draft-ietf-dnsop-nxdomain-cut-03.txt   draft-ietf-dnsop-nxdomain-cut-04.txt 
Domain Name System Operations (dnsop) Working Group S. Bortzmeyer Domain Name System Operations (dnsop) Working Group S. Bortzmeyer
Internet-Draft AFNIC Internet-Draft AFNIC
Updates: 1034, 2308 (if approved) S. Huque Updates: 1034, 2308 (if approved) S. Huque
Intended status: Standards Track Verisign Labs Intended status: Standards Track Verisign Labs
Expires: November 9, 2016 May 8, 2016 Expires: January 19, 2017 July 18, 2016
NXDOMAIN really means there is nothing underneath NXDOMAIN really means there is nothing underneath
draft-ietf-dnsop-nxdomain-cut-03 draft-ietf-dnsop-nxdomain-cut-04
Abstract Abstract
This document states clearly that when a DNS resolver receives a This document states clearly that when a DNS resolver receives a
response with response code of NXDOMAIN, it means that the domain response with response code of NXDOMAIN, it means that the domain
name which is thus denied AND ALL THE NAMES UNDER IT do not exist. name which is thus denied AND ALL THE NAMES UNDER IT do not exist.
REMOVE BEFORE PUBLICATION: this document should be discussed in the REMOVE BEFORE PUBLICATION: this document should be discussed in the
IETF DNSOP (DNS Operations) group, through its mailing list. The IETF DNSOP (DNS Operations) group, through its mailing list. The
source of the document, as well as a list of open issues, is source of the document, as well as a list of open issues, is
currently kept at Github [1]. currently kept at Github [1].
This documents clarifies RFC 1034 and modifies a bit RFC 2308 so it This documents clarifies RFC 1034 and modifies RFC 2308 a bit so it
updates both of them. updates both of them.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
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This Internet-Draft will expire on November 9, 2016. This Internet-Draft will expire on January 19, 2017.
Copyright Notice Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the Copyright (c) 2016 IETF Trust and the persons identified as the
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Table of Contents Table of Contents
1. Introduction and background . . . . . . . . . . . . . . . . . 2 1. Introduction and background . . . . . . . . . . . . . . . . . 2
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Rules . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Rule . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Benefits . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Updates to RFCs . . . . . . . . . . . . . . . . . . . . . . . 4
4. Possible issues . . . . . . . . . . . . . . . . . . . . . . . 5 3.1. Updates to RFC1034 . . . . . . . . . . . . . . . . . . . 5
5. Implementation considerations . . . . . . . . . . . . . . . . 6 3.2. Updates to RFC2308 . . . . . . . . . . . . . . . . . . . 5
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 4. Benefits . . . . . . . . . . . . . . . . . . . . . . . . . . 5
7. Security Considerations . . . . . . . . . . . . . . . . . . . 6 5. Possible issues . . . . . . . . . . . . . . . . . . . . . . . 6
8. Implementation status - RFC EDITOR: REMOVE BEFORE PUBLICATION 7 6. Implementation considerations . . . . . . . . . . . . . . . . 6
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 7 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 8. Security Considerations . . . . . . . . . . . . . . . . . . . 7
10.1. Normative References . . . . . . . . . . . . . . . . . . 8 9. Implementation status - RFC EDITOR: REMOVE BEFORE PUBLICATION 7
10.2. Informative References . . . . . . . . . . . . . . . . . 8 10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8
10.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 9 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
11.1. Normative References . . . . . . . . . . . . . . . . . . 8
11.2. Informative References . . . . . . . . . . . . . . . . . 9
11.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Appendix A. Why can't we just use the owner name of the returned Appendix A. Why can't we just use the owner name of the returned
SOA? . . . . . . . . . . . . . . . . . . . . . . . . 9 SOA? . . . . . . . . . . . . . . . . . . . . . . . . 10
Appendix B. Related approaches . . . . . . . . . . . . . . . . . 10 Appendix B. Related approaches . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction and background 1. Introduction and background
The DNS protocol [RFC1035] defines response code 3 as "Name Error", The DNS protocol [RFC1035] defines response code 3 as "Name Error",
or "NXDOMAIN" [RFC2308], which means that the queried domain name or "NXDOMAIN" [RFC2308], which means that the queried domain name
does not exist in the DNS. Since domain names are represented as a does not exist in the DNS. Since domain names are represented as a
tree of labels ([RFC1034], Section 3.1), non-existence of a node tree of labels ([RFC1034], Section 3.1), non-existence of a node
implies non-existence of the entire sub-tree rooted at this node. implies non-existence of the entire sub-tree rooted at this node.
