RFC7368: IPv6 Home Networking Architecture Principles
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(IPv6)
Internet Engineering Task Force (IETF) T. Chown, Ed.
Request for Comments: 7368 University of Southampton
Category: Informational J. Arkko
ISSN: 2070-1721 Ericsson
A. Brandt
Sigma Designs
O. Troan
Cisco Systems, Inc.
J. Weil
Time Warner Cable
October 2014
IPv6 Home Networking Architecture Principles
Abstract
This text describes evolving networking technology within residential
home networks with increasing numbers of devices and a trend towards
increased internal routing. 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.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7368.
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Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Terminology and Abbreviations . . . . . . . . . . . . . . 5
2. Effects of IPv6 on Home Networking . . . . . . . . . . . . . 6
2.1. Multiple Subnets and Routers . . . . . . . . . . . . . . 7
2.2. Global Addressability and Elimination of NAT . . . . . . 8
2.3. Multi-Addressing of Devices . . . . . . . . . . . . . . . 8
2.4. Unique Local Addresses (ULAs) . . . . . . . . . . . . . . 9
2.5. Avoiding Manual Configuration of IP Addresses . . . . . . 10
2.6. IPv6-Only Operation . . . . . . . . . . . . . . . . . . . 11
3. Homenet Architecture Principles . . . . . . . . . . . . . . . 11
3.1. General Principles . . . . . . . . . . . . . . . . . . . 12
3.1.1. Reuse Existing Protocols . . . . . . . . . . . . . . 12
3.1.2. Minimise Changes to Hosts and Routers . . . . . . . . 13
3.2. Homenet Topology . . . . . . . . . . . . . . . . . . . . 13
3.2.1. Supporting Arbitrary Topologies . . . . . . . . . . . 13
3.2.2. Network Topology Models . . . . . . . . . . . . . . . 14
3.2.3. Dual-Stack Topologies . . . . . . . . . . . . . . . . 18
3.2.4. Multihoming . . . . . . . . . . . . . . . . . . . . . 19
3.2.5. Mobility Support . . . . . . . . . . . . . . . . . . 20
3.3. A Self-Organising Network . . . . . . . . . . . . . . . . 21
3.3.1. Differentiating Neighbouring Homenets . . . . . . . . 21
3.3.2. Largest Practical Subnets . . . . . . . . . . . . . . 21
3.3.3. Handling Varying Link Technologies . . . . . . . . . 22
3.3.4. Homenet Realms and Borders . . . . . . . . . . . . . 22
3.3.5. Configuration Information from the ISP . . . . . . . 23
3.4. Homenet Addressing . . . . . . . . . . . . . . . . . . . 24
3.4.1. Use of ISP-Delegated IPv6 Prefixes . . . . . . . . . 24
3.4.2. Stable Internal IP Addresses . . . . . . . . . . . . 26
3.4.3. Internal Prefix Delegation . . . . . . . . . . . . . 27
3.4.4. Coordination of Configuration Information . . . . . . 28
3.4.5. Privacy . . . . . . . . . . . . . . . . . . . . . . . 28
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3.5. Routing Functionality . . . . . . . . . . . . . . . . . . 28
3.5.1. Unicast Routing within the Homenet . . . . . . . . . 30
3.5.2. Unicast Routing at the Homenet Border . . . . . . . . 31
3.5.3. Multicast Support . . . . . . . . . . . . . . . . . . 31
3.6. Security . . . . . . . . . . . . . . . . . . . . . . . . 32
3.6.1. Addressability vs. Reachability . . . . . . . . . . . 32
3.6.2. Filtering at Borders . . . . . . . . . . . . . . . . 33
3.6.3. Partial Effectiveness of NAT and Firewalls . . . . . 34
3.6.4. Exfiltration Concerns . . . . . . . . . . . . . . . . 34
3.6.5. Device Capabilities . . . . . . . . . . . . . . . . . 34
3.6.6. ULAs as a Hint of Connection Origin . . . . . . . . . 35
3.7. Naming and Service Discovery . . . . . . . . . . . . . . 35
3.7.1. Discovering Services . . . . . . . . . . . . . . . . 35
3.7.2. Assigning Names to Devices . . . . . . . . . . . . . 36
3.7.3. The Homenet Name Service . . . . . . . . . . . . . . 37
3.7.4. Name Spaces . . . . . . . . . . . . . . . . . . . . . 38
3.7.5. Independent Operation . . . . . . . . . . . . . . . . 40
3.7.6. Considerations for LLNs . . . . . . . . . . . . . . . 40
3.7.7. DNS Resolver Discovery . . . . . . . . . . . . . . . 41
3.7.8. Devices Roaming to/from the Homenet . . . . . . . . . 41
3.8. Other Considerations . . . . . . . . . . . . . . . . . . 41
3.8.1. Quality of Service . . . . . . . . . . . . . . . . . 41
3.8.2. Operations and Management . . . . . . . . . . . . . . 42
3.9. Implementing the Architecture on IPv6 . . . . . . . . . . 43
4. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 44
5. Security Considerations . . . . . . . . . . . . . . . . . . . 44
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 44
6.1. Normative References . . . . . . . . . . . . . . . . . . 44
6.2. Informative References . . . . . . . . . . . . . . . . . 44
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 48
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 49
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1. Introduction
This document focuses on evolving networking technology within
residential home networks with increasing numbers of devices and a
trend towards increased internal routing, as well as 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, while others relate to the introduction of specialised networks
for home automation and sensors.
While at the time of writing some complex home network topologies
exist, most are relatively simple single subnet networks and
ostensibly operate using just IPv4. While there may be IPv6 traffic
within the network, e.g., for service discovery, the homenet is
provisioned by the ISP as an IPv4 network. Such networks also
typically employ solutions that should be avoided, such as private
[RFC1918] addressing with (cascaded) Network Address Translation
(NAT) [RFC3022], or they may require expert assistance to set up.
In contrast, emerging IPv6-capable home networks are very likely to
have multiple internal subnets, e.g., to facilitate private and guest
networks, heterogeneous link layers, and smart grid components, and
have enough address space available to allow every device to have a
globally unique address. This implies that internal routing
functionality is required, and that the homenet's ISP delegates a
large enough address block, to allow assignment of a prefix to each
subnet in the home network.
It is not practical to expect home users to configure their networks.
Thus, the assumption of this document is that the homenet is as far
as possible self-organising and self-configuring, i.e., it should
function without proactive management by the residential user.
The architectural constructs in this document are focused on the
problems to be solved when introducing IPv6, with an eye towards a
better result than what we have today with IPv4, as well as aiming
for a more consistent solution that addresses as many of the
identified requirements as possible. This document aims to provide
the basis and guiding principles for how standard IPv6 mechanisms and
addressing [RFC2460] [RFC4291] can be employed in home networking,
while coexisting with existing IPv4 mechanisms. In emerging dual-
stack home networks, it is vital that introducing IPv6 does not
adversely affect IPv4 operation. We assume that the IPv4 network
architecture in home networks is what it is and cannot be modified by
new recommendations. This document does not discuss how IPv4 home
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networks provision or deliver support for multiple subnets. 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.
This document proposes a baseline homenet architecture, using
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. Likewise, we also do not specify the
whole design of a homenet router from top to bottom; rather, we focus
on the Layer 3 aspects. This means that Layer 2 is largely out of
scope, we're assuming a data-link layer that supports IPv6 is
present, and we react accordingly. Any IPv6-over-Foo definitions
occur elsewhere.
[RFC7084], which has obsoleted [RFC6204], defines basic requirements
for Customer Edge (CE) routers. The update includes the definition
of requirements for specific transition tools on the CE router,
specifically Dual-Stack Lite (DS-Lite) [RFC6333] and IPv6 Rapid
Deployment on IPv4 Infrastructures (6rd) [RFC5969]. Such detailed
specification of CE router devices is considered out of scope of this
architecture document, and we assume that any required update of the
CE router device specification as a result of adopting this
architecture will be handled as separate and specific updates to
these existing documents. Further, the scope of this text is the
internal homenet, and thus specific features on the WAN side of the
CE router are out of scope for this text.
1.1. Terminology and Abbreviations
In this section, we define terminology and abbreviations used
throughout the text.
o Border: A point, typically resident on a router, between two
networks, e.g., between the main internal homenet and a guest
network. This defines a point(s) at which filtering and
forwarding policies for different types of traffic may be applied.
o CE router: Customer Edge router. A border router intended for use
in a homenet. A CE router connects the homenet to a service
provider network.
