draft-ietf-dnsext-rfc2672bis-dname-11.txt		draft-ietf-dnsext-rfc2672bis-dname-12.txt
	DNS Extensions Working Group S. Rose		DNS Extensions Working Group S. Rose
	Internet-Draft NIST		Internet-Draft NIST
	Updates: 2672,3363,4294 W. Wijngaards		Obsoletes: 2672 (if approved) W. Wijngaards
	(if approved) NLnet Labs		Updates: 3363,4294 NLnet Labs
	Intended status: Standards Track March 25, 2008		(if approved) April 21, 2008
	Expires: September 26, 2008		Intended status: Standards Track
			Expires: October 23, 2008
	Update to DNAME Redirection in the DNS		Update to DNAME Redirection in the DNS
	draft-ietf-dnsext-rfc2672bis-dname-11		draft-ietf-dnsext-rfc2672bis-dname-12
	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.
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	Task Force (IETF), its areas, and its working groups. Note that		Task Force (IETF), its areas, and its working groups. Note that
	skipping to change at page 1, line 36		skipping to change at page 1, line 37
	and may be updated, replaced, or obsoleted by other documents at any		and may be updated, replaced, or obsoleted by other documents at any
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	This Internet-Draft will expire on September 26, 2008.		This Internet-Draft will expire on October 23, 2008.
	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
	skipping to change at page 2, line 19		skipping to change at page 2, line 19
	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
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
	2. The DNAME Resource Record . . . . . . . . . . . . . . . . . . 3		2. The DNAME Resource Record . . . . . . . . . . . . . . . . . . 3
	2.1. Format . . . . . . . . . . . . . . . . . . . . . . . . . . 3		2.1. Format . . . . . . . . . . . . . . . . . . . . . . . . . . 3
	2.2. The DNAME Substitution . . . . . . . . . . . . . . . . . . 4		2.2. The DNAME Substitution . . . . . . . . . . . . . . . . . . 4
	2.3. DNAME Apex not Redirected itself . . . . . . . . . . . . . 5		2.3. DNAME Apex not Redirected itself . . . . . . . . . . . . . 5
	2.4. Names Next to and Below a DNAME Record . . . . . . . . . . 5		2.4. Names Next to and Below a DNAME Record . . . . . . . . . . 6
	2.5. Compression of the DNAME record. . . . . . . . . . . . . . 6		2.5. Compression of the DNAME record. . . . . . . . . . . . . . 6
	3. Processing . . . . . . . . . . . . . . . . . . . . . . . . . . 6		3. Processing . . . . . . . . . . . . . . . . . . . . . . . . . . 7
	3.1. Wildcards . . . . . . . . . . . . . . . . . . . . . . . . 6		3.1. Server algorithm . . . . . . . . . . . . . . . . . . . . . 7
	3.2. CNAME synthesis . . . . . . . . . . . . . . . . . . . . . 7		3.2. Wildcards . . . . . . . . . . . . . . . . . . . . . . . . 9
	3.3. Acceptance and Intermediate Storage . . . . . . . . . . . 7		3.3. CNAME synthesis and UD bit . . . . . . . . . . . . . . . . 9
	3.4. Server algorithm . . . . . . . . . . . . . . . . . . . . . 8		3.4. Acceptance and Intermediate Storage . . . . . . . . . . . 10
	4. DNAME Discussions in Other Documents . . . . . . . . . . . . . 10		4. DNAME Discussions in Other Documents . . . . . . . . . . . . . 10
	5. Other Issues with DNAME . . . . . . . . . . . . . . . . . . . 11		5. Other Issues with DNAME . . . . . . . . . . . . . . . . . . . 12
	5.1. MX, NS and PTR Records Must Point to Target of DNAME . . . 11		5.1. Canonical hostnames cannot be below DNAME owners . . . . . 12
	5.2. Dynamic Update and DNAME . . . . . . . . . . . . . . . . . 11		5.2. Dynamic Update and DNAME . . . . . . . . . . . . . . . . . 12
	5.3. DNSSEC and DNAME . . . . . . . . . . . . . . . . . . . . . 11		5.3. DNSSEC and DNAME . . . . . . . . . . . . . . . . . . . . . 12
	5.3.1. DNAME bit in NSEC type map . . . . . . . . . . . . . . 11		5.3.1. DNAME bit in NSEC type map . . . . . . . . . . . . . . 12
	5.3.2. Validators Must Understand DNAME . . . . . . . . . . . 12		5.3.2. Validators Must Understand DNAME . . . . . . . . . . . 12
	5.3.2.1. DNAME in Bitmap Causes Invalid Name Error . . . . 12		5.3.2.1. DNAME in Bitmap Causes Invalid Name Error . . . . 13
	5.3.2.2. Valid Name Error Response Involving DNAME in		5.3.2.2. Valid Name Error Response Involving DNAME in
	Bitmap . . . . . . . . . . . . . . . . . . . . . . 12		Bitmap . . . . . . . . . . . . . . . . . . . . . . 13
