Internet Engineering Task Force (IETF)                          C. Lever
Request for Comments: 8167                                        Oracle
Category: Standards Track                                      June 2017
ISSN: 2070-1721
Internet Engineering Task Force (IETF)                          C. Lever
Request for Comments: 8167                                        Oracle
Category: Standards Track                                      June 2017
ISSN: 2070-1721

Bidirectional Remote Procedure Call on RPC-over-RDMA Transports

RPC over RDMA传输上的双向远程过程调用



Minor versions of Network File System (NFS) version 4 newer than minor version 0 work best when Remote Procedure Call (RPC) transports can send RPC transactions in both directions on the same connection. This document describes how RPC transport endpoints capable of Remote Direct Memory Access (RDMA) convey RPCs in both directions on a single connection.


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.

本文件是互联网工程任务组(IETF)的产品。它代表了IETF社区的共识。它已经接受了公众审查,并已被互联网工程指导小组(IESG)批准出版。有关互联网标准的更多信息,请参见RFC 7841第2节。

Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at


Copyright Notice


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

版权所有(c)2017 IETF信托基金和确定为文件作者的人员。版权所有。

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents ( 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.

本文件受BCP 78和IETF信托有关IETF文件的法律规定的约束(自本文件出版之日起生效。请仔细阅读这些文件,因为它们描述了您对本文件的权利和限制。从本文件中提取的代码组件必须包括信托法律条款第4.e节中所述的简化BSD许可证文本,并提供简化BSD许可证中所述的无担保。

Table of Contents


   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Understanding RPC Direction . . . . . . . . . . . . . . . . .   3
   3.  Immediate Uses of Bidirectional RPC-over-RDMA . . . . . . . .   5
   4.  Flow Control  . . . . . . . . . . . . . . . . . . . . . . . .   6
   5.  Sending and Receiving Operations in the Reverse Direction . .   8
   6.  In the Absence of Support for Reverse-Direction Operation . .  11
   7.  Considerations for ULBs . . . . . . . . . . . . . . . . . . .  11
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  12
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  12
   10. Normative References  . . . . . . . . . . . . . . . . . . . .  12
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  13
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  13
   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Understanding RPC Direction . . . . . . . . . . . . . . . . .   3
   3.  Immediate Uses of Bidirectional RPC-over-RDMA . . . . . . . .   5
   4.  Flow Control  . . . . . . . . . . . . . . . . . . . . . . . .   6
   5.  Sending and Receiving Operations in the Reverse Direction . .   8
   6.  In the Absence of Support for Reverse-Direction Operation . .  11
   7.  Considerations for ULBs . . . . . . . . . . . . . . . . . . .  11
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  12
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  12
   10. Normative References  . . . . . . . . . . . . . . . . . . . .  12
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  13
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  13
1. Introduction
1. 介绍

RPC-over-RDMA transports, introduced in [RFC8166], efficiently convey Remote Procedure Call (RPC) transactions on transport layers capable of Remote Direct Memory Access (RDMA). The purpose of this document is to enable concurrent operation in both directions on a single transport connection using RPC-over-RDMA protocol versions that do not have specific facilities for reverse-direction operation.

[RFC8166]中介绍的RPC over RDMA传输在能够远程直接内存访问(RDMA)的传输层上高效地传输远程过程调用(RPC)事务。本文档的目的是使用RPC over RDMA协议版本在单个传输连接上启用双向并发操作,该协议版本没有用于反向操作的特定设施。

Reverse-direction RPC transactions are necessary for the operation of version 4.1 of the Network File System (NFS), and in particular, of Parallel NFS (pNFS) [RFC5661], though any Upper-Layer Protocol (ULP) implementation may make use of them. An Upper-Layer Binding (ULB) for NFS version 4.x callback operation is additionally required (see Section 7) but is not provided in this document.


For example, using the approach described herein, RPC transactions can be conveyed in both directions on the same RPC-over-RDMA version 1 connection without changes to the RPC-over-RDMA version 1 protocol. This document does not update the protocol specified in [RFC8166].