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o FQDN: Fully Qualified Domain Name. A globally unique name.
o Guest network: A part of the home network intended for use by
visitors or guests to the home(net). Devices on the guest network
may typically not see or be able to use all services in the
home(net).
o Homenet: A home network, comprising host and router equipment,
with one or more CE routers providing connectivity to a service
provider network(s).
o ISP: Internet Service Provider. An entity that provides access to
the Internet. In this document, a service provider specifically
offers Internet access using IPv6 and may also offer IPv4 Internet
access. The service provider can provide such access over a
variety of different transport methods such as DSL, cable,
wireless, and others.
o LLN: Low-power and Lossy Network.
o LQDN: Locally Qualified Domain Name. A name local to the homenet.
o NAT: Network Address Translation. Typically referring to IPv4
Network Address Port Translation (NAPT) [RFC3022].
o NPTv6: IPv6-to-IPv6 Network Prefix Translation [RFC6296].
o PCP: Port Control Protocol [RFC6887].
o Realm: A network delimited by a defined border. A guest network
within a homenet may form one realm.
o 'Simple Security': Defined in [RFC4864] and expanded further in
[RFC6092]; describes recommended perimeter security capabilities
for IPv6 networks.
o ULA: IPv6 Unique Local Address [RFC4193].
o VM: Virtual Machine.
2. Effects of IPv6 on Home Networking
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, it 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
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introduction of IPv6 for home networking that are simultaneously both
promising and problematic.
2.1. Multiple Subnets and Routers
While simple Layer 3 topologies involving as few subnets as possible
are preferred in home networks, the incorporation of dedicated
(routed) subnets remains necessary for a variety of reasons. For
instance, 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 home automation or
corporate extension LANs (whereby a home worker can have their
corporate network extended into the home using a virtual private
network, commonly presented as one port on an Ethernet device) 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 links of much lower capacity thus becomes an
important topic.
The introduction of IPv6 for home networking makes it possible for
every home network to be delegated enough address space from its ISP
to provision globally unique prefixes for each such subnet in the
home. While the number of addresses in a standard /64 IPv6 prefix is
practically unlimited, 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; this topic is
discussed in BCP 157 [RFC6177], which recommends that "end sites
always be able to obtain a reasonable amount of address space for
their actual and planned usage."
The addition of routing between subnets raises a number of issues.
One is a method by which prefixes can be efficiently allocated to
each subnet, without user intervention. Another issue is how to
extend mechanisms such as zero-configuration service discovery that
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 in
Section 3.7.
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2.2. Global Addressability and Elimination of NAT
The possibility for direct end-to-end communication on the Internet
to be restored by the introduction of IPv6 is, on the one hand, an
incredible opportunity for innovation and simpler network operation,
but on the other hand, it is also a concern as it potentially exposes
nodes in the internal networks to receipt of unwanted and possibly
malicious traffic from the Internet.
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 they may simply not be robust by design
because it was assumed that either such devices would only be used on
private networks or the devices don't have the computing power to
apply the necessary security methods. In addition, the upgrade cycle
for devices (or their firmware) may be slow and/or lack auto-update
mechanisms.
It is thus important to distinguish between addressability and
reachability. While IPv6 offers global addressability through the
use of globally unique addresses in the home, whether devices are
globally reachable or not would depend on any 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 CE router. [RFC4864] and [RFC6092] discuss such
filtering and the merits of 'default allow' against 'default deny'
policies for external traffic initiated into a homenet. This topic
is discussed further in Section 3.6.1.
2.3. Multi-Addressing of Devices
In an IPv6 network, devices will often acquire multiple addresses,
typically at least a link-local address and one or more globally
unique addresses (GUAs). Where a homenet is multihomed, a device
would typically receive a GUA 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) [RFC4193]
(see below), and one or more IPv6 privacy addresses [RFC4941].
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. In multihoming scenarios,
nodes will be configured with one address from each upstream ISP
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prefix. In such cases, the presence of upstream ingress filtering as
described in BCP 38 [RFC2827] requires such multi-addressed nodes to
select the correct source address to be used for the corresponding
uplink. Default address selection for IPv6 [RFC6724] provides a
solution for this, but a challenge here is that the node may not have
the information it needs to make that decision based on addresses
alone. We discuss this challenge in Section 3.2.4.
2.4. Unique Local Addresses (ULAs)
[RFC4193] defines ULAs for IPv6 that may be used to address devices
within the scope of a single site. Support for ULAs for IPv6 CE
routers is described in [RFC7084]. 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. A homenet using provider-assigned global addresses is
exposed to its ISP renumbering the network to a much larger degree
than before whereas, for IPv4, NAT isolated the user against ISP
renumbering to some extent.
While setting up a network, there may be a period where it has no
external connectivity, in which case ULAs would be required for
inter-subnet communication. In the case where home automation
networks are being set up in a new home/deployment (as early as
during construction of the home), such networks will likely need to
use their own /48 ULA prefix. Depending upon circumstances beyond
the control of the owner of the homenet, it may be impossible to
renumber the ULA used by the home automation network so routing
between ULA /48s may be required. Also, some devices, particularly
constrained devices, may have only a ULA (in addition to a link-
local), while others may have both a GUA and a ULA.
Note that unlike private IPv4 space as described in RFC 1918, the use
of ULAs does not imply use of an IPv6 equivalent of a traditional
IPv4 NAT [RFC3022] or of NPTv6 prefix-based NAT [RFC6296]. When an
IPv6 node in a homenet has both a ULA and a globally unique IPv6
address, it should only use its ULA address internally and use its
additional globally unique IPv6 address as a source address for
external communications. This should be the natural behaviour given
support for default address selection for IPv6 [RFC6724]. By using
such globally unique addresses between hosts and devices in remote
networks, the architectural cost and complexity, particularly to
applications, of NAT or NPTv6 translation are avoided. As such,
neither IPv6 NAT nor NPTv6 is recommended for use in the homenet
architecture. Further, the homenet border router(s) should filter
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packets with ULA source/destination addresses as discussed in
Section 3.4.2.
Devices in a homenet may be given only a ULA as a means to restrict
reachability from outside the homenet. ULAs can be used by default
for devices that, without additional configuration (e.g., via a web
interface), would only offer services to the internal network. For
example, a printer might only accept incoming connections on a ULA
until configured to be globally reachable, at which point it acquires
a global IPv6 address and may be advertised via a global name space.
Where both a ULA and a global prefix are in use, the ULA source
address is used to communicate with ULA destination addresses when
appropriate, i.e., when the ULA source and destination lie within the
/48 ULA prefix(es) known to be used within the same homenet. In
cases where multiple /48 ULA prefixes are in use within a single
homenet (perhaps because multiple homenet routers each independently
auto-generate a /48 ULA prefix and then share prefix/routing
information), utilising a ULA source address and a ULA destination
address from two disjoint internal ULA prefixes is preferable to
using GUAs.
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.
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 should support and use ULAs.
2.5. Avoiding Manual Configuration of IP Addresses
Some IPv4 home networking devices expose IPv4 addresses to users,
e.g., the IPv4 address of a home IPv4 CE router 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 the 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 are imperative for the easy deployment and use of homenet
devices and applications.
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2.6. IPv6-Only Operation
It is likely that IPv6-only networking will be deployed first in new
home network deployments, often referred to as 'greenfield'
scenarios, where there is no existing IPv4 capability, 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.
Some specific transition technologies that may be deployed by the
homenet's ISP are discussed in [RFC7084]. In addition, certain other
functions may be desirable on the CE router, e.g., to access content
in the IPv4 Internet, NAT64 [RFC6144] and DNS64 [RFC6145] may be
applicable.
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 CE router.
3. Homenet Architecture Principles
The aim of this text is to outline how to construct advanced IPv6-
based home networks involving multiple routers and subnets using
standard IPv6 addressing and protocols [RFC2460] [RFC4291] as the
basis. As described in Section 3.1, solutions should as far as
possible reuse existing protocols and minimise changes to hosts and
routers, but some new protocols or extensions are likely to be
required. In this section, we present the elements of the proposed
home networking architecture with discussion of the associated design
principles.
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.
