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rfc:rfc8267

Internet Engineering Task Force (IETF) C. Lever Request for Comments: 8267 Oracle Obsoletes: 5667 October 2017 Category: Standards Track ISSN: 2070-1721

Network File System (NFS) Upper-Layer Binding to RPC-over-RDMA Version 1

Abstract

 This document specifies Upper-Layer Bindings of Network File System
 (NFS) protocol versions to RPC-over-RDMA version 1, thus enabling the
 use of Direct Data Placement.  This document obsoletes RFC 5667.

Status of This Memo

 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in Section 2 of RFC 7841.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 https://www.rfc-editor.org/info/rfc8267.

Lever Standards Track [Page 1] RFC 8267 NFS on RPC-over-RDMA Version 1 October 2017

Copyright Notice

 Copyright (c) 2017 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (https://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.
 This document may contain material from IETF Documents or IETF
 Contributions published or made publicly available before November
 10, 2008.  The person(s) controlling the copyright in some of this
 material may not have granted the IETF Trust the right to allow
 modifications of such material outside the IETF Standards Process.
 Without obtaining an adequate license from the person(s) controlling
 the copyright in such materials, this document may not be modified
 outside the IETF Standards Process, and derivative works of it may
 not be created outside the IETF Standards Process, except to format
 it for publication as an RFC or to translate it into languages other
 than English.

Lever Standards Track [Page 2] RFC 8267 NFS on RPC-over-RDMA Version 1 October 2017

Table of Contents

 1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
 2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   4
 3.  Reply Size Estimation . . . . . . . . . . . . . . . . . . . .   5
   3.1.  Short Reply Chunk Retry . . . . . . . . . . . . . . . . .   5
 4.  Upper-Layer Binding for NFS Versions 2 and 3  . . . . . . . .   6
   4.1.  Reply Size Estimation . . . . . . . . . . . . . . . . . .   7
   4.2.  RPC Binding Considerations  . . . . . . . . . . . . . . .   7
 5.  Upper-Layer Bindings for NFS Versions 2 and 3 Auxiliary
     Protocols . . . . . . . . . . . . . . . . . . . . . . . . . .   7
   5.1.  MOUNT, NLM, and NSM Protocols . . . . . . . . . . . . . .   8
   5.2.  NFSACL Protocol . . . . . . . . . . . . . . . . . . . . .   8
 6.  Upper-Layer Binding for NFS Version 4 . . . . . . . . . . . .   8
   6.1.  DDP-Eligibility . . . . . . . . . . . . . . . . . . . . .   8
   6.2.  Reply Size Estimation . . . . . . . . . . . . . . . . . .   9
   6.3.  RPC Binding Considerations  . . . . . . . . . . . . . . .  10
   6.4.  NFS COMPOUND Requests . . . . . . . . . . . . . . . . . .  10
   6.5.  NFS Callback Requests . . . . . . . . . . . . . . . . . .  13
   6.6.  Session-Related Considerations  . . . . . . . . . . . . .  14
   6.7.  Transport Considerations  . . . . . . . . . . . . . . . .  15
 7.  Extending NFS Upper-Layer Bindings  . . . . . . . . . . . . .  16
 8.  Security Considerations . . . . . . . . . . . . . . . . . . .  16
 9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  17
 10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  17
   10.1.  Normative References . . . . . . . . . . . . . . . . . .  17
   10.2.  Informative References . . . . . . . . . . . . . . . . .  18
 Appendix A.  Changes Since RFC 5667 . . . . . . . . . . . . . . .  20
 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  21
 Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  21

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1. Introduction

 The RPC-over-RDMA version 1 transport may employ Direct Data
 Placement (DDP) to convey data payloads associated with RPC
 transactions [RFC8166].  To enable successful interoperation, RPC
 client and server implementations using RPC-over-RDMA version 1 must
 agree which External Data Representation (XDR) data items and RPC
 procedures are eligible to use DDP.
 An Upper-Layer Binding specifies this agreement for one or more
 versions of one RPC program.  Other operational details, such as RPC
 binding assignments, pairing Write chunks with result data items, and
 reply size estimation, are also specified by this Binding.
 This document contains material required of Upper-Layer Bindings, as
 specified in [RFC8166], 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 are also provided for auxiliary protocols used
 with NFS versions 2 and 3 (see Section 5).
 This document assumes the reader is already familiar with concepts
 and terminology defined in [RFC8166] and the documents it references.

