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Versions: (RFC 5667) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 RFC 8267

Network File System Version 4                              C. Lever, Ed.
Internet-Draft                                                    Oracle
Obsoletes: 5667 (if approved)                          February 24, 2017
Intended status: Standards Track
Expires: August 28, 2017


 Network File System (NFS) Upper Layer Binding To RPC-Over-RDMA Version
                                  One
                     draft-ietf-nfsv4-rfc5667bis-06

Abstract

   This document specifies Upper Layer Bindings of Network File System
   (NFS) protocol versions to RPC-over-RDMA Version One.  Upper Layer
   Bindings are required in order to enable RPC-based protocols such as
   NFS to use Direct Data Placement on RPC-over-RDMA Version One.  This
   document obsoletes RFC 5667.

Requirements Language

   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].

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   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."

   This Internet-Draft will expire on August 28, 2017.

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.





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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
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   it for publication as an RFC or to translate it into languages other
   than English.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Reply Size Estimation . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Short Reply Chunk Retry . . . . . . . . . . . . . . . . .   4
   3.  Upper Layer Binding for NFS Versions 2 and 3  . . . . . . . .   5
     3.1.  Reply Size Estimation . . . . . . . . . . . . . . . . . .   5
     3.2.  RPC Binding Considerations  . . . . . . . . . . . . . . .   5
   4.  Upper Layer Bindings for NFS Version 2 and 3 Auxiliary
       Protocols . . . . . . . . . . . . . . . . . . . . . . . . . .   6
     4.1.  MOUNT, NLM, and NSM Protocols . . . . . . . . . . . . . .   6
     4.2.  NFSACL Protocol . . . . . . . . . . . . . . . . . . . . .   7
   5.  Upper Layer Binding For NFS Version 4 . . . . . . . . . . . .   7
     5.1.  DDP-Eligibility . . . . . . . . . . . . . . . . . . . . .   7
     5.2.  Reply Size Estimation . . . . . . . . . . . . . . . . . .   8
     5.3.  RPC Binding Considerations  . . . . . . . . . . . . . . .   9
     5.4.  NFS COMPOUND Requests . . . . . . . . . . . . . . . . . .  10
     5.5.  NFS Callback Requests . . . . . . . . . . . . . . . . . .  11
     5.6.  Session-Related Considerations  . . . . . . . . . . . . .  12
     5.7.  Transport Considerations  . . . . . . . . . . . . . . . .  13
   6.  Extending NFS Upper Layer Bindings  . . . . . . . . . . . . .  14
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  14
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  15
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  15
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  15
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  16



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   Appendix A.  Changes Since RFC 5667 . . . . . . . . . . . . . . .  17
   Appendix B.  Acknowledgments  . . . . . . . . . . . . . . . . . .  18
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  19

1.  Introduction

   An RPC-over-RDMA Version One transport may employ direct data
   placement to convey certain data payloads associated with RPC
   transactions [I-D.ietf-nfsv4-rfc5666bis].  To enable successful
   interoperation, implementations of RPC Programs running on RPC-over-
   RDMA must agree as to which XDR data items in what particular RPC
   procedures are eligible for direct data placement (DDP).  This
   agreement is specified in an Upper Layer Binding.

   This document contains material required of Upper Layer Bindings, as
   specified in [I-D.ietf-nfsv4-rfc5666bis], for the following NFS
   protocol versions:

   o  NFS Version 2 [RFC1094]

   o  NFS Version 3 [RFC1813]

   o  NFS Version 4.0 [RFC7530]

   o  NFS Version 4.1 [RFC5661]

   o  NFS Version 4.2 [RFC7862]

   This document assumes the reader is already familiar with concepts
   and terminology defined in [I-D.ietf-nfsv4-rfc5666bis] and the
   documents it references.

2.  Reply Size Estimation

   On an RPC-over-RDMA Version One transport, during the construction of
   each RPC Call message, a requester is responsible for allocating
   appropriate resources for receiving the matching Reply message.

   An overrun of these resources can result in corruption of the Reply
   message or termination of the transport connection.  Therefore
   reliable reply size estimation is necessary to ensure successful
   interoperation.  This is particularly critical, for example, when
   allocating a Reply chunk.

