3. Homenet Architecture Principles
The aim of this text is to outline how to construct advanced IPv6-
based home networks involving multiple routers and subnets using
standard IPv6 addressing and protocols [RFC2460] [RFC4291] as the
basis. As described in Section 3.1, solutions should as far as
possible reuse existing protocols and minimise changes to hosts and
routers, but some new protocols or extensions are likely to be
required. In this section, we present the elements of the proposed
home networking architecture with discussion of the associated design
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 the
o Prefix configuration for routers
o Name resolution
o Service discovery
o Network security
The remainder of this document describes the principles by which the
homenet architecture may deliver these properties.
3.1. General Principles
There is little that the Internet standards community can do about
the physical topologies or the need for some networks to be separated
at the network layer for policy or link-layer compatibility reasons.
However, there is a lot of flexibility in using IP addressing and
internetworking mechanisms. This text discusses how such flexibility
should be used to provide the best user experience and ensure that
the network can evolve with new applications in the future. The
principles described in this text should be followed when designing
homenet protocol solutions.
3.1.1. Reuse Existing Protocols
Existing protocols will be used to meet the requirements of home
networks. Where necessary, extensions will be made to those
protocols. When no existing protocol is found to be suitable, a new
or emerging protocol may be used. Therefore, it is important that no
design or architectural decisions be made that would preclude the use
of new or emerging protocols.
A generally conservative approach, giving weight to running (and
available) code, is preferable. Where new protocols are required,
evidence of commitment to implementation by appropriate vendors or
development communities is highly desirable. Protocols used should
be backward compatible and forward compatible where changes are made.
3.1.2. Minimise Changes to Hosts and Routers
In order to maximise the deployability of new homenets, any
requirement for changes to hosts and routers should be minimised
where possible; however, solutions that, for example, incrementally
improve capability via host or router changes may be acceptable.
There may be cases where changes are unavoidable, e.g., to allow a
given homenet routing protocol to be self-configuring or to support
routing based on source addresses in addition to destination
addresses (to improve multihoming support, as discussed in
3.2. Homenet Topology
This section considers homenet topologies and the principles that may
be applied in designing an architecture to support as wide a range of
such topologies as possible.
3.2.1. Supporting Arbitrary Topologies
There should ideally be no built-in assumptions about the topology in
home networks, as users are capable of connecting their devices in
'ingenious' ways. Thus, arbitrary topologies and arbitrary routing
will need to be supported, or at least the failure mode for when the
user makes a mistake should be as robust as possible, e.g.,
deactivating a certain part of the infrastructure to allow the rest
to operate. In such cases, the user should ideally have some useful
indication of the failure mode encountered.
There should be no topology scenarios that cause a loss of
connectivity, except when the user creates a physical island within
the topology. Some potentially pathological cases that can be
created include bridging ports of a router together; however, this
case can be detected and dealt with by the router. Loops within a
routed topology are in a sense good in that they offer redundancy.
Topologies that include potential bridging loops can be dangerous but
are also detectable when a switch learns the Media Access Control
(MAC) address of one of its interfaces on another or runs a spanning
tree or link-state protocol. It is only topologies with such
potential loops using simple repeaters that are truly pathological.
The topology of the homenet may change over time, due to the addition
or removal of equipment but also due to temporary failures or
connectivity problems. In some cases, this may lead to, for example,
a multihomed homenet being split into two isolated homenets or, after
such a fault is remedied, two isolated parts reconfiguring back to a
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
At the time of writing, most IPv4 home network models tend to be
relatively simple, typically a single NAT router to the ISP and a
single internal subnet but, as discussed earlier, evolution in
network architectures is driving more complex topologies, such as the
separation of guest and private networks. There may also be some
cascaded IPv4 NAT scenarios, which we mention in the next section.
For IPv6 homenets, the network architectures described in [RFC7084]
should, as a minimum, be supported.
There are a number of properties or attributes of a home network that
we can use to describe its topology and operation. The following
properties apply to any IPv6 home network:
o Presence of internal routers. The homenet may have one or more
internal routers or may only provide subnetting from interfaces on
the CE router.
o Presence of isolated internal subnets. There may be isolated
internal subnets, with no direct connectivity between them within
the homenet (with each having its own external connectivity).
Isolation may be physical or implemented via IEEE 802.1q VLANs.
