DNSEXT Working Group E. Lewis INTERNET DRAFT NeuStar Expiration Date:
July 20,August 10, 2005 JanuaryFebruary 2005 Clarifying theThe Role of Wild CardWildcard Domains in the Domain Name System draft-ietf-dnsext-wcard-clarify-04.txtdraft-ietf-dnsext-wcard-clarify-05.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of RFC 3668. 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 This Internet-Draft will expire on July 20,August 10, 2005. Copyright Notice Copyright (C) The Internet Society (2004, 2005).(2005). 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 documentis meantan update to supplementthe wildcard definition inof RFC 10341034. The interaction with wildcards and CNAME is changed, an error condition removed, and the words defining some concepts central to wildcards are changed. The overall goal is not to significantly alterchange wildcards, but to refine the spirit or intentdefinition of that definition.RFC 1034. 1 Introduction In RFC 1034 [RFC1034], sections 4.3.2 and 4.3.3 describe the synthesis of answers from special resource records called wildcards. The original definitions are incomplete.definition in RFC 1034 is incomplete and has proven to be confusing. This document clarifies anddescribes the wildcard synthesis by adding to the discussion and making limited modifications. Modifications are made only where necessaryto close inconsistencies that have led to interoperability issues. This description does not expand the service intended by the original definition. Staying within the spirit and style of the original documents, this document avoids specifying rules for DNS implementations regarding wildcards. The intention is to only describe what is needed for interoperability, not restrict implementation choices. In addition, consideration has been given to minimize any backwards compatibility with implementations that have complied with RFC 1034's definition. This document is focused on the concept of wildcards as defined in RFC 1034. Nothing is implied regarding alternative approaches, nor are alternatives discussed. [Note to the WG - this draft is not complete, it is presented as fodder for the upcoming meeting. Sections 4.2.3, 4.6, 3.7, and 4.8 are particularly incomplete. I wanted to make sure there was something recent in the draft repository before setting out on more travel. For 4.2.3, refer to the threads for the most recent discussions... http://ops.ietf.org/lists/namedroppers/namedroppers.2004/msg01601.html http://ops.ietf.org/lists/namedroppers/namedroppers.2004/msg01603.html And you might want to check out the minutes from the last IETF meeting as well as http://www.ietf.org/proceedings/03nov/131.htm.] 1.1 Motivation Over time manyMany DNS implementations have diverged with respect to wildcards in different ways from the original definition, or at from least what had been intended. Although there is clearly a need to clarify the original documents in light of this,this alone, the impetus for this document lay in the engineering of the DNS security extensions [RFC TBD]. With an unclear definition of wildcards the design of authenticated denial became entangled. Although this document is motivated by DNSSEC and the need to have a separate document passed for the sake of DNSSEC, other motivations have arisen. The renewed understanding of wildcards gained is worthy of being documented. 1.2 The Original DefinitionThis document is intended to make just one change,limit changes, only those based on implementation experience, and to remain as close to the original 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 contradict the goal1.2 The Original Definition The context of not changingthe original specification, butwildcard concept involves the changes herein are required because of inconsistencies withalgorithm by which a name server prepares a response (in RFC 1034's section 4.3.2) and the wordingway in RFC 1034.which a resource record (set) is identified as being a source of synthetic data (section 4.3.3). 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. # In the previous algorithm, special treatment was given to RRs with owner # names starting with the label "*". Such RRs are called wildcards. # Wildcard RRs can be thought of as instructions for synthesizing 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 # wildcard RRs. This passage appears after the algorithm in which they are used is presented. The terminology is not consistent,the word "wildcard"term wildcard is clearly definedfirst used. In this definition, wildcard refers to be aresource record. Wildcardrecords. In other usage, wildcard has also been used to referreferred to domain names whose first (i.e., left most or least significant) label consists of an asterisk. 1.3 The Clarification The clarification effort can be divided into three sections: o The introduction of new terminology for clarity of the discussion o Changesnames, and it has been used to describe the wording of passagesoperational practice of RFC 1034 prompted by discoveries of conflicting concepts o Descriptions of special resource record typesrelying on wildcards to generate answers. It is clear from this that there is a need to define clear and unambiguous terminology in the contextprocess of discussing wildcards. 