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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group F. Templin, Ed. 3 Internet-Draft The Boeing Company 4 Updates: rfc1191, rfc4443, rfc7526, A. Whyman 5 rfc8201 (if approved) MWA Ltd c/o Inmarsat Global Ltd 6 Intended status: Standards Track March 11, 2021 7 Expires: September 12, 2021 9 Transmission of IP Packets over Overlay Multilink Network (OMNI) 10 Interfaces 11 draft-templin-6man-omni-interface-95 13 Abstract 15 Mobile nodes (e.g., aircraft of various configurations, terrestrial 16 vehicles, seagoing vessels, enterprise wireless devices, etc.) 17 communicate with networked correspondents over multiple access 18 network data links and configure mobile routers to connect end user 19 networks. A multilink interface specification is therefore needed 20 for coordination with the network-based mobility service. This 21 document specifies the transmission of IP packets over Overlay 22 Multilink Network (OMNI) Interfaces. 24 Status of This Memo 26 This Internet-Draft is submitted in full conformance with the 27 provisions of BCP 78 and BCP 79. 29 Internet-Drafts are working documents of the Internet Engineering 30 Task Force (IETF). Note that other groups may also distribute 31 working documents as Internet-Drafts. The list of current Internet- 32 Drafts is at https://datatracker.ietf.org/drafts/current/. 34 Internet-Drafts are draft documents valid for a maximum of six months 35 and may be updated, replaced, or obsoleted by other documents at any 36 time. It is inappropriate to use Internet-Drafts as reference 37 material or to cite them other than as "work in progress." 39 This Internet-Draft will expire on September 12, 2021. 41 Copyright Notice 43 Copyright (c) 2021 IETF Trust and the persons identified as the 44 document authors. All rights reserved. 46 This document is subject to BCP 78 and the IETF Trust's Legal 47 Provisions Relating to IETF Documents 48 (https://trustee.ietf.org/license-info) in effect on the date of 49 publication of this document. Please review these documents 50 carefully, as they describe your rights and restrictions with respect 51 to this document. Code Components extracted from this document must 52 include Simplified BSD License text as described in Section 4.e of 53 the Trust Legal Provisions and are provided without warranty as 54 described in the Simplified BSD License. 56 Table of Contents 58 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 59 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 60 3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 9 61 4. Overlay Multilink Network (OMNI) Interface Model . . . . . . 9 62 5. OMNI Interface Maximum Transmission Unit (MTU) . . . . . . . 14 63 5.1. OMNI Interface MTU/MRU . . . . . . . . . . . . . . . . . 14 64 5.2. The OMNI Adaptation Layer (OAL) . . . . . . . . . . . . . 15 65 5.3. OAL Addressing Considerations . . . . . . . . . . . . . . 19 66 5.4. OMNI Interface MTU Feedback Messaging . . . . . . . . . . 20 67 5.5. OAL Fragmentation Security Implications . . . . . . . . . 22 68 5.6. OAL Super-Packets . . . . . . . . . . . . . . . . . . . . 23 69 6. Frame Format . . . . . . . . . . . . . . . . . . . . . . . . 25 70 7. Link-Local Addresses (LLAs) . . . . . . . . . . . . . . . . . 25 71 8. Unique-Local Addresses (ULAs) . . . . . . . . . . . . . . . . 27 72 9. Global Unicast Addresses (GUAs) . . . . . . . . . . . . . . . 28 73 10. Node Identification . . . . . . . . . . . . . . . . . . . . . 29 74 11. Address Mapping - Unicast . . . . . . . . . . . . . . . . . . 29 75 11.1. Sub-Options . . . . . . . . . . . . . . . . . . . . . . 31 76 11.1.1. Pad1 . . . . . . . . . . . . . . . . . . . . . . . . 33 77 11.1.2. PadN . . . . . . . . . . . . . . . . . . . . . . . . 33 78 11.1.3. Interface Attributes (Type 1) . . . . . . . . . . . 34 79 11.1.4. Interface Attributes (Type 2) . . . . . . . . . . . 35 80 11.1.5. Traffic Selector . . . . . . . . . . . . . . . . . . 39 81 11.1.6. MS-Register . . . . . . . . . . . . . . . . . . . . 40 82 11.1.7. MS-Release . . . . . . . . . . . . . . . . . . . . . 41 83 11.1.8. Geo Coordinates . . . . . . . . . . . . . . . . . . 41 84 11.1.9. Dynamic Host Configuration Protocol for IPv6 85 (DHCPv6) Message . . . . . . . . . . . . . . . . . . 42 86 11.1.10. Host Identity Protocol (HIP) Message . . . . . . . . 43 87 11.1.11. ICMPv6 Error Message . . . . . . . . . . . . . . . . 44 88 11.1.12. Maximum Reassembly Unit (MRU) . . . . . . . . . . . 45 89 11.1.13. Node Identification . . . . . . . . . . . . . . . . 45 90 11.1.14. Sub-Type Extension . . . . . . . . . . . . . . . . . 47 91 12. Address Mapping - Multicast . . . . . . . . . . . . . . . . . 50 92 13. Multilink Conceptual Sending Algorithm . . . . . . . . . . . 50 93 13.1. Multiple OMNI Interfaces . . . . . . . . . . . . . . . . 51 94 13.2. MN<->AR Traffic Loop Prevention . . . . . . . . . . . . 52 95 14. Router Discovery and Prefix Registration . . . . . . . . . . 52 96 14.1. Router Discovery in IP Multihop and IPv4-Only Networks . 56 97 14.2. MS-Register and MS-Release List Processing . . . . . . . 58 98 14.3. DHCPv6-based Prefix Registration . . . . . . . . . . . . 60 99 15. Secure Redirection . . . . . . . . . . . . . . . . . . . . . 61 100 16. AR and MSE Resilience . . . . . . . . . . . . . . . . . . . . 62 101 17. Detecting and Responding to MSE Failures . . . . . . . . . . 62 102 18. Transition Considerations . . . . . . . . . . . . . . . . . . 62 103 19. OMNI Interfaces on Open Internetworks . . . . . . . . . . . . 63 104 20. Time-Varying MNPs . . . . . . . . . . . . . . . . . . . . . . 65 105 21. (H)HITs and Temporary ULAs . . . . . . . . . . . . . . . . . 65 106 22. Address Selection . . . . . . . . . . . . . . . . . . . . . . 66 107 23. Error Messages . . . . . . . . . . . . . . . . . . . . . . . 67 108 24. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 67 109 24.1. "IPv6 Neighbor Discovery Option Formats" Registry . . . 67 110 24.2. "Ethernet Numbers" Registry . . . . . . . . . . . . . . 67 111 24.3. "ICMPv6 Code Fields: Type 2 - Packet Too Big" Registry . 67 112 24.4. "OMNI Option Sub-Type Values" (New Registry) . . . . . . 68 113 24.5. "OMNI Node Identification ID-Type Values" (New Registry) 68 114 24.6. "OMNI Option Sub-Type Extension Values" (New Registry) . 69 115 24.7. "OMNI RFC4380 UDP/IP Header Option" (New Registry) . . . 69 116 24.8. "OMNI RFC6081 UDP/IP Trailer Option" (New Registry) . . 70 117 24.9. Additional Considerations . . . . . . . . . . . . . . . 70 118 25. Security Considerations . . . . . . . . . . . . . . . . . . . 71 119 26. Implementation Status . . . . . . . . . . . . . . . . . . . . 72 120 27. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 72 121 28. References . . . . . . . . . . . . . . . . . . . . . . . . . 73 122 28.1. Normative References . . . . . . . . . . . . . . . . . . 73 123 28.2. Informative References . . . . . . . . . . . . . . . . . 75 124 Appendix A. Interface Attribute Preferences Bitmap Encoding . . 82 125 Appendix B. VDL Mode 2 Considerations . . . . . . . . . . . . . 84 126 Appendix C. MN / AR Isolation Through L2 Address Mapping . . . . 85 127 Appendix D. Change Log . . . . . . . . . . . . . . . . . . . . . 85 128 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 88 130 1. Introduction 132 Mobile Nodes (MNs) (e.g., aircraft of various configurations, 133 terrestrial vehicles, seagoing vessels, enterprise wireless devices, 134 pedestrians with cellphones, etc.) often have multiple interface 135 connections to wireless and/or wired-line data links used for 136 communicating with networked correspondents. These data links may 137 have diverse performance, cost and availability properties that can 138 change dynamically according to mobility patterns, flight phases, 139 proximity to infrastructure, etc. MNs coordinate their data links in 140 a discipline known as "multilink", in which a single virtual 141 interface is configured over the node's underlying interface 142 connections to the data links. 144 The MN configures a virtual interface (termed the "Overlay Multilink 145 Network Interface (OMNI)") as a thin layer over the underlying 146 interfaces. The OMNI interface is therefore the only interface 147 abstraction exposed to the IP layer and behaves according to the Non- 148 Broadcast, Multiple Access (NBMA) interface principle, while 149 underlying interfaces appear as link layer communication channels in 150 the architecture. The OMNI interface internally employs the "OMNI 151 Adaptation Layer (OAL)" to ensure that packets are delivered without 152 loss due to size restrictions. The OMNI interface connects to a 153 virtual overlay service known as the "OMNI link". The OMNI link 154 spans one or more Internetworks that may include private-use 155 infrastructures and/or the global public Internet itself. 157 Each MN receives a Mobile Network Prefix (MNP) for numbering 158 downstream-attached End User Networks (EUNs) independently of the 159 access network data links selected for data transport. The MN 160 performs router discovery over the OMNI interface (i.e., similar to 161 IPv6 customer edge routers [RFC7084]) and acts as a mobile router on 162 behalf of its EUNs. The router discovery process is iterated over 163 each of the OMNI interface's underlying interfaces in order to 164 register per-link parameters (see Section 14). 166 The OMNI interface provides a multilink nexus for exchanging inbound 167 and outbound traffic via the correct underlying interface(s). The IP 168 layer sees the OMNI interface as a point of connection to the OMNI 169 link. Each OMNI link has one or more associated Mobility Service 170 Prefixes (MSPs), which are typically IP Global Unicast Address (GUA) 171 prefixes from which MNPs are derived. If there are multiple OMNI 172 links, the IPv6 layer will see multiple OMNI interfaces. 174 MNs may connect to multiple distinct OMNI links within the same OMNI 175 domain by configuring multiple OMNI interfaces, e.g., omni0, omni1, 176 omni2, etc. Each OMNI interface is configured over a set of 177 underlying interfaces and provides a nexus for Safety-Based Multilink 178 (SBM) operation. Each OMNI interface within the same OMNI domain 179 configures a common ULA prefix [ULA]::/48, and configures a unique 180 16-bit Subnet ID '*' to construct the sub-prefix [ULA*]::/64 (see: 181 Section 8). The IP layer applies SBM routing to select an OMNI 182 interface, which then applies Performance-Based Multilink (PBM) to 183 select the correct underlying interface. Applications can apply 184 Segment Routing [RFC8402] to select independent SBM topologies for 185 fault tolerance. 187 The OMNI interface interacts with a network-based Mobility Service 188 (MS) through IPv6 Neighbor Discovery (ND) control message exchanges 189 [RFC4861]. The MS provides Mobility Service Endpoints (MSEs) that 190 track MN movements and represent their MNPs in a global routing or 191 mapping system. 193 Many OMNI use cases have been proposed. In particular, the 194 International Civil Aviation Organization (ICAO) Working Group-I 195 Mobility Subgroup is developing a future Aeronautical 196 Telecommunications Network with Internet Protocol Services (ATN/IPS) 197 and has issued a liaison statement requesting IETF adoption [ATN] in 198 support of ICAO Document 9896 [ATN-IPS]. The IETF IP Wireless Access 199 in Vehicular Environments (ipwave) working group has further included 200 problem statement and use case analysis for OMNI in a document now in 201 AD evaluation for RFC publication 202 [I-D.ietf-ipwave-vehicular-networking]. Still other communities of 203 interest include AEEC, RTCA Special Committee 228 (SC-228) and NASA 204 programs that examine commercial aviation, Urban Air Mobility (UAM) 205 and Unmanned Air Systems (UAS). Pedestrians with handheld devices 206 represent another large class of potential OMNI users. 208 This document specifies the transmission of IP packets and MN/MS 209 control messages over OMNI interfaces. The OMNI interface supports 210 either IP protocol version (i.e., IPv4 [RFC0791] or IPv6 [RFC8200]) 211 as the network layer in the data plane, while using IPv6 ND messaging 212 as the control plane independently of the data plane IP protocol(s). 213 The OAL operates as a mid-layer between L3 and L2 based on IP-in-IPv6 214 encapsulation per [RFC2473] as discussed in the following sections. 215 OMNI interfaces enable Multilink, Mobility, Multihop, Multicast and 216 MTU services (i.e., the "five M's"), with provisions for both 217 Vehicle-to-Infrastructure (V2I) communications and Vehicle-to-Vehicle 218 (V2V) communications outside the context of infrastructure. 220 2. Terminology 222 The terminology in the normative references applies; especially, the 223 terms "link" and "interface" are the same as defined in the IPv6 224 [RFC8200] and IPv6 Neighbor Discovery (ND) [RFC4861] specifications. 225 Additionally, this document assumes the following IPv6 ND message 226 types: Router Solicitation (RS), Router Advertisement (RA), Neighbor 227 Solicitation (NS), Neighbor Advertisement (NA) and Redirect. 229 The Protocol Constants defined in Section 10 of [RFC4861] are used in 230 their same format and meaning in this document. The terms "All- 231 Routers multicast", "All-Nodes multicast" and "Subnet-Router anycast" 232 are the same as defined in [RFC4291] (with Link-Local scope assumed). 234 The term "IP" is used to refer collectively to either Internet 235 Protocol version (i.e., IPv4 [RFC0791] or IPv6 [RFC8200]) when a 236 specification at the layer in question applies equally to either 237 version. 239 The following terms are defined within the scope of this document: 241 Mobile Node (MN) 242 an end system with a mobile router having multiple distinct 243 upstream data link connections that are grouped together in one or 244 more logical units. The MN's data link connection parameters can 245 change over time due to, e.g., node mobility, link quality, etc. 246 The MN further connects a downstream-attached End User Network 247 (EUN). The term MN used here is distinct from uses in other 248 documents, and does not imply a particular mobility protocol. 250 End User Network (EUN) 251 a simple or complex downstream-attached mobile network that 252 travels with the MN as a single logical unit. The IP addresses 253 assigned to EUN devices remain stable even if the MN's upstream 254 data link connections change. 256 Mobility Service (MS) 257 a mobile routing service that tracks MN movements and ensures that 258 MNs remain continuously reachable even across mobility events. 259 Specific MS details are out of scope for this document. 261 Mobility Service Endpoint (MSE) 262 an entity in the MS (either singular or aggregate) that 263 coordinates the mobility events of one or more MN. 265 Mobility Service Prefix (MSP) 266 an aggregated IP Global Unicast Address (GUA) prefix (e.g., 267 2001:db8::/32, 192.0.2.0/24, etc.) assigned to the OMNI link and 268 from which more-specific Mobile Network Prefixes (MNPs) are 269 delegated. OMNI link administrators typically obtain MSPs from an 270 Internet address registry, however private-use prefixes can 271 alternatively be used subject to certain limitations (see: 272 Section 9). OMNI links that connect to the global Internet 273 advertise their MSPs to their interdomain routing peers. 275 Mobile Network Prefix (MNP) 276 a longer IP prefix delegated from an MSP (e.g., 277 2001:db8:1000:2000::/56, 192.0.2.8/30, etc.) and assigned to a MN. 278 MNs sub-delegate the MNP to devices located in EUNs. 280 Access Network (ANET) 281 a data link service network (e.g., an aviation radio access 282 network, satellite service provider network, cellular operator 283 network, WiFi network, etc.) that connects MNs. Physical and/or 284 data link level security is assumed, and sometimes referred to as 285 "protected spectrum". Private enterprise networks and ground 286 domain aviation service networks may provide multiple secured IP 287 hops between the MN's point of connection and the nearest Access 288 Router. 290 Access Router (AR) 291 a router in the ANET for connecting MNs to correspondents in 292 outside Internetworks. The AR may be located on the same physical 293 link as the MN, or may be located multiple IP hops away. In the 294 latter case, the MN uses encapsulation to communicate with the AR 295 as though it were on the same physical link. 297 ANET interface 298 a MN's attachment to a link in an ANET. 300 Internetwork (INET) 301 a connected network region with a coherent IP addressing plan that 302 provides transit forwarding services between ANETs and nodes that 303 connect directly to the open INET via unprotected media. No 304 physical and/or data link level security is assumed, therefore 305 security must be applied by upper layers. The global public 306 Internet itself is an example. 308 INET interface 309 a node's attachment to a link in an INET. 311 *NET 312 a "wildcard" term used when a given specification applies equally 313 to both ANET and INET cases. 315 OMNI link 316 a Non-Broadcast, Multiple Access (NBMA) virtual overlay configured 317 over one or more INETs and their connected ANETs. An OMNI link 318 can comprise multiple INET segments joined by bridges the same as 319 for any link; the addressing plans in each segment may be mutually 320 exclusive and managed by different administrative entities. 322 OMNI interface 323 a node's attachment to an OMNI link, and configured over one or 324 more underlying *NET interfaces. If there are multiple OMNI links 325 in an OMNI domain, a separate OMNI interface is configured for 326 each link. 328 OMNI Adaptation Layer (OAL) 329 an OMNI interface process whereby packets admitted into the 330 interface are wrapped in a mid-layer IPv6 header and fragmented/ 331 reassembled if necessary to support the OMNI link Maximum 332 Transmission Unit (MTU). The OAL is also responsible for 333 generating MTU-related control messages as necessary, and for 334 providing addressing context for spanning multiple segments of a 335 bridged OMNI link. 337 OMNI Option 338 an IPv6 Neighbor Discovery option providing multilink parameters 339 for the OMNI interface as specified in Section 11. 341 Mobile Network Prefix Link Local Address (MNP-LLA) 342 an IPv6 Link Local Address that embeds the most significant 64 343 bits of an MNP in the lower 64 bits of fe80::/64, as specified in 344 Section 7. 346 Mobile Network Prefix Unique Local Address (MNP-ULA) 347 an IPv6 Unique-Local Address derived from an MNP-LLA. 349 Administrative Link Local Address (ADM-LLA) 350 an IPv6 Link Local Address that embeds a 32-bit administratively- 351 assigned identification value in the lower 32 bits of fe80::/96, 352 as specified in Section 7. 354 Administrative Unique Local Address (ADM-ULA) 355 an IPv6 Unique-Local Address derived from an ADM-LLA. 357 Multilink 358 an OMNI interface's manner of managing diverse underlying 359 interface connections to data links as a single logical unit. The 360 OMNI interface provides a single unified interface to upper 361 layers, while underlying interface selections are performed on a 362 per-packet basis considering factors such as DSCP, flow label, 363 application policy, signal quality, cost, etc. Multilinking 364 decisions are coordinated in both the outbound (i.e. MN to 365 correspondent) and inbound (i.e., correspondent to MN) directions. 367 Multihop 368 an iterative relaying of IP packets between MNs over an OMNI 369 underlying interface technology (such as omnidirectional wireless) 370 without support of fixed infrastructure. Multihop services entail 371 node-to-node relaying within a Mobile/Vehicular Ad-hoc Network 372 (MANET/VANET) for MN-to-MN communications and/or for "range 373 extension" where MNs within range of communications infrastructure 374 elements provide forwarding services for other MNs. 376 L2 377 The second layer in the OSI network model. Also known as "layer- 378 2", "link-layer", "sub-IP layer", "data link layer", etc. 380 L3 381 The third layer in the OSI network model. Also known as "layer- 382 3", "network-layer", "IP layer", etc. 384 underlying interface 385 a *NET interface over which an OMNI interface is configured. The 386 OMNI interface is seen as a L3 interface by the IP layer, and each 387 underlying interface is seen as a L2 interface by the OMNI 388 interface. The underlying interface either connects directly to 389 the physical communications media or coordinates with another node 390 where the physical media is hosted. 392 Mobility Service Identification (MSID) 393 Each MSE and AR is assigned a unique 32-bit Identification (MSID) 394 (see: Section 7). IDs are assigned according to MS-specific 395 guidelines (e.g., see: [I-D.templin-intarea-6706bis]). 397 Safety-Based Multilink (SBM) 398 A means for ensuring fault tolerance through redundancy by 399 connecting multiple affiliated OMNI interfaces to independent 400 routing topologies (i.e., multiple independent OMNI links). 402 Performance Based Multilink (PBM) 403 A means for selecting underlying interface(s) for packet 404 transmission and reception within a single OMNI interface. 406 OMNI Domain 407 The set of all SBM/PBM OMNI links that collectively provides 408 services for a common set of MSPs. Each OMNI domain consists of a 409 set of affiliated OMNI links that all configure the same ::/48 ULA 410 prefix with a unique 16-bit Subnet ID as discussed in Section 8. 412 3. Requirements 414 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 415 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 416 "OPTIONAL" in this document are to be interpreted as described in BCP 417 14 [RFC2119][RFC8174] when, and only when, they appear in all 418 capitals, as shown here. 420 An implementation is not required to internally use the architectural 421 constructs described here so long as its external behavior is 422 consistent with that described in this document. 424 4. Overlay Multilink Network (OMNI) Interface Model 426 An OMNI interface is a MN virtual interface configured over one or 427 more underlying interfaces, which may be physical (e.g., an 428 aeronautical radio link) or virtual (e.g., an Internet or higher- 429 layer "tunnel"). The MN receives a MNP from the MS, and coordinates 430 with the MS through IPv6 ND message exchanges. The MN uses the MNP 431 to construct a unique Link-Local Address (MNP-LLA) through the 432 algorithmic derivation specified in Section 7 and assigns the LLA to 433 the OMNI interface. 435 The OMNI interface architectural layering model is the same as in 436 [RFC5558][RFC7847], and augmented as shown in Figure 1. The IP layer 437 therefore sees the OMNI interface as a single L3 interface nexus for 438 multiple underlying interfaces that appear as L2 communication 439 channels in the architecture. 441 +----------------------------+ 442 | Upper Layer Protocol | 443 Session-to-IP +---->| | 444 Address Binding | +----------------------------+ 445 +---->| IP (L3) | 446 IP Address +---->| | 447 Binding | +----------------------------+ 448 +---->| OMNI Interface | 449 Logical-to- +---->| (OMNI Adaptation Layer) | 450 Physical | +----------------------------+ 451 Interface +---->| L2 | L2 | | L2 | 452 Binding |(IF#1)|(IF#2)| ..... |(IF#n)| 453 +------+------+ +------+ 454 | L1 | L1 | | L1 | 455 | | | | | 456 +------+------+ +------+ 458 Figure 1: OMNI Interface Architectural Layering Model 460 Each underlying interface provides an L2/L1 abstraction according to 461 one of the following models: 463 o INET interfaces connect to an INET either natively or through one 464 or several IPv4 Network Address Translators (NATs). Native INET 465 interfaces have global IP addresses that are reachable from any 466 INET correspondent. NATed INET interfaces typically have private 467 IP addresses and connect to a private network behind one or more 468 NATs that provide INET access. 470 o ANET interfaces connect to a protected ANET that is separated from 471 the open INET by an AR acting as a proxy. The ANET interface may 472 be either on the same L2 link segment as the AR, or separated from 473 the AR by multiple IP hops. 475 o VPNed interfaces use security encapsulation over a *NET to a 476 Virtual Private Network (VPN) gateway. Other than the link-layer 477 encapsulation format, VPNed interfaces behave the same as for 478 Direct interfaces. 480 o Direct (aka "point-to-point") interfaces connect directly to a 481 peer without crossing any *NET paths. An example is a line-of- 482 sight link between a remote pilot and an unmanned aircraft. 484 The OMNI interface forwards original IP packets from the network 485 layer (L3) using the OMNI Adaptation Layer (OAL) (see: Section 5) as 486 a mid-layer encapsulation and fragmentation service. This "OAL 487 source" then further encapsulates the resulting OAL packets/fragments 488 in *NET headers for transmission over underlying interfaces (L2/L1). 489 In the reverse, the OMNI interface receives *NET-encapsulated OAL 490 packets/fragments from underlying interfaces (L1/L2), then discards 491 the *NET headers. If the OAL packets/fragments are addressed to 492 itself, the OMNI interface acts as an "OAL destination" and performs 493 reassembly if necessary, discards the OAL encapsulation, and delivers 494 the packet to the network layer (L3). If the OAL packets/fragments 495 are addressed to another node, the OMNI interface instead acts as an 496 "OAL intermediate node" by re-encapsulating in new *NET headers and 497 forwarding over an underlying interface without reassembling or 498 discarding the OAL encapsulation. The OAL source and OAL destination 499 are seen as "neighbors" on the OMNI link, while OAL intermediate 500 nodes are seen as "bridges". 