draft-ietf-dnsext-dnssec-bis-updates-20.txt   rfc6840.txt 
Network Working Group S. Weiler Internet Engineering Task Force (IETF) S. Weiler, Ed.
Internet-Draft SPARTA, Inc. Request for Comments: 6840 SPARTA, Inc.
Updates: 4033, 4034, 4035, 5155 D. Blacka Updates: 4033, 4034, 4035, 5155 D. Blacka, Ed.
(if approved) Verisign, Inc. Category: Standards Track Verisign, Inc.
Intended status: Standards Track September 28, 2012 ISSN: 2070-1721 February 2013
Expires: April 1, 2013
Clarifications and Implementation Notes for DNSSEC Clarifications and Implementation Notes for DNS Security (DNSSEC)
draft-ietf-dnsext-dnssec-bis-updates-20
Abstract Abstract
This document is a collection of technical clarifications to the This document is a collection of technical clarifications to the DNS
DNSSEC document set. It is meant to serve as a resource to Security (DNSSEC) document set. It is meant to serve as a resource
implementors as well as a repository of DNSSEC errata. to implementors as well as a collection of DNSSEC errata that existed
at the time of writing.
This document updates the core DNSSEC documents (RFC4033, RFC4034,
and RFC4035) as well as the NSEC3 specification (RFC5155). It also
defines NSEC3 and SHA-2 as core parts of the DNSSEC specification.
Status of this Memo This document updates the core DNSSEC documents (RFC 4033, RFC 4034,
and RFC 4035) as well as the NSEC3 specification (RFC 5155). It also
defines NSEC3 and SHA-2 (RFC 4509 and RFC 5702) as core parts of the
DNSSEC specification.
This Internet-Draft is submitted in full conformance with the Status of This Memo
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering This is an Internet Standards Track document.
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 5741.
This Internet-Draft will expire on April 1, 2013. 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/rfc6840.
Copyright Notice Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the Copyright (c) 2013 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
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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
skipping to change at page 3, line 7 skipping to change at page 3, line 7
modifications of such material outside the IETF Standards Process. modifications of such material outside the IETF Standards Process.
Without obtaining an adequate license from the person(s) controlling Without obtaining an adequate license from the person(s) controlling
the copyright in such materials, this document may not be modified the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other it for publication as an RFC or to translate it into languages other
than English. than English.
Table of Contents Table of Contents
1. Introduction and Terminology . . . . . . . . . . . . . . . . . 4 1. Introduction and Terminology ....................................4
1.1. Structure of this Document . . . . . . . . . . . . . . . . 4 1.1. Structure of This Document .................................4
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 1.2. Terminology ................................................4
2. Important Additions to DNSSEC . . . . . . . . . . . . . . . . 4 2. Important Additions to DNSSEC ...................................4
2.1. NSEC3 Support . . . . . . . . . . . . . . . . . . . . . . 4 2.1. NSEC3 Support ..............................................4
2.2. SHA-2 Support . . . . . . . . . . . . . . . . . . . . . . 5 2.2. SHA-2 Support ..............................................5
3. Scaling Concerns . . . . . . . . . . . . . . . . . . . . . . . 5 3. Scaling Concerns ................................................5
3.1. Implement a BAD cache . . . . . . . . . . . . . . . . . . 5 3.1. Implement a BAD Cache ......................................5
4. Security Concerns . . . . . . . . . . . . . . . . . . . . . . 5 4. Security Concerns ...............................................5
4.1. Clarifications on Non-Existence Proofs . . . . . . . . . . 5 4.1. Clarifications on Nonexistence Proofs ......................5
4.2. Validating Responses to an ANY Query . . . . . . . . . . . 6 4.2. Validating Responses to an ANY Query .......................6
4.3. Check for CNAME . . . . . . . . . . . . . . . . . . . . . 6 4.3. Check for CNAME ............................................6
4.4. Insecure Delegation Proofs . . . . . . . . . . . . . . . . 7 4.4. Insecure Delegation Proofs .................................7
5. Interoperability Concerns . . . . . . . . . . . . . . . . . . 7 5. Interoperability Concerns .......................................7
5.1. Errors in Canonical Form Type Code List . . . . . . . . . 7 5.1. Errors in Canonical Form Type Code List ....................7
5.2. Unknown DS Message Digest Algorithms . . . . . . . . . . . 7 5.2. Unknown DS Message Digest Algorithms .......................7
5.3. Private Algorithms . . . . . . . . . . . . . . . . . . . . 8 5.3. Private Algorithms .........................................8
5.4. Caution About Local Policy and Multiple RRSIGs . . . . . . 9 5.4. Caution about Local Policy and Multiple RRSIGs .............9
5.5. Key Tag Calculation . . . . . . . . . . . . . . . . . . . 9 5.5. Key Tag Calculation ........................................9
5.6. Setting the DO Bit on Replies . . . . . . . . . . . . . . 9 5.6. Setting the DO Bit on Replies ..............................9
5.7. Setting the AD Bit on Queries . . . . . . . . . . . . . . 9 5.7. Setting the AD Bit on Queries .............................10
5.8. Setting the AD Bit on Replies . . . . . . . . . . . . . . 10 5.8. Setting the AD Bit on Replies .............................10
5.9. Always set the CD bit on Queries . . . . . . . . . . . . . 10 5.9. Always Set the CD Bit on Queries ..........................10
5.10. Nested Trust Anchors . . . . . . . . . . . . . . . . . . . 10 5.10. Nested Trust Anchors .....................................11
5.11. Mandatory Algorithm Rules . . . . . . . . . . . . . . . . 11 5.11. Mandatory Algorithm Rules ................................11
5.12. Ignore Extra Signatures From Unknown Keys . . . . . . . . 12 5.12. Ignore Extra Signatures from Unknown Keys ................12
6. Minor Corrections and Clarifications . . . . . . . . . . . . . 12 6. Minor Corrections and Clarifications ...........................12
6.1. Finding Zone Cuts . . . . . . . . . . . . . . . . . . . . 12 6.1. Finding Zone Cuts .........................................12
6.2. Clarifications on DNSKEY Usage . . . . . . . . . . . . . . 12 6.2. Clarifications on DNSKEY Usage ............................12
6.3. Errors in Examples . . . . . . . . . . . . . . . . . . . . 13 6.3. Errors in Examples ........................................13
6.4. Errors in RFC 5155 . . . . . . . . . . . . . . . . . . . . 13 6.4. Errors in RFC 5155 ........................................13
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 7. Security Considerations ........................................13
8. Security Considerations . . . . . . . . . . . . . . . . . . . 13 8. References .....................................................14
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14 8.1. Normative References ......................................14
9.1. Normative References . . . . . . . . . . . . . . . . . . . 14 8.2. Informative References ....................................15
9.2. Informative References . . . . . . . . . . . . . . . . . . 15 Appendix A. Acknowledgments .......................................16
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 15 Appendix B. Discussion of Setting the CD Bit ......................16
Appendix B. Discussion of Setting the CD Bit . . . . . . . . . . 16 Appendix C. Discussion of Trust Anchor Preference Options .........19
Appendix C. Discussion of Trust Anchor Preference Options . . . . 19 C.1. Closest Encloser ..........................................19
C.1. Closest Encloser . . . . . . . . . . . . . . . . . . . . . 19 C.2. Accept Any Success ........................................20
C.2. Accept Any Success . . . . . . . . . . . . . . . . . . . . 20 C.3. Preference Based on Source ................................20
C.3. Preference Based on Source . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 21
1. Introduction and Terminology 1. Introduction and Terminology
This document lists some additions, clarifications and corrections to This document lists some additions, clarifications, and corrections
the core DNSSEC specification, as originally described in [RFC4033], to the core DNSSEC specification, as originally described in
[RFC4034], and [RFC4035], and later amended by [RFC5155]. (See [RFC4033], [RFC4034], and [RFC4035], and later amended by [RFC5155].
section Section 2 for more recent additions to that core document (See Section 2 for more recent additions to that core document set.)
set.)