The DNS iterative resolution algorithm precisely interprets the The DNS iterative resolution algorithm precisely interprets the
NXDOMAIN signal in this manner. If it encounters an NXDOMAIN NXDOMAIN signal in this manner. If it encounters an NXDOMAIN
response code from an authoritative server, it immediately stops response code from an authoritative server, it immediately stops
iteration and returns the NXDOMAIN response to the querier. iteration and returns the NXDOMAIN response to the querier.
However, in most known existing resolvers today, a cached non- However, in most known existing resolvers today, a cached non-
existence for a domain is not considered "proof" that there can be no existence for a domain is not considered "proof" that there can be no
child domains underneath. This is due to an ambiguity in [RFC1034] child domains underneath. This is due to an ambiguity in [RFC1034]
that failed to distinguish Empty Non-Terminal names (ENT) ([RFC7719]) that failed to distinguish Empty Non-Terminal names (ENT) ([RFC7719])
from nonexistent names. The distinction became especially important from nonexistent names (Section 3.1). The distinction became
for the development of DNSSEC, which provides proof of non-existence. especially important for the development of DNSSEC, which provides
proof of non-existence. [RFC4035], section 3.1.3.2, describes how
[RFC4035], section 3.1.3.2, describes how security-aware security-aware authoritative name servers make the distinction, but
authoritative name servers make the distinction, but no existing RFCs no existing RFCs describe the behavior for recursive name servers.
describe the behavior for recursive name servers.
This document specifies that an NXDOMAIN response for a domain name This document specifies that an NXDOMAIN response for a domain name
means that no child domains underneath the queried name exist either. means that no child domains underneath the queried name exist either.
And furthermore, that DNS resolvers should interpret cached non- And furthermore, that DNS resolvers should interpret cached non-
existence in this manner. Since the domain names are organized in a existence in this manner. Since the domain names are organized in a
tree, it is a simple consequence of the tree structure: non-existence tree, it is a simple consequence of the tree structure: non-existence
of a node implies non-existence of the entire sub-tree rooted at this of a node implies non-existence of the entire sub-tree rooted at this
node. node.
1.1. Terminology 1.1. Terminology
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of that tree structure and to describe things in those terms (names of that tree structure and to describe things in those terms (names
under/above, descendent names, subtrees etc). In fact, the DNS under/above, descendent names, subtrees etc). In fact, the DNS
algorithm description in [RFC1034] even states an assumption that the algorithm description in [RFC1034] even states an assumption that the
cache is a tree structure, so the precedent is already well cache is a tree structure, so the precedent is already well
established: see its section 4.3.2 which says "The following established: see its section 4.3.2 which says "The following
algorithm assumes that the RRs are organized in several tree algorithm assumes that the RRs are organized in several tree
structures, one for each zone, and another for the cache..." So, in structures, one for each zone, and another for the cache..." So, in
this document, each time we talk of a tree or tree operations, it this document, each time we talk of a tree or tree operations, it
refers to the model, not to the actual implementation. refers to the model, not to the actual implementation.
2. Rules 2. Rule
When an iterative caching DNS resolver receives a response NXDOMAIN, When an iterative caching DNS resolver receives a response NXDOMAIN,
it SHOULD store it in its cache and all names and RRsets at or below it SHOULD store it in its cache and all names and RRsets at or below
that node SHOULD then be considered to be unreachable. Subsequent that node SHOULD then be considered to be unreachable. Subsequent
queries for such names SHOULD elicit an NXDOMAIN response. queries for such names SHOULD elicit an NXDOMAIN response.
But if a resolver has cached data under the NXDOMAIN cut, it MAY But if a resolver has cached data under the NXDOMAIN cut, it MAY
continue to send it as a reply. (Until the TTL of this cached data continue to send it as a reply. (Until the TTL of this cached data
expires.) expires.)
