Internet DRAFT - draft-boucadair-add-deployment-considerations
draft-boucadair-add-deployment-considerations
Network Working Group M. Boucadair, Ed.
Internet-Draft Orange
Intended status: Informational T. Reddy, Ed.
Expires: 21 April 2023 Nokia
D. Wing
Citrix
N. Cook
Open-Xchange
T. Jensen
Microsoft
18 October 2022
Discovery of Encrypted DNS Resolvers: Deployment Considerations
draft-boucadair-add-deployment-considerations-02
Abstract
The document discusses some deployment considerations of the various
options to discover encrypted DNS resolvers (e.g., DNS-over-HTTPS,
DNS-over-TLS, or DNS-over-QUIC). In particular, the document
describes how Discovery of Network-designated Resolvers (DNR) and
Discovery of Designated Resolvers (DDR) can be used in typical
deployment contexts.
This document does not intend to provide deployment recommendations,
but is meant to exemplify how operators can enable the encrypted DNS
discovery mechanisms. In addition, the document illustrates the
feasibility of hosting encrypted DNS forwarders in Customer Premises
Equipment (CPEs).
Status of This Memo
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provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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Internet-Drafts are draft documents valid for a maximum of six months
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on 21 April 2023.
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Copyright Notice
Copyright (c) 2022 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.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Scope & Target Audience . . . . . . . . . . . . . . . . . . . 3
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Sample Target Deployment Scenarios . . . . . . . . . . . . . 5
4.1. Managed CPEs . . . . . . . . . . . . . . . . . . . . . . 7
4.1.1. Direct DNS . . . . . . . . . . . . . . . . . . . . . 7
4.1.2. Proxied DNS . . . . . . . . . . . . . . . . . . . . . 9
4.2. Unmanaged CPEs . . . . . . . . . . . . . . . . . . . . . 11
4.2.1. ISP-facing Unmanaged CPEs . . . . . . . . . . . . . . 11
4.2.2. Internal Unmanaged CPEs . . . . . . . . . . . . . . . 11
5. Hosting Encrypted DNS Forwarder in Local Networks . . . . . . 12
5.1. DDR/DNR Comparison and Naming Constraints . . . . . . . . 12
5.2. Managed CPEs . . . . . . . . . . . . . . . . . . . . . . 13
5.2.1. DNS Forwarders . . . . . . . . . . . . . . . . . . . 13
5.2.2. ACME . . . . . . . . . . . . . . . . . . . . . . . . 13
5.3. Unmanaged CPEs . . . . . . . . . . . . . . . . . . . . . 14
6. Legacy CPEs . . . . . . . . . . . . . . . . . . . . . . . . . 16
7. Security Considerations . . . . . . . . . . . . . . . . . . . 16
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 16
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 16
10.1. Normative References . . . . . . . . . . . . . . . . . . 16
10.2. Informative References . . . . . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19
1. Introduction
Discovery of Network-designated Resolvers (DNR) [I-D.ietf-add-dnr]
specifies how a local encrypted DNS resolver can be discovered by
connected hosts by means of DHCP [RFC2132], DHCPv6 [RFC8415], and
IPv6 Router Advertisement (RA) [RFC4861] options. 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. The ADN is used as a reference identifier for
authentication purposes, while the list of IP addresses designate
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where to locate the resolver without relying upon an external
resolver. The service parameters provide additional information to
characterize a DNS resolver (e.g., supported encrypted DNS,
customized DNS port number, or URI Template for DNS-over-HTTPS
(DoH)). Such an information is used by a DNS client for DNS resolver
selection and session establishment.
This document discusses some considerations to make use of the
discovery of encrypted DNS resolvers such as DoH [RFC8484], DNS-over-
TLS (DoT) [RFC7858], or DNS-over-QUIC (DoQ) [RFC9250] in local
networks.
Sample target deployment scenarios are discussed in Section 4; both
managed and unmanaged Customer Premises Equipment (CPEs) are covered.
