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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 6lo M. Sethi, Ed. 3 Internet-Draft Ericsson 4 Updates: 6775 (if approved) P. Thubert 5 Intended status: Standards Track Cisco 6 Expires: February 23, 2017 B. Sarikaya, Ed. 7 Huawei USA 8 August 22, 2016 10 Address Protected Neighbor Discovery for Low-power and Lossy Networks 11 draft-sarikaya-6lo-ap-nd-04 13 Abstract 15 This document defines an extension to 6LoWPAN Neighbor Discovery. 16 This extension is designed for low-power and lossy network 17 environments and it supports multi-hop operation. Nodes supporting 18 this extension compute a Cryptographically Unique Interface ID and 19 associate it with one or more of their Registered Addresses. The 20 Cryptographic ID (Crypto-ID) uniquely identifies the owner of the 21 Registered Address. It is used in place of the EUI-64 address that 22 is specified in RFC 6775. Once an address is registered with a 23 Cryptographic ID, only the owner of that ID can modify the state 24 information of the Registered Address in the 6LR and 6LBR. 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 February 23, 2017. 43 Copyright Notice 45 Copyright (c) 2016 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 . . . . . . . . . . . . . . . . . . . . . . . . 2 61 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 62 3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 4 63 4. Protocol Interactions . . . . . . . . . . . . . . . . . . . . 5 64 4.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 5 65 4.2. Updating RFC 6775 . . . . . . . . . . . . . . . . . . . . 7 66 4.2.1. Crypto-ID Calculation . . . . . . . . . . . . . . . . 10 67 4.3. Multihop Operation . . . . . . . . . . . . . . . . . . . 13 68 5. Security Considerations . . . . . . . . . . . . . . . . . . . 14 69 6. IANA considerations . . . . . . . . . . . . . . . . . . . . . 14 70 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14 71 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 14 72 8.1. Normative References . . . . . . . . . . . . . . . . . . 14 73 8.2. Informative references . . . . . . . . . . . . . . . . . 16 74 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17 76 1. Introduction 78 Neighbor discovery for IPv6 [RFC4861] and stateless address 79 autoconfiguration [RFC4862] are together referred to as neighbor 80 discovery protocols (NDP). They are defined for regular hosts that 81 have sufficient memory and computation capabilities. These protocols 82 are however not suitable for resource-constrained devices. 83 Therefore, they require adaptation to work on resource-constrained 84 hosts operating over a low-power and lossy network (LLN). Neighbor 85 Discovery optimizations for 6LoWPAN networks include simple 86 optimizations such as a host address registration feature. This 87 feature uses the address registration option (ARO) which is sent in 88 the unicast Neighbor Solicitation (NS) and Neighbor Advertisement 89 (NA) messages [RFC6775]. 91 With 6LoWPAN ND [RFC6775], the ARO option includes a EUI-64 interface 92 ID to uniquely identify the interface of the Registered Address on 93 the registering device, so as to correlate further registrations for 94 the same address and avoid address duplication. The EUI-64 interface 95 ID is not secure and its ownership cannot be verified. Consequently, 96 any device claiming the same EUI-64 interface ID may take over an 97 existing registration and attract the traffic for that address. The 98 address registration mechanism in [RFC6775] is limited as it does not 99 require a node to prove its ownership of the EUI-64 Interface ID. 100 Therefore, any node connected to the subnet and aware of the 101 registered address to EUI-64 interface ID mapping may effectively 102 fake the same interface ID and steal an address. 104 In this document, we extend 6LoWPAN ND to protect the address 105 ownership with cryptographic material, but as opposed to Secure 106 Neighbor Discovery (SEND) [RFC3971] and Cryptographically Generated 107 Addresses (CGAs) [RFC3972], the cryptographic material generated is 108 not embedded in the Interface ID (IID) as an IPv6 address. Instead, 109 the generated cryptographic ID is used as a correlator associated 110 with the registration of the IP address. This approach is made 111 possible with 6LoWPAN ND [RFC6775], where the 6LR and the 6LBR 112 maintain state information for each Registered Address. If a 113 cryptographic ID is associated with the first 6LoWPAN ND 114 registration, then it can be used to validate any future updates to 115 the registration. 