1.3.1 New Terms The term "wildcard" has become so overloaded it is virtually useless as a description. A few new terms will be introduced to be more descriptive.The new terms that will be introduced are: Asterisk Label - a label consistingmention of an asterisk ("*") and no other characters. Wild Card Domain Name - a domain name whose least significant label (first when reading left to right) is an asterisk label. Other labels might also be asterisk labels. Sourcethe use of Synthesis - a wild card domain name when it is consultedwildcards in the final paragraphpreparation of a response is contained in step 3, part c3c of RFC 1034's section 4.3.2 algorithm. Closest Encloser - in RFC 1034's 4.3.2 algorithm,entitled "Algorithm." Note that "wildcard" does not appear in the name at whichalgorithm, instead references are made to the last match was possible"*" label. The portion of the algorithm relating to wildcards is deconstructed in step 3, part c. Thisdetail in section 3 of this document, this is the longest sequencebeginning of exactly matching labels from the root downward in boththe query name (QNAME) and inpassage. # c. If at some label, a match is impossible (i.e., the zone being examined. Label Match - two labels are equivalent# corresponding label does not exist), look to see if a # the "*" label type and label length are bothexists. The scope of this document is the sameRFC 1034 definition of wildcards and ifthe labelsimplications of updates to those documents, such as DNSSEC. Alternate schemes for synthesizing answers are case-independent equivalent strings. Pattern matching isnot involved. These terms will be more fully described as needed later. These terms will be usedconsidered. (Note that there is no reference listed. No document is known to describe a fewany alternate schemes, although there has been some mention of them in mailing lists.) 1.3 This Document This document accomplishes these three items. o Defines new terms o Makes minor changes to avoid conflicting concepts o Describe the words in RFC 1034. A summaryactions of the changes appear next andcertain resource records as wildcards 1.3.1 New Terms To help in discussing what resource records are wildcards, two terms will be fully covereddefined - "asterisk label" and "wild card domain name". These are defined in later sections. Note that labels other thansection 2.1.1. To assist in clarifying the asterisk label which contain asterisks have no special significance or terminologyrole of wildcards in this document; thusthe fact that a domain names starts with an asteriskname server algorithm in RFC 1034, 4.3.2, "source of synthesis" and "closest encloser" are defined. These definitions are in section 3.3.2. "Label match" is alsodefined in section 3.2. The introduction 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).new terms ought not have an impact on any existing implementations. The new terms are used only to make discussions of wildcards clearer. 1.3.2 Changed Text The definition of "existence" is changed, superficially, to exclude empty domains that have no subdomains with resource records.superficially. This change will not be apparent to implementations; it is needed to make descriptions more concise. Inprecise. The change appears in section 2.2.3. RFC 1034, there is text thatsection 4.3.3., seems to prohibit having two asterisk labels in a wild card domainwildcard owner name. There is no further discussion, no prescribed error handling, nor enforcement described.With this document implementations will have to account for such a name's use.the restriction is removed entirely. This change and its implications are in section 2.1.3. 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 is an addition to the words in RFC 1034, section 4.3.2, step 3, part c. The discussion of this is in section 3.3.3. Only the latter change represents an impact to implementations. The definition of existence is not a protocol impact. The change to the restriction on names is unlikely to have an impact, as there was no discussion of how to enforce the restriction. 1.3.3 Considerations with Special Types This clarification will describe in some detail thedocument describes semantics of wildcard CNAME RRSets,RRSets [RFC2181], wildcard NS RRSets, wildcard SOA RRSets, wildcard DNAME RRSets [RFC2672], wildcard DS RRSets [RFC 2672],TBD], and empty non-terminal wildcards. Understanding these types in the context of wildcards has been clouded because these types incur special processing if they are the result of an exact match. By the definition in RFC 1034, there can be no empty non-terminal "wildcards" ("RRs are called wildcards"). However, in the algorithm, it is possible that an empty non-terminal is sought as the potential owner of a "wildcard."This discussion is one examplein section 4. These discussions do not have an implementation impact, they cover existing knowledge of whythe orderingtypes, but to a greater level of the discussion in RFC 1034 is confusing.detail. 