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'PAC' ** Downref: Normative reference to an Experimental RFC: RFC 2307 ** Obsolete normative reference: RFC 5661 (Obsoleted by RFC 8881) ** Downref: Normative reference to an Informational RFC: RFC 5716 Summary: 4 errors (**), 0 flaws (~~), 2 warnings (==), 4 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 NFSv4 Working Group W. Adamson 3 Internet-Draft NetApp 4 Intended status: Standards Track N. Williams 5 Expires: April 26, 2015 Cryptonector 6 October 23, 2014 8 Multiple NFSv4 Domain File System Requirements 9 draft-ietf-nfsv4-multi-domain-fs-reqs-00 11 Abstract 13 This document describes constraints to the NFSv4.0 and NFSv4.1 14 protocols as well as the use of multi-domain capable file systems, 15 name resolution services, and security services required to fully 16 enable a multiple NFSv4 domain file system, such as a multiple NFSv4 17 domain Federated File System. 19 Requirements Language 21 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 22 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 23 document are to be interpreted as described in [RFC2119]. 25 Status of This Memo 27 This Internet-Draft is submitted in full conformance with the 28 provisions of BCP 78 and BCP 79. 30 Internet-Drafts are working documents of the Internet Engineering 31 Task Force (IETF). Note that other groups may also distribute 32 working documents as Internet-Drafts. The list of current Internet- 33 Drafts is at http://datatracker.ietf.org/drafts/current/. 35 Internet-Drafts are draft documents valid for a maximum of six months 36 and may be updated, replaced, or obsoleted by other documents at any 37 time. It is inappropriate to use Internet-Drafts as reference 38 material or to cite them other than as "work in progress." 40 This Internet-Draft will expire on April 26, 2015. 42 Copyright Notice 44 Copyright (c) 2014 IETF Trust and the persons identified as the 45 document authors. All rights reserved. 47 This document is subject to BCP 78 and the IETF Trust's Legal 48 Provisions Relating to IETF Documents 49 (http://trustee.ietf.org/license-info) in effect on the date of 50 publication of this document. Please review these documents 51 carefully, as they describe your rights and restrictions with respect 52 to this document. Code Components extracted from this document must 53 include Simplified BSD License text as described in Section 4.e of 54 the Trust Legal Provisions and are provided without warranty as 55 described in the Simplified BSD License. 57 Table of Contents 59 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 60 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 61 3. NFSv4 Server Identity Mapping . . . . . . . . . . . . . . . . 4 62 4. Stand-alone NFSv4 Domain Deployment Examples . . . . . . . . 5 63 4.1. AUTH_SYS with Stringified UID/GID . . . . . . . . . . . . . 6 64 4.2. AUTH_SYS with name@domain . . . . . . . . . . . . . . . . . 6 65 4.3. RPCSEC_GSS with name@domain . . . . . . . . . . . . . . . . 6 66 5. Multi-domain Constraints to the NFSv4 Protocol . . . . . . . 7 67 5.1. Name@domain Constraints . . . . . . . . . . . . . . . . . . 7 68 5.1.1. NFSv4 Domain and DNS Services . . . . . . . . . . . . . . 8 69 5.1.2. NFSv4 Domain, Name Service, and Domain Aware File Systems 8 70 5.2. RPC Security Constraints . . . . . . . . . . . . . . . . . 9 71 5.2.1. NFSv4 Domain and Security Services . . . . . . . . . . . 9 72 6. Resolving Multi-domain Authorization Information . . . . . . 10 73 7. Stand-alone Examples and Multi NFSv4 Domain FedFS . . . . . . 11 74 8. Security Considerations . . . . . . . . . . . . . . . . . . . 11 75 9. Normative References . . . . . . . . . . . . . . . . . . . . 12 76 Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . 12 77 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13 79 1. Introduction 81 An NFSv4 domain is defined as a set of users, groups and computers 82 running NFSv4.0 [I-D.ietf-nfsv4-rfc3530bis] and NFSv4.1 [RFC5661] 83 (hereafter referred to as NFSv4) protocols identified by an NFSv4 84 domain name. 86 The Federated File System (FedFS) [RFC5716] describes the 87 requirements and administrative tools to construct a uniform NFSv4 88 file server based namespace that is capable of spanning a whole 89 enterprise and that is easy to manage. 