draft-ietf-dnsop-nsec-aggressiveuse-03.txt   draft-ietf-dnsop-nsec-aggressiveuse-04.txt 
Network Working Group K. Fujiwara Network Working Group K. Fujiwara
Internet-Draft JPRS Internet-Draft JPRS
Updates: 4035 (if approved) A. Kato Updates: 4035 (if approved) A. Kato
Intended status: Standards Track Keio/WIDE Intended status: Standards Track Keio/WIDE
Expires: April 7, 2017 W. Kumari Expires: April 10, 2017 W. Kumari
Google Google
October 4, 2016 October 7, 2016
Aggressive use of NSEC/NSEC3 Aggressive use of NSEC/NSEC3
draft-ietf-dnsop-nsec-aggressiveuse-03 draft-ietf-dnsop-nsec-aggressiveuse-04
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. This increases to generate negative answers within a range, and positive answers
performance / decreases latency, decreases resource utilization on from wildcards. This increases performance / decreases latency,
both authoritative and recursive servers, and also increases privacy. decreases resource utilization on both authoritative and recursive
It may also help increase resilience to certain DoS attacks in some servers, and also increases privacy. It may also help increase
circumstances. resilience to certain DoS attacks in some circumstances.
This document updates RFC4035 by allowing validating resolvers to This document updates RFC4035 by allowing validating resolvers to
generate negative answers based upon NSEC/NSEC3 records. generate negative based upon NSEC/NSEC3 records (and positive answers
in the presence of wildcards).
[ Ed note: Text inside square brackets ([]) is additional background [ Ed note: Text inside square brackets ([]) is additional background
information, answers to frequently asked questions, general musings, information, answers to frequently asked questions, general musings,
etc. They will be removed before publication.This document is being etc. They will be removed before publication.This document is being
collaborated on in Github at: https://github.com/wkumari/draft-ietf- collaborated on in Github at: https://github.com/wkumari/draft-ietf-
dnsop-nsec-aggressiveuse. The most recent version of the document, dnsop-nsec-aggressiveuse. The most recent version of the document,
open issues, etc should all be available here. The authors open issues, etc should all be available here. The authors
(gratefully) accept pull requests.] (gratefully) accept pull requests.]
Status of This Memo Status of This Memo
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 7, 2017.
This Internet-Draft will expire on April 10, 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
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
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
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 . . . . . . . . . . . . . . . . . . . . . . . . 2 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 Negative Caching . . . . . . . . . . . . . . . . . 5 5. Aggressive Caching . . . . . . . . . . . . . . . . . . . . . 5
5.1. NSEC . . . . . . . . . . . . . . . . . . . . . . . . . . 5 5.1. NSEC . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.2. NSEC3 . . . . . . . . . . . . . . . . . . . . . . . . . . 6 5.2. NSEC3 . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.3. Consideration on TTL . . . . . . . . . . . . . . . . . . 6 5.3. Wildcards . . . . . . . . . . . . . . . . . . . . . . . . 7
6. Benefits . . . . . . . . . . . . . . . . . . . . . . . . . . 6 5.4. Consideration on TTL . . . . . . . . . . . . . . . . . . 7
7. Update to RFC 4035 . . . . . . . . . . . . . . . . . . . . . 7 6. Benefits . . . . . . . . . . . . . . . . . . . . . . . . . . 8
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 7. Update to RFC 4035 . . . . . . . . . . . . . . . . . . . . . 8
9. Security Considerations . . . . . . . . . . . . . . . . . . . 8 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
10. Implementation Status . . . . . . . . . . . . . . . . . . . . 8 9. Security Considerations . . . . . . . . . . . . . . . . . . . 9
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8 10. Implementation Status . . . . . . . . . . . . . . . . . . . . 9
12. Change History . . . . . . . . . . . . . . . . . . . . . . . 8 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10
12.1. Version draft-fujiwara-dnsop-nsec-aggressiveuse-01 . . . 10 11.1. Change History . . . . . . . . . . . . . . . . . . . . . 10
