DNSEXT Working Group E. Lewis INTERNET DRAFT NeuStar Expiration Date:
November 16, 2005 May 16,January 6, 2006 July 6, 2005 Updates RFC 1034, RFC 2672 The Role of Wildcards in the Domain Name System draft-ietf-dnsext-wcard-clarify-07.txtdraft-ietf-dnsext-wcard-clarify-08.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 BCP 79. 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 November 16, 2005.January 6, 2006. Copyright Notice Copyright (C) The Internet Society (2005). Abstract This is an update to the wildcard definition of RFC 1034. 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 change wildcards, but to refine the definition of RFC 1034. 1Table of Contents 1. Introduction 1.1 Motivation 1.2 The Original Definition 1.3 Roadmap to This Document 1.3.1 New Terms 1.3.2 Changed Text 1.3.3 Considerations with Special Types 1.4 Standards Terminology 2. Wildcard Syntax 2.1 Identifying a Wildcard 2.1.1 Wild Card Domain Name and Asterisk Label 2.1.2 Asterisks and Other Characters 2.1.3 Non-terminal Wild Card Domain Names 2.2 Existence Rules 2.2.1 An Example 2.2.2 Empty Non-terminals 2.2.3 Yet Another Definition of Existence 2.3 When is a Wild Card Domain Name Not Special 3. Impact of a Wild Card Domain Name On a Response 3.1 Step 2 3.2 Step 3 3.3 Part 'c' 3.3.1 Closest Encloser and the Source of Synthesis 3.3.2 Closest Encloser and Source of Synthesis Examples 3.3.3 Type Matching 4. Considerations with Special Types 4.1 SOA RRSet at a Wild Card Domain Name 4.2 NS RRSet at a Wild Card Domain Name 4.2.1 Discarded Notions 4.3 CNAME RRSet at a Wild Card Domain Name 4.4 DNAME RRSet at a Wild Card Domain Name 4.5 SRV RRSet at a Wild Card Domain Name 4.6 DS RRSet at a Wild Card Domain Name 4.7 NSEC RRSet at a Wild Card Domain Name 4.8 RRSIG at a Wild Card Domain Name 4.9 Empty Non-terminal Wild Card Domain Name 5. Security Considerations 6. IANA Considerations 7. References 8. Editor 9. Others Contributing to the Document 10. Trailing Boilerplate 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 definition in RFC 1034 is incomplete and has proven to be confusing. This document describes the wildcard synthesis by adding to the discussion and making limited modifications. Modifications are made to 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 beenis given to minimize any backwards compatibility issues with implementations that have compliedcomply 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,means of synthesizing resource record sets, nor are alternatives discussed. 1.1 Motivation Many DNS implementations have diverged with respect to wildcardsdiverge, in different waysways, from the original definition, or at from least what had been intended.definition of wildcards. Although there is clearly a need to clarify the original documents in light of this alone, the impetus for this document lay in the engineering of the DNS security extensions [RFC4033]. With an unclear definition of wildcards the design of authenticated denial became entangled. This document is intended to limit its changes, documenting only those based on implementation experience, and to remain as close to the original document as possible. To reinforce this,that this document is meant to clarify and adjust and not redefine wildcards, relevant sections of RFC 1034 are repeated verbatim to help comparefacilitate comparison of the old and new text. 1.2 The Original Definition The contextdefintion of the wildcard concept involvesis comprised by the documentation of the algorithm by which 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 source of synthetic data (section 4.3.3). The beginning of the discussion ought to start withThis is 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 afterfollows the algorithm in which the term wildcard is first used. In this definition, wildcard refers to resource records. In other usage, wildcard has referred to domain names, and it has been used to describe the operational practice of relying on wildcards to generate answers. It is clear from this that there is a need to define clear and unambiguous terminology in the process of discussing wildcards. The mention of the use of wildcards in the preparation of a response is contained in step 3c of RFC 1034's section 4.3.2 entitled "Algorithm." Note that "wildcard" does not appear in the algorithm, instead references are made to the "*" label. The portion of the algorithm relating to wildcards is deconstructed in detail in section 3 of this document, this is the beginning of the passage.relevant portion of the "Algorithm." # c. If at some label, a match is impossible (i.e., the # corresponding label does not exist), look to see if [...] # the "*" label exists. The scope of this document is the RFC 1034 definition of wildcards and the implications of updates to those documents, such as DNSSEC. Alternate schemes for synthesizing answers are not considered. (Note that there is no reference listed. No document is known to describe any alternate schemes, although there has been some mention of them in mailing lists.) 