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(See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- The document date (March 6, 1998) is 9546 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Missing Reference: 'BITLBL' is mentioned on line 80, but not defined == Missing Reference: 'DNSUPD' is mentioned on line 128, but not defined Summary: 11 errors (**), 0 flaws (~~), 4 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 DNSIND Working Group Matt Crawford 2 Internet Draft Fermilab 3 March 6, 1998 5 Non-Terminal DNS Name Redirection 6 8 Status of this Memo 10 This document is an Internet Draft. Internet Drafts are working 11 documents of the Internet Engineering Task Force (IETF), its Areas, 12 and its Working Groups. Note that other groups may also distribute 13 working documents as Internet Drafts. 15 Internet Drafts are draft documents valid for a maximum of six 16 months. Internet Drafts may be updated, replaced, or obsoleted by 17 other documents at any time. It is not appropriate to use Internet 18 Drafts as reference material or to cite them other than as a 19 ``working draft'' or ``work in progress.'' 21 To learn the current status of any Internet-Draft, please check the 22 ``1id-abstracts.txt'' listing contained in the Internet Drafts 23 Shadow Directories on ds.internic.net (US East Coast), nic.nordu.net 24 (Europe), ftp.isi.edu (US West Coast), or munnari.oz.au (Pacific 25 Rim). 27 Distribution of this memo is unlimited. 29 1. Introduction 31 This document defines a new DNS Resource Record called ``DNAME'', 32 which provides the capability to map an entire subtree of the DNS 33 name space to another domain. It differs from the CNAME record 34 which maps a single node of the name space. 36 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 37 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 38 document are to be interpreted as described in [KWORD]. 40 2. Motivation 42 This Resource Record and its processing rules were conceived as a 43 solution to the problem of maintaining address-to-name mappings in a 44 context of network renumbering. Without the DNAME mechanism, an 45 authoritative DNS server for the address-to-name mappings of some 46 network must be reconfigured when that network is renumbered. With 47 DNAME, the zone can be constructed so that it needs no modification 48 when renumbered. DNAME can also be useful in other situations, such 49 as when an organizational unit is renamed. 51 3. The DNAME Resource Record 53 The DNAME RR has mnemonic DNAME and type code TBA (decimal). 55 DNAME has the following format: 57 DNAME 59 The format is not class-sensitive. All fields are required. The 60 RDATA field is a [DNSIS]. 62 The DNAME RR causes type NS additional section processing. 64 The effect of the DNAME record is the substitution of the record's 65 for its as a suffix of a domain name. Two limiting 66 rules govern the use of DNAMEs. 68 Rule One 69 If a DNAME RR is present at a node N, there may be other data at N 70 (except a CNAME or another DNAME), but there MUST be no data at 71 any descendant of N, except for the wildcard node *.N which MAY 72 have data intended to help old DNS clients which do not understand 73 the DNAME record. These restrictions apply only to records of the 74 same class as the DNAME record. 76 Rule Two 77 When resolving a query, it is valid to encounter more than one 78 DNAME record along the way ONLY IF every DNAME record encountered 79 has fewer labels in its than in its . (Note that 80 in the bit-string label [BITLBL], each bit is a separate label.) 81 If a single DNAME is encountered there is no special restriction 82 on the number of labels in its . 84 Rule One assures predictable results when a DNAME record is cached 85 by a server which is not authoritative for the record's zone. Rule 86 Two prevents DNAME loops. 88 Rule One MUST be enforced when authoritative zone data is loaded. 89 Rule Two MUST be enforced during query processing. 91 4. Query Processing 93 To exploit the DNAME mechanism the name resolution algorithms 94 [DNSCF] must be modified slightly for both servers and resolvers. 