Internet DRAFT - draft-ietf-snac-simple
draft-ietf-snac-simple
Internet Engineering Task Force T. Lemon
Internet-Draft Apple Inc.
Intended status: Best Current Practice J. Hui
Expires: 5 September 2024 Google LLC
4 March 2024
Automatically Connecting Stub Networks to Unmanaged Infrastructure
draft-ietf-snac-simple-04
Abstract
This document describes a set of practices for connecting stub
networks to adjacent infrastructure networks. This is applicable in
cases such as constrained (Internet of Things) networks where there
is a need to provide functional parity of service discovery and
reachability between devices on the stub network and devices on an
adjacent infrastructure link (for example, a home 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 https://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 5 September 2024.
Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
Lemon & Hui Expires 5 September 2024 [Page 1]
Internet-Draft Automatic Stub Networks March 2024
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Interoperability Goals . . . . . . . . . . . . . . . . . 4
1.2. Usability Goals . . . . . . . . . . . . . . . . . . . . . 6
2. Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Constants . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4. Conventions and Terminology Used in This Document . . . . . . 8
5. Support for adjacent infrastructure links . . . . . . . . . . 9
5.1. Managing addressability on an adjacent infrastructure
link . . . . . . . . . . . . . . . . . . . . . . . . . . 9
5.1.1. Suitable On-Link Prefixes . . . . . . . . . . . . . . 9
5.1.2. State Machine for maintaining a suitable on-link prefix
on an infrastructure link . . . . . . . . . . . . . . 10
5.2. Managing addressability on the stub network . . . . . . . 14
5.2.1. Maintenance across stub router restarts . . . . . . . 15
5.2.2. Generating a per-stub-router ULA Site Prefix . . . . 16
5.2.3. Using DHCPv6 Prefix Delegation to acquire a prefix to
provide addressability . . . . . . . . . . . . . . . 16
5.3. Managing reachability on the adjacent infrastructure
link . . . . . . . . . . . . . . . . . . . . . . . . . . 17
5.4. Managing reachability on the stub network . . . . . . . . 17
5.5. Providing discoverability between stub network links and
infrastructure network links . . . . . . . . . . . . . . 18
5.5.1. Discoverability by hosts on adjacent infrastructure
links . . . . . . . . . . . . . . . . . . . . . . . . 18
5.5.2. Providing discoverability of adjacent infrastructure
hosts on the stub network . . . . . . . . . . . . . . 19
6. Providing reachability to IPv4 services to the stub
network . . . . . . . . . . . . . . . . . . . . . . . . . 20
6.1. NAT64 provided by infrastructure . . . . . . . . . . . . 22
6.2. NAT64 provided by stub router(s) . . . . . . . . . . . . 22
7. Handling partitioning events on a stub network . . . . . . . 24
8. Services Provided by Stub Routers . . . . . . . . . . . . . . 24
9. Normative References . . . . . . . . . . . . . . . . . . . . 25
10. Informative References . . . . . . . . . . . . . . . . . . . 27
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 27
Lemon & Hui Expires 5 September 2024 [Page 2]
Internet-Draft Automatic Stub Networks March 2024
1. Introduction
This document describes a set of practices for connecting stub
networks to adjacent infrastructure networks. There are several use
cases for stub networks. Motivating factors include:
* Incompatible speed: for example, an 802.15.4 network could not be
easily bridged to a WiFi network because the data rates are so
dissimilar. So either it must be bridged in a very complicated
and careful way to avoid overwhelming the 802.15.4 network with
irrelevant traffic, or the 802.15.4 network needs to be a separate
subnet.
* Incompatible media: for example, a constrained 802.15.4 network
connected as a stub network to a WiFi or ethernet infrastructure
network. In the case of an 802.15.4 network, it is quite possible
that the devices used to link the infrastructure network to the
stub network will not be conceived of by the end user as routers.
Consequently, we cannot assume that these devices will be on all
the time. A solution for this use case will require some sort of
commissioning process for stub routers, and can't assume that any
particular stub router will always be available; rather, any stub
router that is available must be able to adapt to current
conditions to provide reachability.
* Incompatible mechanisms: the medium of the stub network may not,
for example, use neighbor discovery to populate a neighbor table.
If the infrastructure network (as is typical) does use neighbor
discovery, then bridging the two networks together would require
some way of translating between neighbor discovery and whatever
mechanism is used on the stub network, and hence complicates
rather than simplifying the problem of connecting the two
networks.
* Incompatible framing: if the stub network is a 6lowpan [RFC4944]
network, packets on the stub network are expected to use 6lowpan
header compression [RFC6282]. Making this work through a bridge
would be very difficult.
* Convenience: end users often connect devices to each other in
order to extend networks
* Transitory connectivity: a mobile device acting as a router for a
set of co-located devices could connect to a network and gain
access to services for itself and for the co-located devices.
Such a stub network is unlikely to have more than one stub router.
Lemon & Hui Expires 5 September 2024 [Page 3]
Internet-Draft Automatic Stub Networks March 2024
What makes stub networks a distinct type of network is simply that a
stub network never provides transit between networks to which it is
connected. The term "stub" refers to the way the network is seen by
the link to which it is connected: there is reachability through a
stub network router to devices on the stub network from the
infrastructure link, but there is no reachability through the stub
network to any link beyond that one.
Eliminating transit routing is not intended to be seen as a virtue in
itself, but rather as a simplifying assumption that makes it possible
to solve a subset of the general problem of automating multi-link
networks. Stub networks may be globally reachable, or may be only
locally reachable. A host on a locally reachable stub network can
only interoperate with hosts on the network link(s) to which it is
connected. A host on a globally reachable stub network should be
able to interoperate with hosts on other network links in the same
infrastructure as well as hosts on the global internet.
It may be noted that just as you can plug several Home Gateway
devices together in series to form multi-layer NATs, there is nothing
preventing the owner of a stub network router from attaching it to a
stub network as if that network were its infrastructure network. In
the case of an IoT wireless network, there may be no way to do this,
nor would it be desirable, but a stub router that uses ethernet on
both the infrastructure and stub network sides could be connected
this way. Nothing in this document is intended to prevent this from
being done, but neither do we attempt to solve the problems that this
could create.
The goal of this document is to describe the minimal set of changes
or behaviors required to use existing IETF specifications to support
the stub network use case. The result is intended to be deployable
on existing networks without requiring changes to those networks.
1.1. Interoperability Goals
The specific goal is for hosts on the stub network to be able to
interoperate with hosts on the adjacent infrastructure link or links.