91 The FedFS is the standardized method of constructing and 92 administrating an enterprise wide NFSv4 filesystem, and so is 93 referenced in this document. The issues with multiple NFSv4 domain 94 file systems described in this document apply to all multiple NFSv4 95 domain file systems, be they run as a FedFS or not. 97 Stand-alone NFSv4 domains can be run in many ways. While a FedFS can 98 be run within all stand-alone NFSv4 domain configurations some of 99 these configurations (Section 4) are not compatible with joining a 100 multiple NFSv4 domain FedFS namespace. 102 Multi NFSv4 domain file systems require support for global identities 103 in name services, security services, and in the exporting of on-disk 104 local identity representation. Many of the stand-alone NFSv4 domain 105 deployments do not provide full support for global identities. 107 This document describes constraints to the NFSv4 protocols as well as 108 the use of multi-domain capable file systems, name resolution 109 services, and security services required to fully enable a multiple 110 NFSv4 domain file system, such as a multiple NFSv4 domain FedFS. 112 2. Terminology 114 Name Service: provides the mapping between {NFSv4 domain, group or 115 user name} and {NFSv4 domain, local ID}, as well as the mapping 116 between {security principal} and {NFSv4 domain, local ID} via 117 lookups. Can be applied to local or remote domains. Often 118 provided by a Directory Service such as LDAP. 120 Domain: This term is used in multiple contexts where it has 121 different meanings. Here we provide specific definitions used in 122 this document. 124 DNS domain: a set of computers, services, or any internet 125 resource identified by an DNS domain name [RFC1034]. 127 Security realm or domain: a set of configured security 128 providers, users, groups, security roles, and security policies 129 running a single security protocol and administered by a single 130 entity, for example a Kerberos realm. 132 NFSv4 domain: a set of users, groups, and computers running 133 NFSv4 protocols identified by a unique NFSv4 domain name. See 134 [RFC5661] Section 5.9 "Interpreting owner and owner_group". 136 Multi-domain: In this document this always refers to multiple 137 NFSv4 domains. 139 FedFS domain: A file name space that can cross multiple shares 140 on multiple file servers using file-access protocols such as 141 NFSv4. A FedFS domain is typically a single administrative 142 entity, and has a name that is similar to a DNS domain name. 143 Also known as a Federation. 145 Administrative domain: a set of users, groups, computers, and 146 services administered by a single entity. Can include multiple 147 DNS domains, NFSv4 domains, security domains, and FedFS 148 domains. 150 Local representation of identity: an object such as a uidNumber 151 (UID) or gidNumber (GID) [RFC2307], a Windows Security Identifier 152 (SID) [CIFS], or other such representation of a user or a group of 153 users on-disk in a file system. 155 Global identity: An on-the-wire globally unique form of identity 156 that can be mapped to a local representation. For example, the 157 NFSv4 name@domain or the Kerberos principal@REALM. 159 Multi-domain capable filesystem: A local filesystem that uses a 160 local ID form that can represent identities from both local and 161 remote domains. For example, an SSID based local ID form where 162 the SSID contains both a domain and a user or group component. 164 Principal: an RPCSEC_GSS authentication identity. Usually, but 165 not always, a user; rarely, if ever, a group; sometimes a host or 166 server. 168 Authorization Context: A collection of information about a 169 principal such as username, userID, group membership, etcetera 170 used in authorization decisions. 172 Stringified UID or GID: NFSv4 owner and group strings that consist 173 of decimal numeric values with no leading zeros, and which do not 174 contain an '@' sign. See Section 5.9 "Interpreting owner and 175 owner_group" [RFC5661]. 177 3. NFSv4 Server Identity Mapping 179 NFSv4 servers deal with two kinds of identities: authentication 180 identities (referred to here as "principals") and authorization 181 identities ("users" and "groups" of users). NFSv4 supports multiple 182 authentication methods, each authenticating an "initiator principal" 183 (typically representing a user) to an "acceptor principal" (always 184 corresponding to the NFSv4 server). NFSv4 does not prescribe how to 185 represent authorization identities on file systems. All file access 186 decisions constitute "authorization" and are made by NFSv4 servers 187 using authorization context information and file metadata related to 188 authorization, such as a file's access control list (ACL). 