



Internet Engineering Task Force (IETF)                     S. Hollenbeck
Request for Comments: 9874                                    W. Carroll
BCP: 244                                                   Verisign Labs
Category: Best Current Practice                               G. Akiwate
ISSN: 2070-1721                                      Stanford University
                                                          September 2025


Best Practices for Deletion of Domain and Host Objects in the Extensible
                      Provisioning Protocol (EPP)

Abstract

   The Extensible Provisioning Protocol (EPP) includes commands for
   clients to delete domain and host objects, both of which are used to
   publish information in the Domain Name System (DNS).  EPP also
   includes guidance for deletions that is intended to avoid DNS
   resolution disruptions and maintain data consistency.  However,
   operational relationships between objects can make that guidance
   difficult to implement.  Some EPP clients have developed operational
   practices to delete those objects that have unintended impacts on DNS
   resolution and security.  This document describes best current
   practices and proposes new potential practices to delete domain and
   host objects that reduce the risk of DNS resolution failure and
   maintain client-server data consistency.

Status of This Memo

   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/rfc9874.

Copyright Notice

   Copyright (c) 2025 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Revised BSD License text as described in Section 4.e of the
   Trust Legal Provisions and are provided without warranty as described
   in the Revised BSD License.

Table of Contents

   1.  Introduction
   2.  Conventions Used in This Document
   3.  Rationale for "SHOULD NOT be deleted"
     3.1.  DNS Considerations
     3.2.  Client-Server Consistency Considerations
     3.3.  Relational Consistency Considerations
   4.  Host Object Renaming Risk
   5.  Analysis of Practices for Domain and Host Object Deletion
     5.1.  Renaming to Sacrificial Hosts
       5.1.1.  Practice Benefits
       5.1.2.  Practice Detriments
       5.1.3.  Observed Practices for Renaming to Sacrificial Hosts
         5.1.3.1.  Renaming to External, Presumed Non-Existent Hosts
           5.1.3.1.1.  Practice Benefits
           5.1.3.1.2.  Practice Detriments
         5.1.3.2.  Renaming to "AS112.ARPA"
           5.1.3.2.1.  Practice Benefits
           5.1.3.2.2.  Practice Detriments
         5.1.3.3.  Renaming to Non-Authoritative Hosts
           5.1.3.3.1.  Practice Benefits
           5.1.3.3.2.  Practice Detriments
         5.1.3.4.  Renaming to Client-Maintained Dedicated Sacrificial
                 Name Server Host Objects
           5.1.3.4.1.  Practice Benefits
           5.1.3.4.2.  Practice Detriments
       5.1.4.  Potential Practices for Renaming to Sacrificial Hosts
         5.1.4.1.  Renaming to Pseudo-TLD
           5.1.4.1.1.  Practice Benefits
           5.1.4.1.2.  Practice Detriments
         5.1.4.2.  Renaming to Existing Special-Use TLD
           5.1.4.2.1.  Renaming to Reserved TLD
         5.1.4.3.  Renaming to a Special-Use Domain
           5.1.4.3.1.  Practice Benefits
           5.1.4.3.2.  Practice Detriments
         5.1.4.4.  Renaming to Community Sacrificial Name Server
                 Service
           5.1.4.4.1.  Practice Benefits
           5.1.4.4.2.  Practice Detriments
     5.2.  Deletion of Hosts
       5.2.1.  Observed Practices for Deletion of Hosts
         5.2.1.1.  Implicit Deletion of Affected Host Objects
           5.2.1.1.1.  Practice Benefits
           5.2.1.1.2.  Practice Detriments
         5.2.1.2.  Inform Affected Clients
           5.2.1.2.1.  Practice Benefits
           5.2.1.2.2.  Practice Detriments
       5.2.2.  Potential Practices for Deletion of Hosts
         5.2.2.1.  Request Explicit Deletion of Affected Host Objects
           5.2.2.1.1.  Practice Benefits
           5.2.2.1.2.  Practice Detriments
         5.2.2.2.  Provide Additional Deletion Details
           5.2.2.2.1.  Practice Benefits
           5.2.2.2.2.  Practice Detriments
         5.2.2.3.  Allow Explicit Deletion of a Domain with Restore
                 Capability
           5.2.2.3.1.  Practice Benefits
           5.2.2.3.2.  Practice Detriments
   6.  Recommendations
   7.  IANA Considerations
   8.  Security Considerations
   9.  References
     9.1.  Normative References
     9.2.  Informative References
   Acknowledgments
   Authors' Addresses

1.  Introduction

   Section 3.2.2 of [RFC5731] contains text that has led some domain
   name registrars (acting as EPP clients) to adopt an operational
   practice of renaming name server host objects so that they can delete
   domain objects:

   |  A domain object SHOULD NOT be deleted if subordinate host objects
   |  are associated with the domain object.  For example, if domain
   |  "example.com" exists and host object "ns1.example.com" also
   |  exists, then domain "example.com" SHOULD NOT be deleted until host
   |  "ns1.example.com" has either been deleted or renamed to exist in a
   |  different superordinate domain.

