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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group F. Templin, Ed. 3 Internet-Draft The Boeing Company 4 Updates: rfc1191, rfc4443, rfc8201 (if A. Whyman 5 approved) MWA Ltd c/o Inmarsat Global Ltd 6 Intended status: Standards Track October 22, 2020 7 Expires: April 25, 2021 9 Transmission of IP Packets over Overlay Multilink Network (OMNI) 10 Interfaces 11 draft-templin-6man-omni-interface-50 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 April 25, 2021. 41 Copyright Notice 43 Copyright (c) 2020 IETF Trust and the persons identified as the 44 document authors. All rights reserved. 46 This document is subject to BCP 78 and the IETF Trust's Legal 47 Provisions Relating to IETF Documents 48 (https://trustee.ietf.org/license-info) in effect on the date of 49 publication of this document. Please review these documents 50 carefully, as they describe your rights and restrictions with respect 51 to this document. Code Components extracted from this document must 52 include Simplified BSD License text as described in Section 4.e of 53 the Trust Legal Provisions and are provided without warranty as 54 described in the Simplified BSD License. 56 Table of Contents 58 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 59 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 60 3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 8 61 4. Overlay Multilink Network (OMNI) Interface Model . . . . . . 8 62 5. The OMNI Adaptation Layer (OAL) . . . . . . . . . . . . . . . 13 63 5.1. Fragmentation Security Implications . . . . . . . . . . . 17 64 6. Frame Format . . . . . . . . . . . . . . . . . . . . . . . . 18 65 7. Link-Local Addresses (LLAs) . . . . . . . . . . . . . . . . . 18 66 8. Domain-Local Addresses (DLAs) . . . . . . . . . . . . . . . . 20 67 9. Address Mapping - Unicast . . . . . . . . . . . . . . . . . . 21 68 9.1. Sub-Options . . . . . . . . . . . . . . . . . . . . . . . 23 69 9.1.1. Pad1 . . . . . . . . . . . . . . . . . . . . . . . . 24 70 9.1.2. PadN . . . . . . . . . . . . . . . . . . . . . . . . 24 71 9.1.3. Interface Attributes . . . . . . . . . . . . . . . . 24 72 9.1.4. Traffic Selector . . . . . . . . . . . . . . . . . . 28 73 9.1.5. MS-Register . . . . . . . . . . . . . . . . . . . . . 29 74 9.1.6. MS-Release . . . . . . . . . . . . . . . . . . . . . 29 75 9.1.7. Network Access Identifier (NAI) . . . . . . . . . . . 30 76 9.1.8. Geo Coordinates . . . . . . . . . . . . . . . . . . . 31 77 9.1.9. DHCP Unique Identifier (DUID) . . . . . . . . . . . . 31 78 10. Address Mapping - Multicast . . . . . . . . . . . . . . . . . 32 79 11. Multilink Conceptual Sending Algorithm . . . . . . . . . . . 32 80 11.1. Multiple OMNI Interfaces . . . . . . . . . . . . . . . . 33 81 11.2. MN<->AR Traffic Loop Prevention . . . . . . . . . . . . 33 82 12. Router Discovery and Prefix Registration . . . . . . . . . . 34 83 12.1. Router Discovery in IP Multihop and IPv4-Only Access 84 Networks . . . . . . . . . . . . . . . . . . . . . . . . 37 85 12.2. MS-Register and MS-Release List Processing . . . . . . . 39 86 12.3. DHCPv6-based Prefix Registration . . . . . . . . . . . . 41 87 13. Secure Redirection . . . . . . . . . . . . . . . . . . . . . 41 88 14. AR and MSE Resilience . . . . . . . . . . . . . . . . . . . . 42 89 15. Detecting and Responding to MSE Failures . . . . . . . . . . 42 90 16. Transition Considerations . . . . . . . . . . . . . . . . . . 43 91 17. OMNI Interfaces on the Open Internet . . . . . . . . . . . . 43 92 18. Time-Varying MNPs . . . . . . . . . . . . . . . . . . . . . . 44 93 19. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 45 94 20. Security Considerations . . . . . . . . . . . . . . . . . . . 46 95 21. Implementation Status . . . . . . . . . . . . . . . . . . . . 47 96 22. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 47 97 23. References . . . . . . . . . . . . . . . . . . . . . . . . . 48 98 23.1. Normative References . . . . . . . . . . . . . . . . . . 48 99 23.2. Informative References . . . . . . . . . . . . . . . . . 50 100 Appendix A. Interface Attribute Preferences Bitmap Encoding . . 55 101 Appendix B. VDL Mode 2 Considerations . . . . . . . . . . . . . 56 102 Appendix C. MN / AR Isolation Through L2 Address Mapping . . . . 57 103 Appendix D. Change Log . . . . . . . . . . . . . . . . . . . . . 58 104 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 60 106 1. Introduction 108 Mobile Nodes (MNs) (e.g., aircraft of various configurations, 109 terrestrial vehicles, seagoing vessels, enterprise wireless devices, 110 etc.) often have multiple data links for communicating with networked 111 correspondents. These data links may have diverse performance, cost 112 and availability properties that can change dynamically according to 113 mobility patterns, flight phases, proximity to infrastructure, etc. 114 MNs coordinate their data links in a discipline known as "multilink", 115 in which a single virtual interface is configured over the underlying 116 data links. 118 The MN configures a virtual interface (termed the "Overlay Multilink 119 Network (OMNI) interface") as a thin layer over the underlying Access 120 Network (ANET) interfaces. The OMNI interface is therefore the only 121 interface abstraction exposed to the IP layer and behaves according 122 to the Non-Broadcast, Multiple Access (NBMA) interface principle, 123 while underlying interfaces appear as link layer communication 124 channels in the architecture. The OMNI interface connects to a 125 virtual overlay service known as the "OMNI link". The OMNI link 126 spans one or more Internetworks that may include private-use 127 infrastructures and/or the global public Internet itself. 129 Each MN receives a Mobile Network Prefix (MNP) for numbering 130 downstream-attached End User Networks (EUNs) independently of the 131 access network data links selected for data transport. The MN 132 performs router discovery over the OMNI interface (i.e., similar to 133 IPv6 customer edge routers [RFC7084]) and acts as a mobile router on 134 behalf of its EUNs. The router discovery process is iterated over 135 each of the OMNI interface's underlying interfaces in order to 136 register per-link parameters (see Section 12). 138 The OMNI interface provides a multilink nexus for exchanging inbound 139 and outbound traffic via the correct underlying interface(s). The IP 140 layer sees the OMNI interface as a point of connection to the OMNI 141 link. Each OMNI link has one or more associated Mobility Service 142 Prefixes (MSPs) from which OMNI link MNPs are derived. If there are 143 multiple OMNI links, the IPv6 layer will see multiple OMNI 144 interfaces. 146 MNs may connect to multiple distinct OMNI links by configuring 147 multiple OMNI interfaces, e.g., omni0, omni1, omni2, etc. Each OMNI 148 interface is configured over a set of underlying interfaces and 149 provides a nexus for Safety-Based Multilink (SBM) operation. The IP 150 layer selects an OMNI interface based on SBM routing considerations, 151 then the selected interface applies Performance-Based Multilink (PBM) 152 to select the correct underlying interface. Applications can apply 153 Segment Routing [RFC8402] to select independent SBM topologies for 154 fault tolerance. 156 The OMNI interface interacts with a network-based Mobility Service 157 (MS) through IPv6 Neighbor Discovery (ND) control message exchanges 158 [RFC4861]. The MS provides Mobility Service Endpoints (MSEs) that 159 track MN movements and represent their MNPs in a global routing or 160 mapping system. 162 Many OMNI use cases are currenty under active consideration. In 163 particular, the International Civil Aviation Organization (ICAO) 164 Working Group-I Mobility Subgroup is developing a future Aeronautical 165 Telecommunications Network with Internet Protocol Services (ATN/IPS) 166 and has issued a liaison statement requesting IETF adoption [ATN]. 167 The IETF IP Wireless Access in Vehicular Environments (ipwave) 168 working group has further included problem statement and use case 169 analysis for OMNI in a document now in AD evaluation for RFC 170 publication [I-D.ietf-ipwave-vehicular-networking]. Still other 171 communities of interest include AEEC, RTCA Special Committee 228 (SC- 172 228) and NASA programs that examine commercial aviation, Urban Air 173 Mobility (UAM) and Unmanned Air Systems (UAS). Pedestrians with 174 handheld devices represent another large class of potential OMNI 175 users. 177 This document specifies the transmission of IP packets and MN/MS 178 control messages over OMNI interfaces. The OMNI interface supports 179 either IP protocol version (i.e., IPv4 [RFC0791] or IPv6 [RFC8200]) 180 as the network layer in the data plane, while using IPv6 ND messaging 181 as the control plane independently of the data plane IP protocol(s). 182 The OMNI Adaptation Layer (OAL) which operates as a mid-layer between 183 L3 and L2 is based on IP-in-IPv6 encapsulation per [RFC2473] as 184 discussed in the following sections. 186 2. Terminology 188 The terminology in the normative references applies; especially, the 189 terms "link" and "interface" are the same as defined in the IPv6 190 [RFC8200] and IPv6 Neighbor Discovery (ND) [RFC4861] specifications. 191 Additionally, this document assumes the following IPv6 ND message 192 types: Router Solicitation (RS), Router Advertisement (RA), Neighbor 193 Solicitation (NS), Neighbor Advertisement (NA) and Redirect. 195 The Protocol Constants defined in Section 10 of [RFC4861] are used in 196 their same format and meaning in this document. The terms "All- 197 Routers multicast", "All-Nodes multicast" and "Subnet-Router anycast" 198 are the same as defined in [RFC4291] (with Link-Local scope assumed). 200 The term "IP" is used to refer collectively to either Internet 201 Protocol version (i.e., IPv4 [RFC0791] or IPv6 [RFC8200]) when a 202 specification at the layer in question applies equally to either 203 version. 205 The following terms are defined within the scope of this document: 207 Mobile Node (MN) 208 an end system with a mobile router having multiple distinct 209 upstream data link connections that are grouped together in one or 210 more logical units. The MN's data link connection parameters can 211 change over time due to, e.g., node mobility, link quality, etc. 212 The MN further connects a downstream-attached End User Network 213 (EUN). The term MN used here is distinct from uses in other 214 documents, and does not imply a particular mobility protocol. 216 End User Network (EUN) 217 a simple or complex downstream-attached mobile network that 218 travels with the MN as a single logical unit. The IP addresses 219 assigned to EUN devices remain stable even if the MN's upstream 220 data link connections change. 222 Mobility Service (MS) 223 a mobile routing service that tracks MN movements and ensures that 224 MNs remain continuously reachable even across mobility events. 225 Specific MS details are out of scope for this document. 227 Mobility Service Endpoint (MSE) 228 an entity in the MS (either singular or aggregate) that 229 coordinates the mobility events of one or more MN. 231 Mobility Service Prefix (MSP) 232 an aggregated IP prefix (e.g., 2001:db8::/32, 192.0.2.0/24, etc.) 233 advertised to the rest of the Internetwork by the MS, and from 234 which more-specific Mobile Network Prefixes (MNPs) are derived. 236 Mobile Network Prefix (MNP) 237 a longer IP prefix taken from an MSP (e.g., 238 2001:db8:1000:2000::/56, 192.0.2.8/30, etc.) and assigned to a MN. 239 MNs sub-delegate the MNP to devices located in EUNs. 241 Access Network (ANET) 242 a data link service network (e.g., an aviation radio access 243 network, satellite service provider network, cellular operator 244 network, wifi network, etc.) that connects MNs. Physical and/or 245 data link level security between the MN and ANET are assumed. 247 Access Router (AR) 248 a first-hop router in the ANET for connecting MNs to 249 correspondents in outside Internetworks. 251 ANET interface 252 a MN's attachment to a link in an ANET. 254 Internetwork (INET) 255 a connected network region with a coherent IP addressing plan that 256 provides transit forwarding services for ANET MNs and INET 257 correspondents. Examples include private enterprise networks, 258 ground domain aviation service networks and the global public 259 Internet itself. 261 INET interface 262 a node's attachment to a link in an INET. 264 OMNI link 265 a Non-Broadcast, Multiple Access (NBMA) virtual overlay configured 266 over one or more INETs and their connected ANETs. An OMNI link 267 can comprise multiple INET segments joined by bridges the same as 268 for any link; the addressing plans in each segment may be mutually 269 exclusive and managed by different administrative entities. 271 OMNI domain 272 a set of affiliated OMNI links that collectively provide services 273 under a common (set of) Mobility Service Prefixes (MSPs). 275 OMNI interface 276 a node's attachment to an OMNI link, and configured over one or 277 more underlying ANET/INET interfaces. If there are multiple OMNI 278 links in an OMNI domain, a separate OMNI interface is configured 279 for each link. 281 OMNI Adaptation Layer (OAL) 282 an OMNI interface process whereby packets admitted into the 283 interface are wrapped in a mid-layer IPv6 header and fragmented/ 284 reassembled if necessary to support the OMNI link Maximum 285 Transmission Unit (MTU). The OAL is also responsible for 286 generating MTU-related control messages as necessary, and for 287 providing addressing context for spanning multiple segments of a 288 bridged OMNI link. 290 OMNI Link-Local Address (LLA) 291 a link local IPv6 address per [RFC4291] constructed as specified 292 in Section 7. 294 OMNI Domain-Local Address (DLA) 295 an IPv6 address from the prefix [DLA]::/10 constructed as 296 specified in Section 8. OMNI DLAs are statelessly derived from 297 OMNI LLAs, and vice-versa. 299 OMNI Option 300 an IPv6 Neighbor Discovery option providing multilink parameters 301 for the OMNI interface as specified in Section 9. 303 Multilink 304 an OMNI interface's manner of managing diverse underlying data 305 link interfaces as a single logical unit. The OMNI interface 306 provides a single unified interface to upper layers, while 307 underlying data link selections are performed on a per-packet 308 basis considering factors such as DSCP, flow label, application 309 policy, signal quality, cost, etc. Multilinking decisions are 310 coordinated in both the outbound (i.e. MN to correspondent) and 311 inbound (i.e., correspondent to MN) directions. 313 L2 314 The second layer in the OSI network model. Also known as "layer- 315 2", "link-layer", "sub-IP layer", "data link layer", etc. 317 L3 318 The third layer in the OSI network model. Also known as "layer- 319 3", "network-layer", "IP layer", etc. 321 underlying interface 322 an ANET/INET interface over which an OMNI interface is configured. 323 The OMNI interface is seen as a L3 interface by the IP layer, and 324 each underlying interface is seen as a L2 interface by the OMNI 325 interface. 327 Mobility Service Identification (MSID) 328 Each MSE and AR is assigned a unique 32-bit Identification (MSID) 329 as specified in Section 7. 331 Safety-Based Multilink (SBM) 332 A means for ensuring fault tolerance through redundancy by 333 connecting multiple independent OMNI interfaces to independent 334 routing topologies (i.e., multiple independent OMNI links). 336 Performance Based Multilink (PBM) 337 A means for selecting underlying interface(s) for packet 338 transmission and reception within a single OMNI interface. 340 3. Requirements 342 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 343 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 344 "OPTIONAL" in this document are to be interpreted as described in BCP 345 14 [RFC2119][RFC8174] when, and only when, they appear in all 346 capitals, as shown here. 348 OMNI links maintain a constant value "MAX_MSID" selected to provide 349 MNs with an acceptable level of MSE redundancy while minimizing 350 control message amplification. It is RECOMMENDED that MAX_MSID be 351 set to the default value 5; if a different value is chosen, it should 352 be set uniformly by all nodes on the OMNI link. 354 An implementation is not required to internally use the architectural 355 constructs described here so long as its external behavior is 356 consistent with that described in this document. 