190 NFSv4 servers therefore must perform two kinds of mappings: 192 1. Auth-to-authz: A mapping between the authentication identity and 193 the authorization context information. 195 2. Wire-to-disk: A mapping between the on-the-wire authorization 196 identity representation and the on-disk authorization identity 197 representation. 199 A Name Service such as LDAP often provides these mappings. 201 Many aspects of these mappings are entirely implementation specific, 202 but some require multi-domain capable name resolution and security 203 services in order to interoperate in a multiple NFSv4 domain file 204 system. 206 NFSv4 servers use these mappings for: 208 1. File access: Both the auth-to-authz and the wire-to-disk mappings 209 may be required for file access decisions. 211 2. Meta-data setting and listing: The auth-to-authz mapping is 212 usually required to service file metadata setting or listing 213 requests (such as ACL or unix permission setting or listing) as 214 NFSv4 uses the name@domain on-the-wire identity representation 215 which usually differs from the exported on-disk identity 216 representation. 218 4. Stand-alone NFSv4 Domain Deployment Examples 220 In order to service as many environments as possible, the NFSv4 221 protocol is designed to allow administrators freedom to configure 222 their NFSv4 domains as they please. 224 Stand-alone NFSv4 domains can be run in many ways. Here we list some 225 stand-alone NFSv4 domain deployment examples focusing on the NFSv4 226 server's use of name service mappings (Section 3) and security 227 services deployment to demonstrate the need for some multiple NFSv4 228 domain constraints to the NFSv4 protocol, name service configuration, 229 and security service choices. 231 Because all on-disk identities participating in a stand-alone NFSv4 232 domain belong to the same NFSv4 domain, stand-alone NFSv4 domain 233 deployments have no requirement for exporting multi-domain capable 234 file systems. 236 These examples are for a NFSv4 server exporting a 32bit UID/GID based 237 file system, a typical deployment. These examples are listed in the 238 order of increasing NFSv4 administrative complexity. 240 4.1. AUTH_SYS with Stringified UID/GID 242 This example is the closest NFSv4 gets to being run as NFSv3. 244 File access: The AUTH_SYS RPC credential provides a UID as the 245 authentication identity, and a list of GIDs as authorization context 246 information. File access decisions require no name service 247 interaction as the on-the-wire and on-disk representation are the 248 same and the auth-to-authz UID and GID authorization context 249 information is provided in the RPC credential. 251 Meta-data setting and listing: When the NFSv4 clients and servers 252 implement a stringified UID/GID scheme, where a stringified UID or 253 GID is used for the NFSv4 name@domain on-the-wire identity, then a 254 name service is not required for file metadata listing as the UID or 255 GID can be constructed from the stringified form on the fly by the 256 server. 258 4.2. AUTH_SYS with name@domain 260 The next level of complexity is to not use a stringified UID/GID 261 scheme for file metadata listing. 263 File access: This is the same as in Section 4.1. 265 Meta-data setting and listing: The NFSv4 server will need to use a 266 name service for the wire-to-disk mappings to map between the on-the- 267 wire name@domain syntax and the on-disk UID/GID representation. 268 Often, the NFSv4 server will use the nsswitch interface for these 269 mappings. A typical use of the nsswitch name service interface uses 270 no domain component, just the uid attribute [RFC2307] (or login name) 271 as the name component. This is no issue in a stand-alone NFSv4 272 domain deployment as the NFSv4 domain is known to the NFSv4 server 273 and can combined with the login name to form the name@domain syntax 274 after the return of the name service call. 276 4.3. RPCSEC_GSS with name@domain 278 This final example adds the complexity of RPCSEC_GSS with the 279 Kerberos 5 GSS security mechanism. 281 File Access: The RPCSEC_GSS Kerberos credential provides a 282 principal@REALM name as the authentication identity, and (as of this 283 writing) no authorization context information. File access decisions 284 therefore require a wire-to-disk mapping of the principal@REALM to a 285 UID, and an auth-to-authz mapping to obtain the list of GIDs as the 286 authorization context. 