   Similarly, Section 3.2.2 of [RFC5732] contains this text regarding
   deletion of host objects:

   |  A host name object SHOULD NOT be deleted if the host object is
   |  associated with any other object.  For example, if the host object
   |  is associated with a domain object, the host object SHOULD NOT be
   |  deleted until the existing association has been broken.  Deleting
   |  a host object without first breaking existing associations can
   |  cause DNS resolution failure for domain objects that refer to the
   |  deleted host object.

   These recommendations create a dilemma when the sponsoring client for
   "example.com" intends to delete "example.com" but its associated host
   object "ns1.example.com" is also associated with domain objects
   sponsored by another client.  It is advised not to delete the host
   object due to its associated domain objects.  However, the associated
   domain objects cannot be directly updated because they are sponsored
   by another client.  This situation affects all EPP operators that
   have implemented support for host objects.

   Section 3.2.5 of [RFC5732] describes host object renaming:

   |  Host name changes can have an impact on associated objects that
   |  refer to the host object.  A host name change SHOULD NOT require
   |  additional updates of associated objects to preserve existing
   |  associations, with one exception: changing an external host object
   |  that has associations with objects that are sponsored by a
   |  different client.  Attempts to update such hosts directly MUST
   |  fail with EPP error code 2305.  The change can be provisioned by
   |  creating a new external host with a new name and any needed new
   |  attributes, and subsequently updating the other objects sponsored
   |  by the client.

   Section 1.1 of [RFC5732] includes a description of external hosts.
   Some EPP clients have developed operational practices that use host
   object renaming to break association between a domain object and host
   object.  Note that the specific method used to rename the host object
   can create DNS delegation failures and introduce risks of loss of
   management control.  If the new external host refers to an
   unregistered domain, then a malicious actor may register the domain
   and create the host object to gain control of DNS resolution for the
   domain previously associated with "ns1.example.com".  If the new
   external host offers an authoritative DNS service but the domain is
   not assigned to an account, then a malicious actor may add the domain
   to a service account and gain control of (i.e., hijack) DNS
   resolution functionality.  If the new external host offers recursive
   DNS service or no DNS service, then DNS requests for the domain will
   result in SERVFAIL messages or other errors.  Aggressive requeries by
   DNS resolvers may then create large numbers of spurious DNS queries
   for an unresolvable domain.  Note that renaming a host object to a
   name of an external host cannot be reversed by the EPP client.

   This document describes the rationale for the "SHOULD NOT be deleted"
   text in [RFC5731] and [RFC5732] as well as the risk associated with
   host object renaming.  Section 5 includes a detailed analysis of the
   practices that have been and can be used to mitigate that risk.
   Section 6 includes specific recommendations for the best practices.

2.  Conventions Used in This Document

   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.

3.  Rationale for "SHOULD NOT be deleted"

3.1.  DNS Considerations

   The primary consideration when deleting domain and host objects
   concerns the potential impact on DNS resolution.  Deletion of a
   domain object will make all name servers associated with subordinate
   host objects unresolvable.  Deletion of a host object will make any
   domain that has been delegated to the associated name server
   unresolvable.  The text in [RFC5731] and [RFC5732] was written to
   encourage clients to take singular, discrete steps to delete objects
   in a way that avoids breaking DNS resolution functionality.
   Additionally, allowing host objects to exist after deletion of their
   superordinate domain object invites hijacking, as a malicious actor
   may reregister the domain object, potentially controlling resolution
   for the host objects and for their associated domain objects.  It
   also creates orphan glue as described in [SAC048].

3.2.  Client-Server Consistency Considerations

   A server that implicitly deletes subordinate host objects in response
   to a request to delete a domain object can create a data
   inconsistency condition in which the EPP client and the EPP server
   have different views of what remains registered after processing a
   <delete> command.  The text in [RFC5731] and [RFC5732] was written to
   encourage clients to take singular, discrete steps to delete objects
   in a way that maintains client-server data consistency.  Experience
   suggests that this inconsistency poses little operational risk.

