draft-ietf-dnsext-rfc2672bis-dname-13.txt   draft-ietf-dnsext-rfc2672bis-dname-14.txt 
DNS Extensions Working Group S. Rose DNS Extensions Working Group S. Rose
Internet-Draft NIST Internet-Draft NIST
Obsoletes: 2672 (if approved) W. Wijngaards Obsoletes: 2672 (if approved) W. Wijngaards
Updates: 3363,4294 NLnet Labs Updates: 3363,4294 NLnet Labs
(if approved) May 2, 2008 (if approved) July 15, 2008
Intended status: Standards Track Intended status: Standards Track
Expires: November 3, 2008 Expires: January 16, 2009
Update to DNAME Redirection in the DNS Update to DNAME Redirection in the DNS
draft-ietf-dnsext-rfc2672bis-dname-13 draft-ietf-dnsext-rfc2672bis-dname-14
Status of This Memo Status of This Memo
By submitting this Internet-Draft, each author represents that any By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79. aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that Task Force (IETF), its areas, and its working groups. Note that
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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."
The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt. http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at The list of Internet-Draft Shadow Directories can be accessed at
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This Internet-Draft will expire on November 3, 2008. This Internet-Draft will expire on January 16, 2009.
Copyright Notice Copyright Notice
Copyright (C) The IETF Trust (2008). Copyright (C) The IETF Trust (2008).
Abstract Abstract
The DNAME record provides redirection for a sub-tree of the domain 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 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 particular suffix are redirected to another part of the DNS. This is
an update of the original specification in RFC 2672, also aligning a revision of the original specification in RFC 2672, also aligning
RFC 3363 and RFC 4294 with this revision. RFC 3363 and RFC 4294 with this revision.
Requirements Language Requirements Language
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", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]. document are to be interpreted as described in RFC 2119 [RFC2119].
Table of Contents Table of Contents
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different (single) node of the tree. different (single) node of the tree.
Take for example, looking through a zone (see RFC 1034 [RFC1034], Take for example, looking through a zone (see RFC 1034 [RFC1034],
section 4.3.2, step 3) for the domain name "foo.example.com" and a section 4.3.2, step 3) for the domain name "foo.example.com" and a
DNAME resource record is found at "example.com" indicating that all DNAME resource record is found at "example.com" indicating that all
queries under "example.com" be directed to "example.net". The lookup queries under "example.com" be directed to "example.net". The lookup
process will return to step 1 with the new query name of process will return to step 1 with the new query name of
"foo.example.net". Had the query name been "www.foo.example.com" the "foo.example.net". Had the query name been "www.foo.example.com" the
new query name would be "www.foo.example.net". new query name would be "www.foo.example.net".
This document is an update of the original specification of DNAME in This document is a revision of the original specification of DNAME in
RFC 2672 [RFC2672]. DNAME was conceived to help with the problem of RFC 2672 [RFC2672]. DNAME was conceived to help with the problem of
maintaining address-to-name mappings in a context of network maintaining address-to-name mappings in a context of network
renumbering. With a careful set-up, a renumbering event in the renumbering. With a careful set-up, a renumbering event in the
network causes no change to the authoritative server that has the network causes no change to the authoritative server that has the
address-to-name mappings. Examples in practice are classless reverse address-to-name mappings. Examples in practice are classless reverse
address space delegations. address space delegations.
Another usage of DNAME lies in redirection of name spaces. For Another usage of DNAME lies in aliasing of name spaces. For example,
example, a zone administrator may want sub-trees of the DNS to a zone administrator may want sub-trees of the DNS to contain the
contain the same information. Examples include punycode alternates same information. Examples include punycode alternates for domain
for domain spaces. DNAME is also used for the redirection of ENUM spaces.
domains to another maintaining party.
