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doc/draft/draft-ietf-dnsext-insensitive-00.txt → doc/draft/draft-ietf-dnsext-insensitive-01.txt
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INTERNET-DRAFT Donald E. Eastlake 3rd
Clarifies STD0013 Motorola Laboratories
Expires July 2003 January 2003
Expires August 2003 February 2003
Domain Name System (DNS) Case Insensitivity Clarification
------ ---- ------ ----- ---- ------------- -------------
<draft-ietf-dnsext-insensitive-00.txt>
<draft-ietf-dnsext-insensitive-01.txt>
Donald E. Eastlake 3rd
@ -60,42 +60,42 @@ D. Eastlake 3rd [Page 1]
INTERNET-DRAFT DNS Case Insensitivity
Acknowledgements
The contributions to this document of Rob Austein, Olafur
Gudmundsson, Daniel J. Anderson, Alan Barrett, and Andrew Main are
gratefully acknowledged.
Table of Contents
Status of This Document....................................1
Abstract...................................................1
Acknowledgements...........................................2
Table of Contents..........................................2
1. Introduction............................................3
2. Case Insensitivity of DNS Labels........................3
3. Additional DNS Case Insensitivity Considerations........4
3.1 CLASS Case Insensitivity Considerations................4
3.2 Label Type Case Insensitivity Considerations...........5
4. Case on Input and Output................................5
5. Security Considerations.................................6
Normative References.......................................7
Informative References.....................................7
Author's Address...........................................8
Expiration and File Name...................................8
2.1 Escaping Unusual DNS Label Octets......................3
2.2 Example Labels with Escapes............................4
2.3 Name Lookup Case Insensitivity.........................4
2.4 Original DNS Label Types...............................5
3. Additional DNS Case Insensitivity Considerations........5
3.1 CLASS Case Insensitivity Considerations................5
3.2 Extended Label Type Case Insensitivity Considerations..5
4. Case on Input and Output................................6
4.1 DNS Output Case Preservation...........................6
4.2 DNS Input Case Preservation............................6
4.3 Wildcard Matching......................................7
5. Security Considerations.................................7
Normative References.......................................9
Informative References.....................................9
Author's Address..........................................10
Expiration and File Name..................................10
@ -123,7 +123,7 @@ INTERNET-DRAFT DNS Case Insensitivity
The Domain Name System (DNS) is the global hierarchical replicated
distributed database system for Internet addressing, mail proxy, and
other information. Each node in the DNS tree has a name consisting of
zero or more labels [STD 13][RFC 1591, 2606] which have always been
zero or more labels [STD 13][RFC 1591, 2606] which have been
specified as being treated in a case insensitive fashion. This
document clarifies the meaning of "case insensitive" for this
application.
@ -153,21 +153,21 @@ INTERNET-DRAFT DNS Case Insensitivity
WWW.gnu.AI.mit.EDU.
or 69.2.0.192.in-ADDR.ARPA.
The individual bytes of which DNS names consist are not limited to
The individual octets of which DNS names consist are not limited to
valid ASCII character codes. They are defined as 8-bit bytes and all
values are allowed. It is just that they are traditionally interpreted
values are allowed. Most applications, however, interprete them
as ASCII characters.
The typographic convention for bytes that do not correspond to an
ASCII printing graphic is to show them as a back-slash followed by
three hex digits for the value of the byte as an unsigned
integer. This includes all byte values outside of the inclusive range
of 0x21 ("!") to 0x7E ("~"). That is to say, all byte values in the
two inclusive ranges 0x00 to 0x20 and 0x7F to 0xFF. The same
convention can be used for the back-slash character and the special
label separator period ("."). A period can also be protected from
recognition as a separator, so that it will be treated as a normal
label character, by preceeding it with a back-slash. The first example
2.1 Escaping Unusual DNS Label Octets
An escape is needed for all octet values outside of the inclusive
range of 0x21 ("!") to 0x7E ("~"). That is to say, all octet values in
the two inclusive ranges 0x00 to 0x20 and 0x7F to 0xFF.