Another exception is that a validating resolver MAY decide to Another exception is that a validating resolver MAY decide to
implement this behaviour only when the NXDOMAIN response has been implement this behaviour only when the NXDOMAIN response has been
validated with DNSSEC. See Section 7 for the rationale. validated with DNSSEC. See Section 8 for the rationale.
The fact that a subtree does not exist is not forever: [RFC2308],
section 3, already describes the amount of time that an NXDOMAIN
response may be cached (the "negative TTL").
If the NXDOMAIN response due to a cached non-existence is from a
DNSSEC signed zone, then it will have accompanying NSEC or NSEC3
records that authenticate the non-existence of the name. For a
descendant name of the original NXDOMAIN name, the same set of NSEC
or NSEC3 records proves the non-existence of the descendant name.
The iterative, caching resolver MUST return these NSEC or NSEC3
records in the response to the triggering query if the query had the
DNSSEC OK (DO) bit set.
Warning: if there is a chain of CNAME (or DNAME), the name which does
not exist is the last of the chain ([RFC6604]) and not the QNAME.
The NXDOMAIN stored in the cache is for the denied name, not always
for the QNAME.
As an example of the consequence of these rules, consider two As an example of the consequence of these rules, consider two
successive queries to a resolver, with a non-existing domain successive queries to a resolver, with a non-existing domain
'foo.example': the first is for 'foo.example' (which results in an 'foo.example': the first is for 'foo.example' (which results in an
NXDOMAIN) and the second for 'bar.foo.example' (which also results in NXDOMAIN) and the second for 'bar.foo.example' (which also results in
an NXDOMAIN). Many resolvers today will forward both queries, as an NXDOMAIN). Many resolvers today will forward both queries, as
noticed in Section 8. However, following the rules in this document noticed in Section 9. However, following the rules in this document
("NXDOMAIN cut"), a resolver would cache the first NXDOMAIN response, ("NXDOMAIN cut"), a resolver would cache the first NXDOMAIN response,
as a sign of non-existence, and then immediately return an NXDOMAIN as a sign of non-existence, and then immediately return an NXDOMAIN
response for the second query, without transmitting it to an response for the second query, without transmitting it to an
authoritative server. authoritative server.
If the first request is for 'bar.foo.example' and the second for If the first request is for 'bar.foo.example' and the second for
'baz.foo.example', the first NXDOMAIN response won't tell anything 'baz.foo.example', the first NXDOMAIN response won't tell anything
about 'baz.foo.example' and therefore the second query will be about 'baz.foo.example' and therefore the second query will be
transmitted as it was before the use of "NXDOMAIN cut" optimisation transmitted as it was before the use of "NXDOMAIN cut" optimisation
(see Appendix A). (see Appendix A).
These rules replace the second paragraph of section 5 of [RFC2308]. 3. Updates to RFCs
Otherwise, this document does not update any other parts of 3.1. Updates to RFC1034
[RFC2308]. The fact that a subtree does not exist is not forever:
[RFC2308], section 3, already describes the amount of time that an
NXDOMAIN response may be cached (the "negative TTL").
If the NXDOMAIN response due to a cached non-existence is from a This document clarifies possible ambiguities in [RFC1034] that did
DNSSEC signed zone, then it will have accompanying NSEC or NSEC3 not clearly distinguish Empty Non-Terminal names (ENT) ([RFC7719])
records that authenticate the non-existence of the name. For a from nonexistent names, and refers to subsequent documents that do.
descendant name of the original NXDOMAIN name, the same set of NSEC Empty Non-Terminals are nodes in the DNS that have no resource record
or NSEC3 records proves the non-existence of the descendant name. sets associated with them, but have descendant nodes that do. The
The iterative, caching resolver MUST return these NSEC or NSEC3 correct response to Empty Non-Terminals is NODATA (i.e. a response
records in the response to the triggering query if the query had the code of NOERROR and an empty ANSWER section). Additional clarifying
DNSSEC OK (DO) bit set. language on these points is provided in section 7.16 of [RFC2136] and
sections 2.2.2 and 2.2.3 of [RFC4592].