12.2. Version draft-fujiwara-dnsop-nsec-aggressiveuse-02 . . . 10 11.1.1. Version draft-fujiwara-dnsop-nsec-aggressiveuse-01 . 12
12.3. Version draft-fujiwara-dnsop-nsec-aggressiveuse-03 . . . 10 11.1.2. Version draft-fujiwara-dnsop-nsec-aggressiveuse-02 . 12
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 11 11.1.3. Version draft-fujiwara-dnsop-nsec-aggressiveuse-03 . 13
13.1. Normative References . . . . . . . . . . . . . . . . . . 11 11.2. new section . . . . . . . . . . . . . . . . . . . . . . 13
13.2. Informative References . . . . . . . . . . . . . . . . . 11 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
Appendix A. Detailed implementation notes . . . . . . . . . . . 12 12.1. Normative References . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12 12.2. Informative References . . . . . . . . . . . . . . . . . 14
Appendix A. Detailed implementation notes . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15
1. Introduction 1. Introduction
A DNS negative cache exists, and is used to cache the fact that a A DNS negative cache exists, and is used to cache the fact that a
name does not exist. This method of negative caching requires exact name 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 recursive resolvers to use This document updates RFC 4035 to allow recursive resolvers to use
NSEC/NSEC3 resource records to synthetize negative answers from the NSEC/NSEC3 resource records to synthesize negative answers from the
information they have in the cache. This allows validating resolvers information they have in the cache. This allows validating resolvers
to respond with NXDOMAIN immediately if the name in question falls to respond with NXDOMAIN immediately if the name in question falls
into a range expressed by a NSEC/NSEC3 resource record already in the into a range expressed by a NSEC/NSEC3 resource record already in the
cache. cache. It also allows the synthesis of positive answers in the
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.
Section 3 of [I-D.vixie-dnsext-resimprove] "Stopping Downward Cache Section 3 of [I-D.vixie-dnsext-resimprove] "Stopping Downward Cache
Search on NXDOMAIN" and [I-D.ietf-dnsop-nxdomain-cut] proposed Search on NXDOMAIN" and [I-D.ietf-dnsop-nxdomain-cut] proposed
another approach to use NXDOMAIN information effectively. another approach to use NXDOMAIN information effectively.
2. Terminology 2. Terminology
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"Closest Encloser" is also defined in NSEC3 [RFC5155], as is "Next "Closest Encloser" is also defined in NSEC3 [RFC5155], as is "Next
closer name". closer name".
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:
apple.example.com IN A 192.0.2.1 apple.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 *.example.com IN A 192.0.2.3
zebra.example.com IN A 192.0.2.4
zebra.example.com IN A 192.0.2.3
If a validating resolver gets a query for cat.example.com, it will If a validating resolver receives a query for cat.example.com, it
query the example.com servers and will get back an NSEC (or NSEC3) contacts its resolver (which may be itself) to query the example.com
record starting that there are no records between apple and elephant. servers and will get back an NSEC record starting that there are no
The resolver then knows that cat.example.com does not exist; however, records (alphabetically) between apple and elephant, or an NSEC3
it does not use the fact that the proof covers a range (apple to record stating there is nothing between two hashed names. The
resolver then knows that cat.example.com does not exist; however, it
does not use the fact that the proof covers a range (apple 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.
Further, if a query is received for lion.example.com, it 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 records
(alphabetically) between elephant and zebra (or an NSEC3 record
stating there is nothing between two hashed names), as well as an
answer for lion.example.com, with the label count of the signature
set to two (see [RFC7129], section 5.3 for more details).
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 (see additional resources), and also has
privacy implications (e.g: typos leak out further than necessary). privacy implications (e.g: typos leak out further than necessary).
