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draft-ietf-intarea-provisioning-domains.txt
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Network Working Group P. Pfister
Internet-Draft E. Vyncke
Intended status: Standards Track Cisco
Expires: July 26, 2020 T. Pauly
Apple Inc.
D. Schinazi
Google LLC
W. Shao
Cisco
January 23, 2020
Discovering Provisioning Domain Names and Data
draft-ietf-intarea-provisioning-domains-latest
Abstract
Provisioning Domains (PvDs) are defined as consistent sets of network
configuration information. This allows hosts to manage connections
to multiple networks and interfaces simultaneously, such as when a
home router provides connectivity through both a broadband and
cellular network provider.
This document defines a mechanism for explicitly identifying PvDs
through a Router Advertisement (RA) option. This RA option announces
a PvD identifier, which hosts can compare to differentiate between
PvDs. The option can directly carry some information about a PvD and
can optionally point to additional PvD information that can be
retrieved using HTTP over TLS.
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 July 26, 2020.
Pfister, et al. Expires July 26, 2020 [Page 1]
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Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(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 Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Specification of Requirements . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Provisioning Domain Identification using Router
Advertisements . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. PvD ID Option for Router Advertisements . . . . . . . . . 5
3.2. Router Behavior . . . . . . . . . . . . . . . . . . . . . 8
3.3. Non-PvD-aware Host Behavior . . . . . . . . . . . . . . . 9
3.4. PvD-aware Host Behavior . . . . . . . . . . . . . . . . . 9
3.4.1. DHCPv6 configuration association . . . . . . . . . . 10
3.4.2. DHCPv4 configuration association . . . . . . . . . . 11
3.4.3. Connection Sharing by the Host . . . . . . . . . . . 11
3.4.4. Usage of DNS Servers . . . . . . . . . . . . . . . . 12
4. Provisioning Domain Additional Information . . . . . . . . . 13
4.1. Retrieving the PvD Additional Information . . . . . . . . 13
4.2. Operational Consideration to Providing the PvD Additional
Information . . . . . . . . . . . . . . . . . . . . . . . 16
4.3. PvD Additional Information Format . . . . . . . . . . . . 16
4.3.1. Example . . . . . . . . . . . . . . . . . . . . . . . 18
4.4. Detecting misconfiguration and misuse . . . . . . . . . . 18
5. Operational Considerations . . . . . . . . . . . . . . . . . 19
5.1. Exposing Extra RA Options to PvD-Aware Hosts . . . . . . 19
5.2. Different RAs for PvD-Aware and Non-PvD-Aware Hosts . . . 19
5.3. Enabling Multi-homing for PvD-Aware Hosts . . . . . . . . 21
5.4. Providing Additional Information to PvD-Aware Hosts . . . 22
6. Security Considerations . . . . . . . . . . . . . . . . . . . 23
7. Privacy Considerations . . . . . . . . . . . . . . . . . . . 24
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25
8.1. New entry in the Well-Known URIs Registry . . . . . . . . 26
8.2. Additional Information PvD Keys Registry . . . . . . . . 26
8.3. PvD Option Flags Registry . . . . . . . . . . . . . . . . 26
Pfister, et al. Expires July 26, 2020 [Page 2]
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8.4. PvD JSON Media Type Registration . . . . . . . . . . . . 27
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 28
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 28
10.1. Normative References . . . . . . . . . . . . . . . . . . 28
10.2. Informative References . . . . . . . . . . . . . . . . . 30
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 32
1. Introduction
Provisioning Domains (PvDs) are defined in [RFC7556] as consistent
sets of network configuration information. This information includes
properties that are traditionally associated with a single networking
interface, such as source addresses, DNS configuration, proxy
configuration, and gateway addresses.
Clients that are aware of PvDs can take advantage of multiple network
interfaces simultaneously. This enables using two PvDs in parallel
for separate connections or for multi-path transports.
