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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group C. Everhart 3 Internet-Draft W. Adamson 4 Intended status: Standards Track NetApp 5 Expires: March 9, 2009 J. Zhang 6 Google 7 September 5, 2008 9 Using DNS SRV to Specify a Global File Name Space with NFS version 4 10 draft-everhart-nfsv4-namespace-via-dns-srv-03.txt 12 Status of this Memo 14 By submitting this Internet-Draft, each author represents that any 15 applicable patent or other IPR claims of which he or she is aware 16 have been or will be disclosed, and any of which he or she becomes 17 aware will be disclosed, in accordance with Section 6 of BCP 79. 19 Internet-Drafts are working documents of the Internet Engineering 20 Task Force (IETF), its areas, and its working groups. Note that 21 other groups may also distribute working documents as Internet- 22 Drafts. 24 Internet-Drafts are draft documents valid for a maximum of six months 25 and may be updated, replaced, or obsoleted by other documents at any 26 time. It is inappropriate to use Internet-Drafts as reference 27 material or to cite them other than as "work in progress." 29 The list of current Internet-Drafts can be accessed at 30 http://www.ietf.org/ietf/1id-abstracts.txt. 32 The list of Internet-Draft Shadow Directories can be accessed at 33 http://www.ietf.org/shadow.html. 35 This Internet-Draft will expire on March 9, 2009. 37 Abstract 39 The NFS version 4 protocol provides a natural way for a collection of 40 NFS file servers to collaborate in providing an organization-wide 41 file name space. The DNS SRV RR allows a simple and appropriate way 42 for an organization to publish the root of its name space, even to 43 clients that might not be intimately associated with such an 44 organization. DNS SRV can be used to join these organization-wide 45 file name spaces together to allow construction of a global, uniform 46 NFS version 4 file name space. This document refreshes the draft. 48 Table of Contents 50 1. Requirements notation . . . . . . . . . . . . . . . . . . . . 3 51 2. Background . . . . . . . . . . . . . . . . . . . . . . . . . . 3 52 3. Proposed Use of SRV Resource Record in DNS . . . . . . . . . . 3 53 3.1. Deployment of the Resource Record . . . . . . . . . . . . 4 54 4. Integration with Use of NFS Version 4 . . . . . . . . . . . . 5 55 4.1. Globally-useful names: conventional mount point . . . . . 5 56 4.2. Mount options . . . . . . . . . . . . . . . . . . . . . . 5 57 4.3. File system integration issues . . . . . . . . . . . . . . 6 58 5. Where is this integration carried out? . . . . . . . . . . . . 7 59 6. Relationship to DNS NFS4ID RR . . . . . . . . . . . . . . . . 7 60 7. Security Considerations . . . . . . . . . . . . . . . . . . . 8 61 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8 62 8.1. Normative References . . . . . . . . . . . . . . . . . . . 8 63 8.2. Informative References . . . . . . . . . . . . . . . . . . 9 64 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10 65 Intellectual Property and Copyright Statements . . . . . . . . . . 11 67 1. Requirements notation 69 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 70 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 71 document are to be interpreted as described in [RFC2119]. 73 2. Background 75 With the advent of fs_locations attributes in the NFS Version 4 76 protocol [RFC3530], NFS servers can cooperate to build a file name 77 space that crosses server boundaries, as detailed in the description 78 of referrals in [NB0510]. With NFS Version 4 referrals, a file 79 server may indicate to its client that the file system name tree 80 beneath a given name in the server is not present on itself, but is 81 represented by a filesystem in some other set of servers. The 82 mechanism is general, allowing servers to describe any filesystem as 83 being reachable by requests to any of a set of servers. Thus, 84 starting with a single NFS Version 4 server, using these referrals, 85 an NFS Version 4 client might be able to see a large name space 86 associated with a collection of interrelated NFS Version 4 file 87 servers. An organization could use this capability to construct a 88 uniform file name space for itself. 90 An organization might wish to publish the starting point for this 91 name space to its clients. In many cases, the organization will want 92 to publish this starting point to a broader set of possible clients. 93 At the same time, it is useful to require clients to know only the 94 smallest amount of information in order to locate the appropriate 95 name space. Simultaneously, that required information should be 96 constant through the life of an organization if the clients are not 97 to require reconfiguration as administrative events change, for 98 instance, a server's name or address. 