288 Deployments can use the nsswitch name service interface for the 289 principal@REALM to UID mapping by stripping off the REALM portion. 290 This requires that the principal portion of the principal@REALM 291 matches the uid attribute [RFC2307] (or login name) of the user. 293 Meta-data setting and listing: This is the same as in Section 4.2. 295 5. Multi-domain Constraints to the NFSv4 Protocol 297 Joining NFSv4 domains under a single file namespace imposes slightly 298 on the NFSv4 administration freedom. Here we describe the required 299 constraints. 301 5.1. Name@domain Constraints 303 NFSv4 uses a syntax of the form "name@domain" as the on wire 304 representation of the "who" field of an NFSv4 access control entry 305 (ACE) for users and groups. This design provides a level of 306 indirection that allows NFSv4 clients and servers with different 307 internal representations of authorization identity to interoperate 308 even when referring to authorization identities from different NFSv4 309 domains. 311 Multiple NFSv4 domain capable sites need to meet the following 312 requirements in order to ensure that NFSv4 clients and servers can 313 map between name@domain and internal representations reliably. While 314 some of these constraints are basic assumptions in NFSv4.0 315 [I-D.ietf-nfsv4-rfc3530bis] and NFSv4.1 [RFC5661], they need to be 316 clearly stated for the multiple NFSv4 domain case. 318 o The NFSv4 domain portion of name@domain MUST be unique within the 319 multiple NFSv4 domain namespace. See [RFC5661] section 5.9 320 "Interpreting owner and owner_group" for a discussion on NFSv4 321 domain configuration. 323 o The name portion of name@domain MUST be unique within the 324 specified NFSv4 domain. 326 o Every local representation of a user and of a group MUST have a 327 canonical name@domain, and it must be possible to return the 328 canonical name@domain for any identity stored on disk, at least 329 when required infrastructure servers (such as name services) are 330 online. 332 Due to UID and GID collisions, stringified UID/GIDs MUST NOT be used 333 in a multiple NFSv4 domain file system. 335 Note that for stand-alone NFSv4 domains it does not matter if the 336 choice of the NFSv4 domain name is replicated by another stand-alone 337 NFSv4 domain deployment. Indeed, if a stringified UID/GID scheme is 338 used, or just UNIX mode bits are used (NFSv4 ACLs are not set or 339 listed) and the simple nsswitch interface that strips the @domain and 340 the @REALM is used, then the domain portion of name@domain can be 341 ignored, and even be different for each client and server in the 342 domain. 344 5.1.1. NFSv4 Domain and DNS Services 346 Here we address the relationship between NFSv4 domain name and DNS 347 domain name in a multiple NFSv4 domain deployment. 349 The definition of an NFSv4 domain name needs clarification to work in 350 a multiple NFSv4 domain file system name space. Section 5.9 351 [RFC5661] loosely defines the NFSv4 domain name as a DNS domain name. 352 This loose definition for the NFSv4 domain is a good one, as DNS 353 domain names are globally unique. As noted above in Section 5.1, any 354 choice of NFSv4 domain name can work within a stand-alone NFSv4 355 domain deployment whereas the NFSv4 domain is required to be unique 356 in a multiple NFSv4 domain deployment. 358 A typical configuration is that there is a single NFSv4 domain that 359 is served by a single DNS domain. In this case the NFSv4 domain name 360 can be the same as the DNS domain name. 362 An NFSv4 domain can span multiple DNS domains. In this case, one of 363 the DNS domain names can be chosen as the NFSv4 domain name. 365 Multiple NFSv4 domains can also share a DNS domain. In this case, 366 only one of the NFSv4 domains can use the DNS domain name, the other 367 NFSv4 domains must choose another unique NFSv4 domain name. 369 5.1.2. NFSv4 Domain, Name Service, and Domain Aware File Systems 371 As noted above in Section 5.1, each name@domain is unique across the 372 multiple NFSv4 domain namespace, and maps to a local representation 373 of ID in each NFSv4 domain. This means that each NFSv4 domain has a 374 single name resolution service exporting the NFSv4 domain local ID 375 name space. 