358 4. Overlay Multilink Network (OMNI) Interface Model 360 An OMNI interface is a MN virtual interface configured over one or 361 more underlying interfaces, which may be physical (e.g., an 362 aeronautical radio link) or virtual (e.g., an Internet or higher- 363 layer "tunnel"). The MN receives a MNP from the MS, and coordinates 364 with the MS through IPv6 ND message exchanges. The MN uses the MNP 365 to construct a unique OMNI LLA through the algorithmic derivation 366 specified in Section 7 and assigns the LLA to the OMNI interface. 368 The OMNI interface architectural layering model is the same as in 369 [RFC5558][RFC7847], and augmented as shown in Figure 1. The IP layer 370 therefore sees the OMNI interface as a single L3 interface with 371 multiple underlying interfaces that appear as L2 communication 372 channels in the architecture. 374 +----------------------------+ 375 | Upper Layer Protocol | 376 Session-to-IP +---->| | 377 Address Binding | +----------------------------+ 378 +---->| IP (L3) | 379 IP Address +---->| | 380 Binding | +----------------------------+ 381 +---->| OMNI Interface | 382 Logical-to- +---->| (OMNI LLA) | 383 Physical | +----------------------------+ 384 Interface +---->| L2 | L2 | | L2 | 385 Binding |(IF#1)|(IF#2)| ..... |(IF#n)| 386 +------+------+ +------+ 387 | L1 | L1 | | L1 | 388 | | | | | 389 +------+------+ +------+ 391 Figure 1: OMNI Interface Architectural Layering Model 393 Each underlying interface provides an L2/L1 abstraction according to 394 one of the following models: 396 o INET interfaces connect to an INET either natively or through one 397 or several IPv4 Network Address Translators (NATs). Native INET 398 interfaces have global IP addresses that are reachable from any 399 INET correspondent. NATed INET interfaces typically have private 400 IP addresses and connect to a private network behind one or more 401 NATs that provide INET access. 403 o ANET interfaces connect to a protected ANET that is separated from 404 the open INET by an AR acting as a proxy. The ANET interface may 405 be either on the same L2 link segment as the AR, or separated from 406 the AR by multiple IP hops. 408 o VPNed interfaces use security encapsulation over an INET/ANET to a 409 Virtual Private Network (VPN) gateway. Other than the link-layer 410 encapsulation format, VPNed interfaces behave the same as for 411 Direct interfaces. 413 o Direct (aka "point-to-point") interfaces connect directly to a 414 peer without crossing any ANET/INET paths. An example is a line- 415 of-sight link between a remote pilot and an unmanned aircraft. 417 The OMNI virtual interface model gives rise to a number of 418 opportunities: 420 o since OMNI LLAs are uniquely derived from an MNP, no Duplicate 421 Address Detection (DAD) or Multicast Listener Discovery (MLD) 422 messaging is necessary. 424 o ANET interfaces on the same L2 link segment as an AR do not 425 require any L3 addresses (i.e., not even link-local) in 426 environments where communications are coordinated entirely over 427 the OMNI interface. (An alternative would be to also assign the 428 same OMNI LLA to all ANET interfaces.) 430 o as underlying interface properties change (e.g., link quality, 431 cost, availability, etc.), any active interface can be used to 432 update the profiles of multiple additional interfaces in a single 433 message. This allows for timely adaptation and service continuity 434 under dynamically changing conditions. 436 o coordinating underlying interfaces in this way allows them to be 437 represented in a unified MS profile with provisions for mobility 438 and multilink operations. 440 o exposing a single virtual interface abstraction to the IPv6 layer 441 allows for multilink operation (including QoS based link 442 selection, packet replication, load balancing, etc.) at L2 while 443 still permitting L3 traffic shaping based on, e.g., DSCP, flow 444 label, etc. 446 o the OMNI interface allows inter-INET traversal when nodes located 447 in different INETs need to communicate with one another. This 448 mode of operation would not be possible via direct communications 449 over the underlying interfaces themselves. 451 o the OMNI Adaptation Layer (OAL) within the OMNI interface supports 452 lossless and adaptive path MTU mitigations not available for 453 communications directly over the underlying interfaces themselves. 455 o L3 sees the OMNI interface as a point of connection to the OMNI 456 link; if there are multiple OMNI links (i.e., multiple MS's), L3 457 will see multiple OMNI interfaces. 459 o Multiple independent OMNI interfaces can be used for increased 460 fault tolerance through Safety-Based Multilink (SBM), with 461 Performance-Based Multilink (PBM) applied within each interface. 463 Other opportunities are discussed in [RFC7847]. Note that even when 464 the OMNI virtual interface is present, applications can still access 465 underlying interfaces either through the network protocol stack using 466 an Internet socket or directly using a raw socket. This allows for 467 intra-network (or point-to-point) communications without invoking the 468 OMNI interface and/or OAL. For example, when an IPv6 OMNI interface 469 is configured over an underlying IPv4 interface, applications can 470 still invoke IPv4 intra-network communications as long as the 471 communicating endpoints are not subject to mobility dynamics. 472 However, the opportunities discussed above are not available when the 473 architectural layering is bypassed in this way. 475 Figure 2 depicts the architectural model for a MN connecting to the 476 MS via multiple independent ANETs. When an underlying interface 477 becomes active, the MN's OMNI interface sends native (i.e., 478 unencapsulated) IPv6 ND messages via the underlying interface. IPv6 479 ND messages traverse the ground domain ANETs until they reach an 480 Access Router (AR#1, AR#2, .., AR#n). The AR then coordinates with a 481 Mobility Service Endpoint (MSE#1, MSE#2, ..., MSE#m) in the INET and 482 returns an IPv6 ND message response to the MN. IPv6 ND messages 483 traverse the ANET at layer 2; hence, the Hop Limit is not 484 decremented. 486 +--------------+ 487 | MN | 488 +--------------+ 489 |OMNI interface| 490 +----+----+----+ 491 +--------|IF#1|IF#2|IF#n|------ + 492 / +----+----+----+ \ 493 / | \ 494 / <---- Native | IP ----> \ 495 v v v 496 (:::)-. (:::)-. (:::)-. 497 .-(::ANET:::) .-(::ANET:::) .-(::ANET:::) 498 `-(::::)-' `-(::::)-' `-(::::)-' 499 +----+ +----+ +----+ 500 ... |AR#1| .......... |AR#2| ......... |AR#n| ... 501 . +-|--+ +-|--+ +-|--+ . 502 . | | | 503 . v v v . 504 . <----- Encapsulation -----> . 505 . . 506 . +-----+ (:::)-. . 507 . |MSE#2| .-(::::::::) +-----+ . 508 . +-----+ .-(::: INET :::)-. |MSE#m| . 509 . (::::: Routing ::::) +-----+ . 510 . `-(::: System :::)-' . 511 . +-----+ `-(:::::::-' . 512 . |MSE#1| +-----+ +-----+ . 513 . +-----+ |MSE#3| |MSE#4| . 514 . +-----+ +-----+ . 515 . . 516 . . 517 . <----- Worldwide Connected Internetwork ----> . 518 ........................................................... 520 Figure 2: MN/MS Coordination via Multiple ANETs 522 After the initial IPv6 ND message exchange, the MN can send and 523 receive unencapsulated IP data packets over the OMNI interface. OMNI 524 interface multilink services will forward the packets via ARs in the 525 correct underlying ANETs. The AR encapsulates the packets according 526 to the capabilities provided by the MS and forwards them to the next 527 hop within the worldwide connected Internetwork via optimal routes. 529 OMNI links span one or more underlying Internetwork via the OMNI 530 Adaptation Layer (OAL) which is based on a mid-layer overlay 531 encapsulation using [RFC2473]. Each OMNI link corresponds to a 532 different overlay (differentiated by an address codepoint) which may 533 be carried over a completely separate underlying topology. Each MN 534 can facilitate SBM by connecting to multiple OMNI links using a 535 distinct OMNI interface for each link. 537 5. The OMNI Adaptation Layer (OAL) 539 The OMNI interface observes the link nature of tunnels, including the 540 Maximum Transmission Unit (MTU), Maximum Reassembly Unit (MRU) and 541 the role of fragmentation and reassembly [I-D.ietf-intarea-tunnels]. 542 The OMNI interface is configured over one or more underlying 543 interfaces that may have diverse MTUs. OMNI interfaces accommodate 544 MTU diversity through the use of the OMNI Adaptation Layer (OAL) as 545 discussed in this section. 547 IPv6 underlying interfaces are REQUIRED to configure a minimum MTU of 548 1280 bytes and a minimum MRU of 1500 bytes [RFC8200], meaning that 549 the minimum IPv6 path MTU is 1280 bytes since routers on the path are 550 not permitted to perform network fragmentation even though the 551 destination is required to reassemble more. The network therefore 552 MUST forward packets of at least 1280 bytes without generating an 553 IPv6 Path MTU Discovery (PMTUD) Packet Too Big (PTB) message 554 [RFC8201]. (Note: the source can apply "source fragmentation" for 555 locally-generated IPv6 packets up to 1500 bytes and larger still if 556 it if has a way to determine that the destination configures a larger 557 MRU, but this does not affect the minimum IPv6 path MTU.) 559 IPv4 underlying interfaces are REQUIRED to configure a minimum MTU of 560 68 bytes [RFC0791] and a minimum MRU of 576 bytes [RFC0791][RFC1122]. 561 Therefore, when the Don't Fragment (DF) bit in the IPv4 header is set 562 to 0 the minimum IPv4 path MTU is 576 bytes since routers on the path 563 support network fragmentation and the destination is required to 564 reassemble at least that much. The DF bit in the IPv4 encapsulation 565 headers of packets sent over IPv4 underlying interfaces therefore 566 MUST be set to 0. (Note: even if the encapsulation source has a way 567 to determine that the encapsulation destination configures an MRU 568 larger than 576 bytes, it should not assume a larger minimum IPv4 569 path MTU without careful consideration of the issues discussed in 570 Section 5.1.) 572 The OMNI interface configures both an MTU and MRU of 9180 bytes 573 [RFC2492]; the size is therefore not a reflection of the underlying 574 interface MTUs, but rather determines the largest packet the OMNI 575 interface can forward or reassemble. The OMNI interface uses the 576 OMNI Adaptation Layer (OAL) to admit packets from the network layer 577 that are no larger than the OMNI interface MTU while generating 578 ICMPv4 Fragmentation Needed [RFC1191] or ICMPv6 Path MTU Discovery 579 (PMTUD) Packet Too Big (PTB) [RFC8201] messages as necessary. This 580 document refers to both of these ICMPv4/ICMPv6 message types simply 581 as "PTBs", and introduces a distinction between PTB "hard" and "soft" 582 errors as discussed below. 584 For IPv4 packets with DF=0, the network layer performs IPv4 585 fragmentation if necessary then admits the packets/fragments into the 586 OMNI interface; these fragments will be reassembled by the final 587 destination. For IPv4 packets with DF=1 and IPv6 packets, the 588 network layer admits the packet if it is no larger than the OMNI 589 interface MTU; otherwise, it drops the packet and returns a PTB hard 590 error message to the source. 592 For each admitted IP packet/fragment, the OMNI interface internally 593 employs the OAL when necessary by inserting a mid-layer IPv6 header 594 between the inner IP packet/fragment and any outer IP encapsulation 595 headers per [RFC2473] (but without decrementing the inner IP Hop 596 Limit/TTL since the insertion occurs at a layer below IP forwarding). 597 The OAL then calculates the 32-bit CRC over the entire mid-layer 598 packet and writes the value in a trailing 4-octet field at the end of 599 the packet. Next, the OAL fragments this mid-layer IPv6 packet, 600 forwards the fragments (using outer IP encapsulation if necessary), 601 and returns an internally-generated PTB soft error message (subject 602 to rate limiting) if it deems the packet too large according to 603 factors such as link performance characteristics, reassembly 604 congestion, etc. This ensures that the path MTU is adaptive and 605 reflects the current path used for a given data flow. 607 The OAL operates with respect to both the minimum IPv6 and IPv4 path 608 MTUs as follows: 610 o When an OMNI interface sends a packet toward a final destination 611 via an ANET peer, it sends without OAL encapsulation if the packet 612 (including any outer-layer ANET encapsulations) is no larger than 613 the underlying interface MTU for on-link ANET peers or the minimum 614 ANET path MTU for peers separated by multiple IP hops. Otherwise, 615 the OAL inserts an IPv6 header per [RFC2473] with source address 616 set to the node's own OMNI Domain-Local Address (DLA) (see: 617 Section 8) and destination set to the OMNI DLA of the ANET peer. 618 The OAL then calculates and appends the trailing 32-bit CRC, then 619 uses IPv6 fragmentation to break the packet into a minimum number 620 of non-overlapping fragments where the largest fragment size 621 (including both the OMNI and any outer-layer ANET encapsulations) 622 is determined by the underlying interface MTU for on-link ANET 623 peers or the minimum ANET path MTU for peers separated by multiple 624 IP hops. The OAL then encapsulates the fragments in any ANET 625 headers and sends them to the ANET peer, which reassembles before 626 forwarding toward the final destination. 628 o When an OMNI interface sends a packet toward a final destination 629 via an INET interface, it sends packets (including any outer-layer 630 INET encapsulations) no larger than the minimum INET path MTU 631 without OAL encapsulation if the destination is reached via an 632 INET address within the same OMNI link segment. Otherwise, the 633 OAL inserts an IPv6 header per [RFC2473] with source address set 634 to the node's OMNI DLA, destination set to the DLA of the next hop 635 OMNI node toward the final destination and (if necessary) with a 636 Segment Routing Header with the remaining Segment IDs on the path 637 to the final destination. The OAL then calculates and appends the 638 trailing 32-bit CRC, then uses IPv6 fragmentation to break the 639 packet into a minimum number of non-overlapping fragments where 640 the largest fragment size (including both the OMNI and outer-layer 641 INET encapsulations) is the minimum INET path MTU, and the 642 smallest fragment size is no smaller than 256 bytes (i.e., 643 slightly less than half the minimum IPv4 path MTU). The OAL then 644 encapsulates the fragments in any INET headers and sends them to 645 the OMNI link neighbor, which reassembles before forwarding toward 646 the final destination. 648 The OAL unconditionally drops all OAL fragments received from an INET 649 peer that are smaller than 256 bytes (note that no minimum fragment 650 size is specified for ANET peers since the underlying ANET is secured 651 against tiny fragment attacks). In order to set the correct context 652 for reassembly, the OAL of the OMNI interface that inserts the IPv6 653 header MUST also be the one that inserts the IPv6 Fragment Header 654 Identification value. While not strictly required, sending all 655 fragments of the same fragmented OAL packet consecutively over the 656 same underlying interface with minimal inter-fragment delay may 657 increase the likelihood of successful reassembly. 659 Ordinary PTB messages with ICMPv4 header "unused" field or ICMPv6 660 header Code field value 0 are hard errors that always indicate that a 661 packet has been dropped due to a real MTU restriction. However, the 662 OAL can also forward large packets via encapsulation and 663 fragmentation while at the same time returning PTB soft error 664 messages (subject to rate limiting) indicating that a forwarded 665 packet was uncomfortably large. The OMNI interface can therefore 666 continuously forward large packets without loss while returning PTB 667 soft error messages recommending a smaller size. Original sources 668 that receive the soft errors in turn reduce the size of the packets 669 they send, i.e., the same as for hard errors. 671 The OAL sets the ICMPv4 header "unused" field or ICMPv6 header Code 672 field to the value 1 in PTB soft error messages. The OAL sets the 673 PTB destination address to the source address of the original packet, 674 and sets the source address to the MNP Subnet Router Anycast address 675 of the MN (i.e., whether the MN was the source or target of the 676 original packet). When the original source receives the PTB, it 677 reduces its path MTU estimate the same as for hard errors but does 678 not regard the message as a loss indication. (If the original source 679 does not recognize the soft error code, it regards the PTB the same 680 as a hard error but should heed the retransmission advice given in 681 [RFC8201] suggesting retransmission based on normal packetization 682 layer retransmission timers.) This document therefore updates 683 [RFC1191][RFC4443] and [RFC8201]. Furthermore, implementations of 684 [RFC4821] must be aware that PTB hard or soft errors may arrive at 685 any time even if after a successful MTU probe (this is the same 686 consideration as for an ordinary path fluctuation following a 687 successful probe). 