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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 4, 2021 MWA Ltd c/o Inmarsat Global Ltd 6 April 2, 2021 8 Transmission of IP Packets over Overlay Multilink Network (OMNI) 9 Interfaces 10 draft-templin-6man-omni-03 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 4, 2021. 41 Copyright Notice 43 Copyright (c) 2021 IETF Trust and the persons identified as the 44 document authors. All rights reserved. 46 This document is subject to BCP 78 and the IETF Trust's Legal 47 Provisions Relating to IETF Documents 48 (https://trustee.ietf.org/license-info) in effect on the date of 49 publication of this document. Please review these documents 50 carefully, as they describe your rights and restrictions with respect 51 to this document. Code Components extracted from this document must 52 include Simplified BSD License text as described in Section 4.e of 53 the Trust Legal Provisions and are provided without warranty as 54 described in the Simplified BSD License. 56 Table of Contents 58 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 59 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 60 3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 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. Reassembly Limit . . . . . . . . . . . . . . . . . . 55 93 12.1.12. Fragmentation Report . . . . . . . . . . . . . . . . 57 94 12.1.13. Node Identification . . . . . . . . . . . . . . . . 58 95 12.1.14. Sub-Type Extension . . . . . . . . . . . . . . . . . 60 96 13. Address Mapping - Multicast . . . . . . . . . . . . . . . . . 63 97 14. Multilink Conceptual Sending Algorithm . . . . . . . . . . . 63 98 14.1. Multiple OMNI Interfaces . . . . . . . . . . . . . . . . 64 99 14.2. MN<->AR Traffic Loop Prevention . . . . . . . . . . . . 64 100 15. Router Discovery and Prefix Registration . . . . . . . . . . 65 101 15.1. Router Discovery in IP Multihop and IPv4-Only Networks . 69 102 15.2. MS-Register and MS-Release List Processing . . . . . . . 71 103 15.3. DHCPv6-based Prefix Registration . . . . . . . . . . . . 73 104 16. Secure Redirection . . . . . . . . . . . . . . . . . . . . . 74 105 17. AR and MSE Resilience . . . . . . . . . . . . . . . . . . . . 74 106 18. Detecting and Responding to MSE Failures . . . . . . . . . . 75 107 19. Transition Considerations . . . . . . . . . . . . . . . . . . 75 108 20. OMNI Interfaces on Open Internetworks . . . . . . . . . . . . 76 109 21. Time-Varying MNPs . . . . . . . . . . . . . . . . . . . . . . 78 110 22. (H)HITs and Temporary ULAs . . . . . . . . . . . . . . . . . 79 111 23. Address Selection . . . . . . . . . . . . . . . . . . . . . . 80 112 24. Error Messages . . . . . . . . . . . . . . . . . . . . . . . 80 113 25. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 80 114 25.1. "IEEE 802 Numbers" Registry . . . . . . . . . . . . . . 80 115 25.2. "IPv6 Neighbor Discovery Option Formats" Registry . . . 81 116 25.3. "Ethernet Numbers" Registry . . . . . . . . . . . . . . 81 117 25.4. "ICMPv6 Code Fields: Type 2 - Packet Too Big" Registry . 81 118 25.5. "OMNI Option Sub-Type Values" (New Registry) . . . . . . 81 119 25.6. "OMNI Geo Coordinates Type Values" (New Registry) . . . 82 120 25.7. "OMNI Node Identification ID-Type Values" (New Registry) 82 121 25.8. "OMNI Option Sub-Type Extension Values" (New Registry) . 83 122 25.9. "OMNI RFC4380 UDP/IP Header Option" (New Registry) . . . 83 123 25.10. "OMNI RFC6081 UDP/IP Trailer Option" (New Registry) . . 84 124 25.11. Additional Considerations . . . . . . . . . . . . . . . 84 125 26. Security Considerations . . . . . . . . . . . . . . . . . . . 85 126 27. Implementation Status . . . . . . . . . . . . . . . . . . . . 86 127 28. Document Updates . . . . . . . . . . . . . . . . . . . . . . 86 128 29. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 86 129 30. References . . . . . . . . . . . . . . . . . . . . . . . . . 88 130 30.1. Normative References . . . . . . . . . . . . . . . . . . 88 131 30.2. Informative References . . . . . . . . . . . . . . . . . 90 132 Appendix A. Interface Attribute Preferences Bitmap Encoding . . 97 133 Appendix B. VDL Mode 2 Considerations . . . . . . . . . . . . . 99 134 Appendix C. MN / AR Isolation Through L2 Address Mapping . . . . 100 135 Appendix D. Change Log . . . . . . . . . . . . . . . . . . . . . 100 136 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 101 138 1. Introduction 140 Mobile Nodes (MNs) (e.g., aircraft of various configurations, 141 terrestrial vehicles, seagoing vessels, enterprise wireless devices, 142 pedestrians with cellphones, etc.) often have multiple interface 143 connections to wireless and/or wired-line data links used for 144 communicating with networked correspondents. These data links may 145 have diverse performance, cost and availability properties that can 146 change dynamically according to mobility patterns, flight phases, 147 proximity to infrastructure, etc. MNs coordinate their data links in 148 a discipline known as "multilink", in which a single virtual 149 interface is configured over the node's underlying interface 150 connections to the data links. 152 The MN configures a virtual interface (termed the "Overlay Multilink 153 Network Interface (OMNI)") as a thin layer over the underlying 154 interfaces. The OMNI interface is therefore the only interface 155 abstraction exposed to the IP layer and behaves according to the Non- 156 Broadcast, Multiple Access (NBMA) interface principle, while 157 underlying interfaces appear as link layer communication channels in 158 the architecture. The OMNI interface internally employs the "OMNI 159 Adaptation Layer (OAL)" to ensure that original IP packets are 160 delivered without loss due to size restrictions. The OMNI interface 161 connects to a virtual overlay service known as the "OMNI link". The 162 OMNI link spans one or more Internetworks that may include private- 163 use infrastructures and/or the global public Internet itself. 165 Each MN receives a Mobile Network Prefix (MNP) for numbering 166 downstream-attached End User Networks (EUNs) independently of the 167 access network data links selected for data transport. The MN 168 performs router discovery over the OMNI interface (i.e., similar to 169 IPv6 customer edge routers [RFC7084]) and acts as a mobile router on 170 behalf of its EUNs. The router discovery process is iterated over 171 each of the OMNI interface's underlying interfaces in order to 172 register per-link parameters (see Section 15). 174 The OMNI interface provides a multilink nexus for exchanging inbound 175 and outbound traffic via the correct underlying interface(s). The IP 176 layer sees the OMNI interface as a point of connection to the OMNI 177 link. Each OMNI link has one or more associated Mobility Service 178 Prefixes (MSPs), which are typically IP Global Unicast Address (GUA) 179 prefixes from which MNPs are derived. If there are multiple OMNI 180 links, the IPv6 layer will see multiple OMNI interfaces. 182 MNs may connect to multiple distinct OMNI links within the same OMNI 183 domain by configuring multiple OMNI interfaces, e.g., omni0, omni1, 184 omni2, etc. Each OMNI interface is configured over a set of 185 underlying interfaces and provides a nexus for Safety-Based Multilink 186 (SBM) operation. Each OMNI interface within the same OMNI domain 187 configures a common ULA prefix [ULA]::/48, and configures a unique 188 16-bit Subnet ID '*' to construct the sub-prefix [ULA*]::/64 (see: 189 Section 9). The IP layer applies SBM routing to select an OMNI 190 interface, which then applies Performance-Based Multilink (PBM) to 191 select the correct underlying interface. Applications can apply 192 Segment Routing [RFC8402] to select independent SBM topologies for 193 fault tolerance. 195 The OMNI interface interacts with a network-based Mobility Service 196 (MS) through IPv6 Neighbor Discovery (ND) control message exchanges 197 [RFC4861]. The MS provides Mobility Service Endpoints (MSEs) that 198 track MN movements and represent their MNPs in a global routing or 199 mapping system. 201 Many OMNI use cases have been proposed. In particular, the 202 International Civil Aviation Organization (ICAO) Working Group-I 203 Mobility Subgroup is developing a future Aeronautical 204 Telecommunications Network with Internet Protocol Services (ATN/IPS) 205 and has issued a liaison statement requesting IETF adoption [ATN] in 206 support of ICAO Document 9896 [ATN-IPS]. The IETF IP Wireless Access 207 in Vehicular Environments (ipwave) working group has further included 208 problem statement and use case analysis for OMNI in a document now in 209 AD evaluation for RFC publication 210 [I-D.ietf-ipwave-vehicular-networking]. Still other communities of 211 interest include AEEC, RTCA Special Committee 228 (SC-228) and NASA 212 programs that examine commercial aviation, Urban Air Mobility (UAM) 213 and Unmanned Air Systems (UAS). Pedestrians with handheld devices 214 represent another large class of potential OMNI users. 216 This document specifies the transmission of IP packets and MN/MS 217 control messages over OMNI interfaces. The OMNI interface supports 218 either IP protocol version (i.e., IPv4 [RFC0791] or IPv6 [RFC8200]) 219 as the network layer in the data plane, while using IPv6 ND messaging 220 as the control plane independently of the data plane IP protocol(s). 221 The OAL operates as a sublayer between L3 and L2 based on IPv6 222 encapsulation [RFC2473] as discussed in the following sections. OMNI 223 interfaces enable Multilink, Multinet, Mobility, Multihop, Multicast 224 and MTU services (i.e., the "6 M's" of advanced Internetworking), 225 with provisions for both Vehicle-to-Infrastructure (V2I) 226 communications and Vehicle-to-Vehicle (V2V) communications outside 227 the context of infrastructure. 229 2. Terminology 231 The terminology in the normative references applies; especially, the 232 terms "link" and "interface" are the same as defined in the IPv6 233 [RFC8200] and IPv6 Neighbor Discovery (ND) [RFC4861] specifications. 234 Additionally, this document assumes the following IPv6 ND message 235 types: Router Solicitation (RS), Router Advertisement (RA), Neighbor 236 Solicitation (NS), Neighbor Advertisement (NA) and Redirect. 238 The Protocol Constants defined in Section 10 of [RFC4861] are used in 239 their same format and meaning in this document. The terms "All- 240 Routers multicast", "All-Nodes multicast" and "Subnet-Router anycast" 241 are the same as defined in [RFC4291] (with Link-Local scope assumed). 243 The term "IP" is used to refer collectively to either Internet 244 Protocol version (i.e., IPv4 [RFC0791] or IPv6 [RFC8200]) when a 245 specification at the layer in question applies equally to either 246 version. 248 The following terms are defined within the scope of this document: 250 Mobile Node (MN) 251 an end system with a mobile router having multiple distinct 252 upstream data link connections that are grouped together in one or 253 more logical units. The MN's data link connection parameters can 254 change over time due to, e.g., node mobility, link quality, etc. 255 The MN further connects a downstream-attached End User Network 256 (EUN). The term MN used here is distinct from uses in other 257 documents, and does not imply a particular mobility protocol. 259 End User Network (EUN) 260 a simple or complex downstream-attached mobile network that 261 travels with the MN as a single logical unit. The IP addresses 262 assigned to EUN devices remain stable even if the MN's upstream 263 data link connections change. 265 Mobility Service (MS) 266 a mobile routing service that tracks MN movements and ensures that 267 MNs remain continuously reachable even across mobility events. 268 Specific MS details are out of scope for this document. 270 Mobility Service Endpoint (MSE) 271 an entity in the MS (either singular or aggregate) that 272 coordinates the mobility events of one or more MN. 274 Mobility Service Prefix (MSP) 275 an aggregated IP Global Unicast Address (GUA) prefix (e.g., 276 2001:db8::/32, 192.0.2.0/24, etc.) assigned to the OMNI link and 277 from which more-specific Mobile Network Prefixes (MNPs) are 278 delegated. OMNI link administrators typically obtain MSPs from an 279 Internet address registry, however private-use prefixes can 280 alternatively be used subject to certain limitations (see: 281 Section 10). OMNI links that connect to the global Internet 282 advertise their MSPs to their interdomain routing peers. 284 Mobile Network Prefix (MNP) 285 a longer IP prefix delegated from an MSP (e.g., 286 2001:db8:1000:2000::/56, 192.0.2.8/30, etc.) and assigned to a MN. 287 MNs sub-delegate the MNP to devices located in EUNs. Note that 288 OMNI link Relay nodes may also service non-MNP routes (i.e., GUA 289 prefixes not covered by an MSP) but that these correspond to fixed 290 correspondent nodes and not MNs. Other than this distinction, MNP 291 and non-MNP routes are treated exactly the same by the OMNI 292 routing system. 294 Access Network (ANET) 295 a data link service network (e.g., an aviation radio access 296 network, satellite service provider network, cellular operator 297 network, WiFi network, etc.) that connects MNs. Physical and/or 298 data link level security is assumed, and sometimes referred to as 299 "protected spectrum". Private enterprise networks and ground 300 domain aviation service networks may provide multiple secured IP 301 hops between the MN's point of connection and the nearest Access 302 Router. 304 Access Router (AR) 305 a router in the ANET for connecting MNs to correspondents in 306 outside Internetworks. The AR may be located on the same physical 307 link as the MN, or may be located multiple IP hops away. In the 308 latter case, the MN uses encapsulation to communicate with the AR 309 as though it were on the same physical link. 311 ANET interface 312 a MN's attachment to a link in an ANET. 314 Internetwork (INET) 315 a connected network region with a coherent IP addressing plan that 316 provides transit forwarding services between ANETs and nodes that 317 connect directly to the open INET via unprotected media. No 318 physical and/or data link level security is assumed, therefore 319 security must be applied by upper layers. The global public 320 Internet itself is an example. 322 INET interface 323 a node's attachment to a link in an INET. 325 *NET 326 a "wildcard" term used when a given specification applies equally 327 to both ANET and INET cases. 329 OMNI link 330 a Non-Broadcast, Multiple Access (NBMA) virtual overlay configured 331 over one or more INETs and their connected ANETs. An OMNI link 332 can comprise multiple INET segments joined by bridges the same as 333 for any link; the addressing plans in each segment may be mutually 334 exclusive and managed by different administrative entities. 336 OMNI interface 337 a node's attachment to an OMNI link, and configured over one or 338 more underlying *NET interfaces. If there are multiple OMNI links 339 in an OMNI domain, a separate OMNI interface is configured for 340 each link. 342 OMNI Adaptation Layer (OAL) 343 an OMNI interface sublayer service whereby original IP packets 344 admitted into the interface are wrapped in an IPv6 header and 345 subject to fragmentation and reassembly. The OAL is also 346 responsible for generating MTU-related control messages as 347 necessary, and for providing addressing context for spanning 348 multiple segments of a bridged OMNI link. 350 original IP packet 351 a whole IP packet or fragment admitted into the OMNI interface by 352 the network layer prior to OAL encapsulation and fragmentation, or 353 an IP packet delivered to the network layer by the OMNI interface 354 following OAL decapsulation and reassembly. 356 OAL packet 357 an original IP packet encapsulated in OAL headers and trailers 358 before OAL fragmentation, or following OAL reassembly. 360 OAL fragment 361 a portion of an OAL packet following fragmentation but prior to 362 *NET encapsulation, or following *NET encapsulation but prior to 363 OAL reassembly. 365 (OAL) atomic fragment 366 an OAL packet that does not require fragmentation is always 367 encapsulated as an "atomic fragment" with a Fragment Header with 368 Fragment Offset and More Fragments both set to 0, but with a valid 369 Identification value. 371 (OAL) carrier packet 372 an encapsulated OAL fragment following *NET encapsulation or prior 373 to *NET decapsulation. OAL sources and destinations exchange 374 carrier packets over underlying interfaces, and may be separated 375 by one or more OAL intermediate nodes. OAL intermediate nodes may 376 perform re-encapsulation on carrier packets by removing the *NET 377 headers of the first hop network and replacing them with new *NET 378 headers for the next hop network. 380 OAL source 381 an OMNI interface acts as an OAL source when it encapsulates 382 original IP packets to form OAL packets, then performs OAL 383 fragmentation and *NET encapsulation to create carrier packets. 385 OAL destination 386 an OMNI interface acts as an OAL destination when it decapsulates 387 carrier packets, then performs OAL reassembly and decapsulation to 388 derive the original IP packet. 390 OAL intermediate node 391 an OMNI interface acts as an OAL intermediate node when it removes 392 the *NET headers of carrier packets received on a first segment, 393 then re-encapsulates the carrier packets in new *NET headers and 394 forwards them into the next segment. 396 OMNI Option 397 an IPv6 Neighbor Discovery option providing multilink parameters 398 for the OMNI interface as specified in Section 12. 400 Mobile Network Prefix Link Local Address (MNP-LLA) 401 an IPv6 Link Local Address that embeds the most significant 64 402 bits of an MNP in the lower 64 bits of fe80::/64, as specified in 403 Section 8. 405 Mobile Network Prefix Unique Local Address (MNP-ULA) 406 an IPv6 Unique-Local Address derived from an MNP-LLA. 408 Administrative Link Local Address (ADM-LLA) 409 an IPv6 Link Local Address that embeds a 32-bit administratively- 410 assigned identification value in the lower 32 bits of fe80::/96, 411 as specified in Section 8. 413 Administrative Unique Local Address (ADM-ULA) 414 an IPv6 Unique-Local Address derived from an ADM-LLA. 416 Multilink 417 an OMNI interface's manner of managing diverse underlying 418 interface connections to data links as a single logical unit. The 419 OMNI interface provides a single unified interface to upper 420 layers, while underlying interface selections are performed on a 421 per-packet basis considering factors such as DSCP, flow label, 422 application policy, signal quality, cost, etc. Multilinking 423 decisions are coordinated in both the outbound (i.e. MN to 424 correspondent) and inbound (i.e., correspondent to MN) directions. 426 Multinet 427 an OAL intermediate node's manner of bridging multiple diverse IP 428 Internetworks and/or private enterprise networks at the OAL layer 429 below IP. Through intermediate node concatenation of bridged 430 network segments in this way, multiple diverse Internetworks (such 431 as the global public IPv4 and IPv6 Internets) can serve as transit 432 segments in a bridged path for forwarding IP packets end-to-end. 434 This bridging capability proivde benefits such as supporting IPv4/ 435 IPv6 transition and coexsitence, joining multiple diverse operator 436 networks into a cooperative single service network, etc. 438 Multihop 439 an iterative relaying of IP packets between MNs over an OMNI 440 underlying interface technology (such as omnidirectional wireless) 441 without support of fixed infrastructure. Multihop services entail 442 node-to-node relaying within a Mobile/Vehicular Ad-hoc Network 443 (MANET/VANET) for MN-to-MN communications and/or for "range 444 extension" where MNs within range of communications infrastructure 445 elements provide forwarding services for other MNs. 447 L2 448 The second layer in the OSI network model. Also known as "layer- 449 2", "link-layer", "sub-IP layer", "data link layer", etc. 451 L3 452 The third layer in the OSI network model. Also known as "layer- 453 3", "network-layer", "IP layer", etc. 455 underlying interface 456 a *NET interface over which an OMNI interface is configured. The 457 OMNI interface is seen as a L3 interface by the IP layer, and each 458 underlying interface is seen as a L2 interface by the OMNI 459 interface. The underlying interface either connects directly to 460 the physical communications media or coordinates with another node 461 where the physical media is hosted. 463 Mobility Service Identification (MSID) 464 Each MSE and AR is assigned a unique 32-bit Identification (MSID) 465 (see: Section 8). IDs are assigned according to MS-specific 466 guidelines (e.g., see: [I-D.templin-intarea-6706bis]). 468 Safety-Based Multilink (SBM) 469 A means for ensuring fault tolerance through redundancy by 470 connecting multiple affiliated OMNI interfaces to independent 471 routing topologies (i.e., multiple independent OMNI links). 473 Performance Based Multilink (PBM) 474 A means for selecting underlying interface(s) for packet 475 transmission and reception within a single OMNI interface. 477 OMNI Domain 478 The set of all SBM/PBM OMNI links that collectively provides 479 services for a common set of MSPs. Each OMNI domain consists of a 480 set of affiliated OMNI links that all configure the same ::/48 ULA 481 prefix with a unique 16-bit Subnet ID as discussed in Section 9. 483 3. Requirements 485 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 486 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 487 "OPTIONAL" in this document are to be interpreted as described in BCP 488 14 [RFC2119][RFC8174] when, and only when, they appear in all 489 capitals, as shown here. 491 An implementation is not required to internally use the architectural 492 constructs described here so long as its external behavior is 493 consistent with that described in this document. 495 4. Overlay Multilink Network (OMNI) Interface Model 497 An OMNI interface is a virtual interface configured over one or more 498 underlying interfaces, which may be physical (e.g., an aeronautical 499 radio link, etc.) or virtual (e.g., an Internet or higher-layer 500 "tunnel"). The OMNI interface architectural layering model is the 501 same as in [RFC5558][RFC7847], and augmented as shown in Figure 1. 502 The IP layer therefore sees the OMNI interface as a single L3 503 interface nexus for multiple underlying interfaces that appear as L2 504 communication channels in the architecture. 506 +----------------------------+ 507 | Upper Layer Protocol | 508 Session-to-IP +---->| | 509 Address Binding | +----------------------------+ 510 +---->| IP (L3) | 511 IP Address +---->| | 512 Binding | +----------------------------+ 513 +---->| OMNI Interface | 514 Logical-to- +---->| (OMNI Adaptation Layer) | 515 Physical | +----------------------------+ 516 Interface +---->| L2 | L2 | | L2 | 517 Binding |(IF#1)|(IF#2)| ..... |(IF#n)| 518 +------+------+ +------+ 519 | L1 | L1 | | L1 | 520 | | | | | 521 +------+------+ +------+ 523 Figure 1: OMNI Interface Architectural Layering Model 525 Each underlying interface provides an L2/L1 abstraction according to 526 one of the following models: 528 o INET interfaces connect to an INET either natively or through one 529 or several IPv4 Network Address Translators (NATs). Native INET 530 interfaces have global IP addresses that are reachable from any 531 INET correspondent. NATed INET interfaces typically have private 532 IP addresses and connect to a private network behind one or more 533 NATs that provide INET access. 535 o ANET interfaces connect to a protected ANET that is separated from 536 the open INET by an AR acting as a proxy. The ANET interface may 537 be either on the same L2 link segment as the AR, or separated from 538 the AR by multiple IP hops. 540 o VPNed interfaces use security encapsulation over a *NET to a 541 Virtual Private Network (VPN) gateway. Other than the link-layer 542 encapsulation format, VPNed interfaces behave the same as for 543 Direct interfaces. 545 o Direct (aka "point-to-point") interfaces connect directly to a 546 peer without crossing any *NET paths. An example is a line-of- 547 sight link between a remote pilot and an unmanned aircraft. 549 The OMNI interface forwards original IP packets from the network 550 layer (L3) using the OMNI Adaptation Layer (OAL) (see: Section 5) as 551 an encapsulation and fragmentation sublayer service. This "OAL 552 source" then further encapsulates the resulting OAL packets/fragments 553 in *NET headers to create OAL carrier packets for transmission over 554 underlying interfaces (L2/L1). The target OMNI interface receives 555 the carrier packets from underlying interfaces (L1/L2) and discards 556 the *NET headers. If the resulting OAL packets/fragments are 557 addressed to itself, the OMNI interface acts as an "OAL destination" 558 and performs reassembly if necessary, discards the OAL encapsulation, 559 and delivers the original IP packet to the network layer (L3). If 560 the OAL fragments are addressed to another node, the OMNI interface 561 instead acts as an "OAL intermediate node" by re-encapsulating in new 562 *NET headers and forwarding the new carrier packets over an 563 underlying interface without reassembling or discarding the OAL 564 encapsulation. The OAL source and OAL destination are seen as 565 "neighbors" on the OMNI link, while OAL intermediate nodes are seen 566 as "bridges" capable of multinet concatenation. 568 The OMNI interface can send/receive original IP packets to/from 569 underlying interfaces while including/omitting various encapsulations 570 including OAL, UDP, IP and L2. The network layer can also access the 571 underlying interfaces directly while bypassing the OMNI interface 572 entirely when necessary. This architectural flexibility may be 573 beneficial for underlying interfaces (e.g., some aviation data links) 574 for which encapsulation overhead may be a primary consideration. 575 OMNI interfaces that send original IP packets directly over 576 underlying interfaces without invoking the OAL can only reach peers 577 located on the same OMNI link segment. However, an ANET proxy that 578 receives the original IP packet can forward it further by performing 579 OAL encapsulation with source set to its own address and destination 580 set to the OAL destination corresponding to the final destination 581 (i.e., even if the OAL destination is on a different OMNI link 582 segment). 584 Original IP packets sent directly over underlying interfaces are 585 subject to the same path MTU related issues as for any 586 Internetworking path, and do not include per-packet identifications 587 that can be used for data origin verification and/or link-layer 588 retransmissions. Original IP packets presented directly to an 589 underlying interface that exceed the underlying network path MTU are 590 dropped with an ordinary ICMPv6 Packet Too Big (PTB) message 591 returned. These PTB messages are subject to loss [RFC2923] the same 592 as for any non-OMNI IP interface. 594 The OMNI interface encapsulation/decapsulation layering possibilities 595 are shown in Figure 2 below. In the figure, imaginary vertical lines 596 drawn between the Network Layer and Underlying interfaces denote the 597 encapsulation/decapsulation layering combinations possible. Common 598 combinations include NULL (i.e., direct access to underlying 599 interfaces with or without using the OMNI interface), OMNI/IP, 600 OMNI/UDP/IP, OMNI/UDP/IP/L2, OMNI/OAL/UDP/IP, OMNI/OAL/UDP/L2, etc. 602 +------------------------------------------------------------+ 603 | Network Layer | 604 +--+---------------------------------------------------------+ 605 | OMNI Interface | 606 +--------------------------+------------------------------+ 607 | OAL Encaps/Decaps | 608 +------------------------------+ 609 | OAL Frag/Reass | 610 +------------+---------------+--------------+ 611 | UDP Encaps/Decaps/Compress | 612 +----+---+------------+--------+--+ +--------+ 613 | IP E/D | | IP E/D | | IP E/D | 614 +---+------+-+----+ +--+---+----+ +----+---+--+ 615 |L2 E/D| |L2 E/D| |L2 E/D| |L2 E/D| 616 +-------+------+---+------+----+------+---------------+------+ 617 | Underlying Interfaces | 618 +------------------------------------------------------------+ 620 Figure 2: OMNI Interface Layering 622 The OMNI/OAL model gives rise to a number of opportunities: 624 o MNs receive a MNP from the MS, and coordinate with the MS through 625 IPv6 ND message exchanges. The MN uses the MNP to construct a 626 unique Link-Local Address (MNP-LLA) through the algorithmic 627 derivation specified in Section 8 and assigns the LLA to the OMNI 628 interface. Since MNP-LLAs are uniquely derived from an MNP, no 629 Duplicate Address Detection (DAD) or Multicast Listener Discovery 630 (MLD) messaging is necessary. 