1.4 Standards Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in thisThis document are to be interpreteddoes not use terms as describeddefined in the document entitled"Key words for use in RFCs to Indicate Requirement Levels." [RFC2119] Quotations of RFC 1034 (as has already been done once above)are denoted by a '#' in the leftmost column. 2 "Wildcard"Wildcard Syntax The contextsyntax of thea wildcard concept involvesis the algorithm by which a name server prepares a response (in RFC 1034's section 4.3.2)same as any other DNS resource record, across all classes and types. The only significant feature is the way in which a resource record (set) is identified as being a source of synthetic data (section 4.3.3). Tackling the latter first, thereowner name. Because wildcards are two objectives in defining a means to identify a resource record setencoded as a source of synthesis. First, to simplify implementations, one objective is to encode synthesis rules into the domain tree, i.e., avoiding aresource records with special data store for synthesis is desirable. The second objective impacts interoperability, that is a master server of one implementation has to be able to send the synthesis instructions to the slaves. Although therenames, they are alternatives to the use ofincluded in zone transfers via port 53, a truly interoperable record synthesis approach has to be able to insert the synthesis instructions into aand incremental zone transfer. The objectives in describing the synthesis of records in the context of the name server algorithm include knowing whentransfers. [RFC1995]. This feature has been underappreciated until discussions on alternative approaches to employ the process of synthesis and how the synthesis is carried out.wildcards appeared on mailing lists. 2.1 Identifying a wildcard To provide a more accurate description of "wildcards", the definition has to start with a discussion of the domain names that appear as owners. Two new terms are needed, "Asterisk Label" and "Wild Card Domain Name." 2.1.1 Wild Card Domain Name and Asterisk Label 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) This is "*" in presentation format.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][RFC20] for the '*' character. In RFC 1034, ASCII encoding is assumed to be the character encoding.A descriptive name of a label equaling that value is an "asterisk label." 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 orientation between this clarification2.1.2 Asterisks and RFC 1034. Keep in mind,Other Characters No label values other than that in "Clarifications to the DNS Specification" [RFC 2181] the name of the basic unit of DNS data became the resource record set (RRSet)section 2.1.1 are asterisk labels, hence names beginning with other labels are never wild card domain names. Labels such as 'the*' and '**' are not the resource record. 2.1.2 Variations onasterisk labels, they do not start wild card domain names. 2.1.3 Non-terminal Wild Card Domain Names Labels other than the asterisk label which containIn section 4.3.3, the ASCII representationfollowing is stated: # .......................... The owner name of the asterisk (0x2a) have no significance for the purposeswildcard RRs is of this document. RFC 1034 and RFC 1035 do not explicitly mention# the case in which a domain name might be something like "the*.example." The interpretationform "*.<anydomain>", where <anydomain> is that thisany domain name in a zone would only match queries for "the*.example." andname. # <anydomain> should not have any other role. An asterisk ('*') occurringcontain other than as* labels...................... This restriction is lifted because the sole character in a labeloriginal documentation of it is simply a character forming partincomplete and the restriction does not serve any purpose given years of operational experience. Indirectly, the labelabove passage raises questions about wild card domain names having subdomains and has no special meaning. This is notpossibly being an empty non-terminal. By thinking of domain names such as "*.example.*.example." and "*.*.example." and focusing on the right-most asterisk label, simply alabel an asteriskin it. Theeach, the issues become apparent. Although those example names have been restricted per RFC 1034, a name such as "example.*.example." illustrates the same is true for "**.example." and "*the.example."problems. The interpretationsticky issue of a wild card domain specification whichsubdomains and empty non-terminals is not a leafremoved by the restriction. With that conclusion, the restriction appears to be meaningless, worse yet, it implies that an implementation would have to perform checks that do little more than waste CPU cycles. A wild card domain name can have subdomains. There is not clearly defined in RFC 1034. E.g., sub.