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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 February 4, 2021 7 Expires: August 8, 2021 9 Transmission of IP Packets over Overlay Multilink Network (OMNI) 10 Interfaces 11 draft-templin-6man-omni-interface-76 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 August 8, 2021. 41 Copyright Notice 43 Copyright (c) 2021 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 . . . . . . . . . . . . . . . . . . . . . . . . . 5 60 3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 9 61 4. Overlay Multilink Network (OMNI) Interface Model . . . . . . 9 62 5. The OMNI Adaptation Layer (OAL) . . . . . . . . . . . . . . . 14 63 5.1. Fragmentation Security Implications . . . . . . . . . . . 19 64 5.2. OAL "Super-Packet" Packing . . . . . . . . . . . . . . . 20 65 6. Frame Format . . . . . . . . . . . . . . . . . . . . . . . . 22 66 7. Link-Local Addresses (LLAs) . . . . . . . . . . . . . . . . . 22 67 8. Unique-Local Addresses (ULAs) . . . . . . . . . . . . . . . . 23 68 9. Global Unicast Addresses (GUAs) . . . . . . . . . . . . . . . 25 69 10. Node Identification . . . . . . . . . . . . . . . . . . . . . 26 70 11. Address Mapping - Unicast . . . . . . . . . . . . . . . . . . 26 71 11.1. Sub-Options . . . . . . . . . . . . . . . . . . . . . . 28 72 11.1.1. Pad1 . . . . . . . . . . . . . . . . . . . . . . . . 30 73 11.1.2. PadN . . . . . . . . . . . . . . . . . . . . . . . . 30 74 11.1.3. Interface Attributes (Type 1) . . . . . . . . . . . 30 75 11.1.4. Interface Attributes (Type 2) . . . . . . . . . . . 32 76 11.1.5. Traffic Selector . . . . . . . . . . . . . . . . . . 36 77 11.1.6. MS-Register . . . . . . . . . . . . . . . . . . . . 36 78 11.1.7. MS-Release . . . . . . . . . . . . . . . . . . . . . 37 79 11.1.8. Geo Coordinates . . . . . . . . . . . . . . . . . . 38 80 11.1.9. Dynamic Host Configuration Protocol for IPv6 81 (DHCPv6) Message . . . . . . . . . . . . . . . . . . 38 82 11.1.10. Host Identity Protocol (HIP) Message . . . . . . . . 39 83 11.1.11. Node Identification . . . . . . . . . . . . . . . . 40 84 11.1.12. Sub-Type Extension . . . . . . . . . . . . . . . . . 41 85 12. Address Mapping - Multicast . . . . . . . . . . . . . . . . . 43 86 13. Multilink Conceptual Sending Algorithm . . . . . . . . . . . 43 87 13.1. Multiple OMNI Interfaces . . . . . . . . . . . . . . . . 44 88 13.2. MN<->AR Traffic Loop Prevention . . . . . . . . . . . . 45 89 14. Router Discovery and Prefix Registration . . . . . . . . . . 45 90 14.1. Router Discovery in IP Multihop and IPv4-Only Networks . 49 91 14.2. MS-Register and MS-Release List Processing . . . . . . . 51 92 14.3. DHCPv6-based Prefix Registration . . . . . . . . . . . . 53 93 15. Secure Redirection . . . . . . . . . . . . . . . . . . . . . 54 94 16. AR and MSE Resilience . . . . . . . . . . . . . . . . . . . . 54 95 17. Detecting and Responding to MSE Failures . . . . . . . . . . 54 96 18. Transition Considerations . . . . . . . . . . . . . . . . . . 55 97 19. OMNI Interfaces on Open Internetworks . . . . . . . . . . . . 56 98 20. Time-Varying MNPs . . . . . . . . . . . . . . . . . . . . . . 57 99 21. (H)HITs and Temporary ULAs . . . . . . . . . . . . . . . . . 57 100 22. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 58 101 23. Security Considerations . . . . . . . . . . . . . . . . . . . 60 102 24. Implementation Status . . . . . . . . . . . . . . . . . . . . 61 103 25. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 61 104 26. References . . . . . . . . . . . . . . . . . . . . . . . . . 62 105 26.1. Normative References . . . . . . . . . . . . . . . . . . 62 106 26.2. Informative References . . . . . . . . . . . . . . . . . 64 107 Appendix A. Interface Attribute Preferences Bitmap Encoding . . 70 108 Appendix B. VDL Mode 2 Considerations . . . . . . . . . . . . . 72 109 Appendix C. MN / AR Isolation Through L2 Address Mapping . . . . 73 110 Appendix D. Change Log . . . . . . . . . . . . . . . . . . . . . 73 111 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 76 113 1. Introduction 115 Mobile Nodes (MNs) (e.g., aircraft of various configurations, 116 terrestrial vehicles, seagoing vessels, enterprise wireless devices, 117 pedestrians with cellphones, etc.) often have multiple interface 118 connections to wireless and/or wired-link data links used for 119 communicating with networked correspondents. These data links may 120 have diverse performance, cost and availability properties that can 121 change dynamically according to mobility patterns, flight phases, 122 proximity to infrastructure, etc. MNs coordinate their data links in 123 a discipline known as "multilink", in which a single virtual 124 interface is configured over the node's underlying interface 125 connections to the data links. 127 The MN configures a virtual interface (termed the "Overlay Multilink 128 Network (OMNI) interface") as a thin layer over the underlying 129 interfaces. The OMNI interface is therefore the only interface 130 abstraction exposed to the IP layer and behaves according to the Non- 131 Broadcast, Multiple Access (NBMA) interface principle, while 132 underlying interfaces appear as link layer communication channels in 133 the architecture. The OMNI interface connects to a virtual overlay 134 service known as the "OMNI link". The OMNI link spans one or more 135 Internetworks that may include private-use infrastructures and/or the 136 global public Internet itself. 138 Each MN receives a Mobile Network Prefix (MNP) for numbering 139 downstream-attached End User Networks (EUNs) independently of the 140 access network data links selected for data transport. The MN 141 performs router discovery over the OMNI interface (i.e., similar to 142 IPv6 customer edge routers [RFC7084]) and acts as a mobile router on 143 behalf of its EUNs. The router discovery process is iterated over 144 each of the OMNI interface's underlying interfaces in order to 145 register per-link parameters (see Section 14). 147 The OMNI interface provides a multilink nexus for exchanging inbound 148 and outbound traffic via the correct underlying interface(s). The IP 149 layer sees the OMNI interface as a point of connection to the OMNI 150 link. Each OMNI link has one or more associated Mobility Service 151 Prefixes (MSPs), which are typically IP Global Unicast Address (GUA) 152 prefixes from which OMNI link MNPs are derived. If there are 153 multiple OMNI links, the IPv6 layer will see multiple OMNI 154 interfaces. 156 MNs may connect to multiple distinct OMNI links within the same OMNI 157 domain by configuring multiple OMNI interfaces, e.g., omni0, omni1, 158 omni2, etc. Each OMNI interface is configured over a set of 159 underlying interfaces and provides a nexus for Safety-Based Multilink 160 (SBM) operation. Each OMNI interface within the same OMNI domain 161 configures a common ULA prefix [ULA]::/48, and configures a unique 162 16-bit Subnet ID '*' to construct the sub-prefix [ULA*]::/64 (see: 163 Section 8). The IP layer applies SBM routing to select an OMNI 164 interface, which then applies Performance-Based Multilink (PBM) to 165 select the correct underlying interface. Applications can apply 166 Segment Routing [RFC8402] to select independent SBM topologies for 167 fault tolerance. 169 The OMNI interface interacts with a network-based Mobility Service 170 (MS) through IPv6 Neighbor Discovery (ND) control message exchanges 171 [RFC4861]. The MS provides Mobility Service Endpoints (MSEs) that 172 track MN movements and represent their MNPs in a global routing or 173 mapping system. 175 Many OMNI use cases have been proposed. In particular, the 176 International Civil Aviation Organization (ICAO) Working Group-I 177 Mobility Subgroup is developing a future Aeronautical 178 Telecommunications Network with Internet Protocol Services (ATN/IPS) 179 and has issued a liaison statement requesting IETF adoption [ATN] in 180 support of ICAO Document 9896 [ATN-IPS]. The IETF IP Wireless Access 181 in Vehicular Environments (ipwave) working group has further included 182 problem statement and use case analysis for OMNI in a document now in 183 AD evaluation for RFC publication 184 [I-D.ietf-ipwave-vehicular-networking]. Still other communities of 185 interest include AEEC, RTCA Special Committee 228 (SC-228) and NASA 186 programs that examine commercial aviation, Urban Air Mobility (UAM) 187 and Unmanned Air Systems (UAS). Pedestrians with handheld devices 188 represent another large class of potential OMNI users. 190 This document specifies the transmission of IP packets and MN/MS 191 control messages over OMNI interfaces. The OMNI interface supports 192 either IP protocol version (i.e., IPv4 [RFC0791] or IPv6 [RFC8200]) 193 as the network layer in the data plane, while using IPv6 ND messaging 194 as the control plane independently of the data plane IP protocol(s). 195 The OMNI Adaptation Layer (OAL) which operates as a mid-layer between 196 L3 and L2 is based on IP-in-IPv6 encapsulation per [RFC2473] as 197 discussed in the following sections. OMNI interfaces enable 198 multilink, mobility, multihop and multicast services, with provisions 199 for both Vehicle-to-Infrastructure (V2I) communications and Vehicle- 200 to-Vehicle (V2V) communications outside the context of 201 infrastructure. 203 2. Terminology 205 The terminology in the normative references applies; especially, the 206 terms "link" and "interface" are the same as defined in the IPv6 207 [RFC8200] and IPv6 Neighbor Discovery (ND) [RFC4861] specifications. 208 Additionally, this document assumes the following IPv6 ND message 209 types: Router Solicitation (RS), Router Advertisement (RA), Neighbor 210 Solicitation (NS), Neighbor Advertisement (NA) and Redirect. 212 The Protocol Constants defined in Section 10 of [RFC4861] are used in 213 their same format and meaning in this document. The terms "All- 214 Routers multicast", "All-Nodes multicast" and "Subnet-Router anycast" 215 are the same as defined in [RFC4291] (with Link-Local scope assumed). 217 The term "IP" is used to refer collectively to either Internet 218 Protocol version (i.e., IPv4 [RFC0791] or IPv6 [RFC8200]) when a 219 specification at the layer in question applies equally to either 220 version. 222 The following terms are defined within the scope of this document: 224 Mobile Node (MN) 225 an end system with a mobile router having multiple distinct 226 upstream data link connections that are grouped together in one or 227 more logical units. The MN's data link connection parameters can 228 change over time due to, e.g., node mobility, link quality, etc. 229 The MN further connects a downstream-attached End User Network 230 (EUN). The term MN used here is distinct from uses in other 231 documents, and does not imply a particular mobility protocol. 233 End User Network (EUN) 234 a simple or complex downstream-attached mobile network that 235 travels with the MN as a single logical unit. The IP addresses 236 assigned to EUN devices remain stable even if the MN's upstream 237 data link connections change. 239 Mobility Service (MS) 240 a mobile routing service that tracks MN movements and ensures that 241 MNs remain continuously reachable even across mobility events. 242 Specific MS details are out of scope for this document. 244 Mobility Service Endpoint (MSE) 245 an entity in the MS (either singular or aggregate) that 246 coordinates the mobility events of one or more MN. 248 Mobility Service Prefix (MSP) 249 an aggregated IP Global Unicast Address (GUA) prefix (e.g., 250 2001:db8::/32, 192.0.2.0/24, etc.) assigned to the OMNI link and 251 from which more-specific Mobile Network Prefixes (MNPs) are 252 delegated. OMNI link administrators typically obtain MSPs from an 253 Internet address registry, however private-use prefixes can 254 alternatively be used subject to certain limitations (see: 255 Section 9). OMNI links that connect to the global Internet 256 advertise their MSPs to their interdomain routing peers. 258 Mobile Network Prefix (MNP) 259 a longer IP prefix delegated from an MSP (e.g., 260 2001:db8:1000:2000::/56, 192.0.2.8/30, etc.) and assigned to a MN. 261 MNs sub-delegate the MNP to devices located in EUNs. 263 Access Network (ANET) 264 a data link service network (e.g., an aviation radio access 265 network, satellite service provider network, cellular operator 266 network, WiFi network, etc.) that connects MNs. Physical and/or 267 data link level security is assumed, and sometimes referred to as 268 "protected spectrum". Private enterprise networks and ground 269 domain aviation service networks may provide multiple secured IP 270 hops between the MN's point of connection and the nearest Access 271 Router. 273 Access Router (AR) 274 a router in the ANET for connecting MNs to correspondents in 275 outside Internetworks. The AR may be located on the same physical 276 link as the MN, or may be located multiple IP hops away. In the 277 latter case, the MN uses encapsulation to communicate with the AR 278 as though it were on the same physical link. 280 ANET interface 281 a MN's attachment to a link in an ANET. 283 Internetwork (INET) 284 a connected network region with a coherent IP addressing plan that 285 provides transit forwarding services between ANETs and nodes that 286 connect directly to the open INET via unprotected media. No 287 physical and/or data link level security is assumed, therefore 288 security must be applied by upper layers. The global public 289 Internet itself is an example. 291 INET interface 292 a node's attachment to a link in an INET. 294 *NET 295 a "wildcard" term used when a given specification applies equally 296 to both ANET and INET cases. 298 OMNI link 299 a Non-Broadcast, Multiple Access (NBMA) virtual overlay configured 300 over one or more INETs and their connected ANETs. An OMNI link 301 can comprise multiple INET segments joined by bridges the same as 302 for any link; the addressing plans in each segment may be mutually 303 exclusive and managed by different administrative entities. 305 OMNI interface 306 a node's attachment to an OMNI link, and configured over one or 307 more underlying *NET interfaces. If there are multiple OMNI links 308 in an OMNI domain, a separate OMNI interface is configured for 309 each link. 311 OMNI Adaptation Layer (OAL) 312 an OMNI interface process whereby packets admitted into the 313 interface are wrapped in a mid-layer IPv6 header and fragmented/ 314 reassembled if necessary to support the OMNI link Maximum 315 Transmission Unit (MTU). The OAL is also responsible for 316 generating MTU-related control messages as necessary, and for 317 providing addressing context for spanning multiple segments of a 318 bridged OMNI link. 320 OMNI Option 321 an IPv6 Neighbor Discovery option providing multilink parameters 322 for the OMNI interface as specified in Section 11. 324 Mobile Network Prefix Link Local Address (MNP-LLA) 325 an IPv6 Link Local Address that embeds the most significant 64 326 bits of an MNP in the lower 64 bits of fe80::/64, as specified in 327 Section 7. 329 Mobile Network Prefix Unique Local Address (MNP-ULA) 330 an IPv6 Unique-Local Address derived from an MNP-LLA. 332 Administrative Link Local Address (ADM-LLA) 333 an IPv6 Link Local Address that embeds a 32-bit administratively- 334 assigned identification value in the lower 32 bits of fe80::/96, 335 as specified in Section 7. 337 Administrative Unique Local Address (ADM-ULA) 338 an IPv6 Unique-Local Address derived from an ADM-LLA. 340 Multilink 341 an OMNI interface's manner of managing diverse underlying 342 interface connections to data links as a single logical unit. The 343 OMNI interface provides a single unified interface to upper 344 layers, while underlying interface selections are performed on a 345 per-packet basis considering factors such as DSCP, flow label, 346 application policy, signal quality, cost, etc. Multilinking 347 decisions are coordinated in both the outbound (i.e. MN to 348 correspondent) and inbound (i.e., correspondent to MN) directions. 350 Multihop 351 an iterative relaying of IP packets between MNs over an OMNI 352 underlying interface technology (such as omnidirectional wireless) 353 without support of fixed infrastructure. Multihop services entail 354 node-to-node relaying within a Mobile/Vehicular Ad-hoc Network 355 (MANET/VANET) for MN-to-MN communications and/or for "range 356 extension" where MNs within range of communications infrastructure 357 elements provide forwarding services for other MNs. 359 L2 360 The second layer in the OSI network model. Also known as "layer- 361 2", "link-layer", "sub-IP layer", "data link layer", etc. 363 L3 364 The third layer in the OSI network model. Also known as "layer- 365 3", "network-layer", "IP layer", etc. 367 underlying interface 368 a *NET interface over which an OMNI interface is configured. The 369 OMNI interface is seen as a L3 interface by the IP layer, and each 370 underlying interface is seen as a L2 interface by the OMNI 371 interface. The underlying interface either connects directly to 372 the physical communications media or coordinates with another node 373 where the physical media is hosted. 375 Mobility Service Identification (MSID) 376 Each MSE and AR is assigned a unique 32-bit Identification (MSID) 377 (see: Section 7). IDs are assigned according to MS-specific 378 guidelines (e.g., see: [I-D.templin-intarea-6706bis]). 380 Safety-Based Multilink (SBM) 381 A means for ensuring fault tolerance through redundancy by 382 connecting multiple affiliated OMNI interfaces to independent 383 routing topologies (i.e., multiple independent OMNI links). 385 Performance Based Multilink (PBM) 386 A means for selecting underlying interface(s) for packet 387 transmission and reception within a single OMNI interface. 389 OMNI Domain 390 The set of all SBM/PBM OMNI links that collectively provides 391 services for a common set of MSPs. Each OMNI domain consists of a 392 set of affiliated OMNI links that all configure the same ::/48 ULA 393 prefix with a unique 16-bit Subnet ID as discussed in Section 8. 395 3. Requirements 397 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 398 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 399 "OPTIONAL" in this document are to be interpreted as described in BCP 400 14 [RFC2119][RFC8174] when, and only when, they appear in all 401 capitals, as shown here. 403 An implementation is not required to internally use the architectural 404 constructs described here so long as its external behavior is 405 consistent with that described in this document. 407 4. Overlay Multilink Network (OMNI) Interface Model 409 An OMNI interface is a MN virtual interface configured over one or 410 more underlying interfaces, which may be physical (e.g., an 411 aeronautical radio link) or virtual (e.g., an Internet or higher- 412 layer "tunnel"). The MN receives a MNP from the MS, and coordinates 413 with the MS through IPv6 ND message exchanges. The MN uses the MNP 414 to construct a unique Link-Local Address (MNP-LLA) through the 415 algorithmic derivation specified in Section 7 and assigns the LLA to 416 the OMNI interface. 418 The OMNI interface architectural layering model is the same as in 419 [RFC5558][RFC7847], and augmented as shown in Figure 1. The IP layer 420 therefore sees the OMNI interface as a single L3 interface with 421 multiple underlying interfaces that appear as L2 communication 422 channels in the architecture. 424 +----------------------------+ 425 | Upper Layer Protocol | 426 Session-to-IP +---->| | 427 Address Binding | +----------------------------+ 428 +---->| IP (L3) | 429 IP Address +---->| | 430 Binding | +----------------------------+ 431 +---->| OMNI Interface | 432 Logical-to- +---->| (LLA) | 433 Physical | +----------------------------+ 434 Interface +---->| L2 | L2 | | L2 | 435 Binding |(IF#1)|(IF#2)| ..... |(IF#n)| 436 +------+------+ +------+ 437 | L1 | L1 | | L1 | 438 | | | | | 439 +------+------+ +------+ 441 Figure 1: OMNI Interface Architectural Layering Model 443 Each underlying interface provides an L2/L1 abstraction according to 444 one of the following models: 446 o INET interfaces connect to an INET either natively or through one 447 or several IPv4 Network Address Translators (NATs). Native INET 448 interfaces have global IP addresses that are reachable from any 449 INET correspondent. NATed INET interfaces typically have private 450 IP addresses and connect to a private network behind one or more 451 NATs that provide INET access. 453 o ANET interfaces connect to a protected ANET that is separated from 454 the open INET by an AR acting as a proxy. The ANET interface may 455 be either on the same L2 link segment as the AR, or separated from 456 the AR by multiple IP hops. 458 o VPNed interfaces use security encapsulation over a *NET to a 459 Virtual Private Network (VPN) gateway. Other than the link-layer 460 encapsulation format, VPNed interfaces behave the same as for 461 Direct interfaces. 463 o Direct (aka "point-to-point") interfaces connect directly to a 464 peer without crossing any *NET paths. An example is a line-of- 465 sight link between a remote pilot and an unmanned aircraft. 467 The OMNI virtual interface model gives rise to a number of 468 opportunities: 470 o since MNP-LLAs are uniquely derived from an MNP, no Duplicate 471 Address Detection (DAD) or Multicast Listener Discovery (MLD) 472 messaging is necessary. 