689 In summary, the OAL supports continuous transmission and reception of 690 packets of various sizes in the face of dynamically changing network 691 conditions. Moreover, since PTB soft errors do not indicate loss, 692 original sources that receive soft errors can quickly scan for path 693 MTU increases without waiting for the minimum 10 minutes specified 694 for loss-oriented PTB hard errors [RFC1191][RFC8201]. The OAL 695 therefore provides a lossless and adaptive service that accommodates 696 MTU diversity especially well-suited for dynamic multilink 697 environments. 699 Note: In network paths where IPv6/IPv4 protocol translation or IPv6- 700 in-IPv4 encapsulation may be prevalent, it may be prudent for the OAL 701 to always assume the IPv4 minimum path MTU (i.e., 576 bytes) 702 regardless of the underlying interface IP protocol version. Always 703 assuming the IPv4 minimum path MTU even for IPv6 underlying 704 interfaces may produce more fragments and additional header overhead, 705 but will always interoperate and never run the risk of presenting an 706 IPv4 node with a packet that exceeds its MRU. 708 Note: An OMNI interface that reassembles OAL fragments may experience 709 congestion-oriented loss in its reassembly cache and can optionally 710 send PTB soft errors to the original source and/or ICMP "Time 711 Exceeded" messages to the source of the OAL fragments. In 712 environments where the messages may contribute to unacceptable 713 additional congestion, however, the OMNI interface can simply regard 714 the loss as an ordinary unreported congestion event for which the 715 original source will eventually compensate. 717 Note: When the network layer forwards an IPv4 packet/fragment with 718 DF=0 into the OMNI interface, the interface can optionally perform 719 (further) IPv4 fragmentation before invoking the OAL so that the 720 fragments will be reassembled by the final destination. When the 721 network layer performs IPv6 fragmentation for locally-generated IPv6 722 packets, the OMNI interface typically invokes the OAL without first 723 applying (further) IPv6 fragmentation; the network layer should 724 therefore fragment to the minimum IPv6 path MTU (or smaller still) to 725 push the reassembly burden to the final destination and avoid 726 receiving PTB soft errors from the OMNI interface. Aside from these 727 non-normative guidelines, the manner in which any IP fragmentation is 728 invoked prior to OAL encapsulation/fragmentation is an implementation 729 matter. 731 Note: Inclusion of the 32-bit CRC prior to fragmentation assumes that 732 the receiving OAL will discard any packets with incorrect CRC values 733 following reassembly. The 32-bit CRC is sufficient to detect 734 reassembly misassociations for packet sizes up to the OMNI interface 735 MTU 9180 but may not be sufficient to detect errors for larger sizes 736 [CRC]. 738 Note: Some underlying interface types (e.g., VPNs) may already 739 provide their own robust fragmentation and reassembly services even 740 without OAL encapsulation. In those cases, the OAL can invoke the 741 inherent underlying interface schemes instead while employing PTB 742 soft errors in the same fashion as described above. Other underlying 743 interface properties such as header/message compression can also be 744 harnessed in a similar fashion. 746 Note: Applications can dynamically tune the size of the packets they 747 to send to produce the best possible throughput and latency, with the 748 understanding that these parameters may change over time due to 749 factors such as congestion, mobility, network path changes, etc. The 750 receipt or absence of soft errors should be seen as hints of when 751 increasing or decreasing packet sizes may be beneficial. 753 5.1. Fragmentation Security Implications 755 As discussed in Section 3.7 of [RFC8900], there are four basic 756 threats concerning IPv6 fragmentation; each of which is addressed by 757 effective mitigations as follows: 759 1. Overlapping fragment attacks - reassembly of overlapping 760 fragments is forbidden by [RFC8200]; therefore, this threat does 761 not apply to the OAL. 763 2. Resource exhaustion attacks - this threat is mitigated by 764 providing a sufficiently large OAL reassembly cache and 765 instituting "fast discard" of incomplete reassemblies that may be 766 part of a buffer exhaustion attack. The reassembly cache should 767 be sufficiently large so that a sustained attack does not cause 768 excessive loss of good reassemblies but not so large that (timer- 769 based) data structure management becomes computationally 770 expensive. The cache should also be indexed based on the arrival 771 underlying interface such that congestion experienced over a 772 first underlying interface does not cause discard of incomplete 773 reassemblies for uncongested underlying interfaces. 775 3. Attacks based on predictable fragment identification values - 776 this threat is mitigated by selecting a suitably random ID value 777 per [RFC7739]. 779 4. Evasion of Network Intrusion Detection Systems (NIDS) - this 780 threat is mitigated by disallowing "tiny fragments" per the OAL 781 fragmentation procedures specified above. 783 Additionally, IPv4 fragmentation includes a 16-bit Identification (IP 784 ID) field with only 65535 unique values such that at high data rates 785 the field could wrap and apply to new packets while the fragments of 786 old packets using the same ID are still alive in the network 787 [RFC4963]. However, since the largest OAL fragment that will be sent 788 via an IPv4 INET path is 576 bytes any IPv4 fragmentation would occur 789 only on links with an IPv4 MTU smaller than this size, and [RFC3819] 790 recommendations suggest that such links will have low data rates. 791 Since IPv6 provides a 32-bit Identification value, IP ID wraparound 792 at high data rates is not a concern for IPv6 fragmentation. 794 6. Frame Format 796 The OMNI interface transmits IPv6 packets according to the native 797 frame format of each underlying interface. For example, for 798 Ethernet-compatible interfaces the frame format is specified in 799 [RFC2464], for aeronautical radio interfaces the frame format is 800 specified in standards such as ICAO Doc 9776 (VDL Mode 2 Technical 801 Manual), for tunnels over IPv6 the frame format is specified in 802 [RFC2473], etc. 804 7. Link-Local Addresses (LLAs) 806 OMNI nodes are assigned OMNI interface IPv6 Link-Local Addresses 807 (i.e., "OMNI LLAs") through pre-service administrative actions. MN 808 OMNI LLAs embed the MNP assigned to the mobile node, while MS OMNI 809 LLAs include an administratively-unique ID that is guaranteed to be 810 unique on the link. OMNI LLAs are configured as follows: 812 o IPv6 MN OMNI LLAs encode the most-significant 112 bits of a MNP 813 within the least-significant 112 bits of the IPv6 link-local 814 prefix fe80::/16. The Prefix Length is determined by adding 16 to 815 the length of the embedded MNP. For example, for the MNP 816 2001:db8:1000:2000::/56 the corresponding MN OMNI LLA is 817 fe80:2001:db8:1000:2000::/72. This specification updates the IPv6 818 link-local address format specified in Section 2.5.6 of [RFC4291] 819 by defining a use for bits 11 - 63. 821 o IPv4-compatible MN OMNI LLAs are constructed as fe80::ffff:[IPv4], 822 i.e., the most significant 16 bits of the prefix fe80::/16, 823 followed by 64 '0' bits, followed by 16 '1' bits, followed by a 824 32bit IPv4 address/prefix. The Prefix Length is determined by 825 adding 96 to the length of the embedded IPv4 address/prefix. For 826 example, the IPv4-Compatible MN OMNI LLA for 192.0.2.0/24 is 827 fe80::ffff:192.0.2.0/120 (also written as 828 fe80::ffff:c000:0200/120). 830 o MS OMNI LLAs are assigned to ARs and MSEs from the range 831 fe80::/96, and MUST be managed for uniqueness. The lower 32 bits 832 of the LLA includes a unique integer "MSID" value between 833 0x00000001 and 0xfeffffff, e.g., as in fe80::1, fe80::2, fe80::3, 834 etc., fe80::feff:ffff. The MS OMNI LLA Prefix Length is 835 determined by adding 96 to the MSID prefix length. For example, 836 if the MSID '0x10002000' prefix length is 16 then the MS OMNI LLA 837 Prefix Length is set to 112 and the LLA is written as 838 fe80::1000:2000/112. Finally, the MSID 0x00000000 is the 839 "Anycast" MSID and corresponds to the link-local Subnet-Router 840 anycast address (fe80::) [RFC4291]; the MSID range 0xff000000 841 through 0xffffffff is reserved for future use. 843 o Temporary OMNI LLAs are configured from the range 844 fe80:0:0:ffff::/64 with the lower 64 bits set according to the 845 specification in [I-D.ietf-6man-rfc4941bis]. Temporary OMNI LLAs 846 are used for the short-term purpose of procuring an actual MN OMNI 847 LLA upon startup or (re)connecting to the network. 849 o Cryptographically-Generated Address (CGA) OMNI LLAs are configured 850 from the range fe80:0:0:fffe::/64 with the lower 64 bits set 851 according to the specification in [RFC3972]. CGAs are used for 852 operation of the Secure Neighbor Discovery (SEND) protocol. 854 o the remaining /64 sub-prefixes of fe80:0:0::/48 (other than 855 fe80::/64) are available for future assignment to other LLA types 857 Since the prefix 0000::/8 is "Reserved by the IETF" [RFC4291], no 858 MNPs can be allocated from that block ensuring that there is no 859 possibility for overlap between the above OMNI LLA constructs. 861 Since MN OMNI LLAs are based on the distribution of administratively 862 assured unique MNPs, and since MS OMNI LLAs are guaranteed unique 863 through administrative assignment, OMNI interfaces set the 864 autoconfiguration variable DupAddrDetectTransmits to 0 [RFC4862]. 865 Temporary OMNI LLAs employ optimistic DAD principles [RFC4429] since 866 they are probabilistically unique and their use is short-duration in 867 nature. 869 8. Domain-Local Addresses (DLAs) 871 OMNI links use IPv6 Domain-Local Addresses (i.e., "OMNI DLAs") as the 872 source and destination addresses in OAL IPv6 encapsulation headers. 873 This document uses the prefix [DLA]::/10 for mapping OMNI LLAs to 874 routable OMNI DLAs (where the actual prefix assignment for [DLA]::/10 875 is TBD). 877 Each OMNI link instance is identified by bits 10-15 of the OMNI 878 service prefix [DLA]::/10. For example, OMNI DLAs associated with 879 instance 0 are configured from the prefix [DLA0]::/16, instance 1 880 from [DLA1]::/16, instance 2 from [DLA2]::/16, etc. OMNI DLAs and 881 their associated prefix lengths are configured in one-to-one 882 correspondence with OMNI LLAs through stateless prefix translation. 883 For example, for OMNI link instance [DLA0]::/16: 885 o the OMNI DLA corresponding to fe80:2001:db8:1:2::/80 is simply 886 [DLA0]:2001:db8:1:2::/80 888 o the OMNI DLA corresponding to fe80::ffff:192.0.2.0/120 is simply 889 [DLA0]::ffff:192.0.2.0/120 891 o the OMNI DLA corresponding to fe80::1000/112 is simply 892 [DLA0]::1000/112 894 o the OMNI DLA corresponding to fe80::/128 is simply [DLA0]::/128. 896 o the OMNI DLA corresponding to fe80:0:0:ffff:[Temporary]/64 is 897 simply [DLA0]:0:0:ffff:[Temporary]/64. 899 o etc. 901 Each OMNI interface assigns the Anycast OMNI DLA specific to the OMNI 902 link instance, e.g., the OMNI interface connected to instance 3 903 assigns the Anycast OMNI DLA [DLA3]:. Routers that configure OMNI 904 interfaces advertise the OMNI service prefix (e.g., [DLA3]::/16) into 905 the local routing system so that applications can direct traffic 906 according to SBM requirements. 908 The OMNI DLA presents an IPv6 address format that is routable within 909 the OMNI domain routing system and can be used to convey link-scoped 910 IPv6 ND messages across multiple hops using IPv6 encapsulation 911 [RFC2473]. The OMNI link extends across one or more underling 912 Internetworks to include all ARs and MSEs. All MNs are also 913 considered to be connected to the OMNI link, however OAL 914 encapsulation is omitted over ANET links when possible to conserve 915 bandwidth (see: Section 11). 917 Each OMNI link can be subdivided into "segments" that often 918 correspond to different administrative domains or physical 919 partitions. OMNI nodes can use IPv6 Segment Routing [RFC8402] when 920 necessary to support efficient packet forwarding to destinations 921 located in other OMNI link segments. A full discussion of Segment 922 Routing over the OMNI link appears in [I-D.templin-intarea-6706bis]. 924 NOTE: Since DLAs are only routable within the scope of an OMNI 925 domain, [DLA]::/10 need not be based on an IPv6 Globally Unique 926 Address (GUA) prefix. The IPv6 Unique Local Address (ULA) prefix 927 fc00::/7 [RFC4193] could provide an acceptable alternative provided 928 the exact [DLA]::/10 sub-prefix could be annexed for use by this 929 document. Re-purposing the (deprecated) IPv6 "site-local" address 930 block fec0::/10 would seem to be a natural alternative since both 931 fe80::/10 and fec0::/10 have identical prefix lengths and differ only 932 in a single bit setting; they can also be unambiguously allocated in 933 one-to-one correspondence with one another. This alternative would 934 also make good use of an otherwise-wasted address range that has been 935 "parked" since the 2004 deprecation. However, re-purposing the block 936 would require an IETF standards action acknowledging this document as 937 obsoleting [RFC3879] and updating [RFC4291]. 939 9. Address Mapping - Unicast 941 OMNI interfaces maintain a neighbor cache for tracking per-neighbor 942 state and use the link-local address format specified in Section 7. 943 OMNI interface IPv6 Neighbor Discovery (ND) [RFC4861] messages sent 944 over physical underlying interfaces without encapsulation observe the 945 native underlying interface Source/Target Link-Layer Address Option 946 (S/TLLAO) format (e.g., for Ethernet the S/TLLAO is specified in 947 [RFC2464]). OMNI interface IPv6 ND messages sent over underlying 948 interfaces via encapsulation do not include S/TLLAOs which were 949 intended for encoding physical L2 media address formats and not 950 encapsulation IP addresses. Furthermore S/TLLAOs are not intended 951 for encoding additional interface attributes. Hence, this document 952 does not define an S/TLLAO format but instead defines a new option 953 type termed the "OMNI option" designed for these purposes. 955 MNs such as aircraft typically have many wireless data link types 956 (e.g. satellite-based, cellular, terrestrial, air-to-air directional, 957 etc.) with diverse performance, cost and availability properties. 958 The OMNI interface would therefore appear to have multiple L2 959 connections, and may include information for multiple underlying 960 interfaces in a single IPv6 ND message exchange. OMNI interfaces use 961 an IPv6 ND option called the OMNI option formatted as shown in 962 Figure 3: 964 0 1 2 3 965 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 1 966 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 967 | Type | Length | Prefix Length | S/T-ifIndex | 968 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 969 | | 970 ~ Sub-Options ~ 971 | | 972 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 974 Figure 3: OMNI Option Format 976 In this format: 978 o Type is set to TBD. If multiple OMNI option instances appear in 979 the same IPv6 ND message, the first instance is processed and all 980 other instances are ignored. 982 o Length is set to the number of 8 octet blocks in the option. 984 o Prefix Length is determines the length of prefix to be applied to 985 an OMNI MN LLA/DLA. For IPv6 ND messages sent from a MN to the 986 MS, Prefix Length is the length that the MN is requesting or 987 asserting to the MS. For IPv6 ND messages sent from the MS to the 988 MN, Prefix Length indicates the length that the MS is granting to 989 the MN. For IPv6 ND messages sent between MS endpoints, Prefix 990 Length indicates the length associated with the target MN that is 991 subject of the ND message. 