draft-ietf-dnsext-wcard-clarify-03.txt   draft-ietf-dnsext-wcard-clarify-04.txt 
DNSEXT Working Group E. Lewis DNSEXT Working Group E. Lewis
INTERNET DRAFT NeuStar INTERNET DRAFT NeuStar
Expiration Date: April 2005 October 2004 Expiration Date: July 20, 2005 January 2005
Clarifying the Role of Wild Card Domains Clarifying the Role of Wild Card Domains
in the Domain Name System in the Domain Name System
draft-ietf-dnsext-wcard-clarify-03.txt draft-ietf-dnsext-wcard-clarify-04.txt
Status of this Memo Status of this Memo
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aware will be disclosed, in accordance with Section 6 of RFC 3668. aware will be disclosed, in accordance with Section 6 of RFC 3668.
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Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2004). Copyright (C) The Internet Society (2004, 2005).
Abstract Abstract
The definition of wild cards is recast from the original in RFC 1034, The definition of wild cards is recast from the original in RFC 1034,
in words that are more specific and in line with RFC 2119. This in words that are more specific and in line with RFC 2119. This
document is meant to supplement the definition in RFC 1034 and not to document is meant to supplement the definition in RFC 1034 and not to
significantly alter the spirit or intent of that definition. significantly alter the spirit or intent of that definition.
1 Introduction 1 Introduction
In RFC 1034 [RFC1034], sections 4.3.2 and 4.3.3 describe the synthesis In RFC 1034 [RFC1034], sections 4.3.2 and 4.3.3 describe the synthesis
of answers from special records called wildcards. The original of answers from special records called wildcards. The original
definitions are incomplete. This document clarifies and describes definitions are incomplete. This document clarifies and describes
the wildcard synthesis by adding to the discussion and making the wildcard synthesis by adding to the discussion and making
limited modifications. Modifications are made only where necessary limited modifications. Modifications are made only where necessary
to close inconsistencies that have led to interoperability issues. to close inconsistencies that have led to interoperability issues.
1.1 Motivation 1.1 Motivation
Over time many implementations have diverged in different ways from Over time many implementations have diverged in different ways from
the original definition, or at least what had been intended. Although the original definition, or at from least what had been intended. Although
there is clearly a need to clarify the original documents in light there is clearly a need to clarify the original documents in light
of this, the impetus for this document lay in the engineering of of this, the impetus for this document lay in the engineering of
the DNS security extensions [RFC TBD]. With an unclear definition the DNS security extensions [RFC TBD]. With an unclear definition
of wildcards the design of authenticated denial became entangled. of wildcards the design of authenticated denial became entangled.
Although this document is motivated by DNSSEC and the need to Although this document is motivated by DNSSEC and the need to have a
have a separate document passed for the sake of DNSSEC, other separate document passed for the sake of DNSSEC, other motivations have
motivations have risen. The renewed understanding of wildcards gained arisen. The renewed understanding of wildcards gained is worthy of being
is worthy of being documented. documented.
1.2 The Original Definition 1.2 The Original Definition
This document is intended to not make changes. To reinforce This document is intended to make just one change, based on
this, sections of RFC 1034 are repeated verbatim for convenience implementation experience, and to remain as close to the original
of the reader, to help in comparison of old and new text. document as possible. To reinforce this, relevant sections of RFC
1034 are repeated verbatim to help compare the old and new text.
There are a few passages which are changed. This may seem to There are a few passages which are changed. This may seem to
contradict the goal of not changing the original specification, contradict the goal of not changing the original specification,
but the changes herein are required because of inconsistencies but the changes herein are required because of inconsistencies
with the wording in RFC 1034. with the wording in RFC 1034.
The beginning of the discussion ought to start with the definition The beginning of the discussion ought to start with the definition
of the term "wildcard" as it appears in RFC 1034, section 4.3.3. of the term "wildcard" as it appears in RFC 1034, section 4.3.3.
# In the previous algorithm, special treatment was given to RRs with owner # In the previous algorithm, special treatment was given to RRs with owner
# names starting with the label "*". Such RRs are called wildcards. # names starting with the label "*". Such RRs are called wildcards.
# Wildcard RRs can be thought of as instructions for synthesizing RRs. # Wildcard RRs can be thought of as instructions for synthesizing RRs.
# When the appropriate conditions are met, the name server creates RRs # When the appropriate conditions are met, the name server creates RRs
# with an owner name equal to the query name and contents taken from the # with an owner name equal to the query name and contents taken from the
# wildcard RRs. # wildcard RRs.
This passage appears after the algorithm in which they are used is This passage appears after the algorithm in which they are used is
presented. The terminology is not consistent, the word "wildcard" presented. The terminology is not consistent, the word "wildcard"
is clearly defined to be a resource record. In the next sentence is clearly defined to be a resource record. Wildcard has also been
the term is shifted to be an adjective, the first step on the used to refer to domain names whose first (i.e., left most or least
path to overloading the term. Wildcard has also been used to significant) label consists of an asterisk.
refer to domain names that begin with a "*".
1.3 The Clarification 1.3 The Clarification
The clarification effort can be divided into three sections. One The clarification effort can be divided into three sections:
is the use of new terminology to better describe wildcards. Changes
to words in RFC 1034 that have resulted by discovering conflicting o The introduction of new terminology for clarity of the discussion
concepts are presented. Descriptions of special type records in the o Changes to the wording of passages of RFC 1034 prompted by discoveries of
context of being wildcards is discussed. conflicting concepts
o Descriptions of special resource record types in the context of wildcards.
1.3.1 New Terms 1.3.1 New Terms
The term "wildcard" has become so overloaded it is virtually useless The term "wildcard" has become so overloaded it is virtually useless
as a description. A few new terms will be introduced to be more as a description. A few new terms will be introduced to be more
descriptive. The new terms that will be introduced are: descriptive. The new terms that will be introduced are:
Asterisk Label - a label consisting of an asterisk ("*") and no Asterisk Label - a label consisting of an asterisk ("*") and no
other characters. other characters.
