Network Working Group R. R. Stewart
INTERNET-DRAFT Cisco Systems
Q. Xie
Motorola
M. Tuexen
Seimens AG
I. Rytina
Ericsson
expires in six months September 7 ,2000
SCTP Dynamic Addition of IP addresses
<draft-stewart-addip-sctp-sigtran-00.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.
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Abstract
This document describes an extension to the Stream Control
Transmission Protocol (SCTP) [RFCXXXX] to provide a method to add or
delete an IP address from a existing association. Also this document
will provide a generic method for transmitting a reliable control
chunk. The benefits of these extensions are a) uniform methods for the
addition of control chunks that must be reliable and b) for machines
with hot pluggable interface cards the ability to add (and or delete)
IP addresses dynamically without forcing an association restart.
TABLE OF CONTENTS
1. Introduction............................................... 2
2. Conventions................................................ 2
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3. Chunk and Parameter Format................................. 3
3.1 New Chunk Type............................................ 3
3.1.1 Reliable Request Chunk (REL-REQ)....................... 3
3.1.2 Reliable Request Acknowledgement (REL-ACK).............. 4
3.2 New REL-REQ Parameters .................................. 4
3.2.1 Add IP Address.......................................... 5
3.2.2 Delete IP Address....................................... 5
3.3 New Error Causes.......................................... 6
3.3.1 Request to delete last IP address....................... 6
4. Procedures................................................. 6
4.1 Reliable Chunk Procedures................................. 7
4.1.1 Congestion Control of Reliable Chunks................... 8
4.2 Upon reception of a REL-REQ Chunk......................... 8
4.3 IP address addition and deletion.......................... 9
5. Security Considerations....................................11
6. IANA considerations........................................11
7. Authors' Addresses.........................................11
8. References.................................................12
1. Introduction
Taking advantage of the extensibility of SCTP, this document adds a
standard method to SCTP to send and receive reliable control
information. This method is designed to be friendly to the TCP type
congestion control within the the network. This document will also
introduce the first use of the new control chunk, i.e. the ability of
an existing SCTP association to add or delete IP addresses without the
currently required restart of the association. The following are some
of the deemed advantages to this extension:
A) A uniform method for adding control information that must be
sent reliably.
B) The reliable transfer extension is designed NOT to interfere with the
currently defined congestion control mechanisms within SCTP and the
network. This is accomplished by limiting when and how often a
reliable control chunk may be sent.
C) Allowing SCTP to have dynamic IP addresses added and subtracted for
those machines that allow addition of a interface card. This will
provide the same type of services that exist in the SS7 world that
allow a link set to add an additional link without interference with the
operation of the link set.
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].
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3. Chunk and Parameter Formats
This section specifies the two chunks that are used by the
reliable control chunk transfer. Each new chunk is detailed
and described. After all the new chunks are described additional
new parameters are described for adding and deleting IP addresses
to an existing association.
3.1 New Chunk Types
This section defines the two new Chunk types that will be used
to transfer reliable control information. Table 1 illustrates
the two new chunk types chunks. Notice that the two reliable Chunk
formats also call for the receiver to report to the sender if it
does not understand either of the new chunk formats. This is
accomplished by setting the upper bit in the Chunk type as
described in RFCXXXX section 3.2.
Chunk Type Chunk Name
------------------------------------------------------
11000001 Reliable Request Chunk (REL-REQ)
11000010 Reliable Request Acknowledgement (REL-ACK)
Table 1 - New Chunk types
The upper two bits in both chunk types are set to one. As defined
in RFCXXXX section 3.2, these upper bits set in this manner, will
cause the receiver that does not understand these chunks to skip these
chunks and continue processing, but report in an Operation Error
Chunk using the 'Unrecognized Chunk Type' cause of error.
