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Checking references for intended status: Informational ---------------------------------------------------------------------------- ** Obsolete normative reference: RFC 793 (Obsoleted by RFC 9293) == Outdated reference: A later version (-04) exists of draft-bittau-tcp-crypt-01 -- Obsolete informational reference (is this intentional?): RFC 5226 (Obsoleted by RFC 8126) -- Obsolete informational reference (is this intentional?): RFC 6013 (Obsoleted by RFC 7805) Summary: 1 error (**), 0 flaws (~~), 2 warnings (==), 3 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 TCPM Working Group J. Touch 2 Internet Draft USC/ISI 3 Intended status: Informational October 24, 2011 4 Expires: April 2012 6 Shared Use of Experimental TCP Options 7 draft-touch-tcpm-experimental-options-00.txt 9 Status of this Memo 11 This Internet-Draft is submitted in full conformance with the 12 provisions of BCP 78 and BCP 79. 14 Internet-Drafts are working documents of the Internet Engineering 15 Task Force (IETF), its areas, and its working groups. Note that 16 other groups may also distribute working documents as Internet- 17 Drafts. 19 Internet-Drafts are draft documents valid for a maximum of six 20 months and may be updated, replaced, or obsoleted by other documents 21 at any time. It is inappropriate to use Internet-Drafts as 22 reference material or to cite them other than as "work in progress." 24 The list of current Internet-Drafts can be accessed at 25 http://www.ietf.org/ietf/1id-abstracts.txt 27 The list of Internet-Draft Shadow Directories can be accessed at 28 http://www.ietf.org/shadow.html 30 This Internet-Draft will expire on April 24, 2012. 32 Copyright Notice 34 Copyright (c) 2011 IETF Trust and the persons identified as the 35 document authors. All rights reserved. 37 This document is subject to BCP 78 and the IETF Trust's Legal 38 Provisions Relating to IETF Documents 39 (http://trustee.ietf.org/license-info) in effect on the date of 40 publication of this document. Please review these documents 41 carefully, as they describe your rights and restrictions with 42 respect to this document. 44 Abstract 46 This document describes how TCP option codepoints can support 47 concurrent experiments. The suggested mechanism avoids the need for 48 a coordinated registry, and is backward-compatible with currently 49 known uses. 51 Table of Contents 53 1. Introduction...................................................2 54 2. Conventions used in this document..............................3 55 3. TCP Experimental Option Structure..............................3 56 4. Security Considerations........................................4 57 5. IANA Considerations............................................5 58 6. References.....................................................5 59 6.1. Normative References......................................5 60 6.2. Informative References....................................5 61 7. Acknowledgments................................................6 63 1. Introduction 65 TCP includes options to enable new protocol capabilities that can be 66 activated only where needed and supported [RFC793]. The space for 67 identifying such options is small - 256 values, of which 31 are 68 assigned at the time this document was published [IANA]. Two of 69 these codepoints are allocated to support experiments (253, 254) 70 [RFC4727]. These numbers are intended for testing purposes, and 71 implementations need to assume they can be used for other purposes, 72 but this is often not the case. 74 There is no mechanism to support shared use of the experimental 75 option codepoints. Experimental options 245 and 255 are deployed in 76 operational code to support an early version of TCP authentication. 77 Option 253 is also documented for the experimental TCP Cookie 78 Transaction option [RFC6013]. This shared use results in collisions 79 in which a single codepoint can appear multiple times in a single 80 TCP segment and each use is ambiguous. 82 Other options have been used without assignment, notably 31-32 (TCP 83 cookie transactions, as originally distributed and in its API doc) 84 and 76-78 (tcpcrypt) [Bi11][Si11]. Commercial products reportedly 85 also use unassigned options 33 and 76-78 as well. 87 There are a variety of proposed approaches to address this issue. 88 The first is to relax the requirements for assignment of TCP 89 options, allowing them to be assigned more readily for protocols 90 that have not been standardized through the IETF process [RFC5226]. 91 A second would be to assign a larger pool to options, and to manage 92 their sharing through IANA coordination [Ed11]. 94 This document proposes a solution that does not require additional 95 codepoints and also avoids IANA participation. A short nonce is 96 added to the structure of the experimental TCP option structure. The 97 nonce helps reduce the probability of collision of independent 98 experimental uses of the same option codepoint. This feature 99 increases the size of experimental options, but the size can be 100 reduced when the experiment is converted to a standard protocol with 101 a conventional codepoint assignment. 