Internet Engineering Task Force (IETF) M. Boucadair, Ed.

Internet Engineering Task Force (IETF) M. Boucadair, Ed.
Request for Comments: 9463 Orange
Category: Standards Track T. Reddy.K, Ed.
ISSN: 2070-1721 Nokia
D. Wing
Cloud Software Group
N. Cook
Open-Xchange
T. Jensen
Microsoft
November 2023

DHCP and Router Advertisement Options for the Discovery of Network-
designated Resolvers (DNR)

Abstract

This document specifies new DHCP and IPv6 Router Advertisement
options to discover encrypted DNS resolvers (e.g., DNS over HTTPS,
DNS over TLS, and DNS over QUIC). Particularly, it allows a host to
learn an Authentication Domain Name together with a list of IP
addresses and a set of service parameters to reach such encrypted DNS
resolvers.

Status of This Memo

This is an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.

Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9463.

Copyright Notice

Copyright (c) 2023 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 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
2. Terminology
3. Overview
3.1. Configuration Data for Encrypted DNS
3.1.1. ADN as Reference Identifier for DNS Authentication
3.1.2. Avoiding Dependency on External Resolvers
3.1.3. Single vs. Multiple IP Addresses
3.1.4. Why Not Separate Options for the ADN and IP Addresses?
3.1.5. Service Parameters
3.1.6. ADN-Only Mode
3.1.7. Ordering of Encrypted DNS Options
3.1.8. DNR Validation Checks
3.1.9. DNR Information Using Other Provisioning Mechanisms
3.2. Handling Configuration Data Conflicts
3.3. Validating Discovered Resolvers
3.4. Multihoming Considerations
4. DHCPv6 Encrypted DNS Option
4.1. Option Format
4.2. DHCPv6 Client Behavior
5. DHCPv4 Encrypted DNS Option
5.1. Option Format
5.2. DHCPv4 Client Behavior
6. IPv6 RA Encrypted DNS Option
6.1. Option Format
6.2. IPv6 Host Behavior
7. Security Considerations
7.1. Spoofing Attacks
7.2. Deletion Attacks
7.3. Passive Attacks
7.4. Wireless Security - Authentication Attacks
8. Privacy Considerations
9. IANA Considerations
9.1. DHCPv6 Option
9.2. DHCPv4 Option
9.3. Neighbor Discovery Option
10. References
10.1. Normative References
10.2. Informative References
Acknowledgments
Contributors
Authors' Addresses

1. Introduction

This document focuses on the discovery of encrypted DNS resolvers
that are using protocols such as DNS over HTTPS (DoH) [RFC8484], DNS
over TLS (DoT) [RFC7858], or DNS over QUIC (DoQ) [RFC9250] in local
networks.

In particular, this document specifies how a local encrypted DNS
resolver can be discovered by connected hosts by means of DHCPv4
[RFC2132], DHCPv6 [RFC8415], and IPv6 Router Advertisement (RA)
options [RFC4861]. These options are designed to convey the
following information: the DNS Authentication Domain Name (ADN), a
list of IP addresses, and a set of service parameters. This
procedure is called Discovery of Network-designated Resolvers (DNR).

The options defined in this document can be deployed in a variety of
deployments (e.g., local networks with Customer Premises Equipment
(CPEs) that may or may not be managed by an Internet Service Provider
(ISP), or local networks with or without DNS forwarders). Providing
an inventory of such deployments is beyond the scope of this
document.

Resolver selection considerations are out of scope. Likewise,
policies (including any interactions with users) are out of scope.

2. Terminology

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.

This document makes use of the terms defined in [RFC8499]. The
following additional terms are used:

Authentication Domain Name (ADN): Refers to a domain name that is
used by a DNS client to authenticate a DNS resolver.

ADN-only mode: Refers to a DNS discovery mode where only the ADN of
the DNS resolver is retrieved. See Section 3.1.6.

Do53: Refers to unencrypted DNS.

DNR: Refers to the procedure called Discovery of Network-designated
Resolvers.

Encrypted DNS: Refers to a scheme where DNS exchanges are
transported over an encrypted channel. Examples include DoT, DoH,
and DoQ.

Encrypted DNS resolver: Refers to a DNS resolver that supports any
encrypted DNS scheme.

Encrypted DNS options: Refers to the options defined in Sections 4,
5, and 6.

DHCP: Refers to both DHCPv4 and DHCPv6.

3. Overview

This document describes how a DNS client can discover local encrypted
DNS resolvers using DHCP (Sections 4 and 5) and Neighbor Discovery
protocol (Section 6) Encrypted DNS options.

These options configure an ADN, a list of IP addresses, and a set of
service parameters of the encrypted DNS resolver. More information
about the design of these options is provided in the following
subsections.

3.1. Configuration Data for Encrypted DNS

3.1.1. ADN as Reference Identifier for DNS Authentication

In order to allow for a PKIX-based authentication of the encrypted
DNS resolver to the DNS client, the Encrypted DNS options are
designed to always include an ADN. This ADN is presented as a
reference identifier for DNS authentication purposes. This design
accommodates the current best practices for issuing certificates as
per Section 1.7.2 of [RFC6125]:

| Some certification authorities issue server certificates based
| on IP addresses, but preliminary evidence indicates that such
| certificates are a very small percentage (less than 1%) of
| issued certificates.

3.1.2. Avoiding Dependency on External Resolvers

To avoid adding a dependency on another server to resolve the ADN,
the Encrypted DNS options return the IP address(es) to locate an
encrypted DNS resolver. These encrypted DNS resolvers may be hosted
on the same IP address or distinct IP addresses. Such a decision is
deployment specific.

