RFC 8932 | DNS Privacy Service Recommendations | October 2020 |
Dickinson, et al. | Best Current Practice | [Page] |
This document presents operational, policy, and security considerations for DNS recursive resolver operators who choose to offer DNS privacy services. With these recommendations, the operator can make deliberate decisions regarding which services to provide, as well as understanding how those decisions and the alternatives impact the privacy of users.¶
This document also presents a non-normative framework to assist writers of a Recursive operator Privacy Statement, analogous to DNS Security Extensions (DNSSEC) Policies and DNSSEC Practice Statements described in RFC 6841.¶
This memo documents an Internet Best Current Practice.¶
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 BCPs 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/rfc8932.¶
Copyright (c) 2020 IETF Trust and the persons identified as the document authors. All rights reserved.¶
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.¶
The Domain Name System (DNS) is at the core of the Internet; almost every activity on the Internet starts with a DNS query (and often several). However, the DNS was not originally designed with strong security or privacy mechanisms. A number of developments have taken place in recent years that aim to increase the privacy of the DNS, and these are now seeing some deployment. This latest evolution of the DNS presents new challenges to operators, and this document attempts to provide an overview of considerations for privacy-focused DNS services.¶
In recent years, there has also been an increase in the availability of "public resolvers" [RFC8499], which users may prefer to use instead of the default network resolver, either because they offer a specific feature (e.g., good reachability or encrypted transport) or because the network resolver lacks a specific feature (e.g., strong privacy policy or unfiltered responses). These public resolvers have tended to be at the forefront of adoption of privacy-related enhancements, but it is anticipated that operators of other resolver services will follow.¶
Whilst protocols that encrypt DNS messages on the wire provide protection against certain attacks, the resolver operator still has (in principle) full visibility of the query data and transport identifiers for each user. Therefore, a trust relationship (whether explicit or implicit) is assumed to exist between each user and the operator of the resolver(s) used by that user. The ability of the operator to provide a transparent, well-documented, and secure privacy service will likely serve as a major differentiating factor for privacy-conscious users if they make an active selection of which resolver to use.¶
It should also be noted that there are both advantages and disadvantages to a user choosing to configure a single resolver (or a fixed set of resolvers) and an encrypted transport to use in all network environments. For example, the user has a clear expectation of which resolvers have visibility of their query data. However, this resolver/transport selection may provide an added mechanism for tracking them as they move across network environments. Commitments from resolver operators to minimize such tracking as users move between networks are also likely to play a role in user selection of resolvers.¶
More recently, the global legislative landscape with regard to personal data collection, retention, and pseudonymization has seen significant activity. Providing detailed practice advice about these areas to the operator is out of scope, but Section 5.3.3 describes some mitigations of data-sharing risk.¶
This document has two main goals:¶
A desired operational impact is that all operators (both those providing resolvers within networks and those operating large public services) can demonstrate their commitment to user privacy, thereby driving all DNS resolution services to a more equitable footing. Choices for users would (in this ideal world) be driven by other factors -- e.g., differing security policies or minor differences in operator policy -- rather than gross disparities in privacy concerns.¶
Community insight (or judgment?) about operational practices can change quickly, and experience shows that a Best Current Practice (BCP) document about privacy and security is a point-in-time statement. Readers are advised to seek out any updates that apply to this document.¶
"DNS Privacy Considerations" [RFC7626] describes the general privacy issues and threats associated with the use of the DNS by Internet users; much of the threat analysis here is lifted from that document and [RFC6973]. However, this document is limited in scope to best-practice considerations for the provision of DNS privacy services by servers (recursive resolvers) to clients (stub resolvers or forwarders). Choices that are made exclusively by the end user, or those for operators of authoritative nameservers, are out of scope.¶
This document includes (but is not limited to) considerations in the following areas:¶
Whilst the issues raised here are targeted at those operators who choose to offer a DNS privacy service, considerations for areas 2 and 3 could equally apply to operators who only offer DNS over unencrypted transports but who would otherwise like to align with privacy best practice.¶
