaces connected to
Network A, Link F, and Network B. IPv6 Internal Router (IR) has four
interfaces connected to Link F, Network C, Network D and Network E.
Network B and Network E have been bridged, likely inadvertently. This
could be as a result of connecting a wire between a switch for Network B
and a switch for Network E.
</t>
<t>
Any of logical Networks A through F might be wired or wireless.
Where multiple hosts are shown, this might be through one or more
physical ports on the CER or IPv6 (IR), wireless networks, or through
one or more layer-2 only Ethernet switches.
</t>
</section>
<section title="B: Two ISPs, Two CERs, Shared subnet">
<figure align="left" anchor="Figure.2 ">
<preamble></preamble>
<artwork align="left">
+-------+-------+ +-------+-------+ \
| Service | | Service | \
| Provider A | | Provider B | | Service
| Router | | Router | | Provider
+------+--------+ +-------+-------+ | network
| | /
| Customer | /
| Internet connections | /
| |
+------+--------+ +-------+-------+ \
| IPv6 | | IPv6 | \
| Customer Edge | | Customer Edge | \
| Router 1 | | Router 2 | /
+------+--------+ +-------+-------+ /
| | /
| | | End-User
---+---------+---+---------------+--+----------+--- | network(s)
| | | | \
+----+-----+ +-----+----+ +----+-----+ +-----+----+ \
|IPv6 Host | |IPv6 Host | | IPv6 Host| |IPv6 Host | /
| H1 | | H2 | | H3 | | H4 | /
+----------+ +----------+ +----------+ +----------+
</artwork>
<postamble></postamble>
</figure>
<t>
Figure 2 illustrates a multihomed homenet model, where the
customer has connectivity via CER1 to ISP A and via CER2 to ISP B.
This example shows one shared subnet where IPv6 nodes would
potentially be multihomed and receive multiple IPv6 global
addresses, one per ISP. This model may also be combined with
that shown in Figure 1 to create a more complex scenario with multiple
internal routers. Or the above shared subnet may be split in two,
such that each CER serves a separate isolated subnet, which is a
scenario seen with some IPv4 networks today.
</t>
</section>
<section title="C: Two ISPs, One CER, Shared subnet">
<figure align="left" anchor="Figure.3 ">
<preamble></preamble>
<artwork align="left">
+-------+-------+ +-------+-------+ \
| Service | | Service | \
| Provider A | | Provider B | | Service
| Router | | Router | | Provider
+-------+-------+ +-------+-------+ | network
| | /
| Customer | /
| Internet | /
| connections | |
+---------+---------+ \
| IPv6 | \
| Customer Edge | \
| Router | /
+---------+---------+ /
| /
| | End-User
---+------------+-------+--------+-------------+--- | network(s)
| | | | \
+----+-----+ +----+-----+ +----+-----+ +-----+----+ \
|IPv6 Host | |IPv6 Host | | IPv6 Host| |IPv6 Host | /
| H1 | | H2 | | H3 | | H4 | /
+----------+ +----------+ +----------+ +----------+
</artwork>
<postamble></postamble>
</figure>
<t>
Figure 3 illustrates a model where a home network may have multiple
connections to multiple providers or multiple logical connections to
the same provider, with shared internal subnets.
</t>
<t>
In general, while the architecture may focus on likely common
topologies, it should not preclude any arbitrary topology from
being constructed.
</t>
</section>
</section>
<section title="Dual-stack topologies">
<t>
It is expected that most homenet deployments will for the immediate
future be dual-stack IPv4/IPv6. In such networks
it is important not to introduce new IPv6 capabilities that would cause
a failure if used alongside IPv4+NAT, given that such
dual-stack homenets will be commonplace for some time.
That said, it is desirable that IPv6 works better than IPv4 in
as many scenarios as possible. Further, the homenet architecture must
operate in the absence of IPv4.
</t>
<t>
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,
routing or bridging may be used. Routing may have advantages when
compared to bridging together high speed and lower speed shared media,
and in addition bridging
may not be suitable for some media, such as ad-hoc mobile networks.
</t>
<t>
In some cases IPv4 home networks may feature cascaded NATs, which
could include cases where NAT routers are included within VMs, or where
Internet connection sharing services
are used. IPv6 routed versions of such cases will be required.
We should thus note that routers in the homenet may not be
separate physical devices; they may be embedded within other devices.
</t>
</section>
<section title="Multihoming">
<t>
A homenet may be multihomed to multiple providers, as the network
models above illustrate. This may either
take a form where there are multiple isolated networks within the home
or a more integrated network where the connectivity selection
needs to be dynamic.
Current practice is typically of the former kind, but the latter is
expected to become more commonplace.
</t>
<t>In the general homenet architecture, hosts should be multi-addressed
with a global IPv6 address from the global prefix delegated
from each ISP they communicate with or through.
When such multi-addressing is in use, hosts need some way to pick source
and destination address pairs for connections.
A host may choose a source address to use by various methods, most
commonly <xref target="RFC6724"/>. Applications may
of course do different things, and this should not be precluded.
</t>
<t>
For the single CER Network Model C illustrated above, multihoming may
be offered by source routing at the CER. With multiple exit routers,
as in CER Network Model B, the complexity rises.
Given a packet with a source address on the home network, the
packet must be routed to the proper egress to avoid BCP 38
filtering at an ISP. It is highly desirable
that the packet is routed in the most efficient manner to the correct exit,
though as a minimum requirement the packet should not be dropped.
</t>
<t>
The homenet architecture should support both the above models, i.e. one or
more CERs. However,
the general multihoming problem is broad, and solutions suggested to
date within the IETF have
included complex architectures for monitoring connectivity,
traffic engineering, identifier-locator separation, connection survivability
across multihoming events, and so on. It is thus important that
the homenet architecture should as far as possible
minimise the complexity of any multihoming support.
</t>
<t>
An example of such a 'simpler' approach has been documented
in <xref target="I-D.ietf-v6ops-ipv6-multihoming-without-ipv6nat"/>.
Alternatively a flooding/routing protocol could potentially be
used to pass information through the homenet, such that internal
routers and ultimately end hosts could learn per-prefix configuration
information, allowing better address selection decisions to be made.
However, this would imply probably host and certainly router changes.
Or another avenue is to introduce support for source routing
throughout the homenet; while greatly improving the 'intelligence' of
routing decisions within the homenet, such an approach would require
relatively significant router changes.
</t>
<t>
As explained previously, NPTv6 is not recommended in the homenet
architecture.
