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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 Intended status: Informational A. Whyman 5 Expires: October 18, 2021 MWA Ltd c/o Inmarsat Global Ltd 6 April 16, 2021 8 Transmission of IP Packets over Overlay Multilink Network (OMNI) 9 Interfaces 10 draft-templin-6man-omni-04 12 Abstract 14 Mobile nodes (e.g., aircraft of various configurations, terrestrial 15 vehicles, seagoing vessels, enterprise wireless devices, etc.) 16 communicate with networked correspondents over multiple access 17 network data links and configure mobile routers to connect end user 18 networks. A multilink interface specification is presented that 19 enables mobile nodes to coordinate with a network-based mobility 20 service and/or with other mobile node peers. This document specifies 21 the transmission of IP packets over Overlay Multilink Network (OMNI) 22 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 October 18, 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 . . . . . . . . . . . . . . . . . . . . . . . . . 6 60 3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 11 61 4. Overlay Multilink Network (OMNI) Interface Model . . . . . . 11 62 5. OMNI Interface Maximum Transmission Unit (MTU) . . . . . . . 17 63 6. The OMNI Adaptation Layer (OAL) . . . . . . . . . . . . . . . 18 64 6.1. OAL Source Encapsulation and Fragmentation . . . . . . . 18 65 6.2. OAL *NET Encapsulation and Re-Encapsulation . . . . . . . 23 66 6.3. OAL Destination Decapsulation and Reassembly . . . . . . 25 67 6.4. OAL Header Compression . . . . . . . . . . . . . . . . . 25 68 6.5. OAL Fragment Identification Window Maintenance . . . . . 28 69 6.6. OAL Fragment Retransmission . . . . . . . . . . . . . . . 29 70 6.7. OAL MTU Feedback Messaging . . . . . . . . . . . . . . . 30 71 6.8. OAL Requirements . . . . . . . . . . . . . . . . . . . . 32 72 6.9. OAL Fragmentation Security Implications . . . . . . . . . 33 73 6.10. OAL Super-Packets . . . . . . . . . . . . . . . . . . . . 34 74 7. Frame Format . . . . . . . . . . . . . . . . . . . . . . . . 36 75 8. Link-Local Addresses (LLAs) . . . . . . . . . . . . . . . . . 36 76 9. Unique-Local Addresses (ULAs) . . . . . . . . . . . . . . . . 37 77 10. Global Unicast Addresses (GUAs) . . . . . . . . . . . . . . . 39 78 11. Node Identification . . . . . . . . . . . . . . . . . . . . . 40 79 12. Address Mapping - Unicast . . . . . . . . . . . . . . . . . . 40 80 12.1. Sub-Options . . . . . . . . . . . . . . . . . . . . . . 42 81 12.1.1. Pad1 . . . . . . . . . . . . . . . . . . . . . . . . 44 82 12.1.2. PadN . . . . . . . . . . . . . . . . . . . . . . . . 44 83 12.1.3. Interface Attributes (Type 1) . . . . . . . . . . . 45 84 12.1.4. Interface Attributes (Type 2) . . . . . . . . . . . 46 85 12.1.5. Traffic Selector . . . . . . . . . . . . . . . . . . 50 86 12.1.6. MS-Register . . . . . . . . . . . . . . . . . . . . 51 87 12.1.7. MS-Release . . . . . . . . . . . . . . . . . . . . . 52 88 12.1.8. Geo Coordinates . . . . . . . . . . . . . . . . . . 52 89 12.1.9. Dynamic Host Configuration Protocol for IPv6 90 (DHCPv6) Message . . . . . . . . . . . . . . . . . . 53 91 12.1.10. Host Identity Protocol (HIP) Message . . . . . . . . 54 92 12.1.11. PIM-SM Message . . . . . . . . . . . . . . . . . . . 55 93 12.1.12. Reassembly Limit . . . . . . . . . . . . . . . . . . 56 94 12.1.13. Fragmentation Report . . . . . . . . . . . . . . . . 58 95 12.1.14. Node Identification . . . . . . . . . . . . . . . . 59 96 12.1.15. Sub-Type Extension . . . . . . . . . . . . . . . . . 60 98 13. Address Mapping - Multicast . . . . . . . . . . . . . . . . . 64 99 14. Multilink Conceptual Sending Algorithm . . . . . . . . . . . 64 100 14.1. Multiple OMNI Interfaces . . . . . . . . . . . . . . . . 65 101 14.2. MN<->AR Traffic Loop Prevention . . . . . . . . . . . . 65 102 15. Router Discovery and Prefix Registration . . . . . . . . . . 66 103 15.1. Router Discovery in IP Multihop and IPv4-Only Networks . 70 104 15.2. MS-Register and MS-Release List Processing . . . . . . . 72 105 15.3. DHCPv6-based Prefix Registration . . . . . . . . . . . . 74 106 16. Secure Redirection . . . . . . . . . . . . . . . . . . . . . 75 107 17. AR and MSE Resilience . . . . . . . . . . . . . . . . . . . . 75 108 18. Detecting and Responding to MSE Failures . . . . . . . . . . 76 109 19. Transition Considerations . . . . . . . . . . . . . . . . . . 76 110 20. OMNI Interfaces on Open Internetworks . . . . . . . . . . . . 77 111 21. Time-Varying MNPs . . . . . . . . . . . . . . . . . . . . . . 79 112 22. (H)HITs and Temporary ULAs . . . . . . . . . . . . . . . . . 80 113 23. Address Selection . . . . . . . . . . . . . . . . . . . . . . 81 114 24. Error Messages . . . . . . . . . . . . . . . . . . . . . . . 81 115 25. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 81 116 25.1. "IEEE 802 Numbers" Registry . . . . . . . . . . . . . . 81 117 25.2. "IPv6 Neighbor Discovery Option Formats" Registry . . . 82 118 25.3. "Ethernet Numbers" Registry . . . . . . . . . . . . . . 82 119 25.4. "ICMPv6 Code Fields: Type 2 - Packet Too Big" Registry . 82 120 25.5. "OMNI Option Sub-Type Values" (New Registry) . . . . . . 82 121 25.6. "OMNI Geo Coordinates Type Values" (New Registry) . . . 83 122 25.7. "OMNI Node Identification ID-Type Values" (New Registry) 83 123 25.8. "OMNI Option Sub-Type Extension Values" (New Registry) . 84 124 25.9. "OMNI RFC4380 UDP/IP Header Option" (New Registry) . . . 84 125 25.10. "OMNI RFC6081 UDP/IP Trailer Option" (New Registry) . . 85 126 25.11. Additional Considerations . . . . . . . . . . . . . . . 85 127 26. Security Considerations . . . . . . . . . . . . . . . . . . . 86 128 27. Implementation Status . . . . . . . . . . . . . . . . . . . . 87 129 28. Document Updates . . . . . . . . . . . . . . . . . . . . . . 87 130 29. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 87 131 30. References . . . . . . . . . . . . . . . . . . . . . . . . . 89 132 30.1. Normative References . . . . . . . . . . . . . . . . . . 89 133 30.2. Informative References . . . . . . . . . . . . . . . . . 91 134 Appendix A. Interface Attribute Preferences Bitmap Encoding . . 98 135 Appendix B. VDL Mode 2 Considerations . . . . . . . . . . . . . 100 136 Appendix C. MN / AR Isolation Through L2 Address Mapping . . . . 101 137 Appendix D. Change Log . . . . . . . . . . . . . . . . . . . . . 102 138 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 103 140 1. Introduction 142 Mobile Nodes (MNs) (e.g., aircraft of various configurations, 143 terrestrial vehicles, seagoing vessels, enterprise wireless devices, 144 pedestrians with cellphones, etc.) often have multiple interface 145 connections to wireless and/or wired-line data links used for 146 communicating with networked correspondents. These data links may 147 have diverse performance, cost and availability properties that can 148 change dynamically according to mobility patterns, flight phases, 149 proximity to infrastructure, etc. MNs coordinate their data links in 150 a discipline known as "multilink", in which a single virtual 151 interface is configured over the node's underlying interface 152 connections to the data links. 154 The MN configures a virtual interface (termed the "Overlay Multilink 155 Network Interface (OMNI)") as a thin layer over the underlying 156 interfaces. The OMNI interface is therefore the only interface 157 abstraction exposed to the IP layer and behaves according to the Non- 158 Broadcast, Multiple Access (NBMA) interface principle, while 159 underlying interfaces appear as link layer communication channels in 160 the architecture. The OMNI interface internally employs the "OMNI 161 Adaptation Layer (OAL)" to ensure that original IP packets are 162 delivered without loss due to size restrictions. The OMNI interface 163 connects to a virtual overlay service known as the "OMNI link". The 164 OMNI link spans one or more Internetworks that may include private- 165 use infrastructures and/or the global public Internet itself. 167 Each MN receives a Mobile Network Prefix (MNP) for numbering 168 downstream-attached End User Networks (EUNs) independently of the 169 access network data links selected for data transport. The MN 170 performs router discovery over the OMNI interface (i.e., similar to 171 IPv6 customer edge routers [RFC7084]) and acts as a mobile router on 172 behalf of its EUNs. The router discovery process is iterated over 173 each of the OMNI interface's underlying interfaces in order to 174 register per-link parameters (see Section 15). 176 The OMNI interface provides a multilink nexus for exchanging inbound 177 and outbound traffic via the correct underlying interface(s). The IP 178 layer sees the OMNI interface as a point of connection to the OMNI 179 link. Each OMNI link has one or more associated Mobility Service 180 Prefixes (MSPs), which are typically IP Global Unicast Address (GUA) 181 prefixes from which MNPs are derived. If there are multiple OMNI 182 links, the IPv6 layer will see multiple OMNI interfaces. 184 MNs may connect to multiple distinct OMNI links within the same OMNI 185 domain by configuring multiple OMNI interfaces, e.g., omni0, omni1, 186 omni2, etc. Each OMNI interface is configured over a set of 187 underlying interfaces and provides a nexus for Safety-Based Multilink 188 (SBM) operation. Each OMNI interface within the same OMNI domain 189 configures a common ULA prefix [ULA]::/48, and configures a unique 190 16-bit Subnet ID '*' to construct the sub-prefix [ULA*]::/64 (see: 191 Section 9). The IP layer applies SBM routing to select an OMNI 192 interface, which then applies Performance-Based Multilink (PBM) to 193 select the correct underlying interface. Applications can apply 194 Segment Routing [RFC8402] to select independent SBM topologies for 195 fault tolerance. 197 The OMNI interface interacts with a network-based Mobility Service 198 (MS) through IPv6 Neighbor Discovery (ND) control message exchanges 199 [RFC4861]. The MS provides Mobility Service Endpoints (MSEs) that 200 track MN movements and represent their MNPs in a global routing or 201 mapping system. 203 Many OMNI use cases have been proposed. In particular, the 204 International Civil Aviation Organization (ICAO) Working Group-I 205 Mobility Subgroup is developing a future Aeronautical 206 Telecommunications Network with Internet Protocol Services (ATN/IPS) 207 and has issued a liaison statement requesting IETF adoption [ATN] in 208 support of ICAO Document 9896 [ATN-IPS]. The IETF IP Wireless Access 209 in Vehicular Environments (ipwave) working group has further included 210 problem statement and use case analysis for OMNI in a document now in 211 AD evaluation for RFC publication 212 [I-D.ietf-ipwave-vehicular-networking]. Still other communities of 213 interest include AEEC, RTCA Special Committee 228 (SC-228) and NASA 214 programs that examine commercial aviation, Urban Air Mobility (UAM) 215 and Unmanned Air Systems (UAS). Pedestrians with handheld devices 216 represent another large class of potential OMNI users. 218 In addition to many other aspects, OMNI supports the "6M's" of modern 219 Internetworking including: 221 1. Multilink - a mobile node's ability to coordinate multiple 222 diverse underlying data links as a single logical unit (i.e., the 223 OMNI interface) to achieve the required communications 224 performance and reliability objectives. 226 2. Multinet - the ability to span the OMNI link across multiple 227 diverse network administrative segments while maintaining 228 seamless end-to-end communications between mobile nodes and 229 correspondents such as air traffic controllers, fleet 230 administrators, etc. 232 3. Mobility - a mobile node's ability to change network points of 233 attachment (e.g., moving between wireless base stations) which 234 may result in an underlying interface address change, but without 235 disruptions to ongoing communication sessions with peers over the 236 OMNI link. 238 4. Multicast - the ability to send a single network transmission 239 that reaches multiple nodes belonging to the same interest group, 240 but without disturbing other nodes not subscribed to the interest 241 group. 243 5. Multihop - a mobile node vehicle-to-vehicle relaying capability 244 useful when multiple forwarding hops between vehicles may be 245 necessary to "reach back" to an infrastructure access point 246 connection to the OMNI link. 248 6. MTU assurance - the ability to deliver packets of various robust 249 sizes between peers without loss due to a link size restriction, 250 and to dynamically adjust packets sizes to achieve the optimal 251 performance for each independent traffic flow. 253 This document specifies the transmission of IP packets and MN/MS 254 control messages over OMNI interfaces. The OMNI interface supports 255 either IP protocol version (i.e., IPv4 [RFC0791] or IPv6 [RFC8200]) 256 as the network layer in the data plane, while using IPv6 ND messaging 257 as the control plane independently of the data plane IP protocol(s). 258 The OAL operates as a sublayer between L3 and L2 based on IPv6 259 encapsulation [RFC2473] as discussed in the following sections. 261 2. Terminology 263 The terminology in the normative references applies; especially, the 264 terms "link" and "interface" are the same as defined in the IPv6 265 [RFC8200] and IPv6 Neighbor Discovery (ND) [RFC4861] specifications. 266 Additionally, this document assumes the following IPv6 ND message 267 types: Router Solicitation (RS), Router Advertisement (RA), Neighbor 268 Solicitation (NS), Neighbor Advertisement (NA) and Redirect. 270 The Protocol Constants defined in Section 10 of [RFC4861] are used in 271 their same format and meaning in this document. The terms "All- 272 Routers multicast", "All-Nodes multicast" and "Subnet-Router anycast" 273 are the same as defined in [RFC4291] (with Link-Local scope assumed). 275 The term "IP" is used to refer collectively to either Internet 276 Protocol version (i.e., IPv4 [RFC0791] or IPv6 [RFC8200]) when a 277 specification at the layer in question applies equally to either 278 version. 280 The following terms are defined within the scope of this document: 282 Mobile Node (MN) 283 an end system with a mobile router having multiple distinct 284 upstream data link connections that are grouped together in one or 285 more logical units. The MN's data link connection parameters can 286 change over time due to, e.g., node mobility, link quality, etc. 287 The MN further connects a downstream-attached End User Network 288 (EUN). The term MN used here is distinct from uses in other 289 documents, and does not imply a particular mobility protocol. 291 End User Network (EUN) 292 a simple or complex downstream-attached mobile network that 293 travels with the MN as a single logical unit. The IP addresses 294 assigned to EUN devices remain stable even if the MN's upstream 295 data link connections change. 297 Mobility Service (MS) 298 a mobile routing service that tracks MN movements and ensures that 299 MNs remain continuously reachable even across mobility events. 300 Specific MS details are out of scope for this document. 302 Mobility Service Endpoint (MSE) 303 an entity in the MS (either singular or aggregate) that 304 coordinates the mobility events of one or more MN. 306 Mobility Service Prefix (MSP) 307 an aggregated IP Global Unicast Address (GUA) prefix (e.g., 308 2001:db8::/32, 192.0.2.0/24, etc.) assigned to the OMNI link and 309 from which more-specific Mobile Network Prefixes (MNPs) are 310 delegated. OMNI link administrators typically obtain MSPs from an 311 Internet address registry, however private-use prefixes can 312 alternatively be used subject to certain limitations (see: 313 Section 10). OMNI links that connect to the global Internet 314 advertise their MSPs to their interdomain routing peers. 316 Mobile Network Prefix (MNP) 317 a longer IP prefix delegated from an MSP (e.g., 318 2001:db8:1000:2000::/56, 192.0.2.8/30, etc.) and assigned to a MN. 319 MNs sub-delegate the MNP to devices located in EUNs. Note that 320 OMNI link Relay nodes may also service non-MNP routes (i.e., GUA 321 prefixes not covered by an MSP) but that these correspond to fixed 322 correspondent nodes and not MNs. Other than this distinction, MNP 323 and non-MNP routes are treated exactly the same by the OMNI 324 routing system. 326 Access Network (ANET) 327 a data link service network (e.g., an aviation radio access 328 network, satellite service provider network, cellular operator 329 network, WiFi network, etc.) that connects MNs. Physical and/or 330 data link level security is assumed, and sometimes referred to as 331 "protected spectrum". Private enterprise networks and ground 332 domain aviation service networks may provide multiple secured IP 333 hops between the MN's point of connection and the nearest Access 334 Router. 336 Access Router (AR) 337 a router in the ANET for connecting MNs to correspondents in 338 outside Internetworks. The AR may be located on the same physical 339 link as the MN, or may be located multiple IP hops away. In the 340 latter case, the MN uses encapsulation to communicate with the AR 341 as though it were on the same physical link. 343 ANET interface 344 a MN's attachment to a link in an ANET. 346 Internetwork (INET) 347 a connected network region with a coherent IP addressing plan that 348 provides transit forwarding services between ANETs and nodes that 349 connect directly to the open INET via unprotected media. No 350 physical and/or data link level security is assumed, therefore 351 security must be applied by upper layers. The global public 352 Internet itself is an example. 354 INET interface 355 a node's attachment to a link in an INET. 357 *NET 358 a "wildcard" term used when a given specification applies equally 359 to both ANET and INET cases. 361 OMNI link 362 a Non-Broadcast, Multiple Access (NBMA) virtual overlay configured 363 over one or more INETs and their connected ANETs. An OMNI link 364 can comprise multiple INET segments joined by bridges the same as 365 for any link; the addressing plans in each segment may be mutually 366 exclusive and managed by different administrative entities. 368 OMNI interface 369 a node's attachment to an OMNI link, and configured over one or 370 more underlying *NET interfaces. If there are multiple OMNI links 371 in an OMNI domain, a separate OMNI interface is configured for 372 each link. 374 OMNI Adaptation Layer (OAL) 375 an OMNI interface sublayer service whereby original IP packets 376 admitted into the interface are wrapped in an IPv6 header and 377 subject to fragmentation and reassembly. The OAL is also 378 responsible for generating MTU-related control messages as 379 necessary, and for providing addressing context for spanning 380 multiple segments of a bridged OMNI link. 382 original IP packet 383 a whole IP packet or fragment admitted into the OMNI interface by 384 the network layer prior to OAL encapsulation and fragmentation, or 385 an IP packet delivered to the network layer by the OMNI interface 386 following OAL decapsulation and reassembly. 388 OAL packet 389 an original IP packet encapsulated in OAL headers and trailers 390 before OAL fragmentation, or following OAL reassembly. 392 OAL fragment 393 a portion of an OAL packet following fragmentation but prior to 394 *NET encapsulation, or following *NET encapsulation but prior to 395 OAL reassembly. 397 (OAL) atomic fragment 398 an OAL packet that does not require fragmentation is always 399 encapsulated as an "atomic fragment" with a Fragment Header with 400 Fragment Offset and More Fragments both set to 0, but with a valid 401 Identification value. 403 (OAL) carrier packet 404 an encapsulated OAL fragment following *NET encapsulation or prior 405 to *NET decapsulation. OAL sources and destinations exchange 406 carrier packets over underlying interfaces, and may be separated 407 by one or more OAL intermediate nodes. OAL intermediate nodes may 408 perform re-encapsulation on carrier packets by removing the *NET 409 headers of the first hop network and replacing them with new *NET 410 headers for the next hop network. 412 OAL source 413 an OMNI interface acts as an OAL source when it encapsulates 414 original IP packets to form OAL packets, then performs OAL 415 fragmentation and *NET encapsulation to create carrier packets. 417 OAL destination 418 an OMNI interface acts as an OAL destination when it decapsulates 419 carrier packets, then performs OAL reassembly and decapsulation to 420 derive the original IP packet. 422 OAL intermediate node 423 an OMNI interface acts as an OAL intermediate node when it removes 424 the *NET headers of carrier packets received on a first segment, 425 then re-encapsulates the carrier packets in new *NET headers and 426 forwards them into the next segment. 428 OMNI Option 429 an IPv6 Neighbor Discovery option providing multilink parameters 430 for the OMNI interface as specified in Section 12. 432 Mobile Network Prefix Link Local Address (MNP-LLA) 433 an IPv6 Link Local Address that embeds the most significant 64 434 bits of an MNP in the lower 64 bits of fe80::/64, as specified in 435 Section 8. 437 Mobile Network Prefix Unique Local Address (MNP-ULA) 438 an IPv6 Unique-Local Address derived from an MNP-LLA. 440 Administrative Link Local Address (ADM-LLA) 441 an IPv6 Link Local Address that embeds a 32-bit administratively- 442 assigned identification value in the lower 32 bits of fe80::/96, 443 as specified in Section 8. 445 Administrative Unique Local Address (ADM-ULA) 446 an IPv6 Unique-Local Address derived from an ADM-LLA. 448 Multilink 449 an OMNI interface's manner of managing diverse underlying 450 interface connections to data links as a single logical unit. The 451 OMNI interface provides a single unified interface to upper 452 layers, while underlying interface selections are performed on a 453 per-packet basis considering factors such as DSCP, flow label, 454 application policy, signal quality, cost, etc. Multilinking 455 decisions are coordinated in both the outbound (i.e. MN to 456 correspondent) and inbound (i.e., correspondent to MN) directions. 458 Multinet 459 an OAL intermediate node's manner of bridging multiple diverse IP 460 Internetworks and/or private enterprise networks at the OAL layer 461 below IP. Through intermediate node concatenation of bridged 462 network segments in this way, multiple diverse Internetworks (such 463 as the global public IPv4 and IPv6 Internets) can serve as transit 464 segments in a bridged path for forwarding IP packets end-to-end. 465 This bridging capability proivde benefits such as supporting IPv4/ 466 IPv6 transition and coexsitence, joining multiple diverse operator 467 networks into a cooperative single service network, etc. 469 Multihop 470 an iterative relaying of IP packets between MNs over an OMNI 471 underlying interface technology (such as omnidirectional wireless) 472 without support of fixed infrastructure. Multihop services entail 473 node-to-node relaying within a Mobile/Vehicular Ad-hoc Network 474 (MANET/VANET) for MN-to-MN communications and/or for "range 475 extension" where MNs within range of communications infrastructure 476 elements provide forwarding services for other MNs. 478 L2 479 The second layer in the OSI network model. Also known as "layer- 480 2", "link-layer", "sub-IP layer", "data link layer", etc. 482 L3 483 The third layer in the OSI network model. Also known as "layer- 484 3", "network-layer", "IP layer", etc. 486 underlying interface 487 a *NET interface over which an OMNI interface is configured. The 488 OMNI interface is seen as a L3 interface by the IP layer, and each 489 underlying interface is seen as a L2 interface by the OMNI 490 interface. The underlying interface either connects directly to 491 the physical communications media or coordinates with another node 492 where the physical media is hosted. 494 Mobility Service Identification (MSID) 495 Each MSE and AR is assigned a unique 32-bit Identification (MSID) 496 (see: Section 8). IDs are assigned according to MS-specific 497 guidelines (e.g., see: [I-D.templin-6man-aero]). 499 Safety-Based Multilink (SBM) 500 A means for ensuring fault tolerance through redundancy by 501 connecting multiple affiliated OMNI interfaces to independent 502 routing topologies (i.e., multiple independent OMNI links). 504 Performance Based Multilink (PBM) 505 A means for selecting underlying interface(s) for packet 506 transmission and reception within a single OMNI interface. 508 OMNI Domain 509 The set of all SBM/PBM OMNI links that collectively provides 510 services for a common set of MSPs. Each OMNI domain consists of a 511 set of affiliated OMNI links that all configure the same ::/48 ULA 512 prefix with a unique 16-bit Subnet ID as discussed in Section 9. 514 3. Requirements 516 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 517 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 518 "OPTIONAL" in this document are to be interpreted as described in BCP 519 14 [RFC2119][RFC8174] when, and only when, they appear in all 520 capitals, as shown here. 522 An implementation is not required to internally use the architectural 523 constructs described here so long as its external behavior is 524 consistent with that described in this document. 526 4. Overlay Multilink Network (OMNI) Interface Model 528 An OMNI interface is a virtual interface configured over one or more 529 underlying interfaces, which may be physical (e.g., an aeronautical 530 radio link, etc.) or virtual (e.g., an Internet or higher-layer 531 "tunnel"). The OMNI interface architectural layering model is the 532 same as in [RFC5558][RFC7847], and augmented as shown in Figure 1. 533 The IP layer therefore sees the OMNI interface as a single L3 534 interface nexus for multiple underlying interfaces that appear as L2 535 communication channels in the architecture. 537 +----------------------------+ 538 | Upper Layer Protocol | 539 Session-to-IP +---->| | 540 Address Binding | +----------------------------+ 541 +---->| IP (L3) | 542 IP Address +---->| | 543 Binding | +----------------------------+ 544 +---->| OMNI Interface | 545 Logical-to- +---->| (OMNI Adaptation Layer) | 546 Physical | +----------------------------+ 547 Interface +---->| L2 | L2 | | L2 | 548 Binding |(IF#1)|(IF#2)| ..... |(IF#n)| 549 +------+------+ +------+ 550 | L1 | L1 | | L1 | 551 | | | | | 552 +------+------+ +------+ 554 Figure 1: OMNI Interface Architectural Layering Model 556 Each underlying interface provides an L2/L1 abstraction according to 557 one of the following models: 559 o INET interfaces connect to an INET either natively or through one 560 or several IPv4 Network Address Translators (NATs). Native INET 561 interfaces have global IP addresses that are reachable from any 562 INET correspondent. NATed INET interfaces typically have private 563 IP addresses and connect to a private network behind one or more 564 NATs that provide INET access. 566 o ANET interfaces connect to a protected ANET that is separated from 567 the open INET by an AR acting as a proxy. The ANET interface may 568 be either on the same L2 link segment as the AR, or separated from 569 the AR by multiple IP hops. 571 o VPNed interfaces use security encapsulation over a *NET to a 572 Virtual Private Network (VPN) gateway. Other than the link-layer 573 encapsulation format, VPNed interfaces behave the same as for 574 Direct interfaces. 576 o Direct (aka "point-to-point") interfaces connect directly to a 577 peer without crossing any *NET paths. An example is a line-of- 578 sight link between a remote pilot and an unmanned aircraft. 580 The OMNI interface forwards original IP packets from the network 581 layer (L3) using the OMNI Adaptation Layer (OAL) (see: Section 5) as 582 an encapsulation and fragmentation sublayer service. This "OAL 583 source" then further encapsulates the resulting OAL packets/fragments 584 in *NET headers to create OAL carrier packets for transmission over 585 underlying interfaces (L2/L1). The target OMNI interface receives 586 the carrier packets from underlying interfaces (L1/L2) and discards 587 the *NET headers. If the resulting OAL packets/fragments are 588 addressed to itself, the OMNI interface acts as an "OAL destination" 589 and performs reassembly if necessary, discards the OAL encapsulation, 590 and delivers the original IP packet to the network layer (L3). If 591 the OAL fragments are addressed to another node, the OMNI interface 592 instead acts as an "OAL intermediate node" by re-encapsulating in new 593 *NET headers and forwarding the new carrier packets over an 594 underlying interface without reassembling or discarding the OAL 595 encapsulation. The OAL source and OAL destination are seen as 596 "neighbors" on the OMNI link, while OAL intermediate nodes are seen 597 as "bridges" capable of multinet concatenation. 599 The OMNI interface can send/receive original IP packets to/from 600 underlying interfaces while including/omitting various encapsulations 601 including OAL, UDP, IP and L2. The network layer can also access the 602 underlying interfaces directly while bypassing the OMNI interface 603 entirely when necessary. This architectural flexibility may be 604 beneficial for underlying interfaces (e.g., some aviation data links) 605 for which encapsulation overhead may be a primary consideration. 