In order to optimize the size of discovery messages when all DNS
resolvers terminate on the same IP address, early draft versions of
this document considered relying upon the discovery mechanisms
specified in [RFC2132], [RFC3646], and [RFC8106] to retrieve a list
of IP addresses to reach their DNS resolvers. Nevertheless, this
approach requires a client that supports more than one encrypted DNS
protocol (e.g., DoH and DoT) to probe that list of IP addresses. To
avoid such probing, the options defined in Sections 4, 5, and 6
associate an encrypted DNS protocol with an IP address. No probing
is required in such a design.

3.1.3. Single vs. Multiple IP Addresses

A list of IP addresses to reach an encrypted DNS resolver may be
returned in an Encrypted DNS option to accommodate current
deployments relying upon primary and backup resolvers. Also, DNR can
be used in contexts where other DNS redundancy schemes (e.g., anycast
as discussed in BCP 126 [RFC4786]) are used.

Whether one or more IP addresses are returned in an Encrypted DNS
option is deployment specific. For example, a router embedding a
recursive server or a forwarder has to include one single IP address
pointing to one of its LAN-facing interfaces. Typically, this IP
address can be a private IPv4 address, a Link-Local address, an IPv6
Unique Local Address (ULA), or a Global Unicast Address (GUA).

If multiple IP addresses are to be returned in an Encrypted DNS
option, these addresses are returned, ordered by preference, for use
by the client.

3.1.4. Why Not Separate Options for the ADN and IP Addresses?

A single option is used to convey both the ADN and IP addresses.
Otherwise, a means to correlate an IP address conveyed in an option
with an ADN conveyed in another option will be required if, for
example, more than one ADN is supported by the network.

3.1.5. Service Parameters

Because distinct encrypted DNS protocols (e.g., DoT, DoH, and DoQ)
may be provisioned by a network and some of these protocols may make
use of customized port numbers instead of default port numbers, the
Encrypted DNS options are designed to return a set of service
parameters. These parameters are encoded following the same rules
for encoding SvcParams using the wire format specified in Section 2.2
of [RFC9460]. This encoding approach may increase the size of the
options, but it has the merit of relying upon an existing IANA
registry and, thus, accommodating new encrypted DNS protocols and
service parameters that may be defined in the future.

The following service parameters MUST be supported by a DNR
implementation:

alpn: Used to indicate the set of supported protocols (Section 7.1
of [RFC9460]).

port: Used to indicate the target port number for the encrypted DNS
connection (Section 7.2 of [RFC9460]).

In addition, the following service parameter is RECOMMENDED to be
supported by a DNR implementation:

dohpath: Used to supply a relative DoH URI Template (Section 5.1 of
[RFC9461]).

3.1.6. ADN-Only Mode

The provisioning mode in which an ADN, a list of IP addresses, and a
set of service parameters of the encrypted DNS resolver are supplied
to a host SHOULD be used because the Encrypted DNS options are self-
contained and do not require any additional DNS queries. The reader
may refer to [RFC7969] for an overview of advanced capabilities that
are supported by DHCP servers to populate configuration data (e.g.,
issue DNS queries).

In contexts where putting additional complexity on requesting hosts
is acceptable, returning an ADN only can be considered. The supplied
ADN will be passed to a local resolution library (a DNS client,
typically), which will then issue Service Binding (SVCB) queries
[RFC9461]. These SVCB queries can be sent to the discovered
encrypted DNS resolver itself or to the network-designated Do53
resolver. Note that this mode may be subject to active attacks,
which can be mitigated by DNSSEC.

| How an ADN is passed to a local resolution library is
| implementation specific.

3.1.7. Ordering of Encrypted DNS Options

The DHCP options defined in Sections 4 and 5 follow the option
ordering guidelines in Section 17 of [RFC7227].

Likewise, the RA option (Section 6) adheres to the recommendations in
Section 9 of [RFC4861].

3.1.8. DNR Validation Checks

On receipt of an Encrypted DNS option, the DHCP client (or IPv6 host)
makes the following validation checks:

* The ADN is present and encoded as per Section 10 of [RFC8415].

* If additional data is supplied:

- The service parameters are encoded following the rules
specified in Section 2.2 of [RFC9460].

- The option includes at least one valid IP address.

- The service parameters do not include "ipv4hint" or "ipv6hint"
parameters.

If any of the checks fail, the receiver discards the received
Encrypted DNS option.

3.1.9. DNR Information Using Other Provisioning Mechanisms

The provisioning mechanisms specified in this document may not be
available in specific networks (e.g., some cellular networks
exclusively use Protocol Configuration Options (PCOs) [TS.24008]) or
may not be suitable in some contexts (e.g., where secure discovery is
needed). Other mechanisms may be considered in these contexts for
the provisioning of encrypted DNS resolvers. It is RECOMMENDED that
at least the following DNR information be made available to a
requesting host:

* A service priority whenever the discovery mechanism does not rely
on implicit ordering if multiple instances of the encrypted DNS
are used.

* An ADN. This parameter is mandatory.

* A list of IP addresses to locate the encrypted DNS resolver.

* A set of service parameters.

3.2. Handling Configuration Data Conflicts

If encrypted DNS resolvers are discovered by a host using both RA and
DHCP, the rules discussed in Section 5.3.1 of [RFC8106] MUST be
followed.