117 In order to achieve this ownership verification, in this extension 118 specification, the EUI-64 interface ID used in 6LoWPAN ND is replaced 119 with cryptographic material whose ownership can be verified. The 120 extension also provides new means for the 6LR to validate ownership 121 of the registration, and thus, the ownership of registered address. 122 The resulting protocol is called Protected Address Registration 123 protocol (ND-PAR). 125 In ND-PAR, a node typically generates one 64-bit cryptographic ID 126 (Crypto-ID) and uses it as Unique Interface ID in the registration of 127 one (or more) of its addresses with the 6LR, which it attaches to and 128 uses as default router. The 6LR validates ownership of the 129 cryptographic ID typically upon creation or update of a registration 130 state, for instance following an apparent movement from one point of 131 attachment to another. The ARO option is modified to carry the 132 Unique Interface ID, and through the DAR/DAC exchange. 134 Compared with SeND, this specification saves ~1Kbyte in every NS/NA 135 message. Also SeND requires one cryptographic address per IPv6 136 address. This specification separates the cryptographic identifier 137 from the IPv6 address so that a node can have more than one IPv6 138 address protected by the same cryptographic identifier. SeND forces 139 the IPv6 address to be cryptographic since it integrates the CGA as 140 an IID. 6LoWPAN derives the IPv6 address from other things like a 141 short address in 802.15.4 to enable a better compression. 143 2. Terminology 145 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 146 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 147 document are to be interpreted as described in [RFC2119]. 149 Readers are expected to be familiar with all the terms and concepts 150 that are discussed in [RFC3971], [RFC3972], [RFC4861], [RFC4919], 151 [RFC6775], and [I-D.ietf-6lo-backbone-router] which proposes an 152 evolution of [RFC6775] for wider applicability. 154 This document defines Crypto-ID as an identifier of variable size 155 which in most cases is 64 bits long. It is generated using 156 cryptographic means explained later in this document. 158 The document also conforms to the terms and models described in 159 [RFC5889] and uses the vocabulary and the concepts defined in 160 [RFC4291] for the IPv6 Architecture. 162 This document uses [RFC7102] for Terminology in Low power And Lossy 163 Networks. 165 3. Requirements 167 In this section we state requirements of a secure neighbor discovery 168 protocol for low-power and lossy networks. 170 o The protocol MUST be based on the Neighbor Discovery Optimization 171 for Low-power and Lossy Networks protocol defined in [RFC6775]. 172 RFC6775 utilizes optimizations such as host-initiated interactions 173 for sleeping resource-constrained hosts and elimination of 174 multicast address resolution. 176 o New options to be added to Neighbor Solicitation messages MUST 177 lead to small packet sizes, especially compared with existing 178 protocols such as SEcure Neighbor Discovery (SEND). Smaller 179 packet sizes facilitate low-power transmission by resource- 180 constrained nodes on lossy links. 182 o The support for this registration mechanism SHOULD be extensible 183 to more LLN links than IEEE 802.15.4 only. Support for at least 184 the LLN links for which a 6lo "IPv6 over foo" specification 185 exists, as well as Low-Power Wi-Fi SHOULD be possible. 187 o As part of this extension, a mechanism to compute a unique 188 Identifier should be provided with the capability to form a Link 189 Local Address that SHOULD be unique at least within the LLN 190 connected to a 6LBR. 192 o The Address Registration Option used in the ND registration SHOULD 193 be extended to carry the relevant forms of Unique Interface 194 IDentifier. 