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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group F. Templin, Ed. 3 Internet-Draft The Boeing Company 4 Updates: rfc1191, rfc4443, rfc8201 (if A. Whyman 5 approved) MWA Ltd c/o Inmarsat Global Ltd 6 Intended status: Standards Track December 10, 2020 7 Expires: June 13, 2021 9 Transmission of IP Packets over Overlay Multilink Network (OMNI) 10 Interfaces 11 draft-templin-6man-omni-interface-55 13 Abstract 15 Mobile nodes (e.g., aircraft of various configurations, terrestrial 16 vehicles, seagoing vessels, enterprise wireless devices, etc.) 17 communicate with networked correspondents over multiple access 18 network data links and configure mobile routers to connect end user 19 networks. A multilink interface specification is therefore needed 20 for coordination with the network-based mobility service. This 21 document specifies the transmission of IP packets over Overlay 22 Multilink Network (OMNI) Interfaces. 24 Status of This Memo 26 This Internet-Draft is submitted in full conformance with the 27 provisions of BCP 78 and BCP 79. 29 Internet-Drafts are working documents of the Internet Engineering 30 Task Force (IETF). Note that other groups may also distribute 31 working documents as Internet-Drafts. The list of current Internet- 32 Drafts is at https://datatracker.ietf.org/drafts/current/. 34 Internet-Drafts are draft documents valid for a maximum of six months 35 and may be updated, replaced, or obsoleted by other documents at any 36 time. It is inappropriate to use Internet-Drafts as reference 37 material or to cite them other than as "work in progress." 39 This Internet-Draft will expire on June 13, 2021. 41 Copyright Notice 43 Copyright (c) 2020 IETF Trust and the persons identified as the 44 document authors. All rights reserved. 46 This document is subject to BCP 78 and the IETF Trust's Legal 47 Provisions Relating to IETF Documents 48 (https://trustee.ietf.org/license-info) in effect on the date of 49 publication of this document. Please review these documents 50 carefully, as they describe your rights and restrictions with respect 51 to this document. Code Components extracted from this document must 52 include Simplified BSD License text as described in Section 4.e of 53 the Trust Legal Provisions and are provided without warranty as 54 described in the Simplified BSD License. 56 Table of Contents 58 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 59 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 60 3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 8 61 4. Overlay Multilink Network (OMNI) Interface Model . . . . . . 8 62 5. The OMNI Adaptation Layer (OAL) . . . . . . . . . . . . . . . 13 63 5.1. Fragmentation Security Implications . . . . . . . . . . . 17 64 6. Frame Format . . . . . . . . . . . . . . . . . . . . . . . . 18 65 7. Link-Local Addresses (LLAs) . . . . . . . . . . . . . . . . . 18 66 8. Domain-Local Addresses (DLAs) . . . . . . . . . . . . . . . . 20 67 9. Address Mapping - Unicast . . . . . . . . . . . . . . . . . . 21 68 9.1. Sub-Options . . . . . . . . . . . . . . . . . . . . . . . 23 69 9.1.1. Pad1 . . . . . . . . . . . . . . . . . . . . . . . . 24 70 9.1.2. PadN . . . . . . . . . . . . . . . . . . . . . . . . 24 71 9.1.3. Interface Attributes . . . . . . . . . . . . . . . . 24 72 9.1.4. Traffic Selector . . . . . . . . . . . . . . . . . . 28 73 9.1.5. MS-Register . . . . . . . . . . . . . . . . . . . . . 29 74 9.1.6. MS-Release . . . . . . . . . . . . . . . . . . . . . 29 75 9.1.7. Network Access Identifier (NAI) . . . . . . . . . . . 30 76 9.1.8. Geo Coordinates . . . . . . . . . . . . . . . . . . . 31 77 9.1.9. DHCP Unique Identifier (DUID) . . . . . . . . . . . . 31 78 9.1.10. DHCPv6 Message . . . . . . . . . . . . . . . . . . . 32 79 10. Address Mapping - Multicast . . . . . . . . . . . . . . . . . 32 80 11. Multilink Conceptual Sending Algorithm . . . . . . . . . . . 33 81 11.1. Multiple OMNI Interfaces . . . . . . . . . . . . . . . . 33 82 11.2. MN<->AR Traffic Loop Prevention . . . . . . . . . . . . 34 83 12. Router Discovery and Prefix Registration . . . . . . . . . . 34 84 12.1. Router Discovery in IP Multihop and IPv4-Only Access 85 Networks . . . . . . . . . . . . . . . . . . . . . . . . 38 86 12.2. MS-Register and MS-Release List Processing . . . . . . . 40 87 12.3. DHCPv6-based Prefix Registration . . . . . . . . . . . . 41 88 13. Secure Redirection . . . . . . . . . . . . . . . . . . . . . 42 89 14. AR and MSE Resilience . . . . . . . . . . . . . . . . . . . . 43 90 15. Detecting and Responding to MSE Failures . . . . . . . . . . 43 91 16. Transition Considerations . . . . . . . . . . . . . . . . . . 44 92 17. OMNI Interfaces on the Open Internet . . . . . . . . . . . . 44 93 18. Time-Varying MNPs . . . . . . . . . . . . . . . . . . . . . . 45 94 19. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 46 95 20. Security Considerations . . . . . . . . . . . . . . . . . . . 47 96 21. Implementation Status . . . . . . . . . . . . . . . . . . . . 47 97 22. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 48 98 23. References . . . . . . . . . . . . . . . . . . . . . . . . . 48 99 23.1. Normative References . . . . . . . . . . . . . . . . . . 48 100 23.2. Informative References . . . . . . . . . . . . . . . . . 50 101 Appendix A. Interface Attribute Preferences Bitmap Encoding . . 55 102 Appendix B. VDL Mode 2 Considerations . . . . . . . . . . . . . 57 103 Appendix C. MN / AR Isolation Through L2 Address Mapping . . . . 58 104 Appendix D. Change Log . . . . . . . . . . . . . . . . . . . . . 59 105 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 61 107 1. Introduction 109 Mobile Nodes (MNs) (e.g., aircraft of various configurations, 110 terrestrial vehicles, seagoing vessels, enterprise wireless devices, 111 etc.) often have multiple data links for communicating with networked 112 correspondents. These data links may have diverse performance, cost 113 and availability properties that can change dynamically according to 114 mobility patterns, flight phases, proximity to infrastructure, etc. 115 MNs coordinate their data links in a discipline known as "multilink", 116 in which a single virtual interface is configured over the underlying 117 data links. 119 The MN configures a virtual interface (termed the "Overlay Multilink 120 Network (OMNI) interface") as a thin layer over the underlying Access 121 Network (ANET) interfaces. The OMNI interface is therefore the only 122 interface abstraction exposed to the IP layer and behaves according 123 to the Non-Broadcast, Multiple Access (NBMA) interface principle, 124 while underlying interfaces appear as link layer communication 125 channels in the architecture. The OMNI interface connects to a 126 virtual overlay service known as the "OMNI link". The OMNI link 127 spans one or more Internetworks that may include private-use 128 infrastructures and/or the global public Internet itself. 130 Each MN receives a Mobile Network Prefix (MNP) for numbering 131 downstream-attached End User Networks (EUNs) independently of the 132 access network data links selected for data transport. The MN 133 performs router discovery over the OMNI interface (i.e., similar to 134 IPv6 customer edge routers [RFC7084]) and acts as a mobile router on 135 behalf of its EUNs. The router discovery process is iterated over 136 each of the OMNI interface's underlying interfaces in order to 137 register per-link parameters (see Section 12). 139 The OMNI interface provides a multilink nexus for exchanging inbound 140 and outbound traffic via the correct underlying interface(s). The IP 141 layer sees the OMNI interface as a point of connection to the OMNI 142 link. Each OMNI link has one or more associated Mobility Service 143 Prefixes (MSPs) from which OMNI link MNPs are derived. If there are 144 multiple OMNI links, the IPv6 layer will see multiple OMNI 145 interfaces. 147 MNs may connect to multiple distinct OMNI links by configuring 148 multiple OMNI interfaces, e.g., omni0, omni1, omni2, etc. Each OMNI 149 interface is configured over a set of underlying interfaces and 150 provides a nexus for Safety-Based Multilink (SBM) operation. The IP 151 layer selects an OMNI interface based on SBM routing considerations, 152 then the selected interface applies Performance-Based Multilink (PBM) 153 to select the correct underlying interface. Applications can apply 154 Segment Routing [RFC8402] to select independent SBM topologies for 155 fault tolerance. 157 The OMNI interface interacts with a network-based Mobility Service 158 (MS) through IPv6 Neighbor Discovery (ND) control message exchanges 159 [RFC4861]. The MS provides Mobility Service Endpoints (MSEs) that 160 track MN movements and represent their MNPs in a global routing or 161 mapping system. 163 Many OMNI use cases are currently under active consideration. In 164 particular, the International Civil Aviation Organization (ICAO) 165 Working Group-I Mobility Subgroup is developing a future Aeronautical 166 Telecommunications Network with Internet Protocol Services (ATN/IPS) 167 and has issued a liaison statement requesting IETF adoption [ATN]. 168 The IETF IP Wireless Access in Vehicular Environments (ipwave) 169 working group has further included problem statement and use case 170 analysis for OMNI in a document now in AD evaluation for RFC 171 publication [I-D.ietf-ipwave-vehicular-networking]. Still other 172 communities of interest include AEEC, RTCA Special Committee 228 (SC- 173 228) and NASA programs that examine commercial aviation, Urban Air 174 Mobility (UAM) and Unmanned Air Systems (UAS). Pedestrians with 175 handheld devices represent another large class of potential OMNI 176 users. 178 This document specifies the transmission of IP packets and MN/MS 179 control messages over OMNI interfaces. The OMNI interface supports 180 either IP protocol version (i.e., IPv4 [RFC0791] or IPv6 [RFC8200]) 181 as the network layer in the data plane, while using IPv6 ND messaging 182 as the control plane independently of the data plane IP protocol(s). 183 The OMNI Adaptation Layer (OAL) which operates as a mid-layer between 184 L3 and L2 is based on IP-in-IPv6 encapsulation per [RFC2473] as 185 discussed in the following sections. 187 2. Terminology 189 The terminology in the normative references applies; especially, the 190 terms "link" and "interface" are the same as defined in the IPv6 191 [RFC8200] and IPv6 Neighbor Discovery (ND) [RFC4861] specifications. 193 Additionally, this document assumes the following IPv6 ND message 194 types: Router Solicitation (RS), Router Advertisement (RA), Neighbor 195 Solicitation (NS), Neighbor Advertisement (NA) and Redirect. 197 The Protocol Constants defined in Section 10 of [RFC4861] are used in 198 their same format and meaning in this document. The terms "All- 199 Routers multicast", "All-Nodes multicast" and "Subnet-Router anycast" 200 are the same as defined in [RFC4291] (with Link-Local scope assumed). 202 The term "IP" is used to refer collectively to either Internet 203 Protocol version (i.e., IPv4 [RFC0791] or IPv6 [RFC8200]) when a 204 specification at the layer in question applies equally to either 205 version. 207 The following terms are defined within the scope of this document: 209 Mobile Node (MN) 210 an end system with a mobile router having multiple distinct 211 upstream data link connections that are grouped together in one or 212 more logical units. The MN's data link connection parameters can 213 change over time due to, e.g., node mobility, link quality, etc. 214 The MN further connects a downstream-attached End User Network 215 (EUN). The term MN used here is distinct from uses in other 216 documents, and does not imply a particular mobility protocol. 218 End User Network (EUN) 219 a simple or complex downstream-attached mobile network that 220 travels with the MN as a single logical unit. The IP addresses 221 assigned to EUN devices remain stable even if the MN's upstream 222 data link connections change. 224 Mobility Service (MS) 225 a mobile routing service that tracks MN movements and ensures that 226 MNs remain continuously reachable even across mobility events. 227 Specific MS details are out of scope for this document. 229 Mobility Service Endpoint (MSE) 230 an entity in the MS (either singular or aggregate) that 231 coordinates the mobility events of one or more MN. 233 Mobility Service Prefix (MSP) 234 an aggregated IP prefix (e.g., 2001:db8::/32, 192.0.2.0/24, etc.) 235 advertised to the rest of the Internetwork by the MS, and from 236 which more-specific Mobile Network Prefixes (MNPs) are derived. 238 Mobile Network Prefix (MNP) 239 a longer IP prefix taken from an MSP (e.g., 240 2001:db8:1000:2000::/56, 192.0.2.8/30, etc.) and assigned to a MN. 241 MNs sub-delegate the MNP to devices located in EUNs. 243 Access Network (ANET) 244 a data link service network (e.g., an aviation radio access 245 network, satellite service provider network, cellular operator 246 network, wifi network, etc.) that connects MNs. Physical and/or 247 data link level security between the MN and ANET are assumed. 249 Access Router (AR) 250 a first-hop router in the ANET for connecting MNs to 251 correspondents in outside Internetworks. 253 ANET interface 254 a MN's attachment to a link in an ANET. 256 Internetwork (INET) 257 a connected network region with a coherent IP addressing plan that 258 provides transit forwarding services for ANET MNs and INET 259 correspondents. Examples include private enterprise networks, 260 ground domain aviation service networks and the global public 261 Internet itself. 263 INET interface 264 a node's attachment to a link in an INET. 266 OMNI link 267 a Non-Broadcast, Multiple Access (NBMA) virtual overlay configured 268 over one or more INETs and their connected ANETs. An OMNI link 269 can comprise multiple INET segments joined by bridges the same as 270 for any link; the addressing plans in each segment may be mutually 271 exclusive and managed by different administrative entities. 273 OMNI domain 274 a set of affiliated OMNI links that collectively provide services 275 under a common (set of) Mobility Service Prefixes (MSPs). 277 OMNI interface 278 a node's attachment to an OMNI link, and configured over one or 279 more underlying ANET/INET interfaces. If there are multiple OMNI 280 links in an OMNI domain, a separate OMNI interface is configured 281 for each link. 283 OMNI Adaptation Layer (OAL) 284 an OMNI interface process whereby packets admitted into the 285 interface are wrapped in a mid-layer IPv6 header and fragmented/ 286 reassembled if necessary to support the OMNI link Maximum 287 Transmission Unit (MTU). The OAL is also responsible for 288 generating MTU-related control messages as necessary, and for 289 providing addressing context for spanning multiple segments of a 290 bridged OMNI link. 292 OMNI Link-Local Address (LLA) 293 a link local IPv6 address per [RFC4291] constructed as specified 294 in Section 7. 296 OMNI Domain-Local Address (DLA) 297 an IPv6 address from the prefix [DLA]::/48 constructed as 298 specified in Section 8. OMNI DLAs are statelessly derived from 299 OMNI LLAs, and vice-versa. 301 OMNI Option 302 an IPv6 Neighbor Discovery option providing multilink parameters 303 for the OMNI interface as specified in Section 9. 305 Multilink 306 an OMNI interface's manner of managing diverse underlying data 307 link interfaces as a single logical unit. The OMNI interface 308 provides a single unified interface to upper layers, while 309 underlying data link selections are performed on a per-packet 310 basis considering factors such as DSCP, flow label, application 311 policy, signal quality, cost, etc. Multilinking decisions are 312 coordinated in both the outbound (i.e. MN to correspondent) and 313 inbound (i.e., correspondent to MN) directions. 315 L2 316 The second layer in the OSI network model. Also known as "layer- 317 2", "link-layer", "sub-IP layer", "data link layer", etc. 319 L3 320 The third layer in the OSI network model. Also known as "layer- 321 3", "network-layer", "IP layer", etc. 323 underlying interface 324 an ANET/INET interface over which an OMNI interface is configured. 325 The OMNI interface is seen as a L3 interface by the IP layer, and 326 each underlying interface is seen as a L2 interface by the OMNI 327 interface. 329 Mobility Service Identification (MSID) 330 Each MSE and AR is assigned a unique 32-bit Identification (MSID) 331 as specified in Section 7. 333 Safety-Based Multilink (SBM) 334 A means for ensuring fault tolerance through redundancy by 335 connecting multiple independent OMNI interfaces to independent 336 routing topologies (i.e., multiple independent OMNI links). 338 Performance Based Multilink (PBM) 339 A means for selecting underlying interface(s) for packet 340 transmission and reception within a single OMNI interface. 