Wild Card Domain Name - a domain name whose least significant Wild Card Domain Name - a domain name whose least significant
label (first when reading left to right) is an asterisk label. label (first when reading left to right) is an asterisk label.
Other labels might also be asterisk labels. Other labels might also be asterisk labels.
Source of Synthesis - a Wild Card Domain Name when it is consulted in Source of Synthesis - a wild card domain name when it is consulted in
the final paragraph of step 3, part c of RFC 1034's 4.3.2 algorithm. the final paragraph of step 3, part c of RFC 1034's 4.3.2 algorithm.
Closest Encloser - in RFC 1034's 4.3.2 algorithm, the name at which Closest Encloser - in RFC 1034's 4.3.2 algorithm, the name at which
the last match was possible in step 3, part c. This is the longest the last match was possible in step 3, part c. This is the longest
sequence of exactly matching labels from the root downward in both the sequence of exactly matching labels from the root downward in both the
sought name (QNAME) and in the zone being examined. query name (QNAME) and in the zone being examined.
Label Match - two labels are equivalent if the label type and label Label Match - two labels are equivalent if the label type and label
length are the same bit sequence and if the name is the label is length are both the same and if the labels are case-independent
equivalent bit wise after down casing all of the ASCII characters. equivalent strings. Pattern matching is not involved.
[Ed note: do we still call them ASCII?]
These terms will be more fully described as needed later. These These terms will be more fully described as needed later. These
terms will be used to describe a few changes to the words in RFC terms will be used to describe a few changes to the words in RFC
1034. A summary of the changes appear next and will be fully 1034. A summary of the changes appear next and will be fully
covered in later sections. covered in later sections.
Note that labels other than the asterisk label which contain
asterisks have no special significance or terminology in this
document; thus the fact that a domain names starts with an
asterisk is also of no special significance (and has no special
terminology) unless its first label is the asterisk label, e.g.,
"*foo.example." has no special significance).
1.3.2 Changed Text 1.3.2 Changed Text
The definition of "existence" is changed, superficially, to exclude The definition of "existence" is changed, superficially, to exclude
empty domains that have no subdomains with resource records. This empty domains that have no subdomains with resource records. This
change will not be apparent to implementations, it is needed to change will not be apparent to implementations; it is needed to
make descriptions more concise. make descriptions more concise.
In RFC 1034, there is text that seems to bar having two Asterisk In RFC 1034, there is text that seems to prohibit having two asterisk
Labels in a Wild Card Domain Name. There is no further discussion, labels in a wild card domain name. There is no further discussion,
no prescribed error handling, nor enforcement described. In this no prescribed error handling, nor enforcement described. With this
document, the use of such names will be discouraged, but implementations document implementations will have to account for such a name's use.
will have to account for the possibility of such a name's use.
The actions when a Source of Synthesis owns a CNAME RR are changed to The actions when a source of synthesis owns a CNAME RR are changed to
mirror the actions if an exact match name owns a CNAME RR. This mirror the actions if an exact match name owns a CNAME RR. This
is an addition to the words in RFC 1034, section 4.3.2, step 3, is an addition to the words in RFC 1034, section 4.3.2, step 3,
part c. part c.
1.3.3 Considerations with Special Types 1.3.3 Considerations with Special Types
This clarification will describe in some detail the semantics of This clarification will describe in some detail the semantics of
wildcard CNAME RRs, wildcard NS RRs, wildcard SOA RR's, wildcard CNAME RRSets, wildcard NS RRSets, wildcard SOA RRSets,
wildcard DNAME RRs [RFC wxyz], and empty, non-terminal wildcards. wildcard DNAME RRSets [RFC 2672], and empty non-terminal wildcards.
Understanding these types in the context of wildcards has been Understanding these types in the context of wildcards has been
clouded because these types incur special processing if they clouded because these types incur special processing if they
are the result of an exact match. are the result of an exact match.
By the definition in RFC 1034, there can be no empty, non-terminal By the definition in RFC 1034, there can be no empty non-terminal
"wildcards", but in the algorithm, it is possible that an empty "wildcards" ("RRs are called wildcards"). However, in the algorithm,
non-terminal is sought as the potential owner of a "wildcard." This it is possible that an empty non-terminal is sought as the potential
is one example of why the ordering of the discussion in RFC 1034 is owner of a "wildcard." This is one example of why the ordering of the
confusing. discussion in RFC 1034 is confusing.
1.4 Standards Terminology 1.4 Standards Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in the document entitled document are to be interpreted as described in the document entitled
"Key words for use in RFCs to Indicate Requirement Levels." [RFC2119] "Key words for use in RFCs to Indicate Requirement Levels." [RFC2119]
Quotations of RFC 1034 (as has already been done once above) are Quotations of RFC 1034 (as has already been done once above) are
denoted by a '#' in the leftmost column. denoted by a '#' in the leftmost column.
2 "Wildcard" 2 "Wildcard"
The context of the wildcard concept involves the algorithm by which The context of the wildcard concept involves the algorithm by which
a name server prepares a response (in RFC 1034's section 4.3.2) and a name server prepares a response (in RFC 1034's section 4.3.2) and
the way in which a resource record (set) is identified as being a the way in which a resource record (set) is identified as being a
source of synthetic data (section 4.3.3). source of synthetic data (section 4.3.3).
Tackling the latter first, there are two objectives in defining a Tackling the latter first, there are two objectives in defining a
means to identify a resource record set as a source of synthesis. means to identify a resource record set as a source of synthesis.
First is the desire to maintain all DNS data in a consistent manner. First, to simplify implementations, one objective is to encode synthesis
Avoiding the need for implementations to have many internal data rules into the domain tree, i.e., avoiding a special data store for
structures is a good thing. Not that this means limiting quantity, synthesis is desirable. The second objective impacts interoperability,
but rather types of data. The second objective impacts interoperability,
that is a master server of one implementation has to be able to that is a master server of one implementation has to be able to
send the synthesis instructions to the slaves. Although there are send the synthesis instructions to the slaves. Although there are
alternatives to the use of zone transfers via port 53, a truly alternatives to the use of zone transfers via port 53, a truly
interoperable record synthesis approach has to be able to insert the interoperable record synthesis approach has to be able to insert the
synthesis instructions into a zone transfer. synthesis instructions into a zone transfer.