95 In both cases a conceptual per-query variable DFLAG is introduced to 96 enforce Rule Two. Implementations MAY use other means to enforce 97 the rule. DFLAG DFLAG's value is 99 0 when processing of a query begins and whenever no DNAME has been 100 encountered; 102 1 when one or more DNAME records have been encountered, and each 103 had fewer labels in its than in its ; 105 2 when a DNAME record has been encountered which had at least as 106 many labels in its as in its . 108 Both modified algorithms incorporate the operation of making a 109 substitution on a name (either QNAME or SNAME) under control of a 110 DNAME record. For conciseness, this operation is elaborated here 111 and will be referred to as "procedure S". 113 S1. If DFLAG = 2, Rule Two is violated. Go to step S4. 115 S2. If DFLAG = 1 and the DNAME record's 's does not have 116 fewer labels than its , Rule Two is violated. Go to step 117 S4. 119 S3. If substituting the DNAME's for its in the name 120 being operated on would overflow the legal size for a , go to step S4. Otherwise make the substitution. 123 If the has fewer labels than the , set DFLAG to 124 1, otherwise set DFLAG to 2. Return. 126 S4. In a resolver, return an implementation-dependent error to the 127 application. In a server, copy the DNAME record to the answer 128 section, set RCODE to YXDOMAIN [DNSUPD], and exit. 130 4.1. Processing by Servers 132 For a server performing non-recursive service steps 3.c and 4 of 133 section 4.3.2 [DNSCF] are changed to check for a DNAME record before 134 checking for a wildcard ("*") label, and to return certain DNAME 135 records from the cache. The revised algorithm is: 137 1. Set or clear the value of recursion available in the response 138 depending on whether the name server is willing to provide 139 recursive service. If recursive service is available and 140 requested via the RD bit in the query, go to step 5, otherwise 141 step 2. 143 2. Search the available zones for the zone which is the nearest 144 ancestor to QNAME. If such a zone is found, go to step 3, 145 otherwise step 4. 147 3. Start matching down, label by label, in the zone. The matching 148 process can terminate several ways: 150 a. If the whole of QNAME is matched, we have found the node. 152 If the data at the node is a CNAME, and QTYPE doesn't match 153 CNAME, copy the CNAME RR into the answer section of the 154 response, change QNAME to the canonical name in the CNAME 155 RR, and go back to step 1. 157 Otherwise, copy all RRs which match QTYPE into the answer 158 section and go to step 6. 160 b. If a match would take us out of the authoritative data, we 161 have a referral. This happens when we encounter a node with 162 NS RRs marking cuts along the bottom of a zone. 164 Copy the NS RRs for the subzone into the authority section 165 of the reply. Put whatever addresses are available into the 166 additional section, using glue RRs if the addresses are not 167 available from authoritative data or the cache. Go to step 168 4. 170 c. If at some label, a match is impossible (i.e., the 171 corresponding label does not exist), look to see whether the | 172 last label matched has a DNAME record. | 174 If a DNAME record exists at that point, copy that record | 175 into the answer section, substitute its for its | 176 in QNAME according to procedure S, and go back to | 177 step 1. | 179 If there was no DNAME record, look to see if the "*" label | 180 exists. 182 If the "*" label does not exist, check whether the name we 183 are looking for is the original QNAME in the query or a name 184 we have followed due to a CNAME. If the name is original, 185 set an authoritative name error in the response and exit. 187 Otherwise just exit. 189 If the "*" label does exist, match RRs at that node against 190 QTYPE. If any match, copy them into the answer section, but 191 set the owner of the RR to be QNAME, and not the node with 192 the "*" label. Go to step 6. 194 4. Start matching down in the cache. If QNAME is found in the 195 cache, copy all RRs attached to it that match QTYPE into the 196 answer section. If QNAME is not found in the cache but a DNAME | 197 record is present at an ancestor of QNAME, copy that DNAME | 198 record into the answer section. If there was no delegation from | 199 authoritative data, look for the best one from the cache, and 200 put it in the authority section. Go to step 6. 