It is out of the scope of this document to provide an exhaustive
inventory of deployments where Encrypted DNS options can be used.
Considerations related to hosting a DNS forwarder in a local network
are described in Section 5. In contexts where CPEs can't be upgraded
to support DNR, Discovery of Designated Resolvers (DDR)
[I-D.ietf-add-ddr] can be used. See Sections 5.1 and 6 for more
details.
Techniques, such as the one defined in
[I-D.ietf-opsawg-add-encrypted-dns], can be enabled together with
[I-D.ietf-add-dnr] to feed the Encrypted DNS options. However, the
document does not make any assumption about the internal behavior at
the network side to feed the Encrypted DNS options that are supplied
to requesting hosts; only the external observed behavior is detailed
in the following sections.
Policies to guide the activation and selection of encrypted DNS can
be configured by users using implementation specific means (e.g., CPE
management interface).
2. Scope & Target Audience
This document is not setting deployment recommendations or claiming
to share best current practices. It is purposely scoped to exemplify
how encrypted DNS discovery mechanisms can be enabled in typical
networks. A set of considerations are specifically drawn to assist
Internet Service Providers (ISPs), CPE vendors, and home network
security service providers.
Concretely, generalizing the use of encrypted DNS while preserving
services that are offered to users (especially, those services that
require a local DNS forwarder) depend on many actors:
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ISPs and home network security service providers: ISPs who need to
investigate and elaborate plans about how their managed CPEs will
be upgraded to support encrypted DNS forwarders and whether home
network security mechanisms will still be required to enforce per-
device policies.
Some ISPs may also need to investigate plans to offer encrypted
DNS services even for CPE models whose firmware cannot be updated.
For example, ISPs may consider updating the CPE configuration to
point to the ISP's Do53 resolver for DDR to work.
ISPs will also need to assess the impacts of bypassing local DNS
forwarders on their DNS infrastructure and the services they are
offering to their subscribers.
CPE vendors: to help them assess the feasibly of CPEs to host an
encrypted DNS forwarder. To that aim, the document sketches some
realization approaches. For example, CPE vendors may learn from
the effort that was conducted by some DNS providers to optimize
the encrypted DNS forwarder to run in a container in home routers
and how this may be integrated with home network security service
agents.
Users: may want to avoid depending on the capabilities of their ISP-
supplied CPE. They may consider deploying an unmanaged CPE that
uses DNR to advertise the local encrypted DNS information to
connected devices. Section 5.3 discusses how DNR can be used in
such contexts.
OS/Application clients: which need to support the Discovery of
Designated Resolvers (DDR) [I-D.ietf-add-ddr] or the Discovery of
Network-designated Resolvers (DNR) [I-D.ietf-add-dnr] procedures.
This document is meant to assist future deployments and (hopefully)
accelerate the network deployment of encrypted DNS servers.
3. Terminology
This document makes use of the terms defined in [RFC8499].
The following additional terms are used:
DHCP: refers to both DHCPv4 and DHCPv6.
Do53: refers to unencrypted DNS.
DNR: refers to the Discovery of Network-designated Resolvers
procedure defined in [I-D.ietf-add-dnr].
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DDR: refers to the Discovery of Designated Resolvers procedure
defined in [I-D.ietf-add-ddr].
Encrypted DNS: refers to a scheme where DNS exchanges are
transported over an encrypted channel. Examples of encrypted DNS
are DoT, DoH, or DoQ.
Encrypted DNS options: refers to the options defined in
[I-D.ietf-add-dnr].
Managed CPE: refers to a CPE that is managed by an ISP.
Unmanaged CPE: refers to a CPE that is not managed by an ISP.
4. Sample Target Deployment Scenarios
ISPs usually provide DNS resolvers to their customers. To that aim,
ISPs deploy the following mechanisms to advertise a list of DNS
Recursive DNS server(s) to their customers:
* Protocol Configuration Options in cellular networks [TS.24008].