What we mean by "interoperate" is that a host on a stub network:
* is discoverable by hosts attached to adjacent infrastructure links
* is able to discover hosts attached to adjacent infrastructure
links
* is able to discover hosts on the Internet
Lemon & Hui Expires 5 September 2024 [Page 4]
Internet-Draft Automatic Stub Networks March 2024
* is able to acquire an IP address that can be used to communicate
with hosts attached to adjacent infrastructure links
* has reachability to the hosts attached to adjacent infrastructure
links
* is reachable by hosts on the adjacent infrastructure link
* is able to reach hosts on the Internet
Discoverability here means "discoverable using DNS, or DNS Service
Discovery". DNS Service Discovery includes multicast DNS [RFC6762].
As an example, when one host connected to a specific WiFi network
wishes to discover services on hosts connected to that same WiFi
network, it can do so using multicast DNS. Similarly, when a host on
some other network wishes to discover the same service, it must use
DNS-based DNS Service Discovery [RFC6763]. In both cases,
"discoverable using DNS" means that the host has one or more entries
in the DNS that serve to make it discoverable.
We lump discoverability in with reachability and addressability, both
of which are essentially Layer 3 issues. The reason for this is that
it does us no good to automatically set up connectivity between stub
network hosts and infrastructure hosts if the infrastructure hosts
have no means to learn about the availability of services provided by
stub network hosts. For stub network hosts that only consume cloud
services this will not be an issue, but for stub networks that
provide services, such as IoT devices on stub networks with
incompatible media, discoverability is necessary in order for stub
network connectivity to be useful.
Ability to acquire an IP address that can be used to communicate
means that the IP address a host on the stub network acquires can be
used to communicate with it by hosts not on the stub network.
Reachability to hosts on adjacent infrastructure links means that
when a host (A) on the stub network has a datagram destined for the
IP address of a host (B) on an adjacent infrastructure link, host (A)
knows of a next-hop router to which it can send the datagram, so that
it will ultimately reach host (B) on the infrastructure network.
Reachability from hosts on adjacent infrastructure links means that
when host (A) on an adjacent infrastructure link has a datagram
destined for the IP address of a host (B) on the stub network, a
next-hop router is known by host (A) such that, when the datagram is
sent to that router, it will ultimately reach host (B) on the stub
network.
Lemon & Hui Expires 5 September 2024 [Page 5]
Internet-Draft Automatic Stub Networks March 2024
To achieve the reachability goal described above, this document
assumes hosts attempting to reach destinations on the stub network
maintain a routing table - Type C hosts as defined in Section 3.1 of
[RFC4191]). Type A and Type B hosts are out-of-scope for this
document.
1.2. Usability Goals
In addition to the interoperability goals we've described above, the
additional goal for stub networks is that they be able to be
connected automatically, with no user intervention. The experience
of connecting a stub network to an infrastructure should be as
straightforward as connecting a new host to the same infrastructure
network.
2. Glossary
Addressability: The ability to associate each node on a link with
its own IPv6 address.
Reachability: Given an IPv6 destination address that is not on-link
for any link to which a node is attached, the information required
that allows the node to send packets to a router that can forward
those packets towards a link where the destination address is on-
link.
Adjacent Infrastructure Link (AIL): any link to which a stub network
router is directly attached, that is part of an infrastructure
network and is not the stub network.
Home Gateway: A device, such as a CE Router [RFC7084], that is
intended to connect a single uplink network to a Local-Area
Network. A CE router may be provided by an ISP and only capable
of connecting directly to the ISP's means of service delivery,
e.g. Cable or DSL, or it may have an ethernet port on the WAN
side and one or more ethernet ports, plus WiFi, on the LAN side.
Infrastructure network: the network infrastructure to which a stub
router connects. This network can be a single link, or a network
of links. The network is typically formed by a Home Gateway,
which may also provide some services, such as a DNS resolver, a
DHCPv4 server, and a DHCPv6 prefix delegation server, for example.
Off-Stub-Network-Routable (OSNR) Prefix: a prefix advertised on the
stub network that can be used for communication with hosts not on
the stub network.
Stub Network: A network link that is connected by one or more Stub
Lemon & Hui Expires 5 September 2024 [Page 6]
Internet-Draft Automatic Stub Networks March 2024
Routers to an AIL an infrastructure network, but is not used for
transit between that link and any other link. Section 2.1 of
[RFC2328] describes the distinction between stub networks and
transit networks from a topological perspective: a stub network is
simply any network that does not provide transit within a routing
fabric. There is reachability through a stub network router to
hosts on the stub network, but there is no reachability through
the stub network to any link beyond the stub network link.
Stub Router: A router that provides connectivity between a stub
network and an infrastructure network. A stub router may also
provide connectivity between other networks: the term "stub
router" refers specifically to its role in providing connectivity
to a stub network. For example, a Home Gateway may provide
connectivity between a provider network (WAN) and a home network
(LAN), while at the same time providing connectivity between the
LAN and a stub network. What distinguishes the LAN from the stub
network in this case is that the LAN is potentially a candidate to
act as a transit network to reach other routers, whereas the stub
network is not.
RA Beacon: A Router Advertisement (RA) that is multicast on a link
so that hosts can see that the router is still present. This is
in contrast to a unicast RA sent in response to the router
solicit.
ULA Site Prefix: A Unique Local Address /48 prefix [RFC4193]
randomly generated by each stub router for use in allocating ULA
Link Prefixes to the stub network and the adjacent infrastructure
link.
ULA Link Prefix: A Unique Local Address /64 prefix allocated from
the ULA site prefix. Stub routers can use ULA Link prefixes to
provide addressability on the stub network and/or adjacent
infrastructure link as needed. If a stub router is doing NAT64,
the NAT64 prefix is also a ULA Link Prefix. A total of 65,536 ULA
link prefixes can be allocated from the ULA Site prefix.
3. Constants
This section describes the meaning of and gives default values for
various constants used in this document.
STALE_RA_TIME (default: 10 minutes): The amount of time that can
pass after the last time a router advertisement from a particular
router has been received before we assume the router is no longer
present. This is a stopgap in case the router is reachable but
has silently stopped advertising a prefix; this situation is
Lemon & Hui Expires 5 September 2024 [Page 7]
Internet-Draft Automatic Stub Networks March 2024
unlikely, but if it does happen, new devices joining the
infrastructure network will not be able to reach devices on the
stub network until the stub router decides that the router that
advertised the suitable prefix is stale.
STUB_PROVIDED_PREFIX_LIFETIME (default: 30 minutes): The valid and
preferred lifetime the stub router will advertise. This should be
long enough that a host is actually willing to use it, and
obviously should also be long enough that a missed RA will not
cause the host to stop using it. The values suggested here allow
ten RAs to be missed before the host will stop using the prefix.