While most PvDs today are discovered implicitly (such as by receiving
information via Router Advertisements from a router on a network that
a client host directly connects to), [RFC7556] also defines the
notion of Explicit PvDs. IPsec Virtual Private Networks are
considered Explicit PvDs, but Explicit PvDs can also be discovered
via the local network router. Discovering Explicit PvDs allows two
key advancements in managing multiple PvDs:
1. The ability to discover and use multiple PvDs on a single
interface, such as when a local router can provide connectivity
to two different Internet Service Providers.
2. The ability to associate additional information about PvDs to
describe the properties of the network.
While [RFC7556] defines the concept of Explicit PvDs, it does not
define the mechanism for discovering multiple Explicit PvDs on a
single network and their additional information.
This document specifies a way to identify PvDs with Fully Qualified
Domain Names (FQDN), called PvD IDs. Those identifiers are
advertised in a new Router Advertisement (RA) [RFC4861] option called
the PvD ID Router Advertisement option which, when present,
associates the PvD ID with all the information present in the Router
Advertisement as well as any configuration object, such as addresses,
derived from it. The PVD ID Router Advertisement option may also
contain a set of other RA options, along with an optional inner
Router Advertisement message header. These options and optional
Pfister, et al. Expires July 26, 2020 [Page 3]
Internet-Draft Provisioning Domains January 2020
inner header are only visible to 'PvD-aware' hosts, allowing such
hosts to have a specialized view of the network configuration.
Since PvD IDs are used to identify different ways to access the
internet, multiple PvDs (with different PvD IDs) can be provisioned
on a single host interface. Similarly, the same PvD ID could be used
on different interfaces of a host in order to inform that those PvDs
ultimately provide equivalent services.
This document also introduces a mechanism for hosts to retrieve
optional additional information related to a specific PvD by means of
an HTTP over TLS query using a URI derived from the PvD ID. The
retrieved JSON object contains additional information that would
typically be considered too large to be directly included in the
Router Advertisement, but might be considered useful to the
applications, or even sometimes users, when choosing which PvD should
be used.
For example, if Alice has both a cellular network provider and a
broadband provider in her home, her PvD-aware devices and
applications would be aware of both available uplinks. These
applications could fail-over between these networks, or run
connections over both (potentially using multi-path transports).
Applications could also select specific uplinks based on the
properties of the network; for example, if the cellular network
provides free high-quality video streaming, a video-streaming
application could select that network while most of the other traffic
on Alice's device uses the broadband provider.
1.1. Specification of Requirements
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.
2. Terminology
This document uses the following terminology:
Provisioning Domain (PvD): A set of network configuration
information; for more information, see [RFC7556].
PvD ID: A Fully Qualified Domain Name (FQDN) used to identify a PvD.
Explicit PvD: A PvD uniquely identified with a PvD ID. For more
information, see [RFC7556].
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Implicit PvD: A PvD that, in the absence of a PvD ID, is identified
by the host interface to which it is attached and the address of
the advertising router. See also [RFC7556].
PvD-aware host: A host that supports the association of network
configuration information into PvDs and the use of these PvDs as
described in this document. Also named PvD-aware node in
[RFC7556].
3. Provisioning Domain Identification using Router Advertisements
Explicit PvDs are identified by a PvD ID. The PvD ID is a Fully
Qualified Domain Name (FQDN) that identifies the network operator.
Network operators MUST use names that they own or manage to avoid
naming conflicts. The same PvD ID MAY be used in several access
networks when they ultimately provide identical services (e.g., in
all home networks subscribed to the same service); else, the PvD ID
MUST be different to follow Section 2.4 of [RFC7556].
3.1. PvD ID Option for Router Advertisements
This document introduces a Router Advertisement (RA) option called
the PvD Option. It is used to convey the FQDN identifying a given
PvD (see Figure 1), bind the PvD ID with configuration information
received over DHCPv4 (see Section 3.4.2), enable the use of HTTP over
TLS to retrieve the PvD Additional Information JSON object (see
Section 4), as well as contain any other RA options which would
otherwise be valid in the RA.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |H|L|R| Reserved | Delay |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number | ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ...
... PvD ID FQDN ...
... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
... | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ...
... Router Advertisement message header ...