   In most cases, the NFS protocol's XDR definition provides enough
   information to enable an NFS client to predict the maximum size of
   the expected Reply message.  If there are variable-size data items in




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   the result, the maximum size of the RPC Reply message can be
   estimated as follows:

   o  The client requests only a specific portion of an object (for
      example, using the "count" and "offset" fields in an NFS READ).

   o  The client has already cached the size of the whole object it is
      about to request (say, via a previous NFS GETATTR request).

   o  The client and server have negotiated a maximum size for all calls
      and responses (using a CREATE_SESSION operation, for instance).

2.1.  Short Reply Chunk Retry

   In a few cases, either the size of one or more returned data items or
   the number of returned data items cannot be known in advance of
   forming an RPC Call.

   A requester uses a Reply chunk to handle an RPC transaction where the
   expected RPC Reply message might be larger than the requester's
   inline threshold.  If an actual RPC Reply message does not fit in a
   client-provided Reply chunk, the NFS server responds with an
   RDMA_ERROR message with the rdma_err field set to ERR_CHUNK, or it
   could even break the transport connection.

   In response, an NFS client can choose to:

   o  Terminate the RPC transaction with an error, or

   o  Allocate a larger Reply chunk and send the same request as a new
      RPC transaction (to avoid hitting in a Duplicate Reply Cache).
      The NFS client should avoid retrying the request indefinitely
      because a responder may return ERR_CHUNK for a variety of reasons.

   The latter choice is considered heroic recovery, and is only a real
   choice for the few operations where it is not possible for an NFS
   client to predict the size of the Reply message in advance.

   Subsequent sections of this document discuss exactly which operations
   might have ultimate difficulty with Reply size estimation.  These
   operations are eligible for "short Reply chunk retry."  Unless
   explicitly mentioned as applicable, short Reply chunk retry should
   not be used.








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3.  Upper Layer Binding for NFS Versions 2 and 3

   The Upper Layer Binding specification in this section applies to NFS
   Version 2 [RFC1094] and NFS Version 3 [RFC1813].  For brevity, in
   this document a "Legacy NFS client" refers to an NFS client using the
   NFS version 2 or NFS version 3 RPC Programs (100003) to communicate
   with an NFS server.  Likewise, a "Legacy NFS server" is an NFS server
   communicating with clients using NFS version 2 or NFS version 3.

   The following XDR data items in NFS versions 2 and 3 are DDP-
   eligible:

   o  The opaque file data argument in the NFS WRITE procedure

   o  The pathname argument in the NFS SYMLINK procedure

   o  The opaque file data result in the NFS READ procedure

   o  The pathname result in the NFS READLINK procedure

   All other argument or result data items in NFS versions 2 and 3 are
   not DDP-eligible.

   A Legacy NFS client MUST NOT send a reduced Payload stream in a Long
   Call.  A Legacy NFS client MUST NOT enable a Legacy NFS server to
   send a reduced Payload stream in a Long Reply.

   A Legacy server's response to a DDP-eligibility violation does not
   give an indication to Legacy clients of whether the server has
   processed the arguments of the RPC Call, or whether the server has
   accessed or modified client memory associated with that RPC.

3.1.  Reply Size Estimation

   A Legacy NFS client determines the maximum reply size for each
   operation using the criteria outlined in Section 2.  There are no
   operations in NFS version 2 or 3 that benefit from short Reply chunk
   retry.

3.2.  RPC Binding Considerations

   Legacy NFS servers traditionally listen for clients on UDP and TCP
   port 2049.  Additionally, they register these ports with a local
   portmapper [RFC1833] service.

   A Legacy NFS server supporting RPC-over-RDMA Version One on such a
   network and registering itself with the RPC portmapper MAY choose an
   arbitrary port, or MAY use the alternative well-known port number for



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   its RPC-over-RDMA service (see Section 8).  The chosen port MAY be
   registered with the RPC portmapper under the netids assigned in
   [I-D.ietf-nfsv4-rfc5666bis].

4.  Upper Layer Bindings for NFS Version 2 and 3 Auxiliary Protocols

   NFS versions 2 and 3 are typically deployed with several other
   protocols, sometimes referred to as "NFS auxiliary protocols."  These
   are distinct RPC Programs that define procedures which are not part
   of the NFS version 2 or version 3 RPC Programs.  The Upper Layer
   Bindings in this section apply to:

   o  The MOUNT and NLM protocols, introduced in an appendix of
      [RFC1813]

   o  The NSM protocol, described in Chapter 11 of [NSM]

   o  The NFSACL protocol, which does not have a public definition.
      NFSACL is treated in this document as a de facto standard, as
      there are several interoperating implementations.