606 OMNI interfaces that send original IP packets directly over 607 underlying interfaces without invoking the OAL can only reach peers 608 located on the same OMNI link segment. However, an ANET proxy that 609 receives the original IP packet can forward it further by performing 610 OAL encapsulation with source set to its own address and destination 611 set to the OAL destination corresponding to the final destination 612 (i.e., even if the OAL destination is on a different OMNI link 613 segment). 615 Original IP packets sent directly over underlying interfaces are 616 subject to the same path MTU related issues as for any 617 Internetworking path, and do not include per-packet identifications 618 that can be used for data origin verification and/or link-layer 619 retransmissions. Original IP packets presented directly to an 620 underlying interface that exceed the underlying network path MTU are 621 dropped with an ordinary ICMPv6 Packet Too Big (PTB) message 622 returned. These PTB messages are subject to loss [RFC2923] the same 623 as for any non-OMNI IP interface. 625 The OMNI interface encapsulation/decapsulation layering possibilities 626 are shown in Figure 2 below. In the figure, imaginary vertical lines 627 drawn between the Network Layer and Underlying interfaces denote the 628 encapsulation/decapsulation layering combinations possible. Common 629 combinations include NULL (i.e., direct access to underlying 630 interfaces with or without using the OMNI interface), OMNI/IP, 631 OMNI/UDP/IP, OMNI/UDP/IP/L2, OMNI/OAL/UDP/IP, OMNI/OAL/UDP/L2, etc. 633 +------------------------------------------------------------+ 634 | Network Layer | 635 +--+---------------------------------------------------------+ 636 | OMNI Interface | 637 +--------------------------+------------------------------+ 638 | OAL Encaps/Decaps | 639 +------------------------------+ 640 | OAL Frag/Reass | 641 +------------+---------------+--------------+ 642 | UDP Encaps/Decaps/Compress | 643 +----+---+------------+--------+--+ +--------+ 644 | IP E/D | | IP E/D | | IP E/D | 645 +---+------+-+----+ +--+---+----+ +----+---+--+ 646 |L2 E/D| |L2 E/D| |L2 E/D| |L2 E/D| 647 +-------+------+---+------+----+------+---------------+------+ 648 | Underlying Interfaces | 649 +------------------------------------------------------------+ 651 Figure 2: OMNI Interface Layering 653 The OMNI/OAL model gives rise to a number of opportunities: 655 o MNs receive a MNP from the MS, and coordinate with the MS through 656 IPv6 ND message exchanges. The MN uses the MNP to construct a 657 unique Link-Local Address (MNP-LLA) through the algorithmic 658 derivation specified in Section 8 and assigns the LLA to the OMNI 659 interface. Since MNP-LLAs are uniquely derived from an MNP, no 660 Duplicate Address Detection (DAD) or Multicast Listener Discovery 661 (MLD) messaging is necessary. 663 o since Temporary ULAs are statistically unique, they can be used 664 without DAD, e.g. for MN-to-MN communications until an MNP-LLA is 665 obtained. 667 o underlying interfaces on the same L2 link segment as an AR do not 668 require any L3 addresses (i.e., not even link-local) in 669 environments where communications are coordinated entirely over 670 the OMNI interface. 672 o as underlying interface properties change (e.g., link quality, 673 cost, availability, etc.), any active interface can be used to 674 update the profiles of multiple additional interfaces in a single 675 message. This allows for timely adaptation and service continuity 676 under dynamically changing conditions. 678 o coordinating underlying interfaces in this way allows them to be 679 represented in a unified MS profile with provisions for mobility 680 and multilink operations. 682 o exposing a single virtual interface abstraction to the IPv6 layer 683 allows for multilink operation (including QoS based link 684 selection, packet replication, load balancing, etc.) at L2 while 685 still permitting L3 traffic shaping based on, e.g., DSCP, flow 686 label, etc. 688 o the OMNI interface allows inter-INET traversal when nodes located 689 in different INETs need to communicate with one another. This 690 mode of operation would not be possible via direct communications 691 over the underlying interfaces themselves. 693 o the OAL supports lossless and adaptive path MTU mitigations not 694 available for communications directly over the underlying 695 interfaces themselves. The OAL supports "packing" of multiple IP 696 payload packets within a single OAL packet. 698 o the OAL applies per-packet identification values that allow for 699 link-layer reliability and data origin authentication. 701 o L3 sees the OMNI interface as a point of connection to the OMNI 702 link; if there are multiple OMNI links (i.e., multiple MS's), L3 703 will see multiple OMNI interfaces. 705 o Multiple independent OMNI interfaces can be used for increased 706 fault tolerance through Safety-Based Multilink (SBM), with 707 Performance-Based Multilink (PBM) applied within each interface. 709 Other opportunities are discussed in [RFC7847]. Note that even when 710 the OMNI virtual interface is present, applications can still access 711 underlying interfaces either through the network protocol stack using 712 an Internet socket or directly using a raw socket. This allows for 713 intra-network (or point-to-point) communications without invoking the 714 OMNI interface and/or OAL. For example, when an IPv6 OMNI interface 715 is configured over an underlying IPv4 interface, applications can 716 still invoke IPv4 intra-network communications as long as the 717 communicating endpoints are not subject to mobility dynamics. 718 However, the opportunities discussed above are not realized when the 719 architectural layering is bypassed in this way. 721 Figure 3 depicts the architectural model for a MN with an attached 722 EUN connecting to the MS via multiple independent *NETs. When an 723 underlying interface becomes active, the MN's OMNI interface sends 724 IPv6 ND messages without encapsulation if the first-hop Access Router 725 (AR) is on the same underlying link; otherwise, the interface uses 726 IP-in-IP encapsulation. The IPv6 ND messages traverse the ground 727 domain *NETs until they reach an AR (AR#1, AR#2, ..., AR#n), which 728 then coordinates with an INET Mobility Service Endpoint (MSE#1, 729 MSE#2, ..., MSE#m) and returns an IPv6 ND message response to the MN. 730 The Hop Limit in IPv6 ND messages is not decremented due to 731 encapsulation; hence, the OMNI interface appears to be attached to an 732 ordinary link. 734 +--------------+ (:::)-. 735 | MN |<-->.-(::EUN:::) 736 +--------------+ `-(::::)-' 737 |OMNI interface| 738 +----+----+----+ 739 +--------|IF#1|IF#2|IF#n|------ + 740 / +----+----+----+ \ 741 / | \ 742 / | \ 743 v v v 744 (:::)-. (:::)-. (:::)-. 745 .-(::*NET:::) .-(::*NET:::) .-(::*NET:::) 746 `-(::::)-' `-(::::)-' `-(::::)-' 747 +----+ +----+ +----+ 748 ... |AR#1| .......... |AR#2| ......... |AR#n| ... 749 . +-|--+ +-|--+ +-|--+ . 750 . | | | 751 . v v v . 752 . <----- INET Encapsulation -----> . 753 . . 754 . +-----+ (:::)-. . 755 . |MSE#2| .-(::::::::) +-----+ . 756 . +-----+ .-(::: INET :::)-. |MSE#m| . 757 . (::::: Routing ::::) +-----+ . 758 . `-(::: System :::)-' . 759 . +-----+ `-(:::::::-' . 760 . |MSE#1| +-----+ +-----+ . 761 . +-----+ |MSE#3| |MSE#4| . 762 . +-----+ +-----+ . 763 . . 764 . . 765 . <----- Worldwide Connected Internetwork ----> . 766 ........................................................... 768 Figure 3: MN/MS Coordination via Multiple *NETs 770 After the initial IPv6 ND message exchange, the MN (and/or any nodes 771 on its attached EUNs) can send and receive original IP packets over 772 the OMNI interface. OMNI interface multilink services will forward 773 the packets via ARs in the correct underlying *NETs. The AR 774 encapsulates the packets according to the capabilities provided by 775 the MS and forwards them to the next hop within the worldwide 776 connected Internetwork via optimal routes. 778 5. OMNI Interface Maximum Transmission Unit (MTU) 780 The OMNI interface observes the link nature of tunnels, including the 781 Maximum Transmission Unit (MTU), Maximum Reassembly Unit (MRU) and 782 the role of fragmentation and reassembly [I-D.ietf-intarea-tunnels]. 783 The OMNI interface is configured over one or more underlying 784 interfaces as discussed in Section 4, where the interfaces (and their 785 associated *NET paths) may have diverse MTUs. OMNI interface 786 considerations for accommodating original IP packets of various sizes 787 are discussed in the following sections. 789 IPv6 underlying interfaces are REQUIRED to configure a minimum MTU of 790 1280 bytes and a minimum MRU of 1500 bytes [RFC8200]. Therefore, the 791 minimum IPv6 path MTU is 1280 bytes since routers on the path are not 792 permitted to perform network fragmentation even though the 793 destination is required to reassemble more. The network therefore 794 MUST forward original IP packets of at least 1280 bytes without 795 generating an IPv6 Path MTU Discovery (PMTUD) Packet Too Big (PTB) 796 message [RFC8201]. (While the source can apply "source 797 fragmentation" for locally-generated IPv6 packets up to 1500 bytes 798 and larger still if it knows the destination configures a larger MRU, 799 this does not affect the minimum IPv6 path MTU.) 801 IPv4 underlying interfaces are REQUIRED to configure a minimum MTU of 802 68 bytes [RFC0791] and a minimum MRU of 576 bytes [RFC0791][RFC1122]. 803 Therefore, when the Don't Fragment (DF) bit in the IPv4 header is set 804 to 0 the minimum IPv4 path MTU is 576 bytes since routers on the path 805 support network fragmentation and the destination is required to 806 reassemble at least that much. The OMNI interface therefore MUST set 807 DF to 0 in the IPv4 encapsulation headers of carrier packets that are 808 no larger than 576 bytes, and SHOULD set DF to 1 in larger carrier 809 packets. (Note: even if the encapsulation source has a way to 810 determine that the encapsulation destination configures an MRU larger 811 than 576 bytes, it should not assume a larger minimum IPv4 path MTU 812 without careful consideration of the issues discussed in 813 Section 6.9.) 815 The OMNI interface configures an MTU and MRU of 9180 bytes [RFC2492]; 816 the size is therefore not a reflection of the underlying interface or 817 *NET path MTUs, but rather determines the largest original IP packet 818 the OAL (and/or underlying interface) can forward or reassemble. For 819 each OAL destination (i.e., for each OMNI link neighbor), the OAL 820 source may discover "hard" or "soft" Reassembly Limit values smaller 821 than the MRU based on receipt of IPv6 ND messages with OMNI 822 Reassembly Limit sub-options (see: Section 12.1.12). The OMNI 823 interface employs the OAL as an encapsulation sublayer service to 824 transform original IP packets into OAL packets/fragments, and the OAL 825 in turn uses *NET encapsulation to forward carrier packets over the 826 underlying interfaces (see: Section 6). 828 6. The OMNI Adaptation Layer (OAL) 830 When an OMNI interface forwards an original IP packet from the 831 network layer for transmission over one or more underlying 832 interfaces, the OMNI Adaptation Layer (OAL) acting as the OAL source 833 drops the packet and returns a PTB message if the packet exceeds the 834 MRU and/or the hard Reassembly Limit for the intended OAL 835 destination. Otherwise, the OAL source applies encapsulation to form 836 OAL packets and fragmentation to produce resulting OAL fragments 837 suitable for *NET encapsulation and transmission as carrier packets 838 over underlying interfaces as described in Section 6.1. 840 These carrier packets travel over one or more underlying networks 841 bridged by OAL intermediate nodes, which re-encapsulate by removing 842 the *NET headers of the first underlying network and appending *NET 843 headers appropriate for the next underlying network in succession. 844 (This process supports the multinet concatenation capability needed 845 for joining multiple diverse networks.) After re-encapsulation by 846 zero or more OAL intermediate nodes, the carrier packets arrive at 847 the OAL destination. 849 When the OAL destination receives the carrier packets, it discards 850 the *NET headers and reassembles the resulting OAL fragments into an 851 OAL packet as described in Section 6.3. The OAL destination then 852 decapsulates the OAL packet to obtain the original IP packet, which 853 it then delivers to the network layer. 855 The OAL presents an OMNI sublayer abstraction similar to ATM 856 Adaptation Layer 5 (AAL5). Unlike AAL5 which performs segmentation 857 and reassembly with fixed-length 53 octet cells over ATM networks, 858 however, the OAL uses IPv6 encapsulation, fragmentation and 859 reassembly with larger variable-length cells over heterogeneous 860 underlying networks. Detailed operations of the OAL are specified in 861 the following sections. 863 6.1. OAL Source Encapsulation and Fragmentation 865 When the network layer forwards an original IP packet into the OMNI 866 interface, the OAL source inserts an IPv6 encapsulation header but 867 does not decrement the Hop Limit/TTL of the original IP packet since 868 encapsulation occurs at a layer below IP forwarding [RFC2473]. The 869 OAL source copies the "Type of Service/Traffic Class" [RFC2983] and 870 "Congestion Experienced" [RFC3168] values in the original packet's IP 871 header into the corresponding fields in the OAL header, then sets the 872 OAL header "Flow Label" as specified in [RFC6438]. The OAL source 873 finally sets the OAL header IPv6 Hop Limit to a conservative value 874 sufficient to enable loop-free forwarding over multiple concatenated 875 OMNI link segments and sets the Payload Length to the length of the 876 original IP packet. 878 The OAL next selects source and destination addresses for the IPv6 879 header of the resulting OAL packet. MN OMNI interfaces set the OAL 880 IPv6 header source address to a Unique Local Address (ULA) based on 881 the Mobile Network Prefix (MNP-ULA), while AR and MSE OMNI interfaces 882 set the source address to an Administrative ULA (ADM-ULA) (see: 883 Section 9). When a MN OMNI interface does not (yet) have an MNP-ULA, 884 it can use a Temporary ULA and/or Host Identity Tag (HIT) instead 885 (see: Section 22). 887 When the OAL source forwards an original IP packet toward a final 888 destination via an ANET underlying interface, it sets the OAL IPv6 889 header source address to its own ULA and sets the destination to 890 either the Administrative ULA (ADM-ULA) of the ANET peer or the 891 Mobile Network Prefix ULA (MNP-ULA) corresponding to the final 892 destination (see below). The OAL source then fragments the OAL 893 packet if necessary, encapsulates the OAL fragments in any ANET 894 headers and sends the resulting carrier packets to the ANET peer 895 which either reassembles before forwarding if the OAL destination is 896 its own ULA or forwards the fragments toward the true OAL destination 897 without first reassembling otherwise. 899 When the OAL source forwards an original IP packet toward a final 900 destination via an INET underlying interface, it sets the OAL IPv6 901 header source address to its own ULA and sets the destination to the 902 ULA of an OAL destination node on the final *NET segment. The OAL 903 source then fragments the OAL packet if necessary, encapsulates the 904 OAL fragments in any *NET headers and sends the resulting carrier 905 packets toward the OAL destination on the final segment OMNI node 906 which reassembles before forwarding the original IP packets toward 907 the final destination. 909 Following OAL IPv6 encapsulation and address selection, the OAL 910 source next appends a 2 octet trailing Checksum (initialized to 0) at 911 the end of the original IP packet while incrementing the OAL header 912 IPv6 Payload Length field to reflect the addition of the trailer. 913 The format of the resulting OAL packet following encapsulation is 914 shown in Figure 4: 916 +----------+-----+-----+-----+-----+-----+-----+----+ 917 | OAL Hdr | Original IP packet |Csum| 918 +----------+-----+-----+-----+-----+-----+-----+----+ 920 Figure 4: OAL Packet Before Fragmentation 922 The OAL source next selects a 32-bit Identification value for the 923 packet, beginning with an unpredictable value for the initial OAL 924 packet per [RFC7739] and monotonically incrementing for each 925 successive OAL packet until a new initial value is chosen. 927 The OAL source then calculates the 2's complement (mod 256) 928 Fletcher's checksum [CKSUM][RFC2328][RFC0905] over the entire OAL 929 packet beginning with a pseudo-header of the IPv6 header similar to 930 that found in Section 8.1 of [RFC8200]. The OAL IPv6 pseudo-header 931 is formed as shown in Figure 5: 933 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 934 | | 935 + + 936 | | 937 + OAL Source Address + 938 | | 939 + + 940 | | 941 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 942 | | 943 + + 944 | | 945 + OAL Destination Address + 946 | | 947 + + 948 | | 949 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 950 | OAL Payload Length | zero | Next Header | 951 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 952 | Identification | 953 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 955 Figure 5: OAL IPv6 Pseudo-Header 957 The OAL source then inserts a single OMNI Routing Header (ORH) if 958 necessary (see: [I-D.templin-6man-aero]) while incrementing Payload 959 Length to reflect the addition of the ORH (note that the late 960 addition of the ORH is not covered by the trailing checksum). 962 The OAL source next fragments the OAL packet if necessary while 963 assuming the IPv4 minimum path MTU (i.e., 576 bytes) as the worst 964 case for OAL fragmentation regardless of the underlying interface IP 965 protocol version since IPv6/IPv4 protocol translation and/or IPv6-in- 966 IPv4 encapsulation may occur in any *NET path. By always assuming 967 the IPv4 minimum even for IPv6 underlying interfaces, the OAL source 968 may produce smaller fragments with additional encapsulation overhead 969 but will always interoperate and never run the risk of loss due to an 970 MTU restriction or due to presenting an underlying interface with a 971 carrier packet that exceeds its MRU. Additionally, the OAL path 972 could traverse multiple *NET "segments" with intermediate OAL 973 forwarding nodes performing re-encapsulation where the *NET 974 encapsulation of the previous segment is replaced by the *NET 975 encapsulation of the next segment which may be based on a different 976 IP protocol version and/or encapsulation sizes. 978 The OAL source therefore assumes a default minimum path MTU of 576 979 bytes at each *NET segment for the purpose of generating OAL 980 fragments for *NET encapsulation and transmission as carrier packets. 981 In the worst case, each successive *NET segment may re-encapsulate 982 with either a 20 byte IPv4 or 40 byte IPv6 header, an 8 byte UDP 983 header and in some cases an IP security encapsulation (40 bytes 984 maximum assumed). Any *NET segment may also insert a maximum-length 985 (40 byte) ORH as an extension to the existing 40 byte OAL IPv6 header 986 plus 8 byte Fragment Header if an ORH was not already present. 987 Assuming therefore an absolute worst case of (40 + 40 + 8) = 88 bytes 988 for *NET encapsulation plus (40 + 40 + 8) = 88 bytes for OAL 989 encapsulation leaves (576 - 88 - 88) = 400 bytes to accommodate a 990 portion of the original IP packet/fragment. The OAL source therefore 991 sets a minimum Maximum Payload Size (MPS) of 400 bytes as the basis 992 for the minimum-sized OAL fragment that can be assured of traversing 993 all segments without loss due to an MTU/MRU restriction. The Maximum 994 Fragment Size (MFS) for OAL fragmentation is therefore determined by 995 the MPS plus the size of the OAL encapsulation headers. (Note that 996 the OAL source includes the 2 octet trailer as part of the payload 997 during fragmentation, and the OAL destination regards it as ordinary 998 payload until reassembly and checksum verification are complete.) 1000 The OAL source SHOULD maintain "path MPS" values for individual OAL 1001 destinations initialized to the minimum MPS and increased to larger 1002 values (up to the OMNI interface MTU) if better information is known 1003 or discovered. For example, when *NET peers share a common 1004 underlying link or a fixed path with a known larger MTU, the OAL 1005 source can base path MPS on this larger size (i.e., instead of 576 1006 bytes) as long as the *NET peer reassembles before re-encapsulating 1007 and forwarding (while re-fragmenting if necessary). Also, if the OAL 1008 source has a way of knowing the maximum *NET encapsulation size for 1009 all segments along the path it may be able to increase path MPS to 1010 reserve additional room for payload data. The OAL source must 1011 include the uncompressed OAL header size in its path MPS calculation, 1012 since a full header could be included at any time. 1014 The OAL source can also actively probe individual OAL destinations to 1015 discover larger path MPS values using packetization layer probes per 1016 [RFC4821][RFC8899], but care must be taken to avoid setting static 1017 values for dynamically changing paths leading to black holes. The 1018 probe involves sending an OAL packet larger than the current path MPS 1019 and receiving a small acknowledgement message in response (with the 1020 possible receipt of link-layer error message in case the probe was 1021 lost). For this purpose, the OAL source can send an NS message with 1022 one or more OMNI options with large PadN sub-options (see: 1023 Section 12) in order to receive a small NA response from the OAL 1024 destination. While observing the minimum MPS will always result in 1025 robust and secure behavior, the OAL source should optimize path MPS 1026 values when more efficient utilization may result in better 1027 performance (e.g. for wireless aviation data links). 1029 When the OAL source performs fragmentation, it SHOULD produce the 1030 minimum number of non-overlapping fragments under current MPS 1031 constraints, where each non-final fragment MUST be of equal length at 1032 least as large as the minimum MPS, while the final fragment MAY be of 1033 different length. The OAL source also converts all original IP 1034 packets no larger than the current MPS into "atomic fragments" by 1035 including a Fragment Header with Fragment Offset and More Fragments 1036 both set to 0. The OAL source finally encapsulates the fragments in 1037 *NET headers to form carrier packets and forwards them over an 1038 underlying interface, while retaining the fragments and their ordinal 1039 positions (i.e., as Frag #0, Frag #1, Frag #2, etc.) for a timeout 1040 period in case link-layer retransmission is requested. The formats 1041 of OAL fragments and carrier packets are shown in Figure 6. 1043 +----------+--+-------------+ 1044 | OAL Hdr |FH| Frag #0 | 1045 +----------+--+-------------+ 1046 +----------+--+-------------+ 1047 | OAL Hdr |FH| Frag #1 | 1048 +----------+--+-------------+ 1049 +----------+--+-------------+ 1050 | OAL Hdr |FH| Frag #2 | 1051 +----------+--+-------------+ 1052 .... 1053 +----------+--+-------------+----+ 1054 | OAL Hdr |FH| Frag #(N-1) |Csum| 1055 +----------+--+-------------+----+ 1056 a) OAL fragments after fragmentation 1057 (FH = Fragment Header; Csum appears only in final fragment) 1059 +--------+--+-----+-----+-----+-----+-----+----+ 1060 |OAL Hdr |FH| Original IP packet |Csum| 1061 +--------+--+-----+-----+-----+-----+-----+----+ 1062 b) An OAL atomic fragment with FH but no fragmentation. 1064 +--------+----------+--+-------------+ 1065 |*NET Hdr| OAL Hdr |FH| Frag #i | 1066 +--------+----------+--+-------------+ 1067 c) OAL carrier packet after *NET encapsulation 1069 Figure 6: OAL Fragments and Carrier Packets 1071 6.2. OAL *NET Encapsulation and Re-Encapsulation 1073 During *NET encapsulation, OAL sources first encapsulate each OAL 1074 fragment in a UDP header as the first *NET encapsulation sublayer if 1075 NAT traversal, packet filtering middlebox traversal and/or OAL header 1076 compression are necessary. The OAL then optionally appends 1077 additional encapsulation sublayer headers, then presents the *NET 1078 packet to an underlying interface. This layering can be seen in 1079 Figure 2. 1081 When a UDP header is included, the OAL source next sets the UDP 1082 source port to a constant value that it will use in each successive 1083 carrier packet it sends to the next OAL hop. For packets sent to an 1084 MSE, the OAL source sets the UDP destination port to 8060, i.e., the 1085 IANA-registered port number for AERO. For packets sent to a MN peer, 1086 the source sets the UDP destination port to the cached port value for 1087 this peer. The OAL source then sets the UDP length to the total 1088 length of the OAL fragment in correspondence with the OAL header 1089 Payload Length (i.e., the UDP length and IPv6 Payload Length must 1090 agree). The OAL source finally sets the UDP checksum to 0 1091 [RFC6935][RFC6936] since the only fields not already covered by the 1092 OAL checksum or underlying *NET CRCs are the Fragment Header fields, 1093 and any corruption in those fields will be garbage collected by the 1094 reassembly algorithm (however, see Section 20 for additional 1095 considerations). The UDP encapsulation header is often used in 1096 association with IP encapsulation, but may also be used between 1097 neighbors on a shared physical link with a true L2 header format such 1098 as for transmission over IEEE 802 Ethernet links. This document 1099 therefore requests a new Ether Type code assignment TBD1 in the IANA 1100 'ieee-802-numbers' registry for direct User Datagram Protocol (UDP) 1101 encapsulation over IEEE 802 Ethernet links (see: Section 25). 1103 For *NET encapsulations over IP, the OAL source next copies the "Type 1104 of Service/Traffic Class" [RFC2983] and "Congestion Experienced" 1105 [RFC3168] values in the OAL IPv6 header into the corresponding fields 1106 in the *NET IP header, then (for IPv6) sets the *NET IPv6 header 1107 "Flow Label" as specified in [RFC6438]. The OAL source then sets the 1108 *NET IP TTL/Hop Limit the same as for any *NET host, i.e., it does 1109 not copy the Hop Limit value from the OAL header. For carrier 1110 packets undergoing re-encapsulation at an OAL intermediate node, the 1111 node decrements the OAL IPv6 header Hop Limit and discards the 1112 carrier packet if the value reaches 0. The node then copies the 1113 "Type of Service/Traffic Class" and "Congestion Experienced" values 1114 from the previous hop *NET encapsulation header into the OAL IPv6 1115 header before setting the next hop *NET IP encapsulation header 1116 values the same as specified for the OAL source above. 1118 Following *NET encapsulation/re-encapsulation, the OAL source sends 1119 the resulting carrier packets over one or more underlying interfaces. 1120 The underlying interfaces often connect directly to physical media on 1121 the local platform (e.g., a laptop computer with WiFi, etc.), but in 1122 some configurations the physical media may be hosted on a separate 1123 Local Area Network (LAN) node. In that case, the OMNI interface can 1124 establish a Layer-2 VLAN or a point-to-point tunnel (at a layer below 1125 the underlying interface) to the node hosting the physical media. 1126 The OMNI interface may also apply encapsulation at the underlying 1127 interface layer (e.g., as for a tunnel virtual interface) such that 1128 carrier packets would appear "double-encapsulated" on the LAN; the 1129 node hosting the physical media in turn removes the LAN encapsulation 1130 prior to transmission or inserts it following reception. Finally, 1131 the underlying interface must monitor the node hosting the physical 1132 media (e.g., through periodic keepalives) so that it can convey 1133 up/down/status information to the OMNI interface. 1135 6.3. OAL Destination Decapsulation and Reassembly 1137 When an OMNI interface receives a carrier packet from an underlying 1138 interface, the OAL destination discards the *NET encapsulation 1139 headers and examines the OAL header of the enclosed OAL fragment. If 1140 the OAL fragment is addressed to a different node, the OAL 1141 destination re-encapsulates and forwards as discussed below. If the 1142 OAL fragment is addressed to itself, the OAL destination creates or 1143 updates a checklist for this (Source, Destination, Identification)- 1144 tuple to track the fragments already received (i.e., by examining the 1145 Payload Length, Fragment Offset, More Fragments and Identification 1146 values supplied by the OAL source). The OAL destination verifies 1147 that all non-final OAL fragments are of equal length no less than the 1148 minimum MPS and that no fragments overlap or leave "holes", while 1149 dropping any non-conforming fragments. The OAL destination records 1150 each conforming OAL fragment's ordinal position based on the OAL 1151 header Payload Length and Fragment Offset values (i.e., as Frag #0, 1152 Frag #1, Frag #2, etc.) and admits each fragment into the reassembly 1153 cache. 