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Versions: 00 01 02 03 04 05 06 07 08 09 draft-ietf-tsvwg-udp-options

TSGWG                                                          J. Touch
Internet Draft                                                  USC/ISI
Intended status: Experimental                             July 21, 2015
Expires: January 2016



                         Transport Options for UDP
                   draft-touch-tsvwg-udp-options-01.txt


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Abstract

   Transport protocols are extended through the use of transport header
   options. This document experimentally extends UDP to provide a
   location, syntax, and semantics for transport layer options.

Table of Contents


   1. Introduction...................................................2
   2. Conventions used in this document..............................2
   3. Background.....................................................3
   4. The UDP Option Area............................................3
   5. UDP options vs. UDP-Lite.......................................5
   6. Options in a Stateless, Unreliable Transport Protocol..........5
   7. Security Considerations........................................6
   8. IANA Considerations............................................6
   9. References.....................................................6
      9.1. Normative References......................................6
      9.2. Informative References....................................6
   10. Acknowledgments...............................................7

1. Introduction

   Transport protocols use options as a way to extend their
   capabilities. TCP [RFC793], SCTP [RFC4960], and DCCP [RFC4340]
   include space for these options but UDP [RFC768] currently does not.
   This document defines an experimental extension to UDP that provides
   space for transport options including their generic syntax and
   semantics for their use in UDP's stateless, unreliable message
   protocol.

2. Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

   In this document, these words will appear with that interpretation
   only when in ALL CAPS. Lowercase uses of these words are not to be
   interpreted as carrying significance described in RFC 2119.

   In this document, the characters ">>" preceding an indented line(s)
   indicates a statement using the key words listed above. This
   convention aids reviewers in quickly identifying or finding the
   portions of this RFC covered by these key words.



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3. Background

   Many protocols include a default header and an area for header
   options. These options enable the protocol to be extended for use in
   particular environments or in ways unforeseen by the original
   designers. Examples include TCP's Maximum Segment Size, Window
   Scale, Timestamp, and Authentication Options
   [RFC793][RFC5925][RFC7323].

   These options are used both in stateful (connection-oriented, e.g.,
   TCP [RFC793], SCTP [RFC4960], DCCP [RFC4340]) and stateless
   (connectionless, e.g., IPv4 [RFC791], IPv6 [RFC2460] protocols. In
   stateful protocols they can help extend the way in which state is
   managed. In stateless protocols their effect is often limited to
   individual packets, but they can have an aggregate effect on a
   sequence as well. One example of such uses is Substrate Protocol for
   User Datagrams (SPUD) [Tr15], and this document is intended to
   provide an out-of-band option area as an alternative to the in-band
   mechanism currently proposed [Hi15].

   UDP is one of the most popular protocols that lacks space for
   options [RFC768]. The UDP header was intended to be a minimal
   addition to IP, providing only ports and a data checksum for
   protection. This document experimentally extends UDP to provide a
   trailer area for options located after the UDP data payload.

4. The UDP Option Area

   The UDP transport header includes demultiplexing and service
   identification (port numbers), a checksum, and a field that
   indicates the payload length. This length field is typically
   redundant with total IP datagram length and header length.

   For IPv4, the total datagram length (including IP header) is the
   "Total Length" field and the header and its options are 4*IHL
   ("Internet Header Length") [RFC791]. For IPv6, the last IP option
   with "Next Header" = UDP (i.e., 17) indicates the size of the
   transport payload as its "Payload Length" directly [RFC2460]. In
   both cases, the space available for the UDP transport protocol data
   unit is indicated by IP

   As a result of this redundancy, the UDP length field can be used in
   other ways. UDP-Lite uses this field to indicate UDP checksum
   coverage. This document uses this field to create a place for UDP
   transport options.




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   The UDP option area is defined as the location between the end of
   the UDP payload (as indicated by UDP length) and the end of the IP
   datagram (as indicated by the IP length and IP header length), i.e.,
   as a trailing options area. This area can occur at any valid byte
   offset, i.e., it need not be 16-bit or 32-bit aligned. In effect,
   this document redefines the UDP "Length" field as a "trailer
   offset".

   UDP options are defined using a syntax similar to that of TCP
   [RFC793]. They are typically a minimum of two bytes in length as
   shown in Figure 1, excepting only the one byte options "No
   Operation" (NOP) and "End of Options List" (EOL) described below.

                        +--------+--------+
                        |  Kind  | Length |
                        +--------+--------+

                    Figure 1 UDP option default format

   >> UDP options MAY occur at any UDP length offset.

   >> The UDP length MUST be at least as large as the UDP header (8)
   and no larger than the payload of the IP datagram (IPlen -
   IPhdrlen). Values outside this range MUST be silently discarded as
   invalid and logged where rate-limiting permits.

   >> UDP options MUST be interpreted in the order in which they occur
   in the UDP option area.

   The following UDP options are currently defined:

             Kind    Length    Meaning
             ----------------------------------------------
             0       -         End of Options List
             1       -         No operation
             128-253           RESERVED
             254     N(>=4)    RFC 3692-style experiments
             255               RESERVED


   >> NOP options SHOULD be used at the beginning of the UDP options
   area to achieve 32-bit alignment for active (i.e., non-NOP) options.