   RPC-over-RDMA Version One considers these RPC Programs as separate
   Upper Layer Protocols [I-D.ietf-nfsv4-rfc5666bis].  Therefore a
   separate Upper Layer Binding, provided here, is required for each of
   these.

4.1.  MOUNT, NLM, and NSM Protocols

   Typically MOUNT, NLM, and NSM are conveyed via TCP, even in
   deployments where the NFS RPC Program operates on RPC-over-RDMA
   Version One.  When a Legacy server supports these RPC Programs on
   RPC-over-RDMA Version One, it advertises the port address via the
   usual rpcbind service [RFC1833].

   No operation in these protocols conveys a significant data payload,
   and the size of RPC messages in these protocols is uniformly small.
   Therefore, no XDR data items in these protocols are DDP-eligible.

   The largest variable-length XDR data item is an xdr_netobj.  In most
   implementations this data item is never larger than 1024 bytes,
   making reliable reply size estimation straightforward using the
   criteria outlined in Section 2.  There are no operations in these
   protocols that benefit from short Reply chunk retry.








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4.2.  NFSACL Protocol

   Legacy clients and servers that support the NFSACL RPC Program
   typically convey NFSACL procedures on the same connection as NFS RPC
   Programs.  This obviates the need for separate rpcbind queries to
   discover server support for this RPC Program.

   ACLs are typically small, but even large ACLs must be encoded and
   decoded to some degree.  Thus no data item in this Upper Layer
   Protocol is DDP-eligible.

   For procedures whose replies do not include an ACL object, the size
   of a reply is determined directly from the NFSACL RPC Program's XDR
   definition.

   There is no protocol-specified size limit for NFS version 3 ACLs, and
   there is no mechanism in either the NFSACL or NFS RPC Programs for a
   Legacy client to ascertain the largest ACL a Legacy server can
   return.  Legacy client implementations should choose a maximum size
   for ACLs based on their own internal limits.

   Because an NFSACL client cannot know in advance how large a returned
   ACL will be, it can use short Reply chunk retry when an NFSACL GETACL
   operation encounters a transport error.

5.  Upper Layer Binding For NFS Version 4

   The Upper Layer Binding specification in this section applies to RPC
   Programs defined in NFS Version 4.0 [RFC7530], NFS Version 4.1
   [RFC5661], and NFS Version 4.2 [RFC7862].

5.1.  DDP-Eligibility

   Only the following XDR data items in the COMPOUND procedure of all
   NFS version 4 minor versions are DDP-eligible:

   o  The opaque data field in the WRITE4args structure

   o  The linkdata field of the NF4LNK arm in the createtype4 union

   o  The opaque data field in the READ4resok structure

   o  The linkdata field in the READLINK4resok structure

   o  In minor version 2 and newer, the rpc_data field of the
      read_plus_content union (further restrictions on the use of this
      data item follow below).




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5.1.1.  READ_PLUS Replies

   The NFS version 4.2 READ_PLUS operation returns a complex data type
   [RFC7862].  The rpr_contents field in the result of this operation is
   an array of read_plus_content unions, one arm of which contains an
   opaque byte stream (d_data).

   The size of d_data is limited to the value of the rpa_count field,
   but the protocol does not bound the number of elements which can be
   returned in the rpr_contents array.  In order to make the size of
   READ_PLUS replies predictable by NFS version 4.2 clients, the
   following restrictions are placed on the use of the READ_PLUS
   operation on an RPC-over-RDMA Version One transport:

   o  An NFS version 4.2 client MUST NOT provide more than one Write
      chunk for any READ_PLUS operation.  When providing a Write chunk
      for a READ_PLUS operation, an NFS version 4.2 client MUST provide
      a Write chunk that is either empty (which forces all result data
      items for this operation to be returned inline) or large enough to
      receive rpa_count bytes in a single element of the rpr_contents
      array.

   o  If the Write chunk provided for a READ_PLUS operation by an NFS
      version 4.2 client is not empty, an NFS version 4.2 server MUST
      use that chunk for the first element of the rpr_contents array
      that has an rpc_data arm.

   o  An NFS version 4.2 server MUST NOT return more than two elements
      in the rpr_contents array of any READ_PLUS operation.  It returns
      as much of the requested byte range as it can fit within these two
      elements.  If the NFS version 4.2 server has not asserted rpr_eof
      in the reply, the NFS version 4.2 client SHOULD send additional
      READ_PLUS requests for any remaining bytes.

