Stream Control Transmission Protocol (SCTP) Direct Data Placement (DDP) Adaptation
RFC 5043
| Document | Type |
RFC - Proposed Standard
(October 2007; No errata)
Was draft-ietf-rddp-sctp (rddp WG)
|
|
|---|---|---|---|
| Authors | Caitlin Bestler , Randall Stewart | ||
| Last updated | 2015-10-14 | ||
| Stream | Internet Engineering Task Force (IETF) | ||
| Formats | plain text html pdf htmlized bibtex | ||
| Reviews | |||
| Stream | WG state | (None) | |
| Document shepherd | No shepherd assigned | ||
| IESG | IESG state | RFC 5043 (Proposed Standard) | |
| Action Holders |
(None)
|
||
| Consensus Boilerplate | Unknown | ||
| Telechat date | |||
| Responsible AD | Lars Eggert | ||
| Send notices to | (None) | ||
Network Working Group C. Bestler, Ed.
Request for Comments: 5043 Neterion
Category: Standards Track R. Stewart, Ed.
Cisco Systems, Inc.
October 2007
Stream Control Transmission Protocol (SCTP)
Direct Data Placement (DDP) Adaptation
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Abstract
This document specifies an adaptation layer to provide a Lower Layer
Protocol (LLP) service for Direct Data Placement (DDP) using the
Stream Control Transmission Protocol (SCTP).
Bestler & Stewart Standards Track [Page 1]
RFC 5043 SCTP DDP Adaptation October 2007
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Conventions . . . . . . . . . . . . . . . . . . . . . . . 3
2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
5. Data Formats . . . . . . . . . . . . . . . . . . . . . . . . . 5
5.1. Adaptation Layer Indicator . . . . . . . . . . . . . . . . 5
5.2. Payload Data Chunks . . . . . . . . . . . . . . . . . . . 6
5.2.1. DDP Source Sequence Number (DDP-SSN) . . . . . . . . . 6
5.2.2. DDP Segment Chunk . . . . . . . . . . . . . . . . . . 7
5.2.3. DDP Stream Session Control . . . . . . . . . . . . . . 7
6. DDP Stream Sessions . . . . . . . . . . . . . . . . . . . . . 8
6.1. Sequencing . . . . . . . . . . . . . . . . . . . . . . . . 9
6.2. Legal Sequence: Active/Passive Session Accepted . . . . . 9
6.3. Legal Sequence: Active/Passive Session Rejected . . . . . 9
6.4. Legal Sequence: Active/Passive Session Non-ULP Rejected . 10
6.5. ULP-Specific Sequencing . . . . . . . . . . . . . . . . . 10
6.6. Other Sequencing Rules . . . . . . . . . . . . . . . . . . 10
7. SCTP Endpoints . . . . . . . . . . . . . . . . . . . . . . . . 11
7.1. Adaptation Layer Indication Restriction . . . . . . . . . 11
7.2. Multihoming Implications . . . . . . . . . . . . . . . . . 11
8. Number of Streams . . . . . . . . . . . . . . . . . . . . . . 12
9. Fragmentation . . . . . . . . . . . . . . . . . . . . . . . . 12
10. Sequenced Unordered Operation . . . . . . . . . . . . . . . . 13
11. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . 13
11.1. Association Initialization . . . . . . . . . . . . . . . . 13
11.2. Chunk Bundling . . . . . . . . . . . . . . . . . . . . . . 14
11.3. Association Termination . . . . . . . . . . . . . . . . . 14
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
13. Security Considerations . . . . . . . . . . . . . . . . . . . 15
14. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 16
15. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 16
16. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
16.1. Normative References . . . . . . . . . . . . . . . . . . . 16
16.2. Informative References . . . . . . . . . . . . . . . . . . 16
Bestler & Stewart Standards Track [Page 2]
RFC 5043 SCTP DDP Adaptation October 2007
1. Introduction
This document describes a method to adapt Direct Data Placement
[RFC5041] to Stream Control Transmission Protocol (SCTP) [RFC4960].
Some implementations may include this adaptation layer within their
SCTP implementations to obtain maximum performance, but the behavior
of SCTP will be unaffected. An SCTP layer used solely by this
adaptation layer is able to take certain optimizations based on the
limited subset of SCTP capabilities used. In order to allow
optimization for these implementations, we specify the use of the new
adaptation layer indication as defined in [RFC5061]
1.1. Conventions
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 RFC 2119 [RFC2119].