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.¶
DNS terminology is as described in [RFC8499], except with regard to the definition of privacy-enabling DNS server in Section 6 of [RFC8499]. In this document we use the full definition of a DNS over (D)TLS privacy-enabling DNS server as given in [RFC8310], i.e., that such a server should also offer at least one of the credentials described in Section 8 of [RFC8310] and implement the (D)TLS profile described in Section 9 of [RFC8310].¶
Other Terms:¶
In the following sections, we first outline the threats relevant to the specific topic and then discuss the potential actions that can be taken to mitigate them.¶
We describe two classes of threats:¶
Threats described in [RFC6973], "Privacy Considerations for Internet Protocols"¶
DNS Privacy Threats¶
We describe three classes of actions that operators of DNS privacy services can take:¶
This document does not specify policy, only best practice. However, for DNS privacy services to be considered compliant with these best-practice guidelines, they SHOULD implement (where appropriate) all:¶
The rest of this document does not use normative language but instead refers only to the three differing classes of action that correspond to the three named levels of compliance stated above. However, compliance (to the indicated level) remains a normative requirement.¶
In this section, we consider both data on the wire and the service provided to the client.¶
A DNS privacy service can mitigate these threats by providing service over one or more of the following transports:¶
It is noted that a DNS privacy service can also be provided over DNS over DTLS [RFC8094]; however, this is an Experimental specification, and there are no known implementations at the time of writing.¶
It is also noted that DNS privacy service might be provided over DNSCrypt [DNSCrypt], IPsec, or VPNs. However, there are no specific RFCs that cover the use of these transports for DNS, and any discussion of best practice for providing such a service is out of scope for this document.¶
Whilst encryption of DNS traffic can protect against active injection on the paths traversed by the encrypted connection, this does not diminish the need for DNSSEC; see Section 5.1.4.¶
DNS privacy services should ensure clients can authenticate the server. Note that this, in effect, commits the DNS privacy service to a public identity users will trust.¶
When using DoT, clients that select a "Strict Privacy" usage profile [RFC8310] (to mitigate the threat of active attack on the client) require the ability to authenticate the DNS server. To enable this, DNS privacy services that offer DoT need to provide credentials that will be accepted by the client's trust model, in the form of either X.509 certificates [RFC5280] or Subject Public Key Info (SPKI) pin sets [RFC8310].¶
When offering DoH [RFC8484], HTTPS requires authentication of the server as part of the protocol.¶
Anecdotal evidence to date highlights the management of certificates as one of the more challenging aspects for operators of traditional DNS resolvers that choose to additionally provide a DNS privacy service, as management of such credentials is new to those DNS operators.¶
It is noted that SPKI pin set management is described in [RFC7858] but that key-pinning mechanisms in general have fallen out of favor operationally for various reasons, such as the logistical overhead of rolling keys.¶
It is recommended that operators:¶
In the case of DoT, TLS profiles from Section 9 of [RFC8310] and the "Countermeasures to DNS Traffic Analysis" from Section 11.1 of [RFC8310] provide strong mitigations. This includes but is not limited to:¶
The addition of encryption to DNS does not remove the need for DNSSEC [RFC4033]; they are independent and fully compatible protocols, each solving different problems. The use of one does not diminish the need nor the usefulness of the other.¶
While the use of an authenticated and encrypted transport protects origin authentication and data integrity between a client and a DNS privacy service, it provides no proof (for a nonvalidating client) that the data provided by the DNS privacy service was actually DNSSEC authenticated. As with cleartext DNS, the user is still solely trusting the Authentic Data (AD) bit (if present) set by the resolver.¶
It should also be noted that the use of an encrypted transport for DNS actually solves many of the practical issues encountered by DNS validating clients -- e.g., interference by middleboxes with cleartext DNS payloads is completely avoided. In this sense, a validating client that uses a DNS privacy service that supports DNSSEC has a far simpler task in terms of DNSSEC roadblock avoidance [RFC8027].¶
A DNS privacy service should strive to engineer encrypted services to the same availability level as any unencrypted services they provide. Particular care should to be taken to protect DNS privacy services against denial-of-service (DoS) attacks, as experience has shown that unavailability of DNS resolving because of attacks is a significant motivation for users to switch services. See, for example, Section IV-C of [Passive-Observations-of-a-Large-DNS].¶