... (Only present when R-flag is set) ...
... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Options ...
+-+-+-+-+-+-+-+-+-+-+-+-
Figure 1: PvD ID Router Advertisements Option Format
Type: (8 bits) Set to 21.
Length: (8 bits) The length of the option in units of 8 octets,
including the Type and Length fields, the Router Advertisement
message header, if any, as well as the RA options that are
included within the PvD Option.
H-flag: (1 bit) 'HTTP' flag stating whether some PvD Additional
Information is made available through HTTP over TLS, as described
in Section 4.
L-flag: (1 bit) 'Legacy' flag stating whether the PvD is associated
with IPv4 information assigned using DHCPv4 (see Section 3.4.2).
R-flag: (1 bit) 'Router Advertisement' flag stating whether the PvD
Option header is followed (right after padding to the next 64 bits
boundary) by a Router Advertisement message header (see section
4.2 of [RFC4861]). The usage of the inner message header is
described in Section 3.4.
Reserved: (13 bits) Reserved for later use. It MUST be set to zero
by the sender and ignored by the receiver.
Delay: (4 bits) Unsigned integer used to delay HTTP GET queries from
hosts by a randomized backoff (see Section 4.1). If the H-flag is
not set, senders SHOULD set the delay to zero, and receivers
SHOULD ignore the value.
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Sequence Number: (16 bits) Sequence number for the PvD Additional
Information, as described in Section 4. If the H-flag is not set,
senders SHOULD set the Sequence Number to zero, and receivers
SHOULD ignore the value.
PvD ID FQDN: The FQDN used as PvD ID encoded in DNS format, as
described in Section 3.1 of [RFC1035]. Domain name compression
described in Section 4.1.4 of [RFC1035] MUST NOT be used.
Padding: Zero or more padding octets to the next 8 octet boundary
(see Section 4.6 of [RFC4861]). It MUST be set to zero by the
sender, and ignored by the receiver.
RA message header: (16 octets) When the R-flag is set, a full Router
Advertisement message header as specified in [RFC4861]. The
sender MUST set the 'Type' to 134, the value for "Router
Advertisement", and set the 'Code' to 0. Receivers MUST ignore
both of these fields. The 'Checksum' MUST be set to 0 by the
sender; non-zero checksums MUST be ignored by the receiver without
causing the processing of the message to fail. All other fields
are to be set and parsed as specified in [RFC4861] or any updating
documents.
Options: Zero or more RA options that would otherwise be valid as
part of the Router Advertisement main body, but are instead
included in the PvD Option so as to be ignored by hosts that are
not PvD-aware.
Figure 2 shows an example of a PvD Option with "example.org" as the
PvD ID FQDN and including both a Recursive DNS Server (RDNSS) option
and a prefix information option. It has a Sequence Number of 123,
and indicates the presence of additional information that is expected
to be fetched with a delay factor of 1.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+-----------------------------------------------+
| Type: 21 | Length: 12 |1|0|0| Reserved |Delay:1|
+---------------+-------------------------------+---------------+
| Seq number: 123 | 7 | e |
+---------------+-----------------------------------------------+
| x | a | m | p |
+---------------------------------------------------------------+
| l | e | 3 | o |
+---------------------------------------------------------------+
| r | g | 0 | 0 (padding) |
+---------------------------------------------------------------+
| 0 (padding) | 0 (padding) | 0 (padding) | 0 (padding) |
+---------------+---------------+---------------+---------------+
| RDNSS option (RFC 8106) length: 5 ...
... ...
... |
+---------------------------------------------------------------+
| Prefix Information Option (RFC 4861) length: 4 ...
... |
... |
+---------------------------------------------------------------+
Figure 2
3.2. Router Behavior
A router MAY send RAs containing one PvD Option, but MUST NOT include
more than one PvD Option in each RA. The PvD Option MUST NOT contain
further PvD Options.
The PvD Option MAY contain zero, one, or more RA options which would
otherwise be valid as part of the same RA. Such options are
processed by PvD-aware hosts, while ignored by other hosts as per
section 4.2 of [RFC4861].
