STORM A. Kanevsky, Ed. Internet-Draft VMware Updates: 5043, 5044 (if approved) C. Bestler, Ed. Intended status: Standards Track Nexenta Systems Expires: December 15, 2011 R. Sharp Intel S. Wise Open Grid Computing June 13, 2011 Enhanced RDMA Connection Establishment draft-ietf-storm-mpa-peer-connect-05 Abstract This document updates RFC5043 and RFC5044 by extending MPA negotiation for RDMA connection establishment. The first enhancement extends RFC5043, enabling peer-to-peer connection establishment over MPA/TCP. The second enhancement extends both RFC5043 and RFC5044, by providing an option for standardized exchange of RDMA-layer connection configuration. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on December 15, 2011. Copyright Notice Copyright (c) 2011 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 (http://trustee.ietf.org/license-info) in effect on the date of Kanevsky, et al. Expires December 15, 2011 [Page 1] Internet-Draft Enhanced RDMA Connection Establishment June 2011 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. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Summary of changes from RFC 5044 . . . . . . . . . . . . . 4 1.2. Summary of changes from RFC 5043 . . . . . . . . . . . . . 4 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 4 3. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 4 4. Motivations . . . . . . . . . . . . . . . . . . . . . . . . . 5 4.1. Enabling MPA Mode . . . . . . . . . . . . . . . . . . . . 6 4.2. Lack of Explicit RTR in MPA Request/Reply Exchange . . . . 6 4.3. Limitations on ULP Workaround . . . . . . . . . . . . . . 7 4.3.1. Transport Neutral APIs . . . . . . . . . . . . . . . . 8 4.3.2. Work/Completion Queue Accounting . . . . . . . . . . . 8 4.3.3. Host-based Implementation of MPA Fencing . . . . . . . 9 4.4. Standardized RDMA Parameter Negotiation . . . . . . . . . 9 5. Enhanced MPA Connection Establishment . . . . . . . . . . . . 10 6. Enhanced MPA Request/Reply Frames . . . . . . . . . . . . . . 11 7. Enhanced SCTP Session Control Chunks . . . . . . . . . . . . . 12 8. MPA Error Reporting . . . . . . . . . . . . . . . . . . . . . 14 9. Enhanced RDMA Connection Establishment Data . . . . . . . . . 15 10. Interoperability . . . . . . . . . . . . . . . . . . . . . . . 17 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18 12. Security Considerations . . . . . . . . . . . . . . . . . . . 18 13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 18 14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18 14.1. Normative References . . . . . . . . . . . . . . . . . . . 18 14.2. Informative References . . . . . . . . . . . . . . . . . . 19 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 20 Kanevsky, et al. Expires December 15, 2011 [Page 2] Internet-Draft Enhanced RDMA Connection Establishment June 2011 1. Introduction When used over Transmission Control Protocol TCP, the current Remote Direct Data Placement (RDDP) suite of protocols relies on Marker protocol Data Unit PDU Alignment (MPA) [RFC5044] protocol for both connection establishment and for markers for TCP layering. A typical model for establishing an RDMA connection has the following steps: o The passive side Upper Layer Protocol (ULP) listens for connection requests. o The active side ULP submits a connection request using an RDMA endpoint, the desired destination and the parameters to be used for the connection. Those parameters include both RDMA layer characteristics, such as the RDMA Read credits to be allowed and application specific data. o The passive side ULP receives the Connection Request, which includes the identity of the active side and the requested connection characteristics. The passive side ULP uses this information to decide whether to accept the connection, and if it is to be accepted, how to create and/or configure the local RDMA endpoint. o If accepting, the passive side ULP submits its acceptance of the Connection Request. This local accept operation includes the RDMA endpoint to be used and the connection characteristics (both the RDMA configuration and any application specific private data to be returned). o The active side receives confirmation that the connection has been accepted, what the configured connection characteristics are, and any application supplied private data. Currently, MPA only supports a client-server model for connection establishment, forcing peer-to-peer applications to interact as though they had a client/server relationship. In addition negotiation of some of Remote Direct Memory Access Protocol (RDMAP) [RFC5040] specific parameters are left to ULP negotiation. Providing an optional ULP-independent format for exchanging these parameters would be of benefit to transport neutral Remote Direct Memory Access (RDMA) applications. Kanevsky, et al. Expires December 15, 2011 [Page 3] Internet-Draft Enhanced RDMA Connection Establishment June 2011 1.1. Summary of changes from RFC 5044 This draft enhances [RFC5044] MPA connection setup protocol. First, it adds exchange and negotiation of the maximum number of RDMA Read Incoming (IRD) and Outgoing (ORD) messages. Second, it adds a Ready to Receive (RTR) frame from Initiator to Responder as the last message of connection establishment and adds negotiation of an RTR message frame type into MPA request/response frames. 