Transport Options for UDP
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This is an older version of an Internet-Draft whose latest revision state is "Replaced".
|Author||Dr. Joseph D. Touch|
|Replaced by||draft-ietf-tsvwg-udp-options, draft-ietf-tsvwg-udp-options|
|Stream||Stream state||(No stream defined)|
|RFC Editor Note||(None)|
|IESG||IESG state||I-D Exists|
|Send notices to||(None)|
TSGWG J. Touch Internet Draft USC/ISI Intended status: Experimental July 20, 2015 Expires: January 2016 Transport Options for UDP draft-touch-tsvwg-udp-options-00.txt Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. This document may not be modified, and derivative works of it may not be created, and it may not be published except as an Internet-Draft. 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 and may be updated, replaced, or obsoleted by other documents at any 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 http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html This Internet-Draft will expire on January 20, 2016. Copyright Notice Copyright (c) 2015 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 (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. Touch Expires January 20, 2016 [Page 1] Internet-Draft Transport Options for UDP July 2015 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........................................5 8. IANA Considerations............................................5 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. Touch Expires January 20, 2016 [Page 2] Internet-Draft Transport Options for UDP July 2015 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 an area for options. 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 IP datagram length and header length information as follows: UDPlen = IPlen - IPhdrlen - 8 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. 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). This area can occur at any valid byte offset, i.e., it need not be 16-bit or 32-bit aligned. Touch Expires January 20, 2016 [Page 3] Internet-Draft Transport Options for UDP July 2015 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. +--------+--------+ | Kind | Length | +--------+--------+ Figure 1 UDP option default format There are two exceptions: "No Operation" (NOP) and "End of Options List" (EOL), each of which is one byte long. >> UDP options MAY occur at any UDP length offset. >> 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. >> 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. The following UDP options are currently defined: Kind Length Meaning ---------------------------------------------- 0 - End of Options List 1 - No operation 128-253 RESERVED 254 N RFC 3692-style experiments 255 RESERVED 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]. Touch Expires January 20, 2016 [Page 4] Internet-Draft Transport Options for UDP July 2015 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) 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. Touch Expires January 20, 2016 [Page 5] Internet-Draft Transport Options for UDP July 2015 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. [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. Touch Expires January 20, 2016 [Page 6] Internet-Draft Transport Options for UDP July 2015 [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 document was prepared using 2-Word-v2.0.template.dot. Touch Expires January 20, 2016 [Page 7] Internet-Draft Transport Options for UDP July 2015 Authors' Addresses Joe Touch USC/ISI 4676 Admiralty Way Marina del Rey, CA 90292 USA Phone: +1 (310) 448-9151 Email: firstname.lastname@example.org Touch Expires January 20, 2016 [Page 8]