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, accomplished by providing a (DNSSEC secured) record does not exist, accomplished by providing a (DNSSEC secured) record
containing the names which appear alphabetically before and after the containing the names which appear alphabetically before and after the
queried for name. In the example above, if the (DNSSEC validating) queried for name. In the example above, if the (DNSSEC validating)
recursive server were to query for lion.example.com it would receive recursive server were to query for dog.example.com it would receive a
a (signed) NSEC/NSEC3 record stating that there are no labels between (signed) NSEC record stating that there are no labels between "apple"
"elephant" and "zebra". This is a signed, cryptographic proof that and "elephant" (or, for NSEC3, a similar pair of hashed names). This
these names are the ones before and after the queried for label. As is a signed, cryptographic proof that these names are the ones before
lion.example.com falls within this range, the recursive server knows and after the queried for label. As dog.example.com falls within
that lion.example.com really does not exist. This document specifies this range, the recursive server knows that dog.example.com really
that this NSEC/NSEC3 record should be used to generate negative does not exist.
answers for any queries that the recursive server receives that fall
within the range covered by the record (for the TTL for the record). This document specifies that this NSEC/NSEC3 record should be used to
generate negative answers for any queries that the validating server
receives that fall within the range covered by the record (for the
TTL for the record). This document also specifies that a positive
answer should be generated for any queries that the validating server
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 and "The reason for these recommendations is that, between the
initial query and the expiration of the data from the cache, the initial query and the expiration of the data from the cache, the
authoritative data might have been changed (for example, via dynamic authoritative data might have been changed (for example, via dynamic
update).". In other words, if a resolver generates negative answers update).". In other words, if a resolver generates negative answers
from an NSEC record, it will not send any queries for names within 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 that NSEC range (for the TTL). If a new name is added to the zone
during this interval the resolver will not know this. 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
We believe this recommendation can be relaxed because, in the absense We believe this recommendation can be relaxed because, in the absense
of this technique, a lookup for the exact name could have come in of this technique, a lookup for the exact name could have come in
during this interval, and so this could already be cached (see during this interval, and so a negative answer could already be
[RFC2308] for more background). This means that zone operators cached (see [RFC2308] for more background). This means that zone
should have no expectation that an added name would work immediately. operators should have no expectation that an added name would work
With DNSSEC and Aggressive NSEC, the TTL of the NSEC record is the immediately. With DNSSEC and Aggressive NSEC, the TTL of the NSEC
authoritative statement of how quickly a name can start working record is the authoritative statement of how quickly a name can start
within a zone. working within a zone.
5. Aggressive Negative Caching 5. Aggressive Caching
Section 4.5 of [RFC4035] shows that "In theory, a resolver could use Section 4.5 of [RFC4035] says 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".
This document relaxes this this restriction, as follows: This document relaxes this this restriction, as follows:
+--------------------------------------------------------------+ +--------------------------------------------------------------+
| Once the records are validated, DNSSEC enabled validating | | Once the records are validated, DNSSEC enabled validating |
| resolvers SHOULD use NSEC/NSEC3 resource records to generate | | resolvers MAY use wildcards and NSEC/NSEC3 resource records |
| negative responses until their effective TTLs or signatures | | to generate positive and negative responses until the |
| for those records expire. | | effective TTLs or signatures for those records expire. |
+--------------------------------------------------------------+ +--------------------------------------------------------------+
If the validating resolver's cache has sufficient information to If the validating resolver's cache has sufficient information to
validate the query, the resolver SHOULD use NSEC/NSEC3/wildcard validate the query, the resolver SHOULD use NSEC/NSEC3/wildcard
records aggressively. Otherwise, it MUST fall back to send the query records aggressively. Otherwise, it MUST fall back to send the query
to the authoritative DNS servers. to the authoritative DNS servers.
If the query name has the matching NSEC/NSEC3 RR proving the
information requested does not exist, the validating resolver may
respond with a NODATA (empty) answer.
5.1. NSEC 5.1. NSEC
Implementations which support aggressive use of NSEC SHOULD enable Implementations which support aggressive use of NSEC SHOULD enable
this by default. Implementations MAY provide a configuration switch this by default. Implementations MAY provide a configuration switch
to disable aggressive use of NSEC and allow it to be enabled or to disable aggressive use of NSEC and allow it to be enabled or
disabled per domain. disabled per domain.