1.2. Summary of changes from RFC 5043 This draft enhances [RFC5043] by adding new Enhanced Session Control Chunks that extends the currently defined Chunks with the addition of IRD and ORD negotiation. 2. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. 3. Definitions FULPDU: Framed Upper Layer Protocol PDU. See FPDU of [RFC5044]. CRC: Cyclic Redundancy Check. Completion Queue (CQ): A consumer accessible queue where the RDMA device reports completions of Work Requests. A Consumer is able to reap completions from a CQ without requiring per transaction support from the kernel or other privileged entity. See [RDMAC]. Completion Queue Entry (CQE): Transport and device specific representation of a Work Completion. A Completion Queue holds CQEs. See [RDMAC]. Inbound RDMA Read Queue Depth (IRD): The maximum number of incoming outstanding RDMA Read Request Messages an RDMA connection can handle. See [RDMAC]. IRD: See Inbound RDMA Read Queue Depth. MPA Fencing: MPA Responder Connection Establishment logic that ensures that no ULP messages will be transferred until Initiator first message has been received. Kanevsky, et al. Expires December 15, 2011 [Page 4] Internet-Draft Enhanced RDMA Connection Establishment June 2011 ORD: See Outbound RDMA Read Queue Depth. Outbound RDMA Read Queue Depth (ORD): The maximum number of outstanding RDMA Read Requests that can be issued for the RDMA connection. This should be less than or equal to the peer's IRD. See [RDMAC]. Queue Pair (QP): The traditional name for a local Endpoint in a [VIA] derived local interface. A Queue Pair is the set of Work Queues associated exclusively with a single Endpoint. The Send Queue (SQ), Receive Queue (RQ) and Inbound RDMA Read Queue (IRQ) are considered to be part of the Queue Pair. The potentially shared Completion Queue (CQ) and Shared Receive Queue (SRQ) are not. See [RDMAC]. Ready to Receive (RTR): RTR is the last connection establishment message sent from Initiator to Responder indicating that Initiator is ready to receive messages and that connection establishment is completed. See [IBTA]. Shared Receive Queue(SRQ): A shared pool of Receive Work Requests posted by the Consumer that can be allocated by multiple RDMA endpoints (Queue Pair). See [RDMAC]. Tagged (DDP) Message: - A DDP Message that targets a Tagged Buffer that is explicitly Advertised to the Remote Peer through exchange of an STag (memory handle), offset in the memory region identified by STag, and length [RFC5040]. Work Queue: An element of a [VIA] derived local interface that allows user-space applications to submit Work Requests directly to network hardware. Specific Work Queues include the Send Queue (SQ) for transmit requests, Receive Queue (RQ) for receive requests specific to a single Endpoint and Shared Receive Queues (SRQs) for receive requests that can be allocated by one or more Endpoints. See [RDMAC]. Work Queue Element (WQE): Transport and device specific representation of a Work Request. See [RDMAC]. Work Request: An elementary object used by Consumers to enqueue a requested operation (WQEs) onto a Work Queue. See [RDMAC]. 4. Motivations The goal of this draft is twofold. One is to extend support from the current client-server model for RDMA connection setup to a peer-to- Kanevsky, et al. Expires December 15, 2011 [Page 5] Internet-Draft Enhanced RDMA Connection Establishment June 2011 peer model. The second is to add negotiation of RDMA Read queue size for both sides of an RDMA connection. 4.1. Enabling MPA Mode MPA defines encoding of DDP Segments in FULPDUs (Framed Upper Layer Protocol PDUs). Generation of FULPDUs requires the ability to periodically insert MPA Markers and to generate the MPA CRC-32c for each frame. Reception may require parsing/removing the markers after using them to identify MPA Frame boundaries, and validation of the MPA-CRC32c. A major design objective for MPA was to ensure that the resulting TCP stream would be a fully compliant TCP stream for any and all TCP- aware middle-boxes. The challenge is that while only some TCP payload streams are a valid stream of MPA FULPDUs, any sequence of bytes is a valid TCP payload stream. The determination that a given stream is in a