DHCP/RA options to discover encrypted DNS resolvers (including DoH
URI Templates) takes precedence over Discovery of Designated
Resolvers (DDR) [RFC9462], since DDR uses Do53 to an external DNS
resolver, which is susceptible to both internal and external attacks
whereas DHCP/RA is typically protected using the mechanisms discussed
in Section 7.1.

If a client learns both Do53 and encrypted DNS resolvers from the
same network, and absent explicit configuration otherwise, it is
RECOMMENDED that the client use the encrypted DNS resolvers for that
network. If the client cannot establish an authenticated and
encrypted connection with the encrypted DNS resolver, it may fall
back to using the Do53 resolver.

3.3. Validating Discovered Resolvers

This section describes a set of validation checks to confirm that an
encrypted DNS resolver matches what is provided using DNR (e.g., DHCP
or RA). Such validation checks do not intend to validate the
security of the DNR provisioning mechanisms or the user's trust
relationship to the network.

If the local DNS client supports one of the discovered encrypted DNS
protocols identified by Application-Layer Protocol Negotiation (ALPN)
protocol identifiers (or another service parameter that indicates
some other protocol disambiguation mechanism), the DNS client
establishes an encrypted DNS session following the service priority
of the discovered encrypted resolvers.

The DNS client verifies the connection based on PKIX validation
[RFC5280] of the DNS resolver certificate and uses the validation
techniques as described in [RFC6125] to compare the ADN conveyed in
the Encrypted DNS options to the certificate provided (see
Section 8.1 of [RFC8310] for more details). The DNS client uses the
default system or application PKI trust anchors unless configured
otherwise to use explicit trust anchors. ALPN-related considerations
can be found in Section 7.1 of [RFC9460]. Operational considerations
related to checking the revocation status of the certificate of an
encrypted DNS resolver are discussed in Section 10 of [RFC8484].

3.4. Multihoming Considerations

Devices may be connected to multiple networks, each providing their
own DNS configuration using the discovery mechanisms specified in
this document. Nevertheless, discussing DNS selection of multi-
interfaced devices is beyond the scope of this specification. Such
considerations fall under the generic issue of handling multiple
provisioning sources and should not be processed in each option
separately, as per the recommendation in Section 12 of [RFC7227].

The reader may refer to [RFC6731] for a discussion of DNS selection
issues and an example of DNS resolver selection for multi-interfaced
devices. Also, the reader may refer to [Local-DNS-Authority] for a
discussion on how DNR and Provisioning Domain (PvD) key "dnsZones"
(Section 4.3 of [RFC8801]) can be used in "split DNS" environments
(Section 6 of [RFC8499]).

4. DHCPv6 Encrypted DNS Option

4.1. Option Format

The format of the DHCPv6 Encrypted DNS option is shown in Figure 1.

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_V6_DNR | Option-length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Service Priority | ADN Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ authentication-domain-name ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Addr Length | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
~ ipv6-address(es) ~
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
~ Service Parameters (SvcParams) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 1: DHCPv6 Encrypted DNS Option

The fields of the option shown in Figure 1 are as follows:

Option-code: OPTION_V6_DNR (144; see Section 9.1).

Option-length: Length of the enclosed data in octets. The option
length is ('ADN Length' + 4) when only an ADN is included in the
option.

Service Priority: The priority of this OPTION_V6_DNR instance
compared to other instances. This 16-bit unsigned integer is
interpreted following the rules specified in Section 2.4.1 of
[RFC9460].

ADN Length: Length of the authentication-domain-name field in
octets.

authentication-domain-name (variable length): A Fully Qualified
Domain Name (FQDN) of the encrypted DNS resolver. This field is
formatted as specified in Section 10 of [RFC8415].

An example of the authentication-domain-name encoding is shown in
Figure 2. This example conveys the FQDN "doh1.example.com.", and
the resulting ADN Length field is 18.

+------+------+------+------+------+------+------+------+------+
| 0x04 | d | o | h | 1 | 0x07 | e | x | a |
+------+------+------+------+------+------+------+------+------+
| m | p | l | e | 0x03 | c | o | m | 0x00 |
+------+------+------+------+------+------+------+------+------+

Figure 2: An Example of the DNS authentication-domain-name
Encoding

Addr Length: Length of enclosed IPv6 addresses in octets. When
present, it MUST be a multiple of 16.

ipv6-address(es) (variable length): Indicates one or more IPv6
addresses to reach the encrypted DNS resolver. An address can be
a Link-Local address, a ULA, or a GUA. The format of this field
is shown in Figure 3.

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| ipv6-address |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 3: Format of the ipv6-address(es) Field

Service Parameters (SvcParams) (variable length): Specifies a set of
service parameters that are encoded following the rules in
Section 2.2 of [RFC9460]. Service parameters may include, for
example, a list of ALPN protocol identifiers or alternate port
numbers. This field SHOULD include at least the "alpn" SvcParam.
The "alpn" SvcParam may not be required in contexts such as a
variant of DNS over the Constrained Application Protocol (CoAP)
where messages are encrypted using Object Security for Constrained
RESTful Environments (OSCORE) [RFC8613]. The service parameters
MUST NOT include "ipv4hint" or "ipv6hint" SvcParams, as they are
superseded by the included IP addresses.

If no port service parameter is included, this indicates that
default port numbers should be used. As a reminder, the default
port number is 853 for DoT, 443 for DoH, and 853 for DoQ.

The length of this field is ('Option-length' - 6 - 'ADN Length' -
'Addr Length').

