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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group F. Templin, Ed. 3 Internet-Draft The Boeing Company 4 Intended status: Standards Track A. Whyman 5 Expires: November 2, 2020 MWA Ltd c/o Inmarsat Global Ltd 6 May 1, 2020 8 Transmission of IPv6 Packets over Overlay Multilink Network (OMNI) 9 Interfaces 10 draft-templin-6man-omni-interface-19 12 Abstract 14 Mobile nodes (e.g., aircraft of various configurations, terrestrial 15 vehicles, seagoing vessels, mobile enterprise devices, etc.) 16 communicate with networked correspondents over multiple access 17 network data links and configure mobile routers to connect end user 18 networks. A multilink interface specification is therefore needed 19 for coordination with the network-based mobility service. This 20 document specifies the transmission of IPv6 packets over Overlay 21 Multilink Network (OMNI) Interfaces. 23 Status of This Memo 25 This Internet-Draft is submitted in full conformance with the 26 provisions of BCP 78 and BCP 79. 28 Internet-Drafts are working documents of the Internet Engineering 29 Task Force (IETF). Note that other groups may also distribute 30 working documents as Internet-Drafts. The list of current Internet- 31 Drafts is at https://datatracker.ietf.org/drafts/current/. 33 Internet-Drafts are draft documents valid for a maximum of six months 34 and may be updated, replaced, or obsoleted by other documents at any 35 time. It is inappropriate to use Internet-Drafts as reference 36 material or to cite them other than as "work in progress." 38 This Internet-Draft will expire on November 2, 2020. 40 Copyright Notice 42 Copyright (c) 2020 IETF Trust and the persons identified as the 43 document authors. All rights reserved. 45 This document is subject to BCP 78 and the IETF Trust's Legal 46 Provisions Relating to IETF Documents 47 (https://trustee.ietf.org/license-info) in effect on the date of 48 publication of this document. Please review these documents 49 carefully, as they describe your rights and restrictions with respect 50 to this document. Code Components extracted from this document must 51 include Simplified BSD License text as described in Section 4.e of 52 the Trust Legal Provisions and are provided without warranty as 53 described in the Simplified BSD License. 55 Table of Contents 57 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 58 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 59 3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 6 60 4. Overlay Multilink Network (OMNI) Interface Model . . . . . . 6 61 5. Maximum Transmission Unit (MTU) and Fragmentation . . . . . . 10 62 6. Frame Format . . . . . . . . . . . . . . . . . . . . . . . . 11 63 7. Link-Local Addresses . . . . . . . . . . . . . . . . . . . . 12 64 8. The SPAN . . . . . . . . . . . . . . . . . . . . . . . . . . 12 65 9. Address Mapping - Unicast . . . . . . . . . . . . . . . . . . 13 66 9.1. Sub-Options . . . . . . . . . . . . . . . . . . . . . . . 14 67 9.1.1. Pad1 . . . . . . . . . . . . . . . . . . . . . . . . 15 68 9.1.2. PadN . . . . . . . . . . . . . . . . . . . . . . . . 16 69 9.1.3. ifIndex-tuple (Type 1) . . . . . . . . . . . . . . . 16 70 9.1.4. ifIndex-tuple (Type 2) . . . . . . . . . . . . . . . 18 71 9.1.5. MS-Register . . . . . . . . . . . . . . . . . . . . . 19 72 9.1.6. MS-Release . . . . . . . . . . . . . . . . . . . . . 19 73 10. Address Mapping - Multicast . . . . . . . . . . . . . . . . . 20 74 11. Conceptual Sending Algorithm . . . . . . . . . . . . . . . . 20 75 11.1. Multiple OMNI Interfaces . . . . . . . . . . . . . . . . 20 76 12. Router Discovery and Prefix Registration . . . . . . . . . . 21 77 13. Secure Redirection . . . . . . . . . . . . . . . . . . . . . 24 78 14. AR and MSE Resilience . . . . . . . . . . . . . . . . . . . . 24 79 15. Detecting and Responding to MSE Failures . . . . . . . . . . 24 80 16. Transition Considerations . . . . . . . . . . . . . . . . . . 25 81 17. OMNI Interfaces on the Open Internet . . . . . . . . . . . . 26 82 18. Time-Varying MNPs . . . . . . . . . . . . . . . . . . . . . . 26 83 19. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27 84 20. Security Considerations . . . . . . . . . . . . . . . . . . . 27 85 21. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 28 86 22. References . . . . . . . . . . . . . . . . . . . . . . . . . 28 87 22.1. Normative References . . . . . . . . . . . . . . . . . . 28 88 22.2. Informative References . . . . . . . . . . . . . . . . . 30 89 Appendix A. Type 1 ifIndex-tuple Traffic Classifier Preference 90 Encoding . . . . . . . . . . . . . . . . . . . . . . 33 91 Appendix B. VDL Mode 2 Considerations . . . . . . . . . . . . . 35 92 Appendix C. MN / AR Isolation Through L2 Address Mapping . . . . 36 93 Appendix D. Change Log . . . . . . . . . . . . . . . . . . . . . 36 94 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 42 96 1. Introduction 98 Mobile Nodes (MNs) (e.g., aircraft of various configurations, 99 terrestrial vehicles, seagoing vessels, mobile enterprise devices, 100 etc.) often have multiple data links for communicating with networked 101 correspondents. These data links may have diverse performance, cost 102 and availability properties that can change dynamically according to 103 mobility patterns, flight phases, proximity to infrastructure, etc. 104 MNs coordinate their data links in a discipline known as "multilink", 105 in which a single virtual interface is configured over the underlying 106 data links. 108 The MN configures a virtual interface (termed the "Overlay Multilink 109 Network (OMNI) interface") as a thin layer over the underlying Access 110 Network (ANET) interfaces. The OMNI interface is therefore the only 111 interface abstraction exposed to the IPv6 layer and behaves according 112 to the Non-Broadcast, Multiple Access (NBMA) interface principle, 113 while underlying interfaces appear as link layer communication 114 channels in the architecture. The OMNI interface connects to a 115 virtual overlay service known as the "OMNI link". The OMNI link 116 spans a worldwide Internetwork that may include private-use 117 infrastructures and/or the global public Internet itself. 119 Each MN receives a Mobile Network Prefix (MNP) for numbering 120 downstream-attached End User Networks (EUNs) independently of the 121 access network data links selected for data transport. The MN 122 performs router discovery over the OMNI interface (i.e., similar to 123 IPv6 customer edge routers [RFC7084]) and acts as a mobile router on 124 behalf of its EUNs. The router discovery process is iterated over 125 each of the OMNI interface's underlying interfaces in order to 126 register per-link parameters (see Section 12). 128 The OMNI interface provides a multilink nexus for exchanging inbound 129 and outbound traffic via the correct underlying interface(s). The 130 IPv6 layer sees the OMNI interface as a point of connection to the 131 OMNI link. Each OMNI link has one or more associated Mobility 132 Service Prefixes (MSPs) from which OMNI link MNPs are derived. If 133 there are multiple OMNI links, the IPv6 layer will see multiple OMNI 134 interfaces. 136 The OMNI interface interacts with a network-based Mobility Service 137 (MS) through IPv6 Neighbor Discovery (ND) control message exchanges 138 [RFC4861]. The MS provides Mobility Service Endpoints (MSEs) that 139 track MN movements and represent their MNPs in a global routing or 140 mapping system. 142 This document specifies the transmission of IPv6 packets [RFC8200] 143 and MN/MS control messaging over OMNI interfaces. 145 2. Terminology 147 The terminology in the normative references applies; especially, the 148 terms "link" and "interface" are the same as defined in the IPv6 149 [RFC8200] and IPv6 Neighbor Discovery (ND) [RFC4861] specifications. 150 Also, the Protocol Constants defined in Section 10 of [RFC4861] are 151 used in their same format and meaning in this document. The terms 152 "All-Routers multicast", "All-Nodes multicast" and "Subnet-Router 153 anycast" are the same as defined in [RFC4291] (with Link-Local scope 154 assumed). 156 The following terms are defined within the scope of this document: 158 Mobile Node (MN) 159 an end system with multiple distinct upstream data link 160 connections that are managed together as a single logical unit. 161 The MN's data link connection parameters can change over time due 162 to, e.g., node mobility, link quality, etc. The MN further 163 connects a downstream-attached End User Network (EUN). The term 164 MN used here is distinct from uses in other documents, and does 165 not imply a particular mobility protocol. 167 End User Network (EUN) 168 a simple or complex downstream-attached mobile network that 169 travels with the MN as a single logical unit. The IPv6 addresses 170 assigned to EUN devices remain stable even if the MN's upstream 171 data link connections change. 173 Mobility Service (MS) 174 a mobile routing service that tracks MN movements and ensures that 175 MNs remain continuously reachable even across mobility events. 176 Specific MS details are out of scope for this document. 178 Mobility Service Endpoint (MSE) 179 an entity in the MS (either singular or aggregate) that 180 coordinates the mobility events of one or more MN. 182 Mobility Service Prefix (MSP) 183 an aggregated IPv6 prefix (e.g., 2001:db8::/32) advertised to the 184 rest of the Internetwork by the MS, and from which more-specific 185 Mobile Network Prefixes (MNPs) are derived. 187 Mobile Network Prefix (MNP) 188 a longer IPv6 prefix taken from an MSP (e.g., 189 2001:db8:1000:2000::/56) and assigned to a MN. MNs sub-delegate 190 the MNP to devices located in EUNs. 192 Access Network (ANET) 193 a data link service network (e.g., an aviation radio access 194 network, satellite service provider network, cellular operator 195 network, wifi network, etc.) that connects MNs. Physical and/or 196 data link level security between the MN and ANET are assumed. 198 Access Router (AR) 199 a first-hop router in the ANET for connecting MNs to 200 correspondents in outside Internetworks. 202 ANET interface 203 a MN's attachment to a link in an ANET. 205 Internetwork (INET) 206 a connected network region with a coherent IP addressing plan that 207 provides transit forwarding services for ANET MNs and INET 208 correspondents. Examples include private enterprise networks, 209 ground domain aviation service networks and the global public 210 Internet itself. 