* DHCPv4 [RFC2132] (Domain Name Server Option) or DHCPv6
[RFC8415][RFC3646] (OPTION_DNS_SERVERS).
* IPv6 Router Advertisement [RFC4861][RFC8106] (Type 25 (Recursive
DNS Server Option)).
The communication between a customer's device (possibly via a CPE)
and an ISP-supplied DNS resolver takes place by using cleartext DNS
messages (Do53). Some examples are depicted in cases (a) and (c) of
Figure 1. In the case of cellular networks, the cellular network
will provide connectivity directly to a host (e.g., smartphone,
tablet) or via a CPE. Do53 mechanisms used within the Local Area
Network (LAN) are similar in both fixed and cellular CPE-based
broadband service offerings.
Some ISPs rely upon external resolvers (e.g., outsourced service or
public resolvers); these ISPs provide their customers with the IP
addresses of these external DNS resolvers. An example is depicted in
cases (b) and (d) of Figure 1.
The IP addresses of the DNS resolver can also be configured on CPEs
using dedicated management tools. As such, users can modify the
default DNS configuration of their CPEs (e.g., supplied by their ISP)
to configure their favorite DNS servers. This document permits such
deployments.
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(a) Fixed networks with a local DNS resolver
,--,--,--.
+-+ LAN +---+ ,-' `-.
|H+--------------+CPE+---+ ISP )
+-+ +---+ `-. ,-'
| `--'--'--'
| |
|<=============Do53============>|
| |
(b) Fixed networks with a 3rd party DNS resolver
,--,--,--.
+-+ LAN +---+ ,-' `-. 3rd Party
|H+--------------+CPE+---+ ISP )--- DNS Resolver
+-+ +---+ `-. ,-' |
| `--'--'--' |
| |
|<========================Do53===================>|
| |
(c) Cellular networks with a local DNS resolver
| |
|<=============Do53============>|
| |
| ,--,--,-.
+-+ LAN +---+ ,-' .
|H+--------------+CPE+---+ \
+-+ +---+ ,' ISP `-.
( )
+-----+-. ,-'
+-+ | `--'--'--'
|H+----------------+ |
+-+ |
| |
|<=============Do53============>|
| |
(d) Cellular networks with a 3rd party DNS resolver
| |
|<==================Do53=======================>|
| |
| ,--,--,-. |
+-+ LAN +---+ ,-' . |
|H+--------------+CPE+---+ \ |
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+-+ +---+ ,' ISP `-. 3rd Party
( )--- DNS Resolver
+-----+-. ,-' |
+-+ | `--'--'--' |
|H+----------------+ |
+-+ |
| |
|<==================Do53=======================>|
| |
Legend:
* H: refers to a host.
Figure 1: Sample Legacy Deployments
4.1. Managed CPEs
This section focuses on CPEs that are managed by ISPs.
4.1.1. Direct DNS
ISPs have developed an expertise in managing service-specific
configuration information (e.g., CPE WAN Management Protocol
[TR-069]). For example, these tools may be used to provision the DNS
server's ADN and additional service parameters to managed CPEs if an
encrypted DNS is supported by a network similar to what is depicted
in Figure 2.
For example, DoH-capable DNS clients establish the DoH session with
the discovered DoH server.
When the CPE supports DNR, the DNS client discovers whether the
network-designated DNS resolver supports a given encrypted DNS scheme
(e.g., DoT or DoH) by using the "alpn" service parameter
(Section 3.1.5 of [I-D.ietf-add-dnr]). Otherwise, the DNS client
uses DDR with the Do53 resolver advertised by the CPE and upgrades to
encrypted DNS if that succeeds. Otherwise, the DNS client may fall
back to using unencrypted DNS to the IP address advertised by the CPE
or use some other configuration it has.
DNR is attempted first because it requires fewer round trips to any
network peer because all of the necessary information to use
encrypted DNS is presented directly by the CPE. DDR requires the DNS
client to receive Do53 resolver configuration from the CPE and then
further query for encrypted DNS support from the DNS resolver before
any encrypted DNS can be attempted.