2. Requirements Language

 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
 "OPTIONAL" in this document are to be interpreted as described in
 BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
 capitals, as shown here.

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3. Reply Size Estimation

 During the construction of each RPC Call message, a requester is
 responsible for allocating appropriate resources for receiving the
 corresponding Reply message.  If the requester expects the RPC Reply
 message will be larger than its inline threshold, it provides Write
 and/or Reply chunks wherein the responder can place results and the
 Reply's Payload stream.
 A reply resource overrun occurs if the RPC Reply Payload stream does
 not fit into the provided Reply chunk or if no Reply chunk was
 provided and the Payload stream does not fit inline.  This prevents
 the responder from returning the Upper-Layer reply to the requester.
 Therefore, reliable reply size estimation is necessary to ensure
 successful interoperation.
 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
 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 (e.g.,
    using the "count" and "offset" fields in an NFS READ).
 o  The client limits the number of results (e.g., using the "count"
    field of an NFS READDIR request).
 o  The client has already cached the size of the whole object it is
    about to request (e.g., via a previous NFS GETATTR request).
 o  The client and server have negotiated a maximum size for all calls
    and responses (e.g., using a CREATE_SESSION operation).

3.1. 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.
 If an NFS server finds that the NFS client provided inadequate
 receive resources to return the whole Reply, it returns an RPC-level
 error or a transport error, such as ERR_CHUNK.

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 In response to these errors, an NFS client can choose to:
 o  terminate the RPC transaction immediately with an error, or
 o  allocate a larger Reply chunk and send the same request as a new
    RPC transaction (a new Transaction ID (XID) should be assigned to
    the retransmitted request to avoid matching a cached RPC Reply
    that caches the original error).  The NFS client should avoid
    retrying the request indefinitely because a responder may return
    ERR_CHUNK for a variety of reasons.
 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 since accurate reply size estimation is problematic in
 only a few cases.  In all other cases, reply size underestimation is
 considered a correctable implementation bug.
 NFS server implementations can avoid connection loss by first
 confirming that target RDMA segments are large enough to receive
 results before initiating explicit RDMA operations.

4. Upper-Layer Binding for NFS Versions 2 and 3

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

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 A transport error does not give an indication 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.

4.1. Reply Size Estimation

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

4.2. 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 1 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 (see Section 9).  The chosen port MAY be
 registered with the RPC portmapper under the netids assigned in
 [RFC8166].

5. Upper-Layer Bindings for NFS Versions 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 that are not part of
 the NFS RPC program (100003).  The Upper-Layer Bindings in this
 section apply to:
 o  versions 2 and 3 of the MOUNT RPC program (100005) [RFC1813];
 o  versions 1, 3, and 4 of the NLM (Network Lock Manager) RPC program
    (100021) [RFC1813];
 o  version 1 of the NSM (Network Status Monitor) RPC program
    (100024), which is described in Chapter 11 of [XNFS]; and
 o  version 1 of the NFSACL RPC program (100227), which does not have
    a public definition.  NFSACL is treated in this document as a de
    facto standard, as there are several interoperating
    implementations.

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5.1. MOUNT, NLM, and NSM Protocols

 Historically, NFS/RDMA implementations have chosen to convey the
 MOUNT, NLM, and NSM protocols via TCP.  To enable interoperation of
 these protocols when NFS/RDMA is in use, a Legacy NFS server MUST
 provide support for these protocols via TCP.