474 o since Temporary ULAs are statistically unique, they can be used 475 without DAD, e.g. for MN-to-MN communications until an MNP-LLA is 476 obtained. 478 o *NET interfaces on the same L2 link segment as an AR do not 479 require any L3 addresses (i.e., not even link-local) in 480 environments where communications are coordinated entirely over 481 the OMNI interface. (An alternative would be to also assign the 482 same LLA to all *NET interfaces.) 484 o as underlying interface properties change (e.g., link quality, 485 cost, availability, etc.), any active interface can be used to 486 update the profiles of multiple additional interfaces in a single 487 message. This allows for timely adaptation and service continuity 488 under dynamically changing conditions. 490 o coordinating underlying interfaces in this way allows them to be 491 represented in a unified MS profile with provisions for mobility 492 and multilink operations. 494 o exposing a single virtual interface abstraction to the IPv6 layer 495 allows for multilink operation (including QoS based link 496 selection, packet replication, load balancing, etc.) at L2 while 497 still permitting L3 traffic shaping based on, e.g., DSCP, flow 498 label, etc. 500 o the OMNI interface allows inter-INET traversal when nodes located 501 in different INETs need to communicate with one another. This 502 mode of operation would not be possible via direct communications 503 over the underlying interfaces themselves. 505 o the OMNI Adaptation Layer (OAL) within the OMNI interface supports 506 lossless and adaptive path MTU mitigations not available for 507 communications directly over the underlying interfaces themselves. 508 The OAL supports "packing" of multiple IP payload packets within a 509 single OAL packet. 511 o L3 sees the OMNI interface as a point of connection to the OMNI 512 link; if there are multiple OMNI links (i.e., multiple MS's), L3 513 will see multiple OMNI interfaces. 515 o Multiple independent OMNI interfaces can be used for increased 516 fault tolerance through Safety-Based Multilink (SBM), with 517 Performance-Based Multilink (PBM) applied within each interface. 519 Other opportunities are discussed in [RFC7847]. Note that even when 520 the OMNI virtual interface is present, applications can still access 521 underlying interfaces either through the network protocol stack using 522 an Internet socket or directly using a raw socket. This allows for 523 intra-network (or point-to-point) communications without invoking the 524 OMNI interface and/or OAL. For example, when an IPv6 OMNI interface 525 is configured over an underlying IPv4 interface, applications can 526 still invoke IPv4 intra-network communications as long as the 527 communicating endpoints are not subject to mobility dynamics. 528 However, the opportunities discussed above are not available when the 529 architectural layering is bypassed in this way. 531 Figure 2 depicts the architectural model for a MN with an attached 532 EUN connecting to the MS via multiple independent *NETs. When an 533 underlying interface becomes active, the MN's OMNI interface sends 534 IPv6 ND messages without encapsulation if the first-hop Access Router 535 (AR) is on the same underlying link; otherwise, the interface uses 536 IP-in-IP encapsulation. The IPv6 ND messages traverse the ground 537 domain *NETs until they reach an AR (AR#1, AR#2, ..., AR#n), which 538 then coordinates with an INET Mobility Service Endpoint (MSE#1, 539 MSE#2, ..., MSE#m) and returns an IPv6 ND message response to the MN. 540 The Hop Limit in IPv6 ND messages is not decremented due to 541 encapsulation; hence, the OMNI interface appears to be attached to an 542 ordinary link. 544 +--------------+ (:::)-. 545 | MN |<-->.-(::EUN:::) 546 +--------------+ `-(::::)-' 547 |OMNI interface| 548 +----+----+----+ 549 +--------|IF#1|IF#2|IF#n|------ + 550 / +----+----+----+ \ 551 / | \ 552 / | \ 553 v v v 554 (:::)-. (:::)-. (:::)-. 555 .-(::*NET:::) .-(::*NET:::) .-(::*NET:::) 556 `-(::::)-' `-(::::)-' `-(::::)-' 557 +----+ +----+ +----+ 558 ... |AR#1| .......... |AR#2| ......... |AR#n| ... 559 . +-|--+ +-|--+ +-|--+ . 560 . | | | 561 . v v v . 562 . <----- INET Encapsulation -----> . 563 . . 564 . +-----+ (:::)-. . 565 . |MSE#2| .-(::::::::) +-----+ . 566 . +-----+ .-(::: INET :::)-. |MSE#m| . 567 . (::::: Routing ::::) +-----+ . 568 . `-(::: System :::)-' . 569 . +-----+ `-(:::::::-' . 570 . |MSE#1| +-----+ +-----+ . 571 . +-----+ |MSE#3| |MSE#4| . 572 . +-----+ +-----+ . 573 . . 574 . . 575 . <----- Worldwide Connected Internetwork ----> . 576 ........................................................... 578 Figure 2: MN/MS Coordination via Multiple *NETs 580 After the initial IPv6 ND message exchange, the MN (and/or any nodes 581 on its attached EUNs) can send and receive IP data packets over the 582 OMNI interface. OMNI interface multilink services will forward the 583 packets via ARs in the correct underlying *NETs. The AR encapsulates 584 the packets according to the capabilities provided by the MS and 585 forwards them to the next hop within the worldwide connected 586 Internetwork via optimal routes. 588 OMNI links span one or more underlying Internetwork via the OMNI 589 Adaptation Layer (OAL) which is based on a mid-layer overlay 590 encapsulation using [RFC2473]. Each OMNI link corresponds to a 591 different overlay (differentiated by an address codepoint) which may 592 be carried over a completely separate underlying topology. Each MN 593 can facilitate SBM by connecting to multiple OMNI links using a 594 distinct OMNI interface for each link. 596 Note: OMNI interface underlying interfaces often connect directly to 597 physical media on the local platform (e.g., a laptop computer with 598 WiFi, etc.), but in some configurations the physical media may be 599 hosted on a separate Local Area Network (LAN) node. In that case, 600 the OMNI interface can establish a Layer-2 VLAN or a point-to-point 601 tunnel (at a layer below the underlying interface) to the node 602 hosting the physical media. The OMNI interface may also apply 603 encapsulation at a layer above the underlying interface such that 604 packets would appear "double-encapsulated" on the LAN; the node 605 hosting the physical media in turn removes the LAN encapsulation 606 prior to transmission or inserts it following reception. Finally, 607 the underlying interface must monitor the node hosting the physical 608 media (e.g., through periodic keepalives) so that it can convey 609 up/down/status information to the OMNI interface. 611 5. The OMNI Adaptation Layer (OAL) 613 The OMNI interface observes the link nature of tunnels, including the 614 Maximum Transmission Unit (MTU), Maximum Reassembly Unit (MRU) and 615 the role of fragmentation and reassembly [I-D.ietf-intarea-tunnels]. 616 The OMNI interface is configured over one or more underlying 617 interfaces that may have diverse MTUs. OMNI interfaces accommodate 618 MTU diversity through the use of the OMNI Adaptation Layer (OAL) as 619 discussed in this section. 621 IPv6 underlying interfaces are REQUIRED to configure a minimum MTU of 622 1280 bytes and a minimum MRU of 1500 bytes [RFC8200]. Therefore, the 623 minimum IPv6 path MTU is 1280 bytes since routers on the path are not 624 permitted to perform network fragmentation even though the 625 destination is required to reassemble more. The network therefore 626 MUST forward packets of at least 1280 bytes without generating an 627 IPv6 Path MTU Discovery (PMTUD) Packet Too Big (PTB) message 628 [RFC8201]. (Note: the source can apply "source fragmentation" for 629 locally-generated IPv6 packets up to 1500 bytes and larger still if 630 it if has a way to determine that the destination configures a larger 631 MRU, but this does not affect the minimum IPv6 path MTU.) 633 IPv4 underlying interfaces are REQUIRED to configure a minimum MTU of 634 68 bytes [RFC0791] and a minimum MRU of 576 bytes [RFC0791][RFC1122]. 635 Therefore, when the Don't Fragment (DF) bit in the IPv4 header is set 636 to 0 the minimum IPv4 path MTU is 576 bytes since routers on the path 637 support network fragmentation and the destination is required to 638 reassemble at least that much. The "Don't Fragment" (DF) bit in the 639 IPv4 encapsulation headers of packets sent over IPv4 underlying 640 interfaces therefore MUST be set to 0. (Note: even if the 641 encapsulation source has a way to determine that the encapsulation 642 destination configures an MRU larger than 576 bytes, it should not 643 assume a larger minimum IPv4 path MTU without careful consideration 644 of the issues discussed in Section 5.1.) 646 In network paths where IPv6/IPv4 protocol translation or IPv6-in-IPv4 647 encapsulation may be prevalent, it may be prudent for the OAL to 648 always assume the IPv4 minimum path MTU (i.e., 576 bytes) regardless 649 of the underlying interface IP protocol version. By always assuming 650 the IPv4 minimum path MTU even for IPv6 underlying interfaces, the 651 OAL may produce smaller fragments and additional header overhead but 652 will always interoperate and never run the risk of presenting a 653 destination interface with a packet that exceeds its MRU. 655 The OMNI interface configures both an MTU and MRU of 9180 bytes 656 [RFC2492]; the size is therefore not a reflection of the underlying 657 interface MTUs, but rather determines the largest packet the OMNI 658 interface can forward or reassemble. The OMNI interface uses the 659 OMNI Adaptation Layer (OAL) to admit packets from the network layer 660 that are no larger than the OMNI interface MTU while generating 661 ICMPv4 Fragmentation Needed [RFC1191] or ICMPv6 Path MTU Discovery 662 (PMTUD) Packet Too Big (PTB) [RFC8201] messages as necessary. This 663 document refers to both of these ICMPv4/ICMPv6 message types simply 664 as "PTBs", and introduces a distinction between PTB "hard" and "soft" 665 errors as discussed below. 667 For IPv4 packets with DF=0, the network layer performs IPv4 668 fragmentation if necessary then admits the packets/fragments into the 669 OMNI interface; these fragments will be reassembled by the final 670 destination. For IPv4 packets with DF=1 and IPv6 packets, the 671 network layer admits the packet if it is no larger than the OMNI 672 interface MTU; otherwise, it drops the packet and returns a PTB hard 673 error message to the source. 675 For each admitted IP packet/fragment, the OMNI interface internally 676 employs the OAL when necessary by encapsulating the inner IP packet/ 677 fragment in a mid-layer IPv6 header per [RFC2473] before adding any 678 outer IP encapsulations. (The OAL does not decrement the inner IP 679 Hop Limit/TTL during encapsulation since the insertion occurs at a 680 layer below IP forwarding.) If the OAL packet will itself require 681 fragmentation, the OMNI interface then calculates the 32-bit CRC over 682 the entire mid-layer packet and writes the value in a trailing field 683 at the end of the packet. Next, the OAL fragments this mid-layer 684 IPv6 packet, forwards the fragments (using *NET encapsulation if 685 necessary), and returns an internally-generated PTB soft error 686 message (subject to rate limiting) if it deems the packet too large 687 according to factors such as link performance characteristics, 688 reassembly congestion, etc. This ensures that the path MTU is 689 adaptive and reflects the current path used for a given data flow. 691 The OAL operates with respect to both the minimum IPv6 and IPv4 path 692 MTUs as follows: 694 o When an OMNI interface sends a packet toward a final destination 695 via an ANET peer, it sends without OAL encapsulation if the packet 696 (including any outer-layer ANET encapsulations) is no larger than 697 the underlying interface MTU for on-link ANET peers or the minimum 698 ANET path MTU for peers separated by multiple IP hops. Otherwise, 699 the OAL inserts an IPv6 header per [RFC2473] with source address 700 set to the node's own Unique-Local Address (ULA) (see: Section 8) 701 and destination set to either the Administrative ULA (ADM-ULA) of 702 the ANET peer or the Mobile Network Prefix ULA (MNP-ULA) 703 corresponding to the final destination (see below). The OAL then 704 calculates and appends the trailing 32-bit CRC, then uses IPv6 705 fragmentation to break the packet into a minimum number of non- 706 overlapping fragments where the size of each non-final fragment 707 (including both the OMNI and any outer-layer ANET encapsulations) 708 is determined by the underlying interface MTU for on-link ANET 709 peers or the minimum ANET path MTU for peers separated by multiple 710 IP hops. The OAL then encapsulates the fragments in any ANET 711 headers and sends them to the ANET peer, which either reassembles 712 before forwarding if the OAL destination is its own ADM-ULA or 713 forwards the fragments toward the final destination without first 714 reassembling otherwise. 716 o When an OMNI interface sends a packet toward a final destination 717 via an INET interface, it sends packets (including any outer-layer 718 INET encapsulations) no larger than the minimum INET path MTU 719 without OAL encapsulation if the destination is reached via an 720 INET address within the same OMNI link segment. Otherwise, the 721 OAL inserts an IPv6 header per [RFC2473] with source address set 722 to the node's ULA, destination set to the ULA of the next hop OMNI 723 node toward the final destination and (if necessary) with an OMNI 724 Routing Header (ORH) (see: [I-D.templin-intarea-6706bis]) with 725 final segment addressing information. The OAL next calculates and 726 appends the trailing 32-bit CRC, then uses IPv6 fragmentation to 727 break the packet into a minimum number of non-overlapping 728 fragments where the size of each non-final fragment (including 729 both the OMNI and outer-layer INET encapsulations) is determined 730 by the minimum INET path MTU. The OAL then encapsulates the 731 fragments in any INET headers and sends them to the OMNI link 732 neighbor, which reassembles before forwarding toward the final 733 destination. 735 In light of the above considerations, the OAL SHOULD assume a minimum 736 path MTU of 576 bytes for the purpose of generating OAL fragments. 737 Each OAL fragment will undergo *NET encapsulation including either a 738 20 byte IPv4 or 40 byte IPv6 header (plus an 8 byte UDP header for 739 INETs), leaving a minimum of 528 bytes for each fragment. Each OAL 740 fragment must reserve 40 bytes for the OAL IPv6 header plus 8 bytes 741 for the fragment header (while reserving 40 additional bytes in case 742 a maximum-length ORH is inserted during re-encapsulation), leaving 743 440 bytes to accommodate the actual inner IP packet fragment. OAL 744 fragmentation algorithms therefore MUST produce non-final fragments 745 with the OAL IPv6 header Payload Length set to no less than 448 bytes 746 (8 bytes for the fragment header plus 440 bytes for the inner packet 747 fragment), while the Payload Length of the final fragment may be 748 smaller. OAL reassembly algorithms MUST drop any non-final fragments 749 with Payload Length less than 448 bytes. 751 Note that OAL fragmentation algorithms MAY produce larger non-final 752 OAL fragments if better path MTU information is available. For 753 example, for ANETs in which no UDP encapsulation header is needed the 754 algorithm can increase the minimum non-final fragment length by 8 755 bytes. In a second example, for ANETs in which no IPv6 hops will be 756 traversed over the path the algorithm can increase the minimum length 757 by 20 bytes. In a third example, if there is assurance that no ORH 758 will be inserted in the path the algorithm can increase the minimum 759 length by 40 bytes. In a final example, when two ANET peers share a 760 common physical or virtual link with a larger MTU (e.g., 1280 bytes 761 or larger), the OAL can base the minimum non-final fragment length on 762 this larger MTU size as long as the receiving ANET peer reassembles 763 (and possibly also refragments) before forwarding. (Other examples 764 are possible, and dependent on actual ANET/INET deployment 765 scenarios.) 767 In all of the above examples, optimizing the minimum OAL fragment 768 size may be important for accommodating links where performance is 769 dependent on maximum use of the available link MTU, e.g. for wireless 770 aviation data links. Additionally, the OMNI interface that inserts 771 the OAL header MUST also be the one that inserts the IPv6 fragment 772 header Identification value in order to set the correct context for 773 reassembly. While not strictly required, sending all fragments of 774 the same fragmented OAL packet consecutively over the same underlying 775 interface with minimal inter-fragment delay may increase the 776 likelihood of successful reassembly. 778 Ordinary PTB messages with ICMPv4 header "unused" field or ICMPv6 779 header Code field value 0 are hard errors that always indicate that a 780 packet has been dropped due to a real MTU restriction. However, the 781 OAL can also forward large packets via encapsulation and 782 fragmentation while at the same time returning PTB soft error 783 messages (subject to rate limiting) indicating that a forwarded 784 packet was uncomfortably large. The OMNI interface can therefore 785 continuously forward large packets without loss while returning PTB 786 soft error messages recommending a smaller size. Original sources 787 that receive the soft errors in turn reduce the size of the packets 788 they send, i.e., the same as for hard errors. 790 The OAL sets the ICMPv4 header "unused" field or ICMPv6 header Code 791 field to the value 1 in PTB soft error messages. The OAL sets the 792 PTB destination address to the source address of the original packet, 793 and sets the source address to the MNP Subnet Router Anycast address 794 of the MN. The OAL then sets the MTU field to a value no smaller 795 than 576 for ICMPv4 or 1280 for ICMPv6, and returns the PTB soft 796 error to the original source. 798 When the original source receives the PTB, it reduces its path MTU 799 estimate the same as for hard errors but does not regard the message 800 as a loss indication. (If the original source does not recognize the 801 soft error code, it regards the PTB the same as a hard error but 802 should heed the retransmission advice given in [RFC8201] suggesting 803 retransmission based on normal packetization layer retransmission 804 timers.) This document therefore updates [RFC1191][RFC4443] and 805 [RFC8201]. Furthermore, implementations of [RFC4821] must be aware 806 that PTB hard or soft errors may arrive at any time even if after a 807 successful MTU probe (this is the same consideration as for an 808 ordinary path fluctuation following a successful probe). 810 In summary, the OAL supports continuous transmission and reception of 811 packets of various sizes in the face of dynamically changing network 812 conditions. Moreover, since PTB soft errors do not indicate loss, 813 original sources that receive soft errors can quickly scan for path 814 MTU increases without waiting for the minimum 10 minutes specified 815 for loss-oriented PTB hard errors [RFC1191][RFC8201]. The OAL 816 therefore provides a lossless and adaptive service that accommodates 817 MTU diversity especially well-suited for dynamic multilink 818 environments. 820 Note: An OMNI interface that reassembles OAL fragments may experience 821 congestion-oriented loss in its reassembly cache and can optionally 822 send PTB soft errors to the original source and/or ICMP "Time 823 Exceeded" messages to the source of the OAL fragments. In 824 environments where the messages may contribute to unacceptable 825 additional congestion, however, the OMNI interface can refrain from 826 sending PTB soft errors and simply regard the loss as an ordinary 827 unreported congestion event for which the original source will 828 eventually compensate. 830 Note: When the network layer forwards an IPv4 packet/fragment with 831 DF=0 into the OMNI interface, the interface can optionally perform 832 (further) IPv4 fragmentation before invoking the OAL so that the 833 fragments will be reassembled by the final destination. When the 834 network layer performs IPv6 fragmentation for locally-generated IPv6 835 packets, the OMNI interface typically invokes the OAL without first 836 applying (further) IPv6 fragmentation; the network layer should 837 therefore fragment to the minimum IPv6 path MTU (or smaller still) to 838 push the reassembly burden to the final destination and avoid 839 receiving PTB soft errors from the OMNI interface. Aside from these 840 non-normative guidelines, the manner in which any IP fragmentation is 841 invoked prior to OAL encapsulation/fragmentation is an implementation 842 matter. 844 Note: The source OAL includes a trailing 32-bit CRC only for OAL 845 packets that require fragmentation, and the destination OAL discards 846 any OAL packets with incorrect CRC values following reassembly. (The 847 source OAL calculates the CRC over the entire packet, then appends 848 the CRC to the end of the packet and adds the CRC length to the OAL 849 Payload Length prior to fragmentation. The destination OAL subtracts 850 the CRC length from the OAL Payload Length and verifies the CRC 851 following reassembly.) A 32-bit CRC is sufficient for detecting 852 reassembly misassociations for packet sizes no larger than the OMNI 853 interface MTU but may not be sufficient to detect errors for larger 854 sizes [CRC]. 