212 INET interface 213 a node's attachment to a link in an INET. 215 OMNI link 216 a virtual overlay configured over one or more INETs and their 217 connected ANETs. An OMNI link can comprise multiple INET segments 218 joined by bridges the same as for any link; the addressing plans 219 in each segment may be mutually exclusive and managed by different 220 administrative entities. 222 OMNI interface 223 a node's attachment to an OMNI link, and configured over one or 224 more underlying ANET/INET interfaces. 226 OMNI link local address (LLA) 227 an IPv6 link-local address constructed as specified in Section 7, 228 and assigned to an OMNI interface. 230 OMNI Option 231 an IPv6 Neighbor Discovery option providing multilink parameters 232 for the OMNI interface as specified in Section 9. 234 Multilink 235 an OMNI interface's manner of managing diverse underlying data 236 link interfaces as a single logical unit. The OMNI interface 237 provides a single unified interface to upper layers, while 238 underlying data link selections are performed on a per-packet 239 basis considering factors such as DSCP, flow label, application 240 policy, signal quality, cost, etc. Multilinking decisions are 241 coordinated in both the outbound (i.e. MN to correspondent) and 242 inbound (i.e., correspondent to MN) directions. 244 L2 245 The second layer in the OSI network model. Also known as "layer- 246 2", "link-layer", "sub-IP layer", "data link layer", etc. 248 L3 249 The third layer in the OSI network model. Also known as "layer- 250 3", "network-layer", "IPv6 layer", etc. 252 underlying interface 253 an ANET/INET interface over which an OMNI interface is configured. 254 The OMNI interface is seen as a L3 interface by the IP layer, and 255 each underlying interface is seen as a L2 interface by the OMNI 256 interface. 258 Mobility Service Identification (MSID) 259 Each MSE and AR is assigned a unique 32-bit Identification (MSID) 260 as specified in Section 7. 262 Spanning Partitioned Administrative Networks (SPAN) 263 A means for bridging disjoint INET partitions as segments of a 264 unified OMNI link the same as for a bridged campus LAN. The SPAN 265 is a mid-layer IPv6 encapsulation service that supports a unified 266 OMNI link view for all segments. 268 3. Requirements 270 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 271 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 272 "OPTIONAL" in this document are to be interpreted as described in BCP 273 14 [RFC2119][RFC8174] when, and only when, they appear in all 274 capitals, as shown here. 276 An implementation is not required to internally use the architectural 277 constructs described here so long as its external behavior is 278 consistent with that described in this document. 280 4. Overlay Multilink Network (OMNI) Interface Model 282 An OMNI interface is a MN virtual interface configured over one or 283 more underlying interfaces, which may be physical (e.g., an 284 aeronautical radio link) or virtual (e.g., an Internet or higher- 285 layer "tunnel"). The MN receives a MNP from the MS, and coordinates 286 with the MS through IPv6 ND message exchanges. The MN uses the MNP 287 to construct a unique OMNI LLA through the algorithmic derivation 288 specified in Section 7 and assigns the LLA to the OMNI interface. 290 The OMNI interface architectural layering model is the same as in 291 [RFC5558][RFC7847], and augmented as shown in Figure 1. The IP layer 292 therefore sees the OMNI interface as a single L3 interface with 293 multiple underlying interfaces that appear as L2 communication 294 channels in the architecture. 296 +----------------------------+ 297 | Upper Layer Protocol | 298 Session-to-IP +---->| | 299 Address Binding | +----------------------------+ 300 +---->| IP (L3) | 301 IP Address +---->| | 302 Binding | +----------------------------+ 303 +---->| OMNI Interface | 304 Logical-to- +---->| (OMNI LLA) | 305 Physical | +----------------------------+ 306 Interface +---->| L2 | L2 | | L2 | 307 Binding |(IF#1)|(IF#2)| ..... |(IF#n)| 308 +------+------+ +------+ 309 | L1 | L1 | | L1 | 310 | | | | | 311 +------+------+ +------+ 313 Figure 1: OMNI Interface Architectural Layering Model 315 The OMNI virtual interface model gives rise to a number of 316 opportunities: 318 o since OMNI LLAs are uniquely derived from an MNP, no Duplicate 319 Address Detection (DAD) or Muticast Listener Discovery (MLD) 320 messaging is necessary. 322 o ANET interfaces do not require any L3 addresses (i.e., not even 323 link-local) in environments where communications are coordinated 324 entirely over the OMNI interface. (An alternative would be to 325 also assign the same OMNI LLA to all ANET interfaces.) 327 o as ANET interface properties change (e.g., link quality, cost, 328 availability, etc.), any active ANET interface can be used to 329 update the profiles of multiple additional ANET interfaces in a 330 single message. This allows for timely adaptation and service 331 continuity under dynamically changing conditions. 333 o coordinating ANET interfaces in this way allows them to be 334 represented in a unified MS profile with provisions for mobility 335 and multilink operations. 337 o exposing a single virtual interface abstraction to the IPv6 layer 338 allows for multilink operation (including QoS based link 339 selection, packet replication, load balancing, etc.) at L2 while 340 still permitting L3 traffic shaping based on, e.g., DSCP, flow 341 label, etc. 343 o L3 sees the OMNI interface as a point of connection to the OMNI 344 link; if there are multiple OMNI links (i.e., multiple MS's), L3 345 will see multiple OMNI interfaces. 347 Other opportunities are discussed in [RFC7847]. 349 Figure 2 depicts the architectural model for a MN connecting to the 350 MS via multiple independent ANETs. When an underlying interface 351 becomes active, the MN's OMNI interface sends native (i.e., 352 unencapsulated) IPv6 ND messages via the underlying interface. IPv6 353 ND messages traverse the ground domain ANETs until they reach an 354 Access Router (AR#1, AR#2, .., AR#n). The AR then coordinates with a 355 Mobility Service Endpoint (MSE#1, MSE#2, ..., MSE#m) in the INET and 356 returns an IPv6 ND message response to the MN. IPv6 ND messages 357 traverse the ANET at layer 2; hence, the Hop Limit is not 358 decremented. 360 +--------------+ 361 | MN | 362 +--------------+ 363 |OMNI interface| 364 +----+----+----+ 365 +--------|IF#1|IF#2|IF#n|------ + 366 / +----+----+----+ \ 367 / | \ 368 / <---- Native | IP ----> \ 369 v v v 370 (:::)-. (:::)-. (:::)-. 371 .-(::ANET:::) .-(::ANET:::) .-(::ANET:::) 372 `-(::::)-' `-(::::)-' `-(::::)-' 373 +----+ +----+ +----+ 374 ... |AR#1| .......... |AR#2| ......... |AR#n| ... 375 . +-|--+ +-|--+ +-|--+ . 376 . | | | 377 . v v v . 378 . <----- Encapsulation -----> . 379 . . 380 . +-----+ (:::)-. . 381 . |MSE#2| .-(::::::::) +-----+ . 382 . +-----+ .-(::: INET :::)-. |MSE#m| . 383 . (::::: Routing ::::) +-----+ . 384 . `-(::: System :::)-' . 385 . +-----+ `-(:::::::-' . 386 . |MSE#1| +-----+ +-----+ . 387 . +-----+ |MSE#3| |MSE#4| . 388 . +-----+ +-----+ . 389 . . 390 . . 391 . <----- Worldwide Connected Internetwork ----> . 392 ........................................................... 394 Figure 2: MN/MS Coordination via Multiple ANETs 396 After the initial IPv6 ND message exchange, the MN can send and 397 receive unencapsulated IPv6 data packets over the OMNI interface. 398 OMNI interface multilink services will forward the packets via ARs in 399 the correct underlying ANETs. The AR encapsulates the packets 400 according to the capabilities provided by the MS and forwards them to 401 the next hop within the worldwide connected Internetwork via optimal 402 routes. 404 OMNI links span the underlying Internetwork via a mid-layer overlay 405 known as "The SPAN" - see Section 8. Each OMNI link corresponds to a 406 different SPAN overlay (possibly differentiated by a SPAN header 407 codepoint) which may be carried over a completely separate 408 Internetwork topology. The same as for VLANs, each MN can connect to 409 multiple OMNI links (i.e., multiple SPANs) by configuring a distinct 410 OMNI interface for each link. 412 5. Maximum Transmission Unit (MTU) and Fragmentation 414 All IPv6 interfaces are REQUIRED to configure a minimum Maximum 415 Transmission Unit (MTU) of 1280 bytes [RFC8200]. The network 416 therefore MUST forward packets of at least 1280 bytes without 417 generating an IPv6 Path MTU Discovery (PMTUD) Packet Too Big (PTB) 418 message [RFC8201]. 420 The OMNI interface configures an MTU of 9180 bytes [RFC2492]; the 421 size is therefore not a reflection of the underlying interface MTUs, 422 but rather determines the largest packet the OMNI interface can 423 forward or reassemble. The OMNI interface therefore accommodates IP 424 packets up to 9180 bytes while generating IPv6 Path MTU Discovery 425 (PMTUD) Packet Too Big (PTB) messages [RFC8201] as necessary (see 426 below). 428 OMNI interfaces employ mid-layer IPv6 encapsulation and 429 fragmentation/reassembly per [RFC2473] (also known as "SPAN 430 encapsulation" - see Section 8) to accommodate the 9180 byte MTU. 431 The OMNI interface returns internally-generated PTB messages for 432 packets admitted into the interface that it deems too large (e.g., 433 according to link performance characteristics, reassembly cost, etc.) 434 while either dropping or forwarding the packet as necessary. The 435 OMNI interface performs PMTUD even if the destination appears to be 436 on the same link since an OMNI link node on the path may return a 437 PTB. This ensures that the path MTU is adaptive and reflects the 438 current path used for a given data flow. 440 OMNI interfaces perform SPAN encapsulation and fragmentation/ 441 reassembly as follows: 443 o When an OMNI interface sends a packet toward a final destination 444 via an ANET peer, it sends without SPAN encapsulation if the 445 packet is no larger than the underlying interface MTU. Otherwise, 446 it inserts a SPAN header with source address set to the node's own 447 SPAN address and destination set to the SPAN address of the ANET 448 peer. The OMNI interface then uses IPv6 fragmentation to break 449 the packet into a minimum number of non-overlapping fragments, 450 where the largest fragment size is determined by the underlying 451 interface MTU and the smallest fragment is no smaller than 640 452 bytes. The OMNI interface then sends the fragments to the ANET 453 peer, which reassembles before forwarding toward the final 454 destination. 456 o When an OMNI interface sends a packet toward a final destination 457 via an INET interface, it sends encapsulated packets no larger 458 than 1280 bytes without a SPAN header if the destination is 459 reached via an INET address within the same SPAN segment. 