RA_BEACON_INTERVAL (default: 3 minutes): How often the stub router
will transmit an RA beacon. This should be frequent enough that a
missed Router Solicit (e.g. due to congestion on a WiFi link) will
not result in an extremely long outage (assuming the congestion
passes before the RA is sent, of course).
PREFIX_DELEGATION_INTERVAL (default: 30 minutes): The lifetime a
stub router should request for a DHCPv6-delegated prefix. The
longer this is, the more prefixes will be consumed on a network
where stub routers are not stable. The lifetime here is chosen to
be long enough that a reboot of the DHCP server will not prevent
the prefix being renewed. It happens to coincide with the value
of STUB_PROVIDED_PREFIX_LIFETIME, but the two should not be
considered to be equivalent.
MAX_FLAGS_COPY_TIME (default: 150 minutes): The maximum time period,
after receiving an RA, that a stub router can copy flag values
from the header of this RA for use in its own transmitted RAs.
MAX_SUITABLE_REACHABLE_TIME (default: 60 seconds): The maximum
ReachableTime value that a router can have in the Neighbor
Table before any suitable prefixes it has advertised are no longer
considered suitable.
4. Conventions and Terminology Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
Lemon & Hui Expires 5 September 2024 [Page 8]
Internet-Draft Automatic Stub Networks March 2024
5. Support for adjacent infrastructure links
We assume that the AIL supports Neighbor Discovery [RFC4861], and
specifically that routers and on-link prefixes can be advertised
using router advertisements and discovered using neighbor solicits.
The stub network link may also support this, or may use some
different mechanism. This section specifies how advertisement of the
on-link prefix for such links is managed. In this section we will
use the term "Advertising Interface" as described in Section 6.2.2 of
[RFC4861].
Support for AILS on networks where Neighbor Discovery is not
supported is out of scope for this document. Stub routers do not
provide routing between AILs when connected to more than one such
link.
5.1. Managing addressability on an adjacent infrastructure link
In order to provide IPv6 routing to the stub network, IPv6 addressing
must be available on each AIL. Ideally such addressing is already
present on these links, and need not be provided. However, if it is
not present, the stub router must provide it.
5.1.1. Suitable On-Link Prefixes
Stub routers must evaluate prefixes that are advertised on-link as to
their suitability for use in communicating with devices on the stub
network. If no suitable prefix is found, a stub router MUST
advertise one.
An on-link prefix is considered suitable if it is advertised on the
link in a Prefix Information option ([RFC4861], Section 4.6.2) with
the following Prefix Information option header values:
* Prefix Length value is 64,
* 'L' bit is set,
* 'A' bit is set, and
* Preferred Lifetime of 30 minutes or more.
A prefix is not considered a suitable on-link prefix if the 'L' bit
is set, but the 'A' bit is not set. This indicates that node
addressability is being managed using DHCPv6. Nodes are not required
to use DHCPv6 to acquire addresses, so a prefix that requires the use
of DHCPv6 can't be considered "suitable"—not all hosts can actually
use it.
Lemon & Hui Expires 5 September 2024 [Page 9]
Internet-Draft Automatic Stub Networks March 2024
A prefix is considered to be advertised on the link if, when a Router
Solicit message ([RFC4861], Section 4.1) is sent, a Router
Advertisement message is received in response which contains a prefix
information option ([RFC4861], Section 4.6.2) for that prefix.
After an RA message containing a suitable prefix has been received,
it can be assumed for some period of time thereafter that that prefix
is still valid on the link. However, prefix lifetimes and router
lifetimes are often quite long. In addition to knowing that a prefix
has been advertised on the link in the past, and is still valid, we
must therefore ensure that at least one router that has advertised
this prefix is still alive to respond to router advertisements.
5.1.2. State Machine for maintaining a suitable on-link prefix on an
infrastructure link
The possible states of an interface connected to an AIL are described
here, along with actions required to be taken to monitor the state.
The purpose of the state machine described here is to ensure that at
all times, when a new host arrives on the AIL, it is able to acquire
an IPv6 address on that link.
5.1.2.1. Status of IP addressability on adjacent infrastructure link
unknown (STATE-UNKNOWN)
When the stub router interface first connects to the AIL, it MUST
begin router discovery.
If, after router discovery has completed, no suitable on-link prefix
has been found, the router moves this interface to STATE-BEGIN-
ADVERTISING (Section 5.1.2.3).
If, during router discovery, a suitable on-link prefix is found, the
router moves the interface to STATE-SUITABLE (Section 5.1.2.2).
In this state, the stub router MUST NOT treat this interface as an
advertising interface as described in Section 6.2.2 of [RFC4861].
5.1.2.2. IP addressability already present on adjacent infrastructure
link (STATE-SUITABLE)
When entering this state, if the router MUST discontinue treating the
interface as an Advertising Interface as described in Section 6.2.2
of [RFC4861], if it has been doing so.
When a new host appears on the AIL and sends an initial router
solicit, if it does not receive a suitable on-link prefix, it will
not be able to communicate. Consequently, the stub router MUST
Lemon & Hui Expires 5 September 2024 [Page 10]
Internet-Draft Automatic Stub Networks March 2024
monitor router solicits and advertisements on the interface in order
to determine whether a prefix that has been advertised on the link is
still being advertised. To accomplish this we have two complementary
methods: router staleness detection and neighbor unreachability
detection.
5.1.2.2.1. Router staleness detection
The stub router MUST listen for router advertisements on the AIL to
which the interface is attached, and record the time at which each
router advertisement was received. The router MUST NOT consider any
router advertisement that is older than STALE_RA_TIME to be suitable.
When the last non-stale router advertisement containing a suitable
prefixes on the link is marked stale, the stub router MUST move the
interface to STATE-BEGIN-ADVERTISING.
5.1.2.2.2. Router Unreachability Detection
For each suitable route, the stub router MUST monitor the state of
reachability to the router(s) that advertised it as described in
([RFC4861], Section 7.3.1) using a ReachableTime value of no more
than MAX_SUITABLE_REACHABLE_TIME. The reason for this is that if no
router providing the on-link prefix on the AIL is reachable, then
when a new host joins the network, it will have no suitable on-link
prefix to use for autoconfiguration, and thus will be unable to
communicate with hosts on the stub network.
Whenever the ReachableTime for a router advertising a suitable prefix
exceeds MAX_SUITABLE_REACHABLE_TIME, the stub router MUST send
unicast neighbor solicits as described in Section 7.2.2 of [RFC4861]
until either a response is received, which resets ReachableTime to
zero, or the maximum number of retransmissions has been sent.