Techniques such as those described in Section 10 of [RFC7766] can be of use to operators to defend against such attacks.¶
Many monitoring solutions for DNS traffic rely on the plaintext nature of this traffic and work by intercepting traffic on the wire, either using a separate view on the connection between clients and the resolver, or as a separate process on the resolver system that inspects network traffic. Such solutions will no longer function when traffic between clients and resolvers is encrypted. Many DNS privacy service operators still need to inspect DNS traffic -- e.g., to monitor for network security threats. Operators may therefore need to invest in an alternative means of monitoring that relies on either the resolver software directly, or exporting DNS traffic from the resolver using, for example, [dnstap].¶
Some operators may choose to implement DoT using a TLS proxy (e.g., [nginx], [haproxy], or [stunnel]) in front of a DNS nameserver because of proven robustness and capacity when handling large numbers of client connections, load-balancing capabilities, and good tooling. Currently, however, because such proxies typically have no specific handling of DNS as a protocol over TLS or DTLS, using them can restrict traffic management at the proxy layer and the DNS server. For example, all traffic received by a nameserver behind such a proxy will appear to originate from the proxy, and DNS techniques such as Access Control Lists (ACLs), Response Rate Limiting (RRL), or DNS64 [RFC6147] will be hard or impossible to implement in the nameserver.¶
Operators may choose to use a DNS-aware proxy, such as [dnsdist], that offers custom options (similar to those proposed in [DNS-XPF]) to add source information to packets to address this shortcoming. It should be noted that such options potentially significantly increase the leaked information in the event of a misconfiguration.¶
The following are recommendations relating to common activities for DNS service operators; in all cases, data retention should be minimized or completely avoided if possible for DNS privacy services. If data is retained, it should be encrypted and either aggregated, pseudonymized, or anonymized whenever possible. In general, the principle of data minimization described in [RFC6973] should be applied.¶
Data minimization refers to collecting, using, disclosing, and storing the minimal data necessary to perform a task, and this can be achieved by removing or obfuscating privacy-sensitive information in network traffic logs. This is typically personal data or data that can be used to link a record to an individual, but it may also include other confidential information -- for example, on the structure of an internal corporate network.¶
The problem of effectively ensuring that DNS traffic logs contain no or minimal privacy-sensitive information is not one that currently has a generally agreed solution or any standards to inform this discussion. This section presents an overview of current techniques to simply provide reference on the current status of this work.¶
Research into data minimization techniques (and particularly IP address pseudonymization/anonymization) was sparked in the late 1990s / early 2000s, partly driven by the desire to share significant corpuses of traffic captures for research purposes. Several techniques reflecting different requirements in this area and different performance/resource trade-offs emerged over the course of the decade. Developments over the last decade have been both a blessing and a curse; the large increase in size between an IPv4 and an IPv6 address, for example, renders some techniques impractical, but also makes available a much larger amount of input entropy, the better to resist brute-force re-identification attacks that have grown in practicality over the period.¶
Techniques employed may be broadly categorized as either anonymization or pseudonymization. The following discussion uses the definitions from [RFC6973], Section 3, with additional observations from [van-Dijkhuizen-et-al].¶
In practice, there is a fine line between the two; for example, it is difficult to categorize a deterministic algorithm for data minimization of IP addresses that produces a group of pseudonyms for a single given address.¶
A major privacy risk in DNS is connecting DNS queries to an individual, and the major vector for this in DNS traffic is the client IP address.¶
There is active discussion in the space of effective pseudonymization of IP addresses in DNS traffic logs; however, there seems to be no single solution that is widely recognized as suitable for all or most use cases. There are also as yet no standards for this that are unencumbered by patents.¶
Appendix B provides a more detailed survey of various techniques employed or under development in 2020.¶
In this section, we consider both data sent on the wire in upstream queries and data shared with third parties.¶
The server should:¶
If operators do offer a service that sends the ECS options upstream, they should use the shortest prefix that is operationally feasible and ideally use a policy of allowlisting upstream servers to which to send ECS in order to reduce data leakage. Operators should make clear in any policy statement what prefix length they actually send and the specific policy used.¶