1.3 Roadmap to This Document This document accomplishes these three items. o Defines new terms o Makes minor changes to avoid conflicting concepts o Describes the actions of certain resource records as wildcards 1.3.1 New Terms To help in discussing what resource records are wildcards, two terms will be defined - "asterisk label" and "wild card domain name". These are defined in section 2.1.1. To assist in clarifying the role of wildcards in the name 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 defined in section 3.2. The introduction of new terms ought not have an impact on any existing implementations. Thenew terms are used onlyto make discussions of wildcards clearer. Terminology doesn't directly have an impact on implementations. 1.3.2 Changed Text The definition of "existence" is changed,changed superficially. This change will not be apparent to implementations; it is needed to make descriptions more precise. The change appears in section 2.2.3. RFC 1034, section 4.3.3., seems to prohibit having two asterisk labels in a wildcard owner name. With this document 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 wasRFC 1034 contained no discussion ofspecification on when and how to enforce the restriction. 1.3.3 Considerations with Special Types This document describes semantics of wildcard CNAME RRSets [RFC2181], wildcard NS RRSets, wildcard SOA RRSets, wildcard DNAME RRSets [RFC2672],semantics of wildcard DSRRSets [RFC TBD], andfor "interesting" types as well as empty non-terminal wildcards. Understanding these typessituations in the context of wildcards has been clouded because these types incur special processing if they are the result of an exact match. This discussion is in section 4. These discussions do not have an implementation impact, they cover existing knowledge of the types, but to a greater level of detail. 1.4 Standards Terminology This document does not use terms as defined in "Key words for use in RFCs to Indicate Requirement Levels." [RFC2119] Quotations of RFC 1034 are denoted by a '#' in the leftmost column. 2References to section "4.3.2" are assumed to refer to RFC 1034's section 4.3.2, simply titled "Algorithm." 2. Wildcard Syntax The syntax of a wildcard is the same as any other DNS resource record, across all classes and types. The only significant feature is the owner name. Because wildcards are encoded as resource records with special names, they are included in zone transfers and incremental zone transfers[RFC1995].transfers[RFC1995] just as non-wildcard resource records are. This feature has been underappreciated until discussions on alternative approaches to wildcards appeared on mailing lists. 2.1 Identifying a Wildcard To provide a more accurate description of "wildcards",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) The first octet is the normal label type and length for a 1 octet long label, the second octet is the ASCII representation [RFC20] for the '*' character. 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." 2.1.2 Asterisks and Other Characters No label values other than that in 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 asterisk labels, theylabels so these labels do not start wild card domain names. 2.1.3 Non-terminal Wild Card Domain Names In section 4.3.3, the following is stated: # .......................... The owner name of the wildcard RRs is of # the form "*.<anydomain>", where <anydomain> is any domain name. # <anydomain> should not contain other * labels...................... ThisThe restriction is lifted because thenow removed. The original documentation of it is incomplete and the restriction does not serve any purpose given years of operational experience. Indirectly,There are three possible reasons for putting the above passage raises questions aboutrestriction in place, but none of the three has held up over time. One is that the restriction meant that there would never be subdomains of wild card domain names having subdomains and possibly being an empty non-terminal. By thinking ofnames, but the restriciton as stated still permits "example.*.example." for instance. Another is that wild card domain names such as "*.example.*.example." and "*.*.example." and focusing onare not intended to be empty non-terminals, but this situation does not disrupt the right-most asterisk labelalgorithm in each, the issues become apparent. Although those example4.3.2. Finally, "nested" wild card domain names have been restricted per RFC 1034, a name such as "example.