2. Definitions
DDP - See Direct Data Placement Protocol.
DDP Endpoint - The logical sender/receiver of DDP Segments. An SCTP
stream pair is not assumed to have a DDP Endpoint. DDP Segments
may only be sent once a DDP Endpoint has been assigned to an SCTP
stream pair by a local interface.
DDP Source Stream Sequence Number (DDP-SSN) - A stream-specific
sequence number assigned by the adaptation layer for each SCTP
Data Chunk sent. This is the order that chunks were submitted to
SCTP, no matter in what order they are actually sent or received.
DDP Segment - The smallest unit of data transfer for the DDP
protocol. It includes a DDP Header and ULP Payload (if present).
A DDP Segment should be sized to fit within the Lower Layer
Protocol MULPDU (Marker PDU Aligned (MPA) Upper Layer PDU).
DDP Segment Chunk - An SCTP Payload Data Chunk that encapsulates the
DDP-SSN and a DDP Segment.
DDP Stream - A sequence of DDP Segments whose ordering is defined by
the LLP. For SCTP, a DDP stream maps directly to a bidirectional
pair of SCTP streams with the same Stream IDs. Note that DDP has
no ordering guarantees between DDP streams.
Bestler & Stewart Standards Track [Page 3]
RFC 5043 SCTP DDP Adaptation October 2007
DDP Stream Session - A single pairing of DDP Endpoints over a DDP
stream that lasts from an Initiation message through the
Termination message(s).
DDP Stream Session Control Message - A message that is used to
control the association of the DDP Endpoint with the DDP stream.
Direct Data Placement Protocol (DDP) - A wire protocol that supports
Direct Data Placement by associating explicit memory buffer
placement information with the LLP payload units.
Lower Layer Protocol (LLP) - In the context of DDP, the protocol
layer beneath RDMA that provides a reliable transport service.
The SCTP DDP adaption is one of the initially defined LLPs for
DDP.
Protection Domain - A common local interface convention to control
which Steering Tags (STags) are valid with which DDP Endpoints.
Under this convention, both the Steering Tag and DDP Endpoint are
created within the context of a Protection Domain, and the
Steering Tag may only be enabled for DDP Endpoints created under
the same Protection Domain.
RDMA - Remote Direct Memory Access.
RNIC - RDMA Network Interface Card.
SCTP association - A protocol relationship between two SCTP
endpoints. An SCTP association supports multiple SCTP streams.
SCTP Data Chunk - An SCTP Chunk used to convey Payload Data. There
can be multiple Chunks within each SCTP packet. Other Chunks are
used to control the SCTP Association.
SCTP endpoint - The logical sender/receiver of SCTP packets. On a
multihomed host, an SCTP endpoint is represented to its peers as a
combination of an SCTP port number and a set of eligible
destination transport addresses to which SCTP packets can be sent.
SCTP Stream - A unidirectional logical channel established from one
to another associated SCTP endpoint. There can be multiple SCTP
streams within each SCTP association. An SCTP stream is used to
form one direction of a DDP stream.
Transmission Sequence Number (TSN) - A 32-bit sequence number used
internally by SCTP. One TSN is attached to each chunk containing
user data to permit the receiving SCTP endpoint to acknowledge its
receipt and detect duplicate deliveries.
Bestler & Stewart Standards Track [Page 4]
RFC 5043 SCTP DDP Adaptation October 2007
Upper Layer Protocol (ULP) - In the context of RDMA protocol
specifications, this is the layer using RDMA services. Typically,
this is an application or middleware. A primary goal of RDMA
protocols is to enable direct transfer of payload to/from ULP
Buffers.
3. Motivation
This document specifies an adaptation layer which fulfills the
requirements of a Lower Layer Protocol (LLP) for DDP using a specific
subset of SCTP capabilities.
The defined protocol is intended to be implementable over existing
SCTP stacks, while clearly defining what portions of SCTP are
required to enable an implementation to be optimized specifically to
support DDP.
4. Overview
The adaptation layer uses a pair of like-numbered SCTP streams within
an SCTP Association to provide a reliable DDP stream between two DDP
Endpoints. Except as specifically noted, each DDP Segment submitted
by the DDP layer is encoded as a single unordered SCTP Data Chunk.