This update to DNAME does not change the wire format or the handling This revision to DNAME does not change the wire format or the
of DNAME Resource Records by existing software. A new UD (Understand handling of DNAME Resource Records by existing software. A new UD
DNAME) bit in the EDNS flags field can be used to signal that CNAME (Understand DNAME) bit in the EDNS flags field can be used to signal
synthesis is not needed. Discussion is added on problems that may be that CNAME synthesis is not needed. Discussion is added on problems
encountered when using DNAME. that may be encountered when using DNAME.
2. The DNAME Resource Record 2. The DNAME Resource Record
2.1. Format 2.1. Format
The DNAME RR has mnemonic DNAME and type code 39 (decimal). It is The DNAME RR has mnemonic DNAME and type code 39 (decimal). It is
not class-sensitive. not class-sensitive.
Its RDATA is comprised of a single field, <target>, which contains a Its RDATA is comprised of a single field, <target>, which contains a
fully qualified domain name that must be sent in uncompressed form fully qualified domain name that must be sent in uncompressed form
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violates these rules. violates these rules.
2.5. Compression of the DNAME record. 2.5. Compression of the DNAME record.
The DNAME owner name can be compressed like any other owner name. The DNAME owner name can be compressed like any other owner name.
The DNAME RDATA target name MUST NOT be sent out in compressed form, The DNAME RDATA target name MUST NOT be sent out in compressed form,
so that a DNAME RR can be treated as an unknown type [RFC3597]. so that a DNAME RR can be treated as an unknown type [RFC3597].
Although the previous DNAME specification [RFC2672] (that is Although the previous DNAME specification [RFC2672] (that is
obsoleted by this specification) talked about signaling to allow obsoleted by this specification) talked about signaling to allow
compression of the target name, such signaling is not specified. compression of the target name, such signaling has never been
specified and this document also does not specify this signaling
behavior.
RFC 2672 stated that the EDNS version had a meaning for understanding RFC 2672 (obsoleted by this document) stated that the EDNS version
of DNAME and DNAME target name compression. This document updates had a meaning for understanding of DNAME and DNAME target name
RFC 2672, in that there is no EDNS version signaling for DNAME. compression. This document revises RFC 2672, in that there is no
However, the flags section of EDNS(0) is updated with a Understand- EDNS version signaling for DNAME. However, the flags section of
DNAME flag by this document (See Section 3.3). EDNS(0) is updated with a Understand-DNAME flag by this document (See
Section 3.3).
3. Processing 3. Processing
The DNAME RR causes type NS additional section processing. The DNAME RR causes type NS additional section processing.
3.1. CNAME synthesis and UD bit 3.1. CNAME synthesis and UD bit
When preparing an response, a server upon performing a DNAME When preparing an response, a server upon performing a DNAME
substitution will in all cases include the DNAME RR used in the substitution will in all cases include the DNAME RR used in the
answer section. A CNAME RR record with TTL equal to the answer section. A CNAME RR record with TTL equal to the
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2: |DO|UD| Z | 2: |DO|UD| Z |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
Servers MUST be able to answer a query for a synthesized CNAME. Like Servers MUST be able to answer a query for a synthesized CNAME. Like
other query types this invokes the DNAME, and synthesizes the CNAME other query types this invokes the DNAME, and synthesizes the CNAME
into the answer. into the answer.
3.2. Server algorithm 3.2. Server algorithm
Below the server algorithm, which appeared in RFC 2672 Section 4.1, Below the server algorithm, which appeared in RFC 2672 Section 4.1,
is expanded to handle the UD (Understand DNAME) bit. is expanded to handle the UD (Understand-DNAME) bit.
1. Set or clear the value of recursion available in the response 1. Set or clear the value of recursion available in the response
depending on whether the name server is willing to provide depending on whether the name server is willing to provide
recursive service. If recursive service is available and recursive service. If recursive service is available and
requested via the RD bit in the query, go to step 5, otherwise requested via the RD bit in the query, go to step 5, otherwise
step 2. step 2.
