Internet DRAFT - draft-ietf-homenet-arch
draft-ietf-homenet-arch
Network Working Group T. Chown, Ed.
Internet-Draft University of Southampton
Intended status: Informational J. Arkko
Expires: January 5, 2015 Ericsson
A. Brandt
Sigma Designs
O. Troan
Cisco Systems, Inc.
J. Weil
Time Warner Cable
July 4, 2014
IPv6 Home Networking Architecture Principles
draft-ietf-homenet-arch-17
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 Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 5, 2015.
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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
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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 . . . . . . . . 12
3.2. Homenet Topology . . . . . . . . . . . . . . . . . . . . 13
3.2.1. Supporting arbitrary topologies . . . . . . . . . . . 13
3.2.2. Network topology models . . . . . . . . . . . . . . . 13
3.2.3. Dual-stack topologies . . . . . . . . . . . . . . . . 18
3.2.4. Multihoming . . . . . . . . . . . . . . . . . . . . . 19
3.2.5. Mobility support . . . . . . . . . . . . . . . . . . 20
3.3. A Self-Organising Network . . . . . . . . . . . . . . . . 20
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 . . . . . . . . . . . . . . . . . . . 23
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 . . . . . . . . . 29
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 . . . . . 33
3.6.4. Exfiltration concerns . . . . . . . . . . . . . . . . 34
3.6.5. Device capabilities . . . . . . . . . . . . . . . . . 34
3.6.6. ULAs as a hint of connection origin . . . . . . . . . 34
3.7. Naming and Service Discovery . . . . . . . . . . . . . . 34
3.7.1. Discovering services . . . . . . . . . . . . . . . . 35
3.7.2. Assigning names to devices . . . . . . . . . . . . . 36
3.7.3. The homenet name service . . . . . . . . . . . . . . 36
3.7.4. Name spaces . . . . . . . . . . . . . . . . . . . . . 37
3.7.5. Independent operation . . . . . . . . . . . . . . . . 39
3.7.6. Considerations for LLNs . . . . . . . . . . . . . . . 40
3.7.7. DNS resolver discovery . . . . . . . . . . . . . . . 40
3.7.8. Devices roaming to/from the homenet . . . . . . . . . 40
3.8. Other Considerations . . . . . . . . . . . . . . . . . . 41
3.8.1. Quality of Service . . . . . . . . . . . . . . . . . 41
3.8.2. Operations and Management . . . . . . . . . . . . . . 41
3.9. Implementing the Architecture on IPv6 . . . . . . . . . . 42
4. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 43
5. Security Considerations . . . . . . . . . . . . . . . . . . . 43
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 43
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 43
7.1. Normative References . . . . . . . . . . . . . . . . . . 43
7.2. Informative References . . . . . . . . . . . . . . . . . 44
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . 47
Appendix B. Changes . . . . . . . . . . . . . . . . . . . . . . 47
B.1. Version 17 . . . . . . . . . . . . . . . . . . . . . . . 47
B.2. Version 16 . . . . . . . . . . . . . . . . . . . . . . . 47
B.3. Version 15 . . . . . . . . . . . . . . . . . . . . . . . 47
B.4. Version 14 . . . . . . . . . . . . . . . . . . . . . . . 48
B.5. Version 13 . . . . . . . . . . . . . . . . . . . . . . . 48
B.6. Version 12 . . . . . . . . . . . . . . . . . . . . . . . 48
B.7. Version 11 (after IESG review) . . . . . . . . . . . . . 48
B.8. Version 10 (after AD review) . . . . . . . . . . . . . . 49
B.9. Version 09 (after WGLC) . . . . . . . . . . . . . . . . . 49
B.10. Version 08 . . . . . . . . . . . . . . . . . . . . . . . 49
B.11. Version 07 . . . . . . . . . . . . . . . . . . . . . . . 50
B.12. Version 06 . . . . . . . . . . . . . . . . . . . . . . . 51
B.13. Version 05 . . . . . . . . . . . . . . . . . . . . . . . 51
B.14. Version 04 . . . . . . . . . . . . . . . . . . . . . . . 51
B.15. Version 03 . . . . . . . . . . . . . . . . . . . . . . . 51
B.16. Version 02 . . . . . . . . . . . . . . . . . . . . . . . 53
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Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 53
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, and the associated
challenges with their deployment and operation. There is a growing
trend in home networking for the proliferation of networking
technology through an increasingly broad range of devices and media.