5.2. 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 (100003).  This obviates the need for separate rpcbind
 queries to discover server support for this RPC program.
 Access Control Lists (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 NFSACL 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.

6. Upper-Layer Binding for NFS Version 4

 The Upper-Layer Binding specification in this section applies to
 versions of the NFS RPC program defined in NFS versions 4.0
 [RFC7530], 4.1 [RFC5661], and 4.2 [RFC7862].

6.1. 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

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 o  The opaque data field in the READ4resok structure
 o  The linkdata field in the READLINK4resok structure

6.2. 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, and
    fattr4_sacl;
 o  fields in the fs_locations4 and fs_locations_info4 data
    structures; and
 o  fields opaque to the NFS version 4 protocol that pertain to pNFS
    (parallel NFS) layout metadata, such as loc_body, loh_body,
    da_addr_body, lou_body, lrf_body, fattr_layout_types, and
    fs_layout_types.

6.2.1. 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 6.2 (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.  Client implementations might 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., RENAME) 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.

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6.2.2. Reply Size Estimation for Minor Version 1 and Newer Minor

      Versions
 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 precisely
 estimate a reply size upper bound.  In practice, objects such as
 ACLs, named attributes, layout bodies, and security labels are much
 smaller than this maximum.

6.3. 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].
 Therefore, an NFS version 4 server supporting RPC-over-RDMA version 1
 MUST use the alternative well-known port number for its RPC-over-RDMA
 service (see Section 9).  Clients SHOULD connect to this well-known
 port without consulting the RPC portmapper (as for NFS version 4 on
 TCP transports).

6.4. NFS COMPOUND Requests

6.4.1. Multiple DDP-Eligible Data Items

 An NFS version 4 COMPOUND procedure can contain more than one
 operation that carries a DDP-eligible data item.  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.
 In the following list, a "READ operation" refers to any NFS version 4
 operation that has a DDP-eligible result data item.  The mechanism
 specified in Section 4.3.2 of [RFC8166] is applied to this class of
 operations:
 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.

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 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 a READ operation returns a union arm that 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.

6.4.2. Chunk List Complexity

 The RPC-over-RDMA version 1 protocol does not place any limit on the
 number of chunks or segments that may appear in Read or Write lists.
 However, for various reasons, NFS version 4 server implementations
 often have practical limits on the number of chunks or segments they
 are prepared to process in a single RPC transaction conveyed via
 RPC-over-RDMA version 1.
 These implementation limits are especially important when Kerberos
 integrity or privacy is in use [RFC7861].  Generic Security Service
 (GSS) services increase the size of credential material in RPC
 headers, potentially requiring more frequent use of Long messages.
 This can increase the complexity of chunk lists independent of the
 NFS version 4 COMPOUND being conveyed.
 In the absence of explicit knowledge of the server's limits, NFS
 version 4 clients SHOULD follow the prescriptions listed below when
 constructing RPC-over-RDMA version 1 messages.  NFS version 4 servers
 MUST accept and process such requests.
 o  The Read list can contain either a Position Zero Read chunk, one
    Read chunk with a non-zero Position, or both.
 o  The Write list can contain no more than one Write chunk.
 o  Any chunk can contain up to sixteen RDMA segments.

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 NFS version 4 clients wishing to send more complex chunk lists can
 provide configuration interfaces to bound the complexity of NFS
 version 4 COMPOUNDs, limit the number of elements in scatter-gather
 operations, and avoid other sources of chunk overruns at the
 receiving peer.
 An NFS version 4 server SHOULD return one of the following responses
 to a client that has sent an RPC transaction via RPC-over-RDMA
 version 1, which cannot be processed due to chunk list complexity
 limits on the server:
 o  A problem is detected by the transport layer while parsing the
    transport header in an RPC Call message.  The server responds with
    an RDMA_ERROR message with the err field set to ERR_CHUNK.
 o  A problem is detected during XDR decoding of the RPC Call message
    while the RPC layer reassembles the call's XDR stream.  The server
    responds with an RPC Reply with its "reply_stat" field set to
    MSG_ACCEPTED and its "accept_stat" field set to GARBAGE_ARGS.
 After receiving one of these errors, an NFS version 4 client SHOULD
 NOT retransmit the failing request, as the result would be the same
 error.  It SHOULD immediately terminate the RPC transaction
 associated with the XID in the RPC Reply.