	5.3.2.3. Response With Synthesized CNAME . . . . . . . . . 12		5.3.2.3. Response With Synthesized CNAME . . . . . . . . . 13
	6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13		6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
	7. Security Considerations . . . . . . . . . . . . . . . . . . . 13		7. Security Considerations . . . . . . . . . . . . . . . . . . . 14
	8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 13		8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 14
	9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14		9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
	9.1. Normative References . . . . . . . . . . . . . . . . . . . 14		9.1. Normative References . . . . . . . . . . . . . . . . . . . 14
	9.2. Informative References . . . . . . . . . . . . . . . . . . 14		9.2. Informative References . . . . . . . . . . . . . . . . . . 15
	1. Introduction		1. Introduction
	DNAME is a DNS Resource Record type. DNAME provides redirection from		DNAME is a DNS Resource Record type defined in RFC 2672 [RFC2672].
	a part of the DNS name tree to another part of the DNS name tree.		DNAME provides redirection from a part of the DNS name tree to
			another part of the DNS name tree.
			The DNAME RR and the CNAME RR [RFC1034] cause a lookup to
			(potentially) return data corresponding to a domain name different
			from the queried domain name. The difference between the two
			resource records is that the CNAME RR directs the lookup of data at
			its owner to another single name, a DNAME RR directs lookups for data
			at descendents of its owner's name to corresponding names under a
			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".
	The DNAME RR is similar to the CNAME RR in that it provides
	redirection. The CNAME RR only provides redirection for exactly one
	name while the DNAME RR provides redirection for all names in a sub-
	tree of the DNS name tree.
	This document is an update to the original specification of DNAME in		This document is an update to 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 and punycode alternates for domain spaces.		address space delegations and punycode alternates for domain spaces.
	Another usage of DNAME lies in redirection of name spaces. For		Another usage of DNAME lies in redirection of name spaces. For
	example, a zone administrator may want sub-trees of the DNS to		example, a zone administrator may want sub-trees of the DNS to
	skipping to change at page 3, line 46		skipping to change at page 3, line 50
	This update to DNAME does not change the wire format or the handling		This update to DNAME does not change the wire format or the handling
	of DNAME Resource Records by existing software. A new UD (Understand		of DNAME Resource Records by existing software. A new UD (Understand
	Dname) bit in the EDNS flags field can be used to signal that CNAME		Dname) bit in the EDNS flags field can be used to signal that CNAME
	synthesis is not needed. Discussion is added on problems that may be		synthesis is not needed. Discussion is added on problems that may be
	encountered when using DNAME.		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).		The DNAME RR has mnemonic DNAME and type code 39 (decimal). It is
			not class-sensitive.
	The format of the DNAME record has not changed from the original		Its RDATA is comprised of a single field, <target>, which contains a
	specification in RFC 2672. DNAME has the following format:		fully qualified domain name that must be sent in uncompressed form
			[RFC1035], [RFC3597]. The <target> field MUST be present. The
			presentation format of <target> is that of a domain name [RFC1035].
	<owner> <ttl> <class> DNAME <target>		<owner> <ttl> <class> DNAME <target>
	The format is not class-sensitive. All fields are required. The		The effect of the DNAME RR is the substitution of the record's
	RDATA field target is a domain name. The RDATA field target name		<target> for its owner name, as a suffix of a domain name. This
	MUST be sent uncompressed [RFC3597].		substitution has to be applied for every DNAME RR found in the
			resolution process, which allows fairly lengthy valid chains of DNAME
			RRs.
	The DNAME RR causes type NS additional section processing.		Details of the substitution process, methods to avoid conflicting
			resource records, and rules for specific corner cases are given in
			the following subsections.