3.1.1 Reliable Request Chunk (REL-REQ)
This chunk is used to communicate to the remote endpoint reliable
information that must be acknowledged. The information that is being
transfered reliably is always in the form of a Tag-Length Value (TLV)
as described in "3.2.1 Optional/Variable-length Parameter Format" in
[RFCXXXX].
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| REL-REQ Parameter #1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ .... /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| REL-REQ Parameter #N |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Serial Number : 32 bits (unsigned integer)
This value represents a Serial Number for the Reliable Chunk. The
valid range of Serial Number is from 0 to 4294967295 (2**32 - 1).
Serial Numbers wrap back to 0 after reaching 4294967295.
REL-REQ Parameter: TLV format
Each piece of information that the sending endpoint wishes to
communicate reliably is incorporated in a TLV format. The upper
two bits describe the treatment of each REL-REQ Parameter if it is not
understood by the receiving endpoint (refer to RFCXXXX section
3.2.1). Multiple REL-REQ Parameters may be included in a REL-REQ.
3.1.2 Reliable Request Acknowledgement (REL-ACK)
This chunk is used by the receiver of a REL-REQ chunk to acknowledge
its reception. It carries the acknowledgement and may be bundled with
one or more Operational error chunks for any REL-REQ Parameters that
were not understood (based on the reporting bits as defined in 3.2.1
of [RFCXXXX]).
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 = 0xC2 | Chunk Flags | Chunk Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Serial Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Serial Number : 32 bits (unsigned integer)
This value represents the Serial Number for the Reliable Chunk that
was received to which this Chunk is acknowledgment of. This value is
copied from the received REL-REQ message.
3.2 New REL-REQ Parameters
This section describes the addition of two new REL-REQ Parameters to allow for
the dynamic addition and deletion of IP addresses to an existing
association. These are deemed the first parameters to use the reliable
extension chunk described in 3.1. All of the REL-REQ Parameters added follow
the format defined in [RFCXXXX] section 3.2.1. Table 2 describes the
two new REL-REQ Parameter's.
REL-REQ Parameter Type Value
-------------------------------------------------
Add IP Address 32769 (0xC001)
Delete IP Address 32770 (0xC002)
All other REL-REQ Parameter Type Values (i.e. 0 to 32768 and 32771 to
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65535) are currently defined as "Reserved by IETF". New REL-REQ
Parameters may be defined in a similar way as described for
IETF-defined Chunk Parameter Extension (see [RFCXXXX] section 13.2).
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 = 32769 | Length = Variable |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Address Type: TLV
This field contains a IPv4 or IPv6 address type parameter as described
in 3.3.2.1 of RFCXXXX. 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 adding the IPv4 address 10.1.1.1 to an existing
association would look as follows:
+--------------------------------+
| Type=32769 | Length = 12 |
+--------------------------------+
| Type=5 | Length = 8 |
+----------------+---------------+
| Value=0x0a010101 |
+----------------+---------------+
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 = 32769 | Length = Variable |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Address Type: TLV
This field contains a IPv4 or IPv6 address type parameter as described
in 3.3.2.1 of [RFCXXXX]. The complete TLV is wrapped within this 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:
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+--------------------------------+
| Type=32770 | Length = 12 |
+--------------------------------+
| Type=5 | Length = 8 |
+----------------+---------------+
| Value=0x0a010101 |
+----------------+---------------+
3.3 New Error Causes
The following new error cause is being added to the Operational
Errors. These error causes may be used with an Operational
Error or an Abort (as defined in RFCXXXX).
Cause Code
Value Cause Code
--------- ----------------
11 Request to delete last IP address
3.3.1 Request to delete last IP address
Cause of error
---------------
Request to delete last 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.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cause Code=11 | Cause Length=4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ Address Parameter /
/ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
An example of a failed delete in a operational error would
look as follows:
+--------------------------------+
| Chk=9 | Flg=0 | Length = 12 |
+--------------------------------+
| Cause=11 | Length = 8 |
+----------------+---------------+
| Value=0x0a010101 |
+----------------+---------------+
4. Procedures
This section will lay out the procedures for both the reliable chunk
transfer and the add/delete IP address REL-REQ Parameter. Future extensions
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that wish to use the reliable chunk transfer MUST NOT change the
procedures of the chunk transfer itself. Extensions SHOULD detail only
procedures related to the REL-REQ Parameters being defined by them.
