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Listed below is the contents of file draft-ietf-tsvwg-addip-sctp-01.txt.
Network Working Group R. R. Stewart
INTERNET-DRAFT M. A. Ramalho
Cisco Systems
Q. Xie
Motorola
M. Tuexen
Siemens AG
I. Rytina
Ericsson
P. Conrad
Temple University
expires in six months June 6, 2001
SCTP Extensions for Dynamic Reconfiguration of IP Addresses
and Enforcement of Flow and Message Limits
<draft-ietf-tsvwg-addip-sctp-01.txt>
Status of This Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC 2026 [RFC2026]. Internet-Drafts
are working documents of the Internet Engineering Task Force (IETF),
its areas, and its working groups. Note that other groups may also
distribute working documents as Internet-Drafts.
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
Abstract
This document describes extensions to the Stream Control
Transmission Protocol (SCTP) [RFC2960] that provide methods to (1)
reconfigure IP address information on an existing association and
(2) request that a peer set flow limits in units of bytes or
messages, either on a per-stream or per-association basis.
TABLE OF CONTENTS
1. Introduction............................................... 2
2. Conventions................................................ 3
3. Additional Chunks and Parameters........................... 3
3.1 New Chunk Types........................................... 4
3.1.1 Address Configuration Change Chunk (ASCONF)............ 4
3.1.2 Address Configuration Acknowledgment Chunk (ASCONF-ACK). 5
3.2 New Parameter Types....................................... 6
3.2.1 Add IP Address.......................................... 7
3.2.2 Delete IP Address....................................... 7
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3.2.3 Stream Flow Limit Change................................ 8
3.2.4 Error Cause Indication.................................. 9
3.2.5 Set Primary IP Address.................................. 9
3.2.6 Success Indication......................................10
3.2.7 Stream Message Limit Change.............................10
3.2.8 Association Message Limit Change........................11
3.3 New Error Causes..........................................11
3.3.1 Error Cause: Request to Delete Last Remaining
IP Address..............................................12
3.3.2 Error Cause: Operation Refused Due to Resource Shortage.12
3.3.3 Error Cause: Request to Delete Source IP Address........13
4. Procedures.................................................13
4.1 ASCONF Chunk Procedures...................................14
4.1.1 Congestion Control of ASCONF Chunks.....................15
4.2 Upon reception of an ASCONF Chunk.........................16
4.3 General rules for address manipulation....................18
4.3.1 A special case for OOTB ABORT chunks....................20
4.3.2 A special case for changing an address..................21
4.4 Setting of the primary address............................21
4.5 Stream Flow/Message Limit Procedures......................21
4.5.1 Stream receiver side procedures.........................22
4.5.2 Stream sender side procedures...........................23
4.5.3 ULP considerations on the use of SCTP flow limit
facility................................................24
4.6 Association Message Limit Procedures......................24
4.6.1 Receiver side procedures................................25
4.6.2 Sender side procedures..................................25
5. Security Considerations....................................25
6. IANA considerations........................................26
7. Authors' Addresses.........................................26
8. References.................................................27
1. Introduction
To extend the utility and application scenarios of SCTP, this
document introduces optional extensions that provide SCTP with the
ability to reconfigure IP address information on an existing
association or to request that the peer set flow limits in units
of bytes or messages, either on a per-stream or per-association
basis.
These extensions enable SCTP to be utilized in the following
applications:
- Dynamic IP address reconfiguration extension: For
computational or networking platforms that allow addition/removal of
physical interface cards this feature can provide:
A) a graceful method to add to the interfaces of an existing
association. For IPv6 this feature allows renumbering
of existing associations.
B) a method for an endpoint to request that its peer set
its primary destination address. This can be useful
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when an address is about to be deleted, or when an endpoint
has some predetermined knowledge about which is the
preferred address to receive SCTP packets upon.
- The SCTP flow limit extension: This extension enables
a receiver to request that a sender impose a byte limit on the
outstanding data present on a per-stream basis.
The SCTP flow limit extension provides:
A) The ability to minimize the occurrence of a single stream
monopolizing all transport level resources (e.g. a_rwnd
"deadlock").
B) The ability to dynamically change the stream buffering
limits as the application deems appropriate at any particular
instant.
- The SCTP message limit extension: This extension enables a
receiver to request that a sender impose a limit on the number
of outstanding messages present on:
A) each stream, and/or
B) the whole association.
The SCTP message limit extension provides a method for minimizing
the occurrence of a lack of resources needed for messages even
when resources for payload data are still available. This can
become important when handling a large number of short messages.
2. Conventions
The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
SHOULD NOT, RECOMMENDED, NOT RECOMMENDED, MAY, and OPTIONAL, when
they appear in this document, are to be interpreted as described in
RFC 2119 [RFC2119].
3. Additional Chunks and Parameters
This section describes the addition of two new chunks and, eight
new parameters to allow:
- Dynamic addition of IP Addresses to an association.
- Dynamic deletion of IP Addresses to an association.
- A request to set the primary address the peer will
use when sending to an endpoint.
- The setting of stream byte limits.
- The setting of stream message limits.
- The setting of association message limits.
Additionally, this section describes three new error causes that
support these new chunks and parameters.
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3.1 New Chunk Types
This section defines two new chunk types that will be used to
transfer the control information reliably. Table 1 illustrates the
two new chunk types.
Chunk Type Chunk Name
--------------------------------------------------------------
0xC1 Address/Stream Configuration Change Chunk (ASCONF)
0x80 Address Configuration Acknowledgment (ASCONF-ACK)
Table 1: Address/Stream Configuration Chunks
It should be noted that the ASCONF Chunk format requires the
receiver to report to the sender if it does not understand the
ASCONF Chunk. This is accomplished by setting the upper bits in the
chunk type as described in [RFC2960] section 3.2. Note that the
upper two bits in the ASCONF Chunk are set to one. As defined in
[RFC2960] section 3.2, setting these upper bits in this manner will
cause the receiver that does not understand this chunk to skip the
chunk and continue processing, but report in an Operation Error
Chunk using the 'Unrecognized Chunk Type' cause of error.