This evolution in scale and diversity sets requirements on IETF
protocols. Some of these requirements relate to the introduction of
IPv6, others to the introduction of specialised networks for home
automation and sensors.
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 both provides a
large enough prefix to allocate a prefix to each subnet, and that a
method is supported for such prefixes to be delegated efficiently to
those subnets.
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 pro-active 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 at
a more consistent solution that addresses as many of the identified
requirements as possible. The 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
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affect IPv4 operation. We assume that the IPv4 network architecture
in home networks is what it is, and can not be modified by new
recommendations. This document does not discuss how IPv4 home
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 that we react accordingly. Any IPv6-over-Foo
definitions occur elsewhere.
[RFC7084], which has obsoleted [RFC6204], defines basic requirements
for customer edge routers (CERs). The update includes the definition
of requirements for specific transition tools on the CER,
specifically DS-Lite [RFC6333] and 6rd [RFC5969]. Such detailed
specification of CER devices is considered out of scope of this
architecture document, and we assume that any required update of the
CER 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 CER 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 point(s) at which filtering and forwarding
policies for different types of traffic may be applied.
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o CER: Customer Edge Router: A border router intended for use in a
homenet, which connects the homenet to a service provider network.
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 CERs providing connectivity to service provider
network(s).
o Internet Service Provider (ISP): 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 and Port Translation (NAPT) [RFC3022].
o NPTv6: Network Prefix Translation for IPv6 [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,
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through the vastly increased address space, allows globally unique IP
addresses to be used for all devices in a home network. This section
presents an overview of some of the key implications of the
introduction of IPv6 for home networking, that are simultaneously
both promising and problematic.
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 much lower capacity links 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 [RFC6177] (BCP 157), 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 is the issue of how
to extend mechanisms such as zero configuration service discovery
which currently only operate within a single subnet using link-local
traffic. In a typical IPv4 home network, there is only one subnet,
so such mechanisms would normally operate as expected. For multi-
subnet IPv6 home networks there are two broad choices to enable such
protocols to work across the scope of the entire homenet; extend
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existing protocols to work across that scope, or introduce proxies
for existing link layer protocols. This topic is discussed in
Section 3.7.
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 may simply not have robustness designed-in
because it was either assumed such devices would only be used on
private networks or the device itself doesn't have the computing
power to apply the necessary security methods. 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 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 CER. [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. Where a homenet is multihomed, a device would
typically receive a globally unique address (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].
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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
prefix. In such cases the presence of upstream BCP 38 [RFC2827]
ingress filtering 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 Unique Local Addresses (ULAs) for IPv6 that may be
used to address devices within the scope of a single site. Support
for ULAs for IPv6 CERs is described in [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 RFC 1918 space, 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
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globally unique addresses between hosts and devices in remote
networks, the architectural cost and complexity, particularly to
applications, of NAT or NPTv6 translation is avoided. As such,
neither IPv6 NAT or NPTv6 is recommended for use in the homenet
architecture. Further, the homenet border router(s) should filter
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 CER that may be configured via
a web interface. In potentially complex future IPv6 homenets, users
should not be expected to enter IPv6 literal addresses in devices or
applications, given their much greater length and the apparent
randomness of such addresses to a typical home user. Thus, even for
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the simplest of functions, simple naming and the associated (minimal,
and ideally zero configuration) discovery of services is imperative
for the easy deployment and use of homenet devices and applications.
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 which may be deployed by the
homenet's ISP are discussed in [RFC7084]. In addition, certain other
functions may be desirable on the CER, 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 CER.
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 re-use 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.
The homenet needs to be able to handle or provision at least
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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
inter-networking 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 are 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 backwardly compatible, and forward compatible where changes are
made.
3.1.2. Minimise changes to hosts and routers
In order to maximise deployability of new homenets, where possible
any requirement for changes to hosts and routers should be minimised,
though solutions which, for example, incrementally improve capability
with host or router changes may be acceptable. There may be cases
where changes are unavoidable, e.g., to allow a given homenet routing
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protocol to be self-configuring, or to support routing based on
sources 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., de-
activating a certain part of the infrastructure to allow the rest to
operate. In such cases, the user should ideally have some useful
indication of the failure mode encountered.
