Network File System Version 4                              C. Lever, Ed.
Internet-Draft                                                    Oracle
Obsoletes: 5667 (if approved)                           January 20,                           February 3, 2017
Intended status: Standards Track
Expires: July 24, August 7, 2017

     Network File System (NFS) Upper Layer Binding To RPC-Over-RDMA


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

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conveying NFS Operations On RPC-Over-RDMA . . . . . . . . . .   3
   3.  Upper Layer Binding For NFS Versions 2 And 3  . . . . . . . .   5   4
   4.  Upper Layer Binding For NFS Version 4 . . . . . . . . . . . .   7   6
   5.  Extending NFS Upper Layer Bindings  . . . . . . . . . . . . .  13  12
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  14  13
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  14  13
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  15  14
   Appendix A.  Changes Since RFC 5667 . . . . . . . . . . . . . . .  16  15
   Appendix B.  Acknowledgments  . . . . . . . . . . . . . . . . . .  17
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  18  17

1.  Introduction

   An RPC-over-RDMA transport, such as the one defined in
   [I-D.ietf-nfsv4-rfc5666bis], may employ direct data placement to
   convey data payloads associated with RPC transactions.  To enable
   successful interoperation, RPC client and server implementations must
   agree as to which XDR data items in what particular RPC procedures
   are eligible for direct data placement (DDP).

   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]

   Upper Layer Bindings specified in this document apply to all versions
   of RPC-over-RDMA.

2.  Conveying NFS Operations On RPC-Over-RDMA

   Definitions of terminology and a general discussion of how RPC-over-
   RDMA is used to convey RPC transactions can be found in
   [I-D.ietf-nfsv4-rfc5666bis].  In this section, these general
   principles are applied in the context of conveying NFS procedures on
   RPC-over-RDMA.  Some issues common to all NFS protocol versions are

2.1.  The Read List

   The Read list in each RPC-over-RDMA transport header represents a set
   of memory regions containing DDP-eligible NFS argument data.  Large
   data items, such as the data payload of an NFS version 3 WRITE
   procedure, can be referenced by the Read list.  The NFS server pulls
   such payloads from the client and places them directly into its own

   Exactly which XDR data items may be conveyed in this fashion is
   detailed later in this document.

2.2.  The Write List

   The Write list in each RPC-over-RDMA transport header represents a
   set of memory regions that can receive DDP-eligible NFS result data.
   Large data items, such as the payload of an NFS version 3 READ
   procedure, can be referenced by the Write list.  The NFS server
   pushes such payloads to the client, placing them directly into the
   client's memory.

   Each Write chunk corresponds to a specific XDR data item in an NFS
   reply.  This document specifies how NFS client and server
   implementations identify the correspondence between Write chunks and
   XDR results.

   Exactly which XDR data items may be conveyed in this fashion is
   detailed later in this document.

2.3.  Long Calls And Replies

   Small RPC messages are conveyed using RDMA Send operations which are
   of limited size.  If an NFS request is too large to be conveyed
   within the NFS server's responder inline threshold, and there are no
   DDP-eligible data items that can be removed, an NFS client must send
   the request in the form of a Long Call.  The entire NFS request is
   sent in a special Read chunk called a Position Zero Read chunk.

   If an NFS client determines that the maximum size of an NFS reply
   could be too large to be conveyed within it's own responder inline
   threshold, it provides a Reply chunk in the RPC-over-RDMA transport
   header conveying the NFS request.  The server places the entire NFS
   reply in the Reply chunk.

   When the RPC authentication flavor requires that DDP-eligible data
   items are never removed from RPC messages, an NFS client can provide
   both a Position Zero Read chunk and a Reply chunk for the same RPC.

   These special chunks are discussed in further detail in

2.4.  Scatter-Gather Considerations

   A chunk typically corresponds to exactly one XDR data item.  Each
   Read chunk is represented as a list of segments at the same XDR
   Position.  Each Write chunk is represented as an array of segments.
   An NFS client thus has the flexibility to advertise a set of
   discontiguous memory regions in which to convey a single DDP-eligible
   XDR data item.

2.5.  DDP Eligibility Violations

   To report a DDP-eligibity violation, an NFS server MUST return one

   o  An RPC-over-RDMA message of type RDMA_ERROR, with the rdma_xid
      field set to the XID of the matching NFS Call, and the rdma_error
      field set to ERR_CHUNK; or

   o  An RPC message (via an RDMA_MSG message) with the xid field set to
      the XID of the matching NFS Call, the mtype field set to REPLY,
      the stat field set to MSG_ACCEPTED, and the accept_stat field set
      to GARBAGE_ARGS.

