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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: October 15, 2020 MWA Ltd c/o Inmarsat Global Ltd 6 April 13, 2020 8 Transmission of IPv6 Packets over Overlay Multilink Network (OMNI) 9 Interfaces 10 draft-templin-6man-omni-interface-14 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 October 15, 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 . . . . . . . . . . . . . . . . . . . . 11 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 . . . . . . . . . . 25 80 16. Transition Considerations . . . . . . . . . . . . . . . . . . 25 81 17. OMNI Interfaces on the Open Internet . . . . . . . . . . . . 26 82 18. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26 83 19. Security Considerations . . . . . . . . . . . . . . . . . . . 27 84 20. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 27 85 21. References . . . . . . . . . . . . . . . . . . . . . . . . . 28 86 21.1. Normative References . . . . . . . . . . . . . . . . . . 28 87 21.2. Informative References . . . . . . . . . . . . . . . . . 30 88 Appendix A. Type 1 ifIndex-tuple Traffic Classifier Preference 89 Encoding . . . . . . . . . . . . . . . . . . . . . . 32 90 Appendix B. Prefix Length Considerations . . . . . . . . . . . . 34 91 Appendix C. VDL Mode 2 Considerations . . . . . . . . . . . . . 35 92 Appendix D. MN / AR Isolation Through L2 Address Mapping . . . . 36 93 Appendix E. Change Log . . . . . . . . . . . . . . . . . . . . . 36 94 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 41 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 defined in [RFC4291] (with Link-Local scope assumed). 155 The following terms are defined within the scope of this document: 157 Mobile Node (MN) 158 an end system with multiple distinct upstream data link 159 connections that are managed together as a single logical unit. 160 The MN's data link connection parameters can change over time due 161 to, e.g., node mobility, link quality, etc. The MN further 162 connects a downstream-attached End User Network (EUN). The term 163 MN used here is distinct from uses in other documents, and does 164 not imply a particular mobility protocol. 166 End User Network (EUN) 167 a simple or complex downstream-attached mobile network that 168 travels with the MN as a single logical unit. The IPv6 addresses 169 assigned to EUN devices remain stable even if the MN's upstream 170 data link connections change. 172 Mobility Service (MS) 173 a mobile routing service that tracks MN movements and ensures that 174 MNs remain continuously reachable even across mobility events. 175 Specific MS details are out of scope for this document. 177 Mobility Service Endpoint (MSE) 178 an entity in the MS (either singluar or aggregate) that 179 coordinates the mobility events of one or more MN. 181 Mobility Service Prefix (MSP) 182 an aggregated IPv6 prefix (e.g., 2001:db8::/32) advertised to the 183 rest of the Internetwork by the MS, and from which more-specific 184 Mobile Network Prefixes (MNPs) are derived. 186 Mobile Network Prefix (MNP) 187 a longer IPv6 prefix taken from an MSP (e.g., 188 2001:db8:1000:2000::/56) and assigned to a MN. MNs sub-delegate 189 the MNP to devices located in EUNs. 191 Access Network (ANET) 192 a data link service network (e.g., an aviation radio access 193 network, satellite service provider network, cellular operator 194 network, wifi network, etc.) that connects MNs. Physical and/or 195 data link level security between the MN and ANET are assumed. 197 Access Router (AR) 198 a first-hop router in the ANET for connecting MNs to 199 correspondents in outside Internetworks. 201 ANET interface 202 a MN's attachment to a link in an ANET. 204 Internetwork (INET) 205 a connected network region with a coherent IP addressing plan that 206 provides transit forwarding services for ANET MNs and INET 207 correspondents. Examples include private enterprise networks, 208 ground domain aviation service networks and the global public 209 Internet itself. 211 INET interface 212 a node's attachment to a link in an INET. 214 OMNI link 215 a virtual overlay configured over one or more INETs and their 216 connected ANETs. An OMNI link can comprise multiple INET segments 217 joined by bridges the same as for any link; the addressing plans 218 in each segment may be mutually exclusive and managed by different 219 administrative entities. 221 OMNI interface 222 a node's attachment to an OMNI link, and configured over one or 223 more underlying ANET/INET interfaces. 225 OMNI link local address (LLA) 226 an IPv6 link-local address constructed as specified in Section 7, 227 and assigned to an OMNI interface. 229 OMNI Option 230 an IPv6 Neighbor Discovery option providing multilink parameters 231 for the OMNI interface as specified in Section 9. 233 Multilink 234 an OMNI interface's manner of managing diverse underlying data 235 link interfaces as a single logical unit. The OMNI interface 236 provides a single unified interface to upper layers, while 237 underlying data link selections are performed on a per-packet 238 basis considering factors such as DSCP, flow label, application 239 policy, signal quality, cost, etc. Multilinking decisions are 240 coordinated in both the outbound (i.e. MN to correspondent) and 241 inbound (i.e., correspondent to MN) directions. 243 L2 244 The second layer in the OSI network model. Also known as "layer- 245 2", "link-layer", "sub-IP layer", "data link layer", etc. 247 L3 248 The third layer in the OSI network model. Also known as "layer- 249 3", "network-layer", "IPv6 layer", etc. 251 underlying interface 252 an ANET/INET interface over which an OMNI interface is configured. 253 The OMNI interface is seen as a L3 interface by the IP layer, and 254 each underlying interface is seen as a L2 interface by the OMNI 255 interface. 257 Mobility Service Identification (MSID) 258 Each MSE and AR is assigned a unique 32-bit Identification (MSID) 259 as specified in Section 7. 261 Spanning Partitioned Administrative Networks (SPAN) 262 A means for bridging disjoint INET partitions as segments of a 263 unified OMNI link the same as for a bridged campus LAN. The SPAN 264 is a mid-layer IPv6 encapsulation service that supports a unified 265 OMNI link view for all segments. 267 3. Requirements 269 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 270 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 271 "OPTIONAL" in this document are to be interpreted as described in BCP 272 14 [RFC2119][RFC8174] when, and only when, they appear in all 273 capitals, as shown here. 275 An implementation is not required to internally use the architectural 276 constructs described here so long as its external behavior is 277 consistent with that described in this document. 279 4. Overlay Multilink Network (OMNI) Interface Model 281 An OMNI interface is a MN virtual interface configured over one or 282 more underlying interfaces, which may be physical (e.g., an 283 aeronautical radio link) or virtual (e.g., an Internet or higher- 284 layer "tunnel"). The MN receives a MNP from the MS, and coordinates 285 with the MS through IPv6 ND message exchanges. The MN uses the MNP 286 to construct a unique OMNI LLA through the algorithmic derivation 287 specified in Section 7 and assigns the LLA to the OMNI interface. 289 The OMNI interface architectural layering model is the same as in 290 [RFC7847], and augmented as shown in Figure 1. The IP layer 291 therefore sees the OMNI interface as a single L3 interface with 292 multiple underlying interfaces that appear as L2 communication 293 channels in the architecture. 295 +----------------------------+ 296 | Upper Layer Protocol | 297 Session-to-IP +---->| | 298 Address Binding | +----------------------------+ 299 +---->| IP (L3) | 300 IP Address +---->| | 301 Binding | +----------------------------+ 302 +---->| OMNI Interface | 303 Logical-to- +---->| (OMNI LLA) | 304 Physical | +----------------------------+ 305 Interface +---->| L2 | L2 | | L2 | 306 Binding |(IF#1)|(IF#2)| ..... |(IF#n)| 307 +------+------+ +------+ 308 | L1 | L1 | | L1 | 309 | | | | | 310 +------+------+ +------+ 312 Figure 1: OMNI Interface Architectural Layering Model 314 The OMNI virtual interface model gives rise to a number of 315 opportunities: 317 o since OMNI LLAs are uniquely derived from an MNP, no Duplicate 318 Address Detection (DAD) or Muticast Listener Discovery (MLD) 319 messaging is necessary. 