	2.2. The DNAME Substitution		2.2. The DNAME Substitution
	DNAMEs cause a name substitution to happen to query names. This is		When following RFC 1034 [RFC1034], section 4.3.2's algorithm's third
	called the DNAME substitution. The portion of the QNAME ending with		step, "start matching down, label by label, in the zone" and a node
	the root label that matches the owner name of the DNAME RR is		is found to own a DNAME resource record a DNAME substitution occurs.
	replaced with the contents of the DNAME RR's RDATA. The owner name		The name being sought may be the original query name or a name that
	of the DNAME is not itself redirected, only domain names below the		is the result of a CNAME resource record being followed or a
	owner name are redirected. Only whole labels are replaced. A name		previously encountered DNAME. As is the case of finding a CNAME
	is considered below the owner name if it has more labels than the		resource record or NS resource record set, the processing of a DNAME
	owner name, and the labels of the owner name appear at the end of the		will happen prior to finding the desired domain name.
	query name. See the table of examples for common cases and corner
			A DNAME substitution is performed by replacing the suffix labels of
			the name being sought matching the owner name of the DNAME resource
			record with the string of labels in the RDATA field. The matching
			labels end with the root label in all cases. Only whole labels are
			replaced. See the table of examples for common cases and corner
	cases.		cases.
	In the table below, the QNAME refers to the query name. The owner is		In the table below, the QNAME refers to the query name. The owner is
	the DNAME owner domain name, and the target refers to the target of		the DNAME owner domain name, and the target refers to the target of
	the DNAME record. The result is the resulting name after performing		the DNAME record. The result is the resulting name after performing
	the DNAME substitution on the query name. "no match" means that the		the DNAME substitution on the query name. "no match" means that the
	query did not match the DNAME and thus no substitution is performed		query did not match the DNAME and thus no substitution is performed
	and a possible error message is returned (if no other result is		and a possible error message is returned (if no other result is
	possible). In the examples below, 'cyc' and 'shortloop' contain		possible). In the examples below, 'cyc' and 'shortloop' contain
	loops.		loops.
	skipping to change at page 5, line 26		skipping to change at page 5, line 50
	suppose the target name of the DNAME RR is 250 octets in length		suppose the target name of the DNAME RR is 250 octets in length
	(multiple labels), if an incoming QNAME that has a first label over 5		(multiple labels), if an incoming QNAME that has a first label over 5
	octets in length, the result of the result would be a name over 255		octets in length, the result of the result would be a name over 255
	octets. If this occurs the server returns an RCODE of YXDOMAIN		octets. If this occurs the server returns an RCODE of YXDOMAIN
	[RFC2136]. The DNAME record and its signature (if the zone is		[RFC2136]. The DNAME record and its signature (if the zone is
	signed) are included in the answer as proof for the YXDOMAIN (value		signed) are included in the answer as proof for the YXDOMAIN (value
	6) RCODE.		6) RCODE.
	2.3. DNAME Apex not Redirected itself		2.3. DNAME Apex not Redirected itself
	The owner name of a DNAME is not redirected itself. The reason for		Unlike a CNAME RR, a DNAME RR redirects DNS names subordinate to its
	the original decision was that one can have a DNAME at the zone apex		owner name; the owner name of a DNAME is not redirected itself. The
	without problem. Then use this DNAME at the zone apex to point		domain name that owns a DNAME record is allowed to have other
	queries to the target zone. There still is a need to have the		resource record types at that domain name, except DNAMEs or CNAMEs.
	customary SOA and NS resource records at the zone apex. This means
	that DNAME does not mirror a zone completely, as it does not mirror
	the zone apex.
	Another reason for excluding the DNAME owner from the DNAME
	substitution is that one can then query for the DNAME through RFC
	1034 [RFC1034] caches.
	This means that DNAME RRs are not allowed at the parent side of a		This means that DNAME RRs are not allowed at the parent side of a
	delegation point but are allowed at a zone apex.		delegation point but are allowed at a zone apex.
			The reason for this decision was that one can have a DNAME at the
			zone apex. There still is a need to have the customary SOA and NS
			resource records at the zone apex. This means that DNAME does not
			mirror a zone completely, as it does not mirror the zone apex.
			These rules also allow DNAME records to be queried through RFC 1034
			[RFC1034] compliant, DNAME-unaware caches.