202 5. Using the local resolver or a copy of its algorithm (see 203 resolver section of this memo) to answer the query. Store the 204 results, including any intermediate CNAMEs and DNAMEs, in the | 205 answer section of the response. 207 6. Using local data only, attempt to add other RRs which may be 208 useful to the additional section of the query. Exit. 210 Note that there will be at most one ancestor with a DNAME as 211 described in step 4 unless some zone's data is in violation of Rule 212 One. 214 4.2. Processing by Resolvers 216 A resolver or a server providing recursive service must be modified 217 to treat a DNAME as somewhat analogous to a CNAME. The resolver 218 algorithm of [DNSCF] section 5.3.3 is modified to renumber step 4.d 219 as 4.e and insert a new 4.d. The complete algorithm becomes: 221 1. See if the answer is in local information, and if so return it 222 to the client. 224 2. Find the best servers to ask. 226 3. Send them queries until one returns a response. 228 4. Analyze the response, either: 230 a. if the response answers the question or contains a name 231 error, cache the data as well as returning it back to the 232 client. 234 b. if the response contains a better delegation to other 235 servers, cache the delegation information, and go to step 2. 237 c. if the response shows a CNAME and that is not the answer 238 itself, cache the CNAME, change the SNAME to the canonical 239 name in the CNAME RR and go to step 1. 241 d. if the response shows a DNAME the DNAME, substitute the | 242 DNAME's for its in the SNAME according to | 243 procedure S and go to step 1. | 245 e. if the response shows a server failure or other bizarre | 246 contents, delete the server from the SLIST and go back to 247 step 3. 249 5. Examples of Use 251 If an organization with domain name FROBOZZ.TLD became part of an 252 organization with domain name ACME.TLD, it might ease transition by 253 placing information such as this in its old zone. 255 frobozz.tld. DNAME frobozz-division.acme.tld. 256 MX mailhub.acme.tld. 257 *.frobozz.tld. CNAME www.frobozz-division.acme.tld. 259 If IPv4 network renumbering were common, maintenance of address 260 space delegation could be simplified by using DNAME records instead 261 of NS records to delegate. 263 $ORIGIN new-style.in-addr.arpa. 264 189.190 DNAME in-addr.example.net. 266 $ORIGIN in-addr.example.net. 267 188 DNAME in-addr.customer.xy. 269 $ORIGIN in-addr.customer.xy. 270 1 PTR www.customer.xy. 271 2 PTR mailhub.customer.xy. 272 ; etc ... 274 This would allow the address space assigned to the ISP "example.net" 275 to be changed without the necessity of altering the zone files 276 describing the use of that space by the ISP and its customers. 278 6. Discussion (in draft only) 280 Why does [DNSCF] section 4.3.2 step 3.a say "go back to step 1" 281 rather than "go back to step 2"? 283 Would a DNAME with a special be of any use in securely 284 denying anything in a subtree below its ? If so, a special 285 rule could be added about a null label in the , or 286 =. 288 The meaning of NS and DNAME records together at the same node is 289 unclear. Perhaps this ought to be forbidden. 291 YXDOMAIN seems like a reasonable error code to overload for name- 292 length overflow due to DNAME substitution. But a case for NXDOMAIN 293 could be made on the grounds that the resulting too-long name is 294 sure not to exist. 296 Rule Two could be modified to allow up to one (or any fixed finite 297 number) of DNAMEs which don't decrease the label count AND any 298 number of DNAMEs which do decrease it. Would that help anything? 300 7. Acknowledgments 302 Donald Eastlake 3rd suggested the wildcard subdomain to help old 303 clients get something useful. 305 8. References 307 [BITLBL]M. Crawford, "Binary Labels in the Domain Name System", 308 currently draft-ietf-dnsind-binary-labels-00.txt. 310 [DNSCF] P.V. Mockapetris, "Domain names - concepts and facilities", 311 RFC 1034. 313 [DNSIS] P.V. Mockapetris, "Domain names - implementation and 314 specification", RFC 1035. 316 [DNSUPD]P. Vixie, Ed., S. Thomson, Y. Rekhter, J. Bound, "Dynamic 317 Updates in the Domain Name System", RFC 2136. 319 [KWORD] S. Bradner, "Key words for use in RFCs to Indicate 320 Requirement Levels," RFC 2119. 322 9. Author's Address 324 Matt Crawford 325 Fermilab MS 368 326 PO Box 500 327 Batavia, IL 60510 328 USA 330 Phone: +1 630 840-3461 332 EMail: crawdad@fnal.gov