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(a) Fixed Networks
,--,--,--.
+-+ LAN +---+ ,-' `-.
|H+--------------+CPE+---+ ISP )
+-+ +---+ `-. ,-'
| `--'--'--'
| |
|<========Encrypted DNS========>|
| |
(b) Cellular Networks
| |
|<========Encrypted DNS========>|
| |
| ,--,--,-.
+-+ LAN +---+ ,-' .
|H+--------------+CPE+---+ \
+-+ +---+ ,' ISP `-.
( )
+-----+-. ,-'
+-+ | `--'--'--'
|H+----------------+ |
+-+ |
| |
|<========Encrypted DNS========>|
| |
Figure 2: Encrypted DNS in the WAN
Figure 2 shows the scenario where the CPE relays the list of
encrypted DNS resolvers that it learns from the network by using,
e.g., DNR. Direct encrypted DNS sessions will be established between
a host serviced by a CPE and an ISP-supplied encrypted DNS resolver.
Figure 3 shows the example of exchanges that occur for an encrypted
DNS capable host. The DNR exchanges that occur at the CPE WAN may be
terminated by a centralized DHCP server or a router that is located
at the edge of the ISP's network.
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,--,--,--. ,--,--,--.
,-' `-. ,-' ISP `-.
Host---( LAN CPE----( DNS Resolver)
| `-. ,-' `-. ,-'
| `--'--'--' | | `--'--'--'
| |<=DNR=>| |
|<========DNR========>| | |
| | |
| |
|<=========Encrypted DNS===========>|
| |
Figure 3: Direct Encrypted DNS Sessions
4.1.2. Proxied DNS
Figure 4 shows various network setups where the CPE embeds a caching
DNS forwarder. Cases (b) and (d) involves a host (called legacy
host) that does not support DNR. Section 5.1 discusses the
applicability of DDR as a function of the address used by the CPE for
the verification of ownership.
(a)
,--,--,--. ,--,--,--.
,-' `-. ,-' ISP `-.
Host---( LAN CPE----( DNS Resolver)
| `-. ,-'| `-. ,-'
| `--'--'--' | | `--'--'--'
| |<=DNR=>| |
|<========DNR========>| | |
| | |
|<=====Encrypted=====>|<=Encrypted=>|
| DNS | DNS |
(b)
,--,--,--. ,--,--,--.
Legacy ,-' `-. ,-' ISP `-.
Host---( LAN CPE----( DNS Resolver)
| `-. ,-'| `-. ,-'
| `--'--'--' | | `--'--'--'
| |<=DNR=>| |
|<====DHCP/RA(Do53)==>| | |
| | |
|<=======Do53========>|<=Encrypted=>|
| | DNS |
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(c)
,--,--,--. ,--,--,--.
,-' `-. ,-' ISP `-. 3rd Party
Host---( LAN CPE----( )--- DNS Resolver
| `-. ,-'| `-. ,-' |
| `--'--'--' | | `--'--'--' |
| |<=DNR=>| |
|<========DNR========>| | |
| | |
|<=====Encrypted=====>|<=========Encrypted DNS======>|
| DNS | |
(d)
,--,--,--. ,--,--,--.
Legacy ,-' `-. ,-' ISP `-. 3rd Party
Host---( LAN CPE----( )--- DNS Resolver
| `-. ,-'| `-. ,-' |
| `--'--'--' | | `--'--'--' |
| |<=DNR=>| |
|<====DHCP/RA(Do53)==>| | |
| | |
|<========Do53=======>|<=========Encrypted DNS======>|
| | |
Figure 4: Proxied Encrypted DNS Sessions
For all the cases shown in Figure 4, the CPE advertises itself as the
default DNS server to the hosts it serves in the LAN. The CPE relies
upon DHCP or RA to advertise itself to internal hosts as the default
encrypted DNS (cases (a) and (c)) or Do53 resolver (cases (b) and
(d)). When receiving a DNS request it cannot handle locally, the CPE
forwards the request to an upstream encrypted DNS. The upstream
encrypted DNS can be hosted by the ISP (cases (a) and (b)) or
provided by a third party (cases (c) and (d)).