856 Note: Some underlying interface types (e.g., VPNs) may already 857 provide their own robust fragmentation and reassembly services even 858 without OAL encapsulation. In those cases, the OAL can invoke the 859 inherent underlying interface schemes instead while employing PTB 860 soft errors in the same fashion as described above. Other underlying 861 interface facilities such as header/message compression can also be 862 harnessed in a similar fashion. 864 Note: Applications can dynamically tune the size of the packets they 865 to send to produce the best possible throughput and latency, with the 866 understanding that these parameters may change over time due to 867 factors such as congestion, mobility, network path changes, etc. The 868 receipt or absence of soft errors should be seen as hints of when 869 increasing or decreasing packet sizes may be beneficial. 871 5.1. Fragmentation Security Implications 873 As discussed in Section 3.7 of [RFC8900], there are four basic 874 threats concerning IPv6 fragmentation; each of which is addressed by 875 effective mitigations as follows: 877 1. Overlapping fragment attacks - reassembly of overlapping 878 fragments is forbidden by [RFC8200]; therefore, this threat does 879 not apply to the OAL. 881 2. Resource exhaustion attacks - this threat is mitigated by 882 providing a sufficiently large OAL reassembly cache and 883 instituting "fast discard" of incomplete reassemblies that may be 884 part of a buffer exhaustion attack. The reassembly cache should 885 be sufficiently large so that a sustained attack does not cause 886 excessive loss of good reassemblies but not so large that (timer- 887 based) data structure management becomes computationally 888 expensive. The cache should also be indexed based on the arrival 889 underlying interface such that congestion experienced over a 890 first underlying interface does not cause discard of incomplete 891 reassemblies for uncongested underlying interfaces. 893 3. Attacks based on predictable fragment identification values - 894 this threat is mitigated by selecting a suitably random ID value 895 per [RFC7739]. 897 4. Evasion of Network Intrusion Detection Systems (NIDS) - this 898 threat is mitigated by disallowing "tiny fragments" per the OAL 899 fragmentation procedures specified above. 901 Additionally, IPv4 fragmentation includes a 16-bit Identification (IP 902 ID) field with only 65535 unique values such that at high data rates 903 the field could wrap and apply to new packets while the fragments of 904 old packets using the same ID are still alive in the network 905 [RFC4963]. However, since the largest OAL fragment that will be sent 906 via an IPv4 *NET path is 576 bytes any IPv4 fragmentation would occur 907 only on links with an IPv4 MTU smaller than this size, and [RFC3819] 908 recommendations suggest that such links will have low data rates. 909 Since IPv6 provides a 32-bit Identification value, IP ID wraparound 910 at high data rates is not a concern for IPv6 fragmentation. 912 Finally, [RFC6980] documents fragmentation security concerns for 913 large IPv6 ND messages. These concerns are addressed when the OMNI 914 interface employs the OAL instead of directly fragmenting the IPv6 ND 915 message itself. For this reason, OMNI interfaces MUST NOT admit IPv6 916 ND messages larger than the OMNI interface MTU, and MUST employ the 917 OAL for IPv6 ND messages admitted into the OMNI interface the same as 918 discussed above. 920 5.2. OAL "Super-Packet" Packing 922 By default, the source OAL includes a 40-byte IPv6 encapsulation 923 header for each inner IP payload packet during OAL encapsulation. 924 When fragmentation is needed, the source OAL also calculates and 925 includes a 32-bit trailing CRC for the entire packet then performs 926 fragmentation such that a copy of the 40-byte IPv6 header plus an 927 8-byte IPv6 Fragment Header is included in each fragment. However, 928 these encapsulations may represent excessive overhead in some 929 environments. A technique known as "packing" discussed in 930 [I-D.ietf-intarea-tunnels] is therefore supported so that multiple 931 inner IP payload packets can be included within a single OAL packet 932 known as a "super-packet". 934 When the source OAL has multiple inner IP payload packets with total 935 length no larger than the OMNI interface MTU to send to the same 936 destination, it can optionally concatenate them into a super-packet 937 encapsulated in a single OAL header. Within the super-packet, the IP 938 header of the first inner packet (iHa) followed by its data (iDa) is 939 concatenated immediately following the OAL header, then the inner IP 940 header of the next packet (iHb) followed by its data (iDb) is 941 concatenated immediately following the first packet, etc. The super- 942 packet format is transposed from [I-D.ietf-intarea-tunnels] and shown 943 in Figure 3: 945 <-- Multiple inner IP payload packets to be "packed" --> 946 +-----+-----+ 947 | iHa | iDa | 948 +-----+-----+ 949 | 950 | +-----+-----+ 951 | | iHb | iDb | 952 | +-----+-----+ 953 | | 954 | | +-----+-----+ 955 | | | iHc | iDc | 956 | | +-----+-----+ 957 | | | 958 v v v 959 +----------+-----+-----+-----+-----+-----+-----+ 960 | OAL Hdr | iHa | iDa | iHb | iDb | iHc | iDc | 961 +----------+-----+-----+-----+-----+-----+-----+ 962 <-- OMNI "Super-Packet" with single OAL Hdr --> 964 Figure 3: OAL Super-Packet Format 966 When the source OAL sends a super-packet, it calculates a CRC and 967 applies OAL fragmentation if necessary then sends the packet or 968 fragments to the destination OAL. When the destination OAL receives 969 the super-packet as a whole packet or as fragments, it reassembles 970 and verifies the CRC if necessary then regards the OAL header Payload 971 Length (after subtracting the CRC length) as the sum of the lengths 972 of all payload packets. The destination OAL then selectively 973 extracts each individual payload packet (e.g., by setting pointers 974 into the buffer containing the super-packet and maintaining a 975 reference count, by copying each payload packet into its own buffer, 976 etc.) and forwards each payload packet or processes it locally as 977 appropriate. During extraction, the OAL determines the IP protocol 978 version of each successive inner payload packet 'j' by examining the 979 first four bits of iH(j), and determines the length of the inner 980 packet by examining the rest of iH(j) according to the IP protocol 981 version. 983 Note: OMNI interfaces must take care to avoid processing super-packet 984 payload elements that would subvert security. Specifically, if a 985 super-packet contains a mix of data and control payload packets 986 (which could include critical security codes), the node MUST NOT 987 process the data packets before processing the control packets. 989 6. Frame Format 991 The OMNI interface transmits IP packets according to the native frame 992 format of each underlying interface. For example, for Ethernet- 993 compatible interfaces the frame format is specified in [RFC2464], for 994 aeronautical radio interfaces the frame format is specified in 995 standards such as ICAO Doc 9776 (VDL Mode 2 Technical Manual), for 996 tunnels over IPv6 the frame format is specified in [RFC2473], etc. 998 7. Link-Local Addresses (LLAs) 1000 OMNI nodes are assigned OMNI interface IPv6 Link-Local Addresses 1001 (LLAs) through pre-service administrative actions. "MNP-LLAs" embed 1002 the MNP assigned to the mobile node, while "ADM-LLAs" include an 1003 administratively-unique ID that is guaranteed to be unique on the 1004 link. LLAs are configured as follows: 1006 o IPv6 MNP-LLAs encode the most-significant 64 bits of a MNP within 1007 the least-significant 64 bits of the IPv6 link-local prefix 1008 fe80::/64, i.e., in the LLA "interface identifier" portion. The 1009 prefix length for the LLA is determined by adding 64 to the MNP 1010 prefix length. For example, for the MNP 2001:db8:1000:2000::/56 1011 the corresponding MNP-LLA is fe80::2001:db8:1000:2000/120. 1013 o IPv4-compatible MNP-LLAs are constructed as fe80::ffff:[IPv4], 1014 i.e., the interface identifier consists of 16 '0' bits, followed 1015 by 16 '1' bits, followed by a 32bit IPv4 address/prefix. The 1016 prefix length for the LLA is determined by adding 96 to the MNP 1017 prefix length. For example, the IPv4-Compatible MN OMNI LLA for 1018 192.0.2.0/24 is fe80::ffff:192.0.2.0/120 (also written as 1019 fe80::ffff:c000:0200/120). 1021 o ADM-LLAs are assigned to ARs and MSEs and MUST be managed for 1022 uniqueness. The lower 32 bits of the LLA includes a unique 1023 integer "MSID" value between 0x00000001 and 0xfeffffff, e.g., as 1024 in fe80::1, fe80::2, fe80::3, etc., fe80::feffffff. The ADM-LLA 1025 prefix length is determined by adding 96 to the MSID prefix 1026 length. For example, if the prefix length for MSID 0x10012001 is 1027 16 then the ADM-LLA prefix length is set to 112 and the LLA is 1028 written as fe80::1001:2001/112. The "zero" address for each ADM- 1029 LLA prefix is the Subnet-Router anycast address for that prefix 1030 [RFC4291]; for example, the Subnet-Router anycast address for 1031 fe80::1001:2001/112 is simply fe80::1001:2000. The MSID range 1032 0xff000000 through 0xffffffff is reserved for future use. 1034 Since the prefix 0000::/8 is "Reserved by the IETF" [RFC4291], no 1035 MNPs can be allocated from that block ensuring that there is no 1036 possibility for overlap between the different MNP- and ADM-LLA 1037 constructs discussed above. 1039 Since MNP-LLAs are based on the distribution of administratively 1040 assured unique MNPs, and since ADM-LLAs are guaranteed unique through 1041 administrative assignment, OMNI interfaces set the autoconfiguration 1042 variable DupAddrDetectTransmits to 0 [RFC4862]. 1044 Note: If future protocol extensions relax the 64-bit boundary in IPv6 1045 addressing, the additional prefix bits of an MNP could be encoded in 1046 bits 16 through 63 of the MNP-LLA. (The most-significant 64 bits 1047 would therefore still be in bits 64-127, and the remaining bits would 1048 appear in bits 16 through 48.) However, the analysis provided in 1049 [RFC7421] suggests that the 64-bit boundary will remain in the IPv6 1050 architecture for the foreseeable future. 1052 Note: Even though this document honors the 64-bit boundary in IPv6 1053 addressing, it specifies prefix lengths longer than /64 for routing 1054 purposes. This effectively extends IPv6 routing determination into 1055 the interface identifier portion of the IPv6 address, but it does not 1056 redefine the 64-bit boundary. Modern routing protocol 1057 implementations honor IPv6 prefixes of all lengths, up to and 1058 including /128. 1060 8. Unique-Local Addresses (ULAs) 1062 OMNI domains use IPv6 Unique-Local Addresses (ULAs) as the source and 1063 destination addresses in OAL IPv6 encapsulation headers. ULAs are 1064 only routable within the scope of a an OMNI domain, and are derived 1065 from the IPv6 Unique Local Address prefix fc00::/7 followed by the L 1066 bit set to 1 (i.e., as fd00::/8) followed by a 40-bit pseudo-random 1067 Global ID to produce the prefix [ULA]::/48, which is then followed by 1068 a 16-bit Subnet ID then finally followed by a 64 bit Interface ID as 1069 specified in Section 3 of [RFC4193]. All nodes in the same OMNI 1070 domain configure the same 40-bit Global ID as the OMNI domain 1071 identifier. The statistic uniqueness of the 40-bit pseudo-random 1072 Global ID allows different OMNI domains to be joined together in the 1073 future without requiring renumbering. 1075 Each OMNI link instance is identified by a value between 0x0000 and 1076 0xfeff in bits 48-63 of [ULA]::/48; the values 0xff00 through 0xfffe 1077 are reserved for future use, and the value 0xffff denotes the 1078 presence of a Temporary ULA (see below). For example, OMNI ULAs 1079 associated with instance 0 are configured from the prefix 1080 [ULA]:0000::/64, instance 1 from [ULA]:0001::/64, instance 2 from 1081 [ULA]:0002::/64, etc. ULAs and their associated prefix lengths are 1082 configured in correspondence with LLAs through stateless prefix 1083 translation where "MNP-ULAs" are assigned in correspondence to MNP- 1084 LLAs and "ADM-ULAs" are assigned in correspondence to ADM-LLAs. For 1085 example, for OMNI link instance [ULA]:1010::/64: 1087 o the MNP-ULA corresponding to the MNP-LLA fe80::2001:db8:1:2 with a 1088 56-bit MNP length is derived by copying the lower 64 bits of the 1089 LLA into the lower 64 bits of the ULA as 1090 [ULA]:1010:2001:db8:1:2/120 (where, the ULA prefix length becomes 1091 64 plus the IPv6 MNP length). 1093 o the MNP-ULA corresponding to fe80::ffff:192.0.2.0 with a 28-bit 1094 MNP length is derived by simply writing the LLA interface ID into 1095 the lower 64 bits as [ULA]:1010:0:ffff:192.0.2.0/124 (where, the 1096 ULA prefix length is 64 plus 32 plus the IPv4 MNP length). 1098 o the ADM-ULA corresponding to fe80::1000/112 is simply 1099 [ULA]:1010::1000/112. 1101 o the ADM-ULA corresponding to fe80::/128 is simply 1102 [ULA]:1010::/128. 1104 o etc. 1106 Each OMNI interface assigns the Anycast ADM-ULA specific to the OMNI 1107 link instance. For example, the OMNI interface connected to instance 1108 3 assigns the Anycast address [ULA]:0003::/128. Routers that 1109 configure OMNI interfaces advertise the OMNI service prefix (e.g., 1110 [ULA]:0003::/64) into the local routing system so that applications 1111 can direct traffic according to SBM requirements. 1113 The ULA presents an IPv6 address format that is routable within the 1114 OMNI routing system and can be used to convey link-scoped IPv6 ND 1115 messages across multiple hops using IPv6 encapsulation [RFC2473]. 1116 The OMNI link extends across one or more underling Internetworks to 1117 include all ARs and MSEs. All MNs are also considered to be 1118 connected to the OMNI link, however OAL encapsulation is omitted 1119 whenever possible to conserve bandwidth (see: Section 13). 1121 Each OMNI link can be subdivided into "segments" that often 1122 correspond to different administrative domains or physical 1123 partitions. OMNI nodes can use IPv6 Segment Routing [RFC8402] when 1124 necessary to support efficient packet forwarding to destinations 1125 located in other OMNI link segments. A full discussion of Segment 1126 Routing over the OMNI link appears in [I-D.templin-intarea-6706bis]. 1128 Temporary ULAs are constructed per [I-D.ietf-6man-rfc4941bis] based 1129 on the prefix [ULA]:ffff::/64 and used by MNs when they have no other 1130 addresses. Temporary ULAs can be used for MN-to-MN communications 1131 outside the context of any supporting OMNI link infrastructure, and 1132 can also be used as an initial address while the MN is in the process 1133 of procuring an MNP. Temporary ULAs are not routable within the OMNI 1134 routing system, and are therefore useful only for OMNI link "edge" 1135 communications. Temporary ULAs employ optimistic DAD principles 1136 [RFC4429] since they are probabilistically unique. 1138 Note: IPv6 ULAs taken from the prefix fc00::/7 followed by the L bit 1139 set to 0 (i.e., as fc00::/8) are never used for OMNI OAL addressing, 1140 however the range could be used for MSP and MNP addressing under 1141 certain limiting conditions (see: Section 9). 1143 9. Global Unicast Addresses (GUAs) 1145 OMNI domains use IP Global Unicast Address (GUA) prefixes [RFC4291] 1146 as Mobility Service Prefixes (MSPs) from which Mobile Network 1147 Prefixes (MNP) are delegated to Mobile Nodes (MNs). 1149 For IPv6, GUA prefixes are assigned by IANA [IPV6-GUA] and/or an 1150 associated regional assigned numbers authority such that the OMNI 1151 domain can be interconnected to the global IPv6 Internet without 1152 causing inconsistencies in the routing system. An OMNI domain could 1153 instead use ULAs with the 'L' bit set to 0 (i.e., from the prefix 1154 fc00::/8)[RFC4193], however this would require IPv6 NAT if the domain 1155 were ever connected to the global IPv6 Internet. 1157 For IPv4, GUA prefixes are assigned by IANA [IPV4-GUA] and/or an 1158 associated regional assigned numbers authority such that the OMNI 1159 domain can be interconnected to the global IPv4 Internet without 1160 causing routing inconsistencies. An OMNI domain could instead use 1161 private IPv4 prefixes (e.g., 10.0.0.0/8, etc.) [RFC3330], however 1162 this would require IPv4 NAT if the domain were ever connected to the 1163 global IPv4 Internet. 1165 10. Node Identification 1167 OMNI MNs and MSEs that connect over open Internetworks generate a 1168 Host Identity Tag (HIT) as specified in [RFC7401] and use the value 1169 as a robust general-purpose node identification value. Hierarchical 1170 HITs (HHITs) [I-D.ietf-drip-rid] may provide a useful alternative in 1171 certain domains such as the Unmanned (Air) Traffic Management (UTM) 1172 service for Unmanned Air Systems (UAS). MNs and MSEs can then use 1173 their (H)HITs in IPv6 ND control message exchanges. 1175 When a MN is truly outside the context of any infrastructure, it may 1176 have no MNP information at all. In that case, the MN can use its 1177 (H)HIT as an IPv6 source/destination address for sustained 1178 communications in Vehicle-to-Vehicle (V2V) and (multihop) Vehicle-to- 1179 Infrastructure (V2I) scenarios. The MN can also propagate the (H)HIT 1180 into the multihop routing tables of (collective) Mobile/Vehicular Ad- 1181 hoc Networks (MANETs/VANETs) using only the vehicles themselves as 1182 communications relays. 1184 When a MN connects to ARs over (non-multihop) protected-spectrum 1185 ANETs, an alternate form of node identification (e.g., MAC address, 1186 serial number, airframe identification value, VIN, etc.) may be 1187 sufficient. In that case, the MN should still generate a (H)HIT and 1188 maintain it in conjunction with any other node identifiers. The MN 1189 can then include OMNI "Node Identification" sub-options (see: 1190 Section 11.1.11) in IPv6 ND messages should the need to transmit 1191 identification information over the network arise. 1193 11. Address Mapping - Unicast 1195 OMNI interfaces maintain a neighbor cache for tracking per-neighbor 1196 state and use the link-local address format specified in Section 7. 1197 OMNI interface IPv6 Neighbor Discovery (ND) [RFC4861] messages sent 1198 over physical underlying interfaces without encapsulation observe the 1199 native underlying interface Source/Target Link-Layer Address Option 1200 (S/TLLAO) format (e.g., for Ethernet the S/TLLAO is specified in 1201 [RFC2464]). OMNI interface IPv6 ND messages sent over underlying 1202 interfaces via encapsulation do not include S/TLLAOs which were 1203 intended for encoding physical L2 media address formats and not 1204 encapsulation IP addresses. Furthermore, S/TLLAOs are not intended 1205 for encoding additional interface attributes needed for multilink 1206 coordination. Hence, this document does not define an S/TLLAO format 1207 but instead defines a new option type termed the "OMNI option" 1208 designed for these purposes. 1210 MNs such as aircraft typically have many wireless data link types 1211 (e.g. satellite-based, cellular, terrestrial, air-to-air directional, 1212 etc.) with diverse performance, cost and availability properties. 1214 The OMNI interface would therefore appear to have multiple L2 1215 connections, and may include information for multiple underlying 1216 interfaces in a single IPv6 ND message exchange. OMNI interfaces use 1217 an IPv6 ND option called the OMNI option formatted as shown in 1218 Figure 4: 1220 0 1 2 3 1221 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 1222 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1223 | Type | Length | Preflen | S/T-omIndex | 1224 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1225 | | 1226 ~ Sub-Options ~ 1227 | | 1228 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1230 Figure 4: OMNI Option Format 1232 In this format: 1234 o Type is set to TBD1. 1236 o Length is set to the number of 8 octet blocks in the option. The 1237 value 0 is invalid, while the values 1 through 255 (i.e., 8 1238 through 2040 octets, respectively) indicate the total length of 1239 the OMNI option. 1241 o Preflen is an 8 bit field that determines the length of prefix 1242 associated with an LLA. Values 0 through 128 specify a valid 1243 prefix length (all other values are invalid). For IPv6 ND 1244 messages sent from a MN to the MS, Preflen applies to the IPv6 1245 source LLA and provides the length that the MN is requesting or 1246 asserting to the MS. For IPv6 ND messages sent from the MS to the 1247 MN, Preflen applies to the IPv6 destination LLA and indicates the 1248 length that the MS is granting to the MN. For IPv6 ND messages 1249 sent between MS endpoints, Preflen provides the length associated 1250 with the source/target MN that is subject of the ND message. 