draft-ietf-dnsop-kskroll-sentinel-15.txt   draft-ietf-dnsop-kskroll-sentinel-16.txt 
DNSOP G. Huston DNSOP G. Huston
Internet-Draft J. Damas Internet-Draft J. Damas
Intended status: Standards Track APNIC Intended status: Standards Track APNIC
Expires: January 3, 2019 W. Kumari Expires: April 23, 2019 W. Kumari
Google Google
July 02, 2018 October 20, 2018
A Root Key Trust Anchor Sentinel for DNSSEC A Root Key Trust Anchor Sentinel for DNSSEC
draft-ietf-dnsop-kskroll-sentinel-15 draft-ietf-dnsop-kskroll-sentinel-16
Abstract Abstract
The DNS Security Extensions (DNSSEC) were developed to provide origin The DNS Security Extensions (DNSSEC) were developed to provide origin
authentication and integrity protection for DNS data by using digital authentication and integrity protection for DNS data by using digital
signatures. These digital signatures can be verified by building a signatures. These digital signatures can be verified by building a
chain of trust starting from a trust anchor and proceeding down to a chain of trust starting from a trust anchor and proceeding down to a
particular node in the DNS. This document specifies a mechanism that particular node in the DNS. This document specifies a mechanism that
will allow an end user and third parties to determine the trusted key will allow an end user and third parties to determine the trusted key
state for the root key of the resolvers that handle that user's DNS state for the root key of the resolvers that handle that user's DNS
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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 https://datatracker.ietf.org/drafts/current/. Drafts is at https://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 January 3, 2019. This Internet-Draft will expire on April 23, 2019.
Copyright Notice Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the Copyright (c) 2018 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
(https://trustee.ietf.org/license-info) in effect on the date of (https://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
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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 . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. Sentinel Mechanism in Resolvers . . . . . . . . . . . . . . . 4 2. Sentinel Mechanism in Resolvers . . . . . . . . . . . . . . . 4
2.1. Preconditions . . . . . . . . . . . . . . . . . . . . . . 4 2.1. Preconditions . . . . . . . . . . . . . . . . . . . . . . 5
2.2. Special Processing . . . . . . . . . . . . . . . . . . . 5 2.2. Special Processing . . . . . . . . . . . . . . . . . . . 5
3. Sentinel Tests for a Single DNS Resolver . . . . . . . . . . 6 3. Sentinel Tests for a Single DNS Resolver . . . . . . . . . . 6
3.1. Forwarders . . . . . . . . . . . . . . . . . . . . . . . 8 3.1. Forwarders . . . . . . . . . . . . . . . . . . . . . . . 9
4. Sentinel Tests from Hosts with More than One Configured 4. Sentinel Tests for Multiple Resolvers . . . . . . . . . . . . 10
Resolve . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 4.1. Test Scenario and Objective . . . . . . . . . . . . . . . 10
4.1. Test Scenario and Objective . . . . . . . . . . . . . . . 9
4.2. Test Assumptions . . . . . . . . . . . . . . . . . . . . 10 4.2. Test Assumptions . . . . . . . . . . . . . . . . . . . . 10
4.3. Test Procedure . . . . . . . . . . . . . . . . . . . . . 10 4.3. Test Procedure . . . . . . . . . . . . . . . . . . . . . 11
5. Security Considerations . . . . . . . . . . . . . . . . . . . 12 5. Security Considerations . . . . . . . . . . . . . . . . . . . 12
6. Privacy Considerations . . . . . . . . . . . . . . . . . . . 12 6. Privacy Considerations . . . . . . . . . . . . . . . . . . . 13
7. Implementation Experience . . . . . . . . . . . . . . . . . . 12 7. Implementation Experience . . . . . . . . . . . . . . . . . . 13
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14
10. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 14 10. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 15
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 17 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 19
11.1. Normative References . . . . . . . . . . . . . . . . . . 18 11.1. Normative References . . . . . . . . . . . . . . . . . . 19
11.2. Informative References . . . . . . . . . . . . . . . . . 18 11.2. Informative References . . . . . . . . . . . . . . . . . 19
Appendix A. Protocol Walkthrough Example . . . . . . . . . . . . 18 Appendix A. Protocol Walkthrough Example . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22
1. Introduction 1. Introduction
The DNS Security Extensions (DNSSEC) [RFC4033], [RFC4034] and The DNS Security Extensions (DNSSEC) [RFC4033], [RFC4034] and
[RFC4035] were developed to provide origin authentication and [RFC4035] were developed to provide origin authentication and
integrity protection for DNS data by using digital signatures. integrity protection for DNS data by using digital signatures.
