draft-ietf-dnsop-nsec-aggressiveuse-10.txt   rfc8198.txt 
Network Working Group K. Fujiwara Internet Engineering Task Force (IETF) K. Fujiwara
Internet-Draft JPRS Request for Comments: 8198 JPRS
Updates: 4035 (if approved) A. Kato Updates: 4035 A. Kato
Intended status: Standards Track Keio/WIDE Category: Standards Track Keio/WIDE
Expires: November 25, 2017 W. Kumari ISSN: 2070-1721 W. Kumari
Google Google
May 24, 2017 July 2017
Aggressive use of DNSSEC-validated Cache Aggressive Use of DNSSEC-Validated Cache
draft-ietf-dnsop-nsec-aggressiveuse-10
Abstract Abstract
The DNS relies upon caching to scale; however, the cache lookup The DNS relies upon caching to scale; however, the cache lookup
generally requires an exact match. This document specifies the use generally requires an exact match. This document specifies the use
of NSEC/NSEC3 resource records to allow DNSSEC validating resolvers of NSEC/NSEC3 resource records to allow DNSSEC-validating resolvers
to generate negative answers within a range, and positive answers to generate negative answers within a range and positive answers from
from wildcards. This increases performance / decreases latency, wildcards. This increases performance, decreases latency, decreases
decreases resource utilization on both authoritative and recursive resource utilization on both authoritative and recursive servers, and
servers, and also increases privacy. It may also help increase increases privacy. Also, it may help increase resilience to certain
resilience to certain DoS attacks in some circumstances. DoS attacks in some circumstances.
This document updates RFC4035 by allowing validating resolvers to This document updates RFC 4035 by allowing validating resolvers to
generate negative answers based upon NSEC/NSEC3 records and positive generate negative answers based upon NSEC/NSEC3 records and positive
answers in the presence of wildcards. answers in the presence of wildcards.
[ Ed note: Text inside square brackets ([]) is additional background
information, answers to frequently asked questions, general musings,
etc. RFC Editor, please remove before publication. This document is
being collaborated on in Github at: https://github.com/wkumari/draft-
ietf-dnsop-nsec-aggressiveuse. The most recent version of the
document, open issues, etc should all be available here. The authors
(gratefully) accept pull requests.]
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This is an Internet Standards Track document.
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 http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months This document is a product of the Internet Engineering Task Force
and may be updated, replaced, or obsoleted by other documents at any (IETF). It represents the consensus of the IETF community. It has
time. It is inappropriate to use Internet-Drafts as reference received public review and has been approved for publication by the
material or to cite them other than as "work in progress." Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
This Internet-Draft will expire on November 25, 2017. 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/rfc8198.
Copyright Notice Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
skipping to change at page 2, line 30 skipping to change at page 2, line 26
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 3 3. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 3
4. Background . . . . . . . . . . . . . . . . . . . . . . . . . 4 4. Background . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. Aggressive use of Cache . . . . . . . . . . . . . . . . . . . 6 5. Aggressive Use of DNSSEC-Validated Cache . . . . . . . . . . 6
5.1. NSEC . . . . . . . . . . . . . . . . . . . . . . . . . . 6 5.1. NSEC . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.2. NSEC3 . . . . . . . . . . . . . . . . . . . . . . . . . . 6 5.2. NSEC3 . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.3. Wildcards . . . . . . . . . . . . . . . . . . . . . . . . 6 5.3. Wildcards . . . . . . . . . . . . . . . . . . . . . . . . 6
5.4. Consideration on TTL . . . . . . . . . . . . . . . . . . 7 5.4. Consideration on TTL . . . . . . . . . . . . . . . . . . 7
6. Benefits . . . . . . . . . . . . . . . . . . . . . . . . . . 7 6. Benefits . . . . . . . . . . . . . . . . . . . . . . . . . . 7
7. Update to RFC 4035 . . . . . . . . . . . . . . . . . . . . . 8 7. Update to RFC 4035 . . . . . . . . . . . . . . . . . . . . . 8
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
9. Security Considerations . . . . . . . . . . . . . . . . . . . 9 9. Security Considerations . . . . . . . . . . . . . . . . . . . 9
10. Implementation Status . . . . . . . . . . . . . . . . . . . . 9 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9 10.1. Normative References . . . . . . . . . . . . . . . . . . 9
11.1. Change History . . . . . . . . . . . . . . . . . . . . . 10 10.2. Informative References . . . . . . . . . . . . . . . . . 10
11.1.1. Version draft-fujiwara-dnsop-nsec-aggressiveuse-01 . 13 Appendix A. Detailed Implementation Notes . . . . . . . . . . . 11
11.1.2. Version draft-fujiwara-dnsop-nsec-aggressiveuse-02 . 13 Appendix B. Procedure for Determining ENT vs. NXDOMAIN with NSEC 11
11.1.3. Version draft-fujiwara-dnsop-nsec-aggressiveuse-03 . 14 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 12
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 14 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
12.1. Normative References . . . . . . . . . . . . . . . . . . 14
12.2. Informative References . . . . . . . . . . . . . . . . . 15
Appendix A. Detailed implementation notes . . . . . . . . . . . 15
Appendix B. Procedure for determining ENT vs NXDOMAN with NSEC . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16
1. Introduction 1. Introduction
A DNS negative cache exists, and is used to cache the fact that an A DNS negative cache exists, and is used to cache the fact that an
RRset does not exist. This method of negative caching requires exact RRset does not exist. This method of negative caching requires exact
matching; this leads to unnecessary additional lookups, increases matching; this leads to unnecessary additional lookups, increases
latency, leads to extra resource utilization on both authoritative latency, leads to extra resource utilization on both authoritative
and recursive servers, and decreases privacy by leaking queries. and recursive servers, and decreases privacy by leaking queries.