The stub router MUST listen for router solicits on the AIL. When a
router solicit is received, if none of the on-link routers on the AIL
are marked reachable, the stub router MUST move this interface to the
STATE-BEGIN-ADVERTISING state (Section 5.1.2.3).
If a RA beacon interval arrives, and there are no routers advertising
suitable prefixes that have a ReachableTime that is less than
MAX_SUITABLE_REACHABLE_TIME, then the router MUST move this interface
to the STATE-BEGIN-ADVERTISING state.
Lemon & Hui Expires 5 September 2024 [Page 11]
Internet-Draft Automatic Stub Networks March 2024
5.1.2.3. IP addressability not present on adjacent infrastructure link
(STATE-BEGIN-ADVERTISING)
In this state, the stub router generates its own on-link prefix for
the interface. This prefix has a valid and preferred lifetime of
STUB_PROVIDED_PREFIX_LIFETIME seconds. The stub router sends a
router advertisement (RA) containing this prefix in a Prefix
Information Option (PIO). In the PIO, the A (autonomous
configuration) flag Section 4.6.2 of [RFC4861] MUST be set and the L
(on-link) flag SHOULD be set. The exception cases where the L flag
can be cleared is where the specific link-layer technology and/or
configuration requires clearing the L flag.
The Stub Router flag ([I-D.hui-stub-router-ra-flag]) MUST be set in
the RA flags field. The values of the M and O flags MUST be copied
from the respective M/O flag values seen in the most recent (unicast
or multicast) RA received from a non-stub-router. For the selection
of the most recent RA, the following RAs MUST be excluded:
* An RA received from a router longer ago than the Router Lifetime
period indicated in the RA header. This only applies for a non-
zero Router Lifetime value.
* An RA received more than MAX_FLAGS_COPY_TIME ago.
If there is no recent RA from a non-stub-router, both M and O flags
MUST be cleared, unless the stub router rebooted recently. After a
reboot, if no recent RA is received from a non-stub router, but a
recent RA has been received from a stub router, the values for the M
and O flags provided by that stub router MUST be copied. After
MAX_FLAGS_COPY_TIME after reboot, the stub router MUST go back to the
regular behavior defined above. This avoids a situation where a stub
router that has rebooted starts to advertise different M/O flag
values than other stub routers present on the same link.
The sent router advertisement MUST also include a Route Information
option (Section 2.3 of [RFC4191]) for each routable prefix advertised
on the stub network. If the stub router is also a normal router
(e.g. a home WiFi router), it SHOULD include all other routes that it
is advertising in the RA, if there is space.
After having sent the initial router advertisement, the stub router
moves the interface into the STATE-ADVERTISING-SUITABLE state
(Section 5.1.2.4).
Lemon & Hui Expires 5 September 2024 [Page 12]
Internet-Draft Automatic Stub Networks March 2024
5.1.2.4. IP addressability not present on adjacent infrastructure link
(STATE-ADVERTISING-SUITABLE)
When entering this state, if the router MUST begin treating the
interface as an Advertising Interface as described in Section 6.2.2
of [RFC4861] if it is not already doing so.
The stub router sends a router advertisement message, as described in
Section 5.1.2.3, every RA_BEACON_INTERVAL seconds.
The stub router may receive a router advertisement containing one or
more suitable on-link prefixes on the AIL. If any of these prefixes
are different than the prefix the stub router is advertising as the
on-link suitable prefix, and the Stub Router flag is not set in in
the Router Advertisement flags field, the stub router moves the
interface to STATE-DEPRECATING (Section 5.1.2.5).
If the stub router bit is set in the RA header flags field, then one
of the following must be true in order for that prefix to be
considered suitable:
* The prefixes are equal. In this case, the interface remains in
STATE-ADVERTISING-SUITABLE.
* The prefix the stub router is advertising is a ULA prefix
[RFC4193], and the received prefix is a non-ULA prefix. In this
case, the interface moves into the STATE-DEPRECATING
(Section 5.1.2.5) state.
* Both prefixes are ULA prefixes, and the received prefix,
considered as a 128-bit big-endian unsigned integer, is
numerically lower, then the interface moves to STATE-DEPRECATING
(Section 5.1.2.5.
* Otherwise the interface remains in STATE-ADVERTISING-SUITABLE.
5.1.2.5. Stub router deprecating the on-link prefix it is advertising
(STATE-DEPRECATING)
On entry to this state, the stub router has been treating the
interface as an Advertising Interface as described in Section 6.2.2
of [RFC4861], and MUST continue to do so.
When the stub router has detected the availability of suitable on-
link prefix on the AIL to which the interface is attached, and that
prefix is preferable to the one it is advertising, it continues to
advertise its own prefix, but deprecates it:
Lemon & Hui Expires 5 September 2024 [Page 13]
Internet-Draft Automatic Stub Networks March 2024
* the preferred lifetime for its prefix should be set to zero in
subsequent router advertisement messages.
* the valid lifetime for its prefix should be reduced with each
subsequent router advertisement messages.
* the usability of the infrastructure-provided on-link prefix should
be monitored as in the STATE-SUITABLE state; if during the
deprecation period, the stub router detects that there are no
longer any suitable prefixes on the link, as described in
Section 5.1.2.2.1 or in Section 5.1.2.2.2, it MUST return the
interface to the STATE-BEGIN-ADVERTISING (Section 5.1.2.4) state
and resume advertising its prefix with the valid and preferred
lifetimes described there.
In this state, the valid lifetime (VALID) is computed based on three
values: the current time when a router advertisement is being
generated (NOW), the time at which the new suitable on-link prefix
advertisement was received (DEPRECATE_TIME), and
STUB_PROVIDED_PREFIX_LIFETIME. All of these values are in seconds.
VALID is computed as follows:
VALID = STUB_PROVIDED_PREFIX_LIFETIME - (NOW - DEPRECATE_TIME)
If VALID is less than RA_BEACON_INTERVAL, the stub router does not
include the deprecated prefix in the router advertisement. Note that
VALID could be less than zero. Otherwise, the prefix is provided in
the advertisement, but with a valid lifetime of VALID.
5.2. Managing addressability on the stub network
How addressability is managed on stub networks depends on the nature
of the stub network. For some stub networks, the stub router can be
sure that it is the only router. For example, a stub router that is
providing a Wi-Fi network for tethering will advertise its own SSID
and use its own joining credentials; in this case, it can assume that
it is the only router for that network, and advertise a default route
and on-link prefix just like any other router.
However, some stub networks are more cooperative in nature, for
example IP mesh networks. On such networks, multiple stub routers
may be present and be providing addressability and reachability.