The objectives in describing the synthesis of records in the context The objectives in describing the synthesis of records in the context
of the name server algorithm include knowing when to employ the of the name server algorithm include knowing when to employ the
process of synthesis and how the synthesis is carried out. process of synthesis and how the synthesis is carried out.
2.1 Identifying a wildcard 2.1 Identifying a wildcard
To provide a more accurate description of "wildcards", the definition To provide a more accurate description of "wildcards", the definition
has to start with a discussion of the domain names that appear as has to start with a discussion of the domain names that appear as
owners. owners.
2.1.1 Wild Card Domain Name and Asterisk Label 2.1.1 Wild Card Domain Name and Asterisk Label
A "Wild Card Domain Name" is defined by having its initial label be: A "wild card domain name" is defined by having its initial
(i.e., left-most or least significant) label be, in binary format:
0000 0001 0010 1010 (binary) = 0x01 0x2a (hexadecimal) 0000 0001 0010 1010 (binary) = 0x01 0x2a (hexadecimal)
This is "*" in presentation format.
The first octet is the normal label type and length for a 1 octet The first octet is the normal label type and length for a 1 octet
long label, the second octet is the ASCII representation [RFC 20] for long label, the second octet is the ASCII representation [RFC 20] for
the '*' character. In RFC 1034, ASCII encoding is assumed to be the the '*' character. In RFC 1034, ASCII encoding is assumed to be the
character encoding. character encoding.
A descriptive name of a label equaling that value is an "Asterisk A descriptive name of a label equaling that value is an "asterisk
Label." label."
RFC 1034's definition of wildcard would be "a resource record owned RFC 1034's definition of wildcard would be "a resource record owned
by a Wild Card Domain Name." This is mentioned to help maintain some by a wild card domain name." This is mentioned to help maintain some
orientation between this clarification and RFC 1034. Keep in mind, orientation between this clarification and RFC 1034. Keep in mind,
that in "Clarifications to the DNS Specification" [RFC 2181] the name that in "Clarifications to the DNS Specification" [RFC 2181] the name
of the basic unit of DNS data became the resource record set (RRSet) and of the basic unit of DNS data became the resource record set (RRSet) and
not the resource record. not the resource record.
2.1.2 Variations on Wild Card Domain Names 2.1.2 Variations on Wild Card Domain Names
Labels other than the asterisk label which contain the ASCII
representation of the asterisk (0x2a) have no significance for the
purposes of this document.
RFC 1034 and RFC 1035 do not explicitly mention the case in which a RFC 1034 and RFC 1035 do not explicitly mention the case in which a
domain name might be something like "the*.example.com." The domain name might be something like "the*.example." The
interpretation is that this domain name in a zone would only match interpretation is that this domain name in a zone would only match
queries for "the*.example.com" and not have any other role. An queries for "the*.example." and not have any other role. An
asterisk ('*') occurring other than as the sole character in asterisk ('*') occurring other than as the sole character in
a label is simply a character forming part of the label and has no a label is simply a character forming part of the label and has no
special meaning. This is not an Asterisk Label, simply a label special meaning. This is not an asterisk label, simply a label
an asterisk in it. The same is true for "**.example.com." and an asterisk in it. The same is true for "**.example." and
"*the.example.com." "*the.example."
[Ed note: the above paragraph reads too strong. The intent ought to
be that such names do not fall under the rules of wildcards. The
intent is not to bar any future attempts to define other forms of
synthesis - nor is the intent to encourage them.]
The interpretation of a wild card domain specification which is not a The interpretation of a wild card domain specification which is not a
leaf domain is not clearly defined in RFC 1034. E.g., sub.*.example., leaf domain is not clearly defined in RFC 1034. E.g., sub.*.example.,
is not discussed, not barred. In wanting to minimize changes from is not discussed, not barred. In wanting to minimize changes from
the original specification, such names are permitted. Although the original specification, such names are permitted. Although
"sub.*.example." is not a Wild Card Domain Name, "*.example." is. "sub.*.example." is not a wild card domain name, "*.example." is.
RRSets used to synthesize records can be owned by a Wild Card Domain RRSets used to synthesize records can be owned by a wild card domain
Name that has subdomains. name that has subdomains.
2.1.3 Non-terminal Wild Card Domain Names 2.1.3 Non-terminal Wild Card Domain Names
In section 4.3.3, the following is stated: In section 4.3.3, the following is stated:
# .......................... The owner name of the wildcard RRs is of # .......................... The owner name of the wildcard RRs is of
# the form "*.<anydomain>", where <anydomain> is any domain name. # the form "*.<anydomain>", where <anydomain> is any domain name.
# <anydomain> should not contain other * labels...................... # <anydomain> should not contain other * labels......................
This covers names like "*.foo.*.example." The pre-RFC2119 wording uses This covers names like "*.foo.*.example." The pre-RFC2119 wording uses
"should not" which has an ambiguous meaning. The specification does not "should not" which has an ambiguous meaning. The specification does not
proscribe actions upon seeing such a name, such as whether or not a proscribe actions upon seeing such a name, such as whether or not a
zone containing the name should fail to be served. What if a dynamic zone containing the name should fail to be served. What if a dynamic
update (RFC2136) requested to add the name to the zone? The failure update (RFC2136) requested to add the name to the zone? The failure
semantics are not defined. semantics are not defined.
The recommendation is that implementations ought to anticipate the The recommendation is that implementations ought to anticipate the
appearance of such names but generally discourage their use in appearance of such names but generally discourage their use in
operations. No standards statement, such as "MAY NOT" or "SHOULD NOT" operations. No standards statement, such as "MUST NOT" nor "SHOULD NOT"
is made here. is made here.
The interpretation of this is, when seeking a Wild Card Domain Name The interpretation of this is, when seeking a wild card domain name
for the purposes of record synthesis, an implementation ought not to for the purposes of record synthesis, an implementation need not to
check the domain name for subdomains. check the domain name for subdomains.
It is possible that a Wild Card Domain Name is an empty non-terminal. It is possible that a wild card domain name is an empty non-terminal.
