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Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (8 September 2021) is 961 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) No issues found here. Summary: 0 errors (**), 0 flaws (~~), 2 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 CBOR Working Group M. Richardson 3 Internet-Draft Sandelman Software Works 4 Intended status: Standards Track C. Bormann 5 Expires: 12 March 2022 Universität Bremen TZI 6 8 September 2021 8 CBOR tags for IPv4 and IPv6 addresses and prefixes 9 draft-ietf-cbor-network-addresses-08 11 Abstract 13 This specification defines two CBOR Tags to be used with IPv6 and 14 IPv4 addresses and prefixes. 16 // RFC-EDITOR-please-remove: This work is tracked at 17 // https://github.com/cbor-wg/cbor-network-address 19 Status of This Memo 21 This Internet-Draft is submitted in full conformance with the 22 provisions of BCP 78 and BCP 79. 24 Internet-Drafts are working documents of the Internet Engineering 25 Task Force (IETF). Note that other groups may also distribute 26 working documents as Internet-Drafts. The list of current Internet- 27 Drafts is at https://datatracker.ietf.org/drafts/current/. 29 Internet-Drafts are draft documents valid for a maximum of six months 30 and may be updated, replaced, or obsoleted by other documents at any 31 time. It is inappropriate to use Internet-Drafts as reference 32 material or to cite them other than as "work in progress." 34 This Internet-Draft will expire on 12 March 2022. 36 Copyright Notice 38 Copyright (c) 2021 IETF Trust and the persons identified as the 39 document authors. All rights reserved. 41 This document is subject to BCP 78 and the IETF Trust's Legal 42 Provisions Relating to IETF Documents (https://trustee.ietf.org/ 43 license-info) in effect on the date of publication of this document. 44 Please review these documents carefully, as they describe your rights 45 and restrictions with respect to this document. Code Components 46 extracted from this document must include Simplified BSD License text 47 as described in Section 4.e of the Trust Legal Provisions and are 48 provided without warranty as described in the Simplified BSD License. 50 Table of Contents 52 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 53 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 54 3. Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . 3 55 3.1. Three Forms . . . . . . . . . . . . . . . . . . . . . . . 3 56 3.1.1. Addresses . . . . . . . . . . . . . . . . . . . . . . 3 57 3.1.2. Prefixes . . . . . . . . . . . . . . . . . . . . . . 3 58 3.1.3. Interface Definition . . . . . . . . . . . . . . . . 3 59 3.2. IPv6 . . . . . . . . . . . . . . . . . . . . . . . . . . 4 60 3.3. IPv4 . . . . . . . . . . . . . . . . . . . . . . . . . . 4 61 4. Encoder Considerations for Prefixes . . . . . . . . . . . . . 5 62 5. Decoder Considerations for Prefixes . . . . . . . . . . . . . 6 63 6. CDDL . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 64 7. Security Considerations . . . . . . . . . . . . . . . . . . . 7 65 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 66 8.1. Tag 54 - IPv6 . . . . . . . . . . . . . . . . . . . . . . 8 67 8.2. Tag 52 - IPv4 . . . . . . . . . . . . . . . . . . . . . . 8 68 8.3. Tags 260 and 261 . . . . . . . . . . . . . . . . . . . . 8 69 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 70 9.1. Normative References . . . . . . . . . . . . . . . . . . 8 71 9.2. Informative References . . . . . . . . . . . . . . . . . 8 72 Appendix A. Changelog . . . . . . . . . . . . . . . . . . . . . 9 73 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 9 74 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 76 1. Introduction 78 [RFC8949] defines a number of CBOR Tags for common items. Tags 260 79 and 261 were later defined through IANA [IANA.cbor-tags]. These tags 80 cover addresses (260), and prefixes (261). Tag 260 distinguishes 81 between IPv6, IPv4 and Ethernet through the length of the byte string 82 only. Tag 261 was not documented well enough to be used. 84 This specification defines tags 54 and 52. These new tags are 85 intended to be used in preference to tags 260 and 261. They provide 86 formats for IPv6 and IPv4 addresses, prefixes, and addresses with 87 prefixes, achieving an explicit indication of IPv6 or IPv4. The 88 prefix format omits trailing zeroes in the address part. (Due to the 89 complexity of testing, the value of omitting trailing zeros for the 90 pure address format was considered non-essential and support for that 91 is not provided in this specification.) This specification does not 92 deal with 6- or 8-byte Ethernet addresses. 