196 o The Neighbour Discovery should specify the formation of a site- 197 local address that follows the security recommendations from 198 [RFC7217]. 200 4. Protocol Interactions 202 Protected address and registration neighbor discovery protocol (ND- 203 PAR) modifies Neighbor Discovery Optimization for Low-power and Lossy 204 Networks [RFC6775] as explained in this section. 206 4.1. Overview 208 The scope of the present work is a 6LoWPAN Low Power Lossy Network 209 (LLN), typically a stub network connected to a larger IP network via 210 a Border Router called a 6LBR per [RFC6775]. 212 ---+-------- ............ 213 | External Network 214 | 215 +-----+ 216 | | LLN Border 217 | | router 218 +-----+ 219 o o o 220 o o o o 221 o o LLN o o o 222 o o o o 223 o 225 Figure 1: Basic Configuration 227 The 6LBR maintains a registration state for all devices in the 228 attached LLN, and, in conjunction with the first-hop router (the 229 6LR), is in a position to validate uniqueness and grant ownership of 230 an IPv6 address before it can be used in the LLN. This is a 231 fundamental difference with a classical network that relies on IPv6 232 address auto-configuration [RFC4862], where there is no guarantee of 233 ownership from the network, and any IPv6 Neighbor Discovery packet 234 must be individually secured [RFC3971]. 236 In a mesh network, the 6LR is directly connected to the host device. 237 This specification expects that the peer-wise layer-2 security is 238 deployed so that all the packets from a particular host are securely 239 identifiable by the 6LR. The 6LR may be multiple hops away from the 240 6LBR. Packets are routed between the 6LR and the 6LBR via other 241 6LRs. This specification expects that a chain of trust is 242 established so that a packet that was validated by the first 6LR can 243 be safely routed by the next 6LRs to the 6LBR. 245 [I-D.ietf-6tisch-architecture] suggests to use of RPL [RFC6550] as 246 the routing protocol between the 6LRs and the 6LBR, and leveraging a 247 backbone router [I-D.ietf-6lo-backbone-router] to extend the LLN in a 248 larger multilink subnet [RFC4903]. In that model, a registration 249 flow happens as shown in Figure 2. Note that network beyond the 6LBR 250 is out of scope for this document. 252 6LoWPAN Node 6LR 6LBR 253 (RPL leaf) (router) (root) 254 | | | 255 | 6LoWPAN ND |6LoWPAN ND+RPL | Efficient ND 256 | LLN link |Route-Over mesh| IPv6 link 257 | | | 258 | NS(ARO) | | 259 |-------------->| | 260 | 6LoWPAN ND | DAR (then DAO)| 261 | |-------------->| 262 | | | 263 | | | 264 | | | 265 | | | 266 | | | 267 | | | 268 | | | 269 | | DAC | 270 | |<--------------| 271 | NA(ARO) | | 272 |<--------------| | 274 Figure 2: (Re-)Registration Flow over Multi-Link Subnet 276 A new device that joins the network auto-configures an address and 277 performs an initial registration to an on-link 6LR with an NS message 278 that carries a new Address Registration Option (ARO) [RFC6775]. The 279 6LR validates the address with the central 6LBR using a DAR/DAC 280 exchange, and the 6LR confirms (or denies) the address ownership with 281 an NA message that also carries an Address Registration Option. 283 The registration mechanism in [RFC6775] was created for the original 284 purpose of Duplicate Address Detection (DAD), whereby use of an 285 address would be granted as long as the address is not already 286 present in the subnet. But [RFC6775] does not require that the 6LR 287 use the registration for source address validation (SAVI) [RFC7039]. 289 Protected address registration protocol proposed in this document 290 enforces SAVI. With this we ensure that only the correct owner uses 291 the registered address in the source address field. Therefore a 292 destination node can trust that the source is the real owner without 293 using SeND. All packets destined for a node go through the 6LR to 294 which it is attached. The 6LR maintains state information for the 295 registered addressed along with the MAC address, and link-layer 296 cryptographic key associated with that node. The 6LR therefore only 297 delivers packets to the real owner based on its state information. 299 In order to validate address ownership, the registration mechanism 300 (that goes all the way to the 6LBR with the DAR/DAC) enables the 6LBR 301 to correlate further claims for a registered address from the device 302 to which it is granted, based on a Unique Interface IDentifier (UID). 