460 Otherwise, it inserts a SPAN header with source address set to the 461 node's SPAN address, destination set to the SPAN address of the 462 next hop OMNI node toward the final destination and (if necessary) 463 with a Segment Routing Header [RFC8754] with the remaining Segment 464 IDs on the path to the final destination. The OMNI interface then 465 uses IPv6 fragmentation to break the encapsulated packet into a 466 minimum number of non-overlapping fragments, where the largest 467 fragment size (including both SPAN and INET encapsulation) is 1280 468 bytes and the smallest fragment is no smaller than 640 bytes. The 469 OMNI interface then sends the fragments to the SPAN destination, 470 which reassembles before forwarding toward the final destination. 472 In order to avoid a "tiny fragment" attack, OMNI interfaces 473 unconditionally drop all SPAN fragments smaller than 640 bytes. In 474 order to set the correct context for reassembly, the OMNI interface 475 that inserts a SPAN header MUST also be the one that inserts the IPv6 476 Fragment Header Identification value. Although all fragments of the 477 same fragmented SPAN packet are typically sent via the same 478 underlying interface, this is not strictly required since all 479 fragments will arrive at the OMNI interface that performs reassembly 480 even if they travel over different paths. 482 Note that the OMNI interface can forward large packets via 483 encapsulation and fragmentation while at the same time returning 484 advisory PTB messages, e.g., subject to rate limiting. The receiving 485 node that performs reassembly can also send advisory PTB messages if 486 reassembly conditions become unfavorable. The AERO interface can 487 therefore continuously forward large packets without loss while 488 returning advisory messages recommending a smaller size (but no 489 smaller than 1280). Advisory PTB messages are differentiated from 490 PTB messages that report loss by setting the Code field in the ICMPv6 491 message header to the value 1. This document therefore updates 492 [RFC4443] and [RFC8201]. 494 6. Frame Format 496 The OMNI interface transmits IPv6 packets according to the native 497 frame format of each underlying interface. For example, for 498 Ethernet-compatible interfaces the frame format is specified in 499 [RFC2464], for aeronautical radio interfaces the frame format is 500 specified in standards such as ICAO Doc 9776 (VDL Mode 2 Technical 501 Manual), for tunnels over IPv6 the frame format is specified in 502 [RFC2473], etc. 504 7. Link-Local Addresses 506 OMNI interfaces assign IPv6 Link-Local Addresses (i.e., "OMNI LLAs") 507 using the following constructs: 509 o IPv6 MN OMNI LLAs encode the most-significant 112 bits of a MNP 510 within the least-significant 112 bits of the IPv6 link-local 511 prefix fe80::/16. For example, for the MNP 512 2001:db8:1000:2000::/56 the corresponding LLA is 513 fe80:2001:db8:1000:2000::. See: [RFC4291], Section 2.5.6) for a 514 discussion of IPv6 link-local addresses. 516 o IPv4-compatible MN OMNI LLAs are assigned as fe80::ffff:[v4addr], 517 i.e., the most significant 16 bits of the prefix fe80::/16, 518 followed by 64 '0' bits, followed by 16 '1' bits, followed by a 519 32bit IPv4 address. For example, the IPv4-Compatible MN OMNI LLA 520 for 192.0.2.1 is fe80::ffff:192.0.2.1 (also written as 521 fe80::ffff:c000:0201). 523 o MS OMNI LLAs are assigned to ARs and MSEs from the range 524 fe80::/96, and MUST be managed for uniqueness. The lower 32 bits 525 of the LLA includes a unique integer "MSID" value between 526 0x00000001 and 0xfeffffff, e.g., as in fe80::1, fe80::2, fe80::3, 527 etc., fe80::feff:ffff. The MSID 0x00000000 corresponds to the 528 link-local Subnet-Router anycast address (fe80::) [RFC4291]. The 529 MSID range 0xff000000 through 0xffffffff is reserved for future 530 use. 532 o The OMNI LLA range fe80::/32 is used as the service prefix for the 533 address format specified in Section 4 of [RFC4380] (see Section 17 534 for further discussion). 536 Since the prefix 0000::/8 is "Reserved by the IETF" [RFC4291], no 537 MNPs can be allocated from that block ensuring that there is no 538 possibility for overlap between the above OMNI LLA constructs. 540 Since MN OMNI LLAs are based on the distribution of administratively 541 assured unique MNPs, and since MS OMNI LLAs are guaranteed unique 542 through administrative assignment, OMNI interfaces set the 543 autoconfiguration variable DupAddrDetectTransmits to 0 [RFC4862]. 545 8. The SPAN 547 OMNI links employ an overlay network instance called "The SPAN" 548 (Spanning Partitioned Administrative Networks) that supports 549 forwarding of encapsulated link-scoped messages over an IPv6 overlay 550 routing instance that spans the entire link without decrementing the 551 (link-local) Hop Limit. The OMNI link reserves the Unique Local 552 Address (ULA) prefix fd80::/10 [RFC4193] used for mapping OMNI LLAs 553 to routable SPAN addresses. 555 SPAN addresses are configured in one-to-one correspondence with MN/MS 556 OMNI LLAs through stateless translation of the prefix. For example, 557 for the SPAN sub-prefix fd80::/16: 559 o the SPAN address corresponding to fe80:2001:db8:1:2:: is simply 560 fd80:2001:db8:1:2:: 562 o the SPAN address corresponding to fe80::ffff:192.0.2.1 is simply 563 fd80::ffff:192.0.2.1 565 o the SPAN address corresponding to fe80::1000 is simply fd80::1000 567 The SPAN address presents an IPv6 address format that is routable 568 within the OMNI link routing system and can be used to convey link- 569 scoped messages across multiple hops using IPv6 encapsulation 570 [RFC2473]. The SPAN extends over the entire OMNI link to include all 571 ARs and MSEs. All MNs are also considered to be "on the SPAN", 572 however SPAN encapsulation is omitted over ANET links when possible 573 to conserve bandwidth (see: Section 11). 575 The SPAN allows the OMNI link to be subdivided into "segments" that 576 often correspond to administrative domains or physical partitions. 577 OMNI nodes can use IPv6 Segment Routing [RFC8754][RFC8402] when 578 necessary to support efficient packet forwarding to destinations 579 located in other SPAN segments. A full discussion of Segment Routing 580 over the SPAN appears in [I-D.templin-intarea-6706bis]. 582 9. Address Mapping - Unicast 584 OMNI interfaces maintain a neighbor cache for tracking per-neighbor 585 state and use the link-local address format specified in Section 7. 586 IPv6 Neighbor Discovery (ND) [RFC4861] messages on MN OMNI interfaces 587 observe the native Source/Target Link-Layer Address Option (S/TLLAO) 588 formats of the underlying interfaces (e.g., for Ethernet the S/TLLAO 589 is specified in [RFC2464]). 591 MNs such as aircraft typically have many wireless data link types 592 (e.g. satellite-based, cellular, terrestrial, air-to-air directional, 593 etc.) with diverse performance, cost and availability properties. 594 The OMNI interface would therefore appear to have multiple L2 595 connections, and may include information for multiple underlying 596 interfaces in a single IPv6 ND message exchange. 598 OMNI interfaces use an IPv6 ND option called the "OMNI option" 599 formatted as shown in Figure 3: 601 0 1 2 3 602 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 1 603 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 604 | Type | Length | Prefix Length |R| Reserved | 605 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 606 | | 607 ~ Sub-Options ~ 608 | | 609 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 611 Figure 3: OMNI Option Format 613 In this format: 615 o Type is set to TBD. 617 o Length is set to the number of 8 octet blocks in the option. 619 o Prefix Length is set according to the IPv6 source address type. 620 For MN OMNI LLAs, the value is set to the length of the embedded 621 MNP. For IPv4-compatible MN OMNI LLAs, the value is set to 96 622 plus the length of the embedded IPv4 prefix. For MS OMNI LLAs, 623 the value is set to 128. 625 o R (the "Register/Release" bit) is set to 1/0 to request the 626 message recipient to register/release a MN's MNP. The OMNI option 627 may additionally include MSIDs for the recipient to contact to 628 also register/release the MNP. 630 o Reserved is set to the value '0' on transmission and ignored on 631 reception. 633 o Sub-Options is a Variable-length field, of length such that the 634 complete OMNI Option is an integer multiple of 8 octets long. 635 Contains one or more options, as described in Section 9.1. 637 9.1. Sub-Options 639 The OMNI option includes zero or more Sub-Options, some of which may 640 appear multiple times in the same message. Each consecutive Sub- 641 Option is concatenated immediately after its predecessor. All Sub- 642 Options except Pad1 (see below) are type-length-value (TLV) encoded 643 in the following format: 645 0 1 2 646 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 5 647 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 648 | Sub-Type | Sub-length | Sub-Option Data ... 649 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 651 Figure 4: Sub-Option Format 653 o Sub-Type is a 1-byte field that encodes the Sub-Option type. Sub- 654 Options defined in this document are: 656 Option Name Sub-Type 657 Pad1 0 658 PadN 1 659 ifIndex-tuple (Type 1) 2 660 ifIndex-tuple (Type 2) 3 661 MS-Register 4 662 MS-Release 5 664 Figure 5 666 Sub-Types 253 and 254 are reserved for experimentation, as 667 recommended in [RFC3692]. 669 o Sub-Length is a 1-byte field that encodes the length of the Sub- 670 Option Data, in bytes 672 o Sub-Option Data is a byte string with format determined by Sub- 673 Type 675 During processing, unrecognized Sub-Options are ignored and the next 676 Sub-Option processed until the end of the OMNI option. 678 The following Sub-Option types and formats are defined in this 679 document: 681 9.1.1. Pad1 683 0 684 0 1 2 3 4 5 6 7 685 +-+-+-+-+-+-+-+-+ 686 | Sub-Type=0 | 687 +-+-+-+-+-+-+-+-+ 689 Figure 6: Pad1 691 o Sub-Type is set to 0. 693 o No Sub-Length or Sub-Option Data follows (i.e., the "Sub-Option" 694 consists of a single zero octet). 696 9.1.2. PadN 698 0 1 2 699 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 5 700 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 701 | Sub-Type=1 |Sub-length=N-2 | N-2 padding bytes ... 702 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 704 Figure 7: PadN 706 o Sub-Type is set to 1. 708 o Sub-Length is set to N-2 being the number of padding bytes that 709 follow. 711 o Sub-Option Data consists of N-2 zero-valued octets. 