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 the validating resolver's cache contains an NSEC RR covering the If denial of existence can be determined according to the rules set
source of synthesis and the covering NSEC RR of the query name, the out in Section 5.4 of [RFC4035], using NSEC records in the cache,
validating resolver may respond with NXDOMAIN error immediately. then the resolver can immediately return an NXDOMAIN or NODATA (as
appropriate) response.
5.2. NSEC3 5.2. NSEC3
NSEC3 aggressive negative caching is more difficult. If the zone is NSEC3 aggressive negative caching is more difficult than NSEC
signed with NSEC3, the validating resolver needs to check the aggressive caching. If the zone is signed with NSEC3, the validating
existence of non-terminals and wildcards which derive from query resolver needs to check the existence of non-terminals and wildcards
names. which derive from query names.
If the validating resolver's cache contains an NSEC3 RR matching the A validating resolver implementation MAY support aggressive use of
closest encloser, an NSEC3 RR covering the next closer name, and an NSEC3. If it does support aggressive use of NSEC3, it SHOULD enable
NSEC3 RR covering the source of synthesis, it is possible for the this by default. It MAY provide a configuration switch to disable
validating resolver to respond with NXDOMAIN immediately. aggressive use of NSEC3 and allow it to be enabled or disabled for
specific zones.
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
the cache, then the resolver can immediately return an 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 Opt-Out flag, the covering NSEC3 RR does
not prove the non-existence of the domain name and the aggressive not prove the non-existence of the domain name and the aggressive
negative caching is not possible for the domain name. negative caching is not possible for the domain name.
A validating resolver implementation MAY support aggressive use of 5.3. Wildcards
NSEC3. If it does aggressive use of NSEC3, it MAY provide a
configuration switch to disable aggressive use of NSEC3 and allow it
to be enabled or disabled for specific zones.
5.3. Consideration on TTL The last paragraph of [RFC4035] Section 4.5 also discusses the use of
wildcards and NSEC RRs to generate positive responses and recommends
that it not be relied upon. Just like the case for the aggressive
use of NSEC/NSEC3 for negative answers, we revise this
recommendation.
As long as the validating resolver can determine that a name would
not exist without the wildcard match, it MAY synthesize an answer for
that name using the cached deduced wildcard. If the corresponding
wildcard record is not in the cache, it MUST fall back to send the
query to the authoritative DNS servers.
An implementation MAY support aggressive use of wildcards. It SHOULD
provide a configuration switch to disable aggressive use of
wildcards.
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. Section 5 of RFC 2308 states that the information is effective.
maximum number of negative cache TTL value is 3 hours (10800). It is
RECOMMENDED that validating resolvers limit the maximum effective TTL Section 5 of [RFC2308] states that the maximum number of negative
value of negative responses (NSEC/NSEC3 RRs) to this same value. cache TTL value is 3 hours (10800). It is RECOMMENDED that
validating resolvers limit the maximum effective TTL value of
negative responses (NSEC/NSEC3 RRs) to this same value.
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
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
[RFC5155] section 3.)
A resolver that supports aggressive use of NSEC and NSEC3 should
reduce the TTL of NSEC and NSEC3 records to match the TTL of the SOA
record in the authority section of a negative response, if the SOA
TTL 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):
Reduced latency By answering directly from cache, validating Reduced latency: By answering directly from cache, validating
resolvers can immediately inform clients that the name they are resolvers can immediately inform clients that the name they are
looking for does not exist, improving the user experience. looking for does not exist, improving the user experience.
Decreased recursive server load By answering negative queries from Decreased recursive server load: By answering negative queries from
the cache, validating servers avoid having send a query and wait the cache, validating servers avoid having to send a query and
for a response. In addition to decreasing the bandwidth used, it wait for a response. In addition to decreasing the bandwidth
also means that the server does not need to allocate and maintain used, it also means that the server does not need to allocate and
state, thereby decreasing memory and CPU load. maintain state, thereby decreasing memory and CPU load.