342 3. Requirements 344 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 345 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 346 "OPTIONAL" in this document are to be interpreted as described in BCP 347 14 [RFC2119][RFC8174] when, and only when, they appear in all 348 capitals, as shown here. 350 OMNI links maintain a constant value "MAX_MSID" selected to provide 351 MNs with an acceptable level of MSE redundancy while minimizing 352 control message amplification. It is RECOMMENDED that MAX_MSID be 353 set to the default value 5; if a different value is chosen, it should 354 be set uniformly by all nodes on the OMNI link. 356 An implementation is not required to internally use the architectural 357 constructs described here so long as its external behavior is 358 consistent with that described in this document. 360 4. Overlay Multilink Network (OMNI) Interface Model 362 An OMNI interface is a MN virtual interface configured over one or 363 more underlying interfaces, which may be physical (e.g., an 364 aeronautical radio link) or virtual (e.g., an Internet or higher- 365 layer "tunnel"). The MN receives a MNP from the MS, and coordinates 366 with the MS through IPv6 ND message exchanges. The MN uses the MNP 367 to construct a unique OMNI LLA through the algorithmic derivation 368 specified in Section 7 and assigns the LLA to the OMNI interface. 370 The OMNI interface architectural layering model is the same as in 371 [RFC5558][RFC7847], and augmented as shown in Figure 1. The IP layer 372 therefore sees the OMNI interface as a single L3 interface with 373 multiple underlying interfaces that appear as L2 communication 374 channels in the architecture. 376 +----------------------------+ 377 | Upper Layer Protocol | 378 Session-to-IP +---->| | 379 Address Binding | +----------------------------+ 380 +---->| IP (L3) | 381 IP Address +---->| | 382 Binding | +----------------------------+ 383 +---->| OMNI Interface | 384 Logical-to- +---->| (OMNI LLA) | 385 Physical | +----------------------------+ 386 Interface +---->| L2 | L2 | | L2 | 387 Binding |(IF#1)|(IF#2)| ..... |(IF#n)| 388 +------+------+ +------+ 389 | L1 | L1 | | L1 | 390 | | | | | 391 +------+------+ +------+ 393 Figure 1: OMNI Interface Architectural Layering Model 395 Each underlying interface provides an L2/L1 abstraction according to 396 one of the following models: 398 o INET interfaces connect to an INET either natively or through one 399 or several IPv4 Network Address Translators (NATs). Native INET 400 interfaces have global IP addresses that are reachable from any 401 INET correspondent. NATed INET interfaces typically have private 402 IP addresses and connect to a private network behind one or more 403 NATs that provide INET access. 405 o ANET interfaces connect to a protected ANET that is separated from 406 the open INET by an AR acting as a proxy. The ANET interface may 407 be either on the same L2 link segment as the AR, or separated from 408 the AR by multiple IP hops. 410 o VPNed interfaces use security encapsulation over an INET/ANET to a 411 Virtual Private Network (VPN) gateway. Other than the link-layer 412 encapsulation format, VPNed interfaces behave the same as for 413 Direct interfaces. 415 o Direct (aka "point-to-point") interfaces connect directly to a 416 peer without crossing any ANET/INET paths. An example is a line- 417 of-sight link between a remote pilot and an unmanned aircraft. 419 The OMNI virtual interface model gives rise to a number of 420 opportunities: 422 o since MN OMNI LLAs are uniquely derived from an MNP, no Duplicate 423 Address Detection (DAD) or Multicast Listener Discovery (MLD) 424 messaging is necessary. 426 o since Temporary OMNI LLAs are statistically unique, they can be 427 used without DAD for short-term purposes, e.g. until an MN OMNI 428 LLA is obtained. 430 o ANET interfaces on the same L2 link segment as an AR do not 431 require any L3 addresses (i.e., not even link-local) in 432 environments where communications are coordinated entirely over 433 the OMNI interface. (An alternative would be to also assign the 434 same OMNI LLA to all ANET interfaces.) 436 o as underlying interface properties change (e.g., link quality, 437 cost, availability, etc.), any active interface can be used to 438 update the profiles of multiple additional interfaces in a single 439 message. This allows for timely adaptation and service continuity 440 under dynamically changing conditions. 442 o coordinating underlying interfaces in this way allows them to be 443 represented in a unified MS profile with provisions for mobility 444 and multilink operations. 446 o exposing a single virtual interface abstraction to the IPv6 layer 447 allows for multilink operation (including QoS based link 448 selection, packet replication, load balancing, etc.) at L2 while 449 still permitting L3 traffic shaping based on, e.g., DSCP, flow 450 label, etc. 452 o the OMNI interface allows inter-INET traversal when nodes located 453 in different INETs need to communicate with one another. This 454 mode of operation would not be possible via direct communications 455 over the underlying interfaces themselves. 457 o the OMNI Adaptation Layer (OAL) within the OMNI interface supports 458 lossless and adaptive path MTU mitigations not available for 459 communications directly over the underlying interfaces themselves. 461 o L3 sees the OMNI interface as a point of connection to the OMNI 462 link; if there are multiple OMNI links (i.e., multiple MS's), L3 463 will see multiple OMNI interfaces. 465 o Multiple independent OMNI interfaces can be used for increased 466 fault tolerance through Safety-Based Multilink (SBM), with 467 Performance-Based Multilink (PBM) applied within each interface. 469 Other opportunities are discussed in [RFC7847]. Note that even when 470 the OMNI virtual interface is present, applications can still access 471 underlying interfaces either through the network protocol stack using 472 an Internet socket or directly using a raw socket. This allows for 473 intra-network (or point-to-point) communications without invoking the 474 OMNI interface and/or OAL. For example, when an IPv6 OMNI interface 475 is configured over an underlying IPv4 interface, applications can 476 still invoke IPv4 intra-network communications as long as the 477 communicating endpoints are not subject to mobility dynamics. 478 However, the opportunities discussed above are not available when the 479 architectural layering is bypassed in this way. 481 Figure 2 depicts the architectural model for a MN with an attached 482 EUN connecting to the MS via multiple independent ANETs. When an 483 underlying interface becomes active, the MN's OMNI interface sends 484 IPv6 ND messages without encapsulation if the first-hop Access Router 485 (AR) is on the same underlying link; otherwise, the interface uses 486 IP-in-IP encapsulation. The IPv6 ND messages traverse the ground 487 domain ANETs until they reach an AR (AR#1, AR#2, ..., AR#n), which 488 then coordinates with a Mobility Service Endpoint (MSE#1, MSE#2, ..., 489 MSE#m) in the INET and returns an IPv6 ND message response to the MN. 490 The Hop Limit in IPv6 ND messages is not decremented due to 491 encapsulation; hence, the OMNI interface appears to be attached to an 492 ordinary link. 494 +--------------+ (:::)-. 495 | MN |<-->.-(::EUN:::) 496 +--------------+ `-(::::)-' 497 |OMNI interface| 498 +----+----+----+ 499 +--------|IF#1|IF#2|IF#n|------ + 500 / +----+----+----+ \ 501 / | \ 502 / | \ 503 v v v 504 (:::)-. (:::)-. (:::)-. 505 .-(::ANET:::) .-(::ANET:::) .-(::ANET:::) 506 `-(::::)-' `-(::::)-' `-(::::)-' 507 +----+ +----+ +----+ 508 ... |AR#1| .......... |AR#2| ......... |AR#n| ... 509 . +-|--+ +-|--+ +-|--+ . 510 . | | | 511 . v v v . 512 . <----- INET Encapsulation -----> . 513 . . 514 . +-----+ (:::)-. . 515 . |MSE#2| .-(::::::::) +-----+ . 516 . +-----+ .-(::: INET :::)-. |MSE#m| . 517 . (::::: Routing ::::) +-----+ . 518 . `-(::: System :::)-' . 519 . +-----+ `-(:::::::-' . 520 . |MSE#1| +-----+ +-----+ . 521 . +-----+ |MSE#3| |MSE#4| . 522 . +-----+ +-----+ . 523 . . 524 . . 525 . <----- Worldwide Connected Internetwork ----> . 526 ........................................................... 528 Figure 2: MN/MS Coordination via Multiple ANETs 530 After the initial IPv6 ND message exchange, the MN (and/or any nodes 531 on its attached EUNs) can send and receive IP data packets over the 532 OMNI interface. OMNI interface multilink services will forward the 533 packets via ARs in the correct underlying ANETs. The AR encapsulates 534 the packets according to the capabilities provided by the MS and 535 forwards them to the next hop within the worldwide connected 536 Internetwork via optimal routes. 538 OMNI links span one or more underlying Internetwork via the OMNI 539 Adaptation Layer (OAL) which is based on a mid-layer overlay 540 encapsulation using [RFC2473]. Each OMNI link corresponds to a 541 different overlay (differentiated by an address codepoint) which may 542 be carried over a completely separate underlying topology. Each MN 543 can facilitate SBM by connecting to multiple OMNI links using a 544 distinct OMNI interface for each link. 546 5. The OMNI Adaptation Layer (OAL) 548 The OMNI interface observes the link nature of tunnels, including the 549 Maximum Transmission Unit (MTU), Maximum Reassembly Unit (MRU) and 550 the role of fragmentation and reassembly [I-D.ietf-intarea-tunnels]. 551 The OMNI interface is configured over one or more underlying 552 interfaces that may have diverse MTUs. OMNI interfaces accommodate 553 MTU diversity through the use of the OMNI Adaptation Layer (OAL) as 554 discussed in this section. 556 IPv6 underlying interfaces are REQUIRED to configure a minimum MTU of 557 1280 bytes and a minimum MRU of 1500 bytes [RFC8200]. Therefore, the 558 minimum IPv6 path MTU is 1280 bytes since routers on the path are not 559 permitted to perform network fragmentation even though the 560 destination is required to reassemble more. The network therefore 561 MUST forward packets of at least 1280 bytes without generating an 562 IPv6 Path MTU Discovery (PMTUD) Packet Too Big (PTB) message 563 [RFC8201]. (Note: the source can apply "source fragmentation" for 564 locally-generated IPv6 packets up to 1500 bytes and larger still if 565 it if has a way to determine that the destination configures a larger 566 MRU, but this does not affect the minimum IPv6 path MTU.) 568 IPv4 underlying interfaces are REQUIRED to configure a minimum MTU of 569 68 bytes [RFC0791] and a minimum MRU of 576 bytes [RFC0791][RFC1122]. 570 Therefore, when the Don't Fragment (DF) bit in the IPv4 header is set 571 to 0 the minimum IPv4 path MTU is 576 bytes since routers on the path 572 support network fragmentation and the destination is required to 573 reassemble at least that much. The DF bit in the IPv4 encapsulation 574 headers of packets sent over IPv4 underlying interfaces therefore 575 MUST be set to 0. (Note: even if the encapsulation source has a way 576 to determine that the encapsulation destination configures an MRU 577 larger than 576 bytes, it should not assume a larger minimum IPv4 578 path MTU without careful consideration of the issues discussed in 579 Section 5.1.) 581 The OMNI interface configures both an MTU and MRU of 9180 bytes 582 [RFC2492]; the size is therefore not a reflection of the underlying 583 interface MTUs, but rather determines the largest packet the OMNI 584 interface can forward or reassemble. The OMNI interface uses the 585 OMNI Adaptation Layer (OAL) to admit packets from the network layer 586 that are no larger than the OMNI interface MTU while generating 587 ICMPv4 Fragmentation Needed [RFC1191] or ICMPv6 Path MTU Discovery 588 (PMTUD) Packet Too Big (PTB) [RFC8201] messages as necessary. This 589 document refers to both of these ICMPv4/ICMPv6 message types simply 590 as "PTBs", and introduces a distinction between PTB "hard" and "soft" 591 errors as discussed below. 593 For IPv4 packets with DF=0, the network layer performs IPv4 594 fragmentation if necessary then admits the packets/fragments into the 595 OMNI interface; these fragments will be reassembled by the final 596 destination. For IPv4 packets with DF=1 and IPv6 packets, the 597 network layer admits the packet if it is no larger than the OMNI 598 interface MTU; otherwise, it drops the packet and returns a PTB hard 599 error message to the source. 601 For each admitted IP packet/fragment, the OMNI interface internally 602 employs the OAL when necessary by inserting a mid-layer IPv6 header 603 between the inner IP packet/fragment and any outer IP encapsulation 604 headers per [RFC2473]. (The OAL does not decrement the inner IP Hop 605 Limit/TTL during enapsulation since the insertion occurs at a layer 606 below IP forwarding.) The OAL then calculates the 32-bit CRC over 607 the entire mid-layer packet and writes the value in a trailing 608 4-octet field at the end of the packet. Next, the OAL fragments this 609 mid-layer IPv6 packet, forwards the fragments (using outer IP 610 encapsulation if necessary), and returns an internally-generated PTB 611 soft error message (subject to rate limiting) if it deems the packet 612 too large according to factors such as link performance 613 characteristics, reassembly congestion, etc. This ensures that the 614 path MTU is adaptive and reflects the current path used for a given 615 data flow. 617 The OAL operates with respect to both the minimum IPv6 and IPv4 path 618 MTUs as follows: 620 o When an OMNI interface sends a packet toward a final destination 621 via an ANET peer, it sends without OAL encapsulation if the packet 622 (including any outer-layer ANET encapsulations) is no larger than 623 the underlying interface MTU for on-link ANET peers or the minimum 624 ANET path MTU for peers separated by multiple IP hops. Otherwise, 625 the OAL inserts an IPv6 header per [RFC2473] with source address 626 set to the node's own OMNI Domain-Local Address (DLA) (see: 627 Section 8) and destination set to the OMNI DLA of the ANET peer. 628 The OAL then calculates and appends the trailing 32-bit CRC, then 629 uses IPv6 fragmentation to break the packet into a minimum number 630 of non-overlapping fragments where the largest fragment size 631 (including both the OMNI and any outer-layer ANET encapsulations) 632 is determined by the underlying interface MTU for on-link ANET 633 peers or the minimum ANET path MTU for peers separated by multiple 634 IP hops. The OAL then encapsulates the fragments in any ANET 635 headers and sends them to the ANET peer, which reassembles before 636 forwarding toward the final destination. 638 o When an OMNI interface sends a packet toward a final destination 639 via an INET interface, it sends packets (including any outer-layer 640 INET encapsulations) no larger than the minimum INET path MTU 641 without OAL encapsulation if the destination is reached via an 642 INET address within the same OMNI link segment. Otherwise, the 643 OAL inserts an IPv6 header per [RFC2473] with source address set 644 to the node's OMNI DLA, destination set to the DLA of the next hop 645 OMNI node toward the final destination and (if necessary) with a 646 Segment Routing Header with the remaining Segment IDs on the path 647 to the final destination. The OAL then calculates and appends the 648 trailing 32-bit CRC, then uses IPv6 fragmentation to break the 649 packet into a minimum number of non-overlapping fragments where 650 the largest fragment size (including both the OMNI and outer-layer 651 INET encapsulations) is the minimum INET path MTU, and the 652 smallest fragment size is no smaller than 256 bytes (i.e., 653 slightly less than half the minimum IPv4 path MTU). The OAL then 654 encapsulates the fragments in any INET headers and sends them to 655 the OMNI link neighbor, which reassembles before forwarding toward 656 the final destination. 658 The OAL unconditionally drops all OAL fragments received from an INET 659 peer that are smaller than 256 bytes (note that no minimum fragment 660 size is specified for ANET peers since the underlying ANET is secured 661 against tiny fragment attacks). In order to set the correct context 662 for reassembly, the OAL of the OMNI interface that inserts the IPv6 663 header MUST also be the one that inserts the IPv6 Fragment Header 664 Identification value. While not strictly required, sending all 665 fragments of the same fragmented OAL packet consecutively over the 666 same underlying interface with minimal inter-fragment delay may 667 increase the likelihood of successful reassembly. 669 Ordinary PTB messages with ICMPv4 header "unused" field or ICMPv6 670 header Code field value 0 are hard errors that always indicate that a 671 packet has been dropped due to a real MTU restriction. However, the 672 OAL can also forward large packets via encapsulation and 673 fragmentation while at the same time returning PTB soft error 674 messages (subject to rate limiting) indicating that a forwarded 675 packet was uncomfortably large. The OMNI interface can therefore 676 continuously forward large packets without loss while returning PTB 677 soft error messages recommending a smaller size. Original sources 678 that receive the soft errors in turn reduce the size of the packets 679 they send, i.e., the same as for hard errors. 