It is intended to serve as a resource for implementors and as a It is intended to serve as a resource for implementors and as a
repository of items that need to be addressed when advancing the repository of items existing at the time of writing that need to be
DNSSEC documents along the Standards Track. addressed when advancing the DNSSEC documents along the Standards
Track.
1.1. Structure of this Document 1.1. Structure of This Document
The clarifications and changes to DNSSEC are sorted according to The clarifications and changes to DNSSEC are sorted according to
their importance, starting with ones which could, if ignored, lead to their importance, starting with ones which could, if ignored, lead to
security problems and progressing down to clarifications that are security problems and progressing down to clarifications that are
expected to have little operational impact. expected to have little operational impact.
1.2. Terminology 1.2. 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", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
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2.1. NSEC3 Support 2.1. NSEC3 Support
[RFC5155] describes the use and behavior of the NSEC3 and NSEC3PARAM [RFC5155] describes the use and behavior of the NSEC3 and NSEC3PARAM
records for hashed denial of existence. Validator implementations records for hashed denial of existence. Validator implementations
are strongly encouraged to include support for NSEC3 because a number are strongly encouraged to include support for NSEC3 because a number
of highly visible zones use it. Validators that do not support of highly visible zones use it. Validators that do not support
validation of responses using NSEC3 will be hampered in validating validation of responses using NSEC3 will be hampered in validating
large portions of the DNS space. large portions of the DNS space.
[RFC5155] is now considered part of the DNS Security Document Family [RFC5155] is now considered part of the DNS Security Document Family
as described by [RFC4033], Section 10. as described by Section 10 of [RFC4033].
Note that the algorithm identifiers defined in RFC5155 (DSA-NSEC3- Note that the algorithm identifiers defined in [RFC5155] (DSA-NSEC3-
SHA1 and RSASHA1-NSEC3-SHA1) and RFC5702 (RSASHA256 and RSASHA512) SHA1 and RSASHA1-NSEC3-SHA1) and [RFC5702] (RSASHA256 and RSASHA512)
signal that a zone might be using NSEC3, rather than NSEC. The zone signal that a zone might be using NSEC3, rather than NSEC. The zone
may be using either and validators supporting these algorithms MUST may be using either, and validators supporting these algorithms MUST
support both NSEC3 and NSEC responses. support both NSEC3 and NSEC responses.
2.2. SHA-2 Support 2.2. SHA-2 Support
[RFC4509] describes the use of SHA-256 as a digest algorithm in [RFC4509] describes the use of SHA-256 as a digest algorithm in
Delegation Signer (DS) RRs. [RFC5702] describes the use of the Delegation Signer (DS) RRs. [RFC5702] describes the use of the
RSASHA256 and RSASHA512 algorithms in DNSKEY and RRSIG RRs. RSASHA256 and RSASHA512 algorithms in DNSKEY and RRSIG RRs.
Validator implementations are strongly encouraged to include support Validator implementations are strongly encouraged to include support
for these algorithms for DS, DNSKEY, and RRSIG records. for these algorithms for DS, DNSKEY, and RRSIG records.
Both [RFC4509] and [RFC5702] are now considered part of the DNS Both [RFC4509] and [RFC5702] are now considered part of the DNS
Security Document Family as described by [RFC4033], Section 10. Security Document Family as described by Section 10 of [RFC4033].
3. Scaling Concerns 3. Scaling Concerns
3.1. Implement a BAD cache 3.1. Implement a BAD Cache
Section 4.7 of RFC4035 permits security-aware resolvers to implement Section 4.7 of [RFC4035] permits security-aware resolvers to
a BAD cache. That guidance has changed: security-aware resolvers implement a BAD cache. That guidance has changed: security-aware
SHOULD implement a BAD cache as described in RFC4035. resolvers SHOULD implement a BAD cache as described in [RFC4035].
This change in guidance is based on operational experience with This change in guidance is based on operational experience with
DNSSEC administrative errors leading to significant increases in DNS DNSSEC administrative errors leading to significant increases in DNS
traffic, with an accompanying realization that such events are more traffic, with an accompanying realization that such events are more
likely and more damaging than originally supposed. An example of one likely and more damaging than originally supposed. An example of one
such event is documented in "Roll Over and Die" [Huston]. such event is documented in "Rolling Over DNSSEC Keys" [Huston].
4. Security Concerns 4. Security Concerns
This section provides clarifications that, if overlooked, could lead This section provides clarifications that, if overlooked, could lead
to security issues. to security issues.
4.1. Clarifications on Non-Existence Proofs 4.1. Clarifications on Nonexistence Proofs
[RFC4035] Section 5.4 under-specifies the algorithm for checking non- Section 5.4 of [RFC4035] under-specifies the algorithm for checking
existence proofs. In particular, the algorithm as presented would nonexistence proofs. In particular, the algorithm as presented would
allow a validator to interpret an NSEC or NSEC3 RR from an ancestor allow a validator to interpret an NSEC or NSEC3 RR from an ancestor
zone as proving the non-existence of an RR in a child zone. zone as proving the nonexistence of an RR in a child zone.
An "ancestor delegation" NSEC RR (or NSEC3 RR) is one with: An "ancestor delegation" NSEC RR (or NSEC3 RR) is one with:
o the NS bit set, o the NS bit set,
o the SOA bit clear, and
o the Start of Authority (SOA) bit clear, and
o a signer field that is shorter than the owner name of the NSEC RR, o a signer field that is shorter than the owner name of the NSEC RR,
or the original owner name for the NSEC3 RR. or the original owner name for the NSEC3 RR.
Ancestor delegation NSEC or NSEC3 RRs MUST NOT be used to assume non- Ancestor delegation NSEC or NSEC3 RRs MUST NOT be used to assume
existence of any RRs below that zone cut, which include all RRs at nonexistence of any RRs below that zone cut, which include all RRs at
that (original) owner name other than DS RRs, and all RRs below that that (original) owner name other than DS RRs, and all RRs below that
owner name regardless of type. owner name regardless of type.
Similarly, the algorithm would also allow an NSEC RR at the same Similarly, the algorithm would also allow an NSEC RR at the same
owner name as a DNAME RR, or an NSEC3 RR at the same original owner owner name as a DNAME RR, or an NSEC3 RR at the same original owner
name as a DNAME, to prove the non-existence of names beneath that name as a DNAME, to prove the nonexistence of names beneath that
DNAME. An NSEC or NSEC3 RR with the DNAME bit set MUST NOT be used DNAME. An NSEC or NSEC3 RR with the DNAME bit set MUST NOT be used
to assume the non-existence of any subdomain of that NSEC/NSEC3 RR's to assume the nonexistence of any subdomain of that NSEC/NSEC3 RR's
(original) owner name. (original) owner name.
