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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 2460 (Obsoleted by RFC 8200) Summary: 1 error (**), 0 flaws (~~), 1 warning (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 IPv6 maintenance Working Group (6man) F. Gont 3 Internet-Draft SI6 Networks / UTN-FRH 4 Updates: 2460 (if approved) V. Manral 5 Intended status: Standards Track Hewlett-Packard Corp. 6 Expires: February 14, 2014 R. Bonica 7 Juniper Networks 8 August 13, 2013 10 Implications of Oversized IPv6 Header Chains 11 draft-ietf-6man-oversized-header-chain-04 13 Abstract 15 The IPv6 specification allows IPv6 header chains of an arbitrary 16 size. The specification also allows options which can in turn extend 17 each of the headers. In those scenarios in which the IPv6 header 18 chain or options are unusually long and packets are fragmented, or 19 scenarios in which the fragment size is very small, the first 20 fragment of a packet may fail to include the entire IPv6 header 21 chain. This document discusses the interoperability and security 22 problems of such traffic, and updates RFC 2460 such that the first 23 fragment of a packet is required to contain the entire IPv6 header 24 chain. 26 Status of this Memo 28 This Internet-Draft is submitted in full conformance with the 29 provisions of BCP 78 and BCP 79. 31 Internet-Drafts are working documents of the Internet Engineering 32 Task Force (IETF). Note that other groups may also distribute 33 working documents as Internet-Drafts. The list of current Internet- 34 Drafts is at http://datatracker.ietf.org/drafts/current/. 36 Internet-Drafts are draft documents valid for a maximum of six months 37 and may be updated, replaced, or obsoleted by other documents at any 38 time. It is inappropriate to use Internet-Drafts as reference 39 material or to cite them other than as "work in progress." 41 This Internet-Draft will expire on February 14, 2014. 43 Copyright Notice 45 Copyright (c) 2013 IETF Trust and the persons identified as the 46 document authors. All rights reserved. 48 This document is subject to BCP 78 and the IETF Trust's Legal 49 Provisions Relating to IETF Documents 50 (http://trustee.ietf.org/license-info) in effect on the date of 51 publication of this document. Please review these documents 52 carefully, as they describe your rights and restrictions with respect 53 to this document. Code Components extracted from this document must 54 include Simplified BSD License text as described in Section 4.e of 55 the Trust Legal Provisions and are provided without warranty as 56 described in the Simplified BSD License. 58 Table of Contents 60 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 61 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 4 62 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 63 4. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . 7 64 5. Updates to RFC 2460 . . . . . . . . . . . . . . . . . . . . . 8 65 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 66 7. Security Considerations . . . . . . . . . . . . . . . . . . . 10 67 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11 68 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12 69 9.1. Normative References . . . . . . . . . . . . . . . . . . . 12 70 9.2. Informative References . . . . . . . . . . . . . . . . . . 12 71 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13 73 1. Introduction 75 With IPv6, optional internet-layer information is carried in one or 76 more IPv6 Extension Headers [RFC2460]. Extension headers are placed 77 between the IPv6 header and the upper-layer header in a packet. The 78 term "header chain" refers collectively to the IPv6 header, extension 79 headers and upper-layer header occurring in a packet. In those 80 scenarios in which the IPv6 header chain is unusually long and 81 packets are fragmented, or scenarios in which the fragment size is 82 very small, the header chain may span multiple fragments. 84 While IPv4 had a fixed maximum length for the set of all IPv4 options 85 present in a single IPv4 packet, IPv6 does not have any equivalent 86 maximum limit at present. This document updates the set of IPv6 87 specifications to create an overall limit on the size of the 88 combination of IPv6 options and IPv6 Extension Headers that is 89 allowed in a single IPv6 packet. Namely, it updates RFC 2460 such 90 that the first fragment of a fragmented datagram is required to 91 contain the entire IPv6 header chain. 