Note that the "Addr Length", "ipv6-address(es)", and "Service
Parameters (SvcParams)" fields are not present if the ADN-only mode
is used (Section 3.1.6).

4.2. DHCPv6 Client Behavior

To discover an encrypted DNS resolver, the DHCPv6 client MUST include
OPTION_V6_DNR in an Option Request Option (ORO), per Sections 18.2.1,
18.2.2, 18.2.4, 18.2.5, 18.2.6, and 21.7 of [RFC8415].

The DHCPv6 client MUST be prepared to receive multiple instances of
the OPTION_V6_DNR option; each option is to be treated as a separate
encrypted DNS resolver. These instances MUST be processed following
their service priority (i.e., a smaller service priority value
indicates a higher preference).

The DHCPv6 client MUST silently discard any OPTION_V6_DNR that fails
to pass the validation steps defined in Section 3.1.8.

The DHCPv6 client MUST silently discard multicast and host loopback
addresses conveyed in OPTION_V6_DNR.

5. DHCPv4 Encrypted DNS Option

5.1. Option Format

The format of the DHCPv4 Encrypted DNS option is illustrated in
Figure 4.

0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_V4_DNR | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ DNR Instance Data #1 ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ---
. ... . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ optional
~ DNR Instance Data #n ~ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ---

Figure 4: DHCPv4 Encrypted DNS Option

The fields of the option shown in Figure 4 are as follows:

Code: OPTION_V4_DNR (162; see Section 9.2).

Length: Indicates the length of the enclosed data in octets.

DNR Instance Data: Includes the configuration data of an encrypted
DNS resolver. The format of this field is shown in Figure 5.

0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DNR Instance Data Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Service Priority |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ADN Length | |
+-+-+-+-+-+-+-+-+ |
~ authentication-domain-name ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Addr Length | |
+-+-+-+-+-+-+-+-+ |
~ IPv4 Address(es) ~
| +-+-+-+-+-+-+-+-+
| | |
+-+-+-+-+-+-+-+-+ |
~Service Parameters (SvcParams) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 5: DNR Instance Data Format

When several encrypted DNS resolvers are to be included, the "DNR
Instance Data" field is repeated.

The fields shown in Figure 5 are as follows:

DNR Instance Data Length: Length of all following data in octets.
This field is set to ('ADN Length' + 3) when only an ADN is
provided for a DNR instance.

Service Priority: The priority of this instance compared to other
DNR instances. This 16-bit unsigned integer is interpreted
following the rules specified in Section 2.4.1 of [RFC9460].

ADN Length: Length of the authentication-domain-name field in
octets.

authentication-domain-name (variable length): The ADN of the
encrypted DNS resolver. This field is formatted as specified in
Section 10 of [RFC8415]. An example is provided in Figure 2.

Addr Length: Length of included IPv4 addresses in octets. When
present, it MUST be a multiple of 4.

IPv4 Address(es) (variable length): Indicates one or more IPv4
addresses to reach the encrypted DNS resolver. Both private and
public IPv4 addresses can be included in this field. The format
of this field is shown in Figure 6. This format assumes that an
IPv4 address is encoded as a1.a2.a3.a4.

0 8 16 24 32 40 48
+-----+-----+-----+-----+-----+-----+--
| a1 | a2 | a3 | a4 | a1 | a2 | ...
+-----+-----+-----+-----+-----+-----+--
IPv4 Address 1 IPv4 Address 2 ...

Figure 6: Format of the IPv4 Address(es) Field

Service Parameters (SvcParams) (variable length): Specifies a set of
service parameters that are encoded following the rules in
Section 2.2 of [RFC9460]. Service parameters may include, for
example, a list of ALPN protocol identifiers or alternate port
numbers. This field SHOULD include at least the "alpn" SvcParam.
The "alpn" SvcParam may not be required in contexts such as a
variant of DNS over CoAP where messages are encrypted using
OSCORE. The service parameters MUST NOT include "ipv4hint" or
"ipv6hint" SvcParams, as they are superseded by the included IP
addresses.

If no port service parameter is included, this indicates that
default port numbers should be used.

The length of this field is ('DNR Instance Data Length' - 4 - 'ADN
Length' - 'Addr Length').

Note that the "Addr Length", "IPv4 Address(es)", and "Service
Parameters (SvcParams)" fields are not present if the ADN-only mode
is used (Section 3.1.6).

OPTION_V4_DNR is a concatenation-requiring option. As such, the
mechanism specified in [RFC3396] MUST be used if OPTION_V4_DNR
exceeds the maximum DHCPv4 option size of 255 octets.

5.2. DHCPv4 Client Behavior

To discover an encrypted DNS resolver, the DHCPv4 client requests the
encrypted DNS resolver by including OPTION_V4_DNR in a Parameter
Request List option [RFC2132].

The DHCPv4 client MUST be prepared to receive multiple "DNR Instance
Data" field entries in the OPTION_V4_DNR option; each instance is to
be treated as a separate encrypted DNS resolver. These instances
MUST be processed following their service priority (i.e., a smaller
service priority value indicates a higher preference).

The DHCPv4 client MUST silently discard any OPTION_V4_DNR that fails
to pass the validation steps defined in Section 3.1.8.

The DHCPv4 client MUST silently discard multicast and host loopback
addresses conveyed in OPTION_V4_DNR.

6. IPv6 RA Encrypted DNS Option

6.1. Option Format

This section defines a new Neighbor Discovery option [RFC4861]: the
IPv6 RA Encrypted DNS option. This option is useful in contexts
similar to those discussed in Section 1.1 of [RFC8106].