In order to provide multiple different PvDs, a router MUST send
multiple RAs. RAs sent from different link-local source addresses
establish distinct implicit PvDs, in the absence of a PvD Option.
Explicit PvDs MAY share link-local source addresses with an Implicit
PvD and any number of other Explicit PvDs.
In other words, different Explicit PvDs MAY be advertised with RAs
using the same link-local source address; but different Implicit
PvDs, advertised by different RAs, MUST use different link-local
addresses because these Implicit PvDs are identified by the source
addresses of the RAs. If a link-local address on the router is
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changed, then any new RA will be interpreted as a different Implicit
PvD by PvD-aware hosts.
As specified in [RFC4861] and [RFC6980], when the set of options
causes the size of an advertisement to exceed the link MTU, multiple
router advertisements MUST be sent to avoid fragmentation, each
containing a subset of the options. In such cases, the PvD Option
header (i.e., all fields except the 'Options' field) MUST be repeated
in all the transmitted RAs. The options within the 'Options' field,
MAY be transmitted only once, included in one of the transmitted PvD
Options.
3.3. Non-PvD-aware Host Behavior
As the PvD Option has a new option code, non-PvD-aware hosts will
simply ignore the PvD Option and all the options it contains (see
section 4.2 of [RFC4861]. This ensures the backward compatibility
required in Section 3.3 of [RFC7556]. This behavior allows for a
mixed-mode network where a mix of PvD-aware and non-PvD-aware hosts
coexist.
3.4. PvD-aware Host Behavior
Hosts MUST associate received RAs and included configuration
information (e.g., Router Valid Lifetime, Prefix Information
[RFC4861], Recursive DNS Server [RFC8106], Routing Information
[RFC4191] options) with the Explicit PvD identified by the first PvD
Option present in the received RA, if any, or with the Implicit PvD
identified by the host interface and the source address of the
received RA otherwise. If an RA message header is present both
within the PvD Option and outside it, the header within the PvD
Option takes precedence.
In case multiple PvD Options are found in a given RA, hosts MUST
ignore all but the first PvD Option.
If a host receives PvD Options flags that it does not recognize
(currently in the Reserved field), it MUST ignore these flags.
Similarly, hosts MUST associate all network configuration objects
(e.g., default routers, addresses, more specific routes, DNS
Recursive Resolvers) with the PvD associated with the RA that
provisioned the object. For example, addresses that are generated
using a received Prefix Information option (PIO) are associated with
the PvD of the last received RA which included the given PIO.
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PvD IDs MUST be compared in a case-insensitive manner as defined by
[RFC4343]. For example, "pvd.example.com." or "PvD.Example.coM."
would refer to the same PvD.
While performing PvD-specific operations such as resolving names,
executing the default address selection algorithm [RFC6724] or
executing the default router selection algorithm when forwarding
packets ([RFC4861], [RFC4191] and [RFC8028]), hosts and applications
MAY consider only the configuration associated with any non-empty
subset of PvDs. For example, a host MAY associate a given process
with a specific PvD, or a specific set of PvDs, while associating
another process with another PvD. A PvD-aware application might also
be able to select, on a per-connection basis, which PvDs should be
used. In particular, constrained devices such as small battery
operated devices (e.g., IoT), or devices with limited CPU or memory
resources may purposefully use a single PvD while ignoring some
received RAs containing different PvD IDs.
The way an application expresses its desire to use a given PvD, or a
set of PvDs, or the way this selection is enforced, is out of the
scope of this document. Useful insights about these considerations
can be found in [I-D.kline-mif-mpvd-api-reqs].
3.4.1. DHCPv6 configuration association
When a host retrieves stateless configuration elements using DHCPv6
(e.g., DNS recursive resolvers or DNS domain search lists [RFC3646]),
they MUST be associated with all the explicit and implicit PvDs
received on the same interface and contained in a RA with the O-flag
set [RFC4861].
When a host retrieves stateful assignments using DHCPv6, such
assignments MUST be associated with the received PvD which was
received with RAs with the M-flag set and including a matching PIO.
