RFC 4960 - Stream Control Transmission Protocol
(Formats: TXT)
Network Working Group R. Stewart, Ed.
Request for Comments: 4960 September 2007
Obsoletes: 2960, 3309
Category: Standards Track
|
Stream Control Transmission Protocol
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 obsoletes RFC 2960 and RFC 3309. It describes the
Stream Control Transmission Protocol (SCTP). SCTP is designed to
transport Public Switched Telephone Network (PSTN) signaling messages
over IP networks, but is capable of broader applications.
SCTP is a reliable transport protocol operating on top of a
connectionless packet network such as IP. It offers the following
services to its users:
-- acknowledged error-free non-duplicated transfer of user data,
-- data fragmentation to conform to discovered path MTU size,
-- sequenced delivery of user messages within multiple streams, with
an option for order-of-arrival delivery of individual user
messages,
-- optional bundling of multiple user messages into a single SCTP
packet, and
-- network-level fault tolerance through supporting of multi-homing
at either or both ends of an association.
The design of SCTP includes appropriate congestion avoidance behavior
and resistance to flooding and masquerade attacks.
Stewart Standards Track [Page 1]
RFC 4960 Stream Control Transmission Protocol September 2007
Table of Contents
1. Introduction ....................................................5
1.1. Motivation .................................................5
1.2. Architectural View of SCTP .................................6
1.3. Key Terms ..................................................6
1.4. Abbreviations .............................................10
1.5. Functional View of SCTP ...................................10
1.5.1. Association Startup and Takedown ...................11
1.5.2. Sequenced Delivery within Streams ..................12
1.5.3. User Data Fragmentation ............................12
1.5.4. Acknowledgement and Congestion Avoidance ...........12
1.5.5. Chunk Bundling .....................................13
1.5.6. Packet Validation ..................................13
1.5.7. Path Management ....................................13
1.6. Serial Number Arithmetic ..................................14
1.7. Changes from RFC 2960 .....................................15
2. Conventions ....................................................15
3. SCTP Packet Format .............................................15
3.1. SCTP Common Header Field Descriptions .....................16
3.2. Chunk Field Descriptions ..................................17
3.2.1. Optional/Variable-Length Parameter Format ..........19
3.2.2. Reporting of Unrecognized Parameters ...............21
3.3. SCTP Chunk Definitions ....................................21
3.3.1. Payload Data (DATA) (0) ............................22
3.3.2. Initiation (INIT) (1) ..............................24
3.3.2.1. Optional/Variable-Length
Parameters in INIT ........................27
3.3.3. Initiation Acknowledgement (INIT ACK) (2) ..........30
3.3.3.1. Optional or Variable-Length Parameters ....33
3.3.4. Selective Acknowledgement (SACK) (3) ...............34
3.3.5. Heartbeat Request (HEARTBEAT) (4) ..................38
3.3.6. Heartbeat Acknowledgement (HEARTBEAT ACK) (5) ......39
3.3.7. Abort Association (ABORT) (6) ......................40
3.3.8. Shutdown Association (SHUTDOWN) (7) ................41
3.3.9. Shutdown Acknowledgement (SHUTDOWN ACK) (8) ........41
3.3.10. Operation Error (ERROR) (9) .......................42
3.3.10.1. Invalid Stream Identifier (1) ............44
3.3.10.2. Missing Mandatory Parameter (2) ..........44
3.3.10.3. Stale Cookie Error (3) ...................45
3.3.10.4. Out of Resource (4) ......................45
3.3.10.5. Unresolvable Address (5) .................46
3.3.10.6. Unrecognized Chunk Type (6) ..............46
3.3.10.7. Invalid Mandatory Parameter (7) ..........47
3.3.10.8. Unrecognized Parameters (8) ..............47
3.3.10.9. No User Data (9) .........................48
3.3.10.10. Cookie Received While Shutting
Down (10) ...............................48
Stewart Standards Track [Page 2]
RFC 4960 Stream Control Transmission Protocol September 2007
3.3.10.11. Restart of an Association with
New Addresses (11) ......................49
3.3.10.12. User-Initiated Abort (12) ...............49
3.3.10.13. Protocol Violation (13) .................50
3.3.11. Cookie Echo (COOKIE ECHO) (10) ....................50
3.3.12. Cookie Acknowledgement (COOKIE ACK) (11) ..........51
3.3.13. Shutdown Complete (SHUTDOWN COMPLETE) (14) ........51
4. SCTP Association State Diagram .................................52
5. Association Initialization .....................................56
5.1. Normal Establishment of an Association ....................56
5.1.1. Handle Stream Parameters ...........................58
5.1.2. Handle Address Parameters ..........................58
5.1.3. Generating State Cookie ............................61
5.1.4. State Cookie Processing ............................62
5.1.5. State Cookie Authentication ........................62
5.1.6. An Example of Normal Association Establishment .....64
5.2. Handle Duplicate or Unexpected INIT, INIT ACK,
COOKIE ECHO, and ..........................................65
5.2.1. INIT Received in COOKIE-WAIT or
COOKIE-ECHOED State (Item B) .......................66
5.2.2. Unexpected INIT in States Other than
CLOSED, COOKIE-ECHOED, .............................66
5.2.3. Unexpected INIT ACK ................................67
5.2.4. Handle a COOKIE ECHO when a TCB Exists .............67
5.2.4.1. An Example of a Association Restart .......69
5.2.5. Handle Duplicate COOKIE-ACK. .......................71
5.2.6. Handle Stale COOKIE Error ..........................71
5.3. Other Initialization Issues ...............................72
5.3.1. Selection of Tag Value .............................72
5.4. Path Verification .........................................72
6. User Data Transfer .............................................73
6.1. Transmission of DATA Chunks ...............................75
6.2. Acknowledgement on Reception of DATA Chunks ...............78
6.2.1. Processing a Received SACK .........................81
6.3. Management of Retransmission Timer ........................83
6.3.1. RTO Calculation ....................................83
6.3.2. Retransmission Timer Rules .........................85
6.3.3. Handle T3-rtx Expiration ...........................86
6.4. Multi-Homed SCTP Endpoints ................................87
6.4.1. Failover from an Inactive Destination Address ......88
6.5. Stream Identifier and Stream Sequence Number ..............88
6.6. Ordered and Unordered Delivery ............................88
6.7. Report Gaps in Received DATA TSNs .........................89
6.8. CRC32c Checksum Calculation ...............................90
6.9. Fragmentation and Reassembly ..............................91
6.10. Bundling .................................................92
7. Congestion Control .............................................93
7.1. SCTP Differences from TCP Congestion Control ..............94
Stewart Standards Track [Page 3]
RFC 4960 Stream Control Transmission Protocol September 2007
7.2. SCTP Slow-Start and Congestion Avoidance ..................95
7.2.1. Slow-Start .........................................96
7.2.2. Congestion Avoidance ...............................97
7.2.3. Congestion Control .................................98
7.2.4. Fast Retransmit on Gap Reports .....................98
7.3. Path MTU Discovery .......................................100
8. Fault Management ..............................................100
8.1. Endpoint Failure Detection ...............................100
8.2. Path Failure Detection ...................................101
8.3. Path Heartbeat ...........................................102
8.4. Handle "Out of the Blue" Packets .........................104
8.5. Verification Tag .........................................105
8.5.1. Exceptions in Verification Tag Rules ..............105
9. Termination of Association ....................................106
9.1. Abort of an Association ..................................107
9.2. Shutdown of an Association ...............................107
10. Interface with Upper Layer ...................................110
10.1. ULP-to-SCTP .............................................110
10.2. SCTP-to-ULP .............................................120
11. Security Considerations ......................................123
11.1. Security Objectives .....................................123
11.2. SCTP Responses to Potential Threats .....................124
11.2.1. Countering Insider Attacks .......................124
11.2.2. Protecting against Data Corruption in the
Network ..........................................124
11.2.3. Protecting Confidentiality .......................124
11.2.4. Protecting against Blind
Denial-of-Service Attacks ........................125
11.2.4.1. Flooding ................................125
11.2.4.2. Blind Masquerade ........................126
11.2.4.3. Improper Monopolization of Services .....127
11.3. SCTP Interactions with Firewalls ........................127
11.4. Protection of Non-SCTP-Capable Hosts ....................128
12. Network Management Considerations ............................128
13. Recommended Transmission Control Block (TCB) Parameters ......129
13.1. Parameters Necessary for the SCTP Instance ..............129
13.2. Parameters Necessary per Association (i.e., the TCB) ....129
13.3. Per Transport Address Data ..............................131
13.4. General Parameters Needed ...............................132
14. IANA Considerations ..........................................132
14.1. IETF-defined Chunk Extension ............................132
14.2. IETF-Defined Chunk Parameter Extension ..................133
14.3. IETF-Defined Additional Error Causes ....................133
14.4. Payload Protocol Identifiers ............................134
14.5. Port Numbers Registry ...................................134
15. Suggested SCTP Protocol Parameter Values .....................136
16. Acknowledgements .............................................137
Appendix A. Explicit Congestion Notification .....................139
Stewart Standards Track [Page 4]
RFC 4960 Stream Control Transmission Protocol September 2007
Appendix B. CRC32c Checksum Calculation ..........................140
Appendix C. ICMP Handling ........................................142
References .......................................................149
Normative References ..........................................149
Informative References ........................................150
1. Introduction
This section explains the reasoning behind the development of the
Stream Control Transmission Protocol (SCTP), the services it offers,
and the basic concepts needed to understand the detailed description
of the protocol.
This document obsoletes [RFC2960] and [RFC3309].