3.1.1 Address Configuration Change Chunk (ASCONF)
This chunk is used to communicate to the remote endpoint one of the
configuration change requests that MUST be acknowledged. The
information carried in the ASCONF Chunk uses the form of a
Tag-Length-Value (TLV), as described in "3.2.1
Optional/Variable-length Parameter Format" in [RFC2960], for
all variable 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 = 0xC1 | Chunk Flags | Chunk Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Serial Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Addr Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address Bytes 0-3 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address Bytes 4-7 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address Bytes 8-11 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address Bytes 12-15 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ASCONF-Request Correlation ID #1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ASCONF Parameter #1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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\ \
/ .... /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ASCONF-Request Correlation ID #N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ASCONF Parameter #N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Serial Number : 32 bits (unsigned integer)
This value represents a Serial Number for the ASCONF Chunk. The
valid range of Serial Number is from 0 to 4294967295 (2**32 - 1).
Serial Numbers wrap back to 0 after reaching 4294967295.
Reserved: 24 bits
Reserved, set to 0 by the sender and ignored by the
receiver.
Address Type : 8 bits (unsigned char)
This value determines the type of address found in the
Address Bytes field. If the value is 5 then the first
4 bytes of the Address Bytes field contain an IPv4 address,
in network byte order. If the value is 6 then the first
16 bytes of the Address Bytes field contain an IPv6 address,
in network byte order.
Address Bytes: 16 bytes (unsigned chars)
This field contains an address which is part of the association.
This field may be used by the receiver of the ASCONF to help
in finding the association.
ASCONF-Request Correlation ID: 32 bits (unsigned integer)
This is an opaque integer assigned by the sender to identify each
request parameter. It is in host byte order and is only meaningful
to the sender. The receiver of the ASCONF Chunk will copy this 32
bit value into the ASCONF Correlation ID field of the
ASCONF-ACK. The sender of the ASCONF can use this same value in the
ASCONF-ACK to find which request the response is for.
ASCONF Parameter: TLV format
Each Address configuration change is represented by a TLV
parameter as defined in Section 3.2. One or more requests
may be present in an ASCONF Chunk.
3.1.2 Address Configuration Acknowledgment Chunk (ASCONF-ACK)
This chunk is used by the receiver of an ASCONF Chunk to acknowledge
the reception. It carries zero or more results for any ASCONF
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Parameters that were processed by the receiver.
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 = 0x80 | Chunk Flags | Chunk Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Serial Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ASCONF-Request Correlation ID #1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ASCONF Parameter Response#1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ .... /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ASCONF-Request Correlation ID #N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ASCONF Parameter Response#N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Serial Number : 32 bits (unsigned integer)
This value represents the Serial Number for the received ASCONF Chunk
that is acknowledged by this chunk. This value is
copied from the received ASCONF Chunk.
ASCONF-Request Correlation ID: 32 bits (unsigned integer)
This value is copied from the ASCONF Correlation ID received in the
ASCONF Chunk. It is used by the receiver of the ASCONF-ACK to identify
which ASCONF parameter this response is associated with.
ASCONF Parameter Response : TLV format
The ASCONF Parameter Response is used in the ASCONF-ACK to report
status of ASCONF processing. By default, if a responding endpoint
does not include any Error Cause, a success is indicated. Thus a
sender of an ASCONF-ACK MAY indicate complete success of all TLVs in
an ASCONF by returning only the Chunk Type, Chunk Flags, Chunk Length
(set to 8) and the Serial Number.
3.2 New Parameter Types
The eight new parameters added follow the format defined in section
3.2.1 of [RFC2960]. Table 2 describes the parameters.
Address Configuration Parameters Parameter Type
-------------------------------------------------
Add IP Address 0xC001
Delete IP Address 0xC002
Stream Byte Limit Request 0xC003
Error Cause Indication 0xC004
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Set Primary Address 0xC005
Success report 0xC006
Stream Message Limit Request 0xC007
Association Message Limit Request 0xC008
Table 2: Address Configuration Parameters
3.2.1 Add IP Address
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 = 0xC001 | Length = Variable |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address Parameter |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Address Parameter: TLV
This field contains an IPv4 or IPv6 address parameter as described
in 3.3.2.1 of RFC2960. The complete TLV is wrapped within this
parameter. It informs the receiver that the address specified is to
be added to the existing association.
An example TLV requesting that the IPv4 address 10.1.1.1 be
added to the association would look as follows:
+--------------------------------+
| Type=0xC001 | Length = 12 |
+--------------------------------+
| Type=5 | Length = 8 |
+----------------+---------------+
| Value=0x0a010101 |
+----------------+---------------+
Valid Chunk Appearance
The Add IP Address parameter may only appear in the ASCONF Chunk
type.
3.2.2 Delete IP Address
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 =0xC002 | Length = Variable |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address Parameter |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Address Parameter: TLV
This field contains an IPv4 or IPv6 address parameter as described in
3.3.2.1 of [RFC2960]. The complete TLV is wrapped within this
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parameter. It informs the receiver that the address specified is to
be removed from the existing association.
An example TLV deleting the IPv4 address 10.1.1.1 from an existing
association would look as follows:
+--------------------------------+
| Type=0xC002 | Length = 12 |
+--------------------------------+
| Type=5 | Length = 8 |
+----------------+---------------+
| Value=0x0a010101 |
+----------------+---------------+
Valid Chunk Appearance
The Delete IP Address parameter may only appear in the ASCONF Chunk
type.