1155 When reassembly is complete, the OAL destination removes the ORH if 1156 present while decrementing Payload Length to reflect the removal of 1157 the ORH. The OAL destination next verifies the resulting OAL 1158 packet's checksum and discards the packet if the checksum is 1159 incorrect. If the OAL packet was accepted, the OAL destination then 1160 removes the OAL header/trailer, then delivers the original IP packet 1161 to the network layer. Note that link layers include a CRC-32 1162 integrity check which provides effective hop-by-hop error detection 1163 in the underlying network for payload sizes up to the OMNI interface 1164 MTU [CRC], but that some hops may traverse intermediate layers such 1165 as tunnels over IPv4 that do not include integrity checks. The 1166 trailing Fletcher checksum therefore allows the OAL destination to 1167 detect OAL packet splicing errors due to reassembly misassociations 1168 and/or to verify integrity for OAL packets whose fragments may have 1169 traversed unprotected underlying network hops [CKSUM]. The Fletcher 1170 algorithm also provides diversity with respect to both lower layer 1171 CRCs and upper layer Internet checksums as part of a complimentary 1172 multi-layer integrity assurance architecture. 1174 6.4. OAL Header Compression 1176 When the OAL source and destination are on the same *NET segment, no 1177 ORH is needed and carrier packet header compression is possible. 1178 When the OAL source and destination exchange initial IPv6 ND messages 1179 as discussed in the following Sections, each caches the observed *NET 1180 UDP source port and source IP (or L2) address associated with the OAL 1181 IPv6 source address found in the full-length OAL IPv6 header. After 1182 the initial IPv6 ND message exchange, the OAL source can begin 1183 applying OAL Header Compression to significantly reduce the 1184 encapsulation overhead required in each carrier packet. 1186 When the OAL source determines that header compression state has been 1187 established (i.e., following the IPv6 ND message exchange), it can 1188 begin sending OAL fragments with significant portions of the IPv6 1189 header and Fragment Header omitted thereby reducing the amount of 1190 encapsulation overhead. For OAL first-fragments (including atomic 1191 fragments), the OMNI Compressed Header - Type 0 (OCH-0) is used and 1192 formatted as shown in Figure 7: 1194 0 1 2 3 1195 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 1196 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ * 1197 | Source port | Destination port | U 1198 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ D 1199 | Length | Checksum | P 1200 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ * 1201 |Version| Traffic Class | Flow Label | 1202 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1203 | Next Header | Reserved |M| Identification (0 -1) | 1204 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1205 | Identification (2-3) | 1206 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+/ 1208 Figure 7: OMNI Compressed Header - Type 0 (OCH-0) 1210 In this format, the UDP header appears in its entirety in the first 8 1211 octets, then followed by the first 4 octets of the IPv6 header with 1212 the remainder omitted. (The IPv6 Version field is set to the value 0 1213 to distinguish this header from a true IP protocol version number and 1214 from OCH-1 - see below.) The compressed IPv6 header is then followed 1215 by a compressed IPv6 Fragment Header with the Fragment Offset field 1216 and two Reserved bits omitted (since these fields always encode the 1217 value 0 in first-fragments), and with the More Fragments (M) bit 1218 relocated to the least significant bit of the first Reserved field. 1219 The OCH-0 header is then followed by the OAL fragment body, and the 1220 UDP length field is reduced by 38 octets (i.e., the difference in 1221 length between full-length IPv6 and Fragment Headers and the length 1222 of the compressed headers). 1224 For OAL non-first fragments (i.e., those with non-zero Fragment 1225 Offsets), the OMNI Compressed Header - Type 1 (OCH-1) is used and 1226 formatted as shown in Figure 8: 1228 0 1 2 3 1229 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 1230 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ * 1231 | Source port | Destination port | U 1232 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ D 1233 | Length | Checksum | P 1234 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ * 1235 |V|R|M| Fragment Offset | Identification (0-1) | 1236 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1237 | Identification (1-3) | 1238 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1240 Figure 8: OMNI Compressed Header - Type 1 (OCH-1) 1242 In this format, the UDP header appears in its entirety in the first 8 1243 octets, but all IPv6 header fields except for the most significant 1244 Version (V) bit are omitted. (The V bit is set to the value 1 to 1245 distinguish this header from a true IP protocol version number and 1246 from OCH-0.) The V bit is followed by a single Reserved (R) bit and 1247 the More Fragments (M) bit in a compressed IPv6 Fragment Header with 1248 the Next Header and first Reserved fields omitted. The OCH-1 header 1249 is then followed by the OAL fragment body, and the UDP length field 1250 is reduced by 42 octets (i.e., the difference in length between full- 1251 length IPv6 and Fragment Headers and the length of the compressed 1252 headers). 1254 When the OAL destination receives a carrier packet with an OCH, it 1255 first determines the OAL IPv6 source and destination addresses by 1256 examining the UDP source port and L2 source address, then determines 1257 the length by examining the UDP length. The OAL destination then 1258 examines the (V)ersion field immediately following the UDP header. 1259 If the (4-bit) Version field encodes the value 0, the OAL destination 1260 processes the remainder of the header as an OCH-0, then reconstitutes 1261 the full-sized IPv6 and Fragment Headers and adds this OAL fragment 1262 to the reassembly buffer if necessary. If the (1-bit) V bit encodes 1263 the value 1, the OAL destination instead processes the remainder of 1264 the header as an OCH-1, then reconstitutes the full-sized IPv6 and 1265 Fragment Headers and adds this OAL fragment to the reassembly buffer. 1266 Note that, since the OCH-1 does not include Traffic Class, Flow Label 1267 or Next Header information, the OAL destination writes the value 0 1268 into these fields when it reconstitutes the full headers. These 1269 values will be correctly populated during reassembly after an OAL 1270 first fragment with an OCH-0 or uncompressed OAL header arrives. 1272 6.5. OAL Fragment Identification Window Maintenance 1274 As noted above, the OAL source establishes a window of 32-bit 1275 Identifications beginning with an unpredictable value for the initial 1276 message [RFC7739] and monotonically incrementing for each successive 1277 OAL packet until a new initial value is chosen. The OAL source 1278 asserts the starting value by including it as the Identification in 1279 an IPv6 ND NS/RS messages. When the OAL destination receives the 1280 IPv6 ND message, it resets the Identification window for this OAL 1281 source to the new value coded in the message's OAL header and expects 1282 future OAL fragments received from this OAL source to include 1283 sequential Identification values (subject to loss and reordering) 1284 until the neighbor reachable time expires or the OAL source sends a 1285 new IPv6 ND message. 1287 For example, if the OAL destination receives an NS/RS message with 1288 Identification 0x12345678, it resets the window for this OAL source 1289 to begin with 0x12345678 and examines the Identification values in 1290 subsequent OAL fragments received from this OAL source. If the 1291 Identification values of subsequent OAL fragments fall within the 1292 window of (0x12345678 + N) the OAL destination accepts the fragment; 1293 otherwise, it silently drops the fragment (where "N" represents the 1294 maximum number of fragments expected before the neighbor reachable 1295 time expires). 1297 While monitoring the current window, the OAL destination must accept 1298 new NS/RS Identification values even if outside the current window. 1299 The new Identification value resets the OAL destination's window 1300 start, and the window processing continues from this new starting 1301 point while allowing a period of overlap in case OAL fragments with 1302 Identification values from a previous window are still in flight. 1303 Note also that unsolicited NA messages must include Identification 1304 values within the current window, and therefore do not reset the 1305 current window. 1307 This implies that an IPv6 ND message used to reset the Identification 1308 window should fit within a single OAL fragment (i.e., within current 1309 MPS constraints), since a fragmented IPv6 ND message with an out-of- 1310 window Identification value could be part of a DoS attack. While 1311 larger IPv6 ND messages (up to the OMNI interface MTU) can certainly 1312 be subject to OAL fragmentation, their Identification should be 1313 within the current window maintained by the OAL destination to 1314 increase the likelihood that they will be accepted. 1316 6.6. OAL Fragment Retransmission 1318 When the OAL source sends carrier packets with OAL fragments to an 1319 OAL destination, the source caches them for a timeout period in case 1320 retransmission may be necessary. (The timeout duration is an 1321 implementation matter, and may be influenced by factors such as 1322 packet arrival rates, OAL source/destination round trip times, etc.) 1323 The OAL destination in turn maintains a checklist for the (Source, 1324 Destination, Identification)-tuple of each new OAL fragment received 1325 and notes the ordinal positions of fragments already received (i.e., 1326 as Frag #0, Frag #1, Frag #2, etc.). 1328 If the OAL destination notices some OAL fragments missing after most 1329 other fragments within the same Identification window have already 1330 arrived, it may send an IPv6 ND unsolicited Neighbor Advertisement 1331 (uNA) message to the OAL source that originated the fragments to 1332 report loss. The OAL destination creates a uNA message with an OMNI 1333 option containing an authentication sub-option to provide 1334 authentication (if the OAL source is on an open Internetwork) 1335 followed by a Fragmentation Report sub-option that includes a list of 1336 (Identification, Bitmap)-tuples for OAL fragments received and 1337 missing from this OAL source (see: Section 12). The OAL destination 1338 signs the message if an authentication sub-option is included, 1339 performs OAL encapsulation (with the its own address as the OAL 1340 source and the source address of the message that prompted the uNA as 1341 the OAL destination) and sends the message to the OAL source. 1343 When the OAL source receives the uNA message, it authenticates the 1344 message using authentication sub-option (if present) then examines 1345 the Fragmentation Report. For each (Source, Destination, 1346 Identification)-tuple, the OAL source determines whether it still 1347 holds the original OAL fragments in its cache and retransmits any for 1348 which the Bitmap indicated a loss event. For example, if the Bitmap 1349 indicates that the ordinal OAL fragments Frag #3, Frag #7, Frag #10 1350 and Frag #13 from the same OAL packet are missing the OAL source 1351 retransmits these fragments only and no others. 1353 Note that the goal of this service is to provide a light-weight link- 1354 layer Automatic Repeat Request (ARQ) capability in the spirit of 1355 Section 8.1 of [RFC3819]. Rather than provide true end-to-end 1356 reliability, however, the service provides timely link-layer 1357 retransmissions that may improve packet delivery ratios and avoid 1358 some delays inherent in true end-to-end services. 1360 6.7. OAL MTU Feedback Messaging 1362 When the OMNI interface forwards original IP packets from the network 1363 layer, it invokes the OAL and returns internally-generated ICMPv4 1364 Fragmentation Needed [RFC1191] or ICMPv6 Path MTU Discovery (PMTUD) 1365 Packet Too Big (PTB) [RFC8201] messages as necessary. This document 1366 refers to both of these ICMPv4/ICMPv6 message types simply as "PTBs", 1367 and introduces a distinction between PTB "hard" and "soft" errors as 1368 discussed below. 1370 Ordinary PTB messages with ICMPv4 header "unused" field or ICMPv6 1371 header Code field value 0 are hard errors that always indicate that a 1372 packet has been dropped due to a real MTU restriction. In 1373 particular, the OAL source drops the packet and returns a PTB hard 1374 error if the packet exceeds the OAL destination MRU. However, the 1375 OMNI interface can also forward large original IP packets via OAL 1376 encapsulation and fragmentation while at the same time returning PTB 1377 soft error messages (subject to rate limiting) if it deems the 1378 original IP packet too large according to factors such as link 1379 performance characteristics, reassembly congestion, etc. This 1380 ensures that the path MTU is adaptive and reflects the current path 1381 used for a given data flow. The OMNI interface can therefore 1382 continuously forward packets without loss while returning PTB soft 1383 error messages recommending a smaller size if necessary. Original 1384 sources that receive the soft errors in turn reduce the size of the 1385 packets they send (i.e., the same as for hard errors), but can soon 1386 resume sending larger packets if the soft errors subside. 1388 An OAL source sends PTB soft error messages by setting the ICMPv4 1389 header "unused" field or ICMPv6 header Code field to the value 1 if a 1390 original IP packet was deemed lost (e.g., due to reassembly timeout) 1391 or to the value 2 otherwise. The OAL source sets the PTB destination 1392 address to the original IP packet source, and sets the source address 1393 to one of its OMNI interface unicast/anycast addresses that is 1394 routable from the perspective of the original source. The OAL source 1395 then sets the MTU field to a value smaller than the original packet 1396 size but no smaller than 576 for ICMPv4 or 1280 for ICMPv6, writes 1397 the leading portion of the original IP packet into the "packet in 1398 error" field, and returns the PTB soft error to the original source. 1399 When the original source receives the PTB soft error, it temporarily 1400 reduces the size of the packets it sends the same as for hard errors 1401 but may seek to increase future packet sizes dynamically while no 1402 further soft errors are arriving. (If the original source does not 1403 recognize the soft error code, it regards the PTB the same as a hard 1404 error but should heed the retransmission advice given in [RFC8201] 1405 suggesting retransmission based on normal packetization layer 1406 retransmission timers.) 1407 An OAL destination may experience reassembly cache congestion, and 1408 can return uNA messages to the OAL source that originated the 1409 fragments (subject to rate limiting) to advertise reduced hard/soft 1410 Reassembly Limits and/or to report individual reassembly failures. 1411 The OAL destination creates a uNA message with an OMNI option 1412 containing an authentication message sub-option (if the OAL source is 1413 on an open Internetwork) followed optionally by at most one hard and 1414 one soft Reassembly Limit sub-options with reduced hard/soft values, 1415 and with one of them optionally including the leading portion an OAL 1416 first fragment containing the header of an original IP packet whose 1417 source must be notified (see: Section 12). The OAL destination 1418 encapsulates as much of the OAL first fragment (beginning with the 1419 OAL header) as will fit in the "OAL First Fragment" field of sub- 1420 option without causing the entire uNA message to exceed the minimum 1421 MPS, signs the message if an authentication sub-option is included, 1422 performs OAL encapsulation (with the its own address as the OAL 1423 source and the source address of the message that prompted the uNA as 1424 the OAL destination) and sends the message to the OAL source. 1426 When the OAL source receives the uNA message, it records the new 1427 hard/soft Reassembly Limit values for this OAL destination if the 1428 OMNI option includes Reassembly Limit sub-options. If a hard or soft 1429 Reassembly Limit sub-option includes an OAL First Fragment, the OAL 1430 source next sends a corresponding network layer PTB hard or soft 1431 error to the original source to recommend a smaller size. For hard 1432 errors, the OAL source sets the PTB Code field to 0. For soft 1433 errors, the OAL source sets the PTB Code field to 1 if the L flag in 1434 the Reassembly Limit sub-option is 1; otherwise, the OAL source sets 1435 the Code field to 2. The OAL source crafts the PTB by extracting the 1436 leading portion of the original IP packet from the OAL First Fragment 1437 field (i.e., not including the OAL header) and writes it in the 1438 "packet in error" field of a PTB with destination set to the original 1439 IP packet source and source set to one of its OMNI interface unicast/ 1440 anycast addresses that is routable from the perspective of the 1441 original source. For future transmissions, if the original IP packet 1442 is larger than the hard Reassembly Limit for this OAL destination the 1443 OAL source drops the packet and returns a PTB hard error with MTU set 1444 to the hard Reassembly Limit. If the packet is no larger than the 1445 current hard Reassembly Limit but larger than the current soft limit, 1446 the OAL source can also return PTB soft errors (subject to rate 1447 limiting) with Code set to 2 and MTU set to the current soft limit 1448 while still forwarding the packet to the OMNI destination. 1450 Original sources that receive PTB soft errors can dynamically tune 1451 the size of the original IP packets they to send to produce the best 1452 possible throughput and latency, with the understanding that these 1453 parameters may change over time due to factors such as congestion, 1454 mobility, network path changes, etc. The receipt or absence of soft 1455 errors should be seen as hints of when increasing or decreasing 1456 packet sizes may be beneficial. The OMNI interface supports 1457 continuous transmission and reception of packets of various sizes in 1458 the face of dynamically changing network conditions. Moreover, since 1459 PTB soft errors do not indicate a hard limit, original sources that 1460 receive soft errors can begin sending larger packets without waiting 1461 for the recommended 10 minutes specified for PTB hard errors 1462 [RFC1191][RFC8201]. The OMNI interface therefore provides an 1463 adaptive service that accommodates MTU diversity especially well- 1464 suited for dynamic multilink environments. 1466 6.8. OAL Requirements 1468 In light of the above, OAL sources, destinations and intermediate 1469 nodes observe the following normative requirements: 1471 o OAL sources MUST NOT send OAL fragments including original IP 1472 packets larger than the OMNI interface MTU or the OAL destination 1473 hard Reassembly Limit, i.e., whether or not fragmentation is 1474 needed. 1476 o OAL sources MUST NOT perform OAL fragmentation for original IP 1477 packets smaller than the minimum MPS minus the trailer size, and 1478 MUST produce non-final fragments that contain equal-length 1479 payloads no smaller than the minimum MPS when performing 1480 fragmentation. 1482 o OAL sources MUST NOT send OAL fragments that include any extension 1483 headers other than a single ORH and a single Fragment Header. 1485 o OAL intermediate nodes SHOULD and OAL destinations MUST 1486 unconditionally drop OAL packets/fragments including original IP 1487 packets larger than the OMNI interface MRU and/or OAL destination 1488 hard Reassembly Limit, i.e., whether or not reassembly was needed. 1490 o OAL intermediate nodes SHOULD and OAL destinations MUST 1491 unconditionally drop any non-final OAL fragments containing a 1492 payload smaller than the minimum MPS. 1494 o OAL intermediate nodes SHOULD and OAL destinations MUST 1495 unconditionally drop OAL fragments that include any extension 1496 headers other than a single ORH and a single Fragment Header. 1498 o OAL destination nodes MUST drop any new OAL non-final fragments of 1499 different length than other non-final fragments that have already 1500 been received, and MUST drop any new OAL fragments with Offset and 1501 Payload length that would overlap with other fragments and/or 1502 leave too-small holes between fragments that have already been 1503 received. 1505 Note: Under the minimum MPS, ordinary 1500 byte original IP packets 1506 would require at most 4 OAL fragments, with each non-final fragment 1507 containing 400 payload bytes and the final fragment containing 302 1508 payload bytes (i.e., the final 300 bytes of the original IP packet 1509 plus the 2 octet trailer). Likewise, maximum-length 9180 byte 1510 original IP packets would require at most 23 fragments. For all 1511 packet sizes, the likelihood of successful reassembly may improve 1512 when the OMNI interface sends all fragments of the same fragmented 1513 OAL packet consecutively over the same underlying interface. 1514 Finally, an assured minimum/path MPS allows continuous operation over 1515 all paths including those that traverse bridged L2 media with 1516 dissimilar MTUs. 1518 Note: Certain legacy network hardware of the past millennium was 1519 unable to accept packet "bursts" resulting from an IP fragmentation 1520 event - even to the point that the hardware would reset itself when 1521 presented with a burst. This does not seem to be a common problem in 1522 the modern era, where fragmentation and reassembly can be readily 1523 demonstrated at line rate (e.g., using tools such as 'iperf3') even 1524 over fast links on average hardware platforms. Even so, the OAL 1525 source could impose an inter-fragment delay while the OAL destination 1526 is reporting reassembly congestion (see: Section 6.7) and decrease 1527 the delay when reassembly congestion subsides. 1529 6.9. OAL Fragmentation Security Implications 1531 As discussed in Section 3.7 of [RFC8900], there are four basic 1532 threats concerning IPv6 fragmentation; each of which is addressed by 1533 effective mitigations as follows: 1535 1. Overlapping fragment attacks - reassembly of overlapping 1536 fragments is forbidden by [RFC8200]; therefore, this threat does 1537 not apply to the OAL. 1539 2. Resource exhaustion attacks - this threat is mitigated by 1540 providing a sufficiently large OAL reassembly cache and 1541 instituting "fast discard" of incomplete reassemblies that may be 1542 part of a buffer exhaustion attack. The reassembly cache should 1543 be sufficiently large so that a sustained attack does not cause 1544 excessive loss of good reassemblies but not so large that (timer- 1545 based) data structure management becomes computationally 1546 expensive. The cache should also be indexed based on the arrival 1547 underlying interface such that congestion experienced over a 1548 first underlying interface does not cause discard of incomplete 1549 reassemblies for uncongested underlying interfaces. 1551 3. Attacks based on predictable fragment identification values - 1552 this threat is mitigated by selecting an unpredictable 1553 Identification value per [RFC7739]. Additionally, inclusion of 1554 the OAL checksum would make it very difficult for an attacker who 1555 could somehow predict a fragment identification value to inject 1556 malicious fragments resulting in undetected reassemblies of bad 1557 data. 1559 4. Evasion of Network Intrusion Detection Systems (NIDS) - this 1560 threat is mitigated by setting a minimum MPS for OAL 1561 fragmentation, which defeats all "tiny fragment"-based attacks. 1563 Additionally, IPv4 fragmentation includes a 16-bit Identification (IP 1564 ID) field with only 65535 unique values such that at high data rates 1565 the field could wrap and apply to new carrier packets while the 1566 fragments of old packets using the same ID are still alive in the 1567 network [RFC4963]. However, since the largest carrier packet that 1568 will be sent via an IPv4 path with DF = 0 is 576 bytes any IPv4 1569 fragmentation would occur only on links with an IPv4 MTU smaller than 1570 this size, and [RFC3819] recommendations suggest that such links will 1571 have low data rates. Since IPv6 provides a 32-bit Identification 1572 value, IP ID wraparound at high data rates is not a concern for IPv6 1573 fragmentation. 1575 Finally, [RFC6980] documents fragmentation security concerns for 1576 large IPv6 ND messages. These concerns are addressed when the OMNI 1577 interface employs the OAL instead of directly fragmenting the IPv6 ND 1578 message itself. For this reason, OMNI interfaces MUST NOT send IPv6 1579 ND messages larger than the OMNI interface MTU, and MUST employ OAL 1580 encapsulation and fragmentation for IPv6 ND messages larger than the 1581 current MPS for this OAL destination. 1583 6.10. OAL Super-Packets 1585 By default, the OAL source includes a 40-byte IPv6 encapsulation 1586 header for each original IP packet during OAL encapsulation. The OAL 1587 source also calculates and appends a 2 octet trailing Fletcher 1588 checksum then performs fragmentation such that a copy of the 40-byte 1589 IPv6 header plus an 8-byte IPv6 Fragment Header is included in each 1590 OAL fragment (when an ORH is added, the OAL encapsulation headers 1591 become larger still). However, these encapsulations may represent 1592 excessive overhead in some environments. OAL header compression can 1593 dramatically reduce the amount of encapsulation overhead, however a 1594 complimentary technique known as "packing" (see: 1595 [I-D.ietf-intarea-tunnels]) is also supported so that multiple 1596 original IP packets and/or control messages can be included within a 1597 single OAL "super-packet". 1599 When the OAL source has multiple original IP packets to send to the 1600 same OAL destination with total length no larger than the OAL 1601 destination MRU, it can concatenate them into a super-packet 1602 encapsulated in a single OAL header and trailing checksum. Within 1603 the OAL super-packet, the IP header of the first original IP packet 1604 (iHa) followed by its data (iDa) is concatenated immediately 1605 following the OAL header, then the IP header of the next original 1606 packet (iHb) followed by its data (iDb) is concatenated immediately 1607 following the first original packet, etc. with the trailing checksum 1608 included last. The OAL super-packet format is transposed from 1609 [I-D.ietf-intarea-tunnels] and shown in Figure 9: 1611 <------- Original IP packets -------> 1612 +-----+-----+ 1613 | iHa | iDa | 1614 +-----+-----+ 1615 | 1616 | +-----+-----+ 1617 | | iHb | iDb | 1618 | +-----+-----+ 1619 | | 1620 | | +-----+-----+ 1621 | | | iHc | iDc | 1622 | | +-----+-----+ 1623 | | | 1624 v v v 1625 +----------+-----+-----+-----+-----+-----+-----+----+ 1626 | OAL Hdr | iHa | iDa | iHb | iDb | iHc | iDc |Csum| 1627 +----------+-----+-----+-----+-----+-----+-----+----+ 1628 <--- OAL "Super-Packet" with single OAL Hdr/Csum ---> 1630 Figure 9: OAL Super-Packet Format 1632 When the OAL source prepares a super-packet, it applies OAL 1633 fragmentation and *NET encapsulation then sends the carrier packets 1634 to the OAL destination. When the OAL destination receives the super- 1635 packet it reassembles if necessary, verifies and removes the trailing 1636 checksum, then regards the remaining OAL header Payload Length as the 1637 sum of the lengths of all payload packets. The OAL destination then 1638 selectively extracts each original IP packet (e.g., by setting 1639 pointers into the super-packet buffer and maintaining a reference 1640 count, by copying each packet into a separate buffer, etc.) and 1641 forwards each packet to the network layer. During extraction, the 1642 OAL determines the IP protocol version of each successive original IP 1643 packet 'j' by examining the four most-significant bits of iH(j), and 1644 determines the length of the packet by examining the rest of iH(j) 1645 according to the IP protocol version. 1647 Note that OMNI interfaces must take care to avoid processing super- 1648 packet payload elements that would subvert security. Specifically, 1649 if a super-packet contains a mix of data and control payload packets 1650 (which could include critical security codes), the node MUST NOT 1651 process the data packets before processing the control packets 1653 7. Frame Format 1655 The OMNI interface forwards original IP packets from the network 1656 layer by first invoking the OAL to create OAL packets/fragments if 1657 necessary, then including any *NET encapsulations and finally 1658 engaging the native frame format of the underlying interface. For 1659 example, for Ethernet-compatible interfaces the frame format is 1660 specified in [RFC2464], for aeronautical radio interfaces the frame 1661 format is specified in standards such as ICAO Doc 9776 (VDL Mode 2 1662 Technical Manual), for various forms of tunnels the frame format is 1663 found in the appropriate tunneling specification, etc. 1665 See Figure 2 for a map of the various *NET layering combinations 1666 possible. For any layering combination, the final layer (e.g., UDP, 1667 IP, Ethernet, etc.) must have an assigned number and frame format 1668 representation that is compatible with the selected underlying 1669 interface. 