A PIO is considered to match a DHCPv6 assignment when the IPv6 prefix
from the PIO includes the assignment from DHCPv6. For example, if a
PvD's associated PIO defines the prefix 2001:db8:cafe::/64, a DHCPv6
IA_NA message that assigns the address 2001:db8:cafe::1234:4567 would
be considered to match.
In cases where an address would be assigned by DHCPv6 and no matching
PvD could be found, hosts MAY associate the assigned address with any
implicit PvD received on the same interface or to multiple implicit
PvDs received on the same interface. This is intended to resolve
backward compatibility issues with rare deployments choosing to
assign addresses with DHCPv6 while not sending any matching PIO.
Implementations are suggested to flag or log such scenarios as errors
to help detect misconfigurations.
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3.4.2. DHCPv4 configuration association
Associating DHCPv4 [RFC2131] configuration elements with Explicit
PvDs allows hosts to treat a set of IPv4 and IPv6 configurations as a
single PvD with shared properties. For example, consider a router
that provides two different uplinks. One could be a broadband
network that has data rate and streaming properties described in PvD
additional information and that provides both IPv4 and IPv6 network
access. The other could be a cellular network that provides only
IPv6 network access, and uses NAT64 [RFC6146]. The broadband network
can be represented by an Explicit PvD that points to the additional
information, and also marks association with DHCPv4 information. The
cellular network can be represented by a different Explicit PvD that
is not associated with DHCPv4.
When a PvD-aware host retrieves configuration elements from DHCPv4,
the information is associated either with a single Explicit PvD on
that interface, or else with all Implicit PvDs on the same interface.
An Explicit PvD indicates its association with DHCPv4 information by
setting the L-flag in the PvD RA Option. If there is exactly one
Explicit PvD that sets this flag, hosts MUST associate the DHCPv4
information with that PvD. Multiple Explicit PvDs on the same
interface marking this flag is a misconfiguration, and hosts SHOULD
NOT associate the DHCPv4 information with any Explicit PvD in this
case.
If no single Explicit PvD claims association with DHCPv4, the
configuration elements coming from DHCPv4 MUST be associated with all
Implicit PvDs identified by the interface on which the DHCPv4
transaction happened. This maintains existing host behavior.
3.4.3. Connection Sharing by the Host
The situation when a host shares connectivity from an upstream
interface (e.g., cellular) to a downstream interface (e.g., Wi-Fi) is
known as 'tethering'. Techniques such as ND-proxy [RFC4389], 64share
[RFC7278] or prefix delegation (e.g., using DHCPv6-PD [RFC8415]) may
be used for that purpose.
Whenever the RAs received from the upstream interface contain a PVD
RA option, hosts that are sharing connectivity SHOULD include a PVD
option within the RAs sent downstream with:
o The same PVD-ID FQDN
o The same H-flag, Delay and Sequence Number values
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o The L bit set whenever the host is sharing IPv4 connectivity
received from the same upstream interface
o The bits from the Reserved field set to 0
The values of the R-flag, Router Advertisement message header and
Options field depend on whether the connectivity should be shared
only with PvD-aware hosts or not (see Section 3.2). In particular,
all options received within the upstream PvD Option and included in
the downstream RA SHOULD be included in the downstream PvD Option.
3.4.4. Usage of DNS Servers
PvD-aware hosts can be provisioned with recursive DNS servers via RA
options passed within an Explicit PvD, via RA options associated with
an Implicit PvD, via DHCPv6 or DHCPv4, or from some other
provisioning mechanism that creates an Explicit PvD (such as a VPN).
In all of these cases, the recursive DNS server addresses SHOULD be
associated with the corresponding PvD. Specifically, queries sent to
a configured recursive DNS server SHOULD be sent from a local IP
address that was provisioned for the PvD via RA or DHCP. Answers
received from the DNS server SHOULD only be used on the same PvD.