502 The OMNI virtual interface model gives rise to a number of 503 opportunities: 505 o since MNP-LLAs are uniquely derived from an MNP, no Duplicate 506 Address Detection (DAD) or Multicast Listener Discovery (MLD) 507 messaging is necessary. 509 o since Temporary ULAs are statistically unique, they can be used 510 without DAD, e.g. for MN-to-MN communications until an MNP-LLA is 511 obtained. 513 o *NET interfaces on the same L2 link segment as an AR do not 514 require any L3 addresses (i.e., not even link-local) in 515 environments where communications are coordinated entirely over 516 the OMNI interface. (An alternative would be to also assign the 517 same LLA to all *NET interfaces.) 519 o as underlying interface properties change (e.g., link quality, 520 cost, availability, etc.), any active interface can be used to 521 update the profiles of multiple additional interfaces in a single 522 message. This allows for timely adaptation and service continuity 523 under dynamically changing conditions. 525 o coordinating underlying interfaces in this way allows them to be 526 represented in a unified MS profile with provisions for mobility 527 and multilink operations. 529 o exposing a single virtual interface abstraction to the IPv6 layer 530 allows for multilink operation (including QoS based link 531 selection, packet replication, load balancing, etc.) at L2 while 532 still permitting L3 traffic shaping based on, e.g., DSCP, flow 533 label, etc. 535 o the OMNI interface allows inter-INET traversal when nodes located 536 in different INETs need to communicate with one another. This 537 mode of operation would not be possible via direct communications 538 over the underlying interfaces themselves. 540 o the OMNI Adaptation Layer (OAL) within the OMNI interface supports 541 lossless and adaptive path MTU mitigations not available for 542 communications directly over the underlying interfaces themselves. 543 The OAL supports "packing" of multiple IP payload packets within a 544 single OAL packet. 546 o L3 sees the OMNI interface as a point of connection to the OMNI 547 link; if there are multiple OMNI links (i.e., multiple MS's), L3 548 will see multiple OMNI interfaces. 550 o Multiple independent OMNI interfaces can be used for increased 551 fault tolerance through Safety-Based Multilink (SBM), with 552 Performance-Based Multilink (PBM) applied within each interface. 554 Other opportunities are discussed in [RFC7847]. Note that even when 555 the OMNI virtual interface is present, applications can still access 556 underlying interfaces either through the network protocol stack using 557 an Internet socket or directly using a raw socket. This allows for 558 intra-network (or point-to-point) communications without invoking the 559 OMNI interface and/or OAL. For example, when an IPv6 OMNI interface 560 is configured over an underlying IPv4 interface, applications can 561 still invoke IPv4 intra-network communications as long as the 562 communicating endpoints are not subject to mobility dynamics. 563 However, the opportunities discussed above are not available when the 564 architectural layering is bypassed in this way. 566 Figure 2 depicts the architectural model for a MN with an attached 567 EUN connecting to the MS via multiple independent *NETs. When an 568 underlying interface becomes active, the MN's OMNI interface sends 569 IPv6 ND messages without encapsulation if the first-hop Access Router 570 (AR) is on the same underlying link; otherwise, the interface uses 571 IP-in-IP encapsulation. The IPv6 ND messages traverse the ground 572 domain *NETs until they reach an AR (AR#1, AR#2, ..., AR#n), which 573 then coordinates with an INET Mobility Service Endpoint (MSE#1, 574 MSE#2, ..., MSE#m) and returns an IPv6 ND message response to the MN. 575 The Hop Limit in IPv6 ND messages is not decremented due to 576 encapsulation; hence, the OMNI interface appears to be attached to an 577 ordinary link. 579 +--------------+ (:::)-. 580 | MN |<-->.-(::EUN:::) 581 +--------------+ `-(::::)-' 582 |OMNI interface| 583 +----+----+----+ 584 +--------|IF#1|IF#2|IF#n|------ + 585 / +----+----+----+ \ 586 / | \ 587 / | \ 588 v v v 589 (:::)-. (:::)-. (:::)-. 590 .-(::*NET:::) .-(::*NET:::) .-(::*NET:::) 591 `-(::::)-' `-(::::)-' `-(::::)-' 592 +----+ +----+ +----+ 593 ... |AR#1| .......... |AR#2| ......... |AR#n| ... 594 . +-|--+ +-|--+ +-|--+ . 595 . | | | 596 . v v v . 597 . <----- INET Encapsulation -----> . 598 . . 599 . +-----+ (:::)-. . 600 . |MSE#2| .-(::::::::) +-----+ . 601 . +-----+ .-(::: INET :::)-. |MSE#m| . 602 . (::::: Routing ::::) +-----+ . 603 . `-(::: System :::)-' . 604 . +-----+ `-(:::::::-' . 605 . |MSE#1| +-----+ +-----+ . 606 . +-----+ |MSE#3| |MSE#4| . 607 . +-----+ +-----+ . 608 . . 609 . . 610 . <----- Worldwide Connected Internetwork ----> . 611 ........................................................... 613 Figure 2: MN/MS Coordination via Multiple *NETs 615 After the initial IPv6 ND message exchange, the MN (and/or any nodes 616 on its attached EUNs) can send and receive IP data packets over the 617 OMNI interface. OMNI interface multilink services will forward the 618 packets via ARs in the correct underlying *NETs. The AR encapsulates 619 the packets according to the capabilities provided by the MS and 620 forwards them to the next hop within the worldwide connected 621 Internetwork via optimal routes. 623 OMNI links span one or more underlying Internetworks via the OMNI 624 Adaptation Layer (OAL) which is based on a mid-layer overlay 625 encapsulation using [RFC2473]. Each OMNI link corresponds to a 626 different overlay (differentiated by an address codepoint) which may 627 be carried over a completely separate underlying topology. Each MN 628 can facilitate SBM by connecting to multiple OMNI links using a 629 distinct OMNI interface for each link. 631 Note: OMNI interface underlying interfaces often connect directly to 632 physical media on the local platform (e.g., a laptop computer with 633 WiFi, etc.), but in some configurations the physical media may be 634 hosted on a separate Local Area Network (LAN) node. In that case, 635 the OMNI interface can establish a Layer-2 VLAN or a point-to-point 636 tunnel (at a layer below the underlying interface) to the node 637 hosting the physical media. The OMNI interface may also apply 638 encapsulation at the underlying interface layer (e.g., as for a 639 tunnel virtual interface) such that packets would appear "double- 640 encapsulated" on the LAN; the node hosting the physical media in turn 641 removes the LAN encapsulation prior to transmission or inserts it 642 following reception. Finally, the underlying interface must monitor 643 the node hosting the physical media (e.g., through periodic 644 keepalives) so that it can convey up/down/status information to the 645 OMNI interface. 647 5. OMNI Interface Maximum Transmission Unit (MTU) 649 The OMNI interface observes the link nature of tunnels, including the 650 Maximum Transmission Unit (MTU), Maximum Reassembly Unit (MRU) and 651 the role of fragmentation and reassembly [I-D.ietf-intarea-tunnels]. 652 The OMNI interface is configured over one or more underlying 653 interfaces as discussed in Section 4, where the interfaces (and their 654 associated *NET paths) may have diverse MTUs. OMNI interface 655 considerations for accommodating original IP packets of various sizes 656 are discussed in the following sections. 658 5.1. OMNI Interface MTU/MRU 660 IPv6 underlying interfaces are REQUIRED to configure a minimum MTU of 661 1280 bytes and a minimum MRU of 1500 bytes [RFC8200]. Therefore, the 662 minimum IPv6 path MTU is 1280 bytes since routers on the path are not 663 permitted to perform network fragmentation even though the 664 destination is required to reassemble more. The network therefore 665 MUST forward packets of at least 1280 bytes without generating an 666 IPv6 Path MTU Discovery (PMTUD) Packet Too Big (PTB) message 667 [RFC8201]. (Note: the source can apply "source fragmentation" for 668 locally-generated IPv6 packets up to 1500 bytes and larger still if 669 it if has a way to determine that the destination configures a larger 670 MRU, but this does not affect the minimum IPv6 path MTU.) 671 IPv4 underlying interfaces are REQUIRED to configure a minimum MTU of 672 68 bytes [RFC0791] and a minimum MRU of 576 bytes [RFC0791][RFC1122]. 673 Therefore, when the Don't Fragment (DF) bit in the IPv4 header is set 674 to 0 the minimum IPv4 path MTU is 576 bytes since routers on the path 675 support network fragmentation and the destination is required to 676 reassemble at least that much. The OMNI interface therefore MUST set 677 DF to 0 in the IPv4 encapsulation headers of OAL/*NET packets that 678 are no larger than 576 bytes, and MUST set DF to 1 in larger packets. 679 (Note: even if the encapsulation source has a way to determine that 680 the encapsulation destination configures an MRU larger than 576 681 bytes, it should not assume a larger minimum IPv4 path MTU without 682 careful consideration of the issues discussed in Section 5.5.) 684 The OMNI interface configures an MTU of 9180 bytes [RFC2492]; the 685 size is therefore not a reflection of the underlying interface or 686 *NET path MTUs, but rather determines the largest original "inner- 687 layer" IP packet the OAL can forward. For each OAL destination 688 (i.e., for each OMNI link neighbor), the OAL source configures a per- 689 neighbor MRU with default and maximum set to 9180 bytes but may be 690 reduced based on receipt of an IPv6 ND message with an OMNI MRU sub- 691 option (see: Section 11.1.12). The OMNI interface employs the OAL as 692 a "mid-layer" encapsulation, fragmentation and reassembly service for 693 original IP packets, and the OAL in turn uses "outer-layer" *NET 694 encapsulation to forward OAL/*NET packets/fragments over the 695 underlying interfaces (see: Section 5.2). 697 5.2. The OMNI Adaptation Layer (OAL) 699 When an OMNI interface forwards an original IP packet from the 700 network layer for transmission over one or more underlying 701 interfaces, the OMNI Adaptation Layer (OAL) acting as the OAL source 702 drops the packet and returns a PTB message if the packet exceeds the 703 MRU for the intended OAL destination. Next, if fragmentation, 704 integrity verification and/or explicit OAL addressing are required 705 the OAL source inserts a mid-layer IPv6 encapsulation per [RFC2473]; 706 otherwise (e.g., for ANET peers that share a common underlying link), 707 the OAL source MAY omit the encapsulation. When OAL encapsulation is 708 used, the OAL source sets the header fields per standard IPv6 709 procedures but does not decrement the inner IP header Hop Limit/TTL 710 since encapsulation occurs at a layer below IP forwarding. The OAL 711 source next appends a 2 octet trailer (initialized to 0) at the end 712 of the packet while incrementing the OAL header Payload Length to 713 reflect the addition of the trailer. The OAL source then calculates 714 the 2's complement (mod 256) Fletcher's checksum 715 [CKSUM][RFC2328][RFC0905] over the entire OAL packet beginning with 716 an IPv6 pseudo-header based on the OAL header Payload Length (see 717 Section 8.1 of [RFC8200]), then writes the results over the trailer 718 octets. The OAL source then inserts a single OMNI Routing Header 719 (ORH) if necessary (see: [I-D.templin-intarea-6706bis]) while 720 incrementing Payload Length to reflect the addition of the ORH, then 721 fragments the OAL packet if necessary. The OAL source finally 722 forwards the packet/fragments over an underlying interface while 723 adding any necessary *NET encapsulations. The formats of OAL packets 724 and fragments are shown in Figure 3. 726 +----------+-----+-----+-----+-----+-----+-----+----+ 727 | OAL Hdr | Original IP packet |Csum| 728 +----------+-----+-----+-----+-----+-----+-----+----+ 729 a) OAL packet after encapsulation but before fragmentation 731 +--------+----------+--+---------+ 732 |*NET Hdr| OAL Hdr |FH| Frag #1 | 733 +--------+----------+--+---------+ 734 +--------+----------+--+---------+ 735 |*NET Hdr| OAL Hdr |FH| Frag #2 | 736 +--------+----------+--+---------+ 737 +--------+----------+--+---------+ 738 |*NET Hdr| OAL Hdr |FH| Frag #3 | 739 +--------+----------+--+---------+ 740 .... 741 +--------+----------+--+---------+----+ 742 |*NET hdr| OAL Hdr |FH| Frag #n |Csum| 743 +--------+----------+--+---------+----+ 744 b) Fragments after OAL fragmentation and *NET encapsulation 745 (FH = Fragment Header; Csum appears only in final fragment) 747 Figure 3: OAL Packets and Fragments 749 When an OMNI interface receives a *NET encapsulated packet from an 750 underlying interface, the OAL destination discards the *NET 751 encapsulation headers and examines the OAL header if present. If the 752 packet is addressed to a different node, the OAL destination re- 753 encapsulates and forwards as discussed below; otherwise, the OAL 754 destination performs reassembly if necessary then removes the ORH if 755 present while decrementing Payload Length to reflect the removal of 756 the ORH. If the OAL header is present, the OAL destination next 757 verifies the checksum and discards the packet if the checksum is 758 incorrect. If the packet was accepted, the OAL destination then 759 removes the OAL header/trailer, then delivers the original packet to 760 the IP layer. Note that link layers include a CRC-32 integrity check 761 which provides effective hop-by-hop error detection in the underlying 762 network for packet/fragment sizes up to the OMNI interface MTU [CRC], 763 but that some hops may traverse intermediate layers such as tunnels 764 over IPv4 that do not include integrity checks. The OAL source 765 therefore includes a trailing Fletcher checksum to allow the OAL 766 destination to detect packet splicing errors for fragmented OAL 767 packets and/or to verify integrity for packets that may have 768 traversed unprotected underlying network hops [CKSUM]. The Fletcher 769 checksum also provides diversity with respect to both lower layer 770 CRCs and upper layer Internet checksums as part of a complimentary 771 multi-layer integrity assurance architecture. 773 The OAL source assumes the IPv4 minimum path MTU (i.e., 576 bytes) as 774 the worst case for OAL fragmentation regardless of the underlying 775 interface IP protocol version since IPv6/IPv4 protocol translation 776 and/or IPv6-in-IPv4 encapsulation may occur in any *NET path. By 777 always assuming the IPv4 minimum even for IPv6 underlying interfaces, 778 the OAL source may produce smaller fragments with additional 779 encapsulation overhead but will always interoperate and never run the 780 risk of loss due to an MTU restriction or due to presenting an 781 underlying interface with a packet that exceeds its MRU. 782 Additionally, the OAL path could traverse multiple *NET "segments" 783 with intermediate OAL forwarding nodes performing re-encapsulation 784 where the *NET encapsulation of the previous segment is replaced by 785 the *NET encapsulation of the next segment which may be based on a 786 different IP protocol version and/or encapsulation sizes. 788 The OAL source therefore assumes a default minimum path MTU of 576 789 bytes at each *NET segment for the purpose of generating OAL 790 fragments. In the worst case, each successive *NET segment may re- 791 encapsulate with either a 20 byte IPv4 or 40 byte IPv6 header, an 8 792 byte UDP header and in some cases an IP security encapsulation (40 793 bytes maximum assumed). Any *NET segment may also insert a maximum- 794 length (40 byte) ORH as an extension to the existing 40 byte OAL IPv6 795 header plus 8 byte Fragment Header if an ORH was not already present. 796 Assuming therefore an absolute worst case of (40 + 40 + 8) = 88 bytes 797 for *NET encapsulation plus (40 + 40 + 8) = 88 bytes for OAL 798 encapsulation leaves (576 - 88 - 88) = 400 bytes to accommodate a 799 portion of the original IP packet/fragment. The OAL source therefore 800 sets a minimum Maximum Payload Size (MPS) of 400 bytes as the basis 801 for the minimum-sized OAL fragment that can be assured of traversing 802 all segments without loss due to an MTU/MRU restriction. The Maximum 803 Fragment Size (MFS) for OAL fragmentation is therefore determined by 804 the MPS plus the size of the OAL encapsulation headers. (Note that 805 the OAL source must include the 2 octet trailer as part of the 806 payload during fragmentation, and the OAL destination must regard it 807 as ordinary payload until reassembly and checksum verification are 808 complete.) 810 In light of the above, OAL source, intermediate and destination nodes 811 observe the following normative requirements: 813 o OAL sources MUST NOT send OAL packets/fragments including original 814 IP packets larger than the OMNI interface MTU or the OAL 815 destination MRU, i.e., whether or not fragmentation is needed. 817 o OAL sources MUST NOT perform OAL fragmentation for original IP 818 packets smaller than the minimum MPS minus the trailer size, and 819 MUST produce non-final fragments that contain a payload no smaller 820 than the minimum MPS when performing fragmentation. 822 o OAL sources MUST NOT send OAL packets/fragments that include any 823 extension headers other than a single ORH and a single Fragment 824 Header. 826 o OAL intermediate nodes SHOULD and OAL destinations MUST 827 unconditionally drop OAL packets/fragments including original IP 828 packets larger than the OMNI interface MRU, i.e., whether or not 829 reassembly is needed. 831 o OAL intermediate nodes SHOULD and OAL destinations MUST 832 unconditionally drop any non-final OAL fragments containing a 833 payload smaller than the minimum MPS. 835 o OAL intermediate nodes SHOULD and OAL destinations MUST 836 unconditionally drop OAL packets/fragments that include any 837 extension headers other than a single ORH and a single Fragment 838 Header. 840 The OAL source SHOULD maintain "path MPS" values for individual OAL 841 destinations initialized to the minimum MPS and increased to larger 842 values (up to the OMNI interface MTU) if better information is known 843 or discovered. For example, when *NET peers share a common 844 underlying link or a fixed path with a known larger MTU, the OAL 845 source can base path MPS on this larger size (i.e., instead of 576 846 bytes) as long as the *NET peer reassembles before re-encapsulating 847 and forwarding (while re-fragmenting if necessary). Also, if the OAL 848 source has a way of knowing the maximum *NET encapsulation size for 849 all segments along the path it may be able to increase path MPS to 850 reserve additional room for payload data. 852 The OAL source can also actively probe individual OAL destinations to 853 discover larger path MPS values using packetization layer probes 854 [RFC4821][RFC8899], but care must be taken to avoid setting static 855 values for dynamically changing paths leading to black holes. The 856 probe involves sending an OAL packet larger than the current path MPS 857 and receiving a small acknowledgement message in response. For this 858 purpose, the OAL source can send an NS message with one or more OMNI 859 options with large PadN sub-options (see: Section 11) in order to 860 receive a small NA response from the OAL destination. While 861 observing the minimum MPS will always result in robust and secure 862 behavior, the OAL should optimize path MPS values when more efficient 863 utilization may result in better performance (e.g. for wireless 864 aviation data links). 866 Under the minimum MPS, ordinary 1500 byte inner IP packets would 867 require 4 OAL fragments, with each non-final fragment containing 400 868 payload bytes and the final fragment containing 302 payload bytes 869 (i.e., the final 300 bytes of the original IP packet plus the 2 octet 870 trailer). For all packet sizes, the likelihood of successful 871 reassembly may improve when the OMNI interface sends all fragments of 872 the same fragmented OAL packet consecutively over the same underlying 873 interface. Finally, an assured minimum/path MPS allows continuous 874 operation over all paths including those that traverse bridged L2 875 media with dissimilar MTUs. 877 Note: Certain legacy network hardware of the past millennium was 878 unable to accept packet "bursts" resulting from an IP fragmentation 879 event - even to the point that the hardware would reset itself when 880 presented with a burst. This does not seem to be a common problem in 881 the modern era, where fragmentation and reassembly can be readily 882 demonstrated at line rate (e.g., using tools such as 'iperf3') even 883 over fast links on average hardware platforms. Even so, the OAL 884 source could impose an inter-fragment delay while the OAL destination 885 is reporting reassembly congestion (see: Section 5.4) and decrease 886 the delay when reassembly congestion subsides. 888 5.3. OAL Addressing Considerations 890 The OMNI interface performs OAL encapsulation and selects source and 891 destination addresses for the OAL IPv6 header according to the node's 892 *NET orientation. MN OMNI interfaces set the OAL IPv6 header source 893 address to a Unique Local Address (ULA) based on the Mobile Network 894 Prefix (MNP-ULA), while MSE OMNI interfaces set the source address to 895 an Administrative ULA (ADM-ULA) (see: Section 8). When a MN OMNI 896 interface does not (yet) have an MNP-ULA, it can use a Temporary ULA 897 and/or Host Identity Tag (HIT) instead (see: Section 21). The 898 following sections discuss the addressing considerations for OMNI 899 Interfaces configured over *NET interfaces. 901 When an OMNI interface forwards an original IP packet toward a final 902 destination via an ANET underlying interface, it sends without OAL 903 encapsulation if the packet (including any outer-layer ANET 904 encapsulations) is no larger than the underlying interface MTU for 905 on-link ANET peers or the minimum ANET path MTU for peers separated 906 by multiple IP hops. Otherwise, the OAL source inserts an IPv6 907 header per [RFC2473] with source address set to the node's own ULA 908 and destination set to either the Administrative ULA (ADM-ULA) of the 909 ANET peer or the Mobile Network Prefix ULA (MNP-ULA) corresponding to 910 the final destination (see below). The OAL source then fragments if 911 necessary, encapsulates the OAL packet/fragments in any ANET headers 912 and sends them to the ANET peer which either reassembles before 913 forwarding if the OAL destination is its own ULA or forwards the 914 fragments toward the final destination without first reassembling 915 otherwise. 917 When an OMNI interface forwards an original IP packet toward a final 918 destination via an INET underlying interface, it sends packets 919 (including any outer-layer INET encapsulations) no larger than the 920 path MPS without OAL encapsulation if the destination is reached via 921 an INET address within the same OMNI link segment. Otherwise, the 922 OAL source inserts an IPv6 header per [RFC2473] with source address 923 set to the node's ULA and destination set to the ULA of an OMNI node 924 on the final *NET segment. The OAL then fragments if necessary, 925 encapsulates the OAL packet/fragments in any INET headers and sends 926 them toward the final segment OMNI node, which reassembles before 927 forwarding toward the final destination. 929 5.4. OMNI Interface MTU Feedback Messaging 931 When the OMNI interface forwards original IP packets from the network 932 layer, it invokes the OAL and returns internally-generated ICMPv4 933 Fragmentation Needed [RFC1191] or ICMPv6 Path MTU Discovery (PMTUD) 934 Packet Too Big (PTB) [RFC8201] messages as necessary. This document 935 refers to both of these ICMPv4/ICMPv6 message types simply as "PTBs", 936 and introduces a distinction between PTB "hard" and "soft" errors as 937 discussed below. 939 Ordinary PTB messages with ICMPv4 header "unused" field or ICMPv6 940 header Code field value 0 are hard errors that always indicate that a 941 packet has been dropped due to a real MTU restriction. In 942 particular, the OAL source drops the packet and returns a PTB hard 943 error if the packet exceeds the MRU advertised by this OAL 944 destination. However, the OMNI interface can also forward large 945 original IP packets via OAL encapsulation and fragmentation while at 946 the same time returning PTB soft error messages (subject to rate 947 limiting) if it deems the original IP packet too large according to 948 factors such as link performance characteristics, reassembly 949 congestion, etc. This ensures that the path MTU is adaptive and 950 reflects the current path used for a given data flow. The OMNI 951 interface can therefore continuously forward packets without loss 952 while returning PTB soft error messages recommending a smaller size 953 if necessary. Original sources that receive the soft errors in turn 954 reduce the size of the packets they send (i.e., the same as for hard 955 errors), but can soon resume sending larger packets if the soft 956 errors subside. 