   Subsequent sections of this document describe further considerations
   particular to specific NFS protocols or procedures.


2.2.  Reply Size Estimation

   During the construction of each RPC Call message, an NFS client is
   responsible for allocating appropriate resources for receiving the
   matching Reply message.  A Reply buffer overrun 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 many cases the Upper Layer Protocol's XDR definition provides
   enough information to enable the client to make a reliable prediction
   of the maximum size of the expected Reply message.  If there are
   variable-size data items in the result, the maximum size of the RPC
   Reply message can be reliably estimated in most cases:

   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.

   Subsequent sections of this document describe considerations
   particular to specific NFS procedures where it is occasionally not possible to
   determine the maximum Reply message size based solely on the above
   criteria.  NFS client
   implementers can choose to provide the largest possible Reply buffer
   in those cases, based on, for instance, the largest possible NFS READ
   or WRITE payload (which is negotiated at mount time).

   In rare cases, a client may encounter a reply for which no a priori
   determination of reply size bound is possible.  The client SHOULD
   expect a transport error to indicate that it must either terminate
   that RPC transaction, or retry it with a larger Reply chunk.

   The use of NFS COMPOUND operations raises the possibility of non-
   idempotent requests that combine a non-idempotent operation with an
   operation whose reply size is uncertain.  This causes potential
   difficulties with retrying the transaction.  Note however that many
   operations normally considered non-idempotent (e.g WRITE, SETATTR)
   are actually idempotent.  Truly non-idempotent operations are quite
   unusual in COMPOUNDs that include operations with uncertain reply

3.  Upper Layer Binding For NFS Versions 2 And 3

   This Upper Layer Binding specification applies to NFS Version 2
   [RFC1094] and NFS Version 3 [RFC1813].  For brevity, in this section
   a "legacy NFS client" refers to an NFS client using NFS version 2 or
   NFS version 3 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-

   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 server's response to a DDP-eligibility violation (described
   in Section 2.5) 2.1) 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.

   A legacy NFS client determines the maximum reply size for each
   operation using the basic criteria outlined in Section 2.6.  Such
   clients provide a Reply chunk when the maximum possible reply size,
   exclusive of any data items represented by Write chunks, is larger
   than the client's responder inline threshold. 2.2.

3.1.  Auxiliary Protocols

   NFS versions 2 and 3 are typically deployed with several other
   protocols, sometimes referred to as "NFS auxiliary protocols."  These
   are separate RPC programs that define procedures which are not part
   of the NFS version 2 or version 3 RPC programs.  These include:

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

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

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

   RPC-over-RDMA considers these programs as distinct Upper Layer
   Protocols [I-D.ietf-nfsv4-rfc5666bis].  To enable the use of these
   ULPs on an RPC-over-RDMA transport, an Upper Layer Binding
   specification is provided here for each.

3.1.1.  MOUNT, NLM, And NSM Protocols

   Typically MOUNT, NLM, and NSM are conveyed via TCP, even in
   deployments where NFS operations on RPC-over-RDMA.  When a legacy
   server supports these programs on RPC-over-RDMA, 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 not larger than 1024 bytes, making
   reliable reply size estimation straightforward using the criteria
   outlined in Section 2.6. 2.2.

3.1.2.  NFSACL Protocol

   Legacy clients and servers that support the NFSACL RPC program
   typically convey NFSACL procedures on the same connection as the NFS
   RPC program.  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 program's XDR

   There is no protocol-wide size limit for NFS version 3 ACLs, and
   there is no mechanism in either the NFSACL or NFS programs for a
   legacy client to ascertain the largest ACL a legacy server can store.
   Legacy client implementations should choose a maximum size for ACLs
   based on their own internal limits.  A recommended lower bound for
   this maximum is 32,768 bytes, though bytes.

   When an especially large ACL is expected, a larger Reply chunk (up might be
   required.  If a legacy NFS server indicates that it cannot return an
   NFSACL GETACL response because the legacy NFS client has not provided
   a large enough Reply chunk to receive that response, the
   negotiated rsize setting) legacy NFS
   client can be provided. choose to

   o  Terminate the NFSACL GETACL with an error, or

   o  Allocate a larger Reply chunk and send the same NFSACL GETACL
      request as a new RPC transaction.  The NFS client should avoid
      retrying the request indefinitely.

