Network Working Group
Request for Comments: 4820
Category: Standards Track

M. Tuexen
Muenster Univ. of Applied Sciences
R. Stewart
P. Lei
Cisco Systems, Inc.
March 2007

Padding Chunk and Parameter

for the Stream Control Transmission Protocol (SCTP)

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.

Copyright Notice

Abstract

This document defines a padding chunk and a padding parameter and describes the required receiver side procedures. The padding chunk is used to pad a Stream Control Transmission Protocol (SCTP) packet to an arbitrary size. The padding parameter is used to pad an SCTP INIT chunk to an arbitrary size.

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 2
   2.  Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . 2
   3.  Padding Chunk (PAD) . . . . . . . . . . . . . . . . . . . . . . 2
   4.  Padding Parameter (PAD) . . . . . . . . . . . . . . . . . . . . 3
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4
     5.1.  A New Chunk Type  . . . . . . . . . . . . . . . . . . . . . 4
     5.2.  A New Parameter Type  . . . . . . . . . . . . . . . . . . . 4
   6.  Security Considerations . . . . . . . . . . . . . . . . . . . . 4
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 4
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 5
     8.1.  Normative References  . . . . . . . . . . . . . . . . . . . 5
     8.2.  Informative References  . . . . . . . . . . . . . . . . . . 5

1. Introduction

This document defines a padding chunk and a padding parameter and describes the required receiver side procedures. The padding chunk is used to pad an SCTP packet to an arbitrary size. The padding parameter is used to pad an SCTP INIT chunk to an arbitrary size. The usage of the PAD chunk for path MTU discovery is described in PMTU [4]. The inappropriate usage of the PAD parameter or PAD chunk can result in wasted bandwidth.

2. Conventions

The key words "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 [1].

3. Padding Chunk (PAD)

This chunk is used to pad an SCTP packet. A PAD chunk can be used to enlarge the packet by 4 to 65536 bytes in steps of 4 bytes. An SCTP packet MAY contain multiple PAD chunks.

    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 = 0x84   |   Flags=0     |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   \                         Padding Data                          /
   /                                                               \
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 1

   Type: 1 byte (unsigned integer)
   
      This value MUST be set to 0x84 for all PAD chunks.
   
   Flags: 1 byte (unsigned integer)
      This value SHOULD be set to zero on transmit and MUST be ignored
      on receipt.
   
   Length: 2 bytes (unsigned integer)
      This value holds the length of the Padding Data plus 4.

Padding Data: n bytes (unsigned integer): This holds the Padding Data. The Padding Data MUST be ignored by the receiver.

The receiver of the PAD chunk MUST discard this chunk and continue processing the rest of the chunks in the packet. Please note that this is also the required processing behavior for any unknown chunk having the same highest-order two bits of the type as the PAD chunk.

4. Padding Parameter (PAD)

This parameter is used to pad an INIT chunk. A PAD parameter can be used to enlarge the INIT chunk by 4 bytes as the minimum to the maximum size of the INIT chunk in steps of 4 bytes. An INIT chunk MAY contain multiple PAD 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Parameter Type = 0x8005   |       Parameter Length        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   /                                                               /
   \                          Padding Data                         \
   /                                                               /
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 2

Parameter Type: 2 bytes (unsigned integer): This value MUST be set to 0x8005.

Parameter Length: 2 bytes (unsigned integer): This value holds the length of the Padding Data plus 4.

The PAD parameter MAY be included only in the INIT chunk. It MUST NOT be included in any other chunk. The receiver of the PAD parameter MUST silently discard this parameter and continue processing the rest of the INIT chunk. This means that the size of the generated COOKIE parameter in the INIT-ACK MUST NOT depend on the existence of the PAD parameter in the INIT chunk. A receiver of a PAD parameter MUST NOT include the PAD parameter within any State Cookie parameter it generates.

5. IANA Considerations

This document is the reference for all registrations described in this section. All registrations have been listed in the document available at sctp-parameters [3]. The changes are described below.

5.1. A New Chunk Type

A chunk type for the PAD chunk has been assigned by IANA. The value has been assigned as described in Figure 1. The following has been added to the "CHUNK TYPES" table of sctp-parameters [3]:

   CHUNK TYPES
   
   ID Value    Chunk Type                                     Reference
   --------    ----------                                     ---------
   132(0x84)   Padding Chunk (PAD)                            [RFC4820]

5.2. A New Parameter Type

A parameter type has been assigned for the PAD parameter by IANA. The value has been assigned as described in Figure 2. The following has been added to the "CHUNK PARAMETER TYPES" table in sctp- parameters [3]:

INIT Chunk Parameter Types

   Chunk Parameter Type                       Value
   --------------------                       -----
   Padding                            32773(0x8005)

6. Security Considerations

This document does not add any additional security considerations to the ones given in RFC 2960 [2].

7. Acknowledgments

The authors wish to thank Matthew J. Zekauskas and Lars Eggert for their invaluable comments.

8. References

8.1. Normative References

   [1]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", BCP 14, RFC 2119, March 1997.
   
   [2]  Stewart, R., Xie, Q., Morneault, K., Sharp, C., Schwarzbauer,
        H., Taylor, T., Rytina, I., Kalla, M., Zhang, L., and V. Paxson,
        "Stream Control Transmission Protocol", RFC 2960, October 2000.

8.2. Informative References

   [3]  "IANA registry",
        <http://www.iana.org/assignments/sctp-parameters>.
   
   [4]  Mathis, M. and J. Heffner, "Packetization Layer Path MTU
        Discovery", RFC 4821, March 2007.

Authors' Addresses

Michael Tuexen
Muenster Univ. of Applied Sciences
Stegerwaldstr. 39
48565 Steinfurt
Germany

   EMail: tuexen@fh-muenster.de
   
   Randall R. Stewart
   Cisco Systems, Inc.
   4875 Forest Drive
   Suite 200
   Columbia, SC  29206
   USA

EMail:

          rrs@cisco.com
   
   Peter Lei
   Cisco Systems, Inc.
   955 Happfield Dr.
   Arlington Heights, IL  60004
   US
   
   Phone: +1 773 695-8201
   EMail: peterlei@cisco.com

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