713 9.1.3. ifIndex-tuple (Type 1) 715 0 1 2 3 716 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 1 717 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 718 | Sub-Type=2 | Sub-length=4+N| ifIndex | ifType | 719 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 720 | Provider ID | Link |S|I|RSV| Bitmap(0)=0xff|P00|P01|P02|P03| 721 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 722 |P04|P05|P06|P07|P08|P09|P10|P11|P12|P13|P14|P15|P16|P17|P18|P19| 723 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 724 |P20|P21|P22|P23|P24|P25|P26|P27|P28|P29|P30|P31| Bitmap(1)=0xff| 725 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 726 |P32|P33|P34|P35|P36|P37|P38|P39| ... 727 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 729 Figure 8: ifIndex-tuple (Type 1) 731 o Sub-Type is set to 2. 733 o Sub-Length is set to 4+N (the number of Sub-Option Data bytes that 734 follow). 736 o Sub-Option Data contains an "ifIndex-tuple" (Type 1) encoded as 737 follows (note that the first four bytes must be present): 739 * ifIndex is set to an 8-bit integer value corresponding to a 740 specific underlying interface. OMNI options MAY include 741 multiple ifIndex-tuples, and MUST number each with an ifIndex 742 value between '1' and '255' that represents a MN-specific 8-bit 743 mapping for the actual ifIndex value assigned to the underlying 744 interface by network management [RFC2863] (the ifIndex value 745 '0' is reserved for use by the MS). Multiple ifIndex-tuples 746 with the same ifIndex value MAY appear in the same OMNI option. 748 * ifType is set to an 8-bit integer value corresponding to the 749 underlying interface identified by ifIndex. The value 750 represents an OMNI interface-specific 8-bit mapping for the 751 actual IANA ifType value registered in the 'IANAifType-MIB' 752 registry [http://www.iana.org]. 754 * Provider ID is set to an OMNI interface-specific 8-bit ID value 755 for the network service provider associated with this ifIndex. 757 * Link encodes a 4-bit link metric. The value '0' means the link 758 is DOWN, and the remaining values mean the link is UP with 759 metric ranging from '1' ("lowest") to '15' ("highest"). 761 * S is set to '1' if this ifIndex-tuple corresponds to the 762 underlying interface that is the source of the ND message. Set 763 to '0' otherwise. 765 * I is set to '0' ("Simplex") if the index for each singleton 766 Bitmap byte in the Sub-Option Data is inferred from its 767 sequential position (i.e., 0, 1, 2, ...), or set to '1' 768 ("Indexed") if each Bitmap is preceded by an Index byte. 769 Figure 8 shows the simplex case for I set to '0'. For I set to 770 '1', each Bitmap is instead preceded by an Index byte that 771 encodes a value "i" = (0 - 255) as the index for its companion 772 Bitmap as follows: 774 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 775 | Index=i | Bitmap(i) |P[*] values ... 776 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 778 Figure 9 780 * RSV is set to the value 0 on transmission and ignored on 781 reception. 783 * The remainder of the Sub-Option Data contains N = (0 - 251) 784 bytes of traffic classifier preferences consisting of a first 785 (indexed) Bitmap (i.e., "Bitmap(i)") followed by 0-8 1-byte 786 blocks of 2-bit P[*] values, followed by a second Bitmap (i), 787 followed by 0-8 blocks of P[*] values, etc. Reading from bit 0 788 to bit 7, the bits of each Bitmap(i) that are set to '1'' 789 indicate the P[*] blocks from the range P[(i*32)] through 790 P[(i*32) + 31] that follow; if any Bitmap(i) bits are '0', then 791 the corresponding P[*] block is instead omitted. For example, 792 if Bitmap(0) contains 0xff then the block with P[00]-P[03], 793 followed by the block with P[04]-P[07], etc., and ending with 794 the block with P[28]-P[31] are included (as shown in Figure 8). 795 The next Bitmap(i) is then consulted with its bits indicating 796 which P[*] blocks follow, etc. out to the end of the Sub- 797 Option. The first 16 P[*] blocks correspond to the 64 798 Differentiated Service Code Point (DSCP) values P[00] - P[63] 799 [RFC2474]. Any additional P[*] blocks that follow correspond 800 to "pseudo-DSCP" traffic classifier values P[64], P[65], P[66], 801 etc. See Appendix A for further discussion and examples. 803 * Each 2-bit P[*] field is set to the value '0' ("disabled"), '1' 804 ("low"), '2' ("medium") or '3' ("high") to indicate a QoS 805 preference level for underlying interface selection purposes. 806 Not all P[*] values need to be included in all OMNI option 807 instances of a given ifIndex-tuple. Any P[*] values 808 represented in an earlier OMNI option but omitted in the 809 current OMNI option remain unchanged. Any P[*] values not yet 810 represented in any OMNI option default to "medium". 812 9.1.4. ifIndex-tuple (Type 2) 814 0 1 2 3 815 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 1 816 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 817 | Sub-Type=3 | Sub-length=4+N| ifIndex | ifType | 818 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 819 | Provider ID | Link |S|Resvd| ~ 820 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ 821 ~ ~ 822 ~ RFC 6088 Format Traffic Selector ~ 823 ~ ~ 824 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 826 Figure 10: ifIndex-tuple (Type 2) 828 o Sub-Type is set to 3. 830 o Sub-Length is set to 4+N (the number of Sub-Option Data bytes that 831 follow). 833 o Sub-Option Data contains an "ifIndex-tuple" (Type 2) encoded as 834 follows (note that the first four bytes must be present): 836 * ifIndex, ifType, Provider ID, Link and S are set exactly as for 837 Type 1 ifIndex-tuples as specified in Section 9.1.3. 839 * the remainder of the Sub-Option body encodes a variable-length 840 traffic selector formatted per [RFC6088], beginning with the 841 "TS Format" field. 843 9.1.5. MS-Register 845 0 1 2 3 846 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 1 847 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 848 | Sub-Type=4 | Sub-length=4 | MSID (bits 0 - 15) | 849 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 850 | MSID (bits 16 - 32) | 851 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 853 Figure 11: MS-Register Sub-option 855 o Sub-Type is set to 4. 857 o Sub-Length is set to 4. 859 o MSID contains the 32 bit ID of an MSE or AR, in network byte 860 order. OMNI options contain zero or more MS-Register sub-options. 862 9.1.6. MS-Release 864 0 1 2 3 865 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 1 866 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 867 | Sub-Type=5 | Sub-length=4 | MSID (bits 0 - 15) | 868 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 869 | MSID (bits 16 - 32) | 870 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 872 Figure 12: MS-Release Sub-option 874 o Sub-Type is set to 5. 876 o Sub-Length is set to 4. 878 o MSIID contains the 32 bit ID of an MS or AR, in network byte 879 order. OMNI options contain zero or more MS-Release sub-options. 881 10. Address Mapping - Multicast 883 The multicast address mapping of the native underlying interface 884 applies. The mobile router on board the MN also serves as an IGMP/ 885 MLD Proxy for its EUNs and/or hosted applications per [RFC4605] while 886 using the L2 address of the AR as the L2 address for all multicast 887 packets. 889 The MN uses Multicast Listener Discovery (MLDv2) [RFC3810] to 890 coordinate with the AR, and ANET L2 elements use MLD snooping 891 [RFC4541]. 893 11. Conceptual Sending Algorithm 895 The MN's IPv6 layer selects the outbound OMNI interface according to 896 standard IPv6 requirements when forwarding data packets from local or 897 EUN applications to external correspondents. The OMNI interface 898 maintains a neighbor cache the same as for any IPv6 interface, but 899 with additional state for multilink coordination. 901 After a packet enters the OMNI interface, an outbound underlying 902 interface is selected based on multilink parameters such as DSCP, 903 application port number, cost, performance, message size, etc. OMNI 904 interface multilink selections could also be configured to perform 905 replication across multiple underlying interfaces for increased 906 reliability at the expense of packet duplication. 908 When an OMNI interface sends a packet over a selected outbound 909 underlying interface, it omits SPAN encapsulation if the packet does 910 not require fragmentation and the neighbor can determine the SPAN 911 addresses through other means (e.g., the packet's destination, 912 neighbor cache information, etc.). Otherwise, the OMNI interface 913 inserts a SPAN header and performs fragmentation if necessary. 915 OMNI interface multilink service designers MUST observe the BCP 916 guidance in Section 15 [RFC3819] in terms of implications for 917 reordering when packets from the same flow may be spread across 918 multiple underlying interfaces having diverse properties. 920 11.1. Multiple OMNI Interfaces 922 MNs may associate with multiple MS instances concurrently. Each MS 923 instance represents a distinct OMNI link distinguished by its 924 associated MSPs. The MN configures a separate OMNI interface for 925 each link so that multiple interfaces (e.g., omni0, omni1, omni2, 926 etc.) are exposed to the IPv6 layer. 928 Depending on local policy and configuration, an MN may choose between 929 alternative active OMNI interfaces using a packet's DSCP, routing 930 information or static configuration. Each OMNI interface can be 931 configured over the same or different sets of underlying interfaces. 933 Multiple distinct OMNI links can therefore be used to support fault 934 tolerance, load balancing, reliability, etc. The architectural model 935 parallels Layer 2 Virtual Local Area Networks (VLANs). 937 12. Router Discovery and Prefix Registration 939 MNs interface with the MS by sending RS messages with OMNI options 940 under the assumption that a single AR on the ANET will process the 941 message and respond. This places a requirement on each ANET, which 942 may be enforced by physical/logical partitioning, L2 AR beaconing, 943 etc. The manner in which the ANET ensures single AR coordination is 944 link-specific and outside the scope of this document. 946 For each underlying interface, the MN sends an RS message with an 947 OMNI option with prefix registration information, ifIndex-tuples, MS- 948 Register/Release suboptions containing MSIDs, and with destination 949 address set to All-Routers multicast (ff02::2) [RFC4291]. Example 950 MSID discovery methods are given in [RFC5214], including data link 951 login parameters, name service lookups, static configuration, etc. 952 Alternatively, MNs can discover individual MSIDs by sending an 953 initial RS with MS-Register MSID set to 0x00000000. 