</t>
<t>There are some other multihoming considerations for homenet
scenarios. First, it may be the case that
multihoming applies due to an ISP migration from a transition method
to a native deployment, e.g. a 6rd <xref target="RFC5969"/>
sunsetting scenario. Second, one upstream
may be a "walled garden", and thus only appropriate to be used for
connectivity to the services of that provider; an example may be
a VPN service that only routes back to the enterprise business
network of a user in the homenet.
While we should not specifically target walled garden multihoming as
a principal goal, it should not be precluded.
</t>
<t>
The homenet architecture should also not preclude use of host or
application-oriented tools, e.g. Shim6 <xref target="RFC5533"/> or
<xref target="RFC6555">Happy Eyeballs</xref>. In general, any incremental
improvements obtained by host changes should give benefit for the
hosts introducing them, but not be required.
</t>
</section>
</section>
<section title="A Self-Organising Network">
<t>
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.
At the same time, it should be possible for advanced users to
manually adjust (override) the current configuration. </t>
<t>
While a goal of the homenet architecture is for the network to be as
self-organising as possible, there may be instances where some manual
configuration is required, e.g. the entry of a cryptographic key to
apply wireless
security, or to configure a shared routing secret. The latter may be
relevant when considering how to bootstrap a routing configuration.
It is highly desirable that the number of such configurations is minimised.
</t>
<section title="Differentiating neighbouring homenets">
<t>
It is important that self-configuration with 'unintended' devices
is avoided. Methods are needed for devices to know whether they are
intended to be part of the same homenet site or not. Thus methods
to ensure separation between neighbouring homenets are required.
This may require use of some unique 'secret' for devices/protocols in
each homenet. Some existing
mechanisms exist to assist home users to associate devices as simply
as possible, e.g. 'connect' button support.
</t>
</section>
<section title="Largest practical subnets">
<t>
Today's IPv4 home networks generally have a single subnet, and
early dual-stack deployments have a single congruent IPv6 subnet,
possibly with some bridging functionality. More recently,
some vendors have
started to introduce 'home' and 'guest' functions, which in IPv6
would be implemented as two subnets.
</t>
<t>
Future home networks are highly likely to have one or more internal
routers and thus need multiple subnets, for
the reasons described earlier. As part
of the self-organisation of the network, the homenet should subdivide
itself to the largest practical subnets that can be constructed within
the constraints of link layer mechanisms, bridging, physical
connectivity, and policy, and where applicable performance or other
criteria. For example, bridging a busy Gigabit Ethernet subnet and a
wireless subnet together may impact wireless performance.
</t>
<t>
While it may be desirable to maximise the chance of link-local
protocols operating across a homenet by maximising the size of a subnet,
multi-subnet home networks are inevitable, so their support must be
included.
</t>
</section>
<section title="Homenet realms and borders">
<t>
The homenet will need to be aware of the extent of its own 'site',
which will, for example, define the borders for ULA and site
scope multicast traffic, and may require specific security policies to
be applied.
The homenet will have one or more such borders with external
connectivity providers.
</t>
<t>
A homenet will most likely also have internal borders between internal
realms, e.g. a guest realm or a corporate network extension realm. It
should be possible to automatically discover these borders, which will
determine, for example, the scope of where network prefixes, routing
information, network traffic, service discovery and naming may be shared.
The default mode internally should be to share everything.
</t>
<t>
It is expected that a realm would span at least an entire subnet, and thus
the borders lie at routers which receive delegated prefixes within the
homenet. It is also desirable for a richer security model that hosts,
which may be running in a transparent communication mode, are able to
make communication decisions based on available realm and associated
prefix information in the same way that routers at realm borders can.
</t>
<t>
A simple homenet model may just consider three types of realm and
the borders between them, namely the internal homenet, the ISP and a
guest network. In this case
the borders will include that from the homenet to the ISP, that
from the guest network to the ISP, and that from the homenet to
the guest network. Regardless, it should be possible
for additional types of realms and borders to be defined, e.g.
for some specific Grid or LLN-based network, and for these to be detected
automatically, and for an appropriate default policy to be applied
as to what type of traffic/data can flow across such borders.
</t>
<t>
It is desirable to classify the external border of the home network as a
unique logical interface separating the home network from service provider
network/s. This border interface may be a single physical interface to
a single service provider, multiple layer 2 sub-interfaces to a single
service provider, or multiple connections to a single or multiple providers.
This border makes it possible to describe edge operations and interface
requirements across multiple functional areas including security, routing,
service discovery, and router discovery.
</t>
<t>
It should be possible for the homenet user to override any automatically
determined borders and the default policies applied between them.
</t>
<t>
Some initial proposals towards border discovery are presented in
<xref target="I-D.kline-default-perimeter"/>.
</t>
</section>
</section>
<section title="Homenet Addressing">
<t>
The IPv6 addressing scheme used within a homenet must conform to
the IPv6 addressing architecture <xref target="RFC4291"/>. In this
section we discuss how the homenet needs to adapt to the prefixes made
available to it by its upstream ISP, such that internal subnets, hosts
and devices can obtain the and configure the necessary addressing information
to operate.
</t>
<section title="Use of ISP-delegated IPv6 prefixes">
<t>
A homenet may receive an arbitrary length IPv6 prefix from
its provider, e.g. /60, /56 or /48. The offered prefix may be stable
or change from time to time. Some ISPs may offer relatively stable
prefixes, while others may change the prefix whenever the CER is reset.
Some discussion of IPv6 prefix allocation policies is included in
<xref target="RFC6177"></xref> which discusses why, for example, a
one-size-fits-all /48 allocation is not desirable.
</t>
<t>
The homenet architecture expects internal host subnets to be /64 in size.
While it may be possible to operate a DHCPv6-only network with
prefixes longer than /64, doing so would break SLAAC, and is
thus not recommended.
</t>
<t>
The home network needs to be adaptable to ISP prefix allocation policies,
and thus make no assumptions about the stability of the prefix
received from an ISP, or the length of the prefix that may be offered.
However, if only a /64 is offered by the ISP, the homenet may be
severely constrained or even unable to function.
As stated above, attempting to use internal subnet prefixes longer
than /64 would break SLAAC, and is thus not recommended. Using ULA
prefixes internally with NPTv6 at the boundary is not recommended
for reasons given elsewhere. Reverting to bridging would destroy
subnetting, breaks multicast if bridged onto 802.11 wireless
networks and has serious limitations with regard to heterogeneous
link layer technologies and LLNs. For those reasons it is recommended
that DHCP-PD or OSPFv3 capable routers have the ability to issue a warning
upon receipt of a /64 if required to assign further prefixes within
the home network. Though some consideration needs to be given to how
that should be presented to a typical home user.