PvD-aware applications will be able to select which PvD(s) to use for
DNS resolution and connections, which allows them to effectively use
multiple Explicit PvDs. In order to support non-PvD-aware
applications, however, PvD-aware hosts SHOULD ensure that non-PvD-
aware name resolution APIs like "getaddrinfo" only use resolvers from
a single PvD for a given query. Handling DNS across PvDs is
discussed in Section 5.2.1 of [RFC7556], and PvD APIs are discussed
in Section 6 of [RFC7556].
Maintaining the correct usage of DNS within PvDs avoids various
practical errors, such as:
o A PvD associated with a VPN or otherwise private network may
provide DNS answers that contain addresses inaccessible over
another PvD. This includes the DNS queries to retrieve PvD
additional information, which could otherwise send identifying
information to the recursive DNS system (see Section 4.1).
o A PvD that uses a NAT64 [RFC6146] and DNS64 [RFC6147] will
synthesize IPv6 addresses in DNS answers that are not globally
routable, and would be invalid on other PvDs. Conversely, an IPv4
address resolved via DNS on another PvD cannot be directly used on
a NAT64 network.
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4. Provisioning Domain Additional Information
Additional information about the network characteristics can be
retrieved based on the PvD ID. This set of information is called PvD
Additional Information, and is encoded as a JSON object [RFC8259].
This JSON object is restricted to the I-JSON profile, as defined in
[RFC7493].
The purpose of this JSON object is to provide additional information
to applications on a client host about the connectivity that is
provided using a given interface and source address. It typically
includes data that would be considered too large, or not critical
enough, to be provided within an RA option. The information
contained in this object MAY be used by the operating system, network
libraries, applications, or users, in order to decide which set of
PvDs should be used for which connection, as described in
Section 3.4.
The additional information related to a PvD is specifically intended
to be optional, and is targeted at optimizing or informing the
behavior of user-facing hosts. This information can be extended to
provide hints for host system behavior (such as captive portal or
walled-garden PvD detection) or application behavior (describing
application-specific services offered on a given PvD). This content
may not be appropriate for light-weight Internet of Things (IoT)
devices. IoT devices might need only a subset of the information,
and would in some cases prefer a smaller representation like CBOR
([RFC7049]). Delivering a reduced version of the PvD Additional
Information designed for such devices is not defined in this
document.
4.1. Retrieving the PvD Additional Information
When the H-flag of the PvD Option is set, hosts MAY attempt to
retrieve the PvD Additional Information associated with a given PvD
by performing an HTTP over TLS [RFC2818] GET query to https://<PvD-
ID>/.well-known/pvd. Inversely, hosts MUST NOT do so whenever the
H-flag is not set.
Recommendations for how to use TLS securely can be found in
[RFC7525].
When a host retrieves the PvD Additional Information, it MUST verify
that the TLS server certificate is valid for the performed request;
specifically, that a DNS-ID [RFC6125] on the certificate is equal to
the PvD ID expressed as an FQDN. This validation indicates that the
owner of the FQDN authorizes its use with the prefix advertised by
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the router. If this validation fails, hosts MUST close the
connection and treat the PvD as if it has no Additional Information.
HTTP requests and responses for PvD additional information use the
"application/pvd+json" media type (see Section 8). Clients SHOULD
include this media type as an Accept header field in their GET
requests, and servers MUST mark this media type as their Content-Type
header field in responses.
Note that the DNS name resolution of the PvD ID, any connections made
for certficate validation (such as OCSP [RFC6960]), and the HTTP
request itself MUST be performed using the considered PvD. In other
words, the name resolution, PKI checks, source address selection, as
well as the next-hop router selection MUST be performed while using
exclusively the set of configuration information attached with the
PvD, as defined in Section 3.4. In some cases, it may therefore be
necessary to wait for an address to be available for use (e.g., once
the Duplicate Address Detection or DHCPv6 processes are complete)
before initiating the HTTP over TLS query. In order to address
privacy concerns around linkability of the PvD HTTP connection with
future user-initiated connections, if the host has a temporary
address per [RFC4941] in this PvD, then it SHOULD use a temporary
address to fetch the PvD Additional Information and MAY deprecate the
used temporary address and generate a new temporary address
afterward.