*.example." illustrates the same problems. The sticky issue of subdomains and empty non-terminals isare not removed byambiguous once the restriction. With that conclusion,concept of 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.closest encloser had been documented. A wild card domain name can have subdomains. There is no need to inspect the subdomains to see if there is another asterisk label in any subdomain. A wild card domain name can be an 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 domain name 'exists' is mentioned in the definition of wildcards. In section 4.3.3 of RFC 1034: # Wildcard RRs do not apply: # ... # - When the query name or a name between the wildcard domain and # the query name is know[n] to exist. For example, if a wildcard RFC 1034 also refers to non-existence in the process of generating a response that results in a return code of "name error." NXDOMAIN is introduced in RFC 2308, section 2.1 says "In this case the domain ... does not exist." The overloading of the term "existence" is confusing. Forin the purposesdefinition of this document,wildcards. In section 4.3.3 of RFC 1034: # Wildcard RRs do not apply: # ... # - When the query name or a name between the wildcard domain and # the query name is saidknow[n] to existexist. For example, if it playsa rolewildcard "Existence" is therefore an important concept in the executionunderstanding of wildcards. Unfortunately, the algorithmsdefinition of what exists, in RFC 1034. This document avoids discussion determining when an authoritative name error has occurred.1034, is unlcear. So, in sections 2.2.2. and 2.2.3, another look is taken at the definition of existence. 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 188.8.131.52 _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 queriesresponses would be synthesized from one of the wildcards:wildcards in the zone: 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 queriesresponses would not be synthesized from any of the wildcards:wildcards in the zone: QNAME=host1.example., QTYPE=MX, QCLASS=IN because host1.example. exists QNAME=ghost.*.example., QTYPE=MX, QCLASS=IN because *.example. existsQNAME=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) QNAME=ghost.*.example., QTYPE=MX, QCLASS=IN because *.example. exists The final example highlights one common misconception about wildcards. A wildcard "blocks itself" in the sense that a wildcard does not match its own subdomains. I.e. "*.example." does not match all names in the "example." zone, it fails to match the names below "*.example." To cover names under "*.example.", another wild card domain name is needed - "*.*.example." - which covers all but it's own subdomains. 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. In section 2.2.1, "_tcp.host1.example." is an 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, and that empty non-terminals "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 [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, so this apparently is not the intent of the original document.definition, justifying the need for an updated definition in the next section. 2.2.3 Yet Another Definition of Existence RFC1034's wording is fixed by the following paragraph: The domain name space is a tree structure. Nodes in the tree either own at least one RRSet and/or have descendants that collectively own at least onone RRSet. A node may haveexist with no RRSets only if it has descendents that do, this node is aan empty non-terminal. A node may have its own RRSets and have descendants with RRSets too. A nodewith no descendants is a leaf node. Empty leaf nodes do not exist. Note that at a zone boundary, the domain name owns data, including the NS RR set. AtIn the delegating server,zone, 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 doesis a Wild Card Domain Name is notNot 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 ana single, corresponding 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 TheRFC 1034's description of how wildcards impact response generation is in RFC 1034,its 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.wildcard. The algorithm in RFC 1034,section 4.3.2. is not intended to be pseudo code,pseudo-code, i.e., its steps are not intended to be followed in strict order. The "algorithm" is a suggestion.suggested means of implementing the requirements. As such, in step 3, parts a, b, and c, do not have to be implemented in that order.order, provided that the result of the implemented code is compliant with the protocol's specification. 3.1 Step 2 Step 2 of the RFC 1034'ssection 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, 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 step 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. 3.2 Step 3 Step 3 is dominated by three parts, labelled 'a', 'b', and 'c'. But the beginning of the step 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 - 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 (QTYPE). Parts 'a' and 'b' are not an issue for this clarification as they do not relate to record synthesis. Part 'a' is an exact match that results in an answer, part 'b' is a referral. It is possible, from the description given, that a query might fit into both part a and part b, this is not within the scope of this document.in an answer, part 'b' is a referral. 