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Best Practices for Deletion of Domain and Host Objects in the Extensible Provisioning Protocol (EPP)
draft-ietf-regext-epp-delete-bcp-03

Document Type Active Internet-Draft (regext WG)
Authors Scott Hollenbeck , William Carroll , Gautam Akiwate
Last updated 2024-05-14
Replaces draft-hollenbeck-regext-epp-delete-bcp
RFC stream Internet Engineering Task Force (IETF)
Intended RFC status Best Current Practice
Formats
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Stream WG state WG Document
Document shepherd Andy Newton
IESG IESG state I-D Exists
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Send notices to andy@hxr.us
draft-ietf-regext-epp-delete-bcp-03
REGEXT Working Group                                       S. Hollenbeck
Internet-Draft                                             Verisign Labs
Intended status: Best Current Practice                        W. Carroll
Expires: 15 November 2024                                       Verisign
                                                              G. Akiwate
                                                     Stanford University
                                                             14 May 2024

Best Practices for Deletion of Domain and Host Objects in the Extensible
                      Provisioning Protocol (EPP)
                  draft-ietf-regext-epp-delete-bcp-03

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 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 Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 15 November 2024.

Copyright Notice

   Copyright (c) 2024 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   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  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Conventions Used in This Document . . . . . . . . . . . . . .   4
   3.  Rationale for "SHOULD NOT be deleted" . . . . . . . . . . . .   4
     3.1.  DNS Considerations  . . . . . . . . . . . . . . . . . . .   4
     3.2.  Client-Server Consistency Considerations  . . . . . . . .   5
     3.3.  Relational Consistency Considerations . . . . . . . . . .   5
   4.  Host Object Renaming Risk . . . . . . . . . . . . . . . . . .   5
   5.  Analysis of Practices for Domain and Host Object Deletion . .   6
     5.1.  Renaming to Sacrificial Hosts . . . . . . . . . . . . . .   6
       5.1.1.  Practice Benefits . . . . . . . . . . . . . . . . . .   6
       5.1.2.  Practice Detriments . . . . . . . . . . . . . . . . .   7
       5.1.3.  Renaming to External, Presumed Non-Existent Hosts . .   7
       5.1.4.  Renaming to Pseudo-TLD  . . . . . . . . . . . . . . .   7
       5.1.5.  Renaming to Existing Special-Use TLD  . . . . . . . .   8
       5.1.6.  Renaming to "as112.arpa"  . . . . . . . . . . . . . .   8
       5.1.7.  Renaming to a Special-Use Domain  . . . . . . . . . .   9
       5.1.8.  Renaming to Non-Authoritative Hosts . . . . . . . . .  10
       5.1.9.  Renaming to Sacrificial Name Server Host Objects
               Maintained by the Client  . . . . . . . . . . . . . .  10
       5.1.10. Renaming to Community Sacrificial Name Server
               Service . . . . . . . . . . . . . . . . . . . . . . .  11
     5.2.  Deletion of Hosts . . . . . . . . . . . . . . . . . . . .  12
       5.2.1.  Delete affected Host Objects  . . . . . . . . . . . .  12
       5.2.2.  Allow Explicit Delete of Host Objects . . . . . . . .  12
   6.  Best Practice Recommendations . . . . . . . . . . . . . . . .  15
     6.1.  Best Current Practice . . . . . . . . . . . . . . . . . .  16
     6.2.  Best Proposed Practices . . . . . . . . . . . . . . . . .  16
       6.2.1.  Safe Host Deletion  . . . . . . . . . . . . . . . . .  16
       6.2.2.  Rename to a Special-Use Domain  . . . . . . . . . . .  16
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  16
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  16
   9.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  17
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  17
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  17
     10.2.  Informative References . . . . . . . . . . . . . . . . .  18
   Appendix A.  Change Log . . . . . . . . . . . . . . . . . . . . .  19
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  20

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1.  Introduction

   Section 3.2.2 of RFC 5731 [RFC5731] contains text that has led some
   domain name registrars (acting as EPP clients) to adopt an
   operational practice of re-naming 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 RFC 5732 [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 RFC 5732 [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."

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   Section 1.1 of RFC 5732 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 (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 re-queries 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, the risk associated with host object renaming, and the best
   practices that can be used to mitigate that risk.