One typographic convention for octets that do not correspond to an
ASCII printing graphic is to show them as a back-slash followed by the
D. Eastlake 3rd [Page 3]
@ -176,41 +176,90 @@ D. Eastlake 3rd [Page 3]
INTERNET-DRAFT DNS Case Insensitivity
below shows embedded spaces and a period (".") within a label. The
second one show a 4 byte label where the second byte has all bits zero
and the third byte has all bits one.
value of the octet as an unsigned integer represented by exactly three
decimal digits. The same convention can be used for printing ASCII
characters. This includes the back-slash character used in this
convention itself and the special label separator period (".") which
can be expressed as \092 and \046 respectively.
Donald\040E\.\040Eastlake\0403rd.example.
or a\000\377z.example.
A back-slash followed by only one or two decimal digits is
undefined. A back-slash followed by four decimal digits produces two
octets, the first octet having the value of the first three digits
considered as a decimal number and the second octet being the
character code for the fourth decimal digit.
Octets, other than those corresponding to the ASCII digits 0 through
9, can also be protected from recognition, so that they will be
treated as a normal label character, by a second convention:
preceding them with a back-slash. This is the most commonly used
technique for protecting back slash ("\") and period ("."). However,
it is advisable to avoid using this on other than printing ASCII
characters.
2.2 Example Labels with Escapes
The first example below shows embedded spaces and a period (".")
within a label. The second one show a 4 octet label where the second
octet has all bits zero and the third octet has all bits one.
Donald\032E\.\032Eastlake\0323rd.example.
or a\000\255z.example.
2.3 Name Lookup Case Insensitivity
The design decision was made that comparisons on name lookup for DNS
queries should be case insensitive [STD 13]. That is to say, a lookup
string byte with a value in the inclusive range of 0x41 to 0x5A, the
string octet with a value in the inclusive range of 0x41 to 0x5A, the
upper case ASCII letters, MUST match the identical value and also
match the corresponding value in the inclusive range 0x61 to 0x7A,
the lower case ASCII letters. And a lookup string byte with a lower
the lower case ASCII letters. And a lookup string octet with a lower
case ASCII letter value MUST similarly match the identical value and
also match the corresponding value in the upper case ASCII letter
range. One way to implement this rule would be, when comparing bytes,
to subtract 0x20 from all bytes in the inclusive range 0x61 to 0x7A
before the comparison. Such an operation is commonly known as "case
folding".
range.
(Historic Note: the terms "upper case" and "lower case" were invented
after movable type became wide spread for printing. The terms
originally refered to the two font trays for storing, in partitioned
areas, the different physical type elements. Before movable type,
the nearest equivalent terms were "majuscule" and "minuscule".)
(Historical Note: the terms "upper case" and "lower case" were
invented after movable type became wide spread for printing. The
terms originally referred to the two font trays for storing, in
partitioned areas, the different physical type elements. Before
movable type, the nearest equivalent terms were "majuscule" and
D. Eastlake 3rd [Page 4]
INTERNET-DRAFT DNS Case Insensitivity
"minuscule".)
One way to implement this rule would be, when comparing octets, to
subtract 0x20 from all octets in the inclusive range 0x61 to 0x7A
before the comparison. Such an operation is commonly known as "case
folding" but implementation via case folding is not required. Note
that the DNS case insensitivity does NOT correspond to the case
folding specified in iso-8859-1 or iso-8859-2. For example, the
octets 0xDD (\221) and 0xFD (\253) do NOT match although in other
contexts where they are interpreted as the upper and lower case
version of "Y" with an acute accent, they might.
2.4 Original DNS Label Types
DNS labels in wire encoded names have a type associated with them.
The original DNS standard [RFC 1035] had only two types. ASCII
labels, with a length of from zero to 63 bytes and indirect labels
labels, with a length of from zero to 63 octets and indirect labels
which consist of an offset pointer to a name location elsewhere in
the wire encoding. (The ASCII label of length zero is reserved for
use as the name of the root node of the name tree.) ASCII labels
follow the ASCII case conventions described above. Indirect labels
are, in effect, replaced by the name to which they point which is
then treated with the case insensitivity rules in this document.
the wire encoding on a DNS message. (The ASCII label of length zero
is reserved for use as the name of the root node of the name tree.)
ASCII labels follow the ASCII case conventions described above.
Indirect labels are, in effect, replaced by the name to which they
point which is then treated with the case insensitivity rules in this
document.
@ -227,21 +276,22 @@ INTERNET-DRAFT DNS Case Insensitivity
for data location called CLASS. The only CLASS in global use at this
time is the "IN" or Internet CLASS.