1671 8. Link-Local Addresses (LLAs) 1673 OMNI nodes are assigned OMNI interface IPv6 Link-Local Addresses 1674 (LLAs) through pre-service administrative actions. "MNP-LLAs" embed 1675 the MNP assigned to the mobile node, while "ADM-LLAs" include an 1676 administratively-unique ID that is guaranteed to be unique on the 1677 link. LLAs are configured as follows: 1679 o IPv6 MNP-LLAs encode the most-significant 64 bits of a MNP within 1680 the least-significant 64 bits of the IPv6 link-local prefix 1681 fe80::/64, i.e., in the LLA "interface identifier" portion. The 1682 prefix length for the LLA is determined by adding 64 to the MNP 1683 prefix length. For example, for the MNP 2001:db8:1000:2000::/56 1684 the corresponding MNP-LLA is fe80::2001:db8:1000:2000/120. Non- 1685 MNP routes are also represented the same as for MNP-LLAs, but 1686 include a GUA prefix that is not properly covered by the MSP. 1688 o IPv4-compatible MNP-LLAs are constructed as fe80::ffff:[IPv4], 1689 i.e., the interface identifier consists of 16 '0' bits, followed 1690 by 16 '1' bits, followed by a 32bit IPv4 address/prefix. The 1691 prefix length for the LLA is determined by adding 96 to the MNP 1692 prefix length. For example, the IPv4-Compatible MN OMNI LLA for 1693 192.0.2.0/24 is fe80::ffff:192.0.2.0/120 (also written as 1694 fe80::ffff:c000:0200/120). 1696 o ADM-LLAs are assigned to ARs and MSEs and MUST be managed for 1697 uniqueness. The lower 32 bits of the LLA includes a unique 1698 integer "MSID" value between 0x00000001 and 0xfeffffff, e.g., as 1699 in fe80::1, fe80::2, fe80::3, etc., fe80::feffffff. The ADM-LLA 1700 prefix length is determined by adding 96 to the MSID prefix 1701 length. For example, if the prefix length for MSID 0x10012001 is 1702 16 then the ADM-LLA prefix length is set to 112 and the LLA is 1703 written as fe80::1001:2001/112. The "zero" address for each ADM- 1704 LLA prefix is the Subnet-Router anycast address for that prefix 1705 [RFC4291]; for example, the Subnet-Router anycast address for 1706 fe80::1001:2001/112 is simply fe80::1001:2000. The MSID range 1707 0xff000000 through 0xffffffff is reserved for future use. 1709 Since the prefix 0000::/8 is "Reserved by the IETF" [RFC4291], no 1710 MNPs can be allocated from that block ensuring that there is no 1711 possibility for overlap between the different MNP- and ADM-LLA 1712 constructs discussed above. 1714 Since MNP-LLAs are based on the distribution of administratively 1715 assured unique MNPs, and since ADM-LLAs are guaranteed unique through 1716 administrative assignment, OMNI interfaces set the autoconfiguration 1717 variable DupAddrDetectTransmits to 0 [RFC4862]. 1719 Note: If future protocol extensions relax the 64-bit boundary in IPv6 1720 addressing, the additional prefix bits of an MNP could be encoded in 1721 bits 16 through 63 of the MNP-LLA. (The most-significant 64 bits 1722 would therefore still be in bits 64-127, and the remaining bits would 1723 appear in bits 16 through 48.) However, the analysis provided in 1724 [RFC7421] suggests that the 64-bit boundary will remain in the IPv6 1725 architecture for the foreseeable future. 1727 Note: Even though this document honors the 64-bit boundary in IPv6 1728 addressing, it specifies prefix lengths longer than /64 for routing 1729 purposes. This effectively extends IPv6 routing determination into 1730 the interface identifier portion of the IPv6 address, but it does not 1731 redefine the 64-bit boundary. Modern routing protocol 1732 implementations honor IPv6 prefixes of all lengths, up to and 1733 including /128. 1735 9. Unique-Local Addresses (ULAs) 1737 OMNI domains use IPv6 Unique-Local Addresses (ULAs) as the source and 1738 destination addresses in OAL packet IPv6 encapsulation headers. ULAs 1739 are only routable within the scope of a an OMNI domain, and are 1740 derived from the IPv6 Unique Local Address prefix fc00::/7 followed 1741 by the L bit set to 1 (i.e., as fd00::/8) followed by a 40-bit 1742 pseudo-random Global ID to produce the prefix [ULA]::/48, which is 1743 then followed by a 16-bit Subnet ID then finally followed by a 64 bit 1744 Interface ID as specified in Section 3 of [RFC4193]. All nodes in 1745 the same OMNI domain configure the same 40-bit Global ID as the OMNI 1746 domain identifier. The statistic uniqueness of the 40-bit pseudo- 1747 random Global ID allows different OMNI domains to be joined together 1748 in the future without requiring renumbering. 1750 Each OMNI link instance is identified by a value between 0x0000 and 1751 0xfeff in bits 48-63 of [ULA]::/48; the values 0xff00 through 0xfffe 1752 are reserved for future use, and the value 0xffff denotes the 1753 presence of a Temporary ULA (see below). For example, OMNI ULAs 1754 associated with instance 0 are configured from the prefix 1755 [ULA]:0000::/64, instance 1 from [ULA]:0001::/64, instance 2 from 1756 [ULA]:0002::/64, etc. ULAs and their associated prefix lengths are 1757 configured in correspondence with LLAs through stateless prefix 1758 translation where "MNP-ULAs" are assigned in correspondence to MNP- 1759 LLAs and "ADM-ULAs" are assigned in correspondence to ADM-LLAs. For 1760 example, for OMNI link instance [ULA]:1010::/64: 1762 o the MNP-ULA corresponding to the MNP-LLA fe80::2001:db8:1:2 with a 1763 56-bit MNP length is derived by copying the lower 64 bits of the 1764 LLA into the lower 64 bits of the ULA as 1765 [ULA]:1010:2001:db8:1:2/120 (where, the ULA prefix length becomes 1766 64 plus the IPv6 MNP length). 1768 o the MNP-ULA corresponding to fe80::ffff:192.0.2.0 with a 28-bit 1769 MNP length is derived by simply writing the LLA interface ID into 1770 the lower 64 bits as [ULA]:1010:0:ffff:192.0.2.0/124 (where, the 1771 ULA prefix length is 64 plus 32 plus the IPv4 MNP length). 1773 o the ADM-ULA corresponding to fe80::1000/112 is simply 1774 [ULA]:1010::1000/112. 1776 o the ADM-ULA corresponding to fe80::/128 is simply 1777 [ULA]:1010::/128. 1779 o etc. 1781 Each OMNI interface assigns the Anycast ADM-ULA specific to the OMNI 1782 link instance. For example, the OMNI interface connected to instance 1783 3 assigns the Anycast address [ULA]:0003::/128. Routers that 1784 configure OMNI interfaces advertise the OMNI service prefix (e.g., 1785 [ULA]:0003::/64) into the local routing system so that applications 1786 can direct traffic according to SBM requirements. 1788 The ULA presents an IPv6 address format that is routable within the 1789 OMNI routing system and can be used to convey link-scoped IPv6 ND 1790 messages across multiple hops using IPv6 encapsulation [RFC2473]. 1791 The OMNI link extends across one or more underling Internetworks to 1792 include all ARs and MSEs. All MNs are also considered to be 1793 connected to the OMNI link, however OAL encapsulation is omitted 1794 whenever possible to conserve bandwidth (see: Section 14). 1796 Each OMNI link can be subdivided into "segments" that often 1797 correspond to different administrative domains or physical 1798 partitions. OMNI nodes can use IPv6 Segment Routing [RFC8402] when 1799 necessary to support efficient forwarding to destinations located in 1800 other OMNI link segments. A full discussion of Segment Routing over 1801 the OMNI link appears in [I-D.templin-6man-aero]. 1803 Temporary ULAs are constructed per [RFC8981] based on the prefix 1804 [ULA]:ffff::/64 and used by MNs when they have no other addresses. 1805 Temporary ULAs can be used for MN-to-MN communications outside the 1806 context of any supporting OMNI link infrastructure, and can also be 1807 used as an initial address while the MN is in the process of 1808 procuring an MNP. Temporary ULAs are not routable within the OMNI 1809 routing system, and are therefore useful only for OMNI link "edge" 1810 communications. Temporary ULAs employ optimistic DAD principles 1811 [RFC4429] since they are probabilistically unique. 1813 Note: IPv6 ULAs taken from the prefix fc00::/7 followed by the L bit 1814 set to 0 (i.e., as fc00::/8) are never used for OMNI OAL addressing, 1815 however the range could be used for MSP and MNP addressing under 1816 certain limiting conditions (see: Section 10). 1818 10. Global Unicast Addresses (GUAs) 1820 OMNI domains use IP Global Unicast Address (GUA) prefixes [RFC4291] 1821 as Mobility Service Prefixes (MSPs) from which Mobile Network 1822 Prefixes (MNP) are delegated to Mobile Nodes (MNs). Fixed 1823 correspondent node networks reachable from the OMNI domain are 1824 represented by non-MNP GUA prefixes that are not derived from the 1825 MSP, but are treated in all other ways the same as for MNPs. 1827 For IPv6, GUA prefixes are assigned by IANA [IPV6-GUA] and/or an 1828 associated regional assigned numbers authority such that the OMNI 1829 domain can be interconnected to the global IPv6 Internet without 1830 causing inconsistencies in the routing system. An OMNI domain could 1831 instead use ULAs with the 'L' bit set to 0 (i.e., from the prefix 1832 fc00::/8)[RFC4193], however this would require IPv6 NAT if the domain 1833 were ever connected to the global IPv6 Internet. 1835 For IPv4, GUA prefixes are assigned by IANA [IPV4-GUA] and/or an 1836 associated regional assigned numbers authority such that the OMNI 1837 domain can be interconnected to the global IPv4 Internet without 1838 causing routing inconsistencies. An OMNI domain could instead use 1839 private IPv4 prefixes (e.g., 10.0.0.0/8, etc.) [RFC3330], however 1840 this would require IPv4 NAT if the domain were ever connected to the 1841 global IPv4 Internet. 1843 11. Node Identification 1845 OMNI MNs and MSEs that connect over open Internetworks include a 1846 unique node identification value for themselves in the OMNI options 1847 of their IPv6 ND messages (see: Section 12.1.14). One useful 1848 identification value alternative is the Host Identity Tag (HIT) as 1849 specified in [RFC7401], while Hierarchical HITs (HHITs) 1850 [I-D.ietf-drip-rid] may provide a better alternative in certain 1851 domains such as the Unmanned (Air) Traffic Management (UTM) service 1852 for Unmanned Air Systems (UAS). Another alternative is the 1853 Universally Unique IDentifier (UUID) [RFC4122] which can be self- 1854 generated by a node without supporting infrastructure with very low 1855 probability of collision. 1857 When a MN is truly outside the context of any infrastructure, it may 1858 have no MNP information at all. In that case, the MN can use an IPv6 1859 temporary ULA or (H)HIT as an IPv6 source/destination address for 1860 sustained communications in Vehicle-to-Vehicle (V2V) and (multihop) 1861 Vehicle-to-Infrastructure (V2I) scenarios. The MN can also propagate 1862 the ULA/(H)HIT into the multihop routing tables of (collective) 1863 Mobile/Vehicular Ad-hoc Networks (MANETs/VANETs) using only the 1864 vehicles themselves as communications relays. 1866 When a MN connects to ARs over (non-multihop) protected-spectrum 1867 ANETs, an alternate form of node identification (e.g., MAC address, 1868 serial number, airframe identification value, VIN, etc.) may be 1869 sufficient. The MN can then include OMNI "Node Identification" sub- 1870 options (see: Section 12.1.14) in IPv6 ND messages should the need to 1871 transmit identification information over the network arise. 1873 12. Address Mapping - Unicast 1875 OMNI interfaces maintain a neighbor cache for tracking per-neighbor 1876 state and use the link-local address format specified in Section 8. 1877 OMNI interface IPv6 Neighbor Discovery (ND) [RFC4861] messages sent 1878 over physical underlying interfaces without encapsulation observe the 1879 native underlying interface Source/Target Link-Layer Address Option 1880 (S/TLLAO) format (e.g., for Ethernet the S/TLLAO is specified in 1881 [RFC2464]). OMNI interface IPv6 ND messages sent over underlying 1882 interfaces via encapsulation do not include S/TLLAOs which were 1883 intended for encoding physical L2 media address formats and not 1884 encapsulation IP addresses. Furthermore, S/TLLAOs are not intended 1885 for encoding additional interface attributes needed for multilink 1886 coordination. Hence, this document does not define an S/TLLAO format 1887 but instead defines a new option type termed the "OMNI option" 1888 designed for these purposes. 1890 MNs such as aircraft typically have many wireless data link types 1891 (e.g. satellite-based, cellular, terrestrial, air-to-air directional, 1892 etc.) with diverse performance, cost and availability properties. 1893 The OMNI interface would therefore appear to have multiple L2 1894 connections, and may include information for multiple underlying 1895 interfaces in a single IPv6 ND message exchange. OMNI interfaces use 1896 an IPv6 ND option called the OMNI option formatted as shown in 1897 Figure 10: 1899 0 1 2 3 1900 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 1901 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1902 | Type | Length | Preflen | S/T-omIndex | 1903 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1904 | | 1905 ~ Sub-Options ~ 1906 | | 1907 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1909 Figure 10: OMNI Option Format 1911 In this format: 1913 o Type is set to TBD2. 1915 o Length is set to the number of 8 octet blocks in the option. The 1916 value 0 is invalid, while the values 1 through 255 (i.e., 8 1917 through 2040 octets, respectively) indicate the total length of 1918 the OMNI option. 1920 o Preflen is an 8 bit field that determines the length of prefix 1921 associated with an LLA. Values 0 through 128 specify a valid 1922 prefix length (all other values are invalid). For IPv6 ND 1923 messages sent from a MN to the MS, Preflen applies to the IPv6 1924 source LLA and provides the length that the MN is requesting or 1925 asserting to the MS. For IPv6 ND messages sent from the MS to the 1926 MN, Preflen applies to the IPv6 destination LLA and indicates the 1927 length that the MS is granting to the MN. For IPv6 ND messages 1928 sent between MS endpoints, Preflen provides the length associated 1929 with the source/target MN that is subject of the ND message. 1931 o S/T-omIndex is an 8 bit field corresponds to the omIndex value for 1932 source or target underlying interface used to convey this IPv6 ND 1933 message. OMNI interfaces MUST number each distinct underlying 1934 interface with an omIndex value between '1' and '255' that 1935 represents a MN-specific 8-bit mapping for the actual ifIndex 1936 value assigned by network management [RFC2863] (the omIndex value 1937 '0' is reserved for use by the MS). For RS and NS messages, S/ 1938 T-omIndex corresponds to the source underlying interface the 1939 message originated from. For RA and NA messages, S/T-omIndex 1940 corresponds to the target underlying interface that the message is 1941 destined to. (For NS messages used for Neighbor Unreachability 1942 Detection (NUD), S/T-omIndex instead identifies the neighbor's 1943 underlying interface to be used as the target interface to return 1944 the NA.) 1946 o Sub-Options is a Variable-length field, of length such that the 1947 complete OMNI Option is an integer multiple of 8 octets long. 1948 Contains one or more Sub-Options, as described in Section 12.1. 1950 The OMNI option may appear in any IPv6 ND message type; it is 1951 processed by interfaces that recognize the option and ignored by all 1952 other interfaces. If multiple OMNI option instances appear in the 1953 same IPv6 ND message, the interface processes the Preflen and S/ 1954 T-omIndex fields in the first instance and ignores those fields in 1955 all other instances. The interface processes the Sub-Options of all 1956 OMNI option instances in the same IPv6 ND message in the consecutive 1957 order in which they appear. 1959 The OMNI option(s) in each IPv6 ND message may include full or 1960 partial information for the neighbor. The union of the information 1961 in the most recently received OMNI options is therefore retained, and 1962 the information is aged/removed in conjunction with the corresponding 1963 neighbor cache entry. 1965 12.1. Sub-Options 1967 Each OMNI option includes zero or more Sub-Options. Each consecutive 1968 Sub-Option is concatenated immediately after its predecessor. All 1969 Sub-Options except Pad1 (see below) are in type-length-value (TLV) 1970 encoded in the following format: 1972 0 1 2 1973 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 1974 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1975 | Sub-Type| Sub-length | Sub-Option Data ... 1976 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1978 Figure 11: Sub-Option Format 1980 o Sub-Type is a 5-bit field that encodes the Sub-Option type. Sub- 1981 Options defined in this document are: 1983 Sub-Option Name Sub-Type 1984 Pad1 0 1985 PadN 1 1986 Interface Attributes (Type 1) 2 1987 Interface Attributes (Type 2) 3 1988 Traffic Selector 4 1989 MS-Register 5 1990 MS-Release 6 1991 Geo Coordinates 7 1992 DHCPv6 Message 8 1993 HIP Message 9 1994 PIM-SM Message 10 1995 Reassembly Limit 11 1996 Fragmentation Report 12 1997 Node Identification 13 1998 Sub-Type Extension 30 2000 Figure 12 2002 Sub-Types 14-29 are available for future assignment for major 2003 protocol functions. Sub-Type 31 is reserved by IANA. 2005 o Sub-Length is an 11-bit field that encodes the length of the Sub- 2006 Option Data ranging from 0 to 2034 octets. 2008 o Sub-Option Data is a block of data with format determined by Sub- 2009 Type and length determined by Sub-Length. 2011 During transmission, the OMNI interface codes Sub-Type and Sub-Length 2012 together in network byte order in 2 consecutive octets, where Sub- 2013 Option Data may be up to 2034 octets in length. This allows ample 2014 space for coding large objects (e.g., ASCII strings, domain names, 2015 protocol messages, security codes, etc.), while a single OMNI option 2016 is limited to 2040 octets the same as for any IPv6 ND option. If the 2017 Sub-Options to be coded would cause an OMNI option to exceed 2040 2018 octets, the OMNI interface codes any remaining Sub-Options in 2019 additional OMNI option instances in the intended order of processing 2020 in the same IPv6 ND message. Implementations must therefore observe 2021 size limitations, and must refrain from sending IPv6 ND messages 2022 larger than the OMNI interface MTU. If the available OMNI 2023 information would cause a single IPv6 ND message to exceed the OMNI 2024 interface MTU, the OMNI interface codes as much as possible in a 2025 first IPv6 ND message and codes the remainder in additional IPv6 ND 2026 messages. 2028 During reception, the OMNI interface processes each OMNI option Sub- 2029 Option while skipping over and ignoring any unrecognized Sub-Options. 2030 The OMNI interface processes the Sub-Options of all OMNI option 2031 instances in the consecutive order in which they appear in the IPv6 2032 ND message, beginning with the first instance and continuing through 2033 any additional instances to the end of the message. If a Sub-Option 2034 length would cause processing to exceed the OMNI option total length, 2035 the OMNI interface accepts any Sub-Options already processed and 2036 ignores the final Sub-Option. The interface then processes any 2037 remaining OMNI options in the same fashion to the end of the IPv6 ND 2038 message. 2040 Note: large objects that exceed the Sub-Option Data limit of 2034 2041 octets are not supported under the current specification; if this 2042 proves to be limiting in practice, future specifications may define 2043 support for fragmenting large objects across multiple OMNI options 2044 within the same IPv6 ND message. 2046 The following Sub-Option types and formats are defined in this 2047 document: 2049 12.1.1. Pad1 2051 0 2052 0 1 2 3 4 5 6 7 2053 +-+-+-+-+-+-+-+-+ 2054 | S-Type=0|x|x|x| 2055 +-+-+-+-+-+-+-+-+ 2057 Figure 13: Pad1 2059 o Sub-Type is set to 0. If multiple instances appear in OMNI 2060 options of the same message all are processed. 2062 o Sub-Type is followed by 3 'x' bits, set to any value on 2063 transmission (typically all-zeros) and ignored on receipt. Pad1 2064 therefore consists of 1 octet with the most significant 5 bits set 2065 to 0, and with no Sub-Length or Sub-Option Data fields following. 2067 12.1.2. PadN 2069 0 1 2 2070 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 2071 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 2072 | S-Type=1| Sub-length=N | N padding octets ... 2073 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 2075 Figure 14: PadN 2077 o Sub-Type is set to 1. If multiple instances appear in OMNI 2078 options of the same message all are processed. 2080 o Sub-Length is set to N (from 0 to 2034) that encodes the number of 2081 padding octets that follow. 2083 o Sub-Option Data consists of N octets, set to any value on 2084 transmission (typically all-zeros) and ignored on receipt. 2086 12.1.3. Interface Attributes (Type 1) 2088 The Interface Attributes (Type 1) sub-option provides a basic set of 2089 attributes for underlying interfaces. Interface Attributes (Type 1) 2090 is deprecated throughout the rest of this specification, and 2091 Interface Attributes (Type 2) (see: Section 12.1.4) are indicated 2092 wherever the term "Interface Attributes" appears without an 2093 associated Type designation. 2095 Nodes SHOULD NOT include Interface Attributes (Type 1) sub-options in 2096 IPv6 ND messages they send, and MUST ignore any in IPv6 ND messages 2097 they receive. If an Interface Attributes (Type 1) is included, it 2098 must have the following format: 2100 0 1 2 3 2101 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 2102 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2103 | Sub-Type=2| Sub-length=N | omIndex | omType | 2104 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2105 | Provider ID | Link | Resvd |P00|P01|P02|P03|P04|P05|P06|P07| 2106 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2107 |P08|P09|P10|P11|P12|P13|P14|P15|P16|P17|P18|P19|P20|P21|P22|P23| 2108 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2109 |P24|P25|P26|P27|P28|P29|P30|P31|P32|P33|P34|P35|P36|P37|P38|P39| 2110 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2111 |P40|P41|P42|P43|P44|P45|P46|P47|P48|P49|P50|P51|P52|P53|P54|P55| 2112 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2113 |P56|P57|P58|P59|P60|P61|P62|P63| 2114 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2116 Figure 15: Interface Attributes (Type 1) 2118 o Sub-Type is set to 2. If multiple instances with different 2119 omIndex values appear in OMNI option of the same message all are 2120 processed; if multiple instances with the same omIndex value 2121 appear, the first is processed and all others are ignored 2123 o Sub-Length is set to N (from 4 to 2034) that encodes the number of 2124 Sub-Option Data octets that follow. 2126 o omIndex is a 1-octet field containing a value from 0 to 255 2127 identifying the underlying interface for which the attributes 2128 apply. 2130 o omType is a 1-octet field containing a value from 0 to 255 2131 corresponding to the underlying interface identified by omIndex. 2133 o Provider ID is a 1-octet field containing a value from 0 to 255 2134 corresponding to the underlying interface identified by omIndex. 2136 o Link encodes a 4-bit link metric. The value '0' means the link is 2137 DOWN, and the remaining values mean the link is UP with metric 2138 ranging from '1' ("lowest") to '15' ("highest"). 2140 o Resvd is reserved for future use. Set to 0 on transmission and 2141 ignored on reception. 2143 o A 16-octet ""Preferences" field immediately follows 'Resvd', with 2144 values P[00] through P[63] corresponding to the 64 Differentiated 2145 Service Code Point (DSCP) values [RFC2474]. Each 2-bit P[*] field 2146 is set to the value '0' ("disabled"), '1' ("low"), '2' ("medium") 2147 or '3' ("high") to indicate a QoS preference for underlying 2148 interface selection purposes. 2150 12.1.4. Interface Attributes (Type 2) 2152 The Interface Attributes (Type 2) sub-option provides L2 forwarding 2153 information for the multilink conceptual sending algorithm discussed 2154 in Section 14. The L2 information is used for selecting among 2155 potentially multiple candidate underlying interfaces that can be used 2156 to forward carrier packets to the neighbor based on factors such as 2157 DSCP preferences and link quality. Interface Attributes (Type 2) 2158 further includes link-layer address information to be used for either 2159 OAL encapsulation or direct UDP/IP encapsulation (when OAL 2160 encapsulation can be avoided). 2162 Interface Attributes (Type 2) are the sole Interface Attributes 2163 format in this specification that all OMNI nodes must honor. 2164 Wherever the term "Interface Attributes" occurs throughout this 2165 specification without a "Type" designation, the format given below is 2166 indicated: 2168 0 1 2 3 2169 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 2170 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2171 | S-Type=3| Sub-length=N | omIndex | omType | 2172 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2173 | Provider ID | Link |R| API | SRT | FMT | LHS (0 - 7) | 2174 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2175 | LHS (bits 8 - 31) | ~ 2176 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ 2177 ~ ~ 2178 ~ Link Layer Address (L2ADDR) ~ 2179 ~ ~ 2180 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2181 | Bitmap(0)=0xff|P00|P01|P02|P03|P04|P05|P06|P07|P08|P09|P10|P11| 2182 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2183 |P12|P13|P14|P15|P16|P17|P18|P19|P20|P21|P22|P23|P24|P25|P26|P27| 2184 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2185 |P28|P29|P30|P31| Bitmap(1)=0xff|P32|P33|P34|P35|P36| ... 2186 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 2188 Figure 16: Interface Attributes (Type 2) 2190 o Sub-Type is set to 3. If multiple instances with different 2191 omIndex values appear in OMNI options of the same message all are 2192 processed; if multiple instances with the same omIndex value 2193 appear, the first is processed and all others are ignored. 2195 o Sub-Length is set to N (from 4 to 2034) that encodes the number of 2196 Sub-Option Data octets that follow. The 'omIndex', 'omType', 2197 'Provider ID', 'Link', 'R' and 'API' fields are always present; 2198 hence, the remainder of the Sub-Option Data is limited to 2030 2199 octets. 2201 o Sub-Option Data contains an "Interface Attributes (Type 2)" option 2202 encoded as follows: 2204 * omIndex is set to an 8-bit integer value corresponding to a 2205 specific underlying interface the same as specified above for 2206 the OMNI option S/T-omIndex field. The OMNI options of a same 2207 message may include multiple Interface Attributes Sub-Options, 2208 with each distinct omIndex value pertaining to a different 2209 underlying interface. The OMNI option will often include an 2210 Interface Attributes Sub-Option with the same omIndex value 2211 that appears in the S/T-omIndex. In that case, the actual 2212 encapsulation address of the received IPv6 ND message should be 2213 compared with the L2ADDR encoded in the Sub-Option (see below); 2214 if the addresses are different (or, if L2ADDR is absent) the 2215 presence of a NAT is assumed. 2217 * omType is set to an 8-bit integer value corresponding to the 2218 underlying interface identified by omIndex. The value 2219 represents an OMNI interface-specific 8-bit mapping for the 2220 actual IANA ifType value registered in the 'IANAifType-MIB' 2221 registry [http://www.iana.org]. 2223 * Provider ID is set to an OMNI interface-specific 8-bit ID value 2224 for the network service provider associated with this omIndex. 2226 * Link encodes a 4-bit link metric. The value '0' means the link 2227 is DOWN, and the remaining values mean the link is UP with 2228 metric ranging from '1' ("lowest") to '15' ("highest"). 2230 * R is reserved for future use. 2232 * API - a 3-bit "Address/Preferences/Indexed" code that 2233 determines the contents of the remainder of the sub-option as 2234 follows: 2236 + When the most significant bit (i.e., "Address") is set to 1, 2237 the SRT, FMT, LHS and L2ADDR fields are included immediately 2238 following the API code; else, they are omitted. 2240 + When the next most significant bit (i.e., "Preferences") is 2241 set to 1, a preferences block is included next; else, it is 2242 omitted. (Note that if "Address" is set the preferences 2243 block immediately follows L2ADDR; else, it immediately 2244 follows the API code.) 2246 + When a preferences block is present and the least 2247 significant bit (i.e., "Indexed") is set to 0, the block is 2248 encoded in "Simplex" form as shown in Figure 15; else it is 2249 encoded in "Indexed" form as discussed below. 2251 * When API indicates that an "Address" is included, the following 2252 fields appear in consecutive order (else, they are omitted): 2254 + SRT - a 5-bit Segment Routing Topology prefix length value 2255 that (when added to 96) determines the prefix length to 2256 apply to the ULA formed from concatenating [ULA*]::/96 with 2257 the 32 bit LHS MSID value that follows. For example, the 2258 value 16 corresponds to the prefix length 112. 2260 + FMT - a 3-bit "Framework/Mode/Type" code corresponding to 2261 the included Link Layer Address as follows: 2263 - When the most significant bit (i.e., "Framework") is set 2264 to 1, L2ADDR is the INET encapsulation address for the 2265 Source/Target Client itself; otherwise L2ADDR is the 2266 address of the Proxy/Server named in the LHS. 2268 - When the next most significant bit (i.e., "Mode") is set 2269 to 1, the Framework node is (likely) located behind an 2270 INET Network Address Translator (NAT); otherwise, it is 2271 on the open INET. 2273 - When the least significant bit (i.e., "Type") is set to 2274 0, L2ADDR includes a UDP Port Number followed by an IPv4 2275 address; otherwise, it includes a UDP Port Number 2276 followed by an IPv6 address. 