The format of the IPv6 RA Encrypted DNS option is illustrated in
Figure 7.

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 | Service Priority |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ADN Length | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
~ authentication-domain-name ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Addr Length | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
~ ipv6-address(es) ~
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | SvcParams Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Service Parameters (SvcParams) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 7: RA Encrypted DNS Option

The fields of the option shown in Figure 7 are as follows:

Type: 8-bit identifier of the Encrypted DNS option as assigned by
IANA (144; see Section 9.3).

Length: 8-bit unsigned integer. The length of the option (including
the Type and Length fields) is in units of 8 octets.

Service Priority: 16-bit unsigned integer. The priority of this
Encrypted DNS option instance compared to other instances. This
field is interpreted following the rules specified in
Section 2.4.1 of [RFC9460].

Lifetime: 32-bit unsigned integer. This represents the maximum time
in seconds (relative to the time the packet is received) over
which the discovered ADN is valid.

The value of Lifetime SHOULD by default be at least 3 *
MaxRtrAdvInterval, where MaxRtrAdvInterval is the maximum RA
interval as defined in [RFC4861].

A value of all one bits (0xffffffff) represents infinity.

A value of zero means that this ADN MUST no longer be used.

ADN Length: 16-bit unsigned integer. This field indicates the
length of the authentication-domain-name field in octets.

authentication-domain-name (variable length): The ADN of the
encrypted DNS resolver. This field is formatted as specified in
Section 10 of [RFC8415].

Addr Length: 16-bit unsigned integer. This field indicates the
length of enclosed IPv6 addresses in octets. When present, it
MUST be a multiple of 16.

ipv6-address(es) (variable length): One or more IPv6 addresses of
the encrypted DNS resolver. An address can be a Link-Local
address, a ULA, or a GUA.

All of the addresses share the same Lifetime value. As also
discussed in [RFC8106], if it is desirable to have different
Lifetime values per IP address, multiple Encrypted DNS options may
be used.

The format of this field is shown in Figure 3.

SvcParams Length: 16-bit unsigned integer. This field indicates the
length of the "Service Parameters (SvcParams)" field in octets.

Service Parameters (SvcParams) (variable length): Specifies a set of
service parameters that are encoded following the rules in
Section 2.2 of [RFC9460]. Service parameters may include, for
example, a list of ALPN protocol identifiers or alternate port
numbers. This field SHOULD include at least the "alpn" SvcParam.
The "alpn" SvcParam may not be required in contexts such as a
variant of DNS over CoAP where messages are encrypted using
OSCORE. The service parameters MUST NOT include "ipv4hint" or
"ipv6hint" SvcParams, as they are superseded by the included IP
addresses.

If no port service parameter is included, this indicates that
default port numbers should be used.

Note that the "Addr Length", "ipv6-address(es)", and "Service
Parameters (SvcParams)" fields are not present if the ADN-only mode
is used (Section 3.1.6).

The option MUST be padded with zeros so that the full enclosed data
is a multiple of 8 octets (Section 4.6 of [RFC4861]).

6.2. IPv6 Host Behavior

The procedure for DNS configuration is the same as it is with any
other Neighbor Discovery option [RFC4861]. In addition, the host
follows the same procedure as the procedure described in
Section 5.3.1 of [RFC8106] for processing received Encrypted DNS
options, with the formatting requirements listed in Section 6.1 and
the validation checks listed in Section 3.1.8 substituted for length
and field validations.

The host MUST be prepared to receive multiple Encrypted DNS options
in RAs. These instances MUST be processed following their service
priority (i.e., a smaller service priority value indicates a higher
preference).

The host MUST silently discard multicast and host loopback addresses
conveyed in the Encrypted DNS options.

7. Security Considerations

7.1. Spoofing Attacks

DHCP/RA messages are not encrypted or protected against modification
within the LAN. Unless spoofing attacks are mitigated as described
below, the content of DHCP and RA messages can be spoofed or modified
by active attackers, such as compromised devices within the local
network. An active attacker (Section 3.3 of [RFC3552]) can spoof the
DHCP/RA response to provide the attacker's encrypted DNS resolver.
Note that such an attacker can launch other attacks as discussed in
Section 22 of [RFC8415]. The attacker can get a domain name with a
domain-validated public certificate from a Certificate Authority (CA)
and host an encrypted DNS resolver.

Attacks of spoofed or modified DHCP responses and RA messages by
attackers within the local network may be mitigated by making use of
the following mechanisms:

DHCPv6-Shield [RFC7610]: The network access node (e.g., a border
router, a CPE, an Access Point (AP)) discards DHCP response
messages received from any local endpoint.

RA-Guard [RFC7113]: The network access node discards RA messages
received from any local endpoint.

Source Address Validation Improvement (SAVI) solution for DHCP
[RFC7513]: The network access node filters packets with forged
source IP addresses.

The above mechanisms would ensure that the endpoint receives the
correct configuration information of the encrypted DNS resolvers
selected by the DHCP server (or RA sender), but these mechanisms
cannot provide any information about the DHCP server or the entity
hosting the DHCP server (or RA sender).

Encrypted DNS sessions with rogue resolvers that spoof the IP address
of a DNS resolver will fail because the DNS client will fail to
authenticate that rogue resolver based upon PKIX authentication
[RFC6125], particularly the ADN in the Encrypted DNS option. DNS
clients that ignore authentication failures and accept spoofed
certificates will be subject to attacks (e.g., attacks that redirect
to malicious resolvers or intercept sensitive data).