632 o since Temporary ULAs are statistically unique, they can be used 633 without DAD, e.g. for MN-to-MN communications until an MNP-LLA is 634 obtained. 636 o underlying interfaces on the same L2 link segment as an AR do not 637 require any L3 addresses (i.e., not even link-local) in 638 environments where communications are coordinated entirely over 639 the OMNI interface. 641 o as underlying interface properties change (e.g., link quality, 642 cost, availability, etc.), any active interface can be used to 643 update the profiles of multiple additional interfaces in a single 644 message. This allows for timely adaptation and service continuity 645 under dynamically changing conditions. 647 o coordinating underlying interfaces in this way allows them to be 648 represented in a unified MS profile with provisions for mobility 649 and multilink operations. 651 o exposing a single virtual interface abstraction to the IPv6 layer 652 allows for multilink operation (including QoS based link 653 selection, packet replication, load balancing, etc.) at L2 while 654 still permitting L3 traffic shaping based on, e.g., DSCP, flow 655 label, etc. 657 o the OMNI interface allows inter-INET traversal when nodes located 658 in different INETs need to communicate with one another. This 659 mode of operation would not be possible via direct communications 660 over the underlying interfaces themselves. 662 o the OAL supports lossless and adaptive path MTU mitigations not 663 available for communications directly over the underlying 664 interfaces themselves. The OAL supports "packing" of multiple IP 665 payload packets within a single OAL packet. 667 o the OAL applies per-packet identification values that allow for 668 link-layer reliability and data origin authentication. 670 o L3 sees the OMNI interface as a point of connection to the OMNI 671 link; if there are multiple OMNI links (i.e., multiple MS's), L3 672 will see multiple OMNI interfaces. 674 o Multiple independent OMNI interfaces can be used for increased 675 fault tolerance through Safety-Based Multilink (SBM), with 676 Performance-Based Multilink (PBM) applied within each interface. 678 Other opportunities are discussed in [RFC7847]. Note that even when 679 the OMNI virtual interface is present, applications can still access 680 underlying interfaces either through the network protocol stack using 681 an Internet socket or directly using a raw socket. This allows for 682 intra-network (or point-to-point) communications without invoking the 683 OMNI interface and/or OAL. For example, when an IPv6 OMNI interface 684 is configured over an underlying IPv4 interface, applications can 685 still invoke IPv4 intra-network communications as long as the 686 communicating endpoints are not subject to mobility dynamics. 687 However, the opportunities discussed above are not realized when the 688 architectural layering is bypassed in this way. 690 Figure 3 depicts the architectural model for a MN with an attached 691 EUN connecting to the MS via multiple independent *NETs. When an 692 underlying interface becomes active, the MN's OMNI interface sends 693 IPv6 ND messages without encapsulation if the first-hop Access Router 694 (AR) is on the same underlying link; otherwise, the interface uses 695 IP-in-IP encapsulation. The IPv6 ND messages traverse the ground 696 domain *NETs until they reach an AR (AR#1, AR#2, ..., AR#n), which 697 then coordinates with an INET Mobility Service Endpoint (MSE#1, 698 MSE#2, ..., MSE#m) and returns an IPv6 ND message response to the MN. 699 The Hop Limit in IPv6 ND messages is not decremented due to 700 encapsulation; hence, the OMNI interface appears to be attached to an 701 ordinary link. 703 +--------------+ (:::)-. 704 | MN |<-->.-(::EUN:::) 705 +--------------+ `-(::::)-' 706 |OMNI interface| 707 +----+----+----+ 708 +--------|IF#1|IF#2|IF#n|------ + 709 / +----+----+----+ \ 710 / | \ 711 / | \ 712 v v v 713 (:::)-. (:::)-. (:::)-. 714 .-(::*NET:::) .-(::*NET:::) .-(::*NET:::) 715 `-(::::)-' `-(::::)-' `-(::::)-' 716 +----+ +----+ +----+ 717 ... |AR#1| .......... |AR#2| ......... |AR#n| ... 718 . +-|--+ +-|--+ +-|--+ . 719 . | | | 720 . v v v . 721 . <----- INET Encapsulation -----> . 722 . . 723 . +-----+ (:::)-. . 724 . |MSE#2| .-(::::::::) +-----+ . 725 . +-----+ .-(::: INET :::)-. |MSE#m| . 726 . (::::: Routing ::::) +-----+ . 727 . `-(::: System :::)-' . 728 . +-----+ `-(:::::::-' . 729 . |MSE#1| +-----+ +-----+ . 730 . +-----+ |MSE#3| |MSE#4| . 731 . +-----+ +-----+ . 732 . . 733 . . 734 . <----- Worldwide Connected Internetwork ----> . 735 ........................................................... 737 Figure 3: MN/MS Coordination via Multiple *NETs 739 After the initial IPv6 ND message exchange, the MN (and/or any nodes 740 on its attached EUNs) can send and receive original IP packets over 741 the OMNI interface. OMNI interface multilink services will forward 742 the packets via ARs in the correct underlying *NETs. The AR 743 encapsulates the packets according to the capabilities provided by 744 the MS and forwards them to the next hop within the worldwide 745 connected Internetwork via optimal routes. 747 5. OMNI Interface Maximum Transmission Unit (MTU) 749 The OMNI interface observes the link nature of tunnels, including the 750 Maximum Transmission Unit (MTU), Maximum Reassembly Unit (MRU) and 751 the role of fragmentation and reassembly [I-D.ietf-intarea-tunnels]. 752 The OMNI interface is configured over one or more underlying 753 interfaces as discussed in Section 4, where the interfaces (and their 754 associated *NET paths) may have diverse MTUs. OMNI interface 755 considerations for accommodating original IP packets of various sizes 756 are discussed in the following sections. 758 IPv6 underlying interfaces are REQUIRED to configure a minimum MTU of 759 1280 bytes and a minimum MRU of 1500 bytes [RFC8200]. Therefore, the 760 minimum IPv6 path MTU is 1280 bytes since routers on the path are not 761 permitted to perform network fragmentation even though the 762 destination is required to reassemble more. The network therefore 763 MUST forward original IP packets of at least 1280 bytes without 764 generating an IPv6 Path MTU Discovery (PMTUD) Packet Too Big (PTB) 765 message [RFC8201]. (While the source can apply "source 766 fragmentation" for locally-generated IPv6 packets up to 1500 bytes 767 and larger still if it knows the destination configures a larger MRU, 768 this does not affect the minimum IPv6 path MTU.) 770 IPv4 underlying interfaces are REQUIRED to configure a minimum MTU of 771 68 bytes [RFC0791] and a minimum MRU of 576 bytes [RFC0791][RFC1122]. 772 Therefore, when the Don't Fragment (DF) bit in the IPv4 header is set 773 to 0 the minimum IPv4 path MTU is 576 bytes since routers on the path 774 support network fragmentation and the destination is required to 775 reassemble at least that much. The OMNI interface therefore MUST set 776 DF to 0 in the IPv4 encapsulation headers of carrier packets that are 777 no larger than 576 bytes, and SHOULD set DF to 1 in larger carrier 778 packets. (Note: even if the encapsulation source has a way to 779 determine that the encapsulation destination configures an MRU larger 780 than 576 bytes, it should not assume a larger minimum IPv4 path MTU 781 without careful consideration of the issues discussed in 782 Section 6.9.) 784 The OMNI interface configures an MTU and MRU of 9180 bytes [RFC2492]; 785 the size is therefore not a reflection of the underlying interface or 786 *NET path MTUs, but rather determines the largest original IP packet 787 the OAL (and/or underlying interface) can forward or reassemble. For 788 each OAL destination (i.e., for each OMNI link neighbor), the OAL 789 source may discover "hard" or "soft" Reassembly Limit values smaller 790 than the MRU based on receipt of IPv6 ND messages with OMNI 791 Reassembly Limit sub-options (see: Section 12.1.11). The OMNI 792 interface employs the OAL as an encapsulation sublayer service to 793 transform original IP packets into OAL packets/fragments, and the OAL 794 in turn uses *NET encapsulation to forward carrier packets over the 795 underlying interfaces (see: Section 6). 797 6. The OMNI Adaptation Layer (OAL) 799 When an OMNI interface forwards an original IP packet from the 800 network layer for transmission over one or more underlying 801 interfaces, the OMNI Adaptation Layer (OAL) acting as the OAL source 802 drops the packet and returns a PTB message if the packet exceeds the 803 MRU and/or the hard Reassembly Limit for the intended OAL 804 destination. Otherwise, the OAL source applies encapsulation to form 805 OAL packets and fragmentation to produce resulting OAL fragments 806 suitable for *NET encapsulation and transmission as carrier packets 807 over underlying interfaces as described in Section 6.1. 809 These carrier packets travel over one or more underlying networks 810 bridged by OAL intermediate nodes, which re-encapsulate by removing 811 the *NET headers of the first underlying network and appending *NET 812 headers appropriate for the next underlying network in succession. 813 (This process supports the multinet concatenation capability needed 814 for joining multiple diverse networks.) After re-encapsulation by 815 zero or more OAL intermediate nodes, the carrier packets arrive at 816 the OAL destination. 818 When the OAL destination receives the carrier packets, it discards 819 the *NET headers and reassembles the resulting OAL fragments into an 820 OAL packet as described in Section 6.3. The OAL destination then 821 decapsulates the OAL packet to obtain the original IP packet, which 822 it then delivers to the network layer. 824 The OAL presents an OMNI sublayer abstraction similar to ATM 825 Adaptation Layer 5 (AAL5). Unlike AAL5 which performs segmentation 826 and reassembly with fixed-length 53 octet cells over ATM networks, 827 however, the OAL uses IPv6 encapsulation, fragmentation and 828 reassembly with larger variable-length cells over heterogeneous 829 underlying networks. Detailed operations of the OAL are specified in 830 the following sections. 832 6.1. OAL Source Encapsulation and Fragmentation 834 When the network layer forwards an original IP packet into the OMNI 835 interface, the OAL source inserts an IPv6 encapsulation header but 836 does not decrement the Hop Limit/TTL of the original IP packet since 837 encapsulation occurs at a layer below IP forwarding [RFC2473]. The 838 OAL source copies the "Type of Service/Traffic Class" [RFC2983] and 839 "Congestion Experienced" [RFC3168] values in the original packet's IP 840 header into the corresponding fields in the OAL header, then sets the 841 OAL header "Flow Label" as specified in [RFC6438]. The OAL source 842 finally sets the OAL header IPv6 Hop Limit to a conservative value 843 sufficient to enable loop-free forwarding over multiple concatenated 844 OMNI link segments and sets the Payload Length to the length of the 845 original IP packet. 847 The OAL next selects source and destination addresses for the IPv6 848 header of the resulting OAL packet. MN OMNI interfaces set the OAL 849 IPv6 header source address to a Unique Local Address (ULA) based on 850 the Mobile Network Prefix (MNP-ULA), while AR and MSE OMNI interfaces 851 set the source address to an Administrative ULA (ADM-ULA) (see: 852 Section 9). When a MN OMNI interface does not (yet) have an MNP-ULA, 853 it can use a Temporary ULA and/or Host Identity Tag (HIT) instead 854 (see: Section 22). 856 When the OAL source forwards an original IP packet toward a final 857 destination via an ANET underlying interface, it sets the OAL IPv6 858 header source address to its own ULA and sets the destination to 859 either the Administrative ULA (ADM-ULA) of the ANET peer or the 860 Mobile Network Prefix ULA (MNP-ULA) corresponding to the final 861 destination (see below). The OAL source then fragments the OAL 862 packet if necessary, encapsulates the OAL fragments in any ANET 863 headers and sends the resulting carrier packets to the ANET peer 864 which either reassembles before forwarding if the OAL destination is 865 its own ULA or forwards the fragments toward the true OAL destination 866 without first reassembling otherwise. 868 When the OAL source forwards an original IP packet toward a final 869 destination via an INET underlying interface, it sets the OAL IPv6 870 header source address to its own ULA and sets the destination to the 871 ULA of an OAL destination node on the final *NET segment. The OAL 872 source then fragments the OAL packet if necessary, encapsulates the 873 OAL fragments in any *NET headers and sends the resulting carrier 874 packets toward the OAL destination on the final segment OMNI node 875 which reassembles before forwarding the original IP packets toward 876 the final destination. 878 Following OAL IPv6 encapsulation and address selection, the OAL 879 source next appends a 2 octet trailing Checksum (initialized to 0) at 880 the end of the original IP packet while incrementing the OAL header 881 IPv6 Payload Length field to reflect the addition of the trailer. 882 The format of the resulting OAL packet following encapsulation is 883 shown in Figure 4: 885 +----------+-----+-----+-----+-----+-----+-----+----+ 886 | OAL Hdr | Original IP packet |Csum| 887 +----------+-----+-----+-----+-----+-----+-----+----+ 889 Figure 4: OAL Packet Before Fragmentation 891 The OAL source next selects a 32-bit Identification value for the 892 packet, beginning with an unpredictable value for the initial OAL 893 packet per [RFC7739] and monotonically incrementing for each 894 successive OAL packet until a new initial value is chosen. 896 The OAL source then calculates the 2's complement (mod 256) 897 Fletcher's checksum [CKSUM][RFC2328][RFC0905] over the entire OAL 898 packet beginning with a pseudo-header of the IPv6 header similar to 899 that found in Section 8.1 of [RFC8200]. The OAL IPv6 pseudo-header 900 is formed as shown in Figure 5: 902 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 903 | | 904 + + 905 | | 906 + OAL Source Address + 907 | | 908 + + 909 | | 910 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 911 | | 912 + + 913 | | 914 + OAL Destination Address + 915 | | 916 + + 917 | | 918 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 919 | OAL Payload Length | zero | Next Header | 920 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 921 | Identification | 922 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 924 Figure 5: OAL IPv6 Pseudo-Header 926 The OAL source then inserts a single OMNI Routing Header (ORH) if 927 necessary (see: [I-D.templin-intarea-6706bis]) while incrementing 928 Payload Length to reflect the addition of the ORH (note that the late 929 addition of the ORH is not covered by the trailing checksum). 931 The OAL source next fragments the OAL packet if necessary while 932 assuming the IPv4 minimum path MTU (i.e., 576 bytes) as the worst 933 case for OAL fragmentation regardless of the underlying interface IP 934 protocol version since IPv6/IPv4 protocol translation and/or IPv6-in- 935 IPv4 encapsulation may occur in any *NET path. By always assuming 936 the IPv4 minimum even for IPv6 underlying interfaces, the OAL source 937 may produce smaller fragments with additional encapsulation overhead 938 but will always interoperate and never run the risk of loss due to an 939 MTU restriction or due to presenting an underlying interface with a 940 carrier packet that exceeds its MRU. Additionally, the OAL path 941 could traverse multiple *NET "segments" with intermediate OAL 942 forwarding nodes performing re-encapsulation where the *NET 943 encapsulation of the previous segment is replaced by the *NET 944 encapsulation of the next segment which may be based on a different 945 IP protocol version and/or encapsulation sizes. 947 The OAL source therefore assumes a default minimum path MTU of 576 948 bytes at each *NET segment for the purpose of generating OAL 949 fragments for *NET encapsulation and transmission as carrier packets. 950 In the worst case, each successive *NET segment may re-encapsulate 951 with either a 20 byte IPv4 or 40 byte IPv6 header, an 8 byte UDP 952 header and in some cases an IP security encapsulation (40 bytes 953 maximum assumed). Any *NET segment may also insert a maximum-length 954 (40 byte) ORH as an extension to the existing 40 byte OAL IPv6 header 955 plus 8 byte Fragment Header if an ORH was not already present. 956 Assuming therefore an absolute worst case of (40 + 40 + 8) = 88 bytes 957 for *NET encapsulation plus (40 + 40 + 8) = 88 bytes for OAL 958 encapsulation leaves (576 - 88 - 88) = 400 bytes to accommodate a 959 portion of the original IP packet/fragment. The OAL source therefore 960 sets a minimum Maximum Payload Size (MPS) of 400 bytes as the basis 961 for the minimum-sized OAL fragment that can be assured of traversing 962 all segments without loss due to an MTU/MRU restriction. The Maximum 963 Fragment Size (MFS) for OAL fragmentation is therefore determined by 964 the MPS plus the size of the OAL encapsulation headers. (Note that 965 the OAL source includes the 2 octet trailer as part of the payload 966 during fragmentation, and the OAL destination regards it as ordinary 967 payload until reassembly and checksum verification are complete.) 969 The OAL source SHOULD maintain "path MPS" values for individual OAL 970 destinations initialized to the minimum MPS and increased to larger 971 values (up to the OMNI interface MTU) if better information is known 972 or discovered. For example, when *NET peers share a common 973 underlying link or a fixed path with a known larger MTU, the OAL 974 source can base path MPS on this larger size (i.e., instead of 576 975 bytes) as long as the *NET peer reassembles before re-encapsulating 976 and forwarding (while re-fragmenting if necessary). Also, if the OAL 977 source has a way of knowing the maximum *NET encapsulation size for 978 all segments along the path it may be able to increase path MPS to 979 reserve additional room for payload data. The OAL source must 980 include the uncompressed OAL header size in its path MPS calculation, 981 since a full header could be included at any time. 983 The OAL source can also actively probe individual OAL destinations to 984 discover larger path MPS values using packetization layer probes per 985 [RFC4821][RFC8899], but care must be taken to avoid setting static 986 values for dynamically changing paths leading to black holes. The 987 probe involves sending an OAL packet larger than the current path MPS 988 and receiving a small acknowledgement message in response (with the 989 possible receipt of link-layer error message in case the probe was 990 lost). For this purpose, the OAL source can send an NS message with 991 one or more OMNI options with large PadN sub-options (see: 992 Section 12) in order to receive a small NA response from the OAL 993 destination. While observing the minimum MPS will always result in 994 robust and secure behavior, the OAL source should optimize path MPS 995 values when more efficient utilization may result in better 996 performance (e.g. for wireless aviation data links). 998 When the OAL source performs fragmentation, it SHOULD produce the 999 minimum number of non-overlapping fragments under current MPS 1000 constraints, where each non-final fragment MUST be of equal length at 1001 least as large as the minimum MPS, while the final fragment MAY be of 1002 different length. The OAL source also converts all original IP 1003 packets no larger than the current MPS into "atomic fragments" by 1004 including a Fragment Header with Fragment Offset and More Fragments 1005 both set to 0. The OAL source finally encapsulates the fragments in 1006 *NET headers to form carrier packets and forwards them over an 1007 underlying interface, while retaining the fragments and their ordinal 1008 positions (i.e., as Frag #0, Frag #1, Frag #2, etc.) for a timeout 1009 period in case link-layer retransmission is requested. The formats 1010 of OAL fragments and carrier packets are shown in Figure 6. 1012 +----------+--+-------------+ 1013 | OAL Hdr |FH| Frag #0 | 1014 +----------+--+-------------+ 1015 +----------+--+-------------+ 1016 | OAL Hdr |FH| Frag #1 | 1017 +----------+--+-------------+ 1018 +----------+--+-------------+ 1019 | OAL Hdr |FH| Frag #2 | 1020 +----------+--+-------------+ 1021 .... 1022 +----------+--+-------------+----+ 1023 | OAL Hdr |FH| Frag #(N-1) |Csum| 1024 +----------+--+-------------+----+ 1025 a) OAL fragments after fragmentation 1026 (FH = Fragment Header; Csum appears only in final fragment) 1028 +--------+--+-----+-----+-----+-----+-----+----+ 1029 |OAL Hdr |FH| Original IP packet |Csum| 1030 +--------+--+-----+-----+-----+-----+-----+----+ 1031 b) An OAL atomic fragment with FH but no fragmentation. 1033 +--------+----------+--+-------------+ 1034 |*NET Hdr| OAL Hdr |FH| Frag #i | 1035 +--------+----------+--+-------------+ 1036 c) OAL carrier packet after *NET encapsulation 1038 Figure 6: OAL Fragments and Carrier Packets 1040 6.2. OAL *NET Encapsulation and Re-Encapsulation 1042 During *NET encapsulation, OAL sources first encapsulate each OAL 1043 fragment in a UDP header as the first *NET encapsulation sublayer if 1044 NAT traversal, packet filtering middlebox traversal and/or OAL header 1045 compression are necessary. The OAL then optionally appends 1046 additional encapsulation sublayer headers, then presents the *NET 1047 packet to an underlying interface. This layering can be seen in 1048 Figure 2. 1050 When a UDP header is included, the OAL source next sets the UDP 1051 source port to a constant value that it will use in each successive 1052 carrier packet it sends to the next OAL hop. For packets sent to an 1053 MSE, the OAL source sets the UDP destination port to 8060, i.e., the 1054 IANA-registered port number for AERO. For packets sent to a MN peer, 1055 the source sets the UDP destination port to the cached port value for 1056 this peer. The OAL source then sets the UDP length to the total 1057 length of the OAL fragment in correspondence with the OAL header 1058 Payload Length (i.e., the UDP length and IPv6 Payload Length must 1059 agree). The OAL source finally sets the UDP checksum to 0 1060 [RFC6935][RFC6936] since the only fields not already covered by the 1061 OAL checksum or underlying *NET CRCs are the Fragment Header fields, 1062 and any corruption in those fields will be garbage collected by the 1063 reassembly algorithm (however, see Section 20 for additional 1064 considerations). The UDP encapsulation header is often used in 1065 association with IP encapsulation, but may also be used between 1066 neighbors on a shared physical link with a true L2 header format such 1067 as for transmission over IEEE 802 Ethernet links. This document 1068 therefore requests a new Ether Type code assignment TBD1 in the IANA 1069 'ieee-802-numbers' registry for direct User Datagram Protocol (UDP) 1070 encapsulation over IEEE 802 Ethernet links (see: Section 25). 1072 For *NET encapsulations over IP, the OAL source next copies the "Type 1073 of Service/Traffic Class" [RFC2983] and "Congestion Experienced" 1074 [RFC3168] values in the OAL IPv6 header into the corresponding fields 1075 in the *NET IP header, then (for IPv6) sets the *NET IPv6 header 1076 "Flow Label" as specified in [RFC6438]. The OAL source then sets the 1077 *NET IP TTL/Hop Limit the same as for any *NET host, i.e., it does 1078 not copy the Hop Limit value from the OAL header. For carrier 1079 packets undergoing re-encapsulation at an OAL intermediate node, the 1080 node decrements the OAL IPv6 header Hop Limit and discards the 1081 carrier packet if the value reaches 0. The node then copies the 1082 "Type of Service/Traffic Class" and "Congestion Experienced" values 1083 from the previous hop *NET encapsulation header into the OAL IPv6 1084 header before setting the next hop *NET IP encapsulation header 1085 values the same as specified for the OAL source above. 1087 Following *NET encapsulation/re-encapsulation, the OAL source sends 1088 the resulting carrier packets over one or more underlying interfaces. 1089 The underlying interfaces often connect directly to physical media on 1090 the local platform (e.g., a laptop computer with WiFi, etc.), but in 1091 some configurations the physical media may be hosted on a separate 1092 Local Area Network (LAN) node. In that case, the OMNI interface can 1093 establish a Layer-2 VLAN or a point-to-point tunnel (at a layer below 1094 the underlying interface) to the node hosting the physical media. 1095 The OMNI interface may also apply encapsulation at the underlying 1096 interface layer (e.g., as for a tunnel virtual interface) such that 1097 carrier packets would appear "double-encapsulated" on the LAN; the 1098 node hosting the physical media in turn removes the LAN encapsulation 1099 prior to transmission or inserts it following reception. Finally, 1100 the underlying interface must monitor the node hosting the physical 1101 media (e.g., through periodic keepalives) so that it can convey 1102 up/down/status information to the OMNI interface. 1104 6.3. OAL Destination Decapsulation and Reassembly 1106 When an OMNI interface receives a carrier packet from an underlying 1107 interface, the OAL destination discards the *NET encapsulation 1108 headers and examines the OAL header of the enclosed OAL fragment. If 1109 the OAL fragment is addressed to a different node, the OAL 1110 destination re-encapsulates and forwards as discussed below. If the 1111 OAL fragment is addressed to itself, the OAL destination creates or 1112 updates a checklist for this (Source, Destination, Identification)- 1113 tuple to track the fragments already received (i.e., by examining the 1114 Payload Length, Fragment Offset, More Fragments and Identification 1115 values supplied by the OAL source). The OAL destination verifies 1116 that all non-final OAL fragments are of equal length no less than the 1117 minimum MPS and that no fragments overlap or leave "holes", while 1118 dropping any non-conforming fragments. The OAL destination records 1119 each conforming OAL fragment's ordinal position based on the OAL 1120 header Payload Length and Fragment Offset values (i.e., as Frag #0, 1121 Frag #1, Frag #2, etc.) and admits each fragment into the reassembly 1122 cache. 1124 When reassembly is complete, the OAL destination removes the ORH if 1125 present while decrementing Payload Length to reflect the removal of 1126 the ORH. The OAL destination next verifies the resulting OAL 1127 packet's checksum and discards the packet if the checksum is 1128 incorrect. If the OAL packet was accepted, the OAL destination then 1129 removes the OAL header/trailer, then delivers the original IP packet 1130 to the network layer. Note that link layers include a CRC-32 1131 integrity check which provides effective hop-by-hop error detection 1132 in the underlying network for payload sizes up to the OMNI interface 1133 MTU [CRC], but that some hops may traverse intermediate layers such 1134 as tunnels over IPv4 that do not include integrity checks. The 1135 trailing Fletcher checksum therefore allows the OAL destination to 1136 detect OAL packet splicing errors due to reassembly misassociations 1137 and/or to verify integrity for OAL packets whose fragments may have 1138 traversed unprotected underlying network hops [CKSUM]. The Fletcher 1139 algorithm also provides diversity with respect to both lower layer 1140 CRCs and upper layer Internet checksums as part of a complimentary 1141 multi-layer integrity assurance architecture. 1143 6.4. OAL Header Compression 1145 When the OAL source and destination are on the same *NET segment, no 1146 ORH is needed and carrier packet header compression is possible. 1147 When the OAL source and destination exchange initial IPv6 ND messages 1148 as discussed in the following Sections, each caches the observed *NET 1149 UDP source port and source IP (or L2) address associated with the OAL 1150 IPv6 source address found in the full-length OAL IPv6 header. After 1151 the initial IPv6 ND message exchange, the OAL source can begin 1152 applying OAL Header Compression to significantly reduce the 1153 encapsulation overhead required in each carrier packet. 