(See the upcoming sections on empty non-terminals.) In this case, (See the upcoming sections on empty non-terminals.) In this case,
the lookup will terminate as would any empty non-terminal match. the lookup will terminate as would any empty non-terminal match.
2.2 Existence Rules 2.2 Existence Rules
The notion that a domain name 'exists' arises numerous times in The notion that a domain name 'exists' arises numerous times in
discussions about the wildcard concept. RFC 1034 raises the issue discussions about the wildcard concept. RFC 1034 raises the issue
of existence in a number of places, usually in reference to of existence in a number of places, usually in reference to
non-existence and in reference to processing involving wildcards. non-existence and in reference to processing involving wildcards.
RFC 1034 contains algorithms that describe how domain names impact RFC 1034 contains algorithms that describe how domain names impact
skipping to change at line 339 skipping to change at line 346
/ / \ \ / / \ \
/ / \ \ / / \ \
* host1 host2 subdel * host1 host2 subdel
| | | |
| | | |
_tcp _tcp _tcp _tcp
| | | |
| | | |
_ssh _ssh _ssh _ssh
The following queries would be synthesized from the wild card: The following queries would be synthesized from one of the wildcards:
QNAME=host3.example. QTYPE=MX, QCLASS=IN QNAME=host3.example. QTYPE=MX, QCLASS=IN
the answer will be a "host3.example. IN MX ..." the answer will be a "host3.example. IN MX ..."
QNAME=host3.example. QTYPE=A, QCLASS=IN QNAME=host3.example. QTYPE=A, QCLASS=IN
the answer will reflect "no error, but no data" the answer will reflect "no error, but no data"
because there is no A RR set at '*.example.' because there is no A RR set at '*.example.'
QNAME=foo.bar.example. QTYPE=TXT, QCLASS=IN QNAME=foo.bar.example. QTYPE=TXT, QCLASS=IN
the answer will be "foo.bar.example. IN TXT ..." the answer will be "foo.bar.example. IN TXT ..."
because bar.example. does not exist, but the wildcard does. because bar.example. does not exist, but the wildcard does.
The following queries would not be synthesized from the wild card: The following queries would not be synthesized from any of the wildcards:
QNAME=host1.example., QTYPE=MX, QCLASS=IN QNAME=host1.example., QTYPE=MX, QCLASS=IN
because host1.example. exists because host1.example. exists
QNAME=ghost.*.example., QTYPE=MX, QCLASS=IN QNAME=ghost.*.example., QTYPE=MX, QCLASS=IN
because *.example. exists because *.example. exists
QNAME=_telnet._tcp.host1.example., QTYPE=SRV, QCLASS=IN QNAME=_telnet._tcp.host1.example., QTYPE=SRV, QCLASS=IN
because _tcp.host1.example. exists (without data) because _tcp.host1.example. exists (without data)
QNAME=_telnet._tcp.host2.example., QTYPE=SRV, QCLASS=IN
because host2.example. exists (without data)
QNAME=host.subdel.example., QTYPE=A, QCLASS=IN QNAME=host.subdel.example., QTYPE=A, QCLASS=IN
because subdel.example. exists (and is a zone cut) because subdel.example. exists (and is a zone cut)
To the server, all of the domains in the tree exist. The resolver will To the server, all of the domains in the tree exist. The resolver will
get answers to some names off the tree, thanks to synthesis. get answers to some names off the tree, thanks to synthesis.
2.2.2 Empty Non-terminals 2.2.2 Empty Non-terminals
Empty non-terminals are domain names that own no resource records but Empty non-terminals are domain names that own no resource records but
have subdomains which do. This is defined in section 3.1 of RFC 1034: have subdomains that do. This is defined in section 3.1 of RFC 1034:
# The domain name space is a tree structure. Each node and leaf on the # The domain name space is a tree structure. Each node and leaf on the
# tree corresponds to a resource set (which may be empty). The domain # tree corresponds to a resource set (which may be empty). The domain
# system makes no distinctions between the uses of the interior nodes and # system makes no distinctions between the uses of the interior nodes and
# leaves, and this memo uses the term "node" to refer to both. # leaves, and this memo uses the term "node" to refer to both.
The parenthesized "which may be empty" specifies that empty non- The parenthesized "which may be empty" specifies that empty non-
terminals are explicitly recognized. According to the definition of terminals are explicitly recognized. According to the definition of
existence in this document, empty non-terminals do exist at the existence in this document, empty non-terminals do exist at the
server. server.
skipping to change at line 414 skipping to change at line 418
node (with or without a resource set) that has a subdomain that node (with or without a resource set) that has a subdomain that
is a leaf node with a resource set. A QNAME and QCLASS matching is a leaf node with a resource set. A QNAME and QCLASS matching
an existing node never results in a response code of an existing node never results in a response code of
authoritative name error (RCODE==3). authoritative name error (RCODE==3).
The terminology in the above paragraph is chosen to remain as close The terminology in the above paragraph is chosen to remain as close
to that in the original document. The term "with" is a alternate to that in the original document. The term "with" is a alternate
form for "owning" in this case, hence "a leaf node owning resources form for "owning" in this case, hence "a leaf node owning resources
sets, or an interior node, owning or not owning any resource set, sets, or an interior node, owning or not owning any resource set,
that has a leaf node owning a resource set as a subdomain," is the that has a leaf node owning a resource set as a subdomain," is the
proper interpretation of the middle sentence. proper interpretation of the middle sentence. The phrase "resource
set" appears in the original text of RFC 1034, this would now be
replaced by "RRSet."
As an aside, an "authoritative name error", response code (RCODE) 3, As an aside, an "authoritative name error", response code (RCODE) 3,
has been called NXDOMAIN in some RFCs, such as RFC 2136 [RFC 2136]. has been called NXDOMAIN in some RFCs, such as RFC 2136 [RFC 2136].
NXDOMAIN is the mnemonic assigned to such an error by at least one NXDOMAIN is the mnemonic assigned to such an error by at least one
implementation of DNS. implementation of DNS.
