NXDOMAIN: There Really Is Nothing Underneath
RFC 8020
Internet Engineering Task Force (IETF) S. Bortzmeyer
Request for Comments: 8020 AFNIC
Updates: 1034, 2308 S. Huque
Category: Standards Track Verisign Labs
ISSN: 2070-1721 November 2016
NXDOMAIN: There Really Is Nothing Underneath
Abstract
This document states clearly that when a DNS resolver receives a
response with a response code of NXDOMAIN, it means that the domain
name which is thus denied AND ALL THE NAMES UNDER IT do not exist.
This document clarifies RFC 1034 and modifies a portion of RFC 2308:
it updates both of them.
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
http://www.rfc-editor.org/info/rfc8020.
Copyright Notice
Copyright (c) 2016 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
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(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Bortzmeyer & Huque Standards Track [Page 1]
RFC 8020 NXDOMAIN Cut November 2016
Table of Contents
1. Introduction and Background .....................................2
1.1. Terminology ................................................3
2. Rules ...........................................................3
3. Updates to RFCs .................................................5
3.1. Updates to RFC 1034 ........................................5
3.2. Updates to RFC 2308 ........................................5
4. Benefits ........................................................5
5. Possible Issues .................................................6
6. Implementation Considerations ...................................6
7. Security Considerations .........................................7
8. References ......................................................7
8.1. Normative References .......................................7
8.2. Informative References .....................................8
Appendix A. Why can't we just use the owner name of the returned
SOA? ...................................................9
Appendix B. Related Approaches .....................................9
Acknowledgments ....................................................9
Authors' Addresses ................................................10
1. Introduction and Background
The DNS protocol [RFC1035] defines response code 3 as "Name Error",
or "NXDOMAIN" [RFC2308], which means that the queried domain name
does not exist in the DNS. Since domain names are represented as a
tree of labels ([RFC1034], Section 3.1), nonexistence of a node
implies nonexistence of the entire subtree rooted at this node.
The DNS iterative resolution algorithm precisely interprets the
NXDOMAIN signal in this manner. If it encounters an NXDOMAIN
response code from an authoritative server, it immediately stops
iteration and returns the NXDOMAIN response to the querier.
However, in most known existing resolvers today, a cached
nonexistence for a domain is not considered "proof" that there can be
no child domains underneath. This is due to an ambiguity in
[RFC1034] that failed to distinguish Empty Non-Terminal (ENT) names
([RFC7719]) from nonexistent names (Section 3.1). The distinction
became especially important for the development of DNSSEC, which
provides proof of nonexistence. [RFC4035], Section 3.1.3.2,
describes how security-aware authoritative name servers make the
distinction, but no existing RFCs describe the behavior for recursive
name servers.
Bortzmeyer & Huque Standards Track [Page 2]
RFC 8020 NXDOMAIN Cut November 2016
This document specifies that an NXDOMAIN response for a domain name
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