specific MPA mode cannot be made at the MPA or TCP layer. Therefore enabling of MPA mode is handled by the Upper Level Protocol (ULP). The MPA protocol can be viewed as having two parts. o a specification of generation and reception of MPA FULPDUs. This is unchanged by enhanced RDMA connection establishment. o a pre-MPA exchange of messages to enable a specific MPA mode for the TCP connection. enhanced RDMA connection establishment extends this protocol with two new features. In typical implementations, generation and reception of MPA FULPDUs is handled by hardware. The exchange of the MPA Request and Reply frames is then handled by host software. As will be explained, this implementation split impedes applications which are not compatible with the client-server assumptions in the current MPA Request/Reply exchange. 4.2. Lack of Explicit RTR in MPA Request/Reply Exchange The exchange of MPA Request and Reply messages to place a TCP connection in MPA mode is specified in [RFC5044]. This protocol provides many benefits to the design of MPA FULPDU hardware: o The ULP is responsible for specifying the exact MPA Mode (Markers enabled or disabled, CRC-32c enabled or suppressed) and the point in the TCP streams (inbound and outbound) where MPA frames will begin. Kanevsky, et al. Expires December 15, 2011 [Page 6] Internet-Draft Enhanced RDMA Connection Establishment June 2011 o Before the first MPA frame is transmitted, all pre-MPA mode TCP payload will have been acknowledged by the peer. Therefore it is never necessary to generate a retransmission that mixes pre-MPA and MPA payload. o Before MPA reception is enabled, all incoming pre-MPA mode TCP payload will have been acknowledged. Therefore the host will never receive a TCP segment that mixes pre-MPA and MPA payload. The limitation of the current MPA Request/Reply exchange is that it does not define a Ready to Receive (RTR) message that the active side would send, so that the passive side can know that the last non-MPA payload (the MPA Reply) had been received. Instead, the role of an RTR message is piggy-backed on the first MPA FULPDU sent by the active side. This is actually a valuable optimization for all applications that fit the classic client/server model. The client only initiates the connection when it has a request to send to the server, and the server has nothing to send until it has received and processed the client request. Even applications where the server sends some configuration data immediately can easily send the same information as application private data in the MPA Reply. So the currently defined exchange works for almost all applications. Many peer-to-peer applications, especially those involving cluster calculations (frequently using MPI [UsingMPI], or [RDS]), have no natural client or server roles ([PPMPI], [OpenMP]). Typically one member of the cluster is arbitrarily selected to initiate the connection when the distributed task is launched, while the other accepts it. At startup time, however, there is no way to predict which node will have the first message to actually send. Establishing the connections immediately, however, is valuable because it reduces latency once results are ready to transmit and it validates connectivity throughout the cluster. The lack of an explicit RTR message in the MPA Request/Reply exchange forces all applications to have a first message from the connection Initiator, whether this matches the application communication model or not. 4.3. Limitations on ULP Workaround The requirement that the RDMA connection Initiator sends the first message does not appear to be onerous on first examination. The natural question is why the application layer would not simply generate a "nop" message when there was no other message to submit. Kanevsky, et al. Expires December 15, 2011 [Page 7] Internet-Draft Enhanced RDMA Connection Establishment June 2011 There are three factors that make this workaround unsuitable for many peer-to-peer applications. o Transport Neutral APIs. o Work/Completion Queue Accounting. o Host-based implementation of MPA Fencing. 4.3.1. Transport Neutral APIs Many of these applications access RDMA services using a transport neutral API such as [DAPL] or [OFA]. Only RDDP over TCP [RFC5044] has a first message requirement. Other RDMA transports, including RDDP over SCTP (see [RFC5043]) and InfiniBand (see [IBTA]), do not. Application or middleware communications can be expressed as transport neutral RDMA operations, allowing lower software layers to translate to transport and device specifics. Having a distinct extra message that is required only for one transport undermines the application's goal of being transport neutral. 