</t>
<t>
Thus the border CER router should 'hint', most likely via DHCP-PD, that
it would like a /48 prefix from its ISP, i.e. it asks the ISP for the
maximum size prefix it might expect to be offered, but in practice
it may only be offered a /56 or /60. For a typical IPv6
homenet, it is not recommended that an ISP offer less than a /60 prefix,
and should preferably offer at least a /56.
</t>
<t>
In practice, it is expected that ISPs will deliver a relatively stable
home prefix to
customers. The norm for residential customers of large ISPs may be
similar to their single IPv4 address provision; by default it is likely
to remain persistent for some time, but changes in the ISP's own
provisioning systems may lead to the customer's IP (and in the IPv6 case
their prefix pool) changing. It is not expected that ISPs will support
Provider Independent (PI) addressing for general residential homenets.
</t>
<t>
When an ISP does need to restructure, and in doing so renumber its customer
homenets, 'flash' renumbering is likely to be imposed.
This implies a need for the
homenet to be able to handle a sudden renumbering event which, unlike the
process described in <xref target="RFC4192"></xref>, would be a 'flag day"
event, which means that a graceful renumbering process moving through a
state with two active prefixes in use would not be possible.
While renumbering can be viewed as
an extended version of an initial numbering process, the difference
between flash renumbering and an initial 'cold start' is the need to
provide service continuity.
</t>
<t>
There may be cases where local law means some ISPs are required to change
IPv6 prefixes (current IPv4 addresses) for privacy reasons for their
customers. In such cases it may be possible to avoid an instant 'flash'
renumbering and plan a non-flag day renumbering as per RFC 4192.
</t>
<t>
The customer may of course also choose to move
to a new ISP, and thus begin using a new prefix. In such cases the
customer should expect a discontinuity, and not only may the
prefix change but potentially also the prefix length, if the new ISP
offers a different default size prefix. Regardless, it's desirable that
homenet protocols support rapid renumbering and that operational processes
don't add unnecessary complexity for the renumbering process.
Further, the introduction of any new homenet protocols should not make
any form of renumbering any more complex than it already is.
</t>
<t>
Finally, the internal operation of the home network should also not depend
on the availability of the ISP network at any given time, other than
of course for connectivity to services or systems off the home network.
This reinforces the use of ULAs for stable
internal communication, and the need for
a naming and service discovery mechanism
that can operate independently within the homenet.
</t>
</section>
<section title="Stable internal IP addresses">
<t>
The network should by default attempt to
provide IP-layer connectivity between all internal parts of
the homenet as well as to and from the external Internet, subject
to the filtering policies or other policy constraints
discussed later in the security section.</t>
<t>
ULAs should be used within the scope of a homenet
to support routing between subnets regardless of whether
a globally unique ISP-provided prefix is available.
As discussed previously, it would be expected that
ULAs would be used alongside one or more
such global prefixes in a homenet, such that hosts become
multi-addressed with both globally unique and ULA prefixes.
ULAs should be used for all devices, not just those intended to only have
internal connectivity.
Default address selection would then enable ULAs to be preferred for internal
communications between devices that are using ULA prefixes
generated within the same homenet.
</t>
<t>
ULA addresses will allow constrained LLN devices to create permanent
relationships between IPv6 addresses, e.g. from a wall controller to a lamp.
Symbolic host names would require additional non-volatile memory.
Updating global prefixes in sleeping LLN devices might also be problematic.
</t>
<t>
The use of ULAs should be restricted to the homenet
scope through filtering at the border(s) of the homenet, as described
in RFC 6092.
</t>
<t>
Note that it is possible that in some cases multiple /48 ULA prefixes may
be in use within the same homenet, e.g. when the network is being deployed,
perhaps also without external connectivity. It is expect that routers
in the homenet would somehow elect a 'master' that would be responsible
for delegating /64 prefixes to internal requesting routers, much as routers
obtain /64 global prefixes from the prefix pool delegated by the ISP
to the CER.
In cases where multiple ULA /48's are in use, hosts need
to know that each /48 is local to the homenet, e.g. by inclusion in their
local address selection policy table.
</t>
</section>
<section title="Internal prefix delegation">
<t>
As mentioned above, there are various sources of prefixes.
From the homenet perspective, a single global prefix from each ISP should
be received on the border CER <xref target="RFC3633"/>.
Where multiple CERs exist with multiple ISP prefix pools, it is
expected that routers within the homenet would assign themselves prefixes
from each ISP they communicate with/through.
As discussed above, a ULA prefix can be made available for stable internal
communications, or for use on constrained/LLN networks. There may also be
a prefix associated with NAT64, if in use in the homenet.
</t>
<t>The delegation or availability of a prefix pool to the homenet
should allow subsequent
internal autonomous delegation of prefixes for use within the homenet.
Such internal delegation should not assume a flat or
hierarchical model, nor should it make an assumption about whether the
delegation of internal prefixes is distributed or centralised.
The assignment mechanism should provide reasonable efficiency, so
that typical home network prefix allocation sizes can accommodate all
the necessary /64 allocations in most cases, and not waste prefixes.
Further, duplicate assignment of multiple /64s to the same network
should be avoided, and the network should behave as gracefully as possible
in the event of prefix exhaustion (though the options in such cases may
be limited).
</t>
<t>
Where the home network has multiple CERs and these are delegated prefix
pools from their attached ISPs, the internal prefix delegation would
be expected to be served by each CER for each prefix associated with it.
However, where ULAs are used, most likely but not necessarily in parallel
with global prefixes, one router should be elected as 'master' for
delegation of ULA prefixes for the homenet, such that only one /48 ULA
covers the whole homenet where possible. That router should generate a
/48 ULA for
the site, and then delegate /64's from that ULA prefix to subnets.
In cases where two /48 ULAs are generated within a homenet, the
network should still continue to function, meaning that hosts will need
to determine that each ULA is local to the homenet.</t>
<t> Delegation within the homenet should give each subnet a prefix that
is persistent across reboots, power outages and similar short-term
outages.
Addition of a new routing device should not affect existing persistent
prefixes, but persistence may not be expected in the face of
significant 'replumbing' of the homenet.
