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Network Working Group                                          M. TuexenRequest for Comments: 4820            Muenster Univ. of Applied SciencesCategory: Standards Track                                     R. Stewart                                                                  P. Lei                                                     Cisco Systems, Inc.                                                              March 2007Padding Chunk and Parameterfor 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 Contents1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .22.  Conventions . . . . . . . . . . . . . . . . . . . . . . . . . .23.  Padding Chunk (PAD) . . . . . . . . . . . . . . . . . . . . . .24.  Padding Parameter (PAD) . . . . . . . . . . . . . . . . . . . .35.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . .45.1.  A New Chunk Type  . . . . . . . . . . . . . . . . . . . . .45.2.  A New Parameter Type  . . . . . . . . . . . . . . . . . . .46.  Security Considerations . . . . . . . . . . . . . . . . . . . .47.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . .48.  References  . . . . . . . . . . . . . . . . . . . . . . . . . .58.1.  Normative References  . . . . . . . . . . . . . . . . . . .58.2.  Informative References  . . . . . . . . . . . . . . . . . .5Tuexen, et al.              Standards Track                     [Page 1]

RFC 4820          Padding Chunk and Parameter for SCTP        March 20071.  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 inRFC 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.Tuexen, et al.              Standards Track                     [Page 2]

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.Tuexen, et al.              Standards Track                     [Page 3]

RFC 4820          Padding Chunk and Parameter for SCTP        March 20075.  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 inRFC 2960 [2].7.  Acknowledgments   The authors wish to thank Matthew J. Zekauskas and Lars Eggert for   their invaluable comments.Tuexen, et al.              Standards Track                     [Page 4]

RFC 4820          Padding Chunk and Parameter for SCTP        March 20078.  References8.1.  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.comTuexen, et al.              Standards Track                     [Page 5]

RFC 4820          Padding Chunk and Parameter for SCTP        March 2007Full Copyright Statement   Copyright (C) The IETF Trust (2007).   This document is subject to the rights, licenses and restrictions   contained inBCP 78, and except as set forth therein, the authors   retain all their rights.   This document and the information contained herein are provided on an   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND   THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS   OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF   THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Intellectual Property   The IETF takes no position regarding the validity or scope of any   Intellectual Property Rights or other rights that might be claimed to   pertain to the implementation or use of the technology described in   this document or the extent to which any license under such rights   might or might not be available; nor does it represent that it has   made any independent effort to identify any such rights.  Information   on the procedures with respect to rights in RFC documents can be   found inBCP 78 andBCP 79.   Copies of IPR disclosures made to the IETF Secretariat and any   assurances of licenses to be made available, or the result of an   attempt made to obtain a general license or permission for the use of   such proprietary rights by implementers or users of this   specification can be obtained from the IETF on-line IPR repository athttp://www.ietf.org/ipr.   The IETF invites any interested party to bring to its attention any   copyrights, patents or patent applications, or other proprietary   rights that may cover technology that may be required to implement   this standard.  Please address the information to the IETF at   ietf-ipr@ietf.org.Acknowledgement   Funding for the RFC Editor function is currently provided by the   Internet Society.Tuexen, et al.              Standards Track                     [Page 6]