3.2.3 Stream Flow Limit Change
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 =0xC003 | Length = Variable |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Stream Number 1 | Byte Limit 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ /
/ \
\ /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Stream Number N | Byte Limit N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Stream Number n : 16 bits (unsigned integer)
This is the stream number for which a limit is to be enforced.
Byte Limit n : 16 bits (unsigned integer)
This is the limit (in bytes) that the receiver (sending the chunk)
is requesting that the sender (receiver of the chunk) enforce as
the maximum amount of outstanding data permitted at any time on
this stream, as per the rules in Section 4.5. Note that the value
'0' holds a special meaning described in Section 4.5.1
Valid Chunk Appearance
The Stream Flow Limit Change parameter may appear in the ASCONF
chunk, the INIT, or the INIT-ACK chunk type. The inclusion of this
parameter in the INIT or INIT-ACK can be used to indicate initial
byte limits.
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3.2.4 Error Cause Indication
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 = 0xC004 | Length = Variable |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Error Cause(s) or Return Info on Success |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
When reporting an error this response parameter is used to wrap
one or more standard error causes normally found within an SCTP
Operational Error or SCTP Abort (as defined in [RFC2960]). The
Error Cause(s) follow the format defined in section 3.3.10 of
[RFC2960].
Valid Chunk Appearance
The Error Cause Indication parameter may only appear in the
ASCONF-ACK chunk type.
3.2.5 Set Primary IP Address
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 =0xC005 | Length = Variable |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address Parameter |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Address Parameter: TLV
This field contains an IPv4 or IPv6 address parameter as described in
3.3.2.1 of [RFC2960]. The complete TLV is wrapped within this
parameter. It requests the receiver to mark the specified address
as the primary address to send data to (see section 5.1.2 of
[RFC2960]). The receiver MAY mark this as its primary upon
receiving this request.
An example TLV requesting that the IPv4 address 10.1.1.1 be made the
primary destination address would look as follows:
+--------------------------------+
| Type=0xC005 | Length = 12 |
+--------------------------------+
| Type=5 | Length = 8 |
+----------------+---------------+
| Value=0x0a010101 |
+----------------+---------------+
Valid Chunk Appearance
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The Set Primary IP Address parameter may appear in the ASCONF Chunk,
the INIT, or the INIT-ACK chunk type. The inclusion of this parameter
in the INIT or INIT-ACK can be used to indicate an initial preference
of primary address.
3.2.6 Success Indication
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 0xC006 | Length = 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
By default if a responding endpoint does not report an error for any
requested TLV, a success is implicitly indicated. Thus a sender of a
ASCONF-ACK MAY indicate complete success of all TLVs in an ASCONF by
returning only the Chunk Type, Chunk Flags, Chunk Length (set to 8)
and the Serial Number.
The responding endpoint MAY also choose to explicitly report a
success for a requested TLV, by returning a success report ASCONF
Parameter Response.
Valid Chunk Appearance
The Success Indication parameter may only appear in the ASCONF-ACK
chunk type.
3.2.7 Stream Message Limit Change
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 =0xC007 | Length = Variable |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Stream Number 1 | Message Limit 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ /
/ \
\ /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Stream Number N | Message Limit N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Stream Number n : 16 bits (unsigned integer)
This is the stream number for which a limit is to be enforced.
Message Limit n : 16 bits (unsigned integer)
This is the limit (in messages) that the receiver (sending the
chunk) is requesting that the sender (receiver of the chunk)
enforce as the maximum number of outstanding messages permitted at
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any time on this stream, as per the rules in Section 4.5. Note
that the value '0' holds a special meaning described in Section
4.5.1.
Valid Chunk Appearance
The Stream Message Limit Change parameter may appear in the ASCONF
chunk, the INIT, or the INIT-ACK chunk type. The inclusion of this
parameter in the INIT or INIT-ACK can be used to indicate initial
stream message limits.
3.2.8 Association Message Limit Change
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 =0xC008 | Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Association Message Limit |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Association Message Limit n : 32 bits (unsigned integer)
This is the limit (in messages) that the receiver (sending the
chunk) is requesting that the sender (receiver of the chunk)
enforce as the maximum number of outstanding messages permitted at
any time on the association, as per the rules in Section 4.6.
Note that the value 0 holds a special meaning described in Section
4.5.1
Valid Chunk Appearance
The Association Message Limit Change parameter may appear in the
ASCONF Chunk, the INIT, or the INIT-ACK chunk type. The inclusion
of this parameter in the INIT or INIT-ACK can be used to indicate
an initial association message limit.
3.3 New Error Causes
Three new Error Causes are added to the SCTP Operational Errors,
primarily for use in the ASCONF-ACK chunk.
Cause Code
Value Cause Code
--------- ----------------
0xC Request to Delete Last Remaining IP Address.
0xD Operation Refused Due to Resource Shortage.
0xE Request to Delete Source IP Address.
Table 3: New Error Causes
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3.3.1 Error Cause: Request to Delete Last Remaining IP Address
Cause of error
---------------
Request to Delete Last Remaining IP address: The receiver of this
error sent a request to delete the last IP address from its
association with its peer. This error indicates that the request is
rejected.
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=0x000C | Cause Length=Variable |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ TLV-Copied-From-ASCONF /
/ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
An example of a failed delete in an Error Cause TLV would look as
follows in the response ASCONF-ACK message:
+--------------------------------+
| Type = 0xC004 | Length = 20 |
+--------------------------------+
| Cause=0x000C | Length = 16 |
+----------------+---------------+
| Type= 0xC002 | Length = 12 |
+----------------+---------------+
| Type=0x0005 | Length = 8 |
+----------------+---------------+
| Value=0x0A010101 |
+----------------+---------------+
3.3.2 Error Cause: Operation Refused Due to Resource Shortage
Cause of error
---------------
This error cause is used to report a failure by the receiver to
perform the requested operation due to a lack of resources. The
entire TLV that is refused is copied from the ASCONF-REQ into the
error cause.