1.1. Motivation
TCP [RFC0793] has performed immense service as the primary means of
reliable data transfer in IP networks. However, an increasing number
of recent applications have found TCP too limiting, and have
incorporated their own reliable data transfer protocol on top of UDP
[RFC0768]. The limitations that users have wished to bypass include
the following:
-- TCP provides both reliable data transfer and strict order-of-
transmission delivery of data. Some applications need reliable
transfer without sequence maintenance, while others would be
satisfied with partial ordering of the data. In both of these
cases, the head-of-line blocking offered by TCP causes unnecessary
delay.
-- The stream-oriented nature of TCP is often an inconvenience.
Applications must add their own record marking to delineate their
messages, and must make explicit use of the push facility to
ensure that a complete message is transferred in a reasonable
time.
-- The limited scope of TCP sockets complicates the task of providing
highly-available data transfer capability using multi-homed hosts.
-- TCP is relatively vulnerable to denial-of-service attacks, such as
SYN attacks.
Transport of PSTN signaling across the IP network is an application
for which all of these limitations of TCP are relevant. While this
application directly motivated the development of SCTP, other
applications may find SCTP a good match to their requirements.
Stewart Standards Track [Page 5]
RFC 4960 Stream Control Transmission Protocol September 2007
1.2. Architectural View of SCTP
SCTP is viewed as a layer between the SCTP user application ("SCTP
user" for short) and a connectionless packet network service such as
IP. The remainder of this document assumes SCTP runs on top of IP.
The basic service offered by SCTP is the reliable transfer of user
messages between peer SCTP users. It performs this service within
the context of an association between two SCTP endpoints. Section 10
of this document sketches the API that should exist at the boundary
between the SCTP and the SCTP user layers.
SCTP is connection-oriented in nature, but the SCTP association is a
broader concept than the TCP connection. SCTP provides the means for
each SCTP endpoint (Section 1.3) to provide the other endpoint
(during association startup) with a list of transport addresses
(i.e., multiple IP addresses in combination with an SCTP port)
through which that endpoint can be reached and from which it will
originate SCTP packets. The association spans transfers over all of
the possible source/destination combinations that may be generated
from each endpoint's lists.
_____________ _____________
| SCTP User | | SCTP User |
| Application | | Application |
|-------------| |-------------|
| SCTP | | SCTP |
| Transport | | Transport |
| Service | | Service |
|-------------| |-------------|
| |One or more ---- One or more| |
| IP Network |IP address \/ IP address| IP Network |
| Service |appearances /\ appearances| Service |
|_____________| ---- |_____________|
SCTP Node A |<-------- Network transport ------->| SCTP Node B
Figure 1: An SCTP Association
1.3. Key Terms
Some of the language used to describe SCTP has been introduced in the
previous sections. This section provides a consolidated list of the
key terms and their definitions.
o Active destination transport address: A transport address on a
peer endpoint that a transmitting endpoint considers available for
receiving user messages.
Stewart Standards Track [Page 6]
RFC 4960 Stream Control Transmission Protocol September 2007
o Bundling: An optional multiplexing operation, whereby more than
one user message may be carried in the same SCTP packet. Each
user message occupies its own DATA chunk.
o Chunk: A unit of information within an SCTP packet, consisting of
a chunk header and chunk-specific content.
o Congestion window (cwnd): An SCTP variable that limits the data,
in number of bytes, a sender can send to a particular destination
transport address before receiving an acknowledgement.
o Cumulative TSN Ack Point: The TSN of the last DATA chunk
acknowledged via the Cumulative TSN Ack field of a SACK.
o Idle destination address: An address that has not had user
messages sent to it within some length of time, normally the
HEARTBEAT interval or greater.
o Inactive destination transport address: An address that is
considered inactive due to errors and unavailable to transport
user messages.
o Message = user message: Data submitted to SCTP by the Upper Layer
Protocol (ULP).
o Message Authentication Code (MAC): An integrity check mechanism
based on cryptographic hash functions using a secret key.
Typically, message authentication codes are used between two
parties that share a secret key in order to validate information
transmitted between these parties. In SCTP, it is used by an
endpoint to validate the State Cookie information that is returned
from the peer in the COOKIE ECHO chunk. The term "MAC" has
different meanings in different contexts. SCTP uses this term
with the same meaning as in [RFC2104].
o Network Byte Order: Most significant byte first, a.k.a., big
endian.
o Ordered Message: A user message that is delivered in order with
respect to all previous user messages sent within the stream on
which the message was sent.
o Outstanding TSN (at an SCTP endpoint): A TSN (and the associated
DATA chunk) that has been sent by the endpoint but for which it
has not yet received an acknowledgement.
Stewart Standards Track [Page 7]
RFC 4960 Stream Control Transmission Protocol September 2007
o Path: The route taken by the SCTP packets sent by one SCTP
endpoint to a specific destination transport address of its peer
SCTP endpoint. Sending to different destination transport
addresses does not necessarily guarantee getting separate paths.
o Primary Path: The primary path is the destination and source
address that will be put into a packet outbound to the peer
endpoint by default. The definition includes the source address
since an implementation MAY wish to specify both destination and
source address to better control the return path taken by reply
chunks and on which interface the packet is transmitted when the
data sender is multi-homed.
o Receiver Window (rwnd): An SCTP variable a data sender uses to
store the most recently calculated receiver window of its peer, in
number of bytes. This gives the sender an indication of the space
available in the receiver's inbound buffer.
o SCTP association: A protocol relationship between SCTP endpoints,
composed of the two SCTP endpoints and protocol state information
including Verification Tags and the currently active set of
Transmission Sequence Numbers (TSNs), etc. An association can be
uniquely identified by the transport addresses used by the
endpoints in the association. Two SCTP endpoints MUST NOT have
more than one SCTP association between them at any given time.
o SCTP endpoint: The logical sender/receiver of SCTP packets. On a
multi-homed host, an SCTP endpoint is represented to its peers as
a combination of a set of eligible destination transport addresses
to which SCTP packets can be sent and a set of eligible source
transport addresses from which SCTP packets can be received. All
transport addresses used by an SCTP endpoint must use the same
port number, but can use multiple IP addresses. A transport
address used by an SCTP endpoint must not be used by another SCTP
endpoint. In other words, a transport address is unique to an
SCTP endpoint.
o SCTP packet (or packet): The unit of data delivery across the
interface between SCTP and the connectionless packet network
(e.g., IP). An SCTP packet includes the common SCTP header,
possible SCTP control chunks, and user data encapsulated within
SCTP DATA chunks.
o SCTP user application (SCTP user): The logical higher-layer
application entity which uses the services of SCTP, also called
the Upper-Layer Protocol (ULP).
Stewart Standards Track [Page 8]
RFC 4960 Stream Control Transmission Protocol September 2007
o Slow-Start Threshold (ssthresh): An SCTP variable. This is the
threshold that the endpoint will use to determine whether to
perform slow start or congestion avoidance on a particular
destination transport address. Ssthresh is in number of bytes.
o Stream: A unidirectional logical channel established from one to
another associated SCTP endpoint, within which all user messages
are delivered in sequence except for those submitted to the
unordered delivery service.
Note: The relationship between stream numbers in opposite directions
is strictly a matter of how the applications use them. It is the
responsibility of the SCTP user to create and manage these
correlations if they are so desired.
o Stream Sequence Number: A 16-bit sequence number used internally
by SCTP to ensure sequenced delivery of the user messages within a
given stream. One Stream Sequence Number is attached to each user
message.
o Tie-Tags: Two 32-bit random numbers that together make a 64-bit
nonce. These tags are used within a State Cookie and TCB so that
a newly restarting association can be linked to the original
association within the endpoint that did not restart and yet not
reveal the true Verification Tags of an existing association.
o Transmission Control Block (TCB): An internal data structure
created by an SCTP endpoint for each of its existing SCTP
associations to other SCTP endpoints. TCB contains all the status
and operational information for the endpoint to maintain and
manage the corresponding association.
o 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.
o Transport address: A transport address is traditionally defined by
a network-layer address, a transport-layer protocol, and a
transport-layer port number. In the case of SCTP running over IP,
a transport address is defined by the combination of an IP address
and an SCTP port number (where SCTP is the transport protocol).
o Unacknowledged TSN (at an SCTP endpoint): A TSN (and the
associated DATA chunk) that has been received by the endpoint but
for which an acknowledgement has not yet been sent. Or in the
opposite case, for a packet that has been sent but no
acknowledgement has been received.
Stewart Standards Track [Page 9]
RFC 4960 Stream Control Transmission Protocol September 2007
o Unordered Message: Unordered messages are "unordered" with respect
to any other message; this includes both other unordered messages
as well as other ordered messages. An unordered message might be
delivered prior to or later than ordered messages sent on the same
stream.
o User message: The unit of data delivery across the interface
between SCTP and its user.
o Verification Tag: A 32-bit unsigned integer that is randomly
generated. The Verification Tag provides a key that allows a
receiver to verify that the SCTP packet belongs to the current
association and is not an old or stale packet from a previous
association.
1.4. Abbreviations
MAC - Message Authentication Code [RFC2104]
RTO - Retransmission Timeout
RTT - Round-Trip Time
RTTVAR - Round-Trip Time Variation
SCTP - Stream Control Transmission Protocol
SRTT - Smoothed RTT
TCB - Transmission Control Block
TLV - Type-Length-Value coding format
TSN - Transmission Sequence Number
ULP - Upper-Layer Protocol
1.5. Functional View of SCTP
The SCTP transport service can be decomposed into a number of
functions. These are depicted in Figure 2 and explained in the
remainder of this section.
