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+<!DOCTYPE rfc  [
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+<?rfc text-list-symbols="-o*+"?>
+
+<rfc ipr="trust200902" docName="draft-kolkman-in-tree-hints" category="info" tocInclude="true" sortRefs="true" symRefs="true">
+  <front>
+    <title abbrev="in-tree-hints">In-Tree Hints for DNS Resiliency</title>
+
+    <author initials="O." surname="Kolkman" fullname="Olaf Kolkman">
+      <organization></organization>
+      <address>
+        <email>kolkman@isoc.org</email>
+      </address>
+    </author>
+
+    <date year="2026" month="March" day="17"/>
+
+    <area>ops</area>
+    <workgroup>dnsop</workgroup>
+    <keyword>Internet-Draft</keyword>
+
+    <abstract>
+
+
+<?line 47?>
+
+<t>We present a methodology by which networks that rely very strongly on
+specific domain names can become more resilience to failures in the parent domain.</t>
+
+<t>The approach presented uses a hints-file-like mechanism in recursive
+nameservers in addition to having the authoritative servers follow a
+few operational practices.</t>
+
+<t>The suggested method can be seen as a means for increasing digital
+sovereignty. We describe the approach, the necessary operational
+practices, and the dilemmas this approach introduces.</t>
+
+
+
+    </abstract>
+
+
+
+  </front>
+
+  <middle>
+
+
+<?line 60?>
+
+<section anchor="introduction"><name>Introduction</name>
+<t><vspace blankLines='999' /></t>
+
+<t>The Domain Name System (DNS) is a remarkably stable and resilient
+system. However, in many environments people are looking on how they
+can remain in control over the continuity of digital services in their
+own environments and reduce external dependencies. One those
+dependencies is the DNS, on which we focus in this document.</t>
+
+<t>Consider the following failure case:</t>
+
+<t><list style="symbols">
+  <t>A community of interest is highly dependent on services that are
+discoverable with names within the example.net domain;</t>
+  <t>A failure in DNS resolution occurs in the delegation between .net
+and example.net;</t>
+  <t>IP connectivity remains intact: The DNS servers that serve
+example.net authoritatively are still reachable by the community of
+interest. So are the recursive nameservers and the service of
+interest.</t>
+</list></t>
+
+<t>This failure case may sound relatively limited. But here are a few
+less abstract examples of such failure.</t>
+
+<t>Consider an enterprise campus operating under the domain example.net
+that provides essential services, such as logistics, to users on its
+campus. If the transit connection to the broader Internet were to
+fail, the consequences could be significant. Even when all
+infrastructure (DNS recursive and authoritative, and the servers for
+the services themselves, etc) is on premise a failure to resolve the
+delegation between top level domain .net and example.net would
+eventually lead to inability to contact services.</t>
+
+<t>Another example is a small island nation state that has a number of
+its government services running on the island under its own TLD. Now
+considers a cable cut scenario where all upstream connectivity is
+lost. After a while, when authority information starts to time out
+from caches (for some implementations after 24 hours), connections to
+services on the island will start to fail.</t>
+
+<t>A less benign example is an intervention in the DNS root. Where
+delegation data for a country's level top level domain(ccTLD) gets
+altered or removed. Such intervention would eventually debilitate
+users which rely on services within that ccTLDs domain, usually
+government services and local media outlets within that country.</t>
+
+<t>While unthinkable even a few years ago these sort of scenario are now
+being considered in the context of international stability in
+cyberspace.</t>
+
+<t>In this document we document an operational approach that, with minor
+support of recursive nameserver can offer one of the elements towards
+greater autonomy and resilience of infrastructure dependent on a
+specific domain. While certainly not the only approach to increase
+resiliency (e.g. the small island nation state example would be
+solved by having a local anycast instance of the root) we introduce
+this to offer confidence building mechanism that does not
+fundamentally change the DNS design. This approach is consistent with
+the architecture, design, and operation of the DNS. By following
+practices herein we avoid namespace fragmentation. We also avoid
+fundamental protocol changes, in particular we avoid alternative
+roots.</t>
+
+<t>The approach called 'in-tree hints', offers protection against various
+attack vectors that could compromise the delegation process. For
+instance, on-path attackers may attempt to alter delegation records,
+which could lead to denial of service, particularly in systems
+utilizing Domain Name System Security Extensions
+(DNSSEC). Additionally, threats such as DNS supply chain attacks or
+inadvertent errors can result in unauthorized changes to the
+delegation, including DS (Delegation Signer) records. More general, we
+solve for the case that a DNS resolver receives parental data that is
+inconsistent with the intent from the domain owner, i.e. receiving
+data that is inconsistent with what is published on authoritative
+servers. That includes not receiving data at all.</t>
+
+<t>In-tree hints can be seen  as a building block for resiliency of
+critical infrastructure or digital autonomy. The approach is
+complementary to serving stale data from the cache <xref target="RFC8767"/>, more
+on this in section <xref target="stale"/>.</t>
+
+<t>In this memo we describe what the parties that are critically
+dependent on a specific domain and those that serve zones within that
+domain will need to do in order to guarantee continuous operation.</t>
+
+<t>In section <xref target="concept"/> we describe the idea and the requirements for a
+recursive DNS server and the requirements of the zone associated with.