Summarizing the discussion on existence in non-RFC1034 words: Summarizing the discussion on existence in non-RFC1034 words:
An authoritative server is to treat a domain name as existing An authoritative server is to treat a domain name as existing
during the execution of the algorithms in RFC 1034 when the during the execution of the algorithms in RFC 1034 when the
domain name conforms to the following definition. A domain name domain name conforms to the following definition. A domain name
is defined to exist if the domain name owns data or has a is defined to exist if the domain name is on the domain tree and
subdomain that exists, or both. either owns data or has a subdomain that exists.
Note that at a zone boundary, the domain name owns data, including Note that at a zone boundary, the domain name owns data, including
the NS RR set. At the delegating server, the NS RR set is not the NS RR set. At the delegating server, the NS RR set is not
authoritative, but that is of no consequence here. The domain name authoritative, but that is of no consequence here. The domain name
owns data, therefore, it exists. owns data, therefore, it exists.
2.3 When does a Wild Card Domain Name not own a wildcard (record) 2.3 When does a Wild Card Domain Name not own a wildcard (record)
When a Wild Card Domain Name appears in a message's query section, When a wild card domain name appears in a message's query section,
no special processing occurs. Asterisk Labels in such a context no special processing occurs. An asterisk label in a query name
only Label Matches other Asterisk Labels in the existing zone tree only (label) matches an asterisk label in the existing zone tree
when the 4.3.2 algorithm is being followed. when the 4.3.2 algorithm is being followed.
When a Wild Card Domain Name appears in the resource data of a When a wild card domain name appears in the resource data of a
record, no special processing occurs. An Asterisk Label in that record, no special processing occurs. An asterisk label in that
context literally means just an asterisk. context literally means just an asterisk.
3. Impact of a Wild Card Domain On a Response 3. Impact of a Wild Card Domain On a Response
The description of how wild cards impact response generation is in The description of how wild cards impact response generation is in
RFC 1034, section 4.3.2. That passage contains the algorithm RFC 1034, section 4.3.2. That passage contains the algorithm
followed by a server in constructing a response. Within that followed by a server in constructing a response. Within that
algorithm, step 3, part 'c' defines the behavior of the wild card. algorithm, step 3, part 'c' defines the behavior of the wild card.
The algorithm is directly quoted in lines that begin with a '#' sign. The algorithm is directly quoted in lines that begin with a '#' sign.
Commentary is interleaved. Commentary is interleaved.
There is a documentation issue deserving some explanation. The There is a documentation issue deserving some explanation. The
algorithm in RFC 1034, section 4.3.2. is not intended to be pseudo algorithm in RFC 1034, section 4.3.2. is not intended to be pseudo
code, i.e., it's steps are not intended to be followed in strict code, i.e., its steps are not intended to be followed in strict
order. The "algorithm" is a suggestion. As such, in step 3, parts order. The "algorithm" is a suggestion. As such, in step 3, parts
a, b, and c, do not have to be implemented in that order. a, b, and c, do not have to be implemented in that order.
Another issue needing explanation is that RFC 1034 is a full Another issue needing explanation is that RFC 1034 is a full
standard. There is another RFC, RFC 2672, which makes, or proposes standard. There is another RFC, RFC 2672, which makes, or proposes
an adjustment to RFC 1034's section 4.3.2 for the sake of the DNAME an adjustment to RFC 1034's section 4.3.2 for the sake of the DNAME
RR. RFC 2672 is a proposed standard. The dilemma in writing these RR. RFC 2672 is a proposed standard. The dilemma in writing these
clarifications is knowing which document is the one being clarified. clarifications is knowing which document is the one being clarified.
Fortunately, the difference between RFC 1034 and RFC 2672 is not Fortunately, the difference between RFC 1034 and RFC 2672 is not
significant with respect to wild card synthesis, so this document significant with respect to wild card synthesis, so this document
skipping to change at line 480 skipping to change at line 486
3.1 Step 2 3.1 Step 2
Step 2 of the RFC 1034's section 4.3.2 reads: Step 2 of the RFC 1034's section 4.3.2 reads:
# 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.
In this step, the most appropriate zone for the response is chosen. In this step, the most appropriate zone for the response is chosen.
There are two reasons to repeat this. One is that this means all The significance of this step is that it means all of Step 3 is being
of step 3 is done within the context of a zone, which will constrain performed within one zone. This has significance when considering
the discussion. The other is the though behind synthesizing entire whether or not an SOA RR can be ever be used for synthesis.
zones and the use of Wild Card Domain Names to do so.
If an implementation were to attempt to synthesize zones, this would be
the step to do this. Note though that each name server listed in the NS
RRSet for the synthesized zone would have to coherently synthesize the
zone.
3.2 Step 3 3.2 Step 3
Step 3 is dominated by three parts, labelled a, b, and c. But the Step 3 is dominated by three parts, labelled 'a', 'b', and 'c'. But the
beginning of the Step is important and needs explanation. beginning of the Step is important and needs explanation.
# 3. Start matching down, label by label, in the zone. The # 3. Start matching down, label by label, in the zone. The
# matching process can terminate several ways: # matching process can terminate several ways:
The word matching in this care refers to Label Matching. The concept The word 'matching' refers to label matching. The concept
is based in the view of the zone as the tree of existing names. The is based in the view of the zone as the tree of existing names. The
Query Name is considered to be an ordered sequence of labels - as query name is considered to be an ordered sequence of labels - as
if the name were a path from the root to the owner of the desired if the name were a path from the root to the owner of the desired
data. data. (Which it is.)
The process of Label Matching ends in one of three choices, the parts The process of label matching a query name ends in exactly one of three
a, b, and c. Once one of the parts is chosen, the other parts are choices, the parts 'a', 'b', and 'c'. Once one of the parts is chosen,
not considered. (E.g., do not execute part c and then change the the other parts are not considered. (E.g., do not execute part 'c' and
execution path to finish in part b.) The process of Label Matching then change the execution path to finish in part 'b'.) The process of
is also done independent of the Query Type. label matching is also done independent of the Query Type.