7.2. Deletion Attacks

If the DHCP responses or RAs are dropped by the attacker, the client
can fall back to using a preconfigured encrypted DNS resolver.
However, the use of policies to select resolvers is beyond the scope
of this document.

Note that deletion attacks are not specific to DHCP/RA.

7.3. Passive Attacks

A passive attacker (Section 3.2 of [RFC3552]) can determine that a
host is using DHCP/RA to discover an encrypted DNS resolver and can
infer that the host is capable of using DoH/DoT/DoQ to encrypt DNS
messages. However, a passive attacker cannot spoof or modify DHCP/RA
messages.

7.4. Wireless Security - Authentication Attacks

Wireless LANs (WLANs), frequently deployed in local networks (e.g.,
home networks), are vulnerable to various attacks (e.g., [Evil-Twin],
[Krack], [Dragonblood]). Because of these attacks, only
cryptographically authenticated communications are trusted on WLANs.
This means that any information (e.g., regarding NTP servers, DNS
resolvers, or domain search lists) provided by such networks via
DHCP, DHCPv6, or RA is untrusted because DHCP and RA messages are not
authenticated.

If the pre-shared key (PSK) is the same for all clients that connect
to the same WLAN (e.g., Wi-Fi Protected Access Pre-Shared Key (WPA-
PSK)), the shared key will be available to all nodes, including
attackers. As such, it is possible to mount an active on-path
attack. On-path attacks are possible within local networks because
this form of WLAN authentication lacks peer entity authentication.

This leads to the need for provisioning unique credentials for
different clients. Endpoints can be provisioned with unique
credentials (username and password, typically) provided by the local
network administrator to mutually authenticate to the local WLAN AP
(e.g., 802.1x Wireless User Authentication on OpenWrt [dot1x], EAP-
pwd [RFC8146] ("EAP" stands for "Extensible Authentication
Protocol")). Not all endpoint devices (e.g., Internet of Things
(IoT) devices) support 802.1x supplicants and need an alternate
mechanism to connect to the local network. To address this
limitation, unique PSKs can be created for each such device and WPA-
PSK is used (e.g., [IPSK]).

8. Privacy Considerations

Privacy considerations that are also specific to DNR provisioning
mechanisms are discussed in Section 23 of [RFC8415] and in [RFC7824].
Anonymity profiles for DHCP clients are discussed in [RFC7844]. The
mechanisms defined in this document can be used to infer that a DHCP
client or IPv6 host supports Encrypted DNS options, but these
mechanisms do not explicitly reveal whether local DNS clients are
able to consume these options or infer their encryption capabilities.
Other than that, this document does not expose more privacy
information compared to Do53 discovery options.

As discussed in [RFC9076], the use of encrypted DNS does not reduce
the data available in the DNS resolver. For example, the reader may
refer to Section 8 of [RFC8484] or Section 7 of [RFC9250] for a
discussion on specific privacy considerations for encrypted DNS.

9. IANA Considerations

9.1. DHCPv6 Option

IANA has assigned the following new DHCPv6 Option Code in the "Option
Codes" registry maintained at [DHCPV6].

+=======+===============+============+==================+===========+
| Value | Description | Client ORO | Singleton | Reference |
| | | | Option | |
+=======+===============+============+==================+===========+
| 144 | OPTION_V6_DNR | Yes | No | RFC 9463 |
+-------+---------------+------------+------------------+-----------+

Table 1: DHCPv6 Encrypted DNS Option

9.2. DHCPv4 Option

IANA has assigned the following new DHCP Option Code in the "BOOTP
Vendor Extensions and DHCP Options" registry maintained at [BOOTP].

+=====+===============+=============+============+===========+
| Tag | Name | Data Length | Meaning | Reference |
+=====+===============+=============+============+===========+
| 162 | OPTION_V4_DNR | N | Encrypted | RFC 9463 |
| | | | DNS Server | |
+-----+---------------+-------------+------------+-----------+

Table 2: DHCPv4 Encrypted DNS Option

9.3. Neighbor Discovery Option

IANA has assigned the following new IPv6 Neighbor Discovery Option
type in the "IPv6 Neighbor Discovery Option Formats" subregistry
under the "Internet Control Message Protocol version 6 (ICMPv6)
Parameters" registry maintained at [ND].

+======+======================+===========+
| Type | Description | Reference |
+======+======================+===========+
| 144 | Encrypted DNS Option | RFC 9463 |
+------+----------------------+-----------+

Table 3: Neighbor Discovery Encrypted
DNS Option

10. References

10.1. 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>.

[RFC2132] Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
Extensions", RFC 2132, DOI 10.17487/RFC2132, March 1997,
<https://www.rfc-editor.org/info/rfc2132>.

[RFC3396] Lemon, T. and S. Cheshire, "Encoding Long Options in the
Dynamic Host Configuration Protocol (DHCPv4)", RFC 3396,
DOI 10.17487/RFC3396, November 2002,
<https://www.rfc-editor.org/info/rfc3396>.

[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>.

[RFC8106] Jeong, J., Park, S., Beloeil, L., and S. Madanapalli,
"IPv6 Router Advertisement Options for DNS Configuration",
RFC 8106, DOI 10.17487/RFC8106, March 2017,
<https://www.rfc-editor.org/info/rfc8106>.

[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>.

[RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A.,
Richardson, M., Jiang, S., Lemon, T., and T. Winters,
"Dynamic Host Configuration Protocol for IPv6 (DHCPv6)",
RFC 8415, DOI 10.17487/RFC8415, November 2018,
<https://www.rfc-editor.org/info/rfc8415>.