There should be no topology scenarios which cause loss of
connectivity, except when the user creates a physical island within
the topology. Some potentially pathological cases that can be
created include bridging ports of a router together, however this
case can be detected and dealt with by the router. Loops within a
routed topology are in a sense good in that they offer redundancy.
Topologies that include potential bridging loops can be dangerous but
are also detectable when a switch learns the MAC of one of its
interfaces on another or runs a spanning tree or link state protocol.
It is only 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.
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.
Most IPv4 home network models at the time of writing tend to be
relatively simple, typically a single NAT router to the ISP and a
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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 CER.
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 CER. The CER(s) may or may not be managed by
the ISP. If the demarcation point is such that the customer can
provide or manage the CER, its configuration must be simple. Both
models must be supported.
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.
o Number of CERs. The homenet may have a single CER, which might be
used for one or more providers, or multiple CERs. The presence of
multiple CERs adds additional complexity for multihoming
scenarios, and protocols like PCP that may need to manage
connection-oriented state mappings on the same CER 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
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be an exhaustive or complete list, rather an indicative one to
facilitate the discussion in this text.
3.2.2.1. A: Single ISP, Single CER, 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 a LLN link layer technology in another. In this
example there is no single router that a priori understands the
entire topology. The topology itself may also be complex, and it may
not be possible to assume a pure tree form, for instance (because
home users may plug routers together to form arbitrary topologies
including 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 CER. It has a single uplink interface.
It has three additional interfaces connected to Network A, Link F,
and Network B. IPv6 Internal Router (IR) has four interfaces
connected to Link F, Network C, Network D and Network E. Network B
and Network E have been bridged, likely inadvertently. This could be
as a result of connecting a wire between a switch for Network B and a
switch for Network E.
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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 CER or IPv6 (IR), wireless networks, or through
one or more layer-2 only Ethernet switches.
3.2.2.2. B: Two ISPs, Two CERs, Shared subnet
+-------+-------+ +-------+-------+ \
| Service | | Service | \
| Provider A | | Provider B | | Service
| Router | | Router | | Provider
+------+--------+ +-------+-------+ | network
| | /
| Customer | /
| Internet connections | /
| |
+------+--------+ +-------+-------+ \
| IPv6 | | IPv6 | \
| Customer Edge | | Customer Edge | \
| Router 1 | | Router 2 | /
+------+--------+ +-------+-------+ /
| | /
| | | End-User
---+---------+---+---------------+--+----------+--- | network(s)
| | | | \
+----+-----+ +-----+----+ +----+-----+ +-----+----+ \
|IPv6 Host | |IPv6 Host | | IPv6 Host| |IPv6 Host | /
| H1 | | H2 | | H3 | | H4 | /
+----------+ +----------+ +----------+ +----------+
Figure 2
Figure 2 illustrates a multihomed homenet model, where the customer
has connectivity via CER1 to ISP A and via CER2 to ISP B. This
example shows one shared subnet where IPv6 nodes would potentially be
multihomed and receive multiple IPv6 global 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 CER serves a
separate isolated subnet, which is a scenario seen with some IPv4
networks today.
3.2.2.3. C: Two ISPs, One CER, Shared subnet
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+-------+-------+ +-------+-------+ \
| 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
It is expected that most homenet deployments will for the immediate
future be dual-stack IPv4/IPv6. In such networks it is important not
to introduce new IPv6 capabilities that would cause a failure if used
alongside IPv4+NAT, given that such dual-stack homenets will be
commonplace for some time. That said, it is desirable that IPv6
works better than IPv4 in as many scenarios as possible. Further,
the homenet architecture must operate in the absence of IPv4.
A general recommendation is to follow the same topology for IPv6 as
is used for IPv4, but not to use NAT. Thus there should be routed
IPv6 where an IPv4 NAT is used and, where there is no NAT, routing or
bridging may be used. Routing may have advantages when compared to
bridging together high speed and lower speed shared media, and in
addition bridging may not be suitable for some networks, such as ad-
hoc mobile networks.
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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 either take a form where there are
multiple isolated networks within the home or a more integrated
network where the connectivity selection needs to be dynamic.
Current practice is typically of the former kind, but the latter is
expected to become more commonplace.