321 o ANET interfaces do not require any L3 addresses (i.e., not even 322 link-local) in environments where communications are coordinated 323 entirely over the OMNI interface. (An alternative would be to 324 also assign the same OMNI LLA to all ANET interfaces.) 326 o as ANET interface properties change (e.g., link quality, cost, 327 availability, etc.), any active ANET interface can be used to 328 update the profiles of multiple additional ANET interfaces in a 329 single message. This allows for timely adaptation and service 330 continuity under dynamically changing conditions. 332 o coordinating ANET interfaces in this way allows them to be 333 represented in a unified MS profile with provisions for mobility 334 and multilink operations. 336 o exposing a single virtual interface abstraction to the IPv6 layer 337 allows for multilink operation (including QoS based link 338 selection, packet replication, load balancing, etc.) at L2 while 339 still permitting L3 traffic shaping based on, e.g., DSCP, flow 340 label, etc. 342 o L3 sees the OMNI interface as a point of connection to the OMNI 343 link; if there are multiple OMNI links (i.e., multiple MS's), L3 344 will see multiple OMNI interfaces. 346 Other opportunities are discussed in [RFC7847]. 348 Figure 2 depicts the architectural model for a MN connecting to the 349 MS via multiple independent ANETs. When an underlying interface 350 becomes active, the MN's OMNI interface sends native (i.e., 351 unencapsulated) IPv6 ND messages via the underlying interface. IPv6 352 ND messages traverse the ground domain ANETs until they reach an 353 Access Router (AR#1, AR#2, .., AR#n). The AR then coordinates with a 354 Mobility Service Endpoint (MSE#1, MSE#2, ..., MSE#m) in the INET and 355 returns an IPv6 ND message response to the MN. IPv6 ND messages 356 traverse the ANET at layer 2; hence, the Hop Limit is not 357 decremented. 359 +--------------+ 360 | MN | 361 +--------------+ 362 |OMNI interface| 363 +----+----+----+ 364 +--------|IF#1|IF#2|IF#n|------ + 365 / +----+----+----+ \ 366 / | \ 367 / <---- Native | IP ----> \ 368 v v v 369 (:::)-. (:::)-. (:::)-. 370 .-(::ANET:::) .-(::ANET:::) .-(::ANET:::) 371 `-(::::)-' `-(::::)-' `-(::::)-' 372 +----+ +----+ +----+ 373 ... |AR#1| .......... |AR#2| ......... |AR#n| ... 374 . +-|--+ +-|--+ +-|--+ . 375 . | | | 376 . v v v . 377 . <----- Encapsulation -----> . 378 . . 379 . +-----+ (:::)-. . 380 . |MSE#2| .-(::::::::) +-----+ . 381 . +-----+ .-(::: INET :::)-. |MSE#m| . 382 . (::::: Routing ::::) +-----+ . 383 . `-(::: System :::)-' . 384 . +-----+ `-(:::::::-' . 385 . |MSE#1| +-----+ +-----+ . 386 . +-----+ |MSE#3| |MSE#4| . 387 . +-----+ +-----+ . 388 . . 389 . . 390 . <----- Worldwide Connected Internetwork ----> . 391 ........................................................... 393 Figure 2: MN/MS Coordination via Multiple ANETs 395 After the initial IPv6 ND message exchange, the MN can send and 396 receive unencapsulated IPv6 data packets over the OMNI interface. 397 OMNI interface multilink services will forward the packets via ARs in 398 the correct underlying ANETs. The AR encapsulates the packets 399 according to the capabilities provided by the MS and forwards them to 400 the next hop within the worldwide connected Internetwork via optimal 401 routes. 403 5. Maximum Transmission Unit (MTU) and Fragmentation 405 All IPv6 interfaces are REQUIRED to configure a minimum Maximum 406 Transmission Unit (MTU) of 1280 bytes [RFC8200]. The network 407 therefore MUST forward packets of at least 1280 bytes without 408 generating an IPv6 Path MTU Discovery (PMTUD) Packet Too Big (PTB) 409 message [RFC8201]. 411 The OMNI interface configures an MTU of 9180 bytes [RFC2492]; the 412 size is therefore not a reflection of the underlying interface MTUs, 413 but rather determines the largest packet the OMNI interface can 414 forward or reassemble. The OMNI interface therefore accommodates IP 415 packets up to 9180 bytes while generating IPv6 Path MTU Discovery 416 (PMTUD) Packet Too Big (PTB) messages [RFC8201] as necessary (see 417 below). 419 OMNI interfaces employ mid-layer IPv6 encapsulation and 420 fragmentation/reassembly per [RFC2473] (also known as "SPAN 421 encapsulation" - see Section 8) to accommodate the 9180 byte MTU. 422 The OMNI interface returns internally-generated PTB messages for 423 packets admitted into the interface that it deems too large (e.g., 424 according to link performance characteristics, reassembly cost, etc.) 425 while either dropping or forwarding the packet as necessary. The 426 OMNI interface performs PMTUD even if the destination appears to be 427 on the same link since an OMNI link node on the path may return a 428 PTB. This ensures that the path MTU is adaptive and reflects the 429 current path used for a given data flow. 431 OMNI interfaces perform SPAN encapsulation and fragmentation/ 432 reassembly as follows: 434 o When an OMNI interface sends a packet toward a final destination 435 via an ANET peer, it sends without SPAN encapsulation if the 436 packet is no larger than the underlying interface MTU. Otherwise, 437 it encapsulates the packet in a SPAN header with source address 438 set to the node's own SPAN address and destination set to the SPAN 439 address of the ANET peer. The OMNI interface then uses IPv6 440 fragmentation to break the encapsulated packet into a minimum 441 number of non-overlapping fragments, where the largest fragment 442 size is determined by the underlying interface MTU and the 443 smallest fragment is no smaller than 640 bytes. The OMNI 444 interface then sends the fragments to the ANET peer, which 445 reassembles before forwarding toward the final destination. 447 o When an OMNI interface sends a packet toward a final destination 448 via an INET interface, it sends packets no larger than 1280 bytes 449 without SPAN encapsulation if the destination is reached via an 450 INET address within the same SPAN segment. Otherwise, it 451 encapsulates the packet in a SPAN header with source address set 452 to the node's SPAN address and destination set to the SPAN address 453 of the next hop OMNI node toward the final destination. The OMNI 454 interface then uses IPv6 fragmentation to break the encapsulated 455 packet into a minimum number of non-overlapping fragments, where 456 the largest fragment size is 1280 bytes and the smallest fragment 457 is no smaller than 640 bytes. The OMNI interface then sends the 458 fragments to the SPAN destination, which reassembles before 459 forwarding toward the final destination. 461 In order to avoid a "tiny fragment" attack, OMNI interfaces 462 unconditionally drop all SPAN fragments smaller than 640 bytes. In 463 order to set the correct context for reassembly, the OMNI interface 464 that inserts a SPAN header MUST also be the one that inserts the IPv6 465 Fragment Header Identification value. Although all fragmnets of the 466 same fragmented SPAN packet are typically sent via the same 467 underlying interface, this is not strictly required since all 468 fragments will arrive at the OMNI interface that performs reassembly 469 even if they travel over different paths. 471 Note that the OMNI interface can forward large packets via 472 encapsulation and fragmentation while at the same time returning 473 advisory PTB messages, e.g., subject to rate limiting. The receiving 474 node that performs reassembly can also send advisory PTB messages if 475 reassembly conditions become unfavorable. The AERO interface can 476 therefore continuously forward large packets without loss while 477 returning advisory messages recommending a smaller size. Advisory 478 PTB messages are differentiated from PTB messages that report loss by 479 setting the Code field in the ICMPv6 message header to the value 1. 