The handling of DNS label case is not CLASS dependent.
D. Eastlake 3rd [Page 4]
3.2 Extended Label Type Case Insensitivity Considerations
DNS was extended by [RFC 2671] to have additional label type numbers
available. (The only such type defined so far it the BINARY type [RFC
D. Eastlake 3rd [Page 5]
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The handling of DNS label case is not CLASS dependent.
3.2 Label Type Case Insensitivity Considerations
DNS was extended by [RFC 2671] to have additional label type numbers
available. (The only such type defined so far it the BINARY type [RFC
2673].)
The ASCII case insensitivity conventions, or case folding, only apply
@ -256,11 +306,15 @@ INTERNET-DRAFT DNS Case Insensitivity
preserved on output, except when output is optimized by the use of
indirect labels, and preserved when possible on input.
4.1 DNS Output Case Preservation
[STD 13] views the DNS namespace as a node tree. ASCII output is as
if a name was marshalled by taking the label on the node whose name
is to be output, converting it to a typographicly encoded ASCII
is to be output, converting it to a typographically encoded ASCII
string, walking up the tree outputting each label encountered, and
preceeding all labels but the first with a period ("."). Wire output
preceding all labels but the first with a period ("."). Wire output
follows the same sequence but each label is wire encoded and no
periods inserted. No "case conversion" or "case folding" is done
during such output operations. However, to optimize output, indirect
@ -271,6 +325,10 @@ INTERNET-DRAFT DNS Case Insensitivity
destroy the output preservation of case. This type of optimization is
commonly called "name compression".
4.2 DNS Input Case Preservation
Originally, DNS input came from an ASCII Master File as defined in
[STD 13]. DNS Dynamic update has been added as a source of DNS data
[RFC 2136, 3007]. When a node in the DNS name tree is created by such
@ -278,33 +336,44 @@ INTERNET-DRAFT DNS Case Insensitivity
preserved if they are for nodes being creted. However, no change is
made in the name label on nodes that already exist is the DNS data
being augmented or updated. It is quite common for higher level nodes
to already exist. For example, if data with owner name
"foo.bar.example" is input and then later data with owner name
"xyz.BAR.example" is input, the name of the label on the
"bar.example" node, i.e. "bar", is not changed to "BAR". Thus later
retrieval of data stored under "xyz.bar.example" in this case can
easily result is obtaining data with "xyz.BAR.example".
to already exist.
For example, if data with owner name "foo.bar.example" is input and
then later data with owner name "xyz.BAR.example" is input, the name
of the label on the "bar.example" node, i.e. "bar", is not changed to
"BAR". Thus later retrieval of data stored under "xyz.bar.example" in
D. Eastlake 3rd [Page 5]
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INTERNET-DRAFT DNS Case Insensitivity
this case can easily result is obtaining data with "xyz.BAR.example".
The same considerations apply inputting multiple data records with
owner names differing only in case. From the example above, if an "A"
record is stored under owner name "xyz.BAR.example" and then a second
"A" record under "XYZ.BAR.example", the second will be stored at the
node with the first (lower case initial label) name.
Note that the order of insertion into a server database of the DNS
name tree nodes that appear in a Master File is not defined so that
the results of inconsistent capitalization in a Master File are
unpredicatable output capitalization.
There is one additional instance of note, which relfects the general
4.3 Wildcard Matching
There is one additional instance of note, which reflects the general
rules that output case reflects input case unless there is
conflicting capitalization in the DNS database or the output case is
hidden by name compression. This is when a query matches a wild card
in the DNS database at a server. In that case, the answer SHOULD
reflect the input case of the label or labels that matched the
wildcard unless they are replaced by an indirect label which MAY
point to a name with different captialization.
point to a name with different capitalization.
@ -326,6 +395,23 @@ INTERNET-DRAFT DNS Case Insensitivity
canonical ordering for them) appears in Section 8 of [RFC 2535]. See
also [UNKRR].
Finally, a non-DNS name may be stored into DNS with the false
expectation that case will always be preserved. For example, although
this would be quite rare, on a system with case sensitive email
address local parts, an attempt to store two "RP" records that
differed only in case would probably produce unexpected results that
D. Eastlake 3rd [Page 7]
INTERNET-DRAFT DNS Case Insensitivity
might have security implications. That is because the entire email
address, including the possibly case sensitive local or left hand
part, is encoded into a DNS name in a readable fashion where the case
of some letters might be changed on output as described above.