Parts a and b are not an issue for this clarification as they do not Parts 'a' and 'b' are not an issue for this clarification as they do not
relate to record synthesis. Part a generally covers a situation in relate to record synthesis. Part 'a' generally covers a situation in
which all of the labels in the search (query) name have been matched which all of the labels in the query name have a (label) match in the tree.
down the tree, e.g., the sought name exists as an exact Label Match. Part 'b' generally covers a situation in which any label in the query
Part b generally covers a situation in which any label in the sought name (label) matches a tree label and the tree label has a NS RRSet.
name Label Matches a tree label and the tree label has a NS RRSet.
3.3 Part 'c' 3.3 Part 'c'
The context of part 'c' is that the process of Label Matching the The context of part 'c' is that the process of label matching the
labels in the sought name has resulted in a situation in which there labels of the query name has resulted in a situation in which there
is nothing corresponding in the tree. It is as if the lookup has is no corresponding label in the tree. It is as if the lookup has
"fallen off the tree." "fallen off the tree."
# c. If at some label, a match is impossible (i.e., the # c. If at some label, a match is impossible (i.e., the
# corresponding label does not exist), look to see if a # corresponding label does not exist), look to see if a
# the "*" label exists. # the "*" label exists.
To help describe the process of looking "to see is a the [sic] To help describe the process of looking 'to see if a [sic] the "*"
label exists" a term has been coined to describe the last label label exists' a term has been coined to describe the last label
matched. The term is "Closest Encloser." matched. The term is "closest encloser."
3.3.1 Closest Encloser and the Source of Synthesis 3.3.1 Closest Encloser and the Source of Synthesis
The "Closest Encloser" is the node in the zone's tree of existing The closest encloser is the node in the zone's tree of existing
domain names that is has the most matching labels with the sought domain names that has the most labels matching the query name
name. Each match is a "Label Match" and the order of the labels (consecutively, counting from the root label downward). Each match
is also the same. The Closest Encloser is an existing name in the is a "label match" and the order of the labels is the same.
zone, it may be an empty non-terminal, it may even be a Wild Card
Domain Name itself. In no circumstances is the Closest Encloser
the used to synthesize records though.
A "Source of Synthesis" is defined in the context of a lookup The closest encloser is, by definition, an existing name in the zone. The
process as the Wild Card Domain Name immediately descending from closest encloser might be an empty non-terminal or even be a wild card
the Closest Encloser provided the Wild Card Domain Name exists. domain name itself. In no circumstances is the closest encloser
A Source of Synthesis does not guarantee having a RRSet to use the used to synthesize records for the current query.
for synthesis, a Source of Synthesis may even be an empty
non-terminal.
If a Source of Synthesis exists, it will be the Wild Card Domain Name The source of synthesis is defined in the context of a query process
that is identified by an Asterisk Label below the Closest Encloser. as that wild card domain name immediately descending from the
E.g., "<Asterisk Label>.<Closest Encloser> or "*.<Closest Encloser>." closest encloser, provided that this wild card domain name exists.
If the Source of Synthesis does not exist (not on the domain tree), "Immediately descending" means that the source of synthesis has a name
there will be no wildcard synthesis of the form <asterisk label>.<closest encloser>. A source of synthesis
does not guarantee having a RRSet to use for synthesis. The source of
synthesis could be an empty non-terminal.
If the source of synthesis does not exist (not on the domain tree),
there will be no wildcard synthesis. There is no search for an alternate.
The important concept is that for any given lookup process, there The important concept is that for any given lookup process, there
is at most one place at which wildcard synthetic records can be is at most one place at which wildcard synthetic records can be
obtained. If the Source of Synthesis does not exist, the lookup obtained. If the source of synthesis does not exist, the lookup
terminates, the lookup does not look for other wildcard records. terminates, the lookup does not look for other wildcard records.
Other terms have been coined on the mailing list in the past. E.g., Other terms have been coined on the mailing list in the past. E.g.,
it has been said that existing names block the application of it has been said that existing names block the application of
wildcard records. This is still an appropriate viewpoint, but wildcard records. This is still an appropriate viewpoint, but
replacing this notion with the Closest Encloser and Source of replacing this notion with the closest encloser and source of
Synthesis the depiction of the wildcard process is clearer. synthesis terminology depicts the wildcard process is more clearly.
3.3.2 Closest Encloser and Source of Synthesis Examples 3.3.2 Closest Encloser and Source of Synthesis Examples
To illustrate, using the example zone in section 2.2.1 of this document, To illustrate, using the example zone in section 2.2.1 of this document,
the following chart shows QNAMEs and the closest enclosers. the following chart shows QNAMEs and the closest enclosers.
QNAME Closest Encloser Source of Synthesis QNAME Closest Encloser Source of Synthesis
host3.example. example. *.example. host3.example. example. *.example.
_telnet._tcp.host1.example. _tcp.host1.example. no source _telnet._tcp.host1.example. _tcp.host1.example. no source
_telnet._tcp.host2.example. host2.example. no source _telnet._tcp.host2.example. host2.example. no source
_telnet._tcp.host3.example. example. *.example. _telnet._tcp.host3.example. example. *.example.
_chat._udp.host3.example. example. *.example. _chat._udp.host3.example. example. *.example.
The fact that a closest encloser will be the only superdomain that
can have a candidate wild card will have an impact when it comes to
designing pre-calculated authenticated denial of existence proofs.
3.3.3 Non-existent Source of Synthesis 3.3.3 Non-existent Source of Synthesis
In RFC 1034: In RFC 1034:
# If the "*" label does not exist, check whether the name # If the "*" label does not exist, check whether the name
# we are looking for is the original QNAME in the query # we are looking for is the original QNAME in the query
# or a name we have followed due to a CNAME. If the name # or a name we have followed due to a CNAME. If the name
# is original, set an authoritative name error in the # is original, set an authoritative name error in the
# response and exit. Otherwise just exit. # response and exit. Otherwise just exit.
The above passage is clear, evidenced by the lack of discussion and The above passage is clear, evidenced by the lack of discussion and
mis-implementation of it over the years. It is included for mis-implementation of it over the years. It is included for
completeness only. (No attempt is made to re-interpret it lest completeness only. (No attempt is made to re-interpret it lest
a mistake in editing leads to confusion.) a mistake in editing leads to confusion.)