4.2. Validating Responses to an ANY Query 4.2. Validating Responses to an ANY Query
[RFC4035] does not address how to validate responses when QTYPE=*. [RFC4035] does not address how to validate responses when QTYPE=*.
As described in Section 6.2.2 of [RFC1034], a proper response to As described in Section 6.2.2 of [RFC1034], a proper response to
QTYPE=* may include a subset of the RRsets at a given name. That is, QTYPE=* may include a subset of the RRsets at a given name. That is,
it is not necessary to include all RRsets at the QNAME in the it is not necessary to include all RRsets at the QNAME in the
response. response.
When validating a response to QTYPE=*, all received RRsets that match When validating a response to QTYPE=*, all received RRsets that match
QNAME and QCLASS MUST be validated. If any of those RRsets fail QNAME and QCLASS MUST be validated. If any of those RRsets fail
validation, the answer is considered Bogus. If there are no RRsets validation, the answer is considered Bogus. If there are no RRsets
matching QNAME and QCLASS, that fact MUST be validated according to matching QNAME and QCLASS, that fact MUST be validated according to
the rules in [RFC4035] Section 5.4 (as clarified in this document). the rules in Section 5.4 of [RFC4035] (as clarified in this
To be clear, a validator must not expect to receive all records at document). To be clear, a validator must not expect to receive all
the QNAME in response to QTYPE=*. records at the QNAME in response to QTYPE=*.
4.3. Check for CNAME 4.3. Check for CNAME
Section 5 of [RFC4035] says nothing explicit about validating Section 5 of [RFC4035] says nothing explicit about validating
responses based on (or that should be based on) CNAMEs. When responses based on (or that should be based on) CNAMEs. When
validating a NOERROR/NODATA response, validators MUST check the CNAME validating a NOERROR/NODATA response, validators MUST check the CNAME
bit in the matching NSEC or NSEC3 RR's type bitmap in addition to the bit in the matching NSEC or NSEC3 RR's type bitmap in addition to the
bit for the query type. bit for the query type.
Without this check, an attacker could successfully transform a Without this check, an attacker could successfully transform a
positive CNAME response into a NOERROR/NODATA response by (e.g.) positive CNAME response into a NOERROR/NODATA response by (for
simply stripping the CNAME RRset from the response. A naive example) simply stripping the CNAME RRset from the response. A naive
validator would then note that the QTYPE was not present in the validator would then note that the QTYPE was not present in the
matching NSEC/NSEC3 RR, but fail to notice that the CNAME bit was matching NSEC/NSEC3 RR, but fail to notice that the CNAME bit was
set, and thus the response should have been a positive CNAME set; thus, the response should have been a positive CNAME response.
response.
4.4. Insecure Delegation Proofs 4.4. Insecure Delegation Proofs
[RFC4035] Section 5.2 specifies that a validator, when proving a Section 5.2 of [RFC4035] specifies that a validator, when proving a
delegation is not secure, needs to check for the absence of the DS delegation is not secure, needs to check for the absence of the DS
and SOA bits in the NSEC (or NSEC3) type bitmap. The validator also and SOA bits in the NSEC (or NSEC3) type bitmap. The validator also
MUST check for the presence of the NS bit in the matching NSEC (or MUST check for the presence of the NS bit in the matching NSEC (or
NSEC3) RR (proving that there is, indeed, a delegation), or NSEC3) RR (proving that there is, indeed, a delegation), or
alternately make sure that the delegation is covered by an NSEC3 RR alternately make sure that the delegation is covered by an NSEC3 RR
with the Opt-Out flag set. with the Opt-Out flag set.
Without this check, an attacker could reuse an NSEC or NSEC3 RR Without this check, an attacker could reuse an NSEC or NSEC3 RR
matching a non-delegation name to spoof an unsigned delegation at matching a non-delegation name to spoof an unsigned delegation at
that name. This would claim that an existing signed RRset (or set of that name. This would claim that an existing signed RRset (or set of
signed RRsets) is below an unsigned delegation, thus not signed and signed RRsets) is below an unsigned delegation, thus not signed and
vulnerable to further attack. vulnerable to further attack.
5. Interoperability Concerns 5. Interoperability Concerns
5.1. Errors in Canonical Form Type Code List 5.1. Errors in Canonical Form Type Code List
When canonicalizing DNS names (for both ordering and signing), DNS When canonicalizing DNS names (for both ordering and signing), DNS
names in the RDATA section of NSEC resource records are not names in the RDATA section of NSEC resource records are not converted
downcased. DNS names in the RDATA section of RRSIG resource records to lowercase. DNS names in the RDATA section of RRSIG resource
are downcased. records are converted to lowercase.
The guidance in the above paragraph differs from what has been The guidance in the above paragraph differs from what has been
published before but is consistent with current common practice. published before but is consistent with current common practice.
[RFC4034] Section 6.2 item 3 says that names in both of these RR Item 3 of Section 6.2 of [RFC4034] says that names in both of these
types should be downcased. The earlier [RFC3755] says that they RR types should be converted to lowercase. The earlier [RFC3755]
should not. Current practice follows neither document fully. says that they should not. Current practice follows neither document
fully.
Section 6.2 of RFC4034 also erroneously lists HINFO as a record that Section 6.2 of [RFC4034] also erroneously lists HINFO as a record
needs downcasing, and twice at that. Since HINFO records contain no that needs conversion to lowercase, and twice at that. Since HINFO
domain names, they are not subject to downcasing. records contain no domain names, they are not subject to case
conversion.
5.2. Unknown DS Message Digest Algorithms 5.2. Unknown DS Message Digest Algorithms
Section 5.2 of [RFC4035] includes rules for how to handle delegations Section 5.2 of [RFC4035] includes rules for how to handle delegations
to zones that are signed with entirely unsupported public key to zones that are signed with entirely unsupported public key
algorithms, as indicated by the key algorithms shown in those zone's algorithms, as indicated by the key algorithms shown in those zones'
DS RRsets. It does not explicitly address how to handle DS records DS RRsets. It does not explicitly address how to handle DS records
that use unsupported message digest algorithms. In brief, DS records that use unsupported message digest algorithms. In brief, DS records
using unknown or unsupported message digest algorithms MUST be using unknown or unsupported message digest algorithms MUST be
treated the same way as DS records referring to DNSKEY RRs of unknown treated the same way as DS records referring to DNSKEY RRs of unknown
or unsupported public key algorithms. or unsupported public key algorithms.
The existing text says: The existing text says:
If the validator does not support any of the algorithms listed in If the validator does not support any of the algorithms listed in
an authenticated DS RRset, then the resolver has no supported an authenticated DS RRset, then the resolver has no supported
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This document modifies the above text to additionally disregard This document modifies the above text to additionally disregard
authenticated DS records using unknown or unsupported message digest authenticated DS records using unknown or unsupported message digest
algorithms. algorithms.