Stewart Standards Track [Page 10]
RFC 4960 Stream Control Transmission Protocol September 2007
SCTP User Application
-----------------------------------------------------
_____________ ____________________
| | | Sequenced Delivery |
| Association | | within Streams |
| | |____________________|
| Startup |
| | ____________________________
| and | | User Data Fragmentation |
| | |____________________________|
| Takedown |
| | ____________________________
| | | Acknowledgement |
| | | and |
| | | Congestion Avoidance |
| | |____________________________|
| |
| | ____________________________
| | | Chunk Bundling |
| | |____________________________|
| |
| | ________________________________
| | | Packet Validation |
| | |________________________________|
| |
| | ________________________________
| | | Path Management |
|_____________| |________________________________|
Figure 2: Functional View of the SCTP Transport Service
1.5.1. Association Startup and Takedown
An association is initiated by a request from the SCTP user (see the
description of the ASSOCIATE (or SEND) primitive in Section 10).
A cookie mechanism, similar to one described by Karn and Simpson in
[RFC2522], is employed during the initialization to provide
protection against synchronization attacks. The cookie mechanism
uses a four-way handshake, the last two legs of which are allowed to
carry user data for fast setup. The startup sequence is described in
Section 5 of this document.
SCTP provides for graceful close (i.e., shutdown) of an active
association on request from the SCTP user. See the description of
the SHUTDOWN primitive in Section 10. SCTP also allows ungraceful
close (i.e., abort), either on request from the user (ABORT
Stewart Standards Track [Page 11]
RFC 4960 Stream Control Transmission Protocol September 2007
primitive) or as a result of an error condition detected within the
SCTP layer. Section 9 describes both the graceful and the ungraceful
close procedures.
SCTP does not support a half-open state (like TCP) wherein one side
may continue sending data while the other end is closed. When either
endpoint performs a shutdown, the association on each peer will stop
accepting new data from its user and only deliver data in queue at
the time of the graceful close (see Section 9).
1.5.2. Sequenced Delivery within Streams
The term "stream" is used in SCTP to refer to a sequence of user
messages that are to be delivered to the upper-layer protocol in
order with respect to other messages within the same stream. This is
in contrast to its usage in TCP, where it refers to a sequence of
bytes (in this document, a byte is assumed to be 8 bits).
The SCTP user can specify at association startup time the number of
streams to be supported by the association. This number is
negotiated with the remote end (see Section 5.1.1). User messages
are associated with stream numbers (SEND, RECEIVE primitives, Section
10). Internally, SCTP assigns a Stream Sequence Number to each
message passed to it by the SCTP user. On the receiving side, SCTP
ensures that messages are delivered to the SCTP user in sequence
within a given stream. However, while one stream may be blocked
waiting for the next in-sequence user message, delivery from other
streams may proceed.
SCTP provides a mechanism for bypassing the sequenced delivery
service. User messages sent using this mechanism are delivered to
the SCTP user as soon as they are received.
1.5.3. User Data Fragmentation
When needed, SCTP fragments user messages to ensure that the SCTP
packet passed to the lower layer conforms to the path MTU. On
receipt, fragments are reassembled into complete messages before
being passed to the SCTP user.
1.5.4. Acknowledgement and Congestion Avoidance
SCTP assigns a Transmission Sequence Number (TSN) to each user data
fragment or unfragmented message. The TSN is independent of any
Stream Sequence Number assigned at the stream level. The receiving
end acknowledges all TSNs received, even if there are gaps in the
sequence. In this way, reliable delivery is kept functionally
separate from sequenced stream delivery.
Stewart Standards Track [Page 12]
RFC 4960 Stream Control Transmission Protocol September 2007
The acknowledgement and congestion avoidance function is responsible
for packet retransmission when timely acknowledgement has not been
received. Packet retransmission is conditioned by congestion
avoidance procedures similar to those used for TCP. See Section 6
and Section 7 for a detailed description of the protocol procedures
associated with this function.
1.5.5. Chunk Bundling
As described in Section 3, the SCTP packet as delivered to the lower
layer consists of a common header followed by one or more chunks.
Each chunk may contain either user data or SCTP control information.
The SCTP user has the option to request bundling of more than one
user message into a single SCTP packet. The chunk bundling function
of SCTP is responsible for assembly of the complete SCTP packet and
its disassembly at the receiving end.
During times of congestion, an SCTP implementation MAY still perform
bundling even if the user has requested that SCTP not bundle. The
user's disabling of bundling only affects SCTP implementations that
may delay a small period of time before transmission (to attempt to
encourage bundling). When the user layer disables bundling, this
small delay is prohibited but not bundling that is performed during
congestion or retransmission.
1.5.6. Packet Validation
A mandatory Verification Tag field and a 32-bit checksum field (see
Appendix B for a description of the CRC32c checksum) are included in
the SCTP common header. The Verification Tag value is chosen by each
end of the association during association startup. Packets received
without the expected Verification Tag value are discarded, as a
protection against blind masquerade attacks and against stale SCTP
packets from a previous association. The CRC32c checksum should be
set by the sender of each SCTP packet to provide additional
protection against data corruption in the network. The receiver of
an SCTP packet with an invalid CRC32c checksum silently discards the
packet.
1.5.7. Path Management
The sending SCTP user is able to manipulate the set of transport
addresses used as destinations for SCTP packets through the
primitives described in Section 10. The SCTP path management
function chooses the destination transport address for each outgoing
SCTP packet based on the SCTP user's instructions and the currently
perceived reachability status of the eligible destination set. The
path management function monitors reachability through heartbeats
Stewart Standards Track [Page 13]
RFC 4960 Stream Control Transmission Protocol September 2007
when other packet traffic is inadequate to provide this information
and advises the SCTP user when reachability of any far-end transport
address changes. The path management function is also responsible
for reporting the eligible set of local transport addresses to the
far end during association startup, and for reporting the transport
addresses returned from the far end to the SCTP user.
At association startup, a primary path is defined for each SCTP
endpoint, and is used for normal sending of SCTP packets.
On the receiving end, the path management is responsible for
verifying the existence of a valid SCTP association to which the
inbound SCTP packet belongs before passing it for further processing.
Note: Path Management and Packet Validation are done at the same
time, so although described separately above, in reality they cannot
be performed as separate items.
1.6. Serial Number Arithmetic
It is essential to remember that the actual Transmission Sequence
Number space is finite, though very large. This space ranges from 0
to 2**32 - 1. Since the space is finite, all arithmetic dealing with
Transmission Sequence Numbers must be performed modulo 2**32. This
unsigned arithmetic preserves the relationship of sequence numbers as
they cycle from 2**32 - 1 to 0 again. There are some subtleties to
computer modulo arithmetic, so great care should be taken in
programming the comparison of such values. When referring to TSNs,
the symbol "=<" means "less than or equal"(modulo 2**32).
Comparisons and arithmetic on TSNs in this document SHOULD use Serial
Number Arithmetic as defined in [RFC1982] where SERIAL_BITS = 32.
An endpoint SHOULD NOT transmit a DATA chunk with a TSN that is more
than 2**31 - 1 above the beginning TSN of its current send window.
Doing so will cause problems in comparing TSNs.
Transmission Sequence Numbers wrap around when they reach 2**32 - 1.
That is, the next TSN a DATA chunk MUST use after transmitting TSN =
2*32 - 1 is TSN = 0.
Any arithmetic done on Stream Sequence Numbers SHOULD use Serial
Number Arithmetic as defined in [RFC1982] where SERIAL_BITS = 16.
All other arithmetic and comparisons in this document use normal
arithmetic.
Stewart Standards Track [Page 14]
RFC 4960 Stream Control Transmission Protocol September 2007
1.7. Changes from RFC 2960
SCTP was originally defined in [RFC2960], which this document
obsoletes. Readers interested in the details of the various changes
that this document incorporates are asked to consult [RFC4460].
2. 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].
3. SCTP Packet Format
An SCTP packet is composed of a common header and chunks. A chunk
contains either control information or user data.
The SCTP packet format is shown below:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Common Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Chunk #1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Chunk #n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Multiple chunks can be bundled into one SCTP packet up to the MTU
size, except for the INIT, INIT ACK, and SHUTDOWN COMPLETE chunks.
These chunks MUST NOT be bundled with any other chunk in a packet.
See Section 6.10 for more details on chunk bundling.
If a user data message doesn't fit into one SCTP packet it can be
fragmented into multiple chunks using the procedure defined in
Section 6.9.
All integer fields in an SCTP packet MUST be transmitted in network
byte order, unless otherwise stated.
Stewart Standards Track [Page 15]
RFC 4960 Stream Control Transmission Protocol September 2007
3.1. SCTP Common Header Field Descriptions
SCTP Common Header Format
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Port Number | Destination Port Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Verification Tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Source Port Number: 16 bits (unsigned integer)
This is the SCTP sender's port number. It can be used by the
receiver in combination with the source IP address, the SCTP
destination port, and possibly the destination IP address to
identify the association to which this packet belongs. The port
number 0 MUST NOT be used.
Destination Port Number: 16 bits (unsigned integer)
This is the SCTP port number to which this packet is destined.
The receiving host will use this port number to de-multiplex the
SCTP packet to the correct receiving endpoint/application. The
port number 0 MUST NOT be used.
Verification Tag: 32 bits (unsigned integer)
The receiver of this packet uses the Verification Tag to validate
the sender of this SCTP packet. On transmit, the value of this
Verification Tag MUST be set to the value of the Initiate Tag
received from the peer endpoint during the association
initialization, with the following exceptions:
- A packet containing an INIT chunk MUST have a zero Verification
Tag.