*.example., is not discussed, not barred. In wantingno need to minimize changes frominspect the original specification, such names are permitted. Although "sub.*.example."subdomains to see if there is not aanother asterisk label in any subdomain. A wild card domain name, "*.example." is. RRSets used to synthesize recordsname can be owned byan empty non-terminal. (See the upcoming sections on empty non-terminals.) In this case, any lookup encountering it will terminate as would any empty non-terminal match. 2.2 Existence Rules The notion that a wild carddomain name that has subdomains. 2.1.3 Non-terminal Wild Card Domain Names'exists' is mentioned in the definition of wildcards. In section 4.3.3, the following is stated: # .......................... The owner name4.3.3 of the wildcardRFC 1034: # Wildcard RRs is ofdo not apply: # the form "*.<anydomain>", where <anydomain> is any domain name.... # <anydomain> should not contain other * labels...................... This covers names like "*.foo.*.example." The pre-RFC2119 wording uses "should not" which has an ambiguous meaning. The specification does not proscribe actions upon seeing such a name, such as whether or not a zone containing- When the query name should fail to be served. What ifor a dynamic update (RFC2136) requested to add thename to the zone? The failure semantics are not defined. The recommendation is that implementations ought to anticipatebetween the appearance of such names but generally discourage their use in operations. No standards statement, such as "MUST NOT" nor "SHOULD NOT" is made here. The interpretation of this is, when seeking a wild cardwildcard domain name for the purposes of record synthesis, an implementation need not to checkand # the domain name for subdomains. It is possible that a wild card domainquery name is an empty non-terminal. (See the upcoming sections on empty non-terminals.) In this case, the lookup will terminate as would any empty non-terminal match. 2.2 Existence Rules The notion thatknow[n] to exist. For example, if a domain name 'exists' arises numerous times in discussions about thewildcard concept.RFC 1034 raisesalso refers to non-existence in the issueprocess of existencegenerating a response that results in a numberreturn code of places, usually in reference to non-existence and"name error." NXDOMAIN is introduced in reference to processing involving wildcards.RFC 1034 contains algorithms that describe how domain names impact2308, section 2.1 says "In this case the preparation of an answer anddomain ... does define wildcards as a meansnot exist." The overloading of synthesizing answers. Becausethe term "existence" is confusing. For the purposes of this document, a discussion on wildcards needsdomain name is said to cover a definition of existence. To help clarify the topic of wild cards, a positive definition of existence is needed. Complicating matters, though, is the realization 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 wildcard. For the purposes of this document, the point of view of an authoritative server is more interesting. A domain name is said to exist if it playsexist if it plays a role in the execution of the algorithms in RFC 1034. 2.2.1.This document avoids discussion determining when an authoritative name error has occurred. 2.2.1 An Example To illustrate what is meant by existence consider this complete zone: $ORIGIN example. example. 3600 IN SOA <SOA RDATA> example. 3600 NS ns.example.com. example. 3600 NS ns.example.net. *.example. 3600 TXT "this is a wild card" *.example. 3600 MX 10 host1.example. sub.*.example. 3600 TXT "this is not a wild card" host1.example. 3600 A 184.108.40.206 _ssh._tcp.host1.example. 3600 SRV <SRV RDATA> _ssh._tcp.host2.example. 3600 SRV <SRV RDATA> subdel.example. 3600 NS ns.example.com. subdel.example. 3600 NS ns.example.net. A look at the domain names in a tree structure is helpful: | -------------example------------ / / \ \ / / \ \ / / \ \ * host1 host2 subdel | | | | | | sub _tcp _tcp | | | | _ssh _ssh The following queries would be synthesized from one of the wildcards: QNAME=host3.example. QTYPE=MX, QCLASS=IN the answer will be a "host3.example. IN MX ..." QNAME=host3.example. QTYPE=A, QCLASS=IN the answer will reflect "no error, but no data" because there is no A RR set at '*.example.' QNAME=foo.bar.example. QTYPE=TXT, QCLASS=IN the answer will be "foo.bar.example. IN TXT ..." because bar.example. does not exist, but the wildcard does. The following queries would not be synthesized from any of the wildcards: QNAME=host1.example., QTYPE=MX, QCLASS=IN because host1.example. exists QNAME=ghost.*.example., QTYPE=MX, QCLASS=IN because *.example. exists QNAME=sub.*.example., QTYPE=MX, QCLASS=IN because sub.