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Checking references for intended status: Full Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Missing Reference: 'IPv6' is mentioned on line 171, but not defined == Unused Reference: 'I-D.ietf-6man-rfc2460bis' is defined on line 298, but no explicit reference was found in the text ** Obsolete normative reference: RFC 2460 (Obsoleted by RFC 8200) ** Downref: Normative reference to an Proposed Standard RFC: RFC 7045 == Outdated reference: A later version (-13) exists of draft-ietf-6man-rfc2460bis-05 Summary: 3 errors (**), 0 flaws (~~), 4 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 INTERNET-DRAFT T. Herbert 3 Intended Status: Standard Quantonium 4 Expires: November 2017 6 May 8, 2017 8 ICMPv6 errors for discarding packets due to processing limits 9 draft-herbert-6man-icmp-limits-00 11 Abstract 13 Network nodes may discards packets if they are unable to process 14 protocol headers of packets due to processing constraints or limits. 15 When such packets are dropped, the sender receives no indication so 16 it cannot take action to address the cause of discarded packets. This 17 document defines ICMP errors that can be sent by a node that discards 18 packets because it is unable to process the protocol headers. A 19 sender that receives such an ICMP error may be able to modify what it 20 sends in future packets to avoid subsequent packet discards. 22 Status of this Memo 24 This Internet-Draft is submitted to IETF in full conformance with the 25 provisions of BCP 78 and BCP 79. 27 Internet-Drafts are working documents of the Internet Engineering 28 Task Force (IETF), its areas, and its working groups. Note that 29 other groups may also distribute working documents as 30 Internet-Drafts. 32 Internet-Drafts are draft documents valid for a maximum of six months 33 and may be updated, replaced, or obsoleted by other documents at any 34 time. It is inappropriate to use Internet-Drafts as reference 35 material or to cite them other than as "work in progress." 37 The list of current Internet-Drafts can be accessed at 38 http://www.ietf.org/1id-abstracts.html 40 The list of Internet-Draft Shadow Directories can be accessed at 41 http://www.ietf.org/shadow.html 43 Copyright and License Notice 45 Copyright (c) 2017 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 1.1 Extension header limits . . . . . . . . . . . . . . . . . . 3 62 1.2 Aggregate header limits . . . . . . . . . . . . . . . . . . 4 63 2 ICMP message format . . . . . . . . . . . . . . . . . . . . . . 4 64 3 Descriptions of codes . . . . . . . . . . . . . . . . . . . . . 5 65 3.1 Unrecognized Next Header type encountered (code 1) . . . . . 5 66 3.2 Extension header too big (code 4) . . . . . . . . . . . . . 5 67 3.3 Extension header chain too long (code 5) . . . . . . . . . . 6 68 3.4 Too many options in extension header (code 6) . . . . . . . 6 69 3.5 Headers too long (code 7) . . . . . . . . . . . . . . . . . 6 70 4 Security Considerations . . . . . . . . . . . . . . . . . . . . 6 71 5 IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7 72 6 References . . . . . . . . . . . . . . . . . . . . . . . . . . 7 73 6.1 Normative References . . . . . . . . . . . . . . . . . . . 7 74 6.2 Informative References . . . . . . . . . . . . . . . . . . 7 75 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 7 77 1 Introduction 79 This document specifies ICMP Parameter Problem type errors that can 80 sent when a node discards a packet due to it being unable to process 81 the necessary protocol headers because of processing constraints and 82 limits. 84 Four of the errors are specific to processing limits of extension 85 headers; another error is used when the aggregate protocol headers in 86 a packet exceed the processing limits of a node. 88 1.1 Extension header limits 90 With IPv6, optional internet-layer information is carried in one or 91 more IPv6 Extension Headers [RFC2460]. Extension Headers are placed 92 between the IPv6 header and the Upper-Layer Header in a packet. The 93 term "Header Chain" refers collectively to the IPv6 header, Extension 94 Headers, and Upper-Layer Header occurring in a packet. Individual 95 extension headers may have a length of 2048 and must fit into one 96 MTU. Destination Options and Hop by Hop Options contain a list 97 options in Type-length-value (TLV) format. Each option includes a 98 length of the data field in octets and the minimum size of a (non- 99 pad) option is two bytes and the maximum length is 257 bytes. The 100 number of options in an extension header is only limited by the 101 length of the extension header and MTU. Options may also be skipped 102 over by a receiver if they are unknown and the Option Type indicates 103 to skip (first two bits are 00). 