958 An OAL source sends PTB soft error messages by setting the ICMPv4 959 header "unused" field or ICMPv6 header Code field to the value 1 if 960 the packet was deemed lost (e.g., due to reassembly timeout) or to 961 the value 2 otherwise. The OAL source sets the PTB destination 962 address to the original IP packet source, and sets the source address 963 to one of its OMNI interface unicast/anycast addresses that is 964 routable from the perspective of the original source. The OAL source 965 then sets the MTU field to a value smaller than the original packet 966 size but no smaller than 576 for ICMPv4 or 1280 for ICMPv6, and 967 returns the PTB soft error to the original source. When the original 968 source receives the PTB soft error, it temporarily reduces the size 969 of the packets it sends the same as for hard errors but may seek to 970 increase future packet sizes dynamically while no further soft errors 971 are arriving. (If the original source does not recognize the soft 972 error code, it regards the PTB the same as a hard error but should 973 heed the retransmission advice given in [RFC8201] suggesting 974 retransmission based on normal packetization layer retransmission 975 timers.) This document therefore updates [RFC1191][RFC4443] and 976 [RFC8201]. Furthermore, packetization layer probing strategies 977 [RFC4821][RFC8899] must be aware that PTB hard or soft errors may 978 arrive at any time, i.e., even following a successful probe (this is 979 the same consideration as for an ordinary path fluctuation following 980 a successful probe). 982 An OAL destination may experience reassembly cache congestion, and 983 can return unsolicited Neighbor Advertisment (uNA) messages to OAL 984 sources that originated the fragments (subject to rate limiting) to 985 advertise a smaller MRU and/or report individual reassembly failures. 986 The OAL destination creates a uNA message with an OMNI option 987 containing a Host Identity Payload (HIP) message sub-option to 988 provide authentication (if the OAL source is on an open Internetwork) 989 followed optionally by an MRU sub-option with a reduced MRU value. 990 If an OAL first fragment is available, the OAL destination next 991 includes an ICMPv6 error message sub-option (see: Section 11) that 992 encodes a PTB soft error with Code field set to 1 if reassembly 993 failed or 2 if reassembly was successful or still in progress. The 994 OAL destination encapsulates as much of the first fragment (beginning 995 with the OAL header) as will fit in the "packet in error" field of 996 the ICMPv6 error message sub-option without causing the entire uNA 997 message to exceed the minimum MPS, signs the message if the HIP sub- 998 option is included, performs OAL encapsulation (with the its own 999 address as the OAL source and the source address of the message that 1000 prompted the uNA as the OAL destination) and sends the message to the 1001 OAL source. 1003 When the OAL source receives the uNA message, it records the new MRU 1004 value for this neighbor if an OMNI MRU sub-option is included. If 1005 the uNA message includes an ICMPv6 error message sub-option with a 1006 PTB soft error, the OAL source next sends a corresponding inner IP 1007 layer PTB soft error with the same Code value to the original source 1008 to recommend a smaller size. The OAL source crafts the PTB by 1009 extracting the leading portion of the original IP packet from the 1010 "packet in error" field (i.e., not including the OAL header) and 1011 includes it in the "packet in error" field of a PTB with destination 1012 set to the original IP packet source and source set to one of its 1013 OMNI interface unicast/anycast addresses that is routable from the 1014 perspective of the original source. For future packet transmissions, 1015 if the packet is larger than the MRU for this OAL destination the OAL 1016 source drops the packet and returns a PTB hard error with MTU set to 1017 the MRU. The OAL source can also return PTB soft errors with Code 1018 set to 2 and MTU set to a value smaller than the MRU while forwarding 1019 the packet if the OMNI destination has recently reported soft errors. 1021 Original sources that receive PTB soft errors can dynamically tune 1022 the size of the packets they to send to produce the best possible 1023 throughput and latency, with the understanding that these parameters 1024 may change over time due to factors such as congestion, mobility, 1025 network path changes, etc. The receipt or absence of soft errors 1026 should be seen as hints of when increasing or decreasing packet sizes 1027 may be beneficial. The OMNI interface supports continuous 1028 transmission and reception of packets of various sizes in the face of 1029 dynamically changing network conditions. Moreover, since PTB soft 1030 errors do not indicate a hard limit, original sources that receive 1031 soft errors can begin sending larger packets without waiting for the 1032 minimum 10 minutes specified for PTB hard errors [RFC1191][RFC8201]. 1033 The OMNI interface therefore provides an adaptive service that 1034 accommodates MTU diversity especially well-suited for dynamic 1035 multilink environments. 1037 5.5. OAL Fragmentation Security Implications 1039 As discussed in Section 3.7 of [RFC8900], there are four basic 1040 threats concerning IPv6 fragmentation; each of which is addressed by 1041 effective mitigations as follows: 1043 1. Overlapping fragment attacks - reassembly of overlapping 1044 fragments is forbidden by [RFC8200]; therefore, this threat does 1045 not apply to the OAL. 1047 2. Resource exhaustion attacks - this threat is mitigated by 1048 providing a sufficiently large OAL reassembly cache and 1049 instituting "fast discard" of incomplete reassemblies that may be 1050 part of a buffer exhaustion attack. The reassembly cache should 1051 be sufficiently large so that a sustained attack does not cause 1052 excessive loss of good reassemblies but not so large that (timer- 1053 based) data structure management becomes computationally 1054 expensive. The cache should also be indexed based on the arrival 1055 underlying interface such that congestion experienced over a 1056 first underlying interface does not cause discard of incomplete 1057 reassemblies for uncongested underlying interfaces. 1059 3. Attacks based on predictable fragment identification values - 1060 this threat is mitigated by selecting a suitably random ID value 1061 per [RFC7739]. Additionally, inclusion of the trailing Fletcher 1062 checksum would make it very difficult for an attacker who could 1063 somehow predict a fragment identification value to inject 1064 malicious fragments resulting in undetected reassemblies of bad 1065 data. 1067 4. Evasion of Network Intrusion Detection Systems (NIDS) - this 1068 threat is mitigated by setting a minimum MPS for OAL 1069 fragmentation, which defeats all "tiny fragment"-based attacks. 1071 Additionally, IPv4 fragmentation includes a 16-bit Identification (IP 1072 ID) field with only 65535 unique values such that at high data rates 1073 the field could wrap and apply to new packets while the fragments of 1074 old packets using the same ID are still alive in the network 1075 [RFC4963]. However, since the largest OAL fragment that will be sent 1076 via an IPv4 *NET path with DF = 0 is 576 bytes any IPv4 fragmentation 1077 would occur only on links with an IPv4 MTU smaller than this size, 1078 and [RFC3819] recommendations suggest that such links will have low 1079 data rates. Since IPv6 provides a 32-bit Identification value, IP ID 1080 wraparound at high data rates is not a concern for IPv6 1081 fragmentation. 1083 Finally, [RFC6980] documents fragmentation security concerns for 1084 large IPv6 ND messages. These concerns are addressed when the OMNI 1085 interface employs the OAL instead of directly fragmenting the IPv6 ND 1086 message itself. For this reason, OMNI interfaces MUST NOT send IPv6 1087 ND messages larger than the OMNI interface MTU, and MUST employ OAL 1088 encapsulation and fragmentation for IPv6 ND messages larger than the 1089 current MPS for this OAL destination. 1091 5.6. OAL Super-Packets 1093 By default, the OAL source includes a 40-byte IPv6 encapsulation 1094 header for each original IP packet during OAL encapsulation. The OAL 1095 source also calculates and appends a 2 octet trailing Fletcher 1096 checksum then performs fragmentation such that a copy of the 40-byte 1097 IPv6 header plus an 8-byte IPv6 Fragment Header is included in each 1098 OAL fragment (when an ORH is added, the OAL encapsulation headers 1099 become larger still). However, these encapsulations may represent 1100 excessive overhead in some environments. A technique known as 1101 "packing" discussed in [I-D.ietf-intarea-tunnels] is therefore 1102 supported so that multiple original IP packets can be included within 1103 a single OAL "super-packet". 1105 When the OAL source has multiple original IP packets to send to the 1106 same OAL destination with total length no larger than the OAL 1107 destination MRU, it can concatenate them into a super-packet 1108 encapsulated in a single OAL header and trailing checksum. Within 1109 the OAL super-packet, the IP header of the first original packet 1110 (iHa) followed by its data (iDa) is concatenated immediately 1111 following the OAL header, then the IP header of the next original 1112 packet (iHb) followed by its data (iDb) is concatenated immediately 1113 following the first original packet, etc. with the trailing checksum 1114 included last. The OAL super-packet format is transposed from 1115 [I-D.ietf-intarea-tunnels] and shown in Figure 4: 1117 <------- Original IP packets -------> 1118 +-----+-----+ 1119 | iHa | iDa | 1120 +-----+-----+ 1121 | 1122 | +-----+-----+ 1123 | | iHb | iDb | 1124 | +-----+-----+ 1125 | | 1126 | | +-----+-----+ 1127 | | | iHc | iDc | 1128 | | +-----+-----+ 1129 | | | 1130 v v v 1131 +----------+-----+-----+-----+-----+-----+-----+----+ 1132 | OAL Hdr | iHa | iDa | iHb | iDb | iHc | iDc |Csum| 1133 +----------+-----+-----+-----+-----+-----+-----+----+ 1134 <--- OAL "Super-Packet" with single OAL Hdr/Csum ---> 1136 Figure 4: OAL Super-Packet Format 1138 When the OAL source prepares a super-packet, it applies OAL 1139 fragmentation if necessary then sends the packet or fragments to the 1140 OAL destination. When the OAL destination receives the super-packet 1141 it reassembles if necessary, verifies and removes the trailing 1142 checksum, then regards the remaining OAL header Payload Length as the 1143 sum of the lengths of all payload packets. The OAL destination then 1144 selectively extracts each original IP packet (e.g., by setting 1145 pointers into the super-packet buffer and maintaining a reference 1146 count, by copying each packet into a separate buffer, etc.) and 1147 forwards each packet or processes it locally as appropriate. During 1148 extraction, the OAL determines the IP protocol version of each 1149 successive original IP packet 'j' by examining the four most- 1150 significant bits of iH(j), and determines the length of the packet by 1151 examining the rest of iH(j) according to the IP protocol version. 1153 Note that OMNI interfaces must take care to avoid processing super- 1154 packet payload elements that would subvert security. Specifically, 1155 if a super-packet contains a mix of data and control payload packets 1156 (which could include critical security codes), the node MUST NOT 1157 process the data packets before processing the control packets 1159 6. Frame Format 1161 The OMNI interface forwards original IP packets from the network 1162 layer by first invoking the OAL, next including any *NET 1163 encapsulations and finally engaging the native frame format of the 1164 underlying interface. For example, for Ethernet-compatible 1165 interfaces the frame format is specified in [RFC2464], for 1166 aeronautical radio interfaces the frame format is specified in 1167 standards such as ICAO Doc 9776 (VDL Mode 2 Technical Manual), for 1168 various forms of tunnels the frame format is found in the appropriate 1169 tunneling specification, etc. 1171 The OMNI interface SHOULD minimize the amount of *NET encapsulation 1172 for increased efficiency. For example, while an OMNI node may need 1173 to use UDP/IP as a *NET encapsulation over underlying interfaces 1174 connected to an open Internetwork, it may be able to omit the UDP 1175 header over underlying interfaces connected to *NETs that do not 1176 include NATs or packet filtering gateways. Similarly, when an OMNI 1177 MN shares a common underlying link with an AR, the MN may be able to 1178 avoid including any *NET encapsulations and instead directly engage 1179 the underlying interface native frame format. Further considerations 1180 for *NET encapsulation are discussed throughout the document and in 1181 [I-D.templin-intarea-6706bis]. 1183 7. Link-Local Addresses (LLAs) 1185 OMNI nodes are assigned OMNI interface IPv6 Link-Local Addresses 1186 (LLAs) through pre-service administrative actions. "MNP-LLAs" embed 1187 the MNP assigned to the mobile node, while "ADM-LLAs" include an 1188 administratively-unique ID that is guaranteed to be unique on the 1189 link. LLAs are configured as follows: 1191 o IPv6 MNP-LLAs encode the most-significant 64 bits of a MNP within 1192 the least-significant 64 bits of the IPv6 link-local prefix 1193 fe80::/64, i.e., in the LLA "interface identifier" portion. The 1194 prefix length for the LLA is determined by adding 64 to the MNP 1195 prefix length. For example, for the MNP 2001:db8:1000:2000::/56 1196 the corresponding MNP-LLA is fe80::2001:db8:1000:2000/120. 1198 o IPv4-compatible MNP-LLAs are constructed as fe80::ffff:[IPv4], 1199 i.e., the interface identifier consists of 16 '0' bits, followed 1200 by 16 '1' bits, followed by a 32bit IPv4 address/prefix. The 1201 prefix length for the LLA is determined by adding 96 to the MNP 1202 prefix length. For example, the IPv4-Compatible MN OMNI LLA for 1203 192.0.2.0/24 is fe80::ffff:192.0.2.0/120 (also written as 1204 fe80::ffff:c000:0200/120). 1206 o ADM-LLAs are assigned to ARs and MSEs and MUST be managed for 1207 uniqueness. The lower 32 bits of the LLA includes a unique 1208 integer "MSID" value between 0x00000001 and 0xfeffffff, e.g., as 1209 in fe80::1, fe80::2, fe80::3, etc., fe80::feffffff. The ADM-LLA 1210 prefix length is determined by adding 96 to the MSID prefix 1211 length. For example, if the prefix length for MSID 0x10012001 is 1212 16 then the ADM-LLA prefix length is set to 112 and the LLA is 1213 written as fe80::1001:2001/112. The "zero" address for each ADM- 1214 LLA prefix is the Subnet-Router anycast address for that prefix 1215 [RFC4291]; for example, the Subnet-Router anycast address for 1216 fe80::1001:2001/112 is simply fe80::1001:2000. The MSID range 1217 0xff000000 through 0xffffffff is reserved for future use. 1219 Since the prefix 0000::/8 is "Reserved by the IETF" [RFC4291], no 1220 MNPs can be allocated from that block ensuring that there is no 1221 possibility for overlap between the different MNP- and ADM-LLA 1222 constructs discussed above. 1224 Since MNP-LLAs are based on the distribution of administratively 1225 assured unique MNPs, and since ADM-LLAs are guaranteed unique through 1226 administrative assignment, OMNI interfaces set the autoconfiguration 1227 variable DupAddrDetectTransmits to 0 [RFC4862]. 1229 Note: If future protocol extensions relax the 64-bit boundary in IPv6 1230 addressing, the additional prefix bits of an MNP could be encoded in 1231 bits 16 through 63 of the MNP-LLA. (The most-significant 64 bits 1232 would therefore still be in bits 64-127, and the remaining bits would 1233 appear in bits 16 through 48.) However, the analysis provided in 1234 [RFC7421] suggests that the 64-bit boundary will remain in the IPv6 1235 architecture for the foreseeable future. 1237 Note: Even though this document honors the 64-bit boundary in IPv6 1238 addressing, it specifies prefix lengths longer than /64 for routing 1239 purposes. This effectively extends IPv6 routing determination into 1240 the interface identifier portion of the IPv6 address, but it does not 1241 redefine the 64-bit boundary. Modern routing protocol 1242 implementations honor IPv6 prefixes of all lengths, up to and 1243 including /128. 1245 8. Unique-Local Addresses (ULAs) 1247 OMNI domains use IPv6 Unique-Local Addresses (ULAs) as the source and 1248 destination addresses in OAL IPv6 encapsulation headers. ULAs are 1249 only routable within the scope of a an OMNI domain, and are derived 1250 from the IPv6 Unique Local Address prefix fc00::/7 followed by the L 1251 bit set to 1 (i.e., as fd00::/8) followed by a 40-bit pseudo-random 1252 Global ID to produce the prefix [ULA]::/48, which is then followed by 1253 a 16-bit Subnet ID then finally followed by a 64 bit Interface ID as 1254 specified in Section 3 of [RFC4193]. All nodes in the same OMNI 1255 domain configure the same 40-bit Global ID as the OMNI domain 1256 identifier. The statistic uniqueness of the 40-bit pseudo-random 1257 Global ID allows different OMNI domains to be joined together in the 1258 future without requiring renumbering. 1260 Each OMNI link instance is identified by a value between 0x0000 and 1261 0xfeff in bits 48-63 of [ULA]::/48; the values 0xff00 through 0xfffe 1262 are reserved for future use, and the value 0xffff denotes the 1263 presence of a Temporary ULA (see below). For example, OMNI ULAs 1264 associated with instance 0 are configured from the prefix 1265 [ULA]:0000::/64, instance 1 from [ULA]:0001::/64, instance 2 from 1266 [ULA]:0002::/64, etc. ULAs and their associated prefix lengths are 1267 configured in correspondence with LLAs through stateless prefix 1268 translation where "MNP-ULAs" are assigned in correspondence to MNP- 1269 LLAs and "ADM-ULAs" are assigned in correspondence to ADM-LLAs. For 1270 example, for OMNI link instance [ULA]:1010::/64: 1272 o the MNP-ULA corresponding to the MNP-LLA fe80::2001:db8:1:2 with a 1273 56-bit MNP length is derived by copying the lower 64 bits of the 1274 LLA into the lower 64 bits of the ULA as 1275 [ULA]:1010:2001:db8:1:2/120 (where, the ULA prefix length becomes 1276 64 plus the IPv6 MNP length). 1278 o the MNP-ULA corresponding to fe80::ffff:192.0.2.0 with a 28-bit 1279 MNP length is derived by simply writing the LLA interface ID into 1280 the lower 64 bits as [ULA]:1010:0:ffff:192.0.2.0/124 (where, the 1281 ULA prefix length is 64 plus 32 plus the IPv4 MNP length). 1283 o the ADM-ULA corresponding to fe80::1000/112 is simply 1284 [ULA]:1010::1000/112. 1286 o the ADM-ULA corresponding to fe80::/128 is simply 1287 [ULA]:1010::/128. 1289 o etc. 1291 Each OMNI interface assigns the Anycast ADM-ULA specific to the OMNI 1292 link instance. For example, the OMNI interface connected to instance 1293 3 assigns the Anycast address [ULA]:0003::/128. Routers that 1294 configure OMNI interfaces advertise the OMNI service prefix (e.g., 1295 [ULA]:0003::/64) into the local routing system so that applications 1296 can direct traffic according to SBM requirements. 1298 The ULA presents an IPv6 address format that is routable within the 1299 OMNI routing system and can be used to convey link-scoped IPv6 ND 1300 messages across multiple hops using IPv6 encapsulation [RFC2473]. 1301 The OMNI link extends across one or more underling Internetworks to 1302 include all ARs and MSEs. All MNs are also considered to be 1303 connected to the OMNI link, however OAL encapsulation is omitted 1304 whenever possible to conserve bandwidth (see: Section 13). 1306 Each OMNI link can be subdivided into "segments" that often 1307 correspond to different administrative domains or physical 1308 partitions. OMNI nodes can use IPv6 Segment Routing [RFC8402] when 1309 necessary to support efficient packet forwarding to destinations 1310 located in other OMNI link segments. A full discussion of Segment 1311 Routing over the OMNI link appears in [I-D.templin-intarea-6706bis]. 1313 Temporary ULAs are constructed per [RFC8981] based on the prefix 1314 [ULA]:ffff::/64 and used by MNs when they have no other addresses. 1315 Temporary ULAs can be used for MN-to-MN communications outside the 1316 context of any supporting OMNI link infrastructure, and can also be 1317 used as an initial address while the MN is in the process of 1318 procuring an MNP. Temporary ULAs are not routable within the OMNI 1319 routing system, and are therefore useful only for OMNI link "edge" 1320 communications. Temporary ULAs employ optimistic DAD principles 1321 [RFC4429] since they are probabilistically unique. 1323 Note: IPv6 ULAs taken from the prefix fc00::/7 followed by the L bit 1324 set to 0 (i.e., as fc00::/8) are never used for OMNI OAL addressing, 1325 however the range could be used for MSP and MNP addressing under 1326 certain limiting conditions (see: Section 9). 1328 9. Global Unicast Addresses (GUAs) 1330 OMNI domains use IP Global Unicast Address (GUA) prefixes [RFC4291] 1331 as Mobility Service Prefixes (MSPs) from which Mobile Network 1332 Prefixes (MNP) are delegated to Mobile Nodes (MNs). 1334 For IPv6, GUA prefixes are assigned by IANA [IPV6-GUA] and/or an 1335 associated regional assigned numbers authority such that the OMNI 1336 domain can be interconnected to the global IPv6 Internet without 1337 causing inconsistencies in the routing system. An OMNI domain could 1338 instead use ULAs with the 'L' bit set to 0 (i.e., from the prefix 1339 fc00::/8)[RFC4193], however this would require IPv6 NAT if the domain 1340 were ever connected to the global IPv6 Internet. 1342 For IPv4, GUA prefixes are assigned by IANA [IPV4-GUA] and/or an 1343 associated regional assigned numbers authority such that the OMNI 1344 domain can be interconnected to the global IPv4 Internet without 1345 causing routing inconsistencies. An OMNI domain could instead use 1346 private IPv4 prefixes (e.g., 10.0.0.0/8, etc.) [RFC3330], however 1347 this would require IPv4 NAT if the domain were ever connected to the 1348 global IPv4 Internet. 1350 10. Node Identification 1352 OMNI MNs and MSEs that connect over open Internetworks generate a 1353 Host Identity Tag (HIT) as specified in [RFC7401] and use the value 1354 as a robust general-purpose node identification value. Hierarchical 1355 HITs (HHITs) [I-D.ietf-drip-rid] may provide a useful alternative in 1356 certain domains such as the Unmanned (Air) Traffic Management (UTM) 1357 service for Unmanned Air Systems (UAS). MNs and MSEs can then use 1358 their (H)HITs in IPv6 ND control message exchanges. 1360 When a MN is truly outside the context of any infrastructure, it may 1361 have no MNP information at all. In that case, the MN can use its 1362 (H)HIT as an IPv6 source/destination address for sustained 1363 communications in Vehicle-to-Vehicle (V2V) and (multihop) Vehicle-to- 1364 Infrastructure (V2I) scenarios. The MN can also propagate the (H)HIT 1365 into the multihop routing tables of (collective) Mobile/Vehicular Ad- 1366 hoc Networks (MANETs/VANETs) using only the vehicles themselves as 1367 communications relays. 1369 When a MN connects to ARs over (non-multihop) protected-spectrum 1370 ANETs, an alternate form of node identification (e.g., MAC address, 1371 serial number, airframe identification value, VIN, etc.) may be 1372 sufficient. In that case, the MN should still generate a (H)HIT and 1373 maintain it in conjunction with any other node identifiers. The MN 1374 can then include OMNI "Node Identification" sub-options (see: 1375 Section 11.1.13) in IPv6 ND messages should the need to transmit 1376 identification information over the network arise. 1378 11. Address Mapping - Unicast 1380 OMNI interfaces maintain a neighbor cache for tracking per-neighbor 1381 state and use the link-local address format specified in Section 7. 1382 OMNI interface IPv6 Neighbor Discovery (ND) [RFC4861] messages sent 1383 over physical underlying interfaces without encapsulation observe the 1384 native underlying interface Source/Target Link-Layer Address Option 1385 (S/TLLAO) format (e.g., for Ethernet the S/TLLAO is specified in 1386 [RFC2464]). OMNI interface IPv6 ND messages sent over underlying 1387 interfaces via encapsulation do not include S/TLLAOs which were 1388 intended for encoding physical L2 media address formats and not 1389 encapsulation IP addresses. Furthermore, S/TLLAOs are not intended 1390 for encoding additional interface attributes needed for multilink 1391 coordination. Hence, this document does not define an S/TLLAO format 1392 but instead defines a new option type termed the "OMNI option" 1393 designed for these purposes. 1395 MNs such as aircraft typically have many wireless data link types 1396 (e.g. satellite-based, cellular, terrestrial, air-to-air directional, 1397 etc.) with diverse performance, cost and availability properties. 1398 The OMNI interface would therefore appear to have multiple L2 1399 connections, and may include information for multiple underlying 1400 interfaces in a single IPv6 ND message exchange. OMNI interfaces use 1401 an IPv6 ND option called the OMNI option formatted as shown in 1402 Figure 5: 1404 0 1 2 3 1405 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 1406 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1407 | Type | Length | Preflen | S/T-omIndex | 1408 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1409 | | 1410 ~ Sub-Options ~ 1411 | | 1412 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1414 Figure 5: OMNI Option Format 1416 In this format: 1418 o Type is set to TBD1. 1420 o Length is set to the number of 8 octet blocks in the option. The 1421 value 0 is invalid, while the values 1 through 255 (i.e., 8 1422 through 2040 octets, respectively) indicate the total length of 1423 the OMNI option. 