681 The OAL sets the ICMPv4 header "unused" field or ICMPv6 header Code 682 field to the value 1 in PTB soft error messages. The OAL sets the 683 PTB destination address to the source address of the original packet, 684 and sets the source address to the MNP Subnet Router Anycast address 685 of the MN (i.e., whether the MN was the source or target of the 686 original packet). When the original source receives the PTB, it 687 reduces its path MTU estimate the same as for hard errors but does 688 not regard the message as a loss indication. (If the original source 689 does not recognize the soft error code, it regards the PTB the same 690 as a hard error but should heed the retransmission advice given in 691 [RFC8201] suggesting retransmission based on normal packetization 692 layer retransmission timers.) This document therefore updates 693 [RFC1191][RFC4443] and [RFC8201]. Furthermore, implementations of 694 [RFC4821] must be aware that PTB hard or soft errors may arrive at 695 any time even if after a successful MTU probe (this is the same 696 consideration as for an ordinary path fluctuation following a 697 successful probe). 699 In summary, the OAL supports continuous transmission and reception of 700 packets of various sizes in the face of dynamically changing network 701 conditions. Moreover, since PTB soft errors do not indicate loss, 702 original sources that receive soft errors can quickly scan for path 703 MTU increases without waiting for the minimum 10 minutes specified 704 for loss-oriented PTB hard errors [RFC1191][RFC8201]. The OAL 705 therefore provides a lossless and adaptive service that accommodates 706 MTU diversity especially well-suited for dynamic multilink 707 environments. 709 Note: In network paths where IPv6/IPv4 protocol translation or IPv6- 710 in-IPv4 encapsulation may be prevalent, it may be prudent for the OAL 711 to always assume the IPv4 minimum path MTU (i.e., 576 bytes) 712 regardless of the underlying interface IP protocol version. Always 713 assuming the IPv4 minimum path MTU even for IPv6 underlying 714 interfaces may produce more fragments and additional header overhead, 715 but will always interoperate and never run the risk of presenting an 716 IPv4 interface with a packet that exceeds its MRU. 718 Note: An OMNI interface that reassembles OAL fragments may experience 719 congestion-oriented loss in its reassembly cache and can optionally 720 send PTB soft errors to the original source and/or ICMP "Time 721 Exceeded" messages to the source of the OAL fragments. In 722 environments where the messages may contribute to unacceptable 723 additional congestion, however, the OMNI interface can simply regard 724 the loss as an ordinary unreported congestion event for which the 725 original source will eventually compensate. 727 Note: When the network layer forwards an IPv4 packet/fragment with 728 DF=0 into the OMNI interface, the interface can optionally perform 729 (further) IPv4 fragmentation before invoking the OAL so that the 730 fragments will be reassembled by the final destination. When the 731 network layer performs IPv6 fragmentation for locally-generated IPv6 732 packets, the OMNI interface typically invokes the OAL without first 733 applying (further) IPv6 fragmentation; the network layer should 734 therefore fragment to the minimum IPv6 path MTU (or smaller still) to 735 push the reassembly burden to the final destination and avoid 736 receiving PTB soft errors from the OMNI interface. Aside from these 737 non-normative guidelines, the manner in which any IP fragmentation is 738 invoked prior to OAL encapsulation/fragmentation is an implementation 739 matter. 741 Note: Inclusion of the 32-bit CRC prior to fragmentation assumes that 742 the receiving OAL will discard any packets with incorrect CRC values 743 following reassembly. The 32-bit CRC is sufficient to detect 744 reassembly misassociations for packet sizes up to the OMNI interface 745 MTU 9180 but may not be sufficient to detect errors for larger sizes 746 [CRC]. 748 Note: Some underlying interface types (e.g., VPNs) may already 749 provide their own robust fragmentation and reassembly services even 750 without OAL encapsulation. In those cases, the OAL can invoke the 751 inherent underlying interface schemes instead while employing PTB 752 soft errors in the same fashion as described above. Other underlying 753 interface properties such as header/message compression can also be 754 harnessed in a similar fashion. 756 Note: Applications can dynamically tune the size of the packets they 757 to send to produce the best possible throughput and latency, with the 758 understanding that these parameters may change over time due to 759 factors such as congestion, mobility, network path changes, etc. The 760 receipt or absence of soft errors should be seen as hints of when 761 increasing or decreasing packet sizes may be beneficial. 763 5.1. Fragmentation Security Implications 765 As discussed in Section 3.7 of [RFC8900], there are four basic 766 threats concerning IPv6 fragmentation; each of which is addressed by 767 effective mitigations as follows: 769 1. Overlapping fragment attacks - reassembly of overlapping 770 fragments is forbidden by [RFC8200]; therefore, this threat does 771 not apply to the OAL. 773 2. Resource exhaustion attacks - this threat is mitigated by 774 providing a sufficiently large OAL reassembly cache and 775 instituting "fast discard" of incomplete reassemblies that may be 776 part of a buffer exhaustion attack. The reassembly cache should 777 be sufficiently large so that a sustained attack does not cause 778 excessive loss of good reassemblies but not so large that (timer- 779 based) data structure management becomes computationally 780 expensive. The cache should also be indexed based on the arrival 781 underlying interface such that congestion experienced over a 782 first underlying interface does not cause discard of incomplete 783 reassemblies for uncongested underlying interfaces. 785 3. Attacks based on predictable fragment identification values - 786 this threat is mitigated by selecting a suitably random ID value 787 per [RFC7739]. 789 4. Evasion of Network Intrusion Detection Systems (NIDS) - this 790 threat is mitigated by disallowing "tiny fragments" per the OAL 791 fragmentation procedures specified above. 793 Additionally, IPv4 fragmentation includes a 16-bit Identification (IP 794 ID) field with only 65535 unique values such that at high data rates 795 the field could wrap and apply to new packets while the fragments of 796 old packets using the same ID are still alive in the network 797 [RFC4963]. However, since the largest OAL fragment that will be sent 798 via an IPv4 INET path is 576 bytes any IPv4 fragmentation would occur 799 only on links with an IPv4 MTU smaller than this size, and [RFC3819] 800 recommendations suggest that such links will have low data rates. 801 Since IPv6 provides a 32-bit Identification value, IP ID wraparound 802 at high data rates is not a concern for IPv6 fragmentation. 804 6. Frame Format 806 The OMNI interface transmits IPv6 packets according to the native 807 frame format of each underlying interface. For example, for 808 Ethernet-compatible interfaces the frame format is specified in 809 [RFC2464], for aeronautical radio interfaces the frame format is 810 specified in standards such as ICAO Doc 9776 (VDL Mode 2 Technical 811 Manual), for tunnels over IPv6 the frame format is specified in 812 [RFC2473], etc. 814 7. Link-Local Addresses (LLAs) 816 OMNI nodes are assigned OMNI interface IPv6 Link-Local Addresses 817 (i.e., "OMNI LLAs") through pre-service administrative actions. MN 818 OMNI LLAs embed the MNP assigned to the mobile node, while MS OMNI 819 LLAs include an administratively-unique ID that is guaranteed to be 820 unique on the link. OMNI LLAs are configured as follows: 822 o IPv6 MN OMNI LLAs encode the most-significant 64 bits of a MNP 823 within the least-significant 64 bits of the IPv6 link-local prefix 824 fe80::/64, i.e., in the LLA "interface identifier" portion. The 825 prefix length for the LLA is determined by adding 64 to the MNP 826 prefix length. For example, for the MNP 2001:db8:1000:2000::/56 827 the corresponding MN OMNI LLA is fe80::2001:db8:1000:2000/120. 829 o IPv4-compatible MN OMNI LLAs are constructed as fe80::ffff:[IPv4], 830 i.e., the interface identifier consists of 16 '0' bits, followed 831 by 16 '1' bits, followed by a 32bit IPv4 address/prefix. The 832 prefix length for the LLA is determined by adding 96 to the MNP 833 prefix length. For example, the IPv4-Compatible MN OMNI LLA for 834 192.0.2.0/24 is fe80::ffff:192.0.2.0/120 (also written as 835 fe80::ffff:c000:0200/120). 837 o MS OMNI LLAs are assigned to ARs and MSEs and MUST be managed for 838 uniqueness. The lower 32 bits of the LLA includes a unique 839 integer "MSID" value between 0x00000001 and 0xfeffffff, e.g., as 840 in fe80::1, fe80::2, fe80::3, etc., fe80::feff:ffff. The MS OMNI 841 LLA prefix length is determined by adding 96 to the MSID prefix 842 length. For example, if the MSID '0x10002000' prefix length is 16 843 then the MS OMNI LLA prefix length is set to 112 and the LLA is 844 written as fe80::1000:2000/112. The MSID 0x00000000 is the 845 "Anycast" MSID and corresponds to the link-local Subnet-Router 846 anycast address (fe80::) [RFC4291]; the MSID range 0xff000000 847 through 0xffffffff is reserved for future use. 849 o Temporary OMNI LLAs are constructed per [I-D.ietf-6man-rfc4941bis] 850 and used by MNs for the short-term purpose of procuring an actual 851 MN OMNI LLA upon startup or (re)connecting to the network. MNs 852 may use Temporary OMNI LLAs as the IPv6 source address of an RS 853 message in order to request a MN OMNI LLA from the MS. 855 Since the prefix 0000::/8 is "Reserved by the IETF" [RFC4291], no 856 MNPs can be allocated from that block ensuring that there is no 857 possibility for overlap between the various OMNI LLA constructs 858 discussed above. 860 Since MN OMNI LLAs are based on the distribution of administratively 861 assured unique MNPs, and since MS OMNI LLAs are guaranteed unique 862 through administrative assignment, OMNI interfaces set the 863 autoconfiguration variable DupAddrDetectTransmits to 0 [RFC4862]. 865 Temporary OMNI LLAs employ optimistic DAD principles [RFC4429] since 866 they are probabilistically unique and their use is short-duration in 867 nature. 869 Note: If future extensions of the IPv6 protocol permit extension of 870 the /64 boundary, the additional prefix bits of IPv6 MN OMNI LLAs 871 would be encoded in bits 16 through 63 of the LLA. (The most- 872 significant 64 bits would therefore still be in LLA bits 64-127, and 873 the remaining bits would be in bits 16 through 48 of the LLA. This 874 would permit encoding of IPv6 prefix lengths up to /112.) 876 8. Domain-Local Addresses (DLAs) 878 OMNI links use IPv6 Domain-Local Addresses (i.e., "OMNI DLAs") as the 879 source and destination addresses in OAL IPv6 encapsulation headers. 880 This document assumes availability of a prefix [DLA]::/48 for mapping 881 OMNI LLAs to routable OMNI DLAs. Since DLAs are only routable within 882 the scope of an OMNI domain, they are normally derived from the IPv6 883 Unique Local Address (ULA) prefix fc00::/7 followed by the L bit set 884 to 1 (i.e., as fd00::/8) followed by a 40-bit pseudo-random Global ID 885 to produce the prefix [DLA]::/48, which is then followed by a 16-bit 886 Subnet ID then finally followed by a 64 bit Interface ID exactly as 887 described in Section 3 of [RFC4193]. ULA prefixes with the L bit set 888 to 0 a(i.e., as fc00::/8) and IPv6 Globally Unique Address (GUA) 889 prefixes represent other DLA candidates, but their use within an OMNI 890 domain must not conflict with any other uses inside or outside the 891 domain. 893 Each OMNI link instance is identified by a value between 0x0000 and 894 0xfeff in bits 48-63 of [DLA]::/48 (the values 0xff00 through 0xfffe 895 are reserved for future use and the value 0xffff denotes a Temporary 896 OMNI DLA). For example, OMNI DLAs associated with instance 0 are 897 configured from the prefix [DLA]:0000::/64, instance 1 from 898 [DLA]:0001::/64, instance 2 from [DLA]:0002::/64, etc. OMNI DLAs and 899 their associated prefix lengths are configured in correspondence with 900 OMNI LLAs through stateless prefix translation. For example, for 901 OMNI link instance [DLA]:1010::/64: 903 o the OMNI DLA corresponding to the MN OMNI LLA fe80::2001:db8:1:2 904 with a 56-bit MNP length is derived by copying the lower 64 bits 905 of the LLA into the lower 64 bits of the DLA as 906 [DLA]:1010:2001:db8:1:2/120 (where, the DLA prefix length becomes 907 64 plus the IPv6 MNP length). 909 o the OMNI DLA corresponding to fe80::ffff:192.0.2.0 with a 28-bit 910 MNP length is derived by simply writing the LLA interface ID into 911 the lower 64 bits as [DLA]:1010:0:ffff:192.0.2.0/124 (where, the 912 DLA prefix length is 64 plus 32 plus the IPv4 MNP length). 914 o the OMNI DLA corresponding to fe80::1000/112 is simply 915 [DLA]:1010::1000/112. 917 o the OMNI DLA corresponding to fe80::/128 is simply 918 [DLA]:1010::/128. 920 o the OMNI DLA corresponding to a Temporary OMNI LLA is simply 921 [DLA]:ffff:[64-bit Temporary Interface ID]/128. 923 o etc. 925 Each OMNI interface assigns the Anycast OMNI DLA specific to the OMNI 926 link instance. For example, the OMNI interface connected to instance 927 3 assigns the Anycast OMNI DLA [DLA]:0003::/128. Routers that 928 configure OMNI interfaces advertise the OMNI service prefix (e.g., 929 [DLA]:0003::/64) into the local routing system so that applications 930 can direct traffic according to SBM requirements. 932 The OMNI DLA presents an IPv6 address format that is routable within 933 the OMNI domain routing system and can be used to convey link-scoped 934 IPv6 ND messages across multiple hops using IPv6 encapsulation 935 [RFC2473]. The OMNI link extends across one or more underling 936 Internetworks to include all ARs and MSEs. All MNs are also 937 considered to be connected to the OMNI link, however OAL 938 encapsulation is omitted over ANET links when possible to conserve 939 bandwidth (see: Section 11). 941 Each OMNI link can be subdivided into "segments" that often 942 correspond to different administrative domains or physical 943 partitions. OMNI nodes can use IPv6 Segment Routing [RFC8402] when 944 necessary to support efficient packet forwarding to destinations 945 located in other OMNI link segments. A full discussion of Segment 946 Routing over the OMNI link appears in [I-D.templin-intarea-6706bis]. 948 9. Address Mapping - Unicast 950 OMNI interfaces maintain a neighbor cache for tracking per-neighbor 951 state and use the link-local address format specified in Section 7. 952 OMNI interface IPv6 Neighbor Discovery (ND) [RFC4861] messages sent 953 over physical underlying interfaces without encapsulation observe the 954 native underlying interface Source/Target Link-Layer Address Option 955 (S/TLLAO) format (e.g., for Ethernet the S/TLLAO is specified in 956 [RFC2464]). OMNI interface IPv6 ND messages sent over underlying 957 interfaces via encapsulation do not include S/TLLAOs which were 958 intended for encoding physical L2 media address formats and not 959 encapsulation IP addresses. Furthermore, S/TLLAOs are not intended 960 for encoding additional interface attributes needed for multilink 961 coordination. Hence, this document does not define an S/TLLAO format 962 but instead defines a new option type termed the "OMNI option" 963 designed for these purposes. 965 MNs such as aircraft typically have many wireless data link types 966 (e.g. satellite-based, cellular, terrestrial, air-to-air directional, 967 etc.) with diverse performance, cost and availability properties. 968 The OMNI interface would therefore appear to have multiple L2 969 connections, and may include information for multiple underlying 970 interfaces in a single IPv6 ND message exchange. OMNI interfaces use 971 an IPv6 ND option called the OMNI option formatted as shown in 972 Figure 3: 974 0 1 2 3 975 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 1 976 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 977 | Type | Length |T| Preflen | S/T-ifIndex | 978 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 979 | | 980 ~ Sub-Options ~ 981 | | 982 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 984 Figure 3: OMNI Option Format 986 In this format: 988 o Type is set to TBD. If multiple OMNI option instances appear in 989 the same IPv6 ND message, the first instance is processed and all 990 other instances are ignored. 992 o Length is set to the number of 8 octet blocks in the option. 994 o T is a 1-bit flag set to 1 for Temporary OMNI LLAs (otherwise, set 995 to 0) and Preflen is a 7 bit field that determines the length of 996 prefix associated with an MN OMNI LLA. Values 1 through 127 997 specify a prefix length, while the value 0 indicates 998 "unspecified". For IPv6 ND messages sent from a MN to the MS, T 999 and Preflen apply to the IPv6 source LLA and provide the length 1000 that the MN is requesting or asserting to the MS. For IPv6 ND 1001 messages sent from the MS to the MN, T and Preflen apply to the 1002 IPv6 destination LLA and indicate the length that the MS is 1003 granting to the MN. For IPv6 ND messages sent between MS 1004 endpoints, T is set to 0 and Preflen provides the length 1005 associated with the source/target MN that is subject of the ND 1006 message. 