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=0x000D | Cause Length=Variable |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ TLV-Copied-From-ASCONF /
/ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
An example of a failed addition in an Error Cause TLV would look as
follows in the response ASCONF-ACK message:
+--------------------------------+
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| Type = 0xC004 | Length = 20 |
+--------------------------------+
| Cause=0x000D | Length = 16 |
+----------------+---------------+
| Type=0xC001 | Length = 12 |
+--------------------------------+
| Type=0x0005 | Length = 8 |
+----------------+---------------+
| Value=0x0A010101 |
+----------------+---------------+
3.3.3 Error Cause: Request to Delete Source IP Address
Cause of error
---------------
Request to Delete Source IP Address: The receiver of this error sent
a request to delete the source IP address of the ASCONF
message. This error indicates that the request is rejected.
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=0x000E | Cause Length=Variable |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ TLV-Copied-From-ASCONF /
/ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
An example of a failed delete in an Error Cause TLV would look as
follows in the response ASCONF-ACK message:
+--------------------------------+
| Type = 0xC004 | Length = 20 |
+--------------------------------+
| Cause=0x000E | Length = 16 |
+----------------+---------------+
| Type=0xC002 | Length = 12 |
+----------------+---------------+
| Type=0x0005 | Length = 8 |
+----------------+---------------+
| Value=0x0A010101 |
+----------------+---------------+
IMPLEMENTATION NOTE: It is unlikely that an endpoint would source
a packet from the address being deleted, unless the endpoint
does not do proper source address selection.
4. Procedures
This section will lay out the specific procedures for address/stream
configuration change chunk type and its processing.
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4.1 ASCONF Chunk Procedures
When an endpoint has an ASCONF signaled change to be sent to the
remote endpoint it should do the following:
A1) Create an ASCONF Chunk as defined in section 3.1.1. The chunk
should contain all of the TLV(s) of information necessary to be
sent to the remote endpoint, and unique correlation identities for
each request.
A2) A serial number should be assigned to the Chunk. The serial
number should be a monotonically increasing number. All serial
numbers are defined to be initialized at the start of the
association to the same value as the Initial TSN.
A3) If no ASCONF Chunk is outstanding (un-acknowledged) with the
remote peer, AND there is less than cwnd bytes of user data
outstanding, send the chunk.
A4) Start a T-4 RTO timer, using the RTO value of the selected
destination address (normally the primary path; see [RFC2960] section
6.4 for details).
A5) When the ASCONF-ACK that acknowledges the serial number last
sent arrives, stop the T-4 RTO timer, and clear the appropriate
association and destination error counters as defined in [RFC2960]
section 8.1 and 8.2.
A6) Process all of the TLVs within the ASCONF-ACK to find out
particular status information returned to the various requests that
were sent. Use the Correlation IDs to correlate the request and the
responses.
A7) If an error response is received for a TLV parameter,
all TLVs with no response before the failed TLV are considered
successful if not reported. All TLVs after the failed response are
considered unsuccessful unless a specific success indication is
present for the parameter.
A8) If there is no response(s) to specific TLV parameter(s), and no
failures are indicated, then all request(s) are considered
successful.
If the T-4 RTO timer expires the endpoint should do the following:
B1) Increment the error counter and perform path failure detection
on the appropriate destination address as defined in [RFC2960]
section 8.2.
B2) Increment the association error counter and perform endpoint
failure detection on the association as defined in [RFC2960] section
8.1.
B3) Back-off the destination address RTO timer to which the ASCONF
chunk was sent by doubling the RTO timer value.
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B4) Re-transmit the ASCONF Chunk last sent and if possible choose an
alternate destination address (please refer to [RFC2960] section
6.4.1). An endpoint MUST NOT add new parameters to this chunk, it
MUST be the same (including its serial number) as the last ASCONF
sent.
B5) Restart the T-4 RTO timer. Note that if a different destination is
selected, then the RTO used will be that of the new destination
address.
Note: the total number of re-transmissions is limited by B2
above. If the maximum is reached, the association will fail and enter
a CLOSED state (see [RFC2960] section 6.4.1 for details).
4.1.1 Congestion Control of ASCONF Chunks
In defining the ASCONF Chunk transfer procedures, it is essential
that these transfers MUST NOT cause congestion within the network.
To achieve this, we place these restrictions on the transfer of
ASCONF Chunks:
R1) One and only one ASCONF Chunk MAY be in transit and
unacknowledged at any one time. If a sender, after sending an ASCONF
chunk, decides it needs to transfer another ASCONF Chunk, it MUST
wait until the ASCONF-ACK Chunk returns from the previous ASCONF
Chunk before sending a subsequent ASCONF. Note this restriction
binds each side, so at any time two ASCONF may be in-transit on any
given association (one sent from each endpoint).
R2) A ASCONF MUST NOT be sent if there is no room in the current
cwnd. If there is room in the cwnd of the destination network, the
Chunk may be sent regardless of the value of rwnd.
R3) A ASCONF may be bundled with any other chunk type (except other
ASCONF Chunks) as long as the source address in the IP header of
the packet is already a part of the association. If the ASCONF
chunk is using an alternate source address as the source in
the IP header, then NO other chunks may be bundled with the ASCONF
chunk.
R4) A ASCONF-ACK may be bundled with any other chunk type except
other ASCONF-ACKs.
R5) Both ASCONF and ASCONF-ACK chunks MUST NOT be sent in any SCTP
state except ESTABLISHED.
R6) An ASCONF and respective ASCONF-ACK MUST NOT be larger than the
path MTU of the destination.