100 3. Proposed Use of SRV Resource Record in DNS 102 Providing an organization's published file system name space is a 103 service, and it is appropriate to use the DNS [RFC1035] to locate it. 104 As with the AFSDB resource record type [RFC1183], the client need 105 only utter the (relatively) constant domain name for an organization 106 in order to locate its file system name space service. Once a client 107 uses the DNS to locate one or more servers for the root of the 108 organization's name space, it can use the standard NFS Version 4 109 mechanisms to navigate the remainder of the NFS servers for that 110 organization. The use of this proposed mechanism results in a useful 111 cross-organizational name space, just as in AFS [AFS] and DCE/DFS 112 [DFS] before it. A client need know only the name of the 113 organization in order to locate the file system name space published 114 by that organization. 116 We propose the use of the DNS SRV resource record type [RFC2782] to 117 fulfill this function. The format of the DNS SRV record is as 118 follows: 120 _Service._Proto.Name TTL Class SRV Priority Weight Port Target 122 In our case, we use a Service name of "nfs4" and a conventional 123 Protocol of "_tcp". The Target fields give the domain names of the 124 NFS Version 4 servers that export root filesystems. An NFS Version 4 125 client SHOULD interpret any of the exported pseudo-root filesystems 126 as the filesystem published by the organization with the given domain 127 name. 129 Suppose a client wished to locate the root of the file system 130 published by organization example.net. The DNS servers for the 131 domain could publish records like 133 _nfs4._tcp IN SRV 0 0 2049 nfs1tr.example.net 134 _nfs4._tcp IN SRV 1 0 2049 nfs2ex.example.net 136 The result domain names nfs1tr.example.net and nfs2ex.example.net 137 indicate NFS Version 4 file servers that export the root of the 138 published name space for the example.net domain. In accordance with 139 RFC 2782, these records are to be interpreted using the Priority and 140 Weight field values, selecting an appropriate file server with which 141 to begin a network conversation. Subsequent accesses are carried out 142 in accordance with ordinary NFS Version 4 protocol. 144 3.1. Deployment of the Resource Record 146 As with any DNS resource, any server installation needs to concern 147 itself with the likely loads and effects of the presence of the 148 resource record. The answers to requests for RRs might differ 149 depending on what the server can tell about the client. For example, 150 some RRs might be returned only to those clients inside some network 151 perimeter (to provide an intranet service) and requests from other 152 clients might be denied. As the RR directs the clients to ask for 153 service from a given set of servers, the administrator should ensure 154 that the identified servers can handle the expected load. 155 Fortunately, the definition of the DNS SRV resource record offers a 156 mechanism to distribute the load to multiple servers within a 157 priority ordering. 159 4. Integration with Use of NFS Version 4 161 There are at least two remaining questions: whether this DNS SRV 162 record evaluation is done in the NFS server or client, and also how 163 the domain names of the organizations are passed to client or server. 164 A third question is how this might produce a uniform global file name 165 space, and what prefix should be used for such file names. 167 This specification anticipates that these SRV records will most 168 commonly be used to define the second directory level in an inter- 169 organizational file name space. This directory will be populated 170 with domain names pointing to the file systems published for use 171 under those domain names. Thus, the root directory for the file 172 system published by example.net will effectively be mounted 173 underneath the example.net name in a second-level directory. 175 In general, a domain name will appear to a client as a directory name 176 pointing to the root directory of the file system published by the 177 organization responsible for that domain name. 179 4.1. Globally-useful names: conventional mount point 181 For the inter-organizational name space to be a global name space, it 182 is useful for its mount point in local systems to be uniform as well. 183 The name /nfs4/ SHOULD be used so that names on one machine will be 184 directly usable on any machine. Thus, the example.net published file 185 system would be accessible as 187 /nfs4/example.net/ 189 on any client. Using this convention, "/nfs4/" is a mount for a 190 special file system that is populated with the results of SRV record 191 lookups. 193 4.2. Mount options 195 SRV records are necessarily less complete than the information in the 196 existing NFS Version 4 attributes fs_locations and the proposed 197 fs_locations_info. For the rootpath field of fs_location, we assume 198 that the empty string is adequate. Thus, the servers listed as 199 targets for the SRV resource records should export the root of the 200 organization's published file system as the pseudo-root in its 201 exported namespace. 