303 This UID is derived from the MAC address of the device (EUI-64). 305 This document uses a randomly generated value as an alternate UID for 306 the registration. Proof of ownership of the UID is passed with the 307 first registration to a given 6LR, and enforced at the 6LR, which 308 validates the proof. With this new operation, the 6LR allows only 309 packets from a connected host if the connected host owns the 310 registration of the source address of the packet. 312 In a multihop 6LoWPAN, the registration with Crypto-ID is propagated 313 to 6LBR as described in Section 4.3. If a chain of trust is present 314 between the 6LR and the 6LBR, then there is no need to propagate the 315 proof of ownership to the 6LBR. All the 6LBR needs to know is that 316 this particular UID is randomly generated, so as to enforce that any 317 update via a different 6LR is also random. 319 4.2. Updating RFC 6775 321 Protocol interactions are as defined in Figure 2. The Crypto-ID is 322 calculated as described in Section 4.2.1. 324 The Target Address field in NS message is set to the prefix 325 concatenated with the node's address. This address does not need 326 duplicate address detection as Crypto-ID is globally unique. So a 327 host cannot steal an address that is already registered unless it has 328 the key used for generating the Crypto-ID. The same Crypto-ID can 329 thus be used to protect multiple addresses e.g. when the node 330 receives a different prefix. 332 Local or on-link protocol interactions are shown in Figure 3. 333 Crypto-ID and ARO are passed to and stored by the 6LR/6LBR on the 334 first NS and not sent again in the next NS. The operation starts 335 with 6LR sending a Router Advertisement (RA) message to 6LN. 337 The 6LR/6LBR ensures first-come/first-serve by storing the ARO and 338 the Crypto-ID correlated to the node being registered. The node is 339 free to claim any address it likes as long as it is the first to make 340 such a claim. The node becomes owner of that address and the address 341 is bound to the Crypto-ID in the 6LR/6LBR registry. This procedure 342 avoids the constrained device to compute multiple keys for multiple 343 addresses. The registration process allows the node to tie all the 344 addresses to the same Crypto-ID and have the 6LR/6LBR enforce first- 345 come first-serve after that. 347 A condition where a 6LN uses multiple IPv6 addresses may happen when 348 the node moves at a different place and receives a different prefix. 349 In this scenario, the node uses the same Crypto-ID to protect its new 350 IPv6 address. This prevents other nodes from stealing the address 351 and trying to use it as their source address. 353 Note that if the device that moves always forms new MAC and IP 354 address [RFC6775], then this new address can be used for 355 registration. In case of a collision of the new MAC and therefore IP 356 address, the node can easily form a new IPv6 address. This is one 357 case where the use of Crypto-ID would not be needed. Crypto-ID or 358 ND-PAR should be activated when the IP address is claimed at another 359 place, or for a different MAC address at the same place, e.g. for MAC 360 address privacy [I-D.ietf-6man-ipv6-address-generation-privacy]. 362 6LN 6LR 363 | | 364 |<------------------- RA --------------------------| 365 | | 366 |----------- NS with ARO and Crypto-ID ----------->| 367 | | 368 |<---------- NA with ARO (status=req-proof) -------| 369 | | 370 |----------- NS with ARO and Crypto-ID ----------->| 371 | | 372 |<---------------- NA with ARO --------------------| 373 | | 374 ... ... 375 | | 376 |------------ NS with ARO and Crypto-ID ---------->| 377 | | 378 | | 379 |<---------------- NA with ARO --------------------| 380 ... ... 