480 This document therefore updates [RFC4443] and [RFC8201]. 482 6. Frame Format 484 The OMNI interface transmits IPv6 packets according to the native 485 frame format of each underlying interface. For example, for 486 Ethernet-compatible interfaces the frame format is specified in 487 [RFC2464], for aeronautical radio interfaces the frame format is 488 specified in standards such as ICAO Doc 9776 (VDL Mode 2 Technical 489 Manual), for tunnels over IPv6 the frame format is specified in 490 [RFC2473], etc. 492 7. Link-Local Addresses 494 OMNI interfaces assign IPv6 Link-Local Addresses (i.e., "OMNI LLAs") 495 using the following constructs: 497 o IPv6 MN OMNI LLAs encode the most-significant 112 bits of a MNP 498 within the least-significant 112 bits of the the IPv6 link-local 499 prefix fe80::/16. For example, for the MNP 500 2001:db8:1000:2000::/56 the corresponding LLA is 501 fe80:2001:db8:1000:2000::/72. See: [RFC4291], Section 2.5.6) for 502 a discussion of IPv6 link-local addresses, for which this document 503 presents an OMNI interface-specific adaptation. See Appendix B 504 for further discussion on prefix lengths. 506 o IPv4-compatible MN OMNI LLAs are assigned as fe80::ffff:[v4addr], 507 i.e., the most significant 16 bits of the prefix fe80::/16, 508 followed by 64 '0' bits, followed by 16 '1' bits, followed by a 509 32bit IPv4 address. For example, the IPv4-Compatible MN OMNI LLA 510 for 192.0.2.1 is fe80::ffff:192.0.2.1 (also written as 511 fe80::ffff:c000:0201). 513 o MS OMNI LLAs are assigned to ARs and MSEs from the range 514 fe80::/96, and MUST be managed for uniqueness. The lower 32 bits 515 of the LLA includes a unique integer "MSID" value between 516 0x00000001 and 0xfeffffff, e.g., as in fe80::1, fe80::2, fe80::3, 517 etc., fe80::feff:ffff. The MSID 0x00000000 corresponds to the 518 link-local Subnet-Router anycast address (fe80::) [RFC4291]. The 519 MSID range 0xff000000 through 0xffffffff is reserved for future 520 use. (Note that distinct OMNI link segments can avoid overlap by 521 assigning MS OMNI LLAs from unique fe80::/96 sub-prefixes. For 522 example, a first segment could assign from fe80::1000/116, a 523 second from fe80::2000/116, a third from fe80::3000/116, etc. 525 o The OMNI LLA range fe80::/32 is used as the Teredo service prefix 526 for OMNI interfaces according to the format in Section 4 of 527 [RFC4380] (see Section 17 for further discussion). 529 Since the prefix 0000::/8 is "Reserved by the IETF" [RFC4291], no 530 MNPs can be allocated from that block ensuring that there is no 531 possibility for overlap between the above OMNI LLA constructs. 533 Since MN OMNI LLAs are based on the distribution of administratively 534 assured unique MNPs, and since MS OMNI LLAs are guaranteed unique 535 through administrative assignment, OMNI interfaces set the 536 autoconfiguration variable DupAddrDetectTransmits to 0 [RFC4862]. 538 8. The SPAN 540 OMNI links employ an overlay network instance called "The SPAN" 541 (Spanning Partitioned Administrative Networks) that supports 542 forwarding of encapsulated link-scoped messages over a private IPv6 543 routing instance that spans the entire link without decrementing the 544 (link-local) Hop Limit. The OMNI link reserves the Unique Local 545 Address (ULA) prefix fd80::/16 [RFC4193] used for mapping OMNI LLAs 546 to routable SPAN addresses. 548 SPAN addresses are configured in one-to-one correspondence with MN/MS 549 OMNI LLAs by simply zeroing bit 7 of the LLA. For example: 551 o the SPAN address corresponding to fe80:2001:db8:1:2:: is simply 552 fd80:2001:db8:1:2:: 554 o the SPAN address corresponding to fe80::ffff:192.0.2.1 is simply 555 fd80::ffff:192.0.2.1 557 o the SPAN address corresponding to fe80::1000 is simply fd80::1000 559 The SPAN address presents an IPv6 address format that is routable 560 within the OMNI link routing system and can be used to convey link- 561 scoped messages across multiple hops using IPv6 encapsulation 562 [RFC2473]. The SPAN extends over the entire OMNI link to include the 563 MNs, but SPAN encapsulation is omitted over ANET links when possible 564 to conserve bandwidth (see: Section 11). 566 A full discussion of the SPAN appears in 567 [I-D.templin-intarea-6706bis]. 569 9. Address Mapping - Unicast 571 OMNI interfaces maintain a neighbor cache for tracking per-neighbor 572 state and use the link-local address format specified in Section 7. 573 IPv6 Neighbor Discovery (ND) [RFC4861] messages on MN OMNI interfaces 574 observe the native Source/Target Link-Layer Address Option (S/TLLAO) 575 formats of the underlying interfaces (e.g., for Ethernet the S/TLLAO 576 is specified in [RFC2464]). 578 MNs such as aircraft typically have many wireless data link types 579 (e.g. satellite-based, cellular, terrestrial, air-to-air directional, 580 etc.) with diverse performance, cost and availability properties. 581 The OMNI interface would therefore appear to have multiple L2 582 connections, and may include information for multiple underlying 583 interfaces in a single IPv6 ND message exchange. 585 OMNI interfaces use an IPv6 ND option called the "OMNI option" 586 formatted as shown in Figure 3: 588 0 1 2 3 589 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 1 590 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 591 | Type | Length | Prefix Length |R| Reserved | 592 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 593 | | 594 ~ Sub-Options ~ 595 | | 596 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 598 Figure 3: OMNI Option Format 600 In this format: 602 o Type is set to TBD. 604 o Length is set to the number of 8 octet blocks in the option. 606 o Prefix Length is set according to the IPv6 source address type. 607 For MN OMNI LLAs, the value is set to the length of the embedded 608 MNP. For IPv4-compatible MN OMNI LLAs, the value is set to 96 609 plus the length of the embedded IPv4 prefix. For MS OMNI LLAs, 610 the value is set to 128. 612 o R (the "Register/Release" bit) is set to 1/0 to request the 613 message recipient to register/release a MN's MNP. The OMNI option 614 may additionally include MSIDs for the recipient to contact to 615 also register/release the MNP. 617 o Reserved is set to the value '0' on transmission and ignored on 618 reception. 620 o Sub-Options is a Variable-length field, of length such that the 621 complete OMNI Option is an integer multiple of 8 octets long. 622 Contains one or more options, as described in Section 8.1. 624 9.1. Sub-Options 626 The OMNI option includes zero or more Sub-Options, some of which may 627 appear multiple times in the same message. Each consecutive Sub- 628 Option is concatenated immediately after its predecessor. All Sub- 629 Options except Pad1 (see below) are type-length-value (TLV) encoded 630 in the following format: 632 0 1 2 633 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 5 634 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 635 | Sub-Type | Sub-length | Sub-Option Data ... 636 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 638 Figure 4: Sub-Option Format 640 o Sub-Type is a 1-byte field that encodes the Sub-Option type. Sub- 641 Options defined in this document are: 643 Option Name Sub-Type 644 Pad1 0 645 PadN 1 646 ifIndex-tuple (Type 1) 2 647 ifIndex-tuple (Type 2) 3 648 MS-Register 4 649 MS-Release 5 651 Figure 5 653 Sub-Types 253 and 254 are reserved for experimentation, as 654 recommended in[RFC3692]]. 656 o Sub-Length is a 1-byte field that encodes the length of the Sub- 657 Option Data, in bytes 659 o Sub-Option Data is a byte string with format determined by Sub- 660 Type 662 During processing, unrecognized Sub-Options are ignored and the next 663 Sub-Option processed until the end of the OMNI option. 665 The following Sub-Option types and formats are defined in this 666 document: 668 9.1.1. Pad1 670 0 671 0 1 2 3 4 5 6 7 672 +-+-+-+-+-+-+-+-+ 673 | Sub-Type=0 | 674 +-+-+-+-+-+-+-+-+ 676 Figure 6: Pad1 678 o Sub-Type is set to 0. 