+In section <xref target="resilience"/> we shortly point to other measures that must
+be taken in combination with this mechanism. In section <xref target="policy"/> we
+discuss some policy considerations and the dilemmas that exist with
+respect to intentions of the DNS parent and child.</t>
+
+<t>This document uses uppercase SHOULD, RECOMMENDED and MUST in the
+meaning defined by <xref target="RFC2119"/>. Their lowercase equivalents do not
+have normative meaning.</t>
+
+</section>
+<section anchor="concept"><name>The in-tree hints concept</name>
+
+<t><xref target="RFC9499"/> describes the root hints file "Operators who manage a DNS
+recursive resolver typically need to configure a 'root hints
+file'. This file contains the names and IP addresses of the
+authoritative name servers for the root zone, so the software can
+bootstrap the DNS resolution process. For many pieces of software,
+this list comes built into the software."</t>
+
+<t>The in-tree hints borrows this from this idea: by configuring a 'hints
+file' for a specific domain one allows oneself to bootstrap from that
+domain down, even if its parents are not available. Implementing it
+requires a modification in recursive nameservers and adherence to some
+operational practices.</t>
+
+<section anchor="rec"><name>Recursive nameserver</name>
+
+<t>Recursive nameserver software will need to be modified to deal to work
+with in-tree hints.</t>
+
+<t>An in-tree hints is configuration for a recursive resolver that
+provides the names and IP addresses of authoritative name servers for
+a specific domain. A recursive name server may be configured for
+in-tree hints for multiple domains.</t>
+
+<t>When there are no in-domain (in bailiwick) nameservers (<xref target="RFC9499"/>)
+in the NS set for the domain then this mechanism MUST [OMK: SHOULD?] not be
+used. Without this requirement the resiliency properties can
+potentially not be achieved as there are dependencies outside of
+control of the domain. This requirement can be enforced by the
+recursive nameserver software at the moment of configuration
+parsing. In addition the in bailiwick server should fate share IP
+connectivity with its dependendants. For instance, in our island
+example one in-domain name server should be on the isle. In our
+enterprise example one in-domain server should be on campus.</t>
+
+<t>In-tree hints are only useful if the domain owner follows certain
+practices. A recursive nameserver MAY only implement the in-tree hints
+mechanism for a specific domain if the domain owner indicates it does
+so. Section <xref target="signal"/> describes the RECOMMENDED way for domain name
+owners to signal their intent.  [OMK: REVIEW 2019 Keywords]</t>
+
+<t>In-tree hints MUST only be used in combination with a DNSSEC
+trust-anchor. i.e. a trusted public DNSSEC key that is associated with
+the name. The trust-anchor MUST be maintained. It SHOULD be maintained
+by the mechanism described in <xref target="RFC5011"/>. Alternatively an
+appropriate and trustworthy off-band mechanism MAY be used. The
+operator of a recursive nameserver must validate that the domain
+associated with the in-tree hints follows the operational practices