Allowlisting has the benefit that not only does the operator know which upstream servers can use ECS, but also the operator can decide which upstream servers apply privacy policies that the operator is happy with. However, some operators consider allowlisting to incur significant operational overhead compared to dynamic detection of ECS support on authoritative servers.¶
Additional options:¶
Additional options:¶
Since queries from recursive resolvers to authoritative servers are performed using cleartext (at the time of writing), resolver services need to consider the extent to which they may be directly leaking information about their client community via these upstream queries and what they can do to mitigate this further. Note that, even when all the relevant techniques described above are employed, there may still be attacks possible -- e.g., [Pitfalls-of-DNS-Encryption]. For example, a resolver with a very small community of users risks exposing data in this way and ought to obfuscate this traffic by mixing it with "generated" traffic to make client characterization harder. The resolver could also employ aggressive prefetch techniques as a further measure to counter traffic analysis.¶
At the time of writing, there are no standardized or widely recognized techniques to perform such obfuscation or bulk prefetches.¶
Another technique that particularly small operators may consider is forwarding local traffic to a larger resolver (with a privacy policy that aligns with their own practices) over an encrypted protocol, so that the upstream queries are obfuscated among those of the large resolver.¶
Operators should not share identifiable data with third parties.¶
If operators choose to share identifiable data with third parties in specific circumstances, they should publish the terms under which data is shared.¶
Operators should consider including specific guidelines for the collection of aggregated and/or anonymized data for research purposes, within or outside of their own organization. This can benefit not only the operator (through inclusion in novel research) but also the wider Internet community. See the policy published by SURFnet [SURFnet-policy] on data sharing for research as an example.¶
To be compliant with this Best Current Practice document, a DNS recursive operator SHOULD publish a Recursive operator Privacy Statement (RPS). Adopting the outline, and including the headings in the order provided, is a benefit to persons comparing RPSs from multiple operators.¶
Appendix C provides a comparison of some existing policy and privacy statements.¶
The contents of Sections 6.1.1 and 6.1.2 are non-normative, other than the order of the headings. Material under each topic is present to assist the operator developing their own RPS. This material:¶
Appendix D provides an example (also non-normative) of an RPS statement for a specific operator scenario.¶
Data collection and sharing. Specify clearly what data (including IP addresses) is:¶
Shared, sold, or rented to third parties.¶
In each case, specify whether data is aggregated, pseudonymized, or anonymized and the conditions of data transfer. Where possible provide details of the techniques used for the above data minimizations.¶
Result filtering. This section should explain whether the operator filters, edits, or alters in any way the replies that it receives from the authoritative servers for each DNS zone before forwarding them to the clients. For each category listed below, the operator should also specify how the filtering lists are created and managed, whether it employs any third-party sources for such lists, and which ones.¶
Communicate the current operational practices of the service.¶
Client-facing capabilities. With reference to each subsection of Section 5.1, provide specific details of which capabilities (transport, DNSSEC, padding, etc.) are provided on which client-facing addresses/port combination or DoH URI template. For Section 5.1.2, clearly specify which specific authentication mechanisms are supported for each endpoint that offers DoT:¶
Transparency reports may help with building user trust that operators adhere to their policies and practices.¶
Where possible, independent monitoring or analysis could be performed of:¶
This is by analogy with several TLS or website-analysis tools that are currently available -- e.g., [SSL-Labs] or [Internet.nl].¶
Additionally, operators could choose to engage the services of a third-party auditor to verify their compliance with their published RPS.¶
This document has no IANA actions.¶
Security considerations for DNS over TCP are given in [RFC7766], many of which are generally applicable to session-based DNS. Guidance on operational requirements for DNS over TCP are also available in [DNS-OVER-TCP]. Security considerations for DoT are given in [RFC7858] and [RFC8310], and those for DoH in [RFC8484].¶
Security considerations for DNSSEC are given in [RFC4033], [RFC4034], and [RFC4035].¶
This section provides an overview of some DNS privacy-related documents. However, this is neither an exhaustive list nor a definitive statement on the characteristics of any document with regard to potential increases or decreases in DNS privacy.¶