In either case, some stub router connected to the stub network MUST
provide a suitable on-link prefix (the OSNR prefix) for the stub
network. If the stub network is a multicast-capable medium where
Router Advertisements are used for router discovery, the same
mechanism described in Section 5.1.2 is used.
Lemon & Hui Expires 5 September 2024 [Page 14]
Internet-Draft Automatic Stub Networks March 2024
Stub networks that do not support the use of Router Advertisements
for router discovery must use some similar mechanism that is
compatible with that type of network. Describing the process of
establishing a common OSNR prefix on such networks is out of scope
for this document.
5.2.1. Maintenance across stub router restarts
Stub routers may restart from time to time; when a restart occurs,
the stub router may have been advertising state to the network which,
following the restart, is no longer required.
For example, suppose there are two stub routers connected to the same
infrastructure link. When the first stub router is restarted, the
second takes over providing an on-link prefix. Now the first router
rejoins the link. It sees that the second stub router's prefix is
advertised on the infrastructure link, and therefore does not
advertise its own.
This behavior can cause problems because the first stub router no
longer sees the on-link prefix it had been advertising on
infrastructure as on-link. Consequently, if it receives a packet to
forward to such an address, it will forward that packet directly to a
default router, if one is present; otherwise, it will have no route
to the destination, and will drop the packet.
To address this problem, stub routers SHOULD remember the last time a
prefix was advertised across restarts. On restart, the router
configures the prefix on its interface but does not advertise it in
Router Advertisements. Devices that are still using that prefix will
be seen as on-link to the router, and so packets will be delivered
using ND on-link rather than forwarded to the default router.
When a stub router has only flash memory with limited write lifetime,
it may be inappropriate to do a write to flash every time an RA
beacon containing a prefix is sent. In this case, the router SHOULD
record the set of prefixes that have been advertised on
infrastructure and the maximum valid lifetime that was advertised.
On restart, the router should assume that hosts on the infrastructure
link have received advertisements for any such prefixes.
When possible, it is best if all stub routers serving a particular
stub network use the same 64-bit prefix on the AIL. For example,
Thread stub routers use bits from the Thread Extended PAN ID to
generate the ULA prefix's Global ID and Subnet ID. The Global ID
generation conforms to [RFC4193] because the Extended PAN ID is
generated randomly using the same mechanism that is specified in RFC
4193 for the ULA prefix bits.
Lemon & Hui Expires 5 September 2024 [Page 15]
Internet-Draft Automatic Stub Networks March 2024
5.2.2. Generating a per-stub-router ULA Site Prefix
In order to be able to provide addressability either on the stub
network or on an adjacent infrastructure network, a stub router MUST
allocate its own ULA Site Pefix. ULA prefixes, described in Unique
Local IPv6 Unicast Addresses ([RFC4193]) are randomly allocated
prefixes. A stub router MUST allocate a single ULA Site Prefix for
use in providing on-link prefixes to the stub network and the
adjacent infrastructure link, as needed.
Any ULA Link Prefixes allocated by a stub router SHOULD be maintained
across reboots, and SHOULD remain stable over time. (TBD: mention
the SHOULD exception cases) However, for privacy reasons, a stub
router that roams from network to network SHOULD allocate a different
ULA Link Prefix each time it connects to a different infrastructure
network, unless configured to behave otherwise.
5.2.3. Using DHCPv6 Prefix Delegation to acquire a prefix to provide
addressability
If DHCPv6 prefix delegation and IPv6 service are both available on
the infrastructure link, then the stub router MUST attempt to acquire
a prefix using DHCPv6 prefix delegation. Using a prefix provided by
the infrastructure DHCPv6 prefix delegation service means (assuming
the infrastructure is configured correctly) that routing is possible
between the stub network links and all links on the infrastructure
network, and possibly to the general internet.
By contrast, if the prefix generated by the stub router is used,
reachability is only possible between the stub network and the AIL.
The OSNR prefix in this case is not known to the infrastructure
network routing fabric, so even though packets might be able to be
forwarded to the intended destination, there would be no return path.
So when the only prefix that is available is the one provided by the
stub router, cloud services will not be reachable via IPv6, and
infrastructure-provided NAT64 will not work. Therefore, when the
stub router is able to successfully acquire a prefix using DHCPv6 PD,
it MUST use DHCPv6 PD rather than the ULA Link prefix it allocated
for the stub network out of its ULA Site Prefix.
A stub router SHOULD request stub network prefixes with length 64.
If the stub router obtains a prefix with length less than 64, it
SHOULD generate a /64 from the obtained prefix by padding with zeros.
If the stub router obtains a prefix with length greater than 64, the
stub router MUST treat the prefix as unsuitable and allocate a ULA
Link Prefix out of its ULA Site Prefix instead.
Lemon & Hui Expires 5 September 2024 [Page 16]
Internet-Draft Automatic Stub Networks March 2024
5.3. Managing reachability on the adjacent infrastructure link
Stub routers MUST advertise reachability to stub network OSNR
prefixes on any AIL to which they are connected. If the stub router
is advertising a suitable prefix on any interface, any such prefixes
MUST be advertised on that interface in the same router advertisement
that is advertising the suitable prefix, to avoid unnecessary
multicast traffic.
Each stub network will have some set of prefixes that are advertised
as on-link for that network. A stub router connected to that stub
network SHOULD advertise reachability to all such prefixes on any AIL
to which it is attached using router advertisements.
A stub router SHOULD NOT advertise itself as a default router on an
AIL by setting a non-zero Router Lifetime value in the header of its
Router Advertisements. The exception to this rule is the case where
the stub router itself is the default router for a particular AIL:
for example, it may be the home router providing connectivity to an
ISP.
5.4. Managing reachability on the stub network
The stub router MAY advertise itself as a default router on the stub
network, if it itself has a default route on the AIL. In some cases
it may not be desirable to advertise reachability to the Internet as
a whole; in this case the stub router is not required to advertise
itself as a default router.
If the stub router is not advertising itself as a default router on
the stub network, it MUST advertise reachability to any prefixes that
are being advertised as on-link on AILs to which it is attached.
This is true for prefixes it is advertising, and for other prefixes
being advertised on that link.
Note that in some stub network configurations, it is possible for
more than one stub router to be connected to the stub network, and
each stub router may be connected to a different AIL. In this case,
a stub router advertising a default route may receive a packet
destined for a link that is not an AIL for that router, but is an AIL
for a different router. In such a case, if the infrastructure is not
capable of routing between these two AILs, a packet which could have
been delivered by another stub router will be lost by the stub router
that received it.