This document updates RFC 4035 to allow resolvers to use NSEC/NSEC3 This document updates RFC 4035 to allow resolvers to use NSEC/NSEC3
resource records to synthesize negative answers from the information resource records to synthesize negative answers from the information
they have in the cache. This allows validating resolvers to respond they have in the cache. This allows validating resolvers to respond
with a negative answer immediately if the name in question falls into with a negative answer immediately if the name in question falls into
a range expressed by a NSEC/NSEC3 resource record already in the a range expressed by an NSEC/NSEC3 resource record already in the
cache. It also allows the synthesis of positive answers in the cache. It also allows the synthesis of positive answers in the
presence of wildcard records. presence of wildcard records.
Aggressive Negative Caching was first proposed in Section 6 of DNSSEC Aggressive negative caching was first proposed in Section 6 of DNSSEC
Lookaside Validation (DLV) [RFC5074] in order to find covering NSEC Lookaside Validation (DLV) [RFC5074] in order to find covering NSEC
records efficiently. records efficiently.
[RFC8020] and [I-D.vixie-dnsext-resimprove] propose steps to using [RFC8020] and [RES-IMPROVE] propose steps to using NXDOMAIN
NXDOMAIN information for more effective caching. This document takes information for more effective caching. This document takes this
this technique further. technique further.
2. Terminology 2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
document are to be interpreted as described in RFC 2119 [RFC2119]. "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.
Many of the specialized terms used in this document are defined in Many of the specialized terms used in this document are defined in
DNS Terminology [RFC7719]. DNS Terminology [RFC7719].
The key words "Source of Synthesis" in this document are to be The key words "source of synthesis" in this document are to be
interpreted as described in [RFC4592]. interpreted as described in [RFC4592].
3. Problem Statement 3. Problem Statement
The DNS negative cache caches negative (non-existent) information, The DNS negative cache caches negative (non-existent) information,
and requires an exact match in most instances [RFC2308]. and requires an exact match in most instances [RFC2308].
Assume that the (DNSSEC signed) "example.com" zone contains: Assume that the (DNSSEC-signed) "example.com" zone contains:
albatross.example.com IN A 192.0.2.1 albatross.example.com. IN A 192.0.2.1
elephant.example.com IN A 192.0.2.2 elephant.example.com. IN A 192.0.2.2
zebra.example.com IN A 192.0.2.3 zebra.example.com. IN A 192.0.2.3
If a validating resolver receives a query for cat.example.com, it If a validating resolver receives a query for cat.example.com, it
contacts its resolver (which may be itself) to query the example.com contacts its resolver (which may be itself) to query the example.com
servers and will get back an NSEC record stating that there are no servers and will get back an NSEC record stating that there are no
records (alphabetically) between albatross and elephant, or an NSEC3 records (alphabetically) between albatross and elephant, or an NSEC3
record stating there is nothing between two hashed names. The record stating there is nothing between two hashed names. The
resolver then knows that cat.example.com does not exist; however, it resolver then knows that cat.example.com does not exist; however, it
does not use the fact that the proof covers a range (albatross to does not use the fact that the proof covers a range (albatross to
elephant) to suppress queries for other labels that fall within this elephant) to suppress queries for other labels that fall within this
range. This means that if the validating resolver gets a query for range. This means that if the validating resolver gets a query for
ball.example.com (or dog.example.com) it will once again go off and ball.example.com (or dog.example.com) it will once again go off and
query the example.com servers for these names. query the example.com servers for these names.
Apart from wasting bandwidth, this also wastes resources on the Apart from wasting bandwidth, this also wastes resources on the
recursive server (it needs to keep state for outstanding queries), recursive server (it needs to keep state for outstanding queries),
wastes resources on the authoritative server (it has to answer wastes resources on the authoritative server (it has to answer
additional questions), increases latency (the end user has to wait additional questions), increases latency (the end user has to wait
longer than necessary to get back an NXDOMAIN answer), can be used by longer than necessary to get back an NXDOMAIN answer), can be used by
attackers to cause a DoS (see additional resources), and also has attackers to cause a DoS, and also has privacy implications (e.g.,
privacy implications (e.g: typos leak out further than necessary). typos leak out further than necessary).
Another example: assume that the (DNSSEC signed) "example.org" zone Another example: assume that the (DNSSEC-signed) "example.org" zone
contains: contains:
avocado.example.org IN A 192.0.2.1 avocado.example.org. IN A 192.0.2.1
*.example.org IN A 192.0.2.2 *.example.org. IN A 192.0.2.2
zucchini.example.org IN A 192.0.2.3 zucchini.example.org. IN A 192.0.2.3
If a query is received for leek.example.org, the system contacts its If a query is received for leek.example.org, the system contacts its
resolver (which may be itself) to query the example.org servers and resolver (which may be itself) to query the example.org servers and
will get back an NSEC record stating that there are no records will get back an NSEC record stating that there are no records
(alphabetically) between avocado and zucchini (or an NSEC3 record (alphabetically) between avocado and zucchini (or an NSEC3 record
stating there is nothing between two hashed names), as well as an stating there is nothing between two hashed names), as well as an
answer for leek.example.org, with the label count of the signature answer for leek.example.org, with the label count of the signature
set to two (see [RFC7129], section 5.3 for more details). set to two (see [RFC7129], Section 5.3 for more details).