1425 o Preflen is an 8 bit field that determines the length of prefix 1426 associated with an LLA. Values 0 through 128 specify a valid 1427 prefix length (all other values are invalid). For IPv6 ND 1428 messages sent from a MN to the MS, Preflen applies to the IPv6 1429 source LLA and provides the length that the MN is requesting or 1430 asserting to the MS. For IPv6 ND messages sent from the MS to the 1431 MN, Preflen applies to the IPv6 destination LLA and indicates the 1432 length that the MS is granting to the MN. For IPv6 ND messages 1433 sent between MS endpoints, Preflen provides the length associated 1434 with the source/target MN that is subject of the ND message. 1436 o S/T-omIndex is an 8 bit field corresponds to the omIndex value for 1437 source or target underlying interface used to convey this IPv6 ND 1438 message. OMNI interfaces MUST number each distinct underlying 1439 interface with an omIndex value between '1' and '255' that 1440 represents a MN-specific 8-bit mapping for the actual ifIndex 1441 value assigned by network management [RFC2863] (the omIndex value 1442 '0' is reserved for use by the MS). For RS and NS messages, S/ 1443 T-omIndex corresponds to the source underlying interface the 1444 message originated from. For RA and NA messages, S/T-omIndex 1445 corresponds to the target underlying interface that the message is 1446 destined to. (For NS messages used for Neighbor Unreachability 1447 Detection (NUD), S/T-omIndex instead identifies the neighbor's 1448 underlying interface to be used as the target interface to return 1449 the NA.) 1451 o Sub-Options is a Variable-length field, of length such that the 1452 complete OMNI Option is an integer multiple of 8 octets long. 1453 Contains one or more Sub-Options, as described in Section 11.1. 1455 The OMNI option may appear in any IPv6 ND message type; it is 1456 processed by interfaces that recognize the option and ignored by all 1457 other interfaces. If multiple OMNI option instances appear in the 1458 same IPv6 ND message, the interface processes the Preflen and S/ 1459 T-omIndex fields in the first instance and ignores those fields in 1460 all other instances. The interface processes the Sub-Options of all 1461 OMNI option instances in the same IPv6 ND message in the consecutive 1462 order in which they appear. 1464 The OMNI option(s) in each IPv6 ND message may include full or 1465 partial information for the neighbor. The union of the information 1466 in the most recently received OMNI options is therefore retained, and 1467 the information is aged/removed in conjunction with the corresponding 1468 neighbor cache entry. 1470 11.1. Sub-Options 1472 Each OMNI option includes zero or more Sub-Options. Each consecutive 1473 Sub-Option is concatenated immediately after its predecessor. All 1474 Sub-Options except Pad1 (see below) are in type-length-value (TLV) 1475 encoded in the following format: 1477 0 1 2 1478 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 1479 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1480 | Sub-Type| Sub-length | Sub-Option Data ... 1481 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1483 Figure 6: Sub-Option Format 1485 o Sub-Type is a 5-bit field that encodes the Sub-Option type. Sub- 1486 Options defined in this document are: 1488 Sub-Option Name Sub-Type 1489 Pad1 0 1490 PadN 1 1491 Interface Attributes (Type 1) 2 1492 Interface Attributes (Type 2) 3 1493 Traffic Selector 4 1494 MS-Register 5 1495 MS-Release 6 1496 Geo Coordinates 7 1497 DHCPv6 Message 8 1498 HIP Message 9 1499 ICMPv6 Error Message 10 1500 Maximum Reassembly Unit (MRU) 11 1501 Node Identification 12 1502 Sub-Type Extension 30 1504 Figure 7 1506 Sub-Types 11-29 are available for future assignment for major 1507 protocol functions. Sub-Type 31 is reserved by IANA. 1509 o Sub-Length is an 11-bit field that encodes the length of the Sub- 1510 Option Data ranging from 0 to 2034 octets. 1512 o Sub-Option Data is a block of data with format determined by Sub- 1513 Type and length determined by Sub-Length. 1515 During transmission, the OMNI interface codes Sub-Type and Sub-Length 1516 together in network byte order in 2 consecutive octets, where Sub- 1517 Option Data may be up to 2034 octets in length. This allows ample 1518 space for coding large objects (e.g., ASCII strings, domain names, 1519 protocol messages, security codes, etc.), while a single OMNI option 1520 is limited to 2040 octets the same as for any IPv6 ND option. If the 1521 Sub-Options to be coded would cause an OMNI option to exceed 2040 1522 octets, the OMNI interface codes any remaining Sub-Options in 1523 additional OMNI option instances in the intended order of processing 1524 in the same IPv6 ND message. Implementations must therefore observe 1525 size limitations, and must refrain from sending IPv6 ND messages 1526 larger than the OMNI interface MTU. If the available OMNI 1527 information would cause a single IPv6 ND message to exceed the OMNI 1528 interface MTU, the OMNI interface codes as much as possible in a 1529 first IPv6 ND message and codes the remainder in additional IPv6 ND 1530 messages. 1532 During reception, the OMNI interface processes each OMNI option Sub- 1533 Option while skipping over and ignoring any unrecognized Sub-Options. 1534 The OMNI interface processes the Sub-Options of all OMNI option 1535 instances in the consecutive order in which they appear in the IPv6 1536 ND message, beginning with the first instance and continuing through 1537 any additional instances to the end of the message. If a Sub-Option 1538 length would cause processing to exceed the OMNI option total length, 1539 the OMNI interface accepts any Sub-Options already processed and 1540 ignores the final Sub-Option. The interface then processes any 1541 remaining OMNI options in the same fashion to the end of the IPv6 ND 1542 message. 1544 Note: large objects that exceed the Sub-Option Data limit of 2034 1545 octets are not supported under the current specification; if this 1546 proves to be limiting in practice, future specifications may define 1547 support for fragmenting large objects across multiple OMNI options 1548 within the same IPv6 ND message. 1550 The following Sub-Option types and formats are defined in this 1551 document: 1553 11.1.1. Pad1 1555 0 1556 0 1 2 3 4 5 6 7 1557 +-+-+-+-+-+-+-+-+ 1558 | S-Type=0|x|x|x| 1559 +-+-+-+-+-+-+-+-+ 1561 Figure 8: Pad1 1563 o Sub-Type is set to 0. If multiple instances appear in OMNI 1564 options of the same message all are processed. 1566 o Sub-Type is followed by 3 'x' bits, set to any value on 1567 transmission (typically all-zeros) and ignored on receipt. Pad1 1568 therefore consists of 1 octet with the most significant 5 bits set 1569 to 0, and with no Sub-Length or Sub-Option Data fields following. 1571 11.1.2. PadN 1573 0 1 2 1574 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 1575 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1576 | S-Type=1| Sub-length=N | N padding octets ... 1577 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1579 Figure 9: PadN 1581 o Sub-Type is set to 1. If multiple instances appear in OMNI 1582 options of the same message all are processed. 1584 o Sub-Length is set to N (from 0 to 2034) that encodes the number of 1585 padding octets that follow. 1587 o Sub-Option Data consists of N octets, set to any value on 1588 transmission (typically all-zeros) and ignored on receipt. 1590 11.1.3. Interface Attributes (Type 1) 1592 The Interface Attributes (Type 1) sub-option provides a basic set of 1593 attributes for underlying interfaces. Interface Attributes (Type 1) 1594 is deprecated throughout the rest of this specification, and 1595 Interface Attributes (Type 2) (see: Section 11.1.4) are indicated 1596 wherever the term "Interface Attributes" appears without an 1597 associated Type designation. 1599 Nodes SHOULD NOT include Interface Attributes (Type 1) sub-options in 1600 IPv6 ND messages they send, and MUST ignore any in IPv6 ND messages 1601 they receive. If an Interface Attributes (Type 1) is included, it 1602 must have the following format: 1604 0 1 2 3 1605 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 1606 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1607 | Sub-Type=2| Sub-length=N | omIndex | omType | 1608 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1609 | Provider ID | Link | Resvd |P00|P01|P02|P03|P04|P05|P06|P07| 1610 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1611 |P08|P09|P10|P11|P12|P13|P14|P15|P16|P17|P18|P19|P20|P21|P22|P23| 1612 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1613 |P24|P25|P26|P27|P28|P29|P30|P31|P32|P33|P34|P35|P36|P37|P38|P39| 1614 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1615 |P40|P41|P42|P43|P44|P45|P46|P47|P48|P49|P50|P51|P52|P53|P54|P55| 1616 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1617 |P56|P57|P58|P59|P60|P61|P62|P63| 1618 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1620 Figure 10: Interface Attributes (Type 1) 1622 o Sub-Type is set to 2. If multiple instances with different 1623 omIndex values appear in OMNI option of the same message all are 1624 processed; if multiple instances with the same omIndex value 1625 appear, the first is processed and all others are ignored 1627 o Sub-Length is set to N (from 4 to 2034) that encodes the number of 1628 Sub-Option Data octets that follow. 1630 o omIndex is a 1-octet field containing a value from 0 to 255 1631 identifying the underlying interface for which the attributes 1632 apply. 1634 o omType is a 1-octet field containing a value from 0 to 255 1635 corresponding to the underlying interface identified by omIndex. 1637 o Provider ID is a 1-octet field containing a value from 0 to 255 1638 corresponding to the underlying interface identified by omIndex. 1640 o Link encodes a 4-bit link metric. The value '0' means the link is 1641 DOWN, and the remaining values mean the link is UP with metric 1642 ranging from '1' ("lowest") to '15' ("highest"). 1644 o Resvd is reserved for future use. Set to 0 on transmission and 1645 ignored on reception. 1647 o A 16-octet ""Preferences" field immediately follows 'Resvd', with 1648 values P[00] through P[63] corresponding to the 64 Differentiated 1649 Service Code Point (DSCP) values [RFC2474]. Each 2-bit P[*] field 1650 is set to the value '0' ("disabled"), '1' ("low"), '2' ("medium") 1651 or '3' ("high") to indicate a QoS preference for underlying 1652 interface selection purposes. 1654 11.1.4. Interface Attributes (Type 2) 1656 The Interface Attributes (Type 2) sub-option provides L2 forwarding 1657 information for the multilink conceptual sending algorithm discussed 1658 in Section 13. The L2 information is used for selecting among 1659 potentially multiple candidate underlying interfaces that can be used 1660 to forward packets to the neighbor based on factors such as DSCP 1661 preferences and link quality. Interface Attributes (Type 2) further 1662 includes link-layer address information to be used for either OAL 1663 encapsulation or direct UDP/IP encapsulation (when OAL encapsulation 1664 can be avoided). 1666 Interface Attributes (Type 2) are the sole Interface Attributes 1667 format in this specification that all OMNI nodes must honor. 1668 Wherever the term "Interface Attributes" occurs throughout this 1669 specification without a "Type" designation, the format given below is 1670 indicated: 1672 0 1 2 3 1673 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 1674 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1675 | S-Type=3| Sub-length=N | omIndex | omType | 1676 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1677 | Provider ID | Link |R| API | SRT | FMT | LHS (0 - 7) | 1678 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1679 | LHS (bits 8 - 31) | ~ 1680 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ 1681 ~ ~ 1682 ~ Link Layer Address (L2ADDR) ~ 1683 ~ ~ 1684 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1685 | Bitmap(0)=0xff|P00|P01|P02|P03|P04|P05|P06|P07|P08|P09|P10|P11| 1686 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1687 |P12|P13|P14|P15|P16|P17|P18|P19|P20|P21|P22|P23|P24|P25|P26|P27| 1688 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1689 |P28|P29|P30|P31| Bitmap(1)=0xff|P32|P33|P34|P35|P36| ... 1690 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1692 Figure 11: Interface Attributes (Type 2) 1694 o Sub-Type is set to 3. If multiple instances with different 1695 omIndex values appear in OMNI options of the same message all are 1696 processed; if multiple instances with the same omIndex value 1697 appear, the first is processed and all others are ignored. 1699 o Sub-Length is set to N (from 4 to 2034) that encodes the number of 1700 Sub-Option Data octets that follow. The 'omIndex', 'omType', 1701 'Provider ID', 'Link', 'R' and 'API' fields are always present; 1702 hence, the remainder of the Sub-Option Data is limited to 2030 1703 octets. 1705 o Sub-Option Data contains an "Interface Attributes (Type 2)" option 1706 encoded as follows: 1708 * omIndex is set to an 8-bit integer value corresponding to a 1709 specific underlying interface the same as specified above for 1710 the OMNI option S/T-omIndex field. The OMNI options of a same 1711 message may include multiple Interface Attributes Sub-Options, 1712 with each distinct omIndex value pertaining to a different 1713 underlying interface. The OMNI option will often include an 1714 Interface Attributes Sub-Option with the same omIndex value 1715 that appears in the S/T-omIndex. In that case, the actual 1716 encapsulation address of the received IPv6 ND message should be 1717 compared with the L2ADDR encoded in the Sub-Option (see below); 1718 if the addresses are different (or, if L2ADDR is absent) the 1719 presence of a NAT is assumed. 1721 * omType is set to an 8-bit integer value corresponding to the 1722 underlying interface identified by omIndex. The value 1723 represents an OMNI interface-specific 8-bit mapping for the 1724 actual IANA ifType value registered in the 'IANAifType-MIB' 1725 registry [http://www.iana.org]. 1727 * Provider ID is set to an OMNI interface-specific 8-bit ID value 1728 for the network service provider associated with this omIndex. 1730 * Link encodes a 4-bit link metric. The value '0' means the link 1731 is DOWN, and the remaining values mean the link is UP with 1732 metric ranging from '1' ("lowest") to '15' ("highest"). 1734 * R is reserved for future use. 1736 * API - a 3-bit "Address/Preferences/Indexed" code that 1737 determines the contents of the remainder of the sub-option as 1738 follows: 1740 + When the most significant bit (i.e., "Address") is set to 1, 1741 the SRT, FMT, LHS and L2ADDR fields are included immediately 1742 following the API code; else, they are omitted. 1744 + When the next most significant bit (i.e., "Preferences") is 1745 set to 1, a preferences block is included next; else, it is 1746 omitted. (Note that if "Address" is set the preferences 1747 block immediately follows L2ADDR; else, it immediately 1748 follows the API code.) 1750 + When a preferences block is present and the least 1751 significant bit (i.e., "Indexed") is set to 0, the block is 1752 encoded in "Simplex" form as shown in Figure 10; else it is 1753 encoded in "Indexed" form as discussed below. 1755 * When API indicates that an "Address" is included, the following 1756 fields appear in consecutive order (else, they are omitted): 1758 + SRT - a 5-bit Segment Routing Topology prefix length value 1759 that (when added to 96) determines the prefix length to 1760 apply to the ULA formed from concatenating [ULA*]::/96 with 1761 the 32 bit LHS MSID value that follows. For example, the 1762 value 16 corresponds to the prefix length 112. 1764 + FMT - a 3-bit "Framework/Mode/Type" code corresponding to 1765 the included Link Layer Address as follows: 1767 - When the most significant bit (i.e., "Framework") is set 1768 to 1, L2ADDR is the INET encapsulation address for the 1769 Source/Target Client itself; otherwise L2ADDR is the 1770 address of the Server/Proxy named in the LHS. 1772 - When the next most significant bit (i.e., "Mode") is set 1773 to 1, the Framework node is (likely) located behind an 1774 INET Network Address Translator (NAT); otherwise, it is 1775 on the open INET. 1777 - When the least significant bit (i.e., "Type") is set to 1778 0, L2ADDR includes a UDP Port Number followed by an IPv4 1779 address; otherwise, it includes a UDP Port Number 1780 followed by an IPv6 address. 1782 + LHS - the 32 bit MSID of the Last Hop Server/Proxy on the 1783 path to the target. When SRT and LHS are both set to 0, the 1784 LHS is considered unspecified in this IPv6 ND message. When 1785 SRT is set to 0 and LHS is non-zero, the prefix length is 1786 set to 128. SRT and LHS together provide guidance to the 1787 OMNI interface forwarding algorithm. Specifically, if SRT/ 1788 LHS is located in the local OMNI link segment then the OMNI 1789 interface can encapsulate according to FMT/L2ADDR (following 1790 any necessary NAT traversal messaging); else, it must 1791 forward according to the OMNI link spanning tree. See 1792 [I-D.templin-intarea-6706bis] for further discussion. 1794 + Link Layer Address (L2ADDR) - Formatted according to FMT, 1795 and identifies the link-layer address (i.e., the 1796 encapsulation address) of the source/target. The UDP Port 1797 Number appears in the first 2 octets and the IP address 1798 appears in the next 4 octets for IPv4 or 16 octets for IPv6. 1799 The Port Number and IP address are recorded in network byte 1800 order, and in ones-compliment "obfuscated" form per 1801 [RFC4380]. The OMNI interface forwarding algorithm uses 1802 FMT/L2ADDR to determine the encapsulation address for 1803 forwarding when SRT/LHS is located in the local OMNI link 1804 segment. Note that if the target is behind a NAT, L2ADDR 1805 will contain the mapped INET address stored in the NAT; 1806 otherwise, L2ADDR will contain the native INET information 1807 of the target itself. 1809 * When API indicates that "Preferences" are included, a 1810 preferences block appears as the remainder of the Sub-Option as 1811 a series of Bitmaps and P[*] values. In "Simplex" form, the 1812 index for each singleton Bitmap octet is inferred from its 1813 sequential position (i.e., 0, 1, 2, ...) as shown in Figure 11. 1814 In "Indexed" form, each Bitmap is preceded by an Index octet 1815 that encodes a value "i" = (0 - 255) as the index for its 1816 companion Bitmap as follows: 1818 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1819 | Index=i | Bitmap(i) |P[*] values ... 1820 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1822 Figure 12 1824 * The preferences consist of a first (simplex/indexed) Bitmap 1825 (i.e., "Bitmap(i)") followed by 0-8 single-octet blocks of 1826 2-bit P[*] values, followed by a second Bitmap (i), followed by 1827 0-8 blocks of P[*] values, etc. Reading from bit 0 to bit 7, 1828 the bits of each Bitmap(i) that are set to '1'' indicate the 1829 P[*] blocks from the range P[(i*32)] through P[(i*32) + 31] 1830 that follow; if any Bitmap(i) bits are '0', then the 1831 corresponding P[*] block is instead omitted. For example, if 1832 Bitmap(0) contains 0xff then the block with P[00]-P[03], 1833 followed by the block with P[04]-P[07], etc., and ending with 1834 the block with P[28]-P[31] are included (as shown in 1835 Figure 10). The next Bitmap(i) is then consulted with its bits 1836 indicating which P[*] blocks follow, etc. out to the end of the 1837 Sub-Option. 1839 * Each 2-bit P[*] field is set to the value '0' ("disabled"), '1' 1840 ("low"), '2' ("medium") or '3' ("high") to indicate a QoS 1841 preference for underlying interface selection purposes. Not 1842 all P[*] values need to be included in the OMNI option of each 1843 IPv6 ND message received. Any P[*] values represented in an 1844 earlier OMNI option but omitted in the current OMNI option 1845 remain unchanged. Any P[*] values not yet represented in any 1846 OMNI option default to "medium". 1848 * The first 16 P[*] blocks correspond to the 64 Differentiated 1849 Service Code Point (DSCP) values P[00] - P[63] [RFC2474]. Any 1850 additional P[*] blocks that follow correspond to "pseudo-DSCP" 1851 traffic classifier values P[64], P[65], P[66], etc. See 1852 Appendix A for further discussion and examples. 1854 11.1.5. Traffic Selector 1855 0 1 2 3 1856 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 1857 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1858 | S-Type=4| Sub-length=N | omIndex | ~ 1859 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ 1860 ~ ~ 1861 ~ RFC 6088 Format Traffic Selector ~ 1862 ~ ~ 1863 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1865 Figure 13: Traffic Selector 1867 o Sub-Type is set to 4. If multiple instances appear in OMNI 1868 options of the same message all are processed, i.e., even if the 1869 same omIndex value appears multiple times. 1871 o Sub-Length is set to N (from 1 to 2034) that encodes the number of 1872 Sub-Option Data octets that follow. 1874 o Sub-Option Data contains a 1 octet omIndex encoded exactly as 1875 specified in Section 11.1.3, followed by an N-1 octet traffic 1876 selector formatted per [RFC6088] beginning with the "TS Format" 1877 field. The largest traffic selector for a given omIndex is 1878 therefore 2033 octets. 1880 11.1.6. MS-Register 1882 0 1 2 3 1883 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 1884 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1885 | S-Type=5| Sub-length=4n | MSID[1] (bits 0 - 15) | 1886 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1887 | MSID [1] (bits 16 - 32) | MSID[2] (bits 0 - 15) | 1888 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1889 | MSID [2] (bits 16 - 32) | MSID[3] (bits 0 - 15) | 1890 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1891 ... ... ... ... ... ... 1892 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1893 | MSID [n] (bits 16 - 32) | 1894 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1896 Figure 14: MS-Register Sub-option 1898 o Sub-Type is set to 5. If multiple instances appear in OMNI 1899 options of the same message all are processed. Only the first 1900 MAX_MSID values processed (whether in a single instance or 1901 multiple) are retained and all other MSIDs are ignored. 1903 o Sub-Length is set to 4n, with 508 as the maximum value for n. The 1904 length of the Sub-Option Data section is therefore limited to 2032 1905 octets. 1907 o A list of n 4 octet MSIDs is included in the following 4n octets. 1908 The Anycast MSID value '0' in an RS message MS-Register sub-option 1909 requests the recipient to return the MSID of a nearby MSE in a 1910 corresponding RA response. 1912 11.1.7. MS-Release 1914 0 1 2 3 1915 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1916 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1917 | S-Type=6| Sub-length=4n | MSID[1] (bits 0 - 15) | 1918 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1919 | MSID [1] (bits 16 - 32) | MSID[2] (bits 0 - 15) | 1920 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1921 | MSID [2] (bits 16 - 32) | MSID[3] (bits 0 - 15) | 1922 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1923 ... ... ... ... ... ... 1924 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1925 | MSID [n] (bits 16 - 32) | 1926 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1928 Figure 15: MS-Release Sub-option 1930 o Sub-Type is set to 6. If multiple instances appear in OMNI 1931 options of the same message all are processed. Only the first 1932 MAX_MSID values processed (whether in a single instance or 1933 multiple) are retained and all other MSIDs are ignored. 1935 o Sub-Length is set to 4n, with 508 as the maximum value for n. The 1936 length of the Sub-Option Data section is therefore limited to 2032 1937 octets. 1939 o A list of n 4 octet MSIDs is included in the following 4n octets. 1940 The Anycast MSID value '0' is ignored in MS-Release sub-options, 1941 i.e., only non-zero values are processed. 1943 11.1.8. Geo Coordinates 1944 0 1 2 3 1945 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 1946 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1947 | S-Type=7| Sub-length=N | Geo Coordinates 1948 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... 1950 Figure 16: Geo Coordinates Sub-option 1952 o Sub-Type is set to 7. If multiple instances appear in OMNI 1953 options of the same message the first is processed and all others 1954 are ignored. 1956 o Sub-Length is set to N (from 0 to 2034) that encodes the number of 1957 Sub-Option Data octets that follow. 1959 o A set of Geo Coordinates of maximum length 2034 octets. Format(s) 1960 to be specified in future documents; should include Latitude/ 1961 Longitude, plus any additional attributes such as altitude, 1962 heading, speed, etc. 1964 11.1.9. Dynamic Host Configuration Protocol for IPv6 (DHCPv6) Message 1966 The Dynamic Host Configuration Protocol for IPv6 (DHCPv6) sub-option 1967 may be included in the OMNI options of RS messages sent by MNs and RA 1968 messages returned by MSEs. ARs that act as proxys to forward RS/RA 1969 messages between MNs and MSEs also forward DHCPv6 sub-options 1970 unchanged and do not process DHCPv6 sub-options themselves. Note 1971 that DHCPv6 message sub-option integrity is protected by the Checksum 1972 included in the IPv6 ND message header. 