Warning: if there is a chain of CNAME (or DNAME), the name which does 3.2. Updates to RFC2308
not exist is the last of the chain ([RFC6604]) and not the QNAME.
The NXDOMAIN stored in the cache is for the denied name, not always
for the QNAME.
3. Benefits The second paragraph of section 5 of [RFC2308] states the following:
"A negative answer that resulted from a name error (NXDOMAIN) should
be cached such that it can be retrieved and returned in response to
another query for the same <QNAME, QCLASS> that resulted in the
cached negative response."
This document revises that paragraph to the following: "A negative
answer that resulted from a name error (NXDOMAIN) should be cached
such that it can be retrieved and returned in response to another
query for the same <QNAME, QCLASS> that resulted in the cached
negative response, or where QNAME is a descendant of the original
QNAME, and QCLASS is the same."
The above section Section 2 elaborates on the revised rule and
specifies when it may be reasonable to relax or ignore it.
4. Benefits
The main benefit is a better efficiency of the caches. In the The main benefit is a better efficiency of the caches. In the
example above, the resolver sends only one query instead of two, the example above, the resolver sends only one query instead of two, the
second one being answered from the cache. This will benefit the second one being answered from the cache. This will benefit the
entire DNS ecosystem, since the authoritative name servers will have entire DNS ecosystem, since the authoritative name servers will have
less unnecessary traffic to process. less unnecessary traffic to process.
The correct behavior (in [RFC1034] and made clearer in this document) The correct behavior (in [RFC1034] and made clearer in this document)
is specially useful when combined with QNAME minimisation [RFC7816] is specially useful when combined with QNAME minimisation [RFC7816]
since it will allow a resolver to stop searching as soon as an since it will allow a resolver to stop searching as soon as an
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composed of a fixed suffix ("dafa888.wf" in one of the articles composed of a fixed suffix ("dafa888.wf" in one of the articles
above), which is typically nonexistent, and a random prefix, above), which is typically nonexistent, and a random prefix,
different for each request. A resolver receiving these requests have different for each request. A resolver receiving these requests have
to forward them to the authoritative servers. With "NXDOMAIN cut", a to forward them to the authoritative servers. With "NXDOMAIN cut", a
system administrator would just have to send to the resolver a query system administrator would just have to send to the resolver a query
for the fixed suffix, the resolver would get a NXDOMAIN and then for the fixed suffix, the resolver would get a NXDOMAIN and then
would stop forwarding the queries. (It would be better if the SOA would stop forwarding the queries. (It would be better if the SOA
record in the NXDOMAIN response were sufficient to find the non- record in the NXDOMAIN response were sufficient to find the non-
existing domain but it is not the case, see Appendix A.) existing domain but it is not the case, see Appendix A.)
4. Possible issues 5. Possible issues
Let's assume the TLD example exists but foobar.example is not Let's assume the TLD example exists but foobar.example is not
delegated (so the example's name servers will reply NXDOMAIN for a delegated (so the example's name servers will reply NXDOMAIN for a
query about anything.foobar.example). A system administrator decides query about anything.foobar.example). A system administrator decides
to name the internal machines of his organization under to name the internal machines of his organization under
office.foobar.example and uses a trick of his resolver to forward office.foobar.example and uses a trick of his resolver to forward
requests about this zone to his local authoritative name servers. requests about this zone to his local authoritative name servers.
"NXDOMAIN cut" would create problems here, since, depending on the "NXDOMAIN cut" would create problems here, since, depending on the
order of requests to the resolver, it may have cached the non- order of requests to the resolver, it may have cached the non-
existence from example and therefore "deleted" everything under. existence from example and therefore "deleted" everything under.
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RFC-EDITOR: REMOVE THE PARAGRAPH BEFORE PUBLICATION. An example RFC-EDITOR: REMOVE THE PARAGRAPH BEFORE PUBLICATION. An example
today is mta2._domainkey.cbs.nl (which exists) where querying today is mta2._domainkey.cbs.nl (which exists) where querying
_domainkey.cbs.nl yields NXDOMAIN. Another example is www.upenn.edu, _domainkey.cbs.nl yields NXDOMAIN. Another example is www.upenn.edu,
redirected to www.upenn.edu-dscg.edgesuite.net while a query for edu- redirected to www.upenn.edu-dscg.edgesuite.net while a query for edu-
dscg.edgesuite.net returns NXDOMAIN. dscg.edgesuite.net returns NXDOMAIN.