4.1 Reliable Chunk Procedures
When a endpoint has reliable control information to be sent
to the remote endpoint it should do the following:
A1) Create a Reliable Request 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.
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 REL-REQ 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 [RFCXXXX]
section 6.4 for details).
A5) When the REL-ACK which 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
[RFCXXXX] section 8.1 and 8.2.
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 [RFCXXXX]
section 8.2.
B2) Increment the association error counter and perform endpoint
failure detection on the association as defined in [RFCXXXX]
section 8.1.
B3) Retransmit the REL-REQ chunk last sent and if possible choose an
alternate destination address (please refer to [RFCXXXX] section
6.4.1). A endpoint MUST NOT add new parameters to this chunk,
it MUST be the same (including its serial number) as the last
REL-REQ sent.
B4) Restart the T-4 RTO timer.
Note: That the the total number of retransmissions is limited by
B2 above. If the maximum is reached the association will fail
and enter a CLOSED state (see [RFCXXXX] section 6.4.1 for details).
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4.1.1 Congestion Control of Reliable Chunks
In defining the reliable 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
reliable chunks:
R1) One and only one REL-REQ Chunk MAY be in flight and unacknowledged
at any one time. If a sender, after sending a reliable chunk, decides
it needs to transfer another REL-REQ Chunk it MUST wait until the
REL-ACK Chunk returns from the previous Chunk before sending
a subsequent REL-REQ. Note this restriction binds each side, so
at any time two REL-REQ may be inflight on any given association
(one sent from each endpoint).
R2) A REL-REQ 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 REL-REQ MUST carry only
information to be used by the peer SCTP Endpoint.
R4) A REL-REQ may be bundled with any other Chunk type except
other REL-REQ's.
R5) A REL-ACK may be bundled with any other Chunk type except
other REL-ACK's.
4.2 Upon reception of a REL-REQ Chunk.
When an endpoint receives a REL-REQ chunk from the remote peer it
should perform the following:
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 greater than the
value stored in the 'Peer-Serial-Number', the endpoint should:
V1) Process the TLV's contained within the Chunk performing the appropriate
actions as instructed.
V2) In processing the chunk, it should build a response message with the
appropriate Operational Errors, as specified in the REL-REQ Parameter type
bits, for any REL-REQ Parameter it does not understand.
V3) After processing the entire Chunk, it MUST send any operational
errors bundled with a REL-ACK chunk acknowledging the arrival and
processing of the REL-REQ Chunk.
V4) Update the 'Peer-Serial-Number' to the value found in the serial
number field.
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C3) If the value found in the serial number is less than or equal
to the value stored in the 'Peer-Serial-Number', the endpoint should:
X1) Parse the REL-REQ Chunk TLV's but the endpoint MUST not take any
action on the TLV's parsed (since it has already performed these
actions).
X2) Build a response message with the appropriate Operational Errors,
as specified in the REL-REQ Parameter type bits, for any parameter it does
not understand.
X3) After parsing the entire Chunk, it MUST send any operational
errors bundled with a REL-ACK chunk acknowledging the arrival and
processing of the REL-REQ Chunk.
X4) The endpoint MUST NOT update its 'Peer-Serial-Number'.
C4) In both cases C2:V3 and C3:X3 the REL-ACK MUST be sent back
to the source address contained in the IP header of the REL-REQ
being responded to.