- A packet containing a SHUTDOWN COMPLETE chunk with the T bit
set MUST have the Verification Tag copied from the packet with
the SHUTDOWN ACK chunk.
- A packet containing an ABORT chunk may have the verification
tag copied from the packet that caused the ABORT to be sent.
For details see Section 8.4 and Section 8.5.
Stewart Standards Track [Page 16]
RFC 4960 Stream Control Transmission Protocol September 2007
An INIT chunk MUST be the only chunk in the SCTP packet carrying it.
Checksum: 32 bits (unsigned integer)
This field contains the checksum of this SCTP packet. Its
calculation is discussed in Section 6.8. SCTP uses the CRC32c
algorithm as described in Appendix B for calculating the checksum.
3.2. Chunk Field Descriptions
The figure below illustrates the field format for the chunks to be
transmitted in the SCTP packet. Each chunk is formatted with a Chunk
Type field, a chunk-specific Flag field, a Chunk Length field, and a
Value field.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Chunk Type | Chunk Flags | Chunk Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ Chunk Value /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Chunk Type: 8 bits (unsigned integer)
This field identifies the type of information contained in the
Chunk Value field. It takes a value from 0 to 254. The value of
255 is reserved for future use as an extension field.
The values of Chunk Types are defined as follows:
ID Value Chunk Type
----- ----------
0 - Payload Data (DATA)
1 - Initiation (INIT)
2 - Initiation Acknowledgement (INIT ACK)
3 - Selective Acknowledgement (SACK)
4 - Heartbeat Request (HEARTBEAT)
5 - Heartbeat Acknowledgement (HEARTBEAT ACK)
6 - Abort (ABORT)
7 - Shutdown (SHUTDOWN)
8 - Shutdown Acknowledgement (SHUTDOWN ACK)
9 - Operation Error (ERROR)
10 - State Cookie (COOKIE ECHO)
11 - Cookie Acknowledgement (COOKIE ACK)
Stewart Standards Track [Page 17]
RFC 4960 Stream Control Transmission Protocol September 2007
12 - Reserved for Explicit Congestion Notification Echo
(ECNE)
13 - Reserved for Congestion Window Reduced (CWR)
14 - Shutdown Complete (SHUTDOWN COMPLETE)
15 to 62 - available
63 - reserved for IETF-defined Chunk Extensions
64 to 126 - available
127 - reserved for IETF-defined Chunk Extensions
128 to 190 - available
191 - reserved for IETF-defined Chunk Extensions
192 to 254 - available
255 - reserved for IETF-defined Chunk Extensions
Chunk Types are encoded such that the highest-order 2 bits specify
the action that must be taken if the processing endpoint does not
recognize the Chunk Type.
00 - Stop processing this SCTP packet and discard it, do not
process any further chunks within it.
01 - Stop processing this SCTP packet and discard it, do not
process any further chunks within it, and report the
unrecognized chunk in an 'Unrecognized Chunk Type'.
10 - Skip this chunk and continue processing.
11 - Skip this chunk and continue processing, but report in an
ERROR chunk using the 'Unrecognized Chunk Type' cause of
error.
Note: The ECNE and CWR chunk types are reserved for future use of
Explicit Congestion Notification (ECN); see Appendix A.
Chunk Flags: 8 bits
The usage of these bits depends on the Chunk type as given by the
Chunk Type field. Unless otherwise specified, they are set to 0
on transmit and are ignored on receipt.
Chunk Length: 16 bits (unsigned integer)
This value represents the size of the chunk in bytes, including
the Chunk Type, Chunk Flags, Chunk Length, and Chunk Value fields.
Therefore, if the Chunk Value field is zero-length, the Length
field will be set to 4. The Chunk Length field does not count any
chunk padding.
Stewart Standards Track [Page 18]
RFC 4960 Stream Control Transmission Protocol September 2007
Chunks (including Type, Length, and Value fields) are padded out
by the sender with all zero bytes to be a multiple of 4 bytes
long. This padding MUST NOT be more than 3 bytes in total. The
Chunk Length value does not include terminating padding of the
chunk. However, it does include padding of any variable-length
parameter except the last parameter in the chunk. The receiver
MUST ignore the padding.
Note: A robust implementation should accept the chunk whether or
not the final padding has been included in the Chunk Length.
Chunk Value: variable length
The Chunk Value field contains the actual information to be
transferred in the chunk. The usage and format of this field is
dependent on the Chunk Type.
The total length of a chunk (including Type, Length, and Value
fields) MUST be a multiple of 4 bytes. If the length of the chunk is
not a multiple of 4 bytes, the sender MUST pad the chunk with all
zero bytes, and this padding is not included in the Chunk Length
field. The sender MUST NOT pad with more than 3 bytes. The receiver
MUST ignore the padding bytes.
SCTP-defined chunks are described in detail in Section 3.3. The
guidelines for IETF-defined chunk extensions can be found in Section
14.1 of this document.
3.2.1. Optional/Variable-Length Parameter Format
Chunk values of SCTP control chunks consist of a chunk-type-specific
header of required fields, followed by zero or more parameters. The
optional and variable-length parameters contained in a chunk are
defined in a Type-Length-Value format as shown below.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Parameter Type | Parameter Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ Parameter Value /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Stewart Standards Track [Page 19]
RFC 4960 Stream Control Transmission Protocol September 2007
Chunk Parameter Type: 16 bits (unsigned integer)
The Type field is a 16-bit identifier of the type of parameter.
It takes a value of 0 to 65534.
The value of 65535 is reserved for IETF-defined extensions.
Values other than those defined in specific SCTP chunk
descriptions are reserved for use by IETF.
Chunk Parameter Length: 16 bits (unsigned integer)
The Parameter Length field contains the size of the parameter in
bytes, including the Parameter Type, Parameter Length, and
Parameter Value fields. Thus, a parameter with a zero-length
Parameter Value field would have a Length field of 4. The
Parameter Length does not include any padding bytes.
Chunk Parameter Value: variable length
The Parameter Value field contains the actual information to be
transferred in the parameter.
The total length of a parameter (including Type, Parameter Length,
and Value fields) MUST be a multiple of 4 bytes. If the length of
the parameter is not a multiple of 4 bytes, the sender pads the
parameter at the end (i.e., after the Parameter Value field) with
all zero bytes. The length of the padding is not included in the
Parameter Length field. A sender MUST NOT pad with more than 3
bytes. The receiver MUST ignore the padding bytes.
The Parameter Types are encoded such that the highest-order 2 bits
specify the action that must be taken if the processing endpoint
does not recognize the Parameter Type.
00 - Stop processing this parameter; do not process any further
parameters within this chunk.
01 - Stop processing this parameter, do not process any further
parameters within this chunk, and report the unrecognized
parameter in an 'Unrecognized Parameter', as described in
Section 3.2.2.
10 - Skip this parameter and continue processing.
11 - Skip this parameter and continue processing but report the
unrecognized parameter in an 'Unrecognized Parameter', as
described in Section 3.2.2.
Stewart Standards Track [Page 20]
RFC 4960 Stream Control Transmission Protocol September 2007
Please note that in all four cases, an INIT ACK or COOKIE ECHO chunk
is sent. In the 00 or 01 case, the processing of the parameters
after the unknown parameter is canceled, but no processing already
done is rolled back.
The actual SCTP parameters are defined in the specific SCTP chunk
sections. The rules for IETF-defined parameter extensions are
defined in Section 14.2. Note that a parameter type MUST be unique
across all chunks. For example, the parameter type '5' is used to
represent an IPv4 address (see Section 3.3.2.1). The value '5' then
is reserved across all chunks to represent an IPv4 address and MUST
NOT be reused with a different meaning in any other chunk.
3.2.2. Reporting of Unrecognized Parameters
If the receiver of an INIT chunk detects unrecognized parameters and
has to report them according to Section 3.2.1, it MUST put the
'Unrecognized Parameter' parameter(s) in the INIT ACK chunk sent in
response to the INIT chunk. Note that if the receiver of the INIT
chunk is NOT going to establish an association (e.g., due to lack of
resources), an 'Unrecognized Parameter' would NOT be included with
any ABORT being sent to the sender of the INIT.
If the receiver of an INIT ACK chunk detects unrecognized parameters
and has to report them according to Section 3.2.1, it SHOULD bundle
the ERROR chunk containing the 'Unrecognized Parameters' error cause
with the COOKIE ECHO chunk sent in response to the INIT ACK chunk.
If the receiver of the INIT ACK cannot bundle the COOKIE ECHO chunk
with the ERROR chunk, the ERROR chunk MAY be sent separately but not
before the COOKIE ACK has been received.
Note: Any time a COOKIE ECHO is sent in a packet, it MUST be the
first chunk.
3.3. SCTP Chunk Definitions
This section defines the format of the different SCTP chunk types.
Stewart Standards Track [Page 21]
RFC 4960 Stream Control Transmission Protocol September 2007
3.3.1. Payload Data (DATA) (0)
The following format MUST be used for the DATA 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 0 | Reserved|U|B|E| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TSN |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Stream Identifier S | Stream Sequence Number n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Payload Protocol Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ User Data (seq n of Stream S) /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Reserved: 5 bits
Should be set to all '0's and ignored by the receiver.
U bit: 1 bit
The (U)nordered bit, if set to '1', indicates that this is an
unordered DATA chunk, and there is no Stream Sequence Number
assigned to this DATA chunk. Therefore, the receiver MUST ignore
the Stream Sequence Number field.
After reassembly (if necessary), unordered DATA chunks MUST be
dispatched to the upper layer by the receiver without any attempt
to reorder.