Such name servers are definitely wrong and have always been. Their Such name servers are definitely wrong and have always been. Their
behaviour is incompatible with DNSSEC. Given the advantages of behaviour is incompatible with DNSSEC. Given the advantages of
"NXDOMAIN cut", there is little reason to support this behavior. "NXDOMAIN cut", there is little reason to support this behavior.
5. Implementation considerations 6. Implementation considerations
This section is non-normative, and is composed only of various things This section is non-normative, and is composed only of various things
which may be useful for implementors. A recursive resolver may which may be useful for implementors. A recursive resolver may
implement its cache in many ways. The most obvious one is a tree implement its cache in many ways. The most obvious one is a tree
data structure, because it fits the data model of domain names. But, data structure, because it fits the data model of domain names. But,
in practice, other implementations are possible, as well as various in practice, other implementations are possible, as well as various
optimisations (such as a tree, augmented by an index of some common optimisations (such as a tree, augmented by an index of some common
domain names). domain names).
If a resolver implements its cache as a tree (without any If a resolver implements its cache as a tree (without any
optimisation), one way to follow the rules of Section 2 is, when optimisation), one way to follow the rules of Section 2 is, when
receiving the NXDOMAIN, to prune the subtree of positive cache receiving the NXDOMAIN, to prune the subtree of positive cache
entries at that node, or to delete all individual cache entries for entries at that node, or to delete all individual cache entries for
names below that node. Then, when searching downward in its cache, names below that node. Then, when searching downward in its cache,
this iterative caching DNS resolver stop searching if it encounters a this iterative caching DNS resolver will stop searching if it
cached non-existence. encounters a cached non-existence.
Some resolver may have a cache which is NOT organized as a tree (but, Some resolver may have a cache which is NOT organized as a tree (but,
for instance, as a dictionary) and therefore have a reason to ignore for instance, as a dictionary) and therefore have a reason to ignore
the rules of Section 2. So these rules are a SHOULD and not a MUST. the rules of Section 2. So these rules are a SHOULD and not a MUST.
6. IANA Considerations 7. IANA Considerations
This document has no actions for IANA. This document has no actions for IANA.
7. Security Considerations 8. Security Considerations
The technique described here may help against a denial-of-service The technique described here may help against a denial-of-service
attack named "random qnames" and described in Section 3. attack named "random qnames" and described in Section 4.
If a resolver does not validate the answers with DNSSEC, or if the If a resolver does not validate the answers with DNSSEC, or if the
zone is not signed, the resolver can of course be poisoned with a zone is not signed, the resolver can of course be poisoned with a
false NXDOMAIN, thus "deleting" a part of the domain name tree. This false NXDOMAIN, thus "deleting" a part of the domain name tree. This
denial-of-service attack is already possible without the rules of denial-of-service attack is already possible without the rules of
this document (but "NXDOMAIN cut" may increase its effects). The this document (but "NXDOMAIN cut" may increase its effects). The
only solution is to use DNSSEC. only solution is to use DNSSEC.
8. Implementation status - RFC EDITOR: REMOVE BEFORE PUBLICATION 9. Implementation status - RFC EDITOR: REMOVE BEFORE PUBLICATION
This section records the status of known implementations of the This section records the status of known implementations of the
protocol defined by this specification at the time of posting of this protocol defined by this specification at the time of posting of this
Internet-Draft, and is based on a proposal described in [RFC6982]. Internet-Draft, and is based on a proposal described in [RFC6982].