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 CER Network Model C illustrated above, multihoming may
be offered by source-based routing at the CER. With multiple exit
routers, as in CER Network Model B, the complexity rises. Given a
packet with a source address on the home network, the packet must be
routed to the proper egress to avoid BCP 38 ingress filtering 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 CERs. However, the general multihoming problem is broad,
and solutions suggested to date within the IETF have included complex
architectures for monitoring connectivity, traffic engineering,
identifier-locator separation, connection survivability across
multihoming events, and so on. It is thus important that the homenet
architecture should as far as possible minimise the complexity of any
multihoming support.
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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 which 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
multi-homing 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], MPTCP [RFC6824] or
Happy Eyeballs [RFC6555]. In general, any incremental improvements
obtained by host changes should give benefit for the hosts
introducing them, but 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 it may
support mobility protocols to facilitate such roaming where multiple
subnets are used.
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
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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 is
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
enrolment 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
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.
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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
1Mbit/s up to 1Gbit/s, which is a three orders of magnitude
throughput discrepancy. 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
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.
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It is expected that a realm would span at least an entire subnet, and
thus the borders lie at routers which receive delegated prefixes
within the homenet. It is also desirable, for a richer security
model, that hosts 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 realm and the
borders between them, namely the internal homenet, the ISP and a
guest network. In this case the borders will include that from the
homenet to the ISP, that from the guest network to the ISP, and that
from the homenet to the guest network. Regardless, it should be
possible for additional types of realms and borders to be defined,
e.g., for some specific 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
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.
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
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can obtain the 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
thus make no assumptions about the stability of the prefix received
from an ISP, or the length of the prefix that may be offered.
However, if, for example, only a /64 is offered by the ISP, the
homenet may be severely constrained or even unable to function.
[RFC6177] (BCP 157) states that "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]), 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
such a warning or error state should best be presented to a typical
home user.
Thus a homenet CER 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 offer 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
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one. While it may be possible for a homenet CER 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 which, unlike the process described in [RFC4192],
would be a 'flag day" event, which means that a graceful renumbering
process moving through a state with two active prefixes in use would
not be possible. While renumbering 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.
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.
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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.
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 it is possible that in some cases multiple /48 ULA prefixes
may be in use within the same homenet, e.g., when the network is
being deployed, perhaps also without external connectivity. In cases
where multiple ULA /48's are in use, hosts need to know that each /48
is local to the homenet, e.g., by inclusion in their local address
selection policy table.
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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 CER [RFC3633]. Where multiple CERs exist with
multiple ISP prefix pools, it is expected that routers within the
homenet would assign themselves prefixes from each ISP they
communicate with/through. As discussed above, a ULA prefix 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 delegation of prefixes for use
within the homenet. Such internal delegation should not assume a
flat or hierarchical model, nor should it make an assumption about
whether the delegation of internal prefixes is distributed or
centralised. The assignment mechanism should provide reasonable
efficiency, so that typical home network prefix allocation sizes can
accommodate all the necessary /64 allocations in most cases, and not
waste prefixes. Further, duplicate assignment of multiple /64s to
the same network should be avoided, and the network should behave as
gracefully as possible in the event of prefix exhaustion (though the
options in such cases may be limited).
Where the home network has multiple CERs and these are delegated
prefix pools from their attached ISPs, the internal prefix delegation
would be expected to be served by each CER for each prefix associated
with it. Where ULAs are used, it is preferable that only one /48 ULA
covers the whole homenet, from which /64's can be delegated 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.
Delegation 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
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, delegated 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).
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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,
or, more likely, it would involve running an appropriate routing
protocol.
A mechanism is required to discover which router(s) in the homenet
are providing the CER 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 a 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
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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, WiFi,
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
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.
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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 CER 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 upstream ISP BCP 38 ingress filtering problems.
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 a 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 low-
power and lossy networks (LLNs), such as those used for certain types
of sensor devices.
Ideally, LLN or other logically separate networks should be able
exchange routes such that IP traffic may be forwarded among the
networks via gateway routers which 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.
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3.5.2. Unicast Routing at the Homenet Border
The current practice defined in [RFC7084] would suggest that routing
between the homenet CER and the Service Provider Router follow the
model of [RFC7084] Section 4 WAN Side Requirements, at least in
initial deployments. However, consideration of whether a routing
protocol is used between the homenet CER 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, e.g., for homenet-wide service discovery should a
multicast service discovery protocol of scope greater than link-local
be defined, or potentially for multicast-based streaming or
filesharing applications. Where multicast is routed across a homenet
an appropriate multicast routing protocol is required, one that as
per the unicast routing protocol should be self-configuring. As
hinted above, it must be 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.