DNSSEC uses Key Tags to efficiently match signatures to the keys from DNSSEC uses Key Tags to efficiently match signatures to the keys from
which they are generated. The Key Tag is a 16-bit value computed which they are generated. The Key Tag is a 16-bit value computed
from the RDATA of a DNSKEY RR as described in Appendix B of from the RDATA of a DNSKEY RR as described in Appendix B of
[RFC4034]. RRSIG RRs contain a Key Tag field whose value is equal to [RFC4034]. RRSIG RRs contain a Key Tag field whose value is equal to
the Key Tag of the DNSKEY RR that was used to generate the the Key Tag of the DNSKEY RR that was used to generate the
corresponding signature. corresponding signature.
This document specifies how security-aware DNS resolvers that perform This document specifies how security-aware DNS resolvers that perform
validation of their responses can respond to certain queries in a validation of their responses can respond to certain queries in a
manner that allows an agent performing the queries to deduce whether manner that allows an agent performing the queries to deduce whether
a particular key for the root has been loaded into that resolver's a particular key for the root has been loaded into that resolver's
trusted key store. This document also describes a procedure where a trusted key store. This document also describes a procedure where a
collection of resolvers can be tested to determine if at least one of collection of resolvers can be tested to determine if at least one of
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trusted key store. This document also describes a procedure where a trusted key store. This document also describes a procedure where a
collection of resolvers can be tested to determine if at least one of collection of resolvers can be tested to determine if at least one of
these resolvers has loaded a given key into its trusted key store. these resolvers has loaded a given key into its trusted key store.
These tests can be used to determine whether a certain root zone Key These tests can be used to determine whether a certain root zone Key
Signing Key (KSK) is ready to be used as a trusted key, within the Signing Key (KSK) is ready to be used as a trusted key, within the
context of a planned root zone KSK key roll. context of a planned root zone KSK key roll.
There are two primary use cases for this mechanism: There are two primary use cases for this mechanism:
o Users may wish to ascertain whether their DNS resolution o Users may wish to ascertain whether their DNS resolution
environment resolvers is ready for an upcoming root KSK rollover. environment's resolver is ready for an upcoming root KSK rollover.
o Researchers want to perform Internet-wide studies about the o Researchers want to perform Internet-wide studies about the
proportion of users who will be negatively impacted an upcoming proportion of users who will be negatively impacted by an upcoming
root KSK rollover. root KSK rollover.
The mechanism described in this document satisfy the requirements of The mechanism described in this document satisfy the requirements of
both these use-cases. This mechanism is OPTIONAL to implement and both these use-cases. This mechanism is OPTIONAL to implement and
use. If implemented, this mechanism SHOULD be enabled by default to use. If implemented, this mechanism SHOULD be enabled by default to
facilitate Internet-wide measurement. Configuration options MAY be facilitate Internet-wide measurement. Configuration options MAY be
provided to disable the mechanism for reasons of local policy. provided to disable the mechanism for reasons of local policy.
The KSK sentinel tests described in this document use a test The KSK sentinel tests described in this document use a test
comprising of a set of DNS queries to domain names that have special comprising of a set of DNS queries to domain names that have special
values for the left-most label. The test relies on recursive values for the left-most label. The test relies on recursive
resolvers supporting a mechanism that recognises this special name resolvers supporting a mechanism that recognises this special name
pattern in queries, and under certain defined circumstances will pattern in queries, and under certain defined circumstances will
return a DNS SERVFAIL response code (RCODE 2), mimicking the response return a DNS SERVFAIL response code (RCODE 2), mimicking the response
code that is returned by security-aware resolvers when DNSSEC code that is returned by security-aware resolvers when DNSSEC
validation fails. validation fails.
If a browser or operating system is configured with multiple If a browser or operating system is configured with multiple
resolvers, and those resolvers have different properties (for resolvers, and those resolvers have different properties (for
example, one performs DNSSEC validation and one does not), the example, one performs DNSSEC validation and one does not), the
sentinel test described in this document can still be used, but it sentinel test described in this document can still be used. The
makes a number of assumptions about DNS resolution behaviour that may sentinel test makes a number of assumptions about DNS resolution
not necessarily hold in all environments. If these assumptions do behaviour that may not necessarily hold in all environments; if these
not hold (such as, for example, requiring the stub resolver to query assumptions do not hold (such as, for example, requiring the stub
the next recursive resolver in the locally configured set upon resolver to query the next recursive resolver in the locally
receipt of a SERVFAIL response code) then this test may produce configured set upon receipt of a SERVFAIL response code) then this
indeterminate or inconsistent results. In some cases where these test may produce indeterminate or inconsistent results. In some
assumptions do not hold, repeating the same test query set may cases where these assumptions do not hold, repeating the same test
generate different results. query set may generate different results.