The latter is, however, not something a typical user would be
expected to configure.
o Demarcation of the CE router. The CE router(s) may or may not be
managed by the ISP. If the demarcation point is such that the
customer can provide or manage the CE router, its configuration
must be simple. Both models must be supported.
Various forms of multihoming are likely to become more prevalent with
IPv6 home networks, where the homenet may have two or more external
ISP connections, as discussed further below. Thus, the following
properties should also be considered for such networks:
o Number of upstream providers. The majority of home networks today
consist of a single upstream ISP, but it may become more common in
the future for there to be multiple ISPs, whether for resilience
or provision of additional services. Each would offer its own
prefix. Some may or may not provide a default route to the public
o Number of CE routers. The homenet may have a single CE router,
which might be used for one or more providers, or multiple CE
routers. The presence of multiple CE routers adds additional
complexity for multihoming scenarios and protocols like PCP that
may need to manage connection-oriented state mappings on the same
CE router as used for subsequent traffic flows.
In the following sections, we give some examples of the types of
homenet topologies we may see in the future. This is not intended to
be an exhaustive or complete list but rather an indicative one to
facilitate the discussion in this text.
18.104.22.168. A: Single ISP, Single CE Router, and Internal Routers
Figure 1 shows a home network with multiple local area networks.
These may be needed for reasons relating to different link-layer
technologies in use or for policy reasons, e.g., classic Ethernet in
one subnet and an LLN link-layer technology in another. In this
example, there is no single router that a priori understands the
entire topology. The topology itself may also be complex, and it may
not be possible to assume a pure tree form, for instance (because
home users may plug routers together to form arbitrary topologies,
including those with potential loops in them).
Any of logical Networks A through F might be wired or wireless.
Where multiple hosts are shown, this might be through one or more
physical ports on the CE router or IPv6 (IR), wireless networks, or
through one or more Ethernet switches that are Layer 2 only.
22.214.171.124. B: Two ISPs, Two CE Routers, and Shared Subnet
+-------+-------+ +-------+-------+ \
| Service | | Service | \
| Provider A | | Provider B | | Service
| Router | | Router | | Provider
+------+--------+ +-------+-------+ | Network
| | /
| Customer | /
| Internet Connections | /
+------+--------+ +-------+-------+ \
| IPv6 | | IPv6 | \
| Customer Edge | | Customer Edge | \
| Router 1 | | Router 2 | /
+------+--------+ +-------+-------+ /
| | /
| | | End-User
---+---------+---+---------------+--+----------+--- | Network(s)
| | | | \
+----+-----+ +-----+----+ +----+-----+ +-----+----+ \
|IPv6 Host | |IPv6 Host | | IPv6 Host| |IPv6 Host | /
| H1 | | H2 | | H3 | | H4 | /
+----------+ +----------+ +----------+ +----------+
Figure 2Figure 2 illustrates a multihomed homenet model, where the customer
has connectivity via CE router 1 to ISP A and via CE router 2 to ISP
B. This example shows one shared subnet where IPv6 nodes would
potentially be multihomed and receive multiple IPv6 global prefixes,
one per ISP. This model may also be combined with that shown in
Figure 1 to create a more complex scenario with multiple internal
routers. Or, the above shared subnet may be split in two, such that
each CE router serves a separate isolated subnet, which is a scenario
seen with some IPv4 networks today.
126.96.36.199. C: Two ISPs, One CE Router, and Shared Subnet
+-------+-------+ +-------+-------+ \
| Service | | Service | \
| Provider A | | Provider B | | Service
| Router | | Router | | Provider
+-------+-------+ +------+--------+ | Network
| | /
| Customer | /
| Internet | /
| Connections |
| IPv6 | \
| Customer Edge | \
| Router | /
| | End-User
---+------------+-------+--------+-------------+--- | Network(s)
| | | | \
+----+-----+ +----+-----+ +----+-----+ +-----+----+ \
|IPv6 Host | |IPv6 Host | | IPv6 Host| |IPv6 Host | /
| H1 | | H2 | | H3 | | H4 | /
+----------+ +----------+ +----------+ +----------+
Figure 3Figure 3 illustrates a model where a home network may have multiple
connections to multiple providers or multiple logical connections to
the same provider, with shared internal subnets.