680 o No Sub-Length or Sub-Option Data follows (i.e., the "Sub-Option" 681 consists of a single zero octet). 683 9.1.2. PadN 685 0 1 2 686 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 5 687 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 688 | Sub-Type=1 |Sub-length=N-2 | N-2 padding bytes ... 689 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 691 Figure 7: PadN 693 o Sub-Type is set to 1. 695 o Sub-Length is set to N-2 being the number of padding bytes that 696 follow. 698 o Sub-Option Data consists of N-2 zero-valued octets. 700 9.1.3. ifIndex-tuple (Type 1) 702 0 1 2 3 703 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 1 704 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 705 | Sub-Type=2 | Sub-length=4+N| ifIndex | ifType | 706 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 707 | Provider ID | Link |S|I|RSV| Bitmap(0)=0xff|P00|P01|P02|P03| 708 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 709 |P04|P05|P06|P07|P08|P09|P10|P11|P12|P13|P14|P15|P16|P17|P18|P19| 710 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 711 |P20|P21|P22|P23|P24|P25|P26|P27|P28|P29|P30|P31| Bitmap(1)=0xff| 712 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 713 |P32|P33|P34|P35|P36|P37|P38|P39| ... 714 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 716 Figure 8: ifIndex-tuple (Type 1) 718 o Sub-Type is set to 2. 720 o Sub-Length is set to 4+N (the number of Sub-Option Data bytes that 721 follow). 723 o Sub-Option Data contains an "ifIndex-tuple" (Type 1) encoded as 724 follows (note that the first four bytes must be present): 726 * ifIndex is set to an 8-bit integer value corresponding to a 727 specific underlying interface. OMNI options MAY include 728 multiple ifIndex-tuples, and MUST number each with an ifIndex 729 value between '1' and '255' that represents a MN-specific 8-bit 730 mapping for the actual ifIndex value assigned to the underlying 731 interface by network management [RFC2863] (the ifIndex value 732 '0' is reserved for use by the MS). Multiple ifIndex-tuples 733 with the same ifIndex value MAY appear in the same OMNI option. 735 * ifType is set to an 8-bit integer value corresponding to the 736 underlying interface identified by ifIndex. The value 737 represents an OMNI interface-specific 8-bit mapping for the 738 actual IANA ifType value registered in the 'IANAifType-MIB' 739 registry [http://www.iana.org]. 741 * Provider ID is set to an OMNI interface-specific 8-bit ID value 742 for the network service provider associated with this ifIndex. 744 * Link encodes a 4-bit link metric. The value '0' means the link 745 is DOWN, and the remaining values mean the link is UP with 746 metric ranging from '1' ("lowest") to '15' ("highest"). 748 * S is set to '1' if this ifIndex-tuple corresponds to the 749 underlying interface that is the source of the ND message. Set 750 to '0' otherwise. 752 * I is set to '0' ("Simplex") if the index for each singleton 753 Bitmap byte in the Sub-Option Data is inferred from its 754 sequential position (i.e., 0, 1, 2, ...), or set to '1' 755 ("Indexed") if each Bitmap is preceded by an Index byte. 756 Figure 8 shows the simplex case for I set to '0'. For I set to 757 '1', each Bitmap is instead preceded by an Index byte that 758 encodes a value "i" = (0 - 255) as the index for its companion 759 Bitmap as follows: 761 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 762 | Index=i | Bitmap(i) |P[*] values ... 763 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 765 Figure 9 767 * RSV is set to the value 0 on transmission and ignored on 768 reception. 770 * The remainder of the Sub-Option Data contains N = (0 - 251) 771 bytes of traffic classifier preferences consisting of a first 772 (indexed) Bitmap (i.e., "Bitmap(i)") followed by 0-8 1-byte 773 blocks of 2-bit P[*] values, followed by a second Bitmap (i), 774 followed by 0-8 blocks of P[*] values, etc. Reading from bit 0 775 to bit 7, the bits of each Bitmap(i) that are set to '1'' 776 indicate the P[*] blocks from the range P[(i*32)] through 777 P[(i*32) + 31] that follow; if any Bitmap(i) bits are '0', then 778 the corresponding P[*] block is instead omitted. For example, 779 if Bitmap(0) contains 0xff then the block with P[00]-P[03], 780 followed by the block with P[04]-P[07], etc., and ending with 781 the block with P[28]-P[31] are included (as showin in 782 Figure 8). The next Bitmap(i) is then consulted with its bits 783 indicating which P[*] blocks follow, etc. out to the end of the 784 Sub-Option. The first 16 P[*] blocks correspond to the 64 785 Differentiated Service Code Point (DSCP) values P[00] - P[63] 786 [RFC2474]. If additional P[*] blocks follow, their values 787 correspond to "pseudo-DSCP" traffic classifier values P[64], 788 P[65], P[66], etc. See Appendix A for further discussion and 789 examples. 791 * Each 2-bit P[*] field is set to the value '0' ("disabled"), '1' 792 ("low"), '2' ("medium") or '3' ("high") to indicate a QoS 793 preference level for underlying interface selection purposes. 794 Not all P[*] values need to be included in all OMNI option 795 instances of a given ifIndex-tuple. Any P[*] values 796 represented in an earlier OMNI option but ommitted in the 797 current OMNI option remain unchanged. Any P[*] values not yet 798 represented in any OMNI option default to "medium". 800 9.1.4. ifIndex-tuple (Type 2) 802 0 1 2 3 803 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 1 804 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 805 | Sub-Type=3 | Sub-length=4+N| ifIndex | ifType | 806 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 807 | Provider ID | Link |S|Resvd| ~ 808 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ 809 ~ ~ 810 ~ RFC 6088 Format Traffic Selector ~ 811 ~ ~ 812 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 814 Figure 10: ifIndex-tuple (Type 2) 816 o Sub-Type is set to 3. 818 o Sub-Length is set to 4+N (the number of Sub-Option Data bytes that 819 follow). 821 o Sub-Option Data contains an "ifIndex-tuple" (Type 2) encoded as 822 follows (note that the first four bytes must be present): 824 * ifIndex, ifType, Provider ID, Link and S are set exactly as for 825 Type 1 ifIndex-tuples as specified in Section 9.1.3. 827 * the remainder of the Sub-Option body encodes a variable-length 828 traffic selector formatted per [RFC6088], beginning with the 829 "TS Format" field. 831 9.1.5. MS-Register 833 0 1 2 3 834 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 1 835 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 836 | Sub-Type=4 | Sub-length=4 | MSID (bits 0 - 15) | 837 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 838 | MSID (bits 16 - 32) | 839 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 841 Figure 11: MS-Register Sub-option 843 o Sub-Type is set to 4. 845 o Sub-Length is set to 4. 847 o MSID contains the 32 bit ID of an MSE or AR, in network byte 848 order. OMNI options contain zero or more MS-Register sub-options. 850 9.1.6. MS-Release 852 0 1 2 3 853 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 1 854 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 855 | Sub-Type=5 | Sub-length=4 | MSID (bits 0 - 15) | 856 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 857 | MSID (bits 16 - 32) | 858 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 860 Figure 12: MS-Release Sub-option 862 o Sub-Type is set to 5. 864 o Sub-Length is set to 4. 866 o MSIID contains the 32 bit ID of an MS or AR, in network byte 867 order. OMNI options contain zero or more MS-Release sub-options. 869 10. Address Mapping - Multicast 871 The multicast address mapping of the native underlying interface 872 applies. The mobile router on board the aircraft also serves as an 873 IGMP/MLD Proxy for its EUNs and/or hosted applications per [RFC4605] 874 while using the L2 address of the router as the L2 address for all 875 multicast packets. 