例如,使用本文描述的方法,可以在相同的RPC over RDMA版本1连接上在两个方向上传送RPC事务,而不改变RPC over RDMA版本1协议。本文档不更新[RFC8166]中指定的协议。

The remainder of this document assumes familiarity with the terminology and concepts contained in [RFC8166], especially Sections 2 and 3.


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.

本文件中的关键词“必须”、“不得”、“必需”、“应”、“不应”、“建议”、“不建议”、“可”和“可选”在所有大写字母出现时(如图所示)应按照BCP 14[RFC2119][RFC8174]所述进行解释。

2. Understanding RPC Direction
2. 了解RPC方向

The Open Network Computing Remote Procedure Call (ONC RPC) protocol as described in [RFC5531] is architected as a message-passing protocol between one server and one or more clients. ONC RPC transactions are made up of two types of messages.

[RFC5531]中所述的开放网络计算远程过程调用(ONC RPC)协议被设计为一台服务器和一个或多个客户端之间的消息传递协议。ONC RPC事务由两种类型的消息组成。

A CALL message, or "Call", requests work. A Call is designated by the value CALL in the message's msg_type field. An arbitrary unique value is placed in the message's Transaction ID (XID) field. A host that originates a Call is referred to in this document as a "Requester".


A REPLY message, or "Reply", reports the results of work requested by a Call. A Reply is designated by the value REPLY in the message's msg_type field. The value contained in the message's XID field is copied from the Call whose results are being returned. A host that emits a Reply is referred to as a "Responder".


Typically, a Call results in a corresponding Reply. A Reply is never sent without a corresponding Call.


RPC-over-RDMA is a connection-oriented RPC transport. In all cases, when a connection-oriented transport is used, ONC RPC client endpoints are responsible for initiating transport connections, while ONC RPC service endpoints passively await incoming connection requests.

RDMA上的RPC是一种面向连接的RPC传输。在所有情况下,当使用面向连接的传输时,ONC RPC客户端端点负责启动传输连接,而ONC RPC服务端点被动地等待传入的连接请求。

RPC direction on connectionless RPC transports is not addressed in this document.


2.1. Forward Direction
2.1. 前进方向

Traditionally, an ONC RPC client acts as a Requester, while an ONC RPC service acts as a Responder. This form of message passing is referred to as "forward-direction" operation.

传统上,ONC RPC客户端充当请求者,而ONC RPC服务充当响应者。这种形式的消息传递称为“正向”操作。

2.2. Reverse Direction
2.2. 反向

The ONC RPC specification [RFC5531] does not forbid passing messages in the other direction. An ONC RPC service endpoint can act as a Requester, in which case, an ONC RPC client endpoint acts as a Responder. This form of message passing is referred to as "reverse-direction" operation.

ONC RPC规范[RFC5531]并不禁止向另一个方向传递消息。ONC RPC服务端点可以充当请求者,在这种情况下,ONC RPC客户端端点可以充当响应者。这种形式的消息传递称为“反向”操作。

During reverse-direction operation, the ONC RPC client is responsible for establishing transport connections, even though RPC Call messages come from the ONC RPC server.

在反向操作期间,ONC RPC客户端负责建立传输连接,即使RPC调用消息来自ONC RPC服务器。

ONC RPC clients and servers are optimized to perform and scale well while handling traffic in the forward direction and might not be prepared to handle operation in the reverse direction. Not until NFS version 4.1 [RFC5661] has there been a strong need to handle reverse-direction operation.

ONC RPC客户端和服务器经过优化,能够在正向处理流量时良好地执行和扩展,并且可能不准备处理反向操作。直到NFS版本4.1[RFC5661]才强烈需要处理反向操作。

2.3. Bidirectional Operation
2.3. 双向操作

A pair of connected RPC endpoints may choose to use only forward-direction or only reverse-direction operations on a particular transport connection. Or, these endpoints may send Calls in both directions concurrently on the same transport connection.


"Bidirectional operation" occurs when both transport endpoints act as a Requester and a Responder at the same time.


Bidirectionality is an extension of RPC transport connection sharing. Two RPC endpoints wish to exchange independent RPC messages over a shared connection, but in opposite directions. These messages may or may not be related to the same workloads or RPC Programs.