2278 + LHS - the 32 bit MSID of the Last Hop Proxy/Server on the 2279 path to the target. When SRT and LHS are both set to 0, the 2280 LHS is considered unspecified in this IPv6 ND message. When 2281 SRT is set to 0 and LHS is non-zero, the prefix length is 2282 set to 128. SRT and LHS together provide guidance to the 2283 OMNI interface forwarding algorithm. Specifically, if SRT/ 2284 LHS is located in the local OMNI link segment then the OMNI 2285 interface can encapsulate according to FMT/L2ADDR (following 2286 any necessary NAT traversal messaging); else, it must 2287 forward according to the OMNI link spanning tree. See 2288 [I-D.templin-6man-aero] for further discussion. 2290 + Link Layer Address (L2ADDR) - Formatted according to FMT, 2291 and identifies the link-layer address (i.e., the 2292 encapsulation address) of the source/target. The UDP Port 2293 Number appears in the first 2 octets and the IP address 2294 appears in the next 4 octets for IPv4 or 16 octets for IPv6. 2295 The Port Number and IP address are recorded in network byte 2296 order, and in ones-compliment "obfuscated" form per 2297 [RFC4380]. The OMNI interface forwarding algorithm uses 2298 FMT/L2ADDR to determine the encapsulation address for 2299 forwarding when SRT/LHS is located in the local OMNI link 2300 segment. Note that if the target is behind a NAT, L2ADDR 2301 will contain the mapped INET address stored in the NAT; 2302 otherwise, L2ADDR will contain the native INET information 2303 of the target itself. 2305 * When API indicates that "Preferences" are included, a 2306 preferences block appears as the remainder of the Sub-Option as 2307 a series of Bitmaps and P[*] values. In "Simplex" form, the 2308 index for each singleton Bitmap octet is inferred from its 2309 sequential position (i.e., 0, 1, 2, ...) as shown in Figure 16. 2310 In "Indexed" form, each Bitmap is preceded by an Index octet 2311 that encodes a value "i" = (0 - 255) as the index for its 2312 companion Bitmap as follows: 2314 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 2315 | Index=i | Bitmap(i) |P[*] values ... 2316 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 2318 Figure 17 2320 * The preferences consist of a first (simplex/indexed) Bitmap 2321 (i.e., "Bitmap(i)") followed by 0-8 single-octet blocks of 2322 2-bit P[*] values, followed by a second Bitmap (i), followed by 2323 0-8 blocks of P[*] values, etc. Reading from bit 0 to bit 7, 2324 the bits of each Bitmap(i) that are set to '1'' indicate the 2325 P[*] blocks from the range P[(i*32)] through P[(i*32) + 31] 2326 that follow; if any Bitmap(i) bits are '0', then the 2327 corresponding P[*] block is instead omitted. For example, if 2328 Bitmap(0) contains 0xff then the block with P[00]-P[03], 2329 followed by the block with P[04]-P[07], etc., and ending with 2330 the block with P[28]-P[31] are included (as shown in 2331 Figure 15). The next Bitmap(i) is then consulted with its bits 2332 indicating which P[*] blocks follow, etc. out to the end of the 2333 Sub-Option. 2335 * Each 2-bit P[*] field is set to the value '0' ("disabled"), '1' 2336 ("low"), '2' ("medium") or '3' ("high") to indicate a QoS 2337 preference for underlying interface selection purposes. Not 2338 all P[*] values need to be included in the OMNI option of each 2339 IPv6 ND message received. Any P[*] values represented in an 2340 earlier OMNI option but omitted in the current OMNI option 2341 remain unchanged. Any P[*] values not yet represented in any 2342 OMNI option default to "medium". 2344 * The first 16 P[*] blocks correspond to the 64 Differentiated 2345 Service Code Point (DSCP) values P[00] - P[63] [RFC2474]. Any 2346 additional P[*] blocks that follow correspond to "pseudo-DSCP" 2347 traffic classifier values P[64], P[65], P[66], etc. See 2348 Appendix A for further discussion and examples. 2350 12.1.5. Traffic Selector 2351 0 1 2 3 2352 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 2353 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2354 | S-Type=4| Sub-length=N | omIndex | ~ 2355 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ 2356 ~ ~ 2357 ~ RFC 6088 Format Traffic Selector ~ 2358 ~ ~ 2359 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2361 Figure 18: Traffic Selector 2363 o Sub-Type is set to 4. If multiple instances appear in OMNI 2364 options of the same message all are processed, i.e., even if the 2365 same omIndex value appears multiple times. 2367 o Sub-Length is set to N (from 1 to 2034) that encodes the number of 2368 Sub-Option Data octets that follow. 2370 o Sub-Option Data contains a 1 octet omIndex encoded exactly as 2371 specified in Section 12.1.3, followed by an N-1 octet traffic 2372 selector formatted per [RFC6088] beginning with the "TS Format" 2373 field. The largest traffic selector for a given omIndex is 2374 therefore 2033 octets. 2376 12.1.6. MS-Register 2378 0 1 2 3 2379 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 2380 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2381 | S-Type=5| Sub-length=4n | MSID[1] (bits 0 - 15) | 2382 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2383 | MSID [1] (bits 16 - 32) | MSID[2] (bits 0 - 15) | 2384 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2385 | MSID [2] (bits 16 - 32) | MSID[3] (bits 0 - 15) | 2386 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2387 ... ... ... ... ... ... 2388 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2389 | MSID [n] (bits 16 - 32) | 2390 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2392 Figure 19: MS-Register Sub-option 2394 o Sub-Type is set to 5. If multiple instances appear in OMNI 2395 options of the same message all are processed. Only the first 2396 MAX_MSID values processed (whether in a single instance or 2397 multiple) are retained and all other MSIDs are ignored. 2399 o Sub-Length is set to 4n, with 508 as the maximum value for n. The 2400 length of the Sub-Option Data section is therefore limited to 2032 2401 octets. 2403 o A list of n 4 octet MSIDs is included in the following 4n octets. 2404 The Anycast MSID value '0' in an RS message MS-Register sub-option 2405 requests the recipient to return the MSID of a nearby MSE in a 2406 corresponding RA response. 2408 12.1.7. MS-Release 2410 0 1 2 3 2411 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 2412 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2413 | S-Type=6| Sub-length=4n | MSID[1] (bits 0 - 15) | 2414 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2415 | MSID [1] (bits 16 - 32) | MSID[2] (bits 0 - 15) | 2416 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2417 | MSID [2] (bits 16 - 32) | MSID[3] (bits 0 - 15) | 2418 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2419 ... ... ... ... ... ... 2420 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2421 | MSID [n] (bits 16 - 32) | 2422 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2424 Figure 20: MS-Release Sub-option 2426 o Sub-Type is set to 6. If multiple instances appear in OMNI 2427 options of the same message all are processed. Only the first 2428 MAX_MSID values processed (whether in a single instance or 2429 multiple) are retained and all other MSIDs are ignored. 2431 o Sub-Length is set to 4n, with 508 as the maximum value for n. The 2432 length of the Sub-Option Data section is therefore limited to 2032 2433 octets. 2435 o A list of n 4 octet MSIDs is included in the following 4n octets. 2436 The Anycast MSID value '0' is ignored in MS-Release sub-options, 2437 i.e., only non-zero values are processed. 2439 12.1.8. Geo Coordinates 2440 0 1 2 3 2441 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 2442 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2443 | S-Type=7| Sub-length=N | Geo Type |Geo Coordinates 2444 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... 2446 Figure 21: Geo Coordinates Sub-option 2448 o Sub-Type is set to 7. If multiple instances appear in OMNI 2449 options of the same message the first is processed and all others 2450 are ignored. 2452 o Sub-Length is set to N (from 0 to 2034) that encodes the number of 2453 Sub-Option Data octets that follow. 2455 o Geo Type is a 1 octet field that encodes a type designator that 2456 determines the format and contents of the Geo Coordinates field 2457 that follows. The following types are currently defined: 2459 * 0 - NULL, i.e., the Geo Coordinates field is zero-length. 2461 o A set of Geo Coordinates of length 0 - 2033 octets. New formats 2462 to be specified in future documents and may include attributes 2463 such as latitude/longitude, altitude, heading, speed, etc. 2465 12.1.9. Dynamic Host Configuration Protocol for IPv6 (DHCPv6) Message 2467 The Dynamic Host Configuration Protocol for IPv6 (DHCPv6) sub-option 2468 may be included in the OMNI options of RS messages sent by MNs and RA 2469 messages returned by MSEs. ARs that act as proxys to forward RS/RA 2470 messages between MNs and MSEs also forward DHCPv6 sub-options 2471 unchanged and do not process DHCPv6 sub-options themselves. Note 2472 that DHCPv6 message sub-option integrity is protected by the Checksum 2473 included in the IPv6 ND message header. 2475 0 1 2 3 2476 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 2477 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2478 | S-Type=8| Sub-length=N | msg-type | id (octet 0) | 2479 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2480 | transaction-id (octets 1-2) | | 2481 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 2482 | | 2483 . DHCPv6 options . 2484 . (variable number and length) . 2485 | | 2486 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2488 Figure 22: DHCPv6 Message Sub-option 2490 o Sub-Type is set to 8. If multiple instances appear in OMNI 2491 options of the same message the first is processed and all others 2492 are ignored. 2494 o Sub-Length is set to N (from 4 to 2034) that encodes the number of 2495 Sub-Option Data octets that follow. The 'msg-type' and 2496 'transaction-id' fields are always present; hence, the length of 2497 the DHCPv6 options is restricted to 2030 octets. 2499 o 'msg-type' and 'transaction-id' are coded according to Section 8 2500 of [RFC8415]. 2502 o A set of DHCPv6 options coded according to Section 21 of [RFC8415] 2503 follows. 2505 12.1.10. Host Identity Protocol (HIP) Message 2507 The Host Identity Protocol (HIP) Message sub-option may be included 2508 in the OMNI options of RS messages sent by MNs and RA messages 2509 returned by ARs. ARs that act as proxys authenticate and remove HIP 2510 messages in RS messages they forward from a MN to an MSE. ARs that 2511 act as proxys insert and sign HIP messages in the RA messages they 2512 forward from an MSE to a MN. 2514 The HIP message sub-option may also be included in any IPv6 ND 2515 message that may traverse an open Internetwork, i.e., where link- 2516 layer authentication is not already assured by lower layers. 2518 0 1 2 3 2519 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 2520 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2521 | S-Type=9| Sub-length=N |0| Packet Type |Version| RES.|1| 2522 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2523 | Checksum | Controls | 2524 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2525 | Sender's Host Identity Tag (HIT) | 2526 | | 2527 | | 2528 | | 2529 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2530 | Receiver's Host Identity Tag (HIT) | 2531 | | 2532 | | 2533 | | 2534 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2535 | | 2536 / HIP Parameters / 2537 / / 2538 | | 2539 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2541 Figure 23: HIP Message Sub-option 2543 o Sub-Type is set to 9. If multiple instances appear in OMNI 2544 options of the same message the first is processed and all others 2545 are ignored. 2547 o Sub-Length is set to N, i.e., the length of the option in octets 2548 beginning immediately following the Sub-Length field and extending 2549 to the end of the HIP parameters. The length of the entire HIP 2550 message is therefore restricted to 2034 octets. 2552 o The HIP message is coded exactly as specified in Section 5 of 2553 [RFC7401], except that the OMNI "Sub-Type" and "Sub-Length" fields 2554 replace the first 2 octets of the HIP message header (i.e., the 2555 Next Header and Header Length fields). Note that, since the IPv6 2556 ND message header already includes a Checksum, the HIP message 2557 Checksum field is set to 0 on transmission and ignored on 2558 reception. (The Checksum field is still included to retain the 2559 [RFC7401] message format.) 2561 12.1.11. PIM-SM Message 2563 The Protocol Independent Multicast - Sparse Mode (PIM-SM) Message 2564 sub-option may be included in the OMNI options of IPv6 ND messages 2565 sent by MNs and MSEs. PIM-SM messages are formatted as specified in 2566 Section 4.9 of [RFC7761], with the exception that the Checksum field 2567 is omitted since the IPv6 ND message is already protected by a 2568 checksum (and possibly also an authentication signature). The PIM-SM 2569 message sub-option format is shown in Figure 24: 2571 0 1 2 3 2572 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 2573 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2574 |S-Type=10| Sub-length=N |PIM Ver| Type | Reserved | 2575 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2576 | | 2577 / PIM-SM Message / 2578 / / 2579 | | 2580 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2582 Figure 24: PIM-SM Message Option Format 2584 o Sub-Type is set to 10. If multiple instances appear in OMNI 2585 options of the same message all are processed. 2587 o Sub-Length is set to N, i.e., the length of the option in octets 2588 beginning immediately following the Sub-Length field and extending 2589 to the end of the PIM-SM message. The length of the entire PIM-SM 2590 message is therefore restricted to 2034 octets. 2592 o The PIM-SM message is coded exactly as specified in Section 4.9 of 2593 [RFC7761], except that the Checksum field is omitted. The "PIM 2594 Ver" field MUST encode the value 2, and the "Type" field encodes 2595 the PIM message type. (See Section 4.9 of [RFC7761] for a list of 2596 PIM-SM message types and formats.) 2598 12.1.12. Reassembly Limit 2600 The Reassembly Limit sub-option may be included in the OMNI options 2601 of IPv6 ND messages. The message consists of a 14-bit Reassembly 2602 Limit value, followed by two flag bits (H, L) optionally followed by 2603 an (N-2)-octet leading portion of an OAL First Fragment that 2604 triggered the message. 2606 0 1 2 3 2607 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2608 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2609 |S-Type=11| Sub-length=N | Reassembly Limit |H|L| 2610 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2611 | OAL First Fragment (As much of invoking packet | 2612 + as possible without the IPv6 ND message + 2613 | exceeding the minimum IPv6 MTU) | 2614 + + 2616 Figure 25: Reassembly Limit 2618 o Sub-Type is set to 11. If multiple instances appear in OMNI 2619 options of the same message the first occurring "hard" and "soft" 2620 Reassembly Limit values are accepted, and any additional 2621 Reassembly Limit values are ignored. 2623 o Sub-Length is set to 2 if no OAL First Fragment is included, or to 2624 a value N greater than 2 if an OAL First Fragment is included. 2626 o A 14-bit Reassembly Limit follows, and includes a value between 2627 1500 and 9180. If any other value is included, the sub-option is 2628 ignored. The value indicates the hard or soft limit for original 2629 IP packets that the source of the message is currently willing to 2630 reassemble; the source may increase or decrease the hard or soft 2631 limit at any time through the transmission of new IPv6 ND 2632 messages. Until the first IPv6 ND message with a Reassembly Limit 2633 sub-option arrives, OMNI nodes assume initial default hard/soft 2634 limits of 9180 bytes (I.e., the OMNI interface MRU). After IPv6 2635 ND messages with Reassembly Limit sub-options arrive, the OMNI 2636 node retains the most recent hard/soft limit values until new IPv6 2637 ND messages with different values arrive. 2639 o The 'H' flag is set to 1 if the Reassembly Limit is a "Hard" 2640 limit, and set to 0 if the Reassembly Limit is a "Soft" limit. 2642 o The 'L' flag is set to 1 if an OAL First Fragment corresponding to 2643 a reassembly loss event was included; otherwise set to 0. 2645 o If N is greater than 2, the remainder of the Reassembly Limit sub- 2646 option encodes the leading portion of an OAL First Fragment that 2647 prompted this IPv6 ND message. The first fragment is included 2648 beginning with the OAL IPv6 header, and continuing with as much of 2649 the fragment payload as possible without causing the IPv6 ND 2650 message to exceed the minimum IPv6 MTU. (Note that only the OAL 2651 First Fragment is consulted regardless of its size, and without 2652 waiting for additional fragments.) 2654 12.1.13. Fragmentation Report 2656 The Fragmentation Report may be included in the OMNI options of uNA 2657 messages sent from an OAL destination to an OAL source. The message 2658 consists of (N / 8)-many (Identification, Bitmap)-tuples which 2659 include the Identification values of OAL fragments received plus a 2660 Bitmap marking the ordinal positions of individual fragments received 2661 and fragments missing. 2663 0 1 2 3 2664 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 2665 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2666 |S-Type=12| Sub-Length = N | Identification #1 (bits 0 -15)| 2667 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2668 | Identification #1 (bits 15-31)| Bitmap #1 (bits 0 - 15) | 2669 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2670 | Bitmap #1 (bits 16-31) | Identification #2 (bits 0 -15)| 2671 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2672 | Identification #2 (bits 15-31)| Bitmap #2 (bits 0 - 15) | 2673 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2674 | Bitmap #2 (bits 16-31) | Identification #3 (bits 0 -15)| 2675 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2676 | Identification #3 (bits 15-31)| Bitmap #3 (bits 0 - 15) | 2677 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2678 | Bitmap #3 (bits 16-31) | ... | 2679 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... + 2680 | ... | 2681 + ... + 2683 Figure 26: Fragmentation Report 2685 o Sub-Type is set to 12. If multiple instances appear in OMNI 2686 options of the same message all are processed. 2688 o Sub-Length is set to N, i.e., the length of the option in octets 2689 beginning immediately following the Sub-Length field and extending 2690 to the end of the ICMPv6 error message body. N must be an 2691 integral multiple of 8 octets; otherwise, the sub-option is 2692 ignored. The length of the entire sub-option should not cause the 2693 entire IPv6 ND message to exceed the minimum MPS. 2695 o Identification (i) includes the IPv6 Identification value found in 2696 the Fragment Header of a received OAL fragment. (Only those 2697 Identification values included represent fragments for which loss 2698 was unambiguously observed; any Identification values not included 2699 correspond to fragments that were either received in their 2700 entirety or are still in transit.) 2702 o Bitmap (i) includes an ordinal checklist of fragments, with each 2703 bit set to 1 for a fragment received or 0 for a fragment missing. 2704 For example, for a 20-fragment fragmented OAL packet with ordinal 2705 fragments #3, #10, #13 and #17 missing and all other fragments 2706 received, the bitmap would encode: 2708 0 1 2 2709 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 2710 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 2711 |1|1|1|0|1|1|1|1|1|1|0|1|1|0|1|1|1|0|1|1|0|0|0|... 2712 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 2714 Figure 27 2716 (Note that loss of an OAL atomic fragment is indicated by a 2717 Bitmap(i) with all bits set to 0.) 2719 12.1.14. Node Identification 2721 0 1 2 3 2722 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 2723 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2724 |S-Type=13| Sub-length=N | ID-Type | ~ 2725 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ 2726 ~ Node Identification Value (N-1 octets) ~ 2727 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2729 Figure 28: Node Identification 2731 o Sub-Type is set to 13. If multiple instances appear in OMNI 2732 options of the same IPv6 ND message the first instance of a 2733 specific ID-Type is processed and all other instances of the same 2734 ID-Type are ignored. (Note therefore that it is possible for a 2735 single IPv6 ND message to convey multiple Node Identifications - 2736 each having a different ID-Type.) 2738 o Sub-Length is set to N (from 1 to 2034) that encodes the number of 2739 Sub-Option Data octets that follow. The ID-Type field is always 2740 present; hence, the maximum Node Identification Value length is 2741 2033 octets. 2743 o ID-Type is a 1 octet field that encodes the type of the Node 2744 Identification Value. The following ID-Type values are currently 2745 defined: 2747 * 0 - Universally Unique IDentifier (UUID) [RFC4122]. Indicates 2748 that Node Identification Value contains a 16 octet UUID. 2750 * 1 - Host Identity Tag (HIT) [RFC7401]. Indicates that Node 2751 Identification Value contains a 16 octet HIT. 2753 * 2 - Hierarchical HIT (HHIT) [I-D.ietf-drip-rid]. Indicates 2754 that Node Identification Value contains a 16 octet HHIT. 2756 * 3 - Network Access Identifier (NAI) [RFC7542]. Indicates that 2757 Node Identification Value contains an N-1 octet NAI. 2759 * 4 - Fully-Qualified Domain Name (FQDN) [RFC1035]. Indicates 2760 that Node Identification Value contains an N-1 octet FQDN. 2762 * 5 - 252 - Unassigned. 2764 * 253-254 - Reserved for experimentation, as recommended in 2765 [RFC3692]. 2767 * 255 - reserved by IANA. 2769 o Node Identification Value is an (N - 1) octet field encoded 2770 according to the appropriate the "ID-Type" reference above. 2772 When a Node Identification Value is needed for DHCPv6 messaging 2773 purposes, it is encoded as a DHCP Unique IDentifier (DUID) using the 2774 "DUID-EN for OMNI" format with enterprise number 45282 (see: 2775 Section 25) as shown in Figure 29: 2777 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 2778 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2779 | DUID-Type (2) | EN (high bits == 0) | 2780 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2781 | EN (low bits = 45282) | ID-Type | | 2782 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 2783 . Node Identification Value . 2784 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2786 Figure 29: DUID-EN for OMNI Format 2788 In this format, the ID-Type and Node Identification Value fields are 2789 coded exactly as in Figure 28 following the 6 octet DUID-EN header, 2790 and the entire "DUID-EN for OMNI" is included in a DHCPv6 message per 2791 [RFC8415]. 2793 12.1.15. Sub-Type Extension 2795 Since the Sub-Type field is only 5 bits in length, future 2796 specifications of major protocol functions may exhaust the remaining 2797 Sub-Type values available for assignment. This document therefore 2798 defines Sub-Type 30 as an "extension", meaning that the actual sub- 2799 option type is determined by examining a 1 octet "Extension-Type" 2800 field immediately following the Sub-Length field. The Sub-Type 2801 Extension is formatted as shown in Figure 30: 2803 0 1 2 3 2804 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 2805 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2806 |S-Type=30| Sub-length=N | Extension-Type| ~ 2807 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ 2808 ~ ~ 2809 ~ Extension-Type Body ~ 2810 ~ ~ 2811 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2813 Figure 30: Sub-Type Extension 2815 o Sub-Type is set to 30. If multiple instances appear in OMNI 2816 options of the same message all are processed, where each 2817 individual extension defines its own policy for processing 2818 multiple of that type. 2820 o Sub-Length is set to N (from 1 to 2034) that encodes the number of 2821 Sub-Option Data octets that follow. The Extension-Type field is 2822 always present; hence, the maximum Extension-Type Body length is 2823 2033 octets. 2825 o Extension-Type contains a 1 octet Sub-Type Extension value between 2826 0 and 255. 2828 o Extension-Type Body contains an N-1 octet block with format 2829 defined by the given extension specification. 2831 Extension-Type values 2 through 252 are available for assignment by 2832 future specifications, which must also define the format of the 2833 Extension-Type Body and its processing rules. Extension-Type values 2834 253 and 254 are reserved for experimentation, as recommended in 2835 [RFC3692], and value 255 is reserved by IANA. Extension-Type values 2836 0 and 1 are defined in the following subsections: 2838 12.1.15.1. RFC4380 UDP/IP Header Option 2839 0 1 2 3 2840 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 2841 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2842 |S-Type=30| Sub-length=N | Ext-Type=0 | Header Type | 2843 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2844 ~ Header Option Value ~ 2845 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2847 Figure 31: RFC4380 UDP/IP Header Option (Extension-Type 0) 2849 o Sub-Type is set to 30. 2851 o Sub-Length is set to N (from 2 to 2034) that encodes the number of 2852 Sub-Option Data octets that follow. The Extension-Type and Header 2853 Type fields are always present; hence, the maximum-length Header 2854 Option Value is 2032 octets. 2856 o Extension-Type is set to 0. Each instance encodes exactly one 2857 header option per Section 5.1.1 of [RFC4380], with the leading '0' 2858 octet omitted and the following octet coded as Header Type. If 2859 multiple instances of the same Header Type appear in OMNI options 2860 of the same message the first instance is processed and all others 2861 are ignored. 2863 o Header Type and Header Option Value are coded exactly as specified 2864 in Section 5.1.1 of [RFC4380]; the following types are currently 2865 defined: 2867 * 0 - Origin Indication (IPv4) - value coded per Section 5.1.1 of 2868 [RFC4380]. 2870 * 1 - Authentication Encapsulation - value coded per 2871 Section 5.1.1 of [RFC4380]. 2873 * 2 - Origin Indication (IPv6) - value coded per Section 5.1.1 of 2874 [RFC4380], except that the address is a 16-octet IPv6 address 2875 instead of a 4-octet IPv4 address. 2877 o Header Type values 3 through 252 are available for assignment by 2878 future specifications, which must also define the format of the 2879 Header Option Value and its processing rules. Header Type values 2880 253 and 254 are reserved for experimentation, as recommended in 2881 [RFC3692], and value 255 is Reserved by IANA. 2883 12.1.15.2. RFC6081 UDP/IP Trailer Option 2885 0 1 2 3 2886 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 2887 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2888 |S-Type=30| Sub-length=N | Ext-Type=1 | Trailer Type | 2889 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2890 ~ Trailer Option Value ~ 2891 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2893 Figure 32: RFC6081 UDP/IP Trailer Option (Extension-Type 1) 2895 o Sub-Type is set to 30. 2897 o Sub-Length is set to N (from 2 to 2034) that encodes the number of 2898 Sub-Option Data octets that follow. The Extension-Type and 2899 Trailer Type fields are always present; hence, the maximum-length 2900 Trailer Option Value is 2032 octets. 2902 o Extension-Type is set to 1. Each instance encodes exactly one 2903 trailer option per Section 4 of [RFC6081]. If multiple instances 2904 of the same trailer type appear in OMNI options of the same 2905 message the first instance is processed and all others ignored. 2907 o Trailer Type and Trailer Option Value are coded exactly as 2908 specified in Section 4 of [RFC6081]; the following Trailer Types 2909 are currently defined: 2911 * 0 - Unassigned 2913 * 1 - Nonce Trailer - value coded per Section 4.2 of [RFC6081]. 2915 * 2 - Unassigned 2917 * 3 - Alternate Address Trailer (IPv4) - value coded per 2918 Section 4.3 of [RFC6081]. 2920 * 4 - Neighbor Discovery Option Trailer - value coded per 2921 Section 4.4 of [RFC6081]. 2923 * 5 - Random Port Trailer - value coded per Section 4.5 of 2924 [RFC6081]. 2926 * 6 - Alternate Address Trailer (IPv6) - value coded per 2927 Section 4.3 of [RFC6081], except that each address is a 2928 16-octet IPv6 address instead of a 4-octet IPv4 address. 2930 o Trailer Type values 7 through 252 are available for assignment by 2931 future specifications, which must also define the format of the 2932 Trailer Option Value and its processing rules. Trailer Type 2933 values 253 and 254 are reserved for experimentation, as 2934 recommended in [RFC3692], and value 255 is Reserved by IANA. 2936 13. Address Mapping - Multicast 2938 The multicast address mapping of the native underlying interface 2939 applies. The mobile router on board the MN also serves as an IGMP/ 2940 MLD Proxy for its EUNs and/or hosted applications per [RFC4605] while 2941 using the L2 address of the AR as the L2 address for all multicast 2942 packets. 