	2.4. Names Next to and Below a DNAME Record		2.4. Names Next to and Below a DNAME Record
	Other resource records MUST NOT exist at a domain name subordinate to		Resource records MUST NOT exist at any domain name subordinate to the
	the owner of a DNAME RR. To get the contents for names subordinate		owner of a DNAME RR. To get the contents for names subordinate to
	to that owner, the DNAME redirection must be invoked and the		that owner, the DNAME redirection must be invoked and the resulting
	resulting target queried. A server MAY refuse to load a zone that		target queried. A server MAY refuse to load a zone that has data at
	has data at a domain name subordinate to a domain name owning a DNAME		a domain name subordinate to a domain name owning a DNAME RR. If the
	RR. If the server does load the zone, those names below the DNAME RR		server does load the zone, those names below the DNAME RR will be
	will be occluded. Also a server SHOULD refuse to load a zone		occluded, RFC 2136 [RFC2136], section 7.18. Also a server SHOULD
	subordinate to the owner of a DNAME record in the ancestor zone. See		refuse to load a zone subordinate to the owner of a DNAME record in
	Section 5.2 for further discussion related to dynamic update.		the ancestor zone. See Section 5.2 for further discussion related to
			dynamic update.
	DNAME is a singleton type, meaning only one DNAME is allowed per		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		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		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		single domain name only one redirection exists, and thus no confusion
	which one to follow. A server SHOULD refuse to load a zone that		which one to follow. A server SHOULD refuse to load a zone that
	violates these rules.		violates these rules.
	The domain name that owns a DNAME record is allowed to have other
	resource record types at that domain name, except DNAMEs or CNAMEs.
	These rules allow DNAME records to be queried through DNAME unaware
	caches.
	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.		so that a DNAME RR can be treated as an unknown type [RFC3597].
	Although the previous specification [RFC2672] talked about signaling		Although the previous DNAME specification [RFC2672] (that is
	to allow compression of the target name, no such signaling is		obsoleted by this specification) talked about signaling to allow
	explicitly specified.		compression of the target name, such signaling is not specified.
	RFC 2672 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		of DNAME and DNAME target name compression. This document updates
	RFC 2672, 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		yet. However, the flags section of EDNS(0) is updated with a
	Understand-DNAME flag by this document (See Section 3.2).		Understand-DNAME flag by this document (See Section 3.3).
	3. Processing		3. Processing
	3.1. Wildcards		The DNAME RR causes type NS additional section processing.
	The use of DNAME in conjunction with wildcards is discouraged
	[RFC4592]. Thus records of the form "*.example.com DNAME
	example.net" SHOULD NOT be used.
	The interaction between the expansion of the wildcard and the
	redirection of the DNAME is non-deterministic. Because the
	processing is non-deterministic, DNSSEC validating resolvers may not
	be able to validate a wildcarded DNAME.
	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
	load or refuse dynamic update.
	3.2. CNAME synthesis
	On the server side, the DNAME RR record is always included in the
	answer section of a query, when one is encountered. A CNAME RR
	record with TTL equal to the corresponding DNAME RR is synthesized
	for old resolvers, specifically for the QNAME in the query. DNSSEC
	[RFC4033], [RFC4034], [RFC4035] says that the synthesized CNAME does
	not have to be signed. The DNAME has an RRSIG and a validating
	resolver can check the CNAME against the DNAME record and validate
	the DNAME record.
	Resolvers MUST be able to handle a synthesized CNAME TTL of zero or
	equal to the TTL of the corresponding DNAME record. A TTL of zero
	means that the CNAME can be discarded immediately after processing
	the answer. DNAME aware resolvers can set the Understand-DNAME (UD
	bit) to receive a response with only the DNAME RR and no synthesized
	CNAMEs.
	The UD bit is part of the EDNS extended RCODE and Flags field. It is
	used to omit server processing, transmission and resolver processing
	of unsigned synthesized CNAMEs. Resolvers can set this in a query to
	request omission of the synthesized CNAMEs. Servers copy the UD bit
	to the response, and can omit synthesized CNAMEs from the answer.
	Older resolvers do not set the UD bit, and older servers do not copy
	the UD bit to the answer, and will not omit synthesized CNAMEs.
	Updated EDNS extended RCODE and Flags field.
	+0 (MSB) +1 (LSB)
	+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
	0: | EXTENDED-RCODE | VERSION |
	+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
	2: |DO|UD| Z |
	+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
	Servers MUST be able to answer a query for a synthesized CNAME. Like
	other query types this invokes the DNAME, and synthesizes the CNAME
	into the answer.