3.3.4 Type Matching 3.3.4 Type Matching
RFC 1034 concludes part c with this: RFC 1034 concludes part 'c' with this:
# If the "*" label does exist, match RRs at that node # If the "*" label does exist, match RRs at that node
# against QTYPE. If any match, copy them into the answer # against QTYPE. If any match, copy them into the answer
# section, but set the owner of the RR to be QNAME, and # section, but set the owner of the RR to be QNAME, and
# not the node with the "*" label. Go to step 6. # not the node with the "*" label. Go to step 6.
This final paragraph covers the role of the QTYPE in the lookup process. This final paragraph covers the role of the QTYPE in the lookup process.
Based on implementation feedback and similarities between step a and Based on implementation feedback and similarities between step 'a' and
step c a change to this passage a change has been made. step 'c' a change to this passage a change has been made.
The change is to add the following text: The change is to add the following text:
If the data at the source of synthesis is a CNAME, and If the data at the source of synthesis is a CNAME, and
QTYPE doesn't match CNAME, copy the CNAME RR into the QTYPE doesn't match CNAME, copy the CNAME RR into the
answer section of the response changing the owner name answer section of the response changing the owner name
to the QNAME, change QNAME to the canonical name in the to the QNAME, change QNAME to the canonical name in the
CNAME RR, and go back to step 1. CNAME RR, and go back to step 1.
This is essentially the same text in step a covering the processing of This is essentially the same text in step a covering the processing of
CNAME RRSets. CNAME RRSets.
4. Considerations with Special Types 4. Considerations with Special Types
Five types of RRSets owned by a Wild Card Domain Name have caused Five types of RRSets owned by a wild card domain name have caused
confusion. Four explicit types causing confusion are SOA, NS, CNAME, confusion. Four explicit types causing confusion are SOA, NS, CNAME,
DNAME, and the fifth type - "none." DNAME, and the fifth type - "none."
4.1. SOA RR's at a Wild Card Domain Name 4.1. SOA RRSet at a Wild Card Domain Name
A Wild Card Domain Name owning an SOA RRSet means that the domain
is at the root of the zone (apex). The domain can not be a Source of
Synthesis because that is, but definition, a descendent node (of
the Closest Encloser) and a zone apex is at the top of the zone.
Although a Wild Card Domain Name can not be a Source of Synthesis, A wild card domain name owning an SOA RRSet means that the domain
there is no reason to forbid the ownership of an SOA RRSet. This is at the root of the zone (apex). The domain can not be a source of
means that zones with names like "*.<Parent Zone>.", and even synthesis because that is, by definition, a descendent node (of
"*.<Parent Sublabels>.<Parent Zone>." the closest encloser) and a zone apex is at the top of the zone.
Step 2 (section 3.1) does not provide a means to specify a means to Although a wild card domain name owning an SOA RRSet can never be a
synthesize a zone. Therefore, according to the rules there, the source of synthesis, there is no reason to forbid the ownership of
only way in which a zone that has a name which is a Wild Card an SOA RRSet.
Domain Name is if the QNAME is in a domain below the zone's name.
E.g., if *.example. has an SOA record, then only a query like E.g., if *.example. has an SOA record, then only a query like
QNAME=*.example., QTYPE=A, QCLASS=IN would see it. As another QNAME=*.example., QTYPE=A, QCLASS=IN would see it. A query like
example, a QNAME of www.*.example. would also result in passing QNAME=foo.example., QTYPE=A, QCLASS=IN would not see it - a different
through the zone. zone would have been picked in Step 2. A QNAME of www.*.example.
would result in a query referencing the *.example zone.
4.2. NS RR's at a Wild Card Domain Name 4.2. NS RRSet at a Wild Card Domain Name
The semantics of a Wild Card Domain Name ownership of a NS RRSet The semantics of a wild card domain name's ownership of a NS RRSet
has been unclear. Looking through RFC 1034, the recommendation has been unclear. Looking through RFC 1034, the recommendation
is to have the NS RRSet act the same a any non-special type, e.g., is to have the NS RRSet act the same a any non-special type, e.g.,
like an A RR. like an A RRSet.
If the NS RRSet in question is at the top of the zone, i.e., the If the NS RRSet in question is at the top of the zone, i.e., the
name also owns an SOA RRSet, the QNAME equals the zone name. This name also owns an SOA RRSet, the QNAME equals the zone name. This
would trigger part 'a' of Step 3. would trigger part 'a' of Step 3.
In any other case, the Wild Card Domain Name owned NS RRSet would In any other case, the wild card domain name owned NS RRSet would
be the only RRSet (prior to changes instituted by DNSSEC) at the be the only RRSet (prior to changes instituted by DNSSEC) at the
node by DNS rules. If the QNAME equals the Wild Card Domain Name node by DNS rules. If the QNAME equals the wild card domain name
or is a subdomain of it, then the node would be considered in part or is a subdomain of it, then the node would be considered in part
'b' of Step 3. 'b' of Step 3. [should dnssec be left out of this?]
Note that there is no synthesis of records in the authority section Note that there is no synthesis of records in the authority section
because part 'b' does not account for synthesis. The referral because part 'b' does not specify synthesis. The referral returned
returned would have the Wild Card Domain Name in the authority section, would have the wild card domain name in the authority section unchanged.
unchanged.
If the QNAME is not the same as the Wild Card Domain Name nor a If the QNAME is not the same as the wild card domain name nor a
subdomain of it, then part 'c' of Step 3 has been triggered. Once subdomain of it, then part 'c' of Step 3 has been triggered. Once
part 'c' is entered, there is no reverting to part 'b' - i.e., part 'c' is entered, there is no reverting to part 'b' - i.e.,
once an NS RRSet is synthesized it does not mean that the server has once an NS RRSet is synthesized it does not mean that the server has
to consider the name delegated away. I.e., the server is not to consider the name delegated away. I.e., the server is not
synthesizing a record (the NS RRSet) that means the server does not synthesizing a record (the NS RRSet) that means the server does not
have the right to synthesize. have the right to synthesize. (Only an authoritative server can
perform synthesis. By synthesizing an NS RRSet, it appears that the
authority for the name has been delegated to another authority.)