105 Per [RFC2460], except for Hop by Hop options, extension headers are 106 not examined or processed by intermediate nodes. Many intermediate 107 nodes, however, do examine extension header for various purposes. For 108 instance, a node may examine all extension headers to locate the 109 transport header of packet in order to implement transport layer 110 filtering or to track connections to implement a stateful firewall. 112 Destination hosts are expected to process all extensions headers and 113 options in Hop by Hop and Destination Options. 115 Due to the variable lengths and high limits of lengths of extension 116 header and chains, many devices have operational limits of extension 117 headers in packets they can process. [RFC7045] discusses the 118 requirements of intermediate nodes that discard packets because of 119 unrecognized extension headers. When a limit is exceeded, the typical 120 behavior is to silently discard a packet. The limits are non-standard 121 and may be configurable per implementation. Both intermediate nodes 122 and end hosts may institute such limits on extension header 123 processing. 125 This document defines three Parameter Problem codes and extends the 126 applicably of an existing code that are sent by a node that discards 127 a packet due to processing limits of extension headers being 128 exceeded. A source host that receives an ICMP error can modify the 129 use of extension headers in subsequent packets to the destination in 130 order to avoid further occurrences of packets with extension headers 131 being discarded. 133 1.2 Aggregate header limits 135 Many hardware devices implement a parsing buffer of a fixed sized to 136 process packets. The parsing buffer is expected to contain all the 137 headers (often up to a transport layer header for filtering) that a 138 device needs to examine. Parsing buffers have been implemented with 139 various sizes (512 is common, some devices have smaller sizes). 141 When the aggregate length of headers in a packet exceeds the size of 142 the parsing buffer, a device will typically either discard the packet 143 or defer processing to a software slow path. In either case, no 144 indication of a problem is sent back to the sender. 146 This document defines one code for ICMPv6 Parameter Problem type that 147 is sent by a node that is unable to process the headers of a packet 148 due to the aggregate size of the packet headers exceeding a 149 processing limit (e.g. exceeding the size of a parsing buffer). A 150 source host that receives an ICMP error can modify the headers used 151 in subsequent packets to try to avoid further occurrences of packets 152 being discarded or relegated to a slow path. 154 2 ICMP message format 156 The ICMP errors defined in this document are Parameter Problem 157 messages. Four new codes are defined for Parameter Problem type and 158 applicability of one existing code is extended. 160 The format of the ICMP message is: 162 0 1 2 3 163 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 1 164 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 165 | Type | Code | Checksum | 166 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 167 | Pointer | 168 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 169 | As much of invoking packet | 170 + as possible without the ICMPv6 packet + 171 | exceeding the minimum IPv6 MTU [IPv6] | 172 IPv6 Fields: 174 Destination Address 175 Copied from the Source Address field of the invoking packet. 177 ICMPv6 Fields: 179 Type 180 4 (Parameter Problem type) 182 Code (pertinent to this specification) 183 1 - Unrecognized Next Header type encountered 184 4 - Extension header too big 185 5 - Extension header chain too long 186 6 - Too many options in extension header 187 7 - Headers too long 189 Pointer 190 Identifies the octet offset within the invoking packet where a 191 limit was exceeded. 193 The pointer will point beyond the end of the ICMPv6 packet if 194 the field exceeding the limit is beyond what can fit in the 195 maximum size of an ICMPv6 error message. 