5.3. Private Algorithms 5.3. Private Algorithms
As discussed above, Section 5.2 of [RFC4035] requires that validators As discussed above, Section 5.2 of [RFC4035] requires that validators
make decisions about the security status of zones based on the public make decisions about the security status of zones based on the public
key algorithms shown in the DS records for those zones. In the case key algorithms shown in the DS records for those zones. In the case
of private algorithms, as described in [RFC4034] Appendix A.1.1, the of private algorithms, as described in Appendix A.1.1 of [RFC4034],
eight-bit algorithm field in the DS RR is not conclusive about what the eight-bit algorithm field in the DS RR is not conclusive about
algorithm(s) is actually in use. what algorithm(s) is actually in use.
If no private algorithms appear in the DS RRset, or if any supported If no private algorithms appear in the DS RRset, or if any supported
algorithm appears in the DS RRset, no special processing is needed. algorithm appears in the DS RRset, no special processing is needed.
Furthermore, if the validator implementation does not support any Furthermore, if the validator implementation does not support any
private algorithms, or only supports private algorithms using an private algorithms, or only supports private algorithms using an
algorithm number not present in the DS RRset, no special processing algorithm number not present in the DS RRset, no special processing
is needed. is needed.
In the remaining cases, the security status of the zone depends on In the remaining cases, the security status of the zone depends on
whether or not the resolver supports any of the private algorithms in whether or not the resolver supports any of the private algorithms in
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determine the algorithm in use. The security-aware resolver MUST determine the algorithm in use. The security-aware resolver MUST
ensure that the hash of the DNSKEY RR's owner name and RDATA matches ensure that the hash of the DNSKEY RR's owner name and RDATA matches
the digest in the DS RR as described in Section 5.2 of [RFC4035], the digest in the DS RR as described in Section 5.2 of [RFC4035],
authenticating the DNSKEY. If all of the retrieved and authenticated authenticating the DNSKEY. If all of the retrieved and authenticated
DNSKEY RRs use unknown or unsupported private algorithms, then the DNSKEY RRs use unknown or unsupported private algorithms, then the
zone is treated as if it were unsigned. zone is treated as if it were unsigned.
Note that if none of the private algorithm DS RRs can be securely Note that if none of the private algorithm DS RRs can be securely
matched to DNSKEY RRs and no other DS establishes that the zone is matched to DNSKEY RRs and no other DS establishes that the zone is
secure, the referral should be considered Bogus data as discussed in secure, the referral should be considered Bogus data as discussed in
[RFC4035]. [RFC4035].
This clarification facilitates the broader use of private algorithms, This clarification facilitates the broader use of private algorithms,
as suggested by [RFC4955]. as suggested by [RFC4955].
5.4. Caution About Local Policy and Multiple RRSIGs 5.4. Caution about Local Policy and Multiple RRSIGs
When multiple RRSIGs cover a given RRset, [RFC4035] Section 5.3.3 When multiple RRSIGs cover a given RRset, Section 5.3.3 of [RFC4035]
suggests that "the local resolver security policy determines whether suggests that "the local resolver security policy determines whether
the resolver also has to test these RRSIG RRs and how to resolve the resolver also has to test these RRSIG RRs and how to resolve
conflicts if these RRSIG RRs lead to differing results." conflicts if these RRSIG RRs lead to differing results".
This document specifies that a resolver SHOULD accept any valid RRSIG This document specifies that a resolver SHOULD accept any valid RRSIG
as sufficient, and only determine that an RRset is Bogus if all as sufficient, and only determine that an RRset is Bogus if all
RRSIGs fail validation. RRSIGs fail validation.
If a resolver adopts a more restrictive policy, there's a danger that If a resolver adopts a more restrictive policy, there's a danger that
properly-signed data might unnecessarily fail validation due to cache properly signed data might unnecessarily fail validation due to cache
timing issues. Furthermore, certain zone management techniques, like timing issues. Furthermore, certain zone management techniques, like
the Double Signature Zone-signing Key Rollover method described in the Double Signature Zone Signing Key Rollover method described in
section 4.2.1.2 of [RFC4641], will not work reliably. Such a Section 4.2.1.2 of [RFC6781], will not work reliably. Such a
resolver is also vulnerable to malicious insertion of gibberish resolver is also vulnerable to malicious insertion of gibberish
signatures. signatures.
5.5. Key Tag Calculation 5.5. Key Tag Calculation
[RFC4034] Appendix B.1 incorrectly defines the Key Tag field Appendix B.1 of [RFC4034] incorrectly defines the Key Tag field
calculation for algorithm 1. It correctly says that the Key Tag is calculation for algorithm 1. It correctly says that the Key Tag is
the most significant 16 of the least significant 24 bits of the the most significant 16 of the least significant 24 bits of the
public key modulus. However, [RFC4034] then goes on to incorrectly public key modulus. However, [RFC4034] then goes on to incorrectly
say that this is 4th to last and 3rd to last octets of the public key say that this is fourth-to-last and third-to-last octets of the
modulus. It is, in fact, the 3rd to last and 2nd to last octets. public key modulus. It is, in fact, the third-to-last and second-to-
last octets.
5.6. Setting the DO Bit on Replies 5.6. Setting the DO Bit on Replies
As stated in Section 3 of [RFC3225], the DO bit of the query MUST be As stated in Section 3 of [RFC3225], the DNSSEC OK (DO) bit of the
copied in the response. However, in order to interoperate with query MUST be copied in the response. However, in order to
implementations that ignore this rule on sending, resolvers MUST interoperate with implementations that ignore this rule on sending,
ignore the DO bit in responses. resolvers MUST ignore the DO bit in responses.
5.7. Setting the AD Bit on Queries 5.7. Setting the AD Bit on Queries
The semantics of the AD bit in the query were previously undefined. The semantics of the Authentic Data (AD) bit in the query were
Section 4.6 of [RFC4035] instructed resolvers to always clear the AD previously undefined. Section 4.6 of [RFC4035] instructed resolvers
bit when composing queries. to always clear the AD bit when composing queries.
This document defines setting the AD bit in a query as a signal This document defines setting the AD bit in a query as a signal
indicating that the requester understands and is interested in the indicating that the requester understands and is interested in the
value of the AD bit in the response. This allows a requestor to value of the AD bit in the response. This allows a requester to
indicate that it understands the AD bit without also requesting indicate that it understands the AD bit without also requesting
DNSSEC data via the DO bit. DNSSEC data via the DO bit.
5.8. Setting the AD Bit on Replies 5.8. Setting the AD Bit on Replies
Section 3.2.3 of [RFC4035] describes under which conditions a Section 3.2.3 of [RFC4035] describes under which conditions a
validating resolver should set or clear the AD bit in a response. In validating resolver should set or clear the AD bit in a response. In
order to interoperate with legacy stub resolvers and middleboxes that order to interoperate with legacy stub resolvers and middleboxes that
neither understand nor ignore the AD bit, validating resolvers SHOULD neither understand nor ignore the AD bit, validating resolvers SHOULD
only set the AD bit when a response both meets the conditions listed only set the AD bit when a response both meets the conditions listed
in RFC 4035, section 3.2.3, and the request contained either a set DO in Section 3.2.3 of [RFC4035], and the request contained either a set
bit or a set AD bit. DO bit or a set AD bit.