5.2.  Reply Size Estimation

   Within NFS version 4, there are certain variable-length result data
   items whose maximum size cannot be estimated by clients reliably
   because there is no protocol-specified size limit on these arrays.
   These include:

   o  The attrlist4 field

   o  Fields containing ACLs such as fattr4_acl, fattr4_dacl,
      fattr4_sacl

   o  Fields in the fs_locations4 and fs_locations_info4 data structures




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   o  Fields opaque to the NFS version 4 protocol which pertain to pNFS
      layout metadata, such as loc_body, loh_body, da_addr_body,
      lou_body, lrf_body, fattr_layout_types and fs_layout_types,

5.2.1.  Reply Size Estimation for Minor Version 0

   The NFS version 4.0 protocol itself does not impose any bound on the
   size of NFS calls or responses.

   Some of the data items enumerated in Section 5.2 (in particular, the
   items related to ACLs and fs_locations) make it difficult to predict
   the maximum size of NFS version 4.0 replies that interrogate
   variable-length fattr4 attributes.  As discussed in Section 2, client
   implementations can rely on their own internal architectural limits
   to constrain the reply size, but such limits are not always
   guaranteed to be reliable.

   When an especially large fattr4 result is expected, a Reply chunk
   might be required.  An NFS version 4.0 client can use short Reply
   chunk retry when an NFS COMPOUND containing a GETATTR operation
   encounters a transport error.

   The use of NFS COMPOUND operations raises the possibility of requests
   that combine a non-idempotent operation (e.g.  WRITE) with a GETATTR
   operation that requests one or more variable-length results.  This
   combination should be avoided by ensuring that any GETATTR operation
   that requests a result of unpredictable length is sent in an NFS
   COMPOUND by itself.

5.2.2.  Reply Size Estimation for Minor Version 1 and Newer

   In NFS version 4.1 and newer minor versions, the csa_fore_chan_attrs
   argument of the CREATE_SESSION operation contains a
   ca_maxresponsesize field.  The value in this field can be taken as
   the absolute maximum size of replies generated by an NFS version 4.1
   server.

   This value can be used in cases where it is not possible to estimate
   a reply size upper bound precisely.  In practice, objects such as
   ACLs, named attributes, layout bodies, and security labels are much
   smaller than this maximum.

5.3.  RPC Binding Considerations

   NFS version 4 servers are required to listen on TCP port 2049, and
   they are not required to register with an rpcbind service [RFC7530].





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   Therefore, an NFS version 4 server supporting RPC-over-RDMA Version
   One MUST use the alternative well-known port number for its RPC-over-
   RDMA service (see Section 8).  Clients SHOULD connect to this well-
   known port without consulting the RPC portmapper (as for NFS version
   4 on TCP transports).

5.4.  NFS COMPOUND Requests

5.4.1.  Long Calls and Replies

   Each NFS version 4 COMPOUND procedure contains an array of operations
   which may be larger than a connection's inline thresholds, even after
   reduction of DDP-elibible payloads.  Therefore, an NFS version 4
   client MAY send a reduced Payload stream in a Long Call.  An NFS
   version 4 client MAY enable an NFS version 4 server to send a reduced
   Payload stream in a Long Reply.

5.4.2.  Multiple DDP-eligible Data Items

   The NFS version 4 COMPOUND procedure allows the transmission of more
   than one DDP-eligible data item per Call and Reply message.  An NFS
   version 4 client provides XDR Position values in each Read chunk to
   disambiguate which chunk is associated with which argument data item.

   However NFS version 4 server and client implementations must agree in
   advance on how to pair Write chunks with returned result data items.
   The mechanism specified in Section 4.3.2 of
   [I-D.ietf-nfsv4-rfc5666bis]) is applied here, with additional
   restrictions that appear below.