197 3 Descriptions of codes 199 3.1 Unrecognized Next Header type encountered (code 1) 201 [RFC2460] specifies that a destination host should send an 202 "unrecognized next header type" when a Next Header value is 203 unrecognized in a packet. This document extends this to allow 204 intermediate nodes to send this same error a packet that is discarded 205 because a node does not recognize a Next Header type. 207 This code SHOULD be sent by an intermediate node that discards a 208 packet because it encounters a Next Header type that is unknown in 209 its examination. The ICMP Pointer field is set to the offset of the 210 unrecognized value within the original packet. 212 Note that when the original sender receives the ICMP error it can 213 differentiate between the message being sent by a destination host, 214 per [RFC2460], and an error sent by an intermediate host based on 215 matching the source address of the ICMP packet and the destination 216 address of the packet in the ICMP data. 218 3.2 Extension header too big (code 4) 219 An ICMP Parameter Problem with code for "extension header too big" 220 SHOULD be sent when a node discards a packet because the size of 221 extension exceeds its processing limit. The ICMP Pointer field should 222 be set to the offset of length field for the extension header that is 223 too big. 225 3.3 Extension header chain too long (code 5) 227 An ICMP Parameter Problem with code for "extension header chain too 228 long" SHOULD be sent when a node discards a packet with an extension 229 header chain because an extension header chains exceeds it processing 230 limit. The ICMP Pointer field should be set to the offset of the 231 first octet that exceeds the limit. 233 Note there are two different limits that might be applied: a limit on 234 the total size in octets of the header chain, and a limit on the 235 number of extension headers in the chain. This error code is used in 236 both cases. In the case that the an octet limit is exceeded, the ICMP 237 Pointer should be set to first octet beyond the limit. In the case 238 that the number of extension headers is exceeded, the ICMP Pointer 239 should be set to the offset of first octet of the first extension 240 header that is beyond the limit. 242 3.4 Too many options in extension header (code 6) 244 An ICMP Parameter Problem with code for "too many options in 245 extension header" SHOULD be sent when a node discards a packet with 246 an extension header that has a number of options that exceed the 247 processing limits of the node. This code is applicable for 248 Destination options or Hop by Hop options. The ICMP Pointer field 249 should be set to the first octet of the first option that exceeds the 250 limit. 252 3.5 Headers too long (code 7) 254 An ICMP Parameter Problem with code for "headers too long" SHOULD be 255 sent when a node discards a packet because the aggregate length of 256 headers in the packet exceeds the processing limits of the node. The 257 ICMP Pointer should be set to the offset of the first octet that 258 exceeds the limit. 260 4 Security Considerations 262 This document does not introduce any new security concerns for use of 263 ICMP errors. The security considerations for ICMPv6 described in 264 [RFC4443] are applicable. 266 5 IANA Considerations 268 IANA is requested to assign the following codes for ICMPv6 type 4 269 "Parameter Problem": 271 4 - Extension header too big 273 5 - Extension header chain too long 275 6 - Too many options in extension header 277 7 - Headers too long 279 6 References 281 6.1 Normative References 283 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 284 (IPv6) Specification", RFC 2460, December 1998. 286 [RFC7045] Carpenter, B. and S. Jiang, "Transmission and Processing of 287 IPv6 Extension Headers", RFC 7045, DOI 10.17487/RFC7045, 288 December 2013, . 290 [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet 291 Control Message Protocol (ICMPv6) for the Internet Protocol 292 Version 6 (IPv6) Specification", RFC 4443, DOI 293 10.17487/RFC4443, March 2006, . 296 6.2 Informative References 298 [I-D.ietf-6man-rfc2460bis] Deering, S. and R. Hinden, "Internet 299 Protocol, Version 6 (IPv6) Specification", draft-ietf-6man- 300 rfc2460bis-05. 302 Author's Address 304 Tom Herbert 305 Quantonium 306 Santa Clara, CA 307 USA 309 Email: tom@herbertland.com