Decreased authorative server load Because recursive servers can Decreased authorative server load: Because recursive servers can
answer (negative) queries without asking the authoritative server, answer (negative) queries without asking the authoritative server,
the authoritative servers receive less queries. This decreases the authoritative servers receive fewer queries. This decreases
the authoritative server bandwidth, queries per second and CPU the 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, currently around 65% of queries to query distribution. For example, at the time of this writing, around
Root Name servers result in NXDOMAIN responses; this technique will 65% of queries to Root Name servers result in NXDOMAIN responses (see
eliminate a sizable quantity of these. statis [root-servers.org]); this technique will eliminate a 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 sub-domains 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 Aggressive NSEC may help mitigate these attacks by allowing the
resolver to answer directly from cache for any random queries which resolver to answer directly from cache for any random queries which
fall within already requested ranges. It will not always work as an fall within already requested ranges. It will not always work as an
effective defense, not least because not many zones are DNSSEC signed effective defense, not least because not many zones are DNSSEC signed
at all, but it will still provide an additional layer of defense. at all -- but it will still provide an additional layer of defense.
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 MAY use wildcards and NSEC/NSEC3 resource records | | resolvers MAY use wildcards and NSEC/NSEC3 resource records |
| to generate negative responses until their effective TTLs | | to generate positive and negative responses until the |
| 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 has no IANA actions.
9. Security Considerations 9. Security Considerations
Use of NSEC / NSEC3 resource records without DNSSEC validation may
create serious security issues, and so this technique requires DNSSEC
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 suitable TTL value and 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. Implementations which comply with (3hrs), to mitigate this issue. Implementations which comply with
this proposal are recommended to have a configurable maximum value of this proposal are recommended to have a configurable maximum value of
NSEC RRs in the negative cache. NSEC RRs in the negative cache.
Aggressive use of NSEC / NSEC3 resource records without DNSSEC Although the TTL of NSEC/NSEC3 records is typically fairly short
validation may create serious security issues, and so this technique (minutes or hours), their RRSIG expiration time can be much further
requires DNSSEC validation. in the future (weeks). An attacker who is able to successfully spoof
responses might poison a cache with old NSEC/NSEC3 records. If the
resolver is NOT making aggressive use of NSEC/NSEC3, the attacker has
to repeat the attack for every query. If the resolver IS making
aggressive use of NSEC/NSEC3, one successful attack would be able to
suppress many queries for new names, up to the negative TTL.
10. Implementation Status 10. Implementation Status
Unbound currenty implements aggressive negative caching, as does Unbound currenty implements aggressive negative caching, as does
Google Public DNS. Google Public DNS.
11. Acknowledgments 11. Acknowledgments
The authors gratefully acknowledge DLV [RFC5074] author Samuel Weiler The authors gratefully acknowledge DLV [RFC5074] author Samuel Weiler
and the Unbound developers. and the Unbound developers.
The authors would like to specifically thank Tatuya JINMEI for The authors would like to specifically thank Stephane Bortzmeyer,
extensive review and comments, and also Mark Andrews, Stephane Tony Finch, Tatuya JINMEI for extensive review and comments, and also
Bortzmeyer, Casey Deccio, Alexander Dupuy, Olafur Gudmundsson, Bob Mark Andrews, Casey Deccio, Alexander Dupuy, Olafur Gudmundsson, Bob
Harold, Shumon Huque, John Levine, Pieter Lexis and Matthijs Mekking Harold, Shumon Huque, John Levine, Pieter Lexis and Matthijs Mekking
(who even sent pull requests!). (who even sent pull requests!).
12. Change History 11.1. Change History
RFC Editor: Please remove this section prior to publication. RFC Editor: Please remove this section prior to publication.
-03 to -04:
o Working group does want the "positive" answers, not just negative
ones. This requires readding 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, refernces 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: -02 to -03:
o Integrated a bunch of comments from Matthijs Mekking - details in: o Integrated a bunch of comments from Matthijs Mekking - details in:
https://github.com/wkumari/draft-ietf-dnsop-nsec-aggressiveuse/ https://github.com/wkumari/draft-ietf-dnsop-nsec-aggressiveuse/
pull/1. I decided to keep "Aggressive Negative Caching" instead pull/1. I decided to keep "Aggressive Negative Caching" instead
of "Aggressive USE OF Negative Caching" for readability. of "Aggressive USE OF Negative Caching" for readability.