4.3.2. Work/Completion Queue Accounting RDMA local APIs conventionally use work queues to submit requests (work queue elements or WQEs) and to asynchronously receive completions (in completion queues or CQs). Each work request can generate a completion queue entry (CQE). Completions for successful transmit work requests are frequently suppressed, but the completion queue capacity must account for the possibility that each will complete in error. A completion queue can receive completions from multiple work queues. Completion Queues are defined so as to allow hardware RDMA implementations to generate CQEs directly to a user-space mapped buffer. This enables a user-space RDMA consumer to reap completions without requiring kernel intervention. A hardware RDMA implementation cannot reasonably wait for an available slot in the completion queue. The queue must be sized such that an overflow will not occur. When an overflow does occur it is considered catastrophic and will typically require tearing down all RDMA connections using that CQ. This style of interface is very efficient, but places a burden on the application to properly size each Completion Queue to match the Work Queues that feed it. Kanevsky, et al. Expires December 15, 2011 [Page 8] Internet-Draft Enhanced RDMA Connection Establishment June 2011 While the format of both WQEs and CQEs is transport and device dependent, a transport neutral API can deal with WQEs and CQEs as abstract transport and device neutral objects. Therefore the number of WQEs and CQEs required for an application can be transport and device neutral. The capacity of the work queues and completion queues can be calculated in an abstract transport/device neutral fashion. If a nop approach was used, it would require lower layers to know the usage model, and would disrupt the calculations by inserting a dummy "nop" Work Request and filtering out the matching completion. The lower layer does not know the usage model on which the queue sizes are built, nor does it know how frequently an insertion will be required. 4.3.3. Host-based Implementation of MPA Fencing Many hardware implementations of RDDP using MPA/TCP do not handle the MPA Request/Reply exchange in hardware, rather they are handled by the host processor in software. With such designs it is common for the MPA Fencing to be implemented in the user-space device-specific library (commonly referred to as a 'User Verbs' library or module). When the generation and reception of MPA FULPDUs is already dedicated to hardware, a Work Completion can only be generated by an untagged message since arrival of a message for tagged buffer does not necessarily generates a completion and is done without any interaction with ULP [RFC5040]. 4.4. Standardized RDMA Parameter Negotiation Most RDMA applications are developed using a transport neutral API to access RDMA services based on a "queue pair" paradigm as originally defined by the Virtual Interface Architecture [VIA], refined by the Direct Access Programming Library [DAPL] and most commonly deployed with the OpenFabrics API [OFA]. These transport neutral APIs seek to provide a common set of RDMA services whether the underlying transport is, for example, RDDP over MPA, RDDP over SCTP or InfiniBand. The common model for establishing an RDMA connection has the following steps: o The passive side ULP listens for connection requests. o The active side ULP submits a connection request using an RDMA endpoint ("queue pair"), the desired destination and the parameters to be used for the connection. Those parameters Kanevsky, et al. Expires December 15, 2011 [Page 9] Internet-Draft Enhanced RDMA Connection Establishment June 2011 include both RDMA layer characteristics, such as the RDMA Read credits to be allowed and application specific data (typically referred to as "private data"). o The passive side ULP receives the Connection Request, which includes the identity of the active side and the requested connection characteristics. The passive side ULP uses this information to decide whether to accept the connection, and if it is to be accepted, how to create and/or configure the RDMA endpoint. o If accepting, the passive side ULP submits its acceptance of the Connection Request. This local accept operation includes the RDMA endpoint to be used and the connection characteristics (both the RDMA configuration and any application specific private data to be returned). o The active side receives confirmation that the connection has been accepted, what the configured connection characteristics are, and any application supplied private data. As currently defined, DDP connection establishment requires the ULP to encode the RDMA configuration in the application specific private data. This results undesirable duplication of logic to cover both InfiniBand and RDDP, and to specify the extraction of the RDMA characteristics from the ULP for each specific Upper Layer Protocol. Both RDDP and InfiniBand support an initial private data exchange, therefore a standard definition of the RDMA characteristics within the private data section would enable common connection establishment APIs to format the RDMA characteristics based on the same API information used when establishing either protocol to form the connection. The application would then only have to indicate that it was using this standard format to enable common connection establishment procedures to apply common code to properly parse these fields and configure the RDMA endpoints accordingly. 