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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 CERs, the
signalling would need to handle the cases of flows that may use one
or more exit routers. CERs would need to be able to advertise their
existence for such protocols.
[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 CERs 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 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
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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 CERs 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 guest network
subnet(s). Some scenarios/models may as a result involve running
isolated subnet(s) with their own CERs. In such cases connectivity
would only be expected within each isolated network (though traffic
may potentially pass between them via external providers).
LLNs provide an another example of where there may be secure
perimeters inside the homenet. Constrained LLN nodes may implement
network key security but may depend on access policies enforced by
the LLN border router.
Considerations for differentiating neighbouring homenets are
discussed in Section 3.3.1.
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 computer, 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,
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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 CERs 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 to
be able to be initiated to them through security filters in the
homenet, either for all ports or for specific services. Users should
have simple methods to associate devices to services that they wish
to operate transparently through (CER) borders.
3.6.6. ULAs as a hint of connection origin
As noted in Section 3.6, if appropriate filtering is in place on the
CER(s), as mandated by RFC 7084 requirement S-2, 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 which 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
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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,
be the user within the homenet or outside it, i.e., the user should
be able to refer to devices by name, and potentially connect to them,
wherever they may be. The most natural way to think about such
naming and service discovery is to enable it to work across the
entire homenet residence (site), disregarding technical borders such
as subnets but respecting policy borders such as those between guest
and other internal network realms. 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.
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 CER. 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 backwardly 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.
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One of the primary challenges facing service discovery today is lack
of interoperability due to the ever increasing number of service
discovery protocols available. While it is conceivable for consumer
devices to support multiple discovery protocols, this is clearly not
the most efficient use of network and computational resources. One
goal of the homenet architecture should be a path to service
discovery protocol interoperability either through a standards based
translation scheme, hooks into current protocols to allow some for of
communication among discovery protocols, extensions to support a
central service repository in the homenet, or simply convergence
towards a unified protocol suite.
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 which 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 the name a user assigns to a device
may be a label that is stored on the device as an attribute of the
device, and may be distinct from the name used in a name service,
e.g., 'Study Laser Printer' as opposed to printer2.<somedomain>.
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 co-exist with the Internet name service. There should also be
a bias towards proven, existing solutions. The strong implication is
thus that the homenet service is DNS-based, or DNS-compatible. There
are naming protocols that are designed to be configured and operate
Internet-wide, like unicast-based DNS, but also protocols that are
designed for zero-configuration local environments, like mDNS
[RFC6762].
When DNS is used as the homenet name service, it typically includes
both a resolving service and an authoritative service. The
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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 CER 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.
Finally, the impact of a change in CER must be considered. It would
be desirable to retain any relevant state (configuration) that was
held in the old CER. This might imply that state information should
be distributed in the homenet, to be recoverable by/to the new CER,
or to the homenet's ISP or a third party 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 CER. 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
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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 which have link-local
scope, and is thus not appropriate for multi-subnet home networks. A
different name space is thus required for the homenet.
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.
An alternative approach for a local name space would be to use a
Unique Locally Qualified Domain Name (ULQDN) space such as
.<UniqueString>.sitelocal. The <UniqueString> could be generated in
a variety of ways, one potentially being based on the local /48 ULA
prefix being used across the homenet. Such a <UniqueString> should
survive a cold restart, i.e., be consistent after a network power-
down, or, if a value is not set on startup, the CER or device running
the name service should generate a default value. It 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).
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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 gTLD. Thus
qualified names should always be used, whether these are exposed to
the user or not. The IAB has issued a statement which explains why
dotless domains should be considered harmful [IABdotless].
There may be use cases where either different name spaces may be
desired for different realms in the homenet, or for 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 individual device(s) being independently registered in
external name spaces.
It may be the case that if there are two or more CERs serving the
home network, that if each has 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.
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 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.
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The approach described above 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.
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 which 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 use of Mobile IPv6 or Dynamic DNS, either of which would
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put additional requirements on to 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 in a multi-service homenet may be a
requirement, e.g., for a critical system (perhaps healthcare
related), or for differentiation between different types of traffic
(file sharing, cloud storage, live streaming, VoIP, etc). Different
link media types may have different such properties or capabilities.
