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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: January 16, 2014 R. Bonica 7 Juniper Networks 8 July 15, 2013 10 Implications of Oversized IPv6 Header Chains 11 draft-ietf-6man-oversized-header-chain-03 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 January 16, 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 . . . . . . . . . . . . . . . . . . . . . . . . . . 6 64 5. Updates to RFC 2460 . . . . . . . . . . . . . . . . . . . . . 7 65 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 66 7. Security Considerations . . . . . . . . . . . . . . . . . . . 9 67 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10 68 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11 69 9.1. Normative References . . . . . . . . . . . . . . . . . . . 11 70 9.2. Informative References . . . . . . . . . . . . . . . . . . 11 71 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12 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 Extension Header: 109 Extension Headers are defined in Section 4 of [RFC2460]. 110 Currently, six extension header types are defined. [RFC2460] 111 defines the hop-by-hop, routing, fragment and destination options 112 extension header types. [RFC4302] defines the authentication 113 header type and [RFC4303] defines the encapsulating security 114 payload (ESP) header type. 116 First Fragment: 118 An IPv6 fragment with fragment offset equal to 0. 120 IPv6 Header Chain: 122 The initial portion of an IPv6 datagram containing headers, 123 starting from the fixed IPv6 header up to (and including) the 124 upper layer protocol header (TCP, UDP, etc. -- assuming there is 125 one of those), including any intermediate IPv6 extension headers. 126 For a header to qualify as a member of the header chain, it must 127 be referenced by the "Next Header" field of the previous member of 128 the header chain. 130 Upper-layer Header: 132 The first member of the header chain that is neither an IPv6 133 header nor an IPv6 extension header. For the purposes of this 134 document, ICMPv6 is considered to be an upper-layer protocol, even 135 though ICMPv6 operates at the same layer as IPv6. Also for the 136 purposes of this document, the first 32 bits of the ICMPv6 message 137 (i.e., the type, code fields and checksum fields) are considered 138 to be the ICMPv6 header. 140 NOTES: 141 The upper-layer payload is not part of the upper-layer header 142 and therefore, is not part of the IPv6 header chain. For 143 example, if the upper-layer protocol is TCP, the TCP payload is 144 not part of the TCP header or the IPv6 header chain. 146 When a packet contains an ESP header [RFC4303], such header is 147 considered to be the last header in the IPv6 header chain. For 148 the sake of clarity, we note that only the Security Parameters 149 Index (SPI) and the Sequence Number fields (i.e., the first 64 150 bits of the ESP packet) are part of the ESP header (i.e., the 151 Payload Data and trailer are NOT part of the ESP header). 153 4. Motivation 155 Many forwarding devices implement stateless firewalls. A stateless 156 firewall enforces a forwarding policy on packet-by-packet basis. In 157 order to enforce its forwarding policy, the stateless firewall may 158 need to glean information from both the IPv6 and upper-layer headers. 160 For example, assume that a stateless firewall discards all traffic 161 received from an interface unless it destined for a particular TCP 162 port on a particular IPv6 address. When this firewall is presented 163 with a fragmented packet, and the entire header chain is contained 164 within the first fragment, the firewall discards the first fragment 165 and allows subsequent fragments to pass. Because the first fragment 166 was discarded, the packet cannot be reassembled at the destination. 167 Insomuch as the packet cannot be reassembled, the forwarding policy 168 is enforced. 170 However, when the firewall is presented with a fragmented packet and 171 the header chain spans multiple fragments, the first fragment does 172 not contain enough information for the firewall to enforce its 173 forwarding policy. Lacking sufficient information, the stateless 174 firewall either forwards or discards that fragment. Regardless of 175 the action that it takes, it may fail to enforce its forwarding 176 policy. 