2.4. XID Values
2.4. XID值

Section 9 of [RFC5531] introduces the ONC RPC transaction identifier, or "XID" for short. The value of an XID is interpreted in the context of the message's msg_type field.

[RFC5531]的第9节介绍了ONC RPC事务标识符,简称“XID”。XID的值在消息的msg_type字段的上下文中进行解释。

o The XID of a Call is arbitrary but is unique among outstanding Calls from that Requester.

o 调用的XID是任意的,但在来自该请求者的未完成调用中是唯一的。

o The XID of a Reply always matches that of the initiating Call.

o 应答的XID始终与发起呼叫的XID匹配。

When receiving a Reply, a Requester matches the XID value in the Reply with a Call it previously sent.


2.4.1. XID Generation
2.4.1. XID代

During bidirectional operation, forward- and reverse-direction XIDs are typically generated on distinct hosts by possibly different algorithms. There is no coordination between forward- and reverse-direction XID generation.


Therefore, a forward-direction Requester MAY use the same XID value at the same time as a reverse-direction Requester on the same transport connection. Though such concurrent requests use the same XID value, they represent distinct ONC RPC transactions.

因此,前向请求者可以在同一传输连接上与反向请求者同时使用相同的XID值。尽管此类并发请求使用相同的XID值,但它们表示不同的ONC RPC事务。

3. Immediate Uses of Bidirectional RPC-over-RDMA
3. RDMA上双向RPC的即时使用
3.1. NFS Version 4.0 Callback Operation
3.1. NFS版本4.0回调操作

An NFS version 4.0 client employs a traditional ONC RPC client to send NFS requests to an NFS version 4.0 server's traditional ONC RPC service [RFC7530]. NFS version 4.0 requests flow in the forward direction on a connection established by the client. This connection is referred to as a "forechannel" connection.

NFS 4.0版客户端使用传统的ONC RPC客户端向NFS 4.0版服务器的传统ONC RPC服务[RFC7530]发送NFS请求。NFS版本4.0请求在客户端建立的连接上向前流动。此连接称为“前频道”连接。

An NFS version 4.x "delegation" is simply a promise made by a server that it will notify a client before another client or program running on the server is allowed access to a file. With this guarantee, that client can operate as sole accessor of the file. In particular, it can manage the file's data and metadata caches aggressively.


To administer file delegations, NFS version 4.0 introduces the use of callback operations, or "callbacks", in Section 10.2 of [RFC7530]. An NFS version 4.0 server sets up a forward-direction ONC RPC client, and an NFS version 4.0 client sets up a forward-direction ONC RPC service. Callbacks flow in the forward direction on a connection established between the server's callback client and the client's callback service. This connection is distinct from connections being used as forechannels and is referred to as a "backchannel connection".

为了管理文件委派,NFS 4.0版在[RFC7530]的第10.2节中引入了回调操作或“回调”。NFS 4.0版服务器设置正向ONC RPC客户端,NFS 4.0版客户端设置正向ONC RPC服务。回调在服务器的回调客户端和客户端的回调服务之间建立的连接上向前流动。此连接与用作前通道的连接不同,称为“后通道连接”。

When an RDMA transport is used as a forechannel, an NFS version 4.0 client typically provides a TCP-based callback service. The client's SETCLIENTID operation advertises the callback service endpoint with a "tcp" or "tcp6" netid. The server then connects to this service using a TCP socket.

当RDMA传输用作预测通道时,NFS 4.0版客户端通常提供基于TCP的回调服务。客户端的SETCLIENTID操作使用“tcp”或“tcp6”netid播发回调服务端点。然后,服务器使用TCP套接字连接到此服务。

NFS version 4.0 implementations can function without a backchannel in place. In this case, the NFS server does not grant file delegations. This might result in a negative performance effect, but correctness is not affected.


3.2. NFS Version 4.1 Callback Operation
3.2. NFS版本4.1回调操作

NFS version 4.1 supports file delegation in a similar fashion to NFS version 4.0 and extends the callback mechanism to manage pNFS layouts, as discussed in Section 12 of [RFC5661].