@ -344,7 +430,37 @@ INTERNET-DRAFT DNS Case Insensitivity
D. Eastlake 3rd [Page 6]
D. Eastlake 3rd [Page 8]
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@ -402,7 +518,7 @@ Informative References
D. Eastlake 3rd [Page 7]
D. Eastlake 3rd [Page 9]
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@ -424,9 +540,9 @@ Author's Address
Expiration and File Name
This draft expires July 2003.
This draft expires August 2003.
Its file name is draft-ietf-dnsext-insensitive-00.txt.
Its file name is draft-ietf-dnsext-insensitive-01.txt.
@ -460,5 +576,5 @@ Expiration and File Name
D. Eastlake 3rd [Page 8]
D. Eastlake 3rd [Page 10]

599
doc/draft/draft-lewis-dns-wildcard-clarify-00.txt Normal file
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Internet Engineering Task Force E. Lewis
Internet-Draft ARIN
February 4, 2003 Expires: August 4, 2003
Clarifying the Role of Wild Card Domains
in the Domain Name System
<draft-lewis-dns-wildcard-clarify-00.txt>
Status of this Memo
This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering Task
Force (IETF), its areas, and its working groups. Note that other
groups may also distribute working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress".
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
Abstract
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 document
is meant to supplement the definition in RFC 1034 and to alter neither
the spirit nor intent of that definition.
1 Introduction
The first section of this document will give a crisp overview of what
is begin defined, as well as the motivation for what amounts to a
simple rewording of an original document. An example is included to
help orient the reader.
Wild card domain names are defined in Section 4.3.3. of RFC 1034 as
"instructions for synthesizing RRs." [RFC1034] The meaning of this is
that a specific, special domain name is used to construct responses in
instances in which the query name is not otherwise represented in a zone.
A wild card domain name has a specific range of influence on query names
(QNAMEs) within a given class, which is rooted at the domain name
containing the wild card label, and is limited by explicit entries, zone
cuts and empty non-terminal domains (see section 1.3 of this document).
Note that a wild card domain name has no special impact on the search
for a query type (QTYPE). If a domain name is found that matches the
QNAME (exact or a wild card) but the QTYPE is not found at that point,
the proper response is that there is no data available. The search
does not continue on to seek other wild cards that might match the QTYPE.
To illustrate, a wild card owning an MX RR does not 'cover' other names
in the zone that own an A RR.
Why is this document needed? Empirical evidence suggests that the
words in RFC 1034 are not clear enough. There exist a number of
implementations that have strayed from the definition. There also
exists a misconception of operators that the wild card can be used to
add a specific RR type to all names, such as the MX RR example listed
above. This document is also needed as input to efforts to extend
DNS, such as the DNS Security Extensions [RFC 2535]. Lack of a clear
base specification has proven to result in extension documents that
have unpredictable consequences. (This is true in general, not just
for DNS.)
1.1 Existence
The notion that a domain name 'exists' will arise numerous times in this
discussion. RFC 1034 raises the issue of existence in a number of places,
usually in reference to non-existence and often in reference to processing
involving wild card domain names. RFC 1034 does contain algorithms that
describe how domain names impact the preparation of an answer and does
define wild cards as a means of synthesizing answers.
To help clarify the topic of wild cards, a positive definition of existence
is needed. To complicate matters, though, there needs to be a recognition
that existence is relative. To an authoritative server, a domain name
exists if the domain name plays a role following the algorithms of
preparing a response. To a resolver, a domain name exists if there is
any data available corresponding to the name. The difference between the
two is the synthesis of records according to a wild card.
For the purposes of this document, the point of view of an authoritative
server is adopted. A domain name is said to exist if it plays a role in
the execution of the algorithms in RFC 1034.
1.2 An Example
For example, consider this wild card domain name: *.example. Any query
name under example. is a candidate to be matched (answered) by this wild
card. Although any name is a candidate, not all queries will match.
To further illustrate this, consider this example:
$ORIGIN example.
