Commit bd97dba0 authored by Mark Andrews's avatar Mark Andrews
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new draft

parent c5d57a13
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DNS Extensions Working Group S. Rose
Internet-Draft NIST
Intended status: Standards Track W. Wijngaards
Expires: May 17, 2008 NLnet Labs
November 14, 2007
Updates: 2672,3363,4294 W. Wijngaards
(if approved) NLnet Labs
Intended status: Standards Track January 14, 2008
Expires: July 17, 2008
Update to DNAME Redirection in the DNS
draft-ietf-dnsext-rfc2672bis-dname-06
draft-ietf-dnsext-rfc2672bis-dname-08
Status of This Memo
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The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on May 17, 2008.
This Internet-Draft will expire on July 17, 2008.
Copyright Notice
Copyright (C) The IETF Trust (2007).
Copyright (C) The IETF Trust (2008).
Abstract
The DNAME record provides redirection for a sub-tree of the domain
name tree in the DNS system. That is, all names that end with a
particular suffix are redirected to another part of the DNS. This is
an update to the original specification in RFC 2672.
an update to the original specification in RFC 2672, also aligning
RFC 3363 and RFC 4294 with this revision.
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Requirements Language
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5. Other Issues with DNAME . . . . . . . . . . . . . . . . . . . 11
5.1. MX, NS and PTR Records Must Point to Target of DNAME . . . 11
5.2. Dynamic Update and DNAME . . . . . . . . . . . . . . . . . 11
5.3. DNSSEC and DNAME . . . . . . . . . . . . . . . . . . . . . 11
5.3.1. DNAME bit in NSEC type map . . . . . . . . . . . . . . 11
5.3. DNSSEC and DNAME . . . . . . . . . . . . . . . . . . . . . 12
5.3.1. DNAME bit in NSEC type map . . . . . . . . . . . . . . 12
5.3.2. Validators Must Understand DNAME . . . . . . . . . . . 12
5.3.2.1. DNAME in Bitmap Causes Invalid Name Error . . . . 12
5.3.2.2. Valid Name Error Response Involving DNAME in
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7. Security Considerations . . . . . . . . . . . . . . . . . . . 13
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 14
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 13
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
9.1. Normative References . . . . . . . . . . . . . . . . . . . 14
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Internet-Draft DNAME Redirection November 2007
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1. Introduction
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Another usage of DNAME lies in redirection of name spaces. For
example, a zone administrator may want sub-trees of the DNS to
contain the same information. DNAME is also used for redirection of
ENUM domains to another maintaining party.
contain the same information. DNAME is also used for the redirection
of ENUM domains to another maintaining party.
This update to DNAME does not change the wire format or the handling
of DNAME Resource Records by existing software. A new UD (Understand
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The format of the DNAME record has not changed from the original
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Table 1. DNAME Substitution Examples.
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substitution is that one can then query for the DNAME through RFC
1034 [RFC1034] caches.
This means that a DNAME RR is not allowed at the same domain name as
NS records unless there is also a SOA record present. DNAME RRs are
not allowed at the parent side of a delegation point but are allowed
at a zone apex.
This means that DNAME RRs are not allowed at the parent side of a
delegation point but are allowed at a zone apex.
2.4. Names Next to and Below a DNAME Record
Other resource records MUST NOT exist below the owner of a DNAME RR.
To get the contents for names subordinate to that owner, the DNAME
redirection must be invoked and the resulting target queried. A
server SHOULD refuse to load a zone that has data below a domain name
owning a DNAME RR. Also a server SHOULD refuse to load a zone
subordinate to the owner of a DNAME record in the ancestor zone. See
Section 5.2 for further restrictions related to dynamic update.
Other resource records MUST NOT exist at a domain name subordinate to
the owner of a DNAME RR. To get the contents for names subordinate
to that owner, the DNAME redirection must be invoked and the
resulting target queried. A server SHOULD refuse to load a zone that
has data at a domain name subordinate to a domain name owning a DNAME
RR. Also a server SHOULD refuse to load a zone subordinate to the
owner of a DNAME record in the ancestor zone. See Section 5.2 for
further restrictions related to dynamic update.
DNAME is a singleton type, meaning only one DNAME is allowed per
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DNAME is a singleton type, meaning only one DNAME is allowed per
name. The owner name of a DNAME can only have one DNAME RR, and no
CNAME RRs can exist at that name. These rules make sure that for a
single domain name only one redirection exists, and thus no confusion
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to allow compression of the target name, no such signaling is
explicitly specified.
RFC2672 stated that the EDNS version had a meaning for understanding
RFC 2672 stated that the EDNS version had a meaning for understanding
of DNAME and DNAME target name compression. This document updates
RFC2672, in that there is no EDNS version signaling for DNAME as of
RFC 2672, in that there is no EDNS version signaling for DNAME as of
yet. However, the flags section of EDNS(0) is updated with a
Understand-DNAME flag by this document (See Section 3.2).
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3.2. CNAME synthesis
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resolver can check the CNAME against the DNAME record and validate
the DNAME record.
It does not make sense for the authoritative server to follow the
chain of DNAMEs, CNAMEs and wildcards outside of the zone of the
query, as some resolver implementations will remove out-of-zone
information from the answer.