If the sender of an ASCONF Chunk receives a Operational Error
indicating that the ASCONF chunk type is not understood, then the
sender MUST not send subsequent ASCONF Chunks to the peer. The
endpoint should also inform the upper layer application that the
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peer endpoint does not support any of the extensions detailed in this
document.
4.2 Upon reception of an ASCONF Chunk.
When an endpoint receives an ASCONF Chunk from the remote peer
special procedures MAY be needed to identify the association
the ASCONF Chunk is associated with. To properly find the
association the following procedures should be followed:
L1) Use the source address and port number of the sender to
attempt to identify the association (i.e. use the same method
defined in [RFC2960] used for all other SCTP chunks ). If found
proceed to rule L5.
L2) If the association is not found, use the address found
in the Address Bytes field combined with the port number
found in the SCTP common header. If found proceed to rule
L4.
L3) If neither L1 or L2 locates the association, treat
the chunk as an Out Of The Blue chunk as defined in
[RFC2960].
L4) Verify that no other chunk is bundled with the ASCONF
chunk. If other chunks are bundled with the ASCONF Chunk
then the receiver MUST silently discard the ASCONF chunk.
L5) Follow the normal rules to validate the SCTP verification
tag found in [RFC2960].
After identification and verification of the association,
the following should be performed to properly process the ASCONF Chunk:
C1) Compare the value of the serial number to the value the endpoint
stored in a new association variable 'Peer-Serial-Number'. This
value MUST be initialized to the Initial TSN value minus 1.
C2) If the value found in the serial number is equal to the the
('Peer-Serial-Number' + 1), the endpoint should:
V1) Process the TLVs contained within the Chunk performing the
appropriate actions as indicated by each TLV type. The TLVs MUST
be processed in order within the Chunk. For example, if the sender
puts 3 TLVs in one chunk, the first TLV (the one closest to the
Chunk Header) in the Chunk MUST be processed first. The next TLV in
the chunk (the middle one) MUST be processed second and finally the
last TLV in the Chunk MUST be processed last.
V2) In processing the chunk, the receiver should build a response
message with the appropriate error TLVs, as specified in the
Parameter type bits for any ASCONF Parameter it does not understand.
To indicate an unrecognized parameter, parameter type 8 as defined
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in in the INIT-ACK in 3.3.3 of [RFC2960] should be used. The
endpoint may also use the response to carry rejections for other
reasons such as resource shortages etc using the Error Cause TLV and
an appropriate error condition.
Note: a positive response is implied if no error is indicated by the
sender.
V3) All error responses MUST copy the ASCONF-Request Correlation ID
field received in the ASCONF, from the TLV being responded to, into
the ASCONF-Request Correlation ID field. The ASCONF-Request
Correlation ID always precedes the request TLV.
V4) After processing the entire Chunk, it MUST send all TLVs for
both unrecognized parameters and any other status TLVs inside the
ASCONF-ACK chunk that acknowledges the arrival and processing of the
ASCONF Chunk.
V5) Update the 'Peer-Serial-Number' to the value found in the serial
number field.
C3) If the value found in the serial number is equal to the value
stored in the 'Peer-Serial-Number', the endpoint should:
X1) Parse the ASCONF Chunk TLVs but the endpoint MUST NOT take any
action on the TLVs parsed (since it has already performed these
actions).
X2) Build a response message with the appropriate response TLVs
as specified in the ASCONF Parameter type bits, for any
parameter it does not understand or could not process.
X3) After parsing the entire Chunk, it MUST send any response
TLV errors and status with an ASCONF-ACK chunk acknowledging the
arrival and processing of the ASCONF Chunk.
X4) The endpoint MUST NOT update its 'Peer-Serial-Number'.
IMPLEMENTATION NOTE: As an optimization a receiver may wish to save
the last ASCONF-ACK for some predetermined period of time and
instead of re-processing the ASCONF (with the same serial number) it
may just re-transmit the ASCONF-ACK. It may wish to use the arrival
of a new serial number to discard the previously saved ASCONF-ACK or
any other means it may choose to expire the saved ASCONF-ACK.
C4) Otherwise, the ASCONF Chunk is discarded since it must be either
a stale packet or from an attacker. A receiver of such a packet MAY
log the event for security purposes.
C5) In both cases C2 and C3 the ASCONF-ACK MUST be sent back to the
source address contained in the IP header of the ASCONF being
responded to.
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4.3 General rules for address manipulation
When building TLV parameters for the ASCONF Chunk that
will add or delete IP addresses the following rules should be
applied:
D1) When adding an IP address to an association, the IP address is
NOT considered fully added to the association until the ASCONF-ACK
arrives. This means that until such time as the ASCONF containing
the add is acknowledged the sender MUST NOT use the new IP address
as a source for ANY SCTP chunks besides an ASCONF Chunk.
The receiver of the add IP address request may use the
address as a destination immediately.
D2) After the ASCONF-ACK of an IP address add arrives, the
endpoint MAY begin using the added IP address as a source
address for any type of SCTP chunk.
D3) If an endpoint receives an Error Cause TLV indicating that the
IP address Add, IP address Deletion, or Set Primary IP Address
parameters was not understood, the endpoint MUST consider the
operation failed and MUST NOT attempt to send any subsequent Add,
Delete or Set Primary requests to the peer.
D4) When deleting an IP address from an association, the IP address
MUST be considered a valid destination address for the reception of
SCTP packets until the ASCONF-ACK arrives and MUST NOT be used as a
source address for any subsequent packets. This means that any
datagrams that arrive before the ASCONF-ACK destined to the IP address
being deleted MUST be considered part of the current
association. One special consideration is that ABORT chunks arriving
destined to the IP address being deleted MUST be ignored (see
Section 4.3.1 for further details).