*.example. exists QNAME=_telnet._tcp.host1.example., QTYPE=SRV, QCLASS=IN because _tcp.host1.example. exists (without data) QNAME=host.subdel.example., QTYPE=A, QCLASS=IN because subdel.example. exists (and is a zone cut) 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.2.2.2 Empty Non-terminals Empty non-terminals [RFC2136, Section 7.16] are domain names that own no resource records but have subdomains that do. ThisIn section 2.2.1, "_tcp.host1.example." is definedan example of a empty non-terminal name. Empty non-terminals are introduced by this text 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,recognized, and that empty non-terminals do exist at the server."exist." Pedantically 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].[RFC1035]. 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 on 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. 2.2.3 Yet Another Definition of Existence RFC1034's wording is clarifiedfixed by the following paragraph: A nodeThe domain name space is considered toa tree structure. Nodes in the tree either own at least one RRSet and/or have an impactdescendants that collectively own at least on the algorithms of 4.3.2RRSet. A node may have no RRSets if it is a leaf node with any resource sets or an interior node (with or without a resource set) thathas a subdomaindescendents that do, this node is a leafempty non-terminal. A node may have its own RRSets and have descendants with a resource set.RRSets too. A QNAME and QCLASS matching an existingnode never results inwith no descendants is a response code of authoritative name error (RCODE==3). The terminology in the above paragraph is chosen to remain as close to that in the original document. The term "with" is a alternate form for "owning" in this case, hence "aleaf node owning resources sets, or an interior node, owning or not owning any resource set, that has anode. Empty leaf node owning a resource set as a subdomain," is the 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, 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. Summarizing the discussion on existence in non-RFC1034 words: An authoritative server is to 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 is on the domain tree and either owns data or has a subdomain that exists.nodes do not exist. 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. 2.3 When does a Wild Card Domain Name is not own a wildcard (record)Special When a wild card domain name appears in a message's query section, no special processing occurs. An asterisk label in a query name only (label) matches an asterisk label in the existing zone tree when the 4.3.2 algorithm is being followed. When a wild card domain name appears in the resource data of a record, no special processing occurs. An asterisk label in that context literally means just an asterisk. 3. Impact of a Wild Card Domain Name On a Response The description of how wild cardswildcards 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. There is a documentation issue deserving some explanation. The algorithmin RFC 1034, section 4.3.2. is not intended to be pseudo 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 a, b, and c, do not have to be implemented in that order. Another issue needing explanation is that RFC 1034 is a full standard. There is another RFC, RFC 2672, which makes, or proposes an adjustment to3.1 Step 2 Step 2 of the RFC 1034's section 4.3.2 forreads: # 2. Search the sake ofavailable zones for the DNAME RR. RFC 2672 is a proposed standard. The dilemma in writing these clarifications is knowingzone which documentis the one being clarified. Fortunately, the difference between RFC 1034 and RFC 2672nearest # ancestor to QNAME. If such a zone is not significant with respect to wild card synthesis, so this document will continue to state that it is clarifying RFC 1034. If RFC 2672 progresses along the standards track, it will need to refer to modifying RFC 1034's algorithm as amended here. 3.1 Step 2 Step 2 of the RFC 1034's section 4.3.2 reads: # 2. Search the available zones for the zone which is the nearest # ancestor to QNAME. If such a zone is found, gofound, go to step 3, # otherwise step 4. In this step, the most appropriate zone for the response is chosen. The significance of this step is that it means all of Stepstep 3 is being performed within one zone. This has significance when considering whether or not an SOA RR can be ever be used for synthesis. 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 Step 3 is dominated by three parts, labelled 'a', 'b', and 'c'. But the beginning of the Stepstep is important and needs explanation. # 3. Start matching down, label by label, in the zone. The # matching process can terminate several ways: The word 'matching' refers to label matching. The concept 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 if the name were a path from the root to the owner of the desired data. (Which it is.)is - 3rd paragraph of RFC 1034, section 3.1.) The process of label matching a query name ends in exactly one of three choices, the parts 'a', 'b', and 'c'. Either the name is found, the name is below a cut point, or the name is not found. Once one of the parts is chosen, the other parts are not considered. (E.g., do not execute part 'c' and then change the execution path to finish in part 'b'.) The process of label matching is also done independent of the Query Type.query type (QTYPE). 