94 2. Terminology 96 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 97 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 98 "OPTIONAL" in this document are to be interpreted as described in 99 BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all 100 capitals, as shown here. 102 3. Protocol 104 3.1. Three Forms 106 3.1.1. Addresses 108 These tags can be applied to byte strings to represent a single 109 address. 111 This form is called the Address Format. 113 3.1.2. Prefixes 115 When applied to an array that starts with an unsigned integer, they 116 represent a CIDR-style prefix of that length. 118 When the Address Format (i.e., without prefix) appears in a context 119 where a prefix is expected, then it is to be assumed that all bits 120 are relevant. That is, for IPv4, a /32 is implied, and for IPv6, a 121 /128 is implied. 123 This form is called the Prefix Format. 125 3.1.3. Interface Definition 127 When applied to an array that starts with a byte string, which stands 128 for an IP address, followed by an unsigned integer giving the bit 129 length of a prefix built out of the first "length" bits of the 130 address, they represent information that is commonly used to specify 131 both the network prefix and the IP address of an interface. 133 This form is called the Interface Format. 135 3.2. IPv6 137 IANA has allocated tag 54 for IPv6 uses. (Note that this is the 138 ASCII code for '6'.) 140 An IPv6 address is to be encoded as a sixteen-byte byte string 141 (Section 3.1 of [RFC8949], major type 2), enclosed in Tag number 54. 143 For example: 145 54(h'20010db81234DEEDBEEFCAFEFACEFEED') 147 An IPv6 prefix, such as 2001:db8:1234::/48 is to be encoded as a two 148 element array, with the length of the prefix first. Trailing zero 149 bytes MUST be omitted. 151 For example: 153 54([48, h'20010db81234']) 155 An IPv6 address combined with a prefix length, such as being used for 156 configuring an interface, is to be encoded as a two element array, 157 with the (full-length) IPv6 address first and the length of the 158 associated network the prefix next. 160 For example: 162 54([h'20010db81234DEEDBEEFCAFEFACEFEED', 56]) 164 Note that the address-with-prefix form can be reliably distinguished 165 from the prefix form only in the sequence of the array elements. 167 3.3. IPv4 169 IANA has allocated tag 52 for IPv4 uses. (Note that this is the 170 ASCII code for '4'.) 172 An IPv4 address is to be encoded as a four-byte byte string 173 (Section 3.1 of [RFC8949], major type 2), enclosed in Tag number 52. 175 For example: 177 52(h'C0000201') 179 An IPv4 prefix, such as 192.0.2.0/24 is to be encoded as a two 180 element array, with the length of the prefix first. Trailing zero 181 bytes MUST be omitted. 183 For example: 185 52([24, h'C00002']) 187 An IPv4 address combined with a prefix length, such as being used for 188 configuring an interface, is to be encoded as a two element array, 189 with the (full-length) IPv4 address first and the length of the 190 associated network the prefix next. 192 For example, 192.0.2.1/24 is to be encoded as a two element array, 193 with the length of the prefix (implied 192.0.2.0/24) last. 195 52([h'C0000201', 24]) 197 Note that the address-with-prefix form can be reliably distinguished 198 from the prefix form only in the sequence of the array elements. 200 4. Encoder Considerations for Prefixes 202 For the byte strings used in representing prefixes, an encoder MUST 203 omit any right-aligned (trailing) sequence of bytes that are all 204 zero. 206 There is no relationship between the number of bytes omitted and the 207 prefix length. For instance, the prefix 2001:db8::/64 is encoded as: 209 54([64, h'20010db8']) 211 An encoder MUST take care to set all trailing bits in the final byte 212 to zero, if any. While decoders are expected to ignore them, such 213 garbage entities could be used as a covert channel, or may reveal the 214 state of what would otherwise be private memory contents. So for 215 example, "2001:db8:1230::/44" MUST be encoded as: 217 52([44, h'20010db81230']) 219 even though variations like: 221 54([44, h'20010db81233']) WRONG 222 54([45, h'20010db8123f']) WRONG 224 would be parsed in the exact same way. 226 The same considerations apply to IPv4 prefixes. 228 5. Decoder Considerations for Prefixes 230 A decoder MUST consider all bits to the right of the prefix length to 231 be zero. 233 A decoder MUST handle the case where a prefix length specifies that 234 more bits are relevant than are actually present in the byte-string. 