993 o S/T-ifIndex corresponds to the ifIndex value for source or target 994 underlying interface used to convey this IPv6 ND message. OMNI 995 interfaces MUST number each distinct underlying interface with an 996 ifIndex value between '1' and '255' that represents a MN-specific 997 8-bit mapping for the actual ifIndex value assigned by network 998 management [RFC2863] (the ifIndex value '0' is reserved for use by 999 the MS). For RS and NS messages, S/T-ifIndex corresponds to the 1000 source underlying interface the message originated from. For RA 1001 and NA messages, S/T-ifIndex corresponds to the target underlying 1002 interface that the message is destined to. 1004 o Sub-Options is a Variable-length field, of length such that the 1005 complete OMNI Option is an integer multiple of 8 octets long. 1006 Contains one or more Sub-Options, as described in Section 9.1. 1008 9.1. Sub-Options 1010 The OMNI option includes zero or more Sub-Options. Each consecutive 1011 Sub-Option is concatenated immediately after its predecessor. All 1012 Sub-Options except Pad1 (see below) are in type-length-value (TLV) 1013 encoded in the following format: 1015 0 1 2 1016 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 1017 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1018 | Sub-Type | Sub-length | Sub-Option Data ... 1019 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1021 Figure 4: Sub-Option Format 1023 o Sub-Type is a 1-octet field that encodes the Sub-Option type. 1024 Sub-Options defined in this document are: 1026 Option Name Sub-Type 1027 Pad1 0 1028 PadN 1 1029 Interface Attributes 2 1030 Traffic Selector 3 1031 MS-Register 4 1032 MS-Release 5 1033 Network Access Identifier 6 1034 Geo Coordinates 7 1035 DHCP Unique Identifier (DUID) 8 1037 Figure 5 1039 Sub-Types 253 and 254 are reserved for experimentation, as 1040 recommended in [RFC3692]. 1042 o Sub-Length is a 1-octet field that encodes the length of the Sub- 1043 Option Data (i.e., ranging from 0 to 255 octets). 1045 o Sub-Option Data is a block of data with format determined by Sub- 1046 Type. 1048 During processing, unrecognized Sub-Options are ignored and the next 1049 Sub-Option processed until the end of the OMNI option is reached. 1051 The following Sub-Option types and formats are defined in this 1052 document: 1054 9.1.1. Pad1 1056 0 1057 0 1 2 3 4 5 6 7 1058 +-+-+-+-+-+-+-+-+ 1059 | Sub-Type=0 | 1060 +-+-+-+-+-+-+-+-+ 1062 Figure 6: Pad1 1064 o Sub-Type is set to 0. If multiple instances appear in the same 1065 OMNI option all are processed. 1067 o No Sub-Length or Sub-Option Data follows (i.e., the "Sub-Option" 1068 consists of a single zero octet). 1070 9.1.2. PadN 1072 0 1 2 1073 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 1074 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1075 | Sub-Type=1 | Sub-length=N | N padding octets ... 1076 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1078 Figure 7: PadN 1080 o Sub-Type is set to 1. If multiple instances appear in the same 1081 OMNI option all are processed. 1083 o Sub-Length is set to N (from 0 to 255) being the number of padding 1084 octets that follow. 1086 o Sub-Option Data consists of N zero-valued octets. 1088 9.1.3. Interface Attributes 1090 The Interface Attributes sub-option provides L2 forwarding 1091 information for the multilink conceptual sending algorithm discussed 1092 in Section 11. The L2 information is used for selecting among 1093 potentially multiple candidate underlying interfaces that can be used 1094 to forward packets to the neighbor based on factors such as DSCP 1095 preferences and link quality. Interface Attributes further include 1096 link-layer address information to be used for either OAL 1097 encapsulation or direct UDP/IP encapsulation (when OAL encapsulation 1098 can be avoided). The Interface Attributes format and contents are 1099 given in Figure 8 below: 1101 0 1 2 3 1102 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 1103 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1104 | Sub-Type=2 | Sub-length=N | ifIndex | ifType | 1105 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1106 | Provider ID | Link |R| APS | SRT | FMT | LHS (0 - 7) | 1107 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1108 | LHS (bits 8 - 31) | ~ 1109 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ 1110 ~ ~ 1111 ~ Link Layer Address (L2ADDR) ~ 1112 ~ ~ 1113 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1114 | Bitmap(0)=0xff|P00|P01|P02|P03|P04|P05|P06|P07|P08|P09|P10|P11| 1115 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1116 |P12|P13|P14|P15|P16|P17|P18|P19|P20|P21|P22|P23|P24|P25|P26|P27| 1117 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1118 |P28|P29|P30|P31| Bitmap(1)=0xff|P32|P33|P34|P35|P36| ... 1119 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1121 Figure 8: Interface Attributes 1123 o Sub-Type is set to 2. If multiple instances with different 1124 ifIndex values appear in the same OMNI option all are processed; 1125 if multiple instances with the same ifIndex value appear, the 1126 first is processed and all others are ignored. 1128 o Sub-Length is set to N (from 4 to 255) that encodes the number of 1129 Sub-Option Data octets that follow. 1131 o Sub-Option Data contains an "Interface Attribute" option encoded 1132 as follows (note that the first four octets must be present): 1134 * ifIndex is set to an 8-bit integer value corresponding to a 1135 specific underlying interface the same as specified above for 1136 the OMNI option header S/T-ifIndex. An OMNI option may include 1137 multiple Interface Attributes Sub-Options, with each distinct 1138 ifIndex value pertaining to a different underlying interface. 1139 The OMNI option will often include an Interface Attributes Sub- 1140 Option with the same ifIndex value that appears in the S/ 1141 T-ifIndex. In that case, the actual encapsulation address of 1142 the received IPv6 ND message should be compared with the L2ADDR 1143 encoded in the Sub-Option (see below); if the addresses are 1144 different (or, if L2ADDR absent) the presence of a Network 1145 Address Translator (NAT) is indicated. 1147 * ifType is set to an 8-bit integer value corresponding to the 1148 underlying interface identified by ifIndex. The value 1149 represents an OMNI interface-specific 8-bit mapping for the 1150 actual IANA ifType value registered in the 'IANAifType-MIB' 1151 registry [http://www.iana.org]. 1153 * Provider ID is set to an OMNI interface-specific 8-bit ID value 1154 for the network service provider associated with this ifIndex. 1156 * Link encodes a 4-bit link metric. The value '0' means the link 1157 is DOWN, and the remaining values mean the link is UP with 1158 metric ranging from '1' ("lowest") to '15' ("highest"). 1160 * R is reserved for future use. 1162 * APS - a 3-bit "Address/Preferences/Simplex" code that 1163 determines the contents of the remainder of the sub-option as 1164 follows: 1166 + When the most significant bit (i.e., "Address") is set to 1, 1167 the SRT, FMT, LHS and L2ADDR fields are included immediately 1168 following the APS code; else, they are omitted. 1170 + When the next most significant bit (i.e., "Preferences") is 1171 set to 1, a preferences block is included next; else, it is 1172 omitted. (Note that if "Address" is set the preferences 1173 block immediately follows L2ADDR; else, it immediately 1174 follows the APS code.) 1176 + When a preferences block is present and the least 1177 significant bit (i.e., "Simplex") is set to 1, the block is 1178 encoded in "Simplex" form as shown in Figure 8; else it is 1179 encoded in "Indexed" form as discussed below. 1181 * When APS indicates that an "Address" is included, the following 1182 fields appear in consecutive order (else, they are omitted): 1184 + SRT - a 5-bit Segment Routing Topology prefix length value 1185 that (when added to 96) determines the prefix length to 1186 apply to the DLA formed from concatenating fe*::/96 with the 1187 32 bit LHS MSID value that follows. For example, the value 1188 16 corresponds to the prefix length 112. 1190 + FMT - a 3-bit "Framework/Mode/Type" code corresponding to 1191 the included Link Layer Address as follows: 1193 - When the most significant bit (i.e., "Framework") is set 1194 to 0, L2ADDR is the INET encapsulation address of a 1195 Proxy/Server; otherwise, it is the address for the 1196 Source/Target itself 1198 - When the next most significant bit (i.e., "Mode") is set 1199 to 0, the Source/Target L2ADDR is on the open INET; 1200 otherwise, it is (likely) located behind a Network 1201 Address Translator (NAT). 1203 - When the least significant bit (i.e., "Type") is set to 1204 0, L2ADDR includes a UDP Port Number followed by an IPv4 1205 address; else, a UDP Port Number followed by an IPv6 1206 address. 1208 + LHS - the 32 bit MSID of the Last Hop Server/Proxy on the 1209 path to the target. When SRT and LHS are both set to 0, the 1210 LHS is considered unspecified in this IPv6 ND message. When 1211 SRT is set to 0 and LHS is non-zero, the prefix length is 1212 set to 128. SRT and LHS provide guidance to the OMNI 1213 interface forwarding algorithm. Specifically, if SRT/LHS is 1214 located in the local OMNI link segment then the OMNI 1215 interface can encapsulate according to FMT/L2ADDR; else, it 1216 must forward according to the OMNI link spanning tree. See 1217 [I-D.templin-intarea-6706bis] for further discussion. 1219 + Link Layer Address (L2ADDR) - Formatted according to FMT, 1220 and identifies the link-layer address (i.e., the 1221 encapsulation address) of the source/target. The UDP Port 1222 Number appears in the first two octets and the IP address 1223 appears in the next 4 octets for IPv4 or 16 octets for IPv6. 1224 The Port Number and IP address are recorded in ones- 1225 compliment "obfuscated" form per [RFC4380]. The OMNI 1226 interface forwarding algorithm uses FMT/L2ADDR to determine 1227 the encapsulation address for forwarding when SRT/LHS is 1228 located in the local OMNI link segment. 1230 * When APS indicates that "Preferences" are included, a 1231 preferences block appears as the remainder of the Sub-Option as 1232 a series of Bitmaps and P[*] values. In "Simplex" form, the 1233 index for each singleton Bitmap octet is inferred from its 1234 sequential position (i.e., 0, 1, 2, ...) as shown in Figure 8. 1235 In "Indexed" form, each Bitmap is preceded by an Index octet 1236 that encodes a value "i" = (0 - 255) as the index for its 1237 companion Bitmap as follows: 1239 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1240 | Index=i | Bitmap(i) |P[*] values ... 1241 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1243 Figure 9 1245 * The preferences consist of a first (simplex/indexed) Bitmap 1246 (i.e., "Bitmap(i)") followed by 0-8 single-octet blocks of 1247 2-bit P[*] values, followed by a second Bitmap (i), followed by 1248 0-8 blocks of P[*] values, etc. Reading from bit 0 to bit 7, 1249 the bits of each Bitmap(i) that are set to '1'' indicate the 1250 P[*] blocks from the range P[(i*32)] through P[(i*32) + 31] 1251 that follow; if any Bitmap(i) bits are '0', then the 1252 corresponding P[*] block is instead omitted. For example, if 1253 Bitmap(0) contains 0xff then the block with P[00]-P[03], 1254 followed by the block with P[04]-P[07], etc., and ending with 1255 the block with P[28]-P[31] are included (as shown in Figure 8). 1256 The next Bitmap(i) is then consulted with its bits indicating 1257 which P[*] blocks follow, etc. out to the end of the Sub- 1258 Option. 1260 * Each 2-bit P[*] field is set to the value '0' ("disabled"), '1' 1261 ("low"), '2' ("medium") or '3' ("high") to indicate a QoS 1262 preference for underlying interface selection purposes. Not 1263 all P[*] values need to be included in the OMNI option of each 1264 IPv6 ND message received. Any P[*] values represented in an 1265 earlier OMNI option but omitted in the current OMNI option 1266 remain unchanged. Any P[*] values not yet represented in any 1267 OMNI option default to "medium". 1269 * The first 16 P[*] blocks correspond to the 64 Differentiated 1270 Service Code Point (DSCP) values P[00] - P[63] [RFC2474]. Any 1271 additional P[*] blocks that follow correspond to "pseudo-DSCP" 1272 traffic classifier values P[64], P[65], P[66], etc. See 1273 Appendix A for further discussion and examples. 1275 9.1.4. Traffic Selector 1277 0 1 2 3 1278 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 1279 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1280 | Sub-Type=3 | Sub-length=N | ifIndex | ~ 1281 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ 1282 ~ ~ 1283 ~ RFC 6088 Format Traffic Selector ~ 1284 ~ ~ 1285 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1287 Figure 10: Traffic Selector 1289 o Sub-Type is set to 3. If multiple instances appear in the same 1290 OMNI option all are processed, i.e., even if the same ifIndex 1291 value appears multiple times. 1293 o Sub-Length is set to N (the number of Sub-Option Data octets that 1294 follow). 1296 o Sub-Option Data contains a 1-octet ifIndex encoded exactly as 1297 specified in Section 9.1.3, followed by an N-1 octet traffic 1298 selector formatted per [RFC6088] beginning with the "TS Format" 1299 field. The largest traffic selector for a given ifIndex is 1300 therefore 254 octets. 1302 9.1.5. MS-Register 1304 0 1 2 3 1305 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 1306 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1307 | Sub-Type=4 | Sub-length=4n | MSID[1] (bits 0 - 15) | 1308 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1309 | MSID [1] (bits 16 - 32) | MSID[2] (bits 0 - 15) | 1310 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1311 | MSID [2] (bits 16 - 32) | MSID[3] (bits 0 - 15) | 1312 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1313 ... ... ... ... ... ... 1314 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1315 | MSID [n] (bits 16 - 32) | 1316 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1318 Figure 11: MS-Register Sub-option 1320 o Sub-Type is set to 4. If multiple instances appear in the same 1321 OMNI option all are processed. Only the first MAX_MSID values 1322 processed (whether in a single instance or multiple) are retained 1323 and all other MSIDs are ignored. 1325 o Sub-Length is set to 4n. 1327 o A list of n 4-octet MSIDs is included in the following 4n octets. 1328 The Anycast MSID value '0' in an RS message MS-Register sub-option 1329 requests the recipient to return the MSID of a nearby MSE in a 1330 corresponding RA response. 1332 9.1.6. MS-Release 1333 0 1 2 3 1334 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 1335 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1336 | Sub-Type=5 | Sub-length=4n | MSID[1] (bits 0 - 15) | 1337 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1338 | MSID [1] (bits 16 - 32) | MSID[2] (bits 0 - 15) | 1339 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1340 | MSID [2] (bits 16 - 32) | MSID[3] (bits 0 - 15) | 1341 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1342 ... ... ... ... ... ... 1343 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1344 | MSID [n] (bits 16 - 32) | 1345 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1347 Figure 12: MS-Release Sub-option 1349 o Sub-Type is set to 5. If multiple instances appear in the same 1350 IPv6 OMNI option all are processed. Only the first MAX_MSID 1351 values processed (whether in a single instance or multiple) are 1352 retained and all other MSIDs are ignored. 1354 o Sub-Length is set to 4n. 1356 o A list of n 4 octet MSIDs is included in the following 4n octets. 1357 The Anycast MSID value '0' is ignored in MS-Release sub-options, 1358 i.e., only non-zero values are processed. 1360 9.1.7. Network Access Identifier (NAI) 1362 0 1 2 3 1363 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 1364 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1365 | Sub-Type=6 | Sub-length=N |Network Access Identifier (NAI) 1366 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... 1368 Figure 13: Network Access Identifier (NAI) Sub-option 1370 o Sub-Type is set to 6. If multiple instances appear in the same 1371 OMNI option the first is processed and all others are ignored. 1373 o Sub-Length is set to N. 1375 o A Network Access Identifier (NAI) up to 255 octets in length is 1376 coded per [RFC7542]. 1378 9.1.8. Geo Coordinates 1380 0 1 2 3 1381 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 1382 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1383 | Sub-Type=7 | Sub-length=N | Geo Coordinates 1384 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... 1386 Figure 14: Geo Coordinates Sub-option 1388 o Sub-Type is set to 7. If multiple instances appear in the same 1389 OMNI option the first is processed and all others are ignored. 