2. Search the available zones for the zone which is the nearest 2. Search the available zones for the zone which is the nearest
ancestor to QNAME. If such a zone is found, go to step 3, ancestor to QNAME. If such a zone is found, go to step 3,
otherwise step 4. otherwise step 4.
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redirection of the DNAME is non-deterministic. Because the redirection of the DNAME is non-deterministic. Because the
processing is non-deterministic, DNSSEC validating resolvers may not processing is non-deterministic, DNSSEC validating resolvers may not
be able to validate a wildcarded DNAME. be able to validate a wildcarded DNAME.
A server MAY give a warning that the behavior is unspecified if such A server MAY give a warning that the behavior is unspecified if such
a wildcarded DNAME is loaded. The server MAY refuse it, refuse to a wildcarded DNAME is loaded. The server MAY refuse it, refuse to
load or refuse dynamic update. load or refuse dynamic update.
3.4. Acceptance and Intermediate Storage 3.4. Acceptance and Intermediate Storage
DNS caches can encounter data at names below the owner name of a Recursive caching name servers can encounter data at names below the
DNAME RR, due to a change at the authoritative server where data from owner name of a DNAME RR, due to a change at the authoritative server
before and after the change resides in the cache. This conflict where data from before and after the change resides in the cache.
situation is a transitional phase, that ends when the old data times This conflict situation is a transitional phase, that ends when the
out. The cache can opt to store both old and new data and treat each old data times out. The caching name server can opt to store both
as if the other did not exist, or drop the old data, or drop the old and new data and treat each as if the other did not exist, or
longer domain name. In any approach, consistency returns after the drop the old data, or drop the longer domain name. In any approach,
older data TTL times out. consistency returns after the older data TTL times out.
DNS caches MUST perform CNAME synthesis on behalf of DNAME-ignorant Recursive caching name servers MUST perform CNAME synthesis on behalf
clients. A DNS cache that understands DNAMEs can send out queries on of DNAME-ignorant clients. A recursive caching name server that
behalf of clients with the UD bit set (See Section 3.1). After understands DNAMEs can send out queries on behalf of clients with the
receiving the answers the DNS cache sends replies to DNAME ignorant UD bit set (See Section 3.1). After receiving the answers the
clients that include DNAMEs and synthesized CNAMEs. recursive caching name server sends replies to DNAME ignorant clients
that include DNAMEs and synthesized CNAMEs.
4. DNAME Discussions in Other Documents 4. DNAME Discussions in Other Documents
In [RFC2181], in Section 10.3., the discussion on MX and NS records In [RFC2181], in Section 10.3., the discussion on MX and NS records
touches on redirection by CNAMEs, but this also holds for DNAMEs. touches on redirection by CNAMEs, but this also holds for DNAMEs.
Excerpt from 10.3. MX and NS records (in RFC 2181). Excerpt from 10.3. MX and NS records (in RFC 2181).
The domain name used as the value of a NS resource record, The domain name used as the value of a NS resource record,
or part of the value of a MX resource record must not be or part of the value of a MX resource record must not be
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punycode in their RDATA. What must be done then is to have the punycode in their RDATA. What must be done then is to have the
domain names with DNAME substitution already applied to it as the MX, domain names with DNAME substitution already applied to it as the MX,
NS, PTR, SRV data. These are valid canonical hostnames. NS, PTR, SRV data. These are valid canonical hostnames.
5.2. Dynamic Update and DNAME 5.2. Dynamic Update and DNAME
DNAME records can be added, changed and removed in a zone using DNAME records can be added, changed and removed in a zone using
dynamic update transactions. Adding a DNAME RR to a zone occludes dynamic update transactions. Adding a DNAME RR to a zone occludes
any domain names that may exist under the added DNAME. any domain names that may exist under the added DNAME.