Note that the measurements facilitated by the mechanism described in Note that the measurements facilitated by the mechanism described in
this document are different from those of [RFC8145]. RFC 8145 relies this document are different from those of [RFC8145]. RFC 8145 relies
on resolvers reporting towards the root servers a list of locally on resolvers reporting towards the root servers a list of locally
cached trust anchors for the root zone. Those reports can be used to cached trust anchors for the root zone. Those reports can be used to
infer how many resolvers may be impacted by a KSK roll, but not what infer how many resolvers may be impacted by a KSK roll, but not what
the user impact of the KSK roll will be. the user impact of the KSK roll will be.
1.1. Terminology 1.1. 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. "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.
This document contains a number of terms related to the DNS. The
current definitions of these terms can be found in [RFC7719].
2. Sentinel Mechanism in Resolvers 2. Sentinel Mechanism in Resolvers
DNSSEC-Validating resolvers that implement this mechanism MUST DNSSEC-Validating resolvers that implement this mechanism MUST
perform validation of responses in accordance with the DNSSEC perform validation of responses in accordance with the DNSSEC
response validation specification [RFC4035]. response validation specification [RFC4035].
This sentinel mechanism makes use of two special labels: This sentinel mechanism makes use of two special labels:
o root-key-sentinel-is-ta-<key-tag> o root-key-sentinel-is-ta-<key-tag>
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o root-key-sentinel-not-ta-<key-tag> o root-key-sentinel-not-ta-<key-tag>
These labels trigger special processing in the validating DNS These labels trigger special processing in the validating DNS
resolver when responses from authoritative servers are received. resolver when responses from authoritative servers are received.
Labels containing "root-key-sentinel-is-ta-<key-tag>" is used to Labels containing "root-key-sentinel-is-ta-<key-tag>" is used to
answer the question "Is this the Key Tag of a key which the answer the question "Is this the Key Tag of a key which the
validating DNS resolver is currently trusting as a trust anchor?" validating DNS resolver is currently trusting as a trust anchor?"
Labels containing "root-key-sentinel-not-ta-<key-tag>" is used to Labels containing "root-key-sentinel-not-ta-<key-tag>" is used to
answer the question "Is this the Key Tag of a key which the answer the question "Is this the Key Tag of a key which the
validating DNS resolver is *not* currently trusting as a trust validating DNS resolver is *not* currently trusting as a trust
anchor?" anchor?".
The special labels defined here came after extensive IETF evaluation
of alternative patterns and approaches in light of the desired
behaviour (sections 2.1, 2.2) within the resolver and the applied
testing methodology (section 4.3). As one example, underscore
prefixed names were rejected because a number of browsers / operating
systems would not fetch them, as they were not viewed as valid
"hostnames".Attention was paid to the consideration of local
collisions and the reservation of Left Hand Side (LHS) labels of a
domain name, and the impact upon zone operators who might desire to
use a similarly constructed hostname for a purpose other than as
documented here. Therefore, it is important to note that the
reservation of the labels in this manner is definitely not considered
"best practice".
2.1. Preconditions 2.1. Preconditions
All of the following conditions must be met to trigger special All of the following conditions must be met to trigger special
processing inside resolver code: processing inside resolver code:
o The DNS response is DNSSEC validated. o The DNS response is DNSSEC validated.
o The result of validation is "Secure". o The result of validation is "Secure".
o The Checking Disabled (CD) bit in the query is not set. o The EDNS(0) Checking Disabled (CD) bit in the query is not set.
o The QTYPE is either A or AAAA (Query Type value 1 or 28). o The QTYPE is either A or AAAA (Query Type value 1 or 28).
o The OPCODE is QUERY. o The OPCODE is QUERY.
o The leftmost label of the original QNAME (the name sent in the o The leftmost label of the original QNAME (the name sent in the
Question Section in the original query) is either "root-key- Question Section in the original query) is either "root-key-
sentinel-is-ta-<key-tag>" or "root-key-sentinel-not-ta-<key-tag>". sentinel-is-ta-<key-tag>" or "root-key-sentinel-not-ta-<key-tag>".
If any one of the preconditions is not met, the resolver MUST NOT If any one of the preconditions is not met, the resolver MUST NOT
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not-ta | return SERVFAIL | return original answer not-ta | return SERVFAIL | return original answer
Instruction "return SERVFAIL" means that the resolver MUST set Instruction "return SERVFAIL" means that the resolver MUST set
RCODE=SERVFAIL (value 2) and the ANSWER section of the DNS response RCODE=SERVFAIL (value 2) and the ANSWER section of the DNS response
MUST be empty, ignoring all other documents which specify content of MUST be empty, ignoring all other documents which specify content of
the ANSWER section. the ANSWER section.
Instruction "return original answer" means that the resolver MUST Instruction "return original answer" means that the resolver MUST
process the query without any further special processing; that is, process the query without any further special processing; that is,
exactly as if the mechanism described in this document was not exactly as if the mechanism described in this document was not
implemented or disabled. implemented or was disabled. The answer for the A or AAAA query is
sent on to the client.