1974 0 1 2 3 1975 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 1976 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1977 | S-Type=8| Sub-length=N | msg-type | id (octet 0) | 1978 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1979 | transaction-id (octets 1-2) | | 1980 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 1981 | | 1982 . DHCPv6 options . 1983 . (variable number and length) . 1984 | | 1985 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1987 Figure 17: DHCPv6 Message Sub-option 1989 o Sub-Type is set to 8. If multiple instances appear in OMNI 1990 options of the same message the first is processed and all others 1991 are ignored. 1993 o Sub-Length is set to N (from 4 to 2034) that encodes the number of 1994 Sub-Option Data octets that follow. The 'msg-type' and 1995 'transaction-id' fields are always present; hence, the length of 1996 the DHCPv6 options is restricted to 2030 octets. 1998 o 'msg-type' and 'transaction-id' are coded according to Section 8 1999 of [RFC8415]. 2001 o A set of DHCPv6 options coded according to Section 21 of [RFC8415] 2002 follows. 2004 11.1.10. Host Identity Protocol (HIP) Message 2006 The Host Identity Protocol (HIP) Message sub-option may be included 2007 in the OMNI options of RS messages sent by MNs and RA messages 2008 returned by ARs. ARs that act as proxys authenticate and remove HIP 2009 messages in RS messages they forward from a MN to an MSE. ARs that 2010 act as proxys insert and sign HIP messages in the RA messages they 2011 forward from an MSE to a MN. 2013 The HIP message sub-option may also be included in any IPv6 ND 2014 message that may traverse an open Internetwork, i.e., where link- 2015 layer authentication is not already assured by lower layers. 2017 0 1 2 3 2018 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 2019 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2020 | S-Type=9| Sub-length=N |0| Packet Type |Version| RES.|1| 2021 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2022 | Checksum | Controls | 2023 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2024 | Sender's Host Identity Tag (HIT) | 2025 | | 2026 | | 2027 | | 2028 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2029 | Receiver's Host Identity Tag (HIT) | 2030 | | 2031 | | 2032 | | 2033 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2034 | | 2035 / HIP Parameters / 2036 / / 2037 | | 2038 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2040 Figure 18: HIP Message Sub-option 2042 o Sub-Type is set to 9. If multiple instances appear in OMNI 2043 options of the same message the first is processed and all others 2044 are ignored. 2046 o Sub-Length is set to N, i.e., the length of the option in octets 2047 beginning immediately following the Sub-Length field and extending 2048 to the end of the HIP parameters. The length of the entire HIP 2049 message is therefore restricted to 2034 octets. 2051 o The HIP message is coded exactly as specified in Section 5 of 2052 [RFC7401], except that the OMNI "Sub-Type" and "Sub-Length" fields 2053 replace the first 2 octets of the HIP message header (i.e., the 2054 Next Header and Header Length fields). Note that, since the IPv6 2055 ND message header already includes a Checksum, the HIP message 2056 Checksum field is set to 0 on transmission and ignored on 2057 reception. (The Checksum field is still included to retain the 2058 [RFC7401] message format.) 2060 11.1.11. ICMPv6 Error Message 2062 The ICMPv6 Error Message sub-option may be included in the OMNI 2063 options of uNA messages sent from an OAL destination or intermediate 2064 node to an OAL source. The message format and error message types 2065 are found in [RFC4443]. Only those ICMPv6 message Type values 2066 between 0 - 127 (i.e., error messages) are permitted; if the Type 2067 field encodes any other value the message is ignored. 2069 0 1 2 3 2070 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2071 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2072 |S-Type=10| Sub-Length = N | Type | Code | 2073 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2074 | Checksum | | 2075 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + 2076 | | 2077 + Message Body + 2078 | | 2080 Figure 19: ICMPv6 Error Message Sub-option 2082 o Sub-Type is set to 10. If multiple instances appear in OMNI 2083 options of the same message the first is processed and all others 2084 are ignored. 2086 o Sub-Length is set to N, i.e., the length of the option in octets 2087 beginning immediately following the Sub-Length field and extending 2088 to the end of the ICMPv6 error message body. The length of the 2089 entire ICMPv6 error message is therefore restricted to 2034 2090 octets. 2092 o The ICMPv6 error message is coded exactly as specified in 2093 Section 2.1 of [RFC4443]. Note that, since the IPv6 ND message 2094 header already includes a Checksum, the ICMPv6 error message 2095 Checksum field is set to 0 on transmission and ignored on 2096 reception. (The Checksum field is still included to retain the 2097 [RFC4443] message format.) 2099 11.1.12. Maximum Reassembly Unit (MRU) 2101 0 1 2 3 2102 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 2103 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2104 |S-Type=11| Sub-length=2 | Maximum Reassembly Unit (MRU) | 2105 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2107 Figure 20: Maximum Reassembly Unit (MRU) 2109 o Sub-Type is set to 11. If multiple instances appear in OMNI 2110 options of the same message the first is processed and all others 2111 are ignored. 2113 o Sub-Length is set to 2. 2115 o A 2-octet Maximum Reassembly Unit (MRU) follows, and includes a 2116 value between 1500 and 9180. If any other value is included, the 2117 sub-otpion is ignored. The value indicates the maximum amount the 2118 source of the message is currently willing to reassemble; the 2119 source may increase or decrease the value at any time through the 2120 transmission of new IPv6 ND messages. Until the first IPv6 ND 2121 message with an MRU option arrives, OMNI nodes assume an initial 2122 default value of 9180 bytes. After the first IPv6 ND message with 2123 an MRU option arrives, the OMNI node retains the value until a new 2124 IPv6 ND message with a different value arrives. 2126 11.1.13. Node Identification 2128 0 1 2 3 2129 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 2130 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2131 |S-Type=12| Sub-length=N | ID-Type | ~ 2132 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ 2133 ~ Node Identification Value (N-1 octets) ~ 2134 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2136 Figure 21: Node Identification 2138 o Sub-Type is set to 12. If multiple instances appear in OMNI 2139 options of the same IPv6 ND message the first instance of a 2140 specific ID-Type is processed and all other instances of the same 2141 ID-Type are ignored. (Note therefore that it is possible for a 2142 single IPv6 ND message to convey multiple Node Identifications - 2143 each having a different ID-Type.) 2145 o Sub-Length is set to N (from 1 to 2034) that encodes the number of 2146 Sub-Option Data octets that follow. The ID-Type field is always 2147 present; hence, the maximum Node Identification Value length is 2148 2033 octets. 2150 o ID-Type is a 1 octet field that encodes the type of the Node 2151 Identification Value. The following ID-Type values are currently 2152 defined: 2154 * 0 - Universally Unique IDentifier (UUID) [RFC4122]. Indicates 2155 that Node Identification Value contains a 16 octet UUID. 2157 * 1 - Host Identity Tag (HIT) [RFC7401]. Indicates that Node 2158 Identification Value contains a 16 octet HIT. 2160 * 2 - Hierarchical HIT (HHIT) [I-D.ietf-drip-rid]. Indicates 2161 that Node Identification Value contains a 16 octet HHIT. 2163 * 3 - Network Access Identifier (NAI) [RFC7542]. Indicates that 2164 Node Identification Value contains an N-1 octet NAI. 2166 * 4 - Fully-Qualified Domain Name (FQDN) [RFC1035]. Indicates 2167 that Node Identification Value contains an N-1 octet FQDN. 2169 * 5 - 252 - Unassigned. 2171 * 253-254 - Reserved for experimentation, as recommended in 2172 [RFC3692]. 2174 * 255 - reserved by IANA. 2176 o Node Identification Value is an (N - 1) octet field encoded 2177 according to the appropriate the "ID-Type" reference above. 2179 When a Node Identification Value is needed for DHCPv6 messaging 2180 purposes, it is encoded as a DHCP Unique IDentifier (DUID) using the 2181 "DUID-EN for OMNI" format with enterprise number 45282 (see: 2182 Section 24) as shown in Figure 22: 2184 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 2185 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2186 | DUID-Type (2) | EN (high bits == 0) | 2187 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2188 | EN (low bits = 45282) | ID-Type | | 2189 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 2190 . Node Identification Value . 2191 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2193 Figure 22: DUID-EN for OMNI Format 2195 In this format, the ID-Type and Node Identification Value fields are 2196 coded exactly as in Figure 21 following the 6 octet DUID-EN header, 2197 and the entire "DUID-EN for OMNI" is included in a DHCPv6 message per 2198 [RFC8415]. 2200 11.1.14. Sub-Type Extension 2202 Since the Sub-Type field is only 5 bits in length, future 2203 specifications of major protocol functions may exhaust the remaining 2204 Sub-Type values available for assignment. This document therefore 2205 defines Sub-Type 30 as an "extension", meaning that the actual sub- 2206 option type is determined by examining a 1 octet "Extension-Type" 2207 field immediately following the Sub-Length field. The Sub-Type 2208 Extension is formatted as shown in Figure 23: 2210 0 1 2 3 2211 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 2212 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2213 |S-Type=30| Sub-length=N | Extension-Type| ~ 2214 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ 2215 ~ ~ 2216 ~ Extension-Type Body ~ 2217 ~ ~ 2218 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2220 Figure 23: Sub-Type Extension 2222 o Sub-Type is set to 30. If multiple instances appear in OMNI 2223 options of the same message all are processed, where each 2224 individual extension defines its own policy for processing 2225 multiple of that type. 2227 o Sub-Length is set to N (from 1 to 2034) that encodes the number of 2228 Sub-Option Data octets that follow. The Extension-Type field is 2229 always present; hence, the maximum Extension-Type Body length is 2230 2033 octets. 2232 o Extension-Type contains a 1 octet Sub-Type Extension value between 2233 0 and 255. 2235 o Extension-Type Body contains an N-1 octet block with format 2236 defined by the given extension specification. 2238 Extension-Type values 2 through 252 are available for assignment by 2239 future specifications, which must also define the format of the 2240 Extension-Type Body and its processing rules. Extension-Type values 2241 253 and 254 are reserved for experimentation, as recommended in 2242 [RFC3692], and value 255 is reserved by IANA. Extension-Type values 2243 0 and 1 are defined in the following subsections: 2245 11.1.14.1. RFC4380 UDP/IP Header Option 2247 0 1 2 3 2248 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 2249 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2250 |S-Type=30| Sub-length=N | Ext-Type=0 | Header Type | 2251 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2252 ~ Header Option Value ~ 2253 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2255 Figure 24: RFC4380 UDP/IP Header Option (Extension-Type 0) 2257 o Sub-Type is set to 30. 2259 o Sub-Length is set to N (from 2 to 2034) that encodes the number of 2260 Sub-Option Data octets that follow. The Extension-Type and Header 2261 Type fields are always present; hence, the maximum-length Header 2262 Option Value is 2032 octets. 2264 o Extension-Type is set to 0. Each instance encodes exactly one 2265 header option per Section 5.1.1 of [RFC4380], with the leading '0' 2266 octet omitted and the following octet coded as Header Type. If 2267 multiple instances of the same Header Type appear in OMNI options 2268 of the same message the first instance is processed and all others 2269 are ignored. 2271 o Header Type and Header Option Value are coded exactly as specified 2272 in Section 5.1.1 of [RFC4380]; the following types are currently 2273 defined: 2275 * 0 - Origin Indication (IPv4) - value coded per Section 5.1.1 of 2276 [RFC4380]. 2278 * 1 - Authentication Encapsulation - value coded per 2279 Section 5.1.1 of [RFC4380]. 2281 * 2 - Origin Indication (IPv6) - value coded per Section 5.1.1 of 2282 [RFC4380], except that the address is a 16-octet IPv6 address 2283 instead of a 4-octet IPv4 address. 2285 o Header Type values 3 through 252 are available for assignment by 2286 future specifications, which must also define the format of the 2287 Header Option Value and its processing rules. Header Type values 2288 253 and 254 are reserved for experimentation, as recommended in 2289 [RFC3692], and value 255 is Reserved by IANA. 2291 11.1.14.2. RFC6081 UDP/IP Trailer Option 2293 0 1 2 3 2294 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 2295 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2296 |S-Type=30| Sub-length=N | Ext-Type=1 | Trailer Type | 2297 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2298 ~ Trailer Option Value ~ 2299 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2301 Figure 25: RFC6081 UDP/IP Trailer Option (Extension-Type 1) 2303 o Sub-Type is set to 30. 2305 o Sub-Length is set to N (from 2 to 2034) that encodes the number of 2306 Sub-Option Data octets that follow. The Extension-Type and 2307 Trailer Type fields are always present; hence, the maximum-length 2308 Trailer Option Value is 2032 octets. 2310 o Extension-Type is set to 1. Each instance encodes exactly one 2311 trailer option per Section 4 of [RFC6081]. If multiple instances 2312 of the same trailer type appear in OMNI options of the same 2313 message the first instance is processed and all others ignored. 2315 o Trailer Type and Trailer Option Value are coded exactly as 2316 specified in Section 4 of [RFC6081]; the following Trailer Types 2317 are currently defined: 2319 * 0 - Unassigned 2321 * 1 - Nonce Trailer - value coded per Section 4.2 of [RFC6081]. 2323 * 2 - Unassigned 2325 * 3 - Alternate Address Trailer (IPv4) - value coded per 2326 Section 4.3 of [RFC6081]. 2328 * 4 - Neighbor Discovery Option Trailer - value coded per 2329 Section 4.4 of [RFC6081]. 2331 * 5 - Random Port Trailer - value coded per Section 4.5 of 2332 [RFC6081]. 2334 * 6 - Alternate Address Trailer (IPv6) - value coded per 2335 Section 4.3 of [RFC6081], except that each address is a 2336 16-octet IPv6 address instead of a 4-octet IPv4 address. 2338 o Trailer Type values 7 through 252 are available for assignment by 2339 future specifications, which must also define the format of the 2340 Trailer Option Value and its processing rules. Trailer Type 2341 values 253 and 254 are reserved for experimentation, as 2342 recommended in [RFC3692], and value 255 is Reserved by IANA. 2344 12. Address Mapping - Multicast 2346 The multicast address mapping of the native underlying interface 2347 applies. The mobile router on board the MN also serves as an IGMP/ 2348 MLD Proxy for its EUNs and/or hosted applications per [RFC4605] while 2349 using the L2 address of the AR as the L2 address for all multicast 2350 packets. 2352 The MN uses Multicast Listener Discovery (MLDv2) [RFC3810] to 2353 coordinate with the AR, and *NET L2 elements use MLD snooping 2354 [RFC4541]. 2356 13. Multilink Conceptual Sending Algorithm 2358 The MN's IPv6 layer selects the outbound OMNI interface according to 2359 SBM considerations when forwarding data packets from local or EUN 2360 applications to external correspondents. Each OMNI interface 2361 maintains a neighbor cache the same as for any IPv6 interface, but 2362 with additional state for multilink coordination. Each OMNI 2363 interface maintains default routes via ARs discovered as discussed in 2364 Section 14, and may configure more-specific routes discovered through 2365 means outside the scope of this specification. 2367 After a packet enters the OMNI interface, one or more outbound 2368 underlying interfaces are selected based on PBM traffic attributes, 2369 and one or more neighbor underlying interfaces are selected based on 2370 the receipt of Interface Attributes sub-options in IPv6 ND messages 2371 (see: Figure 10). Underlying interface selection for the nodes own 2372 local interfaces are based on attributes such as DSCP, application 2373 port number, cost, performance, message size, etc. OMNI interface 2374 multilink selections could also be configured to perform replication 2375 across multiple underlying interfaces for increased reliability at 2376 the expense of packet duplication. The set of all Interface 2377 Attributes received in IPv6 ND messages determines the multilink 2378 forwarding profile for selecting the neighbor's underlying 2379 interfaces. 2381 When the OMNI interface sends a packet over a selected outbound 2382 underlying interface, the OAL includes or omits a mid-layer 2383 encapsulation header as necessary as discussed in Section 5 and as 2384 determined by the L2 address information received in Interface 2385 Attributes. The OAL also performs encapsulation when the nearest AR 2386 is located multiple hops away as discussed in Section 14.1. (Note 2387 that the OAL MAY employ packing when multiple packets are available 2388 for forwarding to the same destination.) 2390 OMNI interface multilink service designers MUST observe the BCP 2391 guidance in Section 15 [RFC3819] in terms of implications for 2392 reordering when packets from the same flow may be spread across 2393 multiple underlying interfaces having diverse properties. 2395 13.1. Multiple OMNI Interfaces 2397 MNs may connect to multiple independent OMNI links concurrently in 2398 support of SBM. Each OMNI interface is distinguished by its Anycast 2399 ULA (e.g., [ULA]:0002::, [ULA]:1000::, [ULA]:7345::, etc.). The MN 2400 configures a separate OMNI interface for each link so that multiple 2401 interfaces (e.g., omni0, omni1, omni2, etc.) are exposed to the IPv6 2402 layer. A different Anycast ULA is assigned to each interface, and 2403 the MN injects the service prefixes for the OMNI link instances into 2404 the EUN routing system. 2406 Applications in EUNs can use Segment Routing to select the desired 2407 OMNI interface based on SBM considerations. The Anycast ULA is 2408 written into the IPv6 destination address, and the actual destination 2409 (along with any additional intermediate hops) is written into the 2410 Segment Routing Header. Standard IP routing directs the packets to 2411 the MN's mobile router entity, and the Anycast ULA identifies the 2412 OMNI interface to be used for transmission to the next hop. When the 2413 MN receives the message, it replaces the IPv6 destination address 2414 with the next hop found in the routing header and transmits the 2415 message over the OMNI interface identified by the Anycast ULA. 2417 Multiple distinct OMNI links can therefore be used to support fault 2418 tolerance, load balancing, reliability, etc. The architectural model 2419 is similar to Layer 2 Virtual Local Area Networks (VLANs). 2421 13.2. MN<->AR Traffic Loop Prevention 2423 After an AR has registered an MNP for a MN (see: Section 14), the AR 2424 will forward packets destined to an address within the MNP to the MN. 2425 The MN will under normal circumstances then forward the packet to the 2426 correct destination within its internal networks. 2428 If at some later time the MN loses state (e.g., after a reboot), it 2429 may begin returning packets destined to an MNP address to the AR as 2430 its default router. The AR therefore must drop any packets 2431 originating from the MN and destined to an address within the MN's 2432 registered MNP. To do so, the AR institutes the following check: 2434 o if the IP destination address belongs to a neighbor on the same 2435 OMNI interface, and if the link-layer source address is the same 2436 as one of the neighbor's link-layer addresses, drop the packet. 2438 14. Router Discovery and Prefix Registration 2440 MNs interface with the MS by sending RS messages with OMNI options 2441 under the assumption that one or more AR on the *NET will process the 2442 message and respond. The MN then configures default routes for the 2443 OMNI interface via the discovered ARs as the next hop. The manner in 2444 which the *NET ensures AR coordination is link-specific and outside 2445 the scope of this document (however, considerations for *NETs that do 2446 not provide ARs that recognize the OMNI option are discussed in 2447 Section 19). 2449 For each underlying interface, the MN sends an RS message with an 2450 OMNI option to coordinate with MSEs identified by MSID values. 2451 Example MSID discovery methods are given in [RFC5214] and include 2452 data link login parameters, name service lookups, static 2453 configuration, a static "hosts" file, etc. The MN can also send an 2454 RS with an MS-Register sub-option that includes the Anycast MSID 2455 value '0', i.e., instead of or in addition to any non-zero MSIDs. 2456 When the AR receives an RS with a MSID '0', it selects a nearby MSE 2457 (which may be itself) and returns an RA with the selected MSID in an 2458 MS-Register sub-option. The AR selects only a single wildcard MSE 2459 (i.e., even if the RS MS-Register sub-option included multiple '0' 2460 MSIDs) while also soliciting the MSEs corresponding to any non-zero 2461 MSIDs. 2463 MNs configure OMNI interfaces that observe the properties discussed 2464 in the previous section. The OMNI interface and its underlying 2465 interfaces are said to be in either the "UP" or "DOWN" state 2466 according to administrative actions in conjunction with the interface 2467 connectivity status. An OMNI interface transitions to UP or DOWN 2468 through administrative action and/or through state transitions of the 2469 underlying interfaces. When a first underlying interface transitions 2470 to UP, the OMNI interface also transitions to UP. When all 2471 underlying interfaces transition to DOWN, the OMNI interface also 2472 transitions to DOWN. 2474 When an OMNI interface transitions to UP, the MN sends RS messages to 2475 register its MNP and an initial set of underlying interfaces that are 2476 also UP. The MN sends additional RS messages to refresh lifetimes 2477 and to register/deregister underlying interfaces as they transition 2478 to UP or DOWN. The MN's OMNI interface sends initial RS messages 2479 over an UP underlying interface with its MNP-LLA as the source and 2480 with destination set to link-scoped All-Routers multicast (ff02::2) 2481 [RFC4291]. The OMNI interface includes an OMNI option per Section 11 2482 with a Preflen assertion, Interface Attributes appropriate for 2483 underlying interfaces, MS-Register/Release sub-options containing 2484 MSID values, MRU and with any other necessary OMNI sub-options (e.g., 2485 a Node Identification sub-option as an identity for the MN). The 2486 OMNI interface then sets the S/T-omIndex field to the index of the 2487 underlying interface over which the RS message is sent. The OMNI 2488 interface then sends the RS over the underlying interface, using OAL 2489 encapsulation and fragmentation if necessary. If OAL encapsulation 2490 is used, the OMNI interface sets the OAL source address to the ULA 2491 corresponding to the RS source and sets the OAL destination to site- 2492 scoped All-Routers multicast (ff05::2). 2494 ARs process IPv6 ND messages with OMNI options and act as an MSE 2495 themselves and/or as a proxy for other MSEs. ARs receive RS messages 2496 (while performing OAL reassembly if necessary) and create a neighbor 2497 cache entry for the MN, then coordinate with any MSEs named in the 2498 Register/Release lists in a manner outside the scope of this 2499 document. When an MSE processes the OMNI information, it first 2500 validates the prefix registration information then injects/withdraws 2501 the MNP in the routing/mapping system and caches/discards the new 2502 Preflen, MNP and Interface Attributes. The MSE then informs the AR 2503 of registration success/failure, and the AR returns an RA message to 2504 the MN with an OMNI option per Section 11. 2506 The AR's OMNI interface returns the RA message via the same 2507 underlying interface of the MN over which the RS was received, and 2508 with destination address set to the MNP-LLA (i.e., unicast), with 2509 source address set to its own LLA, and with an OMNI option with S/ 2510 T-omIndex set to the value included in the RS. The OMNI option also 2511 includes a Preflen confirmation, Interface Attributes, MS-Register/ 2512 Release and any other necessary OMNI sub-options (e.g., a Node 2513 Identification sub-option as an identity for the AR). The RA also 2514 includes any information for the link, including RA Cur Hop Limit, M 2515 and O flags, Router Lifetime, Reachable Time and Retrans Timer 2516 values, and includes any necessary options such as: 2518 o PIOs with (A; L=0) that include MSPs for the link [RFC8028]. 2520 o RIOs [RFC4191] with more-specific routes. 2522 o an MTU option that specifies the maximum acceptable packet size 2523 for this underlying interface. 