955 MNs configure OMNI interfaces that observe the properties discussed 956 in the previous section. The OMNI interface and its underlying 957 interfaces are said to be in either the "UP" or "DOWN" state 958 according to administrative actions in conjunction with the interface 959 connectivity status. An OMNI interface transitions to UP or DOWN 960 through administrative action and/or through state transitions of the 961 underlying interfaces. When a first underlying interface transitions 962 to UP, the OMNI interface also transitions to UP. When all 963 underlying interfaces transition to DOWN, the OMNI interface also 964 transitions to DOWN. 966 When an OMNI interface transitions to UP, the MN sends RS messages to 967 register its MNP and an initial set of underlying interfaces that are 968 also UP. The MN sends additional RS messages to refresh lifetimes 969 and to register/deregister underlying interfaces as they transition 970 to UP or DOWN. The MN sends initial RS messages over an UP 971 underlying interface with its OMNI LLA as the source and with 972 destination set to All-Routers multicast. The RS messages include an 973 OMNI option per Section 9 with valid prefix registration information, 974 ifIndex-tuples appropriate for underlying interfaces and MS-Register/ 975 Release sub-options. 977 ARs process IPv6 ND messages with OMNI options and act as a proxy for 978 MSEs. ARs receive RS messages and create a neighbor cache entry for 979 the MN, then coordinate with any named MSIDs in a manner outside the 980 scope of this document. The AR returns an RA message with 981 destination address set to the MN OMNI LLA (i.e., unicast), with 982 source address set to its MS OMNI LLA, with the P(roxy) bit set in 983 the RA flags [RFC4389][RFC5175], with an OMNI option with valid 984 prefix registration information, ifIndex-tuples, MS-Register/Release 985 sub-options, and with any information for the link that would 986 normally be delivered in a solicited RA message. ARs return RA 987 messages with configuration information in response to a MN's RS 988 messages. The AR sets the RA Cur Hop Limit, M and O flags, Router 989 Lifetime, Reachable Time and Retrans Timer values, and includes any 990 necessary options such as: 992 o PIOs with (A; L=0) that include MSPs for the link [RFC8028]. 994 o RIOs [RFC4191] with more-specific routes. 996 o an MTU option that specifies the maximum acceptable packet size 997 for this ANET interface. 999 The AR coordinates with each Register/Release MSID then sends an 1000 immediate unicast RA response without delay; therefore, the IPv6 ND 1001 MAX_RA_DELAY_TIME and MIN_DELAY_BETWEEN_RAS constants for multicast 1002 RAs do not apply. The AR MAY send periodic and/or event-driven 1003 unsolicited RA messages according to the standard [RFC4861]. 1005 When the MSE processes the OMNI information, it first validates the 1006 prefix registration information. The MSE then injects/withdraws the 1007 MNP in the routing/mapping system and caches/discards the new Prefix 1008 Length, MNP and ifIndex-tuples. The MSE then informs the AR of 1009 registration success/failure, and the AR adds the MSE to the list of 1010 Register/Release MSIDs to return in an RA message OMNI option per 1011 Section 9. 1013 When the MN receives the RA message, it creates an OMNI interface 1014 neighbor cache entry with the AR's address as an L2 address and 1015 records the MSIDs that have confirmed MNP registration via this AR. 1016 If the MN connects to multiple ANETs, it establishes additional AR L2 1017 addresses (i.e., as a Multilink neighbor). The MN then manages its 1018 underlying interfaces according to their states as follows: 1020 o When an underlying interface transitions to UP, the MN sends an RS 1021 over the underlying interface with an OMNI option with R set to 1. 1022 The OMNI option contains at least one ifIndex-tuple with values 1023 specific to this underlying interface, and may contain additional 1024 ifIndex-tuples specific to this and/or other underlying 1025 interfaces. The option also includes any Register/Release MSIDs. 1027 o When an underlying interface transitions to DOWN, the MN sends an 1028 RS or unsolicited NA message over any UP underlying interface with 1029 an OMNI option containing an ifIndex-tuple for the DOWN underlying 1030 interface with Link set to '0'. The MN sends an RS when an 1031 acknowledgement is required, or an unsolicited NA when reliability 1032 is not thought to be a concern (e.g., if redundant transmissions 1033 are sent on multiple underlying interfaces). 1035 o When the Router Lifetime for a specific AR nears expiration, the 1036 MN sends an RS over the underlying interface to receive a fresh 1037 RA. If no RA is received, the MN marks the underlying interface 1038 as DOWN. 1040 o When a MN wishes to release from one or more current MSIDs, it 1041 sends an RS or unsolicited NA message over any UP underlying 1042 interfaces with an OMNI option with a Release MSID. Each MSID 1043 then withdraws the MNP from the routing/mapping system and informs 1044 the AR that the release was successful. 1046 o When all of a MNs underlying interfaces have transitioned to DOWN 1047 (or if the prefix registration lifetime expires), any associated 1048 MSEs withdraw the MNP the same as if they had received a message 1049 with a release indication. 1051 The MN is responsible for retrying each RS exchange up to 1052 MAX_RTR_SOLICITATIONS times separated by RTR_SOLICITATION_INTERVAL 1053 seconds until an RA is received. If no RA is received over a an UP 1054 underlying interface, the MN declares this underlying interface as 1055 DOWN. 1057 The IPv6 layer sees the OMNI interface as an ordinary IPv6 interface. 1058 Therefore, when the IPv6 layer sends an RS message the OMNI interface 1059 returns an internally-generated RA message as though the message 1060 originated from an IPv6 router. The internally-generated RA message 1061 contains configuration information that is consistent with the 1062 information received from the RAs generated by the MS. Whether the 1063 OMNI interface IPv6 ND messaging process is initiated from the 1064 receipt of an RS message from the IPv6 layer is an implementation 1065 matter. Some implementations may elect to defer the IPv6 ND 1066 messaging process until an RS is received from the IPv6 layer, while 1067 others may elect to initiate the process proactively. 1069 Note: The Router Lifetime value in RA messages indicates the time 1070 before which the MN must send another RS message over this underlying 1071 interface (e.g., 600 seconds), however that timescale may be 1072 significantly longer than the lifetime the MS has committed to retain 1073 the prefix registration (e.g., REACHABLETIME seconds). ARs are 1074 therefore responsible for keeping MS state alive on a shorter 1075 timescale than the MN is required to do on its own behalf. 1077 13. Secure Redirection 1079 If the ANET link model is multiple access, the AR is responsible for 1080 assuring that address duplication cannot corrupt the neighbor caches 1081 of other nodes on the link. When the MN sends an RS message on a 1082 multiple access ANET link, the AR verifies that the MN is authorized 1083 to use the address and returns an RA with a non-zero Router Lifetime 1084 only if the MN is authorized. 1086 After verifying MN authorization and returning an RA, the AR MAY 1087 return IPv6 ND Redirect messages to direct MNs located on the same 1088 ANET link to exchange packets directly without transiting the AR. In 1089 that case, the MNs can exchange packets according to their unicast L2 1090 addresses discovered from the Redirect message instead of using the 1091 dogleg path through the AR. In some ANET links, however, such direct 1092 communications may be undesirable and continued use of the dogleg 1093 path through the AR may provide better performance. In that case, 1094 the AR can refrain from sending Redirects, and/or MNs can ignore 1095 them. 1097 14. AR and MSE Resilience 1099 ANETs SHOULD deploy ARs in Virtual Router Redundancy Protocol (VRRP) 1100 [RFC5798] configurations so that service continuity is maintained 1101 even if one or more ARs fail. Using VRRP, the MN is unaware which of 1102 the (redundant) ARs is currently providing service, and any service 1103 discontinuity will be limited to the failover time supported by VRRP. 1104 Widely deployed public domain implementations of VRRP are available. 1106 MSEs SHOULD use high availability clustering services so that 1107 multiple redundant systems can provide coordinated response to 1108 failures. As with VRRP, widely deployed public domain 1109 implementations of high availability clustering services are 1110 available. Note that special-purpose and expensive dedicated 1111 hardware is not necessary, and public domain implementations can be 1112 used even between lightweight virtual machines in cloud deployments. 1114 15. Detecting and Responding to MSE Failures 1116 In environments where fast recovery from MSE failure is required, ARs 1117 SHOULD use proactive Neighbor Unreachability Detection (NUD) in a 1118 manner that parallels Bidirectional Forwarding Detection (BFD) 1119 [RFC5880] to track MSE reachability. ARs can then quickly detect and 1120 react to failures so that cached information is re-established 1121 through alternate paths. Proactive NUD control messaging is carried 1122 only over well-connected ground domain networks (i.e., and not low- 1123 end ANET links such as aeronautical radios) and can therefore be 1124 tuned for rapid response. 1126 ARs perform proactive NUD for MSEs for which there are currently 1127 active MNs on the ANET. If an MSE fails, ARs can quickly inform MNs 1128 of the outage by sending multicast RA messages on the ANET interface. 1129 The AR sends RA messages to MNs via the ANET interface with an OMNI 1130 option with a Release ID for the failed MSE, and with destination 1131 address set to All-Nodes multicast (ff02::1) [RFC4291]. 