@ IN SOA
NS
NS
* TXT "this is a wild card"
MX 10 mailhost.example.
host1 A 10.0.0.1
_ssh._tcp.host1 SRV
_ssh._tcp.host2 SRV
subdel NS
The following queries would be synthesized from the wild card:
QNAME=host3.example. QTYPE=MX, QCLASS=IN
the answer will be a "host.example. IN MX ..."
QNAME=host3.example. QTYPE=A, QCLASS=IN
the answer will be a "host.example. IN NXT ..."
because there is no A RR set at '*'
The following queries would not be synthesized from the wild card:
QNAME=host1.example., QTYPE=MX, QCLASS=IN
because host1.example. exists
QNAME=_telnet._tcp.host1.example., QTYPE=SRV, QCLASS=IN
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
because subdel.example. exists and is a zone cut
To the server, the following domains are considered to exist in the zone:
*, host1, _tcp.host1, _ssh._tcp.host1, host2, _tcp.host2, _ssh._tcp.host2,
and subdel. To a resolver, many more domains appear to exist via the
synthesis of the wild card.
1.3 Empty Non-terminals
Empty non-terminals are domain names that have no data but have
subdomains. This is defined in section 3.1 of RFC 1034:
# 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
# system makes no distinctions between the uses of the interior nodes and
# leaves, and this memo uses the term "node" to refer to both.
The parenthesized "which may be empty" specifies that empty non-terminals
are explicitly recognized. According to the definition of existence in
this document, empty non-terminals do exist at the server.
Carefully reading the above paragraph can lead to an interpretation that
all possible domains exist - up to the suggested limit of 255 octets for
a domain name [RFC 1035]. For example, www.example. may have an A RR, and
as far as is practically concerned, is a leaf of the domain tree. But the
definition can be taken to mean that sub.www.example. also exists, albeit
with no data. By extension, all possible domains exist, from the root
down. As RFC 1034 also defines "an authoritative name error indicating
that the name does not exist" in section 4.3.1, this is not the intent
of the original document.
RFC1034's wording is to be clarified by adding the following paragraph:
A node is considered to have an impact on the algorithms of 4.3.2
if it is a leaf node with any resource sets or an interior 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 an existing
node never results in a response return code of authoritative name
error.
As an aside, an "authoritative name error" 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 implementation of DNS.
1.3 Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in the document entitled
"Key words for use in RFCs to Indicate Requirement Levels." [RFC2119]
Requirements are denoted by paragraphs that begin with with the following
convention: 'R'<sect>.<count>.
2 Defining the Wild Card Domain Name
A wild card domain name is defined by having the initial label be:
0000 0001 0010 1010 (binary) = 0x01 0x2a (hexadecimal)
This defines domain names that may play a role in being a wild card, that
is, being a source for synthesized answers. Domain names conforming to
this definition that appear in queries and RDATA sections do not have
any special role. These cases will be described in more detail in
following sections.
R2.1 A domain name that is to be interpreted as a wild card MUST begin
with a label of '0000 0001 0010 1010' in binary.
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 the
'*' character. In RFC 1034, ASCII encoding is assumed to be the character
encoding.
In the master file formats used in RFCs, a "*" is a legal representation
for the wild card label. Even if the "*" is escaped, it is still
interpreted as the wild card when it is the only character in the label.
R2.2. A server MUST treat a wild card domain name as the basis of
synthesized answers regardless of any "escape" sequences in
the input format.
RFC 1034 and RFC 1035 ignore the case in which a domain name might be
"the*.example.com." The interpretation is that this domain name in a
zone would only match queries for "the*.example.com" and not have any
other role.
Note: By virtue of this definition, a wild card domain name may have a
subdomain. The subdomain (or sub-subdomain) itself may also be a wild
card. E.g., *.*.example. is a wild card, so is *.sub.*.example.
More discussion on this is given in Appendix A.
3 Defining Existence
As described in the Introduction, a precise definition of existence is
needed.
R3.1 An authoritative server MUST treat a domain name as existing during
the execution of the algorithms in RFC 1034 when the domain name
conforms to the following definition. A domain name is defined
to exist if the domain name owns data and/or has a subdomain that
exists.
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 authoritative,
but that is of no consequence here. The domain name owns data, therefore,
it exists.
R3.2 An authoritative server MUST treat a domain name that has neither
a resource record set nor a subdomain as nonexistent when executing
the algorithm in section 4.3.2. of RFC 1034.