1008 o S/T-ifIndex corresponds to the ifIndex value for source or target 1009 underlying interface used to convey this IPv6 ND message. OMNI 1010 interfaces MUST number each distinct underlying interface with an 1011 ifIndex value between '1' and '255' that represents a MN-specific 1012 8-bit mapping for the actual ifIndex value assigned by network 1013 management [RFC2863] (the ifIndex value '0' is reserved for use by 1014 the MS). For RS and NS messages, S/T-ifIndex corresponds to the 1015 source underlying interface the message originated from. For RA 1016 and NA messages, S/T-ifIndex corresponds to the target underlying 1017 interface that the message is destined to. 1019 o Sub-Options is a Variable-length field, of length such that the 1020 complete OMNI Option is an integer multiple of 8 octets long. 1021 Contains one or more Sub-Options, as described in Section 9.1. 1023 9.1. Sub-Options 1025 The OMNI option includes zero or more Sub-Options. Each consecutive 1026 Sub-Option is concatenated immediately after its predecessor. All 1027 Sub-Options except Pad1 (see below) are in type-length-value (TLV) 1028 encoded in the following format: 1030 0 1 2 1031 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 1032 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1033 | Sub-Type | Sub-length | Sub-Option Data ... 1034 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1036 Figure 4: Sub-Option Format 1038 o Sub-Type is a 1-octet field that encodes the Sub-Option type. 1039 Sub-Options defined in this document are: 1041 Option Name Sub-Type 1042 Pad1 0 1043 PadN 1 1044 Interface Attributes 2 1045 Traffic Selector 3 1046 MS-Register 4 1047 MS-Release 5 1048 Network Access Identifier 6 1049 Geo Coordinates 7 1050 DHCP Unique Identifier (DUID) 8 1051 DHCPv6 Message 9 1053 Figure 5 1055 Sub-Types 253 and 254 are reserved for experimentation, as 1056 recommended in [RFC3692]. 1058 o Sub-Length is a 1-octet field that encodes the length of the Sub- 1059 Option Data (i.e., ranging from 0 to 255 octets). 1061 o Sub-Option Data is a block of data with format determined by Sub- 1062 Type. 1064 During processing, unrecognized Sub-Options are ignored and the next 1065 Sub-Option processed until the end of the OMNI option is reached. 1067 The following Sub-Option types and formats are defined in this 1068 document: 1070 9.1.1. Pad1 1072 0 1073 0 1 2 3 4 5 6 7 1074 +-+-+-+-+-+-+-+-+ 1075 | Sub-Type=0 | 1076 +-+-+-+-+-+-+-+-+ 1078 Figure 6: Pad1 1080 o Sub-Type is set to 0. If multiple instances appear in the same 1081 OMNI option all are processed. 1083 o No Sub-Length or Sub-Option Data follows (i.e., the "Sub-Option" 1084 consists of a single zero octet). 1086 9.1.2. PadN 1088 0 1 2 1089 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 1090 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1091 | Sub-Type=1 | Sub-length=N | N padding octets ... 1092 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1094 Figure 7: PadN 1096 o Sub-Type is set to 1. If multiple instances appear in the same 1097 OMNI option all are processed. 1099 o Sub-Length is set to N (from 0 to 255) being the number of padding 1100 octets that follow. 1102 o Sub-Option Data consists of N zero-valued octets. 1104 9.1.3. Interface Attributes 1106 The Interface Attributes sub-option provides L2 forwarding 1107 information for the multilink conceptual sending algorithm discussed 1108 in Section 11. The L2 information is used for selecting among 1109 potentially multiple candidate underlying interfaces that can be used 1110 to forward packets to the neighbor based on factors such as DSCP 1111 preferences and link quality. Interface Attributes further include 1112 link-layer address information to be used for either OAL 1113 encapsulation or direct UDP/IP encapsulation (when OAL encapsulation 1114 can be avoided). The Interface Attributes format and contents are 1115 given in Figure 8 below: 1117 0 1 2 3 1118 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 1119 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1120 | Sub-Type=2 | Sub-length=N | ifIndex | ifType | 1121 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1122 | Provider ID | Link |R| API | SRT | FMT | LHS (0 - 7) | 1123 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1124 | LHS (bits 8 - 31) | ~ 1125 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ 1126 ~ ~ 1127 ~ Link Layer Address (L2ADDR) ~ 1128 ~ ~ 1129 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1130 | Bitmap(0)=0xff|P00|P01|P02|P03|P04|P05|P06|P07|P08|P09|P10|P11| 1131 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1132 |P12|P13|P14|P15|P16|P17|P18|P19|P20|P21|P22|P23|P24|P25|P26|P27| 1133 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1134 |P28|P29|P30|P31| Bitmap(1)=0xff|P32|P33|P34|P35|P36| ... 1135 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1137 Figure 8: Interface Attributes 1139 o Sub-Type is set to 2. If multiple instances with different 1140 ifIndex values appear in the same OMNI option all are processed; 1141 if multiple instances with the same ifIndex value appear, the 1142 first is processed and all others are ignored. 1144 o Sub-Length is set to N (from 4 to 255) that encodes the number of 1145 Sub-Option Data octets that follow. 1147 o Sub-Option Data contains an "Interface Attribute" option encoded 1148 as follows (note that the first four octets must be present): 1150 * ifIndex is set to an 8-bit integer value corresponding to a 1151 specific underlying interface the same as specified above for 1152 the OMNI option header S/T-ifIndex. An OMNI option may include 1153 multiple Interface Attributes Sub-Options, with each distinct 1154 ifIndex value pertaining to a different underlying interface. 1155 The OMNI option will often include an Interface Attributes Sub- 1156 Option with the same ifIndex value that appears in the S/ 1157 T-ifIndex. In that case, the actual encapsulation address of 1158 the received IPv6 ND message should be compared with the L2ADDR 1159 encoded in the Sub-Option (see below); if the addresses are 1160 different (or, if L2ADDR absent) the presence of a Network 1161 Address Translator (NAT) is indicated. 1163 * ifType is set to an 8-bit integer value corresponding to the 1164 underlying interface identified by ifIndex. The value 1165 represents an OMNI interface-specific 8-bit mapping for the 1166 actual IANA ifType value registered in the 'IANAifType-MIB' 1167 registry [http://www.iana.org]. 1169 * Provider ID is set to an OMNI interface-specific 8-bit ID value 1170 for the network service provider associated with this ifIndex. 1172 * Link encodes a 4-bit link metric. The value '0' means the link 1173 is DOWN, and the remaining values mean the link is UP with 1174 metric ranging from '1' ("lowest") to '15' ("highest"). 1176 * R is reserved for future use. 1178 * API - a 3-bit "Address/Preferences/Indexed" code that 1179 determines the contents of the remainder of the sub-option as 1180 follows: 1182 + When the most significant bit (i.e., "Address") is set to 1, 1183 the SRT, FMT, LHS and L2ADDR fields are included immediately 1184 following the API code; else, they are omitted. 1186 + When the next most significant bit (i.e., "Preferences") is 1187 set to 1, a preferences block is included next; else, it is 1188 omitted. (Note that if "Address" is set the preferences 1189 block immediately follows L2ADDR; else, it immediately 1190 follows the API code.) 1192 + When a preferences block is present and the least 1193 significant bit (i.e., "Indexed") is set to 0, the block is 1194 encoded in "Simplex" form as shown in Figure 8; else it is 1195 encoded in "Indexed" form as discussed below. 1197 * When API indicates that an "Address" is included, the following 1198 fields appear in consecutive order (else, they are omitted): 1200 + SRT - a 5-bit Segment Routing Topology prefix length value 1201 that (when added to 96) determines the prefix length to 1202 apply to the DLA formed from concatenating fe*::/96 with the 1203 32 bit LHS MSID value that follows. For example, the value 1204 16 corresponds to the prefix length 112. 1206 + FMT - a 3-bit "Framework/Mode/Type" code corresponding to 1207 the included Link Layer Address as follows: 1209 - When the most significant bit (i.e., "Framework") is set 1210 to 0, L2ADDR is the INET encapsulation address of a 1211 Proxy/Server; otherwise, it is the address for the 1212 Source/Target itself 1214 - When the next most significant bit (i.e., "Mode") is set 1215 to 0, the Source/Target L2ADDR is on the open INET; 1216 otherwise, it is (likely) located behind a Network 1217 Address Translator (NAT). 1219 - When the least significant bit (i.e., "Type") is set to 1220 0, L2ADDR includes a UDP Port Number followed by an IPv4 1221 address; else, a UDP Port Number followed by an IPv6 1222 address. 1224 + LHS - the 32 bit MSID of the Last Hop Server/Proxy on the 1225 path to the target. When SRT and LHS are both set to 0, the 1226 LHS is considered unspecified in this IPv6 ND message. When 1227 SRT is set to 0 and LHS is non-zero, the prefix length is 1228 set to 128. SRT and LHS provide guidance to the OMNI 1229 interface forwarding algorithm. Specifically, if SRT/LHS is 1230 located in the local OMNI link segment then the OMNI 1231 interface can encapsulate according to FMT/L2ADDR; else, it 1232 must forward according to the OMNI link spanning tree. See 1233 [I-D.templin-intarea-6706bis] for further discussion. 1235 + Link Layer Address (L2ADDR) - Formatted according to FMT, 1236 and identifies the link-layer address (i.e., the 1237 encapsulation address) of the source/target. The UDP Port 1238 Number appears in the first two octets and the IP address 1239 appears in the next 4 octets for IPv4 or 16 octets for IPv6. 1240 The Port Number and IP address are recorded in ones- 1241 compliment "obfuscated" form per [RFC4380]. The OMNI 1242 interface forwarding algorithm uses FMT/L2ADDR to determine 1243 the encapsulation address for forwarding when SRT/LHS is 1244 located in the local OMNI link segment. 1246 * When API indicates that "Preferences" are included, a 1247 preferences block appears as the remainder of the Sub-Option as 1248 a series of Bitmaps and P[*] values. In "Simplex" form, the 1249 index for each singleton Bitmap octet is inferred from its 1250 sequential position (i.e., 0, 1, 2, ...) as shown in Figure 8. 1251 In "Indexed" form, each Bitmap is preceded by an Index octet 1252 that encodes a value "i" = (0 - 255) as the index for its 1253 companion Bitmap as follows: 1255 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1256 | Index=i | Bitmap(i) |P[*] values ... 1257 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1259 Figure 9 1261 * The preferences consist of a first (simplex/indexed) Bitmap 1262 (i.e., "Bitmap(i)") followed by 0-8 single-octet blocks of 1263 2-bit P[*] values, followed by a second Bitmap (i), followed by 1264 0-8 blocks of P[*] values, etc. Reading from bit 0 to bit 7, 1265 the bits of each Bitmap(i) that are set to '1'' indicate the 1266 P[*] blocks from the range P[(i*32)] through P[(i*32) + 31] 1267 that follow; if any Bitmap(i) bits are '0', then the 1268 corresponding P[*] block is instead omitted. For example, if 1269 Bitmap(0) contains 0xff then the block with P[00]-P[03], 1270 followed by the block with P[04]-P[07], etc., and ending with 1271 the block with P[28]-P[31] are included (as shown in Figure 8). 1272 The next Bitmap(i) is then consulted with its bits indicating 1273 which P[*] blocks follow, etc. out to the end of the Sub- 1274 Option. 1276 * Each 2-bit P[*] field is set to the value '0' ("disabled"), '1' 1277 ("low"), '2' ("medium") or '3' ("high") to indicate a QoS 1278 preference for underlying interface selection purposes. Not 1279 all P[*] values need to be included in the OMNI option of each 1280 IPv6 ND message received. Any P[*] values represented in an 1281 earlier OMNI option but omitted in the current OMNI option 1282 remain unchanged. Any P[*] values not yet represented in any 1283 OMNI option default to "medium". 1285 * The first 16 P[*] blocks correspond to the 64 Differentiated 1286 Service Code Point (DSCP) values P[00] - P[63] [RFC2474]. Any 1287 additional P[*] blocks that follow correspond to "pseudo-DSCP" 1288 traffic classifier values P[64], P[65], P[66], etc. See 1289 Appendix A for further discussion and examples. 1291 9.1.4. Traffic Selector 1293 0 1 2 3 1294 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 1295 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1296 | Sub-Type=3 | Sub-length=N | ifIndex | ~ 1297 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ 1298 ~ ~ 1299 ~ RFC 6088 Format Traffic Selector ~ 1300 ~ ~ 1301 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1303 Figure 10: Traffic Selector 1305 o Sub-Type is set to 3. If multiple instances appear in the same 1306 OMNI option all are processed, i.e., even if the same ifIndex 1307 value appears multiple times. 1309 o Sub-Length is set to N (the number of Sub-Option Data octets that 1310 follow). 1312 o Sub-Option Data contains a 1-octet ifIndex encoded exactly as 1313 specified in Section 9.1.3, followed by an N-1 octet traffic 1314 selector formatted per [RFC6088] beginning with the "TS Format" 1315 field. The largest traffic selector for a given ifIndex is 1316 therefore 254 octets. 1318 9.1.5. MS-Register 1320 0 1 2 3 1321 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 1322 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1323 | Sub-Type=4 | Sub-length=4n | MSID[1] (bits 0 - 15) | 1324 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1325 | MSID [1] (bits 16 - 32) | MSID[2] (bits 0 - 15) | 1326 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1327 | MSID [2] (bits 16 - 32) | MSID[3] (bits 0 - 15) | 1328 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1329 ... ... ... ... ... ... 1330 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1331 | MSID [n] (bits 16 - 32) | 1332 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1334 Figure 11: MS-Register Sub-option 1336 o Sub-Type is set to 4. If multiple instances appear in the same 1337 OMNI option all are processed. Only the first MAX_MSID values 1338 processed (whether in a single instance or multiple) are retained 1339 and all other MSIDs are ignored. 1341 o Sub-Length is set to 4n. 1343 o A list of n 4-octet MSIDs is included in the following 4n octets. 1344 The Anycast MSID value '0' in an RS message MS-Register sub-option 1345 requests the recipient to return the MSID of a nearby MSE in a 1346 corresponding RA response. 1348 9.1.6. MS-Release 1349 0 1 2 3 1350 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 1351 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1352 | Sub-Type=5 | Sub-length=4n | MSID[1] (bits 0 - 15) | 1353 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1354 | MSID [1] (bits 16 - 32) | MSID[2] (bits 0 - 15) | 1355 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1356 | MSID [2] (bits 16 - 32) | MSID[3] (bits 0 - 15) | 1357 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1358 ... ... ... ... ... ... 1359 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1360 | MSID [n] (bits 16 - 32) | 1361 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1363 Figure 12: MS-Release Sub-option 1365 o Sub-Type is set to 5. If multiple instances appear in the same 1366 IPv6 OMNI option all are processed. Only the first MAX_MSID 1367 values processed (whether in a single instance or multiple) are 1368 retained and all other MSIDs are ignored. 1370 o Sub-Length is set to 4n. 1372 o A list of n 4 octet MSIDs is included in the following 4n octets. 1373 The Anycast MSID value '0' is ignored in MS-Release sub-options, 1374 i.e., only non-zero values are processed. 1376 9.1.7. Network Access Identifier (NAI) 1378 0 1 2 3 1379 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 1380 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1381 | Sub-Type=6 | Sub-length=N |Network Access Identifier (NAI) 1382 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... 1384 Figure 13: Network Access Identifier (NAI) Sub-option 1386 o Sub-Type is set to 6. If multiple instances appear in the same 1387 OMNI option the first is processed and all others are ignored. 1389 o Sub-Length is set to N. 1391 o A Network Access Identifier (NAI) up to 255 octets in length is 1392 coded per [RFC7542]. 1394 9.1.8. Geo Coordinates 1396 0 1 2 3 1397 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 1398 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1399 | Sub-Type=7 | Sub-length=N | Geo Coordinates 1400 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... 