Consequently, stub routers SHOULD be configurable to not advertise
themselves as default routers on the stub network. Stub routers
SHOULD be configurable to explicitly advertise AIL prefixes on the
Lemon & Hui Expires 5 September 2024 [Page 17]
Internet-Draft Automatic Stub Networks March 2024
stub network even if they are advertising as a default router. The
mechanisms by which such configuration can be accomplished are out of
scope for this document.
It is also possible that stub routers for more than one stub network
may be connected to the same AIL. In this case, the stub routers
will be advertising Router Information options in their router
advertisements for their OSNR prefixes. Stub routers MUST track the
presence of such routes, and MUST advertise reachability to them on
interfaces connected to stub networks.
5.5. Providing discoverability between stub network links and
infrastructure network links
Since DNS-SD is in wide use, and provides for ad-hoc, self-
configuring advertising using the mDNS transport, this is a suitable
mandatory-to-implement protocol for stub networks, which must be able
to attach to infrastructure networks without the help of new
mechanisms provided by the infrastructure. Therefore, stub routers
MUST provide DNS-SD service as described in this section.
5.5.1. Discoverability by hosts on adjacent infrastructure links
The adjacent infrastructure can be assumed to already enable some
service discovery mechanism between hosts on the infrastructure
network, and can be assumed to provide a local DNS resolver.
Therefore, we do not need to define a stub-network-specific mechanism
for providing these services on the infrastructure network.
In some cases it will be necessary for hosts on the AIL to be able to
discover devices on the stub network. In other cases, this will be
unnecessary or even undesirable. For example, it may be undesirable
for devices on an AIL to be able to discover devices on a Wi-Fi
tether provided by a mobile phone.
One example of a use case for stub networks where such discovery is
desirable is the constrained network use case. In this case a low-
power, low-cost stub network provides connectivity for devices that
provide services to the infrastructure. For such networks, it is
necessary that devices on the infrastructure be able to discover
devices on the stub network.
The most basic use case for this is to provide feature parity with
existing solutions like multicast DNS (mDNS). For example, a light
bulb with built-in Wi-Fi connectivity might be discoverable on the
infrastructure link to which it is connected, using mDNS, but likely
is not discoverable on other links. To provide equivalent
functionality for an equivalent device on a constrained network that
Lemon & Hui Expires 5 September 2024 [Page 18]
Internet-Draft Automatic Stub Networks March 2024
is a stub network, the stub network device must be discoverable on
the infrastructure link (which is an AIL from the perspective of the
stub network).
If services are to be advertised using DNS Service Discovery
[RFC6763], there are in principle two ways to accomplish this. One
is to present services on the stub network as a DNS zone which can
then be configured as a browsing domain in the DNS ([RFC6763],
Section 11). The second is to advertise stub network services on the
AIL using multicast DNS (mDNS) [RFC6762].
Because this document defines behavior for stub routers connecting to
infrastructure networks that do not provide any new mechanism for
integrating stub networks, there is no way for a stub router to
provide DNS-SD service on an infrastructure link in the form of a DNS
zone in which to do discovery. Therefore, service on the
infrastructure link MUST be provided using an Advertising Proxy, as
defined in [I-D.ietf-dnssd-advertising-proxy].
One limitation of this solution is that it requires that hosts on the
stub network use the DNS-SD Service Registration Protocol
[I-D.ietf-dnssd-srp] to register their DNS-SD advertisements. This
means that in the case of a stub network used for WiFi tethering,
hosts on the stub network will not be discoverable by hosts on the
infrastructure network. Any solution to this problem would require
that the stub router provide a Discovery Proxy [RFC8766]. However, a
discovery proxy is queried using DNS, not mDNS. This requires
assistance from the infrastructure network, and is therefore out of
scope for this document.
5.5.2. Providing discoverability of adjacent infrastructure hosts on
the stub network
Hosts on the stub network may need to discover hosts on the AIL, or
on the stub network. In the IoT network example we've been using,
there might be a light switch on the stub network which needs to be
able to actuate a light bulb connected to the AIL. In order to know
where to send the actuation messages, the light switch will need to
be able to discover the light bulb's address somehow.
Because the stub network is managed by stub routers, any DNS resolver
that's available on the stub network will necessarily be provided by
one or more stub routers. This means that the stub router can enable
discovery of hosts on the infrastructure network by hosts on the stub
network using a Discovery Proxy [RFC8766]. The Discovery Proxy can
be advertised as available to hosts on the stub network through the
DNS resolver provided on the stub network, as described in Section 11
of [RFC6763].
Lemon & Hui Expires 5 September 2024 [Page 19]
Internet-Draft Automatic Stub Networks March 2024
By implication, this means that stub routers MUST provide a DNS
resolver. In addition, stub routers MUST provide DNS zones for each
AIL, and MUST list these zones in the list of default browsing zones
as defined in RFC6763. [[WG: we need to say how these zones are
named. Or refer to the Advertising Proxy doc and have that doc say
how they are named.]]
The stub router MUST also maintain an SRP registrar and use
registrations made through that registrar to populate a DNS zone
which is advertised as a default browsing domain, as above. This SRP
registrar MUST be advertised on the stub network either using the
dnssd-srp and/or dnssd-srp-tls service names or some stub-network-
specific mechanism, the details of which are out of scope for this
document.
6. Providing reachability to IPv4 services to the stub network
Stub Network routers must be capable of providing NAT64 themselves,
and must be capable of discovering the availability of NAT64 service
on the infrastructure network and providing it when it is available
and suitable.
Some network media may provide their own mechanisms for advertising
NAT64 service to the stub network. If such a mechanism is available,
stub routers MUST use the mechanism provided by the network medium
used on the stub network to advertise NAT64 service. Otherwise,
NAT64 service MUST be advertised using the PREF64 Router
Advertisement option [RFC8781].
There are four possible combinations of circumstances in which to
consider how to provide NAT64 service:
1. Infrastructure provides DHCPv6 PD support, and the infrastructure
network provides NAT64
2. Infrastructure provides no DHCPv6 PD support, Infrastructure is
providing NAT64, and there is no IPv4 on infrastructure
3. Infrastructure provides no DHCPv6 PD support, Infrastructure is
providing NAT64, and there is IPv4 on infrastructure
4. Infrastructure provides no DHCPv6 PD support, infrastructure is
not providing NAT64 (and may also not be providing IPv6), and
there is IPv4 on infrastructure
In the first case, infrastructure-provided NAT64 is preferred, and
the stub router MUST advertise this service to the stub network.