3.3.  Relational Consistency Considerations

   Implementations of EPP can have dependencies on the hierarchical
   domain object / host object relationship, which can exist in a
   relational database.  In such instances, deletion of a domain object
   without addressing the existing subordinate host objects can cause
   relational consistency and integrity issues.  The text in [RFC5731]
   and [RFC5732] was written to reduce the risk of these issues arising
   as a result of implicit object deletion.

4.  Host Object Renaming Risk

   As described in [RFC5731], it is possible to delete a domain object
   that has associated host objects that are managed by other clients by
   renaming the host object to exist in a different superordinate
   domain.  This is commonly required when the sponsoring client is
   unable to disassociate a host object from a domain object managed by
   another client because only the second client is authorized to make
   changes to their domain object and the EPP server requires host
   object disassociation to process a request to delete a domain object.
   For example:

   Domain object "domain1.example" is registered by ClientX.

   Domain object "domain2.example" is registered by ClientY.

   Subordinate host object "ns1.domain1.example" is registered and
   associated with domain object "domain1.example" by ClientX.

   Host object "ns1.domain1.example" is associated with domain object
   "domain2.example" by ClientY.

   ClientX wishes to delete domain object "domain1.example".  It can
   modify domain object "domain1.example" to remove the association of
   host object "ns1.domain1.example", but ClientX cannot remove the
   association of host object "ns1.domain1.example" from domain object
   "domain2.example" because "domain2.example" is sponsored by ClientY
   and ClientX is unable to determine that relationship.  Only ClientY
   can modify domain object "domain2.example", and if they do not do so,
   ClientX will need to rename host object "ns1.domain1.example" so that
   "domain1.example" can be deleted.

   ClientX renames host object "ns1.domain1.example" to
   "ns1.example.org", creating an external host and meeting the EPP
   server's subordinate host object disassociation requirement.  The
   renamed host object "ns1.example.org" is referred to as a
   "sacrificial" host [Risky-BIZness].

   If domain "example.org" does not exist, this practice introduces a
   risk of DNS resolution hijacking if someone were to register the
   "example.org" domain and create a subordinate host object named
   "ns1.example.org".  That name server would receive DNS queries for
   all domains delegated to it, allowing the operator of the name server
   to respond in potentially malicious ways.

5.  Analysis of Practices for Domain and Host Object Deletion

   EPP servers can employ a range of practices for domain and host
   object deletion.  Notably, the scope of any practice discussed here
   is the EPP server that adopts the practice, the domains managed by
   it, and the associated host objects where "associated" is described
   in [RFC5731] and [RFC5732].  The practices described in this document
   fall into two broad categories: renaming objects to use sacrificial
   hosts and allowing objects to be deleted even if there are existing
   data relationships.  These practice categories are described in the
   following sections.  For a broader consideration of practices and
   potential impacts on registries and registrars, [SAC125] offers some
   complementary insight.

5.1.  Renaming to Sacrificial Hosts

   Sacrificial hosts are hosts whose name is intended to remove an
   existing relationship between domain and host objects.  To that end,
   sacrificial hosts are either renamed to an external host or
   associated with a different domain object in the EPP server.  The
   first group of deletion practices use sacrificial hosts leveraging
   existing EPP server support for renaming host objects.

5.1.1.  Practice Benefits

   Affected domains remain delegated in the zone.  Registrars and
   registrants of affected domains may be able to determine the
   intention of the change.

5.1.2.  Practice Detriments

   Zones are crowded with irrelevant records.  Registrars and
   registrants of affected domains are required to clean them up.

5.1.3.  Observed Practices for Renaming to Sacrificial Hosts

5.1.3.1.  Renaming to External, Presumed Non-Existent Hosts

   As described above, this practice renames subordinate host objects to
   an external host in order to allow the deletion of the superordinate
   domain object.  The external host is presumed to be non-existent by
   the deleting EPP client, but no check for existence is typically
   performed.  This practice has been observed in use.  This practice
   MUST NOT be used.

5.1.3.1.1.  Practice Benefits

   The primary benefit is convenience for the deleting EPP client.  The
   deleting EPP client is not required to maintain an authoritative DNS
   service or receive traffic.

5.1.3.1.2.  Practice Detriments

   Malicious actors have registered these parent domains and created
   child host objects to take control of DNS resolution for associated
   domains [Risky-BIZness].

   Sponsoring clients of the associated domains are not informed of the
   change.  Associated domains may no longer resolve if all their hosts
   are renamed.  Associated domains may still resolve if they continue
   to be associated with existent hosts; in which case, their partial
   vulnerability to hijacking is more difficult to detect.

5.1.3.2.  Renaming to "AS112.ARPA"

   Some domain registrars, acting as EPP clients, have renamed host
   objects to subdomains of "AS112.ARPA" or "EMPTY.AS112.ARPA"
   [Risky-BIZness-IRTF].  This practice has been observed in use.

