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INTERNET-DRAFT                                                T. Herbert
Intended Status: Standard                                     Quantonium
Expires: September 2019

                                                          March 11, 2019


                        UDP Surplus Space Header
                     draft-herbert-udp-space-hdr-00


Abstract

   This draft defines a header for surplus space in UDP. The UDP surplus
   space is bytes between the end of the UDP payload and the end of the
   IP packet. The purpose of the header is to disambiguate uses of the
   surplus space. The UDP surplus space header includes a type, length,
   and checksum field that covers the space.

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   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.

   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
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Copyright and License Notice

   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors. All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents



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   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document. Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document. Code Components extracted from this document must
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   described in the Simplified BSD License.


Table of Contents

   1  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2  UDP surplus space header format . . . . . . . . . . . . . . . .  3
   3  Operation . . . . . . . . . . . . . . . . . . . . . . . . . . .  4
     3.1 Sender operation . . . . . . . . . . . . . . . . . . . . . .  4
     3.2 Receiver operation . . . . . . . . . . . . . . . . . . . . .  6
   4  Security Considerations . . . . . . . . . . . . . . . . . . . .  7
   5  IANA Considerations . . . . . . . . . . . . . . . . . . . . . .  7
   6  References  . . . . . . . . . . . . . . . . . . . . . . . . . .  7
     6.1  Normative References  . . . . . . . . . . . . . . . . . . .  7
     6.2  Informative References  . . . . . . . . . . . . . . . . . .  7
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . .  7





























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1  Introduction

   This specification defines a UDP surplus header to provide an
   extensible and generic format of the UDP surplus space. The UDP
   surplus space is bytes between the end of the UDP payload and the end
   of the IP packet. The UDP surplus space is possible since UDP
   contains its own length field for the UDP datagram that is not
   required to coincide with the end of the IP packet.

   The UDP surplus space header includes a type, length, and checksum
   field that covers the space. UDP options [UDPOPT] are being defined
   as the first standard use of the UDP surplus space. This draft
   permits other uses, including private uses of the space.

2  UDP surplus space header format

   The format of the UDP surplus space header is shown below.

     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
                    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                    |           Padding (0 to 3 bytes)              |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |    Type       |   Length      |         Checksum              |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    ~                      Type Specific Data                       ~
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The fields are:

      o Padding: Aligns the header to four bytes. The number of padding
        bytes required is: 3 - ((udp_length - 1) % 4) where the
        udp_length is the length of the UDP header and UDP payload.
        Padding bytes MUST be set to zero on transmission, and MUST be
        verified to be zero when received.

      o Type: The type of the UDP surplus space. One type is defined for
        UDP options.

      o Length: Length of the Type Specific Data in units of four byte
        words. The length of the Type Specific Data is thus zero to 1020
        bytes.

      o Checksum: The standard one's complement checksum that covers the
        UDP surplus space starting from the Type field through the end
        of the Type Specific Data as indicated in the Length field.



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        Preceding Padding Bytes are not included in the checksum
        coverage.

      o Type specific data: Data corresponding to the Type of the
        surplus data. For instance, in the case of UDP options, the Type
        specific data would contain the UDP options including any
        padding options to align the length of the Type Specific Data to
        four bytes.

   Defined Type values are:

      o 0: Reserved

      o 1: UDP options

      0 2-127: Reserved

      0 128-255: Available for private use or experimentation

3  Operation

3.1 Sender operation

   A sender MAY set a UDP surplus space header and data in the surplus
   space when sending a UDP packet. The UDP surplus header immediately
   follows the UDP payload at the offset of UDP Length from the start of
   the UDP header.

   The sender MUST insert up to three bytes of padding to align the UDP
   surplus header to four bytes.

   The sender MUST set the Type field to the type of the data to be
   processed.

   The Length field MUST be set to reflect the length of the Type
   Specific Data.

   The Checksum MUST be set. To compute the checksum:

      1) Set the Checksum field to zero. Compute the standard one's
         complement two byte checksum starting from the Type field
         through the end of the Type Specific Data.

      2) Set the value of the Checksum field to the bitwise "not" of the
         checksum computed in the previous step.

   Note that a sender MAY set multiple UDP surplus area headers in a
   packet. If more than one is set, then they are consecutive where one



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   immediately follows another.


















































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3.2 Receiver operation

   The following steps are for processing a UDP packet with surplus
   space:

      1) Check for minimum length to contain a surplus option header. If
         the surplus space length is less than 3 - ((udp_length - 1) %
         4) + 4, then the UDP surplus space header is not present.

      2) Check padding bytes. If the UDP Length is not a multiple of
         four bytes then verify that the padding bytes following the UDP
         payload are set to zero. Then expected number of padding bytes
         is 3 - ((udp_length - 1) % 4).

      3) Check the Length field. If the length determined from the
         Length field plus the starting offset of the Type specific data
         exceeds the length of the packet then the surplus area header
         is considered invalid.

      4) Verify the checksum. Compute the one's complement checksum
         starting from the Type field through the end of the Type
         specific data as indicated by the Length field. If the result
         of the computation ~0 (-0 checksum value) then the checksum is
         verified. If the checksum is not verified then the surplus area
         header is invalid.

      5) Check the Type. If the Type is unknown to the receiver then the
         surplus header is considered invalid.

      6) Process the Type Specific Data per the Type in the UDP surplus
         space header. In the course of processing the Type specific
         data, the receiver may determine that the surplus data is
         invalid.

      7) If there are additional bytes beyond the surplus header, a
         receiver MAY attempt to process those bytes as an additional
         surplus header. Processing would the same as how the first
         header was processed (although note that subsequent UDP surplus
         headers would not need Padding bytes since they would already
         be aligned to four bytes).

   If the number surplus bytes in a UDP packet are non-zero and
   determined to not contain a valid UDP surplus header, the surplus
   bytes SHOULD be ignored following existing protocol processing
   convention. An implementation MAY allow configuration that would
   discard such packets.





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4  Security Considerations

   The UDP surplus space header does not address nor introduce any new
   security considerations.

5  IANA Considerations

   IANA is requested to create a registry for the Type of UDP surplus
   options.

6  References

6.1  Normative References


6.2  Informative References

   [UDPOPT]   Touch, J., "Transport Options for UDP", draft-ietf-tsvwg-
              udp-options-07


Author's Address

   Tom Herbert
   Quantonium
   Santa Clara, CA
   USA


   Email: tom@quantonium.net





















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