1252 o S/T-omIndex is an 8 bit field corresponds to the omIndex value for 1253 source or target underlying interface used to convey this IPv6 ND 1254 message. OMNI interfaces MUST number each distinct underlying 1255 interface with an omIndex value between '1' and '255' that 1256 represents a MN-specific 8-bit mapping for the actual ifIndex 1257 value assigned by network management [RFC2863] (the omIndex value 1258 '0' is reserved for use by the MS). For RS and NS messages, S/ 1259 T-omIndex corresponds to the source underlying interface the 1260 message originated from. For RA and NA messages, S/T-omIndex 1261 corresponds to the target underlying interface that the message is 1262 destined to. (For NS messages used for Neighbor Unreachability 1263 Detection (NUD), S/T-omIndex instead identifies the neighbor's 1264 underlying interface to be used as the target interface to return 1265 the NA.) 1267 o Sub-Options is a Variable-length field, of length such that the 1268 complete OMNI Option is an integer multiple of 8 octets long. 1269 Contains one or more Sub-Options, as described in Section 11.1. 1271 The OMNI option may appear in any IPv6 ND message type; it is 1272 processed by interfaces that recognize the option and ignored by all 1273 other interfaces. If multiple OMNI option instances appear in the 1274 same IPv6 ND message, the interface processes the Preflen and S/ 1275 T-omIndex fields in the first instance and ignores those fields in 1276 all other instances. The interface processes the Sub-Options of all 1277 OMNI option instances in the consecutive order in which they appear 1278 in the IPv6 ND message, beginning with the first instance and 1279 continuing consecutively through any additional instances to the end 1280 of the message. 1282 The OMNI option(s) in each IPv6 ND message may include full or 1283 partial information for the neighbor. The union of the information 1284 in the most recently received OMNI options is therefore retained, and 1285 the information is aged/removed in conjunction with the corresponding 1286 neighbor cache entry. 1288 11.1. Sub-Options 1290 The OMNI option includes zero or more Sub-Options. Each consecutive 1291 Sub-Option is concatenated immediately after its predecessor. All 1292 Sub-Options except Pad1 (see below) are in type-length-value (TLV) 1293 encoded in the following format: 1295 0 1 2 1296 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 1297 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1298 | Sub-Type| Sub-length | Sub-Option Data ... 1299 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1301 Figure 5: Sub-Option Format 1303 o Sub-Type is a 5-bit field that encodes the Sub-Option type. Sub- 1304 Options defined in this document are: 1306 Sub-Option Name Sub-Type 1307 Pad1 0 1308 PadN 1 1309 Interface Attributes (Type 1) 2 1310 Interface Attributes (Type 2) 3 1311 Traffic Selector 4 1312 MS-Register 5 1313 MS-Release 6 1314 Geo Coordinates 7 1315 DHCPv6 Message 8 1316 HIP Message 9 1317 Node Identification 10 1318 Sub-Type Extension 30 1320 Figure 6 1322 Sub-Types 11-29 are available for future assignment for major 1323 protocol functions. Sub-Type 31 is reserved by IANA. 1325 o Sub-Length is an 11-bit field that encodes the length of the Sub- 1326 Option Data ranging from 0 to 2034 octets (the values 2035 through 1327 2047 are invalid, since each OMNI option is limited to 2040 1328 octets). 1330 o Sub-Option Data is a block of data with format determined by Sub- 1331 Type and length determined by Sub-Length. 1333 Note that Sub-Type and Sub-Length are coded together in network byte 1334 order in two consecutive octets. Note also that Sub-Option Data may 1335 be up to 2034 octets in length. This allows ample space for encoding 1336 large objects (e.g., ascii character strings, protocol messages, 1337 security codes, etc.), while a single OMNI option is limited to 2040 1338 octets the same as for any IPv6 ND option. If the Sub-Options to be 1339 coded would cause an OMNI option to exceed 2040 octets, any remaining 1340 Sub-Options are encoded in additional OMNI options in the consecutive 1341 order of intended processing. Implementations must therefore be 1342 mindful of size limitations, and must refrain from sending IPv6 ND 1343 messages larger than the OMNI interface MTU. (Note: individual large 1344 objects that would on their own cause an OMNI option to exceed 2040 1345 octets cannot be accommodated under the current specification; if 1346 this proves to be limiting in practice, future specifications may 1347 define support for fragmenting large objects across multiple OMNI 1348 options within a single IPv6 ND message.) 1350 During processing, unrecognized Sub-Options are ignored and the next 1351 Sub-Option processed until the end of the OMNI option is reached. 1353 The following Sub-Option types and formats are defined in this 1354 document: 1356 11.1.1. Pad1 1358 0 1359 0 1 2 3 4 5 6 7 1360 +-+-+-+-+-+-+-+-+ 1361 | S-Type=0|x|x|x| 1362 +-+-+-+-+-+-+-+-+ 1364 Figure 7: Pad1 1366 o Sub-Type is set to 0. If multiple instances appear in OMNI 1367 options of the same message all are processed. 1369 o Sub-Type is followed by three 'x' bits, set randomly on 1370 transmission and ignored on receipt. Pad1 therefore consists of a 1371 whole single octet with the most significant 5 bits set to 0, and 1372 with no Sub-Length or Sub-Option Data fields following. 1374 11.1.2. PadN 1376 0 1 2 1377 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 1378 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1379 | S-Type=1| Sub-length=N | N padding octets ... 1380 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1382 Figure 8: PadN 1384 o Sub-Type is set to 1. If multiple instances appear in OMNI 1385 options of the same message all are processed. 1387 o Sub-Length is set to N (from 0 to 2034 being the number of padding 1388 octets that follow. 1390 o Sub-Option Data consists of N zero-valued octets. 1392 11.1.3. Interface Attributes (Type 1) 1394 The Interface Attributes (Type 1) sub-option provides a basic set of 1395 attributes for underlying interfaces. Interface Attributes (Type 1) 1396 is deprecated throughout the rest of this specification, and 1397 Interface Attributes (Type 2) (see: Section 11.1.4) are indicated 1398 wherever the term "Interface Attributes" appears without an 1399 associated Type designation. 1401 Nodes SHOULD NOT include Interface Attributes (Type 1) sub-options in 1402 IPv6 ND messages they send, and MUST ignore any in IPv6 ND messages 1403 they receive. If an Interface Attributes (Type 1) is included, it 1404 must have the following format: 1406 0 1 2 3 1407 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 1408 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1409 | Sub-Type=2| Sub-length=N | omIndex | omType | 1410 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1411 | Provider ID | Link | Resvd |P00|P01|P02|P03|P04|P05|P06|P07| 1412 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1413 |P08|P09|P10|P11|P12|P13|P14|P15|P16|P17|P18|P19|P20|P21|P22|P23| 1414 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1415 |P24|P25|P26|P27|P28|P29|P30|P31|P32|P33|P34|P35|P36|P37|P38|P39| 1416 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1417 |P40|P41|P42|P43|P44|P45|P46|P47|P48|P49|P50|P51|P52|P53|P54|P55| 1418 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1419 |P56|P57|P58|P59|P60|P61|P62|P63| 1420 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1422 Figure 9: Interface Attributes (Type 1) 1424 o Sub-Type is set to 2. If multiple instances with different 1425 omIndex values appear in OMNI option of the same message all are 1426 processed; if multiple instances with the same omIndex value 1427 appear, the first is processed and all others are ignored 1429 o Sub-Length is set to N (from 4 to 2034 that encodes the number of 1430 Sub-Option Data octets that follow. 1432 o omIndex is a 1-octet field containing a value from 0 to 255 1433 identifying the underlying interface for which the attributes 1434 apply. 1436 o omType is a 1-octet field containing a value from 0 to 255 1437 corresponding to the underlying interface identified by omIndex. 1439 o Provider ID is a 1-octet field containing a value from 0 to 255 1440 corresponding to the underlying interface identified by omIndex. 1442 o Link encodes a 4-bit link metric. The value '0' means the link is 1443 DOWN, and the remaining values mean the link is UP with metric 1444 ranging from '1' ("lowest") to '15' ("highest"). 1446 o Resvd is reserved for future use. 1448 o A 16-octet ""Preferences" field immediately follows 'Resvd', with 1449 values P[00] through P[63] corresponding to the 64 Differentiated 1450 Service Code Point (DSCP) values [RFC2474]. Each 2-bit P[*] field 1451 is set to the value '0' ("disabled"), '1' ("low"), '2' ("medium") 1452 or '3' ("high") to indicate a QoS preference for underlying 1453 interface selection purposes. 1455 11.1.4. Interface Attributes (Type 2) 1457 The Interface Attributes (Type 2) sub-option provides L2 forwarding 1458 information for the multilink conceptual sending algorithm discussed 1459 in Section 13. The L2 information is used for selecting among 1460 potentially multiple candidate underlying interfaces that can be used 1461 to forward packets to the neighbor based on factors such as DSCP 1462 preferences and link quality. Interface Attributes (Type 2) further 1463 includes link-layer address information to be used for either OAL 1464 encapsulation or direct UDP/IP encapsulation (when OAL encapsulation 1465 can be avoided). 1467 Interface Attributes (Type 2) are the sole Interface Attributes 1468 format in this specification that all OMNI nodes must honor. 1469 Wherever the term "Interface Attributes" occurs throughout this 1470 specification without a "Type" designation, the format given below is 1471 indicated: 1473 0 1 2 3 1474 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 1475 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1476 | S-Type=3| Sub-length=N | omIndex | omType | 1477 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1478 | Provider ID | Link |R| API | SRT | FMT | LHS (0 - 7) | 1479 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1480 | LHS (bits 8 - 31) | ~ 1481 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ 1482 ~ ~ 1483 ~ Link Layer Address (L2ADDR) ~ 1484 ~ ~ 1485 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1486 | Bitmap(0)=0xff|P00|P01|P02|P03|P04|P05|P06|P07|P08|P09|P10|P11| 1487 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1488 |P12|P13|P14|P15|P16|P17|P18|P19|P20|P21|P22|P23|P24|P25|P26|P27| 1489 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1490 |P28|P29|P30|P31| Bitmap(1)=0xff|P32|P33|P34|P35|P36| ... 1491 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1493 Figure 10: Interface Attributes (Type 2) 1495 o Sub-Type is set to 3. If multiple instances with different 1496 omIndex values appear in OMNI options of the same message all are 1497 processed; if multiple instances with the same omIndex value 1498 appear, the first is processed and all others are ignored. 1500 o Sub-Length is set to N (from 4 to 2034) that encodes the number of 1501 Sub-Option Data octets that follow. 1503 o Sub-Option Data contains an "Interface Attributes (Type 2)" option 1504 encoded as follows (note that the first four octets must be 1505 present): 1507 * omIndex is set to an 8-bit integer value corresponding to a 1508 specific underlying interface the same as specified above for 1509 the OMNI option S/T-omIndex field. The OMNI options of a same 1510 message may include multiple Interface Attributes Sub-Options, 1511 with each distinct omIndex value pertaining to a different 1512 underlying interface. The OMNI option will often include an 1513 Interface Attributes Sub-Option with the same omIndex value 1514 that appears in the S/T-omIndex. In that case, the actual 1515 encapsulation address of the received IPv6 ND message should be 1516 compared with the L2ADDR encoded in the Sub-Option (see below); 1517 if the addresses are different (or, if L2ADDR is absent) the 1518 presence of a NAT is assumed. 1520 * omType is set to an 8-bit integer value corresponding to the 1521 underlying interface identified by omIndex. The value 1522 represents an OMNI interface-specific 8-bit mapping for the 1523 actual IANA ifType value registered in the 'IANAifType-MIB' 1524 registry [http://www.iana.org]. 1526 * Provider ID is set to an OMNI interface-specific 8-bit ID value 1527 for the network service provider associated with this omIndex. 1529 * Link encodes a 4-bit link metric. The value '0' means the link 1530 is DOWN, and the remaining values mean the link is UP with 1531 metric ranging from '1' ("lowest") to '15' ("highest"). 1533 * R is reserved for future use. 1535 * API - a 3-bit "Address/Preferences/Indexed" code that 1536 determines the contents of the remainder of the sub-option as 1537 follows: 1539 + When the most significant bit (i.e., "Address") is set to 1, 1540 the SRT, FMT, LHS and L2ADDR fields are included immediately 1541 following the API code; else, they are omitted. 1543 + When the next most significant bit (i.e., "Preferences") is 1544 set to 1, a preferences block is included next; else, it is 1545 omitted. (Note that if "Address" is set the preferences 1546 block immediately follows L2ADDR; else, it immediately 1547 follows the API code.) 1549 + When a preferences block is present and the least 1550 significant bit (i.e., "Indexed") is set to 0, the block is 1551 encoded in "Simplex" form as shown in Figure 9; else it is 1552 encoded in "Indexed" form as discussed below. 1554 * When API indicates that an "Address" is included, the following 1555 fields appear in consecutive order (else, they are omitted): 1557 + SRT - a 5-bit Segment Routing Topology prefix length value 1558 that (when added to 96) determines the prefix length to 1559 apply to the ULA formed from concatenating [ULA*]::/96 with 1560 the 32 bit LHS MSID value that follows. For example, the 1561 value 16 corresponds to the prefix length 112. 1563 + FMT - a 3-bit "Framework/Mode/Type" code corresponding to 1564 the included Link Layer Address as follows: 1566 - When the most significant bit (i.e., "Framework") is set 1567 to 0, L2ADDR is the INET encapsulation address of a 1568 Proxy/Server; otherwise, it is the address for the 1569 Source/Target itself 1571 - When the next most significant bit (i.e., "Mode") is set 1572 to 0, the Source/Target L2ADDR is on the open INET; 1573 otherwise, it is (likely) located behind one or more 1574 NATs. 1576 - When the least significant bit (i.e., "Type") is set to 1577 0, L2ADDR includes a UDP Port Number followed by an IPv4 1578 address; else, a UDP Port Number followed by an IPv6 1579 address. 1581 + LHS - the 32 bit MSID of the Last Hop Server/Proxy on the 1582 path to the target. When SRT and LHS are both set to 0, the 1583 LHS is considered unspecified in this IPv6 ND message. When 1584 SRT is set to 0 and LHS is non-zero, the prefix length is 1585 set to 128. SRT and LHS together provide guidance to the 1586 OMNI interface forwarding algorithm. Specifically, if SRT/ 1587 LHS is located in the local OMNI link segment then the OMNI 1588 interface can encapsulate according to FMT/L2ADDR (following 1589 any necessary NAT traversal messaging); else, it must 1590 forward according to the OMNI link spanning tree. See 1591 [I-D.templin-intarea-6706bis] for further discussion. 1593 + Link Layer Address (L2ADDR) - Formatted according to FMT, 1594 and identifies the link-layer address (i.e., the 1595 encapsulation address) of the source/target. The UDP Port 1596 Number appears in the first two octets and the IP address 1597 appears in the next 4 octets for IPv4 or 16 octets for IPv6. 1598 The Port Number and IP address are recorded in ones- 1599 compliment "obfuscated" form per [RFC4380]. The OMNI 1600 interface forwarding algorithm uses FMT/L2ADDR to determine 1601 the encapsulation address for forwarding when SRT/LHS is 1602 located in the local OMNI link segment. Note that if the 1603 target is behind a NAT, L2ADDR will contain the mapped INET 1604 address stored in the NAT; otherwise, L2ADDR will contain 1605 the native INET information of the target itself. 1607 * When API indicates that "Preferences" are included, a 1608 preferences block appears as the remainder of the Sub-Option as 1609 a series of Bitmaps and P[*] values. In "Simplex" form, the 1610 index for each singleton Bitmap octet is inferred from its 1611 sequential position (i.e., 0, 1, 2, ...) as shown in Figure 9. 1612 In "Indexed" form, each Bitmap is preceded by an Index octet 1613 that encodes a value "i" = (0 - 255) as the index for its 1614 companion Bitmap as follows: 1616 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1617 | Index=i | Bitmap(i) |P[*] values ... 1618 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1620 Figure 11 1622 * The preferences consist of a first (simplex/indexed) Bitmap 1623 (i.e., "Bitmap(i)") followed by 0-8 single-octet blocks of 1624 2-bit P[*] values, followed by a second Bitmap (i), followed by 1625 0-8 blocks of P[*] values, etc. Reading from bit 0 to bit 7, 1626 the bits of each Bitmap(i) that are set to '1'' indicate the 1627 P[*] blocks from the range P[(i*32)] through P[(i*32) + 31] 1628 that follow; if any Bitmap(i) bits are '0', then the 1629 corresponding P[*] block is instead omitted. For example, if 1630 Bitmap(0) contains 0xff then the block with P[00]-P[03], 1631 followed by the block with P[04]-P[07], etc., and ending with 1632 the block with P[28]-P[31] are included (as shown in Figure 9). 1633 The next Bitmap(i) is then consulted with its bits indicating 1634 which P[*] blocks follow, etc. out to the end of the Sub- 1635 Option. 1637 * Each 2-bit P[*] field is set to the value '0' ("disabled"), '1' 1638 ("low"), '2' ("medium") or '3' ("high") to indicate a QoS 1639 preference for underlying interface selection purposes. Not 1640 all P[*] values need to be included in the OMNI option of each 1641 IPv6 ND message received. Any P[*] values represented in an 1642 earlier OMNI option but omitted in the current OMNI option 1643 remain unchanged. Any P[*] values not yet represented in any 1644 OMNI option default to "medium". 1646 * The first 16 P[*] blocks correspond to the 64 Differentiated 1647 Service Code Point (DSCP) values P[00] - P[63] [RFC2474]. Any 1648 additional P[*] blocks that follow correspond to "pseudo-DSCP" 1649 traffic classifier values P[64], P[65], P[66], etc. See 1650 Appendix A for further discussion and examples. 1652 11.1.5. Traffic Selector 1654 0 1 2 3 1655 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 1656 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1657 | S-Type=4| Sub-length=N | omIndex | ~ 1658 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ 1659 ~ ~ 1660 ~ RFC 6088 Format Traffic Selector ~ 1661 ~ ~ 1662 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1664 Figure 12: Traffic Selector 1666 o Sub-Type is set to 4. If multiple instances appear in OMNI 1667 options of the same message all are processed, i.e., even if the 1668 same omIndex value appears multiple times. 1670 o Sub-Length is set to N (the number of Sub-Option Data octets that 1671 follow). 1673 o Sub-Option Data contains a 1-octet omIndex encoded exactly as 1674 specified in Section 11.1.3, followed by an N-1 octet traffic 1675 selector formatted per [RFC6088] beginning with the "TS Format" 1676 field. The largest traffic selector for a given omIndex is 1677 therefore 2033 octets. 1679 11.1.6. MS-Register 1680 0 1 2 3 1681 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 1682 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1683 | S-Type=5| Sub-length=4n | MSID[1] (bits 0 - 15) | 1684 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1685 | MSID [1] (bits 16 - 32) | MSID[2] (bits 0 - 15) | 1686 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1687 | MSID [2] (bits 16 - 32) | MSID[3] (bits 0 - 15) | 1688 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1689 ... ... ... ... ... ... 1690 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1691 | MSID [n] (bits 16 - 32) | 1692 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1694 Figure 13: MS-Register Sub-option 1696 o Sub-Type is set to 5. If multiple instances appear in OMNI 1697 options of the same message all are processed. Only the first 1698 MAX_MSID values processed (whether in a single instance or 1699 multiple) are retained and all other MSIDs are ignored. 1701 o Sub-Length is set to 4n, with 508 as the maximum value for n. 1703 o A list of n 4-octet MSIDs is included in the following 4n octets. 1704 The Anycast MSID value '0' in an RS message MS-Register sub-option 1705 requests the recipient to return the MSID of a nearby MSE in a 1706 corresponding RA response. 1708 11.1.7. MS-Release 1710 0 1 2 3 1711 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 1712 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1713 | S-Type=6| Sub-length=4n | MSID[1] (bits 0 - 15) | 1714 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1715 | MSID [1] (bits 16 - 32) | MSID[2] (bits 0 - 15) | 1716 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1717 | MSID [2] (bits 16 - 32) | MSID[3] (bits 0 - 15) | 1718 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1719 ... ... ... ... ... ... 1720 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1721 | MSID [n] (bits 16 - 32) | 1722 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1724 Figure 14: MS-Release Sub-option 1726 o Sub-Type is set to 6. If multiple instances appear in OMNI 1727 options of the same message all are processed. Only the first 1728 MAX_MSID values processed (whether in a single instance or 1729 multiple) are retained and all other MSIDs are ignored. 