2944 The MN uses Multicast Listener Discovery (MLDv2) [RFC3810] to 2945 coordinate with the AR, and *NET L2 elements use MLD snooping 2946 [RFC4541]. 2948 14. Multilink Conceptual Sending Algorithm 2950 The MN's IPv6 layer selects the outbound OMNI interface according to 2951 SBM considerations when forwarding original IP packets from local or 2952 EUN applications to external correspondents. Each OMNI interface 2953 maintains a neighbor cache the same as for any IPv6 interface, but 2954 with additional state for multilink coordination. Each OMNI 2955 interface maintains default routes via ARs discovered as discussed in 2956 Section 15, and may configure more-specific routes discovered through 2957 means outside the scope of this specification. 2959 After an original IP packet enters the OMNI interface, one or more 2960 outbound underlying interfaces are selected based on PBM traffic 2961 attributes, and one or more neighbor underlying interfaces are 2962 selected based on the receipt of Interface Attributes sub-options in 2963 IPv6 ND messages (see: Figure 15). Underlying interface selection 2964 for the nodes own local interfaces are based on attributes such as 2965 DSCP, application port number, cost, performance, message size, etc. 2966 OMNI interface multilink selections could also be configured to 2967 perform replication across multiple underlying interfaces for 2968 increased reliability at the expense of packet duplication. The set 2969 of all Interface Attributes received in IPv6 ND messages determines 2970 the multilink forwarding profile for selecting the neighbor's 2971 underlying interfaces. 2973 When the OMNI interface sends an original IP packet over a selected 2974 outbound underlying interface, the OAL employs encapsulation and 2975 fragmentation as discussed in Section 5, then performs *NET 2976 encapsulation as determined by the L2 address information received in 2977 Interface Attributes. The OAL also performs encapsulation when the 2978 nearest AR is located multiple hops away as discussed in 2979 Section 15.1. (Note that the OAL MAY employ packing when multiple 2980 original IP packets and/or control messages are available for 2981 forwarding to the same OAL destination.) 2983 OMNI interface multilink service designers MUST observe the BCP 2984 guidance in Section 15 [RFC3819] in terms of implications for 2985 reordering when original IP packets from the same flow may be spread 2986 across multiple underlying interfaces having diverse properties. 2988 14.1. Multiple OMNI Interfaces 2990 MNs may connect to multiple independent OMNI links concurrently in 2991 support of SBM. Each OMNI interface is distinguished by its Anycast 2992 ULA (e.g., [ULA]:0002::, [ULA]:1000::, [ULA]:7345::, etc.). The MN 2993 configures a separate OMNI interface for each link so that multiple 2994 interfaces (e.g., omni0, omni1, omni2, etc.) are exposed to the IPv6 2995 layer. A different Anycast ULA is assigned to each interface, and 2996 the MN injects the service prefixes for the OMNI link instances into 2997 the EUN routing system. 2999 Applications in EUNs can use Segment Routing to select the desired 3000 OMNI interface based on SBM considerations. The Anycast ULA is 3001 written into an original IP packet's IPv6 destination address, and 3002 the actual destination (along with any additional intermediate hops) 3003 is written into the Segment Routing Header. Standard IP routing 3004 directs the packet to the MN's mobile router entity, and the Anycast 3005 ULA identifies the OMNI interface to be used for transmission to the 3006 next hop. When the MN receives the packet, it replaces the IPv6 3007 destination address with the next hop found in the routing header and 3008 transmits the message over the OMNI interface identified by the 3009 Anycast ULA. 3011 Multiple distinct OMNI links can therefore be used to support fault 3012 tolerance, load balancing, reliability, etc. The architectural model 3013 is similar to Layer 2 Virtual Local Area Networks (VLANs). 3015 14.2. MN<->AR Traffic Loop Prevention 3017 After an AR has registered an MNP for a MN (see: Section 15), the AR 3018 will forward packets destined to an address within the MNP to the MN. 3019 The MN will under normal circumstances then forward the packet to the 3020 correct destination within its internal networks. 3022 If at some later time the MN loses state (e.g., after a reboot), it 3023 may begin returning packets destined to an MNP address to the AR as 3024 its default router. The AR therefore must drop any packets 3025 originating from the MN and destined to an address within the MN's 3026 registered MNP. To do so, the AR institutes the following check: 3028 o if the IP destination address belongs to a neighbor on the same 3029 OMNI interface, and if the link-layer source address is the same 3030 as one of the neighbor's link-layer addresses, drop the packet. 3032 15. Router Discovery and Prefix Registration 3034 MNs interface with the MS by sending RS messages with OMNI options 3035 under the assumption that one or more AR on the *NET will process the 3036 message and respond. The MN then configures default routes for the 3037 OMNI interface via the discovered ARs as the next hop. The manner in 3038 which the *NET ensures AR coordination is link-specific and outside 3039 the scope of this document (however, considerations for *NETs that do 3040 not provide ARs that recognize the OMNI option are discussed in 3041 Section 20). 3043 For each underlying interface, the MN sends an RS message with an 3044 OMNI option to coordinate with MSEs identified by MSID values. 3045 Example MSID discovery methods are given in [RFC5214] and include 3046 data link login parameters, name service lookups, static 3047 configuration, a static "hosts" file, etc. When the AR receives an 3048 RS', it selects a nearby MSE (which may be itself) and returns an RA 3049 with the selected MSID in an MS-Register sub-option. The AR selects 3050 only a single nearby MSE while also soliciting the MSEs corresponding 3051 to any non-zero MSIDs. 3053 MNs configure OMNI interfaces that observe the properties discussed 3054 in the previous section. The OMNI interface and its underlying 3055 interfaces are said to be in either the "UP" or "DOWN" state 3056 according to administrative actions in conjunction with the interface 3057 connectivity status. An OMNI interface transitions to UP or DOWN 3058 through administrative action and/or through state transitions of the 3059 underlying interfaces. When a first underlying interface transitions 3060 to UP, the OMNI interface also transitions to UP. When all 3061 underlying interfaces transition to DOWN, the OMNI interface also 3062 transitions to DOWN. 3064 When an OMNI interface transitions to UP, the MN sends RS messages to 3065 register its MNP and an initial set of underlying interfaces that are 3066 also UP. The MN sends additional RS messages to refresh lifetimes 3067 and to register/deregister underlying interfaces as they transition 3068 to UP or DOWN. The MN's OMNI interface sends initial RS messages 3069 over an UP underlying interface with its MNP-LLA as the source (or 3070 with the unspecified address (::) as the source if it does not yet 3071 have an MNP-LLA) and with destination set to link-scoped All-Routers 3072 multicast (ff02::2) [RFC4291]. The OMNI interface includes an OMNI 3073 option per Section 12 with a Preflen assertion, Interface Attributes 3074 appropriate for underlying interfaces, MS-Register/Release sub- 3075 options containing MSID values, Reassembly Limits, an authentication 3076 sub-option and with any other necessary OMNI sub-options (e.g., a 3077 Node Identification sub-option as an identity for the MN). The OMNI 3078 interface then sets the S/T-omIndex field to the index of the 3079 underlying interface over which the RS message is sent. 3081 The OMNI interface then sends the RS over the underlying interface 3082 using OAL encapsulation and fragmentation if necessary. If OAL 3083 encapsulation is used for RS messages sent over an INET interface, 3084 the entire RS message must appear within a single carrier packet so 3085 that it can be authenticated without requiring reassembly. The OMNI 3086 interface selects an unpredictable initial Identification value per 3087 Section 6.5, sets the OAL source address to the ULA corresponding to 3088 the RS source (Or a Temporary ULA if the RS source is the unspecified 3089 address (::)) and sets the OAL destination to site-scoped All-Routers 3090 multicast (ff05::2) then sends the message. 3092 ARs process IPv6 ND messages with OMNI options and act as an MSE 3093 themselves and/or as a proxy for other MSEs. ARs receive RS messages 3094 and create a neighbor cache entry for the MN, then prepare to act as 3095 an MSE themselves and/or coordinate with any MSEs named in the 3096 Register/Release lists in a manner outside the scope of this 3097 document. When an MSE processes the OMNI information, it first 3098 validates the prefix registration information then injects/withdraws 3099 the MNP in the routing/mapping system and caches/discards the new 3100 Preflen, MNP and Interface Attributes. The MSE then informs the AR 3101 of registration success/failure, and the AR returns an RA message to 3102 the MN with an OMNI option per Section 12. 3104 The AR's OMNI interface returns the RA message via the same 3105 underlying interface of the MN over which the RS was received, and 3106 with destination address set to the MNP-LLA (i.e., unicast), with 3107 source address set to its own LLA, and with an OMNI option with S/ 3108 T-omIndex set to the value included in the RS. The OMNI option also 3109 includes a Preflen confirmation, Interface Attributes, MS-Register/ 3110 Release and any other necessary OMNI sub-options (e.g., a Node 3111 Identification sub-option as an identity for the AR). The RA also 3112 includes any information for the link, including RA Cur Hop Limit, M 3113 and O flags, Router Lifetime, Reachable Time and Retrans Timer 3114 values, and includes any necessary options such as: 3116 o PIOs with (A; L=0) that include MSPs for the link [RFC8028]. 3118 o RIOs [RFC4191] with more-specific routes. 3120 o an MTU option that specifies the maximum acceptable packet size 3121 for this underlying interface. 3123 If the RS message arrived as an OAL atomic fragment, the AR prepares 3124 the RA using OAL encapsulation/fragmentation with the same 3125 Identification value that appeared in the RS message, with source set 3126 to the ULA corresponding to the RA source and with destination set to 3127 the ULA corresponding to the RA destination. The AR then sends the 3128 initial RA message to the MN and MAY later send additional periodic 3129 and/or event-driven unsolicited RA messages per [RFC4861]. In that 3130 case, the S/T-omIndex field in the OMNI option of the unsolicited RA 3131 message identifies the target underlying interface of the destination 3132 MN. 3134 The AR can combine the information from multiple MSEs into one or 3135 more "aggregate" RAs sent to the MN in order conserve *NET bandwidth. 3136 Each aggregate RA includes an OMNI option with MS-Register/Release 3137 sub-options with the MSEs represented by the aggregate. If an 3138 aggregate is sent, the RA message contents must consistently 3139 represent the combined information advertised by all represented 3140 MSEs. Note that since the AR uses its own ADM-LLA as the RA source 3141 address, the MN determines the addresses of the represented MSEs by 3142 examining the MS-Register/Release OMNI sub-options. 3144 When the MN receives the RA message, it creates an OMNI interface 3145 neighbor cache entry for each MSID that has confirmed MNP 3146 registration via the L2 address of this AR. If the MN connects to 3147 multiple *NETs, it records the additional L2 AR addresses in each 3148 MSID neighbor cache entry (i.e., as multilink neighbors). The MN 3149 then configures a default route via the MSE that returned the RA 3150 message, and assigns the Subnet Router Anycast address corresponding 3151 to the MNP (e.g., 2001:db8:1:2::) to the OMNI interface. The MN then 3152 manages its underlying interfaces according to their states as 3153 follows: 3155 o When an underlying interface transitions to UP, the MN sends an RS 3156 over the underlying interface with an OMNI option. The OMNI 3157 option contains at least one Interface Attribute sub-option with 3158 values specific to this underlying interface, and may contain 3159 additional Interface Attributes specific to other underlying 3160 interfaces. The option also includes any MS-Register/Release sub- 3161 options. 3163 o When an underlying interface transitions to DOWN, the MN sends an 3164 RS or unsolicited NA message over any UP underlying interface with 3165 an OMNI option containing an Interface Attribute sub-option for 3166 the DOWN underlying interface with Link set to '0'. The MN sends 3167 an RS when an acknowledgement is required, or an unsolicited NA 3168 when reliability is not thought to be a concern (e.g., if 3169 redundant transmissions are sent on multiple underlying 3170 interfaces). 3172 o When the Router Lifetime for a specific AR nears expiration, the 3173 MN sends an RS over the underlying interface to receive a fresh 3174 RA. If no RA is received, the MN can send RS messages to an 3175 alternate MSID in case the current MSID has failed. If no RS 3176 messages are received even after trying to contact alternate 3177 MSIDs, the MN marks the underlying interface as DOWN. 3179 o When a MN wishes to release from one or more current MSIDs, it 3180 sends an RS or unsolicited NA message over any UP underlying 3181 interfaces with an OMNI option with a Release MSID. Each MSID 3182 then withdraws the MNP from the routing/mapping system and informs 3183 the AR that the release was successful. 3185 o When all of a MNs underlying interfaces have transitioned to DOWN 3186 (or if the prefix registration lifetime expires), any associated 3187 MSEs withdraw the MNP the same as if they had received a message 3188 with a release indication. 3190 The MN is responsible for retrying each RS exchange up to 3191 MAX_RTR_SOLICITATIONS times separated by RTR_SOLICITATION_INTERVAL 3192 seconds until an RA is received. If no RA is received over an UP 3193 underlying interface (i.e., even after attempting to contact 3194 alternate MSEs), the MN declares this underlying interface as DOWN. 3196 The IPv6 layer sees the OMNI interface as an ordinary IPv6 interface. 3197 Therefore, when the IPv6 layer sends an RS message the OMNI interface 3198 returns an internally-generated RA message as though the message 3199 originated from an IPv6 router. The internally-generated RA message 3200 contains configuration information that is consistent with the 3201 information received from the RAs generated by the MS. Whether the 3202 OMNI interface IPv6 ND messaging process is initiated from the 3203 receipt of an RS message from the IPv6 layer is an implementation 3204 matter. Some implementations may elect to defer the IPv6 ND 3205 messaging process until an RS is received from the IPv6 layer, while 3206 others may elect to initiate the process proactively. Still other 3207 deployments may elect to administratively disable the ordinary RS/RA 3208 messaging used by the IPv6 layer over the OMNI interface, since they 3209 are not required to drive the internal RS/RA processing. (Note that 3210 this same logic applies to IPv4 implementations that employ ICMP- 3211 based Router Discovery per [RFC1256].) 3213 Note: The Router Lifetime value in RA messages indicates the time 3214 before which the MN must send another RS message over this underlying 3215 interface (e.g., 600 seconds), however that timescale may be 3216 significantly longer than the lifetime the MS has committed to retain 3217 the prefix registration (e.g., REACHABLETIME seconds). ARs are 3218 therefore responsible for keeping MS state alive on a shorter 3219 timescale than the MN is required to do on its own behalf. 3221 Note: On multicast-capable underlying interfaces, MNs should send 3222 periodic unsolicited multicast NA messages and ARs should send 3223 periodic unsolicited multicast RA messages as "beacons" that can be 3224 heard by other nodes on the link. If a node fails to receive a 3225 beacon after a timeout value specific to the link, it can initiate a 3226 unicast exchange to test reachability. 3228 Note: if an AR acting as a proxy forwards a MN's RS message to 3229 another node acting as an MSE using UDP/IP encapsulation, it must use 3230 a distinct UDP source port number for each MN. This allows the MSE 3231 to distinguish different MNs behind the same AR at the link-layer, 3232 whereas the link-layer addresses would otherwise be 3233 indistinguishable. 3235 Note: when an AR acting as an MSE returns an RA to an INET Client, it 3236 includes an OMNI option with an Interface Attributes sub-option with 3237 omIndex set to 0 and with SRT, FMT, LHS and L2ADDR information for 3238 its INET interface. This provides the Client with partition prefix 3239 context regarding the local OMNI link segment. 3241 15.1. Router Discovery in IP Multihop and IPv4-Only Networks 3243 On some *NETs, a MN may be located multiple IP hops away from the 3244 nearest AR. Forwarding through IP multihop *NETs is conducted 3245 through the application of a routing protocol (e.g., a MANET/VANET 3246 routing protocol over omni-directional wireless interfaces, an inter- 3247 domain routing protocol in an enterprise network, etc.). These *NETs 3248 could be either IPv6-enabled or IPv4-only, while IPv4-only *NETs 3249 could be either multicast-capable or unicast-only (note that for 3250 IPv4-only *NETs the following procedures apply for both single-hop 3251 and multihop cases). 3253 A MN located potentially multiple *NET hops away from the nearest AR 3254 prepares an RS message with source address set to its MNP-LLA (or to 3255 the unspecified address (::) if it does not yet have an MNP-LLA), and 3256 with destination set to link-scoped All-Routers multicast the same as 3257 discussed above. The OMNI interface then employs OAL encapsulation 3258 and fragmentation, and sets the OAL source address to the ULA 3259 corresponding to the RS source (or to a Temporary ULA if the RS 3260 source was the unspecified address (::)) and sets the OAL destination 3261 to site-scoped All-Routers multicast (ff05::2). For IPv6-enabled 3262 *NETs, the MN then encapsulates the message in UDP/IPv6 headers with 3263 source address set to the underlying interface address (or to the ULA 3264 that would be used for OAL encapsulation if the underlying interface 3265 does not yet have an address) and sets the destination to either a 3266 unicast or anycast address of an AR. For IPv4-only *NETs, the MN 3267 instead encapsulates the RS message in UDP/IPv4 headers with source 3268 address set to the IPv4 address of the underlying interface and with 3269 destination address set to either the unicast IPv4 address of an AR 3270 [RFC5214] or an IPv4 anycast address reserved for OMNI. The MN then 3271 sends the encapsulated RS message via the *NET interface, where it 3272 will be forwarded by zero or more intermediate *NET hops. 3274 When an intermediate *NET hop that participates in the routing 3275 protocol receives the encapsulated RS, it forwards the message 3276 according to its routing tables (note that an intermediate node could 3277 be a fixed infrastructure element or another MN). This process 3278 repeats iteratively until the RS message is received by a penultimate 3279 *NET hop within single-hop communications range of an AR, which 3280 forwards the message to the AR. 3282 When the AR receives the message, it decapsulates the RS (while 3283 performing OAL reassembly, if necessary) and coordinates with the MS 3284 the same as for an ordinary link-local RS, since the network layer 3285 Hop Limit will not have been decremented by the multihop forwarding 3286 process. The AR then prepares an RA message with source address set 3287 to its own ADM-LLA and destination address set to the LLA of the 3288 original MN. The AR then performs OAL encapsulation and 3289 fragmentation, with OAL source set to its own ADM-ULA and destination 3290 set to the ULA corresponding to the RA source. The AR then 3291 encapsulates the message in UDP/IPv4 or UDP/IPv6 headers with source 3292 address set to its own address and with destination set to the 3293 encapsulation source of the RS. 3295 The AR then forwards the message to an *NET node within 3296 communications range, which forwards the message according to its 3297 routing tables to an intermediate node. The multihop forwarding 3298 process within the *NET continues repetitively until the message is 3299 delivered to the original MN, which decapsulates the message and 3300 performs autoconfiguration the same as if it had received the RA 3301 directly from the AR as an on-link neighbor. 3303 Note: An alternate approach to multihop forwarding via IPv6 3304 encapsulation would be for the MN and AR to statelessly translate the 3305 IPv6 LLAs into ULAs and forward the RS/RA messages without 3306 encapsulation. This would violate the [RFC4861] requirement that 3307 certain IPv6 ND messages must use link-local addresses and must not 3308 be accepted if received with Hop Limit less than 255. This document 3309 therefore mandates encapsulation since the overhead is nominal 3310 considering the infrequent nature and small size of IPv6 ND messages. 3312 Future documents may consider encapsulation avoidance through 3313 translation while updating [RFC4861]. 3315 Note: An alternate approach to multihop forwarding via IPv4 3316 encapsulation would be to employ IPv6/IPv4 protocol translation. 3317 However, for IPv6 ND messages the LLAs would be truncated due to 3318 translation and the OMNI Router and Prefix Discovery services would 3319 not be able to function. The use of IPv4 encapsulation is therefore 3320 indicated. 3322 Note: An IPv4 anycast address for OMNI in IPv4 networks could be part 3323 of a new IPv4 /24 prefix allocation, but this may be difficult to 3324 obtain given IPv4 address exhaustion. An alternative would be to re- 3325 purpose the prefix 192.88.99.0 which has been set aside from its 3326 former use by [RFC7526]. 3328 15.2. MS-Register and MS-Release List Processing 3330 OMNI links maintain a constant value "MAX_MSID" selected to provide 3331 MNs with an acceptable level of MSE redundancy while minimizing 3332 control message amplification. It is RECOMMENDED that MAX_MSID be 3333 set to the default value 5; if a different value is chosen, it should 3334 be set uniformly by all nodes on the OMNI link. 3336 When a MN sends an RS message with an OMNI option via an underlying 3337 interface to an AR, the MN must convey its knowledge of its 3338 currently-associated MSEs. Initially, the MN will have no associated 3339 MSEs and should therefore send its initial RS messages to the link- 3340 scoped All-Routers multicast address. The AR will then return an RA 3341 message with source address set to the ADM-LLA of the selected MSE 3342 (which may be the address of the AR itself). 3344 As the MN activates additional underlying interfaces, it can 3345 optionally include an MS-Register sub-option with MSIDs for MSEs 3346 discovered from previous RS/RA exchanges. The MN will thus 3347 eventually begin to learn and manage its currently active set of 3348 MSEs, and can register with new MSEs or release from former MSEs with 3349 each successive RS/RA exchange. As the MN's MSE constituency grows, 3350 it alone is responsible for including or omitting MSIDs in the MS- 3351 Register/Release lists it sends in RS messages. The inclusion or 3352 omission of MSIDs determines the MN's interface to the MS and defines 3353 the manner in which MSEs will respond. The only limiting factor is 3354 that the MN should include no more than MAX_MSID values in each list 3355 per each IPv6 ND message, and should avoid duplication of entries in 3356 each list unless it wants to increase likelihood of control message 3357 delivery. 3359 When an AR receives an RS message sent by a MN with an OMNI option, 3360 the option will contain zero or more MS-Register and MS-Release sub- 3361 options containing MSIDs. After processing the OMNI option, the AR 3362 will have a list of zero or more MS-Register MSIDs and a list of zero 3363 or more of MS-Release MSIDs. The AR then processes the lists as 3364 follows: 3366 o For each list, retain the first MAX_MSID values in the list and 3367 discard any additional MSIDs (i.e., even if there are duplicates 3368 within a list). 3370 o Next, for each MSID in the MS-Register list, remove all matching 3371 MSIDs from the MS-Release list. 3373 o Next, proceed as follows: 3375 * If the AR's own MSID appears in the MS-Register list, send an 3376 RA message directly back to the MN and send a proxy copy of the 3377 RS message to each additional MSID in the MS-Register list with 3378 the MS-Register/Release lists omitted. Then, send an 3379 unsolicited NA (uNA) message to each MSID in the MS-Release 3380 list with the MS-Register/Release lists omitted and with an 3381 OMNI option with S/T-omIndex set to 0. 3383 * Otherwise, send a proxy copy of the RS message to each 3384 additional MSID in the MS-Register list with the MS-Register 3385 list omitted. For the first MSID, include the original MS- 3386 Release list; for all other MSIDs, omit the MS-Release list. 3388 Each proxy copy of the RS message will include an OMNI option and OAL 3389 encapsulation header with the ADM-ULA of the AR as the source and the 3390 ADM-ULA of the Register MSE as the destination. When the Register 3391 MSE receives the proxy RS message, if the message includes an MS- 3392 Release list the MSE sends a uNA message to each additional MSID in 3393 the Release list with an OMNI option with S/T-omIndex set to 0. The 3394 Register MSE then sends an RA message back to the (Proxy) AR wrapped 3395 in an OAL encapsulation header with source and destination addresses 3396 reversed, and with RA destination set to the MNP-LLA of the MN. When 3397 the AR receives this RA message, it sends a proxy copy of the RA to 3398 the MN. 3400 Each uNA message (whether sent by the first-hop AR or by a Register 3401 MSE) will include an OMNI option and an OAL encapsulation header with 3402 the ADM-ULA of the Register MSE as the source and the ADM-ULA of the 3403 Release MSE as the destination. The uNA informs the Release MSE that 3404 its previous relationship with the MN has been released and that the 3405 source of the uNA message is now registered. The Release MSE must 3406 then note that the subject MN of the uNA message is now "departed", 3407 and forward any subsequent packets destined to the MN to the Register 3408 MSE. 3410 Note that it is not an error for the MS-Register/Release lists to 3411 include duplicate entries. If duplicates occur within a list, the AR 3412 will generate multiple proxy RS and/or uNA messages - one for each 3413 copy of the duplicate entries. 3415 15.3. DHCPv6-based Prefix Registration 3417 When a MN is not pre-provisioned with an MNP-LLA (or, when the MN 3418 requires additional MNP delegations), it requests the MSE to select 3419 MNPs on its behalf and set up the correct routing state within the 3420 MS. The DHCPv6 service [RFC8415] supports this requirement. 3422 When an MN needs to have the MSE select MNPs, it sends an RS message 3423 with source set to the unspecified address (::) if it has no 3424 MNP_LLAs. If the MN requires only a single MNP delegation, it can 3425 then include a Node Identification sub-option in the OMNI option and 3426 set Preflen to the length of the desired MNP. If the MN requires 3427 multiple MNP delegations and/or more complex DHCPv6 services, it 3428 instead includes a DHCPv6 Message sub-option containing a Client 3429 Identifier, one or more IA_PD options and a Rapid Commit option then 3430 sets the 'msg-type' field to "Solicit", and includes a 3 octet 3431 'transaction-id'. The MN then sets the RS destination to All-Routers 3432 multicast and sends the message using OAL encapsulation and 3433 fragmentation if necessary as discussed above. 3435 When the MSE receives the RS message, it performs OAL reassembly if 3436 necessary. Next, if the RS source is the unspecified address (::) 3437 and/or the OMNI option includes a DHCPv6 message sub-option, the MSE 3438 acts as a "Proxy DHCPv6 Client" in a message exchange with the 3439 locally-resident DHCPv6 server. If the RS did not contain a DHCPv6 3440 message sub-option, the MSE generates a DHCPv6 Solicit message on 3441 behalf of the MN using an IA_PD option with the prefix length set to 3442 the OMNI header Preflen value and with a Client Identifier formed 3443 from the OMNI option Node Identification sub-option; otherwise, the 3444 MSE uses the DHCPv6 Solicit message contained in the OMNI option. 3445 The MSE then sends the DHCPv6 message to the DHCPv6 Server, which 3446 delegates MNPs and returns a DHCPv6 Reply message with PD parameters. 3447 (If the MSE wishes to defer creation of MN state until the DHCPv6 3448 Reply is received, it can instead act as a Lightweight DHCPv6 Relay 3449 Agent per [RFC6221] by encapsulating the DHCPv6 message in a Relay- 3450 forward/reply exchange with Relay Message and Interface ID options. 