	3.3. Acceptance and Intermediate Storage
	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
	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
	behalf of clients with the UD bit set. After receiving the answers
	the DNS cache sends replies to DNAME ignorant clients that include
	DNAMEs and synthesized CNAMEs.
	3.4. Server algorithm		3.1. 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 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.
	skipping to change at page 10, line 11		skipping to change at page 9, line 5
	6. Using local data only, attempt to add other RRs which may be		6. Using local data only, attempt to add other RRs which may be
	useful to the additional section of the query. Exit.		useful to the additional section of the query. Exit.
	Note that there will be at most one ancestor with a DNAME as		Note that there will be at most one ancestor with a DNAME as
	described in step 4 unless some zone's data is in violation of the		described in step 4 unless some zone's data is in violation of the
	no-descendants limitation in section 3. An implementation might take		no-descendants limitation in section 3. An implementation might take
	advantage of this limitation by stopping the search of step 3c or		advantage of this limitation by stopping the search of step 3c or
	step 4 when a DNAME record is encountered.		step 4 when a DNAME record is encountered.
			3.2. Wildcards
			The use of DNAME in conjunction with wildcards is discouraged
			[RFC4592]. Thus records of the form "*.example.com DNAME
			example.net" SHOULD NOT be used.
			The interaction between the expansion of the wildcard and the
			redirection of the DNAME is non-deterministic. Because the
			processing is non-deterministic, DNSSEC validating resolvers may not
			be able to validate a wildcarded DNAME.
			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
			load or refuse dynamic update.
			3.3. CNAME synthesis and UD bit
			When preparing an response, a server upon performing a DNAME
			substitution will in all cases include the DNAME RR used in the
			answer section. A CNAME RR record with TTL equal to the
			corresponding DNAME RR is synthesized and included in the answer
			section for old resolvers. The owner name of the CNAME is the QNAME
			of the query. DNSSEC [RFC4033], [RFC4034], [RFC4035] says that the
			synthesized CNAME does not have to be signed. The DNAME has an RRSIG
			and a validating resolver can check the CNAME against the DNAME
			record and validate the DNAME record.
			Resolvers MUST be able to handle a synthesized CNAME TTL of zero or
			equal to the TTL of the corresponding DNAME record. A TTL of zero
			means that the CNAME can be discarded immediately after processing
			the answer. DNAME aware resolvers can set the Understand-DNAME (UD
			bit) to receive a response with only the DNAME RR and no synthesized
			CNAMEs.
			The UD bit is part of the EDNS [RFC2671] extended RCODE and Flags
			field. It is used to omit server processing, transmission and
			resolver processing of unsigned synthesized CNAMEs. Resolvers can
			set this in a query to request omission of the synthesized CNAMEs.
			Servers copy the UD bit to the response, and can omit synthesized
			CNAMEs from the answer. Older resolvers do not set the UD bit, and
			older servers do not copy the UD bit to the answer, and will not omit
			synthesized CNAMEs.
			Updated EDNS extended RCODE and Flags field.
			+0 (MSB) +1 (LSB)
			+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
			0: | EXTENDED-RCODE | VERSION |
			+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
			2: |DO|UD| Z |
			+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
			Servers MUST be able to answer a query for a synthesized CNAME. Like
			other query types this invokes the DNAME, and synthesizes the CNAME
			into the answer.
			3.4. Acceptance and Intermediate Storage
			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
			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
			behalf of clients with the UD bit set. After receiving the answers
			the DNS cache 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
	an alias. Not only is the specification clear on this		an alias. Not only is the specification clear on this
	skipping to change at page 11, line 20		skipping to change at page 12, line 9
	is to be replaced by		is to be replaced by
	"Those nodes are NOT RECOMMENDED to support the experimental		"Those nodes are NOT RECOMMENDED to support the experimental
	A6 Resource Record [RFC3363]."		A6 Resource Record [RFC3363]."
	5. Other Issues with DNAME		5. Other Issues with DNAME
	There are several issues to be aware of about the use of DNAME.		There are several issues to be aware of about the use of DNAME.