6.4.3. 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.

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6.5. 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.

6.5.1. 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 1 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 are 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 6.2.1 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.

6.5.2. 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 approach described in [RFC8167] when backchannel operations are
 conveyed on RPC-over-RDMA version 1 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 versions 4.1 or 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.

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6.6. Session-Related Considerations

 The presence of an NFS session (defined in [RFC5661]) has no effect
 on the operation of RPC-over-RDMA version 1.  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, in response to an RPC request, a requester might receive
 an RDMA_ERROR message with an rdma_err value of ERR_CHUNK.  These
 situations are not different from existing RPC errors, which an NFS
 session implementation is already prepared to handle for other
 transports.  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 were not done, that slot could be rendered permanently
 unavailable.
 When an NFS session is not present (for example, when NFS version 4.0
 is in use), a transport error does not provide an indication 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.

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6.7. Transport Considerations

6.7.1. 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] also 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 1 is constructed on a platform of RDMA Reliable
 Connections [RFC8166] [RFC5041].  RDMA Reliable Connections are
 reliable, connection-oriented transports that guarantee in-order
 delivery, thus meeting all above requirements for NFS version 4
 transports.

6.7.2. 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,
 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.

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 NFS version 4 clients SHOULD reserve one RPC-over-RDMA credit to use
 for a 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 (i.e., 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.

7. 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 1 transports
 [RFC8166].  Via IETF standards action, the Upper-Layer Binding
 specified in this document can be extended to cover (a) versions of
 the NFS version 4 protocol specified after NFS version 4 minor
 version 2 or (b) separately published extensions to an existing NFS
 version 4 minor version, as described in [RFC8178].

8. Security Considerations

 RPC-over-RDMA version 1 supports all RPC security models, including
 RPCSEC_GSS security and transport-level security [RFC7861].  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
 data transfer.  Because this document defines only the binding of the
 NFS protocols atop [RFC8166], all relevant security considerations
 are, therefore, to be described at that layer.

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9. 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 is listed as the reference for the nfsrdma port
 assignments.

10. References

10.1. Normative References

 [RFC1833]  Srinivasan, R., "Binding Protocols for ONC RPC Version 2",
            RFC 1833, DOI 10.17487/RFC1833, August 1995,
            <https://www.rfc-editor.org/info/rfc1833>.
 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119,
            DOI 10.17487/RFC2119, March 1997,
            <https://www.rfc-editor.org/info/rfc2119>.
 [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,
            <https://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,
            <https://www.rfc-editor.org/info/rfc6335>.

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 [RFC7530]  Haynes, T., Ed. and D. Noveck, Ed., "Network File System
            (NFS) Version 4 Protocol", RFC 7530, DOI 10.17487/RFC7530,
            March 2015, <https://www.rfc-editor.org/info/rfc7530>.
 [RFC7861]  Adamson, A. and N. Williams, "Remote Procedure Call (RPC)
            Security Version 3", RFC 7861, DOI 10.17487/RFC7861,
            November 2016, <https://www.rfc-editor.org/info/rfc7861>.
 [RFC7862]  Haynes, T., "Network File System (NFS) Version 4 Minor
            Version 2 Protocol", RFC 7862, DOI 10.17487/RFC7862,
            November 2016, <https://www.rfc-editor.org/info/rfc7862>.
 [RFC8166]  Lever, C., Ed., Simpson, W., and T. Talpey, "Remote Direct
            Memory Access Transport for Remote Procedure Call Version
            1", RFC 8166, DOI 10.17487/RFC8166, June 2017,
            <https://www.rfc-editor.org/info/rfc8166>.
 [RFC8167]  Lever, C., "Bidirectional Remote Procedure Call on RPC-
            over-RDMA Transports", RFC 8167, DOI 10.17487/RFC8167,
            June 2017, <https://www.rfc-editor.org/info/rfc8167>.
 [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
            2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
            May 2017, <https://www.rfc-editor.org/info/rfc8174>.