If the validating resolver gets a query for banana.example.org it If the validating resolver gets a query for banana.example.org, it
will once again go off and query the example.org servers for will once again go off and query the example.org servers for
banana.example.org (even though it already has proof that there is a banana.example.org (even though it already has proof that there is a
wildcard record) - just like above, this has privacy implications, wildcard record) -- just like above, this has privacy implications,
wastes resources, can be used to contribute to a DoS, etc. wastes resources, can be used to contribute to a DoS, etc.
4. Background 4. Background
DNSSEC [RFC4035] and [RFC5155] both provide "authenticated denial of DNSSEC [RFC4035] and [RFC5155] both provide "authenticated denial of
existence"; this is a cryptographic proof that the queried for name existence"; this is a cryptographic proof that the queried-for name
does not exist or type does not exist. Proof that a name does not does not exist or the type does not exist. Proof that a name does
exist is accomplished by providing a (DNSSEC secured) record not exist is accomplished by providing a (DNSSEC-secured) record
containing the names which appear alphabetically before and after the containing the names that appear alphabetically before and after the
queried for name. In the first example above, if the (DNSSEC queried-for name. In the first example above, if the (DNSSEC-
validating) recursive server were to query for dog.example.com it validating) recursive server were to query for dog.example.com, it
would receive a (signed) NSEC record stating that there are no labels would receive a (signed) NSEC record stating that there are no labels
between "albatross" and "elephant" (or, for NSEC3, a similar pair of between "albatross" and "elephant" (or, for NSEC3, a similar pair of
hashed names). This is a signed, cryptographic proof that these hashed names). This is a signed, cryptographic proof that these
names are the ones before and after the queried for label. As names are the ones before and after the queried-for label. As
dog.example.com falls within this range, the recursive server knows dog.example.com falls within this range, the recursive server knows
that dog.example.com really does not exist. Proof that a type does that dog.example.com really does not exist. Proof that a type does
not exist is accomplished by providing a (DNSSEC secured) record not exist is accomplished by providing a (DNSSEC-secured) record
containing the queried for name, and a type bitmap which does not containing the queried-for name, and a type bitmap that does not
include the requested type. include the requested type.
This document specifies that this NSEC/NSEC3 record should be used to This document specifies that this NSEC/NSEC3 record should be used to
generate negative answers for any queries that the validating server generate negative answers for any queries that the validating server
receives that fall within the range covered by the record (for the receives that fall within the range covered by the record (for the
TTL for the record). This document also specifies that a positive TTL for the record). This document also specifies that a positive
answer should be generated for any queries that the validating server answer should be generated for any queries that the validating server
receives that are proven to be covered by a wildcard record. receives that are proven to be covered by a wildcard record.
Section 4.5 of [RFC4035] says: Section 4.5 of [RFC4035] says:
"In theory, a resolver could use wildcards or NSEC RRs to generate In theory, a resolver could use wildcards or NSEC RRs to generate
positive and negative responses (respectively) until the TTL or positive and negative responses (respectively) until the TTL or
signatures on the records in question expire. However, it seems signatures on the records in question expire. However, it seems
prudent for resolvers to avoid blocking new authoritative data or prudent for resolvers to avoid blocking new authoritative data or
synthesizing new data on their own. Resolvers that follow this synthesizing new data on their own. Resolvers that follow this
recommendation will have a more consistent view of the namespace." recommendation will have a more consistent view of the namespace.
and "The reason for these recommendations is that, between the
initial query and the expiration of the data from the cache, the And, earlier, Section 4.5 of [RFC4035] says:
authoritative data might have been changed (for example, via dynamic
update).". In other words, if a resolver generates negative answers The reason for these recommendations is that, between the initial
from an NSEC record, it will not send any queries for names within query and the expiration of the data from the cache, the
that NSEC range (for the TTL). If a new name is added to the zone authoritative data might have been changed (for example, via
during this interval the resolver will not know this. Similarly, if dynamic update).
the resolver is generating responses from a wildcard record, it will
In other words, if a resolver generates negative answers from an NSEC
record, it will not send any queries for names within that NSEC range
(for the TTL). If a new name is added to the zone during this
interval, the resolver will not know this. Similarly, if the
resolver is generating responses from a wildcard record, it will
continue to do so (for the TTL). continue to do so (for the TTL).
We believe this recommendation can be relaxed because, in the absence We believe that this recommendation can be relaxed because, in the
of this technique, a lookup for the exact name could have come in absence of this technique, a lookup for the exact name could have
during this interval, and so a negative answer could already be come in during this interval, and so a negative answer could already
cached (see [RFC2308] for more background). This means that zone be cached (see [RFC2308] for more background). This means that zone
operators should have no expectation that an added name would work operators should have no expectation that an added name would work
immediately. With DNSSEC and Aggressive NSEC, the TTL of the NSEC/ immediately. With DNSSEC and aggressive use of DNSSEC-validated
NSEC3 record and the SOA.MINIMUM field are the authoritative cache, the TTL of the NSEC/NSEC3 record and the SOA.MINIMUM field are
statement of how quickly a name can start working within a zone. the authoritative statement of how quickly a name can start working
within a zone.
5. Aggressive use of Cache 5. Aggressive Use of DNSSEC-Validated Cache
This document relaxes the restriction given in Section 4.5 of This document relaxes the restriction given in Section 4.5 of
[RFC4035], see Section 7 for more detail. [RFC4035]. See Section 7 for more detail.