If the HTTP status of the answer is greater than or equal to 400 the
host MUST close its connection and consider that there is no
additional PvD information. If the HTTP status of the answer is
between 300 and 399, inclusive, it MUST follow the redirection(s).
If the HTTP status of the answer is between 200 and 299, inclusive,
the response is expected to be a single JSON object.
After retrieval of the PvD Additional Information, hosts MUST
remember the last Sequence Number value received in an RA including
the same PvD ID. Whenever a new RA for the same PvD is received with
a different Sequence Number value, or whenever the expiry date for
the additional information is reached, hosts MUST deprecate the
additional information and stop using it.
Hosts retrieving a new PvD Additional Information object MUST check
for the presence and validity of the mandatory fields specified in
Section 4.3. A retrieved object including an expiration time that is
already past or missing a mandatory element MUST be ignored.
In order to avoid synchronized queries toward the server hosting the
PvD Additional Information when an object expires, object updates are
delayed by a randomized backoff time.
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o When a host performs a JSON object update after it detected a
change in the PvD Option Sequence Number, it MUST add a delay
before sending the query. The target time for the delay is
calculated as a random time between zero and 2**(10 + Delay)
milliseconds, where 'Delay' corresponds to the 4-bit unsigned
integer in the last received PvD Option.
o When a host last retrieved a JSON object at time A that includes a
expiry time B using the "expires" key, and the host is configured
to keep the PvD information up to date, it MUST add some
randomness into its calculation of the time to fetch the update.
The target time for fetching the updated object is calculated as a
uniformly random time in the interval [(B-A)/2,B].
In the example Figure 2, the delay field value is 1, this means that
the host calculates its delay by choosing a uniformly random time
between 0 and 2**(10 + 1) milliseconds, i.e., between 0 and 2048
milliseconds.
Since the 'Delay' value is directly within the PvD Option rather than
the object itself, an operator may perform a push-based update by
incrementing the Sequence Number value while changing the Delay value
depending on the criticality of the update and its PvD Additional
Information servers capacity.
In addition to adding a random delay when fetching Additional
Information, hosts MUST enforce a minimum time between requesting
Additional Information for a given PvD on the same network. This
minimum time is RECOMMENDED to be 10 seconds, in order to avoid hosts
causing a denial-of-service on the PvD server. Hosts also MUST limit
the number of requests that are made to different PvD Additional
Information servers on the same network within a short period of
time. A RECOMMENDED value is to issue no more than five PvD
Additional Information requests in total on a given network within 10
seconds. For more discussion, see Section 6.
The PvD Additional Information object includes a set of IPv6 prefixes
(under the key "prefixes") which MUST be checked against all the
Prefix Information Options advertised in the RA. If any of the
prefixes included in any associated PIO is not covered by at least
one of the listed prefixes, the associated PvD information MUST be
considered to be a misconfiguration, and MUST NOT be used by the
host. See Section 4.4 for more discussion on handling such
misconfigurations.
If the request for PvD Additional Information fails due to a TLS
certificate validation error, an HTTP error, or because the retrieved
file does not contain valid PvD JSON, hosts MUST close any connection
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used to fetch the PvD Additional Information, and MUST NOT request
the information for that PvD ID again for the duration of the local
network attachment. If a host detects 10 or more such failures to
fetch PvD Additional Information, the local network is assumed to be
misconfigured or under attack, and the host MUST NOT make any further
requests for any PvD Additional Information, belonging to any PvD ID,
for the duration of the local network attachment. For more
discussion, see Section 6.
4.2. Operational Consideration to Providing the PvD Additional
Information
Whenever the H-flag is set in the PvD Option, a valid PvD Additional
Information object MUST be made available to all hosts receiving the
RA by the network operator. In particular, when a captive portal is
present, hosts MUST still be allowed to perform DNS, certficate
validation, and HTTP over TLS operations related to the retrieval of
the object, even before logging into the captive portal.