377 An NFSv4 domain administrator that wants to give NFSv4 local file 378 access to a remote user from a remote NFSv4 domain needs to create a 379 local ID for the remote user which can then be assigned on-disk and 380 used for local access decisions. Since the local ID for the remote 381 user must be able to be mapped to a name@remote-domain, only multi- 382 domain capable file systems can be exported in a multiple NFSv4 383 domain FedFS. 385 We note that many file systems exported by NFSv4 use 32 bit POSIX UID 386 and GIDs as a local ID form and as this local ID form has no domain 387 component, these file systems are not domain aware and can not 388 participate in a multiple NFSv4 domain FedFS. There are ways to 389 overcome this deficiency, but these practices are beyond the scope of 390 this document. 392 5.2. RPC Security Constraints 394 As described in [RFC5661] section 2.2.1.1 "RPC Security Flavors": 396 NFSv4.1 clients and servers MUST implement RPCSEC_GSS. 397 (This requirement to implement is not a requirement 398 to use.) Other flavors, such as AUTH_NONE, and AUTH_SYS, 399 MAY be implemented as well. 401 The underlying RPCSEC_GSS security mechanism used in a multiple NFSv4 402 domain FedFS is REQUIRED to employ a method of cross NFSv4 domain 403 trust so that a principal from a security service in one NFSv4 domain 404 can be authenticated in another NFSv4 domain that uses a security 405 service with the same security mechanism. Kerberos, and PKU2U 406 [I-D.zhu-pku2u] are examples of such security services. 408 The AUTH_NONE security flavor can be useful in a multiple NFSv4 409 domain FedFS to grant universal access to public data without any 410 credentials. 412 The AUTH_SYS security flavor uses a host-based authentication model 413 where the weakly authenticated host (the NFSv4 client) asserts the 414 user's authorization identities using small integers, uidNumber, and 415 gidNumber [RFC2307], as user and group identity representations. 416 Because this authorization ID representation has no domain component, 417 AUTH_SYS can only be used in a name space where all NFSv4 clients and 418 servers share an [RFC2307] name service. A shared name service is 419 required because uidNumbers and gidNumbers are passed in the RPC 420 credential; there is no negotiation of namespace in AUTH_SYS. 421 Collisions can occur if multiple name services are used, so AUTH_SYS 422 MUST NOT be used in a multiple NFSv4 domain file system. 424 5.2.1. NFSv4 Domain and Security Services 426 As noted above in Section 5.2, caveat AUTH_NULL, multiple NFSv4 427 domain security services are RPCSEC_GSS based with the Kerberos 5 428 security mechanism being the most commonly (and as of this writing, 429 the only) deployed service. 431 A single Kerberos 5 security service per NFSv4 domain with the upper 432 case NFSv4 domain name as the Kerberos 5 REALM name is a common 433 deployment. 435 Multiple security services per NFSv4 domain is allowed, and brings 436 the issue of mapping multiple Kerberos 5 principal@REALMs to the same 437 local ID. Methods of achieving this are beyond the scope of this 438 document. 440 6. Resolving Multi-domain Authorization Information 442 When an RPCSEC_GSS principal is seeking access to files on an NFSv4 443 server, after authenticating the principal, the server must obtain in 444 a secure manner the principal's authorization context information 445 from an authoritative source such as the name service in the 446 principal's NFSv4 domain. 448 In the stand-alone NFSv4 domain case where the principal is seeking 449 access to files on an NFSv4 server in the principal's home NFSv4 450 domain, the server administrator has knowledge of the local policies 451 and methods for obtaining the principal's authorization information 452 and the mappings to local representation of identity from an 453 authoritative source. E.g., the administrator can configure secure 454 access to the local NFSv4 domain name service. 456 In the multiple NFSv4 domain case where a principal is seeking access 457 to files on an NFSv4 server not in the principal's home NFSv4 domain, 458 the server is REQUIRED to obtain in a secure manner the principal's 459 authorization context information from an authoritative source. In 460 this case there is no assumption of: 462 o Remote name service configuration knowledge 464 o The syntax of the remote authorization context information 465 presented to the NFSv4 server by the remote name service for 466 mapping to a local representation. 