5.9. Always set the CD bit on Queries 5.9. Always Set the CD Bit on Queries
When processing a request with the CD bit set, a resolver SHOULD When processing a request with the Checking Disabled (CD) bit set, a
attempt to return all response data, even data that has failed DNSSEC resolver SHOULD attempt to return all response data, even data that
validation. RFC4035 section 3.2.2 requires a resolver processing a has failed DNSSEC validation. Section 3.2.2 of [RFC4035] requires a
request with the CD bit set to set the CD bit on its upstream resolver processing a request with the CD bit set to set the CD bit
queries. on its upstream queries.
This document further specifies that validating resolvers SHOULD set This document further specifies that validating resolvers SHOULD set
the CD bit on every upstream query. This is regardless of whether the CD bit on every upstream query. This is regardless of whether
the CD bit was set on the incoming query or whether it has a trust the CD bit was set on the incoming query or whether it has a trust
anchor at or above the QNAME. anchor at or above the QNAME.
[RFC4035] is ambiguous about what to do when a cached response was [RFC4035] is ambiguous about what to do when a cached response was
obtained with the CD bit unset, a case that only arises when the obtained with the CD bit unset, a case that only arises when the
resolver chooses not to set the CD bit on all upstream queries, as resolver chooses not to set the CD bit on all upstream queries, as
specified above. In the typical case, no new query is required, nor specified above. In the typical case, no new query is required, nor
skipping to change at page 11, line 25 skipping to change at page 11, line 33
The "Accept Any Success" policy is to try all applicable trust The "Accept Any Success" policy is to try all applicable trust
anchors until one gives a validation result of Secure, in which case anchors until one gives a validation result of Secure, in which case
the final validation result is Secure. If and only if all applicable the final validation result is Secure. If and only if all applicable
trust anchors give a result of Insecure, the final validation result trust anchors give a result of Insecure, the final validation result
is Insecure. If one or more trust anchors lead to a Bogus result and is Insecure. If one or more trust anchors lead to a Bogus result and
there is no Secure result, then the final validation result is Bogus. there is no Secure result, then the final validation result is Bogus.
5.11. Mandatory Algorithm Rules 5.11. Mandatory Algorithm Rules
The last paragraph of RFC4035 Section 2.2 includes rules describing The last paragraph of Section 2.2 of [RFC4035] includes rules
which algorithms must be used to sign a zone. Since these rules have describing which algorithms must be used to sign a zone. Since these
been confusing, they are restated using different language here: rules have been confusing, they are restated using different language
here:
The DS RRset and DNSKEY RRset are used to signal which algorithms The DS RRset and DNSKEY RRset are used to signal which algorithms
are used to sign a zone. The presence of an algorithm in either a are used to sign a zone. The presence of an algorithm in either a
zone's DS or DNSKEY RRset signals that that algorithm is used to zone's DS or DNSKEY RRset signals that that algorithm is used to
sign the entire zone. sign the entire zone.
A signed zone MUST include a DNSKEY for each algorithm present in A signed zone MUST include a DNSKEY for each algorithm present in
the zone's DS RRset and expected trust anchors for the zone. The the zone's DS RRset and expected trust anchors for the zone. The
zone MUST also be signed with each algorithm (though not each key) zone MUST also be signed with each algorithm (though not each key)
present in the DNSKEY RRset. It is possible to add algorithms at present in the DNSKEY RRset. It is possible to add algorithms at
the DNSKEY that aren't in the DS record, but not vice-versa. If the DNSKEY that aren't in the DS record, but not vice versa. If
more than one key of the same algorithm is in the DNSKEY RRset, it more than one key of the same algorithm is in the DNSKEY RRset, it
is sufficient to sign each RRset with any subset of these DNSKEYs. is sufficient to sign each RRset with any subset of these DNSKEYs.
It is acceptable to sign some RRsets with one subset of keys (or It is acceptable to sign some RRsets with one subset of keys (or
key) and other RRsets with a different subset, so long as at least key) and other RRsets with a different subset, so long as at least
one DNSKEY of each algorithm is used to sign each RRset. one DNSKEY of each algorithm is used to sign each RRset.
Likewise, if there are DS records for multiple keys of the same Likewise, if there are DS records for multiple keys of the same
algorithm, any subset of those may appear in the DNSKEY RRset. algorithm, any subset of those may appear in the DNSKEY RRset.
This requirement applies to servers, not validators. Validators This requirement applies to servers, not validators. Validators
SHOULD accept any single valid path. They SHOULD NOT insist that all SHOULD accept any single valid path. They SHOULD NOT insist that all
algorithms signaled in the DS RRset work, and they MUST NOT insist algorithms signaled in the DS RRset work, and they MUST NOT insist
that all algorithms signaled in the DNSKEY RRset work. A validator that all algorithms signaled in the DNSKEY RRset work. A validator
MAY have a configuration option to perform a signature completeness MAY have a configuration option to perform a signature completeness
test to support troubleshooting. test to support troubleshooting.
5.12. Ignore Extra Signatures From Unknown Keys 5.12. Ignore Extra Signatures from Unknown Keys
Validating resolvers MUST disregard RRSIGs in a zone that do not Validating resolvers MUST disregard RRSIGs in a zone that do not
(currently) have a corresponding DNSKEY in the zone. Similarly, a (currently) have a corresponding DNSKEY in the zone. Similarly, a
validating resolver MUST disregard RRSIGs with algorithm types that validating resolver MUST disregard RRSIGs with algorithm types that
don't exist in the DNSKEY RRset. don't exist in the DNSKEY RRset.
Good key rollover and algorithm rollover practices, as discussed in Good key rollover and algorithm rollover practices, as discussed in
RFC4641 and its successor documents and as suggested by the rules in RFC 6781 and its successor documents and as suggested by the rules in
the previous section, may require that such RRSIGs be present in a the previous section, may require that such RRSIGs be present in a
zone. zone.
6. Minor Corrections and Clarifications 6. Minor Corrections and Clarifications
6.1. Finding Zone Cuts 6.1. Finding Zone Cuts
Appendix C.8 of [RFC4035] discusses sending DS queries to the servers Appendix C.8 of [RFC4035] discusses sending DS queries to the servers
for a parent zone but does not state how to find those servers. for a parent zone but does not state how to find those servers.
Specific instructions can be found in Section 4.2 of [RFC4035]. Specific instructions can be found in Section 4.2 of [RFC4035].
skipping to change at page 12, line 42 skipping to change at page 12, line 51
above rules. However, be aware that there is no way to tell above rules. However, be aware that there is no way to tell
resolvers what a particular DNSKEY is supposed to be used for -- any resolvers what a particular DNSKEY is supposed to be used for -- any
DNSKEY in the zone's signed DNSKEY RRset may be used to authenticate DNSKEY in the zone's signed DNSKEY RRset may be used to authenticate
any RRset in the zone. For example, if a weaker or less trusted any RRset in the zone. For example, if a weaker or less trusted
DNSKEY is being used to authenticate NSEC RRsets or all dynamically DNSKEY is being used to authenticate NSEC RRsets or all dynamically
updated records, that same DNSKEY can also be used to sign any other updated records, that same DNSKEY can also be used to sign any other
RRsets from the zone. RRsets from the zone.