However, homenet scenarios should require no new Quality of Service
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 Quality of Service deployment
in home networks. It is likely that QoS, or traffic prioritisation,
methods will be required at the CER, and potentially around
boundaries between different 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 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.
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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 layer and
application layer services is out of scope of this architectural
principles document, but are 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.
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 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 network
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 re-use of existing protocols. Thus
the necessary mechanisms are largely already part of the IPv6
protocol set and common implementations, though there are some
exceptions.
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, a mechanism may be
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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
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. IANA Considerations
This document has no actions for IANA.
7. References
7.1. Normative References
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998.
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[RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
Host Configuration Protocol (DHCP) version 6", RFC 3633,
December 2003.
[RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
Addresses", RFC 4193, October 2005.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, February 2006.
7.2. 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.
[RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.,
and W. Weiss, "An Architecture for Differentiated
Services", RFC 2475, December 1998.
[RFC2775] Carpenter, B., "Internet Transparency", RFC 2775, February
2000.
[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.
[RFC3002] Mitzel, D., "Overview of 2000 IAB Wireless Internetworking
Workshop", RFC 3002, December 2000.
[RFC3022] Srisuresh, P. and K. Egevang, "Traditional IP Network
Address Translator (Traditional NAT)", RFC 3022, January
2001.
[RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "DNS Security Introduction and Requirements", RFC
4033, March 2005.
[RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and
More-Specific Routes", RFC 4191, November 2005.
[RFC4192] Baker, F., Lear, E., and R. Droms, "Procedures for
Renumbering an IPv6 Network without a Flag Day", RFC 4192,
September 2005.
[RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for
IP", RFC 4607, August 2006.
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[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862, September 2007.
[RFC4864] Van de Velde, G., Hain, T., Droms, R., Carpenter, B., and
E. Klein, "Local Network Protection for IPv6", RFC 4864,
May 2007.
[RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy
Extensions for Stateless Address Autoconfiguration in
IPv6", RFC 4941, September 2007.
[RFC5533] Nordmark, E. and M. Bagnulo, "Shim6: Level 3 Multihoming
Shim Protocol for IPv6", RFC 5533, June 2009.
[RFC5890] Klensin, J., "Internationalized Domain Names for
Applications (IDNA): Definitions and Document Framework",
RFC 5890, August 2010.
[RFC5969] Townsley, W. and O. Troan, "IPv6 Rapid Deployment on IPv4
Infrastructures (6rd) -- Protocol Specification", RFC
5969, August 2010.
[RFC6092] Woodyatt, J., "Recommended Simple Security Capabilities in
Customer Premises Equipment (CPE) for Providing
Residential IPv6 Internet Service", RFC 6092, January
2011.
[RFC6144] Baker, F., Li, X., Bao, C., and K. Yin, "Framework for
IPv4/IPv6 Translation", RFC 6144, April 2011.
[RFC6145] Li, X., Bao, C., and F. Baker, "IP/ICMP Translation
Algorithm", RFC 6145, April 2011.
[RFC6177] Narten, T., Huston, G., and L. Roberts, "IPv6 Address
Assignment to End Sites", BCP 157, RFC 6177, March 2011.
[RFC6204] Singh, H., Beebee, W., Donley, C., Stark, B., and O.
Troan, "Basic Requirements for IPv6 Customer Edge
Routers", RFC 6204, April 2011.
[RFC6296] Wasserman, M. and F. Baker, "IPv6-to-IPv6 Network Prefix
Translation", RFC 6296, June 2011.
[RFC6333] Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual-
Stack Lite Broadband Deployments Following IPv4
Exhaustion", RFC 6333, August 2011.
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[RFC6555] Wing, D. and A. Yourtchenko, "Happy Eyeballs: Success with
Dual-Stack Hosts", RFC 6555, April 2012.
[RFC6724] Thaler, D., Draves, R., Matsumoto, A., and T. Chown,
"Default Address Selection for Internet Protocol Version 6
(IPv6)", RFC 6724, September 2012.
[RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
February 2013.
[RFC6824] Ford, A., Raiciu, C., Handley, M., and O. Bonaventure,
"TCP Extensions for Multipath Operation with Multiple
Addresses", RFC 6824, January 2013.
[RFC6887] Wing, D., Cheshire, S., Boucadair, M., Penno, R., and P.