1731 o Sub-Length is set to 4n, with 508 as the maximum value for n. 1733 o A list of n 4 octet MSIDs is included in the following 4n octets. 1734 The Anycast MSID value '0' is ignored in MS-Release sub-options, 1735 i.e., only non-zero values are processed. 1737 11.1.8. Geo Coordinates 1739 0 1 2 3 1740 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 1741 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1742 | S-Type=7| Sub-length=N | Geo Coordinates 1743 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... 1745 Figure 15: Geo Coordinates Sub-option 1747 o Sub-Type is set to 7. If multiple instances appear in OMNI 1748 options of the same message the first is processed and all others 1749 are ignored. 1751 o Sub-Length is set to N (i.e., the length of the encoded Geo 1752 Coordinates up to a maximum of 2034 octets). 1754 o A set of Geo Coordinates. Format(s) to be specified in future 1755 documents; should include Latitude/Longitude, plus any additional 1756 attributes such as altitude, heading, speed, etc. 1758 11.1.9. Dynamic Host Configuration Protocol for IPv6 (DHCPv6) Message 1760 0 1 2 3 1761 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 1762 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1763 | S-Type=8| Sub-length=N | msg-type | id (octet 0) | 1764 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1765 | transaction-id (octets 1-2) | | 1766 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 1767 | | 1768 . DHCPv6 options . 1769 . (variable number and length) . 1770 | | 1771 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1773 Figure 16: DHCPv6 Message Sub-option 1775 o Sub-Type is set to 8. If multiple instances appear in OMNI 1776 options of the same message the first is processed and all others 1777 are ignored. 1779 o Sub-Length is set to N (i.e., the length of the DHCPv6 message 1780 beginning with 'msg-type' and continuing to the end of the DHCPv6 1781 options). The length of the entire DHCPv6 message is therefore 1782 restricted to 2034 octets. 1784 o 'msg-type' and 'transaction-id' are coded according to Section 8 1785 of [RFC8415]. 1787 o A set of DHCPv6 options coded according to Section 21 of [RFC8415] 1788 follows. 1790 11.1.10. Host Identity Protocol (HIP) Message 1792 0 1 2 3 1793 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 1794 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1795 | S-Type=9| Sub-length=N |0| Packet Type |Version| RES.|1| 1796 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1797 | Checksum | Controls | 1798 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1799 | Sender's Host Identity Tag (HIT) | 1800 | | 1801 | | 1802 | | 1803 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1804 | Receiver's Host Identity Tag (HIT) | 1805 | | 1806 | | 1807 | | 1808 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1809 | | 1810 / HIP Parameters / 1811 / / 1812 | | 1813 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1815 Figure 17: HIP Message Sub-option 1817 o Sub-Type is set to 9. If multiple instances appear in OMNI 1818 options of the same message the first is processed and all others 1819 are ignored. 1821 o Sub-Length is set to N, i.e., the length of the option in octets 1822 beginning immediately following the Sub-Length field and extending 1823 to the end of the HIP parameters. The length of the entire HIP 1824 message is therefore restricted to 2034 octets. 1826 o The HIP message is coded exactly as specified in Section 5 of 1827 [RFC7401], with the exception that the OMNI "Sub-Type" and "Sub- 1828 Length" fields replace the first two header octets of the HIP 1829 message (i.e., the Next Header and Header Length fields). 1831 11.1.11. Node Identification 1833 0 1 2 3 1834 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 1835 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1836 |S-Type=10| Sub-length=N | ID-Type | ~ 1837 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ 1838 ~ Node Identification Value (N-1 octets) ~ 1839 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1841 Figure 18: Node Identification 1843 o Sub-Type is set to 10. If multiple instances appear in OMNI 1844 options of the same IPv6 ND message the first instance of a 1845 specific ID-Type is processed and all other instances of the same 1846 ID-Type are ignored. (Note therefore that it is possible for a 1847 single IPv6 ND message to convey multiple Node Identifications - 1848 each having a different ID-Type.) 1850 o Sub-Length is set to N, i.e., the combined length of the ID-Type 1851 and Node Identification Value fields. The maximum Node 1852 Identification Value length is therefore 2033 octets. 1854 o ID-Type is a one-octet field that encodes the type of the Node 1855 Identification Value. The following ID-Type values are currently 1856 defined: 1858 * 0 - Universally Unique IDentifier (UUID) [RFC4122]. Indicates 1859 that Node Identification Value contains a 16 octet UUID. 1861 * 1 - Host Identity Tag (HIT) [RFC7401]. Indicates that Node 1862 Identification Value contains a 16 octet HIT. 1864 * 2 - Hierarchical HIT (HHIT) [I-D.ietf-drip-rid]. Indicates 1865 that Node Identification Value contains a 16 octet HHIT. 1867 * 3 - Network Access Identifier (NAI) [RFC7542]. Indicates that 1868 Node Identification Value contains an N-1 octet NAI. 1870 * 4 - Fully-Qualified Domain Name (FQDN) [RFC1035]. Indicates 1871 that Node Identification Value contains an N-1 octet FQDN. 1873 * 5 - 252 - Unassigned. 1875 * 253-254 - Reserved for experimentation, as recommended in 1876 [RFC3692]. 1878 * 255 - reserved by IANA. 1880 o Node Identification Value is an (N - 1)-octet field encoded 1881 according to the appropriate the "ID-Type" reference above. 1883 When a Node Identification Value is needed for DHCPv6 messaging 1884 purposes, it is encoded as a DHCP Unique IDentifier (DUID) using the 1885 "DUID-EN for OMNI" format with enterprise number 45282 (see: 1886 Section 22) as shown in Figure 19: 1888 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 1889 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1890 | DUID-Type (2) | EN (high bits == 0) | 1891 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1892 | EN (low bits = 45282) | ID-Type | | 1893 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 1894 . Node Identification Value . 1895 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1897 Figure 19: DUID-EN for OMNI Format 1899 In this format, the ID-Type and Node Identification Value fields are 1900 coded exactly as in Figure 18 following the 6 octet DUID-EN header, 1901 and the entire "DUID-EN for OMNI" is included in a DHCPv6 message per 1902 [RFC8415]. 1904 11.1.12. Sub-Type Extension 1906 Since the Sub-Type field is only 5 bits in length, future 1907 specifications of major protocol functions may exhaust the remaining 1908 Sub-Type values available for assignment. This document therefore 1909 defines Sub-Type 30 as an "extension", meaning that the actual sub- 1910 option type is determined by examining a 1 octet "Extension-Type" 1911 field immediately following the Sub-Length field. The Sub-Type 1912 Extension is formatted as shown in Figure 20: 1914 0 1 2 3 1915 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 1916 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1917 |S-Type=30| Sub-length=N | Extension-Type| ~ 1918 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ 1919 ~ ~ 1920 ~ Extension-Type Body ~ 1921 ~ ~ 1922 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1924 Figure 20: Sub-Type Extension 1926 o Sub-Type is set to 30. If multiple instances appear in OMNI 1927 options of the same message all are processed, where each 1928 individual extension defines its own policy for processing 1929 multiple of that type. 1931 o Sub-Length is set to N, i.e., the combined length of the 1932 Extension-Type octet and the Extension-Type Body. The maximum 1933 length Extension-Type Body is therefore 2033 octets. 1935 o Extension-Type contains a 1-octet Sub-Type Extension value between 1936 0 and 255. 1938 o Extension-Type Body contains an N-1 octet block with format 1939 defined by the given extension specification. 1941 Extension-Type values 1 through 252 are available for assignment by 1942 future specifications, which must also define the format of the 1943 Extension-Type Body and its processing rules. Extension-Type values 1944 253 and 254 are reserved for experimentation, as recommended in 1945 [RFC3692]. Extension-Type value 255 is reserved by IANA. 1947 Extension-Type value 0 ("Origin Indication") is defined in this 1948 document according to Section 11.1.12.1: 1950 11.1.12.1. Origin Indication 1952 0 1 2 3 1953 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 1954 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1955 |S-Type=30| Sub-length=7/19 | Ext-Type=0 | Origin Port # | 1956 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1957 | Origin Port # | Origin IPv4/IPv6 Address ~ 1958 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1960 Figure 21: Origin Indication (Extension-Type 0) 1962 o Sub-Type is set to 30. 1964 o Sub-Length is set to either 7 or 19; if Sub-Length encodes any 1965 other value, the Sub-Option is ignored. 1967 o Extension-Type is set to 0. If multiple instances appear in OMNI 1968 options of the same message the first instance is processed and 1969 all others are ignored. 1971 o Extension-Type Body contains a 2-octet Origin Port Number followed 1972 immediately by a 4-octet Origin IPv4 address if Sub-Length encodes 1973 7, or by a 16-octet Origin IPv6 address if Sub-Length encodes 19. 1974 The Port Number and IP address are recorded in ones-compliment 1975 "obfuscated" form per [RFC4380]. 1977 12. Address Mapping - Multicast 1979 The multicast address mapping of the native underlying interface 1980 applies. The mobile router on board the MN also serves as an IGMP/ 1981 MLD Proxy for its EUNs and/or hosted applications per [RFC4605] while 1982 using the L2 address of the AR as the L2 address for all multicast 1983 packets. 1985 The MN uses Multicast Listener Discovery (MLDv2) [RFC3810] to 1986 coordinate with the AR, and *NET L2 elements use MLD snooping 1987 [RFC4541]. 1989 13. Multilink Conceptual Sending Algorithm 1991 The MN's IPv6 layer selects the outbound OMNI interface according to 1992 SBM considerations when forwarding data packets from local or EUN 1993 applications to external correspondents. Each OMNI interface 1994 maintains a neighbor cache the same as for any IPv6 interface, but 1995 with additional state for multilink coordination. Each OMNI 1996 interface maintains default routes via ARs discovered as discussed in 1997 Section 14, and may configure more-specific routes discovered through 1998 means outside the scope of this specification. 2000 After a packet enters the OMNI interface, one or more outbound 2001 underlying interfaces are selected based on PBM traffic attributes, 2002 and one or more neighbor underlying interfaces are selected based on 2003 the receipt of Interface Attributes sub-options in IPv6 ND messages 2004 (see: Figure 9). Underlying interface selection for the nodes own 2005 local interfaces are based on attributes such as DSCP, application 2006 port number, cost, performance, message size, etc. OMNI interface 2007 multilink selections could also be configured to perform replication 2008 across multiple underlying interfaces for increased reliability at 2009 the expense of packet duplication. The set of all Interface 2010 Attributes received in IPv6 ND messages determines the multilink 2011 forwarding profile for selecting the neighbor's underlying 2012 interfaces. 2014 When the OMNI interface sends a packet over a selected outbound 2015 underlying interface, the OAL includes or omits a mid-layer 2016 encapsulation header as necessary as discussed in Section 5 and as 2017 determined by the L2 address information received in Interface 2018 Attributes. The OAL also performs encapsulation when the nearest AR 2019 is located multiple hops away as discussed in Section 14.1. (Note 2020 that the OAL MAY employ packing when multiple packets are available 2021 for forwarding to the same destination.) 2023 OMNI interface multilink service designers MUST observe the BCP 2024 guidance in Section 15 [RFC3819] in terms of implications for 2025 reordering when packets from the same flow may be spread across 2026 multiple underlying interfaces having diverse properties. 2028 13.1. Multiple OMNI Interfaces 2030 MNs may connect to multiple independent OMNI links concurrently in 2031 support of SBM. Each OMNI interface is distinguished by its Anycast 2032 ULA (e.g., [ULA]:0002::, [ULA]:1000::, [ULA]:7345::, etc.). The MN 2033 configures a separate OMNI interface for each link so that multiple 2034 interfaces (e.g., omni0, omni1, omni2, etc.) are exposed to the IPv6 2035 layer. A different Anycast ULA is assigned to each interface, and 2036 the MN injects the service prefixes for the OMNI link instances into 2037 the EUN routing system. 2039 Applications in EUNs can use Segment Routing to select the desired 2040 OMNI interface based on SBM considerations. The Anycast ULA is 2041 written into the IPv6 destination address, and the actual destination 2042 (along with any additional intermediate hops) is written into the 2043 Segment Routing Header. Standard IP routing directs the packets to 2044 the MN's mobile router entity, and the Anycast ULA identifies the 2045 OMNI interface to be used for transmission to the next hop. When the 2046 MN receives the message, it replaces the IPv6 destination address 2047 with the next hop found in the routing header and transmits the 2048 message over the OMNI interface identified by the Anycast ULA. 2050 Multiple distinct OMNI links can therefore be used to support fault 2051 tolerance, load balancing, reliability, etc. The architectural model 2052 is similar to Layer 2 Virtual Local Area Networks (VLANs). 2054 13.2. MN<->AR Traffic Loop Prevention 2056 After an AR has registered an MNP for a MN (see: Section 14), the AR 2057 will forward packets destined to an address within the MNP to the MN. 2058 The MN will under normal circumstances then forward the packet to the 2059 correct destination within its internal networks. 2061 If at some later time the MN loses state (e.g., after a reboot), it 2062 may begin returning packets destined to an MNP address to the AR as 2063 its default router. The AR therefore must drop any packets 2064 originating from the MN and destined to an address within the MN's 2065 registered MNP. To do so, the AR institutes the following check: 2067 o if the IP destination address belongs to a neighbor on the same 2068 OMNI interface, and if the link-layer source address is the same 2069 as one of the neighbor's link-layer addresses, drop the packet. 2071 14. Router Discovery and Prefix Registration 2073 MNs interface with the MS by sending RS messages with OMNI options 2074 under the assumption that one or more AR on the *NET will process the 2075 message and respond. The MN then configures default routes for the 2076 OMNI interface via the discovered ARs as the next hop. The manner in 2077 which the *NET ensures AR coordination is link-specific and outside 2078 the scope of this document (however, considerations for *NETs that do 2079 not provide ARs that recognize the OMNI option are discussed in 2080 Section 19). 2082 For each underlying interface, the MN sends an RS message with an 2083 OMNI option to coordinate with MSEs identified by MSID values. 2084 Example MSID discovery methods are given in [RFC5214] and include 2085 data link login parameters, name service lookups, static 2086 configuration, a static "hosts" file, etc. The MN can also send an 2087 RS with an MS-Register sub-option that includes the Anycast MSID 2088 value '0', i.e., instead of or in addition to any non-zero MSIDs. 2089 When the AR receives an RS with a MSID '0', it selects a nearby MSE 2090 (which may be itself) and returns an RA with the selected MSID in an 2091 MS-Register sub-option. The AR selects only a single wildcard MSE 2092 (i.e., even if the RS MS-Register sub-option included multiple '0' 2093 MSIDs) while also soliciting the MSEs corresponding to any non-zero 2094 MSIDs. 2096 MNs configure OMNI interfaces that observe the properties discussed 2097 in the previous section. The OMNI interface and its underlying 2098 interfaces are said to be in either the "UP" or "DOWN" state 2099 according to administrative actions in conjunction with the interface 2100 connectivity status. An OMNI interface transitions to UP or DOWN 2101 through administrative action and/or through state transitions of the 2102 underlying interfaces. When a first underlying interface transitions 2103 to UP, the OMNI interface also transitions to UP. When all 2104 underlying interfaces transition to DOWN, the OMNI interface also 2105 transitions to DOWN. 2107 When an OMNI interface transitions to UP, the MN sends RS messages to 2108 register its MNP and an initial set of underlying interfaces that are 2109 also UP. The MN sends additional RS messages to refresh lifetimes 2110 and to register/deregister underlying interfaces as they transition 2111 to UP or DOWN. The MN's OMNI interface sends initial RS messages 2112 over an UP underlying interface with its MNP-LLA as the source and 2113 with destination set to link-scoped All-Routers multicast (ff02::2) 2114 [RFC4291]. The OMNI interface includes an OMNI option per Section 11 2115 with a Preflen assertion, Interface Attributes appropriate for 2116 underlying interfaces, MS-Register/Release sub-options containing 2117 MSID values, and with any other necessary OMNI sub-options (e.g., a 2118 Node Identification sub-option as an identity for the MN). The OMNI 2119 interface then sets the S/T-omIndex field to the index of the 2120 underlying interface over which the RS message is sent. The OMNI 2121 interface then sends the RS over the underlying interface, using OAL 2122 encapsulation and fragmentation if necessary. If OAL encapsulation 2123 is used, the OMNI interface sets the OAL source address to the ULA 2124 corresponding to the RS source and sets the OAL destination to site- 2125 scoped All-Routers multicast (ff05::2). 2127 ARs process IPv6 ND messages with OMNI options and act as an MSE 2128 themselves and/or as a proxy for other MSEs. ARs receive RS messages 2129 (while performing OAL reassembly if necessary) and create a neighbor 2130 cache entry for the MN, then coordinate with any MSEs named in the 2131 Register/Release lists in a manner outside the scope of this 2132 document. When an MSE processes the OMNI information, it first 2133 validates the prefix registration information then injects/withdraws 2134 the MNP in the routing/mapping system and caches/discards the new 2135 Preflen, MNP and Interface Attributes. The MSE then informs the AR 2136 of registration success/failure, and the AR returns an RA message to 2137 the MN with an OMNI option per Section 11. 2139 The AR's OMNI interface returns the RA message via the same 2140 underlying interface of the MN over which the RS was received, and 2141 with destination address set to the MNP-LLA (i.e., unicast), with 2142 source address set to its own LLA, and with an OMNI option with S/ 2143 T-omIndex set to the value included in the RS. The OMNI option also 2144 includes a Preflen confirmation, Interface Attributes, MS-Register/ 2145 Release and any other necessary OMNI sub-options (e.g., a Node 2146 Identification sub-option as an identity for the AR). The RA also 2147 includes any information for the link, including RA Cur Hop Limit, M 2148 and O flags, Router Lifetime, Reachable Time and Retrans Timer 2149 values, and includes any necessary options such as: 2151 o PIOs with (A; L=0) that include MSPs for the link [RFC8028]. 2153 o RIOs [RFC4191] with more-specific routes. 2155 o an MTU option that specifies the maximum acceptable packet size 2156 for this underlying interface. 2158 The OMNI interface then sends the RA, using OAL encapsulation and 2159 fragmentation if necessary. If OAL encapsulation is used, the OMNI 2160 interface sets the OAL source address to the ULA corresponding to the 2161 RA source and sets the OAL destination to the ULA corresponding to 2162 the RA destination. The AR MAY also send periodic and/or event- 2163 driven unsolicited RA messages per [RFC4861]. In that case, the S/ 2164 T-omIndex field in the OMNI option of the unsolicited RA message 2165 identifies the target underlying interface of the destination MN. 2167 The AR can combine the information from multiple MSEs into one or 2168 more "aggregate" RAs sent to the MN in order conserve *NET bandwidth. 2169 Each aggregate RA includes an OMNI option with MS-Register/Release 2170 sub-options with the MSEs represented by the aggregate. If an 2171 aggregate is sent, the RA message contents must consistently 2172 represent the combined information advertised by all represented 2173 MSEs. Note that since the AR uses its own ADM-LLA as the RA source 2174 address, the MN determines the addresses of the represented MSEs by 2175 examining the MS-Register/Release OMNI sub-options. 