1402 Figure 14: Geo Coordinates Sub-option 1404 o Sub-Type is set to 7. If multiple instances appear in the same 1405 OMNI option the first is processed and all others are ignored. 1407 o Sub-Length is set to N. 1409 o A set of Geo Coordinates up to 255 octets in length (format TBD). 1410 Includes Latitude/Longitude at a minimum; may also include 1411 additional attributes such as altitude, heading, speed, etc.). 1413 9.1.9. DHCP Unique Identifier (DUID) 1415 0 1 2 3 1416 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 1417 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1418 | Sub-Type=8 | Sub-length=N | DUID-Type | 1419 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1420 . . 1421 . type-specific DUID body (variable length) . 1422 . . 1423 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1425 Figure 15: DHCP Unique Identifier (DUID) Sub-option 1427 o Sub-Type is set to 8. If multiple instances appear in the same 1428 OMNI option the first is processed and all others are ignored. 1430 o Sub-Length is set to N (i.e., the length of the option beginning 1431 with the DUID-Type and continuing to the end of the type-specific 1432 body). 1434 o DUID-Type is a two-octet field coded in network byte order that 1435 determines the format and contents of the type-specific body 1436 according to Section 11 of [RFC8415]. DUID-Type 4 in particular 1437 corresponds to the Universally Unique Identifier (UUID) [RFC6355] 1438 which will occur in common operational practice. 1440 o A type-specific DUID body up to 253 octets in length follows, 1441 formatted according to DUID-type. For example, for type 4 the 1442 body consists of a 128-bit UUID selected according to [RFC6355]. 1444 9.1.10. DHCPv6 Message 1446 0 1 2 3 1447 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 1448 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1449 | Sub-Type=9 | Sub-length=N | msg-type | id (octet 0) | 1450 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1451 | transaction-id (octets 1-2) | | 1452 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 1453 | | 1454 . DHCPv6 options . 1455 . (variable number and length) . 1456 | | 1457 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1459 Figure 16: DHCPv6 Message Sub-option 1461 o Sub-Type is set to 9. If multiple instances appear in the same 1462 OMNI option the first is processed and all others are ignored. 1464 o Sub-Length is set to N (i.e., the length of the DHCPv6 message 1465 beginning with 'msg-type' and continuing to the end of the DHCPv6 1466 options). The length of the entire DHCPv6 message is therefore 1467 restricted to 255 octets. 1469 o 'msg-type' and 'transaction-id' are coded according to Section 8 1470 of [RFC8415]. 1472 o A set of DHCPv6 options coded according to Section 21 of [RFC8415] 1473 follows. 1475 10. Address Mapping - Multicast 1477 The multicast address mapping of the native underlying interface 1478 applies. The mobile router on board the MN also serves as an IGMP/ 1479 MLD Proxy for its EUNs and/or hosted applications per [RFC4605] while 1480 using the L2 address of the AR as the L2 address for all multicast 1481 packets. 1483 The MN uses Multicast Listener Discovery (MLDv2) [RFC3810] to 1484 coordinate with the AR, and ANET L2 elements use MLD snooping 1485 [RFC4541]. 1487 11. Multilink Conceptual Sending Algorithm 1489 The MN's IPv6 layer selects the outbound OMNI interface according to 1490 SBM considerations when forwarding data packets from local or EUN 1491 applications to external correspondents. Each OMNI interface 1492 maintains a neighbor cache the same as for any IPv6 interface, but 1493 with additional state for multilink coordination. Each OMNI 1494 interface maintains default routes via ARs discovered as discussed in 1495 Section 12, and may configure more-specific routes discovered through 1496 means outside the scope of this specification. 1498 After a packet enters the OMNI interface, one or more outbound 1499 underlying interfaces are selected based on PBM traffic attributes, 1500 and one or more neighbor underlying interfaces are selected based on 1501 the receipt of Interface Attributes sub-options in IPv6 ND messages 1502 (see: Figure 8). Underlying interface selection for the nodes own 1503 local interfaces are based on attributes such as DSCP, application 1504 port number, cost, performance, message size, etc. OMNI interface 1505 multilink selections could also be configured to perform replication 1506 across multiple underlying interfaces for increased reliability at 1507 the expense of packet duplication. The set of all Interface 1508 Attributes received in IPv6 ND messages determine the multilink 1509 forwarding profile for selecting the neighbor's underlying 1510 interfaces. 1512 When the OMNI interface sends a packet over a selected outbound 1513 underlying interface, the OAL includes or omits a mid-layer 1514 encapsulation header as necessary as discussed in Section 5 and as 1515 determined by the L2 address information received in Interface 1516 Attributes. The OAL also performs encapsulation when the nearest AR 1517 is located multiple hops away as discussed in Section 12.1. 1519 OMNI interface multilink service designers MUST observe the BCP 1520 guidance in Section 15 [RFC3819] in terms of implications for 1521 reordering when packets from the same flow may be spread across 1522 multiple underlying interfaces having diverse properties. 1524 11.1. Multiple OMNI Interfaces 1526 MNs may connect to multiple independent OMNI links concurrently in 1527 support of SBM. Each OMNI interface is distinguished by its Anycast 1528 OMNI DLA (e.g., [DLA]:0002::, [DLA]:1000::, [DLA]:7345::, etc.). The 1529 MN configures a separate OMNI interface for each link so that 1530 multiple interfaces (e.g., omni0, omni1, omni2, etc.) are exposed to 1531 the IPv6 layer. A different Anycast OMNI DLA is assigned to each 1532 interface, and the MN injects the service prefixes for the OMNI link 1533 instances into the EUN routing system. 1535 Applications in EUNs can use Segment Routing to select the desired 1536 OMNI interface based on SBM considerations. The Anycast OMNI DLA is 1537 written into the IPv6 destination address, and the actual destination 1538 (along with any additional intermediate hops) is written into the 1539 Segment Routing Header. Standard IP routing directs the packets to 1540 the MN's mobile router entity, and the Anycast OMNI DLA identifies 1541 the OMNI interface to be used for transmission to the next hop. When 1542 the MN receives the message, it replaces the IPv6 destination address 1543 with the next hop found in the routing header and transmits the 1544 message over the OMNI interface identified by the Anycast OMNI DLA. 1546 Multiple distinct OMNI links can therefore be used to support fault 1547 tolerance, load balancing, reliability, etc. The architectural model 1548 is similar to Layer 2 Virtual Local Area Networks (VLANs). 1550 11.2. MN<->AR Traffic Loop Prevention 1552 After an AR has registered an MNP for a MN (see: Section 12), the AR 1553 will forward packets destined to an address within the MNP to the MN. 1554 The MN will under normal circumstances then forward the packet to the 1555 correct destination within its internal networks. 1557 If at some later time the MN loses state (e.g., after a reboot), it 1558 may begin returning packets destined to an MNP address to the AR as 1559 its default router. The AR therefore must drop any packets 1560 originating from the MN and destined to an address within the MN's 1561 registered MNP. To do so, the AR institutes the following check: 1563 o if the IP destination address belongs to a neighbor on the same 1564 OMNI interface, and if the link-layer source address is the same 1565 as one of the neighbor's link-layer addresses, drop the packet. 1567 12. Router Discovery and Prefix Registration 1569 MNs interface with the MS by sending RS messages with OMNI options 1570 under the assumption that one or more AR on the ANET will process the 1571 message and respond. The MN then configures default routes for the 1572 OMNI interface via the discovered ARs as the next hop. The manner in 1573 which the ANET ensures AR coordination is link-specific and outside 1574 the scope of this document (however, considerations for ANETs that do 1575 not provide ARs that recognize the OMNI option are discussed in 1576 Section 17). 1578 For each underlying interface, the MN sends an RS message with an 1579 OMNI option to coordinate with MSEs identified by MSID values. 1580 Example MSID discovery methods are given in [RFC5214] and include 1581 data link login parameters, name service lookups, static 1582 configuration, a static "hosts" file, etc. The MN can also send an 1583 RS with an MS-Register suboption that includes the Anycast MSID value 1584 '0', i.e., instead of or in addition to any non-zero MSIDs. When the 1585 AR receives an RS with a MSID '0', it selects a nearby MSE (which may 1586 be itself) and returns an RA with the selected MSID in an MS-Register 1587 suboption. The AR selects only a single wildcard MSE (i.e., even if 1588 the RS MS-Register suboption included multiple '0' MSIDs) while also 1589 soliciting the MSEs corresponding to any non-zero MSIDs. 1591 MNs configure OMNI interfaces that observe the properties discussed 1592 in the previous section. The OMNI interface and its underlying 1593 interfaces are said to be in either the "UP" or "DOWN" state 1594 according to administrative actions in conjunction with the interface 1595 connectivity status. An OMNI interface transitions to UP or DOWN 1596 through administrative action and/or through state transitions of the 1597 underlying interfaces. When a first underlying interface transitions 1598 to UP, the OMNI interface also transitions to UP. When all 1599 underlying interfaces transition to DOWN, the OMNI interface also 1600 transitions to DOWN. 1602 When an OMNI interface transitions to UP, the MN sends RS messages to 1603 register its MNP and an initial set of underlying interfaces that are 1604 also UP. The MN sends additional RS messages to refresh lifetimes 1605 and to register/deregister underlying interfaces as they transition 1606 to UP or DOWN. The MN sends initial RS messages over an UP 1607 underlying interface with its MN OMNI LLA as the source and with 1608 destination set to All-Routers multicast (ff02::2) [RFC4291]. The RS 1609 messages include an OMNI option per Section 9 with a Preflen 1610 assertion, Interface Attributes appropriate for underlying 1611 interfaces, MS-Register/Release sub-options containing MSID values, 1612 and with any other necessary OMNI sub-options (e.g., a DUID suboption 1613 as an identity for the MN). The S/T-ifIndex field is set to the 1614 index of the underlying interface over which the RS message is sent. 1616 ARs process IPv6 ND messages with OMNI options and act as an MSE 1617 themselves and/or as a proxy for other MSEs. ARs receive RS messages 1618 and create a neighbor cache entry for the MN, then coordinate with 1619 any MSEs named in the Register/Release lists in a manner outside the 1620 scope of this document. When an MSE processes the OMNI information, 1621 it first validates the prefix registration information then injects/ 1622 withdraws the MNP in the routing/mapping system and caches/discards 1623 the new Preflen, MNP and Interface Attributes. The MSE then informs 1624 the AR of registration success/failure, and the AR returns an RA 1625 message to the MN with an OMNI option per Section 9. 1627 The AR returns the RA message via the same underlying interface of 1628 the MN over which the RS was received, and with destination address 1629 set to the MN OMNI LLA (i.e., unicast), with source address set to 1630 its own OMNI LLA, and with an OMNI option with S/T-ifIndex set to the 1631 value included in the RS. The OMNI option also includes a Preflen 1632 confirmation, Interface Attributes, MS-Register/Release and any other 1633 necessary OMNI sub-options (e.g., a DUID suboption as an identity for 1634 the AR). The RA also includes any information for the link, 1635 including RA Cur Hop Limit, M and O flags, Router Lifetime, Reachable 1636 Time and Retrans Timer values, and includes any necessary options 1637 such as: 1639 o PIOs with (A; L=0) that include MSPs for the link [RFC8028]. 1641 o RIOs [RFC4191] with more-specific routes. 1643 o an MTU option that specifies the maximum acceptable packet size 1644 for this ANET interface. 1646 The AR MAY also send periodic and/or event-driven unsolicited RA 1647 messages per [RFC4861]. In that case, the S/T-ifIndex field in the 1648 OMNI header of the unsolicited RA message identifies the target 1649 underlying interface of the destination MN. 1651 The AR can combine the information from multiple MSEs into one or 1652 more "aggregate" RAs sent to the MN in order conserve ANET bandwidth. 1653 Each aggregate RA includes an OMNI option with MS-Register/Release 1654 sub-options with the MSEs represented by the aggregate. If an 1655 aggregate is sent, the RA message contents must consistently 1656 represent the combined information advertised by all represented 1657 MSEs. Note that since the AR uses its own OMNI LLA as the RA source 1658 address, the MN determines the addresses of the represented MSEs by 1659 examining the MS-Register/Release OMNI sub-options. 1661 When the MN receives the RA message, it creates an OMNI interface 1662 neighbor cache entry for each MSID that has confirmed MNP 1663 registration via the L2 address of this AR. If the MN connects to 1664 multiple ANETs, it records the additional L2 AR addresses in each 1665 MSID neighbor cache entry (i.e., as multilink neighbors). The MN 1666 then configures a default route via the MSE that returned the RA 1667 message, and assigns the Subnet Router Anycast address corresponding 1668 to the MNP (e.g., 2001:db8:1:2::) to the OMNI interface. The MN then 1669 manages its underlying interfaces according to their states as 1670 follows: 1672 o When an underlying interface transitions to UP, the MN sends an RS 1673 over the underlying interface with an OMNI option. The OMNI 1674 option contains at least one Interface Attribute sub-option with 1675 values specific to this underlying interface, and may contain 1676 additional Interface Attributes specific to other underlying 1677 interfaces. The option also includes any MS-Register/Release sub- 1678 options. 1680 o When an underlying interface transitions to DOWN, the MN sends an 1681 RS or unsolicited NA message over any UP underlying interface with 1682 an OMNI option containing an Interface Attribute sub-option for 1683 the DOWN underlying interface with Link set to '0'. The MN sends 1684 an RS when an acknowledgement is required, or an unsolicited NA 1685 when reliability is not thought to be a concern (e.g., if 1686 redundant transmissions are sent on multiple underlying 1687 interfaces). 1689 o When the Router Lifetime for a specific AR nears expiration, the 1690 MN sends an RS over the underlying interface to receive a fresh 1691 RA. If no RA is received, the MN can send RS messages to an 1692 alternate MSID in case the current MSID has failed. If no RS 1693 messages are received even after trying to contact alternate 1694 MSIDs, the MN marks the underlying interface as DOWN. 1696 o When a MN wishes to release from one or more current MSIDs, it 1697 sends an RS or unsolicited NA message over any UP underlying 1698 interfaces with an OMNI option with a Release MSID. Each MSID 1699 then withdraws the MNP from the routing/mapping system and informs 1700 the AR that the release was successful. 1702 o When all of a MNs underlying interfaces have transitioned to DOWN 1703 (or if the prefix registration lifetime expires), any associated 1704 MSEs withdraw the MNP the same as if they had received a message 1705 with a release indication. 1707 The MN is responsible for retrying each RS exchange up to 1708 MAX_RTR_SOLICITATIONS times separated by RTR_SOLICITATION_INTERVAL 1709 seconds until an RA is received. If no RA is received over an UP 1710 underlying interface (i.e., even after attempting to contact 1711 alternate MSEs), the MN declares this underlying interface as DOWN. 1713 The IPv6 layer sees the OMNI interface as an ordinary IPv6 interface. 1714 Therefore, when the IPv6 layer sends an RS message the OMNI interface 1715 returns an internally-generated RA message as though the message 1716 originated from an IPv6 router. The internally-generated RA message 1717 contains configuration information that is consistent with the 1718 information received from the RAs generated by the MS. Whether the 1719 OMNI interface IPv6 ND messaging process is initiated from the 1720 receipt of an RS message from the IPv6 layer is an implementation 1721 matter. Some implementations may elect to defer the IPv6 ND 1722 messaging process until an RS is received from the IPv6 layer, while 1723 others may elect to initiate the process proactively. Still other 1724 deployments may elect to administratively disable the ordinary RS/RA 1725 messaging used by the IPv6 layer over the OMNI interface, since they 1726 are not required to drive the internal RS/RA processing. (Note that 1727 this same logic applies to IPv4 implementations that employ ICMP- 1728 based Router Discovery per [RFC1256].) 