1133 The AR SHOULD send MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated 1134 by small delays [RFC4861]. Any MNs on the ANET interface that have 1135 been using the (now defunct) MSE will receive the RA messages and 1136 associate with a new MSE. 1138 16. Transition Considerations 1140 When a MN connects to an ANET link for the first time, it sends an RS 1141 message with an OMNI option. If the first hop AR recognizes the 1142 option, it returns an RA with its MS OMNI LLA as the source, the MN 1143 OMNI LLA as the destination, the P(roxy) bit set in the RA flags and 1144 with an OMNI option included. The MN then engages the AR according 1145 to the OMNI link model specified above. If the first hop AR is a 1146 legacy IPv6 router, however, it instead returns an RA message with no 1147 OMNI option and with a non-OMNI unicast source LLA as specified in 1148 [RFC4861]. In that case, the MN engages the ANET according to the 1149 legacy IPv6 link model and without the OMNI extensions specified in 1150 this document. 1152 If the ANET link model is multiple access, there must be assurance 1153 that address duplication cannot corrupt the neighbor caches of other 1154 nodes on the link. When the MN sends an RS message on a multiple 1155 access ANET link with an OMNI LLA source address and an OMNI option, 1156 ARs that recognize the option ensure that the MN is authorized to use 1157 the address and return an RA with a non-zero Router Lifetime only if 1158 the MN is authorized. ARs that do not recognize the option instead 1159 return an RA that makes no statement about the MN's authorization to 1160 use the source address. In that case, the MN should perform 1161 Duplicate Address Detection to ensure that it does not interfere with 1162 other nodes on the link. 1164 An alternative approach for multiple access ANET links to ensure 1165 isolation for MN / AR communications is through L2 address mappings 1166 as discussed in Appendix C. This arrangement imparts a (virtual) 1167 point-to-point link model over the (physical) multiple access link. 1169 17. OMNI Interfaces on the Open Internet 1171 OMNI interfaces configured over INET interfaces that connect to the 1172 open Internet can apply symmetric security services such as VPNs or 1173 establish a direct link through some other means. In environments 1174 where an explicit VPN or direct link may be impractical, OMNI 1175 interfaces can instead use Teredo UDP/IP encapsulation 1176 [RFC6081][RFC4380]. (SEcure Neighbor Discovery (SEND) and 1177 Cryptographically Generated Addresses (CGA) [RFC3971][RFC3972] can 1178 also be used if additional authentication is necessary.) 1180 The IPv6 ND control plane messages used to establish neighbor cache 1181 state must be authenticated while data plane messages are delivered 1182 the same as for ordinary best-effort Internet traffic with basic 1183 source address-based data origin verification. Data plane 1184 communications via OMNI interfaces that connect over the open 1185 Internet without an explicit VPN should therefore employ transport- 1186 or higher-layer security to ensure integrity and/or confidentiality. 1188 OMNI interfaces in the open Internet are often located behind Network 1189 Address Translators (NATs). The OMNI interface accommodates NAT 1190 traversal using UDP/IP encapsulation and the mechanisms discussed in 1191 [RFC6081][RFC4380][I-D.templin-intarea-6706bis]. 1193 18. Time-Varying MNPs 1195 In some use cases, it is desirable, beneficial and efficient for the 1196 MN to receive a constant MNP that travels with the MN wherever it 1197 moves. For example, this would allow air traffic controllers to 1198 easily track aircraft, etc. In other cases, however (e.g., 1199 intelligent transportation systems), the MN may be willing to 1200 sacrifice a modicum of efficiency in order to have time-varying MNPs 1201 that can be changed every so often to defeat adversarial tracking. 1203 Prefix delegation services such as those discussed in 1204 [I-D.templin-6man-dhcpv6-ndopt] and [I-D.templin-intarea-6706bis] 1205 allow OMNI MNs that desire time-varying MNPs to obtain short-lived 1206 prefixes. In that case, the identity of the MN would not be bound to 1207 the MNP but rather to the prefix delegation ID and used as the seed 1208 for Prefix Delegation. The MN would then be obligated to renumber 1209 its internal networks whenever its MNP (and therefore also its OMNI 1210 address) changes. This should not present a challenge for MNs with 1211 automated network renumbering services, however presents limits for 1212 the durations of ongoing sessions that would prefer to use a constant 1213 address. 1215 19. IANA Considerations 1217 The IANA is instructed to allocate an official Type number TBD from 1218 the registry "IPv6 Neighbor Discovery Option Formats" for the OMNI 1219 option. Implementations set Type to 253 as an interim value 1220 [RFC4727]. 1222 The IANA is instructed to allocate one Ethernet unicast address TBD2 1223 (suggest 00-00-5E-00-52-14 [RFC5214]) in the registry "IANA Ethernet 1224 Address Block - Unicast Use". 1226 The OMNI option also defines an 8-bit Sub-Type field, for which IANA 1227 is instructed to create and maintain a new registry entitled "OMNI 1228 option Sub-Type values". Initial values for the OMNI option Sub-Type 1229 values registry are given below; future assignments are to be made 1230 through Expert Review [RFC8126]. 1232 Value Sub-Type name Reference 1233 ----- ------------- ---------- 1234 0 Pad1 [RFCXXXX] 1235 1 PadN [RFCXXXX] 1236 2 ifIndex-tuple (Type 1) [RFCXXXX] 1237 3 ifIndex-tuple (Type 2) [RFCXXXX] 1238 4 MS-Register [RFCXXXX] 1239 5 MS-Release [RFCXXXX] 1240 6-252 Unassigned 1241 253-254 Experimental [RFCXXXX] 1242 255 Reserved [RFCXXXX] 1244 Figure 13: OMNI Option Sub-Type Values 1246 20. Security Considerations 1248 Security considerations for IPv6 [RFC8200] and IPv6 Neighbor 1249 Discovery [RFC4861] apply. OMNI interface IPv6 ND messages SHOULD 1250 include Nonce and Timestamp options [RFC3971] when synchronized 1251 transaction confirmation is needed. 1253 OMNI interfaces configured over secured ANET interfaces inherit the 1254 physical and/or link-layer security properties of the connected 1255 ANETs. OMNI interfaces configured over open INET interfaces can use 1256 symmetric securing services such as VPNs or can by some other means 1257 establish a direct link. When a VPN or direct link may be 1258 impractical, however, an asymmetric security service such as SEcure 1259 Neighbor Discovery (SEND) [RFC3971] with Cryptographically Generated 1260 Addresses (CGAs) [RFC3972] and/or the Teredo Authentication option 1261 [RFC4380] may be necessary. 1263 While the OMNI link protects control plane messaging as discussed 1264 above, applications should still employ transport- or higher-layer 1265 security services to protect the data plane. 1267 Security considerations for specific access network interface types 1268 are covered under the corresponding IP-over-(foo) specification 1269 (e.g., [RFC2464], [RFC2492], etc.). 1271 21. Acknowledgements 1273 The first version of this document was prepared per the consensus 1274 decision at the 7th Conference of the International Civil Aviation 1275 Organization (ICAO) Working Group-I Mobility Subgroup on March 22, 1276 2019. Consensus to take the document forward to the IETF was reached 1277 at the 9th Conference of the Mobility Subgroup on November 22, 2019. 1278 Attendees and contributors included: Guray Acar, Danny Bharj, 1279 Francois D'Humieres, Pavel Drasil, Nikos Fistas, Giovanni Garofolo, 1280 Bernhard Haindl, Vaughn Maiolla, Tom McParland, Victor Moreno, Madhu 1281 Niraula, Brent Phillips, Liviu Popescu, Jacky Pouzet, Aloke Roy, Greg 1282 Saccone, Robert Segers, Michal Skorepa, Michel Solery, Stephane 1283 Tamalet, Fred Templin, Jean-Marc Vacher, Bela Varkonyi, Tony Whyman, 1284 Fryderyk Wrobel and Dongsong Zeng. 1286 The following individuals are acknowledged for their useful comments: 1287 Michael Matyas, Madhu Niraula, Greg Saccone, Stephane Tamalet, Eric 1288 Vyncke. Pavel Drasil, Zdenek Jaron and Michal Skorepa are recognized 1289 for their many helpful ideas and suggestions. 1291 This work is aligned with the NASA Safe Autonomous Systems Operation 1292 (SASO) program under NASA contract number NNA16BD84C. 1294 This work is aligned with the FAA as per the SE2025 contract number 1295 DTFAWA-15-D-00030. 1297 22. References 1299 22.1. Normative References 1301 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1302 Requirement Levels", BCP 14, RFC 2119, 1303 DOI 10.17487/RFC2119, March 1997, 1304 . 1306 [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, 1307 "Definition of the Differentiated Services Field (DS 1308 Field) in the IPv4 and IPv6 Headers", RFC 2474, 1309 DOI 10.17487/RFC2474, December 1998, 1310 . 1312 [RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander, 1313 "SEcure Neighbor Discovery (SEND)", RFC 3971, 1314 DOI 10.17487/RFC3971, March 2005, 1315 . 1317 [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)", 1318 RFC 3972, DOI 10.17487/RFC3972, March 2005, 1319 . 1321 [RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and 1322 More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191, 1323 November 2005, . 1325 [RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast 1326 Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005, 1327 . 1329 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 1330 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 1331 2006, . 1333 [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet 1334 Control Message Protocol (ICMPv6) for the Internet 1335 Protocol Version 6 (IPv6) Specification", STD 89, 1336 RFC 4443, DOI 10.17487/RFC4443, March 2006, 1337 . 1339 [RFC4727] Fenner, B., "Experimental Values In IPv4, IPv6, ICMPv4, 1340 ICMPv6, UDP, and TCP Headers", RFC 4727, 1341 DOI 10.17487/RFC4727, November 2006, 1342 . 1344 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 1345 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 1346 DOI 10.17487/RFC4861, September 2007, 1347 . 1349 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 1350 Address Autoconfiguration", RFC 4862, 1351 DOI 10.17487/RFC4862, September 2007, 1352 . 1354 [RFC6088] Tsirtsis, G., Giarreta, G., Soliman, H., and N. Montavont, 1355 "Traffic Selectors for Flow Bindings", RFC 6088, 1356 DOI 10.17487/RFC6088, January 2011, 1357 . 1359 [RFC8028] Baker, F. and B. Carpenter, "First-Hop Router Selection by 1360 Hosts in a Multi-Prefix Network", RFC 8028, 1361 DOI 10.17487/RFC8028, November 2016, 1362 . 1364 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 1365 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 1366 May 2017, . 1368 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 1369 (IPv6) Specification", STD 86, RFC 8200, 1370 DOI 10.17487/RFC8200, July 2017, 1371 . 1373 [RFC8201] McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed., 1374 "Path MTU Discovery for IP version 6", STD 87, RFC 8201, 1375 DOI 10.17487/RFC8201, July 2017, 1376 . 