o Attempted to address Bob Harold's comment on the readability o Attempted to address Bob Harold's comment on the readability
issues with "But, it will be more effective when both are issues with "But, it will be more effective when both are
enabled..." in Section 5.4 - https://www.ietf.org/mail- enabled..." in Section 5.4 - https://www.ietf.org/mail-
skipping to change at page 10, line 21 skipping to change at page 12, line 32
o Improved wordings (from good comments) o Improved wordings (from good comments)
o Simplified pseudo code for NSEC3 o Simplified pseudo code for NSEC3
o Added Warren as co-author. o Added Warren as co-author.
o Reworded much of the problem statement o Reworded much of the problem statement
o Reworked examples to better explain the problem / solution. o Reworked examples to better explain the problem / solution.
12.1. Version draft-fujiwara-dnsop-nsec-aggressiveuse-01 11.1.1. Version draft-fujiwara-dnsop-nsec-aggressiveuse-01
o Added reference to DLV [RFC5074] and imported some sentences. o Added reference to DLV [RFC5074] and imported some sentences.
o Added Aggressive Negative Caching Flag idea. o Added Aggressive Negative Caching Flag idea.
o Added detailed algorithms. o Added detailed algorithms.
12.2. Version draft-fujiwara-dnsop-nsec-aggressiveuse-02 11.1.2. Version draft-fujiwara-dnsop-nsec-aggressiveuse-02
o Added reference to [I-D.vixie-dnsext-resimprove] o Added reference to [I-D.vixie-dnsext-resimprove]
o Added considerations for the CD bit o Added considerations for the CD bit
o Updated detailed algorithms. o Updated detailed algorithms.
o Moved Aggressive Negative Caching Flag idea into Additional o Moved Aggressive Negative Caching Flag idea into Additional
Proposals Proposals
12.3. Version draft-fujiwara-dnsop-nsec-aggressiveuse-03 11.1.3. Version draft-fujiwara-dnsop-nsec-aggressiveuse-03
o Added "Partial implementation" o Added "Partial implementation"
o Section 4,5,6 reorganized for better representation o Section 4,5,6 reorganized for better representation
o Added NODATA answer in Section 4 o Added NODATA answer in Section 4
o Trivial updates o Trivial updates
o Updated pseudo code o Updated pseudo code
13. References 11.2. new section
13.1. Normative References 12. References
12.1. 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, DOI 10.17487/
RFC2119, March 1997, 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>.
skipping to change at page 11, line 36 skipping to change at page 13, line 50
[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>.
[RFC5155] Laurie, B., Sisson, G., Arends, R., and D. Blacka, "DNS [RFC5155] Laurie, B., Sisson, G., Arends, R., and D. Blacka, "DNS
Security (DNSSEC) Hashed Authenticated Denial of Security (DNSSEC) Hashed Authenticated Denial of
Existence", RFC 5155, DOI 10.17487/RFC5155, March 2008, Existence", RFC 5155, DOI 10.17487/RFC5155, March 2008,
<http://www.rfc-editor.org/info/rfc5155>. <http://www.rfc-editor.org/info/rfc5155>.
[RFC7129] Gieben, R. and W. Mekking, "Authenticated Denial of
Existence in the DNS", RFC 7129, DOI 10.17487/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>.
13.2. Informative References 12.2. Informative References
[I-D.ietf-dnsop-nxdomain-cut] [I-D.ietf-dnsop-nxdomain-cut]
Bortzmeyer, S. and S. Huque, "NXDOMAIN really means there Bortzmeyer, S. and S. Huque, "NXDOMAIN really means there
is nothing underneath", draft-ietf-dnsop-nxdomain-cut-03 is nothing underneath", draft-ietf-dnsop-nxdomain-cut-03
(work in progress), May 2016. (work in progress), May 2016.
[I-D.vixie-dnsext-resimprove] [I-D.vixie-dnsext-resimprove]
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 draft-vixie-dnsext-resimprove-00 (work in progress), June
2010. 2010.
[root-servers.org]
IANA, "Root Server Technical Operations Assn",
<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
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