93 It should be noted that this requirement does not preclude the use of 94 e.g. IPv6 jumbo payloads but instead merely requires that all 95 *headers*, starting from IPv6 base header and continuing up to the 96 upper layer header (e.g. TCP or the like) be present in the first 97 fragment. 99 2. Requirements Language 101 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 102 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 103 document are to be interpreted as described in RFC 2119 [RFC2119]. 105 3. Terminology 107 For the purposes of this document, the terms Extension Header, Header 108 Chain, First Fragment, and Upper-layer Header are used as follows: 110 Extension Header: 112 Extension Headers are defined in Section 4 of [RFC2460]. 113 Currently, six extension header types are defined. [RFC2460] 114 defines the Hop-by-Hop, Routing, Fragment and Destination Options 115 extension header types. [RFC4302] defines the Authentication 116 Header (AH) type and [RFC4303] defines the Encapsulating Security 117 Payload (ESP) header type. 119 First Fragment: 121 An IPv6 fragment with fragment offset equal to 0. 123 IPv6 Header Chain: 125 The header chain contains an initial IPv6 header, zero or more 126 IPv6 extension headers, and optionally, a single upper-layer 127 header. If an upper-layer header is present, it terminates the 128 header chain. 130 The first member of the header chain is always an IPv6 header. 131 For a subsequent header to qualify as a member of the header 132 chain, it must be referenced by the "Next Header" field of the 133 previous member of the header chain. However, if a second IPv6 134 header appears in the header chain, as is the case when IPv6 is 135 tunneled over IPv6, the second IPv6 header is considered to be an 136 upper-layer header and terminates the header chain. Likewise, if 137 an ESP header appears in the header chain it is considered to be 138 an upper-layer header and it terminates the header chain. 140 Upper-layer Header: 142 In the general case, the upper-layer header is the first member of 143 the header chain that is neither an IPv6 header nor an IPv6 144 extension header. However, if either an ESP header, or a second 145 IPv6 header occur in the header chain, they are considered to be 146 upper layer headers and they terminate the header chain. 148 Neither the upper-layer payload, nor any protocol data following 149 the upper-layer payload, is considered to be part of the header 150 chain. In a simple example, if the upper-layer header is a TCP 151 header, the TCP payload is not part of the header chain. In a 152 more complex example, if the upper-layer header is an ESP header, 153 neither the payload data, nor any of the fields that follow the 154 payload data in the ESP header are part of the header chain. 156 4. Motivation 158 Many forwarding devices implement stateless firewalls. A stateless 159 firewall enforces a forwarding policy on packet-by-packet basis. In 160 order to enforce its forwarding policy, the stateless firewall may 161 need to glean information from both the IPv6 and upper-layer headers. 163 For example, assume that a stateless firewall discards all traffic 164 received from an interface unless it destined for a particular TCP 165 port on a particular IPv6 address. When this firewall is presented 166 with a fragmented packet, and the entire header chain is contained 167 within the first fragment, the firewall discards the first fragment 168 and allows subsequent fragments to pass. Because the first fragment 169 was discarded, the packet cannot be reassembled at the destination. 170 Insomuch as the packet cannot be reassembled, the forwarding policy 171 is enforced. 173 However, when the firewall is presented with a fragmented packet and 174 the header chain spans multiple fragments, the first fragment does 175 not contain enough information for the firewall to enforce its 176 forwarding policy. Lacking sufficient information, the stateless 177 firewall either forwards or discards that fragment. Regardless of 178 the action that it takes, it may fail to enforce its forwarding 179 policy. 