NFS version 4.1 transport connections are initiated by NFS version 4.1 clients. Therefore, NFS version 4.1 servers send callbacks to clients in the reverse direction on connections established by NFS version 4.1 clients.

NFS 4.1版传输连接由NFS 4.1版客户端启动。因此,NFS 4.1版服务器在NFS 4.1版客户端建立的连接上以相反的方向向客户端发送回调。

NFS version 4.1 clients and servers indicate to their peers that a backchannel capability is available on a given transport connection in the arguments and results of the NFS CREATE_SESSION or BIND_CONN_TO_SESSION operations.


NFS version 4.1 clients may establish distinct transport connections for forechannel and backchannel operation, or they may combine forechannel and backchannel operation on one transport connection using bidirectional operation.


Without a reverse-direction RPC-over-RDMA capability, an NFS version 4.1 client additionally connects using a transport with reverse-direction capability to use as a backchannel. Opening an independent TCP socket is the only choice for an NFS version 4.1 backchannel connection in this case.

如果没有反向RPC over RDMA功能,NFS 4.1版客户端还可以使用具有反向功能的传输进行连接,以用作反向通道。在这种情况下,打开独立TCP套接字是NFS 4.1版反向通道连接的唯一选择。

Implementations often find it more convenient to use a single combined transport (i.e., a transport that is capable of bidirectional operation). This simplifies connection establishment and recovery during network partitions or when one endpoint restarts. This can also enable better scaling by using fewer transport connections to perform the same work.


As with NFS version 4.0, if a backchannel is not in use, an NFS version 4.1 server does not grant delegations. Because NFS version 4.1 relies on callbacks to manage pNFS layout state, pNFS operation is not possible without a backchannel.

与NFS 4.0版一样,如果未使用反向通道,则NFS 4.1版服务器不会授予委派。因为NFS版本4.1依赖回调来管理pNFS布局状态,所以如果没有反向通道,pNFS操作是不可能的。

4. Flow Control
4. 流量控制

For an RDMA Send operation to work properly, the receiving peer has to have already posted a Receive buffer in which to accept the incoming message. If a receiver hasn't posted enough buffers to accommodate each incoming Send operation, the receiving RDMA provider is allowed to terminate the RDMA connection.


RPC-over-RDMA transport protocols provide built-in send flow control to prevent overrunning the number of pre-posted Receive buffers on a connection's receive endpoint using a "credit grant" mechanism. The use of credits in RPC-over-RDMA version 1 is described in Section 3.3.1 of [RFC8166].

RPC over RDMA传输协议提供内置的发送流控制,以使用“信用授予”机制防止连接的接收端点上预发布的接收缓冲区数量超限。[RFC8166]的第3.3.1节描述了RPC over RDMA版本1中信用的使用。

4.1. Reverse-Direction Credits
4.1. 反向信用证

RPC-over-RDMA credits work the same way in the reverse direction as they do in the forward direction. However, forward-direction credits and reverse-direction credits on the same connection are accounted separately. Direction-independent credit accounting prevents head-of-line blocking in one direction from impacting operation in the other direction.


The forward-direction credit value retains the same meaning whether or not there are reverse-direction resources associated with an RPC-over-RDMA transport connection. This is the number of RPC requests the forward-direction Responder (the ONC RPC server) is prepared to receive concurrently.

无论是否存在与RPC over RDMA传输连接关联的反向资源,正向信用值都保留相同的含义。这是前向响应程序(ONC RPC服务器)准备并发接收的RPC请求数。

The reverse-direction credit value is the number of RPC requests the reverse-direction Responder (the ONC RPC client) is prepared to receive concurrently. The reverse-direction credit value MAY be different than the forward-direction credit value.

反向信用值是反向响应程序(ONC RPC客户端)准备同时接收的RPC请求数。反向信用值可能不同于正向信用值。

During bidirectional operation, each receiver has to decide whether an incoming message contains a credit request (the receiver is acting as a Responder) or a credit grant (the receiver is acting as a requester) and apply the credit value accordingly.