2525 The OMNI interface then sends the RA, using OAL encapsulation and 2526 fragmentation if necessary. If OAL encapsulation is used, the OMNI 2527 interface sets the OAL source address to the ULA corresponding to the 2528 RA source and sets the OAL destination to the ULA corresponding to 2529 the RA destination. The AR MAY also send periodic and/or event- 2530 driven unsolicited RA messages per [RFC4861]. In that case, the S/ 2531 T-omIndex field in the OMNI option of the unsolicited RA message 2532 identifies the target underlying interface of the destination MN. 2534 The AR can combine the information from multiple MSEs into one or 2535 more "aggregate" RAs sent to the MN in order conserve *NET bandwidth. 2536 Each aggregate RA includes an OMNI option with MS-Register/Release 2537 sub-options with the MSEs represented by the aggregate. If an 2538 aggregate is sent, the RA message contents must consistently 2539 represent the combined information advertised by all represented 2540 MSEs. Note that since the AR uses its own ADM-LLA as the RA source 2541 address, the MN determines the addresses of the represented MSEs by 2542 examining the MS-Register/Release OMNI sub-options. 2544 When the MN receives the RA message, it creates an OMNI interface 2545 neighbor cache entry for each MSID that has confirmed MNP 2546 registration via the L2 address of this AR. If the MN connects to 2547 multiple *NETs, it records the additional L2 AR addresses in each 2548 MSID neighbor cache entry (i.e., as multilink neighbors). The MN 2549 then configures a default route via the MSE that returned the RA 2550 message, and assigns the Subnet Router Anycast address corresponding 2551 to the MNP (e.g., 2001:db8:1:2::) to the OMNI interface. The MN then 2552 manages its underlying interfaces according to their states as 2553 follows: 2555 o When an underlying interface transitions to UP, the MN sends an RS 2556 over the underlying interface with an OMNI option. The OMNI 2557 option contains at least one Interface Attribute sub-option with 2558 values specific to this underlying interface, and may contain 2559 additional Interface Attributes specific to other underlying 2560 interfaces. The option also includes any MS-Register/Release sub- 2561 options. 2563 o When an underlying interface transitions to DOWN, the MN sends an 2564 RS or unsolicited NA message over any UP underlying interface with 2565 an OMNI option containing an Interface Attribute sub-option for 2566 the DOWN underlying interface with Link set to '0'. The MN sends 2567 an RS when an acknowledgement is required, or an unsolicited NA 2568 when reliability is not thought to be a concern (e.g., if 2569 redundant transmissions are sent on multiple underlying 2570 interfaces). 2572 o When the Router Lifetime for a specific AR nears expiration, the 2573 MN sends an RS over the underlying interface to receive a fresh 2574 RA. If no RA is received, the MN can send RS messages to an 2575 alternate MSID in case the current MSID has failed. If no RS 2576 messages are received even after trying to contact alternate 2577 MSIDs, the MN marks the underlying interface as DOWN. 2579 o When a MN wishes to release from one or more current MSIDs, it 2580 sends an RS or unsolicited NA message over any UP underlying 2581 interfaces with an OMNI option with a Release MSID. Each MSID 2582 then withdraws the MNP from the routing/mapping system and informs 2583 the AR that the release was successful. 2585 o When all of a MNs underlying interfaces have transitioned to DOWN 2586 (or if the prefix registration lifetime expires), any associated 2587 MSEs withdraw the MNP the same as if they had received a message 2588 with a release indication. 2590 The MN is responsible for retrying each RS exchange up to 2591 MAX_RTR_SOLICITATIONS times separated by RTR_SOLICITATION_INTERVAL 2592 seconds until an RA is received. If no RA is received over an UP 2593 underlying interface (i.e., even after attempting to contact 2594 alternate MSEs), the MN declares this underlying interface as DOWN. 2596 The IPv6 layer sees the OMNI interface as an ordinary IPv6 interface. 2597 Therefore, when the IPv6 layer sends an RS message the OMNI interface 2598 returns an internally-generated RA message as though the message 2599 originated from an IPv6 router. The internally-generated RA message 2600 contains configuration information that is consistent with the 2601 information received from the RAs generated by the MS. Whether the 2602 OMNI interface IPv6 ND messaging process is initiated from the 2603 receipt of an RS message from the IPv6 layer is an implementation 2604 matter. Some implementations may elect to defer the IPv6 ND 2605 messaging process until an RS is received from the IPv6 layer, while 2606 others may elect to initiate the process proactively. Still other 2607 deployments may elect to administratively disable the ordinary RS/RA 2608 messaging used by the IPv6 layer over the OMNI interface, since they 2609 are not required to drive the internal RS/RA processing. (Note that 2610 this same logic applies to IPv4 implementations that employ ICMP- 2611 based Router Discovery per [RFC1256].) 2612 Note: The Router Lifetime value in RA messages indicates the time 2613 before which the MN must send another RS message over this underlying 2614 interface (e.g., 600 seconds), however that timescale may be 2615 significantly longer than the lifetime the MS has committed to retain 2616 the prefix registration (e.g., REACHABLETIME seconds). ARs are 2617 therefore responsible for keeping MS state alive on a shorter 2618 timescale than the MN is required to do on its own behalf. 2620 Note: On multicast-capable underlying interfaces, MNs should send 2621 periodic unsolicited multicast NA messages and ARs should send 2622 periodic unsolicited multicast RA messages as "beacons" that can be 2623 heard by other nodes on the link. If a node fails to receive a 2624 beacon after a timeout value specific to the link, it can initiate a 2625 unicast exchange to test reachability. 2627 Note: if an AR acting as a proxy forwards a MN's RS message to 2628 another node acting as an MSE using UDP/IP encapsulation, it must use 2629 a distinct UDP source port number for each MN. This allows the MSE 2630 to distinguish different MNs behind the same AR at the link-layer, 2631 whereas the link-layer addresses would otherwise be 2632 indistinguishable. 2634 Note: when an AR acting as an MSE returns an RA to an INET Client, it 2635 includes an OMNI option with an Interface Attributes sub-option with 2636 omIndex set to 0 and with SRT, FMT, LHS and L2ADDR information for 2637 its INET interface. This provides the Client with partition prefix 2638 context regarding the local OMNI link segment. 2640 14.1. Router Discovery in IP Multihop and IPv4-Only Networks 2642 On some *NETs, a MN may be located multiple IP hops away from the 2643 nearest AR. Forwarding through IP multihop *NETs is conducted 2644 through the application of a routing protocol (e.g., a MANET/VANET 2645 routing protocol over omni-directional wireless interfaces, an inter- 2646 domain routing protocol in an enterprise network, etc.). These *NETs 2647 could be either IPv6-enabled or IPv4-only, while IPv4-only *NETs 2648 could be either multicast-capable or unicast-only (note that for 2649 IPv4-only *NETs the following procedures apply for both single-hop 2650 and multihop cases). 2652 A MN located potentially multiple *NET hops away from the nearest AR 2653 prepares an RS message with source address set to its MNP-LLA (or to 2654 the unspecified address (::) if it does not yet have an MNP-LLA), and 2655 with destination set to link-scoped All-Routers multicast the same as 2656 discussed above. If OAL encapsulation and fragmentation are 2657 necessary, the OMNI interface sets the OAL source address to the ULA 2658 corresponding to the RS source (or to a Temporary ULA if the RS 2659 source was the unspecified address (::)) and sets the OAL destination 2660 to site-scoped All-Routers multicast (ff05::2). For IPv6-enabled 2661 *NETs, the MN then encapsulates the message in UDP/IPv6 headers with 2662 source address set to the underlying interface address (or to the ULA 2663 that would be used for OAL encapsulation if the underlying interface 2664 does not yet have an address) and sets the destination to either a 2665 unicast or anycast address of an AR. For IPv4-only *NETs, the MN 2666 instead encapsulates the RS message in an IPv4 header with source 2667 address set to the IPv4 address of the underlying interface and with 2668 destination address set to either the unicast IPv4 address of an AR 2669 [RFC5214] or an IPv4 anycast address reserved for OMNI. The MN then 2670 sends the encapsulated RS message via the *NET interface, where it 2671 will be forwarded by zero or more intermediate *NET hops. 2673 When an intermediate *NET hop that participates in the routing 2674 protocol receives the encapsulated RS, it forwards the message 2675 according to its routing tables (note that an intermediate node could 2676 be a fixed infrastructure element or another MN). This process 2677 repeats iteratively until the RS message is received by a penultimate 2678 *NET hop within single-hop communications range of an AR, which 2679 forwards the message to the AR. 2681 When the AR receives the message, it decapsulates the RS (while 2682 performing OAL reassembly, if necessary) and coordinates with the MS 2683 the same as for an ordinary link-local RS, since the inner Hop Limit 2684 will not have been decremented by the multihop forwarding process. 2685 The AR then prepares an RA message with source address set to its own 2686 ADM-LLA and destination address set to the LLA of the original MN. 2687 The AR then performs OAL encapsulation and fragmentation if 2688 necessary, with OAL source set to its own ADM-ULA and destination set 2689 to the ULA corresponding to the RA source. The AR then encapsulates 2690 the message in an IPv4/IPv6 header with source address set to its own 2691 IPv4/ULA address and with destination set to the encapsulation source 2692 of the RS. 2694 The AR then forwards the message to an *NET node within 2695 communications range, which forwards the message according to its 2696 routing tables to an intermediate node. The multihop forwarding 2697 process within the *NET continues repetitively until the message is 2698 delivered to the original MN, which decapsulates the message and 2699 performs autoconfiguration the same as if it had received the RA 2700 directly from the AR as an on-link neighbor. 2702 Note: An alternate approach to multihop forwarding via IPv6 2703 encapsulation would be for the MN and AR to statelessly translate the 2704 IPv6 LLAs into ULAs and forward the RS/RA messages without 2705 encapsulation. This would violate the [RFC4861] requirement that 2706 certain IPv6 ND messages must use link-local addresses and must not 2707 be accepted if received with Hop Limit less than 255. This document 2708 therefore mandates encapsulation since the overhead is nominal 2709 considering the infrequent nature and small size of IPv6 ND messages. 2710 Future documents may consider encapsulation avoidance through 2711 translation while updating [RFC4861]. 2713 Note: An alternate approach to multihop forwarding via IPv4 2714 encapsulation would be to employ IPv6/IPv4 protocol translation. 2715 However, for IPv6 ND messages the LLAs would be truncated due to 2716 translation and the OMNI Router and Prefix Discovery services would 2717 not be able to function. The use of IPv4 encapsulation is therefore 2718 indicated. 2720 Note: An IPv4 anycast address for OMNI in IPv4 networks could be part 2721 of a new IPv4 /24 prefix allocation, but this may be difficult to 2722 obtain given IPv4 address exhaustion. An alternative would be to re- 2723 purpose the prefix 192.88.99.0 which has been set aside from its 2724 former use by [RFC7526]. 2726 14.2. MS-Register and MS-Release List Processing 2728 OMNI links maintain a constant value "MAX_MSID" selected to provide 2729 MNs with an acceptable level of MSE redundancy while minimizing 2730 control message amplification. It is RECOMMENDED that MAX_MSID be 2731 set to the default value 5; if a different value is chosen, it should 2732 be set uniformly by all nodes on the OMNI link. 2734 When a MN sends an RS message with an OMNI option via an underlying 2735 interface to an AR, the MN must convey its knowledge of its 2736 currently-associated MSEs. Initially, the MN will have no associated 2737 MSEs and should therefore include an MS-Register sub-option with the 2738 single "anycast" MSID value 0 which requests the AR to select and 2739 assign an MSE. The AR will then return an RA message with source 2740 address set to the ADM-LLA of the selected MSE. 2742 As the MN activates additional underlying interfaces, it can 2743 optionally include an MS-Register sub-option with MSID value 0, or 2744 with non-zero MSIDs for MSEs discovered from previous RS/RA 2745 exchanges. The MN will thus eventually begin to learn and manage its 2746 currently active set of MSEs, and can register with new MSEs or 2747 release from former MSEs with each successive RS/RA exchange. As the 2748 MN's MSE constituency grows, it alone is responsible for including or 2749 omitting MSIDs in the MS-Register/Release lists it sends in RS 2750 messages. The inclusion or omission of MSIDs determines the MN's 2751 interface to the MS and defines the manner in which MSEs will 2752 respond. The only limiting factor is that the MN should include no 2753 more than MAX_MSID values in each list per each IPv6 ND message, and 2754 should avoid duplication of entries in each list unless it wants to 2755 increase likelihood of control message delivery. 2757 When an AR receives an RS message sent by a MN with an OMNI option, 2758 the option will contain zero or more MS-Register and MS-Release sub- 2759 options containing MSIDs. After processing the OMNI option, the AR 2760 will have a list of zero or more MS-Register MSIDs and a list of zero 2761 or more of MS-Release MSIDs. The AR then processes the lists as 2762 follows: 2764 o For each list, retain the first MAX_MSID values in the list and 2765 discard any additional MSIDs (i.e., even if there are duplicates 2766 within a list). 2768 o Next, for each MSID in the MS-Register list, remove all matching 2769 MSIDs from the MS-Release list. 2771 o Next, proceed according to whether the AR's own MSID or the value 2772 0 appears in the MS-Register list as follows: 2774 * If yes, send an RA message directly back to the MN and send a 2775 proxy copy of the RS message to each additional MSID in the MS- 2776 Register list with the MS-Register/Release lists omitted. 2777 Then, send an unsolicited NA (uNA) message to each MSID in the 2778 MS-Release list with the MS-Register/Release lists omitted and 2779 with an OMNI option with S/T-omIndex set to 0. 2781 * If no, send a proxy copy of the RS message to each additional 2782 MSID in the MS-Register list with the MS-Register list omitted. 2783 For the first MSID, include the original MS-Release list; for 2784 all other MSIDs, omit the MS-Release list. 2786 Each proxy copy of the RS message will include an OMNI option and OAL 2787 encapsulation header with the ADM-ULA of the AR as the source and the 2788 ADM-ULA of the Register MSE as the destination. When the Register 2789 MSE receives the proxy RS message, if the message includes an MS- 2790 Release list the MSE sends a uNA message to each additional MSID in 2791 the Release list with an OMNI option with S/T-omIndex set to 0. The 2792 Register MSE then sends an RA message back to the (Proxy) AR wrapped 2793 in an OAL encapsulation header with source and destination addresses 2794 reversed, and with RA destination set to the MNP-LLA of the MN. When 2795 the AR receives this RA message, it sends a proxy copy of the RA to 2796 the MN. 2798 Each uNA message (whether sent by the first-hop AR or by a Register 2799 MSE) will include an OMNI option and an OAL encapsulation header with 2800 the ADM-ULA of the Register MSE as the source and the ADM-ULA of the 2801 Release MSE as the destination. The uNA informs the Release MSE that 2802 its previous relationship with the MN has been released and that the 2803 source of the uNA message is now registered. The Release MSE must 2804 then note that the subject MN of the uNA message is now "departed", 2805 and forward any subsequent packets destined to the MN to the Register 2806 MSE. 2808 Note that it is not an error for the MS-Register/Release lists to 2809 include duplicate entries. If duplicates occur within a list, the AR 2810 will generate multiple proxy RS and/or uNA messages - one for each 2811 copy of the duplicate entries. 2813 14.3. DHCPv6-based Prefix Registration 2815 When a MN is not pre-provisioned with an MNP-LLA (or, when the MN 2816 requires additional MNP delegations), it requests the MSE to select 2817 MNPs on its behalf and set up the correct routing state within the 2818 MS. The DHCPv6 service [RFC8415] supports this requirement. 2820 When an MN needs to have the MSE select MNPs, it sends an RS message 2821 with source set to the unspecified address (::) if it has no 2822 MNP_LLAs. If the MN requires only a single MNP delegation, it can 2823 then include a Node Identification sub-option in the OMNI option and 2824 set Preflen to the length of the desired MNP. If the MN requires 2825 multiple MNP delegations and/or more complex DHCPv6 services, it 2826 instead includes a DHCPv6 Message sub-option containing a Client 2827 Identifier, one or more IA_PD options and a Rapid Commit option then 2828 sets the 'msg-type' field to "Solicit", and includes a 3 octet 2829 'transaction-id'. The MN then sets the RS destination to All-Routers 2830 multicast and sends the message using OAL encapsulation and 2831 fragmentation if necessary as discussed above. 2833 When the MSE receives the RS message, it performs OAL reassembly if 2834 necessary. Next, if the RS source is the unspecified address (::) 2835 and/or the OMNI option includes a DHCPv6 message sub-option, the MSE 2836 acts as a "Proxy DHCPv6 Client" in a message exchange with the 2837 locally-resident DHCPv6 server. If the RS did not contain a DHCPv6 2838 message sub-option, the MSE generates a DHCPv6 Solicit message on 2839 behalf of the MN using an IA_PD option with the prefix length set to 2840 the OMNI header Preflen value and with a Client Identifier formed 2841 from the OMNI option Node Identification sub-option; otherwise, the 2842 MSE uses the DHCPv6 Solicit message contained in the OMNI option. 2843 The MSE then sends the DHCPv6 message to the DHCPv6 Server, which 2844 delegates MNPs and returns a DHCPv6 Reply message with PD parameters. 2845 (If the MSE wishes to defer creation of MN state until the DHCPv6 2846 Reply is received, it can instead act as a Lightweight DHCPv6 Relay 2847 Agent per [RFC6221] by encapsulating the DHCPv6 message in a Relay- 2848 forward/reply exchange with Relay Message and Interface ID options. 2849 In the process, the MSE packs any state information needed to return 2850 an RA to the MN in the Relay-forward Interface ID option so that the 2851 information will be echoed back in the Relay-reply.) 2852 When the MSE receives the DHCPv6 Reply, it adds routes to the routing 2853 system and creates MNP-LLAs based on the delegated MNPs. The MSE 2854 then sends an RA back to the MN with the DHCPv6 Reply message 2855 included in an OMNI DHCPv6 message sub-option if and only if the RS 2856 message had included an explicit DHCPv6 Solicit. If the RS message 2857 source was the unspecified address (::), the MSE includes one of the 2858 (newly-created) MNP-LLAs as the RA destination address and sets the 2859 OMNI option Preflen accordingly; otherwise, the MSE includes the RS 2860 source address as the RA destination address. The MSE then sets the 2861 RA source address to its own ADM-LLA then performs OAL encapsulation 2862 and fragmentation if necessary and sends the RA to the MN. When the 2863 MN receives the RA, it reassembles and discards the OAL encapsulation 2864 if necessary, then creates a default route, assigns Subnet Router 2865 Anycast addresses and uses the RA destination address as its primary 2866 MNP-LLA. The MN will then use this primary MNP-LLA as the source 2867 address of any IPv6 ND messages it sends as long as it retains 2868 ownership of the MNP. 2870 Note: After a MN performs a DHCPv6-based prefix registration exchange 2871 with a first MSE, it would need to repeat the exchange with each 2872 additional MSE it registers with. In that case, the MN supplies the 2873 MNP delegation information received from the first MSE when it 2874 engages the additional MSEs. 2876 15. Secure Redirection 2878 If the *NET link model is multiple access, the AR is responsible for 2879 assuring that address duplication cannot corrupt the neighbor caches 2880 of other nodes on the link. When the MN sends an RS message on a 2881 multiple access *NET link, the AR verifies that the MN is authorized 2882 to use the address and returns an RA with a non-zero Router Lifetime 2883 only if the MN is authorized. 2885 After verifying MN authorization and returning an RA, the AR MAY 2886 return IPv6 ND Redirect messages to direct MNs located on the same 2887 *NET link to exchange packets directly without transiting the AR. In 2888 that case, the MNs can exchange packets according to their unicast L2 2889 addresses discovered from the Redirect message instead of using the 2890 dogleg path through the AR. In some *NET links, however, such direct 2891 communications may be undesirable and continued use of the dogleg 2892 path through the AR may provide better performance. In that case, 2893 the AR can refrain from sending Redirects, and/or MNs can ignore 2894 them. 2896 16. AR and MSE Resilience 2898 *NETs SHOULD deploy ARs in Virtual Router Redundancy Protocol (VRRP) 2899 [RFC5798] configurations so that service continuity is maintained 2900 even if one or more ARs fail. Using VRRP, the MN is unaware which of 2901 the (redundant) ARs is currently providing service, and any service 2902 discontinuity will be limited to the failover time supported by VRRP. 2903 Widely deployed public domain implementations of VRRP are available. 2905 MSEs SHOULD use high availability clustering services so that 2906 multiple redundant systems can provide coordinated response to 2907 failures. As with VRRP, widely deployed public domain 2908 implementations of high availability clustering services are 2909 available. Note that special-purpose and expensive dedicated 2910 hardware is not necessary, and public domain implementations can be 2911 used even between lightweight virtual machines in cloud deployments. 2913 17. Detecting and Responding to MSE Failures 2915 In environments where fast recovery from MSE failure is required, ARs 2916 SHOULD use proactive Neighbor Unreachability Detection (NUD) in a 2917 manner that parallels Bidirectional Forwarding Detection (BFD) 2918 [RFC5880] to track MSE reachability. ARs can then quickly detect and 2919 react to failures so that cached information is re-established 2920 through alternate paths. Proactive NUD control messaging is carried 2921 only over well-connected ground domain networks (i.e., and not low- 2922 end *NET links such as aeronautical radios) and can therefore be 2923 tuned for rapid response. 2925 ARs perform proactive NUD for MSEs for which there are currently 2926 active MNs on the *NET. If an MSE fails, ARs can quickly inform MNs 2927 of the outage by sending multicast RA messages on the *NET interface. 2928 The AR sends RA messages to MNs via the *NET interface with an OMNI 2929 option with a Release ID for the failed MSE, and with destination 2930 address set to All-Nodes multicast (ff02::1) [RFC4291]. 2932 The AR SHOULD send MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated 2933 by small delays [RFC4861]. Any MNs on the *NET interface that have 2934 been using the (now defunct) MSE will receive the RA messages and 2935 associate with a new MSE. 2937 18. Transition Considerations 2939 When a MN connects to an *NET link for the first time, it sends an RS 2940 message with an OMNI option. If the first hop AR recognizes the 2941 option, it returns an RA with its ADM-LLA as the source, the MNP-LLA 2942 as the destination and with an OMNI option included. The MN then 2943 engages the AR according to the OMNI link model specified above. If 2944 the first hop AR is a legacy IPv6 router, however, it instead returns 2945 an RA message with no OMNI option and with a non-OMNI unicast source 2946 LLA as specified in [RFC4861]. In that case, the MN engages the *NET 2947 according to the legacy IPv6 link model and without the OMNI 2948 extensions specified in this document. 