4 Impact of a Wild Card Domain In a Query Message
When a wild card domain name appears in a question, e.g., the query name
is "*.example.", the response in no way differs from any other query.
In other words, the wild card label in a QNAME has no special meaning,
and query processing will proceed using '*' as a literal query name.
R4.1 A wild card domain name acting as a QNAME MUST be treated as any
other QNAME, there MUST be no special processing accorded it.
If a wild card domain name appears in the RDATA of a CNAME RR or any
other RR that has a domain name in it, the same rule applies. In the
instance of a CNAME RR, the wild card domain name is used in the same
manner of as being the original QNAME. For other RR's, rules vary
regarding what is done with the domain name(s) appearing in them,
in no case does the wild card hold special meaning.
R4.2 A wild card domain name appearing in any RR's RDATA MUST be treated
as any other domain name in that situation, there MUST be no special
processing accorded it.
5 Impact of a Wild Card Domain On a Response
The description of how wild cards impact response generation is in RFC
1034, section 4.3.2. That passage contains the algorithm followed by a
server in constructing a response. Within that algorithm step 3, part
'c' defines the behavior of the wild card. The algorithm is directly
quoted in lines that begin with a '#' sign. Commentary is interleaved.
[Note that are no requirements specifically listed in this section. The
text here is explanatory and interpretative. There is no change to
the algorithm specified in RFC 1034.]
The context of part 'c' is that the search is progressing label by label
through the QNAME. (Note that the data being searched is the authoritative
data in the server, the cache is searched in step 4.) Step 3's part 'a'
covers the case that the QNAME has been matched in full, regardless of the
presence of a CNAME RR. Step 'b' covers crossing a cut point, resulting
in a referral. All that is left is to look for the wild card.
Step 3 of the algorithm also assumes that the search is looking in the
zone closest to the answer, i.e., in the same class as QCLASS and as
close to the authority as possible on this server. If the zone is not
the authority, then a referral is given, possibly one indicating lameness.
# c. If at some label, a match is impossible (i.e., the
# corresponding label does not exist), look to see if a
# the "*" label exists.
The above paragraph refers to finding the domain name that exists in the
zone and that most encloses the QNAME. Such a domain name will mark the
boundary of candidate wild card domain names that might be used to
synthesize an answer. (Remember that at this point, if the most enclosing
name is the same as the QNAME, part 'a' would have recorded an exact
match.) The existence of the enclosing name means that no wild card name
higher in the tree is a candidate to answer the query.
Once the closest enclosing node is identified, there's the matter of what
exists below it. It may have subdomains, but none will be closer to the
QNAME. One of the subdomains just might be a wild card. If it exists,
this is the only wild card eligible to be used to synthesize an answer
for the query. Even if the closest enclosing node conforms to the syntax
rule in section 2 for being a wild card domain name, the closest enclosing
node is not eligible to be a source of a synthesized answer.
The only wild card domain name that is a candidate to synthesize an answer
will be the "*" subdomain of the closest enclosing domain name. Three
possibilities can happen. The "*" subdomain does not exist, the "*"
subdomain does but does not have an RR set of the same type as the QTYPE,
or it exists and has the desired RR set.
For the sake of brevity, the closest enclosing node can be referred to as
the "closest encloser."
To illustrate, using the example in section 1.2 of this document, the
following chart shows QNAMEs and the closest enclosers. In Appendix A
there is another chart showing unusual cases.
QNAME Closest Encloser Wild Card Source
host3.example. example. *.example.
_telnet._tcp.host1.example. _tcp.host1.example. no wild card
_telnet._tcp.host2.example. host2.example. no wild card
_telnet._tcp.host3.example. example. *.example.
_chat._udp.host3.example. example. *.example.
Note that host1.subdel.example. is in a subzone, so the search for it ends
in a referral in part 'b', thus does not enter into finding a closest
encloser.
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 authenticated denial of existence proofs. (This concept
is not introduced until DNS Security Extensions are considered in
upcoming sections.)
# If the "*" label does not exist, check whether the name
# we are looking for is the original QNAME in the query
# or a name we have followed due to a CNAME. If the name
# is original, set an authoritative name error in the
# response and exit. Otherwise just exit.
The above passage says that if there is not even a wild card domain name
to match at this point (failing to find an explicit answer elsewhere),
we are to return an authoritative name error at this point. If we were
following a CNAME, the specification is unclear, but seems to imply that
a no error return code is appropriate, with just the CNAME RR (or sequence
of CNAME RRs) in the answer section.