Such a forwarder presence is required for IPv4 service continuity
purposes (e.g., Section 3.1 of [RFC8585]) or for supporting advanced
services within a local network (e.g., malware filtering, parental
control, Manufacturer Usage Description (MUD) [RFC8520] to only allow
intended communications to and from an IoT device). When the CPE
behaves as a DNS forwarder, DNS communications can be decomposed into
two legs:
* The leg between an internal host and the CPE.
* The leg between the CPE and an upstream DNS resolver.
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An ISP that offers encrypted DNS to its customers may enable
encrypted DNS in one or both legs as shown in Figure 4. Additional
considerations related to this setup are discussed in Section 5.
4.2. Unmanaged CPEs
4.2.1. ISP-facing Unmanaged CPEs
Customers may decide to deploy unmanaged CPEs (assuming the CPE is
compliant with the network access technical specification that is
usually published by ISPs). Upon attachment to the network, an
unmanaged CPE receives from the network its service configuration
(including the network-designated DNS information) by means of, e.g.,
DHCP. That DNS information is shared within the LAN following the
same mechanisms as those discussed in Section 4.1. A host can then
establish encrypted DNS sessions with encrypted DNS resolvers similar
to what is depicted in Figure 3 or Figure 4.
4.2.2. Internal Unmanaged CPEs
Customers may also decide to deploy internal routers (called
hereafter, Internal CPEs) for a variety of reasons that are not
detailed here.
Absent any explicit configuration on the internal CPE to override the
DNS configuration it receives from the ISP-supplied CPE, an Internal
CPE relays the DNS information it receives via DHCP/RA from the ISP-
supplied CPE to connected hosts. Encrypted DNS sessions can be
established by a host with the DNS resolvers that are supplied by the
ISP (see Figure 5).
,--,--,--. ,--,--,--.
,-' Internal ,-' ISP `-.
Host--( Network#A CPE----CPE---( DNS Resolver )
| `-. ,-' | `-. ,-'
| `--'--'--' | | | `--'--'--'
| | |<=DNR=>| |
| |<=DNR=>| |
|<========DNR========>| | |
| | |
| |
|<==============Encrypted DNS=============>|
| |
Figure 5: Direct Encrypted DNS Sessions with the ISP DNS Resolver
(Internal CPE)
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Similar to managed CPEs, a user may modify the default DNS
configuration of an unmanaged CPE to use his/her favorite encrypted
DNS resolvers instead. Encrypted DNS sessions can be established
directly between a host and a 3rd Party DNS resolver (see Figure 6).
,--,--,--. ,--,
,' Internal ,-' '- 3rd Party
Host--( Network#A CPE----CPE---( ISP )--- DNS Resolver
| `. ,-' `-. -' |
| `-'--'--' | `--' |
| | |
|<========DNR=====>| |
| | |
| |
|<=================Encrypted DNS==================>|
| |
Figure 6: Direct Encrypted DNS Sessions with a Third Party DNS
Resolver
Section 5.3 discusses considerations related to hosting a forwarder
in the Internal CPE.
5. Hosting Encrypted DNS Forwarder in Local Networks
This section discusses some deployment considerations to host an
encrypted DNS forwarder within a local network
5.1. DDR/DNR Comparison and Naming Constraints
DDR requires proving possession of an IP address, as the DDR
certificate contains the server's IPv4 and IPv6 addresses and is
signed by a certificate authority. DDR is constrained to public IP
addresses because WebPKI certificate authorities will not sign
special-purpose IP addresses [RFC6890], most notably IPv4 private-use
[RFC1918], IPv4 shared address [RFC6598], or IPv6 Unique-Local
[RFC8190] address space. A tempting solution is to use the CPE's WAN
IP address for DDR and prove possession of that IP address. However,
the CPE's WAN IPv4 address will not be a public IPv4 address if the
CPE is behind another layer of NAT (either Carrier Grade NAT (CGN) or
another on-premise NAT), reducing the success of this mechanism to
CPE's WAN IPv6 address. If the ISP renumbers the subscriber's
network suddenly (rather than slow IPv6 renumbering described in
[RFC4192]) encrypted DNS service will be delayed until that new
certificate is acquired.