In addition to the DDP Segment, the Data Chunk also contains a
sequence number (DDP-SSN) that reflects the order in which DDP
submitted the segments for that stream.
A DDP Stream Session is defined by DDP Stream Session Control Chunks
that manage the state of the DDP Stream Session. These Chunks
dynamically bind DDP Endpoints to the DDP Stream Session, and DDP
Segment Chunks are used to reliably deliver DDP Segments with the
session.
5. Data Formats
5.1. Adaptation Layer Indicator
The DDP/SCTP adaptation layer uses all streams within an SCTP
association. An SCTP Association that has had the DDP Adaptation
Indication negotiated will carry only SCTP Data Chunks as defined in
this document.
It is presumed that the handling of incoming data chunks for DDP-
enabled associations is sufficiently different than for routine SCTP
associations that it is undesirable to require support for mixing DDP
and non-DDP streams in a single association. More than a single
association is required if an application desires to utilize both DDP
and non-DDP traffic with the same remote host.
Bestler & Stewart Standards Track [Page 5]
RFC 5043 SCTP DDP Adaptation October 2007
We define an Adaptation Indication that MUST appear in the INIT or
INIT-ACK with the following format as defined in [RFC5061].
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type =0xC006 | Length = Variable |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Adaptation Indication |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Adaptation Indication:
The following value has been assigned for DDP.
DDP - 0x00000001
5.2. Payload Data Chunks
The DDP SCTP adaptation uses two types of SCTP Payload Data Chunks,
differentiated by the Payload Protocol Identifier:
DDP Segment Chunks are used to reliably deliver DDP Segments sent
between DDP Endpoints.
DDP Stream Session Control Messages are used to establish and tear
down DDP Stream Sessions, specifically by controlling the binding
of DDP Endpoints with SCTP streams.
Payload Protocol Identifier:
The following value are defined for DDP in this document
and have been assigned by IANA:
DDP Segment Chunk - 16
DDP Stream Session Control - 17
5.2.1. DDP Source Sequence Number (DDP-SSN)
All SCTP Payload Data Chunks used by this adaptation layer include a
DDP Source Sequence Number (DDP-SSN). The DDP-SSN tracks the
sequence in which the messages were submitted to the SCTP layer for
the SCTP stream in use. The DDP-SSN MUST have the same value that
the SCTP Stream Sequence Number (SSN) would have been assigned had
ordered SCTP Payload Data Chunks been used rather than unordered.
Bestler & Stewart Standards Track [Page 6]
RFC 5043 SCTP DDP Adaptation October 2007
The rationale for specifying the DDP-SSN is as follows:
o The SCTP Stream Sequence Number (SSN) is not suitable for this
purpose because all messages defined by this document use
unordered Payload Data Chunks to ensure prompt delivery from the
receiving SCTP layer.
o The SCTP Transmission Sequence Number (TSN) is not suitable for
determining the original order of Data Chunks within a stream.
The sending SCTP layer is allowed to optimize the transmission
sequence of unordered Data Chunks to encourage Chunk Bundling, or
for other purposes.
5.2.2. DDP Segment Chunk
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DDP-SSN | DDP Segment |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| |
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
DDP Segments are as defined in [RFC5041]. The DDP Segment Chunk
serves the same purpose as the MPA [RFC5044] Upper Layer PDU (MULPDU)
in that it carries DDP Segments over a reliable protocol with added
sequencing information.
5.2.3. DDP Stream Session Control
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DDP-SSN | Function Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Private Data (Dependent on Function Code) |
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The following function code values are defined for DDP in
this document:
DDP Stream Session Initiate - 0x001
DDP Stream Session Accept - 0x002
DDP Stream Session Reject - 0x003
DDP Stream Session Terminate - 0x004
Bestler & Stewart Standards Track [Page 7]
RFC 5043 SCTP DDP Adaptation October 2007
ULP-supplied Private Data MUST be included for DDP Stream Session
Initiate, DDP Stream Session Accept, and DDP Stream Session Reject
messages. However, the ULP supplied Private DATA MAY be of zero
length.
Private Data length MUST NOT exceed 512 bytes in any message.
Private Data MUST NOT be included in the DDP Stream Session Terminate
message.
Received 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.