1730 Note: The Router Lifetime value in RA messages indicates the time 1731 before which the MN must send another RS message over this underlying 1732 interface (e.g., 600 seconds), however that timescale may be 1733 significantly longer than the lifetime the MS has committed to retain 1734 the prefix registration (e.g., REACHABLETIME seconds). ARs are 1735 therefore responsible for keeping MS state alive on a shorter 1736 timescale than the MN is required to do on its own behalf. 1738 Note: On multicast-capable underlying interfaces, MNs should send 1739 periodic unsolicited multicast NA messages and ARs should send 1740 periodic unsolicited multicast RA messages as "beacons" that can be 1741 heard by other nodes on the link. If a node fails to receive a 1742 beacon after a timeout value specific to the link, it can initiate a 1743 unicast exchange to test reachability. 1745 Note: if an AR acting as a proxy forwards a MN's RS message to 1746 another node acting as an MSE using UDP/IP encapsulation, it must use 1747 a distinct UDP source port number for each MN. This allows the MSE 1748 to distinguish different MNs behind the same AR at the link-layer, 1749 whereas the link-layer addresses would otherwise be 1750 indistinguishable. 1752 12.1. Router Discovery in IP Multihop and IPv4-Only Access Networks 1754 On some ANET types a MN may be located multiple IP hops away from the 1755 nearest AR. Forwarding through IP multihop ANETs is conducted 1756 through the application of a routing protocol (e.g., a Mobile Ad-hoc 1757 Network (MANET) routing protocol over omni-directional wireless 1758 interfaces, an inter-domain routing protocol in an enterprise 1759 network, etc.). These ANETs could be either IPv6-enabled or 1760 IPv4-only, while IPv4-only ANETs could be either multicast-capable or 1761 unicast-only (note that for IPv4-only ANETs the following procedures 1762 apply for both single-hop and multihop cases). 1764 A MN located potentially multiple ANET hops away from the nearest AR 1765 prepares an RS message with source address set to either its MN OMNI 1766 LLA or a Temporary OMNI LLA, and with destination set to link-scoped 1767 All-Routers multicast the same as discussed above. For IPv6-enabled 1768 ANETs, the MN then encapsulates the message in an IPv6 header with 1769 source address set to the DLA corresponding to the LLA source address 1770 and with destination set to either a unicast or anycast DLA. For 1771 IPv4-only ANETs, the MN instead encapsulates the RS message in an 1772 IPv4 header with source address set to the node's own IPv4 address 1773 and with destination address set to either the unicast IPv4 address 1774 of an AR [RFC5214] or an IPv4 anycast address reserved for OMNI. The 1775 MN then sends the encapsulated RS message via the ANET interface, 1776 where it will be forwarded by zero or more intermediate ANET hops. 1778 When an intermediate ANET hop that participates in the routing 1779 protocol receives the encapsulated RS, it forwards the message 1780 according to its routing tables (note that an intermediate node could 1781 be a fixed infrastructure element or another MN). This process 1782 repeats iteratively until the RS message is received by a penultimate 1783 ANET hop within single-hop communications range of an AR, which 1784 forwards the message to the AR. 1786 When the AR receives the message, it decapsulates the RS and 1787 coordinates with the MS the same as for an ordinary link-local RS, 1788 since the inner Hop Limit will not have been decremented by the 1789 multihop forwarding process. The AR then prepares an RA message with 1790 source address set to its own LLA and destination address set to the 1791 LLA of the original MN, then encapsulates the message in an IPv4/IPv6 1792 header with source address set to its own IPv4/DLA address and with 1793 destination set to the encapsulation source of the RS. 1795 The AR then forwards the message to an ANET node within 1796 communications range, which forwards the message according to its 1797 routing tables to an intermediate node. The multihop forwarding 1798 process within the ANET continues repetitively until the message is 1799 delivered to the original MN, which decapsulates the message and 1800 performs autoconfiguration the same as if it had received the RA 1801 directly from the AR as an on-link neighbor. 1803 Note: An alternate approach to multihop forwarding via IPv6 1804 encapsulation would be to statelessly translate the IPv6 LLAs into 1805 DLAs and forward the messages without encapsulation. This would 1806 violate the [RFC4861] requirement that certain IPv6 ND messages must 1807 use link-local addresses and must not be accepted if received with 1808 Hop Limit less than 255. This document therefore advocates 1809 encapsulation since the overhead is nominal considering the 1810 infrequent nature and small size of IPv6 ND messages. Future 1811 documents may consider encapsulation avoidance through translation 1812 while updating [RFC4861]. 1814 Note: An alternate approach to multihop forwarding via IPv4 1815 encapsulation would be to employ IPv6/IPv4 protocol translation. 1816 However, for IPv6 ND messages the OMNI LLA addresses would be 1817 truncated due to translation and the OMNI Router and Prefix Discovery 1818 services would not be able to function. The use of IPv4 1819 encapsulation is therefore indicated. 1821 Note: An IPv4 anycast address for OMNI in IPv4 networks could be part 1822 of a new IPv4 /24 prefix allocation, but this may be difficult to 1823 obtain given IPv4 address exhaustion. An alternative would be to re- 1824 purpose the prefix 192.88.99.0 which has been set aside from its 1825 former use by [RFC7526]. 1827 12.2. MS-Register and MS-Release List Processing 1829 When a MN sends an RS message with an OMNI option via an underlying 1830 interface to an AR, the MN must convey its knowledge of its 1831 currently-associated MSEs. Initially, the MN will have no associated 1832 MSEs and should therefore include an MS-Register sub-option with the 1833 single MSID value 0 which requests the AR to select and assign an 1834 MSE. The AR will then return an RA message with source address set 1835 to the OMNI LLA containing the MSE of the selected MSE. 1837 As the MN activates additional underlying interfaces, it can 1838 optionally include an MS-Register sub-option with MSID value 0, or 1839 with non-zero MSIDs for MSEs discovered from previous RS/RA 1840 exchanges. The MN will thus eventually begin to learn and manage its 1841 currently active set of MSEs, and can register with new MSEs or 1842 release from former MSEs with each successive RS/RA exchange. As the 1843 MN's MSE constituency grows, it alone is responsible for including or 1844 omitting MSIDs in the MS-Register/Release lists it sends in RS 1845 messages. The inclusion or omission of MSIDs determines the MN's 1846 interface to the MS and defines the manner in which MSEs will 1847 respond. The only limiting factor is that the MN should include no 1848 more than MAX_MSID values in each list per each IPv6 ND message, and 1849 should avoid duplication of entries in each list unless it wants to 1850 increase likelihood of control message delivery. 1852 When an AR receives an RS message sent by a MN with an OMNI option, 1853 the option will contain zero or more MS-Register and MS-Release sub- 1854 options containing MSIDs. After processing the OMNI option, the AR 1855 will have a list of zero or more MS-Register MSIDs and a list of zero 1856 or more of MS-Release MSIDs. The AR then processes the lists as 1857 follows: 1859 o For each list, retain the first MAX_MSID values in the list and 1860 discard any additional MSIDs (i.e., even if there are duplicates 1861 within a list). 1863 o Next, for each MSID in the MS-Register list, remove all matching 1864 MSIDs from the MS-Release list. 1866 o Next, proceed according to whether the AR's own MSID or the value 1867 0 appears in the MS-Register list as follows: 1869 * If yes, send an RA message directly back to the MN and send a 1870 proxy copy of the RS message to each additional MSID in the MS- 1871 Register list with the MS-Register/Release lists omitted. 1872 Then, send a uNA message to each MSID in the MS-Release list 1873 with the MS-Register/Release lists omitted and with an OMNI 1874 header with S/T-ifIndex set to 0. 1876 * If no, send a proxy copy of the RS message to each additional 1877 MSID in the MS-Register list with the MS-Register list omitted. 1878 For the first MSID, include the original MS-Release list; for 1879 all other MSIDs, omit the MS-Release list. 1881 Each proxy copy of the RS message will include an OMNI option and 1882 encapsulation header with the DLA of the AR as the source and the DLA 1883 of the Register MSE as the destination. When the Register MSE 1884 receives the proxy RS message, if the message includes an MS-Release 1885 list the MSE sends a uNA message to each additional MSID in the 1886 Release list. The Register MSE then sends an RA message back to the 1887 (Proxy) AR wrapped in an OMNI encapsulation header with source and 1888 destination addresses reversed, and with RA destination set to the 1889 LLA of the MN. When the AR receives this RA message, it sends a 1890 proxy copy of the RA to the MN. 1892 Each uNA message (whether send by the first-hop AR or by a Register 1893 MSE) will include an OMNI option and an encapsulation header with the 1894 DLA of the Register MSE as the source and the DLA of the Release ME 1895 as the destination. The uNA informs the Release MSE that its 1896 previous relationship with the MN has been released and that the 1897 source of the uNA message is now registered. The Release MSE must 1898 then note that the subject MN of the uNA message is now "departed", 1899 and forward any subsequent packets destined to the MN to the Register 1900 MSE. 1902 Note that it is not an error for the MS-Register/Release lists to 1903 include duplicate entries. If duplicates occur within a list, the AR 1904 will generate multiple proxy RS and/or uNA messages - one for each 1905 copy of the duplicate entries. 1907 12.3. DHCPv6-based Prefix Registration 1909 When a MN is not pre-provisioned with an OMNI LLA containing a MNP 1910 (or, when multiple MNPs are needed), it will require the AR to select 1911 MNPs on its behalf and set up the correct routing state within the 1912 MS. The DHCPv6 service [RFC8415] supports this requirement. 1914 When an MN needs to have the AR select MNPs, it sends an RS message 1915 with a DHCPv6 Message suboption containing a Client Identifier, one 1916 or more IA_PD options and a Rapid Commit option. The MN also sets 1917 the 'msg-type' field to "Solicit", and includes a 3-octet 1918 'transaction-id'. 1920 When the AR receives the RS message, it extracts the DHCPv6 message 1921 from the OMNI option. The AR then acts as a "Proxy DHCPv6 Client" in 1922 a message exchange with the locally-resident DHCPv6 server, which 1923 delegates MNPs and returns a DHCPv6 Reply message with PD parameters. 1924 (If the AR wishes to defer creation of MN state until the DHCPv6 1925 Reply is received, it can instead act as a Lightweight DHCPv6 Relay 1926 Agent per [RFC6221] by encapsulating the DHCPv6 message in a Relay- 1927 forward/reply exchange with Relay Message and Interface ID options.) 1929 When the AR receives the DHCPv6 Reply, it adds routes to the routing 1930 system and creates MN OMNI LLAs based on the delegated MNPs. The AR 1931 then sends an RA back to the MN with the DHCPv6 Reply message 1932 included in an OMNI DHCPv6 message sub-option. If the RS message 1933 source address was a Temporary address, the AR includes one of the 1934 (newly-created) MN OMNI LLAs as the RA destination address. The MN 1935 then creates a default route, assigns Subnet Router Anycast addresses 1936 and uses the RA destination address as its primary MN OMNI LLA. The 1937 MN will then use this primary MN OMNI LLA as the source address of 1938 any IPv6 ND messages it sends as long as it retains ownership of the 1939 MNP. 1941 Note: The single-octet OMNI sub-option length field restricts the 1942 DHCPv6 Message sub-option to a maximum of 255 octets for both the RS 1943 and RA messages. This provides sufficient room for the DHCPv6 1944 message header, a Client/Server Identifier option, a Rapid Commit 1945 option, at least 3 Identity Association for Prefix Delegation (IA_PD) 1946 options and any other supporting DHCPv6 options. A MN requiring more 1947 DHCPv6-based configuration information than this can either perform 1948 multiple independent RS/RA exchanges (with each exchange providing a 1949 subset of the total configuration information) or simply perform an 1950 actual DHCPv6 message exchange in addition to any RS/RA exchanges. 1952 Note: After a MN performs a DHCPv6-based prefix registration exchange 1953 with a first AR, it would need to repeat the exchange with each 1954 additional MSE it registers with. In that case, the MN supplies the 1955 MNP delegations received from the first AR in the IA_PD fields of a 1956 DHCPv6 message when it engages the additonal MSEs. 1958 13. Secure Redirection 1960 If the ANET link model is multiple access, the AR is responsible for 1961 assuring that address duplication cannot corrupt the neighbor caches 1962 of other nodes on the link. When the MN sends an RS message on a 1963 multiple access ANET link, the AR verifies that the MN is authorized 1964 to use the address and returns an RA with a non-zero Router Lifetime 1965 only if the MN is authorized. 1967 After verifying MN authorization and returning an RA, the AR MAY 1968 return IPv6 ND Redirect messages to direct MNs located on the same 1969 ANET link to exchange packets directly without transiting the AR. In 1970 that case, the MNs can exchange packets according to their unicast L2 1971 addresses discovered from the Redirect message instead of using the 1972 dogleg path through the AR. In some ANET links, however, such direct 1973 communications may be undesirable and continued use of the dogleg 1974 path through the AR may provide better performance. In that case, 1975 the AR can refrain from sending Redirects, and/or MNs can ignore 1976 them. 1978 14. AR and MSE Resilience 1980 ANETs SHOULD deploy ARs in Virtual Router Redundancy Protocol (VRRP) 1981 [RFC5798] configurations so that service continuity is maintained 1982 even if one or more ARs fail. Using VRRP, the MN is unaware which of 1983 the (redundant) ARs is currently providing service, and any service 1984 discontinuity will be limited to the failover time supported by VRRP. 1985 Widely deployed public domain implementations of VRRP are available. 1987 MSEs SHOULD use high availability clustering services so that 1988 multiple redundant systems can provide coordinated response to 1989 failures. As with VRRP, widely deployed public domain 1990 implementations of high availability clustering services are 1991 available. Note that special-purpose and expensive dedicated 1992 hardware is not necessary, and public domain implementations can be 1993 used even between lightweight virtual machines in cloud deployments. 1995 15. Detecting and Responding to MSE Failures 1997 In environments where fast recovery from MSE failure is required, ARs 1998 SHOULD use proactive Neighbor Unreachability Detection (NUD) in a 1999 manner that parallels Bidirectional Forwarding Detection (BFD) 2000 [RFC5880] to track MSE reachability. ARs can then quickly detect and 2001 react to failures so that cached information is re-established 2002 through alternate paths. Proactive NUD control messaging is carried 2003 only over well-connected ground domain networks (i.e., and not low- 2004 end ANET links such as aeronautical radios) and can therefore be 2005 tuned for rapid response. 2007 ARs perform proactive NUD for MSEs for which there are currently 2008 active MNs on the ANET. If an MSE fails, ARs can quickly inform MNs 2009 of the outage by sending multicast RA messages on the ANET interface. 2010 The AR sends RA messages to MNs via the ANET interface with an OMNI 2011 option with a Release ID for the failed MSE, and with destination 2012 address set to All-Nodes multicast (ff02::1) [RFC4291]. 2014 The AR SHOULD send MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated 2015 by small delays [RFC4861]. Any MNs on the ANET interface that have 2016 been using the (now defunct) MSE will receive the RA messages and 2017 associate with a new MSE. 2019 16. Transition Considerations 2021 When a MN connects to an ANET link for the first time, it sends an RS 2022 message with an OMNI option. If the first hop AR recognizes the 2023 option, it returns an RA with its MS OMNI LLA as the source, the MN 2024 OMNI LLA as the destination and with an OMNI option included. The MN 2025 then engages the AR according to the OMNI link model specified above. 