Network Working Group M. Boucadair, Ed. Internet-Draft Orange Intended status: Informational T. Reddy, Ed. Expires: 11 March 2023 Nokia D. Wing Citrix N. Cook Open-Xchange T. Jensen Microsoft 7 September 2022 Discovery of Encrypted DNS Resolvers: Deployment Considerations draft-boucadair-add-deployment-considerations-01 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). Particularly, this document is meant to exemplify how Discovery of Network-designated Resolvers (DNR) and Discovery of Designated Resolvers (DDR) can be used in typical deployment contexts. Also, the document includes considerations related to hosting a DNS forwarder in local networks. 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 11 March 2023. Copyright Notice Copyright (c) 2022 IETF Trust and the persons identified as the document authors. All rights reserved. Boucadair, et al. Expires 11 March 2023 [Page 1] Internet-Draft Discovery of Encrypted DNS Resolvers September 2022 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 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Sample Target Deployment Scenarios . . . . . . . . . . . . . 4 3.1. Managed CPEs . . . . . . . . . . . . . . . . . . . . . . 6 3.1.1. Direct DNS . . . . . . . . . . . . . . . . . . . . . 6 3.1.2. Proxied DNS . . . . . . . . . . . . . . . . . . . . . 8 3.2. Unmanaged CPEs . . . . . . . . . . . . . . . . . . . . . 10 3.2.1. ISP-facing Unmanaged CPEs . . . . . . . . . . . . . . 10 3.2.2. Internal Unmanaged CPEs . . . . . . . . . . . . . . . 10 4. Hosting Encrypted DNS Forwarder in Local Networks . . . . . . 11 4.1. Managed CPEs . . . . . . . . . . . . . . . . . . . . . . 11 4.1.1. DNS Forwarders . . . . . . . . . . . . . . . . . . . 11 4.1.2. ACME . . . . . . . . . . . . . . . . . . . . . . . . 11 4.2. Unmanaged CPEs . . . . . . . . . . . . . . . . . . . . . 12 5. Legacy CPEs . . . . . . . . . . . . . . . . . . . . . . . . . 14 6. Security Considerations . . . . . . . . . . . . . . . . . . . 14 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 14 9.1. Normative References . . . . . . . . . . . . . . . . . . 14 9.2. Informative References . . . . . . . . . . . . . . . . . 14 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16 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 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 Boucadair, et al. Expires 11 March 2023 [Page 2] Internet-Draft Discovery of Encrypted DNS Resolvers September 2022 (DoH)). Such an information is used by a DNS client for DNS resolver selection and session establishment. This document discusses some deployment considerations for 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 3; 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 4. 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 Section 5 for more details. Techniques, such as the one defined in [I-D.boucadair-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. 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]. 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 Boucadair, et al. Expires 11 March 2023 [Page 3] Internet-Draft Discovery of Encrypted DNS Resolvers September 2022 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 Internet Service Provider (ISP). Unmanaged CPE: refers to a CPE that is not managed by an ISP. 3. 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. Boucadair, et al. Expires 11 March 2023 [Page 4] Internet-Draft Discovery of Encrypted DNS Resolvers September 2022 (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+---+ \ | Boucadair, et al. Expires 11 March 2023 [Page 5] Internet-Draft Discovery of Encrypted DNS Resolvers September 2022 +-+ +---+ ,' ISP `-. 3rd Party ( )--- DNS Resolver +-----+-. ,-' | +-+ | `--'--'--' | |H+----------------+ | +-+ | | | |<==================Do53=======================>| | | Legend: * H: refers to a host. Figure 1: Sample Legacy Deployments 3.1. Managed CPEs This section focuses on CPEs that are managed by ISPs. 3.1.1. 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. 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]). Boucadair, et al. Expires 11 March 2023 [Page 6] Internet-Draft Discovery of Encrypted DNS Resolvers September 2022 (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 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. Boucadair, et al. Expires 11 March 2023 [Page 7] Internet-Draft Discovery of Encrypted DNS Resolvers September 2022 ,--,--,--. ,--,--,--. ,-' `-. ,-' ISP `-. Host---( LAN CPE----( DNS Resolver) | `-. ,-' `-. ,-' | `--'--'--' | | `--'--'--' | |<=DNR=>| | |<========DNR========>| | | | | | | | |<=========Encrypted DNS===========>| | | Figure 3: Direct Encrypted DNS Sessions 3.1.2. Proxied DNS Figure 4 shows various deployments where the CPE embeds a caching DNS forwarder. Cases (b) and (d) involves a host (called legacy host) that does not support DNR. (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 | (c) Boucadair, et al. Expires 11 March 2023 [Page 8] Internet-Draft Discovery of Encrypted DNS Resolvers September 2022 ,--,--,--. ,--,--,--. ,-' `-. ,-' 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 deployment is required for IPv4 service continuity purposes (e.g., Section 5.4.1 of [I-D.ietf-v6ops-rfc7084-bis]) 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. Boucadair, et al. Expires 11 March 2023 [Page 9] Internet-Draft Discovery of Encrypted DNS Resolvers September 2022 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 deployment are discussed in Section 4. 