3. Sentinel Tests for a Single DNS Resolver 3. Sentinel Tests for a Single DNS Resolver
This section describes the use of the sentinel detection mechanism This section describes the use of the sentinel detection mechanism
against a single DNS recursive resolver in order to determine whether against a single DNS recursive resolver in order to determine whether
this resolver is using a particular trust anchor to validate DNSSEC- this resolver is using a particular trust anchor to validate DNSSEC-
signed responses. signed responses.
Note that the test in this section applies to a single DNS resolver. Note that the test in this section applies to a single DNS resolver.
The test described in Section 4 applies instead to a collection of The test described in Section 4 applies instead to a collection of
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user environment. user environment.
The critical aspect of the DNS names used in this mechanism is that The critical aspect of the DNS names used in this mechanism is that
they contain the specified label for either the positive and negative they contain the specified label for either the positive and negative
test as the left-most label in the query name. test as the left-most label in the query name.
The sentinel detection procedure can test a DNS resolver using three The sentinel detection procedure can test a DNS resolver using three
queries: queries:
o A query name containing the left-most label "root-key-sentinel-is- o A query name containing the left-most label "root-key-sentinel-is-
ta-<key-tag>". This corresponds to a a validly-signed RRset in ta-<key-tag>". This corresponds to a a validly-signed label in
the zone, so that responses associated with queried names in this the parent zone, so that responses associated with this query name
zone can be authenticated by a DNSSEC-validating resolver. Any can be authenticated by a DNSSEC-validating resolver. Any
validly-signed DNS zone can be used for this test. validly-signed DNS zone can be used as the parent zone for this
test.
o A query name containing the left-most label "root-key-sentinel- o A query name containing the left-most label "root-key-sentinel-
not-ta-<key-tag>". This is also a validly-signed name. Any not-ta-<key-tag>". This is also a validly-signed label. Any
validly-signed DNS zone can be used for this test. validly-signed DNS zone can be used as the parent zone for this
test.
o A query name that is signed with a DNSSEC signature that cannot be o A query name that is signed with a DNSSEC signature that cannot be
validated (described as a "bogus" RRset in Section 5 of [RFC4033], validated (described as a "bogus" RRset in Section 5 of [RFC4033],
when, for example, an RRset is not signed with a valid RRSIG when, for example, an RRset associated with a label in a zoneis
record). not signed with a valid RRSIG record).
The responses received from queries to resolve each of these names The responses received from queries to resolve each of these query
can be evaluated to infer a trust key state of the DNS resolver. names can be evaluated to infer a trust key state of the DNS
resolver.
An essential assumption here is that this technique relies on An essential assumption here is that this technique relies on
security-aware (DNSSEC validating) resolvers responding with a security-aware (DNSSEC validating) resolvers responding with a
SERVFAIL response code to queries where DNSSEC checking is requested SERVFAIL response code to queries where DNSSEC checking is requested
and the response cannot be validated. Note that a slew of other and the response cannot be validated. Note that other issues can
issues can also cause SERVFAIL responses, and so the sentinel also cause a resolver to return SERVFAIL responses, and so the
processing may sometimes result in incorrect or indeterminate sentinel processing may sometimes result in incorrect or
conclusions. indeterminate conclusions.
To describe this process of classification, DNS resolvers are To describe this process of classification, DNS resolvers are
classified by five distinct behavior types using the labels: "Vnew", classified by five distinct behavior types using the labels: "Vnew",
"Vold", "Vind", "nonV", and "other". These labels correspond to "Vold", "Vind", "nonV", and "other". These labels correspond to
resolver system behaviour types as follows: resolver system behaviour types as follows:
Vnew: A DNS resolver that is configured to implement this mechanism Vnew: A DNS resolver that is configured to implement this mechanism
and has loaded the nominated key into their local trusted key and has loaded the nominated key into their local trusted key
stores will respond with an A or AAAA RRset response for the stores will respond with an A or AAAA RRset response for the
associated "root-key-sentinel-is-ta" queries, SERVFAIL for "root- associated "root-key-sentinel-is-ta" queries, SERVFAIL for "root-
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queries that return "bogus" validation status. queries that return "bogus" validation status.