381 | | 382 |----------- NS with ARO and Crypto-ID ----------->| 383 | | 384 | | 385 |<---------------- NA with ARO --------------------| 387 Figure 3: On-link Protocol Operation 389 Elliptic Curve Cryptography (ECC) is used in the calculation of 390 cryptographic identifier (Crypto-ID). The digital signature is 391 constructed by using the 6LN's private key over its EUI-64 (MAC) 392 address. The signature value is computed using the ECDSA signature 393 algorithm and the hash function used is SHA-256 [RFC6234]. Public 394 Key is the most important parameter in CGA Parameters (sent by 6LN in 395 an NS message). ECC Public Key could be in uncompressed form or in 396 compressed form where the first octet of the OCTET STRING is 0x04 and 397 0x02 or 0x03, respectively. Point compression can further reduce the 398 key size by about 32 octets. 400 After calculating its Crypto-ID, a 6LN sends it along with the CGA 401 parameters in the first NS message, see Figure 3. In order to send 402 Crypto-ID, a modified address registration option called Enhanced 403 Address Registration Option (EARO) is defined in Figure 4. As 404 defined in the figure this ID is variable length, varying between 64 405 to 128 bits. This ID is 128 bits long only if it is used as IPv6 406 address. This may happen when some application uses one IP address 407 of the device as device ID. It would make sense in that case to 408 build a real CGA IPv6 address. The prefix of the address would be 409 obtained from prefix information option (PIO in RA) [RFC4861]. 411 6LN also sends some other parameters to enable 6LR or 6LBR to verify 412 the Crypto-ID. The option shown in Figure 5 can be used. In the 413 figure, CGA Parameters field contains the public key, prefix and some 414 other values. It is a simplified form of CGA Option defined in 415 [RFC3971]. 417 4.2.1. Crypto-ID Calculation 419 First, the modifier is set to a random or pseudo-random 128-bit 420 value. Next, concatenate from left to right the modifier, 9 zero 421 octets and the ECC public key. SHA-256 algorithm is applied on the 422 concatenation. The 112 leftmost bits of the hash value is taken. 423 Concatenate from left to right the modifier value, the subnet prefix 424 and the encoded public key. NIST P-256 is executed on the 425 concatenation. The leftmost bits of the result is used as the 426 Crypto-ID. The length is normally 64 bits, however it could be 128 427 bits. 429 In respecting the cryptographical algorithm agility [RFC7696], Curve 430 25519 [RFC7748] can also be used instead of NIST P-256. This is 431 indicated by 6LN by setting the Crypto Type field in CGA Parameters 432 Option to a value of 1. If 6LBR does not support Curve 25519, it 433 will set Crypto Type field to zero. This means that the default 434 algorithm (NIST P-256) will be used. 436 0 1 2 3 437 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 1 438 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 439 | Type | Length | Status | Reserved | 440 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 441 | Reserved |C|T| TID | Registration Lifetime | 442 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 443 | | 444 + Owner Unique ID (EUI-64 or equivalent) + 445 | | 446 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 448 Figure 4: Enhanced Address Registration Option 450 Type: 452 TBA1 454 Length: 456 8-bit unsigned integer. The length of the option (including the 457 type and length fields) in units of 8 bytes. The value 0 is 458 invalid. A value of 3 with the C flag set indicates a Crypto-ID 459 of 128 bits. 461 Status: 463 8-bit unsigned integer. Indicates the status of a registration in 464 the NA response. MUST be set to 0 in NS messages. See below. 466 Reserved: 468 This field is unused. It MUST be initialized to zero by the 469 sender and MUST be ignored by the receiver. 471 C: 473 C bit when set is used to indicate that Owner Unique ID fields 474 contains Crypto-ID. 476 T and TID: 478 Defined in [I-D.ietf-6lo-backbone-router]. 480 Owner Unique ID: 482 In this specification, this field contains Crypto-ID, a variable 483 length field to carry the Crypto-ID or random UID. This field is 484 normally 64 bits long. It could be 128 bits long if IPv6 address 485 is used as the Crypto-ID. 487 0 1 2 3 488 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 1 489 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 490 | Type | Length | Pad Length | Crypto Type | 491 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 492 | | 493 + + 494 | | 495 + Modifier (16 octets) + 496 | | 497 + + 498 | | 499 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 500 | | 501 + Subnet Prefix (8 octets) + 502 | | 503 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 504 | | 505 | | 506 + Public Key (variable length) + 507 | | 508 | | 509 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 510 | | 511 . . 