Persistent prefixes should not depend on router boot order.
However, such persistent prefixes may imply
the need for stable storage on routing devices, and also a method for
a home user to 'reset' the stored prefix should a significant reconfiguration
be required (though ideally the home user should not be involved at all).</t>
<t>The delegation method should support renumbering, which would
typically be 'flash' renumbering in that the homenet would not have
advance notice of the event or thus be able to apply the types of approach
described in <xref target="RFC4192"></xref>. As a minimum,
delegated ULA prefixes within the homenet should remain persistent
through an ISP-driven renumbering event. </t>
<t>
Several proposals have been made for prefix delegation within a homenet.
One group of proposals is based on DHCPv6 PD, as described in
<xref target="I-D.baker-homenet-prefix-assignment"/>,
<xref target="RFC3315"/> and <xref target="RFC3633"/>.
The other uses OSPFv3, as described in
<xref target="I-D.arkko-homenet-prefix-assignment"/>.
More detailed analysis of these approaches needs to be made against the
requirements/principles described above.
</t>
</section>
<section title="Coordination of configuration information">
<t>
The network elements will need to be integrated in a way that takes
account of the various lifetimes on timers that are used on
different elements, e.g.
DHCPv6 PD, router, valid prefix and preferred prefix timers.
</t>
</section>
<section title="Privacy">
<t>
There are no specific privacy concerns discussed in this text. It should be
noted that, in general, ISPs are expected to offer relatively stable IPv6
prefixes
to customers, and thus the network prefix associated with the host addresses
they use may not change over a reasonably long period of time.
This exposure is similar to IPv4 networks that expose the same IPv4
global address via use of NAT, where the IPv4 address received from the
ISP may change over time, but not necessarily that frequently.
</t>
<t>
Hosts inside an IPv6 homenet may get new IPv6 addresses over time
regardless, e.g. through Privacy Addresses
<xref target="RFC4941"></xref>. This may benefit mutual privacy of users
within a home network, but not mask which home network traffic is sourced
from.
</t>
</section>
</section>
<section title="Routing functionality">
<t>
Routing functionality is required when there are multiple routers
deployed within the internal home network.
This functionality could be as simple as the current 'default route is up'
model of IPv4 NAT, or, more likely, it would involve running an appropriate
routing protocol.
</t>
<t>
The homenet unicast routing protocol should preferably be an existing
deployed protocol that has been shown to be reliable and robust, and it is
preferable that the protocol is 'lightweight'.
It is desirable that the routing protocol has knowledge of the homenet
topology, which implies a link-state protocol is preferable. If so,
it is also desirable that the announcements and use of LSAs and RAs are
appropriately coordinated.
This would mean the routing protocol gives a consistent
view of the network, and that it can pass around more than just routing
information.
</t>
<t>Multiple interface PHYs must be accounted for in the homenet routed topology.
Technologies such as Ethernet, WiFi, MoCA, etc must be capable of coexisting
in the same environment and should be treated as part of any routed
deployment. The inclusion of the PHY layer characteristics including
bandwidth, loss, and latency
in path computation should be considered for optimising communication in the homenet.
Multiple upstreams should be supported, as described in the multihoming
section earlier. This should include load-balancing to multiple providers, and
failover from a primary to a backup link when available.
The protocol however
should not require upstream ISP connectivity to be established to
continue routing within the homenet. </t>
<t> To support multihoming within a homenet, a routing protocol that can
make routing decisions based on source and destination addresses is
desirable, to avoid upstream ISP ingress filtering problems. In general
the routing protocol should support multiple ISP uplinks and delegated prefixes
in concurrent use. </t>
<t> The routing environment should be self-configuring, as discussed previously.
An example of how OSPFv3 can be self-configuring in a homenet is
described in <xref target="I-D.acee-ospf-ospfv3-autoconfig"/>.
Minimising convergence time should be a goal in any routed
environment, but as a guideline a maximum convergence time of around 30 seconds
should be the target.</t>
<t> Any routed solution will require a means for determining the boundaries of the
homenet. Borders may include but are not limited to the interface to the upstream ISP,
or a gateway device to a separate home network such as a LLN network.
In some cases there may be no border present, which may for example occur
before an upstream connection has been
established. The border discovery functionality may be
integrated into the routing protocol itself, but may also be imported via a separate
discovery mechanism. </t>
<t>
In general, LLN or other networks should be able to attach and participate
the same way as the main homenet, or alternatively map/be gatewayed to
the main homenet.
Current home deployments use largely different
mechanisms in sensor and basic Internet connectivity networks.
IPv6 VM solutions may also add additional routing requirements.
</t>
<section title="Multicast support">
<t>
It is desirable that, subject to the capacities of devices on certain media
types, multicast routing is supported across the homenet.
The natural scopes for multicast would be link-local or site-local, with
the latter constrained within the homenet, but other
policy borders, e.g. to a guest subnet, or to certain media types,
may also affect where specific multicast traffic is routed.
</t>
<t>
There may be different drivers for multicast to be supported across the
homenet, e.g. for service discovery should a proposal such as
xmDNS <xref target="I-D.lynn-homenet-site-mdns"></xref> be deployed, or
potentially for novel streaming or filesharing applications.
Where multicast is routed across a homenet an appropriate multicast routing
protocol is required, one that as per the unicast routing protocol
should be self-configuring. It must be possible to scope or filter multicast
traffic to avoid it being flooded to network media where devices cannot
reasonably support it.
</t>
<t>
The multicast environment should support the
ability for applications to pick a unique multicast group to use.
</t>
</section>
</section>
<section title="Security">
<t>
The security of an IPv6 homenet is an important consideration. The most
notable difference to the IPv4 operational model is the removal of NAT,
the introduction of global addressability of devices, and thus a need to
consider whether devices should have global reachability. Regardless,
hosts need to be able to operate securely, end-to-end where required,
and also be robust against malicious traffic direct towards them.
However, there
are other challenges introduced, e.g. default filtering policies at the
borders between other homenet realms.
</t>
<section title="Addressability vs reachability">
<t>
An IPv6-based home network architecture should embrace the transparent
end-to-end communications model as described in <xref target="RFC2775"/>.
Each device should be globally addressable, and those addresses must not
be altered in transit.
However, security perimeters can be applied to restrict end-to-end
communications, and thus while a host may be globally addressable
it may not be globally reachable.