   In the following list, an "NFS Read" operation refers to any NFS
   Version 4 operation which has a DDP-eligible result data item (i.e.,
   either a READ, READ_PLUS, or READLINK operation).

   o  If an NFS version 4 client wishes all DDP-eligible items in an NFS
      reply to be conveyed inline, it leaves the Write list empty.

   o  The first chunk in the Write list MUST be used by the first READ
      operation in an NFS version 4 COMPOUND procedure.  The next Write
      chunk is used by the next READ operation, and so on.

   o  If an NFS version 4 client has provided a matching non-empty Write
      chunk, then the corresponding READ operation MUST return its DDP-
      eligible data item using that chunk.

   o  If an NFS version 4 client has provided an empty matching Write
      chunk, then the corresponding READ operation MUST return all of
      its result data items inline.



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   o  If a READ operation returns a union arm which does not contain a
      DDP-eligible result, and the NFS version 4 client has provided a
      matching non-empty Write chunk, an NFS version 4 server MUST
      return an empty Write chunk in that Write list position.

   o  If there are more READ operations than Write chunks, then
      remaining NFS Read operations in an NFS version 4 COMPOUND that
      have no matching Write chunk MUST return their results inline.

5.4.3.  NFS Version 4 COMPOUND Example

   The following example shows a Write list with three Write chunks, A,
   B, and C.  The NFS version 4 server consumes the provided Write
   chunks by writing the results of the designated operations in the
   compound request (READ and READLINK) back to each chunk.


      Write list:

         A --> B --> C

      NFS version 4 COMPOUND request:

         PUTFH LOOKUP READ PUTFH LOOKUP READLINK PUTFH LOOKUP READ
                       |                   |                   |
                       v                   v                   v
                       A                   B                   C


   If the NFS version 4 client does not want to have the READLINK result
   returned via RDMA, it provides an empty Write chunk for buffer B to
   indicate that the READLINK result must be returned inline.

5.5.  NFS Callback Requests

   The NFS version 4 family of protocols support server-initiated
   callbacks to notify NFS version 4 clients of events such as recalled
   delegations.

5.5.1.  NFS Version 4.0 Callback

   NFS version 4.0 implementations typically employ a separate TCP
   connection to handle callback operations, even when the forward
   channel uses an RPC-over-RDMA Version One transport.

   No operation in the NFS version 4.0 callback RPC Program conveys a
   significant data payload.  Therefore, no XDR data items in this RPC
   Program is DDP-eligible.



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   A CB_RECALL reply is small and fixed in size.  The CB_GETATTR reply
   contains a variable-length fattr4 data item.  See Section 5.2.1 for a
   discussion of reply size prediction for this data item.

   An NFS version 4.0 client advertises netids and ad hoc port addresses
   for contacting its NFS version 4.0 callback service using the
   SETCLIENTID operation.

5.5.2.  NFS Version 4.1 Callback

   In NFS version 4.1 and newer minor versions, callback operations may
   appear on the same connection as is used for NFS version 4 forward
   channel client requests.  NFS version 4 clients and servers MUST use
   the mechanism described in [I-D.ietf-nfsv4-rpcrdma-bidirection] when
   backchannel operations are conveyed on RPC-over-RDMA Version One
   transports.

   The csa_back_chan_attrs argument of the CREATE_SESSION operation
   contains a ca_maxresponsesize field.  The value in this field can be
   taken as the absolute maximum size of backchannel replies generated
   by a replying NFS version 4 client.

   There are no DDP-eligible data items in callback procedures defined
   in NFS version 4.1 or NFS version 4.2.  However, some callback
   operations, such as messages that convey device ID information, can
   be large, in which case a Long Call or Reply might be required.

   When an NFS version 4.1 client can support Long Calls in its
   backchannel, it reports a backchannel ca_maxrequestsize that is
   larger than the connection's inline thresholds.  Otherwise an NFS
   version 4 server MUST use only Short messages to convey backchannel
   operations.

5.6.  Session-Related Considerations

   The presence of an NFS session (defined in [RFC5661]) has no effect
   on the operation of RPC-over-RDMA Version One.  None of the
   operations introduced to support NFS sessions (e.g. the SEQUENCE
   operation) contain DDP-eligible data items.  There is no need to
   match the number of session slots with the number of available RPC-
   over-RDMA credits.

   However, there are a few new cases where an RPC transaction can fail.
   For example, a requester might receive, in response to an RPC
   request, an RDMA_ERROR message with an rdma_err value of ERR_CHUNK,
   or an RDMA_MSG containing an RPC_GARBAGEARGS reply.  These situations
   are no different from existing RPC errors which an NFS session
   implementation is already prepared to handle for other transports.