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The homenet needs to be able to handle or provision at least the
following:
o Routing
o Prefix configuration for routers
o Name resolution
o Service discovery
o Network security
The remainder of this document describes the principles by which the
homenet architecture may deliver these properties.
3.1. General Principles
There is little that the Internet standards community can do about
the physical topologies or the need for some networks to be separated
at the network layer for policy or link-layer compatibility reasons.
However, there is a lot of flexibility in using IP addressing and
internetworking mechanisms. This text discusses how such 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 protocol solutions.
3.1.1. Reuse Existing Protocols
Existing protocols will be used to meet the requirements of home
networks. Where necessary, extensions will be made to those
protocols. When no existing protocol is found to be suitable, a new
or emerging protocol may be used. Therefore, it is important that no
design or architectural decisions be made that would preclude the use
of new or emerging protocols.
A generally conservative approach, giving weight to running (and
available) 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 backward compatible and forward compatible where changes are made.
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3.1.2. Minimise Changes to Hosts and Routers
In order to maximise the deployability of new homenets, any
requirement for changes to hosts and routers should be minimised
where possible; however, solutions that, for example, incrementally
improve capability via host or router changes may be acceptable.
There may be cases where changes are unavoidable, e.g., to allow a
given homenet routing protocol to be self-configuring or to support
routing based on source addresses in addition to destination
addresses (to improve multihoming support, as discussed in
Section 3.2.4).
3.2. Homenet Topology
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.
3.2.1. Supporting Arbitrary Topologies
There should ideally be no built-in assumptions about the topology in
home networks, as users are capable of connecting their devices in
'ingenious' ways. Thus, arbitrary topologies and arbitrary routing
will need to be supported, or at least the failure mode for when the
user makes a mistake should be as robust as possible, e.g.,
deactivating 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.
There should be no topology scenarios that cause a 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.
Topologies that include potential bridging loops can be dangerous but
are also detectable when a switch learns the Media Access Control
(MAC) address of one of its interfaces on another or runs a spanning
tree or link-state protocol. It is only topologies with such
potential loops using simple repeaters that are truly pathological.
The topology of the homenet may change over time, due to the addition
or removal of equipment but also due to temporary failures or
connectivity problems. In some cases, this may lead to, for example,
a multihomed homenet being split into two isolated homenets or, after
such a fault is remedied, two isolated parts reconfiguring back to a
single network.
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3.2.2. Network Topology Models
As hinted above, while the architecture may focus on likely common
topologies, it should not preclude any arbitrary topology from being
constructed.
At the time of writing, most IPv4 home network models tend to be
relatively simple, typically a single NAT router to the ISP and a
single internal subnet but, as discussed earlier, evolution in
network architectures is driving more complex 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.
For IPv6 homenets, the network architectures described in [RFC7084]
should, as a minimum, be supported.
There are a number of properties or attributes of a home network that
we can use to describe its topology and operation. The following
properties apply to any IPv6 home network:
o Presence of internal routers. The homenet may have one or more
internal routers or may only provide subnetting from interfaces on
the CE router.
o 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.
o Demarcation of the CE router. The CE router(s) may or may not be
managed by the ISP. If the demarcation point is such that the
customer can provide or manage the CE router, its configuration
must be simple. Both models must be supported.
Various forms of multihoming are likely to become more prevalent with
IPv6 home networks, where the homenet may have two or more external
ISP connections, as discussed further below. Thus, the following
properties should also be considered for such networks:
o 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.
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o Number of CE routers. The homenet may have a single CE router,
which might be used for one or more providers, or multiple CE
routers. The presence of multiple CE routers adds additional
complexity for multihoming scenarios and protocols like PCP that
may need to manage connection-oriented state mappings on the same
CE router as used for subsequent traffic flows.
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 but rather an indicative one to
facilitate the discussion in this text.
3.2.2.1. A: Single ISP, Single CE Router, and Internal Routers
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 an 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 those with potential loops in them).
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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 | | |
| 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 | /
+----------+ +----------+ +----------+ +----------+ /
Figure 1
In this diagram, there is one CE router. It has a single uplink
interface. It has three additional interfaces connected to Network
A, Link F, and Network B. The 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.
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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 CE router or IPv6 (IR), wireless networks, or
through one or more Ethernet switches that are Layer 2 only.
3.2.2.2. B: Two ISPs, Two CE Routers, and Shared Subnet
+-------+-------+ +-------+-------+ \
| Service | | Service | \
| Provider A | | Provider B | | Service
| Router | | Router | | Provider
+------+--------+ +-------+-------+ | Network
| | /
| Customer | /
| Internet Connections | /
| |
+------+--------+ +-------+-------+ \
| IPv6 | | IPv6 | \
| Customer Edge | | Customer Edge | \
| Router 1 | | Router 2 | /
+------+--------+ +-------+-------+ /
| | /
| | | End-User
---+---------+---+---------------+--+----------+--- | Network(s)
| | | | \
+----+-----+ +-----+----+ +----+-----+ +-----+----+ \
|IPv6 Host | |IPv6 Host | | IPv6 Host| |IPv6 Host | /
| H1 | | H2 | | H3 | | H4 | /
+----------+ +----------+ +----------+ +----------+
Figure 2
Figure 2 illustrates a multihomed homenet model, where the customer
has connectivity via CE router 1 to ISP A and via CE router 2 to ISP
B. This example shows one shared subnet where IPv6 nodes would
potentially be multihomed and receive multiple IPv6 global prefixes,
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 CE router serves a separate isolated subnet, which is a scenario
seen with some IPv4 networks today.
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3.2.2.3. C: Two ISPs, One CE Router, and Shared Subnet
+-------+-------+ +-------+-------+ \
| Service | | Service | \
| Provider A | | Provider B | | Service
| Router | | Router | | Provider
+-------+-------+ +------+--------+ | Network
| | /
| Customer | /
| Internet | /
| Connections |
+-----------+-----------+ \
| IPv6 | \
| Customer Edge | \
| Router | /
+-----------+-----------+ /
| /
| | End-User
---+------------+-------+--------+-------------+--- | Network(s)
| | | | \
+----+-----+ +----+-----+ +----+-----+ +-----+----+ \
|IPv6 Host | |IPv6 Host | | IPv6 Host| |IPv6 Host | /
| H1 | | H2 | | H3 | | H4 | /
+----------+ +----------+ +----------+ +----------+
Figure 3
Figure 3 illustrates a model where a home network may have multiple
connections to multiple providers or multiple logical connections to
the same provider, with shared internal subnets.
3.2.3. Dual-Stack Topologies
For the immediate future, it is expected that most homenet
deployments will be dual-stack IPv4/IPv6. In such networks, it is
important not to introduce new IPv6 capabilities that would cause a
failure if used alongside IPv4+NAT, given that such dual-stack
homenets will be commonplace for some time. That said, it is
desirable that IPv6 works better than IPv4 in as many scenarios as
possible. Further, the homenet architecture must operate in the
absence of IPv4.
A general recommendation is to follow the same topology for IPv6 as
is used for IPv4 but not to use NAT. Thus, there should be routed
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- and lower-speed shared media, and in
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addition, bridging may not be suitable for some networks, such as ad
hoc mobile networks.
In some cases, IPv4 home networks may feature cascaded NATs. End
users are frequently unaware that they have created such networks, as
'home routers' and 'home switches' are frequently confused. In
addition, there are cases where NAT routers are included within
Virtual Machine Hypervisors or where Internet connection-sharing
services have been enabled. This document applies equally to such
hidden NAT 'routers'. IPv6-routed versions of such cases will be
required. We should thus also note that routers in the homenet may
not be separate physical devices; they may be embedded within other
devices.
3.2.4. Multihoming
A homenet may be multihomed to multiple providers, as the network
models above illustrate. This may take a form where there are either
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.
In the general homenet architecture, multihomed 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 [RFC6724].
Applications may of course do different things, and this should not
be precluded.
For the single CE Router Network Model C illustrated above,
multihoming may be offered by source-based routing at the CE router.
With multiple exit routers, as in CE Router 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
ingress filtering as described in BCP 38 if exiting through the wrong
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.
The homenet architecture should support both the above models, i.e.,
one or more CE routers. 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
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homenet architecture should as far as possible minimise the
complexity of any multihoming support.
An example of such a 'simpler' approach has been documented in
[RFC7157]. 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 router and, most
likely, host changes. Another avenue is to introduce support
throughout the homenet for routing that is based on the source as
well as the destination address of each packet. While greatly
improving the 'intelligence' of routing decisions within the homenet,
such an approach would require relatively significant router changes
but avoid host changes.