# If the "*" label does exist, match RRs at that node
# against QTYPE. If any match, copy them into the answer
# section, but set the owner of the RR to be QNAME, and
# not the node with the "*" label. Go to step 6.
This final paragraph covers the role of the QTYPE in the process. Note
that if no resource record set matches the QTYPE the result is that no data
is copied, but the search still ceases ("Go to step 6.").
6 Authenticated Denial and Wild Cards
In unsecured DNS, the only concern when there is no data to return to
a query is whether the domain name from which the answer comes exists or
not, whether or not a name error is indicated in the return code. In
either case the answer section is empty or contained just a sequence of
CNAME RR sets.
In securing DNS, authenticated denial of existence is a service that is
provided. The chosen solution to provide this service is to generate
resource records indicating what is protected in a zone and to digitally
sign these.
The resource records that do this, as defined in RFC 2535, are NXT RRs.
There are three points to consider when clarifying the topic of wild card
domain names. One is the construction of the records. The second is
the inclusion of records in responses. The third is the interpretation
of the records in a response by the resolver.
6.1 Preparing Wild Card Domain Name Owned Non-existence Proofs
During the creation of the authenticated denial records, the wild card
domain name plays no special role, in the same manner as the wild card
domain name playing no special role in a query.
There is one consideration with regards to preparing non-existence
proofs.
R6.1 Any mechanism used to provide authenticated denial MUST reveal the
closest enclosing existing domain for the query. If this is not
provided, the resolver will not be able to ascertain the identity
of an appropriate wild card domain name.
6.2 Role of Wild Cards in Answers
There are three cases to address. The first is synthesizing from wild card
domain name with data, the second is negatively synthesizing from an
existing wild card, and the third is denying that neither an exact match,
referral, nor wild card exist to answer the query.
6.2.1 Synthesizing From a Wild Card
When preparing an answer from a wild card domain name, the answer needs
to include proof that the exact match of the QNAME and QCLASS does not
exist. This is needed because synthesis of the answer replaces the "*"
label with the QNAME without securing the result. The resolver will
realize that the answer was derived from a wild card, but cannot
detect whether an exact match was maliciously omitted.
R6.2 When synthesizing a positive answer from a wild card domain name, the
answer MUST include proof that the exact match for the QNAME and
QCLASS does not exist.
6.2.2. Synthesizing Negatively From a Wild Card
When synthesizing a negative answer that is derived from a wild card,
meaning that a wild card matched the QNAME (no exact match happened for
QNAME) but that there is no match for QTYPE there, two negative answers
are needed, possibly one. As in 6.2.1, a proof that the exact match
failed is needed. A second proof is needed to show that the wild card
domain name does not have the QTYPE. Depending on the method of
authenticated denial, these this could be possible with one statement.
R6.3 When synthesizing a negative answer from a wild card domain name,
the answer MUST include proof that the exact match of the QNAME
and QCLASS does not exist and that the QTYPE matches no RR set at
the wild card. If this answer can be optimized, an implementation
SHOULD reduce the number of records included in the response.
6.2.3. Answering With an Authoritative Name Error
When answering with a result code of a name error, the answer needs to
provide proof that neither the exact match for QNAME and QCLASS exists
nor that a wild card domain name exists as a subdomain of the closest
enclosing domain name.
R6.4 When preparing a reply with an authoritative name error, the answer
MUST include proof that the exact match for the QNAME and QCLASS
does not exist and that no wild card is available to provide a match.
6.2.4. The Remaining Case
When answering negatively because there is a match for QNAME and QCLASS
but no match for the QTYPE, only a proof for that is needed. Just as
the search does not proceed onto a search for the wild card in this
case, neither does the construction of the negative answer proof.
R6.5 When preparing a reply in which there is an exact match of the
QNAME and QCLASS, but there is no RR set matching the QTYPE,
the reply SHOULD NOT contain any proof regarding the wild card
domain name.
6.3 Interpreting Negative Answers Involving Wild Cards
There are two requirements for resolvers when it comes to handling
negative answers generated as described in section 6.2.