1391 o Sub-Length is set to N. 1393 o A set of Geo Coordinates up to 255 octets in length (format TBD). 1394 Includes Latitude/Longitude at a minimum; may also include 1395 additional attributes such as altitude, heading, speed, etc.). 1397 9.1.9. DHCP Unique Identifier (DUID) 1399 0 1 2 3 1400 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 1401 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1402 | Sub-Type=8 | Sub-length=N | DUID-Type | 1403 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1404 . . 1405 . type-specific DUID body (variable length) . 1406 . . 1407 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1409 Figure 15: DHCP Unique Identifier (DUID) Sub-option 1411 o Sub-Type is set to 8. If multiple instances appear in the same 1412 OMNI option the first is processed and all others are ignored. 1414 o Sub-Length is set to N (i.e., the length of the option beginning 1415 with the DUID-Type and continuing to the end of the type-specific 1416 body). 1418 o DUID-Type is a two-octet field coded in network byte order that 1419 determines the format and contents of the type-specific body 1420 according to Section 11 of [RFC8415]. DUID-Type 4 in particular 1421 corresponds to the Universally Unique Identifier (UUID) [RFC6355] 1422 which will occur in common operational practice. 1424 o A type-specific DUID body up to 253 octets in length follows, 1425 formatted according to DUID-type. For example, for type 4 the 1426 body consists of a 128-bit UUID selected according to [RFC6355]. 1428 10. Address Mapping - Multicast 1430 The multicast address mapping of the native underlying interface 1431 applies. The mobile router on board the MN also serves as an IGMP/ 1432 MLD Proxy for its EUNs and/or hosted applications per [RFC4605] while 1433 using the L2 address of the AR as the L2 address for all multicast 1434 packets. 1436 The MN uses Multicast Listener Discovery (MLDv2) [RFC3810] to 1437 coordinate with the AR, and ANET L2 elements use MLD snooping 1438 [RFC4541]. 1440 11. Multilink Conceptual Sending Algorithm 1442 The MN's IPv6 layer selects the outbound OMNI interface according to 1443 SBM considerations when forwarding data packets from local or EUN 1444 applications to external correspondents. Each OMNI interface 1445 maintains a neighbor cache the same as for any IPv6 interface, but 1446 with additional state for multilink coordination. Each OMNI 1447 interface maintains default routes via ARs discovered as discussed in 1448 Section 12, and may configure more-specific routes discovered through 1449 means outside the scope of this specification. 1451 After a packet enters the OMNI interface, one or more outbound 1452 underlying interfaces are selected based on PBM traffic attributes, 1453 and one or more neighbor underlying interfaces are selected based on 1454 the receipt of Interface Attributes sub-options in IPv6 ND messages 1455 (see: Figure 8). Underlying interface selection for the nodes own 1456 local interfaces are based on attributes such as DSCP, application 1457 port number, cost, performance, message size, etc. OMNI interface 1458 multilink selections could also be configured to perform replication 1459 across multiple underlying interfaces for increased reliability at 1460 the expense of packet duplication. The set of all Interface 1461 Attributes received in IPv6 ND messages determine the multilink 1462 forwarding profile for selecting the neighbor's underlying 1463 interfaces. 1465 When the OMNI interface sends a packet over a selected outbound 1466 underlying interface, the OAL includes or omits a mid-layer 1467 encapsulation header as necessary as discussed in Section 5 and as 1468 determined by the L2 address information received in Interface 1469 Attributes. The OAL also performs encapsulation when the nearest AR 1470 is located multiple hops away as discussed in Section 12.1. 1472 OMNI interface multilink service designers MUST observe the BCP 1473 guidance in Section 15 [RFC3819] in terms of implications for 1474 reordering when packets from the same flow may be spread across 1475 multiple underlying interfaces having diverse properties. 1477 11.1. Multiple OMNI Interfaces 1479 MNs may connect to multiple independent OMNI links concurrently in 1480 support of SBM. Each OMNI interface is distinguished by its Anycast 1481 OMNI DLA (e.g., fec0::, fec1::, fec2::). The MN configures a 1482 separate OMNI interface for each link so that multiple interfaces 1483 (e.g., omni0, omni1, omni2, etc.) are exposed to the IPv6 layer. A 1484 different Anycast OMNI DLA is assigned to each interface, and the MN 1485 injects the service prefixes for the OMNI link instances into the EUN 1486 routing system. 1488 Applications in EUNs can use Segment Routing to select the desired 1489 OMNI interface based on SBM considerations. The Anycast OMNI DLA is 1490 written into the IPv6 destination address, and the actual destination 1491 (along with any additional intermediate hops) is written into the 1492 Segment Routing Header. Standard IP routing directs the packets to 1493 the MN's mobile router entity, and the Anycast OMNI DLA identifies 1494 the OMNI interface to be used for transmission to the next hop. When 1495 the MN receives the message, it replaces the IPv6 destination address 1496 with the next hop found in the routing header and transmits the 1497 message over the OMNI interface identified by the Anycast OMNI DLA. 1499 Multiple distinct OMNI links can therefore be used to support fault 1500 tolerance, load balancing, reliability, etc. The architectural model 1501 is similar to Layer 2 Virtual Local Area Networks (VLANs). 1503 11.2. MN<->AR Traffic Loop Prevention 1505 After an AR has registered an MNP for a MN (see: Section 12), the AR 1506 will forward packets destined to an address within the MNP to the MN. 1507 The MN will under normal circumstances then forward the packet to the 1508 correct destination within its internal networks. 1510 If at some later time the MN loses state (e.g., after a reboot), it 1511 may begin returning packets destined to an MNP address to the AR as 1512 its default router. The AR therefore must drop any packets 1513 originating from the MN and destined to an address within the MN's 1514 registered MNP. To do so, the AR institutes the following check: 1516 o if the IP destination address belongs to a neighbor on the same 1517 OMNI interface, and if the link-layer source address is the same 1518 as one of the neighbor's link-layer addresses, drop the packet. 1520 12. Router Discovery and Prefix Registration 1522 MNs interface with the MS by sending RS messages with OMNI options 1523 under the assumption that one or more AR on the ANET will process the 1524 message and respond. The MN then configures default routes for the 1525 OMNI interface via the discovered ARs as the next hop. The manner in 1526 which the ANET ensures AR coordination is link-specific and outside 1527 the scope of this document (however, considerations for ANETs that do 1528 not provide ARs that recognize the OMNI option are discussed in 1529 Section 17). 1531 For each underlying interface, the MN sends an RS message with an 1532 OMNI option to coordinate with MSEs identified by MSID values. 1533 Example MSID discovery methods are given in [RFC5214] and include 1534 data link login parameters, name service lookups, static 1535 configuration, a static "hosts" file, etc. The MN can also send an 1536 RS with an MS-Register suboption that includes the Anycast MSID value 1537 '0', i.e., instead of or in addition to any non-zero MSIDs. When the 1538 AR receives an RS with a MSID '0', it selects a nearby MSE (which may 1539 be itself) and returns an RA with the selected MSID in an MS-Register 1540 suboption. The AR selects only a single wildcard MSE (i.e., even if 1541 the RS MS-Register suboption included multiple '0' MSIDs) while also 1542 soliciting the MSEs corresponding to any non-zero MSIDs. 1544 MNs configure OMNI interfaces that observe the properties discussed 1545 in the previous section. The OMNI interface and its underlying 1546 interfaces are said to be in either the "UP" or "DOWN" state 1547 according to administrative actions in conjunction with the interface 1548 connectivity status. An OMNI interface transitions to UP or DOWN 1549 through administrative action and/or through state transitions of the 1550 underlying interfaces. When a first underlying interface transitions 1551 to UP, the OMNI interface also transitions to UP. When all 1552 underlying interfaces transition to DOWN, the OMNI interface also 1553 transitions to DOWN. 1555 When an OMNI interface transitions to UP, the MN sends RS messages to 1556 register its MNP and an initial set of underlying interfaces that are 1557 also UP. The MN sends additional RS messages to refresh lifetimes 1558 and to register/deregister underlying interfaces as they transition 1559 to UP or DOWN. The MN sends initial RS messages over an UP 1560 underlying interface with its OMNI LLA as the source and with 1561 destination set to All-Routers multicast (ff02::2) [RFC4291]. The RS 1562 messages include an OMNI option per Section 9 with valid prefix 1563 registration information, Interface Attributes appropriate for 1564 underlying interfaces, MS-Register/Release sub-options containing 1565 MSID values, and with any other necessary OMNI sub-options. The S/ 1566 T-ifIndex field is set to the index of the underlying interface over 1567 which the RS message is sent. 1569 ARs process IPv6 ND messages with OMNI options and act as an MSE 1570 themselves and/or as a proxy for other MSEs. ARs receive RS messages 1571 and create a neighbor cache entry for the MN, then coordinate with 1572 any MSEs named in the Register/Release lists in a manner outside the 1573 scope of this document. When an MSE processes the OMNI information, 1574 it first validates the prefix registration information then injects/ 1575 withdraws the MNP in the routing/mapping system and caches/discards 1576 the new Prefix Length, MNP and Interface Attributes. The MSE then 1577 informs the AR of registration success/failure, and the AR returns an 1578 RA message to the MN with an OMNI option per Section 9. 1580 The AR returns the RA message via the same underlying interface of 1581 the MN over which the RS was received, and with destination address 1582 set to the MN OMNI LLA (i.e., unicast), with source address set to 1583 its own OMNI LLA, and with an OMNI option with S/T-ifIndex set to the 1584 value included in the RS. The OMNI option also includes valid prefix 1585 registration information, Interface Attributes, MS-Register/Release 1586 and any other necessary OMNI sub-options. The RA also includes any 1587 information for the link, including RA Cur Hop Limit, M and O flags, 1588 Router Lifetime, Reachable Time and Retrans Timer values, and 1589 includes any necessary options such as: 1591 o PIOs with (A; L=0) that include MSPs for the link [RFC8028]. 1593 o RIOs [RFC4191] with more-specific routes. 1595 o an MTU option that specifies the maximum acceptable packet size 1596 for this ANET interface. 1598 The AR MAY also send periodic and/or event-driven unsolicited RA 1599 messages per [RFC4861]. In that case, the S/T-ifIndex field in the 1600 OMNI header of the unsolicited RA message identifies the target 1601 underlying interface of the destination MN. 1603 The AR can combine the information from multiple MSEs into one or 1604 more "aggregate" RAs sent to the MN in order conserve ANET bandwidth. 1605 Each aggregate RA includes an OMNI option with MS-Register/Release 1606 sub-options with the MSEs represented by the aggregate. If an 1607 aggregate is sent, the RA message contents must consistently 1608 represent the combined information advertised by all represented 1609 MSEs. Note that since the AR uses its own OMNI LLA as the RA source 1610 address, the MN determines the addresses of the represented MSEs by 1611 examining the MS-Register/Release OMNI sub-options. 1613 When the MN receives the RA message, it creates an OMNI interface 1614 neighbor cache entry for each MSID that has confirmed MNP 1615 registration via the L2 address of this AR. If the MN connects to 1616 multiple ANETs, it records the additional L2 AR addresses in each 1617 MSID neighbor cache entry (i.e., as multilink neighbors). The MN 1618 then configures a default route via the MSE that returned the RA 1619 message, and assigns the Subnet Router Anycast address corresponding 1620 to the MNP (e.g., 2001:db8:1:2::) to the omni interface. The MN then 1621 manages its underlying interfaces according to their states as 1622 follows: 1624 o When an underlying interface transitions to UP, the MN sends an RS 1625 over the underlying interface with an OMNI option. The OMNI 1626 option contains at least one Interface Attribute sub-option with 1627 values specific to this underlying interface, and may contain 1628 additional Interface Attributes specific to other underlying 1629 interfaces. The option also includes any MS-Register/Release sub- 1630 options. 1632 o When an underlying interface transitions to DOWN, the MN sends an 1633 RS or unsolicited NA message over any UP underlying interface with 1634 an OMNI option containing an Interface Attribute sub-option for 1635 the DOWN underlying interface with Link set to '0'. The MN sends 1636 an RS when an acknowledgement is required, or an unsolicited NA 1637 when reliability is not thought to be a concern (e.g., if 1638 redundant transmissions are sent on multiple underlying 1639 interfaces). 1641 o When the Router Lifetime for a specific AR nears expiration, the 1642 MN sends an RS over the underlying interface to receive a fresh 1643 RA. If no RA is received, the MN can send RS messages to an 1644 alternate MSID in case the current MSID has failed. If no RS 1645 messages are received even after trying to contact alternate 1646 MSIDs, the MN marks the underlying interface as DOWN. 1648 o When a MN wishes to release from one or more current MSIDs, it 1649 sends an RS or unsolicited NA message over any UP underlying 1650 interfaces with an OMNI option with a Release MSID. Each MSID 1651 then withdraws the MNP from the routing/mapping system and informs 1652 the AR that the release was successful. 1654 o When all of a MNs underlying interfaces have transitioned to DOWN 1655 (or if the prefix registration lifetime expires), any associated 1656 MSEs withdraw the MNP the same as if they had received a message 1657 with a release indication. 1659 The MN is responsible for retrying each RS exchange up to 1660 MAX_RTR_SOLICITATIONS times separated by RTR_SOLICITATION_INTERVAL 1661 seconds until an RA is received. If no RA is received over an UP 1662 underlying interface (i.e., even after attempting to contact 1663 alternate MSEs), the MN declares this underlying interface as DOWN. 1665 The IPv6 layer sees the OMNI interface as an ordinary IPv6 interface. 1666 Therefore, when the IPv6 layer sends an RS message the OMNI interface 1667 returns an internally-generated RA message as though the message 1668 originated from an IPv6 router. The internally-generated RA message 1669 contains configuration information that is consistent with the 1670 information received from the RAs generated by the MS. Whether the 1671 OMNI interface IPv6 ND messaging process is initiated from the 1672 receipt of an RS message from the IPv6 layer is an implementation 1673 matter. Some implementations may elect to defer the IPv6 ND 1674 messaging process until an RS is received from the IPv6 layer, while 1675 others may elect to initiate the process proactively. Still other 1676 deployments may elect to administratively disable the ordinary RS/RA 1677 messaging used by the IPv6 layer over the OMNI interface, since they 1678 are not required to drive the internal RS/RA processing. (Note that 1679 this same logic applies to IPv4 implementations that employ ICMP- 1680 based Router Discovery per [RFC1256].) 1682 Note: The Router Lifetime value in RA messages indicates the time 1683 before which the MN must send another RS message over this underlying 1684 interface (e.g., 600 seconds), however that timescale may be 1685 significantly longer than the lifetime the MS has committed to retain 1686 the prefix registration (e.g., REACHABLETIME seconds). ARs are 1687 therefore responsible for keeping MS state alive on a shorter 1688 timescale than the MN is required to do on its own behalf. 