1155 When the OAL source determines that header compression state has been 1156 established (i.e., following the IPv6 ND message exchange), it can 1157 begin sending OAL fragments with significant portions of the IPv6 1158 header and Fragment Header omitted thereby reducing the amount of 1159 encapsulation overhead. For OAL first-fragments (including atomic 1160 fragments), the OMNI Compressed Header - Type 0 (OCH-0) is used and 1161 formatted as shown in Figure 7: 1163 0 1 2 3 1164 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 1165 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ * 1166 | Source port | Destination port | U 1167 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ D 1168 | Length | Checksum | P 1169 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ * 1170 |Version| Traffic Class | Flow Label | 1171 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1172 | Next Header | Reserved |M| Identification (0 -1) | 1173 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1174 | Identification (2-3) | 1175 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+/ 1177 Figure 7: OMNI Compressed Header - Type 0 (OCH-0) 1179 In this format, the UDP header appears in its entirety in the first 8 1180 octets, then followed by the first 4 octets of the IPv6 header with 1181 the remainder omitted. (The IPv6 Version field is set to the value 0 1182 to distinguish this header from a true IP protocol version number and 1183 from OCH-1 - see below.) The compressed IPv6 header is then followed 1184 by a compressed IPv6 Fragment Header with the Fragment Offset field 1185 and two Reserved bits omitted (since these fields always encode the 1186 value 0 in first-fragments), and with the More Fragments (M) bit 1187 relocated to the least significant bit of the first Reserved field. 1188 The OCH-0 header is then followed by the OAL fragment body, and the 1189 UDP length field is reduced by 38 octets (i.e., the difference in 1190 length between full-length IPv6 and Fragment Headers and the length 1191 of the compressed headers). 1193 For OAL non-first fragments (i.e., those with non-zero Fragment 1194 Offsets), the OMNI Compressed Header - Type 1 (OCH-1) is used and 1195 formatted as shown in Figure 8: 1197 0 1 2 3 1198 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 1199 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ * 1200 | Source port | Destination port | U 1201 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ D 1202 | Length | Checksum | P 1203 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ * 1204 |V|R|M| Fragment Offset | Identification (0-1) | 1205 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1206 | Identification (1-3) | 1207 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1209 Figure 8: OMNI Compressed Header - Type 1 (OCH-1) 1211 In this format, the UDP header appears in its entirety in the first 8 1212 octets, but all IPv6 header fields except for the most significant 1213 Version (V) bit are omitted. (The V bit is set to the value 1 to 1214 distinguish this header from a true IP protocol version number and 1215 from OCH-0.) The V bit is followed by a single Reserved (R) bit and 1216 the More Fragments (M) bit in a compressed IPv6 Fragment Header with 1217 the Next Header and first Reserved fields omitted. The OCH-1 header 1218 is then followed by the OAL fragment body, and the UDP length field 1219 is reduced by 42 octets (i.e., the difference in length between full- 1220 length IPv6 and Fragment Headers and the length of the compressed 1221 headers). 1223 When the OAL destination receives a carrier packet with an OCH, it 1224 first determines the OAL IPv6 source and destination addresses by 1225 examining the UDP source port and L2 source address, then determines 1226 the length by examining the UDP length. The OAL destination then 1227 examines the (V)ersion field immediately following the UDP header. 1228 If the (4-bit) Version field encodes the value 0, the OAL destination 1229 processes the remainder of the header as an OCH-0, then reconstitutes 1230 the full-sized IPv6 and Fragment Headers and adds this OAL fragment 1231 to the reassembly buffer if necessary. If the (1-bit) V bit encodes 1232 the value 1, the OAL destination instead processes the remainder of 1233 the header as an OCH-1, then reconstitutes the full-sized IPv6 and 1234 Fragment Headers and adds this OAL fragment to the reassembly buffer. 1235 Note that, since the OCH-1 does not include Traffic Class, Flow Label 1236 or Next Header information, the OAL destination writes the value 0 1237 into these fields when it reconstitutes the full headers. These 1238 values will be correctly populated during reassembly after an OAL 1239 first fragment with an OCH-0 or uncompressed OAL header arrives. 1241 6.5. OAL Fragment Identification Window Maintenance 1243 As noted above, the OAL source establishes a window of 32-bit 1244 Identifications beginning with an unpredictable value for the initial 1245 message [RFC7739] and monotonically incrementing for each successive 1246 OAL packet until a new initial value is chosen. The OAL source 1247 asserts the starting value by including it as the Identification in 1248 an IPv6 ND NS/RS messages. When the OAL destination receives the 1249 IPv6 ND message, it resets the Identification window for this OAL 1250 source to the new value coded in the message's OAL header and expects 1251 future OAL fragments received from this OAL source to include 1252 sequential Identification values (subject to loss and reordering) 1253 until the neighbor reachable time expires or the OAL source sends a 1254 new IPv6 ND message. 1256 For example, if the OAL destination receives an NS/RS message with 1257 Identification 0x12345678, it resets the window for this OAL source 1258 to begin with 0x12345678 and examines the Identification values in 1259 subsequent OAL fragments received from this OAL source. If the 1260 Identification values of subsequent OAL fragments fall within the 1261 window of (0x12345678 + N) the OAL destination accepts the fragment; 1262 otherwise, it silently drops the fragment (where "N" represents the 1263 maximum number of fragments expected before the neighbor reachable 1264 time expires). 1266 While monitoring the current window, the OAL destination must accept 1267 new NS/RS Identification values even if outside the current window. 1268 The new Identification value resets the OAL destination's window 1269 start, and the window processing continues from this new starting 1270 point while allowing a period of overlap in case OAL fragments with 1271 Identification values from a previous window are still in flight. 1272 Note also that unsolicited NA messages must include Identification 1273 values within the current window, and therefore do not reset the 1274 current window. 1276 This implies that an IPv6 ND message used to reset the Identification 1277 window should fit within a single OAL fragment (i.e., within current 1278 MPS constraints), since a fragmented IPv6 ND message with an out-of- 1279 window Identification value could be part of a DoS attack. While 1280 larger IPv6 ND messages (up to the OMNI interface MTU) can certainly 1281 be subject to OAL fragmentation, their Identification should be 1282 within the current window maintained by the OAL destination to 1283 increase the likelihood that they will be accepted. 1285 6.6. OAL Fragment Retransmission 1287 When the OAL source sends carrier packets with OAL fragments to an 1288 OAL destination, the source caches them for a timeout period in case 1289 retransmission may be necessary. (The timeout duration is an 1290 implementation matter, and may be influenced by factors such as 1291 packet arrival rates, OAL source/destination round trip times, etc.) 1292 The OAL destination in turn maintains a checklist for the (Source, 1293 Destination, Identification)-tuple of each new OAL fragment received 1294 and notes the ordinal positions of fragments already received (i.e., 1295 as Frag #0, Frag #1, Frag #2, etc.). 1297 If the OAL destination notices some OAL fragments missing after most 1298 other fragments within the same Identification window have already 1299 arrived, it may send an IPv6 ND unsolicited Neighbor Advertisement 1300 (uNA) message to the OAL source that originated the fragments to 1301 report loss. The OAL destination creates a uNA message with an OMNI 1302 option containing an authentication sub-option to provide 1303 authentication (if the OAL source is on an open Internetwork) 1304 followed by a Fragmentation Report sub-option that includes a list of 1305 (Identification, Bitmap)-tuples for OAL fragments received and 1306 missing from this OAL source (see: Section 12). The OAL destination 1307 signs the message if an authentication sub-option is included, 1308 performs OAL encapsulation (with the its own address as the OAL 1309 source and the source address of the message that prompted the uNA as 1310 the OAL destination) and sends the message to the OAL source. 1312 When the OAL source receives the uNA message, it authenticates the 1313 message using authentication sub-option (if present) then examines 1314 the Fragmentation Report. For each (Source, Destination, 1315 Identification)-tuple, the OAL source determines whether it still 1316 holds the original OAL fragments in its cache and retransmits any for 1317 which the Bitmap indicated a loss event. For example, if the Bitmap 1318 indicates that the ordinal OAL fragments Frag #3, Frag #7, Frag #10 1319 and Frag #13 from the same OAL packet are missing the OAL source 1320 retransmits these fragments only and no others. 1322 Note that the goal of this service is to provide a light-weight link- 1323 layer Automatic Repeat Request (ARQ) capability in the spirit of 1324 Section 8.1 of [RFC3819]. Rather than provide true end-to-end 1325 reliability, however, the service provides timely link-layer 1326 retransmissions that may improve packet delivery ratios and avoid 1327 some delays inherent in true end-to-end services. 1329 6.7. OAL MTU Feedback Messaging 1331 When the OMNI interface forwards original IP packets from the network 1332 layer, it invokes the OAL and returns internally-generated ICMPv4 1333 Fragmentation Needed [RFC1191] or ICMPv6 Path MTU Discovery (PMTUD) 1334 Packet Too Big (PTB) [RFC8201] messages as necessary. This document 1335 refers to both of these ICMPv4/ICMPv6 message types simply as "PTBs", 1336 and introduces a distinction between PTB "hard" and "soft" errors as 1337 discussed below. 1339 Ordinary PTB messages with ICMPv4 header "unused" field or ICMPv6 1340 header Code field value 0 are hard errors that always indicate that a 1341 packet has been dropped due to a real MTU restriction. In 1342 particular, the OAL source drops the packet and returns a PTB hard 1343 error if the packet exceeds the OAL destination MRU. However, the 1344 OMNI interface can also forward large original IP packets via OAL 1345 encapsulation and fragmentation while at the same time returning PTB 1346 soft error messages (subject to rate limiting) if it deems the 1347 original IP packet too large according to factors such as link 1348 performance characteristics, reassembly congestion, etc. This 1349 ensures that the path MTU is adaptive and reflects the current path 1350 used for a given data flow. The OMNI interface can therefore 1351 continuously forward packets without loss while returning PTB soft 1352 error messages recommending a smaller size if necessary. Original 1353 sources that receive the soft errors in turn reduce the size of the 1354 packets they send (i.e., the same as for hard errors), but can soon 1355 resume sending larger packets if the soft errors subside. 1357 An OAL source sends PTB soft error messages by setting the ICMPv4 1358 header "unused" field or ICMPv6 header Code field to the value 1 if a 1359 original IP packet was deemed lost (e.g., due to reassembly timeout) 1360 or to the value 2 otherwise. The OAL source sets the PTB destination 1361 address to the original IP packet source, and sets the source address 1362 to one of its OMNI interface unicast/anycast addresses that is 1363 routable from the perspective of the original source. The OAL source 1364 then sets the MTU field to a value smaller than the original packet 1365 size but no smaller than 576 for ICMPv4 or 1280 for ICMPv6, writes 1366 the leading portion of the original IP packet into the "packet in 1367 error" field, and returns the PTB soft error to the original source. 1368 When the original source receives the PTB soft error, it temporarily 1369 reduces the size of the packets it sends the same as for hard errors 1370 but may seek to increase future packet sizes dynamically while no 1371 further soft errors are arriving. (If the original source does not 1372 recognize the soft error code, it regards the PTB the same as a hard 1373 error but should heed the retransmission advice given in [RFC8201] 1374 suggesting retransmission based on normal packetization layer 1375 retransmission timers.) 1376 An OAL destination may experience reassembly cache congestion, and 1377 can return uNA messages to the OAL source that originated the 1378 fragments (subject to rate limiting) to advertise reduced hard/soft 1379 Reassembly Limits and/or to report individual reassembly failures. 1380 The OAL destination creates a uNA message with an OMNI option 1381 containing an authentication message sub-option (if the OAL source is 1382 on an open Internetwork) followed optionally by at most one hard and 1383 one soft Reassembly Limit sub-options with reduced hard/soft values, 1384 and with one of them optionally including the leading portion an OAL 1385 first fragment containing the header of an original IP packet whose 1386 source must be notified (see: Section 12). The OAL destination 1387 encapsulates as much of the OAL first fragment (beginning with the 1388 OAL header) as will fit in the "OAL First Fragment" field of sub- 1389 option without causing the entire uNA message to exceed the minimum 1390 MPS, signs the message if an authentication sub-option is included, 1391 performs OAL encapsulation (with the its own address as the OAL 1392 source and the source address of the message that prompted the uNA as 1393 the OAL destination) and sends the message to the OAL source. 1395 When the OAL source receives the uNA message, it records the new 1396 hard/soft Reassembly Limit values for this OAL destination if the 1397 OMNI option includes Reassembly Limit sub-options. If a hard or soft 1398 Reassembly Limit sub-option includes an OAL First Fragment, the OAL 1399 source next sends a corresponding network layer PTB hard or soft 1400 error to the original source to recommend a smaller size. For hard 1401 errors, the OAL source sets the PTB Code field to 0. For soft 1402 errors, the OAL source sets the PTB Code field to 1 if the L flag in 1403 the Reassembly Limit sub-option is 1; otherwise, the OAL source sets 1404 the Code field to 2. The OAL source crafts the PTB by extracting the 1405 leading portion of the original IP packet from the OAL First Fragment 1406 field (i.e., not including the OAL header) and writes it in the 1407 "packet in error" field of a PTB with destination set to the original 1408 IP packet source and source set to one of its OMNI interface unicast/ 1409 anycast addresses that is routable from the perspective of the 1410 original source. For future transmissions, if the original IP packet 1411 is larger than the hard Reassembly Limit for this OAL destination the 1412 OAL source drops the packet and returns a PTB hard error with MTU set 1413 to the hard Reassembly Limit. If the packet is no larger than the 1414 current hard Reassembly Limit but larger than the current soft limit, 1415 the OAL source can also return PTB soft errors (subject to rate 1416 limiting) with Code set to 2 and MTU set to the current soft limit 1417 while still forwarding the packet to the OMNI destination. 1419 Original sources that receive PTB soft errors can dynamically tune 1420 the size of the original IP packets they to send to produce the best 1421 possible throughput and latency, with the understanding that these 1422 parameters may change over time due to factors such as congestion, 1423 mobility, network path changes, etc. The receipt or absence of soft 1424 errors should be seen as hints of when increasing or decreasing 1425 packet sizes may be beneficial. The OMNI interface supports 1426 continuous transmission and reception of packets of various sizes in 1427 the face of dynamically changing network conditions. Moreover, since 1428 PTB soft errors do not indicate a hard limit, original sources that 1429 receive soft errors can begin sending larger packets without waiting 1430 for the recommended 10 minutes specified for PTB hard errors 1431 [RFC1191][RFC8201]. The OMNI interface therefore provides an 1432 adaptive service that accommodates MTU diversity especially well- 1433 suited for dynamic multilink environments. 1435 6.8. OAL Requirements 1437 In light of the above, OAL sources, destinations and intermediate 1438 nodes observe the following normative requirements: 1440 o OAL sources MUST NOT send OAL fragments including original IP 1441 packets larger than the OMNI interface MTU or the OAL destination 1442 hard Reassembly Limit, i.e., whether or not fragmentation is 1443 needed. 1445 o OAL sources MUST NOT perform OAL fragmentation for original IP 1446 packets smaller than the minimum MPS minus the trailer size, and 1447 MUST produce non-final fragments that contain equal-length 1448 payloads no smaller than the minimum MPS when performing 1449 fragmentation. 1451 o OAL sources MUST NOT send OAL fragments that include any extension 1452 headers other than a single ORH and a single Fragment Header. 1454 o OAL intermediate nodes SHOULD and OAL destinations MUST 1455 unconditionally drop OAL packets/fragments including original IP 1456 packets larger than the OMNI interface MRU and/or OAL destination 1457 hard Reassembly Limit, i.e., whether or not reassembly was needed. 1459 o OAL intermediate nodes SHOULD and OAL destinations MUST 1460 unconditionally drop any non-final OAL fragments containing a 1461 payload smaller than the minimum MPS. 1463 o OAL intermediate nodes SHOULD and OAL destinations MUST 1464 unconditionally drop OAL fragments that include any extension 1465 headers other than a single ORH and a single Fragment Header. 1467 o OAL destination nodes MUST drop any new OAL non-final fragments of 1468 different length than other non-final fragments that have already 1469 been received, and MUST drop any new OAL fragments with Offset and 1470 Payload length that would overlap with other fragments and/or 1471 leave too-small holes between fragments that have already been 1472 received. 1474 Note: Under the minimum MPS, ordinary 1500 byte original IP packets 1475 would require at most 4 OAL fragments, with each non-final fragment 1476 containing 400 payload bytes and the final fragment containing 302 1477 payload bytes (i.e., the final 300 bytes of the original IP packet 1478 plus the 2 octet trailer). Likewise, maximum-length 9180 byte 1479 original IP packets would require at most 23 fragments. For all 1480 packet sizes, the likelihood of successful reassembly may improve 1481 when the OMNI interface sends all fragments of the same fragmented 1482 OAL packet consecutively over the same underlying interface. 1483 Finally, an assured minimum/path MPS allows continuous operation over 1484 all paths including those that traverse bridged L2 media with 1485 dissimilar MTUs. 1487 Note: Certain legacy network hardware of the past millennium was 1488 unable to accept packet "bursts" resulting from an IP fragmentation 1489 event - even to the point that the hardware would reset itself when 1490 presented with a burst. This does not seem to be a common problem in 1491 the modern era, where fragmentation and reassembly can be readily 1492 demonstrated at line rate (e.g., using tools such as 'iperf3') even 1493 over fast links on average hardware platforms. Even so, the OAL 1494 source could impose an inter-fragment delay while the OAL destination 1495 is reporting reassembly congestion (see: Section 6.7) and decrease 1496 the delay when reassembly congestion subsides. 1498 6.9. OAL Fragmentation Security Implications 1500 As discussed in Section 3.7 of [RFC8900], there are four basic 1501 threats concerning IPv6 fragmentation; each of which is addressed by 1502 effective mitigations as follows: 1504 1. Overlapping fragment attacks - reassembly of overlapping 1505 fragments is forbidden by [RFC8200]; therefore, this threat does 1506 not apply to the OAL. 1508 2. Resource exhaustion attacks - this threat is mitigated by 1509 providing a sufficiently large OAL reassembly cache and 1510 instituting "fast discard" of incomplete reassemblies that may be 1511 part of a buffer exhaustion attack. The reassembly cache should 1512 be sufficiently large so that a sustained attack does not cause 1513 excessive loss of good reassemblies but not so large that (timer- 1514 based) data structure management becomes computationally 1515 expensive. The cache should also be indexed based on the arrival 1516 underlying interface such that congestion experienced over a 1517 first underlying interface does not cause discard of incomplete 1518 reassemblies for uncongested underlying interfaces. 1520 3. Attacks based on predictable fragment identification values - 1521 this threat is mitigated by selecting an unpredictable 1522 Identification value per [RFC7739]. Additionally, inclusion of 1523 the OAL checksum would make it very difficult for an attacker who 1524 could somehow predict a fragment identification value to inject 1525 malicious fragments resulting in undetected reassemblies of bad 1526 data. 1528 4. Evasion of Network Intrusion Detection Systems (NIDS) - this 1529 threat is mitigated by setting a minimum MPS for OAL 1530 fragmentation, which defeats all "tiny fragment"-based attacks. 1532 Additionally, IPv4 fragmentation includes a 16-bit Identification (IP 1533 ID) field with only 65535 unique values such that at high data rates 1534 the field could wrap and apply to new carrier packets while the 1535 fragments of old packets using the same ID are still alive in the 1536 network [RFC4963]. However, since the largest carrier packet that 1537 will be sent via an IPv4 path with DF = 0 is 576 bytes any IPv4 1538 fragmentation would occur only on links with an IPv4 MTU smaller than 1539 this size, and [RFC3819] recommendations suggest that such links will 1540 have low data rates. Since IPv6 provides a 32-bit Identification 1541 value, IP ID wraparound at high data rates is not a concern for IPv6 1542 fragmentation. 1544 Finally, [RFC6980] documents fragmentation security concerns for 1545 large IPv6 ND messages. These concerns are addressed when the OMNI 1546 interface employs the OAL instead of directly fragmenting the IPv6 ND 1547 message itself. For this reason, OMNI interfaces MUST NOT send IPv6 1548 ND messages larger than the OMNI interface MTU, and MUST employ OAL 1549 encapsulation and fragmentation for IPv6 ND messages larger than the 1550 current MPS for this OAL destination. 1552 6.10. OAL Super-Packets 1554 By default, the OAL source includes a 40-byte IPv6 encapsulation 1555 header for each original IP packet during OAL encapsulation. The OAL 1556 source also calculates and appends a 2 octet trailing Fletcher 1557 checksum then performs fragmentation such that a copy of the 40-byte 1558 IPv6 header plus an 8-byte IPv6 Fragment Header is included in each 1559 OAL fragment (when an ORH is added, the OAL encapsulation headers 1560 become larger still). However, these encapsulations may represent 1561 excessive overhead in some environments. OAL header compression can 1562 dramatically reduce the amount of encapsulation overhead, however a 1563 complimentary technique known as "packing" (see: 1564 [I-D.ietf-intarea-tunnels]) is also supported so that multiple 1565 original IP packets and/or control messages can be included within a 1566 single OAL "super-packet". 1568 When the OAL source has multiple original IP packets to send to the 1569 same OAL destination with total length no larger than the OAL 1570 destination MRU, it can concatenate them into a super-packet 1571 encapsulated in a single OAL header and trailing checksum. Within 1572 the OAL super-packet, the IP header of the first original IP packet 1573 (iHa) followed by its data (iDa) is concatenated immediately 1574 following the OAL header, then the IP header of the next original 1575 packet (iHb) followed by its data (iDb) is concatenated immediately 1576 following the first original packet, etc. with the trailing checksum 1577 included last. The OAL super-packet format is transposed from 1578 [I-D.ietf-intarea-tunnels] and shown in Figure 9: 1580 <------- Original IP packets -------> 1581 +-----+-----+ 1582 | iHa | iDa | 1583 +-----+-----+ 1584 | 1585 | +-----+-----+ 1586 | | iHb | iDb | 1587 | +-----+-----+ 1588 | | 1589 | | +-----+-----+ 1590 | | | iHc | iDc | 1591 | | +-----+-----+ 1592 | | | 1593 v v v 1594 +----------+-----+-----+-----+-----+-----+-----+----+ 1595 | OAL Hdr | iHa | iDa | iHb | iDb | iHc | iDc |Csum| 1596 +----------+-----+-----+-----+-----+-----+-----+----+ 1597 <--- OAL "Super-Packet" with single OAL Hdr/Csum ---> 1599 Figure 9: OAL Super-Packet Format 1601 When the OAL source prepares a super-packet, it applies OAL 1602 fragmentation and *NET encapsulation then sends the carrier packets 1603 to the OAL destination. When the OAL destination receives the super- 1604 packet it reassembles if necessary, verifies and removes the trailing 1605 checksum, then regards the remaining OAL header Payload Length as the 1606 sum of the lengths of all payload packets. The OAL destination then 1607 selectively extracts each original IP packet (e.g., by setting 1608 pointers into the super-packet buffer and maintaining a reference 1609 count, by copying each packet into a separate buffer, etc.) and 1610 forwards each packet to the network layer. During extraction, the 1611 OAL determines the IP protocol version of each successive original IP 1612 packet 'j' by examining the four most-significant bits of iH(j), and 1613 determines the length of the packet by examining the rest of iH(j) 1614 according to the IP protocol version. 1616 Note that OMNI interfaces must take care to avoid processing super- 1617 packet payload elements that would subvert security. Specifically, 1618 if a super-packet contains a mix of data and control payload packets 1619 (which could include critical security codes), the node MUST NOT 1620 process the data packets before processing the control packets 1622 7. Frame Format 1624 The OMNI interface forwards original IP packets from the network 1625 layer by first invoking the OAL to create OAL packets/fragments if 1626 necessary, then including any *NET encapsulations and finally 1627 engaging the native frame format of the underlying interface. For 1628 example, for Ethernet-compatible interfaces the frame format is 1629 specified in [RFC2464], for aeronautical radio interfaces the frame 1630 format is specified in standards such as ICAO Doc 9776 (VDL Mode 2 1631 Technical Manual), for various forms of tunnels the frame format is 1632 found in the appropriate tunneling specification, etc. 1634 See Figure 2 for a map of the various *NET layering combinations 1635 possible. For any layering combination, the final layer (e.g., UDP, 1636 IP, Ethernet, etc.) must have an assigned number and frame format 1637 representation that is compatible with the selected underlying 1638 interface. 1640 8. Link-Local Addresses (LLAs) 1642 OMNI nodes are assigned OMNI interface IPv6 Link-Local Addresses 1643 (LLAs) through pre-service administrative actions. "MNP-LLAs" embed 1644 the MNP assigned to the mobile node, while "ADM-LLAs" include an 1645 administratively-unique ID that is guaranteed to be unique on the 1646 link. LLAs are configured as follows: 1648 o IPv6 MNP-LLAs encode the most-significant 64 bits of a MNP within 1649 the least-significant 64 bits of the IPv6 link-local prefix 1650 fe80::/64, i.e., in the LLA "interface identifier" portion. The 1651 prefix length for the LLA is determined by adding 64 to the MNP 1652 prefix length. For example, for the MNP 2001:db8:1000:2000::/56 1653 the corresponding MNP-LLA is fe80::2001:db8:1000:2000/120. Non- 1654 MNP routes are also represented the same as for MNP-LLAs, but 1655 include a GUA prefix that is not properly covered by the MSP. 1657 o IPv4-compatible MNP-LLAs are constructed as fe80::ffff:[IPv4], 1658 i.e., the interface identifier consists of 16 '0' bits, followed 1659 by 16 '1' bits, followed by a 32bit IPv4 address/prefix. The 1660 prefix length for the LLA is determined by adding 96 to the MNP 1661 prefix length. For example, the IPv4-Compatible MN OMNI LLA for 1662 192.0.2.0/24 is fe80::ffff:192.0.2.0/120 (also written as 1663 fe80::ffff:c000:0200/120). 