If the negative cache of the validating resolver has sufficient If the negative cache of the validating resolver has sufficient
information to validate the query, the resolver SHOULD use NSEC, information to validate the query, the resolver SHOULD use NSEC,
NSEC3 and wildcard records to synthesize answers as described in this NSEC3, and wildcard records to synthesize answers as described in
document. Otherwise, it MUST fall back to send the query to the this document. Otherwise, it MUST fall back to send the query to the
authoritative DNS servers. authoritative DNS servers.
5.1. NSEC 5.1. NSEC
The validating resolver needs to check the existence of an NSEC RR The validating resolver needs to check the existence of an NSEC RR
matching/covering the source of synthesis and an NSEC RR covering the matching/covering the source of synthesis and an NSEC RR covering the
query name. query name.
If denial of existence can be determined according to the rules set If denial of existence can be determined according to the rules set
out in Section 5.4 of [RFC4035], using NSEC records in the cache, out in Section 5.4 of [RFC4035], using NSEC records in the cache,
then the resolver can immediately return an NXDOMAIN or NODATA (as then the resolver can immediately return an NXDOMAIN or NODATA (as
appropriate) response. appropriate) response.
5.2. NSEC3 5.2. NSEC3
NSEC3 aggressive negative caching is more difficult than NSEC NSEC3 aggressive negative caching is more difficult than NSEC
aggressive caching. If the zone is signed with NSEC3, the validating aggressive caching. If the zone is signed with NSEC3, the validating
resolver needs to check the existence of non-terminals and wildcards resolver needs to check the existence of non-terminals and wildcards
which derive from query names. that derive from query names.
If denial of existence can be determined according to the rules set If denial of existence can be determined according to the rules set
out in [RFC5155] Sections 8.4, 8.5, 8.6, 8.7, using NSEC3 records in out in [RFC5155], Sections 8.4, 8.5, 8.6, and 8.7, using NSEC3
the cache, then the resolver can immediately return an NXDOMAIN or records in the cache, then the resolver can immediately return an
NODATA response (as appropriate). NXDOMAIN or NODATA response (as appropriate).
If a covering NSEC3 RR has Opt-Out flag, the covering NSEC3 RR does If a covering NSEC3 RR has an Opt-Out flag, the covering NSEC3 RR
not prove the non-existence of the domain name and the aggressive does not prove the non-existence of the domain name and the
negative caching is not possible for the domain name. aggressive negative caching is not possible for the domain name.
5.3. Wildcards 5.3. Wildcards
The last paragraph of [RFC4035] Section 4.5 also discusses the use of The last paragraph of [RFC4035], Section 4.5 also discusses the use
wildcards and NSEC RRs to generate positive responses and recommends of wildcards and NSEC RRs to generate positive responses and
that it not be relied upon. Just like the case for the aggressive recommends that it not be relied upon. Just like the case for the
use of NSEC/NSEC3 for negative answers, we revise this aggressive use of NSEC/NSEC3 for negative answers, we revise this
recommendation. recommendation.
As long as the validating resolver can determine that a name would As long as the validating resolver can determine that a name would
not exist without the wildcard match, determined according to the not exist without the wildcard match, determined according to the
rules set out in Section 5.3.4 of [RFC4035] (NSEC), or in Section 8.8 rules set out in Section 5.3.4 of [RFC4035] (NSEC), or in Section 8.8
of [RFC5155], it SHOULD synthesize an answer (or NODATA response) for of [RFC5155], it SHOULD synthesize an answer (or NODATA response) for
that name using the cached deduced wildcard. If the corresponding that name using the cache-deduced wildcard. If the corresponding
wildcard record is not in the cache, it MUST fall back to send the wildcard record is not in the cache, it MUST fall back to send the
query to the authoritative DNS servers. query to the authoritative DNS servers.
5.4. Consideration on TTL 5.4. Consideration on TTL
The TTL value of negative information is especially important, The TTL value of negative information is especially important,
because newly added domain names cannot be used while the negative because newly added domain names cannot be used while the negative
information is effective. information is effective.
Section 5 of [RFC2308] suggests a maximum default negative cache TTL Section 5 of [RFC2308] suggests a maximum default negative cache TTL
value of 3 hours (10800). It is RECOMMENDED that validating value of 3 hours (10800). It is RECOMMENDED that validating
resolvers limit the maximum effective TTL value of negative responses resolvers limit the maximum effective TTL value of negative responses
(NSEC/NSEC3 RRs) to this same value. (NSEC/NSEC3 RRs) to this same value.
Section 5 of [RFC2308] also states that a negative cache entry TTL is Section 5 of [RFC2308] also states that a negative cache entry TTL is
taken from the minimum of the SOA.MINIMUM field and SOA's TTL. This taken from the minimum of the SOA.MINIMUM field and SOA's TTL. This
can be less than the TTL of an NSEC or NSEC3 record, since their TTL can be less than the TTL of an NSEC or NSEC3 record, since their TTL
is equal to the SOA.MINIMUM field (see [RFC4035]section 2.3 and is equal to the SOA.MINIMUM field (see [RFC4035], Section 2.3 and
[RFC5155] section 3.) [RFC5155], Section 3).
A resolver that supports aggressive use of NSEC and NSEC3 SHOULD A resolver that supports aggressive use of NSEC and NSEC3 SHOULD
reduce the TTL of NSEC and NSEC3 records to match the SOA.MINIMUM reduce the TTL of NSEC and NSEC3 records to match the SOA.MINIMUM
field in the authority section of a negative response, if SOA.MINIMUM field in the authority section of a negative response, if SOA.MINIMUM
is smaller. is smaller.