[RFC9460] Schwartz, B., Bishop, M., and E. Nygren, "Service Binding
and Parameter Specification via the DNS (SVCB and HTTPS
Resource Records)", RFC 9460, DOI 10.17487/RFC9460,
November 2023, <https://www.rfc-editor.org/info/rfc9460>.

[RFC9461] Schwartz, B., "Service Binding Mapping for DNS Servers",
RFC 9461, DOI 10.17487/RFC9461, November 2023,
<https://www.rfc-editor.org/info/rfc9461>.

10.2. Informative References

[BOOTP] IANA, "BOOTP Vendor Extensions and DHCP Options",
<https://www.iana.org/assignments/bootp-dhcp-parameters/>.

[DHCPV6] IANA, "Option Codes",
<https://www.iana.org/assignments/dhcpv6-parameters/>.

[DNS-TLS-DHCPv6-Opt]
Pusateri, T. and W. Toorop, "DHCPv6 Options for private
DNS Discovery", Work in Progress, Internet-Draft, draft-
pusateri-dhc-dns-driu-00, 2 July 2018,
<https://datatracker.ietf.org/doc/html/draft-pusateri-dhc-
dns-driu-00>.

[dot1x] OpenWrt, "Introduction to 802.1X", December 2021,
<https://openwrt.org/docs/guide-user/network/wifi/
wireless.security.8021x>.

[Dragonblood]
Vanhoef, M. and E. Ronen, "Dragonblood: Analyzing the
Dragonfly Handshake of WPA3 and EAP-pwd", 2020 IEEE
Symposium on Security and Privacy (SP), San Francisco, pp.
517-533, DOI 10.1109/SP40000.2020.00031, May 2020,
<https://ieeexplore.ieee.org/document/9152782>.

[Evil-Twin]
Wikipedia, "Evil twin (wireless networks)", November 2022,
<https://en.wikipedia.org/wiki/
Evil_twin_(wireless_networks)>.

[IPSK] Cisco, "8.5 Identity PSK Feature Deployment Guide",
December 2021,
<https://www.cisco.com/c/en/us/td/docs/wireless/
controller/technotes/8-5/
b_Identity_PSK_Feature_Deployment_Guide.html>.

[Krack] Vanhoef, M. and F. Piessens, "Key Reinstallation Attacks:
Forcing Nonce Reuse in WPA2", CCS '17: Proceedings of the
2017 ACM SIGSAC Conference on Computer and Communications
Security, pp. 1313-1328, DOI 10.1145/3133956.3134027,
October 2017,
<https://dl.acm.org/doi/10.1145/3133956.3134027>.

[Local-DNS-Authority]
Reddy, T., Wing, D., Smith, K., and B. Schwartz,
"Establishing Local DNS Authority in Validated Split-
Horizon Environments", Work in Progress, Internet-Draft,
draft-ietf-add-split-horizon-authority-04, 8 March 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-add-
split-horizon-authority-04>.

[ND] IANA, "IPv6 Neighbor Discovery Option Formats",
<https://www.iana.org/assignments/icmpv6-parameters/>.

[RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC
Text on Security Considerations", BCP 72, RFC 3552,
DOI 10.17487/RFC3552, July 2003,
<https://www.rfc-editor.org/info/rfc3552>.

[RFC3646] Droms, R., Ed., "DNS Configuration options for Dynamic
Host Configuration Protocol for IPv6 (DHCPv6)", RFC 3646,
DOI 10.17487/RFC3646, December 2003,
<https://www.rfc-editor.org/info/rfc3646>.

[RFC4786] Abley, J. and K. Lindqvist, "Operation of Anycast
Services", BCP 126, RFC 4786, DOI 10.17487/RFC4786,
December 2006, <https://www.rfc-editor.org/info/rfc4786>.

[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<https://www.rfc-editor.org/info/rfc5280>.

[RFC6125] Saint-Andre, P. and J. Hodges, "Representation and
Verification of Domain-Based Application Service Identity
within Internet Public Key Infrastructure Using X.509
(PKIX) Certificates in the Context of Transport Layer
Security (TLS)", RFC 6125, DOI 10.17487/RFC6125, March
2011, <https://www.rfc-editor.org/info/rfc6125>.

[RFC6731] Savolainen, T., Kato, J., and T. Lemon, "Improved
Recursive DNS Server Selection for Multi-Interfaced
Nodes", RFC 6731, DOI 10.17487/RFC6731, December 2012,
<https://www.rfc-editor.org/info/rfc6731>.

[RFC7113] Gont, F., "Implementation Advice for IPv6 Router
Advertisement Guard (RA-Guard)", RFC 7113,
DOI 10.17487/RFC7113, February 2014,
<https://www.rfc-editor.org/info/rfc7113>.

[RFC7227] Hankins, D., Mrugalski, T., Siodelski, M., Jiang, S., and
S. Krishnan, "Guidelines for Creating New DHCPv6 Options",
BCP 187, RFC 7227, DOI 10.17487/RFC7227, May 2014,
<https://www.rfc-editor.org/info/rfc7227>.

[RFC7513] Bi, J., Wu, J., Yao, G., and F. Baker, "Source Address
Validation Improvement (SAVI) Solution for DHCP",
RFC 7513, DOI 10.17487/RFC7513, May 2015,
<https://www.rfc-editor.org/info/rfc7513>.