D5) An endpoint MUST NOT delete its last remaining IP address from an
association. In other words if an endpoint is NOT multi-homed it
MUST NOT use the delete IP address. Or if an endpoint sends multiple
requests to delete IP addresses it MUST NOT delete all of the IP
addresses that the peer has listed for the requester.
D6) An endpoint MUST NOT set a IP header source address for an SCTP
packet holding the ASCONF Chunk to be the same as an address being
deleted by the ASCONF Chunk.
D7) If a request is received to delete the last remaining IP address
of a peer endpoint, the receiver MUST send an Error Cause TLV with
the error cause set to the new error code 'Request to Delete Last
Remaining IP Address'. The requested delete MUST NOT be performed or
acted upon, other than to send the ASCONF-ACK.
D8) If a request is received to delete an IP address which is also
the source address of the IP packet which contained the ASCONF
chunk, the receiver MUST reject this request. To reject the request
the receiver MUST send an Error Cause TLV set to the new error code
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'Request to Delete Source IP Address' (unless Rule D5 has also been
violated, in which case the error code 'Request to Delete Last
Remaining IP Address' is sent).
D9) If an endpoint receives an ADD IP address request and does not
have the local resources to add this new address to the association,
it MUST return an Error Cause TLV set to the new error code
'Operation Refused Due to Resource Shortage'.
D10) If an endpoint receives an 'Out of Resource' error in response
to its request to ADD an IP address to an association, it must
either ABORT the association or not consider the address part of the
association. In other words if the endpoint does not ABORT the
association, it must consider the add attempt failed and NOT use
this address and treat SCTP packets destined to the address as Out
Of The Blue packets.
D11) When an endpoint receiving an ASCONF to add an IP address sends
an 'Out of Resource' in its response, it MUST also fail any
subsequent add or delete requests bundled in the ASCONF. The
receiver MUST NOT reject an ADD and then accept a subsequent DELETE
of an IP address in the same ASCONF Chunk. In other words, once a
receiver begins failing any ADD or DELETE request, it must fail all
subsequent ADD or DELETE requests contained in that single ASCONF.
D12) When an endpoint receives a request to delete an IP address
that is the current primary address, it is an implementation
decision as to how that endpoint chooses the new primary address.
D13) When an endpoint receives a valid request to DELETE an IP
address the endpoint MUST consider the address no longer as part of
the association. It MUST NOT send SCTP packets for the association
to that address and it MUST treat subsequent packets received from
that address as Out Of The Blue.
During the time interval between sending out the ASCONF and
receiving the ASCONF-ACK it MAY be possible to receive DATA chunks
out of order. The following examples illustrate these problems:
Endpoint-A Endpoint-Z
---------- ----------
ASCONF[Add-IP:X]------------------------------>
/--ASCONF-ACK
/
/--------/---New DATA:
/ / Destination
<-------------------/ / IP:X
/
<--------------------------/
In the above example we see a new IP address (X) being added to
the Endpoint-A. However due to packet re-ordering in the network
a new DATA chunk is sent and arrives at Endpoint-A before
the ASCONF-ACK confirming the add of the address to the association.
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A similar problem exists with the deletion of an IP address as
follows:
Endpoint-A Endpoint-Z
---------- ----------
/------------New DATA:
/ Destination
/ IP:X
ASCONF [DEL-IP:X]---------/---------------->
<-----------------/------------------ASCONF-ACK
/
/
<-------------/
In this example we see a DATA chunk destined to the IP:X (which is
about to be deleted) arriving after the deletion is complete.
For the ADD case an endpoint SHOULD consider the newly adding IP
address valid for the association to receive data from during the
interval when awaiting the ASCONF-ACK. The endpoint MUST NOT source
data from this new address until the ASCONF-ACK arrives but it may
receive out of order data as illustrated and MUST NOT treat this
data as an OOTB datagram (please see [RFC2960] section 8.4). It MAY
drop the data silently or it MAY consider it part of the association
but it MUST NOT respond with an ABORT.
For the DELETE case, an endpoint MAY respond to the late arriving DATA
packet as an OOTB datagram or it MAY hold the deleting IP address for a
small period of time as still valid. If it treats the DATA packet as
an OOTB the peer will silently discard the ABORT (since by the time
the ABORT is sent the peer will have removed the IP address from this
association). If the endpoint elects to hold the IP address valid for
a period of time, it MUST NOT hold it valid longer than 2 RTO
intervals for the destination being removed.
4.3.1 A special case for OOTB ABORT chunks
Another case worth mentioning is illustrated below:
Endpoint-A Endpoint-Z
---------- ----------
New DATA:------------\
Source IP:X \
\
ASCONF-REQ[DEL-IP:X]----\------------------>
\ /---------ASCONF-ACK
\ /
\----/-----------> OOTB
(Ignored <---------------------/-------------ABORT
by rule D4) /
<---------------------/
For this case, during the deletion of an IP address, an
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Abort MUST be ignored if the destination address of the
Abort message is that of a destination being deleted.
4.3.2 A special case for changing an address.
In some instances the sender may only have one IP address in an
association that is being renumbered. When this occurs, the sender
may not be able to send to the peer the appropriate ADD/DELETE pair
and use the old address as a source in the IP header. For this
reason the sender MUST fill in the Address Bytes field with an
address that is part of the association (in this case the one being
deleted). This will allow the receiver to locate the association
without using the source address found in the IP header. Such
an SCTP packet MUST NOT be bundled with any other chunk.
The receiver of such an ASCONF chunk MUST NOT process the
SCTP packet if any other chunks are contained inside the SCTP
packet. The receiver MUST always first use the source address
found in the IP header in looking up the association. The
receiver should attempt to use the address found in the Address
Bytes field only if the lookup fails using the source address from
the IP header. The receiver MUST NOT reply to the source address
of the packet in this special case, but to the new address that
was added by the ASCONF (since the old address is no longer a part
of the association after processing).