877 11. Conceptual Sending Algorithm 879 The MN's IPv6 layer selects the outbound OMNI interface according to 880 standard IPv6 requirements when forwarding data packets from local or 881 EUN applications to external correspondents. The OMNI interface 882 maintains a neighbor cache the same as for any IPv6 interface, but 883 with additional state for multilink coordination. 885 After a packet enters the OMNI interface, an outbound underlying 886 interface is selected based on multilink parameters such as DSCP, 887 application port number, cost, performance, message size, etc. OMNI 888 interface multilink selections could also be configured to perform 889 replication across multiple underlying interfaces for increased 890 reliability at the expense of packet duplication. 892 When an OMNI interface sends a packet over a selected outbound 893 underlying interface, it omits SPAN encapsulation if the packet does 894 not require fragmentation and the neighbor can determine the SPAN 895 addresses through other means (e.g., the packet's OMNI LLAs, neighbor 896 cache information, etc.). Otherwise, the OMNI interface inserts a 897 SPAN header and performs fragmentation if necessary. 899 OMNI interface multilink service designers MUST observe the BCP 900 guidance in Section 15 [RFC3819] in terms of implications for 901 reordering when packets from the same flow may be spread across 902 multiple underlying interfaces having diverse properties. 904 11.1. Multiple OMNI Interfaces 906 MNs may associate with multiple MS instances concurrently. Each MS 907 instance represents a distinct OMNI link distinguished by its 908 associated MSPs. The MN configures a separate OMNI interface for 909 each link so that multiple interfaces (e.g., omni0, omni1, omni2, 910 etc.) are exposed to the IPv6 layer. 912 Depending on local policy and configuration, an MN may choose between 913 alternative active OMNI interfaces using a packet's DSCP, routing 914 information or static configuration. Interface selection based on 915 per-packet source addresses is also enabled when the MSPs for each 916 OMNI interface are known (e.g., discovered through Prefix Information 917 Options (PIOs) and/or Route Information Options (RIOs)). 919 Each OMNI interface can be configured over the same or different sets 920 of underlying interfaces. Each ANET distinguishes between the 921 different OMNI links based on the MSPs represented in per-packet IPv6 922 addresses. 924 Multiple distinct OMNI links can therefore be used to support fault 925 tolerance, load balancing, reliability, etc. The architectural model 926 parallels Layer 2 Virtual Local Area Networks (VLANs), where the MSPs 927 serve as (virtual) VLAN tags. 929 12. Router Discovery and Prefix Registration 931 MNs interface with the MS by sending RS messages with OMNI options 932 under the assumption that a single AR on the ANET will proocess the 933 message and respond. This places a requirement on each ANET, which 934 may be enforced by physical/logical partitioning, L2 AR beaconing, 935 etc. The manner in which the ANET ensures single AR coordination is 936 link-specific and outside the scope of this document. 938 For each underlying interface, the MN sends an RS message with an 939 OMNI option with prefix registration information, ifIndex-tuples, MS- 940 Register/Release suboptions containing MSIDs, and with destination 941 address set to All-Routers multicast (ff02::2) [RFC4291]. Example 942 MSID discovery methods are given in [RFC5214], including data link 943 login parameters, name service lookups, static configuration, etc. 944 Alternatively, MNs can discover indiviual MSIDs by sending an initial 945 RS with MS-Register MSID set to 0x00000000. 947 MNs configure OMNI interfaces that observe the properties discussed 948 in the previous section. The OMNI interface and its underlying 949 interfaces are said to be in either the "UP" or "DOWN" state 950 according to administrative actions in conjunction with the interface 951 connectivity status. An OMNI interface transitions to UP or DOWN 952 through administrative action and/or through state transitions of the 953 underlying interfaces. When a first underlying interface transitions 954 to UP, the OMNI interface also transitions to UP. When all 955 underlying interfaces transition to DOWN, the OMNI interface also 956 transitions to DOWN. 958 When an OMNI interface transitions to UP, the MN sends RS messages to 959 register its MNP and an initial set of underlying interfaces that are 960 also UP. The MN sends additional RS messages to refresh lifetimes 961 and to register/deregister underlying interfaces as they transition 962 to UP or DOWN. The MN sends initial RS messages over an UP 963 underlying interface with its OMNI LLA as the source and with 964 destination set to All-Routers multicast. The RS messages include an 965 OMNI option per Section 9 with valid prefix registration information, 966 ifIndex-tuples appropriate for underlying interfaces and MS-Register/ 967 Release sub-options. 969 ARs process IPv6 ND messages with OMNI options and act as a proxy for 970 MSEs. ARs receive RS messages and create a neighbor cache entry for 971 the MN, then coordinate with any named MSIDs in a manner outside the 972 scope of this document. The AR returns an RA message with 973 destination address set to the MN OMNI LLA (i.e., unicast), with 974 source address set to its MS OMNI LLA, with the P(roxy) bit set in 975 the RA flags [RFC4389], with an OMNI option with valid prefix 976 registration information, ifIndex-tuples, MS-Register/Release sub- 977 options, and with any information for the link that would normally be 978 delivered in a solicited RA message. ARs return RA messages with 979 configuration information in response to a MN's RS messages. The AR 980 sets the RA Cur Hop Limit, M and O flags, Router Lifetime, Reachable 981 Time and Retrans Timer values, and includes any necessary options 982 such as: 984 o PIOs with (A; L=0) that include MSPs for the link [RFC8028]. 986 o RIOs [RFC4191] with more-specific routes. 988 o an MTU option that specifies the maximum acceptable packet size 989 for this ANET interface. 991 The AR coordinates with each Register/Release MSID then sends an 992 immediate unicast RA response without delay; therefore, the IPv6 ND 993 MAX_RA_DELAY_TIME and MIN_DELAY_BETWEEN_RAS constants for multicast 994 RAs do not apply. The AR MAY send periodic and/or event-driven 995 unsolicited RA messages according to the standard [RFC4861]. 997 When the MSE processes the OMNI information, it first validates the 998 prefix registration information. The MSE then injects/withdraws the 999 MNP in the routing/mapping system and caches/discards the new Prefix 1000 Length, MNP and ifIndex-tuples. The MSE then informs the AR of 1001 registration success/failure, and the AR adds the MSE to the list of 1002 Register/Release MSIDs to return in an RA message OMNI option per 1003 Section 9. 1005 When the MN receives the RA message, it creates an OMNI interface 1006 neighbor cache entry with the AR's address as an L2 address and 1007 records the MSIDs that have confirmed MNP registration via this AR. 1008 If the MN connects to multiple ANETs, it establishes additional AR L2 1009 addresses (i.e., as a Multilink neighbor). The MN then manages its 1010 underlying interfaces according to their states as follows: 1012 o When an underlying interface transitions to UP, the MN sends an RS 1013 over the underlying interface with an OMNI option with R set to 1. 1014 The OMNI option contains at least one ifIndex-tuple with values 1015 specific to this underlying interface, and may contain additional 1016 ifIndex-tuples specific to this and/or other underlying 1017 interfaces. The option also includes any Register/Release MSIDs. 1019 o When an underlying interface transitions to DOWN, the MN sends an 1020 RS or unsolicited NA message over any UP underlying interface with 1021 an OMNI option containing an ifIndex-tuple for the DOWN underlying 1022 interface with Link set to '0'. The MN sends an RS when an 1023 acknowledgement is required, or an unsolicited NA when reliability 1024 is not thought to be a concern (e.g., if redundant transmissions 1025 are sent on multiple underlying interfaces). 