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




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.

これはInternet Standards Trackドキュメントです。

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.

このドキュメントは、IETF(Internet Engineering Task Force)の製品です。これは、IETFコミュニティのコンセンサスを表しています。公開レビューを受け、インターネットエンジニアリングステアリンググループ(IESG)による公開が承認されました。インターネット標準の詳細については、RFC 7841のセクション2をご覧ください。

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.

Copyright(c)2017 IETF Trustおよびドキュメントの作成者として識別された人物。全著作権所有。

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.

この文書は、BCP 78およびこの文書の発行日に有効なIETF文書に関するIETFトラストの法的規定(の対象となります。これらのドキュメントは、このドキュメントに関するあなたの権利と制限を説明しているため、注意深く確認してください。このドキュメントから抽出されたコードコンポーネントには、Trust Legal Provisionsのセクション4.eに記載されているSimplified BSD Licenseのテキストが含まれている必要があり、Simplified BSD Licenseに記載されているように保証なしで提供されます。

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
1. はじめに

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.


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.

ネットワークファイルシステム(NFS)のバージョン4.1、特に並列NFS(pNFS)[RFC5661]の操作には、逆方向RPCトランザクションが必要ですが、上位層プロトコル(ULP)の実装では、それら。 NFSバージョン4.xのコールバック操作用の上位層バインディング(ULB)がさらに必要です(セクション7を参照)が、このドキュメントでは提供されていません。

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].


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.


2. Understanding RPC Direction
2. RPC方向について

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]で説明されているOpen Network Computing Remote Procedure Call(ONC RPC)プロトコルは、1つのサーバーと1つ以上のクライアント間のメッセージ受け渡しプロトコルとして設計されています。 ONC RPCトランザクションは、2つのタイプのメッセージで構成されます。

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.

RPC-over-RDMAは、接続指向のRPCトランスポートです。すべての場合において、コネクション型トランスポートが使用される場合、ONC RPCクライアントエンドポイントはトランスポート接続の開始を担当し、ONC RPCサービスエンドポイントは着信接続要求を受動的に待機します。

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


2.1. Forward Direction
2.1. 順方向

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.

従来、ONC RPCクライアントはリクエスターとして機能し、ONC RPCサービスはレスポンダーとして機能します。この形式のメッセージパッシングは、「順方向」操作と​​呼ばれます。

2.2. Reverse Direction
2.2. 逆方向

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仕様[RFC5531]は、逆方向へのメッセージの受け渡しを禁止していません。 ONC RPCサービスエンドポイントはリクエスタとして機能できます。その場合、ONC RPCクライアントエンドポイントはレスポンダとして機能します。この形式のメッセージパッシングは、「逆方向」操作と​​呼ばれます。

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.

逆方向の操作中、RPC CallメッセージがONC RPCサーバーから送信された場合でも、ONC RPCクライアントはトランスポート接続の確立を担当します。

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クライアントとサーバーは、トラフィックを順方向に処理するときにパフォーマンスとスケーリングが最適化されるように最適化されており、逆方向の操作を処理する準備ができていない場合があります。 NFSバージョン4.1 [RFC5661]になるまでは、逆方向の操作を処理する必要はありませんでした。

2.3. Bidirectional Operation
2.3. 双方向操作

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.

双方向性は、RPCトランスポート接続共有の拡張です。 2つのRPCエンドポイントは、共有接続を介して、逆方向に独立したRPCメッセージを交換したいと考えています。これらのメッセージは、同じワークロードまたはRPCプログラムに関連する場合とそうでない場合があります。

2.4. XID Values
2.4. XID値

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]のセクション9では、ONC RPCトランザクション識別子、または略して「XID」を紹介しています。 XIDの値は、メッセージのmsg_typeフィールドのコンテキストで解釈されます。

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

o コールのXIDは任意ですが、そのリクエスターからの未解決のコール間で一意です。

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

o 返信のXIDは、常に開始コールのXIDと一致します。

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生成

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.

したがって、順方向リクエスターは、同じトランスポート接続で逆方向リクエスターと同時に同じXID値を使用できます(MAY)。このような同時要求は同じXID値を使用しますが、それらは別個のONC RPCトランザクションを表します。

3. Immediate Uses of Bidirectional RPC-over-RDMA
3. 双方向RPC-over-RDMAの即時使用
3.1. NFS Version 4.0 Callback Operation
3.1. NFSバージョン4.0のコールバック操作

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バージョン4.0クライアントは、伝統的なONC RPCクライアントを使用して、NFSリクエストをNFSバージョン4.0サーバーの伝統的なONC RPCサービス[RFC7530]に送信します。 NFSバージョン4.0要求は、クライアントによって確立された接続で順方向に流れます。この接続は、「フォアチャネル」接続と呼ばれます。

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".