The DDP/SCTP adaptation layer MAY limit the number of Session
Initiate requests that it has submitted to the ULP. When a DDP
Stream Session Initiate cannot be forwarded to the ULP due to such a
limit, the adaptation layer MUST respond with a DDP Stream Session
Terminate message.
6. DDP Stream Sessions
A DDP Endpoint is the logical sender/receiver of DDP Segments. A DDP
stream connects two DDP Endpoints using a matched pair of SCTP
streams having the same SCTP Stream Identifiers.
A DDP Stream Session defines the sequence of Data Chunks exchanged
between two DDP Endpoints over a DDP stream that has a distinct
beginning and end as defined in the following section. Data Chunks
from one DDP Stream Session are never carried over to the next
session. Each Data Chunk unambiguously belongs to exactly one
session. The DDP-SSNs assigned to the Data Chunks for a session MUST
NOT have any gaps.
The local interface MAY dynamically associate a DDP Endpoint with the
DDP stream based upon the initial exchanges of a DDP Session, and
dynamically terminate that association at the session's end.
Alternately, a specialized local interface could simply statically
map DDP Endpoints to DDP streams.
Conventionally, local interfaces for RDMA have deferred the selection
of the DDP Endpoint until after the ULP decides to accept an RDMA
connection request. But that is a local interface choice and not a
wire protocol requirement.
A DDP stream is associated with at most one Protection Domain during
a single DDP Stream Session. On the passive side, the association is
typically deferred until the DDP Stream Session Accept message.
Bestler & Stewart Standards Track [Page 8]
RFC 5043 SCTP DDP Adaptation October 2007
6.1. Sequencing
The DDP-SSN is reset to zero at the beginning of each DDP Stream
Session.
The normative sequence for considering Payload Data Chunks within a
given session is based upon each Data Chunk's DDP-SSN. When
considered in this normative sequence, all sessions MUST conform to
one of the patterns defined in this section.
If the adaptation layer receives a Payload Data Chunk that conforms
to none of the enumerated legal patterns, the DDP Stream Session MUST
be terminated.
6.2. Legal Sequence: Active/Passive Session Accepted
In this DDP Stream Session sequence, one DDP Endpoint assumes the
active role in requesting a DDP Stream Session, which the other side
accepts.
Active side sends a DDP Stream Session Initiate message.
Passive side sends a DDP Stream Session Accept message.
Each side may then send zero or more DDP Segments with increasing
DDP-SSNs, subject to any flow control imposed by other protocol
layers.
The final User Data Chunk for each side MAY be a DDP Stream
Terminate. At least one side MUST send a DDP Stream Terminate.
Note that this would follow any RDMAP Terminate message, which to
the adaptation layer is simply another DDP Segment.
6.3. Legal Sequence: Active/Passive Session Rejected
DDP Stream Sessions allow each party to send a single non-payload
message before the other end commits specific resources to the
session. This allows each end to determine which resources are to be
used, and how they are to be configured, or even if the session
should be granted.
These decisions MAY be influenced by the need to assign a specific
Protection Domain, to determine how many RDMA Read Credits are
required, or to determine how many receive operations the ULP should
enable.
Bestler & Stewart Standards Track [Page 9]
RFC 5043 SCTP DDP Adaptation October 2007
Because of these or other factors, the passive side MAY choose to
reject a DDP Stream Session Request. This results in the following
legal sequence:
Active side sends a DDP Stream Session Initiate message.
Passive side sends a DDP Stream Session Reject message.
A DDP Stream Session Reject message MUST NOT be sent unless the
rejection is at the direction of the ULP.
6.4. Legal Sequence: Active/Passive Session Non-ULP Rejected
Acceptance or rejection of DDP Stream Session Initiate messages
SHOULD be under the control of the ULP. This MAY require passing an
event to the ULP. There MUST be a finite limit on the number of such
requests that are pending a ULP decision. When more session requests
are received, the passive side MUST respond to the Initiate message
with a DDP Stream Terminate Message.
6.5. ULP-Specific Sequencing
An implementation MAY choose to support additional ULP-specific
sequences, but MUST NOT do so unless requested to do so by the ULP.
A defined ULP MUST be able to operate using only the defined
mandatory session sequences. Any additional sequences must be used
only for optional optimizations.