	5.1. MX, NS and PTR Records Must Point to Target of DNAME		5.1. Canonical hostnames cannot be below DNAME owners
	The names listed as target names of MX, NS and PTR records must be		The names listed as target names of MX, NS, PTR and SRV [RFC2782]
	canonical hostnames. This means no CNAME or DNAME redirection may be		records must be canonical hostnames. This means no CNAME or DNAME
	present during DNS lookup of the address records for the host. This		redirection may be present during DNS lookup of the address records
	is discussed in RFC 2181 [RFC2181], section 10.3, and RFC 1912		for the host. This is discussed in RFC 2181 [RFC2181], section 10.3,
	[RFC1912], section 2.4.		and RFC 1912 [RFC1912], section 2.4. For SRV see RFC 2782 [RFC2782]
			page 4.
	The upshot of this is that although the lookup of a PTR record can		The upshot of this is that although the lookup of a PTR record can
	involve DNAMEs, the name listed in the PTR record can not fall under		involve DNAMEs, the name listed in the PTR record can not fall under
	a DNAME. The same holds for NS and MX records. For example, when		a DNAME. The same holds for NS, SRV and MX records. For example,
	punycode alternates for a zone use DNAME then the NS, MX and PTR		when punycode alternates for a zone use DNAME then the NS, MX, SRV
	records that point to that zone must use names without punycode in		and PTR records that point to that zone must use names without
	their RDATA. What must be done then is to have the domain names with		punycode in their RDATA. What must be done then is to have the
	DNAME substitution already applied to it as the MX, NS, PTR data.		domain names with DNAME substitution already applied to it as the MX,
	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 ignore 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.
	skipping to change at page 13, line 23		skipping to change at page 14, line 8
	the CNAME has no signature, since the server does not sign online.		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		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		foo.bar.example.com CNAME bla.bla.example. The DNAME record does
	have its signature included, since it does not change for every query		have its signature included, since it does not change for every query
	name. The validator must verify the DNAME signature and then		name. The validator must verify the DNAME signature and then
	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 main purpose of this draft is to discuss issues related to the		The DNAME Resource Record type code 39 (decimal) originally has been
	use of DNAME RRs in a DNS zone. The original document registered the		registered by [RFC2672]. IANA should update the DNS resource record
	DNAME Resource Record type code 39 (decimal). IANA should update the		registry to point to this document for RR type 39.
	DNS resource record registry by adding a pointer 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.
	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.
	skipping to change at page 14, line 5		skipping to change at page 14, line 36
	of wildcarded DNAMEs is discouraged in any case [RFC4592].		of wildcarded DNAMEs is discouraged in any case [RFC4592].
	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 and Sam Weiler for		Lewis, Mark Andrews, Mike StJohns, Niall O'Reilly, Sam Weiler, Alfred
	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
			specification", STD 13, RFC 1035, 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.
	[RFC2136] Vixie, P., Thomson, S., Rekhter, Y., and J. Bound,		[RFC2136] Vixie, P., Thomson, S., Rekhter, Y., and J. Bound,
	"Dynamic Updates in the Domain Name System (DNS UPDATE)",		"Dynamic Updates in the Domain Name System (DNS UPDATE)",
	RFC 2136, April 1997.		RFC 2136, April 1997.
	[RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS		[RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS
	Specification", RFC 2181, July 1997.		Specification", RFC 2181, July 1997.
			[RFC2671] Vixie, P., "Extension Mechanisms for DNS (EDNS0)",
			RFC 2671, August 1999.
	[RFC2672] Crawford, M., "Non-Terminal DNS Name Redirection",		[RFC2672] Crawford, M., "Non-Terminal DNS Name Redirection",
	RFC 2672, August 1999.		RFC 2672, August 1999.
			[RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
			specifying the location of services (DNS SRV)", RFC 2782,
			February 2000.
	[RFC3597] Gustafsson, A., "Handling of Unknown DNS Resource Record		[RFC3597] Gustafsson, A., "Handling of Unknown DNS Resource Record
	(RR) Types", RFC 3597, September 2003.		(RR) Types", RFC 3597, September 2003.
	[RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S.		[RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S.
	Rose, "DNS Security Introduction and Requirements",		Rose, "DNS Security Introduction and Requirements",
	RFC 4033, March 2005.		RFC 4033, March 2005.
	[RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S.		[RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S.
	Rose, "Resource Records for the DNS Security Extensions",		Rose, "Resource Records for the DNS Security Extensions",
	RFC 4034, March 2005.		RFC 4034, March 2005.
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