Routers SHOULD increment the PVD Option Sequence Number by one
whenever a new PvD Additional Information object is available and
should be retrieved by hosts. If the value exceeds what can be
stored in the Sequence Number field, it MUST wrap back to zero.
The server providing the JSON files SHOULD also check whether the
client address is contained by the prefixes listed in the additional
information, and SHOULD return a 403 response code if there is no
match.
4.3. PvD Additional Information Format
The PvD Additional Information is a JSON object.
The following table presents the mandatory keys which MUST be
included in the object:
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+------------+-----------------+-----------+------------------------+
| JSON key | Description | Type | Example |
+------------+-----------------+-----------+------------------------+
| identifier | PvD ID FQDN | String | "pvd.example.com." |
| | | | |
| expires | Date after | [RFC3339] | "2020-05-23T06:00:00Z" |
| | which this | Date | |
| | object is no | | |
| | longer valid | | |
| | | | |
| prefixes | Array of IPv6 | Array of | ["2001:db8:1::/48", |
| | prefixes valid | strings | "2001:db8:4::/48"] |
| | for this PvD | | |
+------------+-----------------+-----------+------------------------+
A retrieved object which does not include all three of these keys at
the root of the JSON object MUST be ignored. All three keys need to
be validated, otherwise the object MUST be ignored. The value stored
for "identifier" MUST be matched against the PvD ID FQDN presented in
the PvD RA option using the comparison mechanism described in
Section 3.4. The value stored for "expires" MUST be a valid date in
the future. If the PIO of the received RA is not covered by at least
one of the "prefixes" key, the retrieved object SHOULD be ignored.
The following table presents some optional keys which MAY be included
in the object.
+------------+-----------------------+---------+--------------------+
| JSON key | Description | Type | Example |
+------------+-----------------------+---------+--------------------+
| dnsZones | DNS zones searchable | Array | ["example.com", |
| | and accessible | of | |
| | | strings | |
| | | | |
| | | | "sub.example.com"] |
| | | | |
| noInternet | No Internet, set to | Boolean | true |
| | "true" when the PvD | | |
| | is restricted. | | |
+------------+-----------------------+---------+--------------------+
It is worth noting that the JSON format allows for extensions.
Whenever an unknown key is encountered, it MUST be ignored along with
its associated elements.
Private-use or experimental keys MAY be used in the JSON dictionary.
In order to avoid such keys colliding with IANA registry keys,
implementers or vendors defining private-use or experimental keys
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MUST create sub-dictionaries. If a set of PvD Additional Information
keys are defined by an organization that has a Formal URN Namespace
[URN], the URN namespace SHOULD be used as the top-level JSON key for
the sub-dictionary. For other private uses, the sub-dictionary key
SHOULD follow the format of "vendor-*", where the "*" is replaced by
the implementer's or vendor's identifier. For example, keys specific
to the FooBar organization could use "vendor-foobar". If a host
receives a sub-dictionary with an unknown key, the host MUST ignore
the contents of the sub-dictionary.
4.3.1. Example
The following two examples show how the JSON keys defined in this
document can be used:
{
"identifier": "cafe.example.com.",
"expires": "2020-05-23T06:00:00Z",
"prefixes": ["2001:db8:1::/48", "2001:db8:4::/48"],
}
{
"identifier": "company.foo.example.com.",
"expires": "2020-05-23T06:00:00Z",
"prefixes": ["2001:db8:1::/48", "2001:db8:4::/48"],
"vendor-foo":
{
"private-key": "private-value",
},
}
4.4. Detecting misconfiguration and misuse
Hosts MUST validate the TLS server certificate when retrieving PvD
Additional Information, as detailed in Section 4.1.
Hosts MUST verify that all prefixes in all the RA PIOs are covered by
a prefix from the PvD Additional Information. An adversarial router
attempting to spoof the definition of an Explicit PvD, without the
ability to modify the PvD Additional Information, would need to
perform NAT66 in order to circumvent this check. Thus, this check
cannot prevent all spoofing, but it can detect misconfiguration or
mismatched routers that are not adding a NAT.