5.1.3.2.1.  Practice Benefits

   The primary benefit is convenience for the deleting EPP client.  The
   deleting EPP client is not required to maintain an authoritative DNS
   service or receive traffic.

5.1.3.2.2.  Practice Detriments

   This is a misuse of AS112, which is for reverse lookups on non-unique
   IPs, primarily so local admins can sinkhole non-global traffic
   [RFC7535].  "EMPTY.AS112.ARPA" is designed to be used with DNAME
   aliasing, not as a parent domain for sacrificial name servers (see
   Section 3 of [RFC7535]).  Unexpected AS112 traffic has previously
   caused problems with intrusion detection systems and firewalls
   [RFC6305].  Local administrators can potentially hijack requests.
   AS112 infrastructure must be maintained.

5.1.3.3.  Renaming to Non-Authoritative Hosts

   Some domain registrars, acting as EPP clients, have maintained host
   objects with glue records pointing to prominent public recursive DNS
   services.  This practice has been observed in use.  This practice
   MUST NOT be used.

5.1.3.3.1.  Practice Benefits

   The primary benefit is convenience for the deleting EPP client.  The
   deleting EPP client is not required to maintain an authoritative DNS
   service or receive traffic.

5.1.3.3.2.  Practice Detriments

   Queries for the associated domains result in SERVFAIL or other
   failure responses.  Some recursive name server implementations may
   aggressively requery for these responses, potentially resulting in
   large numbers of queries for unresolvable domains [RFC9520].

5.1.3.4.  Renaming to Client-Maintained Dedicated Sacrificial Name
          Server Host Objects

   EPP clients MAY rename the host object to be deleted to a sacrificial
   name server host object maintained by the client.  This requires that
   the client maintain the registration of the sacrificial name server's
   superordinate domain.  The client may consider long registration
   periods and the use of registrar and registry lock services to
   maintain and protect the superordinate domain and the host object.
   Failures to maintain these registrations have allowed domain hijacks
   [Risky-BIZness].

   The client-maintained dedicated sacrificial name server MUST resolve
   to one or more IP addresses, and the client MUST operate an
   authoritative DNS name server on those addresses.  The name server
   MAY provide any valid response.

   This practice has been observed in use.

5.1.3.4.1.  Practice Benefits

   Associated domains are not able to be hijacked, remain in the zone,
   and have valid DNS records and a responsive DNS service.  The service
   may provide responses that indicate problems with a domain's
   delegation, such as non-existence or including controlled
   interruption IP addresses [RFC8023].

5.1.3.4.2.  Practice Detriments

   This requires that the client maintain the registration of the
   sacrificial name server's superordinate domain.  The client may
   consider long registration periods and the use of registrar and
   registry lock services to maintain and protect the superordinate
   domain and the host object.  Failures to maintain these registrations
   have allowed domain hijacks [Risky-BIZness].

   Failure responses may cause aggressive requerying (see
   Section 5.1.3.3.2).

5.1.4.  Potential Practices for Renaming to Sacrificial Hosts

5.1.4.1.  Renaming to Pseudo-TLD

   Clients may rename host objects to use ".alt" or another non-DNS
   pseudo-TLD (Top-Level Domain), as suggested in [Risky-BIZness-IRTF].
   This practice has not been observed in use.  This practice MUST NOT
   be used.

5.1.4.1.1.  Practice Benefits

   The primary benefit is convenience for the deleting EPP client.  The
   deleting EPP client is not required to maintain an authoritative DNS
   service or receive traffic.  Dependent domains cannot be hijacked
   through the registration of these identifiers and delegation in the
   DNS.

5.1.4.1.2.  Practice Detriments

   The ".alt" pseudo-TLD is to be used "to signify that this is an
   alternative (non-DNS) namespace and should not be looked up in a DNS
   context" [RFC9476].  Some EPP servers may restrict TLDs to valid
   IANA-delegated TLDs.  These entries would mix DNS and non-DNS
   protocols, risk name collisions, create confusion, and potentially
   result in unpredictable resolver behaviors.  These identifiers may be
   registered in non-DNS namespaces, potentially leading to hijacking
   vulnerabilities based in other systems.

5.1.4.2.  Renaming to Existing Special-Use TLD

   Clients may rename host objects to a special-use TLD that cannot
   resolve in the DNS.  Several variations have been suggested.  This
   practice has not been observed in use.

5.1.4.2.1.  Renaming to Reserved TLD

   Clients may rename host objects to use a reserved special-use
   [RFC6761] TLD, as suggested in [Risky-BIZness].

