1. RFC 8749
Internet Engineering Task Force (IETF)                        W. Mekking
Request for Comments: 8749                                    D. Mahoney
Updates: 6698, 6840                                                  ISC
Category: Standards Track                                     March 2020
ISSN: 2070-1721

      Moving DNSSEC Lookaside Validation (DLV) to Historic Status


   This document retires DNSSEC Lookaside Validation (DLV) and
   reclassifies RFCs 4431 and 5074 as Historic.  Furthermore, this
   document updates RFC 6698 by excluding the DLV resource record from
   certificates and updates RFC 6840 by excluding the DLV registries
   from the trust anchor selection.

Status of This Memo

   This is an Internet Standards Track document.

   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
   Internet Standards 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

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Table of Contents

   1.  Introduction
   2.  Requirements Language
   3.  Discussion
   4.  Moving DLV to Historic Status
     4.1.  Documents That Reference the DLV RFCs
       4.1.1.  Documents That Reference RFC 4431
       4.1.2.  Documents That Reference RFC 5074
   5.  IANA Considerations
   6.  Security Considerations
   7.  Normative References
   Authors' Addresses

1.  Introduction

   DNSSEC Lookaside Validation (DLV) was introduced to assist with the
   adoption of DNSSEC [RFC4033] [RFC4034] [RFC4035] in a time when the
   root zone and many top-level domains (TLDs) were unsigned.  DLV
   allowed entities with signed zones under an unsigned parent zone or
   entities with registrars that did not accept DS records to publish
   trust anchors outside of the normal DNS delegation chain.  The root
   zone was signed in July 2010, and as of May 2019, 1389 out of 1531
   TLDs have a secure delegation from the root; thus, DLV has served its
   purpose and can now retire.

2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "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.  Discussion

   One could argue that DLV is still useful because there are still some
   unsigned TLDs and entities under those zones that will not benefit
   from signing their zone.  However, keeping the DLV mechanism also has

   *  It reduces the pressure to get the parent zone signed.

   *  It reduces the pressure on registrars to accept DS records.

   *  It complicates validation code.

   In addition, not every validator actually implemented DLV (only BIND
   9 and Unbound), so even if an entity can use DLV to set up an
   alternate path to its trust anchor, its effect is limited.
   Furthermore, there was one well-known DLV registry (dlv.isc.org),
   which was deprecated (replaced with a signed empty zone) on September
   30, 2017.  With the absence of a well-known DLV registry service, it
   is unlikely that there is a real benefit for the protocol on the
   Internet nowadays.

   One other possible reason to keep DLV is to distribute trust anchors
   for private enterprises.  There are no known uses of DLV for this.

   All things considered, it is probably not worth the effort of
   maintaining the DLV mechanism.

4.  Moving DLV to Historic Status

   There are two RFCs that specify DLV:

   1.  RFC 4431 [RFC4431] specifies the DLV resource record.

   2.  RFC 5074 [RFC5074] specifies the DLV mechanism for publishing
       trust anchors outside the DNS delegation chain and how validators
       can use them to validate DNSSEC-signed data.

   This document moves both RFC 4431 [RFC4431] and RFC 5074 [RFC5074] to
   Historic status.  This is a clear signal to implementers that the DLV
   resource record and the DLV mechanism SHOULD NOT be implemented or

4.1.  Documents That Reference the DLV RFCs

   The RFCs being moved to Historic status are referenced by a couple of
   other RFCs.  The sections below describe the changes to those
   documents due to the DLV RFCs being reclassified as Historic.

4.1.1.  Documents That Reference RFC 4431

   One RFC makes reference to RFC 4431 [RFC4431].  RFC 5074

   RFC 5074 ("DNSSEC Lookaside Validation (DLV)") [RFC5074] describes
   the DLV mechanism itself.  This document moves RFC 5074 [RFC5074] to
   Historic status as well.

4.1.2.  Documents That Reference RFC 5074

   Three RFCs make reference to RFC 5074 [RFC5074].  RFC 6698

   RFC 6698 ("The DNS-Based Authentication of Named Entities (DANE)
   Transport Layer Security (TLS) Protocol: TLSA") [RFC6698] specifies:

   |  DNSSEC forms certificates (the binding of an identity to a key) by
   |  combining a DNSKEY, DS, or DLV resource record with an associated
   |  RRSIG record.  These records then form a signing chain extending
   |  from the client's trust anchors to the RR of interest.

   This document updates RFC 6698 [RFC6698] to exclude the DLV resource
   record from certificates.  RFC 6840

   RFC 6840 ("Clarifications and Implementation Notes for DNS Security
   (DNSSEC)") [RFC6840] states that when trust anchors come from
   different sources, a validator may choose between them based on the
   perceived reliability of those sources.  But in reality, this does
   not happen in validators (both BIND 9 and Unbound have an option for
   a DLV trust anchor that can be used solely as a fallback).

   This document updates RFC 6840 [RFC6840] to exclude the DLV
   registries from the trust anchor selection.  RFC 8198

   RFC 8198 ("Aggressive Use of DNSSEC-Validated Cache") [RFC8198] only
   references RFC 5074 [RFC5074] because aggressive negative caching was
   first proposed there.

5.  IANA Considerations

   IANA has updated the annotation of the DLV RR type (code 32769) to
   "Obsolete" in the "Domain Name System (DNS) Parameters" registry.

6.  Security Considerations

   Once the DLV mechanism is retired, zones that rely on DLV for their
   validation will be treated as insecure.  The chance that this
   scenario actually occurs is very low, since no well-known DLV
   registry exists.

7.  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,

   [RFC4033]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "DNS Security Introduction and Requirements",
              RFC 4033, DOI 10.17487/RFC4033, March 2005,

   [RFC4034]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "Resource Records for the DNS Security Extensions",
              RFC 4034, DOI 10.17487/RFC4034, March 2005,

   [RFC4035]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "Protocol Modifications for the DNS Security
              Extensions", RFC 4035, DOI 10.17487/RFC4035, March 2005,

   [RFC4431]  Andrews, M. and S. Weiler, "The DNSSEC Lookaside
              Validation (DLV) DNS Resource Record", RFC 4431,
              DOI 10.17487/RFC4431, February 2006,

   [RFC5074]  Weiler, S., "DNSSEC Lookaside Validation (DLV)", RFC 5074,
              DOI 10.17487/RFC5074, November 2007,

   [RFC6698]  Hoffman, P. and J. Schlyter, "The DNS-Based Authentication
              of Named Entities (DANE) Transport Layer Security (TLS)
              Protocol: TLSA", RFC 6698, DOI 10.17487/RFC6698, August
              2012, <https://www.rfc-editor.org/info/rfc6698>.

   [RFC6840]  Weiler, S., Ed. and D. Blacka, Ed., "Clarifications and
              Implementation Notes for DNS Security (DNSSEC)", RFC 6840,
              DOI 10.17487/RFC6840, February 2013,

   [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>.

   [RFC8198]  Fujiwara, K., Kato, A., and W. Kumari, "Aggressive Use of
              DNSSEC-Validated Cache", RFC 8198, DOI 10.17487/RFC8198,
              July 2017, <https://www.rfc-editor.org/info/rfc8198>.


   The authors thank Ondřej Surý for the initial review.

Authors' Addresses

   W. (Matthijs) Mekking

   Email: matthijs@isc.org

   Dan Mahoney
   United States of America

   Email: dmahoney@isc.org
  1. RFC 8749