3.2.3. Dual-Stack Topologies
For the immediate future, it is expected that most homenet
deployments will be dual-stack IPv4/IPv6. In such networks, it is
important not to introduce new IPv6 capabilities that would cause a
failure if used alongside IPv4+NAT, given that such dual-stack
homenets will be commonplace for some time. That said, it is
desirable that IPv6 works better than IPv4 in as many scenarios as
possible. Further, the homenet architecture must operate in the
absence of IPv4.
A general recommendation is to follow the same topology for IPv6 as
is used for IPv4 but not to use NAT. Thus, there should be routed
IPv6 where an IPv4 NAT is used, and where there is no NAT, routing or
bridging may be used. Routing may have advantages when compared to
bridging together high- and lower-speed shared media, and in
addition, bridging may not be suitable for some networks, such as ad
hoc mobile networks.
In some cases, IPv4 home networks may feature cascaded NATs. End
users are frequently unaware that they have created such networks, as
'home routers' and 'home switches' are frequently confused. In
addition, there are cases where NAT routers are included within
Virtual Machine Hypervisors or where Internet connection-sharing
services have been enabled. This document applies equally to such
hidden NAT 'routers'. IPv6-routed versions of such cases will be
required. We should thus also note that routers in the homenet may
not be separate physical devices; they may be embedded within other
A homenet may be multihomed to multiple providers, as the network
models above illustrate. This may take a form where there are either
multiple isolated networks within the home or a more integrated
network where the connectivity selection needs to be dynamic.
Current practice is typically of the former kind, but the latter is
expected to become more commonplace.
In the general homenet architecture, multihomed hosts should be
multi-addressed with a global IPv6 address from the global prefix
delegated from each ISP they communicate with or through. When such
multi-addressing is in use, hosts need some way to pick source and
destination address pairs for connections. A host may choose a
source address to use by various methods, most commonly [RFC6724].
Applications may of course do different things, and this should not
For the single CE Router Network Model C illustrated above,
multihoming may be offered by source-based routing at the CE router.
With multiple exit routers, as in CE Router Network Model B, the
complexity rises. Given a packet with a source address on the home
network, the packet must be routed to the proper egress to avoid
ingress filtering as described in BCP 38 if exiting through the wrong
ISP. It is highly desirable that the packet is routed in the most
efficient manner to the correct exit, though as a minimum requirement
the packet should not be dropped.
The homenet architecture should support both the above models, i.e.,
one or more CE routers. However, the general multihoming problem is
broad, and solutions suggested to date within the IETF have included
complex architectures for monitoring connectivity, traffic
engineering, identifier-locator separation, connection survivability
across multihoming events, and so on. It is thus important that the
homenet architecture should as far as possible minimise the
complexity of any multihoming support.
An example of such a 'simpler' approach has been documented in
[RFC7157]. Alternatively, a flooding/routing protocol could
potentially be used to pass information through the homenet, such
that internal routers and ultimately end hosts could learn per-prefix
configuration information, allowing better address selection
decisions to be made. However, this would imply router and, most
likely, host changes. Another avenue is to introduce support
throughout the homenet for routing that is based on the source as
well as the destination address of each packet. While greatly
improving the 'intelligence' of routing decisions within the homenet,
such an approach would require relatively significant router changes
but avoid host changes.
As explained previously, while NPTv6 has been proposed for providing
multihoming support in networks, its use is not recommended in the
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
The homenet architecture should also not preclude use of host or
application-oriented tools, e.g., Shim6 [RFC5533], Multipath TCP
(MPTCP) [RFC6824], or Happy Eyeballs [RFC6555]. In general, any
incremental improvements obtained by host changes should give benefit
for the hosts introducing them but should not be required.
3.2.5. Mobility Support
Devices may be mobile within the homenet. While resident on the same
subnet, their address will remain persistent, but should devices move
to a different (wireless) subnet, they will acquire a new address in
that subnet. It is desirable that the homenet supports internal
device mobility. To do so, the homenet may either extend the reach
of specific wireless subnets to enable wireless roaming across the
home (availability of a specific subnet across the home) or support
mobility protocols to facilitate such roaming where multiple subnets
3.3. A Self-Organising Network
The home network infrastructure should be naturally self-organising
and self-configuring under different circumstances relating to the
connectivity status to the Internet, number of devices, and physical
topology. At the same time, it should be possible for advanced users
to manually adjust (override) the current configuration.