When message direction is not fully determined by context (e.g., suggested by the definition of the RPC-over-RDMA version that is in use) or by an accompanying RPC message payload with a call direction field, it is not possible for the receiver to tell with certainty whether the header credit value is a request or grant. In such cases, the receiver MUST ignore the header's credit value.

当消息方向未完全由上下文(例如,由正在使用的RPC over RDMA版本的定义所建议)或由带有呼叫方向字段的伴随RPC消息有效负载所确定时,接收器不可能确定地告诉消息头信用值是请求还是授予。在这种情况下,接收方必须忽略标题的信用值。

4.2. Inline Thresholds
4.2. 内联阈值

Forward- and reverse-direction operation on the same connection share the same Receive buffers. Therefore, the inline threshold values for the forward direction and the reverse direction are the same. The call inline threshold for the reverse direction is the same as the reply inline threshold for the forward direction, and vice versa. For more information, see Section 3.3.2 of [RFC8166].


4.3. Managing Receive Buffers
4.3. 管理接收缓冲区

An RPC-over-RDMA transport endpoint posts Receive buffers before it can receive and process incoming RPC-over-RDMA messages. If a sender transmits a message for a receiver that has no posted Receive buffer, the RDMA provider is allowed to drop the RDMA connection.

RPC over RDMA传输终结点在接收和处理传入的RPC over RDMA消息之前发送接收缓冲区。如果发送方为没有发送接收缓冲区的接收方发送消息,则允许RDMA提供程序断开RDMA连接。

4.3.1. Client Receive Buffers
4.3.1. 客户端接收缓冲区

Typically, an RPC-over-RDMA Requester posts only as many Receive buffers as there are outstanding RPC Calls. Therefore, a client endpoint without reverse-direction support might, at times, have no available Receive buffers.


To receive incoming reverse-direction Calls, an RPC-over-RDMA client endpoint posts enough additional Receive buffers to match its advertised reverse-direction credit value. Each outstanding forward-direction RPC requires an additional Receive buffer above this minimum.


When an RDMA transport connection is lost, all active Receive buffers are flushed and are no longer available to receive incoming messages. When a fresh transport connection is established, a client endpoint posts a Receive buffer to handle the Reply for each retransmitted forward-direction Call, and it posts enough Receive buffers to handle reverse-direction Calls.


4.3.2. Server Receive Buffers
4.3.2. 服务器接收缓冲区

A forward-direction RPC-over-RDMA service endpoint posts as many Receive buffers as it expects incoming forward-direction Calls. That is, it posts no fewer buffers than the number of credits granted in the rdma_credit field of forward-direction RPC replies.


To receive incoming reverse-direction replies, an RPC-over-RDMA server endpoint posts enough additional Receive buffers to handle replies for each reverse-direction Call it sends.


When the existing transport connection is lost, all active Receive buffers are flushed and are no longer available to receive incoming messages. When a fresh transport connection is established, a server endpoint posts a Receive buffer to handle the Reply for each retransmitted reverse-direction Call, and it posts enough Receive buffers to handle incoming forward-direction Calls.


5. Sending and Receiving Operations in the Reverse Direction
5. 反向发送和接收操作

The operation of RPC-over-RDMA transports in the forward direction is defined in [RFC5531] and [RFC8166]. In this section, a mechanism for reverse-direction operation on RPC-over-RDMA is defined. Reverse-direction operation used in combination with forward-direction operation enables bidirectional communication on a common RPC-over-RDMA transport connection.

[RFC5531]和[RFC8166]中定义了RDMA上RPC传输的正向操作。在本节中,定义了RDMA上RPC的反向操作机制。反向操作与正向操作结合使用,可在公共RPC over RDMA传输连接上实现双向通信。

Certain fields in the RPC-over-RDMA header have a fixed position in all versions of RPC-over-RDMA. The normative specification of these fields is contained in Section 4 of [RFC8166].

RPC over RDMA标头中的某些字段在所有版本的RPC over RDMA中都有固定位置。这些领域的规范性规范包含在[RFC8166]的第4节中。

5.1. Sending a Call in the Reverse Direction
5.1. 以相反方向发送呼叫

To form a reverse-direction RPC-over-RDMA Call message, an ONC RPC service endpoint constructs an RPC-over-RDMA header containing a fresh RPC XID in the rdma_xid field (see Section 2.4 for full requirements).