3.2. Unmanaged CPEs 3.2.1. 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 3.1. A host can then establish encrypted DNS sessions with encrypted DNS resolvers similar to what is depicted in Figure 3 or Figure 4. 3.2.2. 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) Boucadair, et al. Expires 11 March 2023 [Page 10] Internet-Draft Discovery of Encrypted DNS Resolvers September 2022 Similar to managed CPEs, a user may modify the default DNS configuration of an unmanaged CPE to use his/her favorite encryptdd 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 4.2 discusses considerations related to hosting a forwarder in the Internal CPE. 4. Hosting Encrypted DNS Forwarder in Local Networks This section discusses some deployment considerations to host an encrypted DNS forwarder within a local network. 4.1. Managed CPEs The section discusses mechanisms that can be used to host an encrypted DNS forwarder in a managed CPE (Section 3.1). 4.1.1. 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. 4.1.2. 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. Boucadair, et al. Expires 11 March 2023 [Page 11] Internet-Draft Discovery of Encrypted DNS Resolvers September 2022 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. 4.2. Unmanaged CPEs The approach specified in Section 4.1 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]). Boucadair, et al. Expires 11 March 2023 [Page 12] Internet-Draft Discovery of Encrypted DNS Resolvers September 2022 ,--,--,--. ,--, ,' 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) Boucadair, et al. Expires 11 March 2023 [Page 13] Internet-Draft Discovery of Encrypted DNS Resolvers September 2022 5. 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 fallback 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. 6. 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]. 7. IANA Considerations This document does not require any IANA action. 8. Acknowledgements This text was initially part of [I-D.ietf-add-dnr]. 9. References 9.1. 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, . [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, . 9.2. Informative References Boucadair, et al. Expires 11 March 2023 [Page 14] Internet-Draft Discovery of Encrypted DNS Resolvers September 2022 [I-D.boucadair-opsawg-add-encrypted-dns] Boucadair, M. and T. Reddy, "RADIUS Extensions for Encrypted DNS", Work in Progress, Internet-Draft, draft- boucadair-opsawg-add-encrypted-dns-06, 5 September 2022, . [I-D.ietf-add-split-horizon-authority] Reddy, T., Wing, D., Smith, K., and B. Schwartz, "Establishing Local DNS Authority in Split-Horizon Environments", Work in Progress, Internet-Draft, draft- ietf-add-split-horizon-authority-01, 22 August 2022, . [I-D.ietf-v6ops-rfc7084-bis] Martinez, J. P., "Basic Requirements for IPv6 Customer Edge Routers", Work in Progress, Internet-Draft, draft- ietf-v6ops-rfc7084-bis-04, 12 June 2017, . [RFC2132] Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor Extensions", RFC 2132, DOI 10.17487/RFC2132, March 1997, . [RFC3646] Droms, R., Ed., "DNS Configuration options for Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", RFC 3646, DOI 10.17487/RFC3646, December 2003, . [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, . [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, . [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, . Boucadair, et al. Expires 11 March 2023 [Page 15] Internet-Draft Discovery of Encrypted DNS Resolvers September 2022 [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, . [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, . [RFC8484] Hoffman, P. and P. McManus, "DNS Queries over HTTPS (DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018, . [RFC8499] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS Terminology", BCP 219, RFC 8499, DOI 10.17487/RFC8499, January 2019, . [RFC8520] Lear, E., Droms, R., and D. Romascanu, "Manufacturer Usage Description Specification", RFC 8520, DOI 10.17487/RFC8520, March 2019, . [RFC8555] Barnes, R., Hoffman-Andrews, J., McCarney, D., and J. Kasten, "Automatic Certificate Management Environment (ACME)", RFC 8555, DOI 10.17487/RFC8555, March 2019, . [RFC9250] Huitema, C., Dickinson, S., and A. Mankin, "DNS over Dedicated QUIC Connections", RFC 9250, DOI 10.17487/RFC9250, May 2022, . [TR-069] The Broadband Forum, "CPE WAN Management Protocol", December 2018, . [TS.24008] 3GPP, "Mobile radio interface Layer 3 specification; Core network protocols; Stage 3 (Release 16)", December 2019, . Authors' Addresses Mohamed Boucadair (editor) Orange 35000 Rennes France Boucadair, et al. Expires 11 March 2023 [Page 16] Internet-Draft Discovery of Encrypted DNS Resolvers September 2022 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 Email: tojens@microsoft.com Boucadair, et al. Expires 11 March 2023 [Page 17]