6.6. Other Sequencing Rules
A DDP Stream Session Control message MUST NOT be sent if it may be
received before a prior DDP Stream Session Control message within the
same DDP Stream Session.
An active side of a DDP Stream Session MUST NOT send a DDP Segment
that might be received before the DDP Stream Session Initiate
message.
This MAY be determined by SCTP acking of the Data Chunk used to carry
the DDP Stream Session Initiate message, or by receipt of a
responsive DDP Stream Session Control message.
A DDP Stream Identifier MUST NOT be reused for another DDP Stream
Session while any Data Chunk from a prior session might be
outstanding.
Bestler & Stewart Standards Track [Page 10]
RFC 5043 SCTP DDP Adaptation October 2007
7. SCTP Endpoints
7.1. Adaptation Layer Indication Restriction
The local interface MUST allow the ULP to specify an SCTP endpoint to
use a specific Adaptation Indication. It MAY require the ULP to do
so.
Once an endpoint decides on its acceptable Adaptation Indication(s),
it SHOULD terminate all requests to establish an association with any
different Adaptation Indication.
An SCTP implementation MAY choose to accept association requests for
a given SCTP endpoint only until one association for the endpoint has
been established. At that point, it MAY choose to restrict all
further associations for the same endpoint to use the same Adaptation
Indication.
7.2. Multihoming Implications
SCTP allows an SCTP endpoint to be associated with multiple IP
addresses, potentially representing different interface devices.
Distribution of the logic for a single DDP stream across multiple
input devices can be very undesirable, resulting in complex cache
coherency challenges. Therefore, the local interface MAY restrict
DDP-enabled SCTP endpoints to a single IP address, or to a set of IP
addresses that are all assigned to the same input device ("RNIC").
The default binding of a DDP-enabled SCTP endpoint SHOULD NOT cover
more than a single IP address unless doing so results in neither
additional bus traffic nor duplication of memory registration
resources. This will frequently result in a different default than
for SCTP endpoints that are not DDP enabled.
Applications MAY choose to avoid using out-of-band methods for
communicating the set of IP addresses used by an SCTP endpoint when
there is potential confusion as to the intended scope of the SCTP
endpoint. For example, assuming the SCTP endpoint consists of all IP
addresses Advertised by DNS may work for a general purpose SCTP
endpoint but not a DDP-enabled one.
Even when multihoming is supported, ULPs are cautioned that they
SHOULD NOT use ULP control of the source address in an attempt to
load-balance a stream across multiple paths. A receiving DDP/SCTP
implementation that chooses to support multihoming SHOULD optimize
its design on the assumption that multihoming will be used for
network fault tolerance, and not to load-balance between paths. This
is consistent with recommended SCTP practices.
Bestler & Stewart Standards Track [Page 11]
RFC 5043 SCTP DDP Adaptation October 2007
8. Number of Streams
DDP streams are bidirectional. They are always composed by pairing
the inbound and outbound SCTP streams with the same SCTP Stream
Identifier.
The adaptation layer should request the maximum number of SCTP
streams it will wish to use over the lifetime of the association.
SCTP streams must still be bound to DDP Endpoints, and a DDP-enabled
SCTP association does not support ordered Data Chunks. Therefore,
the mere existence of an SCTP stream is unlikely to require
significant supporting resources.
This mapping uses an SCTP association to carry one or more DDP
streams. Each DDP stream will be mapped to a pair of SCTP streams
with the same SCTP stream number. The adaptation MUST initialize all
of its SCTP associations with the same number of inbound and outbound
streams.
9. Fragmentation
A DDP/SCTP Receiver already deals with fragmentation at both the IP
and DDP layers. Therefore, use of SCTP layer segmenting will be
avoided for most cases.
As a Lower Layer Protocol (LLP) for DDP, the SCTP adaptation layer
MUST inform the DDP layer of the maximum DDP Segment size that will
be supported. This should be the largest value that can be supported
without use of IP or SCTP fragmentation, or 516 bytes, whichever is
larger.
A minimum of 516 bytes is required to allow a DDP Stream Session
Control Message with 512 bytes of Private Data.
SCTP data chunk fragmentation MUST NOT be used unless the alternative
is IP fragmentation.
The SCTP adaptation layer SHOULD set the maximum DDP Segment size
below the theoretical maximum in order to allow bundling of Control
Chunks in the same SCTP packet.