512 . Padding . 513 . . 514 | | 515 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 517 Figure 5: CGA Parameters Option 519 Type: 521 TBA2 523 Length: 525 The length of the option in units of 8 octets. 527 Pad Length: 529 The length of the Padding field. 531 Crypto Type: 533 The type of cryptographic algorithm used in calculation Crypto-ID. 534 Default value of all zeros indicate NIST P-256. A value of 1 is 535 assigned for Curve 25519. New values may be defined later. 537 Modifier: 539 128 bit random value. 541 Subnet Prefix: 543 64 bit subnet prefix. 545 Public Key: 547 ECC public key of 6LN. 549 Padding: 551 A variable-length field making the option length a multiple of 8, 552 containing as many octets as specified in the Pad Length field. 554 4.3. Multihop Operation 556 In multihop 6LoWPAN, 6LBR sends RAs with prefixes downstream and it 557 is the 6LR that receives and relays them to the nodes. 6LR and 6LBR 558 communicate with the ICMPv6 Duplicate Address Request (DAR) and the 559 Duplicate Address Confirmation (DAC) messages. The DAR and DAC use 560 the same message format as NS and NA with different ICMPv6 type 561 values. 563 In ND-PAR we extend DAR/DAC messages to carry cryptographically 564 generated UID. In a multihop 6LoWPAN, the node exchanges the 565 messages shown in Figure 2. The 6LBR must be aware of who owns an 566 address (EUI-64) to defend the first node if there is an attacker on 567 another 6LR. Because of this the content that the source signs and 568 the signature needs to be propagated to the 6LBR in DAR message. For 569 this purpose the DAR message sent by 6LR to 6LBR MUST contain CGA 570 Parameters and Digital Signature Option carrying the CGA that the 571 node calculates and its public key. DAR message also contains ARO. 573 It is possible that occasionally, 6LR may miss the node's UID (that 574 it received in ARO). 6LR should be able to ask for it again. This is 575 done by restarting the exchanges shown in Figure 3. The result 576 enables 6LR to refresh the information that was lost. 6LR MUST send 577 DAR message with ARO to 6LBR. 6LBR as a reply forms a DAC message 578 with the information copied from the DAR and the Status field is set 579 to zero. With this exchange, the 6LBR can (re)validate and store the 580 information to make sure that the 6LR is not a fake. 582 In some cases 6LBR may use DAC message to signal to 6LR that it 583 expects Crypto-ID from 6LR also asks 6LR to verify the EUI-64 6LR 584 received from 6LN. This may happen when a 6LN node is compromised 585 and a fake node is sending the Crypto-ID as if it is the node's EUI- 586 64. Note that the detection in this case can only be done by 6LBR 587 not by 6LR. 589 5. Security Considerations 591 The same considerations regarding the threats to the Local Link 592 Network covered in [RFC3971] apply. 594 The threats discussed in Section 9.2 of [RFC3971] are countered by 595 the protocol described in this document as well. 597 Collisions of Crypto-ID is a possibility that needs to be considered. 598 The formula for calculating probability of a collision is 1 - 599 e^{-k^2/(2n)}. If the Crypto-ID is 64-bit long, then the chance of 600 finding a collision is 0.01% when the network contains 66 million 601 nodes. It is important to note that the collision is only relevant 602 when this happens within one stub network (6LBR). A collision of ID 603 in ND-PAR is a rare event. However, when such a collision does 604 happen, the protocol operation is not affected, although it opens a 605 window for a node to hijack an address from another. The link-layer 606 security ensures that the nodes would normally not be aware of a 607 collision on the subnet. If a malicious node is able to gain 608 knowledge of a collision through other means, the only thing that it 609 could do is to steal addresses from the other honest node. This 610 would be no different from what is already possible in a 6lo network 611 today. 