The description of implementations in this section is intended to The description of implementations in this section is intended to
assist the IETF in its decision processes in progressing drafts to assist the IETF in its decision processes in progressing drafts to
RFCs. Please note that the listing of any individual implementation RFCs. Please note that the listing of any individual implementation
here does not imply endorsement by the IETF. Furthermore, no effort here does not imply endorsement by the IETF. Furthermore, no effort
has been spent to verify the information presented here that was has been spent to verify the information presented here that was
supplied by IETF contributors. This is not intended as, and must not supplied by IETF contributors. This is not intended as, and must not
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As of today, practically all existing DNS resolvers are conservative As of today, practically all existing DNS resolvers are conservative
by default: they consider a NXDOMAIN as only significant for the by default: they consider a NXDOMAIN as only significant for the
denied name itself, not for the names under. Almost all the current denied name itself, not for the names under. Almost all the current
recursive servers will send upstream a query for out-of-cache recursive servers will send upstream a query for out-of-cache
sub.example.com even if their cache contains an NXDOMAIN for sub.example.com even if their cache contains an NXDOMAIN for
example.com. example.com.
There are a few exceptions. The Unbound resolver has a configuration There are a few exceptions. The Unbound resolver has a configuration
parameter called "harden-below-nxdomain" [2], which if set to "yes" parameter called "harden-below-nxdomain" [2], which if set to "yes"
turns on "NXDOMAIN cut" behavior ("only DNSSEC-secure nxdomains are turns on "NXDOMAIN cut" behavior ("only DNSSEC-secure nxdomains are
used", see Section 7). The PowerDNS recursor has optional partial used", see Section 8). The PowerDNS recursor has optional partial
support for "NXDOMAIN cut", for the root domain only, with its "root- support for "NXDOMAIN cut", for the root domain only, with its "root-
nx-trust" setting, described as [3] "If set, an NXDOMAIN from the nx-trust" setting, described as [3] "If set, an NXDOMAIN from the
root-servers will serve as a blanket NXDOMAIN for the entire TLD the root-servers will serve as a blanket NXDOMAIN for the entire TLD the
query belonged to. The effect of this is far fewer queries to the query belonged to. The effect of this is far fewer queries to the
root-servers.". root-servers.".
9. Acknowledgments 10. Acknowledgments
The main idea is in this document is taken from The main idea is in this document is taken from
[I-D.vixie-dnsext-resimprove], section 3, "Stopping Downward Cache [I-D.vixie-dnsext-resimprove], section 3, "Stopping Downward Cache
Search on NXDOMAIN". Thanks to its authors, Paul Vixie, Rodney Search on NXDOMAIN". Thanks to its authors, Paul Vixie, Rodney
Joffe, and Frederico Neves. Additionally Tony Finch, John Levine, Joffe, and Frederico Neves. Additionally Tony Finch, Ted Lemon, John
Jinmei Tatuya, Bob Harold and Duane Wessels provided valuable Levine, Jinmei Tatuya, Bob Harold and Duane Wessels provided valuable
feedback and suggestions. feedback and suggestions.
10. References 11. References
10.1. Normative References 11.1. Normative References
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities", [RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987, STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
<http://www.rfc-editor.org/info/rfc1034>. <http://www.rfc-editor.org/info/rfc1034>.
[RFC1035] Mockapetris, P., "Domain names - implementation and [RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <http://www.rfc-editor.org/info/rfc1035>. November 1987, <http://www.rfc-editor.org/info/rfc1035>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
DOI 10.17487/RFC2119, March 1997, RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>. <http://www.rfc-editor.org/info/rfc2119>.
[RFC2136] Vixie, P., Ed., Thomson, S., Rekhter, Y., and J. Bound,
"Dynamic Updates in the Domain Name System (DNS UPDATE)",
RFC 2136, DOI 10.17487/RFC2136, April 1997,
<http://www.rfc-editor.org/info/rfc2136>.
[RFC2308] Andrews, M., "Negative Caching of DNS Queries (DNS [RFC2308] Andrews, M., "Negative Caching of DNS Queries (DNS
NCACHE)", RFC 2308, DOI 10.17487/RFC2308, March 1998, NCACHE)", RFC 2308, DOI 10.17487/RFC2308, March 1998,
<http://www.rfc-editor.org/info/rfc2308>. <http://www.rfc-editor.org/info/rfc2308>.
[RFC4592] Lewis, E., "The Role of Wildcards in the Domain Name
System", RFC 4592, DOI 10.17487/RFC4592, July 2006,
<http://www.rfc-editor.org/info/rfc4592>.