While a goal of the homenet architecture is for the network to be as
self-organising as possible, there may be instances where some manual
configuration is required, e.g., the entry of a cryptographic key to
apply wireless security or to configure a shared routing secret. The
latter may be relevant when considering how to bootstrap a routing
configuration. It is highly desirable that the number of such
configurations is minimised.
3.3.1. Differentiating Neighbouring Homenets
It is important that self-configuration with 'unintended' devices be
avoided. There should be a way for a user to administratively assert
in a simple way whether or not a device belongs to a given homenet.
The goal is to allow the establishment of borders, particularly
between two adjacent homenets, and to avoid unauthorised devices from
participating in the homenet. Such an authorisation capability may
need to operate through multiple hops in the homenet.
The homenet should thus support a way for a homenet owner to claim
ownership of their devices in a reasonably secure way. This could be
achieved by a pairing mechanism by, for example, pressing buttons
simultaneously on an authenticated and a new homenet device or by an
enrollment process as part of an autonomic networking environment.
While there may be scenarios where one homenet may wish to
intentionally gain access through another, e.g., to share external
connectivity costs, such scenarios are not discussed in this
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.
This text does not, however, make recommendations on how such
subdivision should occur. It is expected that subsequent documents
will address this problem.
While it may be desirable to maximise the chance of link-local
protocols operating across a homenet by maximising the size of a
subnet, multi-subnet home networks are inevitable, so their support
must be included.
3.3.3. Handling Varying Link Technologies
Homenets tend to grow organically over many years, and a homenet will
typically be built over link-layer technologies from different
generations. Current homenets typically use links ranging from 1
Mbit/s up to 1 Gbit/s -- a throughput discrepancy of three orders of
magnitude. We expect this discrepancy to widen further as both high-
speed and low-power technologies are deployed.
Homenet protocols should be designed to deal well with
interconnecting links of very different throughputs. In particular,
flows local to a link should not be flooded throughout the homenet,
even when sent over multicast, and, whenever possible, the homenet
protocols should be able to choose the faster links and avoid the
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.
It is expected that a realm would span at least an entire subnet, and
thus the borders lie at routers that receive delegated prefixes
within the homenet. It is also desirable, for a richer security
model, that hosts are able to make communication decisions based on
available realm and associated prefix information in the same way
that routers at realm borders can.
A simple homenet model may just consider three types of realms and
the borders between them, namely the internal homenet, the ISP, and a
guest network. In this case, the borders will include the border
from the homenet to the ISP, the border from the guest network to the
ISP, and the border from the homenet to the guest network.
Regardless, it should be possible for additional types of realms and
borders to be defined, e.g., for some specific LLN-based network,
such as Smart Grid, and for these to be detected automatically and
for an appropriate default policy to be applied as to what type of
traffic/data can flow across such borders.
It is desirable to classify the external border of the home network
as a unique logical interface separating the home network from a
service provider network(s). This border interface may be a single
physical interface to a single service provider, multiple Layer 2
sub-interfaces to a single service provider, or multiple connections
to a single or multiple providers. This border makes it possible to
describe edge operations and interface requirements across multiple
functional areas including security, routing, service discovery, and
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
can obtain and configure the necessary addressing information to
3.4.1. Use of ISP-Delegated IPv6 Prefixes
Discussion of IPv6 prefix allocation policies is included in
[RFC6177]. In practice, a homenet may receive an arbitrary length
IPv6 prefix from its provider, e.g., /60, /56, or /48. The offered
prefix may be stable or change from time to time; it is generally
expected that ISPs will offer relatively stable prefixes to their
residential customers. Regardless, the home network needs to be
adaptable as far as possible to ISP prefix allocation policies and
assume nothing about the stability of the prefix received from an ISP
or the length of the prefix that may be offered.
However, if, for example, only a /64 is offered by the ISP, the
homenet may be severely constrained or even unable to function. BCP
157 [RFC6177] states the following:
A key principle for address management is that end sites always be
able to obtain a reasonable amount of address space for their
actual and planned usage, and over time ranges specified in years
rather than just months. In practice, that means at least one
/64, and in most cases significantly more. One particular
situation that must be avoided is having an end site feel
compelled to use IPv6-to-IPv6 Network Address Translation or other
burdensome address conservation techniques because it could not
get sufficient address space.
This architecture document assumes that the guidance in the quoted
text is being followed by ISPs.