2177 When the MN receives the RA message, it creates an OMNI interface 2178 neighbor cache entry for each MSID that has confirmed MNP 2179 registration via the L2 address of this AR. If the MN connects to 2180 multiple *NETs, it records the additional L2 AR addresses in each 2181 MSID neighbor cache entry (i.e., as multilink neighbors). The MN 2182 then configures a default route via the MSE that returned the RA 2183 message, and assigns the Subnet Router Anycast address corresponding 2184 to the MNP (e.g., 2001:db8:1:2::) to the OMNI interface. The MN then 2185 manages its underlying interfaces according to their states as 2186 follows: 2188 o When an underlying interface transitions to UP, the MN sends an RS 2189 over the underlying interface with an OMNI option. The OMNI 2190 option contains at least one Interface Attribute sub-option with 2191 values specific to this underlying interface, and may contain 2192 additional Interface Attributes specific to other underlying 2193 interfaces. The option also includes any MS-Register/Release sub- 2194 options. 2196 o When an underlying interface transitions to DOWN, the MN sends an 2197 RS or unsolicited NA message over any UP underlying interface with 2198 an OMNI option containing an Interface Attribute sub-option for 2199 the DOWN underlying interface with Link set to '0'. The MN sends 2200 an RS when an acknowledgement is required, or an unsolicited NA 2201 when reliability is not thought to be a concern (e.g., if 2202 redundant transmissions are sent on multiple underlying 2203 interfaces). 2205 o When the Router Lifetime for a specific AR nears expiration, the 2206 MN sends an RS over the underlying interface to receive a fresh 2207 RA. If no RA is received, the MN can send RS messages to an 2208 alternate MSID in case the current MSID has failed. If no RS 2209 messages are received even after trying to contact alternate 2210 MSIDs, the MN marks the underlying interface as DOWN. 2212 o When a MN wishes to release from one or more current MSIDs, it 2213 sends an RS or unsolicited NA message over any UP underlying 2214 interfaces with an OMNI option with a Release MSID. Each MSID 2215 then withdraws the MNP from the routing/mapping system and informs 2216 the AR that the release was successful. 2218 o When all of a MNs underlying interfaces have transitioned to DOWN 2219 (or if the prefix registration lifetime expires), any associated 2220 MSEs withdraw the MNP the same as if they had received a message 2221 with a release indication. 2223 The MN is responsible for retrying each RS exchange up to 2224 MAX_RTR_SOLICITATIONS times separated by RTR_SOLICITATION_INTERVAL 2225 seconds until an RA is received. If no RA is received over an UP 2226 underlying interface (i.e., even after attempting to contact 2227 alternate MSEs), the MN declares this underlying interface as DOWN. 2229 The IPv6 layer sees the OMNI interface as an ordinary IPv6 interface. 2230 Therefore, when the IPv6 layer sends an RS message the OMNI interface 2231 returns an internally-generated RA message as though the message 2232 originated from an IPv6 router. The internally-generated RA message 2233 contains configuration information that is consistent with the 2234 information received from the RAs generated by the MS. Whether the 2235 OMNI interface IPv6 ND messaging process is initiated from the 2236 receipt of an RS message from the IPv6 layer is an implementation 2237 matter. Some implementations may elect to defer the IPv6 ND 2238 messaging process until an RS is received from the IPv6 layer, while 2239 others may elect to initiate the process proactively. Still other 2240 deployments may elect to administratively disable the ordinary RS/RA 2241 messaging used by the IPv6 layer over the OMNI interface, since they 2242 are not required to drive the internal RS/RA processing. (Note that 2243 this same logic applies to IPv4 implementations that employ ICMP- 2244 based Router Discovery per [RFC1256].) 2245 Note: The Router Lifetime value in RA messages indicates the time 2246 before which the MN must send another RS message over this underlying 2247 interface (e.g., 600 seconds), however that timescale may be 2248 significantly longer than the lifetime the MS has committed to retain 2249 the prefix registration (e.g., REACHABLETIME seconds). ARs are 2250 therefore responsible for keeping MS state alive on a shorter 2251 timescale than the MN is required to do on its own behalf. 2253 Note: On multicast-capable underlying interfaces, MNs should send 2254 periodic unsolicited multicast NA messages and ARs should send 2255 periodic unsolicited multicast RA messages as "beacons" that can be 2256 heard by other nodes on the link. If a node fails to receive a 2257 beacon after a timeout value specific to the link, it can initiate a 2258 unicast exchange to test reachability. 2260 Note: if an AR acting as a proxy forwards a MN's RS message to 2261 another node acting as an MSE using UDP/IP encapsulation, it must use 2262 a distinct UDP source port number for each MN. This allows the MSE 2263 to distinguish different MNs behind the same AR at the link-layer, 2264 whereas the link-layer addresses would otherwise be 2265 indistinguishable. 2267 Note: when an AR acting as an MSE returns an RA to an INET Client, it 2268 includes an OMNI option with an Interface Attributes sub-option with 2269 omIndex set to 0 and with SRT, FMT, LHS and L2ADDR information for 2270 its INET interface. This provides the Client with partition prefix 2271 context regarding the local OMNI link segment. 2273 14.1. Router Discovery in IP Multihop and IPv4-Only Networks 2275 On some *NETs, a MN may be located multiple IP hops away from the 2276 nearest AR. Forwarding through IP multihop *NETs is conducted 2277 through the application of a routing protocol (e.g., a MANET/VANET 2278 routing protocol over omni-directional wireless interfaces, an inter- 2279 domain routing protocol in an enterprise network, etc.). These *NETs 2280 could be either IPv6-enabled or IPv4-only, while IPv4-only *NETs 2281 could be either multicast-capable or unicast-only (note that for 2282 IPv4-only *NETs the following procedures apply for both single-hop 2283 and multihop cases). 2285 A MN located potentially multiple *NET hops away from the nearest AR 2286 prepares an RS message with source address set to its MNP-LLA (or to 2287 the unspecified address (::) if it does not yet have an MNP-LLA), and 2288 with destination set to link-scoped All-Routers multicast the same as 2289 discussed above. If OAL encapsulation and fragmentation are 2290 necessary, the OMNI interface sets the OAL source address to the ULA 2291 corresponding to the RS source (or to a Temporary ULA if the RS 2292 source was unspecified) and sets the OAL destination to site-scoped 2293 All-Routers multicast (ff05::2). For IPv6-enabled *NETs, the MN then 2294 encapsulates the message in UDP/IPv6 headers with source address set 2295 to the underlying interface address (or to the ULA that would be used 2296 for OAL encapsulation if the underlying interface does not yet have 2297 an address) and sets the destination to either a unicast or anycast 2298 address of an AR. For IPv4-only *NETs, the MN instead encapsulates 2299 the RS message in an IPv4 header with source address set to the IPv4 2300 address of the underlying interface and with destination address set 2301 to either the unicast IPv4 address of an AR [RFC5214] or an IPv4 2302 anycast address reserved for OMNI. The MN then sends the 2303 encapsulated RS message via the *NET interface, where it will be 2304 forwarded by zero or more intermediate *NET hops. 2306 When an intermediate *NET hop that participates in the routing 2307 protocol receives the encapsulated RS, it forwards the message 2308 according to its routing tables (note that an intermediate node could 2309 be a fixed infrastructure element or another MN). This process 2310 repeats iteratively until the RS message is received by a penultimate 2311 *NET hop within single-hop communications range of an AR, which 2312 forwards the message to the AR. 2314 When the AR receives the message, it decapsulates the RS (while 2315 performing OAL reassembly, if necessary) and coordinates with the MS 2316 the same as for an ordinary link-local RS, since the inner Hop Limit 2317 will not have been decremented by the multihop forwarding process. 2318 The AR then prepares an RA message with source address set to its own 2319 ADM-LLA and destination address set to the LLA of the original MN. 2320 The AR then performs OAL encapsulation and fragmentation if 2321 necessary, with OAL source set to its own ADM-ULA and destination set 2322 to the ULA corresponding to the RA source. The AR then encapsulates 2323 the message in an IPv4/IPv6 header with source address set to its own 2324 IPv4/ULA address and with destination set to the encapsulation source 2325 of the RS. 2327 The AR then forwards the message to an *NET node within 2328 communications range, which forwards the message according to its 2329 routing tables to an intermediate node. The multihop forwarding 2330 process within the *NET continues repetitively until the message is 2331 delivered to the original MN, which decapsulates the message and 2332 performs autoconfiguration the same as if it had received the RA 2333 directly from the AR as an on-link neighbor. 2335 Note: An alternate approach to multihop forwarding via IPv6 2336 encapsulation would be for the MN and AR to statelessly translate the 2337 IPv6 LLAs into ULAs and forward the RS/RA messages without 2338 encapsulation. This would violate the [RFC4861] requirement that 2339 certain IPv6 ND messages must use link-local addresses and must not 2340 be accepted if received with Hop Limit less than 255. This document 2341 therefore mandates encapsulation since the overhead is nominal 2342 considering the infrequent nature and small size of IPv6 ND messages. 2343 Future documents may consider encapsulation avoidance through 2344 translation while updating [RFC4861]. 2346 Note: An alternate approach to multihop forwarding via IPv4 2347 encapsulation would be to employ IPv6/IPv4 protocol translation. 2348 However, for IPv6 ND messages the LLAs would be truncated due to 2349 translation and the OMNI Router and Prefix Discovery services would 2350 not be able to function. The use of IPv4 encapsulation is therefore 2351 indicated. 2353 Note: An IPv4 anycast address for OMNI in IPv4 networks could be part 2354 of a new IPv4 /24 prefix allocation, but this may be difficult to 2355 obtain given IPv4 address exhaustion. An alternative would be to re- 2356 purpose the prefix 192.88.99.0 which has been set aside from its 2357 former use by [RFC7526]. 2359 14.2. MS-Register and MS-Release List Processing 2361 OMNI links maintain a constant value "MAX_MSID" selected to provide 2362 MNs with an acceptable level of MSE redundancy while minimizing 2363 control message amplification. It is RECOMMENDED that MAX_MSID be 2364 set to the default value 5; if a different value is chosen, it should 2365 be set uniformly by all nodes on the OMNI link. 2367 When a MN sends an RS message with an OMNI option via an underlying 2368 interface to an AR, the MN must convey its knowledge of its 2369 currently-associated MSEs. Initially, the MN will have no associated 2370 MSEs and should therefore include an MS-Register sub-option with the 2371 single "anycast" MSID value 0 which requests the AR to select and 2372 assign an MSE. The AR will then return an RA message with source 2373 address set to the ADM-LLA of the selected MSE. 2375 As the MN activates additional underlying interfaces, it can 2376 optionally include an MS-Register sub-option with MSID value 0, or 2377 with non-zero MSIDs for MSEs discovered from previous RS/RA 2378 exchanges. The MN will thus eventually begin to learn and manage its 2379 currently active set of MSEs, and can register with new MSEs or 2380 release from former MSEs with each successive RS/RA exchange. As the 2381 MN's MSE constituency grows, it alone is responsible for including or 2382 omitting MSIDs in the MS-Register/Release lists it sends in RS 2383 messages. The inclusion or omission of MSIDs determines the MN's 2384 interface to the MS and defines the manner in which MSEs will 2385 respond. The only limiting factor is that the MN should include no 2386 more than MAX_MSID values in each list per each IPv6 ND message, and 2387 should avoid duplication of entries in each list unless it wants to 2388 increase likelihood of control message delivery. 2390 When an AR receives an RS message sent by a MN with an OMNI option, 2391 the option will contain zero or more MS-Register and MS-Release sub- 2392 options containing MSIDs. After processing the OMNI option, the AR 2393 will have a list of zero or more MS-Register MSIDs and a list of zero 2394 or more of MS-Release MSIDs. The AR then processes the lists as 2395 follows: 2397 o For each list, retain the first MAX_MSID values in the list and 2398 discard any additional MSIDs (i.e., even if there are duplicates 2399 within a list). 2401 o Next, for each MSID in the MS-Register list, remove all matching 2402 MSIDs from the MS-Release list. 2404 o Next, proceed according to whether the AR's own MSID or the value 2405 0 appears in the MS-Register list as follows: 2407 * If yes, send an RA message directly back to the MN and send a 2408 proxy copy of the RS message to each additional MSID in the MS- 2409 Register list with the MS-Register/Release lists omitted. 2410 Then, send an unsolicited NA (uNA) message to each MSID in the 2411 MS-Release list with the MS-Register/Release lists omitted and 2412 with an OMNI option with S/T-omIndex set to 0. 2414 * If no, send a proxy copy of the RS message to each additional 2415 MSID in the MS-Register list with the MS-Register list omitted. 2416 For the first MSID, include the original MS-Release list; for 2417 all other MSIDs, omit the MS-Release list. 2419 Each proxy copy of the RS message will include an OMNI option and OAL 2420 encapsulation header with the ADM-ULA of the AR as the source and the 2421 ADM-ULA of the Register MSE as the destination. When the Register 2422 MSE receives the proxy RS message, if the message includes an MS- 2423 Release list the MSE sends a uNA message to each additional MSID in 2424 the Release list with an OMNI option with S/T-omIndex set to 0. The 2425 Register MSE then sends an RA message back to the (Proxy) AR wrapped 2426 in an OAL encapsulation header with source and destination addresses 2427 reversed, and with RA destination set to the MNP-LLA of the MN. When 2428 the AR receives this RA message, it sends a proxy copy of the RA to 2429 the MN. 2431 Each uNA message (whether sent by the first-hop AR or by a Register 2432 MSE) will include an OMNI option and an OAL encapsulation header with 2433 the ADM-ULA of the Register MSE as the source and the ADM-ULA of the 2434 Release MSE as the destination. The uNA informs the Release MSE that 2435 its previous relationship with the MN has been released and that the 2436 source of the uNA message is now registered. The Release MSE must 2437 then note that the subject MN of the uNA message is now "departed", 2438 and forward any subsequent packets destined to the MN to the Register 2439 MSE. 2441 Note that it is not an error for the MS-Register/Release lists to 2442 include duplicate entries. If duplicates occur within a list, the AR 2443 will generate multiple proxy RS and/or uNA messages - one for each 2444 copy of the duplicate entries. 2446 14.3. DHCPv6-based Prefix Registration 2448 When a MN is not pre-provisioned with an MNP-LLA (or, when the MN 2449 requires additional MNP delegations), it requests the AR to select 2450 MNPs on its behalf and set up the correct routing state within the 2451 MS. The DHCPv6 service [RFC8415] supports this requirement. 2453 When an MN needs to have the AR select MNPs, it sends an RS message 2454 with the unspecified address (::) as the source and with DHCPv6 2455 Message sub-option containing a Client Identifier, one or more IA_PD 2456 options and a Rapid Commit option. The MN also sets the 'msg-type' 2457 field to "Solicit", and includes a 3-octet 'transaction-id'. The MN 2458 sets the RS destination to All-Routers multicast and applies OAL 2459 encapsulation and fragmentation if necessary as discussed above. 2461 When the AR receives the RS message, it performs OAL reassembly if 2462 necessary and extracts the DHCPv6 message from the OMNI option. The 2463 AR then acts as a "Proxy DHCPv6 Client" in a message exchange with 2464 the locally-resident DHCPv6 server, which delegates MNPs and returns 2465 a DHCPv6 Reply message with PD parameters. (If the AR wishes to 2466 defer creation of MN state until the DHCPv6 Reply is received, it can 2467 instead act as a Lightweight DHCPv6 Relay Agent per [RFC6221] by 2468 encapsulating the DHCPv6 message in a Relay-forward/reply exchange 2469 with Relay Message and Interface ID options.) 2471 When the AR receives the DHCPv6 Reply, it adds routes to the routing 2472 system and creates MNP-LLAs based on the delegated MNPs. The AR then 2473 sends an RA back to the MN with the DHCPv6 Reply message included in 2474 an OMNI DHCPv6 message sub-option. If the RS message source address 2475 was unspecified, the AR includes one of the (newly-created) MNP-LLAs 2476 as the RA destination address; otherwise, it includes the RS source 2477 address as the RA destination address. The AR then sets the RA 2478 source address to its own ADM-LLA then performs OAL encapsulation and 2479 fragmentation if necessary and sends the RA to the MN. When the MN 2480 receives the RA, it reassembles and discards the OAL encapsulation if 2481 necessary, then creates a default route, assigns Subnet Router 2482 Anycast addresses and uses the RA destination address as its primary 2483 MNP-LLA. The MN will then use this primary MNP-LLA as the source 2484 address of any IPv6 ND messages it sends as long as it retains 2485 ownership of the MNP. 2487 Note: After a MN performs a DHCPv6-based prefix registration exchange 2488 with a first AR, it would need to repeat the exchange with each 2489 additional MSE it registers with. In that case, the MN supplies the 2490 MNP delegations received from the first AR in the IA_PD fields of a 2491 DHCPv6 message when it engages the additional MSEs. 2493 15. Secure Redirection 2495 If the *NET link model is multiple access, the AR is responsible for 2496 assuring that address duplication cannot corrupt the neighbor caches 2497 of other nodes on the link. When the MN sends an RS message on a 2498 multiple access *NET link, the AR verifies that the MN is authorized 2499 to use the address and returns an RA with a non-zero Router Lifetime 2500 only if the MN is authorized. 2502 After verifying MN authorization and returning an RA, the AR MAY 2503 return IPv6 ND Redirect messages to direct MNs located on the same 2504 *NET link to exchange packets directly without transiting the AR. In 2505 that case, the MNs can exchange packets according to their unicast L2 2506 addresses discovered from the Redirect message instead of using the 2507 dogleg path through the AR. In some *NET links, however, such direct 2508 communications may be undesirable and continued use of the dogleg 2509 path through the AR may provide better performance. In that case, 2510 the AR can refrain from sending Redirects, and/or MNs can ignore 2511 them. 2513 16. AR and MSE Resilience 2515 *NETs SHOULD deploy ARs in Virtual Router Redundancy Protocol (VRRP) 2516 [RFC5798] configurations so that service continuity is maintained 2517 even if one or more ARs fail. Using VRRP, the MN is unaware which of 2518 the (redundant) ARs is currently providing service, and any service 2519 discontinuity will be limited to the failover time supported by VRRP. 2520 Widely deployed public domain implementations of VRRP are available. 2522 MSEs SHOULD use high availability clustering services so that 2523 multiple redundant systems can provide coordinated response to 2524 failures. As with VRRP, widely deployed public domain 2525 implementations of high availability clustering services are 2526 available. Note that special-purpose and expensive dedicated 2527 hardware is not necessary, and public domain implementations can be 2528 used even between lightweight virtual machines in cloud deployments. 2530 17. Detecting and Responding to MSE Failures 2532 In environments where fast recovery from MSE failure is required, ARs 2533 SHOULD use proactive Neighbor Unreachability Detection (NUD) in a 2534 manner that parallels Bidirectional Forwarding Detection (BFD) 2536 [RFC5880] to track MSE reachability. ARs can then quickly detect and 2537 react to failures so that cached information is re-established 2538 through alternate paths. Proactive NUD control messaging is carried 2539 only over well-connected ground domain networks (i.e., and not low- 2540 end *NET links such as aeronautical radios) and can therefore be 2541 tuned for rapid response. 2543 ARs perform proactive NUD for MSEs for which there are currently 2544 active MNs on the *NET. If an MSE fails, ARs can quickly inform MNs 2545 of the outage by sending multicast RA messages on the *NET interface. 2546 The AR sends RA messages to MNs via the *NET interface with an OMNI 2547 option with a Release ID for the failed MSE, and with destination 2548 address set to All-Nodes multicast (ff02::1) [RFC4291]. 