Vind: A DNS resolver that has is not configured to implement this Vind: A DNS resolver that has is not configured to implement this
mechanism will respond with an A or AAAA RRset response for "root- mechanism will respond with an A or AAAA RRset response for "root-
key-sentinel-is-ta", an A or AAAA RRset response for "root-key- key-sentinel-is-ta", an A or AAAA RRset response for "root-key-
sentinel-not-ta" and SERVFAIL for the name that returns "bogus" sentinel-not-ta" and SERVFAIL for the name that returns "bogus"
validation status. This set of responses does not give any validation status. This set of responses does not give any
information about the trust anchors used by this resolver. information about the trust anchors used by this resolver.
nonV: A non-security-aware DNS resolver will respond with an A or nonV: A non-security-aware DNS resolver will respond with an A or
AAAA record response for "root-key-sentinel-is-ta", an A record AAAA RRset response for "root-key-sentinel-is-ta", an A or AAAA
response for "root-key-sentinel-not-ta" and an A or AAAA RRset RRset response for "root-key-sentinel-not-ta" and an A or AAAA
response for the name that returns "bogus" validation status. RRset response for the name that returns "bogus" validation
status.
other: There is the potential to admit other combinations of other: There is the potential to admit other combinations of
responses to these three queries. While this may appear self- responses to these three queries. While this may appear self-
contradictory, there are cases where such an outcome is possible. contradictory, there are cases where such an outcome is possible.
For example, in DNS resolver farms what appears to be a single DNS For example, in DNS resolver farms what appears to be a single DNS
resolver that responds to queries passed to a single IP address is resolver that responds to queries passed to a single IP address is
in fact constructed as a a collection of slave resolvers, and the in fact constructed as a a collection of slave resolvers, and the
query is passed to one of these internal resolver engines. If query is passed to one of these internal resolver engines. If
these individual slave resolvers in the farm do not behave these individual slave resolvers in the farm do not behave
identically, then other sets of results can be expected from these identically, then other sets of results can be expected from these
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If a client directs these three queries to a single resolver, the If a client directs these three queries to a single resolver, the
responses should allow the client to determine the capability of the responses should allow the client to determine the capability of the
resolver, and if it supports this sentinel mechanism, whether or not resolver, and if it supports this sentinel mechanism, whether or not
it has a particular key in its trust anchor store, as in the it has a particular key in its trust anchor store, as in the
following table: following table:
Query Query
+----------+-----------+------------+ +----------+-----------+------------+
| is-ta | not-ta | bogus | | is-ta | not-ta | bogus |
+-------+----------+-----------+------------+ +-------+----------+-----------+------------+
| Vnew | A | SERVFAIL | SERVFAIL | | Vnew | Y | SERVFAIL | SERVFAIL |
| Vold | SERVFAIL | A | SERVFAIL | | Vold | SERVFAIL | Y | SERVFAIL |
Type | Vind | A | A | SERVFAIL | Type | Vind | Y | Y | SERVFAIL |
| nonV | A | A | A | | nonV | Y | Y | Y |
| other | * | * | * | | other | * | * | * |
+-------+----------+-----------+------------+ +-------+----------+-----------+------------+
In this table the 'Y' response denotes an A or AAAA RRset response
(depending on the Query Type of A or AAAA records), 'SERVFAIL'
denotes a DNS SERVFAIL response code (RCODE 2), and '*' denotes
either response.
Vnew: The nominated key is trusted by the resolver. Vnew: The nominated key is trusted by the resolver.
Vold: The nominated key is not yet trusted by the resolver. Vold: The nominated key is not yet trusted by the resolver.
Vind: There is no information about the trust anchors of the Vind: There is no information about the trust anchors of the
resolver. resolver.
nonV: The resolver does not perform DNSSEC validation. nonV: The resolver does not perform DNSSEC validation.
other: The properties of the resolver cannot be analyzed by this other: The properties of the resolver cannot be analyzed by this
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3.1. Forwarders 3.1. Forwarders
Some resolvers are configured not to answer queries using the Some resolvers are configured not to answer queries using the
recursive algorithm first described in [RFC1034] section 4.3.2, but recursive algorithm first described in [RFC1034] section 4.3.2, but
instead relay queries to one or more other resolvers. Resolvers instead relay queries to one or more other resolvers. Resolvers
configured in this manner are referred to in this document as configured in this manner are referred to in this document as
"forwarders". "forwarders".
If the resolver is non-validating, and it has a single forwarder, If the resolver is non-validating, and it has a single forwarder,
then the resolver will presumably mirror the capabilities of the then the resolver will presumably mirror the capabilities of the
forwarder target resolver. forwarder's target resolver.
If the validating resolver has a forwarding configuration, and uses If the validating resolver has a forwarding configuration, and it
the CD bit on all forwarded queries, then this resolver is acting in sets the EDNS(0) Checking Disabled (CD) bit as described in
a manner that is identical to a standalone resolver. Section 3.2.2 of [RFC4035] on all forwarded queries, then this
resolver is acting in a manner that is identical to a standalone
resolver.