ファイル委任を管理するために、NFSバージョン4.0では、[RFC7530]のセクション10.2にコールバック操作、つまり「コールバック」の使用が導入されています。 NFSバージョン4.0サーバーは順方向ONC RPCクライアントをセットアップし、NFSバージョン4.0クライアントは順方向ONC RPCサービスをセットアップします。コールバックは、サーバーのコールバッククライアントとクライアントのコールバックサービスの間に確立された接続で順方向に流れます。この接続は、フォアチャネルとして使用されている接続とは異なり、「バックチャネル接続」と呼ばれます。

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.

RDMAトランスポートがフォアチャネルとして使用される場合、NFSバージョン4.0クライアントは通常、TCPベースのコールバックサービスを提供します。クライアントのSETCLIENTID操作は、 "tcp"または "tcp6" netidを使用してコールバックサービスエンドポイントをアドバタイズします。次に、サーバーはTCPソケットを使用してこのサービスに接続します。

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バージョン4.1のコールバック操作

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 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バージョン4.1のクライアントとサーバーは、NFS CREATE_SESSIONまたはBIND_CONN_TO_SESSION操作の引数と結果で、特定のトランスポート接続でバックチャネル機能が利用可能であることをピアに示します。

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.


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.

NFSバージョン4.0と同様に、バックチャネルが使用されていない場合、NFSバージョン4.1サーバーは委任を許可しません。 NFSバージョン4.1はpNFSレイアウト状態を管理するためにコールバックに依存しているため、バックチャネルがないとpNFS操作はできません。

4. Flow Control
4. フロー制御

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トランスポートプロトコルは、組み込みの送信フロー制御を提供し、「クレジット付与」メカニズムを使用して、接続の受信エンドポイントで事前送信された受信バッファの数がオーバーランするのを防ぎます。 RPC-over-RDMAバージョン1でのクレジットの使用については、[RFC8166]のセクション3.3.1で説明されています。

4.1. Reverse-Direction Credits
4.1. 逆方向クレジット

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.

順方向クレジット値は、RPC-over-RDMAトランスポート接続に関連付けられている逆方向リソースがあるかどうかにかかわらず、同じ意味を保持します。これは、順方向レスポンダー(ONC RPCサーバー)が同時に受信する準備ができているRPC要求の数です。

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.

逆方向クレジット値は、逆方向レスポンダ(ONC RPCクライアント)が同時に受信する準備ができているRPC要求の数です。逆方向のクレジット値は、順方向のクレジット値とは異なる場合があります。

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.


4.2. Inline Thresholds
4.2. インラインしきい値

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. 受信バッファーの管理

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.


4.3.1. Client Receive Buffers
4.3.1. クライアント受信バッファー

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. サーバー受信バッファー

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. 逆方向の操作の送受信

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.


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].


5.1. Sending a Call in the Reverse Direction
5.1. 逆方向に電話をかける

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).

逆方向RPC-over-RDMA呼び出しメッセージを形成するために、ONC RPCサービスエンドポイントは、rdma_xidフィールドに新しいRPC XIDを含むRPC-over-RDMAヘッダーを作成します(完全な要件については、セクション2.4を参照)。

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.

ONC RPC Callヘッダーは、インラインまたは個別のチャンクとして提示されるかどうかにかかわらず、RPC-over-RDMAヘッダーに存在するものと同じXID値で開始する必要があり、RPCヘッダーのmsg_typeフィールドには値CALLが含まれている必要があります。

5.2. Sending a Reply in the Reverse Direction
5.2. 逆方向の返信の送信

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).

逆方向RPC-over-RDMA応答メッセージを形成するために、ONC RPCクライアントエンドポイントは、rdma_xidフィールドに一致するONC RPCコールのRPC XIDのコピーを含むRPC-over-RDMAヘッダーを作成します(完全な要件については、セクション2.4を参照) 。

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.

ONC RPC Replyヘッダーは、インラインまたは個別のチャンクとして提示されるかどうかにかかわらず、RPC-over-RDMAヘッダーに存在するものと同じXID値で開始する必要があり、RPCヘッダーのmsg_typeフィールドには値REPLYが含まれている必要があります。

5.3. Using Chunks in Reverse-Direction Operations
5.3. 逆方向操作でのチャンクの使用

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.


5.4. Reverse-Direction Retransmission
5.4. 逆方向再送信

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".

まれに、ONC RPCサービスがRPCトランザクションを完了してから応答を送信できないことがあります。これは、トランスポート接続が失われたか、呼び出しまたは応答メッセージがドロップされたか、ULPがONC RPC要求を遅延またはドロップしたことが原因である可能性があります。通常、リクエスターは同じRPC XIDを再利用して、RPCトランザクションを再度送信します。これは「RPC再送信」と呼ばれます。

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

順方向では、リクエスターはONC RPCクライアントです。クライアントは常に、再送信する前にトランスポート接続を確立する責任があります。

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.