2550 The AR SHOULD send MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated 2551 by small delays [RFC4861]. Any MNs on the *NET interface that have 2552 been using the (now defunct) MSE will receive the RA messages and 2553 associate with a new MSE. 2555 18. Transition Considerations 2557 When a MN connects to an *NET link for the first time, it sends an RS 2558 message with an OMNI option. If the first hop AR recognizes the 2559 option, it returns an RA with its ADM-LLA as the source, the MNP-LLA 2560 as the destination and with an OMNI option included. The MN then 2561 engages the AR according to the OMNI link model specified above. If 2562 the first hop AR is a legacy IPv6 router, however, it instead returns 2563 an RA message with no OMNI option and with a non-OMNI unicast source 2564 LLA as specified in [RFC4861]. In that case, the MN engages the *NET 2565 according to the legacy IPv6 link model and without the OMNI 2566 extensions specified in this document. 2568 If the *NET link model is multiple access, there must be assurance 2569 that address duplication cannot corrupt the neighbor caches of other 2570 nodes on the link. When the MN sends an RS message on a multiple 2571 access *NET link with an LLA source address and an OMNI option, ARs 2572 that recognize the option ensure that the MN is authorized to use the 2573 address and return an RA with a non-zero Router Lifetime only if the 2574 MN is authorized. ARs that do not recognize the option instead 2575 return an RA that makes no statement about the MN's authorization to 2576 use the source address. In that case, the MN should perform 2577 Duplicate Address Detection to ensure that it does not interfere with 2578 other nodes on the link. 2580 An alternative approach for multiple access *NET links to ensure 2581 isolation for MN / AR communications is through L2 address mappings 2582 as discussed in Appendix C. This arrangement imparts a (virtual) 2583 point-to-point link model over the (physical) multiple access link. 2585 19. OMNI Interfaces on Open Internetworks 2587 OMNI interfaces configured over IPv6-enabled underlying interfaces on 2588 an open Internetwork without an OMNI-aware first-hop AR receive RA 2589 messages that do not include an OMNI option, while OMNI interfaces 2590 configured over IPv4-only underlying interfaces do not receive any 2591 (IPv6) RA messages at all. OMNI interfaces that receive RA messages 2592 without an OMNI option configure addresses, on-link prefixes, etc. on 2593 the underlying interface that received the RA according to standard 2594 IPv6 ND and address resolution conventions [RFC4861] [RFC4862]. OMNI 2595 interfaces configured over IPv4-only underlying interfaces configure 2596 IPv4 address information on the underlying interfaces using 2597 mechanisms such as DHCPv4 [RFC2131]. 2599 OMNI interfaces configured over underlying interfaces that connect to 2600 an open Internetwork can apply security services such as VPNs to 2601 connect to an MSE, or can establish a direct link to an MSE through 2602 some other means (see Section 4). In environments where an explicit 2603 VPN or direct link may be impractical, OMNI interfaces can instead 2604 use UDP/IP encapsulation per [RFC6081][RFC4380] and HIP-based message 2605 authentication per [RFC7401]. 2607 For "Vehicle-to-Infrastructure (V2I)" coordination, the MN codes a 2608 HIP "Initiator" message in an OMNI option of an IPv6 RS message and 2609 the MSE responds with a HIP "Responder" message coded in an OMNI 2610 option of an IPv6 RA message. HIP security services are applied per 2611 [RFC7401], using the RS/RA messages as simple "shipping containers" 2612 to convey the HIP parameters. In that case, a "two-message HIP 2613 exchange" through a single RS/RA exchange may be sufficient for 2614 mutual authentication. For "Vehicle-to-Vehicle (V2V)" coordination, 2615 two MNs can coordinate directly with one another with HIP "Initiator/ 2616 Responder" messages coded in OMNI options of IPv6 NS/NA messages. In 2617 that case, a four-message HIP exchange (i.e., two back-to-back NS/NA 2618 exchanges) may be necessary for the two MNs to attain mutual 2619 authentication. 2621 After establishing a VPN or preparing for UDP/IP encapsulation, OMNI 2622 interfaces send control plane messages to interface with the MS, 2623 including RS/RA messages used according to Section 14 and NS/NA 2624 messages used for route optimization and mobility (see: 2625 [I-D.templin-intarea-6706bis]). The control plane messages must be 2626 authenticated while data plane messages are delivered the same as for 2627 ordinary best-effort traffic with basic source address-based data 2628 origin verification. Data plane communications via OMNI interfaces 2629 that connect over open Internetworks without an explicit VPN should 2630 therefore employ transport- or higher-layer security to ensure 2631 integrity and/or confidentiality. 2633 OMNI interfaces configured over open Internetworks are often located 2634 behind NATs. The OMNI interface accommodates NAT traversal using 2635 UDP/IP encapsulation and the mechanisms discussed in 2636 [I-D.templin-intarea-6706bis]. 2638 Note: Following the initial HIP Initiator/Responder exchange, OMNI 2639 interfaces configured over open Internetworks maintain HIP 2640 associations through the transmission of IPv6 ND messages that 2641 include OMNI options with HIP "Update" and "Notify" messages. OMNI 2642 interfaces use the HIP "Update" message when an acknowledgement is 2643 required, and use the "Notify" message in unacknowledged isolated 2644 IPv6 ND messages (e.g., unsolicited NAs). 2646 20. Time-Varying MNPs 2648 In some use cases, it is desirable, beneficial and efficient for the 2649 MN to receive a constant MNP that travels with the MN wherever it 2650 moves. For example, this would allow air traffic controllers to 2651 easily track aircraft, etc. In other cases, however (e.g., 2652 intelligent transportation systems), the MN may be willing to 2653 sacrifice a modicum of efficiency in order to have time-varying MNPs 2654 that can be changed every so often to defeat adversarial tracking. 2656 The prefix delegation services discussed in Section 14.3 allows OMNI 2657 MNs that desire time-varying MNPs to obtain short-lived prefixes to 2658 use the unspecified address (::) as the source address of an RS 2659 message with an OMNI option with DHCPv6 Option sub-options. The MN 2660 would then be obligated to renumber its internal networks whenever 2661 its MNP (and therefore also its OMNI address) changes. This should 2662 not present a challenge for MNs with automated network renumbering 2663 services, however presents limits for the durations of ongoing 2664 sessions that would prefer to use a constant address. 2666 21. (H)HITs and Temporary ULAs 2668 MNs that generate (H)HITs but do not have pre-assigned MNPs can 2669 request MNP delegations by issuing IPv6 ND messages that use the 2670 (H)HIT instead of a Temporary ULA. In particular, when a MN creates 2671 an RS message it can set the source address to the unspecified 2672 address (::) and destination address to All-Routers multicast. The 2673 MN then encapsulates the message in an IPv6 header with the (H)HIT as 2674 the source address and with destination set to either a unicast or 2675 anycast ADM-ULA. The MN then sends the message to the AR as 2676 specified in Section 14.1. 2678 When the AR receives the message, it notes that the RS source address 2679 was unspecified, then examines the RS encapsulation source address to 2680 determine that the source is a (H)HIT and not a Temporary ULA. The 2681 AR next invokes the DHCPv6 protocol to request an MNP prefix 2682 delegation, then prepares an RA message with source address set to 2683 its own ADM-LLA and destination set to the MNP-LLA corresponding to 2684 the delegated MNP. The AR finally encapsulates the RA in an IPv6 2685 header with source address set to its own ADM-ULA and destination set 2686 to the (H)HIT from the RS encapsulation source address, then returns 2687 the encapsulated RA to the MN. 2689 MNs can also use (H)HITs and/or Temporary ULAs for direct MN-to-MN 2690 communications outside the context of any OMNI link supporting 2691 infrastructure. When two MNs encounter one another they can use 2692 their (H)HITs and/or Temporary ULAs as IPv6 packet source and 2693 destination addresses to support direct communications. MNs can also 2694 inject their (H)HITs and/or Temporary ULAs into a MANET/VANET routing 2695 protocol to enable multihop communications. MNs can further exchange 2696 IPv6 ND messages (such as NS/NA) using their (H)HITs and/or Temporary 2697 ULAs as source and destination addresses, however the HIP security 2698 protocols for establishing secure neighbor relationships are based on 2699 (H)HITs. 2701 Lastly, when MNs are within the coverage range of OMNI link 2702 infrastructure a case could be made for injecting (H)HITs and/or 2703 Temporary ULAs into the global MS routing system. For example, when 2704 the MN sends an RS to a MSE it could include a request to inject the 2705 (H)HIT / Temporary ULA into the routing system instead of requesting 2706 an MNP prefix delegation. This would potentially enable OMNI link- 2707 wide communications using only (H)HITs or Temporary ULAs, and not 2708 MNPs. This document notes the opportunity, but makes no 2709 recommendation. 2711 22. IANA Considerations 2713 The IANA has assigned a 4-octet Private Enterprise Number (PEN) code 2714 "45282" in the "enterprise-numbers" registry. This document is the 2715 normative reference for using this code in DHCP Unique IDentifiers 2716 based on Enterprise Numbers ("DUID-EN for OMNI Interfaces") (see: 2717 Section 10). 2719 The IANA is instructed to allocate an official Type number TBD1 from 2720 the registry "IPv6 Neighbor Discovery Option Formats" for the OMNI 2721 option. Implementations set Type to 253 as an interim value 2722 [RFC4727]. 2724 The IANA is instructed to assign a new Code value "1" in the "ICMPv6 2725 Code Fields: Type 2 - Packet Too Big" registry. The registry should 2726 read as follows: 2728 Code Name Reference 2729 --- ---- --------- 2730 0 Diagnostic Packet Too Big [RFC4443] 2731 1 Advisory Packet Too Big [RFCXXXX] 2733 Figure 22: ICMPv6 Code Fields: Type 2 - Packet Too Big Values 2735 The IANA is instructed to allocate one Ethernet unicast address TBD2 2736 (suggest 00-00-5E-00-52-14 [RFC5214]) in the registry "IANA Ethernet 2737 Address Block - Unicast Use". 2739 The OMNI option defines a 5-bit Sub-Type field, for which IANA is 2740 instructed to create and maintain a new registry entitled "OMNI 2741 Option Sub-Type Values". Initial values for the OMNI Option Sub-Type 2742 Values registry are given below (future assignments are to be made 2743 through Standards Action [RFC8126]): 2745 Value Sub-Type name Reference 2746 ----- ------------- ---------- 2747 0 Pad1 [RFCXXXX] 2748 1 PadN [RFCXXXX] 2749 2 Interface Attributes (Type 1) [RFCXXXX] 2750 3 Interface Attributes (Type 2) [RFCXXXX] 2751 4 Traffic Selector [RFCXXXX] 2752 5 MS-Register [RFCXXXX] 2753 6 MS-Release [RFCXXXX] 2754 7 Geo Coordinates [RFCXXXX] 2755 8 DHCPv6 Message [RFCXXXX] 2756 9 HIP Message [RFCXXXX] 2757 10 Node Identification [RFCXXXX] 2758 11-29 Unassigned 2759 30 Sub-Type Extension [RFCXXXX] 2760 31 Reserved by IANA [RFCXXXX] 2762 Figure 23: OMNI Option Sub-Type Values 2764 The OMNI option defines an 8-bit Extension-Type field for Sub-Type 30 2765 (Sub-Type Extension), for which IANA is instructed to create and 2766 maintain a new registry entitled "OMNI Option Extension-Type Values". 2767 Initial values for the OMNI Option Extension-Type Values registry are 2768 given below (future assignments are to be made through Expert Review 2769 [RFC8126]): 2771 Value Sub-Type name Reference 2772 ----- ------------- ---------- 2773 0 Origin Indication [RFCXXXX] 2774 1-252 Unassigned 2775 253-254 Reserved for Experimentation [RFCXXXX] 2776 255 Reserved by IANA [RFCXXXX] 2778 Figure 24: OMNI Option Extension-Type Values 2780 The OMNI Node Identification Sub-Option (see: Section 11.1.11) 2781 contains an 8-bit ID-Type field, for which IANA is instructed to 2782 create and maintain a new registry entitled "OMNI Node Identification 2783 Sub-Option ID-Type values". Initial values for the OMNI Node 2784 Identification Sub-Option ID Type values registry are given below 2785 (future assignments are to be made through Expert Review [RFC8126]): 2787 Value Sub-Type name Reference 2788 ----- ------------- ---------- 2789 0 UUID [RFCXXXX] 2790 1 HIT [RFCXXXX] 2791 2 HHIT [RFCXXXX] 2792 3 Network Access Identifier [RFCXXXX] 2793 4 FQDN [RFCXXXX] 2794 5-252 Unassigned [RFCXXXX] 2795 253-254 Reserved for Experimentation [RFCXXXX] 2796 255 Reserved by IANA [RFCXXXX] 2798 Figure 25: OMNI Node Identification Sub-Option ID-Type Values 2800 23. Security Considerations 2802 Security considerations for IPv4 [RFC0791], IPv6 [RFC8200] and IPv6 2803 Neighbor Discovery [RFC4861] apply. OMNI interface IPv6 ND messages 2804 SHOULD include Nonce and Timestamp options [RFC3971] when transaction 2805 confirmation and/or time synchronization is needed. 2807 MN OMNI interfaces configured over secured ANET interfaces inherit 2808 the physical and/or link-layer security properties (i.e., "protected 2809 spectrum") of the connected ANETs. MN OMNI interfaces configured 2810 over open INET interfaces can use symmetric securing services such as 2811 VPNs or can by some other means establish a direct link. When a VPN 2812 or direct link may be impractical, however, the security services 2813 specified in [RFC7401] can be employed. While the OMNI link protects 2814 control plane messaging, applications must still employ end-to-end 2815 transport- or higher-layer security services to protect the data 2816 plane. 2818 Strong network layer security for control plane messages and 2819 forwarding path integrity for data plane messages between MSEs MUST 2820 be supported. In one example, the AERO service 2821 [I-D.templin-intarea-6706bis] constructs a spanning tree between MSEs 2822 and secures the links in the spanning tree with network layer 2823 security mechanisms such as IPsec [RFC4301] or Wireguard. Control 2824 plane messages are then constrained to travel only over the secured 2825 spanning tree paths and are therefore protected from attack or 2826 eavesdropping. Since data plane messages can travel over route 2827 optimized paths that do not strictly follow the spanning tree, 2828 however, end-to-end transport- or higher-layer security services are 2829 still required. 2831 Identity-based key verification infrastructure services such as iPSK 2832 may be necessary for verifying the identities claimed by MNs. This 2833 requirement should be harmonized with the manner in which (H)HITs are 2834 attested in a given operational environment. 2836 Security considerations for specific access network interface types 2837 are covered under the corresponding IP-over-(foo) specification 2838 (e.g., [RFC2464], [RFC2492], etc.). 2840 Security considerations for IPv6 fragmentation and reassembly are 2841 discussed in Section 5.1. 2843 24. Implementation Status 2845 AERO/OMNI Release-3.0.2 was tagged on October 15, 2020, and is 2846 undergoing internal testing. Additional internal releases expected 2847 within the coming months, with first public release expected end of 2848 1H2021. 2850 25. Acknowledgements 2852 The first version of this document was prepared per the consensus 2853 decision at the 7th Conference of the International Civil Aviation 2854 Organization (ICAO) Working Group-I Mobility Subgroup on March 22, 2855 2019. Consensus to take the document forward to the IETF was reached 2856 at the 9th Conference of the Mobility Subgroup on November 22, 2019. 2857 Attendees and contributors included: Guray Acar, Danny Bharj, 2858 Francois D'Humieres, Pavel Drasil, Nikos Fistas, Giovanni Garofolo, 2859 Bernhard Haindl, Vaughn Maiolla, Tom McParland, Victor Moreno, Madhu 2860 Niraula, Brent Phillips, Liviu Popescu, Jacky Pouzet, Aloke Roy, Greg 2861 Saccone, Robert Segers, Michal Skorepa, Michel Solery, Stephane 2862 Tamalet, Fred Templin, Jean-Marc Vacher, Bela Varkonyi, Tony Whyman, 2863 Fryderyk Wrobel and Dongsong Zeng. 2865 The following individuals are acknowledged for their useful comments: 2866 Stuart Card, Michael Matyas, Robert Moskowitz, Madhu Niraula, Greg 2867 Saccone, Stephane Tamalet, Eric Vyncke. Pavel Drasil, Zdenek Jaron 2868 and Michal Skorepa are especially recognized for their many helpful 2869 ideas and suggestions. Madhuri Madhava Badgandi, Sean Dickson, Don 2870 Dillenburg, Joe Dudkowski, Vijayasarathy Rajagopalan, Ron Sackman and 2871 Katherine Tran are acknowledged for their hard work on the 2872 implementation and technical insights that led to improvements for 2873 the spec. 2875 Discussions on the IETF 6man and atn mailing lists during the fall of 2876 2020 suggested additional points to consider. The authors gratefully 2877 acknowledge the list members who contributed valuable insights 2878 through those discussions. Eric Vyncke and Erik Kline were the 2879 intarea ADs, while Bob Hinden and Ole Troan were the 6man WG chairs 2880 at the time the document was developed; they are all gratefully 2881 acknowledged for their many helpful insights. 2883 This work is aligned with the NASA Safe Autonomous Systems Operation 2884 (SASO) program under NASA contract number NNA16BD84C. 2886 This work is aligned with the FAA as per the SE2025 contract number 2887 DTFAWA-15-D-00030. 2889 This work is aligned with the Boeing Information Technology (BIT) 2890 Mobility Vision Lab (MVL) program. 2892 26. References 2894 26.1. Normative References 2896 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 2897 DOI 10.17487/RFC0791, September 1981, 2898 . 2900 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 2901 Requirement Levels", BCP 14, RFC 2119, 2902 DOI 10.17487/RFC2119, March 1997, 2903 . 2905 [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, 2906 "Definition of the Differentiated Services Field (DS 2907 Field) in the IPv4 and IPv6 Headers", RFC 2474, 2908 DOI 10.17487/RFC2474, December 1998, 2909 . 2911 [RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander, 2912 "SEcure Neighbor Discovery (SEND)", RFC 3971, 2913 DOI 10.17487/RFC3971, March 2005, 2914 . 2916 [RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and 2917 More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191, 2918 November 2005, . 2920 [RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast 2921 Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005, 2922 . 2924 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 2925 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 2926 2006, . 2928 [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet 2929 Control Message Protocol (ICMPv6) for the Internet 2930 Protocol Version 6 (IPv6) Specification", STD 89, 2931 RFC 4443, DOI 10.17487/RFC4443, March 2006, 2932 . 2934 [RFC4727] Fenner, B., "Experimental Values In IPv4, IPv6, ICMPv4, 2935 ICMPv6, UDP, and TCP Headers", RFC 4727, 2936 DOI 10.17487/RFC4727, November 2006, 2937 . 2939 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 2940 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 2941 DOI 10.17487/RFC4861, September 2007, 2942 . 2944 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 2945 Address Autoconfiguration", RFC 4862, 2946 DOI 10.17487/RFC4862, September 2007, 2947 . 2949 [RFC6088] Tsirtsis, G., Giarreta, G., Soliman, H., and N. Montavont, 2950 "Traffic Selectors for Flow Bindings", RFC 6088, 2951 DOI 10.17487/RFC6088, January 2011, 2952 . 2954 [RFC7401] Moskowitz, R., Ed., Heer, T., Jokela, P., and T. 2955 Henderson, "Host Identity Protocol Version 2 (HIPv2)", 2956 RFC 7401, DOI 10.17487/RFC7401, April 2015, 2957 . 2959 [RFC8028] Baker, F. and B. Carpenter, "First-Hop Router Selection by 2960 Hosts in a Multi-Prefix Network", RFC 8028, 2961 DOI 10.17487/RFC8028, November 2016, 2962 . 2964 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2965 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2966 May 2017, . 2968 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 2969 (IPv6) Specification", STD 86, RFC 8200, 2970 DOI 10.17487/RFC8200, July 2017, 2971 . 2973 [RFC8201] McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed., 2974 "Path MTU Discovery for IP version 6", STD 87, RFC 8201, 2975 DOI 10.17487/RFC8201, July 2017, 2976 . 2978 [RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A., 2979 Richardson, M., Jiang, S., Lemon, T., and T. Winters, 2980 "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", 2981 RFC 8415, DOI 10.17487/RFC8415, November 2018, 2982 . 2984 26.2. Informative References 2986 [ATN] Maiolla, V., "The OMNI Interface - An IPv6 Air/Ground 2987 Interface for Civil Aviation, IETF Liaison Statement 2988 #1676, https://datatracker.ietf.org/liaison/1676/", March 2989 2020. 2991 [ATN-IPS] WG-I, ICAO., "ICAO Document 9896 (Manual on the 2992 Aeronautical Telecommunication Network (ATN) using 2993 Internet Protocol Suite (IPS) Standards and Protocol), 2994 Draft Edition 3 (work-in-progress)", December 2020. 2996 [CRC] Jain, R., "Error Characteristics of Fiber Distributed Data 2997 Interface (FDDI), IEEE Transactions on Communications", 2998 August 1990. 