A more complex case is where all of the following conditions hold: A more complex case is where all of the following conditions hold:
o Both the validating resolver and the forwarder target resolver o Both the validating resolver and the forwarder target resolver
support this trusted key sentinel mechanism support this trusted key sentinel mechanism
o The local resolver's queries do not have the CD bit set o The local resolver's queries do not have the EDNS(0) CD bit set
o The trusted key state differs between the forwarding resolver and o The trusted key state differs between the forwarding resolver and
the forwarder target resolver the forwarder's target resolver
In such a case, either the outcome is indeterminate validating In such a case, either the outcome is indeterminate validating
("Vind"), or a case of mixed signals such as SERVFAIL in all three ("Vind"), or a case of mixed signals such as SERVFAIL in all three
responses, ("other") which is similarly an indeterminate response responses, ("other") which is similarly an indeterminate response
with respect to the trusted key state. with respect to the trusted key state.
4. Sentinel Tests from Hosts with More than One Configured Resolve 4. Sentinel Tests for Multiple Resolvers
The description in Section 3 describes a trust anchor test that can The description in Section 3 describes a trust anchor test that can
be used in the simple situation where the test queries were being be used in the simple situation where the test queries were being
passed to a single recursive resolver that directly queries passed to a single recursive resolver that directly queried
authoritative name servers. authoritative name servers.
However, the common end-user scenario is where a user's local DNS However, the common end-user scenario is where a user's local DNS
resolution environment is configured to use more than one recursive resolution environment is configured to use more than one recursive
resolver. The single resolver test technique will not function resolver. The single resolver test technique will not function
reliably in such cases, as a a SERVFAIL response from one resolver reliably in such cases, as a a SERVFAIL response from one resolver
may cause the local stub resolver to repeat the query against one of may cause the local stub resolver to repeat the query against one of
the other configured resolvers and the results may be inconclusive. the other configured resolvers and the results may be inconclusive.
In describing a test procedure that can be used in this environment In describing a test procedure that can be used in this environment
skipping to change at page 10, line 46 skipping to change at page 11, line 29
trust anchor cache. trust anchor cache.
There is no current published measurement data that indicates to what There is no current published measurement data that indicates to what
extent the first two assumptions listed here are valid, and how many extent the first two assumptions listed here are valid, and how many
end users may be impacted by these assumptions. In particular, the end users may be impacted by these assumptions. In particular, the
first assumption, that a consistent SERFAIL response will cause the first assumption, that a consistent SERFAIL response will cause the
local stub DNS resolution environment to query all of its configured local stub DNS resolution environment to query all of its configured
recursive resolvers before concluding that the name cannot be recursive resolvers before concluding that the name cannot be
resolved, is a very critical assumption for this test. resolved, is a very critical assumption for this test.
Note that additional precision / determinism may be achievable by
bypassing the normal OS behavior and explicitly testing using each
configured recursive resolver (e.g using 'dig').
4.3. Test Procedure 4.3. Test Procedure
The sentinel detection process tests a DNS resolution environment The sentinel detection process tests a DNS resolution environment
with three query names: with three query names. Note that these same general categories of
query as in Section 3 but the key tag used is different for some
queries:
o A query name that is signed with a DNSSEC signature that cannot be o A query name that is signed with a DNSSEC signature that cannot be
validated (described as a "bogus" RRset in Section 5 of [RFC4033], validated (described as a "bogus" RRset in Section 5 of [RFC4033],
when, for example, an RRset is not signed with a valid RRSIG when, for example, an RRset is not signed with a valid RRSIG
record). record).
o A query name containing the left-most label "root-key-sentinel- o A query name containing the left-most label "root-key-sentinel-
not-ta-<key-tag-of-KSK-current>". This name MUST be a validly- not-ta-<key-tag-of-KSK-current>". This name MUST be a validly-
signed. Any validly-signed DNS zone can be used for this test. signed name. Any validly-signed DNS zone can be used for this
test.
o A query name containing the left-most label "root-key-sentinel-is- o A query name containing the left-most label "root-key-sentinel-is-
ta-<key-tag-of-KSK-new>". This name MUST be a validly-signed. ta-<key-tag-of-KSK-new>". This name MUST be a validly-signed
Any validly-signed DNS zone can be used for this test. name. Any validly-signed DNS zone can be used for this test.
The responses received from queries to resolve each of these names The responses received from queries to resolve each of these names
can be evaluated to infer a trust key state of the user's DNS can be evaluated to infer a trust key state of the user's DNS
resolution environment. resolution environment.