There are many problems that would arise from a homenet not being
offered a sufficient prefix size for its needs. Rather than attempt
to contrive a method for a homenet to operate in a constrained manner
when faced with insufficient prefixes, such as the use of subnet
prefixes longer than /64 (which would break stateless address
autoconfiguration [RFC4862]), the use of NPTv6, or falling back to
bridging across potentially very different media, it is recommended
that the receiving router instead enters an error state and issues
appropriate warnings. Some consideration may need to be given to how
such a warning or error state should best be presented to a typical
Thus, a homenet CE router should request, for example, via DHCP
Prefix Delegation (DHCP PD) [RFC3633], that it would like a /48
prefix from its ISP, i.e., it asks the ISP for the maximum size
prefix it might expect to be offered, even if in practice it may only
be offered a /56 or /60. For a typical IPv6 homenet, it is not
recommended that an ISP offers less than a /60 prefix, and it is
highly preferable that the ISP offers at least a /56. It is expected
that the allocated prefix to the homenet from any single ISP is a
contiguous, aggregated one. While it may be possible for a homenet
CE router to issue multiple prefix requests to attempt to obtain
multiple delegations, such behaviour is out of scope of this
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
When an ISP does need to restructure, and in doing so renumber its
customer homenets, 'flash' renumbering is likely to be imposed. This
implies a need for the homenet to be able to handle a sudden
renumbering event that, unlike the process described in [RFC4192],
would be a 'flag day' event, which means that a graceful renumbering
process moving through a state with two active prefixes in use would
not be possible. While renumbering can be viewed as an extended
version of an initial numbering process, the difference between flash
renumbering and an initial 'cold start' is the need to provide
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
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
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
Note that in some cases, it is possible that multiple /48 ULA
prefixes may be in use within the same homenet, e.g., when the
network is being deployed, perhaps also without external
connectivity. In cases where multiple ULA /48s are in use, hosts
need to know that each /48 is local to the homenet, e.g., by
inclusion in their local address selection policy table.
3.4.3. Internal Prefix Delegation
As mentioned above, there are various sources of prefixes. From the
homenet perspective, a single global prefix from each ISP should be
received on the border CE router [RFC3633]. Where multiple CE
routers exist with multiple ISP prefix pools, it is expected that
routers within the homenet would assign themselves prefixes from each
ISP they communicate with/through. As discussed above, a ULA prefix
should be provisioned for stable internal communications or for use
on constrained/LLN networks.
The delegation or availability of a prefix pool to the homenet should
allow subsequent internal autonomous assignment of prefixes for use
within the homenet. Such internal assignment should not assume a
flat or hierarchical model, nor should it make an assumption about
whether the assignment of internal prefixes is distributed or
centralised. The assignment mechanism should provide reasonable
efficiency, so that typical home network prefix allocation sizes can
accommodate all the necessary /64 allocations in most cases, and not
waste prefixes. Further, duplicate assignment of multiple /64s to
the same network should be avoided, and the network should behave as
gracefully as possible in the event of prefix exhaustion (though the
options in such cases may be limited).
Where the home network has multiple CE routers and these are
delegated prefix pools from their attached ISPs, the internal prefix
assignment would be expected to be served by each CE router for each
prefix associated with it. Where ULAs are used, it is preferable
that only one /48 ULA covers the whole homenet, from which /64s can
be assigned to the subnets. In cases where two /48 ULAs are
generated within a homenet, the network should still continue to
function, meaning that hosts will need to determine that each ULA is
local to the homenet.
Prefix assignment within the homenet should result in each link being
assigned a stable prefix that is persistent across reboots, power
outages, and similar short-term outages. The availability of
persistent prefixes should not depend on the router boot order. The
addition of a new routing device should not affect existing
persistent prefixes, but persistence may not be expected in the face
of significant 'replumbing' of the homenet. However, assigned ULA
prefixes within the homenet should remain persistent through an ISP-
driven renumbering event.
Provisioning such persistent prefixes may imply the need for stable
storage on routing devices and also a method for a home user to
'reset' the stored prefix should a significant reconfiguration be
required (though ideally the home user should not be involved at
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
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
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
A mechanism is required to discover which router(s) in the homenet is
providing the CE router function. Borders may include but are not
limited to the interface to the upstream ISP, a gateway device to a
separate home network such as an LLN network, or a gateway to a guest
or private corporate extension network. In some cases, there may be
no border present, which may, for example, occur before an upstream
connection has been established.