Furthermore, note that the SEP bit setting has no effect on how a Furthermore, note that the SEP bit setting has no effect on how a
DNSKEY may be used -- the validation process is specifically DNSKEY may be used -- the validation process is specifically
prohibited from using that bit by [RFC4034] section 2.1.2. It is prohibited from using that bit by Section 2.1.2 of [RFC4034]. It is
possible to use a DNSKEY without the SEP bit set as the sole secure possible to use a DNSKEY without the SEP bit set as the sole secure
entry point to the zone, yet use a DNSKEY with the SEP bit set to entry point to the zone, yet use a DNSKEY with the SEP bit set to
sign all RRsets in the zone (other than the DNSKEY RRset). It is sign all RRsets in the zone (other than the DNSKEY RRset). It is
also possible to use a single DNSKEY, with or without the SEP bit also possible to use a single DNSKEY, with or without the SEP bit
set, to sign the entire zone, including the DNSKEY RRset itself. set, to sign the entire zone, including the DNSKEY RRset itself.
6.3. Errors in Examples 6.3. Errors in Examples
The text in [RFC4035] Section C.1 refers to the examples in B.1 as The text in Appendix C.1 of [RFC4035] refers to the examples in
"x.w.example.com" while B.1 uses "x.w.example". This is painfully Appendix B.1 as "x.w.example.com" while B.1 uses "x.w.example". This
obvious in the second paragraph where it states that the RRSIG labels is painfully obvious in the second paragraph where it states that the
field value of 3 indicates that the answer was not the result of RRSIG labels field value of 3 indicates that the answer was not the
wildcard expansion. This is true for "x.w.example" but not for result of wildcard expansion. This is true for "x.w.example" but not
"x.w.example.com", which of course has a label count of 4 for "x.w.example.com", which of course has a label count of 4
(antithetically, a label count of 3 would imply the answer was the (antithetically, a label count of 3 would imply the answer was the
result of a wildcard expansion). result of a wildcard expansion).
The first paragraph of [RFC4035] Section C.6 also has a minor error: The first paragraph of Appendix C.6 of [RFC4035] also has a minor
the reference to "a.z.w.w.example" should instead be "a.z.w.example", error: the reference to "a.z.w.w.example" should instead be
as in the previous line. "a.z.w.example", as in the previous line.
6.4. Errors in RFC 5155 6.4. Errors in RFC 5155
A NSEC3 record that matches an Empty Non-Terminal effectively has no An NSEC3 record that matches an Empty Non-Terminal effectively has no
type associated with it. This NSEC3 record has an empty type bit type associated with it. This NSEC3 record has an empty type bit
map. Section 3.2.1 of [RFC5155] contains the statement: map. Section 3.2.1 of [RFC5155] contains the statement:
Blocks with no types present MUST NOT be included. Blocks with no types present MUST NOT be included.
However, the same section contains a regular expression: However, the same section contains a regular expression:
Type Bit Maps Field = ( Window Block # | Bitmap Length | Bitmap )+ Type Bit Maps Field = ( Window Block # | Bitmap Length | Bitmap )+
The plus sign in the regular expression indicates that there is one The plus sign in the regular expression indicates that there is one
or more of the preceding element. This means that there must be at or more of the preceding element. This means that there must be at
least one window block. If this window block has no types, it least one window block. If this window block has no types, it
contradicts with the first statement. Therefore, the correct text in contradicts with the first statement. Therefore, the correct text in
RFC 5155 3.2.1 should be: Section 3.2.1 of [RFC5155] should be:
Type Bit Maps Field = ( Window Block # | Bitmap Length | Bitmap )* Type Bit Maps Field = ( Window Block # | Bitmap Length | Bitmap )*
7. IANA Considerations 7. Security Considerations
This document specifies no IANA Actions.
8. Security Considerations
This document adds SHA-2 and NSEC3 support to the core DNSSEC This document adds SHA-2 and NSEC3 support to the core DNSSEC
protocol. Security considerations for those features are discussed protocol. Security considerations for those features are discussed
in the documents defining them. Additionally, this document in the documents defining them. Additionally, this document
addresses some ambiguities and omissions in the core DNSSEC documents addresses some ambiguities and omissions in the core DNSSEC documents
that, if not recognized and addressed in implementations, could lead that, if not recognized and addressed in implementations, could lead
to security failures. In particular, the validation algorithm to security failures. In particular, the validation algorithm
clarifications in Section 4 are critical for preserving the security clarifications in Section 4 are critical for preserving the security
properties DNSSEC offers. Furthermore, failure to address some of properties DNSSEC offers. Furthermore, failure to address some of
the interoperability concerns in Section 5 could limit the ability to the interoperability concerns in Section 5 could limit the ability to
later change or expand DNSSEC, including adding new algorithms. later change or expand DNSSEC, including adding new algorithms.
The recommendation in Section 5.9 to always set the CD bit has The recommendation in Section 5.9 to always set the CD bit has
security implications. By setting the CD bit, a resolver will not security implications. By setting the CD bit, a resolver will not
benefit from more stringent validation rules or a more complete set benefit from more stringent validation rules or a more complete set
of trust anchors at an upstream validator. of trust anchors at an upstream validator.
9. References 8. References
9.1. Normative References 8.1. Normative References
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities", [RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, November 1987. STD 13, RFC 1034, November 1987.
[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, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3225] Conrad, D., "Indicating Resolver Support of DNSSEC", [RFC3225] Conrad, D., "Indicating Resolver Support of DNSSEC",
RFC 3225, December 2001. RFC 3225, December 2001.
skipping to change at page 15, line 5 skipping to change at page 15, line 5
(DS) Resource Records (RRs)", RFC 4509, May 2006. (DS) Resource Records (RRs)", RFC 4509, May 2006.
[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, March 2008. Existence", RFC 5155, March 2008.
[RFC5702] Jansen, J., "Use of SHA-2 Algorithms with RSA in DNSKEY [RFC5702] Jansen, J., "Use of SHA-2 Algorithms with RSA in DNSKEY
and RRSIG Resource Records for DNSSEC", RFC 5702, and RRSIG Resource Records for DNSSEC", RFC 5702,
October 2009. October 2009.
9.2. Informative References 8.2. Informative References
[Huston] Michaelson, G., Wallstrom, P., Arends, R., and G. Huston, [Huston] Michaelson, G., Wallstrom, P., Arends, R., and G. Huston,
"Roll Over and Die?", February 2010. "Rolling Over DNSSEC Keys", Internet Protocol
Journal, Vol. 13, No.1, pp. 2-16, March 2010.
[RFC2308] Andrews, M., "Negative Caching of DNS Queries (DNS [RFC2308] Andrews, M., "Negative Caching of DNS Queries (DNS
NCACHE)", RFC 2308, March 1998. NCACHE)", RFC 2308, March 1998.
[RFC3755] Weiler, S., "Legacy Resolver Compatibility for Delegation [RFC3755] Weiler, S., "Legacy Resolver Compatibility for Delegation
Signer (DS)", RFC 3755, May 2004. Signer (DS)", RFC 3755, May 2004.
[RFC4641] Kolkman, O. and R. Gieben, "DNSSEC Operational Practices",
RFC 4641, September 2006.