The responses to these queries are described using a simplified The responses to these queries are described using a simplified
notation. Each query will either result in a SERFVAIL response notation. Each query will either result in a SERFVAIL response
(denoted as "S"), indicating that all of the resolvers in the (denoted as "S"), indicating that all of the resolvers in the
recursive resolver set returned the SERVFAIL response code, or result recursive resolver set returned the SERVFAIL response code, or result
in a response with the desire RRset value (denoted as "A"). The in a response with the desire RRset value (denoted as "A"). The
queries are ordered by the "invalid" name, the "not-ta" label, then queries are ordered by the "invalid" name, the "root-key-sentinel-
the "is-ta" label, and a triplet notation denotes a particular not-ta" label, then the "root-key-sentinel-is-ta" label, and a
response. For example, the triplet "(S S A)" denotes a SERVFAIL triplet notation denotes a particular response. For example, the
response to the invalid query, a SERVFAIL response to the "not-ta" triplet "(S S A)" denotes a SERVFAIL response to the invalid query, a
query and a RRset response to the "is-ta" query. SERVFAIL response to the "root-key-sentinel-not-ta" query and a RRset
response to the "root-key-sentinel-is-ta" query.
The set of all possible responses to these three queries are: The set of all possible responses to these three queries are:
(A * *): If any resolver returns an "A" response for the query for (A * *): If any resolver returns an "A" response for the query for
the invalid name, then the resolver set contains at least one non- the invalid name, then the resolver set contains at least one non-
validating DNS resolver, and the user will not be impacted by the validating DNS resolver, and the user will not be impacted by the
KSK roll. KSK roll.
(S A *): If any of the resolvers returns an "A" response the the (S A *): If any of the resolvers returns an "A" response the the
"not-ta" query, then at least one of the resolvers does not "root-key-sentinel-not-ta" query, then at least one of the
recognise the sentinel mechanism, and the behaviour of the resolvers does not recognise the sentinel mechanism, and the
collection of resolvers during the KSK roll cannot be reliably behaviour of the collection of resolvers during the KSK roll
determined. cannot be reliably determined.
(S S A): This case implies that all of the resolvers in the set (S S A): This case implies that all of the resolvers in the set
perform DNSSEC-validation, all of the resolvers are aware of the perform DNSSEC-validation, all of the resolvers are aware of the
sentinel mechanism, and at least one resolver has loaded KSK-new sentinel mechanism, and at least one resolver has loaded KSK-new
as a local trust anchor. The user will not be impacted by the KSK as a local trust anchor. The user will not be impacted by the KSK
roll. roll.
(S S S): This case implies that all of the resolvers in the set (S S S): This case implies that all of the resolvers in the set
perform DNSSEC-validation, all of the resolvers are aware of the perform DNSSEC-validation, all of the resolvers are aware of the
sentinel mechanism, and none of the resolvers has loaded KSK-new sentinel mechanism, and none of the resolvers has loaded KSK-new
skipping to change at page 14, line 18 skipping to change at page 15, line 9
Hardaker, Paul Hoffman, Matt Larson, Jinmei Tatuya, Edward Lewis, Hardaker, Paul Hoffman, Matt Larson, Jinmei Tatuya, Edward Lewis,
George Michaelson, Benno Overeinder, Matthew Pounsett, Hugo Salgado- George Michaelson, Benno Overeinder, Matthew Pounsett, Hugo Salgado-
Hernandez, Andreas Schulze, Mukund Sivaraman, Petr Spacek, Job Hernandez, Andreas Schulze, Mukund Sivaraman, Petr Spacek, Job
Snijders, Andrew Sullivan, Ondrej Sury, Paul Vixie, Duane Wessels and Snijders, Andrew Sullivan, Ondrej Sury, Paul Vixie, Duane Wessels and
Paul Wouters for their helpful feedback. Paul Wouters for their helpful feedback.
The authors would like to especially call out Paul Hoffman and Duane The authors would like to especially call out Paul Hoffman and Duane
Wessels for providing comments in the form of pull requests. Joe Wessels for providing comments in the form of pull requests. Joe
Abley also helpfully provided extensive review and OLD / NEW text. Abley also helpfully provided extensive review and OLD / NEW text.
Petr Spacek wrote some very early implmentations, and provided Petr Spacek wrote some very early implementations, and provided
significant feedback (including pointing out when the test bed didn't significant feedback (including pointing out when the test bed didn't
match the document!) match the document!)
10. Change Log 10. Change Log
RFC Editor: Please remove this section! RFC Editor: Please remove this section!
Note that this document is being worked on in GitHub - see Abstract. Note that this document is being worked on in GitHub - see Abstract.
The below is mainly large changes, and is not authoritative. The below is mainly large changes, and is not authoritative.
From -15 to -16:
o Addressed IESG comments
o Benjamin Kaduk's Discuss on draft-ietf-dnsop-kskroll-sentinel
o Also added Terry's "This a bad design pattern, but we decided the
benefits outweigh the costs this time." text.
o Suggestion from Adam to clarify that bypassing e.g gethostbyname()
can provide better testing.
o Nit: Forgot 'name' in 'This name MUST be a validly-signed name.'
o Clarified that 'bogus.example.com' is intentionally DNSSEC bogus /
invalid.