5.1.4.2.1.1.  Practice Benefits

   The primary benefit is convenience for the deleting EPP client.
   These TLDs are already reserved and will not resolve.  The deleting
   EPP client is not required to maintain an authoritative DNS service
   or receive traffic.  Dependent domains cannot be hijacked.

5.1.4.2.1.2.  Practice Detriments

   The use of TLDs reserved for special purposes [RFC6761] may be
   confusing without a domain designated by the community for this
   purpose (see "sacrificial.invalid" in Sections 5.1.4.3 and 6).  In
   addition, their use may be prevented by EPP server policy.

5.1.4.3.  Renaming to a Special-Use Domain

   Clients would rename hosts to a special-use domain or subdomain
   thereof.  The domain may be a special-use SLD (Second-Level Domain)
   (e.g., sacrificial.invalid) or a new reserved TLD (e.g.,
   .sacrificial).  Use of this domain would communicate the client's
   intention to create a sacrificial host.  IANA would add this domain
   to the "Special-Use Domain Name" registry if such a new TLD is
   created using either IETF or ICANN processes.  This practice has not
   been observed in use.  In terms of the questions from [RFC6761]:

   1.  These names are not expected to be visible to human users.
       However, the purpose of these domains is expected to be
       semantically recognizable to human users.

   2.  Application software is not expected to recognize these names as
       special or treat them differently than other allowed domain
       names.

   3.  Name resolution APIs and libraries are not expected to recognize
       these names as special or treat them differently than other
       allowed domain names.

   4.  Caching name servers are not expected to recognize these names as
       special or treat them differently than other allowed domain
       names.

   5.  Authoritative name servers are not expected to recognize these
       names as special or treat them differently than other allowed
       domain names.  Requests to the root for this domain would result
       in an NXDOMAIN response [RFC9499].

   6.  DNS server operators will treat this domain and its subdomains as
       they would any other allowed names in the DNS.

   7.  DNS registries/registrars will not be able to register this
       domain and must deny requests to register it or its subdomains.

5.1.4.3.1.  Practice Benefits

   This option would offer clarity concerning the intentions of
   registrars that rename hosts.  It would also enable registrars of
   affected domains ease of detection of renamed hosts.  This option is
   also convenient for the deleting EPP client.  The deleting EPP client
   is not required to maintain an authoritative DNS service or receive
   traffic.  Dependent domains cannot be hijacked through the
   registration of these identifiers and delegation in the DNS.

5.1.4.3.2.  Practice Detriments

   This would require cooperation and policy changes for registrars and
   registries.

5.1.4.4.  Renaming to Community Sacrificial Name Server Service

   A new community-wide service could be created explicitly intended for
   use for renaming host records.  This would require maintenance of
   name servers capable of authoritatively responding with NXDOMAIN or a
   controlled interruption IP addresses [RFC8023] for all queries
   without delegating domains or records.  This service could use a new
   special-use TLD created through ICANN or IETF processes (e.g.,
   ".sacrificial"), as an IAB request that IANA delegate an SLD for
   ".arpa" (e.g., "sacrificial-nameserver.arpa"), or as a contracted
   sinkhole service by ICANN or other DNS ecosystem actors.  This
   practice has not been observed in use.

5.1.4.4.1.  Practice Benefits

   This is convenient for the deleting EPP client.  The deleting EPP
   client is not required to maintain an authoritative DNS service or
   receive traffic.  The associated domains are not vulnerable to
   hijacking.  This would provide a well-understood, industry-standard
   solution, allowing registrars and registrants to easily identify
   associated domains that have been affected.  Infrastructure operators
   could monitor traffic to identify affected associated domains that
   result in significant traffic and attempt to contact registrars and
   registrants.  Economies of scale would allow reduced overall costs to
   the industry (in contrast to each client running an independent
   service).

5.1.4.4.2.  Practice Detriments

   Some entity must maintain the infrastructure for the service.

5.2.  Deletion of Hosts

   The second group of practices is based on EPP server support for
   allowing objects to be deleted even if there are existing data
   relationships.  The recommendations in [RFC5731] are intended to
   maintain consistency.  However, they are not requirements.

5.2.1.  Observed Practices for Deletion of Hosts

5.2.1.1.  Implicit Deletion of Affected Host Objects

   EPP servers may relax their constraints and allow sponsoring clients
   to delete host objects without consideration of associations with
   domain objects sponsored by other clients.  The registry
   automatically disassociates the deleted host objects from domain
   objects sponsored by other clients.  This practice has been observed
   in use.