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 RFCs 5731 and 5732 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 re-register 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

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   (https://itp.cdn.icann.org/en/files/security-and-stability-advisory-
   committee-ssac-reports/sac-048-en.pdf).

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 RFCs 5731 and 5732 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, as 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 RFCs 5731 and 5732 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 RFC 5731, 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.

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   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 and the domains managed by
   it.  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.

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.

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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.  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.

5.1.3.1.  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.

5.1.3.2.  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.

5.1.4.  Renaming to Pseudo-TLD

   Clients may rename host objects to use ".alt" or another non-DNS
   pseudo-TLD as suggested in [risky-bizness-irtf].  This practice has
   not been observed in use.

5.1.4.1.  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.

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5.1.4.2.  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.

5.1.5.  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.

5.1.5.1.  Renaming to Reserved TLD

   Clients may rename host objects to use ".invalid" or another reserved
   special-use ([RFC6761]) TLD as suggested in [risky-bizness].

5.1.5.1.1.  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.

5.1.5.1.2.  Practice Detriments

   These TLDs are reserved for experimentation or testing.  Their use is
   confusing and does not signal the client's intent.  Their use may be
   prevented by policy.

5.1.6.  Renaming to "as112.arpa"

   Some domain registrars, acting as EPP clients, have rename host
   objects to subdomains of "as112.arpa," such as "empty.as112.arpa"
   [risky-bizness-irtf].  This practice has been observed in use.

5.1.6.1.  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.  These subdomains are valid DNS names
   designed to sinkhole traffic.

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5.1.6.2.  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].  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.

5.1.7.  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 (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 NXDOMAIN response [RFC8499].

   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.

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5.1.7.1.  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.

5.1.7.2.  Practice Detriments

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

5.1.8.  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.

5.1.8.1.  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.

5.1.8.2.  Practice Detriments

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

5.1.9.  Renaming to Sacrificial Name Server Host Objects Maintained by
        the Client

   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 sacrificial name server should run a DNS
   resolution service capable of responding with an authoritative non-
   error, non-failure response for requests made for associated domains.
   The service SHOULD provide responses that indicate problems with a

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   domain's delegation, such as non-existence or include controlled
   interruption IP addresses [RFC8023].  This practice has been observed
   in use.

5.1.9.1.  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 include controlled interruption
   IP addresses [RFC8023].

5.1.9.2.  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].

5.1.10.  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 either through ICANN or IETF processes (e.g.,
   ".sacrificial"), as an IAB request that IANA delegate a second-level
   domain (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.

5.1.10.1.  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).

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5.1.10.2.  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.

5.2.1.  Delete affected Host Objects

   The recommendations in RFC 5731 [RFC5731] are intended to maintain
   consistency.  However, they are not requirements.  EPP servers may
   relax their constraints and allow sponsoring clients to delete host
   objects and disassociate them from domain objects sponsored by other
   clients.  This practice has been observed in use.

5.2.1.1.  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.

5.2.1.2.  Practice Detriments

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

5.2.2.  Allow Explicit Delete of Host Objects

   Sponsoring clients may delete host objects and disassociate them from
   domain objects sponsored by other clients.  They would be required to
   explicitly delete these objects.  This practice has been observed in
   use.

5.2.2.1.  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.

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5.2.2.2.  Practice Detriments

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

5.2.2.3.  Options for Allowed Delete of Associated Host Objects

   EPP servers would allow clients to explicitly delete hosts with
   dependent domains.  Hosts would be deleted with restore capability,
   as described in Section 5.2.2.5.  As noted previously, EPP servers
   can allow clients to delete host objects and disassociate them from
   domain objects.

5.2.2.3.1.  Explicit Deletion Request

   EPP servers may require that the EPP client explicitly request the
   deletion of the host object before taking this action.  This practice
   has not been observed in use.

5.2.2.3.1.1.  Practice Benefits

   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.

5.2.2.3.1.2.  Practice Detriments

   This change would require additional development on the part of EPP
   servers and clients.  It may only be relevant if the EPP client is
   also provided additional deletion details about the affected domains.

5.2.2.3.2.  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, 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.

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5.2.2.3.2.1.  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.