2026 If the first hop AR is a legacy IPv6 router, however, it instead 2027 returns an RA message with no OMNI option and with a non-OMNI unicast 2028 source LLA as specified in [RFC4861]. In that case, the MN engages 2029 the ANET according to the legacy IPv6 link model and without the OMNI 2030 extensions specified in this document. 2032 If the ANET link model is multiple access, there must be assurance 2033 that address duplication cannot corrupt the neighbor caches of other 2034 nodes on the link. When the MN sends an RS message on a multiple 2035 access ANET link with an OMNI LLA source address and an OMNI option, 2036 ARs that recognize the option ensure that the MN is authorized to use 2037 the address and return an RA with a non-zero Router Lifetime only if 2038 the MN is authorized. ARs that do not recognize the option instead 2039 return an RA that makes no statement about the MN's authorization to 2040 use the source address. In that case, the MN should perform 2041 Duplicate Address Detection to ensure that it does not interfere with 2042 other nodes on the link. 2044 An alternative approach for multiple access ANET links to ensure 2045 isolation for MN / AR communications is through L2 address mappings 2046 as discussed in Appendix C. This arrangement imparts a (virtual) 2047 point-to-point link model over the (physical) multiple access link. 2049 17. OMNI Interfaces on the Open Internet 2051 OMNI interfaces configured over IPv6-enabled underlying interfaces on 2052 the open Internet without an OMNI-aware first-hop AR receive RA 2053 messages that do not include an OMNI option, while OMNI interfaces 2054 configured over IPv4-only underlying interfaces do not receive any 2055 (IPv6) RA messages at all. OMNI interfaces that receive RA messages 2056 without an OMNI option configure addresses, on-link prefixes, etc. on 2057 the underlying interface that received the RA according to standard 2058 IPv6 ND and address resolution conventions [RFC4861] [RFC4862]. OMNI 2059 interfaces configured over IPv4-only underlying interfaces configure 2060 IPv4 address information on the underlying interfaces using 2061 mechanisms such as DHCPv4 [RFC2131]. 2063 OMNI interfaces configured over underlying interfaces that connect to 2064 the open Internet can apply security services such as VPNs to connect 2065 to an MSE or establish a direct link to an MSE through some other 2066 means (see Section 4). In environments where an explicit VPN or 2067 direct link may be impractical, OMNI interfaces can instead use UDP/ 2068 IP encapsulation and HMAC-based message authentication per 2069 [RFC6081][RFC4380]. 2071 After establishing a VPN or preparing for UDP/IP encapsulation, OMNI 2072 interfaces send control plane messages to interface with the MS, 2073 including Neighbor Solicitation (NS) and Neighbor Advertisement (NA) 2074 messages used for address resolution / route optimization (see: 2075 [I-D.templin-intarea-6706bis]). The control plane messages must be 2076 authenticated while data plane messages are delivered the same as for 2077 ordinary best-effort Internet traffic with basic source address-based 2078 data origin verification. Data plane communications via OMNI 2079 interfaces that connect over the open Internet without an explicit 2080 VPN should therefore employ transport- or higher-layer security to 2081 ensure integrity and/or confidentiality. 2083 OMNI interfaces in the open Internet are often located behind Network 2084 Address Translators (NATs). The OMNI interface accommodates NAT 2085 traversal using UDP/IP encapsulation and the mechanisms discussed in 2086 [RFC6081][RFC4380][I-D.templin-intarea-6706bis]. 2088 18. Time-Varying MNPs 2090 In some use cases, it is desirable, beneficial and efficient for the 2091 MN to receive a constant MNP that travels with the MN wherever it 2092 moves. For example, this would allow air traffic controllers to 2093 easily track aircraft, etc. In other cases, however (e.g., 2094 intelligent transportation systems), the MN may be willing to 2095 sacrifice a modicum of efficiency in order to have time-varying MNPs 2096 that can be changed every so often to defeat adversarial tracking. 2098 The prefix delegation services discussed in Section 12.3 allows OMNI 2099 MNs that desire time-varying MNPs to obtain short-lived prefixes to 2100 use a Temporary OMNI LLA as the source address of an RS message with 2101 an OMNI option with DHCPv6 Option sub-options. The MN would then be 2102 obligated to renumber its internal networks whenever its MNP (and 2103 therefore also its OMNI address) changes. This should not present a 2104 challenge for MNs with automated network renumbering services, 2105 however presents limits for the durations of ongoing sessions that 2106 would prefer to use a constant address. 2108 19. IANA Considerations 2110 The IANA is instructed to allocate an official Type number TBD from 2111 the registry "IPv6 Neighbor Discovery Option Formats" for the OMNI 2112 option. Implementations set Type to 253 as an interim value 2113 [RFC4727]. 2115 The IANA is instructed to assign a new Code value "1" in the "ICMPv6 2116 Code Fields: Type 2 - Packet Too Big" registry. The registry should 2117 read as follows: 2119 Code Name Reference 2120 --- ---- --------- 2121 0 Diagnostic Packet Too Big [RFC4443] 2122 1 Advisory Packet Too Big [RFCXXXX] 2124 Figure 17: OMNI Option Sub-Type Values 2126 The IANA is instructed to allocate one Ethernet unicast address TBD2 2127 (suggest 00-00-5E-00-52-14 [RFC5214]) in the registry "IANA Ethernet 2128 Address Block - Unicast Use". 2130 The OMNI option also defines an 8-bit Sub-Type field, for which IANA 2131 is instructed to create and maintain a new registry entitled "OMNI 2132 option Sub-Type values". Initial values for the OMNI option Sub-Type 2133 values registry are given below; future assignments are to be made 2134 through Expert Review [RFC8126]. 2136 Value Sub-Type name Reference 2137 ----- ------------- ---------- 2138 0 Pad1 [RFCXXXX] 2139 1 PadN [RFCXXXX] 2140 2 Interface Attributes [RFCXXXX] 2141 3 Traffic Selector [RFCXXXX] 2142 4 MS-Register [RFCXXXX] 2143 5 MS-Release [RFCXXXX] 2144 6 Network Access Identifier [RFCXXXX] 2145 7 Geo Coordinates [RFCXXXX] 2146 8 DHCP Unique Identifier (DUID) [RFCXXXX] 2147 9 DHCPv6 Message [RFCXXXX] 2148 10-252 Unassigned 2149 253-254 Experimental [RFCXXXX] 2150 255 Reserved [RFCXXXX] 2152 Figure 18: OMNI Option Sub-Type Values 2154 20. Security Considerations 2156 Security considerations for IPv4 [RFC0791], IPv6 [RFC8200] and IPv6 2157 Neighbor Discovery [RFC4861] apply. OMNI interface IPv6 ND messages 2158 SHOULD include Nonce and Timestamp options [RFC3971] when transaction 2159 confirmation and/or time synchronization is needed. 2161 OMNI interfaces configured over secured ANET interfaces inherit the 2162 physical and/or link-layer security properties of the connected 2163 ANETs. OMNI interfaces configured over open INET interfaces can use 2164 symmetric securing services such as VPNs or can by some other means 2165 establish a direct link. When a VPN or direct link may be 2166 impractical, however, an asymmetric security service such as the 2167 authentication option specified in [RFC4380] or other protocol 2168 control message security mechanisms may be necessary. While the OMNI 2169 link protects control plane messaging, applications must still employ 2170 end-to-end transport- or higher-layer security services to protect 2171 the data plane. 2173 The Mobility Service MUST provide strong network layer security for 2174 control plane messages and forwarding path integrity for data plane 2175 messages. In one example, the AERO service 2176 [I-D.templin-intarea-6706bis] constructs a spanning tree between 2177 mobility service elements and secures the links in the spanning tree 2178 with network layer security mechanisms such as IPsec [RFC4301] or 2179 Wireguard. Control plane messages are then constrained to travel 2180 only over the secured spanning tree paths and are therefore protected 2181 from attack or eavesdropping. Since data plane messages can travel 2182 over route optimized paths that do not strictly follow the spanning 2183 tree, however, end-to-end transport- or higher-layer security 2184 services are still required. 2186 Security considerations for specific access network interface types 2187 are covered under the corresponding IP-over-(foo) specification 2188 (e.g., [RFC2464], [RFC2492], etc.). 2190 Security considerations for IPv6 fragmentation and reassembly are 2191 discussed in Section 5.1. 2193 21. Implementation Status 2195 Draft -29 is implemented in the recently tagged AERO/OMNI 3.0.0 2196 internal release, and Draft -30 is now tagged as the AERO/OMNI 3.0.1. 2197 Newer specification versions will be tagged in upcoming releases. 2198 First public release expected before the end of 2020. 2200 22. Acknowledgements 2202 The first version of this document was prepared per the consensus 2203 decision at the 7th Conference of the International Civil Aviation 2204 Organization (ICAO) Working Group-I Mobility Subgroup on March 22, 2205 2019. Consensus to take the document forward to the IETF was reached 2206 at the 9th Conference of the Mobility Subgroup on November 22, 2019. 2207 Attendees and contributors included: Guray Acar, Danny Bharj, 2208 Francois D'Humieres, Pavel Drasil, Nikos Fistas, Giovanni Garofolo, 2209 Bernhard Haindl, Vaughn Maiolla, Tom McParland, Victor Moreno, Madhu 2210 Niraula, Brent Phillips, Liviu Popescu, Jacky Pouzet, Aloke Roy, Greg 2211 Saccone, Robert Segers, Michal Skorepa, Michel Solery, Stephane 2212 Tamalet, Fred Templin, Jean-Marc Vacher, Bela Varkonyi, Tony Whyman, 2213 Fryderyk Wrobel and Dongsong Zeng. 2215 The following individuals are acknowledged for their useful comments: 2216 Michael Matyas, Madhu Niraula, Michael Richardson, Greg Saccone, 2217 Stephane Tamalet, Eric Vyncke. Pavel Drasil, Zdenek Jaron and Michal 2218 Skorepa are recognized for their many helpful ideas and suggestions. 2219 Madhuri Madhava Badgandi, Katherine Tran, and Vijayasarathy 2220 Rajagopalan are acknowledged for their hard work on the 2221 implementation and insights that led to improvements to the spec. 2223 Discussions on the IETF 6man and atn mailing lists during the fall of 2224 2020 suggested additional points to consider. The authors gratefully 2225 acknowledge the list members who contributed valuable insights 2226 through those discussions. Eric Vyncke and Erik Kline were the 2227 intarea ADs, while Bob Hinden and Ole Troan were the 6man WG chairs 2228 at the time the document was developed; they are all gratefully 2229 acknowledged for their many helpful insights. 2231 This work is aligned with the NASA Safe Autonomous Systems Operation 2232 (SASO) program under NASA contract number NNA16BD84C. 2234 This work is aligned with the FAA as per the SE2025 contract number 2235 DTFAWA-15-D-00030. 2237 23. References 2239 23.1. Normative References 2241 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 2242 DOI 10.17487/RFC0791, September 1981, 2243 . 2245 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 2246 Requirement Levels", BCP 14, RFC 2119, 2247 DOI 10.17487/RFC2119, March 1997, 2248 . 2250 [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, 2251 "Definition of the Differentiated Services Field (DS 2252 Field) in the IPv4 and IPv6 Headers", RFC 2474, 2253 DOI 10.17487/RFC2474, December 1998, 2254 . 2256 [RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander, 2257 "SEcure Neighbor Discovery (SEND)", RFC 3971, 2258 DOI 10.17487/RFC3971, March 2005, 2259 . 2261 [RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and 2262 More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191, 2263 November 2005, . 2265 [RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast 2266 Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005, 2267 . 2269 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 2270 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 2271 2006, . 2273 [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet 2274 Control Message Protocol (ICMPv6) for the Internet 2275 Protocol Version 6 (IPv6) Specification", STD 89, 2276 RFC 4443, DOI 10.17487/RFC4443, March 2006, 2277 . 2279 [RFC4727] Fenner, B., "Experimental Values In IPv4, IPv6, ICMPv4, 2280 ICMPv6, UDP, and TCP Headers", RFC 4727, 2281 DOI 10.17487/RFC4727, November 2006, 2282 . 2284 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 2285 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 2286 DOI 10.17487/RFC4861, September 2007, 2287 . 2289 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 2290 Address Autoconfiguration", RFC 4862, 2291 DOI 10.17487/RFC4862, September 2007, 2292 . 2294 [RFC6088] Tsirtsis, G., Giarreta, G., Soliman, H., and N. Montavont, 2295 "Traffic Selectors for Flow Bindings", RFC 6088, 2296 DOI 10.17487/RFC6088, January 2011, 2297 . 2299 [RFC8028] Baker, F. and B. Carpenter, "First-Hop Router Selection by 2300 Hosts in a Multi-Prefix Network", RFC 8028, 2301 DOI 10.17487/RFC8028, November 2016, 2302 . 2304 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2305 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2306 May 2017, . 2308 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 2309 (IPv6) Specification", STD 86, RFC 8200, 2310 DOI 10.17487/RFC8200, July 2017, 2311 . 2313 [RFC8201] McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed., 2314 "Path MTU Discovery for IP version 6", STD 87, RFC 8201, 2315 DOI 10.17487/RFC8201, July 2017, 2316 . 2318 [RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A., 2319 Richardson, M., Jiang, S., Lemon, T., and T. Winters, 2320 "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", 2321 RFC 8415, DOI 10.17487/RFC8415, November 2018, 2322 . 2324 23.2. Informative References 2326 [ATN] Maiolla, V., "The OMNI Interface - An IPv6 Air/Ground 2327 Interface for Civil Aviation, IETF Liaison Statement 2328 #1676, https://datatracker.ietf.org/liaison/1676/", March 2329 2020. 2331 [CRC] Jain, R., "Error Characteristics of Fiber Distributed Data 2332 Interface (FDDI), IEEE Transactions on Communications", 2333 August 1990. 2335 [I-D.ietf-6man-rfc4941bis] 2336 Gont, F., Krishnan, S., Narten, T., and R. Draves, 2337 "Temporary Address Extensions for Stateless Address 2338 Autoconfiguration in IPv6", draft-ietf-6man-rfc4941bis-12 2339 (work in progress), November 2020. 2341 [I-D.ietf-intarea-tunnels] 2342 Touch, J. and M. Townsley, "IP Tunnels in the Internet 2343 Architecture", draft-ietf-intarea-tunnels-10 (work in 2344 progress), September 2019. 2346 [I-D.ietf-ipwave-vehicular-networking] 2347 Jeong, J., "IPv6 Wireless Access in Vehicular Environments 2348 (IPWAVE): Problem Statement and Use Cases", draft-ietf- 2349 ipwave-vehicular-networking-19 (work in progress), July 2350 2020. 2352 [I-D.templin-6man-dhcpv6-ndopt] 2353 Templin, F., "A Unified Stateful/Stateless Configuration 2354 Service for IPv6", draft-templin-6man-dhcpv6-ndopt-10 2355 (work in progress), June 2020. 2357 [I-D.templin-6man-lla-type] 2358 Templin, F., "The IPv6 Link-Local Address Type Field", 2359 draft-templin-6man-lla-type-02 (work in progress), 2360 November 2020. 2362 [I-D.templin-intarea-6706bis] 2363 Templin, F., "Asymmetric Extended Route Optimization 2364 (AERO)", draft-templin-intarea-6706bis-74 (work in 2365 progress), December 2020. 2367 [RFC1122] Braden, R., Ed., "Requirements for Internet Hosts - 2368 Communication Layers", STD 3, RFC 1122, 2369 DOI 10.17487/RFC1122, October 1989, 2370 . 2372 [RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191, 2373 DOI 10.17487/RFC1191, November 1990, 2374 . 2376 [RFC1256] Deering, S., Ed., "ICMP Router Discovery Messages", 2377 RFC 1256, DOI 10.17487/RFC1256, September 1991, 2378 . 2380 [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", 2381 RFC 2131, DOI 10.17487/RFC2131, March 1997, 2382 . 2384 [RFC2225] Laubach, M. and J. Halpern, "Classical IP and ARP over 2385 ATM", RFC 2225, DOI 10.17487/RFC2225, April 1998, 2386 . 2388 [RFC2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet 2389 Networks", RFC 2464, DOI 10.17487/RFC2464, December 1998, 2390 . 2392 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 2393 IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473, 2394 December 1998, . 2396 [RFC2492] Armitage, G., Schulter, P., and M. Jork, "IPv6 over ATM 2397 Networks", RFC 2492, DOI 10.17487/RFC2492, January 1999, 2398 . 2400 [RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4 2401 Domains without Explicit Tunnels", RFC 2529, 2402 DOI 10.17487/RFC2529, March 1999, 2403 . 2405 [RFC2863] McCloghrie, K. and F. Kastenholz, "The Interfaces Group 2406 MIB", RFC 2863, DOI 10.17487/RFC2863, June 2000, 2407 . 2409 [RFC3692] Narten, T., "Assigning Experimental and Testing Numbers 2410 Considered Useful", BCP 82, RFC 3692, 2411 DOI 10.17487/RFC3692, January 2004, 2412 . 2414 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 2415 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 2416 DOI 10.17487/RFC3810, June 2004, 2417 . 2419 [RFC3819] Karn, P., Ed., Bormann, C., Fairhurst, G., Grossman, D., 2420 Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L. 2421 Wood, "Advice for Internet Subnetwork Designers", BCP 89, 2422 RFC 3819, DOI 10.17487/RFC3819, July 2004, 2423 . 