4.  Upper Layer Binding For NFS Version 4

   This Upper Layer Binding specification applies to all protocols
   defined in NFS Version 4.0 [RFC7530], NFS Version 4.1 [RFC5661], and
   NFS Version 4.2 [RFC7862].

4.1.  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).

4.1.1.  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 RPC-over-RDMA transports:

   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

   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.

4.2.  NFS Version 4 Reply Size Estimation


   Within NFS version 4 client provides a Reply chunk when the maximum
   possible reply size is larger than the client's responder inline

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

   o  The attrlist4 field
   o  Fields containing ACLs such as fattr4_acl, fattr4_dacl,

   o  Fields in the fs_locations4 and fs_locations_info4 data structures

   o  Opaque fields  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,

4.2.1.  Reply Size Estimation For Minor Version 0

   The NFSv4.0 protocol itself does not impose any bound on the size of
   NFS calls or responses.

   Some of the data items enumerated above in Section 4.2 (in particular, the
   items related to ACLs and fs_locations) make it difficult to predict
   the maximum size of NFSv4.0 GETATTR replies that interrogate
   variable-length attributes.  As discussed in Section 2.6, 2.2, client
   implementations can rely on their own internal architectural limits
   to bound the reply size, but such limits are not always guaranteed to
   be reliable.

   If a client implementation

   When an especially large NFSv4.0 GETATTR result is equipped to recognize that expected, a transport
   error could mean Reply
   chunk might be required.  If an NFSv4.0 server indicates that it provisioned
   cannot return an inadequately sized NFSv4.0 GETATTR response because the requesting
   NFSv4.0 client has not provided a large enough Reply
   chunk, it chunk to receive
   that response, the NFSv4.0 client can retry choose to

   o  Terminate the operation NFSv4.0 GETATTR with an error, or

   o  Allocate a larger Reply chunk.
   Otherwise, the client must terminate chunk and send the same NFSv4.0 GETATTR
      request as a new RPC transaction.

   It is best to  The NFS client should avoid issuing single COMPOUNDs that contain both non-
   idempotent operations and
      retrying the request indefinitely.

   The use of NFS COMPOUND operations where raises the maximum reply size
   cannot possibility of requests
   that combine a non-idempotent operation (eg.  NFS WRITE) with an
   NFSv4.0 GETATTR that requests one or more variable length results.
   This combination should be reliably predicted. avoided by ensuring that any NFSv4.0
   GETATTR operation that might return a result of unpredictable length
   is sent in an NFS COMPOUND by itself.

4.2.2.  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 a replying NFS
   version 4 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.

4.3.  NFS Version 4 COMPOUND Requests

   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.

   o  If an 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.

4.3.1.  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:

                       |                   |                   |
                       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.

4.4.  NFS Version 4 Callback

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

4.4.1.  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 a RPC-over-RDMA 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.

   A CB_RECALL reply is small and fixed in size.  The CB_GETATTR reply
   contains a variable-length fattr4 data item.  See Section 4.2.1 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.

4.4.2.  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 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, the NFS version 4 client can support Long Calls. thresholds.  Otherwise an NFS
   version 4 server MUST use only Short messages to convey backchannel

4.5.  Session-Related Considerations

   Typically the presence of an NFS session [RFC5661] has no effect on
   the operation of RPC-over-RDMA.  None of the operations introduced to
   support NFS sessions (eg.  SEQUENCE) 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 some rare error conditions which require special
   handling when

   When an NFS session is operating operates on an RPC-over-RDMA
   transport. transport, there are
   a few additional 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.
   Within RPC-over-RDMA Version One, this class of error can be
   generated for two  These situations are
   no different reasons:

   o  There was an XDR error detected parsing the RPC-over-RDMA headers.

   o  There was from existing RPC errors which an error sending the response, because, for example, a
      necessary reply chunk was not provided or the one provided NFS session
   implementation is of
      insufficient length.

   These two situations, which arise due already prepared to incorrect implementations or
   underestimation of reply size, have different implications handle for other transports.

   As with
   regard other transports during such a failure, there might be no
   SEQUENCE result available to Exactly-Once Semantics.  An XDR error in decoding the
   request precludes the execution of the request on the responder, but
   failure requester to send a reply indicates that some distinguish whether
   failure occurred before or all of after the requested operations were executed.

   In both instances, the client SHOULD NOT retry
   executed on the operation without
   addressing reply resource inadequacy.  Such responder.  When a retry can result in the
   same sort of transport error seen previously.  Instead, it is best to consider occurs (eg.
   RDMA_ERROR), the operation requester proceeds as completed unsuccessfully and report an error usual to match the
   consumer who requested the RPC.