Lemon & Hui Expires 5 September 2024 [Page 20]
Internet-Draft Automatic Stub Networks March 2024
In the second case, there is no way to provide connectivity to the
infrastructure: we don't have IPv6 routing other than to the adjacent
infrastructure link, because we don't have a routable prefix, we
don't have NAT64 for the same reason, and we don't have IPv4, so the
stub router can't do NAT64 on its own. In this case, the stub router
MUST NOT advertise NAT64 service.
In the third case, despite the infrastructure providing NAT64, we
can't use it, so the stub router MUST provide its own NAT64 service.
In the fourth case, the stub router MUST provide its own NAT64
service.
An additional complication is that there may be more than one stub
router connecting the stub network to infrastructure. In this case,
it may be desirable to limit the number of stub routers providing
NAT64 service, or it may be acceptable for all stub routers to
provide it.
In the latter case, this should not be a problem: since each stub
router is using its own ULA Site Prefix to provide NAT64, any 5-tuple
that goes through a stub router's NAT64 translator will necessarily
have as its destination an IPv6 address in a particular NAT64 prefix,
and that address will select the correct stub router through which to
send the packet for translation. This also works on the return path
because each stub router has its own IPv4 address, and the return
packet will be destined for that IPv4 packet, and hence will always
return through the stub router that translated it on the way out.
A further complication is that in some cases, some stub routers
connected to the stub network may not be able to advertise an
infrastructure-provided NAT64 prefix, while others may. In this
case, when the infrastructure-provided NAT64 service appears on the
stub network, stub routers that are not able to advertise an
infrastructure NAT64 service MUST NOT do so.
To differentiate between infrastructure-provided NAT64 service and
stub router-provided NAT64 service, stub routers that advertise
infrastructure-provided NAT64 service MUST use a preference of medium
for this service. Stub routers advertising their own service MUST
use a preference of low.
In some cases a stub router may be administratively configured with a
NAT64 prefix. In this situation, the stub router MUST advertise the
prefix with a preference of high.
Lemon & Hui Expires 5 September 2024 [Page 21]
Internet-Draft Automatic Stub Networks March 2024
Stub routers must monitor the advertisement of other NAT64 prefixes
on the stub network. If a stub router is advertising a NAT64 prefix,
and a NAT64 prefix is advertised on the stub network with a higher
preference, the stub router SHOULD deprecate the prefix it is
advertising.
6.1. NAT64 provided by infrastructure
Stub networks are defined to be IPv6-only because it would be
difficult to implement a stub network using IPv4 technology.
However, stub network devices may need to be able to communicate with
IPv4-only services either on the infrastructure network, or on the
global internet. Ideally, the infrastructure network fully supports
IPv6, and all services on the infrastructure network are
IPv6-capable. In this case, perhaps the infrastructure network
provides NAT64 service to IPv4-only hosts on the internet. In this
ideal setting, the stub router need do nothing—the infrastructure
network is doing it all.
In this situation, if there are multiple stub routers, each connected
to the same AIL, there is no need for special behavior—each stub
router can advertise a default route, and any stub router may be used
to route NAT64 traffic. If some stub routers are connected to
different AILs than others, some of which support NAT64 and some of
which do not, then the default route may not carry traffic to the
correct link for NAT64 service. In this case, a more specific
address to the infrastructure NAT64 prefix(es) MUST be advertised by
those stub routers that are able to discover it.
In order for infrastructure-provided NAT64 to work, the stub network
must have an OSNR prefix that is known to the infrastructure.
Typically this means that the stub router must have acquired this
prefix using DHCPv6 Prefix Delegation. Unless otherwise configured
to do so, the stub router MUST NOT advertise infrastructure-provided
NAT64 service on the stub network if it has not acquired the OSNR
prefix through DHCPv6 Prefix Delegation.
6.2. NAT64 provided by stub router(s)
Most infrastructure networks at present do not provide NAT64 service.
Many infrastructure networks do not provide DHCPv6 Prefix Delegation.
In these cases it is necessary for stub routers to be able to provide
NAT64 service if IPv4 hosts are to be reachable from the stub
network. Therefore, stub routers MUST be capable of providing NAT64
service to the stub network. When infrastructure-provided NAT64
service is not present or is not usable, and when no other NAT64
service is already advertised on the stub network, stub routers MUST,
by default, enable their own NAT64 service and advertise it on the
Lemon & Hui Expires 5 September 2024 [Page 22]
Internet-Draft Automatic Stub Networks March 2024
stub network.
To provide NAT64 service, a stub router must allocate a NAT64 prefix.
For convenience, the stub network allocates a single prefix out of
the ULA Site Prefix that it maintains. Out of the 2^16 possible
subnets of the /48, the stub router SHOULD use the numerically
highest /64 prefix.
If there are multiple stub routers providing connectivity between the
stub network and infrastructure, each stub network uses its own NAT64
prefix—there is no common NAT64 prefix. The reason for this is that
NAT64 translation is not stateless, and is tied to the stub router's
IPv4 address. Therefore each NAT64 egress is not equivalent.
A stub network that services a Wi-Fi stub network SHOULD provide
DNS64 translation: hosts on the stub network cannot be assumed to be
able to do DNS64 synthesis in the stub resolver. In this case the
DNS resolver on the stub router MUST honor the CD and DO bits if
received in a request, since this indicates that the stub resolver on
the requestor intends to do DNSSEC validation. In this case, the
resolver on the stub router MUST NOT perform DNS64 synthesis.
On specific stub networks it may be desirable to require the stub
network device to perform DNS64 synthesis. Stub network routers for
such networks do not need to provide DNS64 synthesis. Instead, they
MUST provide an ipv4only.arpa answer that advertises the NAT64 prefix
for that stub router, and MUST provide an explicit route to that
NAT64 prefix on the stub network using RA or whatever technology is
specific to that stub network type.
In constrained networks it can be very useful if stub network
resolvers provide the information required to do DNS64 translation in
the answer to the AAAA query. If the answer to an AAAA query comes
back with "no data" (not NXDOMAIN), this suggests that there may be
an A record. In this case, the stub network's resolver SHOULD
attempt to look up an A record on the same name. If such a record
exists, the resolver SHOULD return no data in the Answer section of
the DNS response, and SHOULD provide any CNAME records that were
involved in returning the "no data" answer to the AAAA query, and
SHOULD provide any A records that were ultimately returned, in the
Additional section. The resolver should also include an
ipv4only.arpa record in the Additional section.
Lemon & Hui Expires 5 September 2024 [Page 23]
Internet-Draft Automatic Stub Networks March 2024
7. Handling partitioning events on a stub network
Some technologies used for stub networks, for example Thread or
6LoWPAN mesh networks, can produce partitioned networks, where what
is notionally the same stub network winds up looking like two or more
discrete links. For mesh networks, such partitions can form and
rejoin over time as a result of either changes in radio propagation
or the addition of, or removal of, devices on the mesh.