5. Enhanced MPA Connection Establishment Below we provide an overview of Enhanced Connection Setup. The goal is to allow standard negotiation of ORD/IRD setting on both sides of the RDMA connection and/or to negotiate the initial data transfer operation by Initiator when the existing 'client sends first' rule does not match application requirements. The RDMA connection Initiator sends an MPA Request, as specified in [RFC5044]; the new format defined here allows for: Kanevsky, et al. Expires December 15, 2011 [Page 10] Internet-Draft Enhanced RDMA Connection Establishment June 2011 o Standardized negotiation of ORD and IRD. o Negotiation of an RTR message. The RDMA connection Responder processes the MPA Request and generates an MPA Reply, as specified in [RFC5044]; the new format completes the negotiation. The local interface SHOULD require the ULP to explicitly configure on a per-application or per-connection basis when an explicit RTR message will be required. Piggy-backing the RTR on a Client's first message is a valuable optimization for most connections. The RDMA connection Initiator MUST NOT allow any later FULPDUs to be transmitted before the RTR message. One method to achieve that is to delay notifying the ULP that the RDMA connection has been established until after any required RTR Message has been transmitted. All MPA exchanges are performed via TCP prior to RDMA establishment, and are therefore signaled via TCP and not via RDMA completion. 6. Enhanced MPA Request/Reply Frames Enhanced RDMA connection establishment uses an alternate format for MPA Requests and Replies, as follows: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 0 | | + Key (16 bytes containing "MPA ID Req Frame") + 4 | (4D 50 41 20 49 44 20 52 65 71 20 46 72 61 6D 65) | + Or (16 bytes containing "MPA ID Rep Frame") + 8 | (4D 50 41 20 49 44 20 52 65 70 20 46 72 61 6D 65) | + + 12 | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 16 |M|C|R|S| Res | Rev | PD_Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | ~ ~ ~ Private Data ~ | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Kanevsky, et al. Expires December 15, 2011 [Page 11] Internet-Draft Enhanced RDMA Connection Establishment June 2011 Key: Unchanged from [RFC5044]. M: Unchanged from [RFC5044]. C: Unchanged from [RFC5044]. R: Unchanged from [RFC5044]. S: One if the Private Data begins with the enhanced RDMA connection establishment data. Zero otherwise. Res: One bit smaller than in [RFC5044], otherwise unchanged. In [RFC5044] this field plus one more bit S used for enhancement is reserved for future use and since it MUST be set to zero when sending, and not checked on reception. Hence, it is backward compatible to the original MPA frame format. With S bit set to zero when no extra private data used for enhanced RDMA connection establishment the MPA request/reply frame is identical to unenhanced protocol. Unenhenced Responder/Initiator MUST NOT check this field, hence no impact on existing implementations. Rev: This field contains the revision of MPA. To use any enhanced connection establishment feature this MUST be set to two or higher, If no enhanced connection establishment features are desired it MAY be set to one. A host accepting MPA connections MUST continue to accept MPA Requests with version one even if it supports version two. PD_Length: Unchanged from [RFC5044]. This is the total length of the Private Data field, including the enhanced RDMA connection establishment data if present. Private Data: Unchanged from [RFC5044]. However, if the 'S' flag is set, Private Data begins with enhanced RDMA connection establishment data. 7. Enhanced SCTP Session Control Chunks The type of the SCTP Session Control Chunk is defined by a Function Code (see [RFC4960]). [RFC5043] already defines codes for 'DDP Stream Session Initiate' and 'DDP Stream Session Accept', which are equivalent to a MPA Request Frame and an accepting MPA Reply Frame. Enhanced RDMA connection establishment requires three additional Function codes. All DDP Stream Session Functional Codes are listed below: Kanevsky, et al. Expires December 15, 2011 [Page 12] Internet-Draft Enhanced RDMA Connection Establishment June 2011 DDP Stream Session Initiate: 0x001 DDP Stream Session Accept: 0x002 DDP Stream Session Reject: 0x003 DDP Stream Session Terminate: 0x004 Enhanced DDP Stream Session Initiate: 0x005 Enhanced DDP Stream Session Accept: 0x006 Enhanced DDP Stream Session Reject: 0x007 The Enhanced Reject function code MUST be used to indicate rejection of enhanced DDP stream session for a configuration that would have been accepted for unenhanced DDP Stream Session negotiation. The Enhanced DDP stream session establishment follows the same rules as the standard DDP stream session establishment as defined in [RFC5043]. ULP-supplied Private Data MUST be included for Enhanced DDP Stream Session Initiate, Enhanced DDP Stream Session Accept, and Enhanced DDP Stream Session Reject messages. Private Data length MUST NOT exceed 512 bytes in any message, including enhanced RDMA connection establishment data. Private Data MUST NOT be included in the DDP Stream Session Terminate message. Received Extended DDP Stream Session Control messages SHOULD be reported to the ULP. If reported, any supplied Private Data MUST be available for the ULP to examine. An example, when received Extended DDP Stream Session Control message is not reported to ULP if none of the requested RTR message types are supported by receiver. In this case, Provider CAN generate reject reply message indicating which RTR message types it supports. The enhanced DDP stream management MUST use the DDP stream session termination function code to terminate a stream established using enhanced DDP stream session function codes. [RFC5043] already supports either side sending the first DDP Message since the Payload Protocol Identifier (PPID) already distinguishes between Session Establishment and DDP Segments. The enhanced RDMA Connection Establishment provides to the ULP a transport independent way to support peer-to-peer model. Kanevsky, et al. Expires December 15, 2011 [Page 13] Internet-Draft Enhanced RDMA Connection Establishment June 2011 The following additional Legal Sequences of DDP Stream Session messages are defined: o Enhanced Active/Passive Session Accepted: as with section 6.2 of [RFC5043], but with the extended opcodes as defined in this document. o Enhanced Active/Passive Session Rejected: as with section 6.3 of [RFC5043], but with the extended opcodes as defined in this document. o Enhanced Active/Passive Session Non-ULP Rejected: as with section 6.4 of [RFC5043], but with the extended opcodes as defined in this document. 8. MPA Error Reporting The RDMA connection establishment protocol is layered upon [RFC5040] and [RFC5041]. Any enhanced RDMA connection establishment error generates an MPA termination message to a peer. [RFC5040] defines a triplet of protocol layers, error types and error codes for error specification. MPA negotiation for RDMA connection establishment uses the following layer and error type for MPA error reporting: Layer: 0010b - LLP/MPA Error Type: 0x3 - Lower Layer Protocol (LLP) While [RFC5044] defines four error codes, [RFC5043] does not define any. Enhanced RDMA connection establishment extends [RFC5044] error codes by adding two new error codes. Thus, enhanced RDMA connection establishment is backward compatible with both [RFC5043] and [RFC5044]. The following error codes are defined for enhanced RDMA connection establishment negotiation: Error Code Description -------------------------------------------------------- 0x5 Local Catastrophic 0x6 Insufficient IRD resources 0x7 No matching RTR option Kanevsky, et al. Expires December 15, 2011 [Page 14] Internet-Draft Enhanced RDMA Connection Establishment June 2011 9. Enhanced RDMA Connection Establishment Data 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 0 |A|B| IRD |C|D| ORD | 4 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ IRD: In request: Maximum IRD Initiator can support for the requested connection. In reply: Responder local endpoint IRD setting. ORD: In request: Initiator ORD setting for the connection that corresponds to Initiator requested IRD at the peer. In reply: Responder local endpoint ORD setting. A: Control Flag that indicates whether peer-to-peer or client-server model is requested. The TRUE value represents peer-to-peer model with B, C, and D flags representing types of Ready to Receive (RTR) message supported by Initiator and accepted by Responder, respectively. The FALSE value represents client-server model and values of flags B, C, D MUST be set to zero on transmit and ignored on receive by both Initiator and Responder. B: Control Flag for using a zero length FULPDU as the RTR message. C: Control Flag for using a zero length RDMA