Resolvers MUST be able to handle a synthesized CNAME TTL of zero or
equal to the TTL of the corresponding DNAME record. The TTL of zero
means that the CNAME can be discarded immediately after processing
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3.3. Acceptance and Intermediate Storage
DNS Caches MUST NOT allow data to be cached below the owner of a
DNAME RR, except CNAME records and their signatures. CNAME records
DNS caches can encounter data at names below the owner name of a
DNAME RR, due to a change at the authoritative server where data from
before and after the change resides in the cache. This conflict
situation is a transitional phase, that ends when the old data times
out. The cache can opt to store both old and new data and treat each
as if the other did not exist, or drop the old data, or drop the
longer domain name. In any approach, consistency returns after the
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below the owner of a DNAME MUST be re-synthesized from the DNAME, or
checked against the DNAME record before sending them out. This
improves consistency of the DNAME and CNAME records below the owner
of the DNAME.
older data TTL times out.
DNS Caches MUST perform CNAME synthesis on behalf of DNAME-ignorant
clients. A DNS Cache that understands DNAMEs can send out queries on
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C. If at some label, a match is impossible (i.e., the
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Note that there will be at most one ancestor with a DNAME as
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RRs, but never a CNAME RR.
The DNAME RR is discussed in RFC 3363, section 4, on A6 and DNAME.
[RFC3363] does NOT RECOMMENDED the use of DNAME in the IPv6 reverse
tree. (Hence, all references to DNAME should have been removed from
[RFC4294].) Based on the experience gained in the meantime, RFC 3363
should be revised, dropping all constraints on having DNAME RRs in
these zones. This would greatly improve the manageability of the
IPv6 reverse tree. These changes are made explicit below.
In [RFC3363], section 4, DNAME is not recommended for the IPv6
reverse tree. The opening premise of this section is demonstrably
wrong. Everything that follows from that premise is also invalid.
The opening premise of this section is demonstrably wrong, and so the
conclusion based on that premise is wrong. In particular, [RFC3363]
deprecates the use of DNAME in the IPv6 reverse tree, which is then
carried forward as a recommendation in [RFC4294]. Based on the
experience gained in the meantime, [RFC3363] should be revised,
dropping all constraints on having DNAME RRs in these zones. This
would greatly improve the manageability of the IPv6 reverse tree.
These changes are made explicit below.
In [RFC3363], the paragraph
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In [RFC4294], the reference to DNAME was left in as a editorial
In [RFC4294], the reference to DNAME was left in as an editorial
oversight. The paragraph
"Those nodes are NOT RECOMMENDED to support the experimental A6 and
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5.2. Dynamic Update and DNAME
Dynamic update for DNAME records works similar to dynamic update for
delegating NS records. For example, adding a DNAME obscures names in
the zone. DNAME records can be added, changed and removed.
Zones containing a DNAME RR MUST NOT accept a dynamic update message
that would add a record or delegation with a name existing under a
DNAME.
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response to a dynamic update message that would add a resource record
under a DNAME in the zone.
5.3. DNSSEC and DNAME
5.3.1. DNAME bit in NSEC type map
When a validator checks the NSEC RRs returned on a name error
response, it SHOULD check that the DNAME bit is not set. If the
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5.3. DNSSEC and DNAME
5.3.1. DNAME bit in NSEC type map
When a validator checks the NSEC RRs returned on a name error
response, it SHOULD check that the DNAME bit is not set. If the
DNAME bit is set then the DNAME substitution should have been done,
but has not.
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;; Header: QR AA DO RCODE=0(NOERROR)
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foo.bar.example.com. CNAME foo.bar.example.net.
The answer shown above has the synthesized CNAME included. However,
the CNAME has no signature, since the server does not sign online (it
is a slow operation and exposes the signing key). So it cannot be
trusted. It could be altered by an attacker to be
the CNAME has no signature, since the server does not sign online.
So it cannot be trusted. It could be altered by an attacker to be
foo.bar.example.com CNAME bla.bla.example. The DNAME record does
have its signature included, since it does not change for every query
name. The validator must verify the DNAME signature and then
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A validating resolver MUST understand DNAME, according to [RFC4034].
In Section 5.3.2 examples are given that illustrate this need.
8. Acknowledgments
The authors of this draft would like to acknowledge Matt Larson for
beginning this effort to address the issues related to the DNAME RR
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8. Acknowledgments
The authors of this draft would like to acknowledge Matt Larson for
beginning this effort to address the issues related to the DNAME RR
type.
9. References
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[RFC1912] Barr, D., "Common DNS Operational and Configuration
Errors", RFC 1912, February 1996.
[RFC3363] Bush, R., Durand, A., Fink, B., Gudmundsson, O., and T.
Hain, "Representing Internet Protocol version 6 (IPv6)
Addresses in the Domain Name System (DNS)", RFC 3363,
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[RFC3363] Bush, R., Durand, A., Fink, B., Gudmundsson, O., and T.
Hain, "Representing Internet Protocol version 6 (IPv6)
Addresses in the Domain Name System (DNS)", RFC 3363,
August 2002.
[RFC4294] Loughney, J., "IPv6 Node Requirements", RFC 4294,
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Full Copyright Statement
Copyright (C) The IETF Trust (2007).
Copyright (C) The IETF Trust (2008).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
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