Applicability of Remote Direct Memory Access Protocol (RDMA) and Direct Data Placement (DDP)
RFC 5045

Document Type RFC - Informational (October 2007; No errata)
Updated by RFC 7146
Last updated 2013-03-02
Replaces draft-bestler-rddp-applicability
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IESG IESG state RFC 5045 (Informational)
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Responsible AD Jon Peterson
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Network Working Group                                    C. Bestler, Ed.
Request for Comments: 5045                                      Neterion
Category: Informational                                         L. Coene
                                                  Nokia Siemens Networks
                                                            October 2007

      Applicability of Remote Direct Memory Access Protocol (RDMA)
                and Direct Data Placement Protocol (DDP)

Status of This Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Abstract

   This document describes the applicability of Remote Direct Memory
   Access Protocol (RDMAP) and the Direct Data Placement Protocol (DDP).
   It compares and contrasts the different transport options over IP
   that DDP can use, provides guidance to ULP developers on choosing
   between available transports and/or how to be indifferent to the
   specific transport layer used, compares use of DDP with direct use of
   the supporting transports, and compares DDP over IP transports with
   non-IP transports that support RDMA functionality.

Bestler & Coene              Informational                      [Page 1]
RFC 5045                 RDMA/DDP Applicability             October 2007

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Definitions  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Direct Placement . . . . . . . . . . . . . . . . . . . . . . .  5
     3.1.  Direct Placement Using Only the LLP  . . . . . . . . . . .  5
     3.2.  Fewer Required ULP Interactions  . . . . . . . . . . . . .  6
   4.  Tagged Messages  . . . . . . . . . . . . . . . . . . . . . . .  6
     4.1.  Order-Independent Reception  . . . . . . . . . . . . . . .  7
     4.2.  Reduced ULP Notifications  . . . . . . . . . . . . . . . .  7
     4.3.  Simplified ULP Exchanges . . . . . . . . . . . . . . . . .  8
     4.4.  Order-Independent Sending  . . . . . . . . . . . . . . . .  9
     4.5.  Untagged Messages and Tagged Buffers as ULP Credits  . . . 10
   5.  RDMA Read  . . . . . . . . . . . . . . . . . . . . . . . . . . 12
   6.  LLP Comparisons  . . . . . . . . . . . . . . . . . . . . . . . 13
     6.1.  Multistreaming Implications  . . . . . . . . . . . . . . . 13
     6.2.  Out-of-Order Reception Implications  . . . . . . . . . . . 13
     6.3.  Header and Marker Overhead . . . . . . . . . . . . . . . . 13
     6.4.  Middlebox Support  . . . . . . . . . . . . . . . . . . . . 14
     6.5.  Processing Overhead  . . . . . . . . . . . . . . . . . . . 14
     6.6.  Data Integrity Implications  . . . . . . . . . . . . . . . 14
       6.6.1.  MPA/TCP Specifics  . . . . . . . . . . . . . . . . . . 15
       6.6.2.  SCTP Specifics . . . . . . . . . . . . . . . . . . . . 15
     6.7.  Non-IP Transports  . . . . . . . . . . . . . . . . . . . . 15
       6.7.1.  No RDMA-Layer Ack  . . . . . . . . . . . . . . . . . . 16
     6.8.  Other IP Transports  . . . . . . . . . . . . . . . . . . . 16
     6.9.  LLP-Independent Session Establishment  . . . . . . . . . . 17
       6.9.1.  RDMA-Only Session Establishment  . . . . . . . . . . . 17
       6.9.2.  RDMA-Conditional Session Establishment . . . . . . . . 18
   7.  Local Interface Implications . . . . . . . . . . . . . . . . . 18
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 19
     8.1.  Connection/Association Setup . . . . . . . . . . . . . . . 19
     8.2.  Tagged Buffer Exposure . . . . . . . . . . . . . . . . . . 19
     8.3.  Impact of Encrypted Transports . . . . . . . . . . . . . . 19
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 19
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 19
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 19

Bestler & Coene              Informational                      [Page 2]
RFC 5045                 RDMA/DDP Applicability             October 2007

1.  Introduction

   Remote Direct Memory Access Protocol (RDMAP) [RFC5040] and Direct
   Data Placement (DDP) [RFC5041] work together to provide application-
   independent efficient placement of application payload directly into
   buffers specified by the Upper Layer Protocol (ULP).

   The DDP protocol is responsible for direct placement of received
   payload into ULP-specified buffers.  The RDMAP protocol provides
   completion notifications to the ULP and support for Data-Sink-
   initiated fetch of Advertised Buffers (RDMA Reads).

   DDP and RDMAP are both application-independent protocols that allow
   the ULP to perform remote direct data placement.  DDP can use
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