</t>
<t>
In IPv4 NAT networks, the NAT provides an implicit firewall
function. <xref target="RFC4864"></xref> describes a 'Simple Security'
model for IPv6 networks, whereby stateful perimeter filtering
can be applied instead where global addresses are used. RFC 4864
implies an IPv6 'default deny' policy for inbound connections
be used for similar functionality to IPv4 NAT.
It should be noted that such a 'default deny' approach would
effectively replace the need for IPv4 NAT traversal protocols
with a need to
use a signalling protocol to request a firewall hole be opened.
Thus to support applications wanting to accept connections
initiated into
home networks where a 'default deny' policy is in place support
for a signalling protocol such as UPnP or
<xref target="I-D.ietf-pcp-base">PCP</xref> is required. In networks
with multiple CERs, the signalling would need to handle the cases of
flows that may use one or more exit routers. CERs would need to
be able to advertise their existence for such protocols.
</t>
<t>
<xref target="RFC6092"></xref> expands on RFC 4864, giving a more
detailed discussion of IPv6 perimeter security recommendations,
without mandating a 'default deny' approach. Indeed,
RFC 6092 does not enforce a particular mode of operation,
instead stating that CERs must provide an easily selected configuration
option that permits a 'transparent' mode, thus ensuring
a 'default allow' model is available.
The homenet architecture text makes no recommendation on the default
setting, and refers the reader to RFC 6092.
</t>
</section>
<section title="Filtering at borders">
<t>
It is desirable that there are mechanisms to detect different types of
borders within the homenet, as discussed previously,
and further mechanisms to then apply different types of filtering
policies at those borders, e.g. whether naming and service discovery
should pass a given border.
Any such policies should be able to be easily applied by typical
home users, e.g. to give a user in a guest network access to
media services in the home, or access to a printer.
Simple mechanisms to apply policy changes, or associations between
devices, will be required.
</t>
<t>
There are cases where full internal connectivity may not be desirable,
e.g. in
certain utility networking scenarios, or where filtering is required
for policy reasons against guest network subnet(s).
Some scenarios/models may as a result involve running isolated subnet(s)
with their own CERs. In such cases connectivity would only be expected
within each isolated network (though traffic may potentially
pass between them via external providers).
</t>
<t>
LLNs provide an another example of where there may be secure perimeters
inside the homenet. Constrained LLN nodes may implement
network key security but may depend on access policies enforced by
the LLN border router.
</t>
</section>
<section title="Marginal Effectiveness of NAT and Firewalls">
<t>
Security by way of obscurity (address translation) or through
firewalls (filtering) is at best marginally effective. The very poor
security track record of home computer, home networking and business
PC computers and networking is testimony to its ineffectiveness. A
compromise behind the firewall of any device exposes all others,
making an entire network that relies on obscurity or a firewall as
vulnerable as the most insecure device on the private side of the
network.
</t>
<t>
However, given home network products with very poor security, putting
a firewall in place does provide some protection, even if only
marginally effective. The use of firewalls today, whether a
good practice or not, is common practice and whatever protection
afforded, even if marginally effective, must not be lost.
</t>
</section>
<section title="Device capabilities">
<t>
In terms of the devices, homenet hosts should implement their own
security policies in accordance to their computing capabilities.
They should have the means to request transparent communications to
be initiated to them, either for all ports or for specific services.
Users should have simple methods to associate devices to services that
they wish to operate transparently through (CER) borders.
</t>
</section>
<section title="ULAs as a hint of connection origin">
<t>
It has been suggested that using ULAs would provide an indication to
applications that received traffic is locally sourced.
This could then be used with security settings to designate
between which nodes a particular application is allowed to communicate,
provided ULA address space is filtered appropriately at the boundary of
the realm.
</t>
</section>
</section>
<section title="Naming and Service Discovery">
<t>
Naming and service discovery must be supported in the homenet, and
the service(s) providing this function must as far as possible
support unmanaged operation.
</t>
<t>
The naming system will be required to work internally or externally,
be the user within the homenet or outside it, i.e. the user should
be able to refer to devices by name, and potentially connect to them,
wherever they may be.
The most natural way to think about such naming and service discovery
is to enable it to work across the entire homenet
residence (site), disregarding technical borders such as subnets
but respecting policy borders such as those between guest and other
internal network realms.
</t>
<section title="Discovering services">
<t>
Users will typically perform service discovery through GUI interfaces
that allow them to browse services on their network in an appropriate and
intuitive way. Such interfaces
are beyond the scope of this document, but the interface should have an
appropriate API for the discovery to be performed.
</t>
<t>
Such interfaces may also typically hide the local domain name element
from users, especially where only one name space is available.
However, as we discuss below, in some cases the ability to discover
available domains may be useful.
</t>
<t>
We note that current service discovery protocols are generally aimed
at single subnets. There is thus a choice to make for multi-subnet
homenets as to whether such protocols should be proxied or extended
to operate across a whole homenet. In this context, that may mean
bridging a link-local method, taking care to avoid loops, or extending
the scope of multicast traffic used for the purpose. This document does
not mandate
either solution, rather it expresses the principles that should be
used for a homenet naming and service discovery environment.
Or it may be that a new approach is preferable, e.g. flooding information
around the homenet as attributes within the routing protocol (which
could allow per-prefix configuration). In general we should
prefer approaches that are backwardly compatible, and allow current
implementations to continue to be used.
</t>
<t>
One of the primary challenges facing service discovery today is lack
of interoperability due to the ever increasing number of service
discovery protocols available. While it is conceivable for consumer
devices to support multiple discovery protocols, this is clearly not the
most efficient use of network and computational resources. One goal of the
homenet architecture should be a path to service discovery protocol
interoperability either through a standards based translation scheme,
hooks into current protocols to allow some for of communication among
discovery protocols, extensions to support a central service repository
in the homenet, or simply convergence towards a unified protocol suite.
</t>
</section>
<section title="Assigning names to devices">
<t>
Given the large number of devices that may be networked in the future,
devices should have a means to generate their own unique names within
a homenet, and to detect clashes should they arise, e.g. where a second
device of the same type/vendor as an existing device with
the same default name is deployed, or where two
running network elements with such devices are suddenly joined.
For example,
mDNS <xref target="I-D.cheshire-dnsext-multicastdns"></xref>
section 8 describes such a mechanism for a single subnetwork and
the '.local' zone. Before assigning a name to the device and the .local
naming space, the device checks whether the name already belongs to
another device by sending a multicast DNS query.