   >> When the UDP options do not consume the entire option area, the
   last non-NOP option SHOULD be EOL.

   >> All bytes after EOL MUST be ignored by UDP option processing.


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   Note that Kind=254 is reserved for experiments [RFC3692]. Only one
   such value is reserved because it experiments are expected to
   already apply the shared use approach developed for TCP experimental
   options [RFC6994].

   >> The length of the experimental option MUST be at least 4 to
   account for the Kind, Length, and the minimum 16-bit UDP ExID
   identifier (similar to TCP ExIDs [RFC6994]).

5. UDP options vs. UDP-Lite

   UDP Lite provides partial checksum coverage, so that packets with
   errors in some locations can be delivered to the user [RFC3828]. It
   uses a different transport protocol number (136) than UDP (17) to
   interpret the UDP length field as the prefix covered by the UDP
   checksum.

   UDP already defines the UDP length field as the limit of the UDP
   checksum but that would also limit the data provided to the user
   (application). A goal of UDP-Lite is to deliver data beyond that
   length offset, which is why a separate transport protocol number was
   required.

   UDP options do not need a separate transport protocol number because
   the data beyond the UDP length offset is never provided to the user.
   It is interpreted exclusively within the UDP transport layer.

6. Options in a Stateless, Unreliable Transport Protocol

   There are two ways to interpret options for a stateless, unreliable
   protocol -- an option is either local to the message or intended to
   affect a stream of messages in a soft-state manner. Either
   interpretation is valid for defined UDP options.

   It is impossible to know in advance whether an endpoint supports a
   UDP option.

   >> Options MUST allow for silent failure on first receipt.

   >> Options that rely on soft-state exchange MUST allow for message
   reordering and loss.

   >> A UDP option MUST be silently optional until confirmed by
   exchange with an endpoint.

   (I'm sure there will be more here)



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7. Security Considerations

   (to be addressed)

8. IANA Considerations

   Upon publication, IANA is hereby requested to create a new registry
   for UDP Option Kind numbers, similar to that for TCP Option Kinds.
   Values in this registry are to be assigned by IESG Approval or
   Standards Action [RFC5226].

   Upon publication, IANA is hereby requested to create a new registry
   for UDP Experimental Option Experiment Identifiers (UDP ExIDs) for
   use in the same manner as [RFC6994]. Values in this registry are to
   be assigned using first-come, first-served (FCFS) rules [RFC5226].

9. References

9.1. Normative References

   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
             Requirement Levels", BCP 14, RFC 2119, March 1997.

9.2. Informative References

   [Hi15]    Hildebrand, J., B. Trammel, "Substrate Protocol for User
             Datagrams (SPUD) Prototype," draft-hildebrand-spud-
             prototype-03, Mar. 2015.

   [RFC768]  Postel, J., "User Datagram Protocol", RFC 768, August
             1980.

   [RFC791]  Postel, J., "Internet Protocol," RFC 791, Sept. 1981.

   [RFC793]  Postel, J., "Transmission Control Protocol" RFC 793,
             September 1981

   [RFC2460] Deering, S., R. Hinden, "Internet Protocol Version 6
             (IPv6) Specification," RFC 2460, Dec. 1998.

   [RFC4340] Kohler, E., M. Handley, and S. Floyd, "Datagram Congestion
             Control Protocol (DCCP)", RFC 4340, March 2006.

   [RFC4960] Stewart, R. (Ed.), "Stream Control Transmission Protocol",
             RFC 4960, September 2007.




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   [RFC3692] Narten, T., "Assigning Experimental and Testing Numbers
             Considered Useful," RFC 3692, Jan. 2004.

   [RFC3828] Larzon, L-A., M. Degermark, S. Pink, L-E. Jonsson (Ed.),
             G. Fairhurst (Ed.), "The Lightweight User Datagram
             Protocol (UDP-Lite)," RFC 3828, July 2004.

   [RFC5226] Narten, T., H. Alvestrand, "Guidelines for Writing an IANA
             Considerations Section in RFCs," RFC 5226, May 2008.

   [RFC5925] Touch, J., A. Mankin, R. Bonica, "The TCP Authentication
             Option," RFC 5925, June 2010.

   [RFC6994] Touch, J., "Shared Use of Experimental TCP Options," RFC
             6994, Aug. 2013.

   [RFC7323] Borman, D., R. Braden, V. Jacobson, R. Scheffenegger
             (Ed.), "TCP Extensions for High Performance," RFC 7323,
             Sep. 2014.

   [Tr15]    Trammel, B. (Ed.), M. Kuelewind (Ed.), "Requirements for
             the design of a Substrate Protocol for User Datagrams
             (SPUD)," draft-trammell-spud-req-00, July 2015.

10. Acknowledgments

   This work benefitted from feedback from Ken Calvert, Ted Faber, and
   Gorry Fairhurst, as well as discussions on the IETF SPUD email list.

   This document was prepared using 2-Word-v2.0.template.dot.



















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Authors' Addresses

   Joe Touch
   USC/ISI
   4676 Admiralty Way
   Marina del Rey, CA 90292 USA

   Phone: +1 (310) 448-9151
   Email: touch@isi.edu








































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