1690 Note: On multicast-capable underlying interfaces, MNs should send 1691 periodic unsolicited multicast NA messages and ARs should send 1692 periodic unsolicited multicast RA messages as "beacons" that can be 1693 heard by other nodes on the link. If a node fails to receive a 1694 beacon after a timeout value specific to the link, it can initiate a 1695 unicast exchange to test reachability. 1697 Note: if an AR acting as a proxy forwards a MN's RS message to 1698 another node acting as an MSE using UDP/IP encapsulation, it must use 1699 a distinct UDP source port number for each MN. This allows the MSE 1700 to distinguish different MNs behind the same AR at the link-layer, 1701 whereas the link-layer addresses would otherwise be 1702 indistinguishable. 1704 12.1. Router Discovery in IP Multihop and IPv4-Only Access Networks 1706 On some ANET types a MN may be located multiple IP hops away from the 1707 nearest AR. Forwarding through IP multihop ANETs is conducted 1708 through the application of a routing protocol (e.g., a Mobile Ad-hoc 1709 Network (MANET) routing protocol over omni-directional wireless 1710 interfaces, an inter-domain routing protocol in an enterprise 1711 network, etc.). These ANETs could be either IPv6-enabled or 1712 IPv4-only, while IPv4-only ANETs could be either multicast-capable or 1713 unicast-only (note that for IPv4-only ANETs the following procedures 1714 apply for both single-hop and multihop cases). 1716 A MN located potentially multiple ANET hops away from the nearest AR 1717 prepares an RS message with source address set to either its OMNI MN 1718 LLA or an OMNI Temporary LLA, and with destination set to link-scoped 1719 All-Routers multicast the same as discussed above. For IPv6-enabled 1720 ANETs, the MN then encapsulates the message in an IPv6 header with 1721 source address set to the DLA corresponding to the LLA source address 1722 and with destination set to either a unicast or anycast DLA address 1723 (e.g., [DLA]::). For IPv4-only ANETs, the MN instead encapsulates 1724 the RS message in an IPv4 header with source address set to the 1725 node's own IPv4 address and with destination address set to either 1726 the unicast IPv4 address of an AR [RFC5214] or an IPv4 anycast 1727 address reserved for OMNI. The MN then sends the encapsulated RS 1728 message via the ANET interface, where it will be forwarded by zero or 1729 more intermediate ANET hops. 1731 When an intermediate ANET hop that participates in the routing 1732 protocol receives the encapsulated RS, it forwards the message 1733 according to its routing tables (note that an intermediate node could 1734 be a fixed infrastructure element or another MN). This process 1735 repeats iteratively until the RS message is received by a penultimate 1736 ANET hop within single-hop communications range of an AR, which 1737 forwards the message to the AR. 1739 When the AR receives the message, it decapsulates the RS and 1740 coordinates with the MS the same as for an ordinary link-local RS, 1741 since the inner Hop Limit will not have been decremented by the 1742 multihop forwarding process. The AR then prepares an RA message with 1743 source address set to its own LLA and destination address set to the 1744 LLA of the original MN, then encapsulates the message in an IPv4/IPv6 1745 header with source address set to its own IPv4/DLA address and with 1746 destination set to the encapsulation source of the RS. 1748 The AR then forwards the message to an ANET node within 1749 communications range, which forwards the message according to its 1750 routing tables to an intermediate node. The multihop forwarding 1751 process within the ANET continues repetitively until the message is 1752 delivered to the original MN, which decapsulates the message and 1753 performs autoconfiguration the same as if it had received the RA 1754 directly from the AR as an on-link neighbor. 1756 Note: An alternate approach to multihop forwarding via IPv6 1757 encapsulation would be to statelessly translate the IPv6 LLAs into 1758 DLAs and forward the messages without encapsulation. This would 1759 violate the [RFC4861] requirement that certain IPv6 ND messages must 1760 use link-local addresses and must not be accepted if received with 1761 Hop Limit less than 255. This document therefore advocates 1762 encapsulation since the overhead is nominal considering the 1763 infrequent nature and small size of IPv6 ND messages. Future 1764 documents may consider encapsulation avoidance through translation 1765 while updating [RFC4861]. 1767 Note: An alternate approach to multihop forwarding via IPv4 1768 encapsulation would be to employ IPv6/IPv4 protocol translation. 1769 However, for IPv6 ND messages the OMNI LLA addresses would be 1770 truncated due to translation and the OMNI Router and Prefix Discovery 1771 services would not be able to function. The use of IPv4 1772 encapsulation is therefore indicated. 1774 Note: An IPv4 anycast address for OMNI in IPv4 networks could be part 1775 of a new IPv4 /24 prefix allocation, but this may be difficult to 1776 obtain given IPv4 address exhaustion. An alternative would be to re- 1777 purpose the prefix 192.88.99.0 which has been set aside from its 1778 former use by [RFC7526]. 1780 12.2. MS-Register and MS-Release List Processing 1782 When a MN sends an RS message with an OMNI option via an underlying 1783 interface to an AR, the MN must convey its knowledge of its 1784 currently-associated MSEs. Initially, the MN will have no associated 1785 MSEs and should therefore include an MS-Register sub-option with the 1786 single MSID value 0 which requests the AR to select and assign an 1787 MSE. The AR will then return an RA message with source address set 1788 to the OMNI LLA containing the MSE of the selected MSE. 1790 As the MN activates additional underlying interfaces, it can 1791 optionally include an MS-Register sub-option with MSID value 0, or 1792 with non-zero MSIDs for MSEs discovered from previous RS/RA 1793 exchanges. The MN will thus eventually begin to learn and manage its 1794 currently active set of MSEs, and can register with new MSEs or 1795 release from former MSEs with each successive RS/RA exchange. As the 1796 MN's MSE constituency grows, it alone is responsible for including or 1797 omitting MSIDs in the MS-Register/Release lists it sends in RS 1798 messages. The inclusion or omission of MSIDs determines the MN's 1799 interface to the MS and defines the manner in which MSEs will 1800 respond. The only limiting factor is that the MN should include no 1801 more than MAX_MSID values in each list per each IPv6 ND message, and 1802 should avoid duplication of entries in each list unless it wants to 1803 increase likelihood of control message delivery. 1805 When an AR receives an RS message sent by a MN with an OMNI option, 1806 the option will contain zero or more MS-Register and MS-Release sub- 1807 options containing MSIDs. After processing the OMNI option, the AR 1808 will have a list of zero or more MS-Register MSIDs and a list of zero 1809 or more of MS-Release MSIDs. The AR then processes the lists as 1810 follows: 1812 o For each list, retain the first MAX_MSID values in the list and 1813 discard any additional MSIDs (i.e., even if there are duplicates 1814 within a list). 1816 o Next, for each MSID in the MS-Register list, remove all matching 1817 MSIDs from the MS-Release list. 1819 o Next, proceed according to whether the AR's own MSID or the value 1820 0 appears in the MS-Register list as follows: 1822 * If yes, send an RA message directly back to the MN and send a 1823 proxy copy of the RS message to each additional MSID in the MS- 1824 Register list with the MS-Register/Release lists omitted. 1825 Then, send a uNA message to each MSID in the MS-Release list 1826 with the MS-Register/Release lists omitted and with an OMNI 1827 header with S/T-ifIndex set to 0. 1829 * If no, send a proxy copy of the RS message to each additional 1830 MSID in the MS-Register list with the MS-Register list omitted. 1831 For the first MSID, include the original MS-Release list; for 1832 all other MSIDs, omit the MS-Release list. 1834 Each proxy copy of the RS message will include an OMNI option and 1835 encapsulation header with the DLA of the AR as the source and the DLA 1836 of the Register MSE as the destination. When the Register MSE 1837 receives the proxy RS message, if the message includes an MS-Release 1838 list the MSE sends a uNA message to each additional MSID in the 1839 Release list. The Register MSE then sends an RA message back to the 1840 (Proxy) AR wrapped in an OMNI encapsulation header with source and 1841 destination addresses reversed, and with RA destination set to the 1842 LLA of the MN. When the AR receives this RA message, it sends a 1843 proxy copy of the RA to the MN. 1845 Each uNA message (whether send by the first-hop AR or by a Register 1846 MSE) will include an OMNI option and an encapsulation header with the 1847 DLA of the Register MSE as the source and the DLA of the Release ME 1848 as the destination. The uNA informs the Release MSE that its 1849 previous relationship with the MN has been released and that the 1850 source of the uNA message is now registered. The Release MSE must 1851 then note that the subject MN of the uNA message is now "departed", 1852 and forward any subsequent packets destined to the MN to the Register 1853 MSE. 1855 Note that it is not an error for the MS-Register/Release lists to 1856 include duplicate entries. If duplicates occur within a list, the AR 1857 will generate multiple proxy RS and/or uNA messages - one for each 1858 copy of the duplicate entries. 1860 12.3. DHCPv6-based Prefix Registration 1862 When a MN is not pre-provisioned with an OMNI LLA containing a MNP, 1863 it will need for the AR to select an MNP on its behalf and set up the 1864 correct routing state within the MS. The DHCPv6 service [RFC8415] is 1865 used to support this requirement. 1867 When an MN without a pre-provisioned OMNI MN LLA needs to have the AR 1868 select an MNP, it sends an RS message with source address set to an 1869 OMNI Temporary LLA. The RS message includes an OMNI option with a 1870 DUID suboption that contains a unique DUID value for the MN, and a 1871 Prefix Length value corresponding to the length of MNP it wishes to 1872 receive. 1874 When the AR received the RS message, it notes that the source was a 1875 Temporary LLA and derives the DUID and Prefix Length from the OMNI 1876 option. The AR (acting as a "proxy DHCP client") then crafts a well- 1877 formed DHCPv6 Solicit message with Prefix Delegation (PD) parameters, 1878 and forwards the message to a locally-resident DHCPv6 server. The 1879 DHCPv6 server then delegates an MNP and returns a DHCPv6 Reply 1880 message with PD parameters. (Note: the Solicit message should 1881 contain enough identifying information for the MN so that the AR can 1882 correlate the server's Reply with the original Solicit.) 1884 When the AR receives the DHCPv6 Reply, it adds a route to the routing 1885 system and creates an OMNI MN LLA based on the delegated MNP. The AR 1886 then sends an RA back to the MN with the (newly-created) OMNI MN LLA 1887 as the destination address and with Prefix Length set in the OMNI 1888 option. When the MN receives the RA, it creates a default route, 1889 assigns the Subnet Router Anycast addresss and sets its OMNI LLA 1890 based on the delegated MNP. 1892 13. Secure Redirection 1894 If the ANET link model is multiple access, the AR is responsible for 1895 assuring that address duplication cannot corrupt the neighbor caches 1896 of other nodes on the link. When the MN sends an RS message on a 1897 multiple access ANET link, the AR verifies that the MN is authorized 1898 to use the address and returns an RA with a non-zero Router Lifetime 1899 only if the MN is authorized. 1901 After verifying MN authorization and returning an RA, the AR MAY 1902 return IPv6 ND Redirect messages to direct MNs located on the same 1903 ANET link to exchange packets directly without transiting the AR. In 1904 that case, the MNs can exchange packets according to their unicast L2 1905 addresses discovered from the Redirect message instead of using the 1906 dogleg path through the AR. In some ANET links, however, such direct 1907 communications may be undesirable and continued use of the dogleg 1908 path through the AR may provide better performance. In that case, 1909 the AR can refrain from sending Redirects, and/or MNs can ignore 1910 them. 1912 14. AR and MSE Resilience 1914 ANETs SHOULD deploy ARs in Virtual Router Redundancy Protocol (VRRP) 1915 [RFC5798] configurations so that service continuity is maintained 1916 even if one or more ARs fail. Using VRRP, the MN is unaware which of 1917 the (redundant) ARs is currently providing service, and any service 1918 discontinuity will be limited to the failover time supported by VRRP. 1919 Widely deployed public domain implementations of VRRP are available. 1921 MSEs SHOULD use high availability clustering services so that 1922 multiple redundant systems can provide coordinated response to 1923 failures. As with VRRP, widely deployed public domain 1924 implementations of high availability clustering services are 1925 available. Note that special-purpose and expensive dedicated 1926 hardware is not necessary, and public domain implementations can be 1927 used even between lightweight virtual machines in cloud deployments. 1929 15. Detecting and Responding to MSE Failures 1931 In environments where fast recovery from MSE failure is required, ARs 1932 SHOULD use proactive Neighbor Unreachability Detection (NUD) in a 1933 manner that parallels Bidirectional Forwarding Detection (BFD) 1934 [RFC5880] to track MSE reachability. ARs can then quickly detect and 1935 react to failures so that cached information is re-established 1936 through alternate paths. Proactive NUD control messaging is carried 1937 only over well-connected ground domain networks (i.e., and not low- 1938 end ANET links such as aeronautical radios) and can therefore be 1939 tuned for rapid response. 1941 ARs perform proactive NUD for MSEs for which there are currently 1942 active MNs on the ANET. If an MSE fails, ARs can quickly inform MNs 1943 of the outage by sending multicast RA messages on the ANET interface. 1944 The AR sends RA messages to MNs via the ANET interface with an OMNI 1945 option with a Release ID for the failed MSE, and with destination 1946 address set to All-Nodes multicast (ff02::1) [RFC4291]. 1948 The AR SHOULD send MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated 1949 by small delays [RFC4861]. Any MNs on the ANET interface that have 1950 been using the (now defunct) MSE will receive the RA messages and 1951 associate with a new MSE. 1953 16. Transition Considerations 1955 When a MN connects to an ANET link for the first time, it sends an RS 1956 message with an OMNI option. If the first hop AR recognizes the 1957 option, it returns an RA with its MS OMNI LLA as the source, the MN 1958 OMNI LLA as the destination and with an OMNI option included. The MN 1959 then engages the AR according to the OMNI link model specified above. 1960 If the first hop AR is a legacy IPv6 router, however, it instead 1961 returns an RA message with no OMNI option and with a non-OMNI unicast 1962 source LLA as specified in [RFC4861]. In that case, the MN engages 1963 the ANET according to the legacy IPv6 link model and without the OMNI 1964 extensions specified in this document. 1966 If the ANET link model is multiple access, there must be assurance 1967 that address duplication cannot corrupt the neighbor caches of other 1968 nodes on the link. When the MN sends an RS message on a multiple 1969 access ANET link with an OMNI LLA source address and an OMNI option, 1970 ARs that recognize the option ensure that the MN is authorized to use 1971 the address and return an RA with a non-zero Router Lifetime only if 1972 the MN is authorized. ARs that do not recognize the option instead 1973 return an RA that makes no statement about the MN's authorization to 1974 use the source address. In that case, the MN should perform 1975 Duplicate Address Detection to ensure that it does not interfere with 1976 other nodes on the link. 1978 An alternative approach for multiple access ANET links to ensure 1979 isolation for MN / AR communications is through L2 address mappings 1980 as discussed in Appendix C. This arrangement imparts a (virtual) 1981 point-to-point link model over the (physical) multiple access link. 1983 17. OMNI Interfaces on the Open Internet 1985 OMNI interfaces configured over IPv6-enabled underlying interfaces on 1986 the open Internet without an OMNI-aware first-hop AR receive RA 1987 messages that do not include an OMNI option, while OMNI interfaces 1988 configured over IPv4-only underlying interfaces do not receive any 1989 (IPv6) RA messages at all. OMNI interfaces that receive RA messages 1990 without an OMNI option configure addresses, on-link prefixes, etc. on 1991 the underlying interface that received the RA according to standard 1992 IPv6 ND and address resolution conventions [RFC4861] [RFC4862]. OMNI 1993 interfaces configured over IPv4-only underlying interfaces configure 1994 IPv4 address information on the underlying interfaces using 1995 mechanisms such as DHCPv4 [RFC2131]. 