4.4 Setting of the primary address
A sender of this option may elect to send this combined with
a deletion or addition of an address. A sender SHOULD only send
a set primary request to an address that is already considered
part of the association. In other words if a sender combines
a set primary with an add of a new IP address the set primary
will be discarded unless the add request is to be processed
BEFORE the set primary (i.e. it precedes the set primary).
A request to set primary MAY also appear in a INIT or INIT-ACK
chunk. This can give advice to the peer endpoint as to which
of its addresses the sender of the INIT or INIT-ACK would like
to be used as the primary address.
The request to set an address as the primary path is an option the
receiver SHOULD perform. It is considered advice to the receiver of
the best destination address to use in sending SCTP packets (in the
requester's view). If a request arrives that asks the receiver to
set an address as primary that does not exist, the receiver should
NOT honor the request, leaving its existing primary address
unchanged.
4.5 Stream Flow Limit and Message Limit Procedures
A stream in SCTP is an uni-directional 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
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un-ordered delivery service which may arrive out of sequence. Since
each stream is uni-directional and no feedback mechanism exists to
limit a sender, it is possible for one unique stream to monopolize
all of the transport level receiver window space. The mechanism
defined here attempts to alleviate this problem by allowing the
receiver side to communicate to the sender a limit on how much
outstanding data may be sent within a particular stream.
The procedures defined here are broken down into two sides:
o The stream receiver side or peer requesting the limit. And,
o the stream sender side or peer that MUST honor the limit request.
The receiver's side is mainly involved with sending the request to
the peer. The sender's side is where the actual flow or message
limit will be enforced. Note that the stream receiver is the
endpoint that sends the ASCONF, INIT or INIT-ACK message (see
Section 4.5.1), whereas the stream sender is the endpoint that
receives the ASCONF, INIT or INIT-ACK message (see Section 4.5.2).
4.5.1 Stream receiver side procedures
The receiver side SCTP requests byte or message limits in response
to an upper layer request. An upper layer may request, via an API
interface, that a byte or message limit be imposed on all or a
subset of the active streams that send data to the upper layer
receiver, or that a message limit be imposed on the association.
The basis on which the upper layer determines these limits is
outside the scope of this document.
Any time during an association that limits are requested of the SCTP
endpoint by the upper layer, the receiver side SHOULD create an
ASCONF Chunk and attach to a Stream Flow Limit Change, Stream
Message Limit Change, or Association Message Limit Change parameter
as appropriate. These parameter types MAY also be placed in an INIT
or INIT-ACK chunk at the beginning of an association to request
initial values for the appropriate limits.
The Stream Flow Limit Change and Stream Message Limit Changes
parameters contain a sequence of one or more pairs, each of which
consists of a specific stream number, and a byte or message limit
to be applied to that stream.
If the receiver wishes to remove the flow limit or message limit
for a specific stream, it may do so by placing the special value
'0' in the Flow Limit or Message Limit field. Once acknowledged
by the peer endpoint the receiver should consider the limit in
place.
In the case of flow or message limits contained within an INIT
chunk, any such limit is considered acknowledged with the arrival of
the INIT-ACK, provided that the peer indicates that it understands
the requested limit by NOT placing an 'unrecognized parameter' error
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in the INIT-ACK.
Similarly, for flow or message limits contained within an INIT-ACK
chunk, any such limit is considered acknowledged with the arrival of
the cookie, provided that the peer indicates that it understands the
requested limit by NOT placing an 'unrecognized parameter' error in
the cookie.
To send initial limits, ASCONF chunks are NOT bundled with the INIT
or INIT-ACK. Instead the TLV is added to the variable parameters
section of the INIT or INIT-ACK.
Note that the parameter type field upper two bits dictates that any
parameter not understood should be skipped and reported to the
sender with an Operational Error. If an Operational Error is
received that indicates that the 'Stream Byte Limit Request' or
'Stream Message Limit Request' is not understood, the sender of the
limit request MUST not send subsequent limit requests. The endpoint
SHOULD also inform the upper layer application that the peer
endpoint does not support this feature.
4.5.2 Stream Sender side procedures
When a 'Stream Byte Limit Request' or 'Stream Message Limit
Request' is received the sender MUST record each limit with its
appropriate stream.
After a limit is set on a stream the sender MUST obey the following
rules when sending to the peer on that stream:
S1) When the upper layer application attempts to send to the peer on
a stream, check
- the number of outstanding bytes sent to that stream
(those TSNs in queue to be sent, which the Cumulative TSN
Acknowledgment has not passed, on this stream) versus the limit set
for that stream (The last received limit for this stream is
henceforth termed the current limit).
- the number of outstanding messages sent on that stream (for which
not all TSNs are passed by the Cumulative TSN Acknowledgment)
versus the limit for this stream.
S2a) If the number of outstanding bytes is greater than or equal to
the current limit, the SCTP endpoint MUST reject the request and NOT
queue the data for transmit. Instead it SHOULD return an error
to the sending application.
S2b) If the number of outstanding messages is greater or equal to
the current limit, the SCTP endpoint MUST reject the request and NOT
queue the data for transmit. Instead it SHOULD return an error
to the sending application.
S3a) If the number of outstanding bytes is less than the current
limit, validate that the data to be sent plus the number of
outstanding bytes is smaller than or equal to this limit. If the
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user data plus the number of outstanding bytes is smaller than or
equal to the current limit accept the data for transmit and queue
the user data (increasing the number of outstanding data bytes on
this stream). If the user data plus the number of outstanding bytes
is larger than the current limit for this stream, the SCTP endpoint
MUST reject the request and NOT queue the data for transmit and
instead SHOULD return an error to the application.