The SCTP adaptation layer MUST reject DDP Segments that are larger
than the maximum size specified.
Bestler & Stewart Standards Track [Page 12]
RFC 5043 SCTP DDP Adaptation October 2007
10. Sequenced Unordered Operation
The adaptation layer MUST use the Unordered option on all Data Chunks
(U Flag set to one). The SCTP layer is expected to deliver unordered
Data Chunks without delay.
Because DDP employs unordered SCTP delivery, the receiver MUST NOT
rely upon the SCTP Transmission Sequence Number (TSN) to imply
ordering of DDP Segments. The fact that the SCTP Data Chunk for a
DDP Segment is prior to the cumulative ack point does not guarantee
that all prior DDP segments have been placed. The SCTP sender is not
obligated to transmit unordered Data Chunks in the order presented.
The DDP-SSN can be used without special logic to determine the
submission sequence when the maximum number of in-flight messages is
less than 32768. This also applies if the sending SCTP accepts no
more than 32767 Data Chunks for a single stream without assigning
TSNs.
If SCTP does accept more than 32768 Data chunks for a single stream
without assigning TSNs, the sending DDP must simply refrain from
sending more than 32767 Data Chunks for a single stream without
acknowledgment. Note that it MUST NOT rely upon ULP flow control for
this purpose. Typical ULP flow control will deal exclusively with
untagged messages, not with DDP segments.
The receiver MAY perform a validity check on received DDP-SSNs to
ensure that any gap could be accounted for by unreceived Data Chunks.
Implementations SHOULD NOT allocate resources on the assumption that
DDP-SSNs are valid without first performing such a validity check.
An invalid DDP-SSN MAY result in termination of the DDP stream.
11. Procedures
11.1. Association Initialization
At the startup of an association, a DDP/SCTP adaptation layer MUST
include an adaptation layer indication in its INIT or INIT-ACK (as
defined in Section 5.1). After the exchange of the initial first two
SCTP chunks (INIT and INIT-ACK), an endpoint MUST verify and inspect
the Adaptation Indication and compare it to the following table to
determine proper action.
Bestler & Stewart Standards Track [Page 13]
RFC 5043 SCTP DDP Adaptation October 2007
Indication | Action
type |
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
| This indicates that the peer DOES NOT
NONE | support ANY DDP or RDMA adaptation, and thus
| RDMA and DDP procedures MUST NOT be
| performed upon this association.
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
| This indicates that the peer DOES support
DDP | the DDP/SCTP adaptation layer defined here.
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
| This indicates that the peer DOES NOT
ANY-OTHER | support the DDP adaptation, and thus
Indication | DDP procedures MUST NOT be performed
| upon this association.
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
An implementation MAY require that all associations for a given SCTP
endpoint be placed in the same mode.
The local interface MAY allow the ULP to accept only requests to
establish an association in a specified mode.
11.2. Chunk Bundling
SCTP allows multiple Data Chunks to be bundled in a single SCTP
packet. Data chunks containing DDP Segments with untagged messages
SHOULD NOT be delayed to facilitate bundling. Data chunks containing
DDP Segments with tagged messages will generally be full sized, and
hence not subject to bundling. However, partial-size tagged messages
MAY be delayed, as they are frequently followed by a short untagged
message.
11.3. Association Termination
Termination of an SCTP Association due to errors should be handled at
the SCTP layer. The RDMAP-defined RDMAP Terminate Message SHOULD NOT
be sent on each DDP stream when a determination has been made to
terminate an SCTP association. Sending that message on each SCTP
stream could severely delay the termination of the association.
The local interface SHOULD notify all consumers of DDP streams when
the underlying SCTP stream has been terminated.
Other RDMAP-defined Terminate Messages MUST be generated as specified
when a DDP stream is terminated. Note that with the SCTP mapping,
termination of a DDP Stream does not mandate termination of the
Association.
Bestler & Stewart Standards Track [Page 14]
RFC 5043 SCTP DDP Adaptation October 2007
12. IANA Considerations
This document defines a new SCTP Adaptation Layer Indication
codepoint for DDP (0x00000001). [RFC5061] creates the registry from
which this codepoint has been assigned.