+described in this memo. This can be achieved by out-of band
+mechanisms, or by querying the TXT record as described in {#auth}</t>
+
+<t>When a recursive nameserver is configured with an in-tree hint then
+the NS Resource Record set contained in the in-tree hint MUST be used
+during the resolution process. Which means that they always overwrite
+the NS and DS resource records received from the parent.</t>
+
+<t>When the NS RRset on the domain's authoritative server changes and has
+been validated using DNSSEC against configured key then the in-hints
+tree configuration SHOULD be updated with the changed authoritative NS
+set. This requirement guarantees that the intent of the domain holder
+will be followed.</t>
+
+<t>The recursive nameserver should honor the TTLs to regular check a
+change of the authoritative NS RRset. Operators that implement in-tree
+hints SHOULD use tooling, possibly implemented in the recursive
+nameserver, to log and signal inconsistencies between information in
+the parents and the in-tree configuration to the operators of the
+recursive nameserver, these inconsistencies need to be well
+understood. They could be the result of a bona-fide re-delegation (in
+which case the parental records are likely a subset of the
+authoritative NS RR set), the withdrawal of the delegation by the
+parent, or an error or attack.</t>
+
+<t>The trust anchor MUST be used for the validation of record within the
+tree-hint's domain even when a parental DS record exists. Nota bene,
+section 5 of <xref target="RFC5011"/> allows for deletion if a superior trust point
+exists - when a trust anchor is part of an in-tree hint that deletion
+with the motivation that a superior trust point exists MUST not
+happen. When a tree-hint exists for a subordinate domain, that trust
+anchor MUST take precedence.</t>
+
+<t>Recursive nameservers that implement this mechanism SHOULD have a
+fallback mechanism implemented that will eventually allow them to
+reach the in-domain nameserver when other servers in the NS resource
+record set fail. [OMK: I think this is an existing requirement
+somewhere else in the mountain of RFCs]</t>
+
+</section>
+<section anchor="auth"><name>Domain Owner</name>
+
+<t>This section describes the operational practices that the domain owner
+has to follow in order to achieve the resiliency within the domain.</t>
+
+<t>The domain owner MUST maintain its DNSSEC configuration using the
+mechanism described in <xref target="RFC5011"/>.</t>
+
+<t>The domain owner MUST have at least one in-domain authoritative
+nameserver in its NS set. If that nameserver's name is within a
+delegated child domain, then the nameservers for that delegated domain
+MUST also have at least one in-domain authoritative nameserver. This
+requirement is recursive for further delegation.</t>
+
+<t>In order to benefit from the resiliency properties provided by this
+mechanism, the domain owner should require that delegated domains
+(zones) within the domain all have one nameserver that are
+in-domain. Note that delegated domains do not have to maintain a trust
+anchor and can rely on there being a chain of trust established using
+DS records from the trust-anchor down. [OMK: is this actually clear?