3000 [I-D.ietf-6man-rfc4941bis] 3001 Gont, F., Krishnan, S., Narten, T., and R. Draves, 3002 "Temporary Address Extensions for Stateless Address 3003 Autoconfiguration in IPv6", draft-ietf-6man-rfc4941bis-12 3004 (work in progress), November 2020. 3006 [I-D.ietf-drip-rid] 3007 Moskowitz, R., Card, S., Wiethuechter, A., and A. Gurtov, 3008 "UAS Remote ID", draft-ietf-drip-rid-06 (work in 3009 progress), December 2020. 3011 [I-D.ietf-intarea-tunnels] 3012 Touch, J. and M. Townsley, "IP Tunnels in the Internet 3013 Architecture", draft-ietf-intarea-tunnels-10 (work in 3014 progress), September 2019. 3016 [I-D.ietf-ipwave-vehicular-networking] 3017 Jeong, J., "IPv6 Wireless Access in Vehicular Environments 3018 (IPWAVE): Problem Statement and Use Cases", draft-ietf- 3019 ipwave-vehicular-networking-19 (work in progress), July 3020 2020. 3022 [I-D.templin-6man-dhcpv6-ndopt] 3023 Templin, F., "A Unified Stateful/Stateless Configuration 3024 Service for IPv6", draft-templin-6man-dhcpv6-ndopt-11 3025 (work in progress), January 2021. 3027 [I-D.templin-6man-lla-type] 3028 Templin, F., "The IPv6 Link-Local Address Type Field", 3029 draft-templin-6man-lla-type-02 (work in progress), 3030 November 2020. 3032 [I-D.templin-intarea-6706bis] 3033 Templin, F., "Asymmetric Extended Route Optimization 3034 (AERO)", draft-templin-intarea-6706bis-87 (work in 3035 progress), January 2021. 3037 [IPV4-GUA] 3038 Postel, J., "IPv4 Address Space Registry, 3039 https://www.iana.org/assignments/ipv4-address-space/ipv4- 3040 address-space.xhtml", December 2020. 3042 [IPV6-GUA] 3043 Postel, J., "IPv6 Global Unicast Address Assignments, 3044 https://www.iana.org/assignments/ipv6-unicast-address- 3045 assignments/ipv6-unicast-address-assignments.xhtml", 3046 December 2020. 3048 [RFC1035] Mockapetris, P., "Domain names - implementation and 3049 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, 3050 November 1987, . 3052 [RFC1122] Braden, R., Ed., "Requirements for Internet Hosts - 3053 Communication Layers", STD 3, RFC 1122, 3054 DOI 10.17487/RFC1122, October 1989, 3055 . 3057 [RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191, 3058 DOI 10.17487/RFC1191, November 1990, 3059 . 3061 [RFC1256] Deering, S., Ed., "ICMP Router Discovery Messages", 3062 RFC 1256, DOI 10.17487/RFC1256, September 1991, 3063 . 3065 [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", 3066 RFC 2131, DOI 10.17487/RFC2131, March 1997, 3067 . 3069 [RFC2225] Laubach, M. and J. Halpern, "Classical IP and ARP over 3070 ATM", RFC 2225, DOI 10.17487/RFC2225, April 1998, 3071 . 3073 [RFC2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet 3074 Networks", RFC 2464, DOI 10.17487/RFC2464, December 1998, 3075 . 3077 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 3078 IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473, 3079 December 1998, . 3081 [RFC2492] Armitage, G., Schulter, P., and M. Jork, "IPv6 over ATM 3082 Networks", RFC 2492, DOI 10.17487/RFC2492, January 1999, 3083 . 3085 [RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4 3086 Domains without Explicit Tunnels", RFC 2529, 3087 DOI 10.17487/RFC2529, March 1999, 3088 . 3090 [RFC2863] McCloghrie, K. and F. Kastenholz, "The Interfaces Group 3091 MIB", RFC 2863, DOI 10.17487/RFC2863, June 2000, 3092 . 3094 [RFC3330] IANA, "Special-Use IPv4 Addresses", RFC 3330, 3095 DOI 10.17487/RFC3330, September 2002, 3096 . 3098 [RFC3692] Narten, T., "Assigning Experimental and Testing Numbers 3099 Considered Useful", BCP 82, RFC 3692, 3100 DOI 10.17487/RFC3692, January 2004, 3101 . 3103 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 3104 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 3105 DOI 10.17487/RFC3810, June 2004, 3106 . 3108 [RFC3819] Karn, P., Ed., Bormann, C., Fairhurst, G., Grossman, D., 3109 Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L. 3110 Wood, "Advice for Internet Subnetwork Designers", BCP 89, 3111 RFC 3819, DOI 10.17487/RFC3819, July 2004, 3112 . 3114 [RFC3879] Huitema, C. and B. Carpenter, "Deprecating Site Local 3115 Addresses", RFC 3879, DOI 10.17487/RFC3879, September 3116 2004, . 3118 [RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally 3119 Unique IDentifier (UUID) URN Namespace", RFC 4122, 3120 DOI 10.17487/RFC4122, July 2005, 3121 . 3123 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 3124 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 3125 DOI 10.17487/RFC4271, January 2006, 3126 . 3128 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 3129 Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, 3130 December 2005, . 3132 [RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through 3133 Network Address Translations (NATs)", RFC 4380, 3134 DOI 10.17487/RFC4380, February 2006, 3135 . 3137 [RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery 3138 Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April 3139 2006, . 3141 [RFC4429] Moore, N., "Optimistic Duplicate Address Detection (DAD) 3142 for IPv6", RFC 4429, DOI 10.17487/RFC4429, April 2006, 3143 . 3145 [RFC4541] Christensen, M., Kimball, K., and F. Solensky, 3146 "Considerations for Internet Group Management Protocol 3147 (IGMP) and Multicast Listener Discovery (MLD) Snooping 3148 Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006, 3149 . 3151 [RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick, 3152 "Internet Group Management Protocol (IGMP) / Multicast 3153 Listener Discovery (MLD)-Based Multicast Forwarding 3154 ("IGMP/MLD Proxying")", RFC 4605, DOI 10.17487/RFC4605, 3155 August 2006, . 3157 [RFC4821] Mathis, M. and J. Heffner, "Packetization Layer Path MTU 3158 Discovery", RFC 4821, DOI 10.17487/RFC4821, March 2007, 3159 . 3161 [RFC4963] Heffner, J., Mathis, M., and B. Chandler, "IPv4 Reassembly 3162 Errors at High Data Rates", RFC 4963, 3163 DOI 10.17487/RFC4963, July 2007, 3164 . 3166 [RFC5175] Haberman, B., Ed. and R. Hinden, "IPv6 Router 3167 Advertisement Flags Option", RFC 5175, 3168 DOI 10.17487/RFC5175, March 2008, 3169 . 3171 [RFC5213] Gundavelli, S., Ed., Leung, K., Devarapalli, V., 3172 Chowdhury, K., and B. Patil, "Proxy Mobile IPv6", 3173 RFC 5213, DOI 10.17487/RFC5213, August 2008, 3174 . 3176 [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site 3177 Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, 3178 DOI 10.17487/RFC5214, March 2008, 3179 . 3181 [RFC5558] Templin, F., Ed., "Virtual Enterprise Traversal (VET)", 3182 RFC 5558, DOI 10.17487/RFC5558, February 2010, 3183 . 3185 [RFC5798] Nadas, S., Ed., "Virtual Router Redundancy Protocol (VRRP) 3186 Version 3 for IPv4 and IPv6", RFC 5798, 3187 DOI 10.17487/RFC5798, March 2010, 3188 . 3190 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 3191 (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, 3192 . 3194 [RFC6081] Thaler, D., "Teredo Extensions", RFC 6081, 3195 DOI 10.17487/RFC6081, January 2011, 3196 . 3198 [RFC6221] Miles, D., Ed., Ooghe, S., Dec, W., Krishnan, S., and A. 3199 Kavanagh, "Lightweight DHCPv6 Relay Agent", RFC 6221, 3200 DOI 10.17487/RFC6221, May 2011, 3201 . 3203 [RFC6355] Narten, T. and J. Johnson, "Definition of the UUID-Based 3204 DHCPv6 Unique Identifier (DUID-UUID)", RFC 6355, 3205 DOI 10.17487/RFC6355, August 2011, 3206 . 3208 [RFC6543] Gundavelli, S., "Reserved IPv6 Interface Identifier for 3209 Proxy Mobile IPv6", RFC 6543, DOI 10.17487/RFC6543, May 3210 2012, . 3212 [RFC6980] Gont, F., "Security Implications of IPv6 Fragmentation 3213 with IPv6 Neighbor Discovery", RFC 6980, 3214 DOI 10.17487/RFC6980, August 2013, 3215 . 3217 [RFC7084] Singh, H., Beebee, W., Donley, C., and B. Stark, "Basic 3218 Requirements for IPv6 Customer Edge Routers", RFC 7084, 3219 DOI 10.17487/RFC7084, November 2013, 3220 . 3222 [RFC7421] Carpenter, B., Ed., Chown, T., Gont, F., Jiang, S., 3223 Petrescu, A., and A. Yourtchenko, "Analysis of the 64-bit 3224 Boundary in IPv6 Addressing", RFC 7421, 3225 DOI 10.17487/RFC7421, January 2015, 3226 . 3228 [RFC7526] Troan, O. and B. Carpenter, Ed., "Deprecating the Anycast 3229 Prefix for 6to4 Relay Routers", BCP 196, RFC 7526, 3230 DOI 10.17487/RFC7526, May 2015, 3231 . 3233 [RFC7542] DeKok, A., "The Network Access Identifier", RFC 7542, 3234 DOI 10.17487/RFC7542, May 2015, 3235 . 3237 [RFC7739] Gont, F., "Security Implications of Predictable Fragment 3238 Identification Values", RFC 7739, DOI 10.17487/RFC7739, 3239 February 2016, . 3241 [RFC7847] Melia, T., Ed. and S. Gundavelli, Ed., "Logical-Interface 3242 Support for IP Hosts with Multi-Access Support", RFC 7847, 3243 DOI 10.17487/RFC7847, May 2016, 3244 . 3246 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 3247 Writing an IANA Considerations Section in RFCs", BCP 26, 3248 RFC 8126, DOI 10.17487/RFC8126, June 2017, 3249 . 3251 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 3252 Decraene, B., Litkowski, S., and R. Shakir, "Segment 3253 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 3254 July 2018, . 3256 [RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J., 3257 Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header 3258 (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020, 3259 . 3261 [RFC8900] Bonica, R., Baker, F., Huston, G., Hinden, R., Troan, O., 3262 and F. Gont, "IP Fragmentation Considered Fragile", 3263 BCP 230, RFC 8900, DOI 10.17487/RFC8900, September 2020, 3264 . 3266 Appendix A. Interface Attribute Preferences Bitmap Encoding 3268 Adaptation of the OMNI option Interface Attributes Preferences Bitmap 3269 encoding to specific Internetworks such as the Aeronautical 3270 Telecommunications Network with Internet Protocol Services (ATN/IPS) 3271 may include link selection preferences based on other traffic 3272 classifiers (e.g., transport port numbers, etc.) in addition to the 3273 existing DSCP-based preferences. Nodes on specific Internetworks 3274 maintain a map of traffic classifiers to additional P[*] preference 3275 fields beyond the first 64. For example, TCP port 22 maps to P[67], 3276 TCP port 443 maps to P[70], UDP port 8060 maps to P[76], etc. 3278 Implementations use Simplex or Indexed encoding formats for P[*] 3279 encoding in order to encode a given set of traffic classifiers in the 3280 most efficient way. Some use cases may be more efficiently coded 3281 using Simplex form, while others may be more efficient using Indexed. 3282 Once a format is selected for preparation of a single Interface 3283 Attribute the same format must be used for the entire Interface 3284 Attribute sub-option. Different sub-options may use different 3285 formats. 3287 The following figures show coding examples for various Simplex and 3288 Indexed formats: 3290 0 1 2 3 3291 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 3292 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3293 | Sub-Type=3| Sub-length=N | omIndex | omType | 3294 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3295 | Provider ID | Link |R| API | Bitmap(0)=0xff|P00|P01|P02|P03| 3296 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3297 |P04|P05|P06|P07|P08|P09|P10|P11|P12|P13|P14|P15|P16|P17|P18|P19| 3298 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3299 |P20|P21|P22|P23|P24|P25|P26|P27|P28|P29|P30|P31| Bitmap(1)=0xff| 3300 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3301 |P32|P33|P34|P35|P36|P37|P38|P39|P40|P41|P42|P43|P44|P45|P46|P47| 3302 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3303 |P48|P49|P50|P51|P52|P53|P54|P55|P56|P57|P58|P59|P60|P61|P62|P63| 3304 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3305 | Bitmap(2)=0xff|P64|P65|P67|P68| ... 3306 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 3308 Figure 26: Example 1: Dense Simplex Encoding 3310 0 1 2 3 3311 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 3312 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3313 | Sub-Type=3| Sub-length=N | omIndex | omType | 3314 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3315 | Provider ID | Link |R| API | Bitmap(0)=0x00| Bitmap(1)=0x0f| 3316 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3317 |P48|P49|P50|P51|P52|P53|P54|P55|P56|P57|P58|P59|P60|P61|P62|P63| 3318 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3319 | Bitmap(2)=0x00| Bitmap(3)=0x00| Bitmap(4)=0x00| Bitmap(5)=0x00| 3320 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3321 | Bitmap(6)=0xf0|192|193|194|195|196|197|198|199|200|201|202|203| 3322 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3323 |204|205|206|207| Bitmap(7)=0x00| Bitmap(8)=0x0f|272|273|274|275| 3324 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3325 |276|277|278|279|280|281|282|283|284|285|286|287| Bitmap(9)=0x00| 3326 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3327 |Bitmap(10)=0x00| ... 3328 +-+-+-+-+-+-+-+-+-+-+- 3330 Figure 27: Example 2: Sparse Simplex Encoding 3332 0 1 2 3 3333 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 3334 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3335 | Sub-Type=3| Sub-length=N | omIndex | omType | 3336 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3337 | Provider ID | Link |R| API | Index = 0x00 | Bitmap = 0x80 | 3338 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3339 |P00|P01|P02|P03| Index = 0x01 | Bitmap = 0x01 |P60|P61|P62|P63| 3340 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3341 | Index = 0x10 | Bitmap = 0x80 |512|513|514|515| Index = 0x18 | 3342 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3343 | Bitmap = 0x01 |796|797|798|799| ... 3344 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 3346 Figure 28: Example 3: Indexed Encoding 3348 Appendix B. VDL Mode 2 Considerations 3350 ICAO Doc 9776 is the "Technical Manual for VHF Data Link Mode 2" 3351 (VDLM2) that specifies an essential radio frequency data link service 3352 for aircraft and ground stations in worldwide civil aviation air 3353 traffic management. The VDLM2 link type is "multicast capable" 3354 [RFC4861], but with considerable differences from common multicast 3355 links such as Ethernet and IEEE 802.11. 3357 First, the VDLM2 link data rate is only 31.5Kbps - multiple orders of 3358 magnitude less than most modern wireless networking gear. Second, 3359 due to the low available link bandwidth only VDLM2 ground stations 3360 (i.e., and not aircraft) are permitted to send broadcasts, and even 3361 so only as compact layer 2 "beacons". Third, aircraft employ the 3362 services of ground stations by performing unicast RS/RA exchanges 3363 upon receipt of beacons instead of listening for multicast RA 3364 messages and/or sending multicast RS messages. 3366 This beacon-oriented unicast RS/RA approach is necessary to conserve 3367 the already-scarce available link bandwidth. Moreover, since the 3368 numbers of beaconing ground stations operating within a given spatial 3369 range must be kept as sparse as possible, it would not be feasible to 3370 have different classes of ground stations within the same region 3371 observing different protocols. It is therefore highly desirable that 3372 all ground stations observe a common language of RS/RA as specified 3373 in this document. 3375 Note that links of this nature may benefit from compression 3376 techniques that reduce the bandwidth necessary for conveying the same 3377 amount of data. The IETF lpwan working group is considering possible 3378 alternatives: [https://datatracker.ietf.org/wg/lpwan/documents]. 3380 Appendix C. MN / AR Isolation Through L2 Address Mapping 3382 Per [RFC4861], IPv6 ND messages may be sent to either a multicast or 3383 unicast link-scoped IPv6 destination address. However, IPv6 ND 3384 messaging should be coordinated between the MN and AR only without 3385 invoking other nodes on the *NET. This implies that MN / AR control 3386 messaging should be isolated and not overheard by other nodes on the 3387 link. 3389 To support MN / AR isolation on some *NET links, ARs can maintain an 3390 OMNI-specific unicast L2 address ("MSADDR"). For Ethernet-compatible 3391 *NETs, this specification reserves one Ethernet unicast address TBD2 3392 (see: Section 22). For non-Ethernet statically-addressed *NETs, 3393 MSADDR is reserved per the assigned numbers authority for the *NET 3394 addressing space. For still other *NETs, MSADDR may be dynamically 3395 discovered through other means, e.g., L2 beacons. 3397 MNs map the L3 addresses of all IPv6 ND messages they send (i.e., 3398 both multicast and unicast) to MSADDR instead of to an ordinary 3399 unicast or multicast L2 address. In this way, all of the MN's IPv6 3400 ND messages will be received by ARs that are configured to accept 3401 packets destined to MSADDR. Note that multiple ARs on the link could 3402 be configured to accept packets destined to MSADDR, e.g., as a basis 3403 for supporting redundancy. 3405 Therefore, ARs must accept and process packets destined to MSADDR, 3406 while all other devices must not process packets destined to MSADDR. 3407 This model has well-established operational experience in Proxy 3408 Mobile IPv6 (PMIP) [RFC5213][RFC6543]. 3410 Appendix D. Change Log 3412 << RFC Editor - remove prior to publication >> 3414 Differences from draft-templin-6man-omni-interface-35 to draft- 3415 templin-6man-omni-interface-36: 3417 o Major clarifications on aspects such as "hard/soft" PTB error 3418 messages 3420 o Made generic so that either IP protocol version (IPv4 or IPv6) can 3421 be used in the data plane. 3423 Differences from draft-templin-6man-omni-interface-31 to draft- 3424 templin-6man-omni-interface-32: 3426 o MTU 3427 o Support for multi-hop ANETS such as ISATAP. 3429 Differences from draft-templin-6man-omni-interface-29 to draft- 3430 templin-6man-omni-interface-30: 3432 o Moved link-layer addressing information into the OMNI option on a 3433 per-ifIndex basis 3435 o Renamed "ifIndex-tuple" to "Interface Attributes" 3437 Differences from draft-templin-6man-omni-interface-27 to draft- 3438 templin-6man-omni-interface-28: 3440 o Updates based on implementation experience. 3442 Differences from draft-templin-6man-omni-interface-25 to draft- 3443 templin-6man-omni-interface-26: 3445 o Further clarification on "aggregate" RA messages. 3447 o Expanded Security Considerations to discuss expectations for 3448 security in the Mobility Service. 3450 Differences from draft-templin-6man-omni-interface-20 to draft- 3451 templin-6man-omni-interface-21: 3453 o Safety-Based Multilink (SBM) and Performance-Based Multilink 3454 (PBM). 3456 Differences from draft-templin-6man-omni-interface-18 to draft- 3457 templin-6man-omni-interface-19: 3459 o SEND/CGA. 3461 Differences from draft-templin-6man-omni-interface-17 to draft- 3462 templin-6man-omni-interface-18: 3464 o Teredo 3466 Differences from draft-templin-6man-omni-interface-14 to draft- 3467 templin-6man-omni-interface-15: 3469 o Prefix length discussions removed. 3471 Differences from draft-templin-6man-omni-interface-12 to draft- 3472 templin-6man-omni-interface-13: 3474 o Teredo 3475 Differences from draft-templin-6man-omni-interface-11 to draft- 3476 templin-6man-omni-interface-12: 3478 o Major simplifications and clarifications on MTU and fragmentation. 3480 o Document now updates RFC4443 and RFC8201. 3482 Differences from draft-templin-6man-omni-interface-10 to draft- 3483 templin-6man-omni-interface-11: 3485 o Removed /64 assumption, resulting in new OMNI address format. 3487 Differences from draft-templin-6man-omni-interface-07 to draft- 3488 templin-6man-omni-interface-08: 3490 o OMNI MNs in the open Internet 3492 Differences from draft-templin-6man-omni-interface-06 to draft- 3493 templin-6man-omni-interface-07: 3495 o Brought back L2 MSADDR mapping text for MN / AR isolation based on 3496 L2 addressing. 3498 o Expanded "Transition Considerations". 3500 Differences from draft-templin-6man-omni-interface-05 to draft- 3501 templin-6man-omni-interface-06: 3503 o Brought back OMNI option "R" flag, and discussed its use. 3505 Differences from draft-templin-6man-omni-interface-04 to draft- 3506 templin-6man-omni-interface-05: 3508 o Transition considerations, and overhaul of RS/RA addressing with 3509 the inclusion of MSE addresses within the OMNI option instead of 3510 as RS/RA addresses (developed under FAA SE2025 contract number 3511 DTFAWA-15-D-00030). 3513 Differences from draft-templin-6man-omni-interface-02 to draft- 3514 templin-6man-omni-interface-03: 3516 o Added "advisory PTB messages" under FAA SE2025 contract number 3517 DTFAWA-15-D-00030. 3519 Differences from draft-templin-6man-omni-interface-01 to draft- 3520 templin-6man-omni-interface-02: 3522 o Removed "Primary" flag and supporting text. 3524 o Clarified that "Router Lifetime" applies to each ANET interface 3525 independently, and that the union of all ANET interface Router 3526 Lifetimes determines MSE lifetime. 3528 Differences from draft-templin-6man-omni-interface-00 to draft- 3529 templin-6man-omni-interface-01: 3531 o "All-MSEs" OMNI LLA defined. Also reserved fe80::ff00:0000/104 3532 for future use (most likely as "pseudo-multicast"). 3534 o Non-normative discussion of alternate OMNI LLA construction form 3535 made possible if the 64-bit assumption were relaxed. 3537 First draft version (draft-templin-atn-aero-interface-00): 3539 o Draft based on consensus decision of ICAO Working Group I Mobility 3540 Subgroup March 22, 2019. 3542 Authors' Addresses 3544 Fred L. Templin (editor) 3545 The Boeing Company 3546 P.O. Box 3707 3547 Seattle, WA 98124 3548 USA 3550 Email: fltemplin@acm.org 3552 Tony Whyman 3553 MWA Ltd c/o Inmarsat Global Ltd 3554 99 City Road 3555 London EC1Y 1AX 3556 England 3558 Email: tony.whyman@mccallumwhyman.com