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 which all of the labels in the query name have a (label)is an exact match that results in the tree. Partan answer, part 'b' generally coversis a situation in which any label inreferral. It is possible, from the description given, that a query name (label) matchesmight fit into both part a tree labeland part b, this is not within the tree label has a NS RRSet.scope of this document. 3.3 Part 'c' The context of part 'c' is that the process of label matching the labels of the query name has resulted in a situation in which there is no corresponding label in the tree. It is as if the lookup has "fallen off the tree." # 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. 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 matched. The term is "closest encloser." 3.3.1 Closest Encloser and the Source of Synthesis The closest encloser is the node in the zone's tree of existing domain names that has the most labels matching the query name (consecutively, counting from the root label downward). Each match is a "label match" and the order of the labels is the same. The closest encloser is, by definition, an existing name in the zone. The closest encloser might be an empty non-terminal or even be a wild card domain name itself. In no circumstances is the closest encloser the used to synthesize records for the current query. The source of synthesis is defined in the context of a query process as that wild card domain name immediately descending from the closest encloser, provided that this wild card domain name exists. "Immediately descending" means that the source of synthesis has a name 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 is at most one place at which wildcard synthetic records can be obtained. If the source of synthesis does not exist, the lookup terminates, the lookup does not look for other wildcard records. 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 wildcard records. This is still an appropriate viewpoint, but replacing this notion with the closest encloser and source of synthesis terminology depicts the wildcard process is more clearly.3.3.2 Closest Encloser and Source of Synthesis Examples To illustrate, using the example zone in section 2.2.1 of this document, the following chart shows QNAMEs and the closest enclosers. QNAME Closest Encloser Source of Synthesis host3.example. example. *.example. _telnet._tcp.host1.example. _tcp.host1.example. no source _telnet._tcp.host2.example. host2.example. no source _telnet._tcp.host3.example. example. *.example. _chat._udp.host3.example. example. *.example. foobar.*.example. *.example. no source 3.3.3 Non-existent Source of Synthesis InType Matching RFC 1034:1034 concludes part 'c' with this: # 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 is clear, evidenced by the lack of discussion and mis-implementation of it over the years. It is included for completeness only. (No attempt is made to re-interpret it lest a mistake in editing leads to confusion.) 3.3.4 Type Matching RFC 1034 concludes part 'c' with this:# # 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. ThisThe final paragraph covers the role of the QTYPE in the lookup process. Based on implementation feedback and similarities between step 'a' and step 'c' a change to this passage a change has been made. The change is to add the following text:text to step 'c': If the data at the source of synthesis is a CNAME, and QTYPE doesn't match CNAME, copy the CNAME RR into the answer section of the response changing the owner name to the QNAME, change QNAME to the canonical name in the CNAME RR, and go back to step 1. This is essentially the same text in step a covering the processing of CNAME RRSets. 4. Considerations with Special Types FiveSections 2 and 3 of this document discuss wildcard synthesis with respect to names in the domain tree and ignore the impact of types. In this section, the implication of wildcards of specific types are discussed. The types covered are those that have proven to be the most difficult to understand. The types are SOA, NS, CNAME, DNAME, SRV, DS, NSEC, RRSIG and "none," i.e., empty non-terminal wild card domain names. 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 RRSets ownedthe zone (apex). The domain can not be a source of synthesis because that is, by 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 owning an SOA RRSet can never be a source of synthesis, there is no reason to forbid the ownership of an SOA RRSet. E.g., given this zone: $ORIGIN *.example. @ 3600 IN SOA <SOA RDATA> 3600 NS ns1.example.com. 3600 NS ns1.example.net. www 3600 TXT "the www txt record" A query for www.