Network Working Group C. Everhart Internet-Draft Network Appliance, Inc. Expires: August 26, 2006 A. Adamson CITI, University of Michigan J. Zhang University of Michigan E. Brunner-Williams Panasas, Inc. February 22, 2006 Using DNS SRV to Specify a Global File Name Space with NFS version 4 draft-everhart-nfsv4-namespace-via-dns-srv-00.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 August 26, 2006. Copyright Notice Copyright (C) The Internet Society (2006). Abstract The NFS version 4 protocol provides a natural way for a collection of NFS file servers to collaborate in providing an organization-wide file name space. The DNS SRV RR allows a simple and appropriate way Everhart, et al. Expires August 26, 2006 [Page 1] Internet-Draft NFSv4 Global Name Space with DNS SRV February 2006 for an organization to publish the root of its name space, even to clients that might not be intimately associated with such an organization. DNS SRV can be used to join these organization-wide file name spaces together to allow construction of a global, uniform NFS version 4 file name space. Table of Contents 1. Requirements notation . . . . . . . . . . . . . . . . . . . . 3 2. Background . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Proposed Use of SRV Resource Record in DNS . . . . . . . . . . 5 4. Integration with Use of NFS Version 4 . . . . . . . . . . . . 6 4.1. Globally-useful names: conventional mount point . . . . . 6 4.2. Mount options . . . . . . . . . . . . . . . . . . . . . . 7 5. Where is this integration carried out? . . . . . . . . . . . . 8 6. Relationship to DNS NFS4ID RR . . . . . . . . . . . . . . . . 9 7. Security Considerations . . . . . . . . . . . . . . . . . . . 10 8. Normative References . . . . . . . . . . . . . . . . . . . . . 10 9. Informative References . . . . . . . . . . . . . . . . . . . . 11 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12 Intellectual Property and Copyright Statements . . . . . . . . . . 13 Everhart, et al. Expires August 26, 2006 [Page 2] Internet-Draft NFSv4 Global Name Space with DNS SRV February 2006 1. Requirements notation The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. Everhart, et al. Expires August 26, 2006 [Page 3] Internet-Draft NFSv4 Global Name Space with DNS SRV February 2006 2. Background With the advent of fs_locations attributes in the NFS Version 4 protocol [RFC3530], NFS servers can cooperative to build a file name space that crosses server boundaries, as detailed in the description of referrals in [NB0510]. With NFS Version 4 referrals, a file server may indicate to its client that the file system name tree beneath a given name in the server is not present on itself, but is represented by a filesystem in some other set of servers. The mechanism is general, allowing servers to describe any filesystem as being reachable by requests to any of a set of servers. Thus, given one NFS Version 4 server, an NFS Version 4 client might be able to see a large name space associated with a collection of interrelated NFS Version 4 file servers. Given this ability for organizations to construct file name spaces, some organizations may wish to advertise a starting point for clients to use in the navigation of the name spaces. In some cases, the organizations may wish to advertise this starting point (the root of the organization's file system name space) to a broad set of possible clients. At the same time, it is useful to require clients to know only the smallest amount of information in order to begin to locate the appropriate name space. Simultaneously, that required information should be constant through the life of an organization if the clients are not to require reconfiguration as administrative events change, for instance, a server's name or address. Everhart, et al. Expires August 26, 2006 [Page 4] Internet-Draft NFSv4 Global Name Space with DNS SRV February 2006 3. Proposed Use of SRV Resource Record in DNS Providing an organization's published file system name space is a service, and it is appropriate to use the DNS [RFC1035] to locate it. As with the AFSDB resource record type in RFC 1183, the client need only utter the (relatively) constant domain name for an organization in order to locate its file system name space service. Once a client uses the DNS to locate one or more servers for the root of the organization's name space, it can use the standard NFS Version 4 mechanisms to navigate the remainder of the NFS servers for that organization. The use of this proposed mechanism results in a useful cross-organizational name space, just as in AFS [AFS] and DCE/DFS [DFS] before it. A client need know only the name of the organization in order to locate the file system name space published by that organization. We propose the use of the DNS SRV resource record type [RFC2782] to fulfill this function. The format of the DNS SRV record is as follows: _Service._Proto.Name TTL Class SRV Priority Weight Port Target In our case, the protocol need not be given, so we elide it and utter only the Service name. The Target fields give the domain names of the NFS Version 4 servers that export root filesystems. An NFS Version 4 client SHOULD interpret any of the exported pseudo-root filesystems as the filesystem published by the organization with the given domain name. Suppose a client wished to locate the root of the file system published by organization example.com. The DNS servers for the domain could publish records like _nfsv4 IN SRV 0 0 2049 nfs1tr.example.com _nfsv4 IN