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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 (1 August 2021) is 989 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: 2 February 2022 Universität Bremen TZI 6 1 August 2021 8 CBOR tags for IPv4 and IPv6 addresses and prefixes 9 draft-ietf-cbor-network-addresses-07 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 2 February 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 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 69 9.1. Normative References . . . . . . . . . . . . . . . . . . 8 70 9.2. Informative References . . . . . . . . . . . . . . . . . 8 71 Appendix A. Changelog . . . . . . . . . . . . . . . . . . . . . 8 72 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 9 73 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 75 1. Introduction 77 [RFC8949] defines a number of CBOR Tags for common items. Tags 260 78 and 261 were later defined through IANA [IANA.cbor-tags]. These tags 79 cover addresses (260), and prefixes (261). Tag 260 distinguishes 80 between IPv6, IPv4 and Ethernet through the length of the byte string 81 only. Tag 261 was not documented well enough to be used. 83 This specification defines tags 54 and 52. These new tags are 84 intended to be used in preference to tags 260 and 261. They provide 85 formats for IPv6 and IPv4 addresses, prefixes, and addresses with 86 prefixes, achieving an explicit indication of IPv6 or IPv4. The 87 prefix format omits trailing zeroes in the address part. (Due to the 88 complexity of testing, the value of omitting trailing zeros for the 89 pure address format was considered non-essential and support for that 90 is not provided in this specification.) This specification does not 91 deal with 6- or 8-byte Ethernet addresses. 93 2. Terminology 95 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 96 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 97 "OPTIONAL" in this document are to be interpreted as described in 98 BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all 99 capitals, as shown here. 101 3. Protocol 103 3.1. Three Forms 105 3.1.1. Addresses 107 These tags can be applied to byte strings to represent a single 108 address. 110 This form is called the Address Format. 112 3.1.2. Prefixes 114 When applied to an array that starts with an unsigned integer, they 115 represent a CIDR-style prefix of that length. 117 When the Address Format (i.e., without prefix) appears in a context 118 where a prefix is expected, then it is to be assumed that all bits 119 are relevant. That is, for IPv4, a /32 is implied, and for IPv6, a 120 /128 is implied. 122 This form is called the Prefix Format. 124 3.1.3. Interface Definition 126 When applied to an array that starts with a byte string, which stands 127 for an IP address, followed by an unsigned integer giving the bit 128 length of a prefix built out of the first "length" bits of the 129 address, they represent information that is commonly used to specify 130 both the network prefix and the IP address of an interface. 132 This form is called the Interface Format. 134 3.2. IPv6 136 IANA has allocated tag 54 for IPv6 uses. (Note that this is the 137 ASCII code for '6'.) 139 An IPv6 address is to be encoded as a sixteen-byte byte string 140 (Section 3.1 of [RFC8949], major type 2), enclosed in Tag number 54. 142 For example: 144 54(h'20010db81234DEEDBEEFCAFEFACEFEED') 146 An IPv6 prefix, such as 2001:db8:1234::/48 is to be encoded as a two 147 element array, with the length of the prefix first. Trailing zero 148 bytes MUST be omitted. 150 For example: 152 54([48, h'20010db81234']) 154 An IPv6 address combined with a prefix length, such as being used for 155 configuring an interface, is to be encoded as a two element array, 156 with the (full-length) IPv6 address first and the length of the 157 associated network the prefix next. 159 For example: 161 54([h'20010db81234DEEDBEEFCAFEFACEFEED', 56]) 163 Note that the address-with-prefix form can be reliably distinguished 164 from the prefix form only in the sequence of the array elements. 166 3.3. IPv4 168 IANA has allocated tag 52 for IPv4 uses. (Note that this is the 169 ASCII code for '4'.) 171 An IPv4 address is to be encoded as a four-byte byte string 172 (Section 3.1 of [RFC8949], major type 2), enclosed in Tag number 52. 174 For example: 176 52(h'C0000201') 178 An IPv4 prefix, such as 192.0.2.0/24 is to be encoded as a two 179 element array, with the length of the prefix first. Trailing zero 180 bytes MUST be omitted. 182 For example: 184 52([24, h'C00002']) 186 An IPv4 address combined with a prefix length, such as being used for 187 configuring an interface, is to be encoded as a two element array, 188 with the (full-length) IPv4 address first and the length of the 189 associated network the prefix next. 191 For example, 192.0.2.1/24 is to be encoded as a two element array, 192 with the length of the prefix (implied 192.0.2.0/24) last. 194 52([h'C0000201', 24]) 196 Note that the address-with-prefix form can be reliably distinguished 197 from the prefix form only in the sequence of the array elements. 