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PROPOSED STANDARD
Errata Exist
Network Working Group                                          M. Tuexen
Request for Comments: 4820            Muenster Univ. of Applied Sciences
Category: Standards Track                                     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

   Copyright (C) The IETF Trust (2007).

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.

Table of Contents

   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






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RFC 4820          Padding Chunk and Parameter for SCTP        March 2007


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.







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RFC 4820          Padding Chunk and Parameter for SCTP        March 2007


   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.









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RFC 4820          Padding Chunk and Parameter for SCTP        March 2007


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.











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RFC 4820          Padding Chunk and Parameter for SCTP        March 2007


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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RFC 4820          Padding Chunk and Parameter for SCTP        March 2007


Full Copyright Statement

   Copyright (C) The IETF Trust (2007).

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Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.







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