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   And as with other transports during such a failure, there might be no
   SEQUENCE result available to the requester to distinguish whether
   failure occurred before or after the requested operations were
   executed on the responder.

   When a transport error occurs (e.g.  RDMA_ERROR), the requester
   proceeds as usual to match the incoming XID value to a waiting RPC
   Call.  The RPC transaction is terminated, and the result status is
   reported to the Upper Layer Protocol.  The requester's session
   implementation then determines the session ID and slot for the failed
   request, and performs slot recovery to make that slot usable again.
   If this is not done, that slot could be rendered permanently
   unavailable.

5.7.  Transport Considerations

5.7.1.  Congestion Avoidance

   Section 3.1 of [RFC7530] states:

      Where an NFSv4 implementation supports operation over the IP
      network protocol, the supported transport layer between NFS and IP
      MUST be an IETF standardized transport protocol that is specified
      to avoid network congestion; such transports include TCP and the
      Stream Control Transmission Protocol (SCTP).

   Section 2.9.1 of [RFC5661] further states:

      Even if NFSv4.1 is used over a non-IP network protocol, it is
      RECOMMENDED that the transport support congestion control.

      It is permissible for a connectionless transport to be used under
      NFSv4.1; however, reliable and in-order delivery of data combined
      with congestion control by the connectionless transport is
      REQUIRED.  As a consequence, UDP by itself MUST NOT be used as an
      NFSv4.1 transport.

   RPC-over-RDMA Version One is constructed on a platform of RDMA
   Reliable Connections [I-D.ietf-nfsv4-rfc5666bis] [RFC5041].  RDMA
   Reliable Connections are reliable, connection-oriented transports
   that guarantee in-order delivery, meeting all above requirements for
   NFS version 4 transports.

5.7.2.  Retransmission and Keep-alive

   NFS version 4 client implementations often rely on a transport-layer
   keep-alive mechanism to detect when an NFS version 4 server has
   become unresponsive.  When an NFS server is no longer responsive,



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   client-side keep-alive terminates the connection, which in turn
   triggers reconnection and RPC retransmission.

   Some RDMA transports (such as Reliable Connections on InfiniBand)
   have no keep-alive mechanism.  Without a disconnect or new RPC
   traffic, such connections can remain alive long after an NFS server
   has become unresponsive.  Once an NFS client has consumed all
   available RPC-over-RDMA credits on that transport connection, it will
   forever await a reply before sending another RPC request.

   NFS version 4 clients SHOULD reserve one RPC-over-RDMA credit to use
   for periodic server or connection health assessment.  This credit can
   be used to drive an RPC request on an otherwise idle connection,
   triggering either a quick affirmative server response or immediate
   connection termination.

   In addition to network partition and request loss scenarios, RPC-
   over-RDMA transport connections can be terminated when a Transport
   header is malformed, Reply messages are larger than receive
   resources, or when too many RPC-over-RDMA messages are sent at once.
   In such cases:

   o  If there is a transport error indicated (ie, RDMA_ERROR) before
      the disconnect or instead of a disconnect, the requester MUST
      respond to that error as prescribed by the specification of the
      RPC transport.  Then the NFS version 4 rules for handling
      retransmission apply.

   o  If there is a transport disconnect and the responder has provided
      no other response for a request, then only the NFS version 4 rules
      for handling retransmission apply.

6.  Extending NFS Upper Layer Bindings

   RPC Programs such as NFS are required to have an Upper Layer Binding
   specification to interoperate on RPC-over-RDMA Version One transports
   [I-D.ietf-nfsv4-rfc5666bis].  Via standards action, the Upper Layer
   Binding specified in this document can be extended to cover versions
   of the NFS version 4 protocol specified after NFS version 4 minor
   version 2, or separately published extensions to an existing NFS
   version 4 minor version, as described in [I-D.ietf-nfsv4-versioning].

7.  Security Considerations

   RPC-over-RDMA Version One supports all RPC security models, including
   RPCSEC_GSS security and transport-level security [RFC2203].  The
   choice of what Direct Data Placement mechanism to convey RPC argument
   and results does not affect this, since it changes only the method of



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   data transfer.  Specifically, the requirements of
   [I-D.ietf-nfsv4-rfc5666bis] ensure that this choice does not
   introduce new vulnerabilities.