1665 o ADM-LLAs are assigned to ARs and MSEs and MUST be managed for 1666 uniqueness. The lower 32 bits of the LLA includes a unique 1667 integer "MSID" value between 0x00000001 and 0xfeffffff, e.g., as 1668 in fe80::1, fe80::2, fe80::3, etc., fe80::feffffff. The ADM-LLA 1669 prefix length is determined by adding 96 to the MSID prefix 1670 length. For example, if the prefix length for MSID 0x10012001 is 1671 16 then the ADM-LLA prefix length is set to 112 and the LLA is 1672 written as fe80::1001:2001/112. The "zero" address for each ADM- 1673 LLA prefix is the Subnet-Router anycast address for that prefix 1674 [RFC4291]; for example, the Subnet-Router anycast address for 1675 fe80::1001:2001/112 is simply fe80::1001:2000. The MSID range 1676 0xff000000 through 0xffffffff is reserved for future use. 1678 Since the prefix 0000::/8 is "Reserved by the IETF" [RFC4291], no 1679 MNPs can be allocated from that block ensuring that there is no 1680 possibility for overlap between the different MNP- and ADM-LLA 1681 constructs discussed above. 1683 Since MNP-LLAs are based on the distribution of administratively 1684 assured unique MNPs, and since ADM-LLAs are guaranteed unique through 1685 administrative assignment, OMNI interfaces set the autoconfiguration 1686 variable DupAddrDetectTransmits to 0 [RFC4862]. 1688 Note: If future protocol extensions relax the 64-bit boundary in IPv6 1689 addressing, the additional prefix bits of an MNP could be encoded in 1690 bits 16 through 63 of the MNP-LLA. (The most-significant 64 bits 1691 would therefore still be in bits 64-127, and the remaining bits would 1692 appear in bits 16 through 48.) However, the analysis provided in 1693 [RFC7421] suggests that the 64-bit boundary will remain in the IPv6 1694 architecture for the foreseeable future. 1696 Note: Even though this document honors the 64-bit boundary in IPv6 1697 addressing, it specifies prefix lengths longer than /64 for routing 1698 purposes. This effectively extends IPv6 routing determination into 1699 the interface identifier portion of the IPv6 address, but it does not 1700 redefine the 64-bit boundary. Modern routing protocol 1701 implementations honor IPv6 prefixes of all lengths, up to and 1702 including /128. 1704 9. Unique-Local Addresses (ULAs) 1706 OMNI domains use IPv6 Unique-Local Addresses (ULAs) as the source and 1707 destination addresses in OAL packet IPv6 encapsulation headers. ULAs 1708 are only routable within the scope of a an OMNI domain, and are 1709 derived from the IPv6 Unique Local Address prefix fc00::/7 followed 1710 by the L bit set to 1 (i.e., as fd00::/8) followed by a 40-bit 1711 pseudo-random Global ID to produce the prefix [ULA]::/48, which is 1712 then followed by a 16-bit Subnet ID then finally followed by a 64 bit 1713 Interface ID as specified in Section 3 of [RFC4193]. All nodes in 1714 the same OMNI domain configure the same 40-bit Global ID as the OMNI 1715 domain identifier. The statistic uniqueness of the 40-bit pseudo- 1716 random Global ID allows different OMNI domains to be joined together 1717 in the future without requiring renumbering. 1719 Each OMNI link instance is identified by a value between 0x0000 and 1720 0xfeff in bits 48-63 of [ULA]::/48; the values 0xff00 through 0xfffe 1721 are reserved for future use, and the value 0xffff denotes the 1722 presence of a Temporary ULA (see below). For example, OMNI ULAs 1723 associated with instance 0 are configured from the prefix 1724 [ULA]:0000::/64, instance 1 from [ULA]:0001::/64, instance 2 from 1725 [ULA]:0002::/64, etc. ULAs and their associated prefix lengths are 1726 configured in correspondence with LLAs through stateless prefix 1727 translation where "MNP-ULAs" are assigned in correspondence to MNP- 1728 LLAs and "ADM-ULAs" are assigned in correspondence to ADM-LLAs. For 1729 example, for OMNI link instance [ULA]:1010::/64: 1731 o the MNP-ULA corresponding to the MNP-LLA fe80::2001:db8:1:2 with a 1732 56-bit MNP length is derived by copying the lower 64 bits of the 1733 LLA into the lower 64 bits of the ULA as 1734 [ULA]:1010:2001:db8:1:2/120 (where, the ULA prefix length becomes 1735 64 plus the IPv6 MNP length). 1737 o the MNP-ULA corresponding to fe80::ffff:192.0.2.0 with a 28-bit 1738 MNP length is derived by simply writing the LLA interface ID into 1739 the lower 64 bits as [ULA]:1010:0:ffff:192.0.2.0/124 (where, the 1740 ULA prefix length is 64 plus 32 plus the IPv4 MNP length). 1742 o the ADM-ULA corresponding to fe80::1000/112 is simply 1743 [ULA]:1010::1000/112. 1745 o the ADM-ULA corresponding to fe80::/128 is simply 1746 [ULA]:1010::/128. 1748 o etc. 1750 Each OMNI interface assigns the Anycast ADM-ULA specific to the OMNI 1751 link instance. For example, the OMNI interface connected to instance 1752 3 assigns the Anycast address [ULA]:0003::/128. Routers that 1753 configure OMNI interfaces advertise the OMNI service prefix (e.g., 1754 [ULA]:0003::/64) into the local routing system so that applications 1755 can direct traffic according to SBM requirements. 1757 The ULA presents an IPv6 address format that is routable within the 1758 OMNI routing system and can be used to convey link-scoped IPv6 ND 1759 messages across multiple hops using IPv6 encapsulation [RFC2473]. 1760 The OMNI link extends across one or more underling Internetworks to 1761 include all ARs and MSEs. All MNs are also considered to be 1762 connected to the OMNI link, however OAL encapsulation is omitted 1763 whenever possible to conserve bandwidth (see: Section 14). 1765 Each OMNI link can be subdivided into "segments" that often 1766 correspond to different administrative domains or physical 1767 partitions. OMNI nodes can use IPv6 Segment Routing [RFC8402] when 1768 necessary to support efficient forwarding to destinations located in 1769 other OMNI link segments. A full discussion of Segment Routing over 1770 the OMNI link appears in [I-D.templin-intarea-6706bis]. 1772 Temporary ULAs are constructed per [RFC8981] based on the prefix 1773 [ULA]:ffff::/64 and used by MNs when they have no other addresses. 1774 Temporary ULAs can be used for MN-to-MN communications outside the 1775 context of any supporting OMNI link infrastructure, and can also be 1776 used as an initial address while the MN is in the process of 1777 procuring an MNP. Temporary ULAs are not routable within the OMNI 1778 routing system, and are therefore useful only for OMNI link "edge" 1779 communications. Temporary ULAs employ optimistic DAD principles 1780 [RFC4429] since they are probabilistically unique. 1782 Note: IPv6 ULAs taken from the prefix fc00::/7 followed by the L bit 1783 set to 0 (i.e., as fc00::/8) are never used for OMNI OAL addressing, 1784 however the range could be used for MSP and MNP addressing under 1785 certain limiting conditions (see: Section 10). 1787 10. Global Unicast Addresses (GUAs) 1789 OMNI domains use IP Global Unicast Address (GUA) prefixes [RFC4291] 1790 as Mobility Service Prefixes (MSPs) from which Mobile Network 1791 Prefixes (MNP) are delegated to Mobile Nodes (MNs). Fixed 1792 correspondent node networks reachable from the OMNI domain are 1793 represented by non-MNP GUA prefixes that are not derived from the 1794 MSP, but are treated in all other ways the same as for MNPs. 1796 For IPv6, GUA prefixes are assigned by IANA [IPV6-GUA] and/or an 1797 associated regional assigned numbers authority such that the OMNI 1798 domain can be interconnected to the global IPv6 Internet without 1799 causing inconsistencies in the routing system. An OMNI domain could 1800 instead use ULAs with the 'L' bit set to 0 (i.e., from the prefix 1801 fc00::/8)[RFC4193], however this would require IPv6 NAT if the domain 1802 were ever connected to the global IPv6 Internet. 1804 For IPv4, GUA prefixes are assigned by IANA [IPV4-GUA] and/or an 1805 associated regional assigned numbers authority such that the OMNI 1806 domain can be interconnected to the global IPv4 Internet without 1807 causing routing inconsistencies. An OMNI domain could instead use 1808 private IPv4 prefixes (e.g., 10.0.0.0/8, etc.) [RFC3330], however 1809 this would require IPv4 NAT if the domain were ever connected to the 1810 global IPv4 Internet. 1812 11. Node Identification 1814 OMNI MNs and MSEs that connect over open Internetworks include a 1815 unique node identification value for themselves in the OMNI options 1816 of their IPv6 ND messages (see: Section 12.1.13). One useful 1817 identification value alternative is the Host Identity Tag (HIT) as 1818 specified in [RFC7401], while Hierarchical HITs (HHITs) 1819 [I-D.ietf-drip-rid] may provide a better alternative in certain 1820 domains such as the Unmanned (Air) Traffic Management (UTM) service 1821 for Unmanned Air Systems (UAS). Another alternative is the 1822 Universally Unique IDentifier (UUID) [RFC4122] which can be self- 1823 generated by a node without supporting infrastructure with very low 1824 probability of collision. 1826 When a MN is truly outside the context of any infrastructure, it may 1827 have no MNP information at all. In that case, the MN can use an IPv6 1828 temporary ULA or (H)HIT as an IPv6 source/destination address for 1829 sustained communications in Vehicle-to-Vehicle (V2V) and (multihop) 1830 Vehicle-to-Infrastructure (V2I) scenarios. The MN can also propagate 1831 the ULA/(H)HIT into the multihop routing tables of (collective) 1832 Mobile/Vehicular Ad-hoc Networks (MANETs/VANETs) using only the 1833 vehicles themselves as communications relays. 1835 When a MN connects to ARs over (non-multihop) protected-spectrum 1836 ANETs, an alternate form of node identification (e.g., MAC address, 1837 serial number, airframe identification value, VIN, etc.) may be 1838 sufficient. The MN can then include OMNI "Node Identification" sub- 1839 options (see: Section 12.1.13) in IPv6 ND messages should the need to 1840 transmit identification information over the network arise. 1842 12. Address Mapping - Unicast 1844 OMNI interfaces maintain a neighbor cache for tracking per-neighbor 1845 state and use the link-local address format specified in Section 8. 1846 OMNI interface IPv6 Neighbor Discovery (ND) [RFC4861] messages sent 1847 over physical underlying interfaces without encapsulation observe the 1848 native underlying interface Source/Target Link-Layer Address Option 1849 (S/TLLAO) format (e.g., for Ethernet the S/TLLAO is specified in 1850 [RFC2464]). OMNI interface IPv6 ND messages sent over underlying 1851 interfaces via encapsulation do not include S/TLLAOs which were 1852 intended for encoding physical L2 media address formats and not 1853 encapsulation IP addresses. Furthermore, S/TLLAOs are not intended 1854 for encoding additional interface attributes needed for multilink 1855 coordination. Hence, this document does not define an S/TLLAO format 1856 but instead defines a new option type termed the "OMNI option" 1857 designed for these purposes. 1859 MNs such as aircraft typically have many wireless data link types 1860 (e.g. satellite-based, cellular, terrestrial, air-to-air directional, 1861 etc.) with diverse performance, cost and availability properties. 1862 The OMNI interface would therefore appear to have multiple L2 1863 connections, and may include information for multiple underlying 1864 interfaces in a single IPv6 ND message exchange. OMNI interfaces use 1865 an IPv6 ND option called the OMNI option formatted as shown in 1866 Figure 10: 1868 0 1 2 3 1869 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 1870 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1871 | Type | Length | Preflen | S/T-omIndex | 1872 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1873 | | 1874 ~ Sub-Options ~ 1875 | | 1876 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1878 Figure 10: OMNI Option Format 1880 In this format: 1882 o Type is set to TBD2. 1884 o Length is set to the number of 8 octet blocks in the option. The 1885 value 0 is invalid, while the values 1 through 255 (i.e., 8 1886 through 2040 octets, respectively) indicate the total length of 1887 the OMNI option. 1889 o Preflen is an 8 bit field that determines the length of prefix 1890 associated with an LLA. Values 0 through 128 specify a valid 1891 prefix length (all other values are invalid). For IPv6 ND 1892 messages sent from a MN to the MS, Preflen applies to the IPv6 1893 source LLA and provides the length that the MN is requesting or 1894 asserting to the MS. For IPv6 ND messages sent from the MS to the 1895 MN, Preflen applies to the IPv6 destination LLA and indicates the 1896 length that the MS is granting to the MN. For IPv6 ND messages 1897 sent between MS endpoints, Preflen provides the length associated 1898 with the source/target MN that is subject of the ND message. 1900 o S/T-omIndex is an 8 bit field corresponds to the omIndex value for 1901 source or target underlying interface used to convey this IPv6 ND 1902 message. OMNI interfaces MUST number each distinct underlying 1903 interface with an omIndex value between '1' and '255' that 1904 represents a MN-specific 8-bit mapping for the actual ifIndex 1905 value assigned by network management [RFC2863] (the omIndex value 1906 '0' is reserved for use by the MS). For RS and NS messages, S/ 1907 T-omIndex corresponds to the source underlying interface the 1908 message originated from. For RA and NA messages, S/T-omIndex 1909 corresponds to the target underlying interface that the message is 1910 destined to. (For NS messages used for Neighbor Unreachability 1911 Detection (NUD), S/T-omIndex instead identifies the neighbor's 1912 underlying interface to be used as the target interface to return 1913 the NA.) 1915 o Sub-Options is a Variable-length field, of length such that the 1916 complete OMNI Option is an integer multiple of 8 octets long. 1917 Contains one or more Sub-Options, as described in Section 12.1. 1919 The OMNI option may appear in any IPv6 ND message type; it is 1920 processed by interfaces that recognize the option and ignored by all 1921 other interfaces. If multiple OMNI option instances appear in the 1922 same IPv6 ND message, the interface processes the Preflen and S/ 1923 T-omIndex fields in the first instance and ignores those fields in 1924 all other instances. The interface processes the Sub-Options of all 1925 OMNI option instances in the same IPv6 ND message in the consecutive 1926 order in which they appear. 1928 The OMNI option(s) in each IPv6 ND message may include full or 1929 partial information for the neighbor. The union of the information 1930 in the most recently received OMNI options is therefore retained, and 1931 the information is aged/removed in conjunction with the corresponding 1932 neighbor cache entry. 1934 12.1. Sub-Options 1936 Each OMNI option includes zero or more Sub-Options. Each consecutive 1937 Sub-Option is concatenated immediately after its predecessor. All 1938 Sub-Options except Pad1 (see below) are in type-length-value (TLV) 1939 encoded in the following format: 1941 0 1 2 1942 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 1943 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1944 | Sub-Type| Sub-length | Sub-Option Data ... 1945 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1947 Figure 11: Sub-Option Format 1949 o Sub-Type is a 5-bit field that encodes the Sub-Option type. Sub- 1950 Options defined in this document are: 1952 Sub-Option Name Sub-Type 1953 Pad1 0 1954 PadN 1 1955 Interface Attributes (Type 1) 2 1956 Interface Attributes (Type 2) 3 1957 Traffic Selector 4 1958 MS-Register 5 1959 MS-Release 6 1960 Geo Coordinates 7 1961 DHCPv6 Message 8 1962 HIP Message 9 1963 Reassembly Limit 10 1964 Fragmentation Report 11 1965 Node Identification 12 1966 Sub-Type Extension 30 1968 Figure 12 1970 Sub-Types 13-29 are available for future assignment for major 1971 protocol functions. Sub-Type 31 is reserved by IANA. 1973 o Sub-Length is an 11-bit field that encodes the length of the Sub- 1974 Option Data ranging from 0 to 2034 octets. 1976 o Sub-Option Data is a block of data with format determined by Sub- 1977 Type and length determined by Sub-Length. 1979 During transmission, the OMNI interface codes Sub-Type and Sub-Length 1980 together in network byte order in 2 consecutive octets, where Sub- 1981 Option Data may be up to 2034 octets in length. This allows ample 1982 space for coding large objects (e.g., ASCII strings, domain names, 1983 protocol messages, security codes, etc.), while a single OMNI option 1984 is limited to 2040 octets the same as for any IPv6 ND option. If the 1985 Sub-Options to be coded would cause an OMNI option to exceed 2040 1986 octets, the OMNI interface codes any remaining Sub-Options in 1987 additional OMNI option instances in the intended order of processing 1988 in the same IPv6 ND message. Implementations must therefore observe 1989 size limitations, and must refrain from sending IPv6 ND messages 1990 larger than the OMNI interface MTU. If the available OMNI 1991 information would cause a single IPv6 ND message to exceed the OMNI 1992 interface MTU, the OMNI interface codes as much as possible in a 1993 first IPv6 ND message and codes the remainder in additional IPv6 ND 1994 messages. 1996 During reception, the OMNI interface processes each OMNI option Sub- 1997 Option while skipping over and ignoring any unrecognized Sub-Options. 1998 The OMNI interface processes the Sub-Options of all OMNI option 1999 instances in the consecutive order in which they appear in the IPv6 2000 ND message, beginning with the first instance and continuing through 2001 any additional instances to the end of the message. If a Sub-Option 2002 length would cause processing to exceed the OMNI option total length, 2003 the OMNI interface accepts any Sub-Options already processed and 2004 ignores the final Sub-Option. The interface then processes any 2005 remaining OMNI options in the same fashion to the end of the IPv6 ND 2006 message. 2008 Note: large objects that exceed the Sub-Option Data limit of 2034 2009 octets are not supported under the current specification; if this 2010 proves to be limiting in practice, future specifications may define 2011 support for fragmenting large objects across multiple OMNI options 2012 within the same IPv6 ND message. 2014 The following Sub-Option types and formats are defined in this 2015 document: 2017 12.1.1. Pad1 2019 0 2020 0 1 2 3 4 5 6 7 2021 +-+-+-+-+-+-+-+-+ 2022 | S-Type=0|x|x|x| 2023 +-+-+-+-+-+-+-+-+ 2025 Figure 13: Pad1 2027 o Sub-Type is set to 0. If multiple instances appear in OMNI 2028 options of the same message all are processed. 2030 o Sub-Type is followed by 3 'x' bits, set to any value on 2031 transmission (typically all-zeros) and ignored on receipt. Pad1 2032 therefore consists of 1 octet with the most significant 5 bits set 2033 to 0, and with no Sub-Length or Sub-Option Data fields following. 2035 12.1.2. PadN 2037 0 1 2 2038 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 2039 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 2040 | S-Type=1| Sub-length=N | N padding octets ... 2041 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 2043 Figure 14: PadN 2045 o Sub-Type is set to 1. If multiple instances appear in OMNI 2046 options of the same message all are processed. 2048 o Sub-Length is set to N (from 0 to 2034) that encodes the number of 2049 padding octets that follow. 2051 o Sub-Option Data consists of N octets, set to any value on 2052 transmission (typically all-zeros) and ignored on receipt. 2054 12.1.3. Interface Attributes (Type 1) 2056 The Interface Attributes (Type 1) sub-option provides a basic set of 2057 attributes for underlying interfaces. Interface Attributes (Type 1) 2058 is deprecated throughout the rest of this specification, and 2059 Interface Attributes (Type 2) (see: Section 12.1.4) are indicated 2060 wherever the term "Interface Attributes" appears without an 2061 associated Type designation. 2063 Nodes SHOULD NOT include Interface Attributes (Type 1) sub-options in 2064 IPv6 ND messages they send, and MUST ignore any in IPv6 ND messages 2065 they receive. If an Interface Attributes (Type 1) is included, it 2066 must have the following format: 2068 0 1 2 3 2069 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 2070 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2071 | Sub-Type=2| Sub-length=N | omIndex | omType | 2072 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2073 | Provider ID | Link | Resvd |P00|P01|P02|P03|P04|P05|P06|P07| 2074 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2075 |P08|P09|P10|P11|P12|P13|P14|P15|P16|P17|P18|P19|P20|P21|P22|P23| 2076 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2077 |P24|P25|P26|P27|P28|P29|P30|P31|P32|P33|P34|P35|P36|P37|P38|P39| 2078 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2079 |P40|P41|P42|P43|P44|P45|P46|P47|P48|P49|P50|P51|P52|P53|P54|P55| 2080 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2081 |P56|P57|P58|P59|P60|P61|P62|P63| 2082 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2084 Figure 15: Interface Attributes (Type 1) 2086 o Sub-Type is set to 2. If multiple instances with different 2087 omIndex values appear in OMNI option of the same message all are 2088 processed; if multiple instances with the same omIndex value 2089 appear, the first is processed and all others are ignored 2091 o Sub-Length is set to N (from 4 to 2034) that encodes the number of 2092 Sub-Option Data octets that follow. 2094 o omIndex is a 1-octet field containing a value from 0 to 255 2095 identifying the underlying interface for which the attributes 2096 apply. 2098 o omType is a 1-octet field containing a value from 0 to 255 2099 corresponding to the underlying interface identified by omIndex. 2101 o Provider ID is a 1-octet field containing a value from 0 to 255 2102 corresponding to the underlying interface identified by omIndex. 2104 o Link encodes a 4-bit link metric. The value '0' means the link is 2105 DOWN, and the remaining values mean the link is UP with metric 2106 ranging from '1' ("lowest") to '15' ("highest"). 2108 o Resvd is reserved for future use. Set to 0 on transmission and 2109 ignored on reception. 2111 o A 16-octet ""Preferences" field immediately follows 'Resvd', with 2112 values P[00] through P[63] corresponding to the 64 Differentiated 2113 Service Code Point (DSCP) values [RFC2474]. Each 2-bit P[*] field 2114 is set to the value '0' ("disabled"), '1' ("low"), '2' ("medium") 2115 or '3' ("high") to indicate a QoS preference for underlying 2116 interface selection purposes. 2118 12.1.4. Interface Attributes (Type 2) 2120 The Interface Attributes (Type 2) sub-option provides L2 forwarding 2121 information for the multilink conceptual sending algorithm discussed 2122 in Section 14. The L2 information is used for selecting among 2123 potentially multiple candidate underlying interfaces that can be used 2124 to forward carrier packets to the neighbor based on factors such as 2125 DSCP preferences and link quality. Interface Attributes (Type 2) 2126 further includes link-layer address information to be used for either 2127 OAL encapsulation or direct UDP/IP encapsulation (when OAL 2128 encapsulation can be avoided). 2130 Interface Attributes (Type 2) are the sole Interface Attributes 2131 format in this specification that all OMNI nodes must honor. 2132 Wherever the term "Interface Attributes" occurs throughout this 2133 specification without a "Type" designation, the format given below is 2134 indicated: 2136 0 1 2 3 2137 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 2138 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2139 | S-Type=3| Sub-length=N | omIndex | omType | 2140 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2141 | Provider ID | Link |R| API | SRT | FMT | LHS (0 - 7) | 2142 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2143 | LHS (bits 8 - 31) | ~ 2144 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ 2145 ~ ~ 2146 ~ Link Layer Address (L2ADDR) ~ 2147 ~ ~ 2148 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2149 | Bitmap(0)=0xff|P00|P01|P02|P03|P04|P05|P06|P07|P08|P09|P10|P11| 2150 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2151 |P12|P13|P14|P15|P16|P17|P18|P19|P20|P21|P22|P23|P24|P25|P26|P27| 2152 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2153 |P28|P29|P30|P31| Bitmap(1)=0xff|P32|P33|P34|P35|P36| ... 2154 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 2156 Figure 16: Interface Attributes (Type 2) 2158 o Sub-Type is set to 3. If multiple instances with different 2159 omIndex values appear in OMNI options of the same message all are 2160 processed; if multiple instances with the same omIndex value 2161 appear, the first is processed and all others are ignored. 2163 o Sub-Length is set to N (from 4 to 2034) that encodes the number of 2164 Sub-Option Data octets that follow. The 'omIndex', 'omType', 2165 'Provider ID', 'Link', 'R' and 'API' fields are always present; 2166 hence, the remainder of the Sub-Option Data is limited to 2030 2167 octets. 2169 o Sub-Option Data contains an "Interface Attributes (Type 2)" option 2170 encoded as follows: 2172 * omIndex is set to an 8-bit integer value corresponding to a 2173 specific underlying interface the same as specified above for 2174 the OMNI option S/T-omIndex field. The OMNI options of a same 2175 message may include multiple Interface Attributes Sub-Options, 2176 with each distinct omIndex value pertaining to a different 2177 underlying interface. The OMNI option will often include an 2178 Interface Attributes Sub-Option with the same omIndex value 2179 that appears in the S/T-omIndex. In that case, the actual 2180 encapsulation address of the received IPv6 ND message should be 2181 compared with the L2ADDR encoded in the Sub-Option (see below); 2182 if the addresses are different (or, if L2ADDR is absent) the 2183 presence of a NAT is assumed. 2185 * omType is set to an 8-bit integer value corresponding to the 2186 underlying interface identified by omIndex. The value 2187 represents an OMNI interface-specific 8-bit mapping for the 2188 actual IANA ifType value registered in the 'IANAifType-MIB' 2189 registry [http://www.iana.org]. 2191 * Provider ID is set to an OMNI interface-specific 8-bit ID value 2192 for the network service provider associated with this omIndex. 2194 * Link encodes a 4-bit link metric. The value '0' means the link 2195 is DOWN, and the remaining values mean the link is UP with 2196 metric ranging from '1' ("lowest") to '15' ("highest"). 2198 * R is reserved for future use. 2200 * API - a 3-bit "Address/Preferences/Indexed" code that 2201 determines the contents of the remainder of the sub-option as 2202 follows: 2204 + When the most significant bit (i.e., "Address") is set to 1, 2205 the SRT, FMT, LHS and L2ADDR fields are included immediately 2206 following the API code; else, they are omitted. 2208 + When the next most significant bit (i.e., "Preferences") is 2209 set to 1, a preferences block is included next; else, it is 2210 omitted. (Note that if "Address" is set the preferences 2211 block immediately follows L2ADDR; else, it immediately 2212 follows the API code.) 2214 + When a preferences block is present and the least 2215 significant bit (i.e., "Indexed") is set to 0, the block is 2216 encoded in "Simplex" form as shown in Figure 15; else it is 2217 encoded in "Indexed" form as discussed below. 2219 * When API indicates that an "Address" is included, the following 2220 fields appear in consecutive order (else, they are omitted): 2222 + SRT - a 5-bit Segment Routing Topology prefix length value 2223 that (when added to 96) determines the prefix length to 2224 apply to the ULA formed from concatenating [ULA*]::/96 with 2225 the 32 bit LHS MSID value that follows. For example, the 2226 value 16 corresponds to the prefix length 112. 