If an unordered user message is fragmented, each fragment of the
message MUST have its U bit set to '1'.
B bit: 1 bit
The (B)eginning fragment bit, if set, indicates the first fragment
of a user message.
E bit: 1 bit
The (E)nding fragment bit, if set, indicates the last fragment of
a user message.
Stewart Standards Track [Page 22]
RFC 4960 Stream Control Transmission Protocol September 2007
An unfragmented user message shall have both the B and E bits set to
'1'. Setting both B and E bits to '0' indicates a middle fragment of
a multi-fragment user message, as summarized in the following table:
B E Description
============================================================
| 1 0 | First piece of a fragmented user message |
+----------------------------------------------------------+
| 0 0 | Middle piece of a fragmented user message |
+----------------------------------------------------------+
| 0 1 | Last piece of a fragmented user message |
+----------------------------------------------------------+
| 1 1 | Unfragmented message |
============================================================
| Table 1: Fragment Description Flags |
============================================================
When a user message is fragmented into multiple chunks, the TSNs are
used by the receiver to reassemble the message. This means that the
TSNs for each fragment of a fragmented user message MUST be strictly
sequential.
Length: 16 bits (unsigned integer)
This field indicates the length of the DATA chunk in bytes from
the beginning of the type field to the end of the User Data field
excluding any padding. A DATA chunk with one byte of user data
will have Length set to 17 (indicating 17 bytes).
A DATA chunk with a User Data field of length L will have the
Length field set to (16 + L) (indicating 16+L bytes) where L MUST
be greater than 0.
TSN: 32 bits (unsigned integer)
This value represents the TSN for this DATA chunk. The valid
range of TSN is from 0 to 4294967295 (2**32 - 1). TSN wraps back
to 0 after reaching 4294967295.
Stream Identifier S: 16 bits (unsigned integer)
Identifies the stream to which the following user data belongs.
Stream Sequence Number n: 16 bits (unsigned integer)
This value represents the Stream Sequence Number of the following
user data within the stream S. Valid range is 0 to 65535.
Stewart Standards Track [Page 23]
RFC 4960 Stream Control Transmission Protocol September 2007
When a user message is fragmented by SCTP for transport, the same
Stream Sequence Number MUST be carried in each of the fragments of
the message.
Payload Protocol Identifier: 32 bits (unsigned integer)
This value represents an application (or upper layer) specified
protocol identifier. This value is passed to SCTP by its upper
layer and sent to its peer. This identifier is not used by SCTP
but can be used by certain network entities, as well as by the
peer application, to identify the type of information being
carried in this DATA chunk. This field must be sent even in
fragmented DATA chunks (to make sure it is available for agents in
the middle of the network). Note that this field is NOT touched
by an SCTP implementation; therefore, its byte order is NOT
necessarily big endian. The upper layer is responsible for any
byte order conversions to this field.
The value 0 indicates that no application identifier is specified
by the upper layer for this payload data.
User Data: variable length
This is the payload user data. The implementation MUST pad the
end of the data to a 4-byte boundary with all-zero bytes. Any
padding MUST NOT be included in the Length field. A sender MUST
never add more than 3 bytes of padding.
3.3.2. Initiation (INIT) (1)
This chunk is used to initiate an SCTP association between two
endpoints. The format of the INIT chunk is shown below:
Stewart Standards Track [Page 24]
RFC 4960 Stream Control Transmission Protocol September 2007
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 = 1 | Chunk Flags | Chunk Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Initiate Tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertised Receiver Window Credit (a_rwnd) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Number of Outbound Streams | Number of Inbound Streams |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Initial TSN |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ Optional/Variable-Length Parameters /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The INIT chunk contains the following parameters. Unless otherwise
noted, each parameter MUST only be included once in the INIT chunk.
Fixed Parameters Status
----------------------------------------------
Initiate Tag Mandatory
Advertised Receiver Window Credit Mandatory
Number of Outbound Streams Mandatory
Number of Inbound Streams Mandatory
Initial TSN Mandatory
Variable Parameters Status Type Value
-------------------------------------------------------------
IPv4 Address (Note 1) Optional 5 IPv6 Address
(Note 1) Optional 6 Cookie Preservative
Optional 9 Reserved for ECN Capable (Note 2) Optional
32768 (0x8000) Host Name Address (Note 3) Optional
11 Supported Address Types (Note 4) Optional 12
Note 1: The INIT chunks can contain multiple addresses that can be
IPv4 and/or IPv6 in any combination.
Note 2: The ECN Capable field is reserved for future use of Explicit
Congestion Notification.
Note 3: An INIT chunk MUST NOT contain more than one Host Name
Address parameter. Moreover, the sender of the INIT MUST NOT combine
any other address types with the Host Name Address in the INIT. The
receiver of INIT MUST ignore any other address types if the Host Name
Address parameter is present in the received INIT chunk.
Stewart Standards Track [Page 25]
RFC 4960 Stream Control Transmission Protocol September 2007
Note 4: This parameter, when present, specifies all the address types
the sending endpoint can support. The absence of this parameter
indicates that the sending endpoint can support any address type.
IMPLEMENTATION NOTE: If an INIT chunk is received with known
parameters that are not optional parameters of the INIT chunk, then
the receiver SHOULD process the INIT chunk and send back an INIT ACK.
The receiver of the INIT chunk MAY bundle an ERROR chunk with the
COOKIE ACK chunk later. However, restrictive implementations MAY
send back an ABORT chunk in response to the INIT chunk.
The Chunk Flags field in INIT is reserved, and all bits in it should
be set to 0 by the sender and ignored by the receiver. The sequence
of parameters within an INIT can be processed in any order.
Initiate Tag: 32 bits (unsigned integer)
The receiver of the INIT (the responding end) records the value of
the Initiate Tag parameter. This value MUST be placed into the
Verification Tag field of every SCTP packet that the receiver of
the INIT transmits within this association.
The Initiate Tag is allowed to have any value except 0. See
Section 5.3.1 for more on the selection of the tag value.
If the value of the Initiate Tag in a received INIT chunk is found
to be 0, the receiver MUST treat it as an error and close the
association by transmitting an ABORT.
Advertised Receiver Window Credit (a_rwnd): 32 bits (unsigned
integer)
This value represents the dedicated buffer space, in number of
bytes, the sender of the INIT has reserved in association with
this window. During the life of the association, this buffer
space SHOULD NOT be lessened (i.e., dedicated buffers taken away
from this association); however, an endpoint MAY change the value
of a_rwnd it sends in SACK chunks.
Number of Outbound Streams (OS): 16 bits (unsigned integer)
Defines the number of outbound streams the sender of this INIT
chunk wishes to create in this association. The value of 0 MUST
NOT be used.
Note: A receiver of an INIT with the OS value set to 0 SHOULD
abort the association.
Stewart Standards Track [Page 26]
RFC 4960 Stream Control Transmission Protocol September 2007
Number of Inbound Streams (MIS): 16 bits (unsigned integer)
Defines the maximum number of streams the sender of this INIT
chunk allows the peer end to create in this association. The
value 0 MUST NOT be used.
Note: There is no negotiation of the actual number of streams but
instead the two endpoints will use the min(requested, offered).
See Section 5.1.1 for details.
Note: A receiver of an INIT with the MIS value of 0 SHOULD abort
the association.
Initial TSN (I-TSN): 32 bits (unsigned integer)
Defines the initial TSN that the sender will use. The valid range
is from 0 to 4294967295. This field MAY be set to the value of
the Initiate Tag field.
3.3.2.1. Optional/Variable-Length Parameters in INIT
The following parameters follow the Type-Length-Value format as
defined in Section 3.2.1. Any Type-Length-Value fields MUST come
after the fixed-length fields defined in the previous section.
IPv4 Address Parameter (5)
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 = 5 | Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
IPv4 Address: 32 bits (unsigned integer)
Contains an IPv4 address of the sending endpoint. It is binary
encoded.
Stewart Standards Track [Page 27]
RFC 4960 Stream Control Transmission Protocol September 2007
IPv6 Address Parameter (6)
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 = 6 | Length = 20 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| IPv6 Address |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
IPv6 Address: 128 bits (unsigned integer)
Contains an IPv6 [RFC2460] address of the sending endpoint. It is
binary encoded.
Note: A sender MUST NOT use an IPv4-mapped IPv6 address [RFC4291],
but should instead use an IPv4 Address parameter for an IPv4
address.
Combined with the Source Port Number in the SCTP common header,
the value passed in an IPv4 or IPv6 Address parameter indicates a
transport address the sender of the INIT will support for the
association being initiated. That is, during the life time of
this association, this IP address can appear in the source address
field of an IP datagram sent from the sender of the INIT, and can
be used as a destination address of an IP datagram sent from the
receiver of the INIT.
More than one IP Address parameter can be included in an INIT
chunk when the INIT sender is multi-homed. Moreover, a multi-
homed endpoint may have access to different types of network;
thus, more than one address type can be present in one INIT chunk,
i.e., IPv4 and IPv6 addresses are allowed in the same INIT chunk.
If the INIT contains at least one IP Address parameter, then the
source address of the IP datagram containing the INIT chunk and
any additional address(es) provided within the INIT can be used as
destinations by the endpoint receiving the INIT. If the INIT does
not contain any IP Address parameters, the endpoint receiving the
INIT MUST use the source address associated with the received IP
datagram as its sole destination address for the association.
Note that not using any IP Address parameters in the INIT and INIT
ACK is an alternative to make an association more likely to work
across a NAT box.