[RFC4955] Blacka, D., "DNS Security (DNSSEC) Experiments", RFC 4955, [RFC4955] Blacka, D., "DNS Security (DNSSEC) Experiments", RFC 4955,
July 2007. July 2007.
[RFC5011] StJohns, M., "Automated Updates of DNS Security (DNSSEC) [RFC5011] StJohns, M., "Automated Updates of DNS Security (DNSSEC)
Trust Anchors", RFC 5011, September 2007. Trust Anchors", STD 74, RFC 5011, September 2007.
[RFC5074] Weiler, S., "DNSSEC Lookaside Validation (DLV)", RFC 5074, [RFC5074] Weiler, S., "DNSSEC Lookaside Validation (DLV)", RFC 5074,
November 2007. November 2007.
[RFC6781] Kolkman, O., Mekking, W., and R. Gieben, "DNSSEC
Operational Practices, Version 2", RFC 6781,
December 2012.
Appendix A. Acknowledgments Appendix A. Acknowledgments
The editors would like the thank Rob Austein for his previous work as The editors would like the thank Rob Austein for his previous work as
an editor of this document. an editor of this document.
The editors are extremely grateful to those who, in addition to The editors are extremely grateful to those who, in addition to
finding errors and omissions in the DNSSEC document set, have finding errors and omissions in the DNSSEC document set, have
provided text suitable for inclusion in this document. provided text suitable for inclusion in this document.
The lack of specificity about handling private algorithms, as The lack of specificity about handling private algorithms, as
skipping to change at page 16, line 26 skipping to change at page 16, line 50
document. document.
Appendix B. Discussion of Setting the CD Bit Appendix B. Discussion of Setting the CD Bit
[RFC4035] may be read as relying on the implicit assumption that [RFC4035] may be read as relying on the implicit assumption that
there is at most one validating system between the stub resolver and there is at most one validating system between the stub resolver and
the authoritative server for a given zone. It is entirely possible, the authoritative server for a given zone. It is entirely possible,
however, for more than one validator to exist between a stub resolver however, for more than one validator to exist between a stub resolver
and an authoritative server. If these different validators have and an authoritative server. If these different validators have
disjoint trust anchors configured, then it is possible that each disjoint trust anchors configured, then it is possible that each
would be able to validate some portion of the DNS tree but neither is would be able to validate some portion of the DNS tree, but neither
able to validate all of it. Accordingly, it might be argued that it is able to validate all of it. Accordingly, it might be argued that
is desirable not to set the CD bit on upstream queries, because that it is desirable not to set the CD bit on upstream queries, because
allows for maximal validation. that allows for maximal validation.
In section Section 5.9 of this document, it is recommended to set the In Section 5.9 of this document, it is recommended to set the CD bit
CD bit on an upstream query even when the incoming query arrives with on an upstream query even when the incoming query arrives with CD=0.
CD=0. This is for two reasons: it encourages a more predictable This is for two reasons: it encourages a more predictable validation
validation experience as only one validator is always doing the experience as only one validator is always doing the validation, and
validation, and it ensures that all DNSSEC data that exists may be it ensures that all DNSSEC data that exists may be available from the
available from the local cache should a query with CD=1 arrive. local cache should a query with CD=1 arrive.
As a matter of policy, it is possible to set the CD bit differently As a matter of policy, it is possible to set the CD bit differently
than suggested in Section 5.9. A different choice will, of course, than suggested in Section 5.9. A different choice will, of course,
not always yield the benefits listed above. It is beyond the scope not always yield the benefits listed above. It is beyond the scope
of this document to outline all of the considerations and counter of this document to outline all of the considerations and counter
considerations for all possible policies. Nevertheless, it is considerations for all possible policies. Nevertheless, it is
possible to describe three approaches and their underlying philosophy possible to describe three approaches and their underlying philosophy
of operation. These are laid out in the tables below. of operation. These are laid out in the tables below.
The table that describes each model has five columns. The first The table that describes each model has five columns. The first
column indicates the value of the CD bit that the resolver receives column indicates the value of the CD bit that the resolver receives
(for instance, on the name server side in an iterative resolver, or (for instance, on the name server side in an iterative resolver, or
as local policy or from the API in the case of a stub). The second as local policy or from the API in the case of a stub). The second
column indicates whether the query needs to be forwarded for column indicates whether the query needs to be forwarded for
resolution (F) or can be satisfied from a local cache (C). The third resolution (F) or can be satisfied from a local cache (C). The third
column is a line number, so that it can be referred to later in the column is a line number, so that it can be referred to later in the
table. The fourth column indicates any relevant conditions at the table. The fourth column indicates any relevant conditions at the
resolver: whether the resolver has a covering trust anchor and so on. resolver, for example, whether the resolver has a covering trust
If there are no parameters here, the column is empty. The fifth and anchor, and so on. If there are no parameters here, the column is
final column indicates what action the resolver takes. empty. The fifth and final column indicates what action the resolver
takes.
The tables differentiate between "cached data" and "cached RCODE=2". The tables differentiate between "cached data" and "cached RCODE=2".
This is a shorthand; the point is that one has to treat RCODE=2 This is a shorthand; the point is that one has to treat RCODE=2
(server failure) as special, because it might indicate a validation (server failure) as special, because it might indicate a validation
failure somewhere upstream. The distinction is really between failure somewhere upstream. The distinction is really between
"cached RCODE=2" and "cached everything else". "cached RCODE=2" and "cached everything else".
The tables are probably easiest to think of in terms of describing The tables are probably easiest to think of in terms of describing
what happens when a stub resolver sends a query to an intermediate what happens when a stub resolver sends a query to an intermediate
resolver, but they are perfectly general and can be applied to any resolver, but they are perfectly general and can be applied to any
skipping to change at page 17, line 40 skipping to change at page 18, line 18
CD F/C line conditions action CD F/C line conditions action
==================================================================== ====================================================================
1 F A1 Set CD=1 on upstream query 1 F A1 Set CD=1 on upstream query
0 F A2 Set CD=1 on upstream query 0 F A2 Set CD=1 on upstream query
1 C A3 Return the cache contents 1 C A3 Return the cache contents
(data or RCODE=2) (data or RCODE=2)
0 C A4 no covering TA Return cache contents 0 C A4 no covering TA Return cache contents
(data or RCODE=2) (data or RCODE=2)
0 C A5 covering TA Validate cached result and 0 C A5 covering TA Validate cached result and
return it. return it
Model 2: "never set when receiving CD=0" Model 2: "never set when receiving CD=0"
This model is so named because it sets CD=0 on upstream queries for This model is so named because it sets CD=0 on upstream queries for
all received CD=0 queries even if it has a covering trust anchor. all received CD=0 queries, even if it has a covering trust anchor.
The general philosophy represented by this table is that more than The general philosophy represented by this table is that more than
one resolver may take responsibility for validating a QNAME and that one resolver may take responsibility for validating a QNAME and that
a validation failure for a QNAME by any resolver in the chain is a a validation failure for a QNAME by any resolver in the chain is a
validation failure for the query. Using this model is NOT validation failure for the query. Using this model is NOT
RECOMMENDED. RECOMMENDED.