1997 OMNI interfaces configured over underlying interfaces that connect to 1998 the open Internet can apply security services such as VPNs to connect 1999 to an MSE or establish a direct link to an MSE through some other 2000 means (see Section 4). In environments where an explicit VPN or 2001 direct link may be impractical, OMNI interfaces can instead use UDP/ 2002 IP encapsulation per [RFC6081][RFC4380]. (SEcure Neighbor Discovery 2003 (SEND) and Cryptographically Generated Addresses (CGA) 2004 [RFC3971][RFC3972] or other protocol-specific security services can 2005 also be used if additional authentication is necessary.) 2007 After establishing a VPN or preparing for UDP/IP encapsulation, OMNI 2008 interfaces send control plane messages to interface with the MS, 2009 including Neighbor Solcitation (NS) and Neighbor Advertisment (NA) 2010 messages used for address resolution / route optimization (see: 2011 [I-D.templin-intarea-6706bis]). The control plane messages must be 2012 authenticated while data plane messages are delivered the same as for 2013 ordinary best-effort Internet traffic with basic source address-based 2014 data origin verification. Data plane communications via OMNI 2015 interfaces that connect over the open Internet without an explicit 2016 VPN should therefore employ transport- or higher-layer security to 2017 ensure integrity and/or confidentiality. 2019 When SEND/CGA are used over an open Internet underlying interfaces, 2020 each OMNI node configures an OMNI CGA LLA for use as the source 2021 address of IPv6 ND messages. The node then employs OAL encapsulation 2022 and sets the IPv6 source address of the OAL header to the DLA 2023 corresponding to its OMNI LLA. Any Prefix Length values in the IPv6 2024 ND message OMNI option then apply to the DLA found in the OMNI 2025 header, i.e., and not to the CGA found in the IPv6 ND message source 2026 address. 2028 OMNI interfaces in the open Internet are often located behind Network 2029 Address Translators (NATs). The OMNI interface accommodates NAT 2030 traversal using UDP/IP encapsulation and the mechanisms discussed in 2031 [RFC6081][RFC4380][I-D.templin-intarea-6706bis]. 2033 18. Time-Varying MNPs 2035 In some use cases, it is desirable, beneficial and efficient for the 2036 MN to receive a constant MNP that travels with the MN wherever it 2037 moves. For example, this would allow air traffic controllers to 2038 easily track aircraft, etc. In other cases, however (e.g., 2039 intelligent transportation systems), the MN may be willing to 2040 sacrifice a modicum of efficiency in order to have time-varying MNPs 2041 that can be changed every so often to defeat adversarial tracking. 2043 The prefix delegation services discussed in Section 12.3 allows OMNI 2044 MNs that desire time-varying MNPs to obtain short-lived prefixes to 2045 use an OMNI Temporary LLA as the source address of an RS message with 2046 an OMNI option with a DHCPv6 Device Unique IDentifier (DUID) 2047 [RFC8415] sub-option. The MN would then be obligated to renumber its 2048 internal networks whenever its MNP (and therefore also its OMNI 2049 address) changes. This should not present a challenge for MNs with 2050 automated network renumbering services, however presents limits for 2051 the durations of ongoing sessions that would prefer to use a constant 2052 address. 2054 19. IANA Considerations 2056 The IANA is instructed to allocate an official Type number TBD from 2057 the registry "IPv6 Neighbor Discovery Option Formats" for the OMNI 2058 option. Implementations set Type to 253 as an interim value 2059 [RFC4727]. 2061 The IANA is instructed to assign a new Code value "1" in the "ICMPv6 2062 Code Fields: Type 2 - Packet Too Big" registry. The registry should 2063 read as follows: 2065 Code Name Reference 2066 --- ---- --------- 2067 0 Diagnostic Packet Too Big [RFC4443] 2068 1 Advisory Packet Too Big [RFCXXXX] 2070 Figure 16: OMNI Option Sub-Type Values 2072 The IANA is instructed to allocate one Ethernet unicast address TBD2 2073 (suggest 00-00-5E-00-52-14 [RFC5214]) in the registry "IANA Ethernet 2074 Address Block - Unicast Use". 2076 The OMNI option also defines an 8-bit Sub-Type field, for which IANA 2077 is instructed to create and maintain a new registry entitled "OMNI 2078 option Sub-Type values". Initial values for the OMNI option Sub-Type 2079 values registry are given below; future assignments are to be made 2080 through Expert Review [RFC8126]. 2082 Value Sub-Type name Reference 2083 ----- ------------- ---------- 2084 0 Pad1 [RFCXXXX] 2085 1 PadN [RFCXXXX] 2086 2 Interface Attributes [RFCXXXX] 2087 3 Traffic Selector [RFCXXXX] 2088 4 MS-Register [RFCXXXX] 2089 5 MS-Release [RFCXXXX] 2090 6 Network Access Identifier [RFCXXXX] 2091 7 Geo Coordinates [RFCXXXX] 2092 8 DHCP Unique Identifier (DUID) [RFCXXXX] 2093 9-252 Unassigned 2094 253-254 Experimental [RFCXXXX] 2095 255 Reserved [RFCXXXX] 2097 Figure 17: OMNI Option Sub-Type Values 2099 20. Security Considerations 2101 Security considerations for IPv4 [RFC0791], IPv6 [RFC8200] and IPv6 2102 Neighbor Discovery [RFC4861] apply. OMNI interface IPv6 ND messages 2103 SHOULD include Nonce and Timestamp options [RFC3971] when transaction 2104 confirmation and/or time synchronization is needed. 2106 OMNI interfaces configured over secured ANET interfaces inherit the 2107 physical and/or link-layer security properties of the connected 2108 ANETs. OMNI interfaces configured over open INET interfaces can use 2109 symmetric securing services such as VPNs or can by some other means 2110 establish a direct link. When a VPN or direct link may be 2111 impractical, however, an asymmetric security service such as SEcure 2112 Neighbor Discovery (SEND) [RFC3971] with Cryptographically Generated 2113 Addresses (CGAs) [RFC3972], the authentication option specified in 2114 [RFC4380] or other protocol control message security mechanisms may 2115 be necessary. While the OMNI link protects control plane messaging, 2116 applications must still employ end-to-end transport- or higher-layer 2117 security services to protect the data plane. 2119 The Mobility Service MUST provide strong network layer security for 2120 control plane messages and forwarding path integrity for data plane 2121 messages. In one example, the AERO service 2122 [I-D.templin-intarea-6706bis] constructs a spanning tree between 2123 mobility service elements and secures the links in the spanning tree 2124 with network layer security mechanisms such as IPsec [RFC4301] or 2125 Wireguard. Control plane messages are then constrained to travel 2126 only over the secured spanning tree paths and are therefore protected 2127 from attack or eavesdropping. Since data plane messages can travel 2128 over route optimized paths that do not strictly follow the spanning 2129 tree, however, end-to-end transport- or higher-layer security 2130 services are still required. 2132 Security considerations for specific access network interface types 2133 are covered under the corresponding IP-over-(foo) specification 2134 (e.g., [RFC2464], [RFC2492], etc.). 2136 Security considerations for IPv6 fragmentation and reassembly are 2137 discussed in Section 5.1. 2139 21. Implementation Status 2141 Draft -29 is implemented in the recently tagged AERO/OMNI 3.0.0 2142 internal release, and Draft -30 is now tagged as the AERO/OMNI 3.0.1. 2143 Newer specification versions will be tagged in upcoming releases. 2144 First public release expected before the end of 2020. 2146 22. Acknowledgements 2148 The first version of this document was prepared per the consensus 2149 decision at the 7th Conference of the International Civil Aviation 2150 Organization (ICAO) Working Group-I Mobility Subgroup on March 22, 2151 2019. Consensus to take the document forward to the IETF was reached 2152 at the 9th Conference of the Mobility Subgroup on November 22, 2019. 2153 Attendees and contributors included: Guray Acar, Danny Bharj, 2154 Francois D'Humieres, Pavel Drasil, Nikos Fistas, Giovanni Garofolo, 2155 Bernhard Haindl, Vaughn Maiolla, Tom McParland, Victor Moreno, Madhu 2156 Niraula, Brent Phillips, Liviu Popescu, Jacky Pouzet, Aloke Roy, Greg 2157 Saccone, Robert Segers, Michal Skorepa, Michel Solery, Stephane 2158 Tamalet, Fred Templin, Jean-Marc Vacher, Bela Varkonyi, Tony Whyman, 2159 Fryderyk Wrobel and Dongsong Zeng. 2161 The following individuals are acknowledged for their useful comments: 2162 Michael Matyas, Madhu Niraula, Michael Richardson, Greg Saccone, 2163 Stephane Tamalet, Eric Vyncke. Pavel Drasil, Zdenek Jaron and Michal 2164 Skorepa are recognized for their many helpful ideas and suggestions. 2165 Madhuri Madhava Badgandi, Katherine Tran, and Vijayasarathy 2166 Rajagopalan are acknowledged for their hard work on the 2167 implementation and insights that led to improvements to the spec. 2169 Discussions on the IETF 6man and atn mailing lists during the fall of 2170 2020 suggested additional points to consider. The authors gratefully 2171 acknowledge the list members who contributed valuable insights 2172 through those discussions. 2174 This work is aligned with the NASA Safe Autonomous Systems Operation 2175 (SASO) program under NASA contract number NNA16BD84C. 2177 This work is aligned with the FAA as per the SE2025 contract number 2178 DTFAWA-15-D-00030. 2180 23. References 2182 23.1. Normative References 2184 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 2185 DOI 10.17487/RFC0791, September 1981, 2186 . 2188 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 2189 Requirement Levels", BCP 14, RFC 2119, 2190 DOI 10.17487/RFC2119, March 1997, 2191 . 2193 [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, 2194 "Definition of the Differentiated Services Field (DS 2195 Field) in the IPv4 and IPv6 Headers", RFC 2474, 2196 DOI 10.17487/RFC2474, December 1998, 2197 . 2199 [RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander, 2200 "SEcure Neighbor Discovery (SEND)", RFC 3971, 2201 DOI 10.17487/RFC3971, March 2005, 2202 . 2204 [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)", 2205 RFC 3972, DOI 10.17487/RFC3972, March 2005, 2206 . 2208 [RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and 2209 More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191, 2210 November 2005, . 2212 [RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast 2213 Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005, 2214 . 2216 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 2217 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 2218 2006, . 2220 [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet 2221 Control Message Protocol (ICMPv6) for the Internet 2222 Protocol Version 6 (IPv6) Specification", STD 89, 2223 RFC 4443, DOI 10.17487/RFC4443, March 2006, 2224 . 2226 [RFC4727] Fenner, B., "Experimental Values In IPv4, IPv6, ICMPv4, 2227 ICMPv6, UDP, and TCP Headers", RFC 4727, 2228 DOI 10.17487/RFC4727, November 2006, 2229 . 2231 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 2232 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 2233 DOI 10.17487/RFC4861, September 2007, 2234 . 2236 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 2237 Address Autoconfiguration", RFC 4862, 2238 DOI 10.17487/RFC4862, September 2007, 2239 . 2241 [RFC6088] Tsirtsis, G., Giarreta, G., Soliman, H., and N. Montavont, 2242 "Traffic Selectors for Flow Bindings", RFC 6088, 2243 DOI 10.17487/RFC6088, January 2011, 2244 . 2246 [RFC8028] Baker, F. and B. Carpenter, "First-Hop Router Selection by 2247 Hosts in a Multi-Prefix Network", RFC 8028, 2248 DOI 10.17487/RFC8028, November 2016, 2249 . 2251 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2252 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2253 May 2017, . 2255 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 2256 (IPv6) Specification", STD 86, RFC 8200, 2257 DOI 10.17487/RFC8200, July 2017, 2258 . 2260 [RFC8201] McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed., 2261 "Path MTU Discovery for IP version 6", STD 87, RFC 8201, 2262 DOI 10.17487/RFC8201, July 2017, 2263 . 2265 [RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A., 2266 Richardson, M., Jiang, S., Lemon, T., and T. Winters, 2267 "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", 2268 RFC 8415, DOI 10.17487/RFC8415, November 2018, 2269 . 2271 23.2. Informative References 2273 [ATN] Maiolla, V., "The OMNI Interface - An IPv6 Air/Ground 2274 Interface for Civil Aviation, IETF Liaison Statement 2275 #1676, https://datatracker.ietf.org/liaison/1676/", March 2276 2020. 2278 [CRC] Jain, R., "Error Characteristics of Fiber Distributed Data 2279 Interface (FDDI), IEEE Transactions on Communications", 2280 August 1990. 2282 [I-D.ietf-6man-rfc4941bis] 2283 Gont, F., Krishnan, S., Narten, T., and R. Draves, 2284 "Temporary Address Extensions for Stateless Address 2285 Autoconfiguration in IPv6", draft-ietf-6man-rfc4941bis-11 2286 (work in progress), September 2020. 2288 [I-D.ietf-intarea-tunnels] 2289 Touch, J. and M. Townsley, "IP Tunnels in the Internet 2290 Architecture", draft-ietf-intarea-tunnels-10 (work in 2291 progress), September 2019. 2293 [I-D.ietf-ipwave-vehicular-networking] 2294 Jeong, J., "IPv6 Wireless Access in Vehicular Environments 2295 (IPWAVE): Problem Statement and Use Cases", draft-ietf- 2296 ipwave-vehicular-networking-19 (work in progress), July 2297 2020. 2299 [I-D.templin-6man-dhcpv6-ndopt] 2300 Templin, F., "A Unified Stateful/Stateless Configuration 2301 Service for IPv6", draft-templin-6man-dhcpv6-ndopt-10 2302 (work in progress), June 2020. 2304 [I-D.templin-intarea-6706bis] 2305 Templin, F., "Asymmetric Extended Route Optimization 2306 (AERO)", draft-templin-intarea-6706bis-66 (work in 2307 progress), October 2020. 2309 [RFC1122] Braden, R., Ed., "Requirements for Internet Hosts - 2310 Communication Layers", STD 3, RFC 1122, 2311 DOI 10.17487/RFC1122, October 1989, 2312 . 2314 [RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191, 2315 DOI 10.17487/RFC1191, November 1990, 2316 . 2318 [RFC1256] Deering, S., Ed., "ICMP Router Discovery Messages", 2319 RFC 1256, DOI 10.17487/RFC1256, September 1991, 2320 . 2322 [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", 2323 RFC 2131, DOI 10.17487/RFC2131, March 1997, 2324 . 2326 [RFC2225] Laubach, M. and J. Halpern, "Classical IP and ARP over 2327 ATM", RFC 2225, DOI 10.17487/RFC2225, April 1998, 2328 . 2330 [RFC2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet 2331 Networks", RFC 2464, DOI 10.17487/RFC2464, December 1998, 2332 . 2334 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 2335 IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473, 2336 December 1998, . 2338 [RFC2492] Armitage, G., Schulter, P., and M. Jork, "IPv6 over ATM 2339 Networks", RFC 2492, DOI 10.17487/RFC2492, January 1999, 2340 . 2342 [RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4 2343 Domains without Explicit Tunnels", RFC 2529, 2344 DOI 10.17487/RFC2529, March 1999, 2345 . 2347 [RFC2863] McCloghrie, K. and F. Kastenholz, "The Interfaces Group 2348 MIB", RFC 2863, DOI 10.17487/RFC2863, June 2000, 2349 . 2351 [RFC3692] Narten, T., "Assigning Experimental and Testing Numbers 2352 Considered Useful", BCP 82, RFC 3692, 2353 DOI 10.17487/RFC3692, January 2004, 2354 . 2356 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 2357 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 2358 DOI 10.17487/RFC3810, June 2004, 2359 . 2361 [RFC3819] Karn, P., Ed., Bormann, C., Fairhurst, G., Grossman, D., 2362 Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L. 2363 Wood, "Advice for Internet Subnetwork Designers", BCP 89, 2364 RFC 3819, DOI 10.17487/RFC3819, July 2004, 2365 . 2367 [RFC3879] Huitema, C. and B. Carpenter, "Deprecating Site Local 2368 Addresses", RFC 3879, DOI 10.17487/RFC3879, September 2369 2004, . 2371 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 2372 Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, 2373 December 2005, . 2375 [RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through 2376 Network Address Translations (NATs)", RFC 4380, 2377 DOI 10.17487/RFC4380, February 2006, 2378 . 