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 [...] # the "*" label exists. To help describe the process of looking 'to see if [...] the "*" label exists' a term has been coined to describe the last domain (node) 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 to be 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. 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 Type Matching RFC 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. # # 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. The 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 has been made. The change is to add the following text to step 'c':'c' prior to the instructions to "go to step 6": 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 Sections 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 the 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'ssection'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 With the definition of DNSSEC [RFC4033, RFC4034, RFC4035] now in place, the semantics of a wild card domain name owning an NS RRRRSet has come to be poorly defined. The dilemma relates to a conflict between the rules for synthesis in part 'c' and the fact that the resulting synthesis generates a record for which the zone is not authoritative. In a DNSSEC signed zone, the mechanics of signature management (generation and inclusion in a message) become unclear. After some lengthy discussions, there has been no clear "best answer" on how to document the semantics of such a situation. Barring such records from the DNS would requireDNS would require definition of rules for that, as well as introducing a restriction on records that were once legal. Allowing such records and amending the process of signature management would entail complicating the DNSSEC definition. There is one more ingredient to the discussion, that being the utility of a wild card domain name owned NS RRSet. Although there are cases of this use, it is an operational rarity. Expending effort to close this topic has proven to be an exercise in diminishing returns. In summary, there is no definition given for wild card domain names owning an NS RRSet. The semantics are left undefined until there is a clear need to have a set defined, and until there is a clear direction to proceed. Operationally, inclusion of wild card NS RRSets in a zone is discouraged, but not barred. 4.2.1 Discarded Notions Prior to DNSSEC, a wild card domain name owning a NS RRSet appeared to be workable, and there are some instances in which it is found in deployments using implementations that support this. Continuing to allow this in the specificaion is not tenable with DNSSEC. The reason is that the synthesis of the NS RRSet is being done in a zone that has delegated away the responsibility for the name. This "unauthorized" synthesis is not a problem for the base DNS protocol, but DNSSEC, in affirming the authorization model for DNS exposes the problem. Outright banning of wildcards of type NS is also untenable as the DNS protocol does not define how to handle "illegal" data. Implementations may choose not to load a zone, but there is no protocol definition. The lack of the definition of rules for that,is complicated by having to cover dynamic update [RFC 2136], zone transfers, as well as introducing a restriction on records that were once legal. Allowing such records and amendingloading at the processmaster server. The case of signature managementa client (resolver, cacheing server) getting a wildcard of type NS in a reply would entail complicatingalso have to be considered. Given the DNSSEC definition. Combining these observationsdaunting challenge of a complete definition of how to ban such records, dealing with thoughtexisting implementations that permit the records today is a further complication. There are uses of wild card domain name owning anNS record is an operationally uninteresting scenario, i.e., it won't happen in the normal course of events, accomodating this situation in the specificationRRSets. One compromise proposed would also be categorized as "needless complication." Further, expending more effort on this topic has provenhave redefined wildcards of type NS to not be an exerciseused in diminishing returns. In summary, there is no definition given for wild card domain names owning an NS RRSet. The semantics are left undefined until there is a clear need tosynthesis, this compromise fell apart because it would have a set defined,required significant edits to the DNSSEC signing and until there is avalidation work. (Again, DNSSEC catches unauthorized data.) With no clear directionconsensus forming on the solution to proceed. Operationally, inclusionthis dilemma, and the realization that wildcards of wild cardtype NS RRSets inare a zonerarity in operations, the best course of action is discouraged, but not barred.to leave this open-ended until "it matters." 4.3 CNAME RRSet at a Wild Card Domain Name The issue of a CNAME RRSet owned by a wild card domain name 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 3.3.3 of this document. 