Selkirk, "Port Control Protocol (PCP)", RFC 6887, April
2013.
[RFC6950] Peterson, J., Kolkman, O., Tschofenig, H., and B. Aboba,
"Architectural Considerations on Application Features in
the DNS", RFC 6950, October 2013.
[RFC7084] Singh, H., Beebee, W., Donley, C., and B. Stark, "Basic
Requirements for IPv6 Customer Edge Routers", RFC 7084,
November 2013.
[RFC7157] Troan, O., Miles, D., Matsushima, S., Okimoto, T., and D.
Wing, "IPv6 Multihoming without Network Address
Translation", RFC 7157, March 2014.
[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252, June 2014.
[IABdotless]
"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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Appendix A. Acknowledgments
The authors would like to thank Aamer Akhter, Mikael Abrahamsson,
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, Markus Stenberg, Sander Steffann, Don Sturek,
Andrew Sullivan, Dave Taht, Dave Thaler, Michael Thomas, Mark
Townsley, JP Vasseur, Curtis Villamizar, Dan Wing, Russ White, and
James Woodyatt for their comments and contributions within homenet WG
meetings and on the WG mailing list. An acknowledgement generally
means that person's text made it in to the document, or was helpful
in clarifying or reinforcing an aspect of the document. It does not
imply that each contributor agrees with every point in the document.
Appendix B. Changes
This section will be removed in the final version of the text.
B.1. Version 17
Changes made include:
o Updated Section 3.5 on routing functionality.
o Noted consensus in London for a separate configuration protocol.
o Updated text to refer to RFC7084 rather than RFC6204.
o Updated coap reference to the pubished RFC.
B.2. Version 16
Changes made include:
o Reverted back to paragraph on link metric usage.
B.3. Version 15
Changes made include:
o Inserted WG chair compromise text on routing functionality.
Removed paragraph on link metric usage.
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B.4. Version 14
Changes made include:
o Changes for Adrian Farrell discuss/comment.
o Very minor wordsmithing requested by Benoit for OAM text.
o Very minor wordsmithing from IETF89 session.
o Added note to support SSM.
o Emphasised at most one routing protocol in use, possibly none.
B.5. Version 13
Changes made include:
o Changes to address last outstanding IESG DISCUSSes/COMMENTs.
B.6. Version 12
Changes made include:
o Fixed minor typo nits introduced in -11.
o Elwyn Davies' gen-art review comments addressed.
o Some further IESG DISCUSSes/COMMENTs addressed.
B.7. Version 11 (after IESG review)
Changes made include:
o Jouni Korhonen's OPSDIR review comments addressed.
o Elwyn Davies' gen-art review comments addressed.
o Considered secdir review by Samiel Weiler; many points addressed.
o Considered APPSDIR review.
o Addressed a large number of IESG comments and discusses.
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B.8. Version 10 (after AD review)
Changes made include:
o Minor changes/clarifications resulting from AD review
B.9. Version 09 (after WGLC)
Changes made include:
o Added note about multicast into or out of site
o Removed further personal draft references, replaced with covering
text
o Routing functionality text updated to avoid ambiguity
o Added note that devices away from homenet may tunnel home (via
VPN)
o Added note that homenets more exposed to provider renumbering than
with IPv4 and NAT
o Added note about devices that may be ULA-only until configured to
be globally addressable
o Removed paragraph about broken CERs that do not work with prefixes
other than /64
o Noted no recommendation on methods to convey prefix information is
made in this text
o Stated that this text does not recommend how to form largest
possible subnets
o Added text about homenet evolution and handling disparate media
types
o Rephrased NAT/firewall text on marginal effectiveness
o Emphasised that multihoming may be to any number of ISPs
B.10. Version 08
Changes made include:
o Various clarifications made in response to list comments
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o Added note on ULAs with IPv4, where no GUAs in use
o Added note on naming and internationalisation (IDNA)
o Added note on trust relationships when adding devices
o Added note for MPTCP
o Added various naming and SD notes
o Added various notes on delegated ISP prefixes
B.11. Version 07
Changes made include:
o Removed reference to NPTv6 in section 3.2.4. Instead now say it
has an architectural cost to use in the earlier section, and thus
it is not recommended for use in the homenet architecture.
o Removed 'proxy or extend?' section. Included shorter text in main
body, without mandating either approach for service discovery.