The routing environment should be self-configuring, as discussed
previously. The homenet self-configuration process and the routing
protocol must interact in a predictable manner, especially during
startup and reconvergence. The border discovery functionality and
other self-configuration functionality may be integrated into the
routing protocol itself but may also be imported via a separate
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
The homenet architecture is IPv6-only. In practice, dual-stack
homenets are still likely for the foreseeable future, as described in
Section 3.2.3. Whilst support for IPv4 and other address families
may therefore be beneficial, it is not an explicit requirement to
carry the routing information in the same routing protocol.
Multiple types of physical interfaces must be accounted for in the
homenet routing topology. Technologies such as Ethernet, Wi-Fi,
Multimedia over Coax Alliance (MoCA), etc., must be capable of
coexisting in the same environment and should be treated as part of
any routed deployment. The inclusion of physical-layer
characteristics in path computation should be considered for
optimising communication in the homenet.
3.5.1. Unicast Routing within the Homenet
The role of the unicast routing protocol is to provide good enough
end-to-end connectivity often enough, where good/often enough is
defined by user expectations.
Due to the use of a variety of diverse underlying link technologies,
path selection in a homenet may benefit from being more refined than
minimising hop count. It may also be beneficial for traffic to use
multiple paths to a given destination within the homenet where
available rather than just a single best path.
Minimising convergence time should be a goal in any routed
environment. It is reasonable to assume that convergence time should
not be significantly longer than network outages users are accustomed
to should their CE router reboot.
The homenet architecture is agnostic as to the choice of underlying
routing technology, e.g., link state versus Bellman-Ford.
The routing protocol should support the generic use of multiple
customer Internet connections and the concurrent use of multiple
delegated prefixes. A routing protocol that can make routing
decisions based on source and destination addresses is thus highly
desirable, to avoid problems with upstream ISP ingress filtering as
described in BCP 38. Multihoming support may also include load
balancing to multiple providers and failover from a primary to a
backup link when available. The protocol should not require upstream
ISP connectivity to be established to continue routing within the
The homenet architecture is agnostic on a minimum hop count that has
to be supported by the routing protocol. The architecture should,
however, be scalable to other scenarios where homenet technology may
be deployed, which may include small office and small enterprise
sites. To allow for such cases, it would be desirable that the
architecture is scalable to higher hop counts and to larger numbers
of routers than would be typical in a true home network.
At the time of writing, link-layer networking technology is poised to
become more heterogeneous, as networks begin to employ both
traditional Ethernet technology and link layers designed for LLNs,
such as those used for certain types of sensor devices.
Ideally, LLN or other logically separate networks should be able to
exchange routes such that IP traffic may be forwarded among the
networks via gateway routers that interoperate with both the homenet
and any LLNs. Current home deployments use largely different
mechanisms in sensor and basic Internet connectivity networks. IPv6
virtual machine (VM) solutions may also add additional routing
In this homenet architecture, LLNs and other specialised networks are
considered stub areas of the homenet and are thus not expected to act
as a transit for traffic between more traditional media.
3.5.2. Unicast Routing at the Homenet Border
The current practice defined in [RFC7084] would suggest that routing
between the homenet CE router and the service provider router follow
the WAN-side requirements model in [RFC7084], Section 4 (WAN-side
requirements), at least in initial deployments. However,
consideration of whether a routing protocol is used between the
homenet CE router and the service provider router is out of scope of
3.5.3. Multicast Support
It is desirable that, subject to the capacities of devices on certain
media types, multicast routing is supported across the homenet,
including source-specific multicast (SSM) [RFC4607].
[RFC4291] requires that any boundary of scope 4 or higher (i.e.,
admin-local or higher) be administratively configured. Thus, the
boundary at the homenet-ISP border must be administratively
configured, though that may be triggered by an administrative
function such as DHCP PD. Other multicast forwarding policy borders
may also exist within the homenet, e.g., to/from a guest subnet,
whilst the use of certain link media types may also affect where
specific multicast traffic is forwarded or routed.
There may be different drivers for multicast to be supported across
the homenet -- for example,
o for homenet-wide service discovery, should a multicast service
discovery protocol of scope greater than link-local be defined
o for multicast-based streaming or file-sharing applications
Where multicast is routed across a homenet, an appropriate multicast
routing protocol is required, one that as per the unicast routing
protocol should be self-configuring. As hinted above, it must be
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.