5.2.1.1.1.  Practice Benefits

   This is convenient for the deleting EPP client.  The deleting EPP
   client is not required to maintain an authoritative DNS service or
   receive traffic.  The associated domains are not vulnerable to
   hijacking.

5.2.1.1.2.  Practice Detriments

   This could result in domains with no name servers being removed from
   the zone or domains with only one name server remaining in the zone.
   Deletions could potentially affect large numbers of associated
   domains, placing strain on domain registries.

5.2.1.2.  Inform Affected Clients

   The sponsoring clients of affected domain objects may also be
   informed of the change (e.g., through the EPP Change Poll extension
   [RFC8590]).  This practice has been observed in use.

5.2.1.2.1.  Practice Benefits

   Updates help achieve the goals of client-server data consistency and
   minimal interruptions to resolution.  The sponsoring clients of
   affected domain objects are able to update their database to reflect
   the change and would be able to inform the domain's registrant.  The
   sponsoring clients can automatically update the affected domains to
   use another authoritative host.

5.2.1.2.2.  Practice Detriments

   This change requires additional development on the part of EPP
   servers and clients.  There may be scalability concerns if large
   numbers of domain objects are updated in a single transaction.

5.2.2.  Potential Practices for Deletion of Hosts

5.2.2.1.  Request Explicit Deletion of Affected Host Objects

   Sponsoring clients requesting the deletion of host objects would
   explicitly request their disassociation from domain objects sponsored
   by other clients.  This practice has not been observed in use.

5.2.2.1.1.  Practice Benefits

   Registries would not be required to unilaterally take responsibility
   for deletion.  The deleting EPP client is not required to maintain an
   authoritative DNS service or receive traffic.  The associated domains
   are not vulnerable to hijacking.

5.2.2.1.2.  Practice Detriments

   This could result in domains with no name servers being removed from
   the zone or domains with only one name server remaining in the zone.
   Deletions could potentially affect large numbers of associated
   domains, placing strain on domain registries.

5.2.2.2.  Provide Additional Deletion Details

   The EPP server may provide the deleting EPP client with additional
   details of the affected objects.  The deleting EPP client may receive
   a response (e.g., using msg, reason, or msgQ elements of the EPP
   response [RFC5730]) that deletion of the host object would affect
   domain objects sponsored by another client and may receive details
   about those objects (e.g., using the EPP poll command).  This
   practice has not been observed in use.

5.2.2.2.1.  Practice Benefits

   The deleting EPP client would be able to better understand and assess
   the potential harms of host object deletion.  Depending on the
   content of the message, the deleting EPP client might choose
   additional actions, such as delaying the deletion until manual
   approval can be obtained, renaming the host objects, or informing
   affected EPP clients.  This would give EPP clients greater
   flexibility with respect to deletion.  For example, they may choose
   only to exercise deletions that have no impact on other clients.

5.2.2.2.2.  Practice Detriments

   This change would require additional development on the part of EPP
   servers and clients.  There may be scalability concerns if large
   numbers of domain objects are updated in a single transaction.  The
   EPP server must determine the relevant information to provide for the
   EPP client's assessment.

5.2.2.3.  Allow Explicit Deletion of a Domain with Restore Capability

   Explicit deletion of a domain name with a cascade purge of
   subordinate host objects and associations with other domains may be
   an unrecoverable operation, increasing the potential negative effects
   of malicious or accidental actions.

   To mitigate this risk, EPP servers can allow for the explicit
   deletion of a domain with subordinate host objects associated with
   other domains only when the associations can be restored by the
   <restore> operation described in [RFC3915].

   In order to allow restore, EPP servers may keep the subordinate host
   objects with a "pendingDelete" status and keep associations with
   other domains.  This makes the objects unavailable in the DNS and
   provides a preview of the deletion.

   If the action was malicious, accidental, or had negative side
   effects, the domain, its subordinate host objects, and the
   associations with other domains can be restored with the <restore>
   operation [RFC3915] during the redemption period.  The purge of the
   domain will correspond with the purging of the subordinate hosts
   objects and the associations at the end of the pending delete period
   [RFC3915].

   Due to the potentially large number of associations, the server can
   asynchronously update (e.g., add and remove from DNS) and purge the
   associations.

   This practice has not been observed in use.

5.2.2.3.1.  Practice Benefits

   This practice enables the clients to directly delete the domains that
   they need since the server will fully support restoration of the
   associations during the redemption period.  The management of the
   domain and the subordinate hosts will be simplified for the client by
   supporting the explicit deletion of the domain with the capability of
   mitigating a destructive malicious or accidental action.