6. Benefits 6. Benefits
The techniques described in this document provide a number of The techniques described in this document provide a number of
benefits, including (in no specific order): benefits, including (in no specific order):
skipping to change at page 8, line 4 skipping to change at page 8, line 8
Decreased recursive server load: By answering queries from the cache Decreased recursive server load: By answering queries from the cache
by synthesizing answers, validating servers avoid having to send a by synthesizing answers, validating servers avoid having to send a
query and wait for a response. In addition to decreasing the query and wait for a response. In addition to decreasing the
bandwidth used, it also means that the server does not need to bandwidth used, it also means that the server does not need to
allocate and maintain state, thereby decreasing memory and CPU allocate and maintain state, thereby decreasing memory and CPU
load. load.
Decreased authoritative server load: Because recursive servers can Decreased authoritative server load: Because recursive servers can
answer queries without asking the authoritative server, the answer queries without asking the authoritative server, the
authoritative servers receive fewer queries. This decreases the authoritative servers receive fewer queries. This decreases the
authoritative server bandwidth, queries per second and CPU authoritative server bandwidth, queries per second, and CPU
utilization. utilization.
The scale of the benefit depends upon multiple factors, including the The scale of the benefit depends upon multiple factors, including the
query distribution. For example, at the time of this writing, around query distribution. For example, at the time of this writing, around
65% of queries to Root Name servers result in NXDOMAIN responses (see 65% of queries to root name servers result in NXDOMAIN responses (see
statistics from [root-servers.org]); this technique will eliminate a statistics from [ROOT-SERVERS]); this technique will eliminate a
sizable quantity of these. sizable quantity of these.
The technique described in this document may also mitigate so-called The technique described in this document may also mitigate so-called
"random QNAME attacks", in which attackers send many queries for "random QNAME attacks", in which attackers send many queries for
random sub-domains to resolvers. As the resolver will not have the random subdomains to resolvers. As the resolver will not have the
answers cached, it has to ask external servers for each random query, answers cached, it has to ask external servers for each random query,
leading to a DoS on the authoritative servers (and often resolvers). leading to a DoS on the authoritative servers (and often resolvers).
Aggressive NSEC may help mitigate these attacks by allowing the The technique may help mitigate these attacks by allowing the
resolver to answer directly from cache for any random queries which resolver to answer directly from the cache for any random queries
fall within already requested ranges. It will not always work as an that fall within already requested ranges. It will not always work
effective defense, not least because not many zones are DNSSEC signed as an effective defense, not least because not many zones are DNSSEC
at all -- but it will still provide an additional layer of defense. signed at all -- but it will still provide an additional layer of
defense.
As these benefits are only accrued by those using DNSSEC, it is hoped As these benefits are only accrued by those using DNSSEC, it is hoped
that these techniques will lead to more DNSSEC deployment. that these techniques will lead to more DNSSEC deployment.
7. Update to RFC 4035 7. Update to RFC 4035
Section 4.5 of [RFC4035] shows that "In theory, a resolver could use Section 4.5 of [RFC4035] shows that "In theory, a resolver could use
wildcards or NSEC RRs to generate positive and negative responses wildcards or NSEC RRs to generate positive and negative responses
(respectively) until the TTL or signatures on the records in question (respectively) until the TTL or signatures on the records in question
expire. However, it seems prudent for resolvers to avoid blocking expire. However, it seems prudent for resolvers to avoid blocking
new authoritative data or synthesizing new data on their own. new authoritative data or synthesizing new data on their own.
Resolvers that follow this recommendation will have a more consistent Resolvers that follow this recommendation will have a more consistent
view of the namespace". view of the namespace".
The paragraph is updated as follows: The paragraph is updated as follows:
+-----------------------------------------------------------------+ +-----------------------------------------------------------------+
| Once the records are validated, DNSSEC enabled validating | | Once the records are validated, DNSSEC-enabled validating |
| resolvers SHOULD use wildcards and NSEC/NSEC3 resource records | | resolvers SHOULD use wildcards and NSEC/NSEC3 resource records |
| to generate positive and negative responses until the | | to generate positive and negative responses until the |
| effective TTLs or signatures for those records expire. | | effective TTLs or signatures for those records expire. |
+-----------------------------------------------------------------+ +-----------------------------------------------------------------+
8. IANA Considerations 8. IANA Considerations
This document has no IANA actions. This document does not require any IANA actions.
9. Security Considerations 9. Security Considerations
Use of NSEC / NSEC3 resource records without DNSSEC validation may Use of NSEC/NSEC3 resource records without DNSSEC validation may
create serious security issues, and so this technique requires DNSSEC create serious security issues, and so this technique requires DNSSEC
validation. validation.
Newly registered resource records may not be used immediately. Newly registered resource records may not be used immediately.
However, choosing suitable TTL value and negative cache TTL value However, choosing a suitable TTL value and a negative cache TTL value
(SOA MINIMUM field) will mitigate the delay concern, and it is not a (SOA.MINIMUM field) will mitigate the delay concern, and it is not a
security problem. security problem.
It is also suggested to limit the maximum TTL value of NSEC / NSEC3 It is also suggested to limit the maximum TTL value of NSEC/NSEC3
resource records in the negative cache to, for example, 10800 seconds resource records in the negative cache to, for example, 10800 seconds
(3hrs), to mitigate this issue. (3 hours), to mitigate this issue.