1027 o When the Router Lifetime for a specific AR nears expiration, the 1028 MN sends an RS over the underlying interface to receive a fresh 1029 RA. If no RA is received, the MN marks the underlying interface 1030 as DOWN. 1032 o When a MN wishes to release from one or more current MSIDs, it 1033 sends an RS or unsolicited NA message over any UP underlying 1034 interfaces with an OMNI option with a Release MSID. Each MSID 1035 then withdraws the MNP from the routing/mapping system and informs 1036 the AR that the release was successful. 1038 o When all of a MNs underlying interfaces have transitioned to DOWN 1039 (or if the prefix registration lifetime expires), any associated 1040 MSEs withdraw the MNP the same as if they had received a message 1041 with a release indication. 1043 The MN is responsible for retrying each RS exchange up to 1044 MAX_RTR_SOLICITATIONS times separated by RTR_SOLICITATION_INTERVAL 1045 seconds until an RA is received. If no RA is received over a an UP 1046 underlying interface, the MN declares this underlying interface as 1047 DOWN. 1049 The IPv6 layer sees the OMNI interface as an ordinary IPv6 interface. 1050 Therefore, when the IPv6 layer sends an RS message the OMNI interface 1051 returns an internally-generated RA message as though the message 1052 originated from an IPv6 router. The internally-generated RA message 1053 contains configuration information that is consistent with the 1054 information received from the RAs generated by the MS. Whether the 1055 OMNI interface IPv6 ND messaging process is initiated from the 1056 receipt of an RS message from the IPv6 layer is an implementation 1057 matter. Some implementations may elect to defer the IPv6 ND 1058 messaging process until an RS is received from the IPv6 layer, while 1059 others may elect to initiate the process proactively. 1061 Note: The Router Lifetime value in RA messages indicates the time 1062 before which the MN must send another RS message over this underlying 1063 interface (e.g., 600 seconds), however that timescale may be 1064 significantly longer than the lifetime the MS has committed to retain 1065 the prefix registration (e.g., REACHABLETIME seconds). ARs are 1066 therefore responsible for keeping MS state alive on a shorter 1067 timescale than the MN is required to do on its own behalf. 1069 13. Secure Redirection 1071 If the ANET link model is multiple access, the AR is responsible for 1072 assuring that address duplication cannot corrupt the neighbor caches 1073 of other nodes on the link. When the MN sends an RS message on a 1074 multiple access ANET link, the AR verifys that the MN is authorized 1075 to use the address and returns an RA with a non-zero Router Lifetime 1076 only if the MN is authorized. 1078 After verifying MN authorization and returning an RA, the AR MAY 1079 return IPv6 ND Redirect messages to direct MNs located on the same 1080 ANET link to exchange packets directly without transiting the AR. In 1081 that case, the MNs can exchange packets according to their unicast L2 1082 addresses discovered from the Redirect message instead of using the 1083 dogleg path through the AR. In some ANET links, however, such direct 1084 communications may be undesirable and continued use of the dogleg 1085 path through the AR may provide better performance. In that case, 1086 the AR can refrain from sending Redirects, and/or MNs can ignore 1087 them. 1089 14. AR and MSE Resilience 1091 ANETs SHOULD deploy ARs in Virtual Router Redundancy Protocol (VRRP) 1092 [RFC5798] configurations so that service continuity is maintained 1093 even if one or more ARs fail. Using VRRP, the MN is unaware which of 1094 the (redundant) ARs is currently providing service, and any service 1095 discontinuity will be limited to the failover time supported by VRRP. 1096 Widely deployed public domain implementations of VRRP are available. 1098 MSEs SHOULD use high availability clustering services so that 1099 multiple redundant systems can provide coordinated response to 1100 failures. As with VRRP, widely deployed public domain 1101 implementations of high availability clustering services are 1102 available. Note that special-purpose and expensive dedicated 1103 hardware is not necessary, and public domain implementations can be 1104 used even between lightweight virtual machines in cloud deployments. 1106 15. Detecting and Responding to MSE Failures 1108 In environments where fast recovery from MSE failure is required, ARs 1109 SHOULD use proactive Neighbor Unreachability Detection (NUD) in a 1110 manner that parallels Bidirectional Forwarding Detection (BFD) 1111 [RFC5880] to track MSE reachability. ARs can then quickly detect and 1112 react to failures so that cached information is re-established 1113 through alternate paths. Proactive NUD control messaging is carried 1114 only over well-connected ground domain networks (i.e., and not low- 1115 end ANET links such as aeronautical radios) and can therefore be 1116 tuned for rapid response. 1118 ARs perform proactive NUD for MSEs for which there are currently 1119 active MNs on the ANET. If an MSE fails, ARs can quickly inform MNs 1120 of the outage by sending multicast RA messages on the ANET interface. 1121 The AR sends RA messages to the MN via the ANET interface with an 1122 OMNI option with a Release ID for the failed MSE, and with 1123 destination address set to All-Nodes multicast (ff02::1) [RFC4291]. 1125 The AR SHOULD send MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated 1126 by small delays [RFC4861]. Any MNs on the ANET interface that have 1127 been using the (now defunct) MSE will receive the RA messages and 1128 associate with a new MSE. 1130 16. Transition Considerations 1132 When a MN connects to an ANET link for the first time, it sends an RS 1133 message with an OMNI option. If the first hop AR recognizes the 1134 option, it returns an RA with its MS OMNI LLA as the source, the MN 1135 OMNI LLA as the destination, the P(roxy) bit set in the RA flags and 1136 with an OMNI option included. The MN then engages the AR according 1137 to the OMNI link model specified above. If the first hop AR is a 1138 legacy IPv6 router, however, it instead returns an RA message with no 1139 OMNI option and with a non-OMNI unicast source LLA as specified in 1140 [RFC4861]. In that case, the MN engages the ANET according to the 1141 legacy IPv6 link model and without the OMNI extensions specified in 1142 this document. 1144 If the ANET link model is multiple access, there must be assurance 1145 that address duplication cannot corrupt the neighbor caches of other 1146 nodes on the link. When the MN sends an RS message on a multiple 1147 access ANET link with an OMNI LLA source address and an OMNI option, 1148 ARs that recognize the option ensure that the MN is authorized to use 1149 the address and return an RA with a non-zero Router Lifetime only if 1150 the MN is authorized. ARs that do not recognize the option instead 1151 return an RA that makes no statement about the MN's authorization to 1152 use the source address. In that case, the MN should perform 1153 Duplicate Address Detection to ensure that it does not interfere with 1154 other nodes on the link. 1156 An alternative approach for multiple access ANET links to ensure 1157 isolation for MN / AR communications is through L2 address mappings 1158 as discussed in Appendix D. This arrangement imparts a (virtual) 1159 point-to-point link model over the (physical) multiple access link. 1161 17. OMNI Interfaces on the Open Internet 1163 OMNI interfaces that connect to the open Internet via INET interfaces 1164 can apply symmetric security services such as VPNs to establish 1165 secured tunnels to MSEs. In environments where an explicit VPN may 1166 be too restrictive, OMNI interfaces can instead ensure neighbor cache 1167 integrity using SEcure Neighbor Discovery (SEND) [RFC3971] and 1168 Cryptographically Generated Addresses (CGAs) [RFC3972]. 