5.2.2.3.2.  Practice Detriments

   By making it easier for a client to explicitly delete a domain having
   subordinate hosts with associations, there is higher risk of
   inadvertent side effects in a single delete command.  There is
   existing risk in EPP of inadvertent side effects, such as adding the
   "clientHold" status to the domain that will impact the DNS resolution
   of the subordinate hosts and the associated delegations.  The ability
   to easily roll back the command is key to minimize the impact of the
   side effects.  Another issue is the potential size of the database
   transaction to disable, re-enable, or purge the subordinate host
   associations, since there is no limit to the number of associations
   to delegated domains.  Servers can break up the disable, re-enable,
   or purge of the subordinate host associations into smaller
   transactions by implementing it asynchronously.

6.  Recommendations

   EPP servers and clients MUST implement one of the following practices
   to delete domain and host objects with minimal undesired side
   effects:

   *  Rename host objects to a sacrificial name server host object
      maintained by the client (see Section 5.1.3.4).

   *  Delete host objects and associations with the restore option (see
      Section 5.2.2.3) based on explicit client requests (see
      Section 5.2.2.1).  Provide requesting clients additional deletion
      details (see Section 5.2.2.2), and inform affected clients of
      changes (see Section 5.2.1.2).

   *  Rename host objects to a sacrificial name server host object that
      uses a special-use domain (see Section 5.1.4.3) that avoids the
      special-use domain issues described in [RFC8244].  Use of
      "sacrificial.invalid" (see Section 5.1.4.3) as the parent domain
      for the host objects is RECOMMENDED to avoid the overhead of
      creating a new TLD using either IETF or ICANN processes that
      offers no additional operational benefit.

   All other practices described in Section 5 are NOT RECOMMENDED due to
   undesired side effects.

7.  IANA Considerations

   This document has no IANA actions.

8.  Security Considerations

   This document describes guidance found in [RFC5731] and [RFC5732]
   regarding the deletion of domain and host objects by EPP clients.
   That guidance sometimes requires that host objects be renamed such
   that they become "external" hosts (see Section 1.1 of [RFC5731]) in
   order to meet an EPP server's requirements for host object
   disassociation prior to domain object deletion.  Host object renaming
   can introduce a risk of DNS resolution hijack under certain
   operational conditions.  This document provides guidance that is
   intended to reduce the risk of DNS resolution failure or hijacking as
   part of the process of deleting EPP domain or host objects.

   Child domains that depend on host objects associated with domain
   objects sponsored by another EPP client for DNS resolution may be
   protected from hijacking through the use of DNSSEC.  Their resolution
   may be protected from the effects of deletion by using host objects
   associated with multiple domain objects.  DNSSEC and multiple host
   objects may interfere with the use of controlled interruption IP
   addresses to alert registrants to DNS changes.  EPP clients can
   periodically scan sponsored domains for association with sacrificial
   name servers and alert end users concerning those domains.

   In absence of DNSSEC use by the victim, an attacker who gains control
   of a single name server can use DNSSEC to instead take over the
   victim domain completely if the registry operator and registrar
   process for automated DS maintenance neglects to check all name
   servers for consistency in CDS/CDNSKEY records.  In this scenario,
   the domain will end up with DS records derived from the attacker CDS/
   CDNSKEY records if, by chance, the queries happen to hit the
   attacker-controlled name server.  Subsequently, validating resolvers
   will no longer accept responses from the legitimate name servers.
   Moreover, with the use of CSYNC, an attacker may update the domain NS
   records, removing the legitimate name servers entirely.

9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC3915]  Hollenbeck, S., "Domain Registry Grace Period Mapping for
              the Extensible Provisioning Protocol (EPP)", RFC 3915,
              DOI 10.17487/RFC3915, September 2004,
              <https://www.rfc-editor.org/info/rfc3915>.

   [RFC5730]  Hollenbeck, S., "Extensible Provisioning Protocol (EPP)",
              STD 69, RFC 5730, DOI 10.17487/RFC5730, August 2009,
              <https://www.rfc-editor.org/info/rfc5730>.

   [RFC5731]  Hollenbeck, S., "Extensible Provisioning Protocol (EPP)
              Domain Name Mapping", STD 69, RFC 5731,
              DOI 10.17487/RFC5731, August 2009,
              <https://www.rfc-editor.org/info/rfc5731>.

   [RFC5732]  Hollenbeck, S., "Extensible Provisioning Protocol (EPP)
              Host Mapping", STD 69, RFC 5732, DOI 10.17487/RFC5732,
              August 2009, <https://www.rfc-editor.org/info/rfc5732>.