4.3. CNAME RR's at a Wild Card Domain Name In summation, an NS RRSet at a wild card domain name will not result in
the generation of referral messages for non-existent domains.
The issue of CNAME RR's owned by wild card domain names has prompted 4.3. CNAME RRSet at a Wild Card Domain Name
The issue of a CNAME RRSet owned by wild card domain names has prompted
a suggested change to the last paragraph of step 3c of the algorithm a suggested change to the last paragraph of step 3c of the algorithm
in 4.3.2. The changed text appears in section 3.3.4 of this document. in 4.3.2. The changed text appears in section 3.3.4 of this document.
4.4. DNAME RR's at a Wild Card Domain Name 4.4. DNAME RRSet at a Wild Card Domain Name
The specification of the DNAME RR, which is at the proposed level of The specification of the DNAME RR, which is at the proposed level of
standardization, is not as mature as the full standard in RFC 1034. standardization, is not as mature as the full standard in RFC 1034.
Because of this, or the reason for this is, there appears to be a Because of this, or the reason for this is, there appears to be a
a number of issues with that definition and it's rewrite of the algorithm a number of issues with that definition and it's rewrite of the algorithm
in 4.3.2. For the time being, when it comes to wild card processing in 4.3.2. For the time being, when it comes to wild card processing
issues, a DNAME can be considered to be a CNAME synthesizer. A DNAME issues, a DNAME can be considered to be a CNAME synthesizer. A DNAME
at a wild card domain name is effectively the same as a CNAME at a at a wild card domain name is effectively the same as a CNAME at a
wild card domain name. wild card domain name.
4.5 Empty Non-terminal Wild Card Domain Name 4.5 Empty Non-terminal Wild Card Domain Name
If a Source of Synthesis is an empty non-terminal, then the response If a source of synthesis is an empty non-terminal, then the response
will be one of no error in the return code and no RRSet in the answer will be one of no error in the return code and no RRSet in the answer
section. section.
5. Security Considerations 5. Security Considerations
This document is refining the specifications to make it more likely This document is refining the specifications to make it more likely
that security can be added to DNS. No functional additions are being that security can be added to DNS. No functional additions are being
made, just refining what is considered proper to allow the DNS, made, just refining what is considered proper to allow the DNS,
security of the DNS, and extending the DNS to be more predictable. security of the DNS, and extending the DNS to be more predictable.
skipping to change at line 720 skipping to change at line 724
[RFC 1034] Domain Names - Concepts and Facilities, P.V. Mockapetris, [RFC 1034] Domain Names - Concepts and Facilities, P.V. Mockapetris,
Nov-01-1987 Nov-01-1987
[RFC 1035] Domain Names - Implementation and Specification, P.V [RFC 1035] Domain Names - Implementation and Specification, P.V
Mockapetris, Nov-01-1987 Mockapetris, Nov-01-1987
[RFC 2119] Key Words for Use in RFCs to Indicate Requirement Levels, S [RFC 2119] Key Words for Use in RFCs to Indicate Requirement Levels, S
Bradner, March 1997 Bradner, March 1997
[RFC 2181] Clarifications to the DNS Specification, R. Elz and R. Bush,
July 1997.
Informative References Informative References
[RFC 2136] Dynamic Updates in the Domain Name System (DNS UPDATE), P. [RFC 2136] Dynamic Updates in the Domain Name System (DNS UPDATE), P.
Vixie, Ed., S. Thomson, Y. Rekhter, J. Bound, April 1997 Vixie, Ed., S. Thomson, Y. Rekhter, J. Bound, April 1997
[RFC 2535] Domain Name System Security Extensions, D. Eastlake, March 1999 [RFC 2535] Domain Name System Security Extensions, D. Eastlake, March 1999
[RFC 2672] Non-Terminal DNS Name Redirection, M. Crawford, August 1999 [RFC 2672] Non-Terminal DNS Name Redirection, M. Crawford, August 1999
7. Others Contributing to This Document 7. Others Contributing to This Document
Others who have been editors of this document: Bob Halley and Robert Elz. Others who have been editors of this document: Bob Halley.
Others who have directly caused text to appear in the document: Paul Others who have directly caused text to appear in the document: Alex
Vixie and Olaf Kolkman. Many others have indirect influences on the Bligh, Robert Elz, Paul Vixie and Olaf Kolkman.
content. Many others have indirect influences on the content.
8. Editor 8. Editor
Name: Edward Lewis Name: Edward Lewis
Affiliation: NeuStar Affiliation: NeuStar
Address: tbd Address: 46000 Center Oak Plaza, Sterling, VA, 20166, US
Phone: tbd Phone: +1-571-434-5468
Email: tbd (please send comments to namedroppers) Email: ed.lewis@neustar.biz
Comments on this document can be sent to the editors or the mailing Comments on this document can be sent to the editor or the mailing
list for the DNSEXT WG, namedroppers@ops.ietf.org. list for the DNSEXT WG, namedroppers@ops.ietf.org.
9. Trailing Boilerplate 9. Trailing Boilerplate
Copyright (C) The Internet Society (2004). This document is subject Copyright (C) The Internet Society (2004). This document is subject
to the rights, licenses and restrictions contained in BCP 78 and to the rights, licenses and restrictions contained in BCP 78 and
except as set forth therein, the authors retain all their rights. except as set forth therein, the authors retain all their rights.
This document and the information contained herein are provided on an This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
skipping to change at line 790 skipping to change at line 797
that may be required to implement this standard. Please address the that may be required to implement this standard. Please address the
information to the IETF at ietf-ipr@ietf.org. information to the IETF at ietf-ipr@ietf.org.
Acknowledgement Acknowledgement
Funding for the RFC Editor function is currently provided by the Funding for the RFC Editor function is currently provided by the
Internet Society. Internet Society.
Expiration Expiration
This document expires on or about 11 April 2005. This document expires on or about July 20, 2005.
 End of changes. 

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