On stub networks that can partition, one way of detecting that a
partition has occurred is to notice that the stub router that has
advertised the on-link prefix for the stub network is no longer
reachable via the stub network. When this occurs, stub routers that
notice this loss of reachability MUST advertise a ULA Link Prefix
derived from their ULA Site Prefix on the stub network.
An implication of this is that when such a partition forms, the same
ULA Link Prefix can’t be advertised on both partitions, since this
will result in ambiguous routing. We address this problem by
requiring that each stub router generate its own ULA Site Prefix.
This prefix is then available for two purposes: providing addressing
on the AIL, if needed, and providing addressing on the stub network,
if needed.
When partitions of this type occur, they may also heal. When a
partition heals in a situation where two stub routers have both been
advertising a prefix, it will now appear that there are two prefixes
on the stub network.
When the time comes to deprecate one or more prefixes as a result of
a network partition healing, only one prefix should remain. If there
are any GUA prefixes, and if there is no specific configuration
contradicting this, the GUA prefix that is numerically lowest should
be kept, and all others deprecated. If there are no GUA prefixes,
then the ULA Link Prefix that is numerically lowest should be kept,
and the others deprecated. By using this approach, it is not
necessary for the routers to coordinate in advance.
8. Services Provided by Stub Routers
In order to provide network access, stub routers must provide some
network services to the stub network. We have previously discussed
the following services:
DNS Resolver: The stub network MUST provide a DNS resolver. If RAs
Lemon & Hui Expires 5 September 2024 [Page 24]
Internet-Draft Automatic Stub Networks March 2024
are in use on the stub network, the DNS resolver is advertised in
the Router Advertisement Recursive DNS Server option. If RAs are
not in use on the stub network, then the mechanism whereby the DNS
resolver is advertised by the stub router is specific to that type
of stub network.
DHCPv6 Server: The use of DHCPv6 on the stub network is NOT
RECOMMENDED. In some cases it may necessary, but should be
disabled by default if the stub router provides this capability at
all.
Discovery Proxy: In order to discover services on the AIL, stub
routers MUST act as Discovery Proxies for any AILs to which they
are attached.
SRP Registrar: Stub routers MUST provide SRP registrar service.
This service MUST be advertised using DNS-SD in a legacy browsing
domain that is discoverable through the stub router's resolver.
Legacy Browsing Domains: The stub resolver must advertise legacy
browsing domains for each AIL, for the zone that is maintained by
its SRP service, and in addition must list the legacy browsing
domains provided by the infrastructure network, if any.
NAT64: As mentioned above, stub routers may need to provide NAT64
service so that devices on the stub network can communicate with
IPv4 hosts on the infrastructure network and the global internet.
9. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and
More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191,
November 2005, <https://www.rfc-editor.org/info/rfc4191>.
[RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005,
<https://www.rfc-editor.org/info/rfc4193>.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
DOI 10.17487/RFC4861, September 2007,
<https://www.rfc-editor.org/info/rfc4861>.
Lemon & Hui Expires 5 September 2024 [Page 25]
Internet-Draft Automatic Stub Networks March 2024
[RFC5175] Haberman, B., Ed. and R. Hinden, "IPv6 Router
Advertisement Flags Option", RFC 5175,
DOI 10.17487/RFC5175, March 2008,
<https://www.rfc-editor.org/info/rfc5175>.
[RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
DOI 10.17487/RFC6762, February 2013,
<https://www.rfc-editor.org/info/rfc6762>.
[RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service
Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013,
<https://www.rfc-editor.org/info/rfc6763>.
[RFC7084] Singh, H., Beebee, W., Donley, C., and B. Stark, "Basic
Requirements for IPv6 Customer Edge Routers", RFC 7084,
DOI 10.17487/RFC7084, November 2013,
<https://www.rfc-editor.org/info/rfc7084>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8766] Cheshire, S., "Discovery Proxy for Multicast DNS-Based
Service Discovery", RFC 8766, DOI 10.17487/RFC8766, June
2020, <https://www.rfc-editor.org/info/rfc8766>.
[RFC8781] Colitti, L. and J. Linkova, "Discovering PREF64 in Router
Advertisements", RFC 8781, DOI 10.17487/RFC8781, April
2020, <https://www.rfc-editor.org/info/rfc8781>.
[I-D.ietf-dnssd-srp]
Lemon, T. and S. Cheshire, "Service Registration Protocol
for DNS-Based Service Discovery", Work in Progress,
Internet-Draft, draft-ietf-dnssd-srp-25, 4 March 2024,
<https://datatracker.ietf.org/api/v1/doc/document/draft-
ietf-dnssd-srp/>.
[I-D.ietf-dnssd-advertising-proxy]
Cheshire, S. and T. Lemon, "Advertising Proxy for DNS-SD
Service Registration Protocol", Work in Progress,
Internet-Draft, draft-ietf-dnssd-advertising-proxy-03, 28
July 2023, <https://datatracker.ietf.org/doc/html/draft-
ietf-dnssd-advertising-proxy-03>.
Lemon & Hui Expires 5 September 2024 [Page 26]
Internet-Draft Automatic Stub Networks March 2024
[I-D.hui-stub-router-ra-flag]
Hui, J., "Stub Router Flag in ICMPv6 Router Advertisement
Messages", Work in Progress, Internet-Draft, draft-hui-
stub-router-ra-flag-02, 27 February 2024,
<https://datatracker.ietf.org/doc/html/draft-hui-stub-
router-ra-flag-02>.
10. Informative References
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328,
DOI 10.17487/RFC2328, April 1998,
<https://www.rfc-editor.org/info/rfc2328>.
[RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler,
"Transmission of IPv6 Packets over IEEE 802.15.4
Networks", RFC 4944, DOI 10.17487/RFC4944, September 2007,
<https://www.rfc-editor.org/info/rfc4944>.
[RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6
Datagrams over IEEE 802.15.4-Based Networks", RFC 6282,
DOI 10.17487/RFC6282, September 2011,
<https://www.rfc-editor.org/info/rfc6282>.
Authors' Addresses
Ted Lemon
Apple Inc.
One Apple Park Way
Cupertino, California 95014
United States of America
Email: mellon@fugue.com
Jonathan Hui
Google LLC
1600 Amphitheatre Parkway
Mountain View, California 940432
United States of America
Email: jonhui@google.com
Lemon & Hui Expires 5 September 2024 [Page 27]