As explained previously, while NPTv6 has been proposed for providing
multihoming support in networks, its use is not recommended in the
homenet architecture.
It should be noted that some multihoming scenarios may see one
upstream being a "walled garden" and thus only appropriate 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. As per Section 4.2.1 of [RFC3002], we do
not specifically target walled-garden multihoming as a goal of this
document.
The homenet architecture should also not preclude use of host or
application-oriented tools, e.g., Shim6 [RFC5533], Multipath TCP
(MPTCP) [RFC6824], or Happy Eyeballs [RFC6555]. In general, any
incremental improvements obtained by host changes should give benefit
for the hosts introducing them but should not be required.
3.2.5. Mobility Support
Devices may be mobile within the homenet. While resident on the same
subnet, their address will remain persistent, but should devices move
to a different (wireless) subnet, they will acquire a new address in
that subnet. It is desirable that the homenet supports internal
device mobility. To do so, the homenet may either extend the reach
of specific wireless subnets to enable wireless roaming across the
home (availability of a specific subnet across the home) or support
mobility protocols to facilitate such roaming where multiple subnets
are used.
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3.3. A Self-Organising Network
The home network infrastructure 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.
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.
3.3.1. Differentiating Neighbouring Homenets
It is important that self-configuration with 'unintended' devices be
avoided. There should be a way for a user to administratively assert
in a simple way whether or not a device belongs to a given homenet.
The goal is to allow the establishment of borders, particularly
between two adjacent homenets, and to avoid unauthorised devices from
participating in the homenet. Such an authorisation capability may
need to operate through multiple hops in the homenet.
The homenet should thus support a way for a homenet owner to claim
ownership of their devices in a reasonably secure way. This could be
achieved by a pairing mechanism by, for example, pressing buttons
simultaneously on an authenticated and a new homenet device or by an
enrollment process as part of an autonomic networking environment.
While there may be scenarios where one homenet may wish to
intentionally gain access through another, e.g., to share external
connectivity costs, such scenarios are not discussed in this
document.
3.3.2. Largest Practical Subnets
Today's IPv4 home networks generally have a single subnet, and early
dual-stack deployments have a single congruent IPv6 subnet, possibly
with some bridging functionality. More recently, some vendors have
started to introduce 'home' and 'guest' functions, which in IPv6
would be implemented as two subnets.
Future home networks are highly likely to have one or more internal
routers and thus need multiple subnets for the reasons described
earlier. As part of the self-organisation of the network, the
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homenet should subdivide itself into 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. In such subdivisions, the
logical topology may not necessarily match the physical topology.
This text does not, however, make recommendations on how such
subdivision should occur. It is expected that subsequent documents
will address this problem.
While it may be desirable to maximise the chance of link-local
protocols operating across a homenet by maximising the size of a
subnet, multi-subnet home networks are inevitable, so their support
must be included.
3.3.3. Handling Varying Link Technologies
Homenets tend to grow organically over many years, and a homenet will
typically be built over link-layer technologies from different
generations. Current homenets typically use links ranging from 1
Mbit/s up to 1 Gbit/s -- a throughput discrepancy of three orders of
magnitude. We expect this discrepancy to widen further as both high-
speed and low-power technologies are deployed.
Homenet protocols should be designed to deal well with
interconnecting links of very different throughputs. In particular,
flows local to a link should not be flooded throughout the homenet,
even when sent over multicast, and, whenever possible, the homenet
protocols should be able to choose the faster links and avoid the
slower ones.
Links (particularly wireless links) may also have limited numbers of
transmit opportunities (txops), and there is a clear trend driven by
both power and downward compatibility constraints toward aggregation
of packets into these limited txops while increasing throughput.
Transmit opportunities may be a system's scarcest resource and,
therefore, also strongly limit actual throughput available.
3.3.4. Homenet Realms and Borders
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.
A homenet will most likely also have internal borders between
internal realms, e.g., a guest realm or a corporate network extension
realm. It is desirable that appropriate borders can be configured to
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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.
It is expected that a realm would span at least an entire subnet, and
thus the borders lie at routers that receive delegated prefixes
within the homenet. It is also desirable, for a richer security
model, that hosts are able to make communication decisions based on
available realm and associated prefix information in the same way
that routers at realm borders can.
A simple homenet model may just consider three types of realms and
the borders between them, namely the internal homenet, the ISP, and a
guest network. In this case, the borders will include the border
from the homenet to the ISP, the border from the guest network to the
ISP, and the border 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 LLN-based network,
such as Smart Grid, and for these to be detected automatically and
for an appropriate default policy to be applied as to what type of
traffic/data can flow across such borders.
It is desirable to classify the external border of the home network
as a unique logical interface separating the home network from a
service provider network(s). This border interface may be a single
physical interface to a single service provider, multiple Layer 2
sub-interfaces to a single service provider, or multiple connections
to a single or multiple providers. This border makes it possible to
describe edge operations and interface requirements across multiple
functional areas including security, routing, service discovery, and
router discovery.
It should be possible for the homenet user to override any
automatically determined borders and the default policies applied
between them, the exception being that it may not be possible to
override policies defined by the ISP at the external border.
3.3.5. Configuration Information from the ISP
In certain cases, it may be useful for the homenet to get certain
configuration information from its ISP. For example, the homenet
DHCP server may request and forward some options that it gets from
its upstream DHCP server, though the specifics of the options may
vary across deployments. There is potential complexity here, of
course, should the homenet be multihomed.
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3.4. Homenet Addressing
The IPv6 addressing scheme used within a homenet must conform to the
IPv6 addressing architecture [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 and configure the necessary addressing information to
operate.
3.4.1. Use of ISP-Delegated IPv6 Prefixes
Discussion of IPv6 prefix allocation policies is included in
[RFC6177]. In practice, 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; it is generally
expected that ISPs will offer relatively stable prefixes to their
residential customers. Regardless, the home network needs to be
adaptable as far as possible to ISP prefix allocation policies and
assume nothing about the stability of the prefix received from an ISP
or the length of the prefix that may be offered.
However, if, for example, only a /64 is offered by the ISP, the
homenet may be severely constrained or even unable to function. BCP
157 [RFC6177] states the following:
A key principle for address management is that end sites always be
able to obtain a reasonable amount of address space for their
actual and planned usage, and over time ranges specified in years
rather than just months. In practice, that means at least one
/64, and in most cases significantly more. One particular
situation that must be avoided is having an end site feel
compelled to use IPv6-to-IPv6 Network Address Translation or other
burdensome address conservation techniques because it could not
get sufficient address space.
This architecture document assumes that the guidance in the quoted
text is being followed by ISPs.
There are many problems that would arise from a homenet not being
offered a sufficient prefix size for its needs. Rather than attempt
to contrive a method for a homenet to operate in a constrained manner
when faced with insufficient prefixes, such as the use of subnet
prefixes longer than /64 (which would break stateless address
autoconfiguration [RFC4862]), the use of NPTv6, or falling back to
bridging across potentially very different media, it is recommended
that the receiving router instead enters an error state and issues
appropriate warnings. Some consideration may need to be given to how
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such a warning or error state should best be presented to a typical
home user.
Thus, a homenet CE router should request, for example, via DHCP
Prefix Delegation (DHCP PD) [RFC3633], 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, even if in practice it may only
be offered a /56 or /60. For a typical IPv6 homenet, it is not
recommended that an ISP offers less than a /60 prefix, and it is
highly preferable that the ISP offers at least a /56. It is expected
that the allocated prefix to the homenet from any single ISP is a
contiguous, aggregated one. While it may be possible for a homenet
CE router to issue multiple prefix requests to attempt to obtain
multiple delegations, such behaviour is out of scope of this
document.
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
generally support Provider Independent (PI) addressing for
residential homenets.
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 that, unlike the process described in [RFC4192],
would be a 'flag day' event, which means that a graceful renumbering
process moving through a state with two active prefixes in use would
not be possible. While renumbering 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.
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. Similarly, if an ISP has a planned renumbering
process, it may be able to adjust lease timers, etc., appropriately.
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. The homenet may also be forced to renumber itself if
significant internal 'replumbing' is undertaken by the user.
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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.
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.