o Made it clearer that ULAs are expected to be used alongside
globals.
o Removed reference to 'advanced security' as described in draft-
vyncke-advanced-ipv6-security.
o Balanced the text between ULQDN and ALQDN.
o Clarify text does not assume default deny or allow on CER, but
that either mode may be enabled.
o Removed ULA-C reference for 'simple' addresses. Instead only
suggested service discovery to find such devices.
o Reiterated that single/multiple CER models to be supported for
multihoming.
o Reordered section 3.3 to improve flow.
o Added recommendation that homenet is not allocated less than /60,
and a /56 is preferable.
o Tidied up first few intro sections.
o Other minor edits from list feedback.
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B.12. Version 06
Changes made include:
o Stated that unmanaged goal is 'as far as possible'.
o Added note about multiple /48 ULAs potentially being in use.
o Minor edits from list feedback.
B.13. Version 05
Changes made include:
o Some significant changes to naming and SD section.
o Removed some expired drafts.
o Added notes about issues caused by ISP only delegating a /64.
o Recommended against using prefixes longer than /64.
o Suggested CER asks for /48 by DHCP PD, even if it only receives
less.
o Added note about DS-Lite but emphasised transition is out of
scope.
o Added text about multicast routing.
B.14. Version 04
Changes made include:
o Moved border section from IPv6 differences to principles section.
o Restructured principles into areas.
o Added summary of naming and service discovery discussion from WG
list.
B.15. Version 03
Changes made include:
o Various improvements to the readability.
o Removed bullet lists of requirements, as requested by chair.
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o Noted 6204bis has replaced advanced-cpe draft.
o Clarified the topology examples are just that.
o Emphasised we are not targetting walled gardens, but they should
not be precluded.
o Also changed text about requiring support for walled gardens.
o Noted that avoiding falling foul of ingress filtering when
multihomed is desirable.
o Improved text about realms, detecting borders and policies at
borders.
o Stated this text makes no recommendation about default security
model.
o Added some text about failure modes for users plugging things
arbitrarily.
o Expanded naming and service discovery text.
o Added more text about ULAs.
o Removed reference to version 1 on chair feedback.
o Stated that NPTv6 adds architectural cost but is not a homenet
matter if deployed at the CER. This text only considers the
internal homenet.
o Noted multihoming is supported.
o Noted routers may not by separate devices, they may be embedded in
devices.
o Clarified simple and advanced security some more, and RFC 4864 and
6092.
o Stated that there should be just one secret key, if any are used
at all.
o For multihoming, support multiple CERs but note that routing to
the correct CER to avoid ISP filtering may not be optimal within
the homenet.
o Added some ISPs renumber due to privacy laws.
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o Removed extra repeated references to Simple Security.
o Removed some solution creep on RIOs/RAs.
o Load-balancing scenario added as to be supported.
B.16. Version 02
Changes made include:
o Made the IPv6 implications section briefer.
o Changed Network Models section to describe properties of the
homenet with illustrative examples, rather than implying the
number of models was fixed to the six shown in 01.
o Text to state multihoming support focused on single CER model.
Multiple CER support is desirable, but not required.
o Stated that NPTv6 not supported.
o Added considerations section for operations and management.
o Added bullet point principles/requirements to Section 3.4.
o Changed IPv6 solutions must not adversely affect IPv4 to should
not.
o End-to-end section expanded to talk about "Simple Security" and
borders.
o Extended text on naming and service discovery.
o Added reference to RFC 2775, RFC 6177.
o Added reference to the new xmDNS draft.
o Added naming/SD requirements from Ralph Droms.
Authors' Addresses
Tim Chown (editor)
University of Southampton
Highfield
Southampton , Hampshire SO17 1BJ
United Kingdom
Email: tjc@ecs.soton.ac.uk
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Jari Arkko
Ericsson
Jorvas 02420
Finland
Email: jari.arkko@piuha.net
Anders Brandt
Sigma Designs
Emdrupvej 26A, 1
Copenhagen DK-2100
Denmark
Email: abr@sdesigns.dk
Ole Troan
Cisco Systems, Inc.
Drammensveien 145A
Oslo N-0212
Norway
Email: ot@cisco.com
Jason Weil
Time Warner Cable
13820 Sunrise Valley Drive
Herndon, VA 20171
USA
Email: jason.weil@twcable.com
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