</t>
<t>
Users will also want simple ways to (re)name devices, again most likely
through an appropriate and intuitive interface that is beyond the scope
of this document. Note the name a user assigns to a device may be a
label that is stored on the device as an attribute of the device, and
may be distinct from the name used in a name service, e.g. 'Study Laser
Printer' as opposed to printer2.<somedomain>.
</t>
</section>
<section title="Name spaces">
<t>
It is desirable that only one name space is in use in the homenet,
and that this name space is served authoritatively by a server in
the homenet, most likely resident on the CER.
</t>
<t>
If a user wishes to access their home devices remotely from
elsewhere on the Internet
a globally unique name space is required. This may be acquired by
the user or provided/generated by their ISP. It is expected that
the default case is that a homenet will use a global domain provided by
the ISP, but advanced users wishing to use a name space that is independent
of their provider in the longer term should be able to acquire and use
their own domain name.
Examples of provider name space delegation approaches are described
in
<xref target="I-D.mglt-homenet-naming-delegation"></xref> and
<xref target="I-D.mglt-homenet-front-end-naming-delegation"></xref>.
For users wanting to use their own independent domain names, such services
are already available.
</t>
<t>
If however a global name space is not available, the homenet will need to
pick and use a local name space which would only have meaning within
the local homenet (i.e. it would not be used for remote access to the
homenet). The .local name space currently has a special meaning
for certain existing protocols which have link-local scope, and is
thus not appropriate for multi-subnet home networks. A different
name space is thus required for the homenet.
</t>
<t>
One approach for picking a local name space is to use an Ambiguous Local
Qualified Domain Name (ALQDN) space, such as .sitelocal (or an appropriate
name reserved for the purpose). While this is a simple
approach, there is the potential in principle for devices that are
bookmarked somehow by an application in one homenet to be confused with
a device with the same name in another homenet.
</t>
<t>
An alternative approach for a local name space would be to use a Unique
Locally Qualified Domain Name (ULQDN) space
such as .<UniqueString>.sitelocal. The <UniqueString>
could be generated in a variety of ways, one potentially
being based on the local /48 ULA prefix being used
across the homenet. Such a <UniqueString> should survive a cold
restart, i.e. be consistent after a network power-down, or,
if a value is not set on startup, the CER or device
running the name service should generate a default value.
It could be desirable for the homenet user to be able to override
the <UniqueString> with a value of their choice, but that would
increase the likelihood of a name conflict.
</t>
<t>
Whichever approach is used, the intent of using a ULQDN is to disambiguate
the name space
across different homenets, not to create a new IANA name space for such
networks. However, in practice an ALQDN may typically suffice, because
the underlying service discovery protocols should be capable of handling
moving to a network where a new device is using the same name as a device
used previously in another homenet.
And regardless, if remote access to a homenet is required, a global domain
is required, which implicitly disambiguates devices.
</t>
<t>
With the introduction of new "dotless" top level domains, there
is also potential for ambiguity between, for example, a local host called
'computer' and (if it is registered) a .computer gTLD. Thus qualified
names should always be used, whether these are exposed to the user or not.
</t>
<t>
There may be use cases where segmentation of the name space
is desirable, e.g. for use in different realms within the homenet.
Thus hierarchical name space management is likely to be required.
</t>
<t>
Where a user may be in a remote network wishing to access devices
in their home network, there may be a requirement to consider the
domain search order presented where two accompanying name spaces exist.
In such cases, a GUI may present the user a choice of domains to
use, where the name of their devices is thus relative to that domain.
This implies that a domain discovery function is desirable.
</t>
<t>
It may be the case that not all devices in the homenet are made available
by name via an Internet name space, and that a 'split view' is preferred
for certain devices.
</t>
<t>
This document makes no assumption about the presence or omission of
a reverse lookup service. There is an argument that it may be useful
for presenting logging information to users with meaningful device names
rather than literal addresses.
</t>
</section>
<section title="The homenet name service">
<t>
The homenet name service should support both lookups and discovery.
A lookup would operate via a direct query to a known service, while
discovery may use multicast messages or a service where applications
register in order to be found.
</t>
<t>
It is highly desirable that the homenet name service must at the very
least co-exist with the Internet name service. There should also be
a bias towards proven, existing solutions. The strong implication is
thus that the homenet service is DNS-based, or DNS-compatible.
There are naming protocols that are designed to be configured and
operate Internet-wide, like unicast-based DNS, but also protocols
that are designed for zero-configuration local environments, like
mDNS <xref target="I-D.cheshire-dnsext-multicastdns"></xref>.
Note that when DNS is used as the homenet name service, it includes
both a resolving service and an authoritative service. The authoritative
service hosts the homenet related zone, that may be requested by
the resolving service.
</t>
<t>
As described in
<xref target="I-D.mglt-homenet-naming-delegation"></xref>, one approach
is to run an authoritative name service in the homenet as well as a
resolving name service, most likely on the CER. The homenet resolving
name service relies both on the homenet authoritative service as well
as on a secondary resolving name service provided by the ISP, for
global Internet naming resolution.
</t>
<t>
For a service such as mDNS to coexist with an Internet name service,
where the homenet is preferably using a global domain name, it is
desirable that the zeroconf devices have a way to add their names
to the global name space in use. One solution could be for zeroconf
protocols to be used to indicate global FQDNs, e.g. an mDNS service
could return a FQDN in a SRV record.
</t>
<t>
Regardless, a method for local name service
entries to be populated automatically by devices is desirable.
Interfaces to devices might choose to give users the option as to
whether the device should register itself in the global name space.
There should also be a defined mechanism for device entries to be
removed or expired from the global name space.
</t>
<t>
It has been suggested that Dynamic DNS could be made to operate
in a zero-configuration mode using a locally significant root domain
and with minimal configuration or, using a DHCPv6 based
means of automated delegation, populate a global DNS zone.
</t>
<t>
To protect against attacks such as cache poisoning, it is desirable
to support appropriate name service security methods, including DNSSEC.
</t>
<t>
The CER is an appropriate location to host the naming service. However,
it introduces an additional load due to the name service management, e.g.
signing the zone, or resolving naming queries. This additional load must
be balanced with the CER capabilities, else the function(s) may need to
be offloaded elsewhere, e.g. with the ISP, though this may impact on the
independent operation principle.
</t>
<t>
Finally, the impact of a change in CER must be considered. It
would be desirable
to retain any relevant state (configuration) that was held in the old CER.
This might imply that state information should be distributed in the
homenet, to be recoverable by/to the new CER, or to the homenet's ISP
or a third party service by some means.