[RFC7610] Gont, F., Liu, W., and G. Van de Velde, "DHCPv6-Shield:
Protecting against Rogue DHCPv6 Servers", BCP 199,
RFC 7610, DOI 10.17487/RFC7610, August 2015,
<https://www.rfc-editor.org/info/rfc7610>.

[RFC7824] Krishnan, S., Mrugalski, T., and S. Jiang, "Privacy
Considerations for DHCPv6", RFC 7824,
DOI 10.17487/RFC7824, May 2016,
<https://www.rfc-editor.org/info/rfc7824>.

[RFC7844] Huitema, C., Mrugalski, T., and S. Krishnan, "Anonymity
Profiles for DHCP Clients", RFC 7844,
DOI 10.17487/RFC7844, May 2016,
<https://www.rfc-editor.org/info/rfc7844>.

[RFC7858] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D.,
and P. Hoffman, "Specification for DNS over Transport
Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May
2016, <https://www.rfc-editor.org/info/rfc7858>.

[RFC7969] Lemon, T. and T. Mrugalski, "Customizing DHCP
Configuration on the Basis of Network Topology", RFC 7969,
DOI 10.17487/RFC7969, October 2016,
<https://www.rfc-editor.org/info/rfc7969>.

[RFC8146] Harkins, D., "Adding Support for Salted Password Databases
to EAP-pwd", RFC 8146, DOI 10.17487/RFC8146, April 2017,
<https://www.rfc-editor.org/info/rfc8146>.

[RFC8310] Dickinson, S., Gillmor, D., and T. Reddy, "Usage Profiles
for DNS over TLS and DNS over DTLS", RFC 8310,
DOI 10.17487/RFC8310, March 2018,
<https://www.rfc-editor.org/info/rfc8310>.

[RFC8484] Hoffman, P. and P. McManus, "DNS Queries over HTTPS
(DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018,
<https://www.rfc-editor.org/info/rfc8484>.

[RFC8499] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
Terminology", BCP 219, RFC 8499, DOI 10.17487/RFC8499,
January 2019, <https://www.rfc-editor.org/info/rfc8499>.

[RFC8613] Selander, G., Mattsson, J., Palombini, F., and L. Seitz,
"Object Security for Constrained RESTful Environments
(OSCORE)", RFC 8613, DOI 10.17487/RFC8613, July 2019,
<https://www.rfc-editor.org/info/rfc8613>.

[RFC8801] Pfister, P., Vyncke, É., Pauly, T., Schinazi, D., and W.
Shao, "Discovering Provisioning Domain Names and Data",
RFC 8801, DOI 10.17487/RFC8801, July 2020,
<https://www.rfc-editor.org/info/rfc8801>.

[RFC9076] Wicinski, T., Ed., "DNS Privacy Considerations", RFC 9076,
DOI 10.17487/RFC9076, July 2021,
<https://www.rfc-editor.org/info/rfc9076>.

[RFC9250] Huitema, C., Dickinson, S., and A. Mankin, "DNS over
Dedicated QUIC Connections", RFC 9250,
DOI 10.17487/RFC9250, May 2022,
<https://www.rfc-editor.org/info/rfc9250>.

[RFC9462] Pauly, T., Kinnear, E., Wood, C. A., McManus, P., and T.
Jensen, "Discovery of Designated Resolvers", RFC 9462,
DOI 10.17487/RFC9462, November 2023,
<https://www.rfc-editor.org/info/rfc9462>.

[TS.24008] 3GPP, "Technical Specification Group Core Network and
Terminals; Mobile radio interface Layer 3 specification;
Core network protocols; Stage 3 (Release 18)", version
18.4.0, September 2023,
<https://www.3gpp.org/DynaReport/24008.htm>.

Acknowledgments

Many thanks to Christian Jacquenet and Michael Richardson for their
reviews.

Thanks to Stephen Farrell, Martin Thomson, Vittorio Bertola, Stéphane
Bortzmeyer, Ben Schwartz, Iain Sharp, and Chris Box for their
comments.

Thanks to Mark Nottingham for the feedback on HTTP redirection that
was discussed in previous draft versions of this specification.

The use of DHCP as a candidate protocol to retrieve an ADN was
mentioned in Section 7.3.1 of [RFC8310] and in an Internet-Draft
authored by Tom Pusateri and Willem Toorop [DNS-TLS-DHCPv6-Opt].

Thanks to Bernie Volz for the review of the DHCP part.

Christian Amsüss reported a case where the ALPN service parameter
cannot be used.

Thanks to Andrew Campling for the Shepherd review and Éric Vyncke for
the AD review.

Thanks to Rich Salz for the secdir reviews, Joe Clarke for the opsdir
review, Robert Sparks for the artart review, and David Blacka for the
dnsdir review.

Thanks to Lars Eggert, Roman Danyliw, Erik Kline, Martin Duke, Robert
Wilton, Paul Wouters, and Zaheduzzaman Sarker for the IESG review.

Contributors

Nicolai Leymann
Deutsche Telekom
Germany
Email: [email protected]

Zhiwei Yan
CNNIC
No.4 South 4th Street, Zhongguancun
Beijing
100190
China
Email: [email protected]

Authors' Addresses

Mohamed Boucadair (editor)
Orange
35000 Rennes
France
Email: [email protected]

Tirumaleswar Reddy.K (editor)
Nokia
India
Email: [email protected]

Dan Wing
Cloud Software Group Holdings, Inc.
United States of America
Email: [email protected]

Neil Cook
Open-Xchange
United Kingdom
Email: [email protected]

Tommy Jensen
Microsoft
United States of America
Email: [email protected]