   Because this document defines only the binding of the NFS protocols
   atop [I-D.ietf-nfsv4-rfc5666bis], all relevant security
   considerations are therefore to be described at that layer.

8.  IANA Considerations

   The use of direct data placement in NFS introduces a need for an
   additional port number assignment for networks that share traditional
   UDP and TCP port spaces with RDMA services.  The iWARP protocol is
   such an example [RFC5041] [RFC5040].

   For this purpose, a set of transport protocol port number assignments
   is specified by this document.  IANA has assigned the following ports
   for NFS/RDMA in the IANA port registry, according to the guidelines
   described in [RFC6335].


     nfsrdma 20049/tcp Network File System (NFS) over RDMA
     nfsrdma 20049/udp Network File System (NFS) over RDMA
     nfsrdma 20049/sctp Network File System (NFS) over RDMA


   This document should be listed as the reference for the nfsrdma port
   assignments.  This document does not alter these assignments.

9.  References

9.1.  Normative References

   [I-D.ietf-nfsv4-rfc5666bis]
              Lever, C., Simpson, W., and T. Talpey, "Remote Direct
              Memory Access Transport for Remote Procedure Call, Version
              One", draft-ietf-nfsv4-rfc5666bis-10 (work in progress),
              February 2017.

   [I-D.ietf-nfsv4-rpcrdma-bidirection]
              Lever, C., "Bi-directional Remote Procedure Call On RPC-
              over-RDMA Transports", draft-ietf-nfsv4-rpcrdma-
              bidirection-07 (work in progress), February 2017.

   [RFC1833]  Srinivasan, R., "Binding Protocols for ONC RPC Version 2",
              RFC 1833, DOI 10.17487/RFC1833, August 1995,
              <http://www.rfc-editor.org/info/rfc1833>.




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   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC2203]  Eisler, M., Chiu, A., and L. Ling, "RPCSEC_GSS Protocol
              Specification", RFC 2203, DOI 10.17487/RFC2203, September
              1997, <http://www.rfc-editor.org/info/rfc2203>.

   [RFC5661]  Shepler, S., Ed., Eisler, M., Ed., and D. Noveck, Ed.,
              "Network File System (NFS) Version 4 Minor Version 1
              Protocol", RFC 5661, DOI 10.17487/RFC5661, January 2010,
              <http://www.rfc-editor.org/info/rfc5661>.

   [RFC6335]  Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S.
              Cheshire, "Internet Assigned Numbers Authority (IANA)
              Procedures for the Management of the Service Name and
              Transport Protocol Port Number Registry", BCP 165,
              RFC 6335, DOI 10.17487/RFC6335, August 2011,
              <http://www.rfc-editor.org/info/rfc6335>.

   [RFC7530]  Haynes, T., Ed. and D. Noveck, Ed., "Network File System
              (NFS) Version 4 Protocol", RFC 7530, DOI 10.17487/RFC7530,
              March 2015, <http://www.rfc-editor.org/info/rfc7530>.

   [RFC7862]  Haynes, T., "Network File System (NFS) Version 4 Minor
              Version 2 Protocol", RFC 7862, DOI 10.17487/RFC7862,
              November 2016, <http://www.rfc-editor.org/info/rfc7862>.

9.2.  Informative References

   [I-D.ietf-nfsv4-versioning]
              Noveck, D., "Rules for NFSv4 Extensions and Minor
              Versions", draft-ietf-nfsv4-versioning-09 (work in
              progress), December 2016.

   [NSM]      The Open Group, "Protocols for Interworking: XNFS, Version
              3W", February 1998.

   [RFC1094]  Nowicki, B., "NFS: Network File System Protocol
              specification", RFC 1094, DOI 10.17487/RFC1094, March
              1989, <http://www.rfc-editor.org/info/rfc1094>.

   [RFC1813]  Callaghan, B., Pawlowski, B., and P. Staubach, "NFS
              Version 3 Protocol Specification", RFC 1813,
              DOI 10.17487/RFC1813, June 1995,
              <http://www.rfc-editor.org/info/rfc1813>.




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   [RFC5040]  Recio, R., Metzler, B., Culley, P., Hilland, J., and D.
              Garcia, "A Remote Direct Memory Access Protocol
              Specification", RFC 5040, DOI 10.17487/RFC5040, October
              2007, <http://www.rfc-editor.org/info/rfc5040>.