CD F/C line conditions action CD F/C line conditions action
==================================================================== ====================================================================
1 F N1 Set CD=1 on upstream query 1 F N1 Set CD=1 on upstream query
0 F N2 Set CD=0 on upstream query 0 F N2 Set CD=0 on upstream query
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0 C N6 covering TA & Treat as line N2 0 C N6 covering TA & Treat as line N2
cached data was cached data was
generated with CD=1 generated with CD=1
0 C N7 covering TA & Validate and return 0 C N7 covering TA & Validate and return
cached data was cached data was
generated with CD=0 generated with CD=0
Model 3: "sometimes set" Model 3: "sometimes set"
This model is so named because it sets the CD bit on upstream queries This model is so named because it sets the CD bit on upstream queries
triggered by received CD=0 queries based on whether the validator has triggered by received CD=0 queries, based on whether the validator
a trust anchor configured that covers the query. If there is no has a trust anchor configured that covers the query. If there is no
covering trust anchor, the resolver clears the CD bit in the upstream covering trust anchor, the resolver clears the CD bit in the upstream
query. If there is a covering trust anchor, the resolver sets CD=1 query. If there is a covering trust anchor, the resolver sets CD=1
and performs validation itself. The general philosophy represented and performs validation itself. The general philosophy represented
by this table is that a resolver should try and validate QNAMEs for by this table is that a resolver should try and validate QNAMEs for
which is has trust anchors and should not preclude validation by which it has trust anchors and should not preclude validation by
other resolvers for QNAMEs for which it does not have covering trust other resolvers for QNAMEs for which it does not have covering trust
anchors. Using this model is NOT RECOMMENDED. anchors. Using this model is NOT RECOMMENDED.
CD F/C line conditions action CD F/C line conditions action
==================================================================== ====================================================================
1 F S1 Set CD=1 on upstream query 1 F S1 Set CD=1 on upstream query
0 F S2 covering TA Set CD=1 on upstream query 0 F S2 covering TA Set CD=1 on upstream query
0 F S3 no covering TA Set CD=0 on upstream query 0 F S3 no covering TA Set CD=0 on upstream query
1 C S4 cached data Return cached data 1 C S4 cached data Return cached data
1 C S5 cached RCODE=2 Treat as line S1 1 C S5 cached RCODE=2 Treat as line S1
skipping to change at page 20, line 17 skipping to change at page 20, line 12
override a parent zone's trust anchor with one that the operator can override a parent zone's trust anchor with one that the operator can
validate in a stronger way, perhaps because the resolver operator is validate in a stronger way, perhaps because the resolver operator is
affiliated with the zone in question. This policy also minimizes the affiliated with the zone in question. This policy also minimizes the
number of public key operations needed, which is of benefit in number of public key operations needed, which is of benefit in
resource-constrained environments. resource-constrained environments.
This policy has the disadvantage of giving the user some unexpected This policy has the disadvantage of giving the user some unexpected
and unnecessary validation failures when sub-zone trust anchors are and unnecessary validation failures when sub-zone trust anchors are
neglected. As a concrete example, consider a validator that neglected. As a concrete example, consider a validator that
configured a trust anchor for "zone.example." in 2009 and one for configured a trust anchor for "zone.example." in 2009 and one for
"example." in 2011. In 2012, "zone.example." rolls its KSK and "example." in 2011. In 2012, "zone.example." rolls its Key Signing
updates its DS records, but the validator operator doesn't update its Key (KSK) and updates its DS records, but the validator operator
trust anchor. With the "closest encloser" policy, the validator gets doesn't update its trust anchor. With the "Closest Encloser" policy,
validation failures. the validator gets validation failures.
C.2. Accept Any Success C.2. Accept Any Success
Another policy is to try all applicable trust anchors until one gives Another policy is to try all applicable trust anchors until one gives
a validation result of Secure, in which case the final validation a validation result of Secure, in which case the final validation
result is Secure. If and only if all applicable trust anchors give a result is Secure. If and only if all applicable trust anchors give a
result of Insecure, the final validation result is Insecure. If one result of Insecure, the final validation result is Insecure. If one
or more trust anchors lead to a Bogus result and there is no Secure or more trust anchors lead to a Bogus result and there is no Secure
result, then the final validation result is Bogus. result, then the final validation result is Bogus.
This has the advantage of causing the fewest validation failures, This has the advantage of causing the fewest validation failures,
which may deliver a better user experience. If one trust anchor is which may deliver a better user experience. If one trust anchor is
out of date (as in our above example), the user may still be able to out of date (as in our above example), the user may still be able to
get a Secure validation result (and see DNS responses). get a Secure validation result (and see DNS responses).
This policy has the disadvantage of making the validator subject to This policy has the disadvantage of making the validator subject to
the compromise of the weakest of these trust anchors while making it the compromise of the weakest of these trust anchors, while making it
relatively painless to keep old trust anchors configured in relatively painless to keep old trust anchors configured in
perpetuity. perpetuity.
C.3. Preference Based on Source C.3. Preference Based on Source
When the trust anchors have come from different sources (e.g. When the trust anchors have come from different sources (e.g.,
automated updates ([RFC5011]), one or more DLV registries automated updates ([RFC5011]), one or more DNSSEC Lookaside
([RFC5074]), and manually configured), a validator may wish to choose Validation (DLV) registries ([RFC5074]), and manual configuration), a
between them based on the perceived reliability of those sources. validator may wish to choose between them based on the perceived
The order of precedence might be exposed as a configuration option. reliability of those sources. The order of precedence might be
exposed as a configuration option.
For example, a validator might choose to prefer trust anchors found For example, a validator might choose to prefer trust anchors found
in a DLV registry over those manually configured on the theory that in a DLV registry over those manually configured on the theory that
the manually configured ones will not be as aggressively maintained. the manually configured ones will not be as aggressively maintained.
Conversely, a validator might choose to prefer manually configured Conversely, a validator might choose to prefer manually configured
trust anchors over those obtained from a DLV registry on the theory trust anchors over those obtained from a DLV registry on the theory
that the manually configured ones have been more carefully that the manually configured ones have been more carefully
authenticated. authenticated.
Or the validator might do something more complex: prefer a sub-set of Or the validator might do something more complex: prefer a sub-set of
manually configured trust anchors (based on a configuration option), manually configured trust anchors (based on a configuration option),
then trust anchors that have been updated using the RFC5011 then trust anchors that have been updated using the mechanism in
mechanism, then trust anchors from one DLV registry, then trust [RFC5011], then trust anchors from one DLV registry, then trust
anchors from a different DLV registry, then the rest of the manually anchors from a different DLV registry, then the rest of the manually
configured trust anchors. configured trust anchors.
Authors' Addresses Authors' Addresses
Samuel Weiler Samuel Weiler (editor)
SPARTA, Inc. SPARTA, Inc.
7110 Samuel Morse Drive 7110 Samuel Morse Drive
Columbia, Maryland 21046 Columbia, MD 21046
US US
Email: weiler@tislabs.com EMail: weiler@tislabs.com
David Blacka David Blacka (editor)
Verisign, Inc. Verisign, Inc.
12061 Bluemont Way 12061 Bluemont Way
Reston, VA 20190 Reston, VA 20190
US US
Email: davidb@verisign.com EMail: davidb@verisign.com
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