3451 In the process, the MSE packs any state information needed to return 3452 an RA to the MN in the Relay-forward Interface ID option so that the 3453 information will be echoed back in the Relay-reply.) 3454 When the MSE receives the DHCPv6 Reply, it adds routes to the routing 3455 system and creates MNP-LLAs based on the delegated MNPs. The MSE 3456 then sends an RA back to the MN with the DHCPv6 Reply message 3457 included in an OMNI DHCPv6 message sub-option if and only if the RS 3458 message had included an explicit DHCPv6 Solicit. If the RS message 3459 source was the unspecified address (::), the MSE includes one of the 3460 (newly-created) MNP-LLAs as the RA destination address and sets the 3461 OMNI option Preflen accordingly; otherwise, the MSE includes the RS 3462 source address as the RA destination address. The MSE then sets the 3463 RA source address to its own ADM-LLA then performs OAL encapsulation 3464 and fragmentation and sends the RA to the MN. When the MN receives 3465 the RA, it reassembles and discards the OAL encapsulation, then 3466 creates a default route, assigns Subnet Router Anycast addresses and 3467 uses the RA destination address as its primary MNP-LLA. The MN will 3468 then use this primary MNP-LLA as the source address of any IPv6 ND 3469 messages it sends as long as it retains ownership of the MNP. 3471 Note: After a MN performs a DHCPv6-based prefix registration exchange 3472 with a first MSE, it would need to repeat the exchange with each 3473 additional MSE it registers with. In that case, the MN supplies the 3474 MNP delegation information received from the first MSE when it 3475 engages the additional MSEs. 3477 16. Secure Redirection 3479 If the *NET link model is multiple access, the AR is responsible for 3480 assuring that address duplication cannot corrupt the neighbor caches 3481 of other nodes on the link. When the MN sends an RS message on a 3482 multiple access *NET link, the AR verifies that the MN is authorized 3483 to use the address and returns an RA with a non-zero Router Lifetime 3484 only if the MN is authorized. 3486 After verifying MN authorization and returning an RA, the AR MAY 3487 return IPv6 ND Redirect messages to direct MNs located on the same 3488 *NET link to exchange packets directly without transiting the AR. In 3489 that case, the MNs can exchange packets according to their unicast L2 3490 addresses discovered from the Redirect message instead of using the 3491 dogleg path through the AR. In some *NET links, however, such direct 3492 communications may be undesirable and continued use of the dogleg 3493 path through the AR may provide better performance. In that case, 3494 the AR can refrain from sending Redirects, and/or MNs can ignore 3495 them. 3497 17. AR and MSE Resilience 3499 *NETs SHOULD deploy ARs in Virtual Router Redundancy Protocol (VRRP) 3500 [RFC5798] configurations so that service continuity is maintained 3501 even if one or more ARs fail. Using VRRP, the MN is unaware which of 3502 the (redundant) ARs is currently providing service, and any service 3503 discontinuity will be limited to the failover time supported by VRRP. 3504 Widely deployed public domain implementations of VRRP are available. 3506 MSEs SHOULD use high availability clustering services so that 3507 multiple redundant systems can provide coordinated response to 3508 failures. As with VRRP, widely deployed public domain 3509 implementations of high availability clustering services are 3510 available. Note that special-purpose and expensive dedicated 3511 hardware is not necessary, and public domain implementations can be 3512 used even between lightweight virtual machines in cloud deployments. 3514 18. Detecting and Responding to MSE Failures 3516 In environments where fast recovery from MSE failure is required, ARs 3517 SHOULD use proactive Neighbor Unreachability Detection (NUD) in a 3518 manner that parallels Bidirectional Forwarding Detection (BFD) 3519 [RFC5880] to track MSE reachability. ARs can then quickly detect and 3520 react to failures so that cached information is re-established 3521 through alternate paths. Proactive NUD control messaging is carried 3522 only over well-connected ground domain networks (i.e., and not low- 3523 end *NET links such as aeronautical radios) and can therefore be 3524 tuned for rapid response. 3526 ARs perform proactive NUD for MSEs for which there are currently 3527 active MNs on the *NET. If an MSE fails, ARs can quickly inform MNs 3528 of the outage by sending multicast RA messages on the *NET interface. 3529 The AR sends RA messages to MNs via the *NET interface with an OMNI 3530 option with a Release ID for the failed MSE, and with destination 3531 address set to All-Nodes multicast (ff02::1) [RFC4291]. 3533 The AR SHOULD send MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated 3534 by small delays [RFC4861]. Any MNs on the *NET interface that have 3535 been using the (now defunct) MSE will receive the RA messages and 3536 associate with a new MSE. 3538 19. Transition Considerations 3540 When a MN connects to an *NET link for the first time, it sends an RS 3541 message with an OMNI option. If the first hop AR recognizes the 3542 option, it returns an RA with its ADM-LLA as the source, the MNP-LLA 3543 as the destination and with an OMNI option included. The MN then 3544 engages the AR according to the OMNI link model specified above. If 3545 the first hop AR is a legacy IPv6 router, however, it instead returns 3546 an RA message with no OMNI option and with a non-OMNI unicast source 3547 LLA as specified in [RFC4861]. In that case, the MN engages the *NET 3548 according to the legacy IPv6 link model and without the OMNI 3549 extensions specified in this document. 3551 If the *NET link model is multiple access, there must be assurance 3552 that address duplication cannot corrupt the neighbor caches of other 3553 nodes on the link. When the MN sends an RS message on a multiple 3554 access *NET link with an LLA source address and an OMNI option, ARs 3555 that recognize the option ensure that the MN is authorized to use the 3556 address and return an RA with a non-zero Router Lifetime only if the 3557 MN is authorized. ARs that do not recognize the option instead 3558 return an RA that makes no statement about the MN's authorization to 3559 use the source address. In that case, the MN should perform 3560 Duplicate Address Detection to ensure that it does not interfere with 3561 other nodes on the link. 3563 An alternative approach for multiple access *NET links to ensure 3564 isolation for MN / AR communications is through L2 address mappings 3565 as discussed in Appendix C. This arrangement imparts a (virtual) 3566 point-to-point link model over the (physical) multiple access link. 3568 20. OMNI Interfaces on Open Internetworks 3570 OMNI interfaces configured over IPv6-enabled underlying interfaces on 3571 an open Internetwork without an OMNI-aware first-hop AR receive RA 3572 messages that do not include an OMNI option, while OMNI interfaces 3573 configured over IPv4-only underlying interfaces do not receive any 3574 (IPv6) RA messages at all (although they may receive IPv4 RA messages 3575 [RFC1256]). OMNI interfaces that receive RA messages without an OMNI 3576 option configure addresses, on-link prefixes, etc. on the underlying 3577 interface that received the RA according to standard IPv6 ND and 3578 address resolution conventions [RFC4861] [RFC4862]. OMNI interfaces 3579 configured over IPv4-only underlying interfaces configure IPv4 3580 address information on the underlying interfaces using mechanisms 3581 such as DHCPv4 [RFC2131]. 3583 OMNI interfaces configured over underlying interfaces that connect to 3584 an open Internetwork can apply security services such as VPNs to 3585 connect to an MSE, or can establish a direct link to an MSE through 3586 some other means (see Section 4). In environments where an explicit 3587 VPN or direct link may be impractical, OMNI interfaces can instead 3588 use UDP/IP encapsulation while including authentication signatures in 3589 IPv6 ND messages. 3591 OMNI interfaces use UDP service port number 8060 (see: Section 25.11 3592 and Section 3.6 of [I-D.templin-6man-aero]) according to the simple 3593 UDP/IP encapsulation format specified in [RFC4380] for both IPv4 and 3594 IPv6 underlying interfaces. OMNI interfaces do not include the UDP/ 3595 IP header/trailer extensions specified in [RFC4380][RFC6081], but may 3596 include them as OMNI sub-options instead when necessary. Since the 3597 OAL includes an integrity check over the OAL packet, OAL sources 3598 selectively disable UDP checksums for OAL packets that do not require 3599 UDP/IP address integrity, but enable UDP checksums for others 3600 including non-OAL packets, IPv6 ND messages used to establish link- 3601 layer addresses, etc. If the OAL source discovers that packets with 3602 UDP checksums disabled are being dropped in the path it should enable 3603 UDP checksums in future packets. Further considerations for UDP 3604 encapsulation checksums are found in [RFC6935][RFC6936]. 3606 For "Vehicle-to-Infrastructure (V2I)" coordination, the MN includes 3607 an authentication sub-option in the OMNI option of IPv6 RS/NS 3608 messages and the MSE responds with an authentication sub-option in an 3609 OMNI option of an IPv6 RA/NA message. HIP security services can be 3610 applied per [RFC7401] using the IPv6 ND messages as simple "shipping 3611 containers" to convey the sender's HIP authentication signature 3612 (e.g., enclosed in a HIP "Notify" message). Alternatively, a simple 3613 Hashed Message Authentication Code (HMAC) can be included in the 3614 manner specified in [RFC4380]. For "Vehicle-to-Vehicle (V2V)" 3615 coordination, two MNs can coordinate directly with one another with 3616 HIP "Initiator/Responder" messages coded in OMNI options of IPv6 NS/ 3617 NA messages. In that case, a four-message HIP exchange (i.e., two 3618 back-to-back NS/NA exchanges) may be necessary for the two MNs to 3619 attain mutual authentication. 3621 After establishing a VPN or preparing for UDP/IP encapsulation, OMNI 3622 interfaces send control plane messages to interface with the MSE, 3623 including RS/RA messages used according to Section 15 and NS/NA 3624 messages used for route optimization and mobility (see: 3625 [I-D.templin-6man-aero]). The control plane messages must be 3626 authenticated while data plane messages are delivered the same as for 3627 ordinary best-effort traffic with basic source address-based data 3628 origin verification. Data plane communications via OMNI interfaces 3629 that connect over open Internetworks without an explicit VPN should 3630 therefore employ transport- or higher-layer security to ensure 3631 integrity and/or confidentiality. 3633 OMNI interfaces configured over open Internetworks are often located 3634 behind NATs. The OMNI interface accommodates NAT traversal using 3635 UDP/IP encapsulation and the mechanisms discussed in 3636 [I-D.templin-6man-aero]. To support NAT determination, MSEs include 3637 an Origin Indication sub-option in RA messages sent in response to RS 3638 messages received from a Client via UDP/IP encapsulation. 3640 Note: Following the initial HIP exchange, OMNI interfaces configured 3641 over open Internetworks maintain HIP associations through the 3642 transmission of IPv6 ND messages that include OMNI options with HIP 3643 "Update" and "Notify" messages. OMNI interfaces use the HIP "Update" 3644 message when an acknowledgement is required, and use the "Notify" 3645 message in unacknowledged isolated IPv6 ND messages (e.g., 3646 unsolicited NAs). When HMAC authentication is used instead of HIP, 3647 the MN and MSE exchange all IPv6 ND messages with HMAC signatures 3648 included based on a shared-secret. 3650 Note: ARs that act as proxys on an open Internetwork authenticate and 3651 remove authentication OMNI sub-options from IPv6 ND messages they 3652 forward from a MN, and insert and sign authentication Origin 3653 Indication sub-options in IPv6 ND messages they forward from the 3654 network to the MN. Conversely, ARs that act as proxys forward 3655 without processing any DHCPv6 information in RS/RA message exchanges 3656 between MNs and MSEs. The AR is therefore responsible for MN 3657 authentication while the MSE is responsible for registering/ 3658 delegating MNPs. Note also that a simpler arrangement is possible 3659 when the AR also acts as a MSE itself, i.e., when the proxy and MSE 3660 functions are combined on a single physical or logical platform 3661 located somewhere in the Internetwork. 3663 Note: The [RFC4380] HMAC and/or HIP message [RFC7401] authentication 3664 sub-options appear in the OMNI option, which may occur anywhere 3665 within the IPv6 ND message body. When a node that inserts an 3666 authentication sub-option generates the authentication signature, it 3667 calculates the signature over the entire length of the IPv6 ND 3668 message but with the sub-option authentication field itself set to 0. 3669 The node then writes the resulting signature into the authentication 3670 field then continues to prepare the message for transmission. For 3671 this reason, if an IPv6 ND message includes multiple authentication 3672 sub-options, the first sub-option is consulted and any additional 3673 sub-options are ignored. 3675 21. Time-Varying MNPs 3677 In some use cases, it is desirable, beneficial and efficient for the 3678 MN to receive a constant MNP that travels with the MN wherever it 3679 moves. For example, this would allow air traffic controllers to 3680 easily track aircraft, etc. In other cases, however (e.g., 3681 intelligent transportation systems), the MN may be willing to 3682 sacrifice a modicum of efficiency in order to have time-varying MNPs 3683 that can be changed every so often to defeat adversarial tracking. 3685 The prefix delegation services discussed in Section 15.3 allows OMNI 3686 MNs that desire time-varying MNPs to obtain short-lived prefixes to 3687 send RS messages with source set to the unspecified address (::) and/ 3688 or with an OMNI option with DHCPv6 Option sub-options. The MN would 3689 then be obligated to renumber its internal networks whenever its MNP 3690 (and therefore also its OMNI address) changes. This should not 3691 present a challenge for MNs with automated network renumbering 3692 services, however presents limits for the durations of ongoing 3693 sessions that would prefer to use a constant address. 3695 22. (H)HITs and Temporary ULAs 3697 MNs that generate (H)HITs but do not have pre-assigned MNPs can 3698 request MNP delegations by issuing IPv6 ND messages that use the 3699 (H)HIT instead of a Temporary ULA. In particular, when a MN creates 3700 an RS message it can set the source to the unspecified address (::) 3701 and destination to All-Routers multicast. The IPv6 ND message 3702 includes an OMNI option with a HIP message sub-option, and need not 3703 include a Node Identification sub-option since the MN's HIT appears 3704 in the HIP message. The MN then encapsulates the message in an IPv6 3705 header with the (H)HIT as the source address and with destination set 3706 to either a unicast or anycast ADM-ULA. The MN then sends the 3707 message to the MSE as specified in Section 15.1. 3709 When the MSE receives the message, it notes that the RS source was 3710 the unspecified address (::), then examines the RS encapsulation 3711 source address to determine that the source is a (H)HIT and not a 3712 Temporary ULA. The MSE next invokes the DHCPv6 protocol to request 3713 an MNP prefix delegation while using the HIT as the Client 3714 Identifier, then prepares an RA message with source address set to 3715 its own ADM-LLA and destination set to the MNP-LLA corresponding to 3716 the delegated MNP. The MSE next includes an OMNI option with a HIP 3717 message sub-option and any DHCPv6 prefix delegation parameters. The 3718 MSE then finally encapsulates the RA in an IPv6 header with source 3719 address set to its own ADM-ULA and destination set to the (H)HIT from 3720 the RS encapsulation source address, then returns the encapsulated RA 3721 to the MN. 3723 MNs can also use (H)HITs and/or Temporary ULAs for direct MN-to-MN 3724 communications outside the context of any OMNI link supporting 3725 infrastructure. When two MNs encounter one another they can use 3726 their (H)HITs and/or Temporary ULAs as original IPv6 packet source 3727 and destination addresses to support direct communications. MNs can 3728 also inject their (H)HITs and/or Temporary ULAs into a MANET/VANET 3729 routing protocol to enable multihop communications. MNs can further 3730 exchange IPv6 ND messages (such as NS/NA) using their (H)HITs and/or 3731 Temporary ULAs as source and destination addresses. Note that the 3732 HIP security protocols for establishing secure neighbor relationships 3733 are based on (H)HITs. IPv6 ND messages that use Temporary ULAs 3734 instead use the HMAC authentication service specified in [RFC4380]. 3736 Lastly, when MNs are within the coverage range of OMNI link 3737 infrastructure a case could be made for injecting (H)HITs and/or 3738 Temporary ULAs into the global MS routing system. For example, when 3739 the MN sends an RS to a MSE it could include a request to inject the 3740 (H)HIT / Temporary ULA into the routing system instead of requesting 3741 an MNP prefix delegation. This would potentially enable OMNI link- 3742 wide communications using only (H)HITs or Temporary ULAs, and not 3743 MNPs. This document notes the opportunity, but makes no 3744 recommendation. 3746 23. Address Selection 3748 OMNI MNs use LLAs only for link-scoped communications on the OMNI 3749 link. Typically, MNs use LLAs as source/destination IPv6 addresses 3750 of IPv6 ND messages, but may also use them for addressing ordinary 3751 original IP packets exchanged with an OMNI link neighbor. 3753 OMNI MNs use MNP-ULAs as source/destination IPv6 addresses in the 3754 encapsulation headers of OAL packets. OMNI MNs use Temporary ULAs 3755 for OAL addressing when an MNP-ULA is not available, or as source/ 3756 destination IPv6 addresses for communications within a MANET/VANET 3757 local area. OMNI MNs use HITs instead of Temporary ULAs when 3758 operation outside the context of a specific ULA domain and/or source 3759 address attestation is necessary. 3761 OMNI MNs use MNP-based GUAs as original IP packet source and 3762 destination addresses for communications with Internet destinations 3763 when they are within range of OMNI link supporting infrastructure 3764 that can inject the MNP into the routing system. 3766 24. Error Messages 3768 An OAL destination or intermediate node may need to return ICMPv6 3769 error messages (e.g., Destination Unreachable, Packet Too Big, Time 3770 Exceeded, etc.) [RFC4443] to an OAL source. Since ICMPv6 error 3771 messages do not themselves include authentication codes, the OAL 3772 includes the ICMPv6 error message as an OMNI sub-option in an IPv6 ND 3773 uNA message. The OAL also includes a HIP message sub-option if the 3774 uNA needs to travel over an open Internetwork. 3776 25. IANA Considerations 3778 The following IANA actions are requested in accordance with [RFC8126] 3779 and [RFC8726]: 3781 25.1. "IEEE 802 Numbers" Registry 3783 The IANA is instructed to allocate an official Ethertype number TBD1 3784 from the 'ieee-802-numbers' registry for User Datagram Protocol (UDP) 3785 encapsulation on Ethernet networks. Guidance is found in [RFC7042] 3786 (registration procedure is Expert Review). 3788 25.2. "IPv6 Neighbor Discovery Option Formats" Registry 3790 The IANA is instructed to allocate an official Type number TBD2 from 3791 the "IPv6 Neighbor Discovery Option Formats" registry for the OMNI 3792 option (registration procedure is RFC required). Implementations set 3793 Type to 253 as an interim value [RFC4727]. 3795 25.3. "Ethernet Numbers" Registry 3797 The IANA is instructed to allocate one Ethernet unicast address TBD3 3798 (suggested value '00-52-14') in the 'ethernet-numbers' registry under 3799 "IANA Unicast 48-bit MAC Addresses" (registration procedure is Expert 3800 Review). The registration should appear as follows: 3802 Addresses Usage Reference 3803 --------- ----- --------- 3804 00-52-14 Overlay Multilink Network (OMNI) Interface [RFCXXXX] 3806 Figure 33: IANA Unicast 48-bit MAC Addresses 3808 25.4. "ICMPv6 Code Fields: Type 2 - Packet Too Big" Registry 3810 The IANA is instructed to assign two new Code values in the "ICMPv6 3811 Code Fields: Type 2 - Packet Too Big" registry (registration 3812 procedure is Standards Action or IESG Approval). The registry should 3813 appear as follows: 3815 Code Name Reference 3816 --- ---- --------- 3817 0 PTB Hard Error [RFC4443] 3818 1 PTB Soft Error (loss) [RFCXXXX] 3819 2 PTB Soft Error (no loss) [RFCXXXX] 3821 Figure 34: ICMPv6 Code Fields: Type 2 - Packet Too Big Values 3823 (Note: this registry also to be used to define values for setting the 3824 "unused" field of ICMPv4 "Destination Unreachable - Fragmentation 3825 Needed" messages.) 3827 25.5. "OMNI Option Sub-Type Values" (New Registry) 3829 The OMNI option defines a 5-bit Sub-Type field, for which IANA is 3830 instructed to create and maintain a new registry entitled "OMNI 3831 Option Sub-Type Values". Initial values are given below 3832 (registration procedure is RFC required): 3834 Value Sub-Type name Reference 3835 ----- ------------- ---------- 3836 0 Pad1 [RFCXXXX] 3837 1 PadN [RFCXXXX] 3838 2 Interface Attributes (Type 1) [RFCXXXX] 3839 3 Interface Attributes (Type 2) [RFCXXXX] 3840 4 Traffic Selector [RFCXXXX] 3841 5 MS-Register [RFCXXXX] 3842 6 MS-Release [RFCXXXX] 3843 7 Geo Coordinates [RFCXXXX] 3844 8 DHCPv6 Message [RFCXXXX] 3845 9 HIP Message [RFCXXXX] 3846 11 PIM-SM Message [RFCXXXX] 3847 11 Reassembly Limit [RFCXXXX] 3848 12 Fragmentation Report [RFCXXXX] 3849 13 Node Identification [RFCXXXX] 3850 14-29 Unassigned 3851 30 Sub-Type Extension [RFCXXXX] 3852 31 Reserved by IANA [RFCXXXX] 3854 Figure 35: OMNI Option Sub-Type Values 3856 25.6. "OMNI Geo Coordinates Type Values" (New Registry) 3858 The OMNI Geo Coordinates Sub-Option (see: Section 12.1.8) contains an 3859 8-bit Type field, for which IANA is instructed to create and maintain 3860 a new registry entitled "OMNI Geo Coordinates Type Values". Initial 3861 values are given below (registration procedure is RFC required): 3863 Value Sub-Type name Reference 3864 ----- ------------- ---------- 3865 0 NULL [RFCXXXX] 3866 255 Reserved by IANA [RFCXXXX] 3868 Figure 36: OMNI Geo Coordinates Type 3870 25.7. "OMNI Node Identification ID-Type Values" (New Registry) 3872 The OMNI Node Identification Sub-Option (see: Section 12.1.14) 3873 contains an 8-bit ID-Type field, for which IANA is instructed to 3874 create and maintain a new registry entitled "OMNI Node Identification 3875 ID-Type Values". Initial values are given below (registration 3876 procedure is RFC required): 3878 Value Sub-Type name Reference 3879 ----- ------------- ---------- 3880 0 UUID [RFCXXXX] 3881 1 HIT [RFCXXXX] 3882 2 HHIT [RFCXXXX] 3883 3 Network Access Identifier [RFCXXXX] 3884 4 FQDN [RFCXXXX] 3885 5-252 Unassigned [RFCXXXX] 3886 253-254 Reserved for Experimentation [RFCXXXX] 3887 255 Reserved by IANA [RFCXXXX] 3889 Figure 37: OMNI Node Identification ID-Type Values 3891 25.8. "OMNI Option Sub-Type Extension Values" (New Registry) 3893 The OMNI option defines an 8-bit Extension-Type field for Sub-Type 30 3894 (Sub-Type Extension), for which IANA is instructed to create and 3895 maintain a new registry entitled "OMNI Option Sub-Type Extension 3896 Values". Initial values are given below (registration procedure is 3897 RFC required): 3899 Value Sub-Type name Reference 3900 ----- ------------- ---------- 3901 0 RFC4380 UDP/IP Header Option [RFCXXXX] 3902 1 RFC6081 UDP/IP Trailer Option [RFCXXXX] 3903 2-252 Unassigned 3904 253-254 Reserved for Experimentation [RFCXXXX] 3905 255 Reserved by IANA [RFCXXXX] 3907 Figure 38: OMNI Option Sub-Type Extension Values 3909 25.9. "OMNI RFC4380 UDP/IP Header Option" (New Registry) 3911 The OMNI Sub-Type Extension "RFC4380 UDP/IP Header Option" defines an 3912 8-bit Header Type field, for which IANA is instructed to create and 3913 maintain a new registry entitled "OMNI RFC4380 UDP/IP Header Option". 3914 Initial registry values are given below (registration procedure is 3915 RFC required): 3917 Value Sub-Type name Reference 3918 ----- ------------- ---------- 3919 0 Origin Indication (IPv4) [RFC4380] 3920 1 Authentication Encapsulation [RFC4380] 3921 2 Origin Indication (IPv6) [RFCXXXX] 3922 3-252 Unassigned 3923 253-254 Reserved for Experimentation [RFCXXXX] 3924 255 Reserved by IANA [RFCXXXX] 3926 Figure 39: OMNI RFC4380 UDP/IP Header Option 3928 25.10. "OMNI RFC6081 UDP/IP Trailer Option" (New Registry) 3930 The OMNI Sub-Type Extension for "RFC6081 UDP/IP Trailer Option" 3931 defines an 8-bit Trailer Type field, for which IANA is instructed to 3932 create and maintain a new registry entitled "OMNI RFC6081 UDP/IP 3933 Trailer Option". Initial registry values are given below 3934 (registration procedure is RFC required): 3936 Value Sub-Type name Reference 3937 ----- ------------- ---------- 3938 0 Unassigned 3939 1 Nonce [RFC6081] 3940 2 Unassigned 3941 3 Alternate Address (IPv4) [RFC6081] 3942 4 Neighbor Discovery Option [RFC6081] 3943 5 Random Port [RFC6081] 3944 6 Alternate Address (IPv6) [RFCXXXX] 3945 7-252 Unassigned 3946 253-254 Reserved for Experimentation [RFCXXXX] 3947 255 Reserved by IANA [RFCXXXX] 3949 Figure 40: OMNI RFC6081 Trailer Option 3951 25.11. Additional Considerations 3953 The IANA has assigned the UDP port number "8060" for an earlier 3954 experimental version of AERO [RFC6706]. This document together with 3955 [I-D.templin-6man-aero] reclaims the UDP port number "8060" for 3956 'aero' as the service port for UDP/IP encapsulation. (Note that, 3957 although [RFC6706] was not widely implemented or deployed, any 3958 messages coded to that specification can be easily distinguished and 3959 ignored since they use an invalid ICMPv6 message type number '0'.) 3960 The IANA is therefore instructed to update the reference for UDP port 3961 number "8060" from "RFC6706" to "RFCXXXX" (i.e., this document). 3963 The IANA has assigned a 4 octet Private Enterprise Number (PEN) code 3964 "45282" in the "enterprise-numbers" registry. This document is the 3965 normative reference for using this code in DHCP Unique IDentifiers 3966 based on Enterprise Numbers ("DUID-EN for OMNI Interfaces") (see: 3967 Section 11). The IANA is therefore instructed to change the 3968 enterprise designation for PEN code "45282" from "LinkUp Networks" to 3969 "Overlay Multilink Network Interface (OMNI)". 3971 The IANA has assigned the ifType code "301 - omni - Overlay Multilink 3972 Network Interface (OMNI)" in accordance with Section 6 of [RFC8892]. 3973 The registration appears under the IANA "Structure of Management 3974 Information (SMI) Numbers (MIB Module Registrations) - Interface 3975 Types (ifType)" registry. 3977 No further IANA actions are required. 3979 26. Security Considerations 3981 Security considerations for IPv4 [RFC0791], IPv6 [RFC8200] and IPv6 3982 Neighbor Discovery [RFC4861] apply. OMNI interface IPv6 ND messages 3983 SHOULD include Nonce and Timestamp options [RFC3971] when transaction 3984 confirmation and/or time synchronization is needed. (Note however 3985 that when OAL encapsulation is used the (echoed) OAL Identification 3986 value can provide sufficient transaction confirmation.) 3988 MN OMNI interfaces configured over secured ANET interfaces inherit 3989 the physical and/or link-layer security properties (i.e., "protected 3990 spectrum") of the connected ANETs. MN OMNI interfaces configured 3991 over open INET interfaces can use symmetric securing services such as 3992 VPNs or can by some other means establish a direct link. When a VPN 3993 or direct link may be impractical, however, the security services 3994 specified in [RFC7401] and/or [RFC4380] can be employed. While the 3995 OMNI link protects control plane messaging, applications must still 3996 employ end-to-end transport- or higher-layer security services to 3997 protect the data plane. 3999 Strong network layer security for control plane messages and 4000 forwarding path integrity for data plane messages between MSEs MUST 4001 be supported. In one example, the AERO service 4002 [I-D.templin-6man-aero] constructs a spanning tree between MSEs and 4003 secures the links in the spanning tree with network layer security 4004 mechanisms such as IPsec [RFC4301] or Wireguard. Control plane 4005 messages are then constrained to travel only over the secured 4006 spanning tree paths and are therefore protected from attack or 4007 eavesdropping. Since data plane messages can travel over route 4008 optimized paths that do not strictly follow the spanning tree, 4009 however, end-to-end transport- or higher-layer security services are 4010 still required. 4012 Identity-based key verification infrastructure services such as iPSK 4013 may be necessary for verifying the identities claimed by MNs. This 4014 requirement should be harmonized with the manner in which (H)HITs are 4015 attested in a given operational environment. 4017 Security considerations for specific access network interface types 4018 are covered under the corresponding IP-over-(foo) specification 4019 (e.g., [RFC2464], [RFC2492], etc.). 