*.example.'s TXT record would still find the "the www txt record" answer. The reason is that the asterisk label only becomes significant when RFC 1034's 4.3.2, step 3 part 'c' in in effect. Of course, there would need to be a delegation in the parent zone, "example." for this to work too. This is covered in the next section. 4.2 NS RRSet at a Wild Card Domain Name The semantics of a wild card domain name's ownership of a NS RRSet has been unclear. There are three considerations to cover. One is is that if the query processing lands in part 'a' or part 'b' of RFC 1034's 4.3.2, step 3, the incidence of the wild card domain name owning an NS RRset has no special meaning. Second, synthesized records never appear in the authority section of a response, meaning that referrals are never synthesized. And finally, DNSSEC validators will have to be aware of a quirk in ownership rules. 4.2.1 NS, *, and answers 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 would trigger part 'a' of step 3. 4.2.2 NS, *, and referrals If the NS RRset is not at the top of the zone and part 'b' is triggered, this implies that the labels being matched are an asterisk label in the QNAME and the asterisk label owning the NS RRset. In either case, what is copied to the response will have the asterisk label in it - no synthesis, no name substitution. E.g., consider the parent zone for the example in section 4.1. $ORIGIN example. @ 3600 IN SOA <SOA RDATA> 3600 NS ns0.example.com. 3600 NS ns0.example.net. * 3600 NS ns1.example.com. 3600 NS ns1.example.net. If the query for www.*.example.'s TXT set arrived here, the response would be a referral as in part 'b'. Response, non-authoritative, no error rcode ANSWER: (empty) AUTHORITY: * 3600 NS ns1.example.com. 3600 NS ns1.example.net. ADDITIIONAL: (empty, or with OPT RR) The same response message would be sent to a query for *.example.'s NS set. Note that the NS records in the response are not expanded, simply copied verbatim. (Compare this the case where "*" is "star".) There is no synthesis of records in the authority section because part 'b' does not specify synthesis. The referral returned would have caused confusion. Four explicit types causing confusion are SOA, NS, CNAME, DNAME, andthe fifth type - "none." 4.1. SOA RRSet at a Wild Card Domain Name Awild card domain name owning an SOA RRSet means that the domain is at the root ofin the zone (apex). The domain can not be a source ofauthority section unchanged. 4.2.3 NS, *, and synthesis because that is, by definition, a descendent node (ofIf the closest encloser) and a zone apexQNAME is atnot the top ofsame as the zone. Although awild card domain name owning an SOA RRSet can never benor a sourcesubdomain of synthesis, there is no reason to forbid the ownershipit, then part 'c' of an SOA RRSet. E.g., if *.example.step 3 has an SOA record, then only a query like QNAME=*.example., QTYPE=A, QCLASS=IN would see it. A query like QNAME=foo.example., QTYPE=A, QCLASS=IN would not see it - a different zone would havebeen picked in Step 2. A QNAME of www.*.example. would result in a query referencing the *.example zone. 4.2. NS RRSet at a Wild Card Domain Name The semantics oftriggered. Assuming that "a match is impossible" a wild card domain name's ownershipsource of a NS RRSet has been unclear. Looking through RFC 1034, the recommendationsynthesis is to havesought. If the source of synthesis owns an NS RRSet actRRset and the sameQTYPE is NS, then a any non-special type, e.g., like an A RRSet. If theNS RRSet in questionRRset is at the top of the zone, i.e.,synthesized and put into the name also ownsanswer section and marked as an SOA RRSet,authoritative answer. If the QNAME equalsQTYPE is not NS, then the zone name. ThisNS RRset is ignored, as it would trigger part 'a' of Step 3. In any other case,have been if it were an A RR and the QTYPE was AAAA. An NS RRSet at a wild card domain name owned NS RRSet would bewill not result in the only RRSet (prior to changes instituted by DNSSEC) atgeneration of referral messages for non-existent domains because part 'c' does not write anything into the node by DNS rules.authority section. (If we choose this, then we have to have a section 4.2.4 on DNSSEC implications.) OR If the QNAME equalsis not the same as the wild card domain name or isnor a subdomain of it, then the node would be considered inpart 'b' of Step 3. [should dnssec be left out'c' of this?] Notestep 3 has been triggered. Assuming that there"a match is noimpossible" a source of synthesis is sought. If the source of records insynthesis owns an NS RRset and the authority section because part 'b' does not specify synthesis.QTYPE is NS, then no synthesis happens. A NS RRset is never synthesized. The referral returned would have the wild card domain name in the authority section unchanged.proper response is, what, no error/no data? Name error? OR If the QNAME is not the same as the wild card domain name nor a subdomain of it, then part 'c' of Stepstep 3 has been triggered. Once part 'c' is entered, there is no reverting to part 'b' - i.e., once an NS RRSet is synthesized it does not meanAssuming that the server has to consider the name delegated away. I.e., the server"a match is not synthesizingimpossible" a record (the NS RRSet) that means the server does not have the right to synthesize. (Only an authoritative server can perform synthesis. By synthesizing an NS RRSet, it appears that the authority forsource of synthesis is sought. If the name has been delegated to another authority.) In summation,source of synthesis owns an NS RRSet atRRset then no synthesis happens. A cut point is never a wild card domain name will not result in the generationsource of referral messages for non-existent domains. 