SRV 1 0 2049 nfs2ex.example.com The result domain names nfs1tr.example.com and nfs2ex.example.com indicate NFS Version 4 file servers that export the root of the published name space for the example.com domain. In accordance with RFC 2782, these records are to be interpreted using the Priority and Weight field values, selecting an appropriate file server with which to begin a network conversation. Subsequent accesses are carried out in accordance with ordinary NFS Version 4 protocol. Everhart, et al. Expires August 26, 2006 [Page 5] Internet-Draft NFSv4 Global Name Space with DNS SRV February 2006 4. Integration with Use of NFS Version 4 There are at least two remaining questions: whether this DNS SRV record evaluation is done in the NFS server or client, and also how the domain names of the organizations are passed to client or server. A third question is whether how this might produce a uniform global file name space, and what prefix should be used for such file names. This specification anticipates that these SRV records will most commonly be used to define the second directory level in an inter- organizational file name space. This directory will be populated principally with domain names pointing to the file systems published for use under those domain names. Thus, the root directory for the file system published by example.com will effectively be mounted underneath the example.com name in a second-level directory. Arguably, clients intimately associated with the example.com organization, as well as clients without prior association, SHOULD be able to refer to files in the example.com published name space with the example.com/ (or example.com\) prefix, thus allowing greater sharing of published content across organizational boundaries. Ideally, also, the client should represent the '..' entry of the published root filesystem as the full example.com directory name, so that 'getcwd' and similar functions might display a content name that would be usable inside and outside the organization. Thus, a domain name will appear to a client as a directory name pointing to the root directory of the file system published by the organization responsible for that domain name. Symbolic links, and other DNS navigational artifacts like case-folding, might appear to the client as relative symbolic names in that directory, pointing to the case-folded full domain name under which the published file system is mounted. 4.1. Globally-useful names: conventional mount point For the inter-organizational name space to be a global name space, it may be useful for its mount point in local systems to be uniform as well. We suggest mounting it as /nfs4/ so that names on one machine will be directly usable on any machine. Thus, the example.com published file system would be accessible as /nfs4/example.com/ on any client. Using this convention, "/nfs4/" is a mount for a special file system that is populated with the results of SRV record lookups. This is the convention that we will observe in examples in the current document. Everhart, et al. Expires August 26, 2006 [Page 6] Internet-Draft NFSv4 Global Name Space with DNS SRV February 2006 4.2. Mount options SRV records are necessarily less complete than the information in the existing NFS Version 4 attributes fs_locations and location_info. For the rootpath field of fs_location, we assume that the empty string is adequate. Thus, the servers listed as targets for the SRV resource records should export the root of the organization's published file system as the pseudo-root in its exported namespace. As for the other attributes in location_info, the recommended approach is for a client to make its first possible contact with any of the referred-to servers, obtain the location_info structure from that server, and use the information from that obtained structure as the basis for its judgment of whether it would be better to use a different server representative from the set of servers for that filesystem. We recommend, though, that the process of mounting an organization's name space should permit the use of what is likely to impose the lowest cost on the server. Thus, we suggest that the client not insist on using a writable copy of the filesystem if read-only copies exist, or a zero-age copy rather than a copy that may be a little older. We presume that the organization's file name space can be navigated to provide access to higher-cost properties such as writability or currency as necessary, but that the default use when navigating to the base information for an organization ought to be as low-overhead as possible. One extension of this rule that we might choose to inherit from AFS, though, is to give a special meaning to the domain name of an organization preceded by a period ("."). It might be reasonable to have names mounting the filesystem for a period-prefixed domain name (e.g., ".example.com") attempt to mount only a read-write instance of that organization's root filesystem, rather than permitting the use of read-only instances of that filesystem. Thus, /nfs4/example.com/users might be a directory in a read-only instance of the root filesystem of the organization "example.com", while /nfs4/.example.com/users would be a writable form of that same directory. A small benefit of following this convention is that names with the period prefix are treated as "hidden" in many operating systems, so that the visible name remains the lowest-overhead name. Everhart, et al. Expires August 26, 2006 [Page 7] Internet-Draft