10.2. Informative References

 [RFC1094]  Nowicki, B., "NFS: Network File System Protocol
            specification", RFC 1094, DOI 10.17487/RFC1094, March
            1989, <https://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,
            <https://www.rfc-editor.org/info/rfc1813>.
 [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, <https://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,
            <https://www.rfc-editor.org/info/rfc5041>.

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 [RFC5666]  Talpey, T. and B. Callaghan, "Remote Direct Memory Access
            Transport for Remote Procedure Call", RFC 5666,
            DOI 10.17487/RFC5666, January 2010,
            <https://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, <https://www.rfc-editor.org/info/rfc5667>.
 [RFC8178]  Noveck, D., "Rules for NFSv4 Extensions and Minor
            Versions", RFC 8178, DOI 10.17487/RFC8178, July 2017,
            <https://www.rfc-editor.org/info/rfc8178>.
 [XNFS]     The Open Group, "Protocols for Interworking: XNFS, Version
            3W", Document Number C702, ISBN 1-85912-184-5, February
            1998.

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Appendix A. Changes Since RFC 5667

 Corrections and updates made necessary by new language in [RFC8166]
 have been introduced.  For example, references to deprecated features
 of RPC-over-RDMA version 1 (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.  Material that duplicates what is
 in [RFC8166] has been deleted.
 Material required by [RFC8166] for Upper-Layer Bindings that was not
 present in [RFC5667] has been added.  A complete discussion of reply
 size estimation has been introduced for all protocols covered by the
 Upper-Layer Bindings in this document.
 Technical corrections have been made.  For example, the mention of
 12KB and 36KB inline thresholds has been removed.  The reference to a
 nonexistent 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 versions 2 and 3 Upper-Layer Binding, as they conflict
 with [RFC8166].
 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 versions 4.0 and 4.1 backchannel
    operation have replaced the previous treatment of callback
    operations.
 o  A section describing considerations when an NFS session is in use
    has been added.
 o  An Upper-Layer Binding for NFS version 4.2 has been added.
 o  A section suggesting a mechanism for periodically assessing
    connection health has been introduced.
 o  Ambiguous or erroneous uses of key words from RFC 2119 have been
    corrected.

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 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.

Acknowledgments

 The author gratefully acknowledges the work of Brent Callaghan and
 Tom Talpey on the original NFS Direct Data Placement specification
 [RFC5667].  Tom contributed the text of Section 6.4.2.
 Dave Noveck provided an excellent review, constructive suggestions,
 and consistent navigational guidance throughout the process of
 drafting this document.  Dave contributed the text of Sections 6.6
 and 7 and insisted on precise discussion of reply size estimation.
 Thanks to Karen Deitke for her sharp observations about idempotency,
 NFS COMPOUNDs, and NFS sessions.
 Special thanks go to Transport Area Director Spencer Dawkins, NFSV4
 Working Group Chair and Document Shepherd Spencer Shepler, and NFSV4
 Working Group Secretary Thomas Haynes for their support.  The author
 also wishes to thank Bill Baker and Greg Marsden for their support of
 this work.

Author's Address

 Charles Lever
 Oracle Corporation
 1015 Granger Avenue
 Ann Arbor, MI  48104
 United States of America
 Phone: +1 248 816 6463
 Email: chuck.lever@oracle.com

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