4.3.synthesis. The proper response is, what, no error/no data? Name error? 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 in 4.3.2. The changed text appears in section 220.127.116.11.3 of this document. 18.104.22.168 DNAME RRSet at a Wild Card Domain Name A DNAME RRset at a wild card domain name is effectively the same as a CNAME at a wild card domain name. 4.5 SRV RRSet at a Wild Card Domain Name The specificationdefinition of the DNAME RR, whichSRV RRset is atRFC 2782 [RFC2782]. In the proposed leveldefinition of standardization,the record, there is not as maturesome confusion over the term "Name." The definition reads as follows: # The format of the full standardSRV RR ... # _Service._Proto.Name TTL Class SRV Priority Weight Port Target ... # Name # The domain this RR refers to. The SRV RR is unique in RFC 1034. Because of this, orthat the reason# name one searches for is not this is, there appears to be a a number of issues with thatname; the example near the end # shows this clearly. Do not confuse the definition "Name" with a domain name. I.e., once removing the _Service and it's rewrite of_Proto labels from the algorithm in 4.3.2. Forowner name of the time being, when it comes toSRV RRSet, what remains could be a wild card processing issues, a DNAME can be considereddomain name but this is immaterial to be a CNAME synthesizer. A DNAME atthe SRV RRSet. E.g., If an SRV record is: _foo._udp.*.example. 10800 IN SRV 0 1 9 old-slow-box.example. *.example is a wild card domain name and although it it the Name of the SRV RR, it is effectivelynot the same as a CNAME atowner (domain name). The owner domain name is "_foo._udp.*.example." which is not a wild card domain name. 4.5The confusion is likely based on the mixture of the specification of the SRV RR and the description of a "use case." 4.6 DS RRSet at a Wild Card Domain Name ...probably harmless... 4.7 NSEC RRSet at a Wild Card Domain Name ...will be present, don't know if it should be synthesized... 4.8 RRSIG at a Wild Card Domain Name ...need to cross check with DNSSECbis to see what is said about querying for RRSIG... 4.9 Empty Non-terminal Wild Card Domain Name 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 section. 5. 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 DNS, security of the DNS, and extending the DNS to be more predictable. 6. References Normative References [RFC 20][RFC20] ASCII Format for Network Interchange, V.G. Cerf, Oct-16-1969 [RFC 1034][RFC1034] Domain Names - Concepts and Facilities, P.V. Mockapetris, Nov-01-1987 [RFC 1035][RFC1035] Domain Names - Implementation and Specification, P.V Mockapetris, Nov-01-1987 [RFC 2119][RFC1995] IXFR ... Ohta [RFC2119] Key Words for Use in RFCs to Indicate Requirement Levels, S Bradner, March 1997 [RFC 2181][RFC2181] Clarifications to the DNS Specification, R. Elz and R. Bush, July 1997. [RFC2782] A DNS RR for specifying the location of services (DNS SRV), A. Gulbrandsen, et.al., February 2000. Informative References [RFC 2136][RFC2136] Dynamic Updates in the Domain Name System (DNS UPDATE), P. Vixie, Ed., S. Thomson, Y. Rekhter, J. Bound, April 1997 [RFC 2535][RFC2535] Domain Name System Security Extensions, D. Eastlake, March 1999 [RFC 2672][RFC2672] Non-Terminal DNS Name Redirection, M. Crawford, August 1999 7. Others Contributing to This Document Others who have been editors of this document: Bob Halley. Others who have directly caused text to appear in the document: Alex Bligh, Robert Elz, Paul VixieVixie, David Blacka and Olaf Kolkman. Many others have indirect influences on the content. 8. Editor Name: Edward Lewis Affiliation: NeuStar Address: 46000 Center Oak Plaza, Sterling, VA, 20166, US Phone: +1-571-434-5468 Email: email@example.com Comments on this document can be sent to the editor or the mailing list for the DNSEXT WG, firstname.lastname@example.org. 9. Trailing Boilerplate Copyright (C) The Internet Society (2004). This document is subject to the rights, licenses and restrictions contained in BCP 78 and except as set forth therein, the authors retain all their rights. This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Intellectual Property The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at email@example.com. Acknowledgement Funding for the RFC Editor function is currently provided by the Internet Society. Expiration This document expires on or about July 20,August 10, 2005.