These documents are limited in scope to communications between stub clients and recursive resolvers:¶
These documents apply to recursive and authoritative DNS but are relevant when considering the operation of a recursive server:¶
These documents relate to functionality that could provide increased tracking of user activity as a side effect:¶
The following table presents a high-level comparison of various techniques employed or under development in 2019 and classifies them according to categorization of technique and other properties. Both the specific techniques and the categorizations are described in more detail in the following sections. The list of techniques includes the main techniques in current use but does not claim to be comprehensive.¶
Categorization/Property | GA | d | TC | C | TS | i | B |
---|---|---|---|---|---|---|---|
Anonymization | X | X | X | X | |||
Pseudonymization | X | X | X | ||||
Format preserving | X | X | X | X | X | X | |
Prefix preserving | X | X | X | ||||
Replacement | X | ||||||
Filtering | X | ||||||
Generalization | X | ||||||
Enumeration | X | ||||||
Reordering/Shuffling | X | ||||||
Random substitution | X | ||||||
Cryptographic permutation | X | X | X | ||||
IPv6 issues | X | ||||||
CPU intensive | X | ||||||
Memory intensive | X | ||||||
Security concerns | X |
Legend of techniques:¶
The choice of which method to use for a particular application will depend on the requirements of that application and consideration of the threat analysis of the particular situation.¶
For example, a common goal is that distributed packet captures must be in an existing data format, such as PCAP [pcap] or Compacted-DNS (C-DNS) [RFC8618], that can be used as input to existing analysis tools. In that case, use of a format-preserving technique is essential. This, though, is not cost free; several authors (e.g., [Brekne-and-Arnes]) have observed that, as the entropy in an IPv4 address is limited, if an attacker can¶
any format-preserving pseudonymization is vulnerable to an attack along the lines of a cryptographic chosen-plaintext attack.¶
Data minimization methods may be categorized by the processing used and the properties of their outputs. The following builds on the categorization employed in [RFC6235]:¶
Since May 2010, Google Analytics has provided a facility [IP-Anonymization-in-Analytics] that allows website owners to request that all their users' IP addresses are anonymized within Google Analytics processing. This very basic anonymization simply sets to zero the least significant 8 bits of IPv4 addresses, and the least significant 80 bits of IPv6 addresses. The level of anonymization this produces is perhaps questionable. There are some analysis results [Geolocation-Impact-Assessment] that suggest that the impact of this on reducing the accuracy of determining the user's location from their IP address is less than might be hoped; the average discrepancy in identification of the user city for UK users is no more than 17%.¶
Since 2006, PowerDNS has included a de-identification tool, dnswasher [PowerDNS-dnswasher], with their PowerDNS product. This is a PCAP filter that performs a one-to-one mapping of end-user IP addresses with an anonymized address. A table of user IP addresses and their de-identified counterparts is kept; the first IPv4 user addresses is translated to 0.0.0.1, the second to 0.0.0.2, and so on. The de-identified address therefore depends on the order that addresses arrive in the input, and when running over a large amount of data, the address translation tables can grow to a significant size.¶
Used in [tcpdpriv], this algorithm stores a set of original and anonymized IP address pairs. When a new IP address arrives, it is compared with previous addresses to determine the longest prefix match. The new address is anonymized by using the same prefix, with the remainder of the address anonymized with a random value. The use of a random value means that TCPdpriv is not deterministic; different anonymized values will be generated on each run. The need to store previous addresses means that TCPdpriv has significant and unbounded memory requirements. The need to allocate anonymized addresses sequentially means that TCPdpriv cannot be used in parallel processing.¶
Cryptographic prefix-preserving pseudonymization was originally proposed as an improvement to the prefix-preserving map implemented in TCPdpriv, described in [Xu-et-al] and implemented in the [Crypto-PAn] tool. Crypto-PAn is now frequently used as an acronym for the algorithm. Initially, it was described for IPv4 addresses only; extension for IPv6 addresses was proposed in [Harvan]. This uses a cryptographic algorithm rather than a random value, and thus pseudonymity is determined uniquely by the encryption key, and is deterministic. It requires a separate AES encryption for each output bit and so has a nontrivial calculation overhead. This can be mitigated to some extent (for IPv4, at least) by precalculating results for some number of prefix bits.¶