Although the TTL of NSEC/NSEC3 records is typically fairly short Although the TTL of NSEC/NSEC3 records is typically fairly short
(minutes or hours), their RRSIG expiration time can be much further (minutes or hours), their RRSIG expiration time can be much further
in the future (weeks). An attacker who is able to successfully spoof in the future (weeks). An attacker who is able to successfully spoof
responses might poison a cache with old NSEC/NSEC3 records. If the responses might poison a cache with old NSEC/NSEC3 records. If the
resolver is not making aggressive use of NSEC/NSEC3, the attacker has resolver is not making aggressive use of NSEC/NSEC3, the attacker has
to repeat the attack for every query. If the resolver is making to repeat the attack for every query. If the resolver is making
aggressive use of NSEC/NSEC3, one successful attack would be able to aggressive use of NSEC/NSEC3, one successful attack would be able to
suppress many queries for new names, up to the negative TTL. suppress many queries for new names, up to the negative TTL.
10. Implementation Status 10. References
[ Editor note: RFC Editor, please remove this entire section.
RFC6982 says: "Since this information is necessarily time dependent,
it is inappropriate for inclusion in a published RFC." ]
Unbound currently implements aggressive negative caching, as does
Google Public DNS.
11. Acknowledgments
The authors gratefully acknowledge DLV [RFC5074] author Samuel Weiler
and the Unbound developers.
Thanks to Mark Andrews for providing the helpful notes for
implementors provided in Appendix B.
The authors would like to specifically thank Stephane Bortzmeyer (for
standing next to and helping edit), Ralph Dolmans, Tony Finch, Tatuya
JINMEI for extensive review and comments, and also Mark Andrews,
Casey Deccio, Alexander Dupuy, Olafur Gudmundsson, Bob Harold, Shumon
Huque, John Levine, Pieter Lexis, Matthijs Mekking (who even sent
pull requests!) and Ondrej Sury.
11.1. Change History
RFC Editor: Please remove this section prior to publication.
-09 to -10:
o Addressed IESG comments at https://datatracker.ietf.org/doc/draft-
ietf-dnsop-nsec-aggressiveuse/ballot/
o Main change "the resolver SHOULD use NSEC, NSEC3 and wildcard
records aggressively." -> "HOULD use NSEC, NSEC3 and wildcard
records to synthesize answers as described in this document"
(Mirja) - aggressively wasn't really described...
-08 to -09:
o Made RFC5074 Informative (after discussions with chairs.
o Addressed SecDir comments.
o Addressed OpsDir comments.
-06 to -08:
o Largely editorial, but please see the diffs (editors forgot to
update change log when editing, backfilling change log.)
o Changed "replacement" text to be "DNSSEC enabled validating
resolvers SHOULD use wildcards ..." to align with text in doc.
o "A resolver that supports aggressive use of NSEC and NSEC3 SHOULD"
(should -> SHOULD) - to align with rest of text.
-05 to -06:
o Moved some dangling text around - when the examples were added
some text added in the wrong place.
o There were some bits which mentioned "negative" in the title.
o We had the cut-and-paste of what changed in 4035 twice.
o Clarified that this also allows NODATA responses to be
synthesized.
-04 to -05:
o Bob pointed out that I did a stupid - when I added the wildcard to
'example.com' I made the example wrong / confusing. I have
attempted to fix this by adding a second example zone
(example.org) with the wildcard instead.
o More helpful changes (in a pull request, thanks!) from Matthijs
o Included Mark Andrew's useful explanation of how to tell ENT from
NXD as an Appendix.
-03 to -04:
o Working group does want the "positive" answers, not just negative
ones. This requires reading what used to be Section 7, and a
bunch of cleanup, including:
* Additional text in the Problem Statement
* Added a wildcard record to the zone.
* Added "or positive answers from wildcards" type text (where
appropriate) to explain that this isn't just for negative
answers.
* Reworded much of the Wildcard text.
o Incorporated pull request from Tony Finch (thanks!):
https://github.com/wkumari/draft-ietf-dnsop-nsec-aggressiveuse/
pull/1
o More fixups from Tony (including text): https://www.ietf.org/mail-
archive/web/dnsop/current/msg18271.html. This included much
clearer text on TTL, references to the NSEC / NSEC3 RFCs (instead
of my clumsy summary), good text on replays, etc.
o Converted the "zone file" to a figure to make it more readable.
o Text from Tim W: "If a validating resolver receives a query for
cat.example.com, it contacts its resolver (which may be itself) to
query..." - which satisfies Jinmei's concern (which I was too
dense to grock).
o Fixup of the "validation required" in security considerations.
-02 to -03:
o Integrated a bunch of comments from Matthijs Mekking - details in:
https://github.com/wkumari/draft-ietf-dnsop-nsec-aggressiveuse/
pull/1. I decided to keep "Aggressive Negative Caching" instead
of "Aggressive USE OF Negative Caching" for readability.
o Attempted to address Bob Harold's comment on the readability
issues with "But, it will be more effective when both are
enabled..." in Section 5.4 - https://www.ietf.org/mail-
archive/web/dnsop/current/msg17997.html
o MAYs and SHOULD drifted in the text block. Fixed - thanks to
https://mailarchive.ietf.org/arch/msg/
dnsop/2ljmmzxtIMCFMLOZmWcSbTYVOy4
o A number of good edits from Stephane in: https://www.ietf.org/
mail-archive/web/dnsop/current/msg18109.html
o A bunch more edits from Jinmei, as in: https://www.ietf.org/mail-
archive/web/dnsop/current/msg18206.html
-01 to -02:
o Added Section 6 - Benefits (as suggested by Jinmei).
o Removed Appendix B (Jinmei)
o Replaced "full-service" with "validating" (where applicable)
o Integrated other comments from Jinmei from https://www.ietf.org/
mail-archive/web/dnsop/current/msg17875.html
o Integrated comment from co-authors, including re-adding parts of
Appendix B, terminology, typos.
o Tried to explain under what conditions this may actually mitigate
attacks.