Stewart Standards Track [Page 28]
RFC 4960 Stream Control Transmission Protocol September 2007
Cookie Preservative (9)
The sender of the INIT shall use this parameter to suggest to the
receiver of the INIT for a longer life-span of the State Cookie.
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 = 9 | Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Suggested Cookie Life-Span Increment (msec.) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Suggested Cookie Life-Span Increment: 32 bits (unsigned integer)
This parameter indicates to the receiver how much increment in
milliseconds the sender wishes the receiver to add to its default
cookie life-span.
This optional parameter should be added to the INIT chunk by the
sender when it reattempts establishing an association with a peer
to which its previous attempt of establishing the association
failed due to a stale cookie operation error. The receiver MAY
choose to ignore the suggested cookie life-span increase for its
own security reasons.
Host Name Address (11)
The sender of INIT uses this parameter to pass its Host Name (in
place of its IP addresses) to its peer. The peer is responsible for
resolving the name. Using this parameter might make it more likely
for the association to work across a NAT box.
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 = 11 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ Host Name /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Host Name: variable length
This field contains a host name in "host name syntax" per RFC 1123
Section 2.1 [RFC1123]. The method for resolving the host name is
out of scope of SCTP.
Stewart Standards Track [Page 29]
RFC 4960 Stream Control Transmission Protocol September 2007
Note: At least one null terminator is included in the Host Name
string and must be included in the length.
Supported Address Types (12)
The sender of INIT uses this parameter to list all the address types
it can support.
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 = 12 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address Type #1 | Address Type #2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ...... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+
Address Type: 16 bits (unsigned integer)
This is filled with the type value of the corresponding address
TLV (e.g., IPv4 = 5, IPv6 = 6, Host name = 11).
3.3.3. Initiation Acknowledgement (INIT ACK) (2)
The INIT ACK chunk is used to acknowledge the initiation of an SCTP
association.
The parameter part of INIT ACK is formatted similarly to the INIT
chunk. It uses two extra variable parameters: The State Cookie and
the Unrecognized Parameter:
Stewart Standards Track [Page 30]
RFC 4960 Stream Control Transmission Protocol September 2007
The format of the INIT ACK chunk is shown below:
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 = 2 | Chunk Flags | Chunk Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Initiate Tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertised Receiver Window Credit |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Number of Outbound Streams | Number of Inbound Streams |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Initial TSN |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ Optional/Variable-Length Parameters /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Initiate Tag: 32 bits (unsigned integer)
The receiver of the INIT ACK records the value of the Initiate Tag
parameter. This value MUST be placed into the Verification Tag
field of every SCTP packet that the INIT ACK receiver transmits
within this association.
The Initiate Tag MUST NOT take the value 0. See Section 5.3.1 for
more on the selection of the Initiate Tag value.
If the value of the Initiate Tag in a received INIT ACK chunk is
found to be 0, the receiver MUST destroy the association
discarding its TCB. The receiver MAY send an ABORT for debugging
purpose.
Advertised Receiver Window Credit (a_rwnd): 32 bits (unsigned
integer)
This value represents the dedicated buffer space, in number of
bytes, the sender of the INIT ACK has reserved in association with
this window. During the life of the association, this buffer
space SHOULD NOT be lessened (i.e., dedicated buffers taken away
from this association).
Number of Outbound Streams (OS): 16 bits (unsigned integer)
Defines the number of outbound streams the sender of this INIT ACK
chunk wishes to create in this association. The value of 0 MUST
Stewart Standards Track [Page 31]
RFC 4960 Stream Control Transmission Protocol September 2007
NOT be used, and the value MUST NOT be greater than the MIS value
sent in the INIT chunk.
Note: A receiver of an INIT ACK with the OS value set to 0 SHOULD
destroy the association discarding its TCB.
Number of Inbound Streams (MIS): 16 bits (unsigned integer)
Defines the maximum number of streams the sender of this INIT ACK
chunk allows the peer end to create in this association. The
value 0 MUST NOT be used.
Note: There is no negotiation of the actual number of streams but
instead the two endpoints will use the min(requested, offered).
See Section 5.1.1 for details.
Note: A receiver of an INIT ACK with the MIS value set to 0 SHOULD
destroy the association discarding its TCB.
Initial TSN (I-TSN): 32 bits (unsigned integer)
Defines the initial TSN that the INIT ACK sender will use. The
valid range is from 0 to 4294967295. This field MAY be set to the
value of the Initiate Tag field.
Fixed Parameters Status
----------------------------------------------
Initiate Tag Mandatory
Advertised Receiver Window Credit Mandatory
Number of Outbound Streams Mandatory
Number of Inbound Streams Mandatory
Initial TSN Mandatory
Variable Parameters Status Type Value
-------------------------------------------------------------
State Cookie Mandatory 7
IPv4 Address (Note 1) Optional 5
IPv6 Address (Note 1) Optional 6
Unrecognized Parameter Optional 8
Reserved for ECN Capable (Note 2) Optional 32768 (0x8000)
Host Name Address (Note 3) Optional 11
Note 1: The INIT ACK chunks can contain any number of IP address
parameters that can be IPv4 and/or IPv6 in any combination.
Note 2: The ECN Capable field is reserved for future use of Explicit
Congestion Notification.
Stewart Standards Track [Page 32]
RFC 4960 Stream Control Transmission Protocol September 2007
Note 3: The INIT ACK chunks MUST NOT contain more than one Host Name
Address parameter. Moreover, the sender of the INIT ACK MUST NOT
combine any other address types with the Host Name Address in the
INIT ACK. The receiver of the INIT ACK MUST ignore any other address
types if the Host Name Address parameter is present.
IMPLEMENTATION NOTE: An implementation MUST be prepared to receive an
INIT ACK that is quite large (more than 1500 bytes) due to the
variable size of the State Cookie AND the variable address list. For
example if a responder to the INIT has 1000 IPv4 addresses it wishes
to send, it would need at least 8,000 bytes to encode this in the
INIT ACK.
IMPLEMENTATION NOTE: If an INIT ACK chunk is received with known
parameters that are not optional parameters of the INIT ACK chunk,
then the receiver SHOULD process the INIT ACK chunk and send back a
COOKIE ECHO. The receiver of the INIT ACK chunk MAY bundle an ERROR
chunk with the COOKIE ECHO chunk. However, restrictive
implementations MAY send back an ABORT chunk in response to the INIT
ACK chunk.
In combination with the Source Port carried in the SCTP common
header, each IP Address parameter in the INIT ACK indicates to the
receiver of the INIT ACK a valid transport address supported by the
sender of the INIT ACK for the life time of the association being
initiated.
If the INIT ACK contains at least one IP Address parameter, then the
source address of the IP datagram containing the INIT ACK and any
additional address(es) provided within the INIT ACK may be used as
destinations by the receiver of the INIT ACK. If the INIT ACK does
not contain any IP Address parameters, the receiver of the INIT ACK
MUST use the source address associated with the received IP datagram
as its sole destination address for the association.
The State Cookie and Unrecognized Parameters use the Type-Length-
Value format as defined in Section 3.2.1 and are described below.
The other fields are defined the same as their counterparts in the
INIT chunk.
3.3.3.1. Optional or Variable-Length Parameters
State Cookie
Parameter Type Value: 7
Parameter Length: Variable size, depending on size of Cookie.
Stewart Standards Track [Page 33]
RFC 4960 Stream Control Transmission Protocol September 2007
Parameter Value:
This parameter value MUST contain all the necessary state and
parameter information required for the sender of this INIT ACK to
create the association, along with a Message Authentication Code
(MAC). See Section 5.1.3 for details on State Cookie definition.
Unrecognized Parameter:
Parameter Type Value: 8
Parameter Length: Variable size.
Parameter Value:
This parameter is returned to the originator of the INIT chunk
when the INIT contains an unrecognized parameter that has a value
that indicates it should be reported to the sender. This
parameter value field will contain unrecognized parameters copied
from the INIT chunk complete with Parameter Type, Length, and
Value fields.
3.3.4. Selective Acknowledgement (SACK) (3)
This chunk is sent to the peer endpoint to acknowledge received DATA
chunks and to inform the peer endpoint of gaps in the received
subsequences of DATA chunks as represented by their TSNs.
The SACK MUST contain the Cumulative TSN Ack, Advertised Receiver
Window Credit (a_rwnd), Number of Gap Ack Blocks, and Number of
Duplicate TSNs fields.
By definition, the value of the Cumulative TSN Ack parameter is the
last TSN received before a break in the sequence of received TSNs
occurs; the next TSN value following this one has not yet been
received at the endpoint sending the SACK. This parameter therefore
acknowledges receipt of all TSNs less than or equal to its value.
The handling of a_rwnd by the receiver of the SACK is discussed in
detail in Section 6.2.1.
The SACK also contains zero or more Gap Ack Blocks. Each Gap Ack
Block acknowledges a subsequence of TSNs received following a break
in the sequence of received TSNs. By definition, all TSNs
acknowledged by Gap Ack Blocks are greater than the value of the
Cumulative TSN Ack.
Stewart Standards Track [Page 34]
RFC 4960 Stream Control Transmission Protocol September 2007
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 = 3 |Chunk Flags | Chunk Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cumulative TSN Ack |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertised Receiver Window Credit (a_rwnd) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Number of Gap Ack Blocks = N | Number of Duplicate TSNs = X |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Gap Ack Block #1 Start | Gap Ack Block #1 End |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ /
\ ... \
/ /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Gap Ack Block #N Start | Gap Ack Block #N End |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Duplicate TSN 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ /
\ ... \
/ /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Duplicate TSN X |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Chunk Flags: 8 bits
Set to all '0's on transmit and ignored on receipt.