2950 If the *NET link model is multiple access, there must be assurance 2951 that address duplication cannot corrupt the neighbor caches of other 2952 nodes on the link. When the MN sends an RS message on a multiple 2953 access *NET link with an LLA source address and an OMNI option, ARs 2954 that recognize the option ensure that the MN is authorized to use the 2955 address and return an RA with a non-zero Router Lifetime only if the 2956 MN is authorized. ARs that do not recognize the option instead 2957 return an RA that makes no statement about the MN's authorization to 2958 use the source address. In that case, the MN should perform 2959 Duplicate Address Detection to ensure that it does not interfere with 2960 other nodes on the link. 2962 An alternative approach for multiple access *NET links to ensure 2963 isolation for MN / AR communications is through L2 address mappings 2964 as discussed in Appendix C. This arrangement imparts a (virtual) 2965 point-to-point link model over the (physical) multiple access link. 2967 19. OMNI Interfaces on Open Internetworks 2969 OMNI interfaces configured over IPv6-enabled underlying interfaces on 2970 an open Internetwork without an OMNI-aware first-hop AR receive RA 2971 messages that do not include an OMNI option, while OMNI interfaces 2972 configured over IPv4-only underlying interfaces do not receive any 2973 (IPv6) RA messages at all. OMNI interfaces that receive RA messages 2974 without an OMNI option configure addresses, on-link prefixes, etc. on 2975 the underlying interface that received the RA according to standard 2976 IPv6 ND and address resolution conventions [RFC4861] [RFC4862]. OMNI 2977 interfaces configured over IPv4-only underlying interfaces configure 2978 IPv4 address information on the underlying interfaces using 2979 mechanisms such as DHCPv4 [RFC2131]. 2981 OMNI interfaces configured over underlying interfaces that connect to 2982 an open Internetwork can apply security services such as VPNs to 2983 connect to an MSE, or can establish a direct link to an MSE through 2984 some other means (see Section 4). In environments where an explicit 2985 VPN or direct link may be impractical, OMNI interfaces can instead 2986 use UDP/IP encapsulation per [RFC6081][RFC4380] and HIP-based message 2987 authentication per [RFC7401]. 2989 OMNI interfaces use UDP service port number 8060 (see: Section 24.9 2990 and Section 3.6 of [I-D.templin-intarea-6706bis]) according to the 2991 simple UDP/IP encapsulation format specified in [RFC4380] for both 2992 IPv4 and IPv6 underlying interfaces. OMNI interfaces do not include 2993 the UDP/IP header/trailer extensions specified in [RFC4380][RFC6081], 2994 but may include them as OMNI sub-options instead when necessary. 2995 Since the OAL includes an integrity check over the OAL packet, OAL 2996 sources selectively disable UDP checksums for OAL packets that do not 2997 require UDP/IP address integrity, but enable UDP checksums for others 2998 including non-OAL packets, IPv6 ND messages used to establish link- 2999 layer addresses, etc. If the OAL source discovers that packets with 3000 UDP checksums disabled are being dropped in the path it should enable 3001 UDP checksums in future packets. Further considerations for UDP 3002 encapsulation checksums are found in [RFC6935][RFC6936]. 3004 For "Vehicle-to-Infrastructure (V2I)" coordination, the MN codes a 3005 HIP "Initiator" message in an OMNI option of an IPv6 RS message and 3006 the AR responds with a HIP "Responder" message coded in an OMNI 3007 option of an IPv6 RA message. HIP security services are applied per 3008 [RFC7401], using the RS/RA messages as simple "shipping containers" 3009 to convey the HIP parameters. In that case, a "two-message HIP 3010 exchange" through a single RS/RA exchange may be sufficient for 3011 mutual authentication. For "Vehicle-to-Vehicle (V2V)" coordination, 3012 two MNs can coordinate directly with one another with HIP "Initiator/ 3013 Responder" messages coded in OMNI options of IPv6 NS/NA messages. In 3014 that case, a four-message HIP exchange (i.e., two back-to-back NS/NA 3015 exchanges) may be necessary for the two MNs to attain mutual 3016 authentication. 3018 After establishing a VPN or preparing for UDP/IP encapsulation, OMNI 3019 interfaces send control plane messages to interface with the MS, 3020 including RS/RA messages used according to Section 14 and NS/NA 3021 messages used for route optimization and mobility (see: 3022 [I-D.templin-intarea-6706bis]). The control plane messages must be 3023 authenticated while data plane messages are delivered the same as for 3024 ordinary best-effort traffic with basic source address-based data 3025 origin verification. Data plane communications via OMNI interfaces 3026 that connect over open Internetworks without an explicit VPN should 3027 therefore employ transport- or higher-layer security to ensure 3028 integrity and/or confidentiality. 3030 OMNI interfaces configured over open Internetworks are often located 3031 behind NATs. The OMNI interface accommodates NAT traversal using 3032 UDP/IP encapsulation and the mechanisms discussed in 3033 [I-D.templin-intarea-6706bis]. To support NAT determination, ARs 3034 include an Origin Indication sub-option in RA messages sent in 3035 response to RS messages received from a Client via UDP/IP 3036 encapsulation. 3038 Note: Following the initial HIP Initiator/Responder exchange, OMNI 3039 interfaces configured over open Internetworks maintain HIP 3040 associations through the transmission of IPv6 ND messages that 3041 include OMNI options with HIP "Update" and "Notify" messages. OMNI 3042 interfaces use the HIP "Update" message when an acknowledgement is 3043 required, and use the "Notify" message in unacknowledged isolated 3044 IPv6 ND messages (e.g., unsolicited NAs). 3046 Note: ARs that act as proxys on an open Internetwork authenticate and 3047 remove HIP message OMNI sub-options from RSes they forward from a MN 3048 to an MSE, and insert and sign HIP message and Origin Indication sub- 3049 options in RAs they forward from an MSE to an MN. Conversely, ARs 3050 that act as proxys forward without processing any DHCPv6 information 3051 in RS/RA message exchanges between MNs and MSEs. The AR is therefore 3052 responsible for MN authentication while the MSE is responsible for 3053 registering/delegating MNPs. 3055 20. Time-Varying MNPs 3057 In some use cases, it is desirable, beneficial and efficient for the 3058 MN to receive a constant MNP that travels with the MN wherever it 3059 moves. For example, this would allow air traffic controllers to 3060 easily track aircraft, etc. In other cases, however (e.g., 3061 intelligent transportation systems), the MN may be willing to 3062 sacrifice a modicum of efficiency in order to have time-varying MNPs 3063 that can be changed every so often to defeat adversarial tracking. 3065 The prefix delegation services discussed in Section 14.3 allows OMNI 3066 MNs that desire time-varying MNPs to obtain short-lived prefixes to 3067 send RS messages with source set to the unspecified address (::) and/ 3068 or with an OMNI option with DHCPv6 Option sub-options. The MN would 3069 then be obligated to renumber its internal networks whenever its MNP 3070 (and therefore also its OMNI address) changes. This should not 3071 present a challenge for MNs with automated network renumbering 3072 services, however presents limits for the durations of ongoing 3073 sessions that would prefer to use a constant address. 3075 21. (H)HITs and Temporary ULAs 3077 MNs that generate (H)HITs but do not have pre-assigned MNPs can 3078 request MNP delegations by issuing IPv6 ND messages that use the 3079 (H)HIT instead of a Temporary ULA. In particular, when a MN creates 3080 an RS message it can set the source to the unspecified address (::) 3081 and destination to All-Routers multicast. The IPv6 ND message 3082 includes an OMNI option with a HIP "Initiator" message sub-option, 3083 and need not include a Node Identification sub-option since the MN's 3084 HIT appears in the HIP message. The MN then encapsulates the message 3085 in an IPv6 header with the (H)HIT as the source address and with 3086 destination set to either a unicast or anycast ADM-ULA. The MN then 3087 sends the message to the AR as specified in Section 14.1. 3089 When the AR receives the message, it notes that the RS source was the 3090 unspecified address (::), then examines the RS encapsulation source 3091 address to determine that the source is a (H)HIT and not a Temporary 3092 ULA. The AR next invokes the DHCPv6 protocol to request an MNP 3093 prefix delegation while using the HIT as the Client Identifier, then 3094 prepares an RA message with source address set to its own ADM-LLA and 3095 destination set to the MNP-LLA corresponding to the delegated MNP. 3096 The AR next includes an OMNI option with a HIP "Responder" message 3097 and any DHCPv6 prefix delegation parameters. The AR then finally 3098 encapsulates the RA in an IPv6 header with source address set to its 3099 own ADM-ULA and destination set to the (H)HIT from the RS 3100 encapsulation source address, then returns the encapsulated RA to the 3101 MN. 3103 MNs can also use (H)HITs and/or Temporary ULAs for direct MN-to-MN 3104 communications outside the context of any OMNI link supporting 3105 infrastructure. When two MNs encounter one another they can use 3106 their (H)HITs and/or Temporary ULAs as IPv6 packet source and 3107 destination addresses to support direct communications. MNs can also 3108 inject their (H)HITs and/or Temporary ULAs into a MANET/VANET routing 3109 protocol to enable multihop communications. MNs can further exchange 3110 IPv6 ND messages (such as NS/NA) using their (H)HITs and/or Temporary 3111 ULAs as source and destination addresses. Note that the HIP security 3112 protocols for establishing secure neighbor relationships are based on 3113 (H)HITs; therefore, Temporary ULAs would presumably utilize some 3114 alternate form of message authentication such as the [RFC4380] 3115 authentication service. 3117 Lastly, when MNs are within the coverage range of OMNI link 3118 infrastructure a case could be made for injecting (H)HITs and/or 3119 Temporary ULAs into the global MS routing system. For example, when 3120 the MN sends an RS to a MSE it could include a request to inject the 3121 (H)HIT / Temporary ULA into the routing system instead of requesting 3122 an MNP prefix delegation. This would potentially enable OMNI link- 3123 wide communications using only (H)HITs or Temporary ULAs, and not 3124 MNPs. This document notes the opportunity, but makes no 3125 recommendation. 3127 22. Address Selection 3129 OMNI MNs use LLAs only for link-scoped communications on the OMNI 3130 link. Typically, MNs use LLAs as source/destination IPv6 addresses 3131 of IPv6 ND messages, but may also use them for addressing ordinary 3132 data packets exchanged with an OMNI link neighbor. 3134 OMNI MNs use MNP-ULAs as source/destination IPv6 addresses in the OAL 3135 headers of OAL-encapsulated packets. OMNI MNs use Temporary ULAs for 3136 OAL addressing when an MNP-ULA is not available, or as source/ 3137 destination IPv6 addresses for communications within a MANET/VANET 3138 local area. OMNI MNs use HITs instead of Temporary ULAs when 3139 operation outside the context of a specific ULA domain and/or source 3140 address attestation is necessary. 3142 OMNI MNs use MNP-based GUAs for communications with Internet 3143 destinations when they are within range of OMNI link supporting 3144 infrastructure that can inject the MNP into the routing system. 3146 23. Error Messages 3148 An OAL destination or intermediate node may need to return ICMPv6 3149 error messages (e.g., Destination Unreachable, Packet Too Big, Time 3150 Exceeded, etc.) [RFC4443] to an OAL source. Since ICMPv6 error 3151 messages do not themselves include authentication codes, the OAL 3152 includes the ICMPv6 error message as an OMNI sub-option in an IPv6 ND 3153 uNA message. The OAL also includes a HIP message sub-option if the 3154 uNA needs to travel over an open Internetwork. 3156 24. IANA Considerations 3158 The following IANA actions are requested: 3160 24.1. "IPv6 Neighbor Discovery Option Formats" Registry 3162 The IANA is instructed to allocate an official Type number TBD1 from 3163 the registry "IPv6 Neighbor Discovery Option Formats" for the OMNI 3164 option. Implementations set Type to 253 as an interim value 3165 [RFC4727]. 3167 24.2. "Ethernet Numbers" Registry 3169 The IANA is instructed to allocate one Ethernet unicast address TBD2 3170 (suggested value '00-52-14') in the 'ethernet-numbers' registry under 3171 "IANA Unicast 48-bit MAC Addresses" as follows: 3173 Addresses Usage Reference 3174 --------- ----- --------- 3175 00-52-14 Overlay Multilink Network (OMNI) Interface [RFCXXXX] 3177 Figure 26: IANA Unicast 48-bit MAC Addresses 3179 24.3. "ICMPv6 Code Fields: Type 2 - Packet Too Big" Registry 3181 The IANA is instructed to assign two new Code values in the "ICMPv6 3182 Code Fields: Type 2 - Packet Too Big" registry. The registry should 3183 appear as follows: 3185 Code Name Reference 3186 --- ---- --------- 3187 0 PTB Hard Error [RFC4443] 3188 1 PTB Soft Error (loss) [RFCXXXX] 3189 2 PTB Soft Error (no loss) [RFCXXXX] 3191 Figure 27: ICMPv6 Code Fields: Type 2 - Packet Too Big Values 3193 (Note: this registry also to be used to define values for setting the 3194 "unused" field of ICMPv4 "Destination Unreachable - Fragmentation 3195 Needed" messages.) 3197 24.4. "OMNI Option Sub-Type Values" (New Registry) 3199 The OMNI option defines a 5-bit Sub-Type field, for which IANA is 3200 instructed to create and maintain a new registry entitled "OMNI 3201 Option Sub-Type Values". Initial values are given below (future 3202 assignments are to be made through Standards Action [RFC8126]): 3204 Value Sub-Type name Reference 3205 ----- ------------- ---------- 3206 0 Pad1 [RFCXXXX] 3207 1 PadN [RFCXXXX] 3208 2 Interface Attributes (Type 1) [RFCXXXX] 3209 3 Interface Attributes (Type 2) [RFCXXXX] 3210 4 Traffic Selector [RFCXXXX] 3211 5 MS-Register [RFCXXXX] 3212 6 MS-Release [RFCXXXX] 3213 7 Geo Coordinates [RFCXXXX] 3214 8 DHCPv6 Message [RFCXXXX] 3215 9 HIP Message [RFCXXXX] 3216 10 ICMPv6 Error Message [RFCXXXX] 3217 11 Maximum Reassembly Unit (MRU) [RFCXXXX] 3218 12 Node Identification [RFCXXXX] 3219 13-29 Unassigned 3220 30 Sub-Type Extension [RFCXXXX] 3221 31 Reserved by IANA [RFCXXXX] 3223 Figure 28: OMNI Option Sub-Type Values 3225 24.5. "OMNI Node Identification ID-Type Values" (New Registry) 3227 The OMNI Node Identification Sub-Option (see: Section 11.1.13) 3228 contains an 8-bit ID-Type field, for which IANA is instructed to 3229 create and maintain a new registry entitled "OMNI Node Identification 3230 ID-Type Values". Initial values are given below (future assignments 3231 are to be made through Expert Review [RFC8126]): 3233 Value Sub-Type name Reference 3234 ----- ------------- ---------- 3235 0 UUID [RFCXXXX] 3236 1 HIT [RFCXXXX] 3237 2 HHIT [RFCXXXX] 3238 3 Network Access Identifier [RFCXXXX] 3239 4 FQDN [RFCXXXX] 3240 5-252 Unassigned [RFCXXXX] 3241 253-254 Reserved for Experimentation [RFCXXXX] 3242 255 Reserved by IANA [RFCXXXX] 3244 Figure 29: OMNI Node Identification ID-Type Values 3246 24.6. "OMNI Option Sub-Type Extension Values" (New Registry) 3248 The OMNI option defines an 8-bit Extension-Type field for Sub-Type 30 3249 (Sub-Type Extension), for which IANA is instructed to create and 3250 maintain a new registry entitled "OMNI Option Sub-Type Extension 3251 Values". Initial values are given below (future assignments are to 3252 be made through Expert Review [RFC8126]): 3254 Value Sub-Type name Reference 3255 ----- ------------- ---------- 3256 0 RFC4380 UDP/IP Header Option [RFCXXXX] 3257 1 RFC6081 UDP/IP Trailer Option [RFCXXXX] 3258 2-252 Unassigned 3259 253-254 Reserved for Experimentation [RFCXXXX] 3260 255 Reserved by IANA [RFCXXXX] 3262 Figure 30: OMNI Option Sub-Type Extension Values 3264 24.7. "OMNI RFC4380 UDP/IP Header Option" (New Registry) 3266 The OMNI Sub-Type Extension "RFC4380 UDP/IP Header Option" defines an 3267 8-bit Header Type field, for which IANA is instructed to create and 3268 maintain a new registry entitled "OMNI RFC4380 UDP/IP Header Option". 3269 Initial registry values are given below (future assignments are to be 3270 made through Expert Review [RFC8126]): 3272 Value Sub-Type name Reference 3273 ----- ------------- ---------- 3274 0 Origin Indication (IPv4) [RFC4380] 3275 1 Authentication Encapsulation [RFC4380] 3276 2 Origin Indication (IPv6) [RFCXXXX] 3277 3-252 Unassigned 3278 253-254 Reserved for Experimentation [RFCXXXX] 3279 255 Reserved by IANA [RFCXXXX] 3281 Figure 31: OMNI RFC4380 UDP/IP Header Option 3283 24.8. "OMNI RFC6081 UDP/IP Trailer Option" (New Registry) 3285 The OMNI Sub-Type Extension for "RFC6081 UDP/IP Trailer Option" 3286 defines an 8-bit Trailer Type field, for which IANA is instructed to 3287 create and maintain a new registry entitled "OMNI RFC6081 UDP/IP 3288 Trailer Option". Initial registry values are given below (future 3289 assignments are to be made through Expert Review [RFC8126]): 3291 Value Sub-Type name Reference 3292 ----- ------------- ---------- 3293 0 Unassigned 3294 1 Nonce [RFC6081] 3295 2 Unassigned 3296 3 Alternate Address (IPv4) [RFC6081] 3297 4 Neighbor Discovery Option [RFC6081] 3298 5 Random Port [RFC6081] 3299 6 Alternate Address (IPv6) [RFCXXXX] 3300 7-252 Unassigned 3301 253-254 Reserved for Experimentation [RFCXXXX] 3302 255 Reserved by IANA [RFCXXXX] 3304 Figure 32: OMNI RFC6081 Trailer Option 3306 24.9. Additional Considerations 3308 The IANA has assigned the UDP port number "8060" for an earlier 3309 experimental version of AERO [RFC6706]. This document together with 3310 [I-D.templin-intarea-6706bis] reclaims the UDP port number "8060" for 3311 'aero' as the service port for UDP/IP encapsulation. (Note that, 3312 although [RFC6706] was not widely implemented or deployed, any 3313 messages coded to that specification can be easily distinguished and 3314 ignored since they use the invalid ICMPv6 message type number '0'.) 3315 The IANA is therefore instructed to update the reference for UDP port 3316 number "8060" from "RFC6706" to "RFCXXXX" (i.e., this document). 3318 The IANA has assigned a 4 octet Private Enterprise Number (PEN) code 3319 "45282" in the "enterprise-numbers" registry. This document is the 3320 normative reference for using this code in DHCP Unique IDentifiers 3321 based on Enterprise Numbers ("DUID-EN for OMNI Interfaces") (see: 3322 Section 10). The IANA is therefore instructed to change the 3323 enterprise designation for PEN code "45282" from "LinkUp Networks" to 3324 "Overlay Multilink Network Interface (OMNI)". 3326 The IANA has assigned the ifType code "301 - omni - Overlay Multilink 3327 Network Interface (OMNI)" in accordance with Section 6 of [RFC8892]. 3328 The registration appears under the IANA "Structure of Management 3329 Information (SMI) Numbers (MIB Module Registrations) - Interface 3330 Types (ifType)" registry. 3332 No further IANA actions are required. 3334 25. Security Considerations 3336 Security considerations for IPv4 [RFC0791], IPv6 [RFC8200] and IPv6 3337 Neighbor Discovery [RFC4861] apply. OMNI interface IPv6 ND messages 3338 SHOULD include Nonce and Timestamp options [RFC3971] when transaction 3339 confirmation and/or time synchronization is needed. 3341 MN OMNI interfaces configured over secured ANET interfaces inherit 3342 the physical and/or link-layer security properties (i.e., "protected 3343 spectrum") of the connected ANETs. MN OMNI interfaces configured 3344 over open INET interfaces can use symmetric securing services such as 3345 VPNs or can by some other means establish a direct link. When a VPN 3346 or direct link may be impractical, however, the security services 3347 specified in [RFC7401] and/or [RFC4380] can be employed. While the 3348 OMNI link protects control plane messaging, applications must still 3349 employ end-to-end transport- or higher-layer security services to 3350 protect the data plane. 3352 Strong network layer security for control plane messages and 3353 forwarding path integrity for data plane messages between MSEs MUST 3354 be supported. In one example, the AERO service 3355 [I-D.templin-intarea-6706bis] constructs a spanning tree between MSEs 3356 and secures the links in the spanning tree with network layer 3357 security mechanisms such as IPsec [RFC4301] or Wireguard. Control 3358 plane messages are then constrained to travel only over the secured 3359 spanning tree paths and are therefore protected from attack or 3360 eavesdropping. Since data plane messages can travel over route 3361 optimized paths that do not strictly follow the spanning tree, 3362 however, end-to-end transport- or higher-layer security services are 3363 still required. 3365 Identity-based key verification infrastructure services such as iPSK 3366 may be necessary for verifying the identities claimed by MNs. This 3367 requirement should be harmonized with the manner in which (H)HITs are 3368 attested in a given operational environment. 3370 Security considerations for specific access network interface types 3371 are covered under the corresponding IP-over-(foo) specification 3372 (e.g., [RFC2464], [RFC2492], etc.). 3374 Security considerations for IPv6 fragmentation and reassembly are 3375 discussed in Section 5.5. 3377 26. Implementation Status 3379 AERO/OMNI Release-3.0.2 was tagged on October 15, 2020, and is 3380 undergoing internal testing. Additional internal releases expected 3381 within the coming months, with first public release expected end of 3382 1H2021. 3384 27. Acknowledgements 3386 The first version of this document was prepared per the consensus 3387 decision at the 7th Conference of the International Civil Aviation 3388 Organization (ICAO) Working Group-I Mobility Subgroup on March 22, 3389 2019. Consensus to take the document forward to the IETF was reached 3390 at the 9th Conference of the Mobility Subgroup on November 22, 2019. 3391 Attendees and contributors included: Guray Acar, Danny Bharj, 3392 Francois D'Humieres, Pavel Drasil, Nikos Fistas, Giovanni Garofolo, 3393 Bernhard Haindl, Vaughn Maiolla, Tom McParland, Victor Moreno, Madhu 3394 Niraula, Brent Phillips, Liviu Popescu, Jacky Pouzet, Aloke Roy, Greg 3395 Saccone, Robert Segers, Michal Skorepa, Michel Solery, Stephane 3396 Tamalet, Fred Templin, Jean-Marc Vacher, Bela Varkonyi, Tony Whyman, 3397 Fryderyk Wrobel and Dongsong Zeng. 3399 The following individuals are acknowledged for their useful comments: 3400 Stuart Card, Michael Matyas, Robert Moskowitz, Madhu Niraula, Greg 3401 Saccone, Stephane Tamalet, Eric Vyncke. Pavel Drasil, Zdenek Jaron 3402 and Michal Skorepa are especially recognized for their many helpful 3403 ideas and suggestions. Madhuri Madhava Badgandi, Sean Dickson, Don 3404 Dillenburg, Joe Dudkowski, Vijayasarathy Rajagopalan, Ron Sackman and 3405 Katherine Tran are acknowledged for their hard work on the 3406 implementation and technical insights that led to improvements for 3407 the spec. 3409 Discussions on the IETF 6man and atn mailing lists during the fall of 3410 2020 suggested additional points to consider. The authors gratefully 3411 acknowledge the list members who contributed valuable insights 3412 through those discussions. Eric Vyncke and Erik Kline were the 3413 intarea ADs, while Bob Hinden and Ole Troan were the 6man WG chairs 3414 at the time the document was developed; they are all gratefully 3415 acknowledged for their many helpful insights. Many of the ideas in 3416 this document have further built on IETF experiences beginning as 3417 early as Y2K, with insights from colleagues including Brian 3418 Carpenter, Ralph Droms, Christian Huitema, Thomas Narten, Dave 3419 Thaler, Joe Touch, and many others who deserve recognition. 3421 Early observations on IP fragmentation performance implications were 3422 noted in the 1986 Digital Equipment Corporation (DEC) "qe reset" 3423 investigation, where fragment bursts from NFS UDP traffic triggered 3424 hardware resets resulting in communication failures. Jeff Chase, 3425 Fred Glover and Chet Juzsczak of the Ultrix Engineering Group led the 3426 investigation, and determined that setting a smaller NFS mount block 3427 size reduced the amount of fragmentation and suppressed the resets. 3428 Early observations on L2 media MTU issues were noted in the 1988 DEC 3429 FDDI investigation, where Raj Jain, KK Ramakrishnan and Kathy Wilde 3430 represented architectural considerations for FDDI networking in 3431 general including FDDI/Ethernet bridging. Jeff Mogul (who led the 3432 IETF Path MTU Discovery working group) and other DEC colleagues who 3433 supported these early investigations are also acknowledged. 3435 This work is aligned with the NASA Safe Autonomous Systems Operation 3436 (SASO) program under NASA contract number NNA16BD84C. 3438 This work is aligned with the FAA as per the SE2025 contract number 3439 DTFAWA-15-D-00030. 3441 This work is aligned with the Boeing Information Technology (BIT) 3442 Mobility Vision Lab (MVL) program. 3444 28. References 3446 28.1. Normative References 3448 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 3449 DOI 10.17487/RFC0791, September 1981, 3450 . 3452 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 3453 Requirement Levels", BCP 14, RFC 2119, 3454 DOI 10.17487/RFC2119, March 1997, 3455 . 3457 [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, 3458 "Definition of the Differentiated Services Field (DS 3459 Field) in the IPv4 and IPv6 Headers", RFC 2474, 3460 DOI 10.17487/RFC2474, December 1998, 3461 . 3463 [RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander, 3464 "SEcure Neighbor Discovery (SEND)", RFC 3971, 3465 DOI 10.17487/RFC3971, March 2005, 3466 . 3468 [RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and 3469 More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191, 3470 November 2005, . 3472 [RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast 3473 Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005, 3474 . 