R6.6 A resolver MUST be able to identify negative answer data that
indicate when a match for QNAME and QCLASS does not exist.
R6.7 From a negative answer, a resolver MUST be able to determine
the closest enclosing domain name in a negative answer and
MUST be able to process a negative answer involving the one
wild card domain name that is a candidate to provide a
synthesized answer.
6.4 Authenticated Denial, Wild Card Domain Names, and Opt-In
When considering the Opt-In proposal [WIP], it is wise to not combine
a zone that adheres to both opt-in and that has a wild card domain
name. The reason is rooted in that the synthesis of an answer is done
by substituting the QNAME for the wild card domain name in the answer.
Because this is unsecured, and the is ambiguity regarding whether a
negative proof can be provided for the exact match (when it is outside
the opt-in secured area), a definitive proof of authenticated denial
is not possible.
7 Security Considerations
This document is refining the specifications to make it more likely that
security can be added to DNS. No functional additions are being made,
just refining what is considered proper to allow the system, security
of the system, and extending the system more predictable.
8 References
Normative References
[RFC 20] ASCII Format for Network Interchange, V.G. Cerf, Oct-16-1969
[RFC 1034] Domain Names - Concepts and Facilities, P.V. Mockapetris,
Nov-01-1987
[RFC 1035] Domain Names - Implementation and Specification, P.V
Mockapetris, Nov-01-1987
[RFC 2119] Key Words for Use in RFCs to Indicate Requirement Levels, S
Bradner, March 1997
Non-normative References
[RFC 2136] Dynamic Updates in the Domain Name System (DNS UPDATE), P. Vixie,
Ed., S. Thomson, Y. Rekhter, J. Bound, April 1997
[RFC 2535] Domain Name System Security Extensions, D. Eastlake, March 1999
[WIP] DNSSEC Opt-In, Internet Draft, R. Arends, M. Kosters, D. Blacka, 2002
9 Other Contributing to This Document
Others who have directly caused text to appear in the document: Paul Vixie
and Olaf Kolkman. Many others have indirect influences on the content.
10 Editor
Name: Edward Lewis
Title: Research Engineer
Affiliation: ARIN
Email: edlewis@arin.net
Phone: +1-703-227-9854
Appendix A: Subdomains of Wild Card Domain Names
In reading the definition of section 2 carefully, it is possible to
rationalize unusual names as legal. In the example given, *.example.
could have subdomains of *.sub.*.example. and even the more direct
*.*.example. (The implication here is that these domain names own
explicit resource records sets.) Although defining these names is not
easy to justify, it is important that implementations account for the
possibility. This section will give some further guidance on handling
these names.
The first thing to realize is that by all definitions, subdomains of
wild card domain names are legal. In analyzing them, one realizes
that they cause no harm by their existence. Because of this, they are
allowed to exist, i.e., there are no special case rules made to disallow
them. The reason for not preventing these names is that the prevention
would just introduce more code paths to put into implementations.
The concept of "closest enclosing" existing names is important to keep in
mind. It is also important to realize that a wild card domain name can
be a closest encloser of a query name. For example, if *.*.example. is
defined in a zone, and the query name is a.*.example., then the closest
enclosing domain name is *.example. Keep in mind that the closest
encloser is not eligible to be a source of synthesized answers, just the
subdomain of it that has the first label "*".
To illustrate this, the following chart shows some matches. Assume that
the names *.example., *.*.example., and *.sub.*.example. are defined
in the zone.
QNAME Closest Encloser Wild Card Source
a.example. example. *.example.
b.a.example. example. *.example.
a.*.example. *.example. *.*.example.
b.a.*.example. *.example. *.*.example.
b.a.*.*.example. *.*.example. no wild card
a.sub.*.example. sub.*.example. *.sub.*.example.
b.a.sub.*.example. sub.*.example. *.sub.*.example.
a.*.sub.*.example. *.sub.*.example. no wild card
*.a.example. example. *.example.
a.sub.b.example. example. *.example.
Recall that the closest encloser itself cannot be the wild card. Therefore
the match for b.a.*.*.example. has no applicable wild card.
Finally, if a query name is sub.*.example., any answer available will come
from an exact name match for sub.*.example. No wild card synthesis is
performed in this case.
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--
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Edward Lewis +1-703-227-9854
ARIN Research Engineer