Cumulative TSN Ack: 32 bits (unsigned integer)
This parameter contains the TSN of the last DATA chunk received in
sequence before a gap. In the case where no DATA chunk has been
received, this value is set to the peer's Initial TSN minus one.
Advertised Receiver Window Credit (a_rwnd): 32 bits (unsigned
integer)
This field indicates the updated receive buffer space in bytes of
the sender of this SACK; see Section 6.2.1 for details.
Number of Gap Ack Blocks: 16 bits (unsigned integer)
Indicates the number of Gap Ack Blocks included in this SACK.
Stewart Standards Track [Page 35]
RFC 4960 Stream Control Transmission Protocol September 2007
Number of Duplicate TSNs: 16 bit
This field contains the number of duplicate TSNs the endpoint has
received. Each duplicate TSN is listed following the Gap Ack
Block list.
Gap Ack Blocks:
These fields contain the Gap Ack Blocks. They are repeated for
each Gap Ack Block up to the number of Gap Ack Blocks defined in
the Number of Gap Ack Blocks field. All DATA chunks with TSNs
greater than or equal to (Cumulative TSN Ack + Gap Ack Block
Start) and less than or equal to (Cumulative TSN Ack + Gap Ack
Block End) of each Gap Ack Block are assumed to have been received
correctly.
Gap Ack Block Start: 16 bits (unsigned integer)
Indicates the Start offset TSN for this Gap Ack Block. To
calculate the actual TSN number the Cumulative TSN Ack is added to
this offset number. This calculated TSN identifies the first TSN
in this Gap Ack Block that has been received.
Gap Ack Block End: 16 bits (unsigned integer)
Indicates the End offset TSN for this Gap Ack Block. To calculate
the actual TSN number, the Cumulative TSN Ack is added to this
offset number. This calculated TSN identifies the TSN of the last
DATA chunk received in this Gap Ack Block.
Stewart Standards Track [Page 36]
RFC 4960 Stream Control Transmission Protocol September 2007
For example, assume that the receiver has the following DATA chunks
newly arrived at the time when it decides to send a Selective ACK,
----------
| TSN=17 |
----------
| | <- still missing
----------
| TSN=15 |
----------
| TSN=14 |
----------
| | <- still missing
----------
| TSN=12 |
----------
| TSN=11 |
----------
| TSN=10 |
----------
then the parameter part of the SACK MUST be constructed as follows
(assuming the new a_rwnd is set to 4660 by the sender):
+--------------------------------+
| Cumulative TSN Ack = 12 |
+--------------------------------+
| a_rwnd = 4660 |
+----------------+---------------+
| num of block=2 | num of dup=0 |
+----------------+---------------+
|block #1 strt=2 |block #1 end=3 |
+----------------+---------------+
|block #2 strt=5 |block #2 end=5 |
+----------------+---------------+
Duplicate TSN: 32 bits (unsigned integer)
Indicates the number of times a TSN was received in duplicate
since the last SACK was sent. Every time a receiver gets a
duplicate TSN (before sending the SACK), it adds it to the list of
duplicates. The duplicate count is reinitialized to zero after
sending each SACK.
For example, if a receiver were to get the TSN 19 three times it
would list 19 twice in the outbound SACK. After sending the SACK, if
it received yet one more TSN 19 it would list 19 as a duplicate once
in the next outgoing SACK.
Stewart Standards Track [Page 37]
RFC 4960 Stream Control Transmission Protocol September 2007
3.3.5. Heartbeat Request (HEARTBEAT) (4)
An endpoint should send this chunk to its peer endpoint to probe the
reachability of a particular destination transport address defined in
the present association.
The parameter field contains the Heartbeat Information, which is a
variable-length opaque data structure understood only by the sender.
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 = 4 | Chunk Flags | Heartbeat Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ Heartbeat Information TLV (Variable-Length) /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Chunk Flags: 8 bits
Set to 0 on transmit and ignored on receipt.
Heartbeat Length: 16 bits (unsigned integer)
Set to the size of the chunk in bytes, including the chunk header
and the Heartbeat Information field.
Heartbeat Information: variable length
Defined as a variable-length parameter using the format described
in Section 3.2.1, i.e.:
Variable Parameters Status Type Value
-------------------------------------------------------------
Heartbeat Info Mandatory 1
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Heartbeat Info Type=1 | HB Info Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ Sender-Specific Heartbeat Info /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Sender-Specific Heartbeat Info field should normally include
information about the sender's current time when this HEARTBEAT
Stewart Standards Track [Page 38]
RFC 4960 Stream Control Transmission Protocol September 2007
chunk is sent and the destination transport address to which this
HEARTBEAT is sent (see Section 8.3). This information is simply
reflected back by the receiver in the HEARTBEAT ACK message (see
Section 3.3.6). Note also that the HEARTBEAT message is both for
reachability checking and for path verification (see Section 5.4).
When a HEARTBEAT chunk is being used for path verification
purposes, it MUST hold a 64-bit random nonce.
3.3.6. Heartbeat Acknowledgement (HEARTBEAT ACK) (5)
An endpoint should send this chunk to its peer endpoint as a response
to a HEARTBEAT chunk (see Section 8.3). A HEARTBEAT ACK is always
sent to the source IP address of the IP datagram containing the
HEARTBEAT chunk to which this ack is responding.
The parameter field contains a variable-length opaque data structure.
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 = 5 | Chunk Flags | Heartbeat Ack Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ Heartbeat Information TLV (Variable-Length) /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Chunk Flags: 8 bits
Set to 0 on transmit and ignored on receipt.
Heartbeat Ack Length: 16 bits (unsigned integer)
Set to the size of the chunk in bytes, including the chunk header
and the Heartbeat Information field.
Heartbeat Information: variable length
This field MUST contain the Heartbeat Information parameter of the
Heartbeat Request to which this Heartbeat Acknowledgement is
responding.
Variable Parameters Status Type Value
-------------------------------------------------------------
Heartbeat Info Mandatory 1
Stewart Standards Track [Page 39]
RFC 4960 Stream Control Transmission Protocol September 2007
3.3.7. Abort Association (ABORT) (6)
The ABORT chunk is sent to the peer of an association to close the
association. The ABORT chunk may contain Cause Parameters to inform
the receiver about the reason of the abort. DATA chunks MUST NOT be
bundled with ABORT. Control chunks (except for INIT, INIT ACK, and
SHUTDOWN COMPLETE) MAY be bundled with an ABORT, but they MUST be
placed before the ABORT in the SCTP packet or they will be ignored by
the receiver.
If an endpoint receives an ABORT with a format error or no TCB is
found, it MUST silently discard it. Moreover, under any
circumstances, an endpoint that receives an ABORT MUST NOT respond to
that ABORT by sending an ABORT of its own.
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 = 6 |Reserved |T| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ zero or more Error Causes /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Chunk Flags: 8 bits
Reserved: 7 bits
Set to 0 on transmit and ignored on receipt.
T bit: 1 bit
The T bit is set to 0 if the sender filled in the Verification Tag
expected by the peer. If the Verification Tag is reflected, the T
bit MUST be set to 1. Reflecting means that the sent Verification
Tag is the same as the received one.
Note: Special rules apply to this chunk for verification; please
see Section 8.5.1 for details.
Length: 16 bits (unsigned integer)
Set to the size of the chunk in bytes, including the chunk header
and all the Error Cause fields present.
See Section 3.3.10 for Error Cause definitions.
Stewart Standards Track [Page 40]
RFC 4960 Stream Control Transmission Protocol September 2007
3.3.8. Shutdown Association (SHUTDOWN) (7)
An endpoint in an association MUST use this chunk to initiate a
graceful close of the association with its peer. This chunk has the
following format.
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 = 7 | Chunk Flags | Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cumulative TSN Ack |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Chunk Flags: 8 bits
Set to 0 on transmit and ignored on receipt.
Length: 16 bits (unsigned integer)
Indicates the length of the parameter. Set to 8.
Cumulative TSN Ack: 32 bits (unsigned integer)
This parameter contains the TSN of the last chunk received in
sequence before any gaps.
Note: Since the SHUTDOWN message does not contain Gap Ack Blocks,
it cannot be used to acknowledge TSNs received out of order. In a
SACK, lack of Gap Ack Blocks that were previously included
indicates that the data receiver reneged on the associated DATA
chunks. Since SHUTDOWN does not contain Gap Ack Blocks, the
receiver of the SHUTDOWN shouldn't interpret the lack of a Gap Ack
Block as a renege. (See Section 6.2 for information on reneging.)
3.3.9. Shutdown Acknowledgement (SHUTDOWN ACK) (8)
This chunk MUST be used to acknowledge the receipt of the SHUTDOWN
chunk at the completion of the shutdown process; see Section 9.2 for
details.
The SHUTDOWN ACK chunk has no parameters.
Stewart Standards Track [Page 41]
RFC 4960 Stream Control Transmission Protocol September 2007
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 = 8 |Chunk Flags | Length = 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Chunk Flags: 8 bits
Set to 0 on transmit and ignored on receipt.
3.3.10. Operation Error (ERROR) (9)
An endpoint sends this chunk to its peer endpoint to notify it of
certain error conditions. It contains one or more error causes. An
Operation Error is not considered fatal in and of itself, but may be
used with an ABORT chunk to report a fatal condition. It has the
following parameters:
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 = 9 | Chunk Flags | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ one or more Error Causes /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Chunk Flags: 8 bits
Set to 0 on transmit and ignored on receipt.
Length: 16 bits (unsigned integer)
Set to the size of the chunk in bytes, including the chunk header
and all the Error Cause fields present.