</t>
</section>
<section title="Independent operation">
<t>
Name resolution and service discovery for reachable devices must
continue to function if the local network is disconnected from
the global Internet,
e.g. a local media server should still be available even if
the Internet link is down for an extended period.
This implies the local network should also be able to perform
a complete restart in the absence of external connectivity,
and have local naming and service discovery operate correctly.
</t>
<t>
The approach described above of a local authoritative name service
with a cache would allow local operation for sustained ISP outages.
</t>
<t>
Having an independent local trust anchor is desirable, to support
secure exchanges should external connectivity be unavailable.
</t>
<t>
A change in ISP should not affect local naming and service
discovery. However, if the homenet uses a global name space provided by
the ISP, then this will obviously have an impact if the user changes
their network provider.
</t>
</section>
<section title="Considerations for LLNs">
<t>
In some parts of the homenet, in particular LLNs, devices may be sleeping,
in which case a proxy for such nodes may be required, that could
respond (for example)
to multicast service discovery requests. Those same parts
of the network may have less capacity for multicast traffic that
may be flooded from other parts of the network.
In general, message utilisation should be efficient considering
the network technologies the service may need to operate over.
</t>
<t>
There are efforts underway to determine naming and discovery
solutions for use by the Constrained Application Protocol (CoAP) in
LLN networks. These are outside the scope of this document.
</t>
</section>
<section title="DNS resolver discovery">
<t>
Automatic discovery of a name service to allow client devices in the
homenet to resolve external domains on the Internet is required,
and such discovery must support clients that may be a
number of router hops away from the name service. Similarly the
search domains for local FQDN-derived zones should be included.
</t>
</section>
</section>
<section title="Other Considerations">
<t>
This section discusses two other considerations for home networking that
the architecture should not preclude, but that this text is neutral towards.
</t>
<section title="Quality of Service">
<t>
Support for QoS in a multi-service homenet may be a requirement,
e.g. for a critical system (perhaps healthcare related), or for
differentiation between different types of traffic (file sharing,
cloud storage, live streaming, VoIP, etc). Different media types
may have different such properties or capabilities.
</t>
<t>
However, homenet scenarios should require no new QoS protocols.
A DiffServ
<xref target="RFC2475"/> approach with a small number of predefined
traffic classes may generally be sufficient, though at present there
is little experience of QoS deployment in home networks. It is likely
that QoS, or traffic prioritisation, methods will be required at the
CER, and potentially around boundaries between different media types
(where for example some traffic may simply not be appropriate for
some media, and need to be dropped to avoid drowning the constrained
media).
</t>
<t>
There may also be complementary mechanisms that could be beneficial
to application performance and behaviour in
the homenet domain, such as ensuring proper buffering algorithms are
used as described in <xref target="Gettys11"/>.
</t>
</section>
<section title="Operations and Management">
<t>
The homenet should be self-organising and configuring as far as possible,
and thus not be pro-actively managed by the home user. Thus protocols
to manage the network are not discussed in this architecture text.
</t>
<t>
However, users may be interested in the status of their networks and
devices on the network, in which case simplified monitoring mechanisms
may be desirable. It may also be the case that an ISP, or a third party,
might offer management of the homenet on behalf of a user, in which case
management protocols would be required. How such management is done
is out of scope of this document; many solutions exist.
</t>
</section>
</section>
<section title="Implementing the Architecture on IPv6">
<t>This architecture text encourages re-use of existing protocols.
Thus the necessary mechanisms are largely already part of the IPv6
protocol set and common implementations, though there are some
exceptions.
</t>
<t>
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.
</t>
<t>
Some functionality, if required by the architecture, would add significant
changes or require development of new protocols, e.g. support for
multihoming with multiple exit routers would likely
require extensions to support
source and destination address based routing within the homenet.
</t>
<t>
Some protocol changes are however required in the architecture, e.g.
for name resolution and service discovery, extensions to existing
multicast-based name
resolution protocols are needed to enable them to work across subnets,
within the scope of the home network site.</t>
<t>Some of the hardest problems in developing solutions for home networking
IPv6 architectures include discovering the right borders where the
'home' domain ends and the service provider domain begins, deciding
whether some of the necessary discovery mechanism extensions should affect
only the network infrastructure or also hosts, and the ability to turn
on routing, prefix delegation and other functions in a backwards
compatible manner.</t>
</section>
</section>
<section title="Conclusions">
<t>
This text defines principles and requirements for a homenet architecture.
The principles and requirements documented here should be observed by
any future texts describing homenet protocols for routing, prefix
management, security, naming or service discovery.
</t>
</section>
</middle>
<back>
<references title="Normative References">
&rfc2460;
&rfc3315;
&rfc3633;
&rfc3736;
&rfc4193;
&rfc4291;
&rfc4864;
</references>
<references title="Informative References">
&rfc1918;
&rfc2475;
&rfc2775;
&rfc2827;
&rfc3022;
&rfc3646;
&rfc4192;
&rfc4941;
&rfc5533;
&rfc5969;
&rfc6092;
&rfc6106;
&rfc6144;
&rfc6145;
&rfc6177;
&rfc6204;
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&rfc6724;
&I-D.mglt-homenet-front-end-naming-delegation;
&I-D.mglt-homenet-naming-delegation;
&I-D.lynn-homenet-site-mdns;
&I-D.ietf-v6ops-ipv6-multihoming-without-ipv6nat;
&I-D.baker-homenet-prefix-assignment;
&I-D.arkko-homenet-prefix-assignment;
&I-D.acee-ospf-ospfv3-autoconfig;
&I-D.cheshire-dnsext-multicastdns;
&I-D.ietf-pcp-base;
&I-D.kline-default-perimeter;
&I-D.ietf-v6ops-6204bis;
<reference anchor='Gettys11' target="http://www.ietf.org/proceedings/80/slides/tsvarea-1.pdf">
<front>
<title>Bufferbloat: Dark Buffers in the Internet</title>
<author initials="J." surname="Gettys" fullname=" Jim Gettys"> <organization />
</author>
<date month="March" year="2011" />
</front>
</reference>
<reference anchor="IGD-2" target="http://upnp.org/specs/gw/UPnP-gw-WANIPConnection-v2-Service.pdf">
<front>
<title>Internet Gateway Device (IGD) V 2.0</title>
<author fullname="UPnP Gateway Committee"
surname="UPnP Gateway Committee">
<organization>UPnP Forum</organization>
</author>
<date month="September" year="2010" />
</front>
</reference>
</references>
<section title="Acknowledgments">
<t>The authors would like to thank
Aamer Akhter,
Mark Andrews,
Dmitry Anipko,
Ran Atkinson,
Fred Baker,
Ray Bellis,
Cameron Byrne,
Brian Carpenter,
Stuart Cheshire,
Lorenzo Colitti,
Robert Cragie,
Ralph Droms,
Lars Eggert,
Jim Gettys,
Olafur Gudmundsson,
Wassim Haddad,
Joel M. Halpern,
David Harrington,
Lee Howard,
Ray Hunter,
Joel Jaeggli,
Heather Kirksey,
Ted Lemon,
Acee Lindem,
Kerry Lynn,
Daniel Migault,
Erik Nordmark,
Michael Richardson,
Mattia Rossi,
Barbara Stark,
Sander Steffann,
Don Sturek,
Dave Taht,
Dave Thaler,
Michael Thomas,
Mark Townsley,
JP Vasseur,
Curtis Villamizar,
Dan Wing,
Russ White,
and James Woodyatt
for their comments and
contributions within homenet WG meetings and on the WG mailing list.