Write as the RTR message. D: Control Flag for using a zero length RDMA Read as the RTR message. For ORD/IRD negotiation both Responder and Initiator MUST pass the remote side provided IRD and ORD to ULP. Responder SHOULD set its IRD at least to Initiator ORD, unless it does not have sufficient resources for it. Responder SHOULD NOT set its IRD higher than Initiator ORD. For example, Responder MAY set IRD to one if Initiator ORD is zero and Responder supports zero-size RDMA Read RTR message. Responder MUST set its ORD at most to the Initiator IRD. Responder CAN reject connection request if Initiator IRD is not sufficient for ULP required ORD and specify in MPA Reject frame Responder required ORD. An all ones value (0x3FFF) indicates that automatic negotiation of the IRD and ORD is not desired, and that the ULP will be responsible for doing this configuration. Upon receiving MPA Accept frame from Responder, Initiator MUST set Kanevsky, et al. Expires December 15, 2011 [Page 15] Internet-Draft Enhanced RDMA Connection Establishment June 2011 its IRD at least to Responder ORD. Upon receiving MPA Accept frame from Responder, Initiator MUST set its ORD at most to Responder IRD. If Initiator does not have sufficient resources to satisfy Responder ORD it MUST terminate the connection and report to local ULP Responder's ORD and IRD with an indicator of insufficient resources to satisfy Responder ORD, and MUST send termination message to Responder indicating insufficient resources. Thus, TERM message MUST contain Layer 2, Error Type 3, Error Code 6. Initiator MUST pass the remote side provided IRD and ORD to ULP for both MPA Accept and Reject. Initiator ULP CAN terminate the established connection if Responder IRD is not sufficient. In the following rules, TRUE value for each Control Flag field corresponds to one, and FALSE corresponds to zero. In the MPA Request, Initiator MUST set Control Flag A to TRUE if peer-to-peer model is requested, zero otherwise. In the MPA Request, Initiator MUST set each Control Flags B, C and D to TRUE for each of the options it supports, if Control Flag A is set to TRUE. If Control Flag A is not set, then Initiator MUST set Control Flags B, C, and D to zero. In the MPA Reply, the Control Flag A MUST match the Control Flag value of MPA Request. If Control Flag A is not set in MPA Reply, then Responder MUST ignore values of remaining Control Flags. In the MPA Reply, if Control Flag A is set then Responder SHOULD set Control Flags B, C and D for the options that Responder will accept as an RTR message. Responder MAY include only RTR options it CAN support that match Initiator Control Flags specified RTR options. MPA Reply SHOULD include all options that Responder CAN support without requiring a connection specific enabling action. For example, if Responder only supports one choice of RTR message, then Responder SHOULD set Control Flag for it only, irrespective what Initiator options specified. Options which require connection specific enabling actions SHOULD NOT be set unless the corresponding flag was set in the MPA Request. Responder MAY choose to limit the number of RTR modes that it enables. For example, it may clear the C flag to disallow zero size RDMA read as RTR message if it does not have sufficient resources to support it, or if negotiated IRD/ORD do not allow this option. When Control Flags B, C, and D are not set, but A is set in the MPA Reply indicates that an RDMA Send message will be required. As this option will require Initiator ULP to be involved it MUST NOT be used Kanevsky, et al. Expires December 15, 2011 [Page 16] Internet-Draft Enhanced RDMA Connection Establishment June 2011 unless necessary. It SHOULD only be used if ULP requires peer-to- peer model support and Responder does not support any RTR options presented by Initiator. Upon receiving MPA accept frame with Control Flag A set, Initiator MUST generate any of the negotiated RTR messages. If Initiator CAN NOT generate any of the Responder supported RTR messages, then it MUST terminate the connection and report to local ULP inability to support peer-to-peer connection model to satisfy Responder RTR message options, and MUST send termination message to Responder indicating no matching RTR option. Thus, TERM message MUST contain Layer 2, Error Type 3, Error Code 7. ULP CAN negotiate ULP level RTR message when local and remote Providers do not have an RTR match. The RTR message type and ORD/IRD negotiation follows the following order: Initiator -->: Sets Control Flags to indicate Initiator connection model, and for peer-to-peer one the Initiator-supported forms of RTR and Initiator initial IRD, and ORD setting on local Endpoint of the connection Responder <--: Sets Control Flags to indicate Responder-supported forms of RTR or peer-to-peer connection model and the ORD/IRD depth Responder will support Initiator -->: After Initiator modifies its ORD/IRD to match Responder's ones s stated above, and if peer-to-peer model is requested and at least one form of RTR is supported by both Initiator and Responder, then the first message sent by Initiator MUST be an RTR using a form supported by both the Initiator and Responder. Initiator or Responder MUST generate the TERM message that contains Layer 2, Error Type 3, Error Code 5 when it encounters any error locally for which the special Error Code is not defined in section Section 8 before resetting the connection. 