   [RFC6761]  Cheshire, S. and M. Krochmal, "Special-Use Domain Names",
              RFC 6761, DOI 10.17487/RFC6761, February 2013,
              <https://www.rfc-editor.org/info/rfc6761>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8244]  Lemon, T., Droms, R., and W. Kumari, "Special-Use Domain
              Names Problem Statement", RFC 8244, DOI 10.17487/RFC8244,
              October 2017, <https://www.rfc-editor.org/info/rfc8244>.

   [RFC9476]  Kumari, W. and P. Hoffman, "The .alt Special-Use Top-Level
              Domain", RFC 9476, DOI 10.17487/RFC9476, September 2023,
              <https://www.rfc-editor.org/info/rfc9476>.

9.2.  Informative References

   [RFC6305]  Abley, J. and W. Maton, "I'm Being Attacked by
              PRISONER.IANA.ORG!", RFC 6305, DOI 10.17487/RFC6305, July
              2011, <https://www.rfc-editor.org/info/rfc6305>.

   [RFC7535]  Abley, J., Dickson, B., Kumari, W., and G. Michaelson,
              "AS112 Redirection Using DNAME", RFC 7535,
              DOI 10.17487/RFC7535, May 2015,
              <https://www.rfc-editor.org/info/rfc7535>.

   [RFC8023]  Thomas, M., Mankin, A., and L. Zhang, "Report from the
              Workshop and Prize on Root Causes and Mitigation of Name
              Collisions", RFC 8023, DOI 10.17487/RFC8023, November
              2016, <https://www.rfc-editor.org/info/rfc8023>.

   [RFC8590]  Gould, J. and K. Feher, "Change Poll Extension for the
              Extensible Provisioning Protocol (EPP)", RFC 8590,
              DOI 10.17487/RFC8590, May 2019,
              <https://www.rfc-editor.org/info/rfc8590>.

   [RFC9499]  Hoffman, P. and K. Fujiwara, "DNS Terminology", BCP 219,
              RFC 9499, DOI 10.17487/RFC9499, March 2024,
              <https://www.rfc-editor.org/info/rfc9499>.

   [RFC9520]  Wessels, D., Carroll, W., and M. Thomas, "Negative Caching
              of DNS Resolution Failures", RFC 9520,
              DOI 10.17487/RFC9520, December 2023,
              <https://www.rfc-editor.org/info/rfc9520>.

   [Risky-BIZness]
              Akiwate, G., Savage, S., Voelker, G., and K. Claffy,
              "Risky BIZness: Risks Derived from Registrar Name
              Management", IMC '21: Proceedings of the 21st ACM Internet
              Measurement Conference, DOI 10.1145/3487552.3487816,
              November 2021, <https://doi.org/10.1145/3487552.3487816>.

   [Risky-BIZness-IRTF]
              Akiwate, G., Savage, S., Voelker, G., and K. Claffy,
              "Risky BIZness: Risks Derived from Registrar Name
              Management", IETF 115 Proceedings, November 2022,
              <https://datatracker.ietf.org/doc/slides-115-irtfopen-
              risky-bizness-risks-derived-from-registrar-name-
              management/>.

   [SAC048]   ICANN Security and Stability Advisory Committee, "SSAC
              Comment on Orphan Glue Records in the Draft Applicant
              Guidebook", SAC 048, 12 May 2011,
              <https://itp.cdn.icann.org/en/files/security-and-
              stability-advisory-committee-ssac-reports/sac-048-en.pdf>.

   [SAC125]   ICANN Security and Stability Advisory Committee, "SSAC
              Report on Registrar Nameserver Management", SAC 125, 9 May
              2024, <https://itp.cdn.icann.org/en/files/security-and-
              stability-advisory-committee-ssac-reports/sac-
              125-09-05-2024-en.pdf>.

Acknowledgments

   The authors would like to thank the following people for their
   contributions to this document: David Blacka, Brian Dickson, James
   Gould, Pawel Kowalik, Mario Loffredo, James Mitchell, Matthew Thomas,
   Peter Thomassen, and Duane Wessels.

Authors' Addresses

   Scott Hollenbeck
   Verisign Labs
   12061 Bluemont Way
   Reston, VA 20190
   United States of America
   Email: shollenbeck@verisign.com
   URI:   https://www.verisignlabs.com/


   William Carroll
   Verisign Labs
   12061 Bluemont Way
   Reston, VA 20190
   United States of America
   Phone: +1 703 948-3200
   Email: wicarroll@verisign.com
   URI:   https://verisign.com


   Gautam Akiwate
   Stanford University
   450 Jane Stanford Way
   Stanford, CA 94305
   United States of America
   Phone: +1 650 723-2300
   Email: gakiwate@cs.stanford.edu
   URI:   https://cs.stanford.edu/~gakiwate/