+Domain, sub-domain, in-domain, may become confusing]</t>
+
+<t>Furthermore, the in-domain nameserver SHOULD be positioned in a
+network that shares connectivity fate with the clients. For instance,
+in our enterprise example it should be in the enterprise campus
+network. More generally the location is subject to a risk based
+assessment about the likelihood of not being able to obtain an IP
+connection the in-domain nameserver.</t>
+
+<t>[OMK: should there be language here about out-of-domain nameservers?]</t>
+
+<t>The domain owner should communicate to its community that it is
+deploying practices that support in-tree hints. That communication MAY
+be out of band. A RECOMMENDED in-band signaling mechanism in-band
+described in section <xref target="signal"/>.</t>
+
+</section>
+</section>
+<section anchor="operational"><name>Operational Considerations</name>
+
+<t>bla</t>
+
+<section anchor="signal"><name>Signaling</name>
+
+<t>It is RECOMMENDED that a domain owner (the owner of <spanx style="verb">&lt;domain&gt;</spanx>)
+signals to its user community that they are using the mechanism
+described in this section. Signaling is done by putting a TXT
+resource record with owner name <spanx style="verb">_in-tree.&lt;domain&gt;</spanx> containing an
+expiry timestamp in <xref target="RFC3339"/> format. The expiry timestamp indicates
+the date to which the owner is committed to follow the instructions in
+section <xref target="auth"/>.</t>
+
+<t>The recursive nameserver operator should at first opportunity, but not
+longer than 30 days after the expiration, validate if a new expiry
+record has been published by the domain owner. If not, they SHOULD
+disable the in-tree hints configuration for the domain.</t>
+
+<t><spanx style="verb">
+   _in-tree.&lt;domain&gt;   TXT  &lt;expiry timestamp&gt; 
+</spanx></t>
+
+<t>[OMK: Alternatively we create a trivial RR type for this. EXP RR
+containing a timestamp as defined in RFC4034 section-3.1.5 ]</t>
+
+<t>Out of band signaling is not in scope for this memo.</t>
+
+</section>
+<section anchor="resilience"><name>Achieving true resiliency of services within the domain.</name>
+
+<t>This memo describes a method to achieve resiliency of name resolution
+for a community of interest of a particular domain. This is, by far,
+not sufficient to achieve actual resiliency for services that are
+provided within the domain. While a detailed discussion is out of
+scope for this memo we like to remind the reader of the following:</t>
+
+<t><list style="symbols">
+  <t>The in-domain nameservers should run on IP addresses that can
+reasonably be expected to be reachable by the community of use. For
+example, if a service is critical for on-campus enterprise use then
+the in-domain nameserver should run on the campus network.</t>
+  <t>Any service provider that offers a service under a certain name
+within the domain should make sure that those services itself can be
+reasonably expected to be reachable by the community of use. Any
+service dependencies should also be local.</t>
+  <t>In an effort to create local resiliency one should not forget that
+resiliency is also achieved by having no single source of
+failure. Having in-domain nameservers, and having services in reach
+of the community of interest does not mean that one deploys
+infrastructure elsewhere.</t>
+</list></t>
+
+</section>
+<section anchor="stale"><name>Serving stale data</name>
+
+<t>In-tree hints are complementary to serving stale data
+<xref target="RFC8767"/>. Serving stale data will allow continuity for all zones
+when their authoritative servers are not reachable and the data
+happens to be in the resolvers cache. In-tree hints works for specific
+domains when data does not happen to be available in recursive
+nameserver caches or when the parent's server(s) deliver faulty
+delegation data.</t>
+
+<t>In-tree hints is not scalable in the sense that there is significant
+operational overhead for both the domain owner, they have to run
+in-domain nameservers and follow <xref target="RFC5011"/>, and the recursive
+nameserver operator as they will have to troubleshoot
+inconsistencies. Serving stale data is highly scalable as it only
+needs one configuration within the recursive nameserver and then it
+applies for all domains.</t>
+
+</section>
+</section>
+<section anchor="conclusions"><name>Conclusions</name>
+
+<t>[TODO]</t>
+
+</section>
+<section anchor="security-considerations"><name>Security Considerations</name>
+
+<t>In-tree hints can be used in recursive nameservers in combination with
+protective block-lists and does therefore not debilitate the available
+mechanism to protect the community of users of a recursive nameserver.</t>