[RFC6604] Eastlake 3rd, D., "xNAME RCODE and Status Bits [RFC6604] Eastlake 3rd, D., "xNAME RCODE and Status Bits
Clarification", RFC 6604, DOI 10.17487/RFC6604, April Clarification", RFC 6604, DOI 10.17487/RFC6604, April
2012, <http://www.rfc-editor.org/info/rfc6604>. 2012, <http://www.rfc-editor.org/info/rfc6604>.
10.2. Informative References 11.2. Informative References
[RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S. [RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "Protocol Modifications for the DNS Security Rose, "Protocol Modifications for the DNS Security
Extensions", RFC 4035, DOI 10.17487/RFC4035, March 2005, Extensions", RFC 4035, DOI 10.17487/RFC4035, March 2005,
<http://www.rfc-editor.org/info/rfc4035>. <http://www.rfc-editor.org/info/rfc4035>.
[RFC6982] Sheffer, Y. and A. Farrel, "Improving Awareness of Running [RFC6982] Sheffer, Y. and A. Farrel, "Improving Awareness of Running
Code: The Implementation Status Section", RFC 6982, Code: The Implementation Status Section", RFC 6982, DOI
DOI 10.17487/RFC6982, July 2013, 10.17487/RFC6982, July 2013,
<http://www.rfc-editor.org/info/rfc6982>. <http://www.rfc-editor.org/info/rfc6982>.
[RFC7719] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS [RFC7719] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
Terminology", RFC 7719, DOI 10.17487/RFC7719, December Terminology", RFC 7719, DOI 10.17487/RFC7719, December
2015, <http://www.rfc-editor.org/info/rfc7719>. 2015, <http://www.rfc-editor.org/info/rfc7719>.
[RFC7816] Bortzmeyer, S., "DNS Query Name Minimisation to Improve [RFC7816] Bortzmeyer, S., "DNS Query Name Minimisation to Improve
Privacy", RFC 7816, DOI 10.17487/RFC7816, March 2016, Privacy", RFC 7816, DOI 10.17487/RFC7816, March 2016,
<http://www.rfc-editor.org/info/rfc7816>. <http://www.rfc-editor.org/info/rfc7816>.
skipping to change at page 9, line 27 skipping to change at page 10, line 16
Joost, M., "About DNS Attacks and ICMP Destination Joost, M., "About DNS Attacks and ICMP Destination
Unreachable Reports", December 2014, Unreachable Reports", December 2014,
<http://www.michael-joost.de/dnsterror.html>. <http://www.michael-joost.de/dnsterror.html>.
[balakrichenan-dafa888] [balakrichenan-dafa888]
Balakrichenan, S., "Disturbance in the DNS - "Random Balakrichenan, S., "Disturbance in the DNS - "Random
qnames", the dafa888 DoS attack"", October 2014, qnames", the dafa888 DoS attack"", October 2014,
<https://indico.dns-oarc.net/event/20/session/3/ <https://indico.dns-oarc.net/event/20/session/3/
contribution/37>. contribution/37>.
10.3. URIs 11.3. URIs
[1] https://github.com/bortzmeyer/ietf-dnsop-nxdomain
[2] https://www.unbound.net/documentation/unbound.conf.html [1] https://www.unbound.net/documentation/unbound.conf.html
[3] https://doc.powerdns.com/md/recursor/settings/#root-nx-trust [2] https://doc.powerdns.com/md/recursor/settings/#root-nx-trust
Appendix A. Why can't we just use the owner name of the returned SOA? Appendix A. Why can't we just use the owner name of the returned SOA?
In this document, we deduce the non-existence of a domain only for In this document, we deduce the non-existence of a domain only for
NXDOMAIN answers where the denied name was this exact domain. If a NXDOMAIN answers where the denied name was this exact domain. If a
resolver sends a query to the name servers of the TLD example, and resolver sends a query to the name servers of the TLD example, and
asks the MX record for www.foobar.example, and receives a NXDOMAIN, asks the MX record for www.foobar.example, and receives a NXDOMAIN,
it can only register the fact that www.foobar.example (and everything it can only register the fact that www.foobar.example (and everything
underneath) does not exist. Even if the accompanying SOA record is underneath) does not exist. Even if the accompanying SOA record is
for example only, one cannot infer that foobar.example is for example only, one cannot infer that foobar.example is
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