为了形成反向RPC over RDMA调用消息,ONC RPC服务端点构造一个RPC over RDMA报头,该报头在RDMA_XID字段中包含一个新的RPC XID(有关完整要求,请参见第2.4节)。

The rdma_vers field MUST contain the same value in reverse- and forward-direction Call messages on the same connection.


The number of requested reverse-direction credits is placed in the rdma_credit field (see Section 4).


Whether presented inline or as a separate chunk, the ONC RPC Call header MUST start with the same XID value that is present in the RPC-over-RDMA header, and the RPC header's msg_type field MUST contain the value CALL.


5.2. Sending a Reply in the Reverse Direction
5.2. 以相反的方向发送回复

To form a reverse-direction RPC-over-RDMA Reply message, an ONC RPC client endpoint constructs an RPC-over-RDMA header containing a copy of the matching ONC RPC Call's RPC XID in the rdma_xid field (see Section 2.4 for full requirements).

为了形成反向RPC over RDMA回复消息,ONC RPC客户端端点在RDMA_XID字段中构造一个包含匹配ONC RPC调用的RPC XID副本的RPC over RDMA报头(有关完整要求,请参阅第2.4节)。

The rdma_vers field MUST contain the same value in a reverse-direction Reply message as in the matching Call message.


The number of granted reverse-direction credits is placed in the rdma_credit field (see Section 4).


Whether presented inline or as a separate chunk, the ONC RPC Reply header MUST start with the same XID value that is present in the RPC-over-RDMA header, and the RPC header's msg_type field MUST contain the value REPLY.


5.3. Using Chunks in Reverse-Direction Operations
5.3. 在反向操作中使用块

A "chunk" refers to a portion of a message's Payload stream that is DDP-eligible and that is placed directly in the receiver's memory by the transport. Chunk data may be moved by an explicit RDMA operation, for example. Chunks are defined in Section 3.4.4 and DDP-eligibility is covered in Section 6.1 of [RFC8166].


Chunks MAY be used in the reverse direction. They operate the same way as in the forward direction.


An implementation might support only ULPs that have no DDP-eligible data items. Such ULPs may use only small messages, or they may have a native mechanism for restricting the size of reverse-direction RPC messages, obviating the need to handle Long Messages in the reverse direction.


When there is no ULP requirement for chunks in the reverse direction, implementers can choose not to provide support for chunks in the reverse direction. This avoids the complexity of adding support for performing RDMA Reads and Writes in the reverse direction.


When chunks are not implemented, RPC messages in the reverse direction are always sent using a Short Message; therefore, they can be no larger than what can be sent inline (that is, without chunks). Sending an inline message larger than the inline threshold can result in loss of connection.


If a reverse-direction requester provides a non-empty chunk list to a Responder that does not support chunks, the Responder MUST reply with an RDMA_ERROR message with rdma_err field set to ERR_CHUNK.

如果反向请求者向不支持区块的响应者提供非空区块列表,响应者必须回复RDMA_错误消息,并将RDMA_err field设置为err_chunk。

5.4. Reverse-Direction Retransmission
5.4. 反向重传

In rare cases, an ONC RPC service cannot complete an RPC transaction and then send a reply. This can be because the transport connection was lost, because the Call or Reply message was dropped, or because the ULP delayed or dropped the ONC RPC request. Typically, the Requester sends the RPC transaction again, reusing the same RPC XID. This is known as an "RPC retransmission".

在极少数情况下,ONC RPC服务无法完成RPC事务,然后发送回复。这可能是因为传输连接丢失、呼叫或应答消息被丢弃,或者ULP延迟或丢弃了ONC RPC请求。通常,请求者再次发送RPC事务,重用相同的RPC XID。这称为“RPC重传”。

In the forward direction, the Requester is the ONC RPC client. The client is always responsible for establishing a transport connection before sending again.