199 4. Encoder Considerations for Prefixes 201 For the byte strings used in representing prefixes, an encoder MUST 202 omit any right-aligned (trailing) sequence of bytes that are all 203 zero. 205 There is no relationship between the number of bytes omitted and the 206 prefix length. For instance, the prefix 2001:db8::/64 is encoded as: 208 54([64, h'20010db8']) 210 An encoder MUST take care to set all trailing bits in the final byte 211 to zero, if any. While decoders are expected to ignore them, such 212 garbage entities could be used as a covert channel, or may reveal the 213 state of what would otherwise be private memory contents. So for 214 example, "2001:db8:1230::/44" MUST be encoded as: 216 52([44, h'20010db81230']) 218 even though variations like: 220 54([44, h'20010db81233']) WRONG 221 54([45, h'20010db8123f']) WRONG 223 would be parsed in the exact same way. 225 The same considerations apply to IPv4 prefixes. 227 5. Decoder Considerations for Prefixes 229 A decoder MUST consider all bits to the right of the prefix length to 230 be zero. 232 A decoder MUST handle the case where a prefix length specifies that 233 more bits are relevant than are actually present in the byte-string. 234 As a pathological case, ::/128 can be encoded as 236 54([128, h'']) 238 A recommendation for implementations is to first create an array of 239 16 (or 4) zero bytes. 241 Then taking whichever is smaller between (a) the length of the 242 included byte-string, and (b) the number of bytes covered by the 243 prefix-length rounded up to the next multiple of 8: fail if that 244 number is greater than 16 (or 4), and then copy that many bytes from 245 the byte-string into the array. 247 Finally, looking at the last three bits of the prefix-length in bits 248 (that is, the prefix-length modulo 8), use a static array of 8 values 249 to force the lower, non-relevant bits to zero, or simply: 251 unused_bits = (-prefix_length_in_bits) & 7; 252 if (length_in_bytes > 0) 253 address_bytes[length_in_bytes - 1] &= (0xFF << unused_bits); 255 A particularly paranoid decoder could examine the lower non-relevant 256 bits to determine if they are non-zero, and reject the prefix. This 257 would detect non-compliant encoders, or a possible covert channel. 259 if (length_in_bytes > 0 && 260 (address_bytes[length_in_bytes - 1] & ~(0xFF << unused_bits)) 261 != 0) 262 fail(); 264 6. CDDL 266 For use with CDDL [RFC8610], the typenames defined in Figure 1 are 267 recommended: 269 ip-address-or-prefix = ipv6-address-or-prefix / 270 ipv4-address-or-prefix 272 ipv6-address-or-prefix = #6.54(ipv6-address / 273 ipv6-address-with-prefix / 274 ipv6-prefix) 275 ipv4-address-or-prefix = #6.52(ipv4-address / 276 ipv4-address-with-prefix / 277 ipv4-prefix) 279 ipv6-address = bytes .size 16 280 ipv4-address = bytes .size 4 282 ipv6-address-with-prefix = [ipv6-address, ipv6-prefix-length] 283 ipv4-address-with-prefix = [ipv4-address, ipv4-prefix-length] 285 ipv6-prefix-length = 0..128 286 ipv4-prefix-length = 0..32 288 ipv6-prefix = [ipv6-prefix-length, ipv6-prefix-bytes] 289 ipv4-prefix = [ipv4-prefix-length, ipv4-prefix-bytes] 291 ipv6-prefix-bytes = bytes .size (uint .le 16) 292 ipv4-prefix-bytes = bytes .size (uint .le 4) 294 Figure 1 296 7. Security Considerations 298 Identifying which byte sequences in a protocol are addresses may 299 allow an attacker or eavesdropper to better understand what parts of 300 a packet to attack. That information, however, is likely to be found 301 in the relevant RFCs anyway, so this is not a significant exposure. 303 The right-hand bits of the prefix, after the prefix-length, are 304 ignored by this protocol. A malicious party could use them to 305 transmit covert data in a way that would not affect the primary use 306 of this encoding. Such abuse would be detected by examination of the 307 raw protocol bytes. Users of this encoding should be aware of this 308 possibility. 310 8. IANA Considerations 312 IANA has allocated two tags from the Specification Required area of 313 the Concise Binary Object Representation (CBOR) Tags 314 [IANA.cbor-tags]: 316 8.1. Tag 54 - IPv6 318 Data Item: byte string or array 319 Semantics: IPv6, [prefixlen,IPv6], [IPv6,prefixpart] 321 8.2. Tag 52 - IPv4 323 Data Item: byte string or array 324 Semantics: IPv4, [prefixlen,IPv4], [IPv4,prefixpart] 326 9. References 328 9.1. Normative References 330 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 331 Requirement Levels", BCP 14, RFC 2119, 332 DOI 10.17487/RFC2119, March 1997, 333 . 335 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 336 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 337 May 2017, . 339 [RFC8610] Birkholz, H., Vigano, C., and C. Bormann, "Concise Data 340 Definition Language (CDDL): A Notational Convention to 341 Express Concise Binary Object Representation (CBOR) and 342 JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610, 343 June 2019, . 345 [RFC8949] Bormann, C. and P. Hoffman, "Concise Binary Object 346 Representation (CBOR)", STD 94, RFC 8949, 347 DOI 10.17487/RFC8949, December 2020, 348 . 350 9.2. Informative References 352 [IANA.cbor-tags] 353 IANA, "Concise Binary Object Representation (CBOR) Tags", 354 . 356 Appendix A. Changelog 358 This section is to be removed before publishing as an RFC. 360 * 03 362 * 02 363 * 01 added security considerations about covert channel 365 Acknowledgements 367 none yet 369 Authors' Addresses 371 Michael Richardson 372 Sandelman Software Works 374 Email: mcr+ietf@sandelman.ca 376 Carsten Bormann 377 Universität Bremen TZI 378 Germany 380 Email: cabo@tzi.org