S3b) If the number of outstanding messages is less than the current
limit, accept the data for transmit and queue the user data
(increasing the number of outstanding messages on this stream).
S4) Any time a stream limit is updated to the value of 0, consider
this indication to mean no limit is in effect for this stream.
NOTE: Stream limits do NOT change the underlying SCTP rwnd and
its usage as defined in [RFC2960]. The association MUST still
honor the rwnd when sending to the peer endpoint as defined in
[RFC2960].
4.5.3 ULP considerations on the use of SCTP flow limit facility
A side-effect of rule S3 in section 4.5.2 is that an upper limit
is imposed on the size of messages that may be sent to any stream
where a flow limit is in place. Once a flow limit is in effect,
if the sending Upper Layer Protocol (ULP) wishes to send a message
that is larger than that permitted by the imposed stream limit,
the ULP will need to provide a mechanism for fragmentation and
re-assembly.
This ULP mechanism is in addition to any fragmentation and
re-assembly that may be provided by SCTP. It is the sole
responsibility of the ULP to handle the case of a single user
message being larger than the stream byte limit, if applicable.
4.6 Association Message Limit Procedures
Using the stream flow/message limit functionality described
in 4.5 it is possible for a receiver to limit the sender in
a way the receiver thinks is appropriate. For an overall
(per association) byte based limit the receiver can make use
of the rwnd field in SACK-chunks.
An overall message based limit is provided by the 'Association
Message Limit Request'. This can be useful to make better use of
message oriented pools (e.g. mbufs) and to limit the delivery time
for messages.
The procedures defined here are broken down into two sides:
o The receiver side or peer requesting the limit. And,
o the sender side or peer that MUST honor the limit request.
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The receiver's side is mainly involved with sending the request to
the peer. The sender's side is where the actual limitations and flow
message limit will occur. Note in section 4.6.1 the receiver
is the endpoint that sends the ASCONF, INIT or INIT-ACK message, in
section 4.6.2 the sender side is the endpoint that receives
the ASCONF, INIT or INIT-ACK message.
4.6.1 Receiver side procedures
The same rules as given in 4.5.1 for the stream limits apply to the
association limit.
4.6.2 Sender side procedures
When an 'Association Message Limit Request' is received the sender MUST
record this limit for the association.
After a limit is set for the association the sender MUST obey the
following rules when sending to the peer on that stream:
S1) When the upper layer application attempts to send to the peer on
a stream, check the number of outstanding messages sent on the
association (for which not all TSNs are passed by the Cumulative TSN
Acknowledgment) versus the limit for this association.
S2) If the number of outstanding messages is greater or equal to
the current limit, the SCTP endpoint MUST reject the request and NOT
queue the data for transmit. Instead it SHOULD return an error
to the sending application.
S3) If the number of outstanding messages is less than the current
limit, accept the data for transmit and queue the user data
(increasing the number of outstanding messages on this association).
S4) Any time the association limit is updated to the value of 0,
consider this indication to mean no limit is in effect for the
Association.
5. Security Considerations
The ADD/DELETE of an IP address to an existing association does
provide an additional mechanism by which existing associations can
be hijacked. Where the attacker is able to intercept and or alter
the packets sent and received in an association, the use of this
feature MAY increase the ease with which an association may be
overtaken. This threat SHOULD be considered when deploying a version
of SCTP that makes use of this feature. The IP Authentication Header
[RFC2402] SHOULD be used when the threat environment requires
stronger integrity protections, but does not require
confidentiality. It should be noted that in the base SCTP
specification [RFC2960], if an attacker is able to intercept and or
alter packets, even without this feature it is possible to hijack an
existing association; please refer to Section 11 of RFC2960.
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6. IANA considerations
This document defines the following new SCTP parameters, chunks
and errors:
- Two new chunk types,
- Eight parameter types, and
- Three new SCTP error causes.
7. Acknowledgments
The authors wish to thank Jon Berger, John Loughney, Ivan Arias
Rodriguez, Marshall Rose, and Chip Sharp for their invaluable
comments.
8. Authors' Addresses
Randall R. Stewart Tel: +1-815-477-2127
Cisco Systems, Inc. EMail: [email protected]
8745 W. Higgins Road, Suite 200
Chicago, Ill 60631
USA
Micheal A. Ramalho Tel: +1-732-809-0188
Cisco Systems, Inc. EMail: [email protected]
1802 Rue de la Porte
Wall Township, NJ 0719-3784
Qiaobing Xie Tel: +1-847-632-3028
Motorola, Inc. EMail: [email protected]
1501 W. Shure Drive, #2309
Arlington Heights, IL 60004
USA
Michael Tuexen Tel: +49-89-722-47210
SIEMENS AG EMail: [email protected]
Hofmannstr. 51
81359 Munich
Germany
Ian Rytina Tel: +61-3-9301-6164
Ericsson Australia EMail:[email protected]
37/360 Elizabeth Street
Melbourne, Victoria 3000
Australia
Phil Conrad Tel: +1-215-204-7910
Netlab Research Group Email [email protected]
Dept. Of Computer &
Information Sciences
Temple University
1805 N Broad St.
Philadelphia, PA 19122
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USA
9. References
[RFC2960] R. R. Stewart, Q. Xie, K. Morneault, C. Sharp,
H. J. Schwarzbauer, T. Taylor, I. Rytina, M. Kalla, L. Zhang,
and, V. Paxson, "Stream Control Transmission Protocol," RFC
2960, October 2000.
[RFC2026] Bradner, S., "The Internet Standards Process -- Revision
3", RFC 2026, October 1996.
[RFC2119] Bradner, S. "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2402] S. Kent, R. Atkinson., "IP Authentication Header.", RFC
2402, November 1998.
This Internet Draft expires in 6 months from May, 2001
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