2380 [RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery 2381 Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April 2382 2006, . 2384 [RFC4429] Moore, N., "Optimistic Duplicate Address Detection (DAD) 2385 for IPv6", RFC 4429, DOI 10.17487/RFC4429, April 2006, 2386 . 2388 [RFC4541] Christensen, M., Kimball, K., and F. Solensky, 2389 "Considerations for Internet Group Management Protocol 2390 (IGMP) and Multicast Listener Discovery (MLD) Snooping 2391 Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006, 2392 . 2394 [RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick, 2395 "Internet Group Management Protocol (IGMP) / Multicast 2396 Listener Discovery (MLD)-Based Multicast Forwarding 2397 ("IGMP/MLD Proxying")", RFC 4605, DOI 10.17487/RFC4605, 2398 August 2006, . 2400 [RFC4821] Mathis, M. and J. Heffner, "Packetization Layer Path MTU 2401 Discovery", RFC 4821, DOI 10.17487/RFC4821, March 2007, 2402 . 2404 [RFC4963] Heffner, J., Mathis, M., and B. Chandler, "IPv4 Reassembly 2405 Errors at High Data Rates", RFC 4963, 2406 DOI 10.17487/RFC4963, July 2007, 2407 . 2409 [RFC5175] Haberman, B., Ed. and R. Hinden, "IPv6 Router 2410 Advertisement Flags Option", RFC 5175, 2411 DOI 10.17487/RFC5175, March 2008, 2412 . 2414 [RFC5213] Gundavelli, S., Ed., Leung, K., Devarapalli, V., 2415 Chowdhury, K., and B. Patil, "Proxy Mobile IPv6", 2416 RFC 5213, DOI 10.17487/RFC5213, August 2008, 2417 . 2419 [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site 2420 Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, 2421 DOI 10.17487/RFC5214, March 2008, 2422 . 2424 [RFC5558] Templin, F., Ed., "Virtual Enterprise Traversal (VET)", 2425 RFC 5558, DOI 10.17487/RFC5558, February 2010, 2426 . 2428 [RFC5798] Nadas, S., Ed., "Virtual Router Redundancy Protocol (VRRP) 2429 Version 3 for IPv4 and IPv6", RFC 5798, 2430 DOI 10.17487/RFC5798, March 2010, 2431 . 2433 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 2434 (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, 2435 . 2437 [RFC6081] Thaler, D., "Teredo Extensions", RFC 6081, 2438 DOI 10.17487/RFC6081, January 2011, 2439 . 2441 [RFC6221] Miles, D., Ed., Ooghe, S., Dec, W., Krishnan, S., and A. 2442 Kavanagh, "Lightweight DHCPv6 Relay Agent", RFC 6221, 2443 DOI 10.17487/RFC6221, May 2011, 2444 . 2446 [RFC6355] Narten, T. and J. Johnson, "Definition of the UUID-Based 2447 DHCPv6 Unique Identifier (DUID-UUID)", RFC 6355, 2448 DOI 10.17487/RFC6355, August 2011, 2449 . 2451 [RFC6543] Gundavelli, S., "Reserved IPv6 Interface Identifier for 2452 Proxy Mobile IPv6", RFC 6543, DOI 10.17487/RFC6543, May 2453 2012, . 2455 [RFC7084] Singh, H., Beebee, W., Donley, C., and B. Stark, "Basic 2456 Requirements for IPv6 Customer Edge Routers", RFC 7084, 2457 DOI 10.17487/RFC7084, November 2013, 2458 . 2460 [RFC7421] Carpenter, B., Ed., Chown, T., Gont, F., Jiang, S., 2461 Petrescu, A., and A. Yourtchenko, "Analysis of the 64-bit 2462 Boundary in IPv6 Addressing", RFC 7421, 2463 DOI 10.17487/RFC7421, January 2015, 2464 . 2466 [RFC7526] Troan, O. and B. Carpenter, Ed., "Deprecating the Anycast 2467 Prefix for 6to4 Relay Routers", BCP 196, RFC 7526, 2468 DOI 10.17487/RFC7526, May 2015, 2469 . 2471 [RFC7542] DeKok, A., "The Network Access Identifier", RFC 7542, 2472 DOI 10.17487/RFC7542, May 2015, 2473 . 2475 [RFC7739] Gont, F., "Security Implications of Predictable Fragment 2476 Identification Values", RFC 7739, DOI 10.17487/RFC7739, 2477 February 2016, . 2479 [RFC7847] Melia, T., Ed. and S. Gundavelli, Ed., "Logical-Interface 2480 Support for IP Hosts with Multi-Access Support", RFC 7847, 2481 DOI 10.17487/RFC7847, May 2016, 2482 . 2484 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 2485 Writing an IANA Considerations Section in RFCs", BCP 26, 2486 RFC 8126, DOI 10.17487/RFC8126, June 2017, 2487 . 2489 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 2490 Decraene, B., Litkowski, S., and R. Shakir, "Segment 2491 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 2492 July 2018, . 2494 [RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J., 2495 Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header 2496 (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020, 2497 . 2499 [RFC8900] Bonica, R., Baker, F., Huston, G., Hinden, R., Troan, O., 2500 and F. Gont, "IP Fragmentation Considered Fragile", 2501 BCP 230, RFC 8900, DOI 10.17487/RFC8900, September 2020, 2502 . 2504 Appendix A. Interface Attribute Preferences Bitmap Encoding 2506 Adaptation of the OMNI option Interface Attributes Preferences Bitmap 2507 encoding to specific Internetworks such as the Aeronautical 2508 Telecommunications Network with Internet Protocol Services (ATN/IPS) 2509 may include link selection preferences based on other traffic 2510 classifiers (e.g., transport port numbers, etc.) in addition to the 2511 existing DSCP-based preferences. Nodes on specific Internetworks 2512 maintain a map of traffic classifiers to additional P[*] preference 2513 fields beyond the first 64. For example, TCP port 22 maps to P[67], 2514 TCP port 443 maps to P[70], UDP port 8060 maps to P[76], etc. 2516 Implementations use Simplex or Indexed encoding formats for P[*] 2517 encoding in order to encode a given set of traffic classifiers in the 2518 most efficient way. Some use cases may be more efficiently coded 2519 using Simplex form, while others may be more efficient using Indexed. 2520 Once a format is selected for preparation of a single Interface 2521 Attribute the same format must be used for the entire Interface 2522 Attribute sub-option. Different sub-options may use different 2523 formats. 2525 The following figures show coding examples for various Simplex and 2526 Indexed formats: 2528 0 1 2 3 2529 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 2530 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2531 | Sub-Type=2 | Sub-length=N | ifIndex | ifType | 2532 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2533 | Provider ID | Link |R| APS | Bitmap(0)=0xff|P00|P01|P02|P03| 2534 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2535 |P04|P05|P06|P07|P08|P09|P10|P11|P12|P13|P14|P15|P16|P17|P18|P19| 2536 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2537 |P20|P21|P22|P23|P24|P25|P26|P27|P28|P29|P30|P31| Bitmap(1)=0xff| 2538 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2539 |P32|P33|P34|P35|P36|P37|P38|P39|P40|P41|P42|P43|P44|P45|P46|P47| 2540 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2541 |P48|P49|P50|P51|P52|P53|P54|P55|P56|P57|P58|P59|P60|P61|P62|P63| 2542 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2543 | Bitmap(2)=0xff|P64|P65|P67|P68| ... 2544 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 2546 Figure 18: Example 1: Dense Simplex Encoding 2548 0 1 2 3 2549 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 2550 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2551 | Sub-Type=2 | Sub-length=N | ifIndex | ifType | 2552 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2553 | Provider ID | Link |R| APS | Bitmap(0)=0x00| Bitmap(1)=0x0f| 2554 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2555 |P48|P49|P50|P51|P52|P53|P54|P55|P56|P57|P58|P59|P60|P61|P62|P63| 2556 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2557 | Bitmap(2)=0x00| Bitmap(3)=0x00| Bitmap(4)=0x00| Bitmap(5)=0x00| 2558 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2559 | Bitmap(6)=0xf0|192|193|194|195|196|197|198|199|200|201|202|203| 2560 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2561 |204|205|206|207| Bitmap(7)=0x00| Bitmap(8)=0x0f|272|273|274|275| 2562 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2563 |276|277|278|279|280|281|282|283|284|285|286|287| Bitmap(9)=0x00| 2564 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2565 |Bitmap(10)=0x00| ... 2566 +-+-+-+-+-+-+-+-+-+-+- 2568 Figure 19: Example 2: Sparse Simplex Encoding 2570 0 1 2 3 2571 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 2572 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2573 | Sub-Type=2 | Sub-length=N | ifIndex | ifType | 2574 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2575 | Provider ID | Link |R| APS | Index = 0x00 | Bitmap = 0x80 | 2576 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2577 |P00|P01|P02|P03| Index = 0x01 | Bitmap = 0x01 |P60|P61|P62|P63| 2578 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2579 | Index = 0x10 | Bitmap = 0x80 |512|513|514|515| Index = 0x18 | 2580 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2581 | Bitmap = 0x01 |796|797|798|799| ... 2582 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 2584 Figure 20: Example 3: Indexed Encoding 2586 Appendix B. VDL Mode 2 Considerations 2588 ICAO Doc 9776 is the "Technical Manual for VHF Data Link Mode 2" 2589 (VDLM2) that specifies an essential radio frequency data link service 2590 for aircraft and ground stations in worldwide civil aviation air 2591 traffic management. The VDLM2 link type is "multicast capable" 2592 [RFC4861], but with considerable differences from common multicast 2593 links such as Ethernet and IEEE 802.11. 2595 First, the VDLM2 link data rate is only 31.5Kbps - multiple orders of 2596 magnitude less than most modern wireless networking gear. Second, 2597 due to the low available link bandwidth only VDLM2 ground stations 2598 (i.e., and not aircraft) are permitted to send broadcasts, and even 2599 so only as compact layer 2 "beacons". Third, aircraft employ the 2600 services of ground stations by performing unicast RS/RA exchanges 2601 upon receipt of beacons instead of listening for multicast RA 2602 messages and/or sending multicast RS messages. 2604 This beacon-oriented unicast RS/RA approach is necessary to conserve 2605 the already-scarce available link bandwidth. Moreover, since the 2606 numbers of beaconing ground stations operating within a given spatial 2607 range must be kept as sparse as possible, it would not be feasible to 2608 have different classes of ground stations within the same region 2609 observing different protocols. It is therefore highly desirable that 2610 all ground stations observe a common language of RS/RA as specified 2611 in this document. 2613 Note that links of this nature may benefit from compression 2614 techniques that reduce the bandwidth necessary for conveying the same 2615 amount of data. The IETF lpwan working group is considering possible 2616 alternatives: [https://datatracker.ietf.org/wg/lpwan/documents]. 2618 Appendix C. MN / AR Isolation Through L2 Address Mapping 2620 Per [RFC4861], IPv6 ND messages may be sent to either a multicast or 2621 unicast link-scoped IPv6 destination address. However, IPv6 ND 2622 messaging should be coordinated between the MN and AR only without 2623 invoking other nodes on the ANET. This implies that MN / AR control 2624 messaging should be isolated and not overheard by other nodes on the 2625 link. 2627 To support MN / AR isolation on some ANET links, ARs can maintain an 2628 OMNI-specific unicast L2 address ("MSADDR"). For Ethernet-compatible 2629 ANETs, this specification reserves one Ethernet unicast address TBD2 2630 (see: Section 19). For non-Ethernet statically-addressed ANETs, 2631 MSADDR is reserved per the assigned numbers authority for the ANET 2632 addressing space. For still other ANETs, MSADDR may be dynamically 2633 discovered through other means, e.g., L2 beacons. 2635 MNs map the L3 addresses of all IPv6 ND messages they send (i.e., 2636 both multicast and unicast) to MSADDR instead of to an ordinary 2637 unicast or multicast L2 address. In this way, all of the MN's IPv6 2638 ND messages will be received by ARs that are configured to accept 2639 packets destined to MSADDR. Note that multiple ARs on the link could 2640 be configured to accept packets destined to MSADDR, e.g., as a basis 2641 for supporting redundancy. 2643 Therefore, ARs must accept and process packets destined to MSADDR, 2644 while all other devices must not process packets destined to MSADDR. 2645 This model has well-established operational experience in Proxy 2646 Mobile IPv6 (PMIP) [RFC5213][RFC6543]. 2648 Appendix D. Change Log 2650 << RFC Editor - remove prior to publication >> 2652 Differences from draft-templin-6man-omni-interface-35 to draft- 2653 templin-6man-omni-interface-36: 2655 o Major clarifications on aspects such as "hard/soft" PTB error 2656 messages 2658 o Made generic so that either IP protocol version (IPv4 or IPv6) can 2659 be used in the data plane. 2661 Differences from draft-templin-6man-omni-interface-31 to draft- 2662 templin-6man-omni-interface-32: 2664 o MTU 2666 o Support for multi-hop ANETS such as ISATAP. 2668 Differences from draft-templin-6man-omni-interface-29 to draft- 2669 templin-6man-omni-interface-30: 2671 o Moved link-layer addressing information into the OMNI option on a 2672 per-ifIndex basis 2674 o Renamed "ifIndex-tuple" to "Interface Attributes" 2676 Differences from draft-templin-6man-omni-interface-27 to draft- 2677 templin-6man-omni-interface-28: 2679 o Updates based on implementation expereince. 2681 Differences from draft-templin-6man-omni-interface-25 to draft- 2682 templin-6man-omni-interface-26: 2684 o Further clarification on "aggregate" RA messages. 2686 o Expanded Security Considerations to discuss expectations for 2687 security in the Mobility Service. 2689 Differences from draft-templin-6man-omni-interface-20 to draft- 2690 templin-6man-omni-interface-21: 2692 o Safety-Based Multilink (SBM) and Performance-Based Multilink 2693 (PBM). 2695 Differences from draft-templin-6man-omni-interface-18 to draft- 2696 templin-6man-omni-interface-19: 2698 o SEND/CGA. 2700 Differences from draft-templin-6man-omni-interface-17 to draft- 2701 templin-6man-omni-interface-18: 2703 o Teredo 2705 Differences from draft-templin-6man-omni-interface-14 to draft- 2706 templin-6man-omni-interface-15: 2708 o Prefix length discussions removed. 2710 Differences from draft-templin-6man-omni-interface-12 to draft- 2711 templin-6man-omni-interface-13: 2713 o Teredo 2715 Differences from draft-templin-6man-omni-interface-11 to draft- 2716 templin-6man-omni-interface-12: 2718 o Major simplifications and clarifications on MTU and fragmentation. 2720 o Document now updates RFC4443 and RFC8201. 2722 Differences from draft-templin-6man-omni-interface-10 to draft- 2723 templin-6man-omni-interface-11: 2725 o Removed /64 assumption, resulting in new OMNI address format. 2727 Differences from draft-templin-6man-omni-interface-07 to draft- 2728 templin-6man-omni-interface-08: 2730 o OMNI MNs in the open Internet 2732 Differences from draft-templin-6man-omni-interface-06 to draft- 2733 templin-6man-omni-interface-07: 2735 o Brought back L2 MSADDR mapping text for MN / AR isolation based on 2736 L2 addressing. 2738 o Expanded "Transition Considerations". 2740 Differences from draft-templin-6man-omni-interface-05 to draft- 2741 templin-6man-omni-interface-06: 2743 o Brought back OMNI option "R" flag, and discussed its use. 2745 Differences from draft-templin-6man-omni-interface-04 to draft- 2746 templin-6man-omni-interface-05: 2748 o Transition considerations, and overhaul of RS/RA addressing with 2749 the inclusion of MSE addresses within the OMNI option instead of 2750 as RS/RA addresses (developed under FAA SE2025 contract number 2751 DTFAWA-15-D-00030). 2753 Differences from draft-templin-6man-omni-interface-02 to draft- 2754 templin-6man-omni-interface-03: 2756 o Added "advisory PTB messages" under FAA SE2025 contract number 2757 DTFAWA-15-D-00030. 2759 Differences from draft-templin-6man-omni-interface-01 to draft- 2760 templin-6man-omni-interface-02: 2762 o Removed "Primary" flag and supporting text. 2764 o Clarified that "Router Lifetime" applies to each ANET interface 2765 independently, and that the union of all ANET interface Router 2766 Lifetimes determines MSE lifetime. 2768 Differences from draft-templin-6man-omni-interface-00 to draft- 2769 templin-6man-omni-interface-01: 2771 o "All-MSEs" OMNI LLA defined. Also reserved fe80::ff00:0000/104 2772 for future use (most likely as "pseudo-multicast"). 2774 o Non-normative discussion of alternate OMNI LLA construction form 2775 made possible if the 64-bit assumption were relaxed. 2777 First draft version (draft-templin-atn-aero-interface-00): 2779 o Draft based on consensus decision of ICAO Working Group I Mobility 2780 Subgroup March 22, 2019. 2782 Authors' Addresses 2783 Fred L. Templin (editor) 2784 The Boeing Company 2785 P.O. Box 3707 2786 Seattle, WA 98124 2787 USA 2789 Email: fltemplin@acm.org 2791 Tony Whyman 2792 MWA Ltd c/o Inmarsat Global Ltd 2793 99 City Road 2794 London EC1Y 1AX 2795 England 2797 Email: tony.whyman@mccallumwhyman.com