1170 When SEND/CGA are used, the IPv6 ND control plane messages used to 1171 establish neighbor cache state are authenticated while data plane 1172 messages are delivered the same as for ordinary best-effort Internet 1173 traffic. Instead, data plane communications via OMNI interfaces that 1174 connect over the open Internet without an explicit VPN must emply 1175 transport- or higher-layer security to ensure integrity and/or 1176 confidentiality. 1178 In addition to secured OMNI interface RS/RA exchanges, SEND/CGA 1179 supports safe address resolution and neighbor unreachability 1180 detection as discused in Asymmetric Extended Route Optimization 1181 (AERO) [I-D.templin-intarea-6706bis]. This allows for efficient 1182 multilink operations over the open Internet with assured neighbor 1183 cache integrity. 1185 OMNI interfaces in the open Internet are often located behind Network 1186 Address Translators (NATs). The OMNI interface accommodates NAT 1187 traversal using the OMNI LLA prefix fe80::/32 for Teredo IPv6 1188 addresses formatted as discussed in Section 4 of [RFC4380]. Further 1189 specifications for NAT traversal are discussed in 1190 [I-D.templin-intarea-6706bis][RFC6081][RFC4380]. 1192 18. IANA Considerations 1194 The IANA is instructed to allocate an official Type number TBD from 1195 the registry "IPv6 Neighbor Discovery Option Formats" for the OMNI 1196 option. Implementations set Type to 253 as an interim value 1197 [RFC4727]. 1199 The IANA is instructed to allocate one Ethernet unicast address TBD2 1200 (suggest 00-00-5E-00-52-14 [RFC5214]) in the registry "IANA Ethernet 1201 Address Block - Unicast Use". 1203 The OMNI option also defines an 8-bit Sub-Type field, for which IANA 1204 is instructed to create and maintain a new registry entitled "OMNI 1205 option Sub-Type values". Initial values for the OMNI option Sub-Type 1206 values registry are given below; future assignments are to be made 1207 through Expert Review [RFC8126]. 1209 Value Sub-Type name Reference 1210 ----- ------------- ---------- 1211 0 Pad1 [RFCXXXX] 1212 1 PadN [RFCXXXX] 1213 2 ifIndex-tuple (Type 1) [RFCXXXX] 1214 3 ifIndex-tuple (Type 2) [RFCXXXX] 1215 4 MS-Register [RFCXXXX] 1216 5 MS-Release [RFCXXXX] 1217 6-252 Unassigned 1218 253-254 Experimental [RFCXXXX] 1219 255 Reserved [RFCXXXX] 1221 Figure 13: OMNI Option Sub-Type Values 1223 19. Security Considerations 1225 Security considerations for IPv6 [RFC8200] and IPv6 Neighbor 1226 Discovery [RFC4861] apply. OMNI interface IPv6 ND messages SHOULD 1227 include Nonce and Timestamp options [RFC3971] when synchronized 1228 transaction confirmation is needed. 1230 OMNI interfaces configured over secured underlying ANET interfaces 1231 inherit the physical and/or link-layer security aspects of the 1232 connected ANETs. OMNI interfaces configured over open Internet 1233 interfaces must use symmetric securing services such as VPNs or 1234 asymmetric services such as SEND/CGA [RFC3971][RFC3972]. 1236 Security considerations for specific access network interface types 1237 are covered under the corresponding IP-over-(foo) specification 1238 (e.g., [RFC2464], [RFC2492], etc.). 1240 20. Acknowledgements 1242 The first version of this document was prepared per the consensus 1243 decision at the 7th Conference of the International Civil Aviation 1244 Organization (ICAO) Working Group-I Mobility Subgroup on March 22, 1245 2019. Consensus to take the document forward to the IETF was reached 1246 at the 9th Conference of the Mobility Subgroup on November 22, 2019. 1248 Attendees and contributors included: Guray Acar, Danny Bharj, 1249 Francois D'Humieres, Pavel Drasil, Nikos Fistas, Giovanni Garofolo, 1250 Bernhard Haindl, Vaughn Maiolla, Tom McParland, Victor Moreno, Madhu 1251 Niraula, Brent Phillips, Liviu Popescu, Jacky Pouzet, Aloke Roy, Greg 1252 Saccone, Robert Segers, Michal Skorepa, Michel Solery, Stephane 1253 Tamalet, Fred Templin, Jean-Marc Vacher, Bela Varkonyi, Tony Whyman, 1254 Fryderyk Wrobel and Dongsong Zeng. 1256 The following individuals are acknowledged for their useful comments: 1257 Michael Matyas, Madhu Niraula, Greg Saccone, Stephane Tamalet, Eric 1258 Vyncke. Pavel Drasil, Zdenek Jaron and Michal Skorepa are recognized 1259 for their many helpful ideas and suggestions. 1261 This work is aligned with the NASA Safe Autonomous Systems Operation 1262 (SASO) program under NASA contract number NNA16BD84C. 1264 This work is aligned with the FAA as per the SE2025 contract number 1265 DTFAWA-15-D-00030. 1267 21. References 1269 21.1. Normative References 1271 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1272 Requirement Levels", BCP 14, RFC 2119, 1273 DOI 10.17487/RFC2119, March 1997, 1274 . 1276 [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, 1277 "Definition of the Differentiated Services Field (DS 1278 Field) in the IPv4 and IPv6 Headers", RFC 2474, 1279 DOI 10.17487/RFC2474, December 1998, 1280 . 1282 [RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander, 1283 "SEcure Neighbor Discovery (SEND)", RFC 3971, 1284 DOI 10.17487/RFC3971, March 2005, 1285 . 1287 [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)", 1288 RFC 3972, DOI 10.17487/RFC3972, March 2005, 1289 . 1291 [RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and 1292 More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191, 1293 November 2005, . 1295 [RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast 1296 Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005, 1297 . 1299 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 1300 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 1301 2006, . 1303 [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet 1304 Control Message Protocol (ICMPv6) for the Internet 1305 Protocol Version 6 (IPv6) Specification", STD 89, 1306 RFC 4443, DOI 10.17487/RFC4443, March 2006, 1307 . 1309 [RFC4727] Fenner, B., "Experimental Values In IPv4, IPv6, ICMPv4, 1310 ICMPv6, UDP, and TCP Headers", RFC 4727, 1311 DOI 10.17487/RFC4727, November 2006, 1312 . 1314 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 1315 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 1316 DOI 10.17487/RFC4861, September 2007, 1317 . 1319 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 1320 Address Autoconfiguration", RFC 4862, 1321 DOI 10.17487/RFC4862, September 2007, 1322 . 1324 [RFC6088] Tsirtsis, G., Giarreta, G., Soliman, H., and N. Montavont, 1325 "Traffic Selectors for Flow Bindings", RFC 6088, 1326 DOI 10.17487/RFC6088, January 2011, 1327 . 1329 [RFC8028] Baker, F. and B. Carpenter, "First-Hop Router Selection by 1330 Hosts in a Multi-Prefix Network", RFC 8028, 1331 DOI 10.17487/RFC8028, November 2016, 1332 . 1334 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 1335 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 1336 May 2017, . 1338 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 1339 (IPv6) Specification", STD 86, RFC 8200, 1340 DOI 10.17487/RFC8200, July 2017, 1341 . 1343 [RFC8201] McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed., 1344 "Path MTU Discovery for IP version 6", STD 87, RFC 8201, 1345 DOI 10.17487/RFC8201, July 2017, 1346 . 1348 21.2. Informative References 1350 [I-D.templin-intarea-6706bis] 1351 Templin, F., "Asymmetric Extended Route Optimization 1352 (AERO)", draft-templin-intarea-6706bis-41 (work in 1353 progress), April 2020. 1355 [RFC2225] Laubach, M. and J. Halpern, "Classical IP and ARP over 1356 ATM", RFC 2225, DOI 10.17487/RFC2225, April 1998, 1357 . 1359 [RFC2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet 1360 Networks", RFC 2464, DOI 10.17487/RFC2464, December 1998, 1361 . 1363 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 1364 IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473, 1365 December 1998, . 1367 [RFC2492] Armitage, G., Schulter, P., and M. Jork, "IPv6 over ATM 1368 Networks", RFC 2492, DOI 10.17487/RFC2492, January 1999, 1369 . 1371 [RFC2863] McCloghrie, K. and F. Kastenholz, "The Interfaces Group 1372 MIB", RFC 2863, DOI 10.17487/RFC2863, June 2000, 1373 . 1375 [RFC3692] Narten, T., "Assigning Experimental and Testing Numbers 1376 Considered Useful", BCP 82, RFC 3692, 1377 DOI 10.17487/RFC3692, January 2004, 1378 . 