2228 + FMT - a 3-bit "Framework/Mode/Type" code corresponding to 2229 the included Link Layer Address as follows: 2231 - When the most significant bit (i.e., "Framework") is set 2232 to 1, L2ADDR is the INET encapsulation address for the 2233 Source/Target Client itself; otherwise L2ADDR is the 2234 address of the Proxy/Server named in the LHS. 2236 - When the next most significant bit (i.e., "Mode") is set 2237 to 1, the Framework node is (likely) located behind an 2238 INET Network Address Translator (NAT); otherwise, it is 2239 on the open INET. 2241 - When the least significant bit (i.e., "Type") is set to 2242 0, L2ADDR includes a UDP Port Number followed by an IPv4 2243 address; otherwise, it includes a UDP Port Number 2244 followed by an IPv6 address. 2246 + LHS - the 32 bit MSID of the Last Hop Proxy/Server on the 2247 path to the target. When SRT and LHS are both set to 0, the 2248 LHS is considered unspecified in this IPv6 ND message. When 2249 SRT is set to 0 and LHS is non-zero, the prefix length is 2250 set to 128. SRT and LHS together provide guidance to the 2251 OMNI interface forwarding algorithm. Specifically, if SRT/ 2252 LHS is located in the local OMNI link segment then the OMNI 2253 interface can encapsulate according to FMT/L2ADDR (following 2254 any necessary NAT traversal messaging); else, it must 2255 forward according to the OMNI link spanning tree. See 2256 [I-D.templin-intarea-6706bis] for further discussion. 2258 + Link Layer Address (L2ADDR) - Formatted according to FMT, 2259 and identifies the link-layer address (i.e., the 2260 encapsulation address) of the source/target. The UDP Port 2261 Number appears in the first 2 octets and the IP address 2262 appears in the next 4 octets for IPv4 or 16 octets for IPv6. 2263 The Port Number and IP address are recorded in network byte 2264 order, and in ones-compliment "obfuscated" form per 2265 [RFC4380]. The OMNI interface forwarding algorithm uses 2266 FMT/L2ADDR to determine the encapsulation address for 2267 forwarding when SRT/LHS is located in the local OMNI link 2268 segment. Note that if the target is behind a NAT, L2ADDR 2269 will contain the mapped INET address stored in the NAT; 2270 otherwise, L2ADDR will contain the native INET information 2271 of the target itself. 2273 * When API indicates that "Preferences" are included, a 2274 preferences block appears as the remainder of the Sub-Option as 2275 a series of Bitmaps and P[*] values. In "Simplex" form, the 2276 index for each singleton Bitmap octet is inferred from its 2277 sequential position (i.e., 0, 1, 2, ...) as shown in Figure 16. 2278 In "Indexed" form, each Bitmap is preceded by an Index octet 2279 that encodes a value "i" = (0 - 255) as the index for its 2280 companion Bitmap as follows: 2282 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 2283 | Index=i | Bitmap(i) |P[*] values ... 2284 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 2286 Figure 17 2288 * The preferences consist of a first (simplex/indexed) Bitmap 2289 (i.e., "Bitmap(i)") followed by 0-8 single-octet blocks of 2290 2-bit P[*] values, followed by a second Bitmap (i), followed by 2291 0-8 blocks of P[*] values, etc. Reading from bit 0 to bit 7, 2292 the bits of each Bitmap(i) that are set to '1'' indicate the 2293 P[*] blocks from the range P[(i*32)] through P[(i*32) + 31] 2294 that follow; if any Bitmap(i) bits are '0', then the 2295 corresponding P[*] block is instead omitted. For example, if 2296 Bitmap(0) contains 0xff then the block with P[00]-P[03], 2297 followed by the block with P[04]-P[07], etc., and ending with 2298 the block with P[28]-P[31] are included (as shown in 2299 Figure 15). The next Bitmap(i) is then consulted with its bits 2300 indicating which P[*] blocks follow, etc. out to the end of the 2301 Sub-Option. 2303 * Each 2-bit P[*] field is set to the value '0' ("disabled"), '1' 2304 ("low"), '2' ("medium") or '3' ("high") to indicate a QoS 2305 preference for underlying interface selection purposes. Not 2306 all P[*] values need to be included in the OMNI option of each 2307 IPv6 ND message received. Any P[*] values represented in an 2308 earlier OMNI option but omitted in the current OMNI option 2309 remain unchanged. Any P[*] values not yet represented in any 2310 OMNI option default to "medium". 2312 * The first 16 P[*] blocks correspond to the 64 Differentiated 2313 Service Code Point (DSCP) values P[00] - P[63] [RFC2474]. Any 2314 additional P[*] blocks that follow correspond to "pseudo-DSCP" 2315 traffic classifier values P[64], P[65], P[66], etc. See 2316 Appendix A for further discussion and examples. 2318 12.1.5. Traffic Selector 2319 0 1 2 3 2320 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 2321 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2322 | S-Type=4| Sub-length=N | omIndex | ~ 2323 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ 2324 ~ ~ 2325 ~ RFC 6088 Format Traffic Selector ~ 2326 ~ ~ 2327 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2329 Figure 18: Traffic Selector 2331 o Sub-Type is set to 4. If multiple instances appear in OMNI 2332 options of the same message all are processed, i.e., even if the 2333 same omIndex value appears multiple times. 2335 o Sub-Length is set to N (from 1 to 2034) that encodes the number of 2336 Sub-Option Data octets that follow. 2338 o Sub-Option Data contains a 1 octet omIndex encoded exactly as 2339 specified in Section 12.1.3, followed by an N-1 octet traffic 2340 selector formatted per [RFC6088] beginning with the "TS Format" 2341 field. The largest traffic selector for a given omIndex is 2342 therefore 2033 octets. 2344 12.1.6. MS-Register 2346 0 1 2 3 2347 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 2348 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2349 | S-Type=5| Sub-length=4n | MSID[1] (bits 0 - 15) | 2350 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2351 | MSID [1] (bits 16 - 32) | MSID[2] (bits 0 - 15) | 2352 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2353 | MSID [2] (bits 16 - 32) | MSID[3] (bits 0 - 15) | 2354 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2355 ... ... ... ... ... ... 2356 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2357 | MSID [n] (bits 16 - 32) | 2358 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2360 Figure 19: MS-Register Sub-option 2362 o Sub-Type is set to 5. If multiple instances appear in OMNI 2363 options of the same message all are processed. Only the first 2364 MAX_MSID values processed (whether in a single instance or 2365 multiple) are retained and all other MSIDs are ignored. 2367 o Sub-Length is set to 4n, with 508 as the maximum value for n. The 2368 length of the Sub-Option Data section is therefore limited to 2032 2369 octets. 2371 o A list of n 4 octet MSIDs is included in the following 4n octets. 2372 The Anycast MSID value '0' in an RS message MS-Register sub-option 2373 requests the recipient to return the MSID of a nearby MSE in a 2374 corresponding RA response. 2376 12.1.7. MS-Release 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=6| 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 20: MS-Release Sub-option 2394 o Sub-Type is set to 6. 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' is ignored in MS-Release sub-options, 2405 i.e., only non-zero values are processed. 2407 12.1.8. Geo Coordinates 2408 0 1 2 3 2409 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 2410 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2411 | S-Type=7| Sub-length=N | Geo Type |Geo Coordinates 2412 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... 2414 Figure 21: Geo Coordinates Sub-option 2416 o Sub-Type is set to 7. If multiple instances appear in OMNI 2417 options of the same message the first is processed and all others 2418 are ignored. 2420 o Sub-Length is set to N (from 0 to 2034) that encodes the number of 2421 Sub-Option Data octets that follow. 2423 o Geo Type is a 1 octet field that encodes a type designator that 2424 determines the format and contents of the Geo Coordinates field 2425 that follows. The following types are currently defined: 2427 * 0 - NULL, i.e., the Geo Coordinates field is zero-length. 2429 o A set of Geo Coordinates of length 0 - 2033 octets. New formats 2430 to be specified in future documents and may include attributes 2431 such as latitude/longitude, altitude, heading, speed, etc. 2433 12.1.9. Dynamic Host Configuration Protocol for IPv6 (DHCPv6) Message 2435 The Dynamic Host Configuration Protocol for IPv6 (DHCPv6) sub-option 2436 may be included in the OMNI options of RS messages sent by MNs and RA 2437 messages returned by MSEs. ARs that act as proxys to forward RS/RA 2438 messages between MNs and MSEs also forward DHCPv6 sub-options 2439 unchanged and do not process DHCPv6 sub-options themselves. Note 2440 that DHCPv6 message sub-option integrity is protected by the Checksum 2441 included in the IPv6 ND message header. 2443 0 1 2 3 2444 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 2445 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2446 | S-Type=8| Sub-length=N | msg-type | id (octet 0) | 2447 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2448 | transaction-id (octets 1-2) | | 2449 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 2450 | | 2451 . DHCPv6 options . 2452 . (variable number and length) . 2453 | | 2454 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2456 Figure 22: DHCPv6 Message Sub-option 2458 o Sub-Type is set to 8. If multiple instances appear in OMNI 2459 options of the same message the first is processed and all others 2460 are ignored. 2462 o Sub-Length is set to N (from 4 to 2034) that encodes the number of 2463 Sub-Option Data octets that follow. The 'msg-type' and 2464 'transaction-id' fields are always present; hence, the length of 2465 the DHCPv6 options is restricted to 2030 octets. 2467 o 'msg-type' and 'transaction-id' are coded according to Section 8 2468 of [RFC8415]. 2470 o A set of DHCPv6 options coded according to Section 21 of [RFC8415] 2471 follows. 2473 12.1.10. Host Identity Protocol (HIP) Message 2475 The Host Identity Protocol (HIP) Message sub-option may be included 2476 in the OMNI options of RS messages sent by MNs and RA messages 2477 returned by ARs. ARs that act as proxys authenticate and remove HIP 2478 messages in RS messages they forward from a MN to an MSE. ARs that 2479 act as proxys insert and sign HIP messages in the RA messages they 2480 forward from an MSE to a MN. 2482 The HIP message sub-option may also be included in any IPv6 ND 2483 message that may traverse an open Internetwork, i.e., where link- 2484 layer authentication is not already assured by lower layers. 2486 0 1 2 3 2487 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 2488 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2489 | S-Type=9| Sub-length=N |0| Packet Type |Version| RES.|1| 2490 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2491 | Checksum | Controls | 2492 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2493 | Sender's Host Identity Tag (HIT) | 2494 | | 2495 | | 2496 | | 2497 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2498 | Receiver's Host Identity Tag (HIT) | 2499 | | 2500 | | 2501 | | 2502 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2503 | | 2504 / HIP Parameters / 2505 / / 2506 | | 2507 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2509 Figure 23: HIP Message Sub-option 2511 o Sub-Type is set to 9. If multiple instances appear in OMNI 2512 options of the same message the first is processed and all others 2513 are ignored. 2515 o Sub-Length is set to N, i.e., the length of the option in octets 2516 beginning immediately following the Sub-Length field and extending 2517 to the end of the HIP parameters. The length of the entire HIP 2518 message is therefore restricted to 2034 octets. 2520 o The HIP message is coded exactly as specified in Section 5 of 2521 [RFC7401], except that the OMNI "Sub-Type" and "Sub-Length" fields 2522 replace the first 2 octets of the HIP message header (i.e., the 2523 Next Header and Header Length fields). Note that, since the IPv6 2524 ND message header already includes a Checksum, the HIP message 2525 Checksum field is set to 0 on transmission and ignored on 2526 reception. (The Checksum field is still included to retain the 2527 [RFC7401] message format.) 2529 12.1.11. Reassembly Limit 2531 The Reassembly Limit sub-option may be included in the OMNI options 2532 of IPv6 ND messages. The message consists of a 14-bit Reassembly 2533 Limit value, followed by two flag bits (H, L) optionally followed by 2534 an (N-2)-octet leading portion of an OAL First Fragment that 2535 triggered the message. 2537 0 1 2 3 2538 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 2539 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2540 |S-Type=10| Sub-length=N | Reassembly Limit |H|L| 2541 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2542 | OAL First Fragment (As much of invoking packet | 2543 + as possible without the IPv6 ND message + 2544 | exceeding the minimum IPv6 MTU) | 2545 + + 2547 Figure 24: Reassembly Limit 2549 o Sub-Type is set to 10. If multiple instances appear in OMNI 2550 options of the same message the first occurring "hard" and "soft" 2551 Reassembly Limit values are accepted, and any additional 2552 Reassembly Limit values are ignored. 2554 o Sub-Length is set to 2 if no OAL First Fragment is included, or to 2555 a value N greater than 2 if an OAL First Fragment is included. 2557 o A 14-bit Reassembly Limit follows, and includes a value between 2558 1500 and 9180. If any other value is included, the sub-option is 2559 ignored. The value indicates the hard or soft limit for original 2560 IP packets that the source of the message is currently willing to 2561 reassemble; the source may increase or decrease the hard or soft 2562 limit at any time through the transmission of new IPv6 ND 2563 messages. Until the first IPv6 ND message with a Reassembly Limit 2564 sub-option arrives, OMNI nodes assume initial default hard/soft 2565 limits of 9180 bytes (I.e., the OMNI interface MRU). After IPv6 2566 ND messages with Reassembly Limit sub-options arrive, the OMNI 2567 node retains the most recent hard/soft limit values until new IPv6 2568 ND messages with different values arrive. 2570 o The 'H' flag is set to 1 if the Reassembly Limit is a "Hard" 2571 limit, and set to 0 if the Reassembly Limit is a "Soft" limit. 2573 o The 'L' flag is set to 1 if an OAL First Fragment corresponding to 2574 a reassembly loss event was included; otherwise set to 0. 2576 o If N is greater than 2, the remainder of the Reassembly Limit sub- 2577 option encodes the leading portion of an OAL First Fragment that 2578 prompted this IPv6 ND message. The first fragment is included 2579 beginning with the OAL IPv6 header, and continuing with as much of 2580 the fragment payload as possible without causing the IPv6 ND 2581 message to exceed the minimum IPv6 MTU. (Note that only the OAL 2582 First Fragment is consulted regardless of its size, and without 2583 waiting for additional fragments.) 2585 12.1.12. Fragmentation Report 2587 The Fragmentation Report may be included in the OMNI options of uNA 2588 messages sent from an OAL destination to an OAL source. The message 2589 consists of (N / 8)-many (Identification, Bitmap)-tuples which 2590 include the Identification values of OAL fragments received plus a 2591 Bitmap marking the ordinal positions of individual fragments received 2592 and fragments missing. 2594 0 1 2 3 2595 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 2596 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2597 |S-Type=11| Sub-Length = N | Identification #1 (bits 0 -15)| 2598 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2599 | Identification #1 (bits 15-31)| Bitmap #1 (bits 0 - 15) | 2600 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2601 | Bitmap #1 (bits 16-31) | Identification #2 (bits 0 -15)| 2602 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2603 | Identification #2 (bits 15-31)| Bitmap #2 (bits 0 - 15) | 2604 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2605 | Bitmap #2 (bits 16-31) | Identification #3 (bits 0 -15)| 2606 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2607 | Identification #3 (bits 15-31)| Bitmap #3 (bits 0 - 15) | 2608 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2609 | Bitmap #3 (bits 16-31) | ... | 2610 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... + 2611 | ... | 2612 + ... + 2614 Figure 25: Fragmentation Report 2616 o Sub-Type is set to 11. If multiple instances appear in OMNI 2617 options of the same message all are processed. 2619 o Sub-Length is set to N, i.e., the length of the option in octets 2620 beginning immediately following the Sub-Length field and extending 2621 to the end of the ICMPv6 error message body. N must be an 2622 integral multiple of 8 octets; otherwise, the sub-option is 2623 ignored. The length of the entire sub-option should not cause the 2624 entire IPv6 ND message to exceed the minimum MPS. 2626 o Identification (i) includes the IPv6 Identification value found in 2627 the Fragment Header of a received OAL fragment. (Only those 2628 Identification values included represent fragments for which loss 2629 was unambiguously observed; any Identification values not included 2630 correspond to fragments that were either received in their 2631 entirety or are still in transit.) 2633 o Bitmap (i) includes an ordinal checklist of fragments, with each 2634 bit set to 1 for a fragment received or 0 for a fragment missing. 2635 For example, for a 20-fragment fragmented OAL packet with ordinal 2636 fragments #3, #10, #13 and #17 missing and all other fragments 2637 received, the bitmap would encode: 2639 0 1 2 2640 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 2641 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 2642 |1|1|1|0|1|1|1|1|1|1|0|1|1|0|1|1|1|0|1|1|0|0|0|... 2643 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 2645 Figure 26 2647 (Note that loss of an OAL atomic fragment is indicated by a 2648 Bitmap(i) with all bits set to 0.) 2650 12.1.13. Node Identification 2652 0 1 2 3 2653 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 2654 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2655 |S-Type=12| Sub-length=N | ID-Type | ~ 2656 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ 2657 ~ Node Identification Value (N-1 octets) ~ 2658 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2660 Figure 27: Node Identification 2662 o Sub-Type is set to 12. If multiple instances appear in OMNI 2663 options of the same IPv6 ND message the first instance of a 2664 specific ID-Type is processed and all other instances of the same 2665 ID-Type are ignored. (Note therefore that it is possible for a 2666 single IPv6 ND message to convey multiple Node Identifications - 2667 each having a different ID-Type.) 2669 o Sub-Length is set to N (from 1 to 2034) that encodes the number of 2670 Sub-Option Data octets that follow. The ID-Type field is always 2671 present; hence, the maximum Node Identification Value length is 2672 2033 octets. 2674 o ID-Type is a 1 octet field that encodes the type of the Node 2675 Identification Value. The following ID-Type values are currently 2676 defined: 2678 * 0 - Universally Unique IDentifier (UUID) [RFC4122]. Indicates 2679 that Node Identification Value contains a 16 octet UUID. 2681 * 1 - Host Identity Tag (HIT) [RFC7401]. Indicates that Node 2682 Identification Value contains a 16 octet HIT. 2684 * 2 - Hierarchical HIT (HHIT) [I-D.ietf-drip-rid]. Indicates 2685 that Node Identification Value contains a 16 octet HHIT. 2687 * 3 - Network Access Identifier (NAI) [RFC7542]. Indicates that 2688 Node Identification Value contains an N-1 octet NAI. 2690 * 4 - Fully-Qualified Domain Name (FQDN) [RFC1035]. Indicates 2691 that Node Identification Value contains an N-1 octet FQDN. 2693 * 5 - 252 - Unassigned. 2695 * 253-254 - Reserved for experimentation, as recommended in 2696 [RFC3692]. 2698 * 255 - reserved by IANA. 2700 o Node Identification Value is an (N - 1) octet field encoded 2701 according to the appropriate the "ID-Type" reference above. 2703 When a Node Identification Value is needed for DHCPv6 messaging 2704 purposes, it is encoded as a DHCP Unique IDentifier (DUID) using the 2705 "DUID-EN for OMNI" format with enterprise number 45282 (see: 2706 Section 25) as shown in Figure 28: 2708 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 2709 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2710 | DUID-Type (2) | EN (high bits == 0) | 2711 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2712 | EN (low bits = 45282) | ID-Type | | 2713 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 2714 . Node Identification Value . 2715 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2717 Figure 28: DUID-EN for OMNI Format 2719 In this format, the ID-Type and Node Identification Value fields are 2720 coded exactly as in Figure 27 following the 6 octet DUID-EN header, 2721 and the entire "DUID-EN for OMNI" is included in a DHCPv6 message per 2722 [RFC8415]. 2724 12.1.14. Sub-Type Extension 2726 Since the Sub-Type field is only 5 bits in length, future 2727 specifications of major protocol functions may exhaust the remaining 2728 Sub-Type values available for assignment. This document therefore 2729 defines Sub-Type 30 as an "extension", meaning that the actual sub- 2730 option type is determined by examining a 1 octet "Extension-Type" 2731 field immediately following the Sub-Length field. The Sub-Type 2732 Extension is formatted as shown in Figure 29: 2734 0 1 2 3 2735 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 2736 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2737 |S-Type=30| Sub-length=N | Extension-Type| ~ 2738 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ 2739 ~ ~ 2740 ~ Extension-Type Body ~ 2741 ~ ~ 2742 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2744 Figure 29: Sub-Type Extension 2746 o Sub-Type is set to 30. If multiple instances appear in OMNI 2747 options of the same message all are processed, where each 2748 individual extension defines its own policy for processing 2749 multiple of that type. 2751 o Sub-Length is set to N (from 1 to 2034) that encodes the number of 2752 Sub-Option Data octets that follow. The Extension-Type field is 2753 always present; hence, the maximum Extension-Type Body length is 2754 2033 octets. 2756 o Extension-Type contains a 1 octet Sub-Type Extension value between 2757 0 and 255. 2759 o Extension-Type Body contains an N-1 octet block with format 2760 defined by the given extension specification. 2762 Extension-Type values 2 through 252 are available for assignment by 2763 future specifications, which must also define the format of the 2764 Extension-Type Body and its processing rules. Extension-Type values 2765 253 and 254 are reserved for experimentation, as recommended in 2766 [RFC3692], and value 255 is reserved by IANA. Extension-Type values 2767 0 and 1 are defined in the following subsections: 2769 12.1.14.1. RFC4380 UDP/IP Header Option 2771 0 1 2 3 2772 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 2773 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2774 |S-Type=30| Sub-length=N | Ext-Type=0 | Header Type | 2775 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2776 ~ Header Option Value ~ 2777 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2779 Figure 30: RFC4380 UDP/IP Header Option (Extension-Type 0) 2781 o Sub-Type is set to 30. 2783 o Sub-Length is set to N (from 2 to 2034) that encodes the number of 2784 Sub-Option Data octets that follow. The Extension-Type and Header 2785 Type fields are always present; hence, the maximum-length Header 2786 Option Value is 2032 octets. 2788 o Extension-Type is set to 0. Each instance encodes exactly one 2789 header option per Section 5.1.1 of [RFC4380], with the leading '0' 2790 octet omitted and the following octet coded as Header Type. If 2791 multiple instances of the same Header Type appear in OMNI options 2792 of the same message the first instance is processed and all others 2793 are ignored. 2795 o Header Type and Header Option Value are coded exactly as specified 2796 in Section 5.1.1 of [RFC4380]; the following types are currently 2797 defined: 2799 * 0 - Origin Indication (IPv4) - value coded per Section 5.1.1 of 2800 [RFC4380]. 2802 * 1 - Authentication Encapsulation - value coded per 2803 Section 5.1.1 of [RFC4380]. 2805 * 2 - Origin Indication (IPv6) - value coded per Section 5.1.1 of 2806 [RFC4380], except that the address is a 16-octet IPv6 address 2807 instead of a 4-octet IPv4 address. 2809 o Header Type values 3 through 252 are available for assignment by 2810 future specifications, which must also define the format of the 2811 Header Option Value and its processing rules. Header Type values 2812 253 and 254 are reserved for experimentation, as recommended in 2813 [RFC3692], and value 255 is Reserved by IANA. 2815 12.1.14.2. RFC6081 UDP/IP Trailer Option 2817 0 1 2 3 2818 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 2819 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2820 |S-Type=30| Sub-length=N | Ext-Type=1 | Trailer Type | 2821 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2822 ~ Trailer Option Value ~ 2823 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2825 Figure 31: RFC6081 UDP/IP Trailer Option (Extension-Type 1) 2827 o Sub-Type is set to 30. 2829 o Sub-Length is set to N (from 2 to 2034) that encodes the number of 2830 Sub-Option Data octets that follow. The Extension-Type and 2831 Trailer Type fields are always present; hence, the maximum-length 2832 Trailer Option Value is 2032 octets. 2834 o Extension-Type is set to 1. Each instance encodes exactly one 2835 trailer option per Section 4 of [RFC6081]. If multiple instances 2836 of the same trailer type appear in OMNI options of the same 2837 message the first instance is processed and all others ignored. 2839 o Trailer Type and Trailer Option Value are coded exactly as 2840 specified in Section 4 of [RFC6081]; the following Trailer Types 2841 are currently defined: 2843 * 0 - Unassigned 2845 * 1 - Nonce Trailer - value coded per Section 4.2 of [RFC6081]. 2847 * 2 - Unassigned 2849 * 3 - Alternate Address Trailer (IPv4) - value coded per 2850 Section 4.3 of [RFC6081]. 2852 * 4 - Neighbor Discovery Option Trailer - value coded per 2853 Section 4.4 of [RFC6081]. 2855 * 5 - Random Port Trailer - value coded per Section 4.5 of 2856 [RFC6081]. 2858 * 6 - Alternate Address Trailer (IPv6) - value coded per 2859 Section 4.3 of [RFC6081], except that each address is a 2860 16-octet IPv6 address instead of a 4-octet IPv4 address. 2862 o Trailer Type values 7 through 252 are available for assignment by 2863 future specifications, which must also define the format of the 2864 Trailer Option Value and its processing rules. Trailer Type 2865 values 253 and 254 are reserved for experimentation, as 2866 recommended in [RFC3692], and value 255 is Reserved by IANA. 2868 13. Address Mapping - Multicast 2870 The multicast address mapping of the native underlying interface 2871 applies. The mobile router on board the MN also serves as an IGMP/ 2872 MLD Proxy for its EUNs and/or hosted applications per [RFC4605] while 2873 using the L2 address of the AR as the L2 address for all multicast 2874 packets. 2876 The MN uses Multicast Listener Discovery (MLDv2) [RFC3810] to 2877 coordinate with the AR, and *NET L2 elements use MLD snooping 2878 [RFC4541]. 2880 14. Multilink Conceptual Sending Algorithm 2882 The MN's IPv6 layer selects the outbound OMNI interface according to 2883 SBM considerations when forwarding original IP packets from local or 2884 EUN applications to external correspondents. Each OMNI interface 2885 maintains a neighbor cache the same as for any IPv6 interface, but 2886 with additional state for multilink coordination. Each OMNI 2887 interface maintains default routes via ARs discovered as discussed in 2888 Section 15, and may configure more-specific routes discovered through 2889 means outside the scope of this specification. 2891 After an original IP packet enters the OMNI interface, one or more 2892 outbound underlying interfaces are selected based on PBM traffic 2893 attributes, and one or more neighbor underlying interfaces are 2894 selected based on the receipt of Interface Attributes sub-options in 2895 IPv6 ND messages (see: Figure 15). Underlying interface selection 2896 for the nodes own local interfaces are based on attributes such as 2897 DSCP, application port number, cost, performance, message size, etc. 2898 OMNI interface multilink selections could also be configured to 2899 perform replication across multiple underlying interfaces for 2900 increased reliability at the expense of packet duplication. The set 2901 of all Interface Attributes received in IPv6 ND messages determines 2902 the multilink forwarding profile for selecting the neighbor's 2903 underlying interfaces. 