Stewart Standards Track [Page 42]
RFC 4960 Stream Control Transmission Protocol September 2007
Error causes are defined as variable-length parameters using the
format described in Section 3.2.1, that is:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cause Code | Cause Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ Cause-Specific Information /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Cause Code: 16 bits (unsigned integer)
Defines the type of error conditions being reported.
Cause Code
Value Cause Code
--------- ----------------
1 Invalid Stream Identifier
2 Missing Mandatory Parameter
3 Stale Cookie Error
4 Out of Resource
5 Unresolvable Address
6 Unrecognized Chunk Type
7 Invalid Mandatory Parameter
8 Unrecognized Parameters
9 No User Data
10 Cookie Received While Shutting Down
11 Restart of an Association with New Addresses
12 User Initiated Abort
13 Protocol Violation
Cause Length: 16 bits (unsigned integer)
Set to the size of the parameter in bytes, including the Cause
Code, Cause Length, and Cause-Specific Information fields.
Cause-Specific Information: variable length
This field carries the details of the error condition.
Section 3.3.10.1 - Section 3.3.10.13 define error causes for SCTP.
Guidelines for the IETF to define new error cause values are
discussed in Section 14.3.
Stewart Standards Track [Page 43]
RFC 4960 Stream Control Transmission Protocol September 2007
3.3.10.1. Invalid Stream Identifier (1)
Cause of error
---------------
Invalid Stream Identifier: Indicates endpoint received a DATA chunk
sent to a nonexistent stream.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cause Code=1 | Cause Length=8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Stream Identifier | (Reserved) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Stream Identifier: 16 bits (unsigned integer)
Contains the Stream Identifier of the DATA chunk received in
error.
Reserved: 16 bits
This field is reserved. It is set to all 0's on transmit and
ignored on receipt.
3.3.10.2. Missing Mandatory Parameter (2)
Cause of error
---------------
Missing Mandatory Parameter: Indicates that one or more mandatory TLV
parameters are missing in a received INIT or INIT ACK.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cause Code=2 | Cause Length=8+N*2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Number of missing params=N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Missing Param Type #1 | Missing Param Type #2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Missing Param Type #N-1 | Missing Param Type #N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Number of Missing params: 32 bits (unsigned integer)
This field contains the number of parameters contained in the
Cause-Specific Information field.
Stewart Standards Track [Page 44]
RFC 4960 Stream Control Transmission Protocol September 2007
Missing Param Type: 16 bits (unsigned integer)
Each field will contain the missing mandatory parameter number.
3.3.10.3. Stale Cookie Error (3)
Cause of error
--------------
Stale Cookie Error: Indicates the receipt of a valid State Cookie
that has expired.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cause Code=3 | Cause Length=8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Measure of Staleness (usec.) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Measure of Staleness: 32 bits (unsigned integer)
This field contains the difference, in microseconds, between the
current time and the time the State Cookie expired.
The sender of this error cause MAY choose to report how long past
expiration the State Cookie is by including a non-zero value in
the Measure of Staleness field. If the sender does not wish to
provide this information, it should set the Measure of Staleness
field to the value of zero.
3.3.10.4. Out of Resource (4)
Cause of error
---------------
Out of Resource: Indicates that the sender is out of resource. This
is usually sent in combination with or within an ABORT.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cause Code=4 | Cause Length=4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Stewart Standards Track [Page 45]
RFC 4960 Stream Control Transmission Protocol September 2007
3.3.10.5. Unresolvable Address (5)
Cause of error
---------------
Unresolvable Address: Indicates that the sender is not able to
resolve the specified address parameter (e.g., type of address is not
supported by the sender). This is usually sent in combination with
or within an ABORT.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cause Code=5 | Cause Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ Unresolvable Address /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Unresolvable Address: variable length
The Unresolvable Address field contains the complete Type, Length,
and Value of the address parameter (or Host Name parameter) that
contains the unresolvable address or host name.
3.3.10.6. Unrecognized Chunk Type (6)
Cause of error
---------------
Unrecognized Chunk Type: This error cause is returned to the
originator of the chunk if the receiver does not understand the chunk
and the upper bits of the 'Chunk Type' are set to 01 or 11.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cause Code=6 | Cause Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ Unrecognized Chunk /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Unrecognized Chunk: variable length
The Unrecognized Chunk field contains the unrecognized chunk from
the SCTP packet complete with Chunk Type, Chunk Flags, and Chunk
Length.
Stewart Standards Track [Page 46]
RFC 4960 Stream Control Transmission Protocol September 2007
3.3.10.7. Invalid Mandatory Parameter (7)
Cause of error
---------------
Invalid Mandatory Parameter: This error cause is returned to the
originator of an INIT or INIT ACK chunk when one of the mandatory
parameters is set to an invalid value.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cause Code=7 | Cause Length=4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3.3.10.8. Unrecognized Parameters (8)
Cause of error
---------------
Unrecognized Parameters: This error cause is returned to the
originator of the INIT ACK chunk if the receiver does not recognize
one or more Optional TLV parameters in the INIT ACK chunk.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cause Code=8 | Cause Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ Unrecognized Parameters /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Unrecognized Parameters: variable length
The Unrecognized Parameters field contains the unrecognized
parameters copied from the INIT ACK chunk complete with TLV. This
error cause is normally contained in an ERROR chunk bundled with
the COOKIE ECHO chunk when responding to the INIT ACK, when the
sender of the COOKIE ECHO chunk wishes to report unrecognized
parameters.
Stewart Standards Track [Page 47]
RFC 4960 Stream Control Transmission Protocol September 2007
3.3.10.9. No User Data (9)
Cause of error
---------------
No User Data: This error cause is returned to the originator of a
DATA chunk if a received DATA chunk has no user data.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cause Code=9 | Cause Length=8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ TSN value /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
TSN value: 32 bits (unsigned integer)
The TSN value field contains the TSN of the DATA chunk received
with no user data field.
This cause code is normally returned in an ABORT chunk (see
Section 6.2).
3.3.10.10. Cookie Received While Shutting Down (10)
Cause of error
---------------
Cookie Received While Shutting Down: A COOKIE ECHO was received while
the endpoint was in the SHUTDOWN-ACK-SENT state. This error is
usually returned in an ERROR chunk bundled with the retransmitted
SHUTDOWN ACK.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cause Code=10 | Cause Length=4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Stewart Standards Track [Page 48]
RFC 4960 Stream Control Transmission Protocol September 2007
3.3.10.11. Restart of an Association with New Addresses (11)
Cause of error
--------------
Restart of an association with new addresses: An INIT was received on
an existing association. But the INIT added addresses to the
association that were previously NOT part of the association. The
new addresses are listed in the error code. This ERROR is normally
sent as part of an ABORT refusing the INIT (see Section 5.2).
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cause Code=11 | Cause Length=Variable |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ New Address TLVs /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Note: Each New Address TLV is an exact copy of the TLV that was found
in the INIT chunk that was new, including the Parameter Type and the
Parameter Length.
3.3.10.12. User-Initiated Abort (12)
Cause of error
--------------
This error cause MAY be included in ABORT chunks that are sent
because of an upper-layer request. The upper layer can specify an
Upper Layer Abort Reason that is transported by SCTP transparently
and MAY be delivered to the upper-layer protocol at the peer.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cause Code=12 | Cause Length=Variable |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ Upper Layer Abort Reason /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Stewart Standards Track [Page 49]
RFC 4960 Stream Control Transmission Protocol September 2007
3.3.10.13. Protocol Violation (13)
Cause of error
--------------
This error cause MAY be included in ABORT chunks that are sent
because an SCTP endpoint detects a protocol violation of the peer
that is not covered by the error causes described in Section 3.3.10.1
to Section 3.3.10.12. An implementation MAY provide additional
information specifying what kind of protocol violation has been
detected.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cause Code=13 | Cause Length=Variable |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ Additional Information /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3.3.11. Cookie Echo (COOKIE ECHO) (10)
This chunk is used only during the initialization of an association.
It is sent by the initiator of an association to its peer to complete
the initialization process. This chunk MUST precede any DATA chunk
sent within the association, but MAY be bundled with one or more DATA
chunks in the same packet.
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 = 10 |Chunk Flags | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ Cookie /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Chunk Flags: 8 bit
Set to 0 on transmit and ignored on receipt.
Length: 16 bits (unsigned integer)
Set to the size of the chunk in bytes, including the 4 bytes of
the chunk header and the size of the cookie.
Stewart Standards Track [Page 50]
RFC 4960 Stream Control Transmission Protocol September 2007
Cookie: variable size
This field must contain the exact cookie received in the State
Cookie parameter from the previous INIT ACK.
An implementation SHOULD make the cookie as small as possible to
ensure interoperability.
Note: A Cookie Echo does NOT contain a State Cookie parameter;
instead, the data within the State Cookie's Parameter Value
becomes the data within the Cookie Echo's Chunk Value. This
allows an implementation to change only the first 2 bytes of the
State Cookie parameter to become a COOKIE ECHO chunk.
3.3.12. Cookie Acknowledgement (COOKIE ACK) (11)
This chunk is used only during the initialization of an association.
It is used to acknowledge the receipt of a COOKIE ECHO chunk. This
chunk MUST precede any DATA or SACK chunk sent within the
association, but MAY be bundled with one or more DATA chunks or SACK
chunk's in the same SCTP packet.
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 = 11 |Chunk Flags | Length = 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Chunk Flags: 8 bits
Set to 0 on transmit and ignored on receipt.
3.3.13. Shutdown Complete (SHUTDOWN COMPLETE) (14)
T |