+
+<t>Malwares that use their own recursive nameservers configured with
+in-trees for their command and control domains to circumvent
+de-delegation by the parents. However, those recursive nameservers are
+likely under the control of the malware administrators and the risk
+of disproportional damage for blocking these recursive nameservers DNS
+after it has been established that they are used in command and
+control seems proportionate.</t>
+
+<t>This mechanism intends to provide resilience for network
+failures. However, it adds complexity in software and operational
+procedures, thereby increasing the fragility.</t>
+
+<t>When DNS validation takes place by clients that are 'behind' a
+recursive nameserver that is configured with in-tree hints for a
+particular domain then behavior in case of inconsistencies between the
+domain and its parent will lead to undefined behavior. These
+validating clients SHOULD also implement in-tree hints.</t>
+
+</section>
+<section anchor="policy"><name>Policy Considerations</name>
+
+<t>Inherently the approach described in this memo provides a mechanism
+for a community of users of a domain to overwrite the policies from
+the parent domain. For instance, it allows the community of users to
+continue to use the domain even when e.g. the delegation for that
+domain expires.  As such, this mechanism allows a community to
+continue to use a domain when the parent has de-delegated the domain
+for instance in the context of a court order. At the same time this
+in-tree approach can be a building block to create resilience for a
+critical infrastructure. It can potentially be applied to a country
+code top-level domain (CCTLD) and its user community. While the
+failure mode at CCTLD level is extremely low, this approach may add to
+confidence in the domain name system as a whole in times of
+international tensions.</t>
+
+<t>When an inconsistency exists between what is published in the parent
+and what is used as in-tree-hints there is a fragmentation of the DNS
+namespace. The operators of the recursive nameservers should
+pro-actively restore the situation to consistency. Note that there is
+no technical enforcement mechanism to aid that restoration but it is
+expected that if a recursive nameserver operator configures an in-tree
+domain he is part of the community of interest and therefore has out
+of band means to contact the domain administrator. Also note that the
+operators of the domain (e.g. example.net) do not have communication
+mechanism that can enforce the use or non-use of in-tree hints by
+recursive nameserver operators.</t>
+
+<t>The authority for using or not using in-tree hints is with the
+operator of the recursive nameserver - as a user agent for its
+community.  Users have in general been able to overwrite their DNS
+configuration since the first deployment of the DNS system.  Users can
+use a recursive nameserver that does not use in-tree hints for a
+particular domain and therefore can opt-out of the mechanism.</t>
+
+</section>
+<section anchor="iana-considerations"><name>IANA Considerations</name>
+
+<t>No IANA considerations herein.</t>
+
+</section>
+<section anchor="acknowledgments"><name>Acknowledgments</name>
+
+<t>This document is inspired by various hallway conversations about digital autonomy.</t>
+
+<t>The author is an employee of the Internet Society, this document does
+not necessarily reflect the position of the Internet Society.</t>
+
+<t>{olaf: source="olaf"}</t>
+
+</section>
+
+
+  </middle>
+
+  <back>
+
+
+<references title='References' anchor="sec-combined-references">
+
+    <references title='Normative References' anchor="sec-normative-references">
+
+
+
+<reference anchor="RFC2119">
+  <front>
+    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
+    <author fullname="S. Bradner" initials="S." surname="Bradner"/>
+    <date month="March" year="1997"/>
+    <abstract>
+      <t>In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.</t>
+    </abstract>
+  </front>
+  <seriesInfo name="BCP" value="14"/>
+  <seriesInfo name="RFC" value="2119"/>
+  <seriesInfo name="DOI" value="10.17487/RFC2119"/>
+</reference>
+<reference anchor="RFC3339">
+  <front>
+    <title>Date and Time on the Internet: Timestamps</title>
+    <author fullname="G. Klyne" initials="G." surname="Klyne"/>
+    <author fullname="C. Newman" initials="C." surname="Newman"/>
+    <date month="July" year="2002"/>
+    <abstract>
+      <t>This document defines a date and time format for use in Internet protocols that is a profile of the ISO 8601 standard for representation of dates and times using the Gregorian calendar.</t>
+    </abstract>
+  </front>