3.4.2. Stable Internal IP Addresses
The network should by default attempt to provide IP-layer
connectivity between all internal parts of the homenet as well as to
and from the external Internet, subject to the filtering policies or
other policy constraints discussed later in the security section.
ULAs should be used within the scope of a homenet to support stable
routing and connectivity between subnets and hosts regardless of
whether a globally unique ISP-provided prefix is available. In the
case of a prolonged external connectivity outage, ULAs allow internal
operations across routed subnets to continue. ULA addresses also
allow constrained devices to create permanent relationships between
IPv6 addresses, e.g., from a wall controller to a lamp, where
symbolic host names would require additional non-volatile memory, and
updating global prefixes in sleeping devices might also be
problematic.
As discussed previously, it would be expected that ULAs would
normally be used alongside one or more 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.
In cases where ULA prefixes are in use within a homenet but there is
no external IPv6 connectivity (and thus no GUAs in use),
recommendations ULA-5, L-3, and L-4 in RFC 7084 should be followed to
ensure correct operation, in particular where the homenet may be dual
stack with IPv4 external connectivity. The use of the Route
Information Option described in [RFC4191] provides a mechanism to
advertise such more-specific ULA routes.
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The use of ULAs should be restricted to the homenet scope through
filtering at the border(s) of the homenet, as mandated by RFC 7084
requirement S-2.
Note that in some cases, it is possible that 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. In cases where multiple ULA /48s 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.
3.4.3. Internal Prefix Delegation
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 CE router [RFC3633]. Where multiple CE
routers 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
should be provisioned for stable internal communications or for use
on constrained/LLN networks.
The delegation or availability of a prefix pool to the homenet should
allow subsequent internal autonomous assignment of prefixes for use
within the homenet. Such internal assignment should not assume a
flat or hierarchical model, nor should it make an assumption about
whether the assignment 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).
Where the home network has multiple CE routers and these are
delegated prefix pools from their attached ISPs, the internal prefix
assignment would be expected to be served by each CE router for each
prefix associated with it. Where ULAs are used, it is preferable
that only one /48 ULA covers the whole homenet, from which /64s can
be assigned to the 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.
Prefix assignment within the homenet should result in each link being
assigned a stable prefix that is persistent across reboots, power
outages, and similar short-term outages. The availability of
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persistent prefixes should not depend on the router boot order. The
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. However, assigned ULA
prefixes within the homenet should remain persistent through an ISP-
driven renumbering event.
Provisioning 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).
This document makes no specific recommendation towards solutions but
notes that it is very likely that all routing devices participating
in a homenet must use the same internal prefix delegation method.
This implies that only one delegation method should be in use.
3.4.4. Coordination of Configuration Information
The network elements will need to be integrated in a way that takes
account of the various lifetimes on timers that are used on different
elements, e.g., DHCPv6 PD, router, valid prefix, and preferred prefix
timers.
3.4.5. Privacy
If ISPs offer relatively stable IPv6 prefixes to customers, the
network prefix part of addresses associated with the homenet may not
change over a reasonably long period of time.
The exposure of which traffic is sourced from the same homenet is
thus similar to IPv4; the single IPv4 global address seen through use
of IPv4 NAT gives the same hint as the global IPv6 prefix seen for
IPv6 traffic.
While IPv4 NAT may obfuscate to an external observer which internal
devices traffic is sourced from, IPv6, even with use of privacy
addresses [RFC4941], adds additional exposure of which traffic is
sourced from the same internal device through use of the same IPv6
source address for a period of time.
3.5. Routing Functionality
Routing functionality is required when there are multiple routers
deployed within the internal home network. This functionality could
be as simple as the current 'default route is up' model of IPv4 NAT,
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or more likely, it would involve running an appropriate routing
protocol.
A mechanism is required to discover which router(s) in the homenet is
providing the CE router function. Borders may include but are not
limited to the interface to the upstream ISP, a gateway device to a
separate home network such as an LLN network, or a gateway to a guest
or private corporate extension network. In some cases, there may be
no border present, which may, for example, occur before an upstream
connection has been established.
The routing environment should be self-configuring, as discussed
previously. The homenet self-configuration process and the routing
protocol must interact in a predictable manner, especially during
startup and reconvergence. The border discovery functionality and
other self-configuration functionality may be integrated into the
routing protocol itself but may also be imported via a separate
discovery mechanism.
It is preferable that configuration information is distributed and
synchronised within the homenet by a separate configuration protocol.
The homenet routing protocol should be based on a previously deployed
protocol that has been shown to be reliable and robust. This does
not preclude the selection of a newer protocol for which a high-
quality open source implementation becomes available. The resulting
code must support lightweight implementations and be suitable for
incorporation into consumer devices, where both fixed and temporary
storage and processing power are at a premium.
At most, one unicast and one multicast routing protocol should be in
use at a given time in a given homenet. In some simple topologies,
no routing protocol may be needed. If more than one routing protocol
is supported by routers in a given homenet, then a mechanism is
required to ensure that all routers in that homenet use the same
protocol.
The homenet architecture is IPv6-only. In practice, dual-stack
homenets are still likely for the foreseeable future, as described in
Section 3.2.3. Whilst support for IPv4 and other address families
may therefore be beneficial, it is not an explicit requirement to
carry the routing information in the same routing protocol.
Multiple types of physical interfaces must be accounted for in the
homenet routing topology. Technologies such as Ethernet, Wi-Fi,
Multimedia over Coax Alliance (MoCA), etc., must be capable of
coexisting in the same environment and should be treated as part of
any routed deployment. The inclusion of physical-layer
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characteristics in path computation should be considered for
optimising communication in the homenet.
3.5.1. Unicast Routing within the Homenet
The role of the unicast routing protocol is to provide good enough
end-to-end connectivity often enough, where good/often enough is
defined by user expectations.
Due to the use of a variety of diverse underlying link technologies,
path selection in a homenet may benefit from being more refined than
minimising hop count. It may also be beneficial for traffic to use
multiple paths to a given destination within the homenet where
available rather than just a single best path.
Minimising convergence time should be a goal in any routed
environment. It is reasonable to assume that convergence time should
not be significantly longer than network outages users are accustomed
to should their CE router reboot.
The homenet architecture is agnostic as to the choice of underlying
routing technology, e.g., link state versus Bellman-Ford.
The routing protocol should support the generic use of multiple
customer Internet connections and the concurrent use of multiple
delegated prefixes. A routing protocol that can make routing
decisions based on source and destination addresses is thus highly
desirable, to avoid problems with upstream ISP ingress filtering as
described in BCP 38. Multihoming support may also include load
balancing to multiple providers and failover from a primary to a
backup link when available. The protocol should not require upstream
ISP connectivity to be established to continue routing within the
homenet.
The homenet architecture is agnostic on a minimum hop count that has
to be supported by the routing protocol. The architecture should,
however, be scalable to other scenarios where homenet technology may
be deployed, which may include small office and small enterprise
sites. To allow for such cases, it would be desirable that the
architecture is scalable to higher hop counts and to larger numbers
of routers than would be typical in a true home network.
At the time of writing, link-layer networking technology is poised to
become more heterogeneous, as networks begin to employ both
traditional Ethernet technology and link layers designed for LLNs,
such as those used for certain types of sensor devices.
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Ideally, LLN or other logically separate networks should be able to
exchange routes such that IP traffic may be forwarded among the
networks via gateway routers that interoperate with both the homenet
and any LLNs. Current home deployments use largely different
mechanisms in sensor and basic Internet connectivity networks. IPv6
virtual machine (VM) solutions may also add additional routing
requirements.
In this homenet architecture, LLNs and other specialised networks are
considered stub areas of the homenet and are thus not expected to act
as a transit for traffic between more traditional media.
3.5.2. Unicast Routing at the Homenet Border
The current practice defined in [RFC7084] would suggest that routing
between the homenet CE router and the service provider router follow
the WAN-side requirements model in [RFC7084], Section 4 (WAN-side
requirements), at least in initial deployments. However,
consideration of whether a routing protocol is used between the
homenet CE router and the service provider router is out of scope of
this document.
3.5.3. Multicast Support
It is desirable that, subject to the capacities of devices on certain
media types, multicast routing is supported across the homenet,
including source-specific multicast (SSM) [RFC4607].