203 As for the other attributes in fs_locations_info, the recommended 204 approach is for a client to make its first possible contact with any 205 of the referred-to servers, obtain the fs_locations_info structure 206 from that server, and use the information from that obtained 207 structure as the basis for its judgment of whether it would be better 208 to use a different server representative from the set of servers for 209 that filesystem. 211 We recommend, though, that the process of mounting an organization's 212 name space should permit the use of what is likely to impose the 213 lowest cost on the server. Thus, we recommend that the client not 214 insist on using a writable copy of the filesystem if read-only copies 215 exist, or a zero-age copy rather than a copy that may be a little 216 older. We presume that the organization's file name space can be 217 navigated to provide access to higher-cost properties such as 218 writability or currency as necessary, but that the default use when 219 navigating to the base information for an organization ought to be as 220 low-overhead as possible. 222 One extension of this rule that we might choose to inherit from AFS, 223 though, is to give a special meaning to the domain name of an 224 organization preceded by a period ("."). It might be reasonable to 225 have names mounting the filesystem for a period-prefixed domain name 226 (e.g., ".example.net") attempt to mount only a read-write instance of 227 that organization's root filesystem, rather than permitting the use 228 of read-only instances of that filesystem. Thus, 230 /nfs4/example.net/users 232 might be a directory in a read-only instance of the root filesystem 233 of the organization "example.net", while 235 /nfs4/.example.net/users 237 would be a writable form of that same directory. A small benefit of 238 following this convention is that names with the period prefix are 239 treated as "hidden" in many operating systems, so that the visible 240 name remains the lowest-overhead name. 242 4.3. File system integration issues 244 The result of the DNS search SHOULD appear as a (pseudo-)directory in 245 the client name space, cached for a time no longer than the RR's TTL. 246 A further refinement is advisable, and SHOULD be deployed: that only 247 fully-qualified domain names appear as directories. That is, in many 248 environments, DNS names may be abbreviated from their fully-qualified 249 form. In such circumstances, multiple names might be given to file 250 system code that all resolve to the same DNS SRV RRs. The 251 abbreviated form SHOULD be represented in the client's name space 252 cache as a symbolic link, pointing to the fully-qualified name, case- 253 canonicalized when appropriate. This will allow pathnames obtained 254 with, say, getcwd() to include the DNS name that is most likely to be 255 usable outside the scope of any particular DNS abbreviation 256 convention. 258 5. Where is this integration carried out? 260 Another consideration is what agent should be responsible for 261 interpreting the SRV records. It could be done just as well by the 262 client or by the server, though we expect that most clients will 263 include this function themselves. Using something like Automounter 264 [AMD] technology, the client would be responsible for interpreting 265 names under a particular directory, discovering the appropriate 266 filesystem to mount, and mounting it in the appropriate place in the 267 client name space before returning control to the application doing a 268 lookup. Alternatively, one could imagine the existence of an NFS 269 version 4 server that awaited similar domain-name lookups, then 270 consulted the DNS SRV records to determine the servers for the 271 indicated published file system, and then returned that information 272 via NFS Version 4 attributes as a referral in the way outlined by 273 Noveck and Burnett [NB0510]. In either case, the result of the DNS 274 lookup should be cached (obeying TTL) so that the result could be 275 returned more quickly the next time. 277 We strongly suggest that this functionality be implemented by NFS 278 clients. While we recognize that it would be possible to configure 279 clients so that they relied on a specially-configured server to do 280 their SRV lookups for them, we feel that such a requirement would 281 impose unusual dependencies and vulnerabilities for the deployers of 282 such clients. 