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DNR requires proving possession of an FQDN as the encrypted
resolver's certificate contains the FQDN. The entity (e.g., ISP,
network administrator) managing the CPE would assign a unique FQDN to
the CPE. There are two mechanisms for the CPE to obtain the
certificate for the FQDN: using one of its WAN IP addresses or
requesting its signed certificate from an Internet-facing server used
for remote CPE management (e.g., the Auto Configuration Server (ACS)
in the CPE WAN Management Protocol [TR-069]). If using a CPE's WAN
IP address, the CPE needs a public IPv4 or a global unicast IPv6
address together with DNS A or AAAA records pointing to that CPE's
WAN address to prove possession of the DNS name to obtain a WebPKI
CA-signed certificate (that is, the CPE fulfills the DNS or HTTP
challenge discussed in ACME [RFC8555]). However, a CPE's WAN address
will not be a public IPv4 address if the CPE is behind another layer
of NAT (either a CGN or another on-premise NAT), reducing the success
of this mechanism to a CPE's WAN IPv6 address. If the subscribers
IPv4 or IPv6 address is included in the certificate name (e.g., "dyn-
192-0-2-1.example.net") then DNR will experience IP renumbering
complications identical to DDR, described above. The former
mechanism has the following limitations when ACME protocol is used
for certificate issuance:
* Each CPE would have to create a different account for ordering a
certificate. When a large scale of CPEs request certificate
issuance for a large number of subdomains, it could be treated as
an attacker by the certificate authorities to overwhelm it.
* The CPE would have to host an Internet-facing HTTP server or a DNS
authoritative server to complete the HTTP or DNS challenge.
5.2. Managed CPEs
The section discusses mechanisms that can be used to host an
encrypted DNS forwarder in a managed CPE (Section 4.1).
5.2.1. DNS Forwarders
The managed CPE should support a configuration parameter to instruct
the CPE whether it has to relay the encrypted DNS resolver received
from the ISP's network or has to announce itself as a forwarder
within the local network. The default behavior of the CPE is to
supply the encrypted DNS resolver received from the ISP's network.
5.2.2. ACME
The ISP can assign a unique FQDN (e.g., "cpe1.example.com") and a
domain-validated public certificate to the encrypted DNS forwarder
hosted on the CPE.
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Automatic Certificate Management Environment (ACME) [RFC8555] can be
used by the ISP to automate certificate management functions such as
domain validation procedure, certificate issuance, and certificate
revocation.
5.3. Unmanaged CPEs
The approach specified in Section 5.2 does not apply for hosting a
DNS forwarder in an unmanaged CPE.
The unmanaged CPE administrator can host an encrypted DNS forwarder
on the unmanaged CPE. This assumes the following:
* The encrypted DNS resolver certificate is managed by the entity
in-charge of hosting the encrypted DNS forwarder.
Alternatively, a security service provider can assign a unique
FQDN to the CPE. The encrypted DNS forwarder will act like a
private encrypted DNS resolver only be accessible from within the
local network.
* The encrypted DNS forwarder will either be configured to use the
ISP's or a 3rd party encrypted DNS resolver.
* The unmanaged CPE will advertise the encrypted DNS forwarder ADN
using DHCP/RA to internal hosts as per [I-D.ietf-add-dnr].
