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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) ** Obsolete normative reference: RFC 793 (Obsoleted by RFC 9293) Summary: 1 error (**), 0 flaws (~~), 1 warning (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 TCP Maintenance and Minor Extensions F. Gont 3 (tcpm) UTN-FRH / SI6 Networks 4 Internet-Draft March 29, 2012 5 Updates: 793 (if approved) 6 Intended status: Standards Track 7 Expires: September 30, 2012 9 Processing of TCP segments with Mirrored End-points 10 draft-gont-tcpm-tcp-mirrored-endpoints-00.txt 12 Abstract 14 This document describes a problem found in some popular 15 implementations regarding the processing of TCP segments in which the 16 local endpoint is equal to the remote endpoint. Additionally, it 17 formally updates RFC 793 clarifying how this scenario should be 18 handled. 20 Status of this Memo 22 This Internet-Draft is submitted in full conformance with the 23 provisions of BCP 78 and BCP 79. 25 Internet-Drafts are working documents of the Internet Engineering 26 Task Force (IETF). Note that other groups may also distribute 27 working documents as Internet-Drafts. The list of current Internet- 28 Drafts is at http://datatracker.ietf.org/drafts/current/. 30 Internet-Drafts are draft documents valid for a maximum of six months 31 and may be updated, replaced, or obsoleted by other documents at any 32 time. It is inappropriate to use Internet-Drafts as reference 33 material or to cite them other than as "work in progress." 35 This Internet-Draft will expire on September 30, 2012. 37 Copyright Notice 39 Copyright (c) 2012 IETF Trust and the persons identified as the 40 document authors. All rights reserved. 42 This document is subject to BCP 78 and the IETF Trust's Legal 43 Provisions Relating to IETF Documents 44 (http://trustee.ietf.org/license-info) in effect on the date of 45 publication of this document. Please review these documents 46 carefully, as they describe your rights and restrictions with respect 47 to this document. Code Components extracted from this document must 48 include Simplified BSD License text as described in Section 4.e of 49 the Trust Legal Provisions and are provided without warranty as 50 described in the Simplified BSD License. 52 Table of Contents 54 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 55 2. Updating RFC 793 . . . . . . . . . . . . . . . . . . . . . . . 3 56 3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 3 57 4. Security Considerations . . . . . . . . . . . . . . . . . . . . 3 58 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 4 59 6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 4 60 6.1. Normative References . . . . . . . . . . . . . . . . . . . 4 61 6.2. Informative References . . . . . . . . . . . . . . . . . . 4 62 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 4 64 1. Introduction 66 Some systems have been found to be unable to process TCP segments in 67 which the source endpoint {Source Address, Source Port} is the same 68 than the destination end-point {Destination Address, Destination 69 Port}. Such TCP segments have been reported to cause malfunction of 70 a number of implementations [CERT1996], and have been exploited in 71 the past to perform Denial of Service (DoS) attacks [Meltman1997]. 72 While these packets are very very unlikely to exist in legitimate 73 scenarios, TCP should nevertheless be able to process them without 74 the need of any "extra" code. 76 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 77 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 78 document are to be interpreted as described in RFC 2119 [RFC2119]. 80 2. Updating RFC 793 82 TCP MUST be able to gracefully handle the case where the source end- 83 point (IP Source Address, TCP Source Port) is the same as the 84 destination end-point (IP Destination Address, TCP Destination Port). 86 A SYN segment in which the source end-point {Source Address, 87 Source Port} is the same as the destination end-point {Destination 88 Address, Destination Port} will result in a "simultaneous open" 89 scenario, such as the one described in page 32 of RFC 793 90 [RFC0793]. Therefore, those TCP implementations that correctly 91 handle simultaneous opens should already be prepared to handle 92 these unusual TCP segments. 94 3. IANA Considerations 96 This document has no IANA actions. The RFC Editor is requested to 97 remove this section before publishing this document as an RFC. 99 4. Security Considerations 101 This document describes a problem found in some popular 102 implementations regarding the processing of TCP instances in which 103 the local and the remote TCP endpoints are the equal. It formally 104 updates RFC 793, clarifying how such packets should be handled, thus 105 helping prevent unexpected behaviors in host implementations. 107 5. Acknowledgements 109 The author would like to thank David Borman for a fruitful discussion 110 about this topic at IETF 73 (Minneapolis). 112 This document is based on the technical report "Security Assessment 113 of the Transmission Control Protocol (TCP)" [CPNI-TCP] written by 114 Fernando Gont on behalf of the UK CPNI. 116 Fernando Gont would like to thank the UK CPNI for their continued 117 support. 119 6. References 121 6.1. Normative References 123 [RFC0793] Postel, J., "Transmission Control Protocol", STD 7, 124 RFC 793, September 1981. 126 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 127 Requirement Levels", BCP 14, RFC 2119, March 1997. 129 6.2. Informative References 131 [CERT1996] 132 CERT, "CERT Advisory CA-1996-21: TCP SYN Flooding and IP 133 Spoofing Attacks", 1996, 134 . 136 [CPNI-TCP] 137 Gont, F., "CPNI Technical Note 3/2009: Security Assessment 138 of the Transmission Control Protocol (TCP)", 2009, . 142 [Meltman1997] 143 Meltman, "new TCP/IP bug in win95. Post to the bugtraq 144 mailing-list", 1996, 145 . 147 Author's Address 149 Fernando Gont 150 UTN-FRH / SI6 Networks 151 Evaristo Carriego 2644 152 Haedo, Provincia de Buenos Aires 1706 153 Argentina 155 Phone: +54 11 4650 8472 156 Email: fgont@si6networks.com 157 URI: http://www.si6networks.com