181 5. Updates to RFC 2460 183 When a host fragments a IPv6 datagram, it MUST include the entire 184 header chain in the first fragment. 186 A host that receives a first-fragment that does not satisfy the 187 above-stated requirements SHOULD discard that packet, and also MAY 188 send an ICMPv6 error message to the source address of the offending 189 packet (subject to the rules for ICMPv6 errors specified in 190 [RFC4443]). 192 Likewise, an intermediate system (e.g. router, firewall) that 193 receives an IPv6 first-fragment that does not satisfy the above- 194 stated requirements MAY discard that packet, and MAY send an ICMPv6 195 error message to the source address of the offending packet (subject 196 to the rules for ICMPv6 error messages specified in [RFC4443]). 197 Intermediate systems having this capability SHOULD support 198 configuration (e.g. enable/disable) of whether such packets are 199 dropped or not by the intermediate system. 201 If a host or intermediate system discards an first-fragment because 202 it does not satisfy the above-stated requirements, and sends an 203 ICMPv6 error message due to the discard, then the ICMPv6 error 204 message MUST be Type 4 ("Parameter Problem") and MUST use Code TBD 205 ("First-fragment has incomplete IPv6 Header Chain"). 207 6. IANA Considerations 209 IANA is requested to add a the following entry to the "Reason Code" 210 registry for ICMPv6 "Type 4 - Parameter Problem" messages: 212 CODE NAME/DESCRIPTION 213 TBD IPv6 first-fragment has incomplete IPv6 header chain 215 7. Security Considerations 217 This document describes how improperly-fragmented packets can prevent 218 traditional stateless packet filtering. 220 This document updates RFC 2460 such that those packets are forbidden, 221 thus enabling stateless packet filtering for IPv6. 223 This specification allows nodes that drop the aforementioned packets 224 to signal such packet drops with ICMPv6 "Parameter Problem, IPv6 225 first-fragment has incomplete IPv6 header chain" (Type 4, Code TBD) 226 error messages. 228 As with all ICMPv6 error/diagnostic messages, deploying Source 229 Address Forgery Prevention filters helps reduce the chances of an 230 attacker successfully performing a reflection attack by sending 231 forged illegal packets with the victim/target's IPv6 address as the 232 IPv6 Source Address of the illegal packet [RFC2827] [RFC3704]. 234 8. Acknowledgements 236 The authors of this document would like to thank Ran Atkinson for 237 contributing text and ideas that were incorporated into this 238 document. 240 The authors would like to thank (in alphabetical order) Ran Atkinson, 241 Fred Baker, Brian Carpenter, Dominik Elsbroek, Bill Jouris, Suresh 242 Krishnan, Dave Thaler, and Eric Vyncke, for providing valuable 243 comments on earlier versions of this document. 245 9. References 247 9.1. Normative References 249 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 250 Requirement Levels", BCP 14, RFC 2119, March 1997. 252 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 253 (IPv6) Specification", RFC 2460, December 1998. 255 [RFC4302] Kent, S., "IP Authentication Header", RFC 4302, 256 December 2005. 258 [RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)", 259 RFC 4303, December 2005. 261 [RFC4443] Conta, A., Deering, S., and M. Gupta, "Internet Control 262 Message Protocol (ICMPv6) for the Internet Protocol 263 Version 6 (IPv6) Specification", RFC 4443, March 2006. 265 9.2. Informative References 267 [RFC2827] Ferguson, P. and D. Senie, "Network Ingress Filtering: 268 Defeating Denial of Service Attacks which employ IP Source 269 Address Spoofing", BCP 38, RFC 2827, May 2000. 271 [RFC3704] Baker, F. and P. Savola, "Ingress Filtering for Multihomed 272 Networks", BCP 84, RFC 3704, March 2004. 274 Authors' Addresses 276 Fernando Gont 277 SI6 Networks / UTN-FRH 278 Evaristo Carriego 2644 279 Haedo, Provincia de Buenos Aires 1706 280 Argentina 282 Phone: +54 11 4650 8472 283 Email: fgont@si6networks.com 284 URI: http://www.si6networks.com 286 Vishwas Manral 287 Hewlett-Packard Corp. 288 191111 Pruneridge Ave. 289 Cupertino, CA 95014 290 US 292 Phone: 408-447-1497 293 Email: vishwas.manral@hp.com 294 URI: 296 Ronald P. Bonica 297 Juniper Networks 298 2251 Corporate Park Drive 299 Herndon, VA 20171 300 US 302 Phone: 571 250 5819 303 Email: rbonica@juniper.net