+  <seriesInfo name="RFC" value="3339"/>
+  <seriesInfo name="DOI" value="10.17487/RFC3339"/>
+</reference>
+<reference anchor="RFC5011">
+  <front>
+    <title>Automated Updates of DNS Security (DNSSEC) Trust Anchors</title>
+    <author fullname="M. StJohns" initials="M." surname="StJohns"/>
+    <date month="September" year="2007"/>
+    <abstract>
+      <t>This document describes a means for automated, authenticated, and authorized updating of DNSSEC "trust anchors". The method provides protection against N-1 key compromises of N keys in the trust point key set. Based on the trust established by the presence of a current anchor, other anchors may be added at the same place in the hierarchy, and, ultimately, supplant the existing anchor(s).</t>
+      <t>This mechanism will require changes to resolver management behavior (but not resolver resolution behavior), and the addition of a single flag bit to the DNSKEY record. [STANDARDS-TRACK]</t>
+    </abstract>
+  </front>
+  <seriesInfo name="STD" value="74"/>
+  <seriesInfo name="RFC" value="5011"/>
+  <seriesInfo name="DOI" value="10.17487/RFC5011"/>
+</reference>
+<reference anchor="RFC7344">
+  <front>
+    <title>Automating DNSSEC Delegation Trust Maintenance</title>
+    <author fullname="W. Kumari" initials="W." surname="Kumari"/>
+    <author fullname="O. Gudmundsson" initials="O." surname="Gudmundsson"/>
+    <author fullname="G. Barwood" initials="G." surname="Barwood"/>
+    <date month="September" year="2014"/>
+    <abstract>
+      <t>This document describes a method to allow DNS Operators to more easily update DNSSEC Key Signing Keys using the DNS as a communication channel. The technique described is aimed at delegations in which it is currently hard to move information from the Child to Parent.</t>
+    </abstract>
+  </front>
+  <seriesInfo name="RFC" value="7344"/>
+  <seriesInfo name="DOI" value="10.17487/RFC7344"/>
+</reference>
+
+
+
+    </references>
+
+    <references title='Informative References' anchor="sec-informative-references">
+
+
+
+<reference anchor="RFC9499">
+  <front>
+    <title>DNS Terminology</title>
+    <author fullname="P. Hoffman" initials="P." surname="Hoffman"/>
+    <author fullname="K. Fujiwara" initials="K." surname="Fujiwara"/>
+    <date month="March" year="2024"/>
+    <abstract>
+      <t>The Domain Name System (DNS) is defined in literally dozens of different RFCs. The terminology used by implementers and developers of DNS protocols, and by operators of DNS systems, has changed in the decades since the DNS was first defined. This document gives current definitions for many of the terms used in the DNS in a single document.</t>
+      <t>This document updates RFC 2308 by clarifying the definitions of "forwarder" and "QNAME". It obsoletes RFC 8499 by adding multiple terms and clarifications. Comprehensive lists of changed and new definitions can be found in Appendices A and B.</t>
+    </abstract>
+  </front>
+  <seriesInfo name="BCP" value="219"/>
+  <seriesInfo name="RFC" value="9499"/>
+  <seriesInfo name="DOI" value="10.17487/RFC9499"/>
+</reference>
+<reference anchor="RFC8767">
+  <front>
+    <title>Serving Stale Data to Improve DNS Resiliency</title>
+    <author fullname="D. Lawrence" initials="D." surname="Lawrence"/>
+    <author fullname="W. Kumari" initials="W." surname="Kumari"/>
+    <author fullname="P. Sood" initials="P." surname="Sood"/>
+    <date month="March" year="2020"/>
+    <abstract>
+      <t>This document defines a method (serve-stale) for recursive resolvers to use stale DNS data to avoid outages when authoritative nameservers cannot be reached to refresh expired data. One of the motivations for serve-stale is to make the DNS more resilient to DoS attacks and thereby make them less attractive as an attack vector. This document updates the definitions of TTL from RFCs 1034 and 1035 so that data can be kept in the cache beyond the TTL expiry; it also updates RFC 2181 by interpreting values with the high-order bit set as being positive, rather than 0, and suggests a cap of 7 days.</t>
+    </abstract>
+  </front>
+  <seriesInfo name="RFC" value="8767"/>
+  <seriesInfo name="DOI" value="10.17487/RFC8767"/>
+</reference>
+
+<reference anchor="E-Gov-Resilience" >
+  <front>
+    <title>Assessing e-Government DNS Resilience</title>
+    <author initials="" surname="Sommese et al">
+      <organization></organization>
+    </author>
+    <date year="2022"/>
+  </front>
+  <seriesInfo name="IEEE" value="Proceedings of the 2022 International Conference on Network and Service Management (CNSM 2022)"/>
+</reference>
+
+
+    </references>
+
+</references>
+
+
+
+  </back>
+
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