3476 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 3477 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 3478 2006, . 3480 [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet 3481 Control Message Protocol (ICMPv6) for the Internet 3482 Protocol Version 6 (IPv6) Specification", STD 89, 3483 RFC 4443, DOI 10.17487/RFC4443, March 2006, 3484 . 3486 [RFC4727] Fenner, B., "Experimental Values In IPv4, IPv6, ICMPv4, 3487 ICMPv6, UDP, and TCP Headers", RFC 4727, 3488 DOI 10.17487/RFC4727, November 2006, 3489 . 3491 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 3492 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 3493 DOI 10.17487/RFC4861, September 2007, 3494 . 3496 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 3497 Address Autoconfiguration", RFC 4862, 3498 DOI 10.17487/RFC4862, September 2007, 3499 . 3501 [RFC6088] Tsirtsis, G., Giarreta, G., Soliman, H., and N. Montavont, 3502 "Traffic Selectors for Flow Bindings", RFC 6088, 3503 DOI 10.17487/RFC6088, January 2011, 3504 . 3506 [RFC7401] Moskowitz, R., Ed., Heer, T., Jokela, P., and T. 3507 Henderson, "Host Identity Protocol Version 2 (HIPv2)", 3508 RFC 7401, DOI 10.17487/RFC7401, April 2015, 3509 . 3511 [RFC8028] Baker, F. and B. Carpenter, "First-Hop Router Selection by 3512 Hosts in a Multi-Prefix Network", RFC 8028, 3513 DOI 10.17487/RFC8028, November 2016, 3514 . 3516 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 3517 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 3518 May 2017, . 3520 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 3521 (IPv6) Specification", STD 86, RFC 8200, 3522 DOI 10.17487/RFC8200, July 2017, 3523 . 3525 [RFC8201] McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed., 3526 "Path MTU Discovery for IP version 6", STD 87, RFC 8201, 3527 DOI 10.17487/RFC8201, July 2017, 3528 . 3530 [RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A., 3531 Richardson, M., Jiang, S., Lemon, T., and T. Winters, 3532 "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", 3533 RFC 8415, DOI 10.17487/RFC8415, November 2018, 3534 . 3536 28.2. Informative References 3538 [ATN] Maiolla, V., "The OMNI Interface - An IPv6 Air/Ground 3539 Interface for Civil Aviation, IETF Liaison Statement 3540 #1676, https://datatracker.ietf.org/liaison/1676/", March 3541 2020. 3543 [ATN-IPS] WG-I, ICAO., "ICAO Document 9896 (Manual on the 3544 Aeronautical Telecommunication Network (ATN) using 3545 Internet Protocol Suite (IPS) Standards and Protocol), 3546 Draft Edition 3 (work-in-progress)", December 2020. 3548 [CKSUM] Stone, J., Greenwald, M., Partridge, C., and J. Hughes, 3549 "Performance of Checksums and CRC's Over Real Data, IEEE/ 3550 ACM Transactions on Networking, Vol. 6, No. 5", October 3551 1998. 3553 [CRC] Jain, R., "Error Characteristics of Fiber Distributed Data 3554 Interface (FDDI), IEEE Transactions on Communications", 3555 August 1990. 3557 [I-D.ietf-drip-rid] 3558 Moskowitz, R., Card, S., Wiethuechter, A., and A. Gurtov, 3559 "UAS Remote ID", draft-ietf-drip-rid-06 (work in 3560 progress), December 2020. 3562 [I-D.ietf-intarea-tunnels] 3563 Touch, J. and M. Townsley, "IP Tunnels in the Internet 3564 Architecture", draft-ietf-intarea-tunnels-10 (work in 3565 progress), September 2019. 3567 [I-D.ietf-ipwave-vehicular-networking] 3568 Jeong, J., "IPv6 Wireless Access in Vehicular Environments 3569 (IPWAVE): Problem Statement and Use Cases", draft-ietf- 3570 ipwave-vehicular-networking-19 (work in progress), July 3571 2020. 3573 [I-D.templin-6man-dhcpv6-ndopt] 3574 Templin, F., "A Unified Stateful/Stateless Configuration 3575 Service for IPv6", draft-templin-6man-dhcpv6-ndopt-11 3576 (work in progress), January 2021. 3578 [I-D.templin-6man-lla-type] 3579 Templin, F., "The IPv6 Link-Local Address Type Field", 3580 draft-templin-6man-lla-type-02 (work in progress), 3581 November 2020. 3583 [I-D.templin-intarea-6706bis] 3584 Templin, F., "Asymmetric Extended Route Optimization 3585 (AERO)", draft-templin-intarea-6706bis-87 (work in 3586 progress), January 2021. 3588 [IPV4-GUA] 3589 Postel, J., "IPv4 Address Space Registry, 3590 https://www.iana.org/assignments/ipv4-address-space/ipv4- 3591 address-space.xhtml", December 2020. 3593 [IPV6-GUA] 3594 Postel, J., "IPv6 Global Unicast Address Assignments, 3595 https://www.iana.org/assignments/ipv6-unicast-address- 3596 assignments/ipv6-unicast-address-assignments.xhtml", 3597 December 2020. 3599 [RFC0905] "ISO Transport Protocol specification ISO DP 8073", 3600 RFC 905, DOI 10.17487/RFC0905, April 1984, 3601 . 3603 [RFC1035] Mockapetris, P., "Domain names - implementation and 3604 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, 3605 November 1987, . 3607 [RFC1122] Braden, R., Ed., "Requirements for Internet Hosts - 3608 Communication Layers", STD 3, RFC 1122, 3609 DOI 10.17487/RFC1122, October 1989, 3610 . 3612 [RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191, 3613 DOI 10.17487/RFC1191, November 1990, 3614 . 3616 [RFC1256] Deering, S., Ed., "ICMP Router Discovery Messages", 3617 RFC 1256, DOI 10.17487/RFC1256, September 1991, 3618 . 3620 [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", 3621 RFC 2131, DOI 10.17487/RFC2131, March 1997, 3622 . 3624 [RFC2225] Laubach, M. and J. Halpern, "Classical IP and ARP over 3625 ATM", RFC 2225, DOI 10.17487/RFC2225, April 1998, 3626 . 3628 [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, 3629 DOI 10.17487/RFC2328, April 1998, 3630 . 3632 [RFC2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet 3633 Networks", RFC 2464, DOI 10.17487/RFC2464, December 1998, 3634 . 3636 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 3637 IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473, 3638 December 1998, . 3640 [RFC2492] Armitage, G., Schulter, P., and M. Jork, "IPv6 over ATM 3641 Networks", RFC 2492, DOI 10.17487/RFC2492, January 1999, 3642 . 3644 [RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4 3645 Domains without Explicit Tunnels", RFC 2529, 3646 DOI 10.17487/RFC2529, March 1999, 3647 . 3649 [RFC2863] McCloghrie, K. and F. Kastenholz, "The Interfaces Group 3650 MIB", RFC 2863, DOI 10.17487/RFC2863, June 2000, 3651 . 3653 [RFC3330] IANA, "Special-Use IPv4 Addresses", RFC 3330, 3654 DOI 10.17487/RFC3330, September 2002, 3655 . 3657 [RFC3692] Narten, T., "Assigning Experimental and Testing Numbers 3658 Considered Useful", BCP 82, RFC 3692, 3659 DOI 10.17487/RFC3692, January 2004, 3660 . 3662 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 3663 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 3664 DOI 10.17487/RFC3810, June 2004, 3665 . 3667 [RFC3819] Karn, P., Ed., Bormann, C., Fairhurst, G., Grossman, D., 3668 Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L. 3669 Wood, "Advice for Internet Subnetwork Designers", BCP 89, 3670 RFC 3819, DOI 10.17487/RFC3819, July 2004, 3671 . 3673 [RFC3879] Huitema, C. and B. Carpenter, "Deprecating Site Local 3674 Addresses", RFC 3879, DOI 10.17487/RFC3879, September 3675 2004, . 3677 [RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally 3678 Unique IDentifier (UUID) URN Namespace", RFC 4122, 3679 DOI 10.17487/RFC4122, July 2005, 3680 . 3682 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 3683 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 3684 DOI 10.17487/RFC4271, January 2006, 3685 . 3687 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 3688 Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, 3689 December 2005, . 3691 [RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through 3692 Network Address Translations (NATs)", RFC 4380, 3693 DOI 10.17487/RFC4380, February 2006, 3694 . 3696 [RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery 3697 Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April 3698 2006, . 3700 [RFC4429] Moore, N., "Optimistic Duplicate Address Detection (DAD) 3701 for IPv6", RFC 4429, DOI 10.17487/RFC4429, April 2006, 3702 . 3704 [RFC4541] Christensen, M., Kimball, K., and F. Solensky, 3705 "Considerations for Internet Group Management Protocol 3706 (IGMP) and Multicast Listener Discovery (MLD) Snooping 3707 Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006, 3708 . 3710 [RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick, 3711 "Internet Group Management Protocol (IGMP) / Multicast 3712 Listener Discovery (MLD)-Based Multicast Forwarding 3713 ("IGMP/MLD Proxying")", RFC 4605, DOI 10.17487/RFC4605, 3714 August 2006, . 3716 [RFC4821] Mathis, M. and J. Heffner, "Packetization Layer Path MTU 3717 Discovery", RFC 4821, DOI 10.17487/RFC4821, March 2007, 3718 . 3720 [RFC4963] Heffner, J., Mathis, M., and B. Chandler, "IPv4 Reassembly 3721 Errors at High Data Rates", RFC 4963, 3722 DOI 10.17487/RFC4963, July 2007, 3723 . 3725 [RFC5175] Haberman, B., Ed. and R. Hinden, "IPv6 Router 3726 Advertisement Flags Option", RFC 5175, 3727 DOI 10.17487/RFC5175, March 2008, 3728 . 3730 [RFC5213] Gundavelli, S., Ed., Leung, K., Devarapalli, V., 3731 Chowdhury, K., and B. Patil, "Proxy Mobile IPv6", 3732 RFC 5213, DOI 10.17487/RFC5213, August 2008, 3733 . 3735 [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site 3736 Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, 3737 DOI 10.17487/RFC5214, March 2008, 3738 . 3740 [RFC5558] Templin, F., Ed., "Virtual Enterprise Traversal (VET)", 3741 RFC 5558, DOI 10.17487/RFC5558, February 2010, 3742 . 3744 [RFC5798] Nadas, S., Ed., "Virtual Router Redundancy Protocol (VRRP) 3745 Version 3 for IPv4 and IPv6", RFC 5798, 3746 DOI 10.17487/RFC5798, March 2010, 3747 . 3749 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 3750 (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, 3751 . 3753 [RFC6081] Thaler, D., "Teredo Extensions", RFC 6081, 3754 DOI 10.17487/RFC6081, January 2011, 3755 . 3757 [RFC6221] Miles, D., Ed., Ooghe, S., Dec, W., Krishnan, S., and A. 3758 Kavanagh, "Lightweight DHCPv6 Relay Agent", RFC 6221, 3759 DOI 10.17487/RFC6221, May 2011, 3760 . 3762 [RFC6355] Narten, T. and J. Johnson, "Definition of the UUID-Based 3763 DHCPv6 Unique Identifier (DUID-UUID)", RFC 6355, 3764 DOI 10.17487/RFC6355, August 2011, 3765 . 3767 [RFC6543] Gundavelli, S., "Reserved IPv6 Interface Identifier for 3768 Proxy Mobile IPv6", RFC 6543, DOI 10.17487/RFC6543, May 3769 2012, . 3771 [RFC6706] Templin, F., Ed., "Asymmetric Extended Route Optimization 3772 (AERO)", RFC 6706, DOI 10.17487/RFC6706, August 2012, 3773 . 3775 [RFC6935] Eubanks, M., Chimento, P., and M. Westerlund, "IPv6 and 3776 UDP Checksums for Tunneled Packets", RFC 6935, 3777 DOI 10.17487/RFC6935, April 2013, 3778 . 3780 [RFC6936] Fairhurst, G. and M. Westerlund, "Applicability Statement 3781 for the Use of IPv6 UDP Datagrams with Zero Checksums", 3782 RFC 6936, DOI 10.17487/RFC6936, April 2013, 3783 . 3785 [RFC6980] Gont, F., "Security Implications of IPv6 Fragmentation 3786 with IPv6 Neighbor Discovery", RFC 6980, 3787 DOI 10.17487/RFC6980, August 2013, 3788 . 3790 [RFC7084] Singh, H., Beebee, W., Donley, C., and B. Stark, "Basic 3791 Requirements for IPv6 Customer Edge Routers", RFC 7084, 3792 DOI 10.17487/RFC7084, November 2013, 3793 . 3795 [RFC7421] Carpenter, B., Ed., Chown, T., Gont, F., Jiang, S., 3796 Petrescu, A., and A. Yourtchenko, "Analysis of the 64-bit 3797 Boundary in IPv6 Addressing", RFC 7421, 3798 DOI 10.17487/RFC7421, January 2015, 3799 . 3801 [RFC7526] Troan, O. and B. Carpenter, Ed., "Deprecating the Anycast 3802 Prefix for 6to4 Relay Routers", BCP 196, RFC 7526, 3803 DOI 10.17487/RFC7526, May 2015, 3804 . 3806 [RFC7542] DeKok, A., "The Network Access Identifier", RFC 7542, 3807 DOI 10.17487/RFC7542, May 2015, 3808 . 3810 [RFC7739] Gont, F., "Security Implications of Predictable Fragment 3811 Identification Values", RFC 7739, DOI 10.17487/RFC7739, 3812 February 2016, . 3814 [RFC7847] Melia, T., Ed. and S. Gundavelli, Ed., "Logical-Interface 3815 Support for IP Hosts with Multi-Access Support", RFC 7847, 3816 DOI 10.17487/RFC7847, May 2016, 3817 . 3819 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 3820 Writing an IANA Considerations Section in RFCs", BCP 26, 3821 RFC 8126, DOI 10.17487/RFC8126, June 2017, 3822 . 3824 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 3825 Decraene, B., Litkowski, S., and R. Shakir, "Segment 3826 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 3827 July 2018, . 3829 [RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J., 3830 Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header 3831 (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020, 3832 . 3834 [RFC8892] Thaler, D. and D. Romascanu, "Guidelines and Registration 3835 Procedures for Interface Types and Tunnel Types", 3836 RFC 8892, DOI 10.17487/RFC8892, August 2020, 3837 . 3839 [RFC8899] Fairhurst, G., Jones, T., Tuexen, M., Ruengeler, I., and 3840 T. Voelker, "Packetization Layer Path MTU Discovery for 3841 Datagram Transports", RFC 8899, DOI 10.17487/RFC8899, 3842 September 2020, . 3844 [RFC8900] Bonica, R., Baker, F., Huston, G., Hinden, R., Troan, O., 3845 and F. Gont, "IP Fragmentation Considered Fragile", 3846 BCP 230, RFC 8900, DOI 10.17487/RFC8900, September 2020, 3847 . 3849 [RFC8981] Gont, F., Krishnan, S., Narten, T., and R. Draves, 3850 "Temporary Address Extensions for Stateless Address 3851 Autoconfiguration in IPv6", RFC 8981, 3852 DOI 10.17487/RFC8981, February 2021, 3853 . 3855 Appendix A. Interface Attribute Preferences Bitmap Encoding 3857 Adaptation of the OMNI option Interface Attributes Preferences Bitmap 3858 encoding to specific Internetworks such as the Aeronautical 3859 Telecommunications Network with Internet Protocol Services (ATN/IPS) 3860 may include link selection preferences based on other traffic 3861 classifiers (e.g., transport port numbers, etc.) in addition to the 3862 existing DSCP-based preferences. Nodes on specific Internetworks 3863 maintain a map of traffic classifiers to additional P[*] preference 3864 fields beyond the first 64. For example, TCP port 22 maps to P[67], 3865 TCP port 443 maps to P[70], UDP port 8060 maps to P[76], etc. 3867 Implementations use Simplex or Indexed encoding formats for P[*] 3868 encoding in order to encode a given set of traffic classifiers in the 3869 most efficient way. Some use cases may be more efficiently coded 3870 using Simplex form, while others may be more efficient using Indexed. 3871 Once a format is selected for preparation of a single Interface 3872 Attribute the same format must be used for the entire Interface 3873 Attribute sub-option. Different sub-options may use different 3874 formats. 3876 The following figures show coding examples for various Simplex and 3877 Indexed formats: 3879 0 1 2 3 3880 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 3881 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3882 | Sub-Type=3| Sub-length=N | omIndex | omType | 3883 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3884 | Provider ID | Link |R| API | Bitmap(0)=0xff|P00|P01|P02|P03| 3885 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3886 |P04|P05|P06|P07|P08|P09|P10|P11|P12|P13|P14|P15|P16|P17|P18|P19| 3887 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3888 |P20|P21|P22|P23|P24|P25|P26|P27|P28|P29|P30|P31| Bitmap(1)=0xff| 3889 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3890 |P32|P33|P34|P35|P36|P37|P38|P39|P40|P41|P42|P43|P44|P45|P46|P47| 3891 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3892 |P48|P49|P50|P51|P52|P53|P54|P55|P56|P57|P58|P59|P60|P61|P62|P63| 3893 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3894 | Bitmap(2)=0xff|P64|P65|P67|P68| ... 3895 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 3897 Figure 33: Example 1: Dense Simplex Encoding 3899 0 1 2 3 3900 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 3901 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3902 | Sub-Type=3| Sub-length=N | omIndex | omType | 3903 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3904 | Provider ID | Link |R| API | Bitmap(0)=0x00| Bitmap(1)=0x0f| 3905 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3906 |P48|P49|P50|P51|P52|P53|P54|P55|P56|P57|P58|P59|P60|P61|P62|P63| 3907 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3908 | Bitmap(2)=0x00| Bitmap(3)=0x00| Bitmap(4)=0x00| Bitmap(5)=0x00| 3909 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3910 | Bitmap(6)=0xf0|192|193|194|195|196|197|198|199|200|201|202|203| 3911 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3912 |204|205|206|207| Bitmap(7)=0x00| Bitmap(8)=0x0f|272|273|274|275| 3913 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3914 |276|277|278|279|280|281|282|283|284|285|286|287| Bitmap(9)=0x00| 3915 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3916 |Bitmap(10)=0x00| ... 3917 +-+-+-+-+-+-+-+-+-+-+- 3919 Figure 34: Example 2: Sparse Simplex Encoding 3921 0 1 2 3 3922 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 3923 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3924 | Sub-Type=3| Sub-length=N | omIndex | omType | 3925 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3926 | Provider ID | Link |R| API | Index = 0x00 | Bitmap = 0x80 | 3927 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3928 |P00|P01|P02|P03| Index = 0x01 | Bitmap = 0x01 |P60|P61|P62|P63| 3929 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3930 | Index = 0x10 | Bitmap = 0x80 |512|513|514|515| Index = 0x18 | 3931 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3932 | Bitmap = 0x01 |796|797|798|799| ... 3933 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 3935 Figure 35: Example 3: Indexed Encoding 3937 Appendix B. VDL Mode 2 Considerations 3939 ICAO Doc 9776 is the "Technical Manual for VHF Data Link Mode 2" 3940 (VDLM2) that specifies an essential radio frequency data link service 3941 for aircraft and ground stations in worldwide civil aviation air 3942 traffic management. The VDLM2 link type is "multicast capable" 3943 [RFC4861], but with considerable differences from common multicast 3944 links such as Ethernet and IEEE 802.11. 3946 First, the VDLM2 link data rate is only 31.5Kbps - multiple orders of 3947 magnitude less than most modern wireless networking gear. Second, 3948 due to the low available link bandwidth only VDLM2 ground stations 3949 (i.e., and not aircraft) are permitted to send broadcasts, and even 3950 so only as compact layer 2 "beacons". Third, aircraft employ the 3951 services of ground stations by performing unicast RS/RA exchanges 3952 upon receipt of beacons instead of listening for multicast RA 3953 messages and/or sending multicast RS messages. 3955 This beacon-oriented unicast RS/RA approach is necessary to conserve 3956 the already-scarce available link bandwidth. Moreover, since the 3957 numbers of beaconing ground stations operating within a given spatial 3958 range must be kept as sparse as possible, it would not be feasible to 3959 have different classes of ground stations within the same region 3960 observing different protocols. It is therefore highly desirable that 3961 all ground stations observe a common language of RS/RA as specified 3962 in this document. 3964 Note that links of this nature may benefit from compression 3965 techniques that reduce the bandwidth necessary for conveying the same 3966 amount of data. The IETF lpwan working group is considering possible 3967 alternatives: [https://datatracker.ietf.org/wg/lpwan/documents]. 3969 Appendix C. MN / AR Isolation Through L2 Address Mapping 3971 Per [RFC4861], IPv6 ND messages may be sent to either a multicast or 3972 unicast link-scoped IPv6 destination address. However, IPv6 ND 3973 messaging should be coordinated between the MN and AR only without 3974 invoking other nodes on the *NET. This implies that MN / AR control 3975 messaging should be isolated and not overheard by other nodes on the 3976 link. 3978 To support MN / AR isolation on some *NET links, ARs can maintain an 3979 OMNI-specific unicast L2 address ("MSADDR"). For Ethernet-compatible 3980 *NETs, this specification reserves one Ethernet unicast address TBD2 3981 (see: Section 24). For non-Ethernet statically-addressed *NETs, 3982 MSADDR is reserved per the assigned numbers authority for the *NET 3983 addressing space. For still other *NETs, MSADDR may be dynamically 3984 discovered through other means, e.g., L2 beacons. 3986 MNs map the L3 addresses of all IPv6 ND messages they send (i.e., 3987 both multicast and unicast) to MSADDR instead of to an ordinary 3988 unicast or multicast L2 address. In this way, all of the MN's IPv6 3989 ND messages will be received by ARs that are configured to accept 3990 packets destined to MSADDR. Note that multiple ARs on the link could 3991 be configured to accept packets destined to MSADDR, e.g., as a basis 3992 for supporting redundancy. 3994 Therefore, ARs must accept and process packets destined to MSADDR, 3995 while all other devices must not process packets destined to MSADDR. 3996 This model has well-established operational experience in Proxy 3997 Mobile IPv6 (PMIP) [RFC5213][RFC6543]. 3999 Appendix D. Change Log 4001 << RFC Editor - remove prior to publication >> 4003 Differences from draft-templin-6man-omni-interface-35 to draft- 4004 templin-6man-omni-interface-36: 4006 o Major clarifications on aspects such as "hard/soft" PTB error 4007 messages 4009 o Made generic so that either IP protocol version (IPv4 or IPv6) can 4010 be used in the data plane. 4012 Differences from draft-templin-6man-omni-interface-31 to draft- 4013 templin-6man-omni-interface-32: 4015 o MTU 4016 o Support for multi-hop ANETS such as ISATAP. 4018 Differences from draft-templin-6man-omni-interface-29 to draft- 4019 templin-6man-omni-interface-30: 4021 o Moved link-layer addressing information into the OMNI option on a 4022 per-ifIndex basis 4024 o Renamed "ifIndex-tuple" to "Interface Attributes" 4026 Differences from draft-templin-6man-omni-interface-27 to draft- 4027 templin-6man-omni-interface-28: 4029 o Updates based on implementation experience. 4031 Differences from draft-templin-6man-omni-interface-25 to draft- 4032 templin-6man-omni-interface-26: 4034 o Further clarification on "aggregate" RA messages. 4036 o Expanded Security Considerations to discuss expectations for 4037 security in the Mobility Service. 4039 Differences from draft-templin-6man-omni-interface-20 to draft- 4040 templin-6man-omni-interface-21: 4042 o Safety-Based Multilink (SBM) and Performance-Based Multilink 4043 (PBM). 4045 Differences from draft-templin-6man-omni-interface-18 to draft- 4046 templin-6man-omni-interface-19: 4048 o SEND/CGA. 4050 Differences from draft-templin-6man-omni-interface-17 to draft- 4051 templin-6man-omni-interface-18: 4053 o Teredo 4055 Differences from draft-templin-6man-omni-interface-14 to draft- 4056 templin-6man-omni-interface-15: 4058 o Prefix length discussions removed. 4060 Differences from draft-templin-6man-omni-interface-12 to draft- 4061 templin-6man-omni-interface-13: 4063 o Teredo 4064 Differences from draft-templin-6man-omni-interface-11 to draft- 4065 templin-6man-omni-interface-12: 4067 o Major simplifications and clarifications on MTU and fragmentation. 4069 o Document now updates RFC4443 and RFC8201. 4071 Differences from draft-templin-6man-omni-interface-10 to draft- 4072 templin-6man-omni-interface-11: 4074 o Removed /64 assumption, resulting in new OMNI address format. 4076 Differences from draft-templin-6man-omni-interface-07 to draft- 4077 templin-6man-omni-interface-08: 4079 o OMNI MNs in the open Internet 4081 Differences from draft-templin-6man-omni-interface-06 to draft- 4082 templin-6man-omni-interface-07: 4084 o Brought back L2 MSADDR mapping text for MN / AR isolation based on 4085 L2 addressing. 4087 o Expanded "Transition Considerations". 4089 Differences from draft-templin-6man-omni-interface-05 to draft- 4090 templin-6man-omni-interface-06: 4092 o Brought back OMNI option "R" flag, and discussed its use. 4094 Differences from draft-templin-6man-omni-interface-04 to draft- 4095 templin-6man-omni-interface-05: 4097 o Transition considerations, and overhaul of RS/RA addressing with 4098 the inclusion of MSE addresses within the OMNI option instead of 4099 as RS/RA addresses (developed under FAA SE2025 contract number 4100 DTFAWA-15-D-00030). 4102 Differences from draft-templin-6man-omni-interface-02 to draft- 4103 templin-6man-omni-interface-03: 4105 o Added "advisory PTB messages" under FAA SE2025 contract number 4106 DTFAWA-15-D-00030. 4108 Differences from draft-templin-6man-omni-interface-01 to draft- 4109 templin-6man-omni-interface-02: 4111 o Removed "Primary" flag and supporting text. 4113 o Clarified that "Router Lifetime" applies to each ANET interface 4114 independently, and that the union of all ANET interface Router 4115 Lifetimes determines MSE lifetime. 4117 Differences from draft-templin-6man-omni-interface-00 to draft- 4118 templin-6man-omni-interface-01: 4120 o "All-MSEs" OMNI LLA defined. Also reserved fe80::ff00:0000/104 4121 for future use (most likely as "pseudo-multicast"). 4123 o Non-normative discussion of alternate OMNI LLA construction form 4124 made possible if the 64-bit assumption were relaxed. 4126 First draft version (draft-templin-atn-aero-interface-00): 4128 o Draft based on consensus decision of ICAO Working Group I Mobility 4129 Subgroup March 22, 2019. 4131 Authors' Addresses 4133 Fred L. Templin (editor) 4134 The Boeing Company 4135 P.O. Box 3707 4136 Seattle, WA 98124 4137 USA 4139 Email: fltemplin@acm.org 4141 Tony Whyman 4142 MWA Ltd c/o Inmarsat Global Ltd 4143 99 City Road 4144 London EC1Y 1AX 4145 England 4147 Email: tony.whyman@mccallumwhyman.com