[RFC4291] requires that any boundary of scope 4 or higher (i.e.,
admin-local or higher) be administratively configured. Thus, the
boundary at the homenet-ISP border must be administratively
configured, though that may be triggered by an administrative
function such as DHCP PD. Other multicast forwarding policy borders
may also exist within the homenet, e.g., to/from a guest subnet,
whilst the use of certain link media types may also affect where
specific multicast traffic is forwarded or routed.
There may be different drivers for multicast to be supported across
the homenet -- for example,
o for homenet-wide service discovery, should a multicast service
discovery protocol of scope greater than link-local be defined
o for multicast-based streaming or file-sharing 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. As hinted above, it must be
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possible to scope or filter multicast traffic to avoid it being
flooded to network media where devices cannot reasonably support it.
A homenet may not only use multicast internally, it may also be a
consumer or provider of external multicast traffic, where the
homenet's ISP supports such multicast operation. This may be
valuable, for example, where live video applications are being
sourced to/from the homenet.
The multicast environment should support the ability for applications
to pick a unique multicast group to use.
3.6. Security
The security of an IPv6 homenet is an important consideration. The
most notable difference to the IPv4 operational model is the removal
of NAT, the introduction of global addressability of devices, and
thus a need to consider whether devices should have global
reachability. Regardless, hosts need to be able to operate securely,
end to end where required, and also be robust against malicious
traffic directed towards them. However, there are other challenges
introduced, e.g., default filtering policies at the borders between
various homenet realms.
3.6.1. Addressability vs. Reachability
An IPv6-based home network architecture should embrace the
transparent end-to-end communications model as described in
[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.
[RFC4864] describes a 'Simple Security' model for IPv6 networks,
whereby stateful perimeter filtering can be applied to control the
reachability of devices in a homenet. RFC 4864 states in Section 4.2
that "the use of firewalls...is recommended for those that want
boundary protection in addition to host defences." It should be
noted that a 'default deny' filtering 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, e.g., a
protocol such as PCP [RFC6887]. In networks with multiple CE
routers, the signalling would need to handle the cases of flows that
may use one or more exit routers. CE routers would need to be able
to advertise their existence for such protocols.
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[RFC6092] expands on RFC 4864, giving a more detailed discussion of
IPv6 perimeter security recommendations, without mandating a 'default
deny' approach. Indeed, RFC 6092 does not enforce a particular mode
of operation, instead stating that CE routers must provide an easily
selected configuration option that permits a 'transparent' mode, thus
ensuring a 'default allow' model is available.
The topic of whether future home networks as described in this
document should have a 'default deny' or 'default allow' position has
been discussed at length in various IETF meetings without any
consensus being reached on which approach is more appropriate.
Further, the choice of which default to apply may be situational, and
thus this text makes no recommendation on the default setting beyond
what is written on this topic in RFC 6092. We note in Section 3.6.3
below that the implicit firewall function of an IPv4 NAT is
commonplace today, and thus future CE routers targeted at home
networks should continue to support the option of running in 'default
deny mode', whether or not that is the default setting.
3.6.2. Filtering at Borders
It is desirable that there are mechanisms to detect different types
of borders within the homenet, as discussed previously, and 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.
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 a guest network
subnet(s). As a result, some scenarios/models may involve running an
isolated subnet(s) with their own CE routers. In such cases,
connectivity would only be expected within each isolated network
(though traffic may potentially pass between them via external
providers).
LLNs provide 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.
Considerations for differentiating neighbouring homenets are
discussed in Section 3.3.1.
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3.6.3. Partial Effectiveness of NAT and Firewalls
Security by way of obscurity (address translation) or through
firewalls (filtering) is at best only partially effective. The very
poor security track record of home computers, home networking, and
business PC computers and networking is testimony to this. A
security 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.
However, given current evidence of home network products with very
poor default device security, putting a firewall in place does
provide some level of protection. The use of firewalls today,
whether a good practice or not, is common practice, and the
capability to afford protection via a 'default deny' setting, even if
marginally effective, should not be lost. Thus, while it is highly
desirable that all hosts in a homenet be adequately protected by
built-in security functions, it should also be assumed that all CE
routers will continue to support appropriate perimeter defence
functions, as per [RFC7084].
3.6.4. Exfiltration Concerns
As homenets become more complex, with more devices, and with service
discovery potentially enabled across the whole home, there are
potential concerns over the leakage of information should devices use
discovery protocols to gather information and report it to equipment
vendors or application service providers.
While it is not clear how such exfiltration could be easily avoided,
the threat should be recognised, be it from a new piece of hardware
or some 'app' installed on a personal device.
3.6.5. Device Capabilities
In terms of the devices, homenet hosts should implement their own
security policies in accordance to their computing capabilities.
They should have the means to request transparent communications that
can be initiated to them through security filters in the homenet, for
either all ports or specific services. Users should have simple
methods to associate devices to services that they wish to operate
transparently through (CE router) borders.
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3.6.6. ULAs as a Hint of Connection Origin
As noted in Section 3.6, if appropriate filtering is in place on the
CE router(s), as mandated by requirement S-2 in RFC 7084, a ULA
source address may be taken as an indication of locally sourced
traffic. This indication 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.
3.7. Naming and Service Discovery
The homenet requires devices to be able to determine and use unique
names by which they can be accessed on the network and that are not
used by other devices on the network. Users and devices will need to
be able to discover devices and services available on the network,
e.g., media servers, printers, displays, or specific home automation
devices. Thus, naming and service discovery must be supported in the
homenet, and given the nature of typical home network users, the
service(s) providing this function must as far as possible support
unmanaged operation.
The naming system will be required to work internally or externally,
whether the user is within or outside of the homenet, 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. Remote access may be desired by
the homenet residents while travelling but also potentially by
manufacturers or other 'benevolent' third parties.
3.7.1. Discovering Services
Users will typically perform service discovery through graphical user
interfaces (GUIs) that allow them to browse services on their network
in an appropriate and intuitive way. Devices may also need to
discover other devices, without any user intervention or choice.
Either way, such interfaces are beyond the scope of this document,
but the interface should have an appropriate application programming
interface (API) for the discovery to be performed.
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.
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We note that current zero-configuration 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 packets entering looping paths, or extending the scope of
multicast traffic used for the purpose. It may mean that some proxy
or hybrid service is utilised, perhaps co-resident on the CE router.
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). However, we
should prefer approaches that are backward compatible and allow
current implementations to continue to be used. Note that this
document does not mandate a particular solution; rather, it expresses
the principles that should be used for a homenet naming and service
discovery environment.
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 through either a standards-based
translation scheme, hooks into current protocols to allow some form
of communication among discovery protocols, extensions to support a
central service repository in the homenet, or simply convergence
towards a unified protocol suite.
3.7.2. Assigning Names to Devices
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 a new subnet is added
to the homenet that already has a device of the same name. It is
expected that a device should have a fixed name while within the
scope of the homenet.
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 that 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 it may be distinct from the name used in a name
service, e.g., 'Study Laser Printer' as opposed to
printer2.<somedomain>.
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3.7.3. The Homenet Name Service
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.
It is highly desirable that the homenet name service must at the very
least coexist 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 Multicast
DNS (mDNS) [RFC6762].
When DNS is used as the homenet name service, it typically includes
both a resolving service and an authoritative service. The
authoritative service hosts the homenet-related zone. One approach
when provisioning such a name service, which is designed to
facilitate name resolution from the global Internet, is to run an
authoritative name service on the CE router and a secondary
authoritative name service provided by the ISP or perhaps an external
third party.
Where zero-configuration name services are used, it is desirable that
these can also coexist with the Internet name service. In
particular, where the homenet is using a global name space, it is
desirable that devices have the ability, where desired, to add
entries to that name space. There should also be a mechanism for
such entries to be removed or expired from the global name space.
To protect against attacks such as cache poisoning, where an attacker
is able to insert a bogus DNS entry in the local cache, it is
desirable to support appropriate name service security methods,
including DNS Security Extensions (DNSSEC) [RFC4033], on both the
authoritative server and the resolver sides. Where DNS is used, the
homenet router or naming service must not prevent DNSSEC from
operating.
While this document does not specify hardware requirements, it is
worth noting briefly here that, e.g., in support of DNSSEC,
appropriate homenet devices should have good random number generation
capability, and future homenet specifications should indicate where
high-quality random number generators, i.e., with decent entropy, are
needed.
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Finally, the impact of a change in the CE router must be considered.