1378 22.2. Informative References 1380 [I-D.templin-6man-dhcpv6-ndopt] 1381 Templin, F., "A Unified Stateful/Stateless Configuration 1382 Service for IPv6", draft-templin-6man-dhcpv6-ndopt-09 1383 (work in progress), January 2020. 1385 [I-D.templin-intarea-6706bis] 1386 Templin, F., "Asymmetric Extended Route Optimization 1387 (AERO)", draft-templin-intarea-6706bis-47 (work in 1388 progress), April 2020. 1390 [RFC2225] Laubach, M. and J. Halpern, "Classical IP and ARP over 1391 ATM", RFC 2225, DOI 10.17487/RFC2225, April 1998, 1392 . 1394 [RFC2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet 1395 Networks", RFC 2464, DOI 10.17487/RFC2464, December 1998, 1396 . 1398 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 1399 IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473, 1400 December 1998, . 1402 [RFC2492] Armitage, G., Schulter, P., and M. Jork, "IPv6 over ATM 1403 Networks", RFC 2492, DOI 10.17487/RFC2492, January 1999, 1404 . 1406 [RFC2863] McCloghrie, K. and F. Kastenholz, "The Interfaces Group 1407 MIB", RFC 2863, DOI 10.17487/RFC2863, June 2000, 1408 . 1410 [RFC3692] Narten, T., "Assigning Experimental and Testing Numbers 1411 Considered Useful", BCP 82, RFC 3692, 1412 DOI 10.17487/RFC3692, January 2004, 1413 . 1415 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 1416 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 1417 DOI 10.17487/RFC3810, June 2004, 1418 . 1420 [RFC3819] Karn, P., Ed., Bormann, C., Fairhurst, G., Grossman, D., 1421 Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L. 1422 Wood, "Advice for Internet Subnetwork Designers", BCP 89, 1423 RFC 3819, DOI 10.17487/RFC3819, July 2004, 1424 . 1426 [RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through 1427 Network Address Translations (NATs)", RFC 4380, 1428 DOI 10.17487/RFC4380, February 2006, 1429 . 1431 [RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery 1432 Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April 1433 2006, . 1435 [RFC4541] Christensen, M., Kimball, K., and F. Solensky, 1436 "Considerations for Internet Group Management Protocol 1437 (IGMP) and Multicast Listener Discovery (MLD) Snooping 1438 Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006, 1439 . 1441 [RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick, 1442 "Internet Group Management Protocol (IGMP) / Multicast 1443 Listener Discovery (MLD)-Based Multicast Forwarding 1444 ("IGMP/MLD Proxying")", RFC 4605, DOI 10.17487/RFC4605, 1445 August 2006, . 1447 [RFC5175] Haberman, B., Ed. and R. Hinden, "IPv6 Router 1448 Advertisement Flags Option", RFC 5175, 1449 DOI 10.17487/RFC5175, March 2008, 1450 . 1452 [RFC5213] Gundavelli, S., Ed., Leung, K., Devarapalli, V., 1453 Chowdhury, K., and B. Patil, "Proxy Mobile IPv6", 1454 RFC 5213, DOI 10.17487/RFC5213, August 2008, 1455 . 1457 [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site 1458 Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, 1459 DOI 10.17487/RFC5214, March 2008, 1460 . 1462 [RFC5558] Templin, F., Ed., "Virtual Enterprise Traversal (VET)", 1463 RFC 5558, DOI 10.17487/RFC5558, February 2010, 1464 . 1466 [RFC5798] Nadas, S., Ed., "Virtual Router Redundancy Protocol (VRRP) 1467 Version 3 for IPv4 and IPv6", RFC 5798, 1468 DOI 10.17487/RFC5798, March 2010, 1469 . 1471 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 1472 (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, 1473 . 1475 [RFC6081] Thaler, D., "Teredo Extensions", RFC 6081, 1476 DOI 10.17487/RFC6081, January 2011, 1477 . 1479 [RFC6543] Gundavelli, S., "Reserved IPv6 Interface Identifier for 1480 Proxy Mobile IPv6", RFC 6543, DOI 10.17487/RFC6543, May 1481 2012, . 1483 [RFC7084] Singh, H., Beebee, W., Donley, C., and B. Stark, "Basic 1484 Requirements for IPv6 Customer Edge Routers", RFC 7084, 1485 DOI 10.17487/RFC7084, November 2013, 1486 . 1488 [RFC7421] Carpenter, B., Ed., Chown, T., Gont, F., Jiang, S., 1489 Petrescu, A., and A. Yourtchenko, "Analysis of the 64-bit 1490 Boundary in IPv6 Addressing", RFC 7421, 1491 DOI 10.17487/RFC7421, January 2015, 1492 . 1494 [RFC7847] Melia, T., Ed. and S. Gundavelli, Ed., "Logical-Interface 1495 Support for IP Hosts with Multi-Access Support", RFC 7847, 1496 DOI 10.17487/RFC7847, May 2016, 1497 . 1499 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 1500 Writing an IANA Considerations Section in RFCs", BCP 26, 1501 RFC 8126, DOI 10.17487/RFC8126, June 2017, 1502 . 1504 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 1505 Decraene, B., Litkowski, S., and R. Shakir, "Segment 1506 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 1507 July 2018, . 1509 [RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J., 1510 Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header 1511 (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020, 1512 . 1514 Appendix A. Type 1 ifIndex-tuple Traffic Classifier Preference Encoding 1516 Adaptation of the OMNI option Type 1 ifIndex-tuple's traffic 1517 classifier Bitmap to specific Internetworks such as the Aeronautical 1518 Telecommunications Network with Internet Protocol Services (ATN/IPS) 1519 may include link selection preferences based on other traffic 1520 classifiers (e.g., transport port numbers, etc.) in addition to the 1521 existing DSCP-based preferences. Nodes on specific Internetworks 1522 maintain a map of traffic classifiers to additional P[*] preference 1523 fields beyond the first 64. For example, TCP port 22 maps to P[67], 1524 TCP port 443 maps to P[70], UDP port 8060 maps to P[76], etc. 1526 Implementations use Simplex or Indexed encoding formats for P[*] 1527 encoding in order to encode a given set of traffic classifiers in the 1528 most efficient way. Some use cases may be more efficiently coded 1529 using Simplex form, while others may be more efficient using Indexed. 1530 Once a format is selected for preparation of a single ifIndex-tuple 1531 the same format must be used for the entire Sub-Option. Different 1532 Sub-Options may use different formats. 1534 The following figures show coding examples for various Simplex and 1535 Indexed formats: 1537 0 1 2 3 1538 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 1539 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1540 | Sub-Type=2 | Sub-length=4+N| ifIndex | ifType | 1541 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1542 | Provider ID | Link |S|0|RSV| Bitmap(0)=0xff|P00|P01|P02|P03| 1543 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1544 |P04|P05|P06|P07|P08|P09|P10|P11|P12|P13|P14|P15|P16|P17|P18|P19| 1545 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1546 |P20|P21|P22|P23|P24|P25|P26|P27|P28|P29|P30|P31| Bitmap(1)=0xff| 1547 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1548 |P32|P33|P34|P35|P36|P37|P38|P39|P40|P41|P42|P43|P44|P45|P46|P47| 1549 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1550 |P48|P49|P50|P51|P52|P53|P54|P55|P56|P57|P58|P59|P60|P61|P62|P63| 1551 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1552 | Bitmap(2)=0xff|P64|P65|P67|P68| ... 1553 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1555 Figure 14: Example 1: Dense Simplex Encoding 1557 0 1 2 3 1558 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 1559 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1560 | Sub-Type=2 | Sub-length=4+N| ifIndex | ifType | 1561 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1562 | Provider ID | Link |S|0|RSV| Bitmap(0)=0x00| Bitmap(1)=0x0f| 1563 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1564 |P48|P49|P50|P51|P52|P53|P54|P55|P56|P57|P58|P59|P60|P61|P62|P63| 1565 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1566 | Bitmap(2)=0x00| Bitmap(3)=0x00| Bitmap(4)=0x00| Bitmap(5)=0x00| 1567 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1568 | Bitmap(6)=0xf0|192|193|194|195|196|197|198|199|200|201|202|203| 1569 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1570 |204|205|206|207| Bitmap(7)=0x00| Bitmap(8)=0x0f|272|273|274|275| 1571 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1572 |276|277|278|279|280|281|282|283|284|285|286|287| Bitmap(9)=0x00| 1573 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1574 |Bitmap(10)=0x00| ... 1575 +-+-+-+-+-+-+-+-+-+-+- 1577 Figure 15: Example 2: Sparse Simplex Encoding 1579 0 1 2 3 1580 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 1581 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1582 | Sub-Type=2 | Sub-length=4+N| ifIndex | ifType | 1583 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1584 | Provider ID | Link |S|1|RSV| Index = 0x00 | Bitmap = 0x80 | 1585 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1586 |P00|P01|P02|P03| Index = 0x01 | Bitmap = 0x01 |P60|P61|P62|P63| 1587 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1588 | Index = 0x10 | Bitmap = 0x80 |512|513|514|515| Index = 0x18 | 1589 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1590 | Bitmap = 0x01 |796|797|798|799| ... 1591 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1593 Figure 16: Example 3: Indexed Encoding 1595 Appendix B. VDL Mode 2 Considerations 1597 ICAO Doc 9776 is the "Technical Manual for VHF Data Link Mode 2" 1598 (VDLM2) that specifies an essential radio frequency data link service 1599 for aircraft and ground stations in worldwide civil aviation air 1600 traffic management. The VDLM2 link type is "multicast capable" 1601 [RFC4861], but with considerable differences from common multicast 1602 links such as Ethernet and IEEE 802.11. 1604 First, the VDLM2 link data rate is only 31.5Kbps - multiple orders of 1605 magnitude less than most modern wireless networking gear. Second, 1606 due to the low available link bandwidth only VDLM2 ground stations 1607 (i.e., and not aircraft) are permitted to send broadcasts, and even 1608 so only as compact layer 2 "beacons". Third, aircraft employ the 1609 services of ground stations by performing unicast RS/RA exchanges 1610 upon receipt of beacons instead of listening for multicast RA 1611 messages and/or sending multicast RS messages. 1613 This beacon-oriented unicast RS/RA approach is necessary to conserve 1614 the already-scarce available link bandwidth. Moreover, since the 1615 numbers of beaconing ground stations operating within a given spatial 1616 range must be kept as sparse as possible, it would not be feasible to 1617 have different classes of ground stations within the same region 1618 observing different protocols. It is therefore highly desirable that 1619 all ground stations observe a common language of RS/RA as specified 1620 in this document. 