   [RFC5041]  Shah, H., Pinkerton, J., Recio, R., and P. Culley, "Direct
              Data Placement over Reliable Transports", RFC 5041,
              DOI 10.17487/RFC5041, October 2007,
              <http://www.rfc-editor.org/info/rfc5041>.

   [RFC5666]  Talpey, T. and B. Callaghan, "Remote Direct Memory Access
              Transport for Remote Procedure Call", RFC 5666,
              DOI 10.17487/RFC5666, January 2010,
              <http://www.rfc-editor.org/info/rfc5666>.

   [RFC5667]  Talpey, T. and B. Callaghan, "Network File System (NFS)
              Direct Data Placement", RFC 5667, DOI 10.17487/RFC5667,
              January 2010, <http://www.rfc-editor.org/info/rfc5667>.

Appendix A.  Changes Since RFC 5667

   Corrections and updates made necessary by new language in
   [I-D.ietf-nfsv4-rfc5666bis] have been introduced.  For example,
   references to deprecated features of RPC-over-RDMA Version One, such
   as RDMA_MSGP, and the use of the Read list for handling RPC replies,
   have been removed.  The term "mapping" has been replaced with the
   term "binding" or "Upper Layer Binding" throughout the document.
   Some material that duplicates what is in [I-D.ietf-nfsv4-rfc5666bis]
   has been deleted.

   Material required by [I-D.ietf-nfsv4-rfc5666bis] for Upper Layer
   Bindings that was not present in [RFC5667] has been added, including
   discussion of how each NFS version properly estimates the maximum
   size of RPC replies.

   Technical corrections have been made.  For example, the mention of
   12KB and 36KB inline thresholds have been removed.  The reference to
   a non-existant NFS version 4 SYMLINK operation has been replaced.

   The discussion of NFS version 4 COMPOUND handling has been completed.
   Some changes were made to the algorithm for matching DDP-eligible
   results to Write chunks.

   Requirements to ignore extra Read or Write chunks have been removed
   from the NFS version 2 and 3 Upper Layer Binding, as they conflict
   with [I-D.ietf-nfsv4-rfc5666bis].





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   A complete discussion of reply size estimation has been introduced
   for all protocols covered by the Upper Layer Bindings in this
   document.

   A section discussing NFS version 4 retransmission and connection loss
   has been added.

   The following additional improvements have been made, relative to
   [RFC5667]:

   o  An explicit discussion of NFS version 4.0 and NFS version 4.1
      backchannel operation has replaced the previous treatment of
      callback operations.

   o  A binding for NFS version 4.2 has been added that includes
      discussion of new data-bearing operations like READ_PLUS.

   o  A section suggesting a mechanism for periodically assessing
      connection health has been introduced.

   o  Language inconsistent with or contradictory to
      [I-D.ietf-nfsv4-rfc5666bis] has been removed from the present
      document.

   o  Ambiguous or erroneous uses of RFC2119 terms have been corrected.

   o  References to obsolete RFCs have been updated.

   o  An IANA Considerations Section has been added, which specifies the
      port assignments for NFS/RDMA.  This replaces the example
      assignment that appeared in [RFC5666].

   o  Code excerpts have been removed, and figures have been modernized.

Appendix B.  Acknowledgments

   The author gratefully acknowledges the work of Brent Callaghan and
   Tom Talpey on the original NFS Direct Data Placement specification
   [RFC5667].  The author also wishes to thank Bill Baker and Greg
   Marsden for their support of this work.

   Dave Noveck provided excellent review, constructive suggestions, and
   consistent navigational guidance throughout the process of drafting
   this document.  Dave also contributed the text of Section 5.6 and
   Section 6, and insisted on precise discussion of reply size
   estimation.





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   Thanks to Karen Deitke for her sharp observations about idempotency,
   and the clarity of the discussion of NFS COMPOUNDs and NFS sessions.

   Special thanks go to Transport Area Director Spencer Dawkins, nfsv4
   Working Group Chair Spencer Shepler, and nfsv4 Working Group
   Secretary Thomas Haynes for their support.

Author's Address

   Charles Lever (editor)
   Oracle Corporation
   1015 Granger Avenue
   Ann Arbor, MI  48104
   USA

   Phone: +1 248 816 6463
   Email: chuck.lever@oracle.com


































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