4.4 DNAME RRSet at a Wild Card Domain Name Ownership of a DNAME [RFC2672] RRSet by a wild card domain name represents a threat to the coherency of the DNS and is to be avoided or outright rejected. Such a DNAME RRSet represents non-deterministic synthesis of rules fed to different caches. As caches are fed the different rules (in an unpredictable manner) the caches will cease to be coherent. ("As caches are fed" refers to the storage in a cache of records obtained in responses by recursive or iterative servers.) For example, assume one cache, responding to a recursive request, obtains the recordrecord: "a.b.example. DNAME foo.bar.tld."foo.bar.example.net." and another cache obtainsobtains: "b.example. DNAME foo.bar.tld.",foo.bar.example.net." both generated from the recordrecord: "*.example. DNAME foo.bar.tld."foo.bar.example.net." by an authoritative server. The DNAME specification is not clear on whether DNAME records in a cache are used to rewrite queries. In some interpretations, the rewrite occurs, in some, it is not. Allowing for the occurrence of rewriting, queries for "sub.a.b.example. A" may be rewritten as "sub.foo.bar.tld. A" by the former caching server and may be rewritten as "sub.a.foo.bar.tld. A" by the latter. Coherency is lost, an operational nightmare ensues. Another justification for banning or avoiding wildcard DNAME records is the observation that such a record could synthesize a DNAME owned by "sub.foo.bar.example." and "foo.bar.example." There is a restriction in the DNAME definition that no domain exist below a DNAME-owning domain, hence, the wildcard DNAME is not to be permitted. 4.5 SRV RRSet at a Wild Card Domain Name The definition of the SRV RRset is RFC 2782 [RFC2782]. In the definition of the record, there is some confusion over the term "Name." The definition reads as follows: # The format of the SRV RR ... # _Service._Proto.Name TTL Class SRV Priority Weight Port Target ... # Name # The domain this RR refers to. The SRV RR is unique in that the # name one searches for is not this name; the example near the end # shows this clearly. Do not confuse the definition "Name" with a domainthe owner name. I.e., once removing the _Service and _Proto labels from the owner name of the SRV RRSet, what remains could be a wild card domain name but this is immaterial to the 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 not the owner (domain name). The owner domain name is "_foo._udp.*.example." which is not a wild card domain name. The 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 A DS RRSet owned by a wild card domain name is meaningless and harmless. This statement is made in the context that an NS RRSet at a wild card domain name is undefined. At a non-delegation point, a DS RRSet has no value (no corresponding DNSKEY RRSet will be used in DNSSEC validation). If there is a synthesized DS RRSet, it alone will not be very useful as it exists in the context of a delegation point. 4.7 NSEC RRSet at a Wild Card Domain Name Wild card domain names in DNSSEC signed zones will have an NSEC RRSet. Synthesis of these records will only occur when the query exactly matches the record. Synthesized NSEC RR's will not be harmful as they will never be used in negative caching or to generate a negative response. 4.8 RRSIG at a Wild Card Domain Name RRSIG records will be present at a wild card domain name in a signed zone, and will be synthesized along with data sought in a query. The fact that the owner name is synthesized is not a problem as the label count in the RRSIG will instruct the verifying code to ignore it. 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. IANA Considerations None. 7. References Normative References [RFC20] ASCII Format for Network Interchange, V.G. Cerf, Oct-16-1969 [RFC1034] Domain Names - Concepts and Facilities, P.V. Mockapetris, Nov-01-1987 [RFC1035] Domain Names - Implementation and Specification, P.V Mockapetris, Nov-01-1987 [RFC1995] Incremental Zone Transfer in DNS, M. Ohta, August 1996 [RFC2119] Key Words for Use in RFCs to Indicate Requirement Levels, S Bradner, March 1997 [RFC2181] Clarifications to the DNS Specification, R. Elz and R. Bush, July 1997 [RFC2308] Negative Caching of DNS Queries (DNS NCACHE), M. Andrews, March 1998 [RFC2672] Non-Terminal DNS Name Redirection, M. Crawford, August 1999. [RFC2782] A DNS RR for specifying the location of services (DNS SRV), A. Gulbrandsen, et.al., February 2000 [RFC4033] DNS Security Introduction and Requirements, R. Arends, et.al., March 2005 [RFC4034] Resource Records for the DNS Security Extensions, R. Arends, et.al., March 2005 [RFC4035] Protocol Modifications for the DNS Security Extensions, R. Arends, et.al., March 2005 [RFC2672] Non-Terminal DNS Name Redirection, M. Crawford, August 1999 Informative References [RFC2136] Dynamic Updates in the Domain Name System (DNS UPDATE), P. Vixie, Ed., S. Thomson, Y. Rekhter, J. Bound, April 1997 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. Others Contributing to the Document This document represents the work of a large working group. 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