With reverse-direction operation, the Requester is the ONC RPC server. Because an ONC RPC server does not establish transport connections with clients, it cannot retransmit if there is no transport connection. It is forced to wait for the ONC RPC client to re-establish a transport connection before it can retransmit ONC RPC transactions in the reverse direction.

使用反向操作时,请求者是ONC RPC服务器。由于ONC RPC服务器不与客户端建立传输连接,因此如果没有传输连接,则无法重新传输。它必须等待ONC RPC客户端重新建立传输连接,然后才能反向重新传输ONC RPC事务。

If the ONC RPC client peer has no work to do, it can be some time before it re-establishes a transport connection. A waiting reverse-direction ONC RPC Call may time out to avoid waiting indefinitely for a connection to be established.


Therefore, forward-direction Requesters SHOULD maintain a transport connection as long as there is the possibility that the connection peer can send reverse-direction requests. For example, while an NFS version 4.1 client has open delegated files or active pNFS layouts, it maintains one or more transport connections to enable the NFS server to perform callback operations.

因此,只要连接对等方有可能发送反向请求,前向请求方就应该保持传输连接。例如,尽管NFS 4.1版客户端具有打开的委托文件或活动的pNFS布局,但它维护一个或多个传输连接以使NFS服务器能够执行回调操作。

6. In the Absence of Support for Reverse-Direction Operation
6. 在没有支持反向操作的情况下

An RPC-over-RDMA transport endpoint might not support reverse-direction operation (and thus it does not support bidirectional operation). There might be no mechanism in the transport implementation to do so. Or in an implementation that can support operation in the reverse direction, the ULP might not yet have configured or enabled the transport to handle reverse-direction traffic.

RPC over RDMA传输终结点可能不支持反向操作(因此不支持双向操作)。传输实现中可能没有这样做的机制。或者,在支持反向操作的实现中,ULP可能尚未配置或启用传输以处理反向流量。

If an endpoint is not prepared to receive an incoming reverse-direction message, loss of the RDMA connection might result. Thus, denial of service could result if a sender continues to send reverse-direction messages after every transport reconnect to an endpoint that is not prepared to receive them.


When dealing with the possibility that the remote peer has no transport-level support for reverse-direction operation, the ULP becomes responsible for informing peers when reverse-direction operation is supported. Otherwise, even a simple reverse-direction RPC NULL procedure from a peer could result in a lost connection.

当处理远程对等方不支持反向操作的传输级别的可能性时,ULP负责在支持反向操作时通知对等方。否则,即使来自对等方的简单反向RPC NULL过程也可能导致连接丢失。

Therefore, a ULP MUST NOT perform reverse-direction ONC RPC operations until the peer has indicated it is prepared to handle them. A description of ULP mechanisms used for this indication is outside the scope of this document.

因此,ULP必须在对等方表示准备处理这些操作之前,才能执行反向ONC RPC操作。用于该指示的ULP机制的描述不在本文件范围内。

For example, an NFS version 4.1 server does not send backchannel messages to an NFS version 4.1 client before the NFS version 4.1 client has sent a CREATE_SESSION or a BIND_CONN_TO_SESSION operation. As long as an NFS version 4.1 client has prepared appropriate resources to receive reverse-direction operations before sending one of these NFS operations, denial of service is avoided.

例如,在NFS 4.1版客户端发送创建会话或绑定连接到会话操作之前,NFS 4.1版服务器不会向NFS 4.1版客户端发送反向通道消息。只要NFS 4.1版客户端在发送其中一个NFS操作之前准备了适当的资源来接收反向操作,就可以避免拒绝服务。

7. Considerations for ULBs
7. ULBs的考虑因素

A ULP that operates on RPC-over-RDMA transports may have procedures that include DDP-eligible data items. DDP-eligibility is specified in an Upper-Layer Binding (ULB). Direction of operation does not obviate the need for DDP-eligibility statements.

在RPC over RDMA传输上运行的ULP可能具有包括DDP合格数据项的过程。DDP合格性在上层绑定(ULB)中指定。操作指导并不排除DDP资格声明的必要性。

Reverse-direction-only operation requires the client endpoint to establish a fresh connection. The ULB can specify appropriate RPC binding parameters for such connections.