468 There are several methods the NFSv4 server can use to obtain the 469 NFSv4 domain authoritative authorization information for a remote 470 principal from an authoritative source. While any detail is beyond 471 the scope of this document, some general methods are listed here. 473 1. A mechanism specific GSS-API authorization payload containing 474 credential authorization data such as a "privilege attribute 475 certificate" (PAC) [PAC] or a "general PAD" (PAD) 476 [I-D.sorce-krbwg-general-pac]. This is the preferred method as 477 the payload is delivered as part of GSS-API authentication, 478 avoids requiring any knowledge of the remote authoritative 479 service configuration, and its syntax is well known. 481 2. When there is a security agreement between the local and remote 482 NFSv4 domain name services plus regular update data feeds, the 483 NFSv4 server local NFSv4 domain name service can be authoritative 484 for principal's in the remote NFSv4 domain. In this case, the 485 NFSv4 server makes a query to it's local NFSv4 domain name 486 service just as it does when servicing a local domain principal. 487 While this requires detailed knowledge of the remote NFSv4 488 domains name service, the authorization context information 489 presented to the NFSv4 server is in the same form as a query for 490 a local principal. 492 3. An authenticated direct query from the NFSv4 server to the 493 principal's NFSv4 domain authoritative name service. This 494 requires the NFSv4 server to have detailed knowledge of the 495 remote NFSv4 domain's authoritative name service and detailed 496 knowledge of the syntax of the resultant authorization context 497 information. 499 7. Stand-alone Examples and Multi NFSv4 Domain FedFS 501 Revisiting the stand-alone (Section 4) NFSv4 domain deployment 502 examples, we note that due to the use of AUTH_SYS, neither 503 Section 4.1 nor Section 4.2 configurations are suitable for multiple 504 NFSv4 domain deployments. 506 The Section 4.3 configuration example can participate in a multiple 507 NFSv4 domain FedFS deployment if: 509 o The NFSv4 domain name is unique across the FedFS. 511 o All exported file systems are multi-domain capable. 513 o A secure method is used to resolve remote NFSv4 domain principals 514 authorization information from an authoritative source. 516 8. Security Considerations 518 There are no security considerations introduced by this document 519 beyond those described in NFSv4.0 [I-D.ietf-nfsv4-rfc3530bis] and 520 NFSv4.1 [RFC5661]. 522 9. Normative References 524 [CIFS] Microsoft Corporation, "[MS-CIFS] -- v20130118 Common 525 Internet File System (CIFS) Protocol", January 2013. 527 [I-D.ietf-nfsv4-rfc3530bis] 528 Haynes, T. and D. Noveck, "Network File System (NFS) 529 version 4 Protocol", draft-ietf-nfsv4-rfc3530bis-25 (Work 530 In Progress), February 2013. 532 [I-D.sorce-krbwg-general-pac] 533 Sorce, S., Yu, T., and T. Hardjono, "A Generalized PAC for 534 Kerberos V5", draft-ietf-krb-wg-general-pac-02 (Work In 535 Progress awaiting merge with other document ), June 2011. 537 [I-D.zhu-pku2u] 538 Zhu, L., Altman, J., and N. Williams, "Public Key 539 Cryptography Based User-to-User Authentication - (PKU2U)", 540 draft-zhu-pku2u-09 (Work In Progress), November 2008. 542 [PAC] Brezak, J., "Utilizing the Windows 2000 Authorization Data 543 in Kerberos Tickets for Access Control to Resources", 544 October 2002. 546 [RFC1034] Mockapetris, P., "DOMAIN NAMES - CONCEPTS AND FACILITIES", 547 RFC 1034, November 1987. 549 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 550 Requirement Levels", RFC 2119, March 1997. 552 [RFC2307] Howard, L., "An Approach for Using LDAP as a Network 553 Information Service", RFC 2307, March 1998. 555 [RFC5661] Shepler, S., Eisler, M., and D. Noveck, "Network File 556 System (NFS) Version 4 Minor Version 1 Protocol", RFC 557 5661, January 2010. 559 [RFC5716] Lentini, J., Everhart, C., Ellard, D., Tewari, R., and M. 560 Naik, "Requirements for Federated File Systems", RFC 5716, 561 January 2010. 563 Appendix A. Acknowledgments 565 Andy Adamson would like to thank NetApp, Inc. for its funding of his 566 time on this project. 568 We thank Chuck Lever, Tom Haynes, Brian Reitz, and Bruce Fields for 569 their review. 571 Authors' Addresses 573 William A. (Andy) Adamson 574 NetApp 576 Email: andros@netapp.com 578 Nicolas Williams 579 Cryptonector 581 Email: nico@cryptonector.com