Figure 7 illustrates an example of an unmanaged CPE hosting a
forwarder which connects to a 3rd party encrypted DNS resolver. In
this example, the DNS information received from the managed CPE (and
therefore from the ISP) is ignored by the Internal CPE hosting the
forwarder. The internal CPE may support a mechanism (e.g.,
[I-D.ietf-add-split-horizon-authority]) to resolve split-horizon
domains (e.g., provider's private name discussed in Section 2 of
[RFC6731]).
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,--,--,--. ,--,
,' Internal Managed ,-' '- 3rd Party
Host--( Network#A CPE--------CPE------( ISP )--- DNS Resolver
| `. ,-'| | `-. -' |
| `-'--'--' | |<==DNR===>|`--' |
| X<==DNR===>| | |
|<=======DNR=======>| | |
| {ADN, @i} | |
| | |
|<==Encrypted DNS==>|<==========Encrypted DNS==========>|
| | |
Legend:
* @i: IP address of the DNS forwarder hosted in the Internal
CPE.
Figure 7: Example of an Internal CPE Hosting a Forwarder
An unmanaged CPE can be used to host an encrypted DNS forwarder even
if the managed CPE does not support DNR. In the example depicted in
Figure 8, the ISP uses DHCP to provision Do53 resolvers to managed
CPEs, while DNR is enabled between the internal CPE and the hosts it
services. The internal CPE ignores the DNS configuration that it
receives from the managed CPE.
,--,--,--. ,--,
,' Internal Managed ,-' '- 3rd Party
Host--( Network#A CPE--------CPE------( ISP )--- DNS Server
| `. ,-'| | `-. -' |
| `-'--'--' | |<==DHCP==>|`--' |
| X<==DHCP==>| Do53 | |
|<=======DNR=======>| Do53 | |
| {ADN, @i} | |
|<==Encrypted DNS==>|<==========Encrypted DNS==========>|
| | |
Legend:
* @i: IP address of the DNS forwarder hosted in the Internal
CPE.
Figure 8: Example of an Internal CPE Hosting a Forwarder (2)
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6. Legacy CPEs
Hosts serviced by legacy CPEs that can't be upgraded to support the
options defined in Sections 4, 5, and 6 of [I-D.ietf-add-dnr] won't
be able to learn the encrypted DNS resolver hosted by the ISP, in
particular. If the ADN is not discovered using DHCP/RA, such hosts
will have to fall back to use discovery using the resolver IP address
as defined in Section 4 of [I-D.ietf-add-ddr] to discover the
designated resolvers.
The guidance in Sections 4.1 and 4.2 of [I-D.ietf-add-ddr] related to
the designated resolver verification has to be followed in such a
case.
7. Security Considerations
DNR-related security considerations are discussed in Section 7 of
[I-D.ietf-add-dnr]. Likewise, DDR-related security considerations
are discussed in Section 7 of [I-D.ietf-add-ddr].
8. IANA Considerations
This document does not require any IANA action.
9. Acknowledgements
This text was initially part of [I-D.ietf-add-dnr].
Thanks to Eliot Lear for the ISE review.
10. References
10.1. Normative References
[I-D.ietf-add-ddr]
Pauly, T., Kinnear, E., Wood, C. A., McManus, P., and T.
Jensen, "Discovery of Designated Resolvers", Work in
Progress, Internet-Draft, draft-ietf-add-ddr-10, 5 August
2022, <https://www.ietf.org/archive/id/draft-ietf-add-ddr-
10.txt>.
[I-D.ietf-add-dnr]
Boucadair, M., Reddy, T., Wing, D., Cook, N., and T.
Jensen, "DHCP and Router Advertisement Options for the
Discovery of Network-designated Resolvers (DNR)", Work in
Progress, Internet-Draft, draft-ietf-add-dnr-13, 13 August
2022, <https://www.ietf.org/archive/id/draft-ietf-add-dnr-
13.txt>.