NFSv4 Global Name Space with DNS SRV February 2006 5. Where is this integration carried out? Another consideration is what agent should be responsible for interpreting the SRV records. It could be done just as well on the client or on the server, and this specification takes no position. Using something like Automounter [AMT] technology, the client might be responsible for interpreting names under a given directory, discovering the appropriate filesystem to mount, and mounting it in the appropriate place in the client name space before returning control to the application doing a lookup. Alternatively, one could imagine the existence of an NFS version 4 server that awaited similar domain-name lookups, then consulted the DNS SRV records to determine the servers for the indicated published file system, then returned that information via NFS Version 4 attributes as a referral in the way outlined by Noveck and Burnett [NB0510]. The server would likely cache the DNS results (obeying TTL) so that it could return the results more quickly the next time. Everhart, et al. Expires August 26, 2006 [Page 8] Internet-Draft NFSv4 Global Name Space with DNS SRV February 2006 6. Relationship to DNS NFS4ID RR This DNS use has no obvious relationship to the NFS4ID RR. The NFS4ID RR is a mechanism to help clients and servers configure themselves with respect to the domain strings used in "who" strings in ACL entries and in owner and group names. The authentication/ authorization domain string of a server need have no direct relationship to the name of the organization that is publishing a file name space of which this server's filesystems form a part. At the same time, it might be seen as straightforward or normal for such a server to refer to the ownership of most of its files using a domain string with an evident relationship to that NFS4ID-given domain name, but this document imposes no such requirement. Everhart, et al. Expires August 26, 2006 [Page 9] Internet-Draft NFSv4 Global Name Space with DNS SRV February 2006 7. Security Considerations Naive use of the DNS may effectively give clients published server referrals that are intrusive substitutes for the servers intended by domain administrators. It may be possible to build a trust chain by using DNSSEC [RFC4033] to implement this function on the client, or by implementing this function on an NFS Version 4 server that uses DNSSEC and maintaining a trust relationship with that server. This trust chain also breaks if the SRV interpreter accepts responses from insecure DNS zones. Thus, it would likely be prudent also to use domain-based service principal names for the servers for the root filesystems as indicated as the targets of the SRV records. The idea is that you want to authenticate {nfs, domainname, host.fqdn}, not {nfs, host.fqdn} when the server is a domain root server obtained through an insecure DNS SRV RR lookup. Then the domain administrator could ensure that only domain root NFSv4 servers have credentials for such domain-based service principal names. Domain-based service principal names are being proposed in the KITTEN WG [KITTEN]. 8. Normative References [RFC1035] Mockapetris, P., "Domain Names - Implementation And Specification," RFC 1035, November 1987. [RFC2782] Golbrandsen, A. et al., "A DNS RR for specifying the location of services (DNS SRV)," RFC 2782, February 2000. [RFC3530] Shepler, S. et al., "Network File System (NFS) version 4 Protocol," RFC 3530, April 2003. Everhart, et al. Expires August 26, 2006 [Page 10] Internet-Draft NFSv4 Global Name Space with DNS SRV February 2006 9. Informative References [AFS] Howard, J. et al., "An Overview of the Andrew File System," in Proc. USENIX Winter Tech. Conf., Dallas, February 1988. [AMT] Pendry, J.-S. and N. Williams, "Amd: The 4.4 BSD Automounter Reference Manual," Imperial College, London, March 1991. Also: http://docs.freebsd.org/info/amdref/amdref.pdf [DFS] Kazar, M. L. et al., "DEcorum File System Architectural Overview," in Proc. USENIX Summer Conf., Anaheim, Calif., June 1990. [KITTEN] IETF working group, GSS-API Next Generation, reference http://ietf.org/html.charters/kitten-charter.html, October 2005. [NB0510] Noveck, D., and C. Burnett, "Next Steps for NFSv4 Migration/Replication," Internet Draft draft-noveck-nfsv4-migrep-00.txt, October 2005. [RFC1183] Everhart, C. et al., "New DNS RR Definitions," RFC 1183, October 1990. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC4033] Arends, P. et al., "DNS Security Introduction and Requirements," RFC 4033, March 2005. Everhart, et al. Expires August 26, 2006 [Page 11] Internet-Draft NFSv4 Global Name Space with DNS SRV February 2006 Authors' Addresses Craig Everhart Network Appliance, Inc. 7301 Kit Creek Road P.O. Box 13917 Research Triangle Park, NC 27709 US Phone: +1 919 476 5320 Email: everhart@netapp.com Andy Adamson CITI, University of Michigan CITI, 3rd Floor Argus 535 W. William Street Ann Arbor, MI 48103 US Phone: +1 734 764 9465 Email: andros@umich.edu Jiaying Zhang University of Michigan 535 W. William Street, Suite 3100 Ann Arbor, MI 48103 US Phone: +1 734 647 4216 Email: jiajingz@umich.edu Eric Brunner-Williams Panasas, Inc. 1501 Reedsdale Street Suite 400 Pittsburgh, PA 15233-2341 US Phone: +1 412 323 6408 Email: ebw@panasas.com Everhart, et al. Expires August 26, 2006 [Page 12] Internet-Draft NFSv4 Global Name Space with DNS SRV February 2006 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. 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