It would be desirable to retain any relevant state (configuration)
that was held in the old CE router. This might imply that state
information should be distributed in the homenet, to be recoverable
by/to the new CE router, or to the homenet's ISP or a third-party
externally provided service by some means.
3.7.4. Name Spaces
If access to homenet devices is required remotely from anywhere on
the Internet, then at least one globally unique name space is
required, though the use of multiple name spaces should not be
precluded. One approach is that the name space(s) used for the
homenet would be served authoritatively by the homenet, most likely
by a server resident on the CE router. Such name spaces may be
acquired by the user or provided/generated by their ISP or an
alternative externally provided service. It is likely 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. For users wanting to use
their own independent domain names, such services are already
available.
Devices may also be assigned different names in different name
spaces, e.g., by third parties who may manage systems or devices in
the homenet on behalf of the resident(s). Remote management of the
homenet is out of scope of this document.
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 that have link-local
scope and is thus not appropriate for multi-subnet home networks. A
different name space is thus required for the homenet.
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 name by an application in one homenet to be
confused with a device with the same name in another homenet. In
practice, however, 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.
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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 CE router or device
running the name service should generate a default value. It would
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. Any generated <UniqueString>
should not be predictable; thus, adding a salt/hash function would be
desirable.
In the (likely) event that the homenet is accessible from outside the
homenet (using the global name space), it is vital that the homenet
name space follow the rules and conventions of the global name space.
In this mode of operation, names in the homenet (including those
automatically generated by devices) must be usable as labels in the
global name space. [RFC5890] describes considerations for
Internationalizing Domain Names in Applications (IDNA).
Also, 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 Generic Top
Level Domain (gTLD). Thus, qualified names should always be used,
whether these are exposed to the user or not. The IAB has issued a
statement that explains why dotless domains should be considered
harmful [IABdotless].
There may be use cases where different name spaces may be desired for
either different realms in the homenet or segmentation of a single
name space within the homenet. Thus, hierarchical name space
management is likely to be required. There should also be nothing to
prevent an individual device(s) from being independently registered
in external name spaces.
It may be the case that if there are two or more CE routers serving
the home network, if each has a name space delegated from a different
ISP, there is the potential for devices in the home to have multiple
fully qualified names under multiple domains.
Where a user is 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 multiple associated name spaces exist.
This also implies that a domain discovery function is desirable.
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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'
(as described in [RFC6950], Section 4) is preferred for certain
devices, whereby devices inside the homenet see different DNS
responses to those outside.
Finally, 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. There are
also some services, most notably email mail exchangers, where some
operators have chosen to require a valid reverse lookup before
accepting connections.
3.7.5. Independent Operation
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 that 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.
As described above, the approach of a local authoritative name
service with a cache would allow local operation for sustained ISP
outages.
Having an independent local trust anchor is desirable, to support
secure exchanges should external connectivity be unavailable.
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.
3.7.6. Considerations for LLNs
In some parts of the homenet, in particular LLNs or any devices where
battery power is used, 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 devices or 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
and constrained devices that the service may need to operate over.
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There are efforts underway to determine naming and discovery
solutions for use by the Constrained Application Protocol (CoAP)
[RFC7252] in LLN networks. These are outside the scope of this
document.
3.7.7. DNS Resolver Discovery
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, it may be desirable to
convey any DNS domain search list that may be in effect for the
homenet.
3.7.8. Devices Roaming to/from the Homenet
It is likely that some devices that have registered names within the
homenet Internet name space and that are mobile will attach to the
Internet at other locations and acquire an IP address at those
locations. Devices may move between different homenets. In such
cases, it is desirable that devices may be accessed by the same name
as is used in their home network.
Solutions to this problem are not discussed in this document. They
may include the use of Mobile IPv6 or Dynamic DNS -- either of which
would put additional requirements on the homenet -- or establishment
of a (VPN) tunnel to a server in the home network.
3.8. Other Considerations
This section discusses two other considerations for home networking
that the architecture should not preclude but that this text is
neutral towards.
3.8.1. Quality of Service
Support for Quality of Service (QoS) in a multi-service homenet may
be a requirement, e.g., for a critical system (perhaps health care
related) or for differentiation between different types of traffic
(file sharing, cloud storage, live streaming, Voice over IP (VoIP),
etc). Different link media types may have different such properties
or capabilities.
However, homenet scenarios should require no new QoS protocols. A
Diffserv [RFC2475] approach with a small number of predefined traffic
classes 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
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CE router and potentially around boundaries between different link
media types (where, for example, some traffic may simply not be
appropriate for some media and need to be dropped to avoid
overloading the constrained media).
There may also be complementary mechanisms that could be beneficial
to application performance and behaviour in the homenet domain, such
as ensuring proper buffering algorithms are used as described in
[Gettys11].
3.8.2. Operations and Management
In this section, we briefly review some initial considerations for
operations and management in the type of homenet described in this
document. It is expected that a separate document will define an
appropriate operations and management framework for such homenets.
As described in this document, the homenet should have the general
goal of being self-organising and self-configuring from the network-
layer perspective, e.g., prefixes should be able to be assigned to
router interfaces. Further, applications running on devices should
be able to use zero-configuration service discovery protocols to
discover services of interest to the home user. In contrast, a home
user would not be expected, for example, to have to assign prefixes
to links or manage the DNS entries for the home network. Such expert
operation should not be precluded, but it is not the norm.
The user may still be required to, or wish to, perform some
configuration of the network and the devices on it. Examples might
include entering a security key to enable access to their wireless
network or choosing to give a 'friendly name' to a device presented
to them through service discovery. Configuration of link- and
application-layer services is out of scope of this architectural
principles document but is likely to be required in an operational
homenet.
While not being expected to actively configure the networking
elements of their homenet, users may be interested in being able to
view the status of their networks and the devices connected to it, in
which case appropriate network monitoring protocols will be required
to allow them to view their network, and its status, e.g., via a web
interface or equivalent. While the user may not understand how the
network operates, it is reasonable to assume they are interested in
understanding what faults or problems may exist on it. Such
monitoring may extend to other devices on the network, e.g., storage
devices or web cameras, but such devices are beyond the scope of this
document.
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It may also be the case that an ISP, or a third party, might wish to
offer a remote management service for the homenet on behalf of the
user, or to be able to assist the user in the event of some problem
they are experiencing, in which case appropriate management and
monitoring protocols would be required.
Specifying the required protocols to facilitate homenet management
and monitoring is out of scope of this document. As stated above, it
is expected that a separate document will be produced to describe the
operations and management framework for the types of home networks
presented in this document.
As a final point, we note that it is desirable that all network
management and monitoring functions should be available over IPv6
transport, even where the homenet is dual stack.
3.9. Implementing the Architecture on IPv6
This architecture text encourages reuse of existing protocols. Thus,
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 solutions can be found
based on existing protocols. Some relatively smaller updates are
likely to be required, e.g., a new mechanism may be needed in order
to turn a selected protocol on by default, or a mechanism may be
required to automatically assign prefixes to links within the
homenet.
Some functionality, if required by the architecture, may need more
significant changes or require development of new protocols, e.g.,
support for multihoming with multiple exit routers would likely
require extensions to support source and destination address-based
routing within the homenet.
Some protocol changes are, however, required in the architecture,
e.g., for name resolution and service discovery, extensions to
existing zero-configuration link-local name resolution protocols are
needed to enable them to work across subnets, within the scope of the
home network site.
Some of the hardest problems in developing solutions for home
networking IPv6 architectures include discovering the right borders
where the '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
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ability to turn on routing, prefix delegation, and other functions in
a backwards-compatible manner.
4. Conclusions
This text defines principles and requirements for a homenet
architecture. The principles and requirements documented here should
be observed by any future texts describing homenet protocols for
routing, prefix management, security, naming, or service discovery.
5. Security Considerations
Security considerations for the homenet architecture are discussed in
Section 3.6 above.
6. References
6.1. Normative References
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998,
<http://www.rfc-editor.org/info/rfc2460>.
[RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
Host Configuration Protocol (DHCP) version 6", RFC 3633,
December 2003, <http://www.rfc-editor.org/info/rfc3633>.
[RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
Addresses", RFC 4193, October 2005,
<http://www.rfc-editor.org/info/rfc4193>.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, February 2006,
<http://www.rfc-editor.org/info/rfc4291>.
6.2. Informative References
[RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
E. Lear, "Address Allocation for Private Internets", BCP
5, RFC 1918, February 1996,
<http://www.rfc-editor.org/info/rfc1918>.
[RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.,
and W. Weiss, "An Architecture for Differentiated
Services", RFC 2475, December 1998,
<http://www.rfc-editor.org/info/rfc2475>.
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[RFC2775] Carpenter, B., "Internet Transparency", RFC 2775, February
2000, <http://www.rfc-editor.org/info/rfc2775>.
[RFC2827] Ferguson, P. and D. Senie, "Network Ingress Filtering:
Defeating Denial of Service Attacks which employ IP Source
Address Spoofing", BCP 38, RFC 2827, May 2000,
<http://www.rfc-editor.org/info/rfc2827>.
[RFC3002] Mitzel, D., "Overview of 2000 IAB Wireless Internetworking
Workshop", RFC 3002, December 2000,
<http://www.rfc-editor.org/info/rfc3002>.
[RFC3022] Srisuresh, P. and K. Egevang, "Traditional IP Network
Address Translator (Traditional NAT)", RFC 3022, January
2001, <http://www.rfc-editor.org/info/rfc3022>.
[RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "DNS Security Introduction and Requirements", RFC
4033, March 2005,
<http://www.rfc-editor.org/info/rfc4033>.
[RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and
More-Specific Routes", RFC 4191, November 2005,
<http://www.rfc-editor.org/info/rfc4191>.
[RFC4192] Baker, F., Lear, E., and R. Droms, "Procedures for
Renumbering an IPv6 Network without a Flag Day", RFC 4192,
September 2005, <http://www.rfc-editor.org/info/rfc4192>.
[RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for
IP", RFC 4607, August 2006,
<http://www.rfc-editor.org/info/rfc4607>.
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862, September 2007,
<http://www.rfc-editor.org/info/rfc4862>.
[RFC4864] Van de Velde, G., Hain, T., Droms, R., Carpenter, B., and
E. Klein, "Local Network Protection for IPv6", RFC 4864,
May 2007, <http://www.rfc-editor.org/info/rfc4864>.
[RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy
Extensions for Stateless Address Autoconfiguration in
IPv6", RFC 4941, September 2007,
<http://www.rfc-editor.org/info/rfc4941>.
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[RFC5533] Nordmark, E. and M. Bagnulo, "Shim6: Level 3 Multihoming
Shim Protocol for IPv6", RFC 5533, June 2009,
<http://www.rfc-editor.org/info/rfc5533>.
[RFC5890] Klensin, J., "Internationalized Domain Names for
Applications (IDNA): Definitions and Document Framework",
RFC 5890, August 2010,
<http://www.rfc-editor.org/info/rfc5890>.
[RFC5969] Townsley, W. and O. Troan, "IPv6 Rapid Deployment on IPv4
Infrastructures (6rd) -- Protocol Specification", RFC
5969, August 2010,
<http://www.rfc-editor.org/info/rfc5969>.
[RFC6092] Woodyatt, J., "Recommended Simple Security Capabilities in
Customer Premises Equipment (CPE) for Providing
Residential IPv6 Internet Service", RFC 6092, January
2011, <http://www.rfc-editor.org/info/rfc6092>.
[RFC6144] Baker, F., Li, X., Bao, C., and K. Yin, "Framework for
IPv4/IPv6 Translation", RFC 6144, April 2011,
<http://www.rfc-editor.org/info/rfc6144>.
[RFC6145] Li, X., Bao, C., and F. Baker, "IP/ICMP Translation
Algorithm", RFC 6145, April 2011,
<http://www.rfc-editor.org/info/rfc6145>.
[RFC6177] Narten, T., Huston, G., and L. Roberts, "IPv6 Address
Assignment to End Sites", BCP 157, RFC 6177, March 2011,
<http://www.rfc-editor.org/info/rfc6177>.
[RFC6204] Singh, H., Beebee, W., Donley, C., Stark, B., and O.
Troan, "Basic Requirements for IPv6 Customer Edge
Routers", RFC 6204, April 2011,
<http://www.rfc-editor.org/info/rfc6204>.
[RFC6296] Wasserman, M. and F. Baker, "IPv6-to-IPv6 Network Prefix
Translation", RFC 6296, June 2011,
<http://www.rfc-editor.org/info/rfc6296>.
[RFC6333] Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual-
Stack Lite Broadband Deployments Following IPv4
Exhaustion", RFC 6333, August 2011,
<http://www.rfc-editor.org/info/rfc6333>.
[RFC6555] Wing, D. and A. Yourtchenko, "Happy Eyeballs: Success with
Dual-Stack Hosts", RFC 6555, April 2012,
<http://www.rfc-editor.org/info/rfc6555>.
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[RFC6724] Thaler, D., Draves, R., Matsumoto, A., and T. Chown,
"Default Address Selection for Internet Protocol Version 6
(IPv6)", RFC 6724, September 2012,
<http://www.rfc-editor.org/info/rfc6724>.
[RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
February 2013, <http://www.rfc-editor.org/info/rfc6762>.
[RFC6824] Ford, A., Raiciu, C., Handley, M., and O. Bonaventure,
"TCP Extensions for Multipath Operation with Multiple
Addresses", RFC 6824, January 2013,
<http://www.rfc-editor.org/info/rfc6824>.
[RFC6887] Wing, D., Cheshire, S., Boucadair, M., Penno, R., and P.
Selkirk, "Port Control Protocol (PCP)", RFC 6887, April
2013, <http://www.rfc-editor.org/info/rfc6887>.
[RFC6950] Peterson, J., Kolkman, O., Tschofenig, H., and B. Aboba,
"Architectural Considerations on Application Features in
the DNS", RFC 6950, October 2013,
<http://www.rfc-editor.org/info/rfc6950>.
[RFC7084] Singh, H., Beebee, W., Donley, C., and B. Stark, "Basic
Requirements for IPv6 Customer Edge Routers", RFC 7084,
November 2013, <http://www.rfc-editor.org/info/rfc7084>.
[RFC7157] Troan, O., Miles, D., Matsushima, S., Okimoto, T., and D.
Wing, "IPv6 Multihoming without Network Address
Translation", RFC 7157, March 2014,
<http://www.rfc-editor.org/info/rfc7157>.
[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252, June 2014,
<http://www.rfc-editor.org/info/rfc7252>.
[IABdotless]
IAB, "IAB Statement: Dotless Domains Considered Harmful",
February 2013, <http://www.iab.org/documents/
correspondence-reports-documents/2013-2/
iab-statement-dotless-domains-considered-harmful>.
[Gettys11]
Gettys, J., "Bufferbloat: Dark Buffers in the Internet",
March 2011,
<http://www.ietf.org/proceedings/80/slides/tsvarea-1.pdf>.
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Acknowledgments
The authors would like to thank Mikael Abrahamsson, Aamer Akhter,
Mark Andrews, Dmitry Anipko, Ran Atkinson, Fred Baker, Ray Bellis,
Teco Boot, John Brzozowski, Cameron Byrne, Brian Carpenter, Stuart
Cheshire, Julius Chroboczek, Lorenzo Colitti, Robert Cragie, Elwyn
Davies, 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, Markus Stenberg, Don Sturek,
Andrew Sullivan, Dave Taht, Dave Thaler, Michael Thomas, Mark
Townsley, JP Vasseur, Curtis Villamizar, Russ White, Dan Wing, and
James Woodyatt for their comments and contributions within homenet WG
meetings and on the WG mailing list. An acknowledgment generally
means that a person's text made it into the document or was helpful
in clarifying or reinforcing an aspect of the document. It does not
imply that each contributor agrees with every point in the document.
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Authors' Addresses
Tim Chown (editor)
University of Southampton
Highfield
Southampton, Hampshire SO17 1BJ
United Kingdom
EMail: tjc@ecs.soton.ac.uk
Jari Arkko
Ericsson
Jorvas 02420
Finland
EMail: jari.arkko@piuha.net
Anders Brandt
Sigma Designs
Emdrupvej 26A, 1
Copenhagen DK-2100
Denmark
EMail: anders_brandt@sigmadesigns.com
Ole Troan
Cisco Systems, Inc.
Philip Pedersensvei 1
Lysaker, N-1325
Norway
EMail: ot@cisco.com
Jason Weil
Time Warner Cable
13820 Sunrise Valley Drive
Herndon, VA 20171
United States
EMail: jason.weil@twcable.com
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