Proposed in [Ramaswamy-and-Wolf], Top-hash Subtree-replicated Anonymization (TSA) originated in response to the requirement for faster processing than Crypto-PAn. It used hashing for the most significant byte of an IPv4 address and a precalculated binary-tree structure for the remainder of the address. To save memory space, replication is used within the tree structure, reducing the size of the precalculated structures to a few megabytes for IPv4 addresses. Address pseudonymization is done via hash and table lookup and so requires minimal computation. However, due to the much-increased address space for IPv6, TSA is not memory efficient for IPv6.¶
A recently released proposal from PowerDNS, ipcipher [ipcipher1] [ipcipher2], is a simple pseudonymization technique for IPv4 and IPv6 addresses. IPv6 addresses are encrypted directly with AES-128 using a key (which may be derived from a passphrase). IPv4 addresses are similarly encrypted, but using a recently proposed encryption [ipcrypt] suitable for 32-bit block lengths. However, the author of ipcrypt has since indicated [ipcrypt-analysis] that it has low security, and further analysis has revealed it is vulnerable to attack.¶
van Rijswijk-Deij et al. have recently described work using Bloom Filters [Bloom-filter] to categorize query traffic and record the traffic as the state of multiple filters. The goal of this work is to allow operators to identify so-called Indicators of Compromise (IOCs) originating from specific subnets without storing information about, or being able to monitor, the DNS queries of an individual user. By using a Bloom Filter, it is possible to determine with a high probability if, for example, a particular query was made, but the set of queries made cannot be recovered from the filter. Similarly, by mixing queries from a sufficient number of users in a single filter, it becomes practically impossible to determine if a particular user performed a particular query. Large numbers of queries can be tracked in a memory-efficient way. As filter status is stored, this approach cannot be used to regenerate traffic and so cannot be used with tools used to process live traffic.¶
A tabular comparison of policy and privacy statements from various DNS privacy service operators based loosely on the proposed RPS structure can be found at [policy-comparison]. The analysis is based on the data available in December 2019.¶
We note that the existing policies vary widely in style, content, and detail, and it is not uncommon for the full text for a given operator to equate to more than 10 pages (A4 size) of text in a moderate-sized font. It is a nontrivial task today for a user to extract a meaningful overview of the different services on offer.¶
It is also noted that Mozilla has published a DoH resolver policy [DoH-resolver-policy] that describes the minimum set of policy requirements that a party must satisfy to be considered as a potential partner for Mozilla's Trusted Recursive Resolver (TRR) program.¶
The following example RPS is very loosely based on some elements of published privacy statements for some public resolvers, with additional fields populated to illustrate what the full contents of an RPS might look like. This should not be interpreted as¶
This is a purely hypothetical example of an RPS to outline example contents -- in this case, for a public resolver operator providing a basic DNS Privacy service via one IP address and one DoH URI with security-based filtering. It does aim to meet minimal compliance as specified in Section 5.¶
Data collection and sharing.¶
Data collected in logs. We do keep some generalized location information (at the city / metropolitan-area level) so that we can conduct debugging and analyze abuse phenomena. We also use the collected information for the creation and sharing of telemetry (timestamp, geolocation, number of hits, first seen, last seen) for contributors, public publishing of general statistics of system use (protections, threat types, counts, etc.). When you use our DNS services, here is the full list of items that are included in our logs:¶
Transport protocol on which the request arrived -- i.e., UDP, TCP, DoT, DoH¶
We may keep the following data as summary information, including all the above EXCEPT for data about the DNS record requested:¶
All the above data may be kept in full or partial form in permanent archives.¶
Result filtering.¶
Filtering. We utilize cyber-threat intelligence about malicious domains from a variety of public and private sources and block access to those malicious domains when your system attempts to contact them. An NXDOMAIN is returned for blocked sites.¶
Client-facing capabilities.¶
We offer DNS over TLS as specified in RFC 7858 on (insert IP address). It is available on port 853 and port 443. We also implement RFC 7766.¶
Both services provide DNSSEC validation.¶
Upstream capabilities.¶
Many thanks to Amelia Andersdotter for a very thorough review of the first draft of this document and Stephen Farrell for a thorough review at Working Group Last Call and for suggesting the inclusion of an example RPS. Thanks to John Todd for discussions on this topic, and to Stéphane Bortzmeyer, Puneet Sood, and Vittorio Bertola for review. Thanks to Daniel Kahn Gillmor, Barry Green, Paul Hoffman, Dan York, Jon Reed, and Lorenzo Colitti for comments at the mic. Thanks to Loganaden Velvindron for useful updates to the text.¶
Sara Dickinson thanks the Open Technology Fund for a grant to support the work on this document.¶
The below individuals contributed significantly to the document:¶