2905 When the OMNI interface sends an original IP packet over a selected 2906 outbound underlying interface, the OAL employs encapsulation and 2907 fragmentation as discussed in Section 5, then performs *NET 2908 encapsulation as determined by the L2 address information received in 2909 Interface Attributes. The OAL also performs encapsulation when the 2910 nearest AR is located multiple hops away as discussed in 2911 Section 15.1. (Note that the OAL MAY employ packing when multiple 2912 original IP packets and/or control messages are available for 2913 forwarding to the same OAL destination.) 2915 OMNI interface multilink service designers MUST observe the BCP 2916 guidance in Section 15 [RFC3819] in terms of implications for 2917 reordering when original IP packets from the same flow may be spread 2918 across multiple underlying interfaces having diverse properties. 2920 14.1. Multiple OMNI Interfaces 2922 MNs may connect to multiple independent OMNI links concurrently in 2923 support of SBM. Each OMNI interface is distinguished by its Anycast 2924 ULA (e.g., [ULA]:0002::, [ULA]:1000::, [ULA]:7345::, etc.). The MN 2925 configures a separate OMNI interface for each link so that multiple 2926 interfaces (e.g., omni0, omni1, omni2, etc.) are exposed to the IPv6 2927 layer. A different Anycast ULA is assigned to each interface, and 2928 the MN injects the service prefixes for the OMNI link instances into 2929 the EUN routing system. 2931 Applications in EUNs can use Segment Routing to select the desired 2932 OMNI interface based on SBM considerations. The Anycast ULA is 2933 written into an original IP packet's IPv6 destination address, and 2934 the actual destination (along with any additional intermediate hops) 2935 is written into the Segment Routing Header. Standard IP routing 2936 directs the packet to the MN's mobile router entity, and the Anycast 2937 ULA identifies the OMNI interface to be used for transmission to the 2938 next hop. When the MN receives the packet, it replaces the IPv6 2939 destination address with the next hop found in the routing header and 2940 transmits the message over the OMNI interface identified by the 2941 Anycast ULA. 2943 Multiple distinct OMNI links can therefore be used to support fault 2944 tolerance, load balancing, reliability, etc. The architectural model 2945 is similar to Layer 2 Virtual Local Area Networks (VLANs). 2947 14.2. MN<->AR Traffic Loop Prevention 2949 After an AR has registered an MNP for a MN (see: Section 15), the AR 2950 will forward packets destined to an address within the MNP to the MN. 2951 The MN will under normal circumstances then forward the packet to the 2952 correct destination within its internal networks. 2954 If at some later time the MN loses state (e.g., after a reboot), it 2955 may begin returning packets destined to an MNP address to the AR as 2956 its default router. The AR therefore must drop any packets 2957 originating from the MN and destined to an address within the MN's 2958 registered MNP. To do so, the AR institutes the following check: 2960 o if the IP destination address belongs to a neighbor on the same 2961 OMNI interface, and if the link-layer source address is the same 2962 as one of the neighbor's link-layer addresses, drop the packet. 2964 15. Router Discovery and Prefix Registration 2966 MNs interface with the MS by sending RS messages with OMNI options 2967 under the assumption that one or more AR on the *NET will process the 2968 message and respond. The MN then configures default routes for the 2969 OMNI interface via the discovered ARs as the next hop. The manner in 2970 which the *NET ensures AR coordination is link-specific and outside 2971 the scope of this document (however, considerations for *NETs that do 2972 not provide ARs that recognize the OMNI option are discussed in 2973 Section 20). 2975 For each underlying interface, the MN sends an RS message with an 2976 OMNI option to coordinate with MSEs identified by MSID values. 2977 Example MSID discovery methods are given in [RFC5214] and include 2978 data link login parameters, name service lookups, static 2979 configuration, a static "hosts" file, etc. When the AR receives an 2980 RS', it selects a nearby MSE (which may be itself) and returns an RA 2981 with the selected MSID in an MS-Register sub-option. The AR selects 2982 only a single nearby MSE while also soliciting the MSEs corresponding 2983 to any non-zero MSIDs. 2985 MNs configure OMNI interfaces that observe the properties discussed 2986 in the previous section. The OMNI interface and its underlying 2987 interfaces are said to be in either the "UP" or "DOWN" state 2988 according to administrative actions in conjunction with the interface 2989 connectivity status. An OMNI interface transitions to UP or DOWN 2990 through administrative action and/or through state transitions of the 2991 underlying interfaces. When a first underlying interface transitions 2992 to UP, the OMNI interface also transitions to UP. When all 2993 underlying interfaces transition to DOWN, the OMNI interface also 2994 transitions to DOWN. 2996 When an OMNI interface transitions to UP, the MN sends RS messages to 2997 register its MNP and an initial set of underlying interfaces that are 2998 also UP. The MN sends additional RS messages to refresh lifetimes 2999 and to register/deregister underlying interfaces as they transition 3000 to UP or DOWN. The MN's OMNI interface sends initial RS messages 3001 over an UP underlying interface with its MNP-LLA as the source (or 3002 with the unspecified address (::) as the source if it does not yet 3003 have an MNP-LLA) and with destination set to link-scoped All-Routers 3004 multicast (ff02::2) [RFC4291]. The OMNI interface includes an OMNI 3005 option per Section 12 with a Preflen assertion, Interface Attributes 3006 appropriate for underlying interfaces, MS-Register/Release sub- 3007 options containing MSID values, Reassembly Limits, an authentication 3008 sub-option and with any other necessary OMNI sub-options (e.g., a 3009 Node Identification sub-option as an identity for the MN). The OMNI 3010 interface then sets the S/T-omIndex field to the index of the 3011 underlying interface over which the RS message is sent. 3013 The OMNI interface then sends the RS over the underlying interface 3014 using OAL encapsulation and fragmentation if necessary. If OAL 3015 encapsulation is used for RS messages sent over an INET interface, 3016 the entire RS message must appear within a single carrier packet so 3017 that it can be authenticated without requiring reassembly. The OMNI 3018 interface selects an unpredictable initial Identification value per 3019 Section 6.5, sets the OAL source address to the ULA corresponding to 3020 the RS source (Or a Temporary ULA if the RS source is the unspecified 3021 address (::)) and sets the OAL destination to site-scoped All-Routers 3022 multicast (ff05::2) then sends the message. 3024 ARs process IPv6 ND messages with OMNI options and act as an MSE 3025 themselves and/or as a proxy for other MSEs. ARs receive RS messages 3026 and create a neighbor cache entry for the MN, then prepare to act as 3027 an MSE themselves and/or coordinate with any MSEs named in the 3028 Register/Release lists in a manner outside the scope of this 3029 document. When an MSE processes the OMNI information, it first 3030 validates the prefix registration information then injects/withdraws 3031 the MNP in the routing/mapping system and caches/discards the new 3032 Preflen, MNP and Interface Attributes. The MSE then informs the AR 3033 of registration success/failure, and the AR returns an RA message to 3034 the MN with an OMNI option per Section 12. 3036 The AR's OMNI interface returns the RA message via the same 3037 underlying interface of the MN over which the RS was received, and 3038 with destination address set to the MNP-LLA (i.e., unicast), with 3039 source address set to its own LLA, and with an OMNI option with S/ 3040 T-omIndex set to the value included in the RS. The OMNI option also 3041 includes a Preflen confirmation, Interface Attributes, MS-Register/ 3042 Release and any other necessary OMNI sub-options (e.g., a Node 3043 Identification sub-option as an identity for the AR). The RA also 3044 includes any information for the link, including RA Cur Hop Limit, M 3045 and O flags, Router Lifetime, Reachable Time and Retrans Timer 3046 values, and includes any necessary options such as: 3048 o PIOs with (A; L=0) that include MSPs for the link [RFC8028]. 3050 o RIOs [RFC4191] with more-specific routes. 3052 o an MTU option that specifies the maximum acceptable packet size 3053 for this underlying interface. 3055 If the RS message arrived as an OAL atomic fragment, the AR prepares 3056 the RA using OAL encapsulation/fragmentation with the same 3057 Identification value that appeared in the RS message, with source set 3058 to the ULA corresponding to the RA source and with destination set to 3059 the ULA corresponding to the RA destination. The AR then sends the 3060 initial RA message to the MN and MAY later send additional periodic 3061 and/or event-driven unsolicited RA messages per [RFC4861]. In that 3062 case, the S/T-omIndex field in the OMNI option of the unsolicited RA 3063 message identifies the target underlying interface of the destination 3064 MN. 3066 The AR can combine the information from multiple MSEs into one or 3067 more "aggregate" RAs sent to the MN in order conserve *NET bandwidth. 3068 Each aggregate RA includes an OMNI option with MS-Register/Release 3069 sub-options with the MSEs represented by the aggregate. If an 3070 aggregate is sent, the RA message contents must consistently 3071 represent the combined information advertised by all represented 3072 MSEs. Note that since the AR uses its own ADM-LLA as the RA source 3073 address, the MN determines the addresses of the represented MSEs by 3074 examining the MS-Register/Release OMNI sub-options. 3076 When the MN receives the RA message, it creates an OMNI interface 3077 neighbor cache entry for each MSID that has confirmed MNP 3078 registration via the L2 address of this AR. If the MN connects to 3079 multiple *NETs, it records the additional L2 AR addresses in each 3080 MSID neighbor cache entry (i.e., as multilink neighbors). The MN 3081 then configures a default route via the MSE that returned the RA 3082 message, and assigns the Subnet Router Anycast address corresponding 3083 to the MNP (e.g., 2001:db8:1:2::) to the OMNI interface. The MN then 3084 manages its underlying interfaces according to their states as 3085 follows: 3087 o When an underlying interface transitions to UP, the MN sends an RS 3088 over the underlying interface with an OMNI option. The OMNI 3089 option contains at least one Interface Attribute sub-option with 3090 values specific to this underlying interface, and may contain 3091 additional Interface Attributes specific to other underlying 3092 interfaces. The option also includes any MS-Register/Release sub- 3093 options. 3095 o When an underlying interface transitions to DOWN, the MN sends an 3096 RS or unsolicited NA message over any UP underlying interface with 3097 an OMNI option containing an Interface Attribute sub-option for 3098 the DOWN underlying interface with Link set to '0'. The MN sends 3099 an RS when an acknowledgement is required, or an unsolicited NA 3100 when reliability is not thought to be a concern (e.g., if 3101 redundant transmissions are sent on multiple underlying 3102 interfaces). 3104 o When the Router Lifetime for a specific AR nears expiration, the 3105 MN sends an RS over the underlying interface to receive a fresh 3106 RA. If no RA is received, the MN can send RS messages to an 3107 alternate MSID in case the current MSID has failed. If no RS 3108 messages are received even after trying to contact alternate 3109 MSIDs, the MN marks the underlying interface as DOWN. 3111 o When a MN wishes to release from one or more current MSIDs, it 3112 sends an RS or unsolicited NA message over any UP underlying 3113 interfaces with an OMNI option with a Release MSID. Each MSID 3114 then withdraws the MNP from the routing/mapping system and informs 3115 the AR that the release was successful. 3117 o When all of a MNs underlying interfaces have transitioned to DOWN 3118 (or if the prefix registration lifetime expires), any associated 3119 MSEs withdraw the MNP the same as if they had received a message 3120 with a release indication. 3122 The MN is responsible for retrying each RS exchange up to 3123 MAX_RTR_SOLICITATIONS times separated by RTR_SOLICITATION_INTERVAL 3124 seconds until an RA is received. If no RA is received over an UP 3125 underlying interface (i.e., even after attempting to contact 3126 alternate MSEs), the MN declares this underlying interface as DOWN. 3128 The IPv6 layer sees the OMNI interface as an ordinary IPv6 interface. 3129 Therefore, when the IPv6 layer sends an RS message the OMNI interface 3130 returns an internally-generated RA message as though the message 3131 originated from an IPv6 router. The internally-generated RA message 3132 contains configuration information that is consistent with the 3133 information received from the RAs generated by the MS. Whether the 3134 OMNI interface IPv6 ND messaging process is initiated from the 3135 receipt of an RS message from the IPv6 layer is an implementation 3136 matter. Some implementations may elect to defer the IPv6 ND 3137 messaging process until an RS is received from the IPv6 layer, while 3138 others may elect to initiate the process proactively. Still other 3139 deployments may elect to administratively disable the ordinary RS/RA 3140 messaging used by the IPv6 layer over the OMNI interface, since they 3141 are not required to drive the internal RS/RA processing. (Note that 3142 this same logic applies to IPv4 implementations that employ ICMP- 3143 based Router Discovery per [RFC1256].) 3145 Note: The Router Lifetime value in RA messages indicates the time 3146 before which the MN must send another RS message over this underlying 3147 interface (e.g., 600 seconds), however that timescale may be 3148 significantly longer than the lifetime the MS has committed to retain 3149 the prefix registration (e.g., REACHABLETIME seconds). ARs are 3150 therefore responsible for keeping MS state alive on a shorter 3151 timescale than the MN is required to do on its own behalf. 3153 Note: On multicast-capable underlying interfaces, MNs should send 3154 periodic unsolicited multicast NA messages and ARs should send 3155 periodic unsolicited multicast RA messages as "beacons" that can be 3156 heard by other nodes on the link. If a node fails to receive a 3157 beacon after a timeout value specific to the link, it can initiate a 3158 unicast exchange to test reachability. 3160 Note: if an AR acting as a proxy forwards a MN's RS message to 3161 another node acting as an MSE using UDP/IP encapsulation, it must use 3162 a distinct UDP source port number for each MN. This allows the MSE 3163 to distinguish different MNs behind the same AR at the link-layer, 3164 whereas the link-layer addresses would otherwise be 3165 indistinguishable. 3167 Note: when an AR acting as an MSE returns an RA to an INET Client, it 3168 includes an OMNI option with an Interface Attributes sub-option with 3169 omIndex set to 0 and with SRT, FMT, LHS and L2ADDR information for 3170 its INET interface. This provides the Client with partition prefix 3171 context regarding the local OMNI link segment. 3173 15.1. Router Discovery in IP Multihop and IPv4-Only Networks 3175 On some *NETs, a MN may be located multiple IP hops away from the 3176 nearest AR. Forwarding through IP multihop *NETs is conducted 3177 through the application of a routing protocol (e.g., a MANET/VANET 3178 routing protocol over omni-directional wireless interfaces, an inter- 3179 domain routing protocol in an enterprise network, etc.). These *NETs 3180 could be either IPv6-enabled or IPv4-only, while IPv4-only *NETs 3181 could be either multicast-capable or unicast-only (note that for 3182 IPv4-only *NETs the following procedures apply for both single-hop 3183 and multihop cases). 3185 A MN located potentially multiple *NET hops away from the nearest AR 3186 prepares an RS message with source address set to its MNP-LLA (or to 3187 the unspecified address (::) if it does not yet have an MNP-LLA), and 3188 with destination set to link-scoped All-Routers multicast the same as 3189 discussed above. The OMNI interface then employs OAL encapsulation 3190 and fragmentation, and sets the OAL source address to the ULA 3191 corresponding to the RS source (or to a Temporary ULA if the RS 3192 source was the unspecified address (::)) and sets the OAL destination 3193 to site-scoped All-Routers multicast (ff05::2). For IPv6-enabled 3194 *NETs, the MN then encapsulates the message in UDP/IPv6 headers with 3195 source address set to the underlying interface address (or to the ULA 3196 that would be used for OAL encapsulation if the underlying interface 3197 does not yet have an address) and sets the destination to either a 3198 unicast or anycast address of an AR. For IPv4-only *NETs, the MN 3199 instead encapsulates the RS message in UDP/IPv4 headers with source 3200 address set to the IPv4 address of the underlying interface and with 3201 destination address set to either the unicast IPv4 address of an AR 3202 [RFC5214] or an IPv4 anycast address reserved for OMNI. The MN then 3203 sends the encapsulated RS message via the *NET interface, where it 3204 will be forwarded by zero or more intermediate *NET hops. 3206 When an intermediate *NET hop that participates in the routing 3207 protocol receives the encapsulated RS, it forwards the message 3208 according to its routing tables (note that an intermediate node could 3209 be a fixed infrastructure element or another MN). This process 3210 repeats iteratively until the RS message is received by a penultimate 3211 *NET hop within single-hop communications range of an AR, which 3212 forwards the message to the AR. 3214 When the AR receives the message, it decapsulates the RS (while 3215 performing OAL reassembly, if necessary) and coordinates with the MS 3216 the same as for an ordinary link-local RS, since the network layer 3217 Hop Limit will not have been decremented by the multihop forwarding 3218 process. The AR then prepares an RA message with source address set 3219 to its own ADM-LLA and destination address set to the LLA of the 3220 original MN. The AR then performs OAL encapsulation and 3221 fragmentation, with OAL source set to its own ADM-ULA and destination 3222 set to the ULA corresponding to the RA source. The AR then 3223 encapsulates the message in UDP/IPv4 or UDP/IPv6 headers with source 3224 address set to its own address and with destination set to the 3225 encapsulation source of the RS. 3227 The AR then forwards the message to an *NET node within 3228 communications range, which forwards the message according to its 3229 routing tables to an intermediate node. The multihop forwarding 3230 process within the *NET continues repetitively until the message is 3231 delivered to the original MN, which decapsulates the message and 3232 performs autoconfiguration the same as if it had received the RA 3233 directly from the AR as an on-link neighbor. 3235 Note: An alternate approach to multihop forwarding via IPv6 3236 encapsulation would be for the MN and AR to statelessly translate the 3237 IPv6 LLAs into ULAs and forward the RS/RA messages without 3238 encapsulation. This would violate the [RFC4861] requirement that 3239 certain IPv6 ND messages must use link-local addresses and must not 3240 be accepted if received with Hop Limit less than 255. This document 3241 therefore mandates encapsulation since the overhead is nominal 3242 considering the infrequent nature and small size of IPv6 ND messages. 3244 Future documents may consider encapsulation avoidance through 3245 translation while updating [RFC4861]. 3247 Note: An alternate approach to multihop forwarding via IPv4 3248 encapsulation would be to employ IPv6/IPv4 protocol translation. 3249 However, for IPv6 ND messages the LLAs would be truncated due to 3250 translation and the OMNI Router and Prefix Discovery services would 3251 not be able to function. The use of IPv4 encapsulation is therefore 3252 indicated. 3254 Note: An IPv4 anycast address for OMNI in IPv4 networks could be part 3255 of a new IPv4 /24 prefix allocation, but this may be difficult to 3256 obtain given IPv4 address exhaustion. An alternative would be to re- 3257 purpose the prefix 192.88.99.0 which has been set aside from its 3258 former use by [RFC7526]. 3260 15.2. MS-Register and MS-Release List Processing 3262 OMNI links maintain a constant value "MAX_MSID" selected to provide 3263 MNs with an acceptable level of MSE redundancy while minimizing 3264 control message amplification. It is RECOMMENDED that MAX_MSID be 3265 set to the default value 5; if a different value is chosen, it should 3266 be set uniformly by all nodes on the OMNI link. 3268 When a MN sends an RS message with an OMNI option via an underlying 3269 interface to an AR, the MN must convey its knowledge of its 3270 currently-associated MSEs. Initially, the MN will have no associated 3271 MSEs and should therefore send its initial RS messages to the link- 3272 scoped All-Routers multicast address. The AR will then return an RA 3273 message with source address set to the ADM-LLA of the selected MSE 3274 (which may be the address of the AR itself). 3276 As the MN activates additional underlying interfaces, it can 3277 optionally include an MS-Register sub-option with MSIDs for MSEs 3278 discovered from previous RS/RA exchanges. The MN will thus 3279 eventually begin to learn and manage its currently active set of 3280 MSEs, and can register with new MSEs or release from former MSEs with 3281 each successive RS/RA exchange. As the MN's MSE constituency grows, 3282 it alone is responsible for including or omitting MSIDs in the MS- 3283 Register/Release lists it sends in RS messages. The inclusion or 3284 omission of MSIDs determines the MN's interface to the MS and defines 3285 the manner in which MSEs will respond. The only limiting factor is 3286 that the MN should include no more than MAX_MSID values in each list 3287 per each IPv6 ND message, and should avoid duplication of entries in 3288 each list unless it wants to increase likelihood of control message 3289 delivery. 3291 When an AR receives an RS message sent by a MN with an OMNI option, 3292 the option will contain zero or more MS-Register and MS-Release sub- 3293 options containing MSIDs. After processing the OMNI option, the AR 3294 will have a list of zero or more MS-Register MSIDs and a list of zero 3295 or more of MS-Release MSIDs. The AR then processes the lists as 3296 follows: 3298 o For each list, retain the first MAX_MSID values in the list and 3299 discard any additional MSIDs (i.e., even if there are duplicates 3300 within a list). 3302 o Next, for each MSID in the MS-Register list, remove all matching 3303 MSIDs from the MS-Release list. 3305 o Next, proceed as follows: 3307 * If the AR's own MSID appears in the MS-Register list, send an 3308 RA message directly back to the MN and send a proxy copy of the 3309 RS message to each additional MSID in the MS-Register list with 3310 the MS-Register/Release lists omitted. Then, send an 3311 unsolicited NA (uNA) message to each MSID in the MS-Release 3312 list with the MS-Register/Release lists omitted and with an 3313 OMNI option with S/T-omIndex set to 0. 3315 * Otherwise, send a proxy copy of the RS message to each 3316 additional MSID in the MS-Register list with the MS-Register 3317 list omitted. For the first MSID, include the original MS- 3318 Release list; for all other MSIDs, omit the MS-Release list. 3320 Each proxy copy of the RS message will include an OMNI option and OAL 3321 encapsulation header with the ADM-ULA of the AR as the source and the 3322 ADM-ULA of the Register MSE as the destination. When the Register 3323 MSE receives the proxy RS message, if the message includes an MS- 3324 Release list the MSE sends a uNA message to each additional MSID in 3325 the Release list with an OMNI option with S/T-omIndex set to 0. The 3326 Register MSE then sends an RA message back to the (Proxy) AR wrapped 3327 in an OAL encapsulation header with source and destination addresses 3328 reversed, and with RA destination set to the MNP-LLA of the MN. When 3329 the AR receives this RA message, it sends a proxy copy of the RA to 3330 the MN. 3332 Each uNA message (whether sent by the first-hop AR or by a Register 3333 MSE) will include an OMNI option and an OAL encapsulation header with 3334 the ADM-ULA of the Register MSE as the source and the ADM-ULA of the 3335 Release MSE as the destination. The uNA informs the Release MSE that 3336 its previous relationship with the MN has been released and that the 3337 source of the uNA message is now registered. The Release MSE must 3338 then note that the subject MN of the uNA message is now "departed", 3339 and forward any subsequent packets destined to the MN to the Register 3340 MSE. 3342 Note that it is not an error for the MS-Register/Release lists to 3343 include duplicate entries. If duplicates occur within a list, the AR 3344 will generate multiple proxy RS and/or uNA messages - one for each 3345 copy of the duplicate entries. 3347 15.3. DHCPv6-based Prefix Registration 3349 When a MN is not pre-provisioned with an MNP-LLA (or, when the MN 3350 requires additional MNP delegations), it requests the MSE to select 3351 MNPs on its behalf and set up the correct routing state within the 3352 MS. The DHCPv6 service [RFC8415] supports this requirement. 3354 When an MN needs to have the MSE select MNPs, it sends an RS message 3355 with source set to the unspecified address (::) if it has no 3356 MNP_LLAs. If the MN requires only a single MNP delegation, it can 3357 then include a Node Identification sub-option in the OMNI option and 3358 set Preflen to the length of the desired MNP. If the MN requires 3359 multiple MNP delegations and/or more complex DHCPv6 services, it 3360 instead includes a DHCPv6 Message sub-option containing a Client 3361 Identifier, one or more IA_PD options and a Rapid Commit option then 3362 sets the 'msg-type' field to "Solicit", and includes a 3 octet 3363 'transaction-id'. The MN then sets the RS destination to All-Routers 3364 multicast and sends the message using OAL encapsulation and 3365 fragmentation if necessary as discussed above. 3367 When the MSE receives the RS message, it performs OAL reassembly if 3368 necessary. Next, if the RS source is the unspecified address (::) 3369 and/or the OMNI option includes a DHCPv6 message sub-option, the MSE 3370 acts as a "Proxy DHCPv6 Client" in a message exchange with the 3371 locally-resident DHCPv6 server. If the RS did not contain a DHCPv6 3372 message sub-option, the MSE generates a DHCPv6 Solicit message on 3373 behalf of the MN using an IA_PD option with the prefix length set to 3374 the OMNI header Preflen value and with a Client Identifier formed 3375 from the OMNI option Node Identification sub-option; otherwise, the 3376 MSE uses the DHCPv6 Solicit message contained in the OMNI option. 3377 The MSE then sends the DHCPv6 message to the DHCPv6 Server, which 3378 delegates MNPs and returns a DHCPv6 Reply message with PD parameters. 3379 (If the MSE wishes to defer creation of MN state until the DHCPv6 3380 Reply is received, it can instead act as a Lightweight DHCPv6 Relay 3381 Agent per [RFC6221] by encapsulating the DHCPv6 message in a Relay- 3382 forward/reply exchange with Relay Message and Interface ID options. 3383 In the process, the MSE packs any state information needed to return 3384 an RA to the MN in the Relay-forward Interface ID option so that the 3385 information will be echoed back in the Relay-reply.) 