Bidirectional operation occurs on an already-established connection. Specification of RPC binding parameters is usually not necessary in this case.


For bidirectional operation, other considerations may apply when distinct RPC Programs share an RPC-over-RDMA transport connection concurrently. Consult Section 6 of [RFC8166] for details about what else may be contained in a ULB.

对于双向操作,当不同的RPC程序同时共享一个RPC over RDMA传输连接时,可能需要考虑其他因素。有关ULB中可能包含的其他内容的详细信息,请参阅[RFC8166]第6节。

8. Security Considerations
8. 安全考虑

RPC security is handled in the RPC layer, which is above the transport layer where RPC-over-RDMA operates.

RPC安全性在RPC层中处理,RPC层位于传输层之上,RPC over RDMA在传输层上运行。

Reverse-direction operations make use of an authentication mechanism and credentials that are independent of forward-direction operation but otherwise operate in the same fashion as outlined in Section 8.2 of [RFC8166].


9. IANA Considerations
9. IANA考虑

This document does not require any IANA actions.


10. Normative References
10. 规范性引用文件

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

[RFC2119]Bradner,S.,“RFC中用于表示需求水平的关键词”,BCP 14,RFC 2119,DOI 10.17487/RFC2119,1997年3月<>.

[RFC5531] Thurlow, R., "RPC: Remote Procedure Call Protocol Specification Version 2", RFC 5531, DOI 10.17487/RFC5531, May 2009, <>.

[RFC5531]Thurlow,R.,“RPC:远程过程调用协议规范版本2”,RFC 5531,DOI 10.17487/RFC5531,2009年5月<>.

[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, <>.

[RFC5661]Shepler,S.,Ed.,Eisler,M.,Ed.,和D.Noveck,Ed.,“网络文件系统(NFS)版本4次要版本1协议”,RFC 5661,DOI 10.17487/RFC5661,2010年1月<>.

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

[RFC7530]Haynes,T.,Ed.和D.Noveck,Ed.,“网络文件系统(NFS)第4版协议”,RFC 7530,DOI 10.17487/RFC7530,2015年3月<>.

[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, <>.

[RFC8166]Lever,C.,Ed.,Simpson,W.,和T.Talpey,“远程过程调用版本1的远程直接内存访问传输”,RFC 8166,DOI 10.17487/RFC8166,2017年6月<>.

[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, <>.

[RFC8174]Leiba,B.,“RFC 2119关键词中大写与小写的歧义”,BCP 14,RFC 8174,DOI 10.17487/RFC8174,2017年5月<>.



Tom Talpey was an indispensable resource, in addition to creating the foundation upon which this work is based. The author's warmest regards go to him for his help and support.

Tom Talpey是一个不可缺少的资源,除了创造的基础上,这项工作的基础。作者向他的帮助和支持致以最热烈的问候。

Dave Noveck provided excellent review, constructive suggestions, and navigational guidance throughout the process of drafting this document.

在起草本文件的整个过程中,Dave Noveck提供了出色的审查、建设性建议和导航指导。

Dai Ngo was a solid partner and collaborator. Together we constructed and tested independent prototypes of the changes described in this document.

Dai Ngo是一个可靠的合作伙伴和合作者。我们共同构建并测试了本文档中描述的变更的独立原型。

The author wishes to thank Bill Baker and Greg Marsden for their unwavering support of this work. In addition, the author gratefully acknowledges the expert contributions of Karen Deitke, Chunli Zhang, Mahesh Siddheshwar, Steve Wise, and Tom Tucker.

作者希望感谢比尔·贝克和格雷格·马斯登对这项工作的坚定支持。此外,作者感谢Karen Deitke、张春丽、Mahesh Siddheshwar、Steve Wise和Tom Tucker的专家贡献。

Special thanks go to Transport Area Director Spencer Dawkins, NFSV4 Working Group Chair and Document Shepherd Spencer Shepler, and NFSV4 Working Group Secretary Tom Haynes for their support.


Author's Address


Charles Lever Oracle Corporation 1015 Granger Avenue Ann Arbor, MI 48104 United States of America


   Phone: +1 248 816 6463
   Phone: +1 248 816 6463