From -14 to -15: From -14 to -15:
o Addressed Joe Abley's thorough review, at: o Addressed Joe Abley's thorough review, at:
https://mailarchive.ietf.org/arch/msg/dnsop/8ZnN1xj55Yimet2cg- https://mailarchive.ietf.org/arch/msg/dnsop/8ZnN1xj55Yimet2cg-
LrdoJafEA LrdoJafEA
From -13 to -14: From -13 to -14:
o Addressed nits from Bob Harold - o Addressed nits from Bob Harold -
https://mailarchive.ietf.org/arch/msg/dnsop/ https://mailarchive.ietf.org/arch/msg/dnsop/
skipping to change at page 18, line 35 skipping to change at page 19, line 38
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,
<https://www.rfc-editor.org/info/rfc4035>. <https://www.rfc-editor.org/info/rfc4035>.
[RFC5011] StJohns, M., "Automated Updates of DNS Security (DNSSEC) [RFC5011] StJohns, M., "Automated Updates of DNS Security (DNSSEC)
Trust Anchors", STD 74, RFC 5011, DOI 10.17487/RFC5011, Trust Anchors", STD 74, RFC 5011, DOI 10.17487/RFC5011,
September 2007, <https://www.rfc-editor.org/info/rfc5011>. September 2007, <https://www.rfc-editor.org/info/rfc5011>.
11.2. Informative References 11.2. Informative References
[RFC7719] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
Terminology", RFC 7719, DOI 10.17487/RFC7719, December
2015, <https://www.rfc-editor.org/info/rfc7719>.
[RFC8145] Wessels, D., Kumari, W., and P. Hoffman, "Signaling Trust [RFC8145] Wessels, D., Kumari, W., and P. Hoffman, "Signaling Trust
Anchor Knowledge in DNS Security Extensions (DNSSEC)", Anchor Knowledge in DNS Security Extensions (DNSSEC)",
RFC 8145, DOI 10.17487/RFC8145, April 2017, RFC 8145, DOI 10.17487/RFC8145, April 2017,
<https://www.rfc-editor.org/info/rfc8145>. <https://www.rfc-editor.org/info/rfc8145>.
Appendix A. Protocol Walkthrough Example Appendix A. Protocol Walkthrough Example
This Appendix provides a non-normative example of how the sentinel This Appendix provides a non-normative example of how the sentinel
mechanism could be used, and what each participant does. It is mechanism could be used, and what each participant does. It is
provided in a conversational tone to be easier to follow. The provided in a conversational tone to be easier to follow. The
skipping to change at page 19, line 34 skipping to change at page 20, line 41
webserver (www.example.com). He adds three address records to webserver (www.example.com). He adds three address records to
example.com: example.com:
bogus.example.com. IN AAAA 2001:db8::1 bogus.example.com. IN AAAA 2001:db8::1
root-key-sentinel-is-ta-02323.example.com. IN AAAA 2001:db8::1 root-key-sentinel-is-ta-02323.example.com. IN AAAA 2001:db8::1
root-key-sentinel-not-ta-11112.example.com. IN AAAA 2001:db8::1 root-key-sentinel-not-ta-11112.example.com. IN AAAA 2001:db8::1
Note that the use of "example.com" names and the addresses here are Note that the use of "example.com" names and the addresses here are
examples. In a real deployment, the domain names need to be under examples, and 'bogus' intentionally has invalid DNSSEC signatures.
control of the researcher, and the addresses must be real, reachable In a real deployment, the domain names need to be under control of
addresses. the researcher, and the addresses must be real, reachable addresses.
Geoff then DNSSEC signs the example.com zone, and intentionally makes Geoff then DNSSEC signs the example.com zone, and intentionally makes
the bogus.example.com record have bogus validation status (for the bogus.example.com record have bogus validation status (for
example, by editing the signed zone and entering garbage for the example, by editing the signed zone and entering garbage for the
signature). Geoff also configures his webserver to listen on signature). Geoff also configures his webserver to listen on
2001:db8::1 and serve a resource (for example, a 1x1 GIF, 1x1.gif) 2001:db8::1 and serve a resource (for example, a 1x1 GIF, 1x1.gif)
for all of these names. The webserver also serves a webpage for all of these names. The webserver also serves a webpage
(www.example.com) which contains links to these 3 resources (www.example.com) which contains links to these 3 resources
(http://bogus.example.com/1x1.gif, http://root-key-sentinel-is-ta- (http://bogus.example.com/1x1.gif, http://root-key-sentinel-is-ta-
02323.example.com/1x1.gif, http://root-key-sentinel-not-ta- 02323.example.com/1x1.gif, http://root-key-sentinel-not-ta-
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