4021 Security considerations for IPv6 fragmentation and reassembly are 4022 discussed in Section 6.9. 4024 27. Implementation Status 4026 AERO/OMNI Release-3.2 was tagged on March 30, 2021, and is undergoing 4027 internal testing. Additional internal releases expected within the 4028 coming months, with first public release expected end of 1H2021. 4030 28. Document Updates 4032 This document does not itself update other RFCs, but suggests that 4033 the following could be updated through future IETF initiatives: 4035 o [RFC1191] 4037 o [RFC4443] 4039 o [RFC8201] 4041 o [RFC7526] 4043 Updates can be through, e.g., standards action, the errata process, 4044 etc. as appropriate. 4046 29. Acknowledgements 4048 The first version of this document was prepared per the consensus 4049 decision at the 7th Conference of the International Civil Aviation 4050 Organization (ICAO) Working Group-I Mobility Subgroup on March 22, 4051 2019. Consensus to take the document forward to the IETF was reached 4052 at the 9th Conference of the Mobility Subgroup on November 22, 2019. 4053 Attendees and contributors included: Guray Acar, Danny Bharj, 4054 Francois D'Humieres, Pavel Drasil, Nikos Fistas, Giovanni Garofolo, 4055 Bernhard Haindl, Vaughn Maiolla, Tom McParland, Victor Moreno, Madhu 4056 Niraula, Brent Phillips, Liviu Popescu, Jacky Pouzet, Aloke Roy, Greg 4057 Saccone, Robert Segers, Michal Skorepa, Michel Solery, Stephane 4058 Tamalet, Fred Templin, Jean-Marc Vacher, Bela Varkonyi, Tony Whyman, 4059 Fryderyk Wrobel and Dongsong Zeng. 4061 The following individuals are acknowledged for their useful comments: 4062 Stuart Card, Michael Matyas, Robert Moskowitz, Madhu Niraula, Greg 4063 Saccone, Stephane Tamalet, Eric Vyncke. Pavel Drasil, Zdenek Jaron 4064 and Michal Skorepa are especially recognized for their many helpful 4065 ideas and suggestions. Madhuri Madhava Badgandi, Sean Dickson, Don 4066 Dillenburg, Joe Dudkowski, Vijayasarathy Rajagopalan, Ron Sackman and 4067 Katherine Tran are acknowledged for their hard work on the 4068 implementation and technical insights that led to improvements for 4069 the spec. 4071 Discussions on the IETF 6man and atn mailing lists during the fall of 4072 2020 suggested additional points to consider. The authors gratefully 4073 acknowledge the list members who contributed valuable insights 4074 through those discussions. Eric Vyncke and Erik Kline were the 4075 intarea ADs, while Bob Hinden and Ole Troan were the 6man WG chairs 4076 at the time the document was developed; they are all gratefully 4077 acknowledged for their many helpful insights. Many of the ideas in 4078 this document have further built on IETF experiences beginning as 4079 early as Y2K, with insights from colleagues including Brian 4080 Carpenter, Ralph Droms, Christian Huitema, Thomas Narten, Dave 4081 Thaler, Joe Touch, and many others who deserve recognition. 4083 Early observations on IP fragmentation performance implications were 4084 noted in the 1986 Digital Equipment Corporation (DEC) "qe reset" 4085 investigation, where fragment bursts from NFS UDP traffic triggered 4086 hardware resets resulting in communication failures. Jeff Chase, 4087 Fred Glover and Chet Juzsczak of the Ultrix Engineering Group led the 4088 investigation, and determined that setting a smaller NFS mount block 4089 size reduced the amount of fragmentation and suppressed the resets. 4090 Early observations on L2 media MTU issues were noted in the 1988 DEC 4091 FDDI investigation, where Raj Jain, KK Ramakrishnan and Kathy Wilde 4092 represented architectural considerations for FDDI networking in 4093 general including FDDI/Ethernet bridging. Jeff Mogul (who led the 4094 IETF Path MTU Discovery working group) and other DEC colleagues who 4095 supported these early investigations are also acknowledged. 4097 Throughout the 1990's and into the 2000's, many colleagues supported 4098 and encouraged continuation of the work. Beginning with the DEC 4099 Project Sequoia effort at the University of California, Berkeley, 4100 then moving to the DEC research lab offices in Palo Alto CA, then to 4101 the NASA Ames Research Center, then to SRI in Menlo Park, CA, then to 4102 Nokia in Mountain View, CA and finally to the Boeing Company in 2005 4103 the work saw continuous advancement through the encouragement of 4104 many. Those who offered their support and encouragement are 4105 gratefully acknowledged. 4107 This work is aligned with the NASA Safe Autonomous Systems Operation 4108 (SASO) program under NASA contract number NNA16BD84C. 4110 This work is aligned with the FAA as per the SE2025 contract number 4111 DTFAWA-15-D-00030. 4113 This work is aligned with the Boeing Information Technology (BIT) 4114 Mobility Vision Lab (MVL) program. 4116 30. References 4118 30.1. Normative References 4120 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 4121 DOI 10.17487/RFC0791, September 1981, 4122 . 4124 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 4125 Requirement Levels", BCP 14, RFC 2119, 4126 DOI 10.17487/RFC2119, March 1997, 4127 . 4129 [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, 4130 "Definition of the Differentiated Services Field (DS 4131 Field) in the IPv4 and IPv6 Headers", RFC 2474, 4132 DOI 10.17487/RFC2474, December 1998, 4133 . 4135 [RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander, 4136 "SEcure Neighbor Discovery (SEND)", RFC 3971, 4137 DOI 10.17487/RFC3971, March 2005, 4138 . 4140 [RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and 4141 More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191, 4142 November 2005, . 4144 [RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast 4145 Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005, 4146 . 4148 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 4149 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 4150 2006, . 4152 [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet 4153 Control Message Protocol (ICMPv6) for the Internet 4154 Protocol Version 6 (IPv6) Specification", STD 89, 4155 RFC 4443, DOI 10.17487/RFC4443, March 2006, 4156 . 4158 [RFC4727] Fenner, B., "Experimental Values In IPv4, IPv6, ICMPv4, 4159 ICMPv6, UDP, and TCP Headers", RFC 4727, 4160 DOI 10.17487/RFC4727, November 2006, 4161 . 4163 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 4164 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 4165 DOI 10.17487/RFC4861, September 2007, 4166 . 4168 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 4169 Address Autoconfiguration", RFC 4862, 4170 DOI 10.17487/RFC4862, September 2007, 4171 . 4173 [RFC6088] Tsirtsis, G., Giarreta, G., Soliman, H., and N. Montavont, 4174 "Traffic Selectors for Flow Bindings", RFC 6088, 4175 DOI 10.17487/RFC6088, January 2011, 4176 . 4178 [RFC7401] Moskowitz, R., Ed., Heer, T., Jokela, P., and T. 4179 Henderson, "Host Identity Protocol Version 2 (HIPv2)", 4180 RFC 7401, DOI 10.17487/RFC7401, April 2015, 4181 . 4183 [RFC8028] Baker, F. and B. Carpenter, "First-Hop Router Selection by 4184 Hosts in a Multi-Prefix Network", RFC 8028, 4185 DOI 10.17487/RFC8028, November 2016, 4186 . 4188 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 4189 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 4190 May 2017, . 4192 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 4193 (IPv6) Specification", STD 86, RFC 8200, 4194 DOI 10.17487/RFC8200, July 2017, 4195 . 4197 [RFC8201] McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed., 4198 "Path MTU Discovery for IP version 6", STD 87, RFC 8201, 4199 DOI 10.17487/RFC8201, July 2017, 4200 . 4202 [RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A., 4203 Richardson, M., Jiang, S., Lemon, T., and T. Winters, 4204 "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", 4205 RFC 8415, DOI 10.17487/RFC8415, November 2018, 4206 . 4208 30.2. Informative References 4210 [ATN] Maiolla, V., "The OMNI Interface - An IPv6 Air/Ground 4211 Interface for Civil Aviation, IETF Liaison Statement 4212 #1676, https://datatracker.ietf.org/liaison/1676/", March 4213 2020. 4215 [ATN-IPS] WG-I, ICAO., "ICAO Document 9896 (Manual on the 4216 Aeronautical Telecommunication Network (ATN) using 4217 Internet Protocol Suite (IPS) Standards and Protocol), 4218 Draft Edition 3 (work-in-progress)", December 2020. 4220 [CKSUM] Stone, J., Greenwald, M., Partridge, C., and J. Hughes, 4221 "Performance of Checksums and CRC's Over Real Data, IEEE/ 4222 ACM Transactions on Networking, Vol. 6, No. 5", October 4223 1998. 4225 [CRC] Jain, R., "Error Characteristics of Fiber Distributed Data 4226 Interface (FDDI), IEEE Transactions on Communications", 4227 August 1990. 4229 [I-D.ietf-drip-rid] 4230 Moskowitz, R., Card, S., Wiethuechter, A., and A. Gurtov, 4231 "UAS Remote ID", draft-ietf-drip-rid-06 (work in 4232 progress), December 2020. 4234 [I-D.ietf-intarea-tunnels] 4235 Touch, J. and M. Townsley, "IP Tunnels in the Internet 4236 Architecture", draft-ietf-intarea-tunnels-10 (work in 4237 progress), September 2019. 4239 [I-D.ietf-ipwave-vehicular-networking] 4240 Jeong, J., "IPv6 Wireless Access in Vehicular Environments 4241 (IPWAVE): Problem Statement and Use Cases", draft-ietf- 4242 ipwave-vehicular-networking-19 (work in progress), July 4243 2020. 4245 [I-D.ietf-tsvwg-udp-options] 4246 Touch, J., "Transport Options for UDP", draft-ietf-tsvwg- 4247 udp-options-09 (work in progress), November 2020. 4249 [I-D.templin-6man-aero] 4250 Templin, F. L., "Automatic Extended Route Optimization 4251 (AERO)", draft-templin-6man-aero-01 (work in progress), 4252 April 2021. 4254 [I-D.templin-6man-dhcpv6-ndopt] 4255 Templin, F., "A Unified Stateful/Stateless Configuration 4256 Service for IPv6", draft-templin-6man-dhcpv6-ndopt-11 4257 (work in progress), January 2021. 4259 [I-D.templin-6man-lla-type] 4260 Templin, F., "The IPv6 Link-Local Address Type Field", 4261 draft-templin-6man-lla-type-02 (work in progress), 4262 November 2020. 4264 [IPV4-GUA] 4265 Postel, J., "IPv4 Address Space Registry, 4266 https://www.iana.org/assignments/ipv4-address-space/ipv4- 4267 address-space.xhtml", December 2020. 4269 [IPV6-GUA] 4270 Postel, J., "IPv6 Global Unicast Address Assignments, 4271 https://www.iana.org/assignments/ipv6-unicast-address- 4272 assignments/ipv6-unicast-address-assignments.xhtml", 4273 December 2020. 4275 [RFC0905] "ISO Transport Protocol specification ISO DP 8073", 4276 RFC 905, DOI 10.17487/RFC0905, April 1984, 4277 . 4279 [RFC1035] Mockapetris, P., "Domain names - implementation and 4280 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, 4281 November 1987, . 4283 [RFC1122] Braden, R., Ed., "Requirements for Internet Hosts - 4284 Communication Layers", STD 3, RFC 1122, 4285 DOI 10.17487/RFC1122, October 1989, 4286 . 4288 [RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191, 4289 DOI 10.17487/RFC1191, November 1990, 4290 . 4292 [RFC1256] Deering, S., Ed., "ICMP Router Discovery Messages", 4293 RFC 1256, DOI 10.17487/RFC1256, September 1991, 4294 . 4296 [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", 4297 RFC 2131, DOI 10.17487/RFC2131, March 1997, 4298 . 4300 [RFC2225] Laubach, M. and J. Halpern, "Classical IP and ARP over 4301 ATM", RFC 2225, DOI 10.17487/RFC2225, April 1998, 4302 . 4304 [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, 4305 DOI 10.17487/RFC2328, April 1998, 4306 . 4308 [RFC2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet 4309 Networks", RFC 2464, DOI 10.17487/RFC2464, December 1998, 4310 . 4312 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 4313 IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473, 4314 December 1998, . 4316 [RFC2492] Armitage, G., Schulter, P., and M. Jork, "IPv6 over ATM 4317 Networks", RFC 2492, DOI 10.17487/RFC2492, January 1999, 4318 . 4320 [RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4 4321 Domains without Explicit Tunnels", RFC 2529, 4322 DOI 10.17487/RFC2529, March 1999, 4323 . 4325 [RFC2863] McCloghrie, K. and F. Kastenholz, "The Interfaces Group 4326 MIB", RFC 2863, DOI 10.17487/RFC2863, June 2000, 4327 . 4329 [RFC2923] Lahey, K., "TCP Problems with Path MTU Discovery", 4330 RFC 2923, DOI 10.17487/RFC2923, September 2000, 4331 . 4333 [RFC2983] Black, D., "Differentiated Services and Tunnels", 4334 RFC 2983, DOI 10.17487/RFC2983, October 2000, 4335 . 4337 [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition 4338 of Explicit Congestion Notification (ECN) to IP", 4339 RFC 3168, DOI 10.17487/RFC3168, September 2001, 4340 . 4342 [RFC3330] IANA, "Special-Use IPv4 Addresses", RFC 3330, 4343 DOI 10.17487/RFC3330, September 2002, 4344 . 4346 [RFC3692] Narten, T., "Assigning Experimental and Testing Numbers 4347 Considered Useful", BCP 82, RFC 3692, 4348 DOI 10.17487/RFC3692, January 2004, 4349 . 4351 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 4352 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 4353 DOI 10.17487/RFC3810, June 2004, 4354 . 4356 [RFC3819] Karn, P., Ed., Bormann, C., Fairhurst, G., Grossman, D., 4357 Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L. 4358 Wood, "Advice for Internet Subnetwork Designers", BCP 89, 4359 RFC 3819, DOI 10.17487/RFC3819, July 2004, 4360 . 4362 [RFC3879] Huitema, C. and B. Carpenter, "Deprecating Site Local 4363 Addresses", RFC 3879, DOI 10.17487/RFC3879, September 4364 2004, . 4366 [RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally 4367 Unique IDentifier (UUID) URN Namespace", RFC 4122, 4368 DOI 10.17487/RFC4122, July 2005, 4369 . 4371 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 4372 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 4373 DOI 10.17487/RFC4271, January 2006, 4374 . 4376 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 4377 Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, 4378 December 2005, . 4380 [RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through 4381 Network Address Translations (NATs)", RFC 4380, 4382 DOI 10.17487/RFC4380, February 2006, 4383 . 4385 [RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery 4386 Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April 4387 2006, . 4389 [RFC4429] Moore, N., "Optimistic Duplicate Address Detection (DAD) 4390 for IPv6", RFC 4429, DOI 10.17487/RFC4429, April 2006, 4391 . 4393 [RFC4541] Christensen, M., Kimball, K., and F. Solensky, 4394 "Considerations for Internet Group Management Protocol 4395 (IGMP) and Multicast Listener Discovery (MLD) Snooping 4396 Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006, 4397 . 4399 [RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick, 4400 "Internet Group Management Protocol (IGMP) / Multicast 4401 Listener Discovery (MLD)-Based Multicast Forwarding 4402 ("IGMP/MLD Proxying")", RFC 4605, DOI 10.17487/RFC4605, 4403 August 2006, . 4405 [RFC4821] Mathis, M. and J. Heffner, "Packetization Layer Path MTU 4406 Discovery", RFC 4821, DOI 10.17487/RFC4821, March 2007, 4407 . 4409 [RFC4963] Heffner, J., Mathis, M., and B. Chandler, "IPv4 Reassembly 4410 Errors at High Data Rates", RFC 4963, 4411 DOI 10.17487/RFC4963, July 2007, 4412 . 4414 [RFC5175] Haberman, B., Ed. and R. Hinden, "IPv6 Router 4415 Advertisement Flags Option", RFC 5175, 4416 DOI 10.17487/RFC5175, March 2008, 4417 . 4419 [RFC5213] Gundavelli, S., Ed., Leung, K., Devarapalli, V., 4420 Chowdhury, K., and B. Patil, "Proxy Mobile IPv6", 4421 RFC 5213, DOI 10.17487/RFC5213, August 2008, 4422 . 4424 [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site 4425 Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, 4426 DOI 10.17487/RFC5214, March 2008, 4427 . 4429 [RFC5558] Templin, F., Ed., "Virtual Enterprise Traversal (VET)", 4430 RFC 5558, DOI 10.17487/RFC5558, February 2010, 4431 . 4433 [RFC5798] Nadas, S., Ed., "Virtual Router Redundancy Protocol (VRRP) 4434 Version 3 for IPv4 and IPv6", RFC 5798, 4435 DOI 10.17487/RFC5798, March 2010, 4436 . 4438 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 4439 (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, 4440 . 4442 [RFC6081] Thaler, D., "Teredo Extensions", RFC 6081, 4443 DOI 10.17487/RFC6081, January 2011, 4444 . 4446 [RFC6221] Miles, D., Ed., Ooghe, S., Dec, W., Krishnan, S., and A. 4447 Kavanagh, "Lightweight DHCPv6 Relay Agent", RFC 6221, 4448 DOI 10.17487/RFC6221, May 2011, 4449 . 4451 [RFC6355] Narten, T. and J. Johnson, "Definition of the UUID-Based 4452 DHCPv6 Unique Identifier (DUID-UUID)", RFC 6355, 4453 DOI 10.17487/RFC6355, August 2011, 4454 . 4456 [RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label 4457 for Equal Cost Multipath Routing and Link Aggregation in 4458 Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011, 4459 . 4461 [RFC6543] Gundavelli, S., "Reserved IPv6 Interface Identifier for 4462 Proxy Mobile IPv6", RFC 6543, DOI 10.17487/RFC6543, May 4463 2012, . 4465 [RFC6706] Templin, F., Ed., "Asymmetric Extended Route Optimization 4466 (AERO)", RFC 6706, DOI 10.17487/RFC6706, August 2012, 4467 . 4469 [RFC6935] Eubanks, M., Chimento, P., and M. Westerlund, "IPv6 and 4470 UDP Checksums for Tunneled Packets", RFC 6935, 4471 DOI 10.17487/RFC6935, April 2013, 4472 . 4474 [RFC6936] Fairhurst, G. and M. Westerlund, "Applicability Statement 4475 for the Use of IPv6 UDP Datagrams with Zero Checksums", 4476 RFC 6936, DOI 10.17487/RFC6936, April 2013, 4477 . 4479 [RFC6980] Gont, F., "Security Implications of IPv6 Fragmentation 4480 with IPv6 Neighbor Discovery", RFC 6980, 4481 DOI 10.17487/RFC6980, August 2013, 4482 . 4484 [RFC7042] Eastlake 3rd, D. and J. Abley, "IANA Considerations and 4485 IETF Protocol and Documentation Usage for IEEE 802 4486 Parameters", BCP 141, RFC 7042, DOI 10.17487/RFC7042, 4487 October 2013, . 4489 [RFC7084] Singh, H., Beebee, W., Donley, C., and B. Stark, "Basic 4490 Requirements for IPv6 Customer Edge Routers", RFC 7084, 4491 DOI 10.17487/RFC7084, November 2013, 4492 . 4494 [RFC7421] Carpenter, B., Ed., Chown, T., Gont, F., Jiang, S., 4495 Petrescu, A., and A. Yourtchenko, "Analysis of the 64-bit 4496 Boundary in IPv6 Addressing", RFC 7421, 4497 DOI 10.17487/RFC7421, January 2015, 4498 . 4500 [RFC7526] Troan, O. and B. Carpenter, Ed., "Deprecating the Anycast 4501 Prefix for 6to4 Relay Routers", BCP 196, RFC 7526, 4502 DOI 10.17487/RFC7526, May 2015, 4503 . 4505 [RFC7542] DeKok, A., "The Network Access Identifier", RFC 7542, 4506 DOI 10.17487/RFC7542, May 2015, 4507 . 4509 [RFC7739] Gont, F., "Security Implications of Predictable Fragment 4510 Identification Values", RFC 7739, DOI 10.17487/RFC7739, 4511 February 2016, . 4513 [RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I., 4514 Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent 4515 Multicast - Sparse Mode (PIM-SM): Protocol Specification 4516 (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March 4517 2016, . 4519 [RFC7847] Melia, T., Ed. and S. Gundavelli, Ed., "Logical-Interface 4520 Support for IP Hosts with Multi-Access Support", RFC 7847, 4521 DOI 10.17487/RFC7847, May 2016, 4522 . 4524 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 4525 Writing an IANA Considerations Section in RFCs", BCP 26, 4526 RFC 8126, DOI 10.17487/RFC8126, June 2017, 4527 . 4529 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 4530 Decraene, B., Litkowski, S., and R. Shakir, "Segment 4531 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 4532 July 2018, . 4534 [RFC8726] Farrel, A., "How Requests for IANA Action Will Be Handled 4535 on the Independent Stream", RFC 8726, 4536 DOI 10.17487/RFC8726, November 2020, 4537 . 4539 [RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J., 4540 Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header 4541 (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020, 4542 . 4544 [RFC8892] Thaler, D. and D. Romascanu, "Guidelines and Registration 4545 Procedures for Interface Types and Tunnel Types", 4546 RFC 8892, DOI 10.17487/RFC8892, August 2020, 4547 . 4549 [RFC8899] Fairhurst, G., Jones, T., Tuexen, M., Ruengeler, I., and 4550 T. Voelker, "Packetization Layer Path MTU Discovery for 4551 Datagram Transports", RFC 8899, DOI 10.17487/RFC8899, 4552 September 2020, . 4554 [RFC8900] Bonica, R., Baker, F., Huston, G., Hinden, R., Troan, O., 4555 and F. Gont, "IP Fragmentation Considered Fragile", 4556 BCP 230, RFC 8900, DOI 10.17487/RFC8900, September 2020, 4557 . 4559 [RFC8981] Gont, F., Krishnan, S., Narten, T., and R. Draves, 4560 "Temporary Address Extensions for Stateless Address 4561 Autoconfiguration in IPv6", RFC 8981, 4562 DOI 10.17487/RFC8981, February 2021, 4563 . 4565 Appendix A. Interface Attribute Preferences Bitmap Encoding 4567 Adaptation of the OMNI option Interface Attributes Preferences Bitmap 4568 encoding to specific Internetworks such as the Aeronautical 4569 Telecommunications Network with Internet Protocol Services (ATN/IPS) 4570 may include link selection preferences based on other traffic 4571 classifiers (e.g., transport port numbers, etc.) in addition to the 4572 existing DSCP-based preferences. Nodes on specific Internetworks 4573 maintain a map of traffic classifiers to additional P[*] preference 4574 fields beyond the first 64. For example, TCP port 22 maps to P[67], 4575 TCP port 443 maps to P[70], UDP port 8060 maps to P[76], etc. 4577 Implementations use Simplex or Indexed encoding formats for P[*] 4578 encoding in order to encode a given set of traffic classifiers in the 4579 most efficient way. Some use cases may be more efficiently coded 4580 using Simplex form, while others may be more efficient using Indexed. 4581 Once a format is selected for preparation of a single Interface 4582 Attribute the same format must be used for the entire Interface 4583 Attribute sub-option. Different sub-options may use different 4584 formats. 4586 The following figures show coding examples for various Simplex and 4587 Indexed formats: 4589 0 1 2 3 4590 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 4591 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4592 | Sub-Type=3| Sub-length=N | omIndex | omType | 4593 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4594 | Provider ID | Link |R| API | Bitmap(0)=0xff|P00|P01|P02|P03| 4595 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4596 |P04|P05|P06|P07|P08|P09|P10|P11|P12|P13|P14|P15|P16|P17|P18|P19| 4597 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4598 |P20|P21|P22|P23|P24|P25|P26|P27|P28|P29|P30|P31| Bitmap(1)=0xff| 4599 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4600 |P32|P33|P34|P35|P36|P37|P38|P39|P40|P41|P42|P43|P44|P45|P46|P47| 4601 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4602 |P48|P49|P50|P51|P52|P53|P54|P55|P56|P57|P58|P59|P60|P61|P62|P63| 4603 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4604 | Bitmap(2)=0xff|P64|P65|P67|P68| ... 4605 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 4607 Figure 41: Example 1: Dense Simplex Encoding 4609 0 1 2 3 4610 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 4611 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4612 | Sub-Type=3| Sub-length=N | omIndex | omType | 4613 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4614 | Provider ID | Link |R| API | Bitmap(0)=0x00| Bitmap(1)=0x0f| 4615 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4616 |P48|P49|P50|P51|P52|P53|P54|P55|P56|P57|P58|P59|P60|P61|P62|P63| 4617 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4618 | Bitmap(2)=0x00| Bitmap(3)=0x00| Bitmap(4)=0x00| Bitmap(5)=0x00| 4619 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4620 | Bitmap(6)=0xf0|192|193|194|195|196|197|198|199|200|201|202|203| 4621 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4622 |204|205|206|207| Bitmap(7)=0x00| Bitmap(8)=0x0f|272|273|274|275| 4623 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4624 |276|277|278|279|280|281|282|283|284|285|286|287| Bitmap(9)=0x00| 4625 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4626 |Bitmap(10)=0x00| ... 4627 +-+-+-+-+-+-+-+-+-+-+- 4629 Figure 42: Example 2: Sparse Simplex Encoding 4631 0 1 2 3 4632 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 4633 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4634 | Sub-Type=3| Sub-length=N | omIndex | omType | 4635 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4636 | Provider ID | Link |R| API | Index = 0x00 | Bitmap = 0x80 | 4637 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4638 |P00|P01|P02|P03| Index = 0x01 | Bitmap = 0x01 |P60|P61|P62|P63| 4639 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4640 | Index = 0x10 | Bitmap = 0x80 |512|513|514|515| Index = 0x18 | 4641 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4642 | Bitmap = 0x01 |796|797|798|799| ... 4643 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 4645 Figure 43: Example 3: Indexed Encoding 4647 Appendix B. VDL Mode 2 Considerations 4649 ICAO Doc 9776 is the "Technical Manual for VHF Data Link Mode 2" 4650 (VDLM2) that specifies an essential radio frequency data link service 4651 for aircraft and ground stations in worldwide civil aviation air 4652 traffic management. The VDLM2 link type is "multicast capable" 4653 [RFC4861], but with considerable differences from common multicast 4654 links such as Ethernet and IEEE 802.11. 4656 First, the VDLM2 link data rate is only 31.5Kbps - multiple orders of 4657 magnitude less than most modern wireless networking gear. Second, 4658 due to the low available link bandwidth only VDLM2 ground stations 4659 (i.e., and not aircraft) are permitted to send broadcasts, and even 4660 so only as compact layer 2 "beacons". Third, aircraft employ the 4661 services of ground stations by performing unicast RS/RA exchanges 4662 upon receipt of beacons instead of listening for multicast RA 4663 messages and/or sending multicast RS messages. 4665 This beacon-oriented unicast RS/RA approach is necessary to conserve 4666 the already-scarce available link bandwidth. Moreover, since the 4667 numbers of beaconing ground stations operating within a given spatial 4668 range must be kept as sparse as possible, it would not be feasible to 4669 have different classes of ground stations within the same region 4670 observing different protocols. It is therefore highly desirable that 4671 all ground stations observe a common language of RS/RA as specified 4672 in this document. 4674 Note that links of this nature may benefit from compression 4675 techniques that reduce the bandwidth necessary for conveying the same 4676 amount of data. The IETF lpwan working group is considering possible 4677 alternatives: [https://datatracker.ietf.org/wg/lpwan/documents]. 4679 Appendix C. MN / AR Isolation Through L2 Address Mapping 4681 Per [RFC4861], IPv6 ND messages may be sent to either a multicast or 4682 unicast link-scoped IPv6 destination address. However, IPv6 ND 4683 messaging should be coordinated between the MN and AR only without 4684 invoking other nodes on the *NET. This implies that MN / AR control 4685 messaging should be isolated and not overheard by other nodes on the 4686 link. 4688 To support MN / AR isolation on some *NET links, ARs can maintain an 4689 OMNI-specific unicast L2 address ("MSADDR"). For Ethernet-compatible 4690 *NETs, this specification reserves one Ethernet unicast address TBD3 4691 (see: Section 25). For non-Ethernet statically-addressed *NETs, 4692 MSADDR is reserved per the assigned numbers authority for the *NET 4693 addressing space. For still other *NETs, MSADDR may be dynamically 4694 discovered through other means, e.g., L2 beacons. 4696 MNs map the L3 addresses of all IPv6 ND messages they send (i.e., 4697 both multicast and unicast) to MSADDR instead of to an ordinary 4698 unicast or multicast L2 address. In this way, all of the MN's IPv6 4699 ND messages will be received by ARs that are configured to accept 4700 packets destined to MSADDR. Note that multiple ARs on the link could 4701 be configured to accept packets destined to MSADDR, e.g., as a basis 4702 for supporting redundancy. 4704 Therefore, ARs must accept and process packets destined to MSADDR, 4705 while all other devices must not process packets destined to MSADDR. 4706 This model has well-established operational experience in Proxy 4707 Mobile IPv6 (PMIP) [RFC5213][RFC6543]. 4709 Appendix D. Change Log 4711 << RFC Editor - remove prior to publication >> 4713 Differences from draft-templin-6man-omni-03 to draft-templin-6man- 4714 omni-04: 4716 o Changed reference citations to "draft-templin-6man-aero". 4718 o Included introductory description of the "6M's". 4720 o Included new OMNI sub-option for PIM-SM. 4722 Differences from draft-templin-6man-omni-02 to draft-templin-6man- 4723 omni-03: 4725 o Added citation of RFC8726. 4727 Differences from draft-templin-6man-omni-01 to draft-templin-6man- 4728 omni-02: 4730 o Updated IANA registration policies for OMNI registries. 4732 Differences from draft-templin-6man-omni-00 to draft-templin-6man- 4733 omni-01: 4735 o Changed intended document status to Informational, and removed 4736 documents from "updates" category. 4738 o Updated implementation status. 4740 o Minor edits to HIP message specifications. 4742 o Clarified OAL and *NET IP header field settings during 4743 encapsulation and re-encapsulation. 4745 Differences from earlier versions to draft-templin-6man-omni-00: 4747 o Established working baseline reference. 4749 Authors' Addresses 4751 Fred L. Templin (editor) 4752 The Boeing Company 4753 P.O. Box 3707 4754 Seattle, WA 98124 4755 USA 4757 Email: fltemplin@acm.org 4759 Tony Whyman 4760 MWA Ltd c/o Inmarsat Global Ltd 4761 99 City Road 4762 London EC1Y 1AX 4763 England 4765 Email: tony.whyman@mccallumwhyman.com