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10.2. Informative References
[I-D.ietf-add-split-horizon-authority]
Reddy.K, T., Wing, D., Smith, K., and B. M. Schwartz,
"Establishing Local DNS Authority in Split-Horizon
Environments", Work in Progress, Internet-Draft, draft-
ietf-add-split-horizon-authority-02, 20 September 2022,
<https://www.ietf.org/archive/id/draft-ietf-add-split-
horizon-authority-02.txt>.
[I-D.ietf-opsawg-add-encrypted-dns]
Boucadair, M. and T. Reddy.K, "RADIUS Extensions for
Encrypted DNS", Work in Progress, Internet-Draft, draft-
ietf-opsawg-add-encrypted-dns-03, 6 October 2022,
<https://www.ietf.org/archive/id/draft-ietf-opsawg-add-
encrypted-dns-03.txt>.
[RFC1918] Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G.
J., and E. Lear, "Address Allocation for Private
Internets", BCP 5, RFC 1918, DOI 10.17487/RFC1918,
February 1996, <https://www.rfc-editor.org/info/rfc1918>.
[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>.
[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>.
[RFC4192] Baker, F., Lear, E., and R. Droms, "Procedures for
Renumbering an IPv6 Network without a Flag Day", RFC 4192,
DOI 10.17487/RFC4192, September 2005,
<https://www.rfc-editor.org/info/rfc4192>.
[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>.
[RFC6598] Weil, J., Kuarsingh, V., Donley, C., Liljenstolpe, C., and
M. Azinger, "IANA-Reserved IPv4 Prefix for Shared Address
Space", BCP 153, RFC 6598, DOI 10.17487/RFC6598, April
2012, <https://www.rfc-editor.org/info/rfc6598>.
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[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>.
[RFC6890] Cotton, M., Vegoda, L., Bonica, R., Ed., and B. Haberman,
"Special-Purpose IP Address Registries", BCP 153,
RFC 6890, DOI 10.17487/RFC6890, April 2013,
<https://www.rfc-editor.org/info/rfc6890>.
[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>.
[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>.
[RFC8190] Bonica, R., Cotton, M., Haberman, B., and L. Vegoda,
"Updates to the Special-Purpose IP Address Registries",
BCP 153, RFC 8190, DOI 10.17487/RFC8190, June 2017,
<https://www.rfc-editor.org/info/rfc8190>.
[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>.
[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>.
[RFC8520] Lear, E., Droms, R., and D. Romascanu, "Manufacturer Usage
Description Specification", RFC 8520,
DOI 10.17487/RFC8520, March 2019,
<https://www.rfc-editor.org/info/rfc8520>.
[RFC8555] Barnes, R., Hoffman-Andrews, J., McCarney, D., and J.
Kasten, "Automatic Certificate Management Environment
(ACME)", RFC 8555, DOI 10.17487/RFC8555, March 2019,
<https://www.rfc-editor.org/info/rfc8555>.
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[RFC8585] Palet Martinez, J., Liu, H. M.-H., and M. Kawashima,
"Requirements for IPv6 Customer Edge Routers to Support
IPv4-as-a-Service", RFC 8585, DOI 10.17487/RFC8585, May
2019, <https://www.rfc-editor.org/info/rfc8585>.
[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>.
[TR-069] The Broadband Forum, "CPE WAN Management Protocol",
December 2018, <https://www.broadband-
forum.org/technical/download/TR-069.pdf>.
[TS.24008] 3GPP, "Mobile radio interface Layer 3 specification; Core
network protocols; Stage 3 (Release 16)", December 2019,
<http://www.3gpp.org/DynaReport/24008.htm>.
Authors' Addresses
Mohamed Boucadair (editor)
Orange
35000 Rennes
France
Email: mohamed.boucadair@orange.com
Tirumaleswar Reddy (editor)
Nokia
India
Email: kondtir@gmail.com
Dan Wing
Citrix Systems, Inc.
United States of America
Email: dwing-ietf@fuggles.com
Neil Cook
Open-Xchange
United Kingdom
Email: neil.cook@noware.co.uk
Tommy Jensen
Microsoft
United States of America
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Email: tojens@microsoft.com
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