103 2. Conventions used in this document 105 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 106 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 107 document are to be interpreted as described in RFC-2119 [RFC2119]. 109 In this document, these words will appear with that interpretation 110 only when in ALL CAPS. Lower case uses of these words are not to be 111 interpreted as carrying RFC-2119 significance. 113 In this document, the characters ">>" preceding an indented line(s) 114 indicates a compliance requirement statement using the key words 115 listed above. This convention aids reviewers in quickly identifying 116 or finding the explicit compliance requirements of this RFC. 118 3. TCP Experimental Option Structure 120 TCP options have the current common structure, where the first byte 121 is the codepoint (Kind) and the second is the length of the option 122 in bytes (Length): 124 +--------+--------+--------+--------+ 125 | Kind | Length | ... | 126 +--------+--------+--------+--------+ 127 | ... 128 +-------- 130 Figure 1 TCP Option Structure [RFC793] 132 This document extends the option structure for experimental 133 codepoints (253, 254) as follows: 135 +--------+--------+--------+--------+ 136 | Kind | Length | Nonce | 137 +--------+--------+--------+--------+ 138 | Nonce | ... 139 +--------+--------+--------+--- 141 Figure 2 TCP Experimental Option with a Nonce 143 >> Protocols using the TCP experimental option codepoints (253, 254) 144 SHOULD use nonces as described in this document. 146 The nonce is selected by the protocol designer when the experimental 147 option is defined. The Nonce is selected any of a variety of ways, 148 e.g., using the Unix time() command or bits selected by an arbitrary 149 function (such as a hash). 151 >> The nonce SHOULD be selected to reduce the probability of 152 collision. 154 The length of the nonce is intended to be 32 bit in network standard 155 byte order. It can be shorter if desired (e.g., 16 bits), with a 156 corresponding increased probability of collision and thus false 157 positives. 159 During TCP processing, experimental options are matched against both 160 the experimental codepoints and the Nonce value for each implemented 161 protocol. 163 >> Experimental options that have nonces that do not match 164 implemented protocols MUST be ignored. 166 The remainder of the option is specified by the particular 167 experimental protocol. 169 Use of a nonce uses additional space in the TCP header and requires 170 additional protocol processing by experimental protocols. Because 171 these are experiments, neither consideration is a substantial 172 impediment; a finalized protocol can avoid both issues with the 173 assignment of a dedicated option codepoint later. 175 4. Security Considerations 177 The mechanism described in this document is not intended to provide 178 security for TCP option processing. False positives are always 179 possible, where a Nonce matches a legacy use of these options or a 180 protocol that does not implement the mechanism described in this 181 document. 183 >> Protocols that are not robust to such false positives SHOULD 184 implement other measures to ensure they process options for their 185 protocol only, such as checksums or digital signatures among 186 cooperating parties of their protocol. 188 5. IANA Considerations 190 This document has no IANA considerations. This section should be 191 removed prior to publication. 193 6. References 195 6.1. Normative References 197 [RFC793] Postel, J., "Transmission Control Protocol", STD 7, RFC 198 793, Sep. 1981. 200 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 201 Requirement Levels", BCP 14, RFC 2119, March 1997. 203 [RFC4727] Fenner, B., "Experimental Values in IPv4, IPv6, ICMPv4, 204 ICMPv6, UDP, and TCP Headers", RFC 4727, Nov. 2006. 206 6.2. Informative References 208 [Bi11] Bittau, A., D. Boneh, M. Hamburg, M. Handley, D. Mazieres, 209 Q. Slack, "Cryptographic protection of TCP Streams 210 (tcpcrypt)", work in progress, draft-bittau-tcp-crypt-01, 211 Aug. 29, 2011. 213 [Ed11] Eddy, W., "Additional TCP Experimental-Use Options", work 214 in progress, draft-eddy-tcpm-addl-exp-options-00, Aug. 16, 215 2011. 217 [IANA] IANA web pages, http://www.iana.org/ 219 [RFC5226] Narten, T., H. Alvestrand, "Guidelines for Writing an IANA 220 Considerations Section in RFCs", BCP 26, RFC 5226, May 221 2008. 223 [RFC6013] Simpson, W., "TCP Cookie Transactions (TCPCT)", RFC 6013, 224 Jan. 2011. 226 [Si11] Simpson, W., "TCP Cookie Transactions (TCPCT) Sockets 227 Application Program Interface (API)", work in progress, 228 draft-simpson-tcpct-api-04, Apr. 7, 2011. 230 7. Acknowledgments 232 This document was motivated by discussions on the IETF TCPM mailing 233 list and by Wes Eddy's proposal [Ed11]. 235 This document was prepared using 2-Word-v2.0.template.dot. 237 Authors' Addresses 239 Joe Touch 240 USC/ISI 241 4676 Admiralty Way 242 Marina del Rey, CA 90292-6695 U.S.A. 244 Phone: +1 (310) 448-9151 245 Email: touch@isi.edu