5.2.2.3.2.2.  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.

5.2.2.4.  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.

5.2.2.4.1.  Practice Benefits

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

5.2.2.4.2.  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.

5.2.2.5.  Allow Explicit Delete of Domain with Restore Capability

   EPP servers can allow for the explicit deletion of a domain with
   subordinate host objects associated with other domains as long as the
   associations can be restored by the <restore> operation described in
   RFC 3915 [RFC3915].  Allowing for the explicit deletion of a domain
   name that performs a cascade purge of the subordinate host objects
   and the association with other domains is unrecoverable and would be
   a risk to malicious or accidental actions.  Instead of purging the

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   subordinate host objects, the server can keep them with the
   "pendingDelete" status and keep the associations with other domains,
   but they will not be available in DNS.  This will provide for a
   preview of the operation that is restorable.  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 in RFC 3915 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 in RFC 3915.  Due to the potential
   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.

5.2.2.5.1.  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.

5.2.2.5.2.  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 rollback 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 with 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.  Best Practice Recommendations

   The practices in this section are described as "best practices"
   because they address the operational risk with minimal undesired side
   effects.  The "Best Current Practice" recommendation has been
   observed in operation.  The "Best Proposed Practices" have not been
   observed in operation.  The analysis presented in this document
   suggests that they could become best practices if deployed.

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6.1.  Best Current Practice

   Host objects SHOULD be renamed to a sacrificial name server host
   object maintained by the client (see section 5.1.9).

6.2.  Best Proposed Practices

6.2.1.  Safe Host Deletion

   Deletion with restore (see 5.2.2.5) SHOULD be allowed with explicit
   client requests (see 5.2.2.3.1).  Deletion SHOULD include additional
   deletion details to the client (see 5.2.2.3.2).  Affected clients
   SHOULD be informed of changes (see 5.2.2.4).

6.2.2.  Rename to a Special-Use Domain

   Host objects SHOULD be renamed to a sacrificial name server host
   object that uses a special-use domain (see 5.1.7).

7.  IANA Considerations

   This document does not contain any instructions for IANA.

8.  Security Considerations

   This document describes guidance found in RFCs 5731 and 5732
   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 RFC 5731
   [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.

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   In absence of DNSSEC use by the victim, an attacker who gains control
   of a single nameserver 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 nameservers 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 nameserver.  Subsequently, validating resolvers will no
   longer accept responses from the legitimate nameservers.  Moreover,
   with the use of CSYNC an attacker may update the domain NS records
   removing the legitimate nameservers entirely.

9.  Acknowledgments

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

10.  References

10.1.  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>.

   [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>.

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   [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>.

10.2.  Informative References

   [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>.

   [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>.

   [RFC8499]  Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
              Terminology", RFC 8499, DOI 10.17487/RFC8499, January
              2019, <https://www.rfc-editor.org/info/rfc8499>.

   [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>.

   [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", 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

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              Management", November 2022,
              <https://datatracker.ietf.org/doc/slides-115-irtfopen-
              risky-bizness-risks-derived-from-registrar-name-
              management/>.

Appendix A.  Change Log

   This section is to be removed before publishing as an RFC.

   This section lists substantial changes to the document as it is being
   worked on.

   00:

   1.  Initial working group version.

   01:

   1.  Addressed feedback received during the WG adoption request.  Re-
       included text to indicate if approaches have been observed in
       practice or not.

   02:

   1.  Section 1: Added sentence to bridge between renaming host objects
       and deletion dilemma.

   2.  Section 1: Noted that renaming a host object to a name of an
       external host is an operation that might not be possible to
       reverse.

   3.  Section 4: Added mention of "sacrificial" hosts.
       "ns1.example.org" is a sacrificial host.

   4.  Section 5.1: Added text to give some more context on
       "sacrificial" hosts.

   5.  Section 8: Added text describing DNSSEC risk.

   6.  Acknowledged Brian Dickson.

   03:

   1.  Added reference to SAC048 in Section 3.1.

   2.  Added note about minimal risk in Section 3.2.

   3.  Added context to the best practice recommendations in Section 6.

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   4.  Added "Sacrificial Name Server" to the title of Section 5.1.9.

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
   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/

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