-00 to -01:
o Comments from DNSOP meeting in Berlin.
o Changed intended status to Standards Track (updates RFC 4035)
o Added a section "Updates to RFC 4035"
o Some language clarification / typo / cleanup
o Cleaned up the TTL section a bit.
o Removed Effects section, Additional proposal section, and pseudo
code.
o Moved "mitigation of random subdomain attacks" to Appendix.
From draft-fujiwara-dnsop-nsec-aggressiveuse-03 -> draft-ietf-dnsop-
nsec-aggressiveuse
o Document adopted by DNSOP WG.
o Adoption comments
o Changed main purpose to performance
o Use NSEC3/Wildcard keywords
o Improved wordings (from good comments)
o Simplified pseudo code for NSEC3
o Added Warren as co-author.
o Reworded much of the problem statement
o Reworked examples to better explain the problem / solution.
11.1.1. Version draft-fujiwara-dnsop-nsec-aggressiveuse-01
o Added reference to DLV [RFC5074] and imported some sentences.
o Added Aggressive Negative Caching Flag idea.
o Added detailed algorithms.
11.1.2. Version draft-fujiwara-dnsop-nsec-aggressiveuse-02
o Added reference to [I-D.vixie-dnsext-resimprove]
o Added considerations for the CD bit
o Updated detailed algorithms.
o Moved Aggressive Negative Caching Flag idea into Additional
Proposals
11.1.3. Version draft-fujiwara-dnsop-nsec-aggressiveuse-03
o Added "Partial implementation"
o Section 4,5,6 reorganized for better representation
o Added NODATA answer in Section 4
o Trivial updates
o Updated pseudo code
12. References
12.1. Normative References 10.1. Normative References
[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, DOI 10.17487/ Requirement Levels", BCP 14, RFC 2119,
RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>. <http://www.rfc-editor.org/info/rfc2119>.
[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>.
[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>.
skipping to change at page 15, line 5 skipping to change at page 10, line 22
<http://www.rfc-editor.org/info/rfc5155>. <http://www.rfc-editor.org/info/rfc5155>.
[RFC7129] Gieben, R. and W. Mekking, "Authenticated Denial of [RFC7129] Gieben, R. and W. Mekking, "Authenticated Denial of
Existence in the DNS", RFC 7129, DOI 10.17487/RFC7129, Existence in the DNS", RFC 7129, DOI 10.17487/RFC7129,
February 2014, <http://www.rfc-editor.org/info/rfc7129>. February 2014, <http://www.rfc-editor.org/info/rfc7129>.
[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>.
12.2. Informative References [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <http://www.rfc-editor.org/info/rfc8174>.
[I-D.vixie-dnsext-resimprove] 10.2. Informative References
[RES-IMPROVE]
Vixie, P., Joffe, R., and F. Neves, "Improvements to DNS Vixie, P., Joffe, R., and F. Neves, "Improvements to DNS
Resolvers for Resiliency, Robustness, and Responsiveness", Resolvers for Resiliency, Robustness, and Responsiveness",
draft-vixie-dnsext-resimprove-00 (work in progress), June Work in Progress, draft-vixie-dnsext-resimprove-00, June
2010. 2010.
[RFC5074] Weiler, S., "DNSSEC Lookaside Validation (DLV)", RFC 5074, [RFC5074] Weiler, S., "DNSSEC Lookaside Validation (DLV)", RFC 5074,
DOI 10.17487/RFC5074, November 2007, DOI 10.17487/RFC5074, November 2007,
<http://www.rfc-editor.org/info/rfc5074>. <http://www.rfc-editor.org/info/rfc5074>.
[RFC8020] Bortzmeyer, S. and S. Huque, "NXDOMAIN: There Really Is [RFC8020] Bortzmeyer, S. and S. Huque, "NXDOMAIN: There Really Is
Nothing Underneath", RFC 8020, DOI 10.17487/RFC8020, Nothing Underneath", RFC 8020, DOI 10.17487/RFC8020,
November 2016, <http://www.rfc-editor.org/info/rfc8020>. November 2016, <http://www.rfc-editor.org/info/rfc8020>.
[root-servers.org] [ROOT-SERVERS]
IANA, "Root Server Technical Operations Assn", "Root Server Technical Operations Assn",
<http://www.root-servers.org/>. <http://www.root-servers.org/>.
Appendix A. Detailed implementation notes Appendix A. Detailed Implementation Notes
o Previously, cached negative responses were indexed by QNAME, o Previously, cached negative responses were indexed by QNAME,
QCLASS, QTYPE, and the setting of the CD bit (see RFC 4035, QCLASS, QTYPE, and the setting of the CD bit (see RFC 4035,
Section 4.7), and only queries matching the index key would be Section 4.7), and only queries matching the index key would be
answered from the cache. With aggressive negative caching, the answered from the cache. With aggressive negative caching, the
validator, in addition to checking to see if the answer is in its validator, in addition to checking to see if the answer is in its
cache before sending a query, checks to see whether any cached and cache before sending a query, checks to see whether any cached and
validated NSEC record denies the existence of the sought validated NSEC record denies the existence of the sought
record(s). Using aggressive negative caching, a validator will record(s). Using aggressive negative caching, a validator will
not make queries for any name covered by a cached and validated not make queries for any name covered by a cached and validated
NSEC record. Furthermore, a validator answering queries from NSEC record. Furthermore, a validator answering queries from
clients will synthesize a negative answer (or NODATA response) clients will synthesize a negative answer (or NODATA response)
whenever it has an applicable validated NSEC in its cache unless whenever it has an applicable validated NSEC in its cache unless
the CD bit was set on the incoming query. (Imported from the CD bit was set on the incoming query. (Imported from
Section 6 of [RFC5074]). Section 6 of [RFC5074].)