3386 When the MSE receives the DHCPv6 Reply, it adds routes to the routing 3387 system and creates MNP-LLAs based on the delegated MNPs. The MSE 3388 then sends an RA back to the MN with the DHCPv6 Reply message 3389 included in an OMNI DHCPv6 message sub-option if and only if the RS 3390 message had included an explicit DHCPv6 Solicit. If the RS message 3391 source was the unspecified address (::), the MSE includes one of the 3392 (newly-created) MNP-LLAs as the RA destination address and sets the 3393 OMNI option Preflen accordingly; otherwise, the MSE includes the RS 3394 source address as the RA destination address. The MSE then sets the 3395 RA source address to its own ADM-LLA then performs OAL encapsulation 3396 and fragmentation and sends the RA to the MN. When the MN receives 3397 the RA, it reassembles and discards the OAL encapsulation, then 3398 creates a default route, assigns Subnet Router Anycast addresses and 3399 uses the RA destination address as its primary MNP-LLA. The MN will 3400 then use this primary MNP-LLA as the source address of any IPv6 ND 3401 messages it sends as long as it retains ownership of the MNP. 3403 Note: After a MN performs a DHCPv6-based prefix registration exchange 3404 with a first MSE, it would need to repeat the exchange with each 3405 additional MSE it registers with. In that case, the MN supplies the 3406 MNP delegation information received from the first MSE when it 3407 engages the additional MSEs. 3409 16. Secure Redirection 3411 If the *NET link model is multiple access, the AR is responsible for 3412 assuring that address duplication cannot corrupt the neighbor caches 3413 of other nodes on the link. When the MN sends an RS message on a 3414 multiple access *NET link, the AR verifies that the MN is authorized 3415 to use the address and returns an RA with a non-zero Router Lifetime 3416 only if the MN is authorized. 3418 After verifying MN authorization and returning an RA, the AR MAY 3419 return IPv6 ND Redirect messages to direct MNs located on the same 3420 *NET link to exchange packets directly without transiting the AR. In 3421 that case, the MNs can exchange packets according to their unicast L2 3422 addresses discovered from the Redirect message instead of using the 3423 dogleg path through the AR. In some *NET links, however, such direct 3424 communications may be undesirable and continued use of the dogleg 3425 path through the AR may provide better performance. In that case, 3426 the AR can refrain from sending Redirects, and/or MNs can ignore 3427 them. 3429 17. AR and MSE Resilience 3431 *NETs SHOULD deploy ARs in Virtual Router Redundancy Protocol (VRRP) 3432 [RFC5798] configurations so that service continuity is maintained 3433 even if one or more ARs fail. Using VRRP, the MN is unaware which of 3434 the (redundant) ARs is currently providing service, and any service 3435 discontinuity will be limited to the failover time supported by VRRP. 3436 Widely deployed public domain implementations of VRRP are available. 3438 MSEs SHOULD use high availability clustering services so that 3439 multiple redundant systems can provide coordinated response to 3440 failures. As with VRRP, widely deployed public domain 3441 implementations of high availability clustering services are 3442 available. Note that special-purpose and expensive dedicated 3443 hardware is not necessary, and public domain implementations can be 3444 used even between lightweight virtual machines in cloud deployments. 3446 18. Detecting and Responding to MSE Failures 3448 In environments where fast recovery from MSE failure is required, ARs 3449 SHOULD use proactive Neighbor Unreachability Detection (NUD) in a 3450 manner that parallels Bidirectional Forwarding Detection (BFD) 3451 [RFC5880] to track MSE reachability. ARs can then quickly detect and 3452 react to failures so that cached information is re-established 3453 through alternate paths. Proactive NUD control messaging is carried 3454 only over well-connected ground domain networks (i.e., and not low- 3455 end *NET links such as aeronautical radios) and can therefore be 3456 tuned for rapid response. 3458 ARs perform proactive NUD for MSEs for which there are currently 3459 active MNs on the *NET. If an MSE fails, ARs can quickly inform MNs 3460 of the outage by sending multicast RA messages on the *NET interface. 3461 The AR sends RA messages to MNs via the *NET interface with an OMNI 3462 option with a Release ID for the failed MSE, and with destination 3463 address set to All-Nodes multicast (ff02::1) [RFC4291]. 3465 The AR SHOULD send MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated 3466 by small delays [RFC4861]. Any MNs on the *NET interface that have 3467 been using the (now defunct) MSE will receive the RA messages and 3468 associate with a new MSE. 3470 19. Transition Considerations 3472 When a MN connects to an *NET link for the first time, it sends an RS 3473 message with an OMNI option. If the first hop AR recognizes the 3474 option, it returns an RA with its ADM-LLA as the source, the MNP-LLA 3475 as the destination and with an OMNI option included. The MN then 3476 engages the AR according to the OMNI link model specified above. If 3477 the first hop AR is a legacy IPv6 router, however, it instead returns 3478 an RA message with no OMNI option and with a non-OMNI unicast source 3479 LLA as specified in [RFC4861]. In that case, the MN engages the *NET 3480 according to the legacy IPv6 link model and without the OMNI 3481 extensions specified in this document. 3483 If the *NET link model is multiple access, there must be assurance 3484 that address duplication cannot corrupt the neighbor caches of other 3485 nodes on the link. When the MN sends an RS message on a multiple 3486 access *NET link with an LLA source address and an OMNI option, ARs 3487 that recognize the option ensure that the MN is authorized to use the 3488 address and return an RA with a non-zero Router Lifetime only if the 3489 MN is authorized. ARs that do not recognize the option instead 3490 return an RA that makes no statement about the MN's authorization to 3491 use the source address. In that case, the MN should perform 3492 Duplicate Address Detection to ensure that it does not interfere with 3493 other nodes on the link. 3495 An alternative approach for multiple access *NET links to ensure 3496 isolation for MN / AR communications is through L2 address mappings 3497 as discussed in Appendix C. This arrangement imparts a (virtual) 3498 point-to-point link model over the (physical) multiple access link. 3500 20. OMNI Interfaces on Open Internetworks 3502 OMNI interfaces configured over IPv6-enabled underlying interfaces on 3503 an open Internetwork without an OMNI-aware first-hop AR receive RA 3504 messages that do not include an OMNI option, while OMNI interfaces 3505 configured over IPv4-only underlying interfaces do not receive any 3506 (IPv6) RA messages at all (although they may receive IPv4 RA messages 3507 [RFC1256]). OMNI interfaces that receive RA messages without an OMNI 3508 option configure addresses, on-link prefixes, etc. on the underlying 3509 interface that received the RA according to standard IPv6 ND and 3510 address resolution conventions [RFC4861] [RFC4862]. OMNI interfaces 3511 configured over IPv4-only underlying interfaces configure IPv4 3512 address information on the underlying interfaces using mechanisms 3513 such as DHCPv4 [RFC2131]. 3515 OMNI interfaces configured over underlying interfaces that connect to 3516 an open Internetwork can apply security services such as VPNs to 3517 connect to an MSE, or can establish a direct link to an MSE through 3518 some other means (see Section 4). In environments where an explicit 3519 VPN or direct link may be impractical, OMNI interfaces can instead 3520 use UDP/IP encapsulation while including authentication signatures in 3521 IPv6 ND messages. 3523 OMNI interfaces use UDP service port number 8060 (see: Section 25.11 3524 and Section 3.6 of [I-D.templin-intarea-6706bis]) according to the 3525 simple UDP/IP encapsulation format specified in [RFC4380] for both 3526 IPv4 and IPv6 underlying interfaces. OMNI interfaces do not include 3527 the UDP/IP header/trailer extensions specified in [RFC4380][RFC6081], 3528 but may include them as OMNI sub-options instead when necessary. 3529 Since the OAL includes an integrity check over the OAL packet, OAL 3530 sources selectively disable UDP checksums for OAL packets that do not 3531 require UDP/IP address integrity, but enable UDP checksums for others 3532 including non-OAL packets, IPv6 ND messages used to establish link- 3533 layer addresses, etc. If the OAL source discovers that packets with 3534 UDP checksums disabled are being dropped in the path it should enable 3535 UDP checksums in future packets. Further considerations for UDP 3536 encapsulation checksums are found in [RFC6935][RFC6936]. 3538 For "Vehicle-to-Infrastructure (V2I)" coordination, the MN includes 3539 an authentication sub-option in the OMNI option of IPv6 RS/NS 3540 messages and the MSE responds with an authentication sub-option in an 3541 OMNI option of an IPv6 RA/NA message. HIP security services can be 3542 applied per [RFC7401] using the IPv6 ND messages as simple "shipping 3543 containers" to convey the sender's HIP authentication signature 3544 (e.g., enclosed in a HIP "Notify" message). Alternatively, a simple 3545 Hashed Message Authentication Code (HMAC) can be included in the 3546 manner specified in [RFC4380]. For "Vehicle-to-Vehicle (V2V)" 3547 coordination, two MNs can coordinate directly with one another with 3548 HIP "Initiator/Responder" messages coded in OMNI options of IPv6 NS/ 3549 NA messages. In that case, a four-message HIP exchange (i.e., two 3550 back-to-back NS/NA exchanges) may be necessary for the two MNs to 3551 attain mutual authentication. 3553 After establishing a VPN or preparing for UDP/IP encapsulation, OMNI 3554 interfaces send control plane messages to interface with the MSE, 3555 including RS/RA messages used according to Section 15 and NS/NA 3556 messages used for route optimization and mobility (see: 3557 [I-D.templin-intarea-6706bis]). The control plane messages must be 3558 authenticated while data plane messages are delivered the same as for 3559 ordinary best-effort traffic with basic source address-based data 3560 origin verification. Data plane communications via OMNI interfaces 3561 that connect over open Internetworks without an explicit VPN should 3562 therefore employ transport- or higher-layer security to ensure 3563 integrity and/or confidentiality. 3565 OMNI interfaces configured over open Internetworks are often located 3566 behind NATs. The OMNI interface accommodates NAT traversal using 3567 UDP/IP encapsulation and the mechanisms discussed in 3568 [I-D.templin-intarea-6706bis]. To support NAT determination, MSEs 3569 include an Origin Indication sub-option in RA messages sent in 3570 response to RS messages received from a Client via UDP/IP 3571 encapsulation. 3573 Note: Following the initial HIP exchange, OMNI interfaces configured 3574 over open Internetworks maintain HIP associations through the 3575 transmission of IPv6 ND messages that include OMNI options with HIP 3576 "Update" and "Notify" messages. OMNI interfaces use the HIP "Update" 3577 message when an acknowledgement is required, and use the "Notify" 3578 message in unacknowledged isolated IPv6 ND messages (e.g., 3579 unsolicited NAs). When HMAC authentication is used instead of HIP, 3580 the MN and MSE exchange all IPv6 ND messages with HMAC signatures 3581 included based on a shared-secret. 3583 Note: ARs that act as proxys on an open Internetwork authenticate and 3584 remove authentication OMNI sub-options from IPv6 ND messages they 3585 forward from a MN, and insert and sign authentication Origin 3586 Indication sub-options in IPv6 ND messages they forward from the 3587 network to the MN. Conversely, ARs that act as proxys forward 3588 without processing any DHCPv6 information in RS/RA message exchanges 3589 between MNs and MSEs. The AR is therefore responsible for MN 3590 authentication while the MSE is responsible for registering/ 3591 delegating MNPs. Note also that a simpler arrangement is possible 3592 when the AR also acts as a MSE itself, i.e., when the proxy and MSE 3593 functions are combined on a single physical or logical platform 3594 located somewhere in the Internetwork. 3596 Note: The [RFC4380] HMAC and/or HIP message [RFC7401] authentication 3597 sub-options appear in the OMNI option, which may occur anywhere 3598 within the IPv6 ND message body. When a node that inserts an 3599 authentication sub-option generates the authentication signature, it 3600 calculates the signature over the entire length of the IPv6 ND 3601 message but with the sub-option authentication field itself set to 0. 3602 The node then writes the resulting signature into the authentication 3603 field then continues to prepare the message for transmission. For 3604 this reason, if an IPv6 ND message includes multiple authentication 3605 sub-options, the first sub-option is consulted and any additional 3606 sub-options are ignored. 3608 21. Time-Varying MNPs 3610 In some use cases, it is desirable, beneficial and efficient for the 3611 MN to receive a constant MNP that travels with the MN wherever it 3612 moves. For example, this would allow air traffic controllers to 3613 easily track aircraft, etc. In other cases, however (e.g., 3614 intelligent transportation systems), the MN may be willing to 3615 sacrifice a modicum of efficiency in order to have time-varying MNPs 3616 that can be changed every so often to defeat adversarial tracking. 3618 The prefix delegation services discussed in Section 15.3 allows OMNI 3619 MNs that desire time-varying MNPs to obtain short-lived prefixes to 3620 send RS messages with source set to the unspecified address (::) and/ 3621 or with an OMNI option with DHCPv6 Option sub-options. The MN would 3622 then be obligated to renumber its internal networks whenever its MNP 3623 (and therefore also its OMNI address) changes. This should not 3624 present a challenge for MNs with automated network renumbering 3625 services, however presents limits for the durations of ongoing 3626 sessions that would prefer to use a constant address. 3628 22. (H)HITs and Temporary ULAs 3630 MNs that generate (H)HITs but do not have pre-assigned MNPs can 3631 request MNP delegations by issuing IPv6 ND messages that use the 3632 (H)HIT instead of a Temporary ULA. In particular, when a MN creates 3633 an RS message it can set the source to the unspecified address (::) 3634 and destination to All-Routers multicast. The IPv6 ND message 3635 includes an OMNI option with a HIP message sub-option, and need not 3636 include a Node Identification sub-option since the MN's HIT appears 3637 in the HIP message. The MN then encapsulates the message in an IPv6 3638 header with the (H)HIT as the source address and with destination set 3639 to either a unicast or anycast ADM-ULA. The MN then sends the 3640 message to the MSE as specified in Section 15.1. 3642 When the MSE receives the message, it notes that the RS source was 3643 the unspecified address (::), then examines the RS encapsulation 3644 source address to determine that the source is a (H)HIT and not a 3645 Temporary ULA. The MSE next invokes the DHCPv6 protocol to request 3646 an MNP prefix delegation while using the HIT as the Client 3647 Identifier, then prepares an RA message with source address set to 3648 its own ADM-LLA and destination set to the MNP-LLA corresponding to 3649 the delegated MNP. The MSE next includes an OMNI option with a HIP 3650 message sub-option and any DHCPv6 prefix delegation parameters. The 3651 MSE then finally encapsulates the RA in an IPv6 header with source 3652 address set to its own ADM-ULA and destination set to the (H)HIT from 3653 the RS encapsulation source address, then returns the encapsulated RA 3654 to the MN. 3656 MNs can also use (H)HITs and/or Temporary ULAs for direct MN-to-MN 3657 communications outside the context of any OMNI link supporting 3658 infrastructure. When two MNs encounter one another they can use 3659 their (H)HITs and/or Temporary ULAs as original IPv6 packet source 3660 and destination addresses to support direct communications. MNs can 3661 also inject their (H)HITs and/or Temporary ULAs into a MANET/VANET 3662 routing protocol to enable multihop communications. MNs can further 3663 exchange IPv6 ND messages (such as NS/NA) using their (H)HITs and/or 3664 Temporary ULAs as source and destination addresses. Note that the 3665 HIP security protocols for establishing secure neighbor relationships 3666 are based on (H)HITs. IPv6 ND messages that use Temporary ULAs 3667 instead use the HMAC authentication service specified in [RFC4380]. 3669 Lastly, when MNs are within the coverage range of OMNI link 3670 infrastructure a case could be made for injecting (H)HITs and/or 3671 Temporary ULAs into the global MS routing system. For example, when 3672 the MN sends an RS to a MSE it could include a request to inject the 3673 (H)HIT / Temporary ULA into the routing system instead of requesting 3674 an MNP prefix delegation. This would potentially enable OMNI link- 3675 wide communications using only (H)HITs or Temporary ULAs, and not 3676 MNPs. This document notes the opportunity, but makes no 3677 recommendation. 3679 23. Address Selection 3681 OMNI MNs use LLAs only for link-scoped communications on the OMNI 3682 link. Typically, MNs use LLAs as source/destination IPv6 addresses 3683 of IPv6 ND messages, but may also use them for addressing ordinary 3684 original IP packets exchanged with an OMNI link neighbor. 3686 OMNI MNs use MNP-ULAs as source/destination IPv6 addresses in the 3687 encapsulation headers of OAL packets. OMNI MNs use Temporary ULAs 3688 for OAL addressing when an MNP-ULA is not available, or as source/ 3689 destination IPv6 addresses for communications within a MANET/VANET 3690 local area. OMNI MNs use HITs instead of Temporary ULAs when 3691 operation outside the context of a specific ULA domain and/or source 3692 address attestation is necessary. 3694 OMNI MNs use MNP-based GUAs as original IP packet source and 3695 destination addresses for communications with Internet destinations 3696 when they are within range of OMNI link supporting infrastructure 3697 that can inject the MNP into the routing system. 3699 24. Error Messages 3701 An OAL destination or intermediate node may need to return ICMPv6 3702 error messages (e.g., Destination Unreachable, Packet Too Big, Time 3703 Exceeded, etc.) [RFC4443] to an OAL source. Since ICMPv6 error 3704 messages do not themselves include authentication codes, the OAL 3705 includes the ICMPv6 error message as an OMNI sub-option in an IPv6 ND 3706 uNA message. The OAL also includes a HIP message sub-option if the 3707 uNA needs to travel over an open Internetwork. 3709 25. IANA Considerations 3711 The following IANA actions are requested in accordance with [RFC8126] 3712 and [RFC8726]: 3714 25.1. "IEEE 802 Numbers" Registry 3716 The IANA is instructed to allocate an official Ethertype number TBD1 3717 from the 'ieee-802-numbers' registry for User Datagram Protocol (UDP) 3718 encapsulation on Ethernet networks. Guidance is found in [RFC7042] 3719 (registration procedure is Expert Review). 3721 25.2. "IPv6 Neighbor Discovery Option Formats" Registry 3723 The IANA is instructed to allocate an official Type number TBD2 from 3724 the "IPv6 Neighbor Discovery Option Formats" registry for the OMNI 3725 option (registration procedure is RFC required). Implementations set 3726 Type to 253 as an interim value [RFC4727]. 3728 25.3. "Ethernet Numbers" Registry 3730 The IANA is instructed to allocate one Ethernet unicast address TBD3 3731 (suggested value '00-52-14') in the 'ethernet-numbers' registry under 3732 "IANA Unicast 48-bit MAC Addresses" (registration procedure is Expert 3733 Review). The registration should appear as follows: 3735 Addresses Usage Reference 3736 --------- ----- --------- 3737 00-52-14 Overlay Multilink Network (OMNI) Interface [RFCXXXX] 3739 Figure 32: IANA Unicast 48-bit MAC Addresses 3741 25.4. "ICMPv6 Code Fields: Type 2 - Packet Too Big" Registry 3743 The IANA is instructed to assign two new Code values in the "ICMPv6 3744 Code Fields: Type 2 - Packet Too Big" registry (registration 3745 procedure is Standards Action or IESG Approval). The registry should 3746 appear as follows: 3748 Code Name Reference 3749 --- ---- --------- 3750 0 PTB Hard Error [RFC4443] 3751 1 PTB Soft Error (loss) [RFCXXXX] 3752 2 PTB Soft Error (no loss) [RFCXXXX] 3754 Figure 33: ICMPv6 Code Fields: Type 2 - Packet Too Big Values 3756 (Note: this registry also to be used to define values for setting the 3757 "unused" field of ICMPv4 "Destination Unreachable - Fragmentation 3758 Needed" messages.) 3760 25.5. "OMNI Option Sub-Type Values" (New Registry) 3762 The OMNI option defines a 5-bit Sub-Type field, for which IANA is 3763 instructed to create and maintain a new registry entitled "OMNI 3764 Option Sub-Type Values". Initial values are given below 3765 (registration procedure is RFC required): 3767 Value Sub-Type name Reference 3768 ----- ------------- ---------- 3769 0 Pad1 [RFCXXXX] 3770 1 PadN [RFCXXXX] 3771 2 Interface Attributes (Type 1) [RFCXXXX] 3772 3 Interface Attributes (Type 2) [RFCXXXX] 3773 4 Traffic Selector [RFCXXXX] 3774 5 MS-Register [RFCXXXX] 3775 6 MS-Release [RFCXXXX] 3776 7 Geo Coordinates [RFCXXXX] 3777 8 DHCPv6 Message [RFCXXXX] 3778 9 HIP Message [RFCXXXX] 3779 10 Reassembly Limit [RFCXXXX] 3780 11 Fragmentation Report [RFCXXXX] 3781 12 Node Identification [RFCXXXX] 3782 13-29 Unassigned 3783 30 Sub-Type Extension [RFCXXXX] 3784 31 Reserved by IANA [RFCXXXX] 3786 Figure 34: OMNI Option Sub-Type Values 3788 25.6. "OMNI Geo Coordinates Type Values" (New Registry) 3790 The OMNI Geo Coordinates Sub-Option (see: Section 12.1.8) contains an 3791 8-bit Type field, for which IANA is instructed to create and maintain 3792 a new registry entitled "OMNI Geo Coordinates Type Values". Initial 3793 values are given below (registration procedure is RFC required): 3795 Value Sub-Type name Reference 3796 ----- ------------- ---------- 3797 0 NULL [RFCXXXX] 3798 255 Reserved by IANA [RFCXXXX] 3800 Figure 35: OMNI Geo Coordinates Type 3802 25.7. "OMNI Node Identification ID-Type Values" (New Registry) 3804 The OMNI Node Identification Sub-Option (see: Section 12.1.13) 3805 contains an 8-bit ID-Type field, for which IANA is instructed to 3806 create and maintain a new registry entitled "OMNI Node Identification 3807 ID-Type Values". Initial values are given below (registration 3808 procedure is RFC required): 3810 Value Sub-Type name Reference 3811 ----- ------------- ---------- 3812 0 UUID [RFCXXXX] 3813 1 HIT [RFCXXXX] 3814 2 HHIT [RFCXXXX] 3815 3 Network Access Identifier [RFCXXXX] 3816 4 FQDN [RFCXXXX] 3817 5-252 Unassigned [RFCXXXX] 3818 253-254 Reserved for Experimentation [RFCXXXX] 3819 255 Reserved by IANA [RFCXXXX] 3821 Figure 36: OMNI Node Identification ID-Type Values 3823 25.8. "OMNI Option Sub-Type Extension Values" (New Registry) 3825 The OMNI option defines an 8-bit Extension-Type field for Sub-Type 30 3826 (Sub-Type Extension), for which IANA is instructed to create and 3827 maintain a new registry entitled "OMNI Option Sub-Type Extension 3828 Values". Initial values are given below (registration procedure is 3829 RFC required): 3831 Value Sub-Type name Reference 3832 ----- ------------- ---------- 3833 0 RFC4380 UDP/IP Header Option [RFCXXXX] 3834 1 RFC6081 UDP/IP Trailer Option [RFCXXXX] 3835 2-252 Unassigned 3836 253-254 Reserved for Experimentation [RFCXXXX] 3837 255 Reserved by IANA [RFCXXXX] 3839 Figure 37: OMNI Option Sub-Type Extension Values 3841 25.9. "OMNI RFC4380 UDP/IP Header Option" (New Registry) 3843 The OMNI Sub-Type Extension "RFC4380 UDP/IP Header Option" defines an 3844 8-bit Header Type field, for which IANA is instructed to create and 3845 maintain a new registry entitled "OMNI RFC4380 UDP/IP Header Option". 3846 Initial registry values are given below (registration procedure is 3847 RFC required): 3849 Value Sub-Type name Reference 3850 ----- ------------- ---------- 3851 0 Origin Indication (IPv4) [RFC4380] 3852 1 Authentication Encapsulation [RFC4380] 3853 2 Origin Indication (IPv6) [RFCXXXX] 3854 3-252 Unassigned 3855 253-254 Reserved for Experimentation [RFCXXXX] 3856 255 Reserved by IANA [RFCXXXX] 3858 Figure 38: OMNI RFC4380 UDP/IP Header Option 3860 25.10. "OMNI RFC6081 UDP/IP Trailer Option" (New Registry) 3862 The OMNI Sub-Type Extension for "RFC6081 UDP/IP Trailer Option" 3863 defines an 8-bit Trailer Type field, for which IANA is instructed to 3864 create and maintain a new registry entitled "OMNI RFC6081 UDP/IP 3865 Trailer Option". Initial registry values are given below 3866 (registration procedure is RFC required): 3868 Value Sub-Type name Reference 3869 ----- ------------- ---------- 3870 0 Unassigned 3871 1 Nonce [RFC6081] 3872 2 Unassigned 3873 3 Alternate Address (IPv4) [RFC6081] 3874 4 Neighbor Discovery Option [RFC6081] 3875 5 Random Port [RFC6081] 3876 6 Alternate Address (IPv6) [RFCXXXX] 3877 7-252 Unassigned 3878 253-254 Reserved for Experimentation [RFCXXXX] 3879 255 Reserved by IANA [RFCXXXX] 3881 Figure 39: OMNI RFC6081 Trailer Option 3883 25.11. Additional Considerations 3885 The IANA has assigned the UDP port number "8060" for an earlier 3886 experimental version of AERO [RFC6706]. This document together with 3887 [I-D.templin-intarea-6706bis] reclaims the UDP port number "8060" for 3888 'aero' as the service port for UDP/IP encapsulation. (Note that, 3889 although [RFC6706] was not widely implemented or deployed, any 3890 messages coded to that specification can be easily distinguished and 3891 ignored since they use an invalid ICMPv6 message type number '0'.) 3892 The IANA is therefore instructed to update the reference for UDP port 3893 number "8060" from "RFC6706" to "RFCXXXX" (i.e., this document). 3895 The IANA has assigned a 4 octet Private Enterprise Number (PEN) code 3896 "45282" in the "enterprise-numbers" registry. This document is the 3897 normative reference for using this code in DHCP Unique IDentifiers 3898 based on Enterprise Numbers ("DUID-EN for OMNI Interfaces") (see: 3899 Section 11). The IANA is therefore instructed to change the 3900 enterprise designation for PEN code "45282" from "LinkUp Networks" to 3901 "Overlay Multilink Network Interface (OMNI)". 3903 The IANA has assigned the ifType code "301 - omni - Overlay Multilink 3904 Network Interface (OMNI)" in accordance with Section 6 of [RFC8892]. 3905 The registration appears under the IANA "Structure of Management 3906 Information (SMI) Numbers (MIB Module Registrations) - Interface 3907 Types (ifType)" registry. 3909 No further IANA actions are required. 3911 26. Security Considerations 3913 Security considerations for IPv4 [RFC0791], IPv6 [RFC8200] and IPv6 3914 Neighbor Discovery [RFC4861] apply. OMNI interface IPv6 ND messages 3915 SHOULD include Nonce and Timestamp options [RFC3971] when transaction 3916 confirmation and/or time synchronization is needed. (Note however 3917 that when OAL encapsulation is used the (echoed) OAL Identification 3918 value can provide sufficient transaction confirmation.) 3920 MN OMNI interfaces configured over secured ANET interfaces inherit 3921 the physical and/or link-layer security properties (i.e., "protected 3922 spectrum") of the connected ANETs. MN OMNI interfaces configured 3923 over open INET interfaces can use symmetric securing services such as 3924 VPNs or can by some other means establish a direct link. When a VPN 3925 or direct link may be impractical, however, the security services 3926 specified in [RFC7401] and/or [RFC4380] can be employed. While the 3927 OMNI link protects control plane messaging, applications must still 3928 employ end-to-end transport- or higher-layer security services to 3929 protect the data plane. 3931 Strong network layer security for control plane messages and 3932 forwarding path integrity for data plane messages between MSEs MUST 3933 be supported. In one example, the AERO service 3934 [I-D.templin-intarea-6706bis] constructs a spanning tree between MSEs 3935 and secures the links in the spanning tree with network layer 3936 security mechanisms such as IPsec [RFC4301] or Wireguard. Control 3937 plane messages are then constrained to travel only over the secured 3938 spanning tree paths and are therefore protected from attack or 3939 eavesdropping. Since data plane messages can travel over route 3940 optimized paths that do not strictly follow the spanning tree, 3941 however, end-to-end transport- or higher-layer security services are 3942 still required. 