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Jinmei 5 Intended status: Standards Track Infoblox 6 Expires: September 10, 2021 March 9, 2021 8 Inserting, Processing And Deleting IPv6 Extension Headers 9 draft-bonica-6man-ext-hdr-update-05 11 Abstract 13 This document provides guidance regarding the processing, insertion, 14 and deletion of IPv6 extension headers. It updates RFC 8200. 16 Status of This Memo 18 This Internet-Draft is submitted in full conformance with the 19 provisions of BCP 78 and BCP 79. 21 Internet-Drafts are working documents of the Internet Engineering 22 Task Force (IETF). Note that other groups may also distribute 23 working documents as Internet-Drafts. The list of current Internet- 24 Drafts is at https://datatracker.ietf.org/drafts/current/. 26 Internet-Drafts are draft documents valid for a maximum of six months 27 and may be updated, replaced, or obsoleted by other documents at any 28 time. It is inappropriate to use Internet-Drafts as reference 29 material or to cite them other than as "work in progress." 31 This Internet-Draft will expire on September 10, 2021. 33 Copyright Notice 35 Copyright (c) 2021 IETF Trust and the persons identified as the 36 document authors. All rights reserved. 38 This document is subject to BCP 78 and the IETF Trust's Legal 39 Provisions Relating to IETF Documents 40 (https://trustee.ietf.org/license-info) in effect on the date of 41 publication of this document. Please review these documents 42 carefully, as they describe your rights and restrictions with respect 43 to this document. Code Components extracted from this document must 44 include Simplified BSD License text as described in Section 4.e of 45 the Trust Legal Provisions and are provided without warranty as 46 described in the Simplified BSD License. 48 Table of Contents 50 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 51 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2 52 3. Updates To RFC 8200 . . . . . . . . . . . . . . . . . . . . . 3 53 3.1. Original Text . . . . . . . . . . . . . . . . . . . . . . 3 54 3.2. Updated Text . . . . . . . . . . . . . . . . . . . . . . 3 55 4. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 4 56 5. Security Considerations . . . . . . . . . . . . . . . . . . . 5 57 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 58 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5 59 8. Normative References . . . . . . . . . . . . . . . . . . . . 5 60 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6 62 1. Introduction 64 In IPv6 [RFC8200] optional internet-layer information is encoded in 65 extension headers. As specified by [RFC8200], "extension headers 66 (except for the Hop-by-Hop Options header) are not processed, 67 inserted, or deleted by any node along a packet's delivery path, 68 until the packet reaches the node (or each of the set of nodes, in 69 the case of multicast) identified in the Destination Address field of 70 the IPv6 header". 72 The statement quoted above identifies nodes upon which extension 73 headers are not processed, inserted, or deleted. It does not imply 74 that extension headers can be processed, inserted, or deleted on any 75 other node along a packet's delivery path. 77 This document provides guidance regarding the processing, insertion, 78 and deletion of IPv6 extension headers. It clarifies the statement 79 quoted above and updates [RFC8200]. 81 2. Terminology 83 The following terms are used in this document: 85 o Source node - An IPv6 source node accepts data from an upper-layer 86 protocol, prepends an IPv6 header, and sends the resulting IPv6 87 packet to a destination node. 89 o Final destination node - An IPv6 final destination node receives 90 an IPv6 packet and delivers its payload to an upper-layer 91 protocol. 93 o Delivery path - A packet's delivery path is a series of nodes that 94 a packet traverses on route to its final destination. The 95 delivery path includes the final destination node. 97 o Segment - A segment is a series of links and nodes in a packet's 98 delivery path. An IPv6 Routing header steers packets from segment 99 to segment along the delivery path. If a packet contains a 100 Routing header, its delivery path can contain multiple segments. 101 If a packet does not contain a Routing header, its delivery path 102 contains only one segment. 104 o Segment egress node - A segment egress node terminates a segment. 105 When a packet arrives at a segment egress node, its IPv6 106 Destination Address identifies an interface that belongs to the 107 node. All final destination nodes are also segment egress nodes. 109 o Extension header processing - Each IPv6 extension header is 110 associated with a procedure. For example, the Fragment header is 111 associated with fragmentation and reassembly procedures. 112 Extension header processing is the reception of an extension 113 header and the execution of its associated procedure. 115 3. Updates To RFC 8200 117 The terms defined in Section 2 of this document should be added to 118 Section 2 of [RFC8200]. 120 Section 3.1 of this document quotes text from [RFC8200]. That text 121 should be replaced with the text contained by Section 3.2 of this 122 document. 