o Implementing aggressive negative caching suggests that a validator o Implementing aggressive negative caching suggests that a validator
will need to build an ordered data structure of NSEC and NSEC3 will need to build an ordered data structure of NSEC and NSEC3
records for each signer domain name of NSEC / NSEC3 records in records for each signer domain name of NSEC/NSEC3 records in order
order to efficiently find covering NSEC / NSEC3 records. Call the to efficiently find covering NSEC/NSEC3 records. Call the table
table as NSEC_TABLE. (Imported from Section 6.1 of [RFC5074] and as "NSEC_TABLE". (Imported from Section 6.1 of [RFC5074] and
expanded.) expanded.)
o The aggressive negative caching may be inserted at the cache o The aggressive negative caching may be inserted at the cache
lookup part of the recursive resolvers. lookup part of the recursive resolvers.
o If errors happen in aggressive negative caching algorithm, o If errors happen in an aggressive negative caching algorithm,
resolvers MUST fall back to resolve the query as usual. "Resolve resolvers MUST fall back to resolve the query as usual. "Resolve
the query as usual" means that the resolver must process the query the query as usual" means that the resolver must process the query
as though it does not implement aggressive negative caching. as though it does not implement aggressive negative caching.
Appendix B. Procedure for determining ENT vs NXDOMAN with NSEC Appendix B. Procedure for Determining ENT vs. NXDOMAIN with NSEC
This procedure outlines how to determine if a given name does not This procedure outlines how to determine if a given name does not
exist, or is an ENT (Empty Non-Terminal, see [RFC5155] Section 1.3) exist, or is an ENT (empty non-terminal; see [RFC5155], Section 1.3)
with NSEC. with NSEC.
If the NSEC record has not been verified as secure discard it. If the NSEC record has not been verified as secure, discard it.
If the given name sorts before or matches the NSEC owner name discard If the given name sorts before or matches the NSEC owner name,
it as it does not prove the NXDOMAIN or ENT. discard it as it does not prove the NXDOMAIN or ENT.
If the given name is a subdomain of the NSEC owner name and the NS If the given name is a subdomain of the NSEC owner name and the NS
bit is present and the SOA bit is absent then discard the NSEC as it bit is present and the SOA bit is absent, then discard the NSEC as it
is from a parent zone. is from a parent zone.
If the next domain name sorts after the NSEC owner name and the given If the next domain name sorts after the NSEC owner name and the given
name sorts after or matches next domain name then discard the NSEC name sorts after or matches next domain name, then discard the NSEC
record as it does not prove the NXDOMAIN or ENT. record as it does not prove the NXDOMAIN or ENT.
If the next domain name sorts before or matches the NSEC owner name If the next domain name sorts before or matches the NSEC owner name
and the given name is not a subdomain of the next domain name then and the given name is not a subdomain of the next domain name, then
discard the NSEC as it does not prove the NXDOMAIN or ENT. discard the NSEC as it does not prove the NXDOMAIN or ENT.
You now have a NSEC record that proves the NXDOMAIN or ENT. You now have an NSEC record that proves the NXDOMAIN or ENT.
If the next domain name is a subdomain of the given name you have a If the next domain name is a subdomain of the given name, you have an
ENT otherwise you have a NXDOMAIN. ENT. Otherwise, you have an NXDOMAIN.
Acknowledgments
The authors gratefully acknowledge DNSSEC Lookaside Validation (DLV)
[RFC5074] author Samuel Weiler and the Unbound developers.
Thanks to Mark Andrews for providing the helpful notes for
implementors provided in Appendix B.
The authors would like to specifically thank Stephane Bortzmeyer (for
standing next to and helping edit), Ralph Dolmans, Tony Finch, Tatuya
JINMEI for extensive review and comments, and also Mark Andrews,
Casey Deccio, Alexander Dupuy, Olafur Gudmundsson, Bob Harold, Shumon
Huque, John Levine, Pieter Lexis, Matthijs Mekking (who even sent
pull requests!), and Ondrej Sury.
Authors' Addresses Authors' Addresses
Kazunori Fujiwara Kazunori Fujiwara
Japan Registry Services Co., Ltd. Japan Registry Services Co., Ltd.
Chiyoda First Bldg. East 13F, 3-8-1 Nishi-Kanda Chiyoda First Bldg. East 13F, 3-8-1 Nishi-Kanda
Chiyoda-ku, Tokyo 101-0065 Chiyoda-ku, Tokyo 101-0065
Japan Japan
Phone: +81 3 5215 8451 Phone: +81 3 5215 8451
skipping to change at page 17, line 17 skipping to change at page 13, line 29
Kohoku, Yokohama 223-8526 Kohoku, Yokohama 223-8526
Japan Japan
Phone: +81 45 564 2490 Phone: +81 45 564 2490
Email: kato@wide.ad.jp Email: kato@wide.ad.jp
Warren Kumari Warren Kumari
Google Google
1600 Amphitheatre Parkway 1600 Amphitheatre Parkway
Mountain View, CA 94043 Mountain View, CA 94043
US United States of America
Email: warren@kumari.net Email: warren@kumari.net
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