   In addition, within the error response, the requester does not have incoming
   XID value to a waiting RPC Call.  The RPC transaction is terminated,
   and the result of the execution of the SEQUENCE operation, which
   identifies the session, slot, and sequence id for status is reported to the request which
   has failed. Upper Layer Protocol.  The xid associated with the request, obtained from the
   rdma_xid field of the RDMA_ERROR or RDMA_MSG message, must be used to
   requester's session implementation then determines the session ID and
   slot for the request which failed, failed request, and the performs slot must be properly retired. recovery to make that
   slot usable again.  If this is not done, the that slot could be rendered
   permanently unavailable.

4.6.  Connection  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,
   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 connections can be terminated when a Transport header is
   malformed, 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.

5.  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 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].

6.  IANA Considerations

   NFS use of direct data placement introduces a need for an additional
   NFS port number assignment for networks that share traditional UDP
   and TCP port spaces with RDMA services.  The iWARP [RFC5041]
   [RFC5040] protocol is such an example (InfiniBand is not).

   NFS servers for versions 2 and 3 [RFC1094] [RFC1813] traditionally
   listen for clients on UDP and TCP port 2049, and additionally, they
   register these with the portmapper and/or rpcbind [RFC1833] service.
   However, [RFC7530] requires NFS version 4 servers to listen on TCP
   port 2049, and they are not required to register.

   An NFS version 2 or version 3 server supporting RPC-over-RDMA 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 its RPC-over-RDMA service.  The chosen port MAY be registered
   with the RPC portmapper under the netid assigned by the requirement
   in [I-D.ietf-nfsv4-rfc5666bis].

   An NFS version 4 server supporting RPC-over-RDMA on such a network
   MUST use the alternative well-known port number for its RPC-over-RDMA
   service.  Clients SHOULD connect to this well-known port without
   consulting the RPC portmapper (as for NFS version 4 on TCP

   The port number assigned to an NFS service over an RPC-over-RDMA
   transport is available from the IANA port registry [RFC3232].

7.  Security Considerations

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

8.1.  Normative References

              Lever, C., Simpson, W., and T. Talpey, "Remote Direct
              Memory Access Transport for Remote Procedure Call, Version
              One", draft-ietf-nfsv4-rfc5666bis-09 (work in progress),
              January 2017.

              Lever, C., "Bi-directional Remote Procedure Call On RPC-
              over-RDMA Transports", draft-ietf-nfsv4-rpcrdma-
              bidirection-06 (work in progress), January 2017.

   [RFC1833]  Srinivasan, R., "Binding Protocols for ONC RPC Version 2",
              RFC 1833, DOI 10.17487/RFC1833, August 1995,

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC2203]  Eisler, M., Chiu, A., and L. Ling, "RPCSEC_GSS Protocol
              Specification", RFC 2203, DOI 10.17487/RFC2203, September
              1997, <>.

   [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,

   [RFC7530]  Haynes, T., Ed. and D. Noveck, Ed., "Network File System
              (NFS) Version 4 Protocol", RFC 7530, DOI 10.17487/RFC7530,
              March 2015, <>.

   [RFC7862]  Haynes, T., "Network File System (NFS) Version 4 Minor
              Version 2 Protocol", RFC 7862, DOI 10.17487/RFC7862,
              November 2016, <>.

8.2.  Informative References

              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, <>.

   [RFC1813]  Callaghan, B., Pawlowski, B., and P. Staubach, "NFS
              Version 3 Protocol Specification", RFC 1813,
              DOI 10.17487/RFC1813, June 1995,

   [RFC3232]  Reynolds, J., Ed., "Assigned Numbers: RFC 1700 is Replaced
              by an On-line Database", RFC 3232, DOI 10.17487/RFC3232,
              January 2002, <>.

   [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, <>.

   [RFC5041]  Shah, H., Pinkerton, J., Recio, R., and P. Culley, "Direct
              Data Placement over Reliable Transports", RFC 5041,
              DOI 10.17487/RFC5041, October 2007,

   [RFC5667]  Talpey, T. and B. Callaghan, "Network File System (NFS)
              Direct Data Placement", RFC 5667, DOI 10.17487/RFC5667,
              January 2010, <>.

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 with
   NFS version 4 CREATE(NF4LNK).

   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].

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

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

   The following additional improvements have been made, relative to

   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 Sections 2 and
      3, and both Sections have been combined into Section 2 in 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 replaced the "Port Usage
      Considerations" Section.

   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 4.5

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

   Phone: +1 248 816 6463