A server MUST ignore a dynamic update message that attempts to add a A server MUST reject a dynamic update message that attempts to add a
DNAME RR at a name that already has a CNAME RR or another DNAME RR DNAME RR at a name that already has a CNAME RR or another DNAME RR
associated with that name. associated with that name.
5.3. DNSSEC and DNAME 5.3. DNSSEC and DNAME
5.3.1. DNAME bit in NSEC type map 5.3.1. DNAME bit in NSEC type map
When a validator checks the NSEC RRs returned on a name error 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 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, DNAME bit is set then the DNAME substitution should have been done,
but has not. but has not.
5.3.2. Validators Must Understand DNAME 5.3.2. Validators Must Understand DNAME
Examples of why DNSSEC validators MUST understand DNAME. Below are examples of why DNSSEC validators MUST understand DNAME.
5.3.2.1. DNAME in Bitmap Causes Invalid Name Error 5.3.2.1. DNAME in Bitmap Causes Invalid Name Error
;; Header: QR AA DO RCODE=3(NXDOMAIN) ;; Header: QR AA DO RCODE=3(NXDOMAIN)
;; Question ;; Question
foo.bar.example.com. IN A foo.bar.example.com. IN A
;; Answer ;; Answer
bar.example.com. NSEC dub.example.com. A DNAME bar.example.com. NSEC dub.example.com. A DNAME
bar.example.com. RRSIG NSEC [valid signature] bar.example.com. RRSIG NSEC [valid signature]
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recursively resolve further to query for the foo.bar.example.net A recursively resolve further to query for the foo.bar.example.net A
record. record.
6. IANA Considerations 6. IANA Considerations
The DNAME Resource Record type code 39 (decimal) originally has been The DNAME Resource Record type code 39 (decimal) originally has been
registered by [RFC2672]. IANA should update the DNS resource record registered by [RFC2672]. IANA should update the DNS resource record
registry to point to this document for RR type 39. registry to point to this document for RR type 39.
This draft requests the second highest bit in the EDNS flags field This draft requests the second highest bit in the EDNS flags field
for the Understand-DNAME (UD) flag. for the Understand-DNAME (UD) flag as described in Section 3.1.
7. Security Considerations 7. Security Considerations
DNAME redirects queries elsewhere, which may impact security based on DNAME redirects queries elsewhere, which may impact security based on
policy and the security status of the zone with the DNAME and the policy and the security status of the zone with the DNAME and the
redirection zone's security status. redirection zone's security status.
If a validating resolver accepts wildcarded DNAMEs, this creates If a validating resolver accepts wildcarded DNAMEs, this creates
security issues. Since the processing of a wildcarded DNAME is non- security issues. Since the processing of a wildcarded DNAME is non-
deterministic and the CNAME that was substituted by the server has no deterministic and the CNAME that was substituted by the server has no
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A validating resolver MUST understand DNAME, according to [RFC4034]. A validating resolver MUST understand DNAME, according to [RFC4034].
In Section 5.3.2 examples are given that illustrate this need. In Section 5.3.2 examples are given that illustrate this need.
8. Acknowledgments 8. Acknowledgments
The authors of this draft would like to acknowledge Matt Larson for The authors of this draft would like to acknowledge Matt Larson for
beginning this effort to address the issues related to the DNAME RR beginning this effort to address the issues related to the DNAME RR
type. The authors would also like to acknowledge Paul Vixie, Ed type. The authors would also like to acknowledge Paul Vixie, Ed
Lewis, Mark Andrews, Mike StJohns, Niall O'Reilly, Sam Weiler, Alfred Lewis, Mark Andrews, Mike StJohns, Niall O'Reilly, Sam Weiler, Alfred
Hines and Kevin Darcy for their review and comments on this document. Hoenes and Kevin Darcy for their review and comments on this
document.
9. References 9. References
9.1. Normative References 9.1. 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.
[RFC1035] Mockapetris, P., "Domain names - implementation and [RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987. specification", STD 13, RFC 1035, November 1987.
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