284 6. Relationship to DNS NFS4ID RR 286 This DNS use has no obvious relationship to the NFS4ID RR. The 287 NFS4ID RR is a mechanism to help clients and servers configure 288 themselves with respect to the domain strings used in "who" strings 289 in ACL entries and in owner and group names. The authentication/ 290 authorization domain string of a server need have no direct 291 relationship to the name of the organization that is publishing a 292 file name space of which this server's filesystems form a part. At 293 the same time, it might be seen as straightforward or normal for such 294 a server to refer to the ownership of most of its files using a 295 domain string with an evident relationship to that NFS4ID-given 296 domain name, but this document imposes no such requirement. 298 7. Security Considerations 300 Naive use of the DNS may effectively give clients published server 301 referrals that are intrusive substitutes for the servers intended by 302 domain administrators. 304 It may be possible to build a trust chain by using DNSSEC [RFC4033] 305 to implement this function on the client, or by implementing this 306 function on an NFS Version 4 server that uses DNSSEC and maintaining 307 a trust relationship with that server. This trust chain also breaks 308 if the SRV interpreter accepts responses from insecure DNS zones. 309 Thus, it would likely be prudent also to use domain-based service 310 principal names for the servers for the root filesystems as indicated 311 as the targets of the SRV records. The idea here is that one wants 312 to authenticate {nfs, domainname, host.fqdn}, not simply {nfs, 313 host.fqdn}, when the server is a domain's root file server obtained 314 through an insecure DNS SRV RR lookup. The domain administrator can 315 thus ensure that only domain root NFSv4 servers have credentials for 316 such domain-based service principal names. 318 Domain-based service principal names are defined in RFCs 5178 319 [RFC3530] and 5179 [RFC3530]. To make use of RFC 5178's domain-based 320 names, the syntax for "domain-based-name" MUST be used with a service 321 of "nfs", a domain matching the name of the organization whose root 322 filesystem is being sought, and a hostname given in the target of the 323 DNS SRV resource record. Thus, in the example above, two file 324 servers (nfs1tr.example.net and nfs2ex.example.net) are located as 325 hosting the root filesystem for the organization example.net. To 326 communicate with, for instance, the second of the given file servers, 327 GSS-API should be used with the name-type of 328 GSS_C_NT_DOMAINBASED_SERVICE defined in RFC 5178 and with a symbolic 329 name of 331 nfs@example.net@nfs2ex.example.net 333 in order to verify that the named server (nfs2ex.example.net) is 334 authorized to provide the root filesystem for the example.net 335 organization. 337 8. References 339 8.1. Normative References 341 [RFC1034] Mockapetris, P., "Domain Names - Concepts and Facilities", 342 RFC 1034, November 1987. 344 [RFC1035] Mockapetris, P., "Domain Names - Implementation and 345 Specification", RFC 1035, November 1987. 347 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 348 Requirement Levels", March 1997. 350 [RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for 351 specifying the location of services (DNS SRV)", RFC 2782, 352 February 2000. 354 [RFC3530] Shepler, S., Callaghan, B., Robinson, D., Thurlow, R., 355 Beame, C., Eisler, M., and D. Noveck, "Network File System 356 (NFS) version 4 Protocol", RFC 3530, April 2003. 358 [RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S. 359 Rose, "DNS Security Introduction and Requirements", 360 RFC 4033, March 2005. 362 [RFC5178] Williams, N. and A. Melnikov, "Generic Security Service 363 Application Program Interface (GSS-API) 364 Internationalization and Domain-Based Service Names and 365 Name Type", RFC 5178, May 2008. 367 [RFC5179] Williams, N., "Generic Security Service Application 368 Program Interface (GSS-API) Domain-Based Service Names 369 Mapping for the Kerberos V GSS Mechanism", RFC 5179, 370 May 2008. 372 8.2. Informative References 374 [AFS] Howard, J., "An Overview of the Andrew File System"", 375 Proc. USENIX Winter Tech. Conf. Dallas, February 1988. 377 [AMD] Pendry, J. and N. Williams, "Amd: The 4.4 BSD Automounter 378 Reference Manual", March 1991, 379 . 381 [DFS] Kazar, M., Leverett, B., Anderson, O., Apostolides, V., 382 Bottos, B., Chutani, S., Everhart, C., Mason, W., Tu, S., 383 and E. Zayas, "DEcorum File System Architectural 384 Overview", Proc. USENIX Summer Conf. Anaheim, Calif., 385 June 1990. 387 [NB0510] Noveck, D. and R. Burnett, "Next Steps for NFSv4 388 Migration/Replication", October 2005, . 391 [RFC1183] Everhart, C., Mamakos, L., Ullmann, R., and P. 392 Mockapetris, "New DNS RR Definitions", RFC 1183, 393 October 1990. 395 Authors' Addresses 397 Craig Everhart 398 NetApp 399 7301 Kit Creek Road 400 P.O. Box 13917 401 Research Triangle Park, NC 27709 402 US 404 Phone: +1 919 476 5320 405 Email: everhart@netapp.com 407 Andy Adamson 408 NetApp 409 495 East Java Drive 410 Sunnyvale, CA 94089 411 US 413 Phone: +1 734 665 1204 414 Email: andros@netapp.com 416 Jiaying Zhang 417 Google 418 535 W. 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