613 6. IANA considerations 615 IANA is requested to assign two new option type values, TBA1 and TBA2 616 under the subregistry "IPv6 Neighbor Discovery Option Formats". 618 7. Acknowledgements 620 We are grateful to Rene Struik and Robert Moskowitz for their 621 comments that lead to many improvements to this document. 623 8. References 625 8.1. Normative References 627 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 628 Requirement Levels", BCP 14, RFC 2119, 629 DOI 10.17487/RFC2119, March 1997, 630 . 632 [RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander, 633 "SEcure Neighbor Discovery (SEND)", RFC 3971, 634 DOI 10.17487/RFC3971, March 2005, 635 . 637 [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)", 638 RFC 3972, DOI 10.17487/RFC3972, March 2005, 639 . 641 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 642 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 643 2006, . 645 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 646 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 647 DOI 10.17487/RFC4861, September 2007, 648 . 650 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 651 Address Autoconfiguration", RFC 4862, 652 DOI 10.17487/RFC4862, September 2007, 653 . 655 [RFC4903] Thaler, D., "Multi-Link Subnet Issues", RFC 4903, 656 DOI 10.17487/RFC4903, June 2007, 657 . 659 [RFC4919] Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6 660 over Low-Power Wireless Personal Area Networks (6LoWPANs): 661 Overview, Assumptions, Problem Statement, and Goals", 662 RFC 4919, DOI 10.17487/RFC4919, August 2007, 663 . 665 [RFC5889] Baccelli, E., Ed. and M. Townsley, Ed., "IP Addressing 666 Model in Ad Hoc Networks", RFC 5889, DOI 10.17487/RFC5889, 667 September 2010, . 669 [RFC6234] Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms 670 (SHA and SHA-based HMAC and HKDF)", RFC 6234, 671 DOI 10.17487/RFC6234, May 2011, 672 . 674 [RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., 675 Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, 676 JP., and R. Alexander, "RPL: IPv6 Routing Protocol for 677 Low-Power and Lossy Networks", RFC 6550, 678 DOI 10.17487/RFC6550, March 2012, 679 . 681 [RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C. 682 Bormann, "Neighbor Discovery Optimization for IPv6 over 683 Low-Power Wireless Personal Area Networks (6LoWPANs)", 684 RFC 6775, DOI 10.17487/RFC6775, November 2012, 685 . 687 [RFC7102] Vasseur, JP., "Terms Used in Routing for Low-Power and 688 Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January 689 2014, . 691 [RFC7039] Wu, J., Bi, J., Bagnulo, M., Baker, F., and C. Vogt, Ed., 692 "Source Address Validation Improvement (SAVI) Framework", 693 RFC 7039, DOI 10.17487/RFC7039, October 2013, 694 . 696 [RFC7217] Gont, F., "A Method for Generating Semantically Opaque 697 Interface Identifiers with IPv6 Stateless Address 698 Autoconfiguration (SLAAC)", RFC 7217, 699 DOI 10.17487/RFC7217, April 2014, 700 . 702 [RFC7696] Housley, R., "Guidelines for Cryptographic Algorithm 703 Agility and Selecting Mandatory-to-Implement Algorithms", 704 BCP 201, RFC 7696, DOI 10.17487/RFC7696, November 2015, 705 . 707 [RFC7748] Langley, A., Hamburg, M., and S. Turner, "Elliptic Curves 708 for Security", RFC 7748, DOI 10.17487/RFC7748, January 709 2016, . 711 8.2. Informative references 713 [I-D.ietf-6lo-backbone-router] 714 Thubert, P., "IPv6 Backbone Router", draft-ietf-6lo- 715 backbone-router-01 (work in progress), March 2016. 717 [I-D.ietf-6tisch-architecture] 718 Thubert, P., "An Architecture for IPv6 over the TSCH mode 719 of IEEE 802.15.4", draft-ietf-6tisch-architecture-10 (work 720 in progress), June 2016. 722 [I-D.ietf-6man-ipv6-address-generation-privacy] 723 Cooper, A., Gont, F., and D. Thaler, "Privacy 724 Considerations for IPv6 Address Generation Mechanisms", 725 draft-ietf-6man-ipv6-address-generation-privacy-08 (work 726 in progress), September 2015. 728 Authors' Addresses 730 Mohit Sethi (editor) 731 Ericsson 732 Hirsalantie 733 Jorvas 02420 735 Email: mohit@piuha.net 737 Pascal Thubert 738 Cisco Systems, Inc 739 Building D 740 45 Allee des Ormes - BP1200 741 MOUGINS - Sophia Antipolis 06254 742 FRANCE 744 Phone: +33 497 23 26 34 745 Email: pthubert@cisco.com 747 Behcet Sarikaya (editor) 748 Huawei USA 749 5340 Legacy Dr. Building 3 750 Plano, TX 75024 752 Email: sarikaya@ieee.org