1622 Note that links of this nature may benefit from compression 1623 techniques that reduce the bandwidth necessary for conveying the same 1624 amount of data. The IETF lpwan working group is considering possible 1625 alternatives: [https://datatracker.ietf.org/wg/lpwan/documents]. 1627 Appendix C. MN / AR Isolation Through L2 Address Mapping 1629 Per [RFC4861], IPv6 ND messages may be sent to either a multicast or 1630 unicast link-scoped IPv6 destination address. However, IPv6 ND 1631 messaging should be coordinated between the MN and AR only without 1632 invoking other nodes on the ANET. This implies that MN / AR control 1633 messaging should be isolated and not overheard by other nodes on the 1634 link. 1636 To support MN / AR isolation on some ANET links, ARs can maintain an 1637 OMNI-specific unicast L2 address ("MSADDR"). For Ethernet-compatible 1638 ANETs, this specification reserves one Ethernet unicast address TBD2 1639 (see: Section 19). For non-Ethernet statically-addressed ANETs, 1640 MSADDR is reserved per the assigned numbers authority for the ANET 1641 addressing space. For still other ANETs, MSADDR may be dynamically 1642 discovered through other means, e.g., L2 beacons. 1644 MNs map the L3 addresses of all IPv6 ND messages they send (i.e., 1645 both multicast and unicast) to MSADDR instead of to an ordinary 1646 unicast or multicast L2 address. In this way, all of the MN's IPv6 1647 ND messages will be received by ARs that are configured to accept 1648 packets destined to MSADDR. Note that multiple ARs on the link could 1649 be configured to accept packets destined to MSADDR, e.g., as a basis 1650 for supporting redundancy. 1652 Therefore, ARs must accept and process packets destined to MSADDR, 1653 while all other devices must not process packets destined to MSADDR. 1654 This model has well-established operational experience in Proxy 1655 Mobile IPv6 (PMIP) [RFC5213][RFC6543]. 1657 Appendix D. Change Log 1659 << RFC Editor - remove prior to publication >> 1661 Differences from draft-templin-6man-omni-interface-18 to draft- 1662 templin-6man-omni-interface-19: 1664 o SEND/CGA. 1666 Differences from draft-templin-6man-omni-interface-17 to draft- 1667 templin-6man-omni-interface-18: 1669 o Teredo 1671 Differences from draft-templin-6man-omni-interface-14 to draft- 1672 templin-6man-omni-interface-15: 1674 o Prefix length discussions removed. 1676 Differences from draft-templin-6man-omni-interface-12 to draft- 1677 templin-6man-omni-interface-13: 1679 o Teredo 1681 Differences from draft-templin-6man-omni-interface-11 to draft- 1682 templin-6man-omni-interface-12: 1684 o Major simplifications and clarifications on MTU and fragmentation. 1686 o Document now updates RFC4443 and RFC8201. 1688 Differences from draft-templin-6man-omni-interface-10 to draft- 1689 templin-6man-omni-interface-11: 1691 o Removed /64 assumption, resulting in new OMNI address format. 1693 Differences from draft-templin-6man-omni-interface-07 to draft- 1694 templin-6man-omni-interface-08: 1696 o OMNI MNs in the open Internet 1698 Differences from draft-templin-6man-omni-interface-06 to draft- 1699 templin-6man-omni-interface-07: 1701 o Brought back L2 MSADDR mapping text for MN / AR isolation based on 1702 L2 addressing. 1704 o Expanded "Transition Considerations". 1706 Differences from draft-templin-6man-omni-interface-05 to draft- 1707 templin-6man-omni-interface-06: 1709 o Brought back OMNI option "R" flag, and discussed its use. 1711 Differences from draft-templin-6man-omni-interface-04 to draft- 1712 templin-6man-omni-interface-05: 1714 o Transition considerations, and overhaul of RS/RA addressing with 1715 the inclusion of MSE addresses within the OMNI option instead of 1716 as RS/RA addresses (developed under FAA SE2025 contract number 1717 DTFAWA-15-D-00030). 1719 Differences from draft-templin-6man-omni-interface-02 to draft- 1720 templin-6man-omni-interface-03: 1722 o Added "advisory PTB messages" under FAA SE2025 contract number 1723 DTFAWA-15-D-00030. 1725 Differences from draft-templin-6man-omni-interface-01 to draft- 1726 templin-6man-omni-interface-02: 1728 o Removed "Primary" flag and supporting text. 1730 o Clarified that "Router Lifetime" applies to each ANET interface 1731 independently, and that the union of all ANET interface Router 1732 Lifetimes determines MSE lifetime. 1734 Differences from draft-templin-6man-omni-interface-00 to draft- 1735 templin-6man-omni-interface-01: 1737 o "All-MSEs" OMNI LLA defined. Also reserved fe80::ff00:0000/104 1738 for future use (most likely as "pseudo-multicast"). 1740 o Non-normative discussion of alternate OMNI LLA construction form 1741 made possible if the 64-bit assumption were relaxed. 1743 Differences from draft-templin-atn-aero-interface-21 to draft- 1744 templin-6man-omni-interface-00: 1746 o Minor clarification on Type-2 ifIndex-tuple encoding. 1748 o Draft filename change (replaces draft-templin-atn-aero-interface). 1750 Differences from draft-templin-atn-aero-interface-20 to draft- 1751 templin-atn-aero-interface-21: 1753 o OMNI option format 1755 o MTU 1757 Differences from draft-templin-atn-aero-interface-19 to draft- 1758 templin-atn-aero-interface-20: 1760 o MTU 1762 Differences from draft-templin-atn-aero-interface-18 to draft- 1763 templin-atn-aero-interface-19: 1765 o MTU 1767 Differences from draft-templin-atn-aero-interface-17 to draft- 1768 templin-atn-aero-interface-18: 1770 o MTU and RA configuration information updated. 1772 Differences from draft-templin-atn-aero-interface-16 to draft- 1773 templin-atn-aero-interface-17: 1775 o New "Primary" flag in OMNI option. 1777 Differences from draft-templin-atn-aero-interface-15 to draft- 1778 templin-atn-aero-interface-16: 1780 o New note on MSE OMNI LLA uniqueness assurance. 1782 o General cleanup. 1784 Differences from draft-templin-atn-aero-interface-14 to draft- 1785 templin-atn-aero-interface-15: 1787 o General cleanup. 1789 Differences from draft-templin-atn-aero-interface-13 to draft- 1790 templin-atn-aero-interface-14: 1792 o General cleanup. 1794 Differences from draft-templin-atn-aero-interface-12 to draft- 1795 templin-atn-aero-interface-13: 1797 o Minor re-work on "Notify-MSE" (changed to Notification ID). 1799 Differences from draft-templin-atn-aero-interface-11 to draft- 1800 templin-atn-aero-interface-12: 1802 o Removed "Request/Response" OMNI option formats. Now, there is 1803 only one OMNI option format that applies to all ND messages. 1805 o Added new OMNI option field and supporting text for "Notify-MSE". 1807 Differences from draft-templin-atn-aero-interface-10 to draft- 1808 templin-atn-aero-interface-11: 1810 o Changed name from "aero" to "OMNI" 1812 o Resolved AD review comments from Eric Vyncke (posted to atn list) 1814 Differences from draft-templin-atn-aero-interface-09 to draft- 1815 templin-atn-aero-interface-10: 1817 o Renamed ARO option to AERO option 1819 o Re-worked Section 13 text to discuss proactive NUD. 1821 Differences from draft-templin-atn-aero-interface-08 to draft- 1822 templin-atn-aero-interface-09: 1824 o Version and reference update 1826 Differences from draft-templin-atn-aero-interface-07 to draft- 1827 templin-atn-aero-interface-08: 1829 o Removed "Classic" and "MS-enabled" link model discussion 1831 o Added new figure for MN/AR/MSE model. 1833 o New Section on "Detecting and responding to MSE failure". 1835 Differences from draft-templin-atn-aero-interface-06 to draft- 1836 templin-atn-aero-interface-07: 1838 o Removed "nonce" field from AR option format. Applications that 1839 require a nonce can include a standard nonce option if they want 1840 to. 1842 o Various editorial cleanups. 1844 Differences from draft-templin-atn-aero-interface-05 to draft- 1845 templin-atn-aero-interface-06: 1847 o New Appendix C on "VDL Mode 2 Considerations" 1849 o New Appendix D on "RS/RA Messaging as a Single Standard API" 1851 o Various significant updates in Section 5, 10 and 12. 1853 Differences from draft-templin-atn-aero-interface-04 to draft- 1854 templin-atn-aero-interface-05: 1856 o Introduced RFC6543 precedent for focusing IPv6 ND messaging to a 1857 reserved unicast link-layer address 1859 o Introduced new IPv6 ND option for Aero Registration 1861 o Specification of MN-to-MSE message exchanges via the ANET access 1862 router as a proxy 1864 o IANA Considerations updated to include registration requests and 1865 set interim RFC4727 option type value. 1867 Differences from draft-templin-atn-aero-interface-03 to draft- 1868 templin-atn-aero-interface-04: 1870 o Removed MNP from aero option format - we already have RIOs and 1871 PIOs, and so do not need another option type to include a Prefix. 1873 o Clarified that the RA message response must include an aero option 1874 to indicate to the MN that the ANET provides a MS. 1876 o MTU interactions with link adaptation clarified. 1878 Differences from draft-templin-atn-aero-interface-02 to draft- 1879 templin-atn-aero-interface-03: 1881 o Sections re-arranged to match RFC4861 structure. 1883 o Multiple aero interfaces 1885 o Conceptual sending algorithm 1887 Differences from draft-templin-atn-aero-interface-01 to draft- 1888 templin-atn-aero-interface-02: 1890 o Removed discussion of encapsulation (out of scope) 1892 o Simplified MTU section 1894 o Changed to use a new IPv6 ND option (the "aero option") instead of 1895 S/TLLAO 1897 o Explained the nature of the interaction between the mobility 1898 management service and the air interface 1900 Differences from draft-templin-atn-aero-interface-00 to draft- 1901 templin-atn-aero-interface-01: 1903 o Updates based on list review comments on IETF 'atn' list from 1904 4/29/2019 through 5/7/2019 (issue tracker established) 1906 o added list of opportunities afforded by the single virtual link 1907 model 1909 o added discussion of encapsulation considerations to Section 6 1911 o noted that DupAddrDetectTransmits is set to 0 1913 o removed discussion of IPv6 ND options for prefix assertions. The 1914 aero address already includes the MNP, and there are many good 1915 reasons for it to continue to do so. Therefore, also including 1916 the MNP in an IPv6 ND option would be redundant. 1918 o Significant re-work of "Router Discovery" section. 1920 o New Appendix B on Prefix Length considerations 1922 First draft version (draft-templin-atn-aero-interface-00): 1924 o Draft based on consensus decision of ICAO Working Group I Mobility 1925 Subgroup March 22, 2019. 1927 Authors' Addresses 1929 Fred L. Templin (editor) 1930 The Boeing Company 1931 P.O. Box 3707 1932 Seattle, WA 98124 1933 USA 1935 Email: fltemplin@acm.org 1937 Tony Whyman 1938 MWA Ltd c/o Inmarsat Global Ltd 1939 99 City Road 1940 London EC1Y 1AX 1941 England 1943 Email: tony.whyman@mccallumwhyman.com