2425 [RFC3879] Huitema, C. and B. Carpenter, "Deprecating Site Local 2426 Addresses", RFC 3879, DOI 10.17487/RFC3879, September 2427 2004, . 2429 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 2430 Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, 2431 December 2005, . 2433 [RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through 2434 Network Address Translations (NATs)", RFC 4380, 2435 DOI 10.17487/RFC4380, February 2006, 2436 . 2438 [RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery 2439 Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April 2440 2006, . 2442 [RFC4429] Moore, N., "Optimistic Duplicate Address Detection (DAD) 2443 for IPv6", RFC 4429, DOI 10.17487/RFC4429, April 2006, 2444 . 2446 [RFC4541] Christensen, M., Kimball, K., and F. Solensky, 2447 "Considerations for Internet Group Management Protocol 2448 (IGMP) and Multicast Listener Discovery (MLD) Snooping 2449 Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006, 2450 . 2452 [RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick, 2453 "Internet Group Management Protocol (IGMP) / Multicast 2454 Listener Discovery (MLD)-Based Multicast Forwarding 2455 ("IGMP/MLD Proxying")", RFC 4605, DOI 10.17487/RFC4605, 2456 August 2006, . 2458 [RFC4821] Mathis, M. and J. Heffner, "Packetization Layer Path MTU 2459 Discovery", RFC 4821, DOI 10.17487/RFC4821, March 2007, 2460 . 2462 [RFC4963] Heffner, J., Mathis, M., and B. Chandler, "IPv4 Reassembly 2463 Errors at High Data Rates", RFC 4963, 2464 DOI 10.17487/RFC4963, July 2007, 2465 . 2467 [RFC5175] Haberman, B., Ed. and R. Hinden, "IPv6 Router 2468 Advertisement Flags Option", RFC 5175, 2469 DOI 10.17487/RFC5175, March 2008, 2470 . 2472 [RFC5213] Gundavelli, S., Ed., Leung, K., Devarapalli, V., 2473 Chowdhury, K., and B. Patil, "Proxy Mobile IPv6", 2474 RFC 5213, DOI 10.17487/RFC5213, August 2008, 2475 . 2477 [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site 2478 Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, 2479 DOI 10.17487/RFC5214, March 2008, 2480 . 2482 [RFC5558] Templin, F., Ed., "Virtual Enterprise Traversal (VET)", 2483 RFC 5558, DOI 10.17487/RFC5558, February 2010, 2484 . 2486 [RFC5798] Nadas, S., Ed., "Virtual Router Redundancy Protocol (VRRP) 2487 Version 3 for IPv4 and IPv6", RFC 5798, 2488 DOI 10.17487/RFC5798, March 2010, 2489 . 2491 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 2492 (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, 2493 . 2495 [RFC6081] Thaler, D., "Teredo Extensions", RFC 6081, 2496 DOI 10.17487/RFC6081, January 2011, 2497 . 2499 [RFC6221] Miles, D., Ed., Ooghe, S., Dec, W., Krishnan, S., and A. 2500 Kavanagh, "Lightweight DHCPv6 Relay Agent", RFC 6221, 2501 DOI 10.17487/RFC6221, May 2011, 2502 . 2504 [RFC6355] Narten, T. and J. Johnson, "Definition of the UUID-Based 2505 DHCPv6 Unique Identifier (DUID-UUID)", RFC 6355, 2506 DOI 10.17487/RFC6355, August 2011, 2507 . 2509 [RFC6543] Gundavelli, S., "Reserved IPv6 Interface Identifier for 2510 Proxy Mobile IPv6", RFC 6543, DOI 10.17487/RFC6543, May 2511 2012, . 2513 [RFC7084] Singh, H., Beebee, W., Donley, C., and B. Stark, "Basic 2514 Requirements for IPv6 Customer Edge Routers", RFC 7084, 2515 DOI 10.17487/RFC7084, November 2013, 2516 . 2518 [RFC7421] Carpenter, B., Ed., Chown, T., Gont, F., Jiang, S., 2519 Petrescu, A., and A. Yourtchenko, "Analysis of the 64-bit 2520 Boundary in IPv6 Addressing", RFC 7421, 2521 DOI 10.17487/RFC7421, January 2015, 2522 . 2524 [RFC7526] Troan, O. and B. Carpenter, Ed., "Deprecating the Anycast 2525 Prefix for 6to4 Relay Routers", BCP 196, RFC 7526, 2526 DOI 10.17487/RFC7526, May 2015, 2527 . 2529 [RFC7542] DeKok, A., "The Network Access Identifier", RFC 7542, 2530 DOI 10.17487/RFC7542, May 2015, 2531 . 2533 [RFC7739] Gont, F., "Security Implications of Predictable Fragment 2534 Identification Values", RFC 7739, DOI 10.17487/RFC7739, 2535 February 2016, . 2537 [RFC7847] Melia, T., Ed. and S. Gundavelli, Ed., "Logical-Interface 2538 Support for IP Hosts with Multi-Access Support", RFC 7847, 2539 DOI 10.17487/RFC7847, May 2016, 2540 . 2542 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 2543 Writing an IANA Considerations Section in RFCs", BCP 26, 2544 RFC 8126, DOI 10.17487/RFC8126, June 2017, 2545 . 2547 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 2548 Decraene, B., Litkowski, S., and R. Shakir, "Segment 2549 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 2550 July 2018, . 2552 [RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J., 2553 Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header 2554 (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020, 2555 . 2557 [RFC8900] Bonica, R., Baker, F., Huston, G., Hinden, R., Troan, O., 2558 and F. Gont, "IP Fragmentation Considered Fragile", 2559 BCP 230, RFC 8900, DOI 10.17487/RFC8900, September 2020, 2560 . 2562 Appendix A. Interface Attribute Preferences Bitmap Encoding 2564 Adaptation of the OMNI option Interface Attributes Preferences Bitmap 2565 encoding to specific Internetworks such as the Aeronautical 2566 Telecommunications Network with Internet Protocol Services (ATN/IPS) 2567 may include link selection preferences based on other traffic 2568 classifiers (e.g., transport port numbers, etc.) in addition to the 2569 existing DSCP-based preferences. Nodes on specific Internetworks 2570 maintain a map of traffic classifiers to additional P[*] preference 2571 fields beyond the first 64. For example, TCP port 22 maps to P[67], 2572 TCP port 443 maps to P[70], UDP port 8060 maps to P[76], etc. 2574 Implementations use Simplex or Indexed encoding formats for P[*] 2575 encoding in order to encode a given set of traffic classifiers in the 2576 most efficient way. Some use cases may be more efficiently coded 2577 using Simplex form, while others may be more efficient using Indexed. 2578 Once a format is selected for preparation of a single Interface 2579 Attribute the same format must be used for the entire Interface 2580 Attribute sub-option. Different sub-options may use different 2581 formats. 2583 The following figures show coding examples for various Simplex and 2584 Indexed formats: 2586 0 1 2 3 2587 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 2588 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2589 | Sub-Type=2 | Sub-length=N | ifIndex | ifType | 2590 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2591 | Provider ID | Link |R| API | Bitmap(0)=0xff|P00|P01|P02|P03| 2592 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2593 |P04|P05|P06|P07|P08|P09|P10|P11|P12|P13|P14|P15|P16|P17|P18|P19| 2594 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2595 |P20|P21|P22|P23|P24|P25|P26|P27|P28|P29|P30|P31| Bitmap(1)=0xff| 2596 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2597 |P32|P33|P34|P35|P36|P37|P38|P39|P40|P41|P42|P43|P44|P45|P46|P47| 2598 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2599 |P48|P49|P50|P51|P52|P53|P54|P55|P56|P57|P58|P59|P60|P61|P62|P63| 2600 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2601 | Bitmap(2)=0xff|P64|P65|P67|P68| ... 2602 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 2604 Figure 19: Example 1: Dense Simplex Encoding 2606 0 1 2 3 2607 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 2608 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2609 | Sub-Type=2 | Sub-length=N | ifIndex | ifType | 2610 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2611 | Provider ID | Link |R| API | Bitmap(0)=0x00| Bitmap(1)=0x0f| 2612 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2613 |P48|P49|P50|P51|P52|P53|P54|P55|P56|P57|P58|P59|P60|P61|P62|P63| 2614 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2615 | Bitmap(2)=0x00| Bitmap(3)=0x00| Bitmap(4)=0x00| Bitmap(5)=0x00| 2616 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2617 | Bitmap(6)=0xf0|192|193|194|195|196|197|198|199|200|201|202|203| 2618 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2619 |204|205|206|207| Bitmap(7)=0x00| Bitmap(8)=0x0f|272|273|274|275| 2620 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2621 |276|277|278|279|280|281|282|283|284|285|286|287| Bitmap(9)=0x00| 2622 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2623 |Bitmap(10)=0x00| ... 2624 +-+-+-+-+-+-+-+-+-+-+- 2626 Figure 20: Example 2: Sparse Simplex Encoding 2628 0 1 2 3 2629 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 2630 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2631 | Sub-Type=2 | Sub-length=N | ifIndex | ifType | 2632 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2633 | Provider ID | Link |R| API | Index = 0x00 | Bitmap = 0x80 | 2634 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2635 |P00|P01|P02|P03| Index = 0x01 | Bitmap = 0x01 |P60|P61|P62|P63| 2636 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2637 | Index = 0x10 | Bitmap = 0x80 |512|513|514|515| Index = 0x18 | 2638 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2639 | Bitmap = 0x01 |796|797|798|799| ... 2640 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 2642 Figure 21: Example 3: Indexed Encoding 2644 Appendix B. VDL Mode 2 Considerations 2646 ICAO Doc 9776 is the "Technical Manual for VHF Data Link Mode 2" 2647 (VDLM2) that specifies an essential radio frequency data link service 2648 for aircraft and ground stations in worldwide civil aviation air 2649 traffic management. The VDLM2 link type is "multicast capable" 2650 [RFC4861], but with considerable differences from common multicast 2651 links such as Ethernet and IEEE 802.11. 2653 First, the VDLM2 link data rate is only 31.5Kbps - multiple orders of 2654 magnitude less than most modern wireless networking gear. Second, 2655 due to the low available link bandwidth only VDLM2 ground stations 2656 (i.e., and not aircraft) are permitted to send broadcasts, and even 2657 so only as compact layer 2 "beacons". Third, aircraft employ the 2658 services of ground stations by performing unicast RS/RA exchanges 2659 upon receipt of beacons instead of listening for multicast RA 2660 messages and/or sending multicast RS messages. 2662 This beacon-oriented unicast RS/RA approach is necessary to conserve 2663 the already-scarce available link bandwidth. Moreover, since the 2664 numbers of beaconing ground stations operating within a given spatial 2665 range must be kept as sparse as possible, it would not be feasible to 2666 have different classes of ground stations within the same region 2667 observing different protocols. It is therefore highly desirable that 2668 all ground stations observe a common language of RS/RA as specified 2669 in this document. 2671 Note that links of this nature may benefit from compression 2672 techniques that reduce the bandwidth necessary for conveying the same 2673 amount of data. The IETF lpwan working group is considering possible 2674 alternatives: [https://datatracker.ietf.org/wg/lpwan/documents]. 2676 Appendix C. MN / AR Isolation Through L2 Address Mapping 2678 Per [RFC4861], IPv6 ND messages may be sent to either a multicast or 2679 unicast link-scoped IPv6 destination address. However, IPv6 ND 2680 messaging should be coordinated between the MN and AR only without 2681 invoking other nodes on the ANET. This implies that MN / AR control 2682 messaging should be isolated and not overheard by other nodes on the 2683 link. 2685 To support MN / AR isolation on some ANET links, ARs can maintain an 2686 OMNI-specific unicast L2 address ("MSADDR"). For Ethernet-compatible 2687 ANETs, this specification reserves one Ethernet unicast address TBD2 2688 (see: Section 19). For non-Ethernet statically-addressed ANETs, 2689 MSADDR is reserved per the assigned numbers authority for the ANET 2690 addressing space. For still other ANETs, MSADDR may be dynamically 2691 discovered through other means, e.g., L2 beacons. 2693 MNs map the L3 addresses of all IPv6 ND messages they send (i.e., 2694 both multicast and unicast) to MSADDR instead of to an ordinary 2695 unicast or multicast L2 address. In this way, all of the MN's IPv6 2696 ND messages will be received by ARs that are configured to accept 2697 packets destined to MSADDR. Note that multiple ARs on the link could 2698 be configured to accept packets destined to MSADDR, e.g., as a basis 2699 for supporting redundancy. 2701 Therefore, ARs must accept and process packets destined to MSADDR, 2702 while all other devices must not process packets destined to MSADDR. 2703 This model has well-established operational experience in Proxy 2704 Mobile IPv6 (PMIP) [RFC5213][RFC6543]. 2706 Appendix D. Change Log 2708 << RFC Editor - remove prior to publication >> 2710 Differences from draft-templin-6man-omni-interface-35 to draft- 2711 templin-6man-omni-interface-36: 2713 o Major clarifications on aspects such as "hard/soft" PTB error 2714 messages 2716 o Made generic so that either IP protocol version (IPv4 or IPv6) can 2717 be used in the data plane. 2719 Differences from draft-templin-6man-omni-interface-31 to draft- 2720 templin-6man-omni-interface-32: 2722 o MTU 2724 o Support for multi-hop ANETS such as ISATAP. 2726 Differences from draft-templin-6man-omni-interface-29 to draft- 2727 templin-6man-omni-interface-30: 2729 o Moved link-layer addressing information into the OMNI option on a 2730 per-ifIndex basis 2732 o Renamed "ifIndex-tuple" to "Interface Attributes" 2734 Differences from draft-templin-6man-omni-interface-27 to draft- 2735 templin-6man-omni-interface-28: 2737 o Updates based on implementation expereince. 2739 Differences from draft-templin-6man-omni-interface-25 to draft- 2740 templin-6man-omni-interface-26: 2742 o Further clarification on "aggregate" RA messages. 2744 o Expanded Security Considerations to discuss expectations for 2745 security in the Mobility Service. 2747 Differences from draft-templin-6man-omni-interface-20 to draft- 2748 templin-6man-omni-interface-21: 2750 o Safety-Based Multilink (SBM) and Performance-Based Multilink 2751 (PBM). 2753 Differences from draft-templin-6man-omni-interface-18 to draft- 2754 templin-6man-omni-interface-19: 2756 o SEND/CGA. 2758 Differences from draft-templin-6man-omni-interface-17 to draft- 2759 templin-6man-omni-interface-18: 2761 o Teredo 2763 Differences from draft-templin-6man-omni-interface-14 to draft- 2764 templin-6man-omni-interface-15: 2766 o Prefix length discussions removed. 2768 Differences from draft-templin-6man-omni-interface-12 to draft- 2769 templin-6man-omni-interface-13: 2771 o Teredo 2773 Differences from draft-templin-6man-omni-interface-11 to draft- 2774 templin-6man-omni-interface-12: 2776 o Major simplifications and clarifications on MTU and fragmentation. 2778 o Document now updates RFC4443 and RFC8201. 2780 Differences from draft-templin-6man-omni-interface-10 to draft- 2781 templin-6man-omni-interface-11: 2783 o Removed /64 assumption, resulting in new OMNI address format. 2785 Differences from draft-templin-6man-omni-interface-07 to draft- 2786 templin-6man-omni-interface-08: 2788 o OMNI MNs in the open Internet 2790 Differences from draft-templin-6man-omni-interface-06 to draft- 2791 templin-6man-omni-interface-07: 2793 o Brought back L2 MSADDR mapping text for MN / AR isolation based on 2794 L2 addressing. 2796 o Expanded "Transition Considerations". 2798 Differences from draft-templin-6man-omni-interface-05 to draft- 2799 templin-6man-omni-interface-06: 2801 o Brought back OMNI option "R" flag, and discussed its use. 2803 Differences from draft-templin-6man-omni-interface-04 to draft- 2804 templin-6man-omni-interface-05: 2806 o Transition considerations, and overhaul of RS/RA addressing with 2807 the inclusion of MSE addresses within the OMNI option instead of 2808 as RS/RA addresses (developed under FAA SE2025 contract number 2809 DTFAWA-15-D-00030). 2811 Differences from draft-templin-6man-omni-interface-02 to draft- 2812 templin-6man-omni-interface-03: 2814 o Added "advisory PTB messages" under FAA SE2025 contract number 2815 DTFAWA-15-D-00030. 2817 Differences from draft-templin-6man-omni-interface-01 to draft- 2818 templin-6man-omni-interface-02: 2820 o Removed "Primary" flag and supporting text. 2822 o Clarified that "Router Lifetime" applies to each ANET interface 2823 independently, and that the union of all ANET interface Router 2824 Lifetimes determines MSE lifetime. 2826 Differences from draft-templin-6man-omni-interface-00 to draft- 2827 templin-6man-omni-interface-01: 2829 o "All-MSEs" OMNI LLA defined. Also reserved fe80::ff00:0000/104 2830 for future use (most likely as "pseudo-multicast"). 2832 o Non-normative discussion of alternate OMNI LLA construction form 2833 made possible if the 64-bit assumption were relaxed. 2835 First draft version (draft-templin-atn-aero-interface-00): 2837 o Draft based on consensus decision of ICAO Working Group I Mobility 2838 Subgroup March 22, 2019. 2840 Authors' Addresses 2841 Fred L. Templin (editor) 2842 The Boeing Company 2843 P.O. Box 3707 2844 Seattle, WA 98124 2845 USA 2847 Email: fltemplin@acm.org 2849 Tony Whyman 2850 MWA Ltd c/o Inmarsat Global Ltd 2851 99 City Road 2852 London EC1Y 1AX 2853 England 2855 Email: tony.whyman@mccallumwhyman.com