124 3.1. Original Text 126 "Extension headers (except for the Hop-by-Hop Options header) are not 127 processed, inserted, or deleted by any node along a packet's delivery 128 path, until the packet reaches the node (or each of the set of nodes, 129 in the case of multicast) identified in the Destination Address field 130 of the IPv6 header. 132 The Hop-by-Hop Options header is not inserted or deleted, but may be 133 examined or processed by any node along a packet's delivery path, 134 until the packet reaches the node (or each of the set of nodes, in 135 the case of multicast) identified in the Destination Address field of 136 the IPv6 header. The Hop-by-Hop Options header, when present, must 137 immediately follow the IPv6 header. Its presence is indicated by the 138 value zero in the Next Header field of the IPv6 header." 140 3.2. Updated Text 142 Source nodes can send packets that include extension headers. 143 Extension headers are not inserted by subsequent nodes along a 144 packet's delivery path. 146 The Hop-by-Hop Options header, when present, must immediately follow 147 the IPv6 header. Its presence is indicated by the value zero in the 148 Next Header field of the IPv6 header. 150 The Hop-by-Hop Options header can be processed by any node in a 151 packet's delivery path. All remaining extension headers can be 152 processed at segment egress nodes only. While some extension headers 153 are processed at any segment egress node, others (e.g., the Fragment 154 header) can only be processed at the final destination node. 156 Except for the Routing header, extension headers cannot be deleted by 157 any node along a packet's delivery path. If the following conditions 158 are true, a Routing header can be deleted by any segment egress node: 160 o The Segments Left field in the routing header is equal to zero. 162 o The packet does not contain an Authentication header. 164 Extension headers can be inspected for various purposes (e.g., 165 firewall filtering) by any node along a packet's delivery path. 167 4. Motivation 169 The following are reasons why extension headers are not inserted by 170 nodes along a packet's delivery path: 172 o Nodes that execute Path MTU Discovery (PMTUD) [RFC8201] procedures 173 can send packets that are nearly as large as the Path MTU. Adding 174 an extension header to such a packet can cause MTU black holing. 176 o IPv6 Authentication Header [RFC4302] processing relies on the 177 immutability of the Payload Length field in the IPv6 header. When 178 a node along a packet's delivery path inserts an extension header, 179 it must also update the Payload Length field in the IPv6 header. 180 Therefore, it causes IPv6 Authentication Header processing to fail 181 on the final destination node. 183 o When a source node sends a packet to a final destination node, and 184 a node along the packet's delivery path inserts an extension 185 header, the final destination node will mistakenly attribute the 186 extension header to the source node. Attackers can leverage this 187 mistaken attribution. 189 The following are reasons why extension headers, except for the 190 Routing header, are not deleted by any node along a packet's delivery 191 path: 193 o IPv6 Authentication Header processing relies on the immutability 194 of the Payload Length field in the IPv6 header. When a node along 195 a packet's delivery path inserts an extension header, it must also 196 update the Payload Length field in the IPv6 header. Therefore, it 197 causes IPv6 Authentication Header processing to fail on the final 198 destination node. 200 o When a source node sends a packet to a final destination node, and 201 a node along the packet's delivery path removes an extension 202 header, the resulting packet may not elicit the behavior intended 203 by the source node. For example, if a Destination Options header 204 is removed, none of the options that it contains will be delivered 205 to the final destination node. 207 The following are reasons why Routing headers can be deleted by any 208 segment egress node when the Segments Left field is equal to zero and 209 the packet does not contain an authentication header: 211 o Because every segment that the routing header contains has already 212 been processed. 214 o Because [RFC8986] has set a precedent for deletion in this case. 216 5. Security Considerations 218 This document does not introduce any new security considerations. 220 6. IANA Considerations 222 This document does not request any IANA actions. 224 7. Acknowledgements 226 Thanks to Bob Hinden, Brian Carpenter, Tom Herbert and Fernando Gont 227 for their comments and review. 229 8. Normative References 231 [RFC4302] Kent, S., "IP Authentication Header", RFC 4302, 232 DOI 10.17487/RFC4302, December 2005, 233 . 235 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 236 (IPv6) Specification", STD 86, RFC 8200, 237 DOI 10.17487/RFC8200, July 2017, 238 . 240 [RFC8201] McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed., 241 "Path MTU Discovery for IP version 6", STD 87, RFC 8201, 242 DOI 10.17487/RFC8201, July 2017, 243 . 245 [RFC8986] Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer, 246 D., Matsushima, S., and Z. Li, "Segment Routing over IPv6 247 (SRv6) Network Programming", RFC 8986, 248 DOI 10.17487/RFC8986, February 2021, 249 . 251 Authors' Addresses 253 Ron Bonica 254 Juniper Networks 255 2251 Corporate Park Drive 256 Herndon, Virginia 20171 257 USA 259 Email: rbonica@juniper.net 261 Tatuya Jinmei 262 Infoblox 264 Email: jinmei@wide.ad.jp