3944 Identity-based key verification infrastructure services such as iPSK 3945 may be necessary for verifying the identities claimed by MNs. This 3946 requirement should be harmonized with the manner in which (H)HITs are 3947 attested in a given operational environment. 3949 Security considerations for specific access network interface types 3950 are covered under the corresponding IP-over-(foo) specification 3951 (e.g., [RFC2464], [RFC2492], etc.). 3953 Security considerations for IPv6 fragmentation and reassembly are 3954 discussed in Section 6.9. 3956 27. Implementation Status 3958 AERO/OMNI Release-3.2 was tagged on March 30, 2021, and is undergoing 3959 internal testing. Additional internal releases expected within the 3960 coming months, with first public release expected end of 1H2021. 3962 28. Document Updates 3964 This document does not itself update other RFCs, but suggests that 3965 the following could be updated through future IETF initiatives: 3967 o [RFC1191] 3969 o [RFC4443] 3971 o [RFC8201] 3973 o [RFC7526] 3975 Updates can be through, e.g., standards action, the errata process, 3976 etc. as appropriate. 3978 29. Acknowledgements 3980 The first version of this document was prepared per the consensus 3981 decision at the 7th Conference of the International Civil Aviation 3982 Organization (ICAO) Working Group-I Mobility Subgroup on March 22, 3983 2019. Consensus to take the document forward to the IETF was reached 3984 at the 9th Conference of the Mobility Subgroup on November 22, 2019. 3985 Attendees and contributors included: Guray Acar, Danny Bharj, 3986 Francois D'Humieres, Pavel Drasil, Nikos Fistas, Giovanni Garofolo, 3987 Bernhard Haindl, Vaughn Maiolla, Tom McParland, Victor Moreno, Madhu 3988 Niraula, Brent Phillips, Liviu Popescu, Jacky Pouzet, Aloke Roy, Greg 3989 Saccone, Robert Segers, Michal Skorepa, Michel Solery, Stephane 3990 Tamalet, Fred Templin, Jean-Marc Vacher, Bela Varkonyi, Tony Whyman, 3991 Fryderyk Wrobel and Dongsong Zeng. 3993 The following individuals are acknowledged for their useful comments: 3994 Stuart Card, Michael Matyas, Robert Moskowitz, Madhu Niraula, Greg 3995 Saccone, Stephane Tamalet, Eric Vyncke. Pavel Drasil, Zdenek Jaron 3996 and Michal Skorepa are especially recognized for their many helpful 3997 ideas and suggestions. Madhuri Madhava Badgandi, Sean Dickson, Don 3998 Dillenburg, Joe Dudkowski, Vijayasarathy Rajagopalan, Ron Sackman and 3999 Katherine Tran are acknowledged for their hard work on the 4000 implementation and technical insights that led to improvements for 4001 the spec. 4003 Discussions on the IETF 6man and atn mailing lists during the fall of 4004 2020 suggested additional points to consider. The authors gratefully 4005 acknowledge the list members who contributed valuable insights 4006 through those discussions. Eric Vyncke and Erik Kline were the 4007 intarea ADs, while Bob Hinden and Ole Troan were the 6man WG chairs 4008 at the time the document was developed; they are all gratefully 4009 acknowledged for their many helpful insights. Many of the ideas in 4010 this document have further built on IETF experiences beginning as 4011 early as Y2K, with insights from colleagues including Brian 4012 Carpenter, Ralph Droms, Christian Huitema, Thomas Narten, Dave 4013 Thaler, Joe Touch, and many others who deserve recognition. 4015 Early observations on IP fragmentation performance implications were 4016 noted in the 1986 Digital Equipment Corporation (DEC) "qe reset" 4017 investigation, where fragment bursts from NFS UDP traffic triggered 4018 hardware resets resulting in communication failures. Jeff Chase, 4019 Fred Glover and Chet Juzsczak of the Ultrix Engineering Group led the 4020 investigation, and determined that setting a smaller NFS mount block 4021 size reduced the amount of fragmentation and suppressed the resets. 4022 Early observations on L2 media MTU issues were noted in the 1988 DEC 4023 FDDI investigation, where Raj Jain, KK Ramakrishnan and Kathy Wilde 4024 represented architectural considerations for FDDI networking in 4025 general including FDDI/Ethernet bridging. Jeff Mogul (who led the 4026 IETF Path MTU Discovery working group) and other DEC colleagues who 4027 supported these early investigations are also acknowledged. 4029 This work is aligned with the NASA Safe Autonomous Systems Operation 4030 (SASO) program under NASA contract number NNA16BD84C. 4032 This work is aligned with the FAA as per the SE2025 contract number 4033 DTFAWA-15-D-00030. 4035 This work is aligned with the Boeing Information Technology (BIT) 4036 Mobility Vision Lab (MVL) program. 4038 30. References 4040 30.1. Normative References 4042 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 4043 DOI 10.17487/RFC0791, September 1981, 4044 . 4046 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 4047 Requirement Levels", BCP 14, RFC 2119, 4048 DOI 10.17487/RFC2119, March 1997, 4049 . 4051 [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, 4052 "Definition of the Differentiated Services Field (DS 4053 Field) in the IPv4 and IPv6 Headers", RFC 2474, 4054 DOI 10.17487/RFC2474, December 1998, 4055 . 4057 [RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander, 4058 "SEcure Neighbor Discovery (SEND)", RFC 3971, 4059 DOI 10.17487/RFC3971, March 2005, 4060 . 4062 [RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and 4063 More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191, 4064 November 2005, . 4066 [RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast 4067 Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005, 4068 . 4070 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 4071 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 4072 2006, . 4074 [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet 4075 Control Message Protocol (ICMPv6) for the Internet 4076 Protocol Version 6 (IPv6) Specification", STD 89, 4077 RFC 4443, DOI 10.17487/RFC4443, March 2006, 4078 . 4080 [RFC4727] Fenner, B., "Experimental Values In IPv4, IPv6, ICMPv4, 4081 ICMPv6, UDP, and TCP Headers", RFC 4727, 4082 DOI 10.17487/RFC4727, November 2006, 4083 . 4085 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 4086 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 4087 DOI 10.17487/RFC4861, September 2007, 4088 . 4090 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 4091 Address Autoconfiguration", RFC 4862, 4092 DOI 10.17487/RFC4862, September 2007, 4093 . 4095 [RFC6088] Tsirtsis, G., Giarreta, G., Soliman, H., and N. Montavont, 4096 "Traffic Selectors for Flow Bindings", RFC 6088, 4097 DOI 10.17487/RFC6088, January 2011, 4098 . 4100 [RFC7401] Moskowitz, R., Ed., Heer, T., Jokela, P., and T. 4101 Henderson, "Host Identity Protocol Version 2 (HIPv2)", 4102 RFC 7401, DOI 10.17487/RFC7401, April 2015, 4103 . 4105 [RFC8028] Baker, F. and B. Carpenter, "First-Hop Router Selection by 4106 Hosts in a Multi-Prefix Network", RFC 8028, 4107 DOI 10.17487/RFC8028, November 2016, 4108 . 4110 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 4111 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 4112 May 2017, . 4114 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 4115 (IPv6) Specification", STD 86, RFC 8200, 4116 DOI 10.17487/RFC8200, July 2017, 4117 . 4119 [RFC8201] McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed., 4120 "Path MTU Discovery for IP version 6", STD 87, RFC 8201, 4121 DOI 10.17487/RFC8201, July 2017, 4122 . 4124 [RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A., 4125 Richardson, M., Jiang, S., Lemon, T., and T. Winters, 4126 "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", 4127 RFC 8415, DOI 10.17487/RFC8415, November 2018, 4128 . 4130 30.2. Informative References 4132 [ATN] Maiolla, V., "The OMNI Interface - An IPv6 Air/Ground 4133 Interface for Civil Aviation, IETF Liaison Statement 4134 #1676, https://datatracker.ietf.org/liaison/1676/", March 4135 2020. 4137 [ATN-IPS] WG-I, ICAO., "ICAO Document 9896 (Manual on the 4138 Aeronautical Telecommunication Network (ATN) using 4139 Internet Protocol Suite (IPS) Standards and Protocol), 4140 Draft Edition 3 (work-in-progress)", December 2020. 4142 [CKSUM] Stone, J., Greenwald, M., Partridge, C., and J. Hughes, 4143 "Performance of Checksums and CRC's Over Real Data, IEEE/ 4144 ACM Transactions on Networking, Vol. 6, No. 5", October 4145 1998. 4147 [CRC] Jain, R., "Error Characteristics of Fiber Distributed Data 4148 Interface (FDDI), IEEE Transactions on Communications", 4149 August 1990. 4151 [I-D.ietf-drip-rid] 4152 Moskowitz, R., Card, S., Wiethuechter, A., and A. Gurtov, 4153 "UAS Remote ID", draft-ietf-drip-rid-06 (work in 4154 progress), December 2020. 4156 [I-D.ietf-intarea-tunnels] 4157 Touch, J. and M. Townsley, "IP Tunnels in the Internet 4158 Architecture", draft-ietf-intarea-tunnels-10 (work in 4159 progress), September 2019. 4161 [I-D.ietf-ipwave-vehicular-networking] 4162 Jeong, J., "IPv6 Wireless Access in Vehicular Environments 4163 (IPWAVE): Problem Statement and Use Cases", draft-ietf- 4164 ipwave-vehicular-networking-19 (work in progress), July 4165 2020. 4167 [I-D.ietf-tsvwg-udp-options] 4168 Touch, J., "Transport Options for UDP", draft-ietf-tsvwg- 4169 udp-options-09 (work in progress), November 2020. 4171 [I-D.templin-6man-dhcpv6-ndopt] 4172 Templin, F., "A Unified Stateful/Stateless Configuration 4173 Service for IPv6", draft-templin-6man-dhcpv6-ndopt-11 4174 (work in progress), January 2021. 4176 [I-D.templin-6man-lla-type] 4177 Templin, F., "The IPv6 Link-Local Address Type Field", 4178 draft-templin-6man-lla-type-02 (work in progress), 4179 November 2020. 4181 [I-D.templin-intarea-6706bis] 4182 Templin, F., "Asymmetric Extended Route Optimization 4183 (AERO)", draft-templin-intarea-6706bis-87 (work in 4184 progress), January 2021. 4186 [IPV4-GUA] 4187 Postel, J., "IPv4 Address Space Registry, 4188 https://www.iana.org/assignments/ipv4-address-space/ipv4- 4189 address-space.xhtml", December 2020. 4191 [IPV6-GUA] 4192 Postel, J., "IPv6 Global Unicast Address Assignments, 4193 https://www.iana.org/assignments/ipv6-unicast-address- 4194 assignments/ipv6-unicast-address-assignments.xhtml", 4195 December 2020. 4197 [RFC0905] "ISO Transport Protocol specification ISO DP 8073", 4198 RFC 905, DOI 10.17487/RFC0905, April 1984, 4199 . 4201 [RFC1035] Mockapetris, P., "Domain names - implementation and 4202 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, 4203 November 1987, . 4205 [RFC1122] Braden, R., Ed., "Requirements for Internet Hosts - 4206 Communication Layers", STD 3, RFC 1122, 4207 DOI 10.17487/RFC1122, October 1989, 4208 . 4210 [RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191, 4211 DOI 10.17487/RFC1191, November 1990, 4212 . 4214 [RFC1256] Deering, S., Ed., "ICMP Router Discovery Messages", 4215 RFC 1256, DOI 10.17487/RFC1256, September 1991, 4216 . 4218 [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", 4219 RFC 2131, DOI 10.17487/RFC2131, March 1997, 4220 . 4222 [RFC2225] Laubach, M. and J. Halpern, "Classical IP and ARP over 4223 ATM", RFC 2225, DOI 10.17487/RFC2225, April 1998, 4224 . 4226 [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, 4227 DOI 10.17487/RFC2328, April 1998, 4228 . 4230 [RFC2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet 4231 Networks", RFC 2464, DOI 10.17487/RFC2464, December 1998, 4232 . 4234 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 4235 IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473, 4236 December 1998, . 4238 [RFC2492] Armitage, G., Schulter, P., and M. Jork, "IPv6 over ATM 4239 Networks", RFC 2492, DOI 10.17487/RFC2492, January 1999, 4240 . 4242 [RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4 4243 Domains without Explicit Tunnels", RFC 2529, 4244 DOI 10.17487/RFC2529, March 1999, 4245 . 4247 [RFC2863] McCloghrie, K. and F. Kastenholz, "The Interfaces Group 4248 MIB", RFC 2863, DOI 10.17487/RFC2863, June 2000, 4249 . 4251 [RFC2923] Lahey, K., "TCP Problems with Path MTU Discovery", 4252 RFC 2923, DOI 10.17487/RFC2923, September 2000, 4253 . 4255 [RFC2983] Black, D., "Differentiated Services and Tunnels", 4256 RFC 2983, DOI 10.17487/RFC2983, October 2000, 4257 . 4259 [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition 4260 of Explicit Congestion Notification (ECN) to IP", 4261 RFC 3168, DOI 10.17487/RFC3168, September 2001, 4262 . 4264 [RFC3330] IANA, "Special-Use IPv4 Addresses", RFC 3330, 4265 DOI 10.17487/RFC3330, September 2002, 4266 . 4268 [RFC3692] Narten, T., "Assigning Experimental and Testing Numbers 4269 Considered Useful", BCP 82, RFC 3692, 4270 DOI 10.17487/RFC3692, January 2004, 4271 . 4273 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 4274 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 4275 DOI 10.17487/RFC3810, June 2004, 4276 . 4278 [RFC3819] Karn, P., Ed., Bormann, C., Fairhurst, G., Grossman, D., 4279 Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L. 4280 Wood, "Advice for Internet Subnetwork Designers", BCP 89, 4281 RFC 3819, DOI 10.17487/RFC3819, July 2004, 4282 . 4284 [RFC3879] Huitema, C. and B. Carpenter, "Deprecating Site Local 4285 Addresses", RFC 3879, DOI 10.17487/RFC3879, September 4286 2004, . 4288 [RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally 4289 Unique IDentifier (UUID) URN Namespace", RFC 4122, 4290 DOI 10.17487/RFC4122, July 2005, 4291 . 4293 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 4294 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 4295 DOI 10.17487/RFC4271, January 2006, 4296 . 4298 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 4299 Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, 4300 December 2005, . 4302 [RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through 4303 Network Address Translations (NATs)", RFC 4380, 4304 DOI 10.17487/RFC4380, February 2006, 4305 . 4307 [RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery 4308 Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April 4309 2006, . 4311 [RFC4429] Moore, N., "Optimistic Duplicate Address Detection (DAD) 4312 for IPv6", RFC 4429, DOI 10.17487/RFC4429, April 2006, 4313 . 4315 [RFC4541] Christensen, M., Kimball, K., and F. Solensky, 4316 "Considerations for Internet Group Management Protocol 4317 (IGMP) and Multicast Listener Discovery (MLD) Snooping 4318 Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006, 4319 . 4321 [RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick, 4322 "Internet Group Management Protocol (IGMP) / Multicast 4323 Listener Discovery (MLD)-Based Multicast Forwarding 4324 ("IGMP/MLD Proxying")", RFC 4605, DOI 10.17487/RFC4605, 4325 August 2006, . 4327 [RFC4821] Mathis, M. and J. Heffner, "Packetization Layer Path MTU 4328 Discovery", RFC 4821, DOI 10.17487/RFC4821, March 2007, 4329 . 4331 [RFC4963] Heffner, J., Mathis, M., and B. Chandler, "IPv4 Reassembly 4332 Errors at High Data Rates", RFC 4963, 4333 DOI 10.17487/RFC4963, July 2007, 4334 . 4336 [RFC5175] Haberman, B., Ed. and R. Hinden, "IPv6 Router 4337 Advertisement Flags Option", RFC 5175, 4338 DOI 10.17487/RFC5175, March 2008, 4339 . 4341 [RFC5213] Gundavelli, S., Ed., Leung, K., Devarapalli, V., 4342 Chowdhury, K., and B. Patil, "Proxy Mobile IPv6", 4343 RFC 5213, DOI 10.17487/RFC5213, August 2008, 4344 . 4346 [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site 4347 Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, 4348 DOI 10.17487/RFC5214, March 2008, 4349 . 4351 [RFC5558] Templin, F., Ed., "Virtual Enterprise Traversal (VET)", 4352 RFC 5558, DOI 10.17487/RFC5558, February 2010, 4353 . 4355 [RFC5798] Nadas, S., Ed., "Virtual Router Redundancy Protocol (VRRP) 4356 Version 3 for IPv4 and IPv6", RFC 5798, 4357 DOI 10.17487/RFC5798, March 2010, 4358 . 4360 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 4361 (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, 4362 . 4364 [RFC6081] Thaler, D., "Teredo Extensions", RFC 6081, 4365 DOI 10.17487/RFC6081, January 2011, 4366 . 4368 [RFC6221] Miles, D., Ed., Ooghe, S., Dec, W., Krishnan, S., and A. 4369 Kavanagh, "Lightweight DHCPv6 Relay Agent", RFC 6221, 4370 DOI 10.17487/RFC6221, May 2011, 4371 . 4373 [RFC6355] Narten, T. and J. Johnson, "Definition of the UUID-Based 4374 DHCPv6 Unique Identifier (DUID-UUID)", RFC 6355, 4375 DOI 10.17487/RFC6355, August 2011, 4376 . 4378 [RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label 4379 for Equal Cost Multipath Routing and Link Aggregation in 4380 Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011, 4381 . 4383 [RFC6543] Gundavelli, S., "Reserved IPv6 Interface Identifier for 4384 Proxy Mobile IPv6", RFC 6543, DOI 10.17487/RFC6543, May 4385 2012, . 4387 [RFC6706] Templin, F., Ed., "Asymmetric Extended Route Optimization 4388 (AERO)", RFC 6706, DOI 10.17487/RFC6706, August 2012, 4389 . 4391 [RFC6935] Eubanks, M., Chimento, P., and M. Westerlund, "IPv6 and 4392 UDP Checksums for Tunneled Packets", RFC 6935, 4393 DOI 10.17487/RFC6935, April 2013, 4394 . 4396 [RFC6936] Fairhurst, G. and M. Westerlund, "Applicability Statement 4397 for the Use of IPv6 UDP Datagrams with Zero Checksums", 4398 RFC 6936, DOI 10.17487/RFC6936, April 2013, 4399 . 4401 [RFC6980] Gont, F., "Security Implications of IPv6 Fragmentation 4402 with IPv6 Neighbor Discovery", RFC 6980, 4403 DOI 10.17487/RFC6980, August 2013, 4404 . 4406 [RFC7042] Eastlake 3rd, D. and J. Abley, "IANA Considerations and 4407 IETF Protocol and Documentation Usage for IEEE 802 4408 Parameters", BCP 141, RFC 7042, DOI 10.17487/RFC7042, 4409 October 2013, . 4411 [RFC7084] Singh, H., Beebee, W., Donley, C., and B. Stark, "Basic 4412 Requirements for IPv6 Customer Edge Routers", RFC 7084, 4413 DOI 10.17487/RFC7084, November 2013, 4414 . 4416 [RFC7421] Carpenter, B., Ed., Chown, T., Gont, F., Jiang, S., 4417 Petrescu, A., and A. Yourtchenko, "Analysis of the 64-bit 4418 Boundary in IPv6 Addressing", RFC 7421, 4419 DOI 10.17487/RFC7421, January 2015, 4420 . 4422 [RFC7526] Troan, O. and B. Carpenter, Ed., "Deprecating the Anycast 4423 Prefix for 6to4 Relay Routers", BCP 196, RFC 7526, 4424 DOI 10.17487/RFC7526, May 2015, 4425 . 4427 [RFC7542] DeKok, A., "The Network Access Identifier", RFC 7542, 4428 DOI 10.17487/RFC7542, May 2015, 4429 . 4431 [RFC7739] Gont, F., "Security Implications of Predictable Fragment 4432 Identification Values", RFC 7739, DOI 10.17487/RFC7739, 4433 February 2016, . 4435 [RFC7847] Melia, T., Ed. and S. Gundavelli, Ed., "Logical-Interface 4436 Support for IP Hosts with Multi-Access Support", RFC 7847, 4437 DOI 10.17487/RFC7847, May 2016, 4438 . 4440 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 4441 Writing an IANA Considerations Section in RFCs", BCP 26, 4442 RFC 8126, DOI 10.17487/RFC8126, June 2017, 4443 . 4445 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 4446 Decraene, B., Litkowski, S., and R. Shakir, "Segment 4447 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 4448 July 2018, . 4450 [RFC8726] Farrel, A., "How Requests for IANA Action Will Be Handled 4451 on the Independent Stream", RFC 8726, 4452 DOI 10.17487/RFC8726, November 2020, 4453 . 4455 [RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J., 4456 Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header 4457 (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020, 4458 . 4460 [RFC8892] Thaler, D. and D. Romascanu, "Guidelines and Registration 4461 Procedures for Interface Types and Tunnel Types", 4462 RFC 8892, DOI 10.17487/RFC8892, August 2020, 4463 . 4465 [RFC8899] Fairhurst, G., Jones, T., Tuexen, M., Ruengeler, I., and 4466 T. Voelker, "Packetization Layer Path MTU Discovery for 4467 Datagram Transports", RFC 8899, DOI 10.17487/RFC8899, 4468 September 2020, . 4470 [RFC8900] Bonica, R., Baker, F., Huston, G., Hinden, R., Troan, O., 4471 and F. Gont, "IP Fragmentation Considered Fragile", 4472 BCP 230, RFC 8900, DOI 10.17487/RFC8900, September 2020, 4473 . 4475 [RFC8981] Gont, F., Krishnan, S., Narten, T., and R. Draves, 4476 "Temporary Address Extensions for Stateless Address 4477 Autoconfiguration in IPv6", RFC 8981, 4478 DOI 10.17487/RFC8981, February 2021, 4479 . 4481 Appendix A. Interface Attribute Preferences Bitmap Encoding 4483 Adaptation of the OMNI option Interface Attributes Preferences Bitmap 4484 encoding to specific Internetworks such as the Aeronautical 4485 Telecommunications Network with Internet Protocol Services (ATN/IPS) 4486 may include link selection preferences based on other traffic 4487 classifiers (e.g., transport port numbers, etc.) in addition to the 4488 existing DSCP-based preferences. Nodes on specific Internetworks 4489 maintain a map of traffic classifiers to additional P[*] preference 4490 fields beyond the first 64. For example, TCP port 22 maps to P[67], 4491 TCP port 443 maps to P[70], UDP port 8060 maps to P[76], etc. 4493 Implementations use Simplex or Indexed encoding formats for P[*] 4494 encoding in order to encode a given set of traffic classifiers in the 4495 most efficient way. Some use cases may be more efficiently coded 4496 using Simplex form, while others may be more efficient using Indexed. 4497 Once a format is selected for preparation of a single Interface 4498 Attribute the same format must be used for the entire Interface 4499 Attribute sub-option. Different sub-options may use different 4500 formats. 4502 The following figures show coding examples for various Simplex and 4503 Indexed formats: 4505 0 1 2 3 4506 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 4507 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4508 | Sub-Type=3| Sub-length=N | omIndex | omType | 4509 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4510 | Provider ID | Link |R| API | Bitmap(0)=0xff|P00|P01|P02|P03| 4511 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4512 |P04|P05|P06|P07|P08|P09|P10|P11|P12|P13|P14|P15|P16|P17|P18|P19| 4513 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4514 |P20|P21|P22|P23|P24|P25|P26|P27|P28|P29|P30|P31| Bitmap(1)=0xff| 4515 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4516 |P32|P33|P34|P35|P36|P37|P38|P39|P40|P41|P42|P43|P44|P45|P46|P47| 4517 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4518 |P48|P49|P50|P51|P52|P53|P54|P55|P56|P57|P58|P59|P60|P61|P62|P63| 4519 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4520 | Bitmap(2)=0xff|P64|P65|P67|P68| ... 4521 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 4523 Figure 40: Example 1: Dense Simplex Encoding 4525 0 1 2 3 4526 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 4527 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4528 | Sub-Type=3| Sub-length=N | omIndex | omType | 4529 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4530 | Provider ID | Link |R| API | Bitmap(0)=0x00| Bitmap(1)=0x0f| 4531 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4532 |P48|P49|P50|P51|P52|P53|P54|P55|P56|P57|P58|P59|P60|P61|P62|P63| 4533 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4534 | Bitmap(2)=0x00| Bitmap(3)=0x00| Bitmap(4)=0x00| Bitmap(5)=0x00| 4535 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4536 | Bitmap(6)=0xf0|192|193|194|195|196|197|198|199|200|201|202|203| 4537 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4538 |204|205|206|207| Bitmap(7)=0x00| Bitmap(8)=0x0f|272|273|274|275| 4539 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4540 |276|277|278|279|280|281|282|283|284|285|286|287| Bitmap(9)=0x00| 4541 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4542 |Bitmap(10)=0x00| ... 4543 +-+-+-+-+-+-+-+-+-+-+- 4545 Figure 41: Example 2: Sparse Simplex Encoding 4547 0 1 2 3 4548 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 4549 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4550 | Sub-Type=3| Sub-length=N | omIndex | omType | 4551 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4552 | Provider ID | Link |R| API | Index = 0x00 | Bitmap = 0x80 | 4553 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4554 |P00|P01|P02|P03| Index = 0x01 | Bitmap = 0x01 |P60|P61|P62|P63| 4555 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4556 | Index = 0x10 | Bitmap = 0x80 |512|513|514|515| Index = 0x18 | 4557 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4558 | Bitmap = 0x01 |796|797|798|799| ... 4559 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 4561 Figure 42: Example 3: Indexed Encoding 4563 Appendix B. VDL Mode 2 Considerations 4565 ICAO Doc 9776 is the "Technical Manual for VHF Data Link Mode 2" 4566 (VDLM2) that specifies an essential radio frequency data link service 4567 for aircraft and ground stations in worldwide civil aviation air 4568 traffic management. The VDLM2 link type is "multicast capable" 4569 [RFC4861], but with considerable differences from common multicast 4570 links such as Ethernet and IEEE 802.11. 4572 First, the VDLM2 link data rate is only 31.5Kbps - multiple orders of 4573 magnitude less than most modern wireless networking gear. Second, 4574 due to the low available link bandwidth only VDLM2 ground stations 4575 (i.e., and not aircraft) are permitted to send broadcasts, and even 4576 so only as compact layer 2 "beacons". Third, aircraft employ the 4577 services of ground stations by performing unicast RS/RA exchanges 4578 upon receipt of beacons instead of listening for multicast RA 4579 messages and/or sending multicast RS messages. 4581 This beacon-oriented unicast RS/RA approach is necessary to conserve 4582 the already-scarce available link bandwidth. Moreover, since the 4583 numbers of beaconing ground stations operating within a given spatial 4584 range must be kept as sparse as possible, it would not be feasible to 4585 have different classes of ground stations within the same region 4586 observing different protocols. It is therefore highly desirable that 4587 all ground stations observe a common language of RS/RA as specified 4588 in this document. 4590 Note that links of this nature may benefit from compression 4591 techniques that reduce the bandwidth necessary for conveying the same 4592 amount of data. The IETF lpwan working group is considering possible 4593 alternatives: [https://datatracker.ietf.org/wg/lpwan/documents]. 4595 Appendix C. MN / AR Isolation Through L2 Address Mapping 4597 Per [RFC4861], IPv6 ND messages may be sent to either a multicast or 4598 unicast link-scoped IPv6 destination address. However, IPv6 ND 4599 messaging should be coordinated between the MN and AR only without 4600 invoking other nodes on the *NET. This implies that MN / AR control 4601 messaging should be isolated and not overheard by other nodes on the 4602 link. 4604 To support MN / AR isolation on some *NET links, ARs can maintain an 4605 OMNI-specific unicast L2 address ("MSADDR"). For Ethernet-compatible 4606 *NETs, this specification reserves one Ethernet unicast address TBD3 4607 (see: Section 25). For non-Ethernet statically-addressed *NETs, 4608 MSADDR is reserved per the assigned numbers authority for the *NET 4609 addressing space. For still other *NETs, MSADDR may be dynamically 4610 discovered through other means, e.g., L2 beacons. 4612 MNs map the L3 addresses of all IPv6 ND messages they send (i.e., 4613 both multicast and unicast) to MSADDR instead of to an ordinary 4614 unicast or multicast L2 address. In this way, all of the MN's IPv6 4615 ND messages will be received by ARs that are configured to accept 4616 packets destined to MSADDR. Note that multiple ARs on the link could 4617 be configured to accept packets destined to MSADDR, e.g., as a basis 4618 for supporting redundancy. 4620 Therefore, ARs must accept and process packets destined to MSADDR, 4621 while all other devices must not process packets destined to MSADDR. 4622 This model has well-established operational experience in Proxy 4623 Mobile IPv6 (PMIP) [RFC5213][RFC6543]. 4625 Appendix D. Change Log 4627 << RFC Editor - remove prior to publication >> 4629 Differences from draft-templin-6man-omni-00 to draft-templin-6man- 4630 omni-01: 4632 o Changed intended document status to Informational, and removed 4633 documents from "updates" category. 4635 o Updated implementation status. 4637 o Minor edits to HIP message specifications. 4639 o Clarified OAL and *NET IP header field settings during 4640 encapsulation and re-encapsulation. 4642 Differences from earlier versions to draft-templin-6man-omni-00: 4644 o Established working baseline reference. 4646 Authors' Addresses 4648 Fred L. Templin (editor) 4649 The Boeing Company 4650 P.O. Box 3707 4651 Seattle, WA 98124 4652 USA 4654 Email: fltemplin@acm.org 4656 Tony Whyman 4657 MWA Ltd c/o Inmarsat Global Ltd 4658 99 City Road 4659 London EC1Y 1AX 4660 England 4662 Email: tony.whyman@mccallumwhyman.com