逆方向操作では、リクエスターはONC RPCサーバーです。 ONC RPCサーバーはクライアントとのトランスポート接続を確立しないため、トランスポート接続がない場合は再送信できません。 ONC RPCクライアントが逆方向にONC RPCトランザクションを再送信する前に、ONC RPCクライアントがトランスポート接続を再確立するまで待機する必要があります。

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.

ONC RPCクライアントピアに実行する作業がない場合、トランスポート接続を再確立するまでに時間がかかることがあります。待機中の逆方向ONC RPC呼び出しは、接続が確立されるまで無期限に待機することを回避するためにタイムアウトする場合があります。

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.


6. In the Absence of Support for Reverse-Direction Operation
6. 逆方向操作のサポートがない場合

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.


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.

リモートピアが逆方向操作のトランスポートレベルのサポートを持たない可能性に対処する場合、逆方向操作がサポートされている場合、ULPはピアに通知する責任があります。そうしないと、ピアからの単純な逆方向RPC NULLプロシージャでさえ、接続が失われる可能性があります。

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.

したがって、ULPは、ピアがそれらを処理する準備ができていることを示すまで、逆方向のONC RPC操作を実行してはなりません(MUST NOT)。この表示に使用されるULPメカニズムの説明は、このドキュメントの範囲外です。

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.

たとえば、NFSバージョン4.1サーバーは、NFSバージョン4.1クライアントがCREATE_SESSIONまたはBIND_CONN_TO_SESSION操作を送信する前に、NFSバージョン4.1クライアントにバックチャネルメッセージを送信しません。 NFSバージョン4.1クライアントが、これらのNFS操作の1つを送信する前に、逆方向操作を受信するための適切なリソースを準備している限り、サービス拒否は回避されます。

7. Considerations for ULBs
7. ULBに関する考慮事項

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.

RPC-over-RDMAトランスポートで動作するULPには、DDPに適格なデータ項目を含む手順がある場合があります。 DDP適格性は、Upper-Layer Binding(ULB)で指定されます。操作の方向は、DDP適格性ステートメントの必要性を未然に防ぎません。

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

逆方向のみの操作では、クライアントエンドポイントが新しい接続を確立する必要があります。 ULBは、そのような接続に適切なRPCバインディングパラメータを指定できます。

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.

双方向操作の場合、個別のRPCプログラムがRPC-over-RDMAトランスポート接続を同時に共有する場合、他の考慮事項が適用される場合があります。 ULBに他に何が含まれる可能性があるかについての詳細は、[RFC8166]のセクション6を参照してください。

8. Security Considerations
8. セキュリティに関する考慮事項

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


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に関する考慮事項

This document does not require any IANA actions.


10. Normative References
10. 引用文献

[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。、「要件レベルを示すためにRFCで使用するキーワード」、BCP 14、RFC 2119、DOI 10.17487 / RFC2119、1997年3月、< rfc2119>。

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

[RFC5531] Thurlow、R。、「RPC:Remote Procedure Call Protocol Specification Version 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。、and D. Noveck、Ed。、 "Network File System(NFS)Version 4 Minor Version 1 Protocol"、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]ヘインズ、T。、エド。およびD. Noveck編、「Network File System(NFS)Version 4 Protocol」、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。、およびT. Talpey、「リモートプロシージャコールバージョン1のリモートダイレクトメモリアクセストランスポート」、RFC 8166、DOI 10.17487 / RFC8166、2017年6月、<http:/ />。

[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。、「あいまいな大文字と小文字のRFC 2119キーワード」、BCP 14、RFC 8174、DOI 10.17487 / RFC8174、2017年5月、< rfc8174>。



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.


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

Dave Noveckは、このドキュメントの草案作成プロセス全体を通じて、優れたレビュー、建設的な提案、およびナビゲーションガイダンスを提供しました。

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

Dai Ngoは確かなパートナーであり、協力者でもありました。このドキュメントに記載されている変更の独立したプロトタイプを作成してテストしました。

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.

著者は、この作業に対する揺るぎないサポートを提供してくれたBill BakerとGreg Marsdenに感謝します。さらに、著者は、Karen Deitke、Chunli Zhang、Mahesh Siddheshwar、Steve Wise、およびTom Tuckerの専門家の貢献に感謝します。

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.

Transport Area Director Spencer Dawkins、NFSV4 Working Group Chair and Document Shepherd Spencer Shepler、およびNFSV4 Working Group Secretary Tom Haynesのサポートに特に感謝します。

Author's Address


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

Charles Lever Oracle Corporation 1015 Granger Avenueアナーバー、ミシガン州48104アメリカ合衆国

   Phone: +1 248 816 6463