10. Interoperability Initiator MUST NOT use the enhanced RDMA connection establishment formats or function codes when no enhanced functionality is desired. Responder MUST continue to accept the unenhanced connection requests. There are three Initiator/Responder cases that involve enhanced MPA: both Initiator and Responder, only Responder, and only Initiator. The enhanced MPA frame is defined by field 'S' set to 1. Kanevsky, et al. Expires December 15, 2011 [Page 17] Internet-Draft Enhanced RDMA Connection Establishment June 2011 Enhanced MPA Initiator and Responder: If Responder receives an enhanced MPA message, it MUST respond with an enhanced MPA message. Enhanced MPA Responder only: If Responder receives an unenhanced MPA message ('S' is set to 0), it MUST respond with an unenhanced MPA message. Enhanced MPA Initiator only: If Responder receives an enhanced MPA message and it does not support enhanced RDMA connection establishment, it MUST close the TCP connection and exit MPA. From standard RDMA connection establishment point of view enhanced MPA frame is improperly formatted as stated in [RFC5044]. Thus, both Initiator and Responder report TCP connection termination to an application locally. In this case Initiator MAY attempt to establish RDMA connection using unenhanced MPA protocol as defined in [RFC5044] if this protocol is compatible with the application, and let ULP deal with ORD and IRD, and peer-to-peer negotiations. 11. IANA Considerations This document has no IANA considerations. 12. Security Considerations The security considerations from RFC 5044 apply and the changes in this document do not introduce new security considerations. 13. Acknowledgements The authors wish to thank Sean Hefty, Dave Minturn, Tom Talpey and David Black for their valuable contributions and reviews of this document. 14. References 14.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC4960] Stewart, R., "Stream Control Transmission Protocol", RFC 4960, September 2007. Kanevsky, et al. Expires December 15, 2011 [Page 18] Internet-Draft Enhanced RDMA Connection Establishment June 2011 [RFC5040] Recio, R., Metzler, B., Culley, P., Hilland, J., and D. Garcia, "A Remote Direct Memory Access Protocol Specification", RFC 5040, October 2007. [RFC5041] Shah, H., Pinkerton, J., Recio, R., and P. Culley, "Direct Data Placement over Reliable Transports", RFC 5041, October 2007. [RFC5043] Bestler, C. and R. Stewart, "Stream Control Transmission Protocol (SCTP) Direct Data Placement (DDP) Adaptation", RFC 5043, October 2007. [RFC5044] Culley, P., Elzur, U., Recio, R., Bailey, S., and J. Carrier, "Marker PDU Aligned Framing for TCP Specification", RFC 5044, October 2007. 14.2. Informative References [DAPL] "Direct Access Programming Library", . [IBTA] "InfiniBand Architecture Specification Release 1.2.1", . [OFA] "OFA verbs & APIs", . [OpenMP] McGraw-Hill, "Parallel Programming in C with MPI and OpenMP", 2003. [PPMPI] Morgan Kaufmann Publishers Inc., "Parallel Programming with MPI", 2008. [RDMAC] "RDMA Protocol Verbs Specification (Version 1.0)", . [RDS] Open Fabrics Association, "Reliable Datagram Socket", 2008, . [UsingMPI] MIT Press, "Using MPI-2: Advanced Features of the Message Passing Interface", 1999. [VIA] Compaq, Intel, Microsoft, "Virtual Interface Architecture Specification", 1997, . Kanevsky, et al. Expires December 15, 2011 [Page 19] Internet-Draft Enhanced RDMA Connection Establishment June 2011 Authors' Addresses Arkady Kanevsky (editor) VMware 5 Cambridge Center Cambridge, MA 02142 USA Phone: +1-617-528-7721 Email: arkady.kanevsky@gmail.com Caitlin Bestler (editor) Nexenta Systems 555 E El Camino Real #104 Sunnyvale, CA 94087 USA Phone: +1-949-528-3085 Email: Caitlin.Bestler@nexenta.com Robert Sharp Intel LAD High Performance Message Passing, Mailstop: AN1-WTR1 1501 South Mopac, Suite 400 Austin, TX 78746 USA Phone: +1-512-493-3242 Email: robert.o.sharp@intel.com Steve Wise Open Grid Computing 4030 Braker Lane STE 130 Austin, TX 78759 USA Phone: +1-512-343-9196 x101 Email: swise@opengridcomputing.com Kanevsky, et al. Expires December 15, 2011 [Page 20]