235 As a pathological case, ::/128 can be encoded as 237 54([128, h'']) 239 A recommendation for implementations is to first create an array of 240 16 (or 4) zero bytes. 242 Then taking whichever is smaller between (a) the length of the 243 included byte-string, and (b) the number of bytes covered by the 244 prefix-length rounded up to the next multiple of 8: fail if that 245 number is greater than 16 (or 4), and then copy that many bytes from 246 the byte-string into the array. 248 Finally, looking at the last three bits of the prefix-length in bits 249 (that is, the prefix-length modulo 8), use a static array of 8 values 250 to force the lower, non-relevant bits to zero, or simply: 252 unused_bits = (-prefix_length_in_bits) & 7; 253 if (length_in_bytes > 0) 254 address_bytes[length_in_bytes - 1] &= (0xFF << unused_bits); 256 A particularly paranoid decoder could examine the lower non-relevant 257 bits to determine if they are non-zero, and reject the prefix. This 258 would detect non-compliant encoders, or a possible covert channel. 260 if (length_in_bytes > 0 && 261 (address_bytes[length_in_bytes - 1] & ~(0xFF << unused_bits)) 262 != 0) 263 fail(); 265 6. CDDL 267 For use with CDDL [RFC8610], the typenames defined in Figure 1 are 268 recommended: 270 ip-address-or-prefix = ipv6-address-or-prefix / 271 ipv4-address-or-prefix 273 ipv6-address-or-prefix = #6.54(ipv6-address / 274 ipv6-address-with-prefix / 275 ipv6-prefix) 276 ipv4-address-or-prefix = #6.52(ipv4-address / 277 ipv4-address-with-prefix / 278 ipv4-prefix) 280 ipv6-address = bytes .size 16 281 ipv4-address = bytes .size 4 283 ipv6-address-with-prefix = [ipv6-address, ipv6-prefix-length] 284 ipv4-address-with-prefix = [ipv4-address, ipv4-prefix-length] 286 ipv6-prefix-length = 0..128 287 ipv4-prefix-length = 0..32 289 ipv6-prefix = [ipv6-prefix-length, ipv6-prefix-bytes] 290 ipv4-prefix = [ipv4-prefix-length, ipv4-prefix-bytes] 292 ipv6-prefix-bytes = bytes .size (uint .le 16) 293 ipv4-prefix-bytes = bytes .size (uint .le 4) 295 Figure 1 297 7. Security Considerations 299 Identifying which byte sequences in a protocol are addresses may 300 allow an attacker or eavesdropper to better understand what parts of 301 a packet to attack. That information, however, is likely to be found 302 in the relevant RFCs anyway, so this is not a significant exposure. 304 The right-hand bits of the prefix, after the prefix-length, are 305 ignored by this protocol. A malicious party could use them to 306 transmit covert data in a way that would not affect the primary use 307 of this encoding. Such abuse would be detected by examination of the 308 raw protocol bytes. Users of this encoding should be aware of this 309 possibility. 311 8. IANA Considerations 313 IANA has allocated two tags from the Specification Required area of 314 the Concise Binary Object Representation (CBOR) Tags 315 [IANA.cbor-tags]: 317 8.1. Tag 54 - IPv6 319 Data Item: byte string or array 320 Semantics: IPv6, [prefixlen,IPv6], [IPv6,prefixpart] 322 8.2. Tag 52 - IPv4 324 Data Item: byte string or array 325 Semantics: IPv4, [prefixlen,IPv4], [IPv4,prefixpart] 327 8.3. Tags 260 and 261 329 IANA is requested to add the note "DEPRECATED in favor of 52 and 54" 330 to registrations 260 and 261" 332 9. References 334 9.1. Normative References 336 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 337 Requirement Levels", BCP 14, RFC 2119, 338 DOI 10.17487/RFC2119, March 1997, 339 . 341 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 342 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 343 May 2017, . 345 [RFC8610] Birkholz, H., Vigano, C., and C. Bormann, "Concise Data 346 Definition Language (CDDL): A Notational Convention to 347 Express Concise Binary Object Representation (CBOR) and 348 JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610, 349 June 2019, . 351 [RFC8949] Bormann, C. and P. Hoffman, "Concise Binary Object 352 Representation (CBOR)", STD 94, RFC 8949, 353 DOI 10.17487/RFC8949, December 2020, 354 . 356 9.2. Informative References 358 [IANA.cbor-tags] 359 IANA, "Concise Binary Object Representation (CBOR) Tags", 360 . 362 Appendix A. Changelog 364 This section is to be removed before publishing as an RFC. 366 * 03 368 * 02 370 * 01 added security considerations about covert channel 372 Acknowledgements 374 none yet 376 Authors' Addresses 378 Michael Richardson 379 Sandelman Software Works 381 Email: mcr+ietf@sandelman.ca 383 Carsten Bormann 384 Universität Bremen TZI 385 Germany 387 Email: cabo@tzi.org