This document also defines two new SCTP Payload Protocol Identifiers
(PPIDs). RFC 4960 [RFC4960] creates the registry from which these
identifiers have been assigned. The following values have been
assigned:
DDP Segment Chunk - 16
DDP Stream Session Control - 17
13. Security Considerations
Any direct placement of memory could pose a significant security risk
if adequate local controls are not provided. These threats are
addressed in the appropriate DDP [RFC5041], RDMA [RFC5040], or
Security [RFC5042] documents. This document does not add any
additional security risks over those found in RFC 4960 [RFC4960].
The IPsec requirements for Remote Direct Data Placement (RDDP) are
based on the version of IPsec specified in RFC 2401 [RFC2401] and
related RFCs, as profiled by RFC 3723 [RFC3723], despite the
existence of a newer version of IPsec specified in RFC 4301 [RFC4301]
and related RFCs. One of the important early applications of the
RDDP protocols is their use with iSCSI iSER [RFC5046]; RDDP's IPsec
requirements follow those of IPsec in order to facilitate that usage
by allowing a common profile of IPsec to be used with iSCSI and the
RDDP protocols. In the future, RFC 3723 may be updated to the newer
version of IPsec; the IPsec security requirements of any such update
should apply uniformly to iSCSI and the RDDP protocols.
Additional requirements apply to security for RDDP over SCTP, due to
the use of SCTP as the transport protocol. An implementation of
IPsec for RDDP over SCTP:
1) MUST support IPsec functionality for SCTP equivalent to the IPsec
functionality for TCP that is required by RFC 3723,
2) SHOULD support the same level of IPsec functionality for SCTP and
TCP unless there is no support for TCP, and
3) MUST support at least the level of protocol and port selector
functionality for SCTP that is supported for TCP.
Bestler & Stewart Standards Track [Page 15]
RFC 5043 SCTP DDP Adaptation October 2007
14. Contributors
Many thanks to our contributors who have spent many hours reading and
reviewing keeping us straight: Sukanta Ganguly an independent
consultant, Vivek Kashyap of IBM, Jim Pinkerton of Microsoft, and
Hemal Shah of Broadcom. Thanks for all your hard work.
15. Acknowledgments
The authors would like to thank the following people that have
provided comments and input: Stephen Bailey, David Black, Douglas
Otis, Allyn Romanow, and Jim Williams.
16. References
16.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3723] Aboba, B., Tseng, J., Walker, J., Rangan, V., and F.
Travostino, "Securing Block Storage Protocols over IP",
RFC 3723, April 2004.
[RFC4960] Stewart, R., "Stream Control Transmission Protocol",
RFC 4960, September 2007.
[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.
[RFC5042] Pinkerton, J. and E. Deleganes, "Direct Data Placement
Protocol (DDP) / Remote Direct Memory Access Protocol
(RDMAP) Security", RFC 5042, October 2007.
[RFC5061] Stewart, R., Xie, Q., Tuexen, M., Maruyama, S., and M.
Kozuka, "Stream Control Transmission Protocol (SCTP)
Dynamic Address Reconfiguration", RFC 5061,
September 2007.
16.2. Informative References
[RFC2401] Kent, S. and R. Atkinson, "Security Architecture for the
Internet Protocol", RFC 2401, November 1998.
Bestler & Stewart Standards Track [Page 16]
RFC 5043 SCTP DDP Adaptation October 2007
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, December 2005.
[RFC5044] Culley, P., Elzur, U., Recio, R., Bailey, S., and J.
Carrier, "Marker PDU Aligned Framing for TCP
Specification", RFC 5044, October 2007.
[RFC5046] Ko, M., Chadalapaka, M., Elzur, U., Shah, H., and P.
Thaler, "Internet Small Computer System Interface (iSCSI)
Extensions for Remote Direct Memory Access (RDMA)",
RFC 5046, October 2007.
Authors' Addresses
Caitlin Bestler (editor)
Neterion
20230 Stevens Creek Blvd.
Suite C
Cupertino, CA 95014
USA
Phone: 408-366-4639
EMail: caitlin.bestler@neterion.com
Randall R. Stewart (editor)
Cisco Systems, Inc.
Forest Drive
Columbia, SC 29036
USA
Phone: +1-815-342-5222
EMail: rrs@cisco.com
Bestler & Stewart Standards Track [Page 17]
RFC 5043 SCTP DDP Adaptation October 2007
Full Copyright Statement
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Bestler & Stewart Standards Track [Page 18]