178 5. Updates to RFC 2460 180 When a host fragments a IPv6 datagram, it MUST include the entire 181 header chain in the first fragment. 183 A host that receives a first-fragment that does not satisfy the 184 above-stated requirements SHOULD discard that packet, and also MAY 185 send an ICMPv6 error message to the source address of the offending 186 packet (subject to the rules for ICMPv6 errors specified in 187 [RFC4443]). 189 Likewise, an intermediate system (e.g. router, firewall) that 190 receives an IPv6 first-fragment that does not satisfy the above- 191 stated requirements MAY discard that packet, and MAY send an ICMPv6 192 error message to the source address of the offending packet (subject 193 to the rules for ICMPv6 error messages specified in [RFC4443]). 194 Intermediate systems having this capability SHOULD support 195 configuration (e.g. enable/disable) of whether such packets are 196 dropped or not by the intermediate system. 198 If a host or intermediate system discards an first-fragment because 199 it does not satisfy the above-stated requirements, and sends an 200 ICMPv6 error message due to the discard, then the ICMPv6 error 201 message MUST be Type 4 ("Parameter Problem") and MUST use Code TBD 202 ("First-fragment has incomplete IPv6 Header Chain"). 204 6. IANA Considerations 206 IANA is requested to add a the following entry to the "Reason Code" 207 registry for ICMPv6 "Type 4 - Parameter Problem" messages: 209 CODE NAME/DESCRIPTION 210 TBD IPv6 first-fragment has incomplete IPv6 header chain 212 7. Security Considerations 214 This document describes how improperly-fragmented packets can prevent 215 traditional stateless packet filtering. 217 This document updates RFC 2460 such that those packets are forbidden, 218 thus enabling stateless packet filtering for IPv6. 220 This specification allows nodes that drop the aforementioned packets 221 to signal such packet drops with ICMPv6 "Parameter Problem, IPv6 222 first-fragment has incomplete IPv6 header chain" (Type 4, Code TBD) 223 error messages. 225 As with all ICMPv6 error/diagnostic messages, deploying Source 226 Address Forgery Prevention filters helps reduce the chances of an 227 attacker successfully performing a reflection attack by sending 228 forged illegal packets with the victim/target's IPv6 address as the 229 IPv6 Source Address of the illegal packet [RFC2827] [RFC3704]. 231 8. Acknowledgements 233 The authors of this document would like to thank Ran Atkinson for 234 contributing text and ideas that were incorporated into this 235 document. 237 The authors would like to thank (in alphabetical order) Ran Atkinson, 238 Fred Baker, Brian Carpenter, Dominik Elsbroek, Bill Jouris, Suresh 239 Krishnan, Dave Thaler, and Eric Vyncke, for providing valuable 240 comments on earlier versions of this document. 242 9. References 244 9.1. Normative References 246 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 247 Requirement Levels", BCP 14, RFC 2119, March 1997. 249 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 250 (IPv6) Specification", RFC 2460, December 1998. 252 [RFC4302] Kent, S., "IP Authentication Header", RFC 4302, 253 December 2005. 255 [RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)", 256 RFC 4303, December 2005. 258 [RFC4443] Conta, A., Deering, S., and M. Gupta, "Internet Control 259 Message Protocol (ICMPv6) for the Internet Protocol 260 Version 6 (IPv6) Specification", RFC 4443, March 2006. 262 9.2. Informative References 264 [RFC2827] Ferguson, P. and D. Senie, "Network Ingress Filtering: 265 Defeating Denial of Service Attacks which employ IP Source 266 Address Spoofing", BCP 38, RFC 2827, May 2000. 268 [RFC3704] Baker, F. and P. Savola, "Ingress Filtering for Multihomed 269 Networks", BCP 84, RFC 3704, March 2004. 271 Authors' Addresses 273 Fernando Gont 274 SI6 Networks / UTN-FRH 275 Evaristo Carriego 2644 276 Haedo, Provincia de Buenos Aires 1706 277 Argentina 279 Phone: +54 11 4650 8472 280 Email: fgont@si6networks.com 281 URI: http://www.si6networks.com 283 Vishwas Manral 284 Hewlett-Packard Corp. 285 191111 Pruneridge Ave. 286 Cupertino, CA 95014 287 US 289 Phone: 408-447-1497 290 Email: vishwas.manral@hp.com 291 URI: 293 Ronald P. Bonica 294 Juniper Networks 295 2251 Corporate Park Drive 296 Herndon, VA 20171 297 US 299 Phone: 571 250 5819 300 Email: rbonica@juniper.net