An acknowledgement generally means that person's text made it in to
the document, or was helpful in clarifying or reinforcing an aspect
of the document.
</t>
</section>
<section title="Changes">
<t>This section will be removed in the final version of the text.
</t>
<section title="Version 07">
<t>Changes made include:</t>
<t>
<list style="symbols">
<t>Removed reference to NPTv6 in section 3.2.4. Instead now say it has
an architectural cost to use in the earlier section, and thus it is
not recommended for use in the homenet architecture.</t>
<t>Removed 'proxy or extend?' section. Included shorter text in main
body, without mandating either approach for service discovery.</t>
<t>Made it clearer that ULAs are expected to be used alongside globals.</t>
<t>Removed reference to 'advanced security' as described in
draft-vyncke-advanced-ipv6-security.</t>
<t>Balanced the text between ULQDN and ALQDN.</t>
<t>Clarify text does not assume default deny or allow on CER, but that either mode may be enabled.</t>
<t>Removed ULA-C reference for 'simple' addresses. Instead only suggested service discovery to find such devices.</t>
<t>Reiterated that single/multiple CER models to be supported for multihoming.</t>
<t>Reordered section 3.3 to improve flow.</t>
<t>Added recommendation that homenet is not allocated less than /60, and a /56 is preferable.</t>
<t>Tidied up first few intro sections.</t>
<t>Other minor edits from list feedback.</t>
</list>
</t>
</section>
<section title="Version 06">
<t>Changes made include:</t>
<t>
<list style="symbols">
<t>Stated that unmanaged goal is 'as far as possible'.</t>
<t>Added note about multiple /48 ULAs potentially being in use.</t>
<t>Minor edits from list feedback.</t>
</list>
</t>
</section>
<section title="Version 05">
<t>Changes made include:</t>
<t>
<list style="symbols">
<t>Some significant changes to naming and SD section.</t>
<t>Removed some expired drafts.</t>
<t>Added notes about issues caused by ISP only delegating a /64.</t>
<t>Recommended against using prefixes longer than /64.</t>
<t>Suggested CER asks for /48 by DHCP-PD, even if it only receives less.</t>
<t>Added note about DS-Lite but emphasised transition is out of scope.</t>
<t>Added text about multicast routing.</t>
</list>
</t>
</section>
<section title="Version 04">
<t>Changes made include:</t>
<t>
<list style="symbols">
<t>Moved border section from IPv6 differences to principles section.</t>
<t>Restructured principles into areas.</t>
<t>Added summary of naming and service discovery discussion from WG list.</t>
</list>
</t>
</section>
<section title="Version 03">
<t>Changes made include:</t>
<t>
<list style="symbols">
<t>Various improvements to the readability.</t>
<t>Removed bullet lists of requirements, as requested by chair.</t>
<t>Noted 6204bis has replaced advanced-cpe draft.</t>
<t>Clarified the topology examples are just that.</t>
<t>Emphasised we are not targetting walled gardens, but they should not be precluded.</t>
<t>Also changed text about requiring support for walled gardens.</t>
<t>Noted that avoiding falling foul of ingress filtering when multihomed is desirable.</t>
<t>Improved text about realms, detecting borders and policies at borders.</t>
<t>Stated this text makes no recommendation about default security model.</t>
<t>Added some text about failure modes for users plugging things arbitrarily.</t>
<t>Expanded naming and service discovery text.</t>
<t>Added more text about ULAs.</t>
<t>Removed reference to version 1 on chair feedback.</t>
<t>Stated that NPTv6 adds architectural cost but is not a homenet matter if
deployed at the CER. This text only considers the internal homenet.</t>
<t>Noted multihoming is supported.</t>
<t>Noted routers may not by separate devices, they may be embedded in devices.</t>
<t>Clarified simple and advanced security some more, and RFC 4864 and 6092.</t>
<t>Stated that there should be just one secret key, if any are used at all.</t>
<t>For multihoming, support multiple CERs but note that routing to the correct CER to avoid ISP filtering may not be optimal within the homenet.</t>
<t>Added some ISPs renumber due to privacy laws.</t>
<t>Removed extra repeated references to Simple Security.</t>
<t>Removed some solution creep on RIOs/RAs.</t>
<t>Load-balancing scenario added as to be supported.</t>
</list>
</t>
</section>
<section title="Version 02">
<t>Changes made include:</t>
<t>
<list style="symbols">
<t>Made the IPv6 implications section briefer.</t>
<t>Changed Network Models section to describe properties of the homenet
with illustrative examples, rather than implying the number of models
was fixed to the six shown in 01. </t>
<t>Text to state multihoming support focused on single CER model.
Multiple CER support is desirable, but not required.</t>
<t>Stated that NPTv6 not supported.</t>
<t>Added considerations section for operations and management.</t>
<t>Added bullet point principles/requirements to Section 3.4.</t>
<t>Changed IPv6 solutions must not adversely affect IPv4 to should not.</t>
<t>End-to-end section expanded to talk about "Simple Security" and borders.</t>
<t>Extended text on naming and service discovery.</t>
<t>Added reference to RFC 2775, RFC 6177.</t>
<t>Added reference to the new xmDNS draft.</t>
<t>Added naming/SD requirements from Ralph Droms.</t>
</list>
</t>
</section>
</section>
</back>
</rfc>
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