4.3 IP address addition and deletion
When building TLV parameters for the REL-REQ Chunk messages that
will add or delete IP addresses the following rules should be applied:
D1) When adding a IP address to an association, the IP address
is NOT considered fully added to the association until the
REL-ACK arrives. This means that until such time as the
REL-REQ containing the add is acknowledged the sender MUST NOT
use the new IP address as a source for ANY SCTP packet.
D2) After the REL-ACK of a IP address add arrives, the endpoint
MAY begin using the added IP address as a source address.
D3) If a endpoint receives a Operational Error indicating that the
IP address Add or IP address Deletion was not understood, the
endpoint MUST consider the operation failed and MUST NOT
attempt to send any subsequent Add or Delete request to the
peer.
D4) When deleting an IP address from an association, the IP
address MUST be considered part of the association until
the REL-ACK arrives. This means that any datagrams that
arrive before the REL-ACK destined to the IP address being
deleted MUST be considered part of the current association.
D5) A endpoint MUST NOT delete its last 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 a endpoint sends
multiple requests to delete IP addresses it MUST NOT delete
all of the IP addresses that the peer has listed for the
requestor.
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D6) If a request is received to delete the last IP address of
a peer endpoint, the receiver MUST send an Operational error
with the error cause set to the new error code 'Request to
delete last IP address'. The requested delete MUST NOT be
performed or acted upon, other than to send the Operational
Error.
D7) After the REL-ACK of a IP address deletion arrives, the
endpoint MUST NOT use the deleted IP address as a source
of any SCTP packet.
During the time interval between sending out the REL-REQ and receiving
the REL-ACK it MAY be possible to receive DATA chunks out of
order. The following examples illustrate these problems:
Endpoint-A Endpoint-Z
---------- ----------
REL-REQ[Add-IP:X]------------------------------>
/--REL-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 REL-ACK confirming the add of the address to the association.
A similar problem exists with the deletion of an IP address as
follows:
Endpoint-A Endpoint-Z
---------- ----------
/------------New DATA:
/ Destination
/ IP:X
REL-REQ[DEL-IP:X]-------------/---------------->
<-----------------/------------------REL-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 REL-ACK. The endpoint MUST NOT source data
from this new address until the REL-ACK arrives but it may receive out
of order data as illustrated and MUST NOT treat this data as a OOTB
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datagram (please see [RFCXXXX] 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 a 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.
5. Security Considerations
The reliable chunk passing mechanism itself does not add any security
considerations other than those addressed by the base level SCTP
protocol. However each new extension MAY result in new security
threats and each extension SHOULD make appropriate consideration of
these threats.
The ADD/DELETE of an IP address to an existing association does
provide a 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 at which an association may be overtaken. This
threat SHOULD be considered when deploying a version of SCTP that use
this feature. The IP Authentication Header [RFC2402] SHOULD be used
when the threat environment requires stronger integrity protections,
but does not require confidentiality.
6. IANA considerations
Two new
Chunk types are being allocated
for use by this feature.
New REL-REQ Parameters may be defined in a similar way as described
for IETF-defined Chunk Parameter Extension (see [RFCXXXX] section
13.2).
7. Authors' Addresses
Randall R. Stewart Tel: +1-815-477-2127
Cisco Systems, Inc. EMail: rrs@cisco.com
8745 W. Higgins Road, Suite 200
Chicago, Ill 60631
USA
Qiaobing Xie Tel: +1-847-632-3028
Motorola, Inc. EMail: qxie1@email.mot.com
1501 W. Shure Drive, #2309
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Arlington Heights, IL 60004
USA
Micheal Tuexen Tel: +49-89-xxx-xxxx
SIEMENS AG EMail: Michael.Tuexen@icn.siemens.de
Hofmannstr. 51
81359 Munich
Germany
Ian Rytina Tel: +61-3-9301-6164
Ericsson Australia EMail:ian.rytina@ericsson.com
37/360 Elizabeth Street
Melbourne, Victoria 3000
Australia
8. References
[RFCXXXX] 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 XXXX, July 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 September, 2000
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