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Bhatia 11 Alcatel-Lucent 12 March 14, 2011 14 An uniform format for IPv6 extension headers 15 draft-ietf-6man-exthdr-02 17 Abstract 19 In IPv6, optional internet-layer information is encoded in separate 20 headers that may be placed between the IPv6 header and the transport 21 layer header. There are a small number of such extension headers 22 currently defined. This document defines a format for defining new 23 IPv6 extension headers. 25 Status of this Memo 27 This Internet-Draft is submitted in full conformance with the 28 provisions of BCP 78 and BCP 79. 30 Internet-Drafts are working documents of the Internet Engineering 31 Task Force (IETF). Note that other groups may also distribute 32 working documents as Internet-Drafts. The list of current Internet- 33 Drafts is at http://datatracker.ietf.org/drafts/current/. 35 Internet-Drafts are draft documents valid for a maximum of six months 36 and may be updated, replaced, or obsoleted by other documents at any 37 time. It is inappropriate to use Internet-Drafts as reference 38 material or to cite them other than as "work in progress." 40 This Internet-Draft will expire on September 15, 2011. 42 Copyright Notice 44 Copyright (c) 2011 IETF Trust and the persons identified as the 45 document authors. All rights reserved. 47 This document is subject to BCP 78 and the IETF Trust's Legal 48 Provisions Relating to IETF Documents 49 (http://trustee.ietf.org/license-info) in effect on the date of 50 publication of this document. Please review these documents 51 carefully, as they describe your rights and restrictions with respect 52 to this document. Code Components extracted from this document must 53 include Simplified BSD License text as described in Section 4.e of 54 the Trust Legal Provisions and are provided without warranty as 55 described in the Simplified BSD License. 57 Table of Contents 59 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 60 2. Conventions used in this document . . . . . . . . . . . . . . . 3 61 3. Applicability . . . . . . . . . . . . . . . . . . . . . . . . . 3 62 4. Proposed IPv6 Extension Header format . . . . . . . . . . . . . 4 63 5. Backward Compatibility . . . . . . . . . . . . . . . . . . . . 4 64 6. Future work . . . . . . . . . . . . . . . . . . . . . . . . . . 4 65 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5 66 8. Security Considerations . . . . . . . . . . . . . . . . . . . . 5 67 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5 68 10. Normative References . . . . . . . . . . . . . . . . . . . . . 5 69 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 5 71 1. Introduction 73 The base IPv6 standard [RFC2460] defines extension headers as an 74 expansion mechanism to carry optional internet layer information. 75 Extension headers, with the exception of the hop-by-hop options 76 header, are not usually processed on intermediate nodes. However, 77 some intermediate nodes such as firewalls, may need to look at the 78 transport layer header fields in order to make a decision to allow or 79 deny the packet. If new extension headers are defined and the 80 intermediate node is not aware of them, the intermediate node cannot 81 proceed further in the header chain since it does not know where the 82 unknown header ends and the next header begins. The main issue is 83 that the extension header format is not standardized and hence it is 84 not possible to skip past the unknown header. This document intends 85 to define a standard format for IPv6 extension headers. 87 2. Conventions used in this document 89 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL","SHALL NOT", 90 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 91 document are to be interpreted as described in [RFC2119]. 93 3. Applicability 95 The base IPv6 standard [RFC2460] allows the use of both extension 96 headers and destination options in order to encode optional 97 destination information in an IPv6 packet. The use of destination 98 options to encode this information, provides more flexible handling 99 characteristics and better backward compatibility than using 100 extension headers. Because of this, implementations SHOULD use 101 destination options as the preferred mechanism for encoding optional 102 destination information, and use a new extension header only if 103 destination options do not satisfy their needs. The request for 104 creation of a new IPv6 extension header MUST be accompanied by an 105 specific explanation of why destination options could not be used to 106 convey this information. 108 4. Proposed IPv6 Extension Header format 110 This document proposes that all IPv6 extension headers be encoded in 111 a consistent TLV format so that it is possible for nodes to skip over 112 unknown extension headers and continue to further process the header 113 chain. 115 0 1 2 3 116 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 1 117 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 118 | Next Header | Hdr Ext Len | | 119 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + 120 | | 121 . . 122 . Header Specific Data . 123 . . 124 | | 125 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 127 Next Header 8-bit selector. Identifies the type of header 128 immediately following the Extension header. 129 Uses the same values as the IPv4 Protocol 130 field. 131 Hdr Ext Len 8-bit unsigned integer. Length of the 132 Extension header in 8-octet units, not 133 including the first 8 octets. 134 Header Specific Variable length. Fields specific to the 135 Data extension header 137 Figure 1: Extension header layout 139 5. Backward Compatibility 141 The scheme proposed in this document is not intended to be backward 142 compatible with all the currently defined IPv6 extension headers. It 143 applies only to newly defined extension headers. Specifically, the 144 fragment header predates this document and does not follow the format 145 proposed in this document. 147 6. Future work 149 This document proposes one step in easing the inspection of extension 150 headers by middleboxes. There is further work required in this area. 151 Some issues that are left unresolved beyond this document include 152 o There can be an arbitrary number of extension headers. 153 o Extension headers must be processed in the order they appear. 154 o Extension headers may alter the processing of the payload itself, 155 and hence the packet may not be processed properly without 156 knowledge of said header. 158 7. IANA Considerations 160 This document does not require any IANA actions. 162 8. Security Considerations 164 This document proposes a standard format for the IPv6 extension 165 headers so that intermediate nodes that do not understand the 166 contents of these headers can look past them. Intermediate nodes, 167 such as firewalls, skipping over unknown headers might end up 168 allowing the setup of a covert channel from the outside of the 169 firewall to the inside using the data field(s) of the unknown 170 extension headers. 172 9. Acknowledgements 174 The authors would like to thank Albert Manfredi, Bob Hinden, Brian 175 Carpenter, Erik Nordmark, Hemant Singh, Lars Westberg, Markku Savela, 176 Tatuya Jinmei, Thomas Narten, Vishwas Manral, Alfred Hoenes, Joel 177 Halpern and Ran Atkinson for their reviews and suggestions that made 178 this document better. 180 10. Normative References 182 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 183 Requirement Levels", BCP 14, RFC 2119, March 1997. 185 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 186 (IPv6) Specification", RFC 2460, December 1998. 188 Authors' Addresses 190 Suresh Krishnan 191 Ericsson 192 8400 Decarie Blvd. 193 Town of Mount Royal, QC 194 Canada 196 Phone: +1 514 345 7900 x42871 197 Email: suresh.krishnan@ericsson.com 199 james woodyatt 200 Apple Inc. 201 1 Infinite Loop 202 Cupertino, CA 95014 203 US 205 Email: jhw@apple.com 207 Erik Kline 208 Google 209 604 Arizona Avenue 210 Santa Monica, CA 90401 211 US 213 Phone: +1 310 460 4080 214 Email: ek@google.com 216 James Hoagland 217 Symantec Corporation 218 350 Ellis St. 219 Mountain View, CA 94043 220 US 222 Email: Jim_Hoagland@symantec.com 223 URI: http://symantec.com/ 225 Manav Bhatia 226 Alcatel-Lucent 227 Bangalore 228 India 230 Email: manav.bhatia@alcatel-lucent.com