1380 [RFC3819] Karn, P., Ed., Bormann, C., Fairhurst, G., Grossman, D., 1381 Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L. 1382 Wood, "Advice for Internet Subnetwork Designers", BCP 89, 1383 RFC 3819, DOI 10.17487/RFC3819, July 2004, 1384 . 1386 [RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through 1387 Network Address Translations (NATs)", RFC 4380, 1388 DOI 10.17487/RFC4380, February 2006, 1389 . 1391 [RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery 1392 Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April 1393 2006, . 1395 [RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick, 1396 "Internet Group Management Protocol (IGMP) / Multicast 1397 Listener Discovery (MLD)-Based Multicast Forwarding 1398 ("IGMP/MLD Proxying")", RFC 4605, DOI 10.17487/RFC4605, 1399 August 2006, . 1401 [RFC5213] Gundavelli, S., Ed., Leung, K., Devarapalli, V., 1402 Chowdhury, K., and B. Patil, "Proxy Mobile IPv6", 1403 RFC 5213, DOI 10.17487/RFC5213, August 2008, 1404 . 1406 [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site 1407 Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, 1408 DOI 10.17487/RFC5214, March 2008, 1409 . 1411 [RFC5798] Nadas, S., Ed., "Virtual Router Redundancy Protocol (VRRP) 1412 Version 3 for IPv4 and IPv6", RFC 5798, 1413 DOI 10.17487/RFC5798, March 2010, 1414 . 1416 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 1417 (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, 1418 . 1420 [RFC6081] Thaler, D., "Teredo Extensions", RFC 6081, 1421 DOI 10.17487/RFC6081, January 2011, 1422 . 1424 [RFC6543] Gundavelli, S., "Reserved IPv6 Interface Identifier for 1425 Proxy Mobile IPv6", RFC 6543, DOI 10.17487/RFC6543, May 1426 2012, . 1428 [RFC7084] Singh, H., Beebee, W., Donley, C., and B. Stark, "Basic 1429 Requirements for IPv6 Customer Edge Routers", RFC 7084, 1430 DOI 10.17487/RFC7084, November 2013, 1431 . 1433 [RFC7421] Carpenter, B., Ed., Chown, T., Gont, F., Jiang, S., 1434 Petrescu, A., and A. Yourtchenko, "Analysis of the 64-bit 1435 Boundary in IPv6 Addressing", RFC 7421, 1436 DOI 10.17487/RFC7421, January 2015, 1437 . 1439 [RFC7847] Melia, T., Ed. and S. Gundavelli, Ed., "Logical-Interface 1440 Support for IP Hosts with Multi-Access Support", RFC 7847, 1441 DOI 10.17487/RFC7847, May 2016, 1442 . 1444 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 1445 Writing an IANA Considerations Section in RFCs", BCP 26, 1446 RFC 8126, DOI 10.17487/RFC8126, June 2017, 1447 . 1449 Appendix A. Type 1 ifIndex-tuple Traffic Classifier Preference Encoding 1451 Adaptation of the OMNI option Type 1 ifIndex-tuple's traffic 1452 classifier Bitmap to specific Internetworks such as the Aeronautical 1453 Telecommunications Network with Internet Protocol Services (ATN/IPS) 1454 may include link selection preferences based on other traffic 1455 classifiers (e.g., transport port numbers, etc.) in addition to the 1456 existing DSCP-based preferences. Nodes on specific Internetworks 1457 maintain a map of traffic classifiers to additional P[*] preference 1458 fields beyond the first 64. For example, TCP port 22 maps to P[67], 1459 TCP port 443 maps to P[70], UDP port 8060 maps to P[76], etc. 1461 Implementations use Simplex or Indexed encoding formats for P[*] 1462 encoding in order to encode a given set of traffic classifiers in the 1463 most efficient way. Some use cases may be more efficiently coded 1464 using Simplex form, while others may be more efficient using Indexed. 1465 Once a format is selected for preparation of a single ifIndex-tuple 1466 the same format must be used for the entire Sub-Option. Different 1467 Sub-Options may use different formats. 1469 The following figures show coding examples for various Simplex and 1470 Indexed formats: 1472 0 1 2 3 1473 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 1474 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1475 | Sub-Type=2 | Sub-length=4+N| ifIndex | ifType | 1476 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1477 | Provider ID | Link |S|0|RSV| Bitmap(0)=0xff|P00|P01|P02|P03| 1478 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1479 |P04|P05|P06|P07|P08|P09|P10|P11|P12|P13|P14|P15|P16|P17|P18|P19| 1480 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1481 |P20|P21|P22|P23|P24|P25|P26|P27|P28|P29|P30|P31| Bitmap(1)=0xff| 1482 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1483 |P32|P33|P34|P35|P36|P37|P38|P39|P40|P41|P42|P43|P44|P45|P46|P47| 1484 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1485 |P48|P49|P50|P51|P52|P53|P54|P55|P56|P57|P58|P59|P60|P61|P62|P63| 1486 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1487 | Bitmap(2)=0xff|P64|P65|P67|P68| ... 1488 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1490 Figure 14: Example 1: Dense Simplex Encoding 1492 0 1 2 3 1493 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 1494 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1495 | Sub-Type=2 | Sub-length=4+N| ifIndex | ifType | 1496 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1497 | Provider ID | Link |S|0|RSV| Bitmap(0)=0x00| Bitmap(1)=0x0f| 1498 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1499 |P48|P49|P50|P51|P52|P53|P54|P55|P56|P57|P58|P59|P60|P61|P62|P63| 1500 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1501 | Bitmap(2)=0x00| Bitmap(3)=0x00| Bitmap(4)=0x00| Bitmap(5)=0x00| 1502 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1503 | Bitmap(6)=0xf0|192|193|194|195|196|197|198|199|200|201|202|203| 1504 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1505 |204|205|206|207| Bitmap(7)=0x00| Bitmap(8)=0x0f|272|273|274|275| 1506 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1507 |276|277|278|279|280|281|282|283|284|285|286|287| Bitmap(9)=0x00| 1508 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1509 |Bitmap(10)=0x00| ... 1510 +-+-+-+-+-+-+-+-+-+-+- 1512 Figure 15: Example 2: Sparse Simplex Encoding 1514 0 1 2 3 1515 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 1516 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1517 | Sub-Type=2 | Sub-length=4+N| ifIndex | ifType | 1518 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1519 | Provider ID | Link |S|1|RSV| Index = 0x00 | Bitmap = 0x80 | 1520 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1521 |P00|P01|P02|P03| Index = 0x01 | Bitmap = 0x01 |P60|P61|P62|P63| 1522 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1523 | Index = 0x10 | Bitmap = 0x80 |512|513|514|515| Index = 0x18 | 1524 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1525 | Bitmap = 0x01 |796|797|798|799| ... 1526 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1528 Figure 16: Example 3: Indexed Encoding 1530 Appendix B. Prefix Length Considerations 1532 The 64-bit boundary in IPv6 addresses [RFC7421] would suggest an MN 1533 OMNI LLA that encodes the most-significant 64 MNP bits into the 1534 least-significant 64 bits of the prefix fe80::/64. For example, the 1535 MNP 2001:db8:1000:2000::/56 would be encoded as the OMNI addresss 1536 fe80::2001:db8:1000:2000. However, the address juxtapositioning does 1537 not present a form compatible with natural longest-prefix-match 1538 routing. 1540 [RFC4291] defines the link-local address format as the most 1541 significant 10 bits of the prefix fe80::/10, followed by 54 unused 1542 bits, followed by the least-significant 64 bits of the address. If 1543 the 64-bit boundary is ignored for the purpose of this specification, 1544 then the 54 unused bits can be employed for extended coding of MNPs 1545 longer than /64. 1547 One possible extended coding format would continue to encode MNP bits 1548 0-63 in bits 64-127 of the OMNI LLA, while including MNP bits 64-117 1549 in bits 10-63. For example, the OMNI LLA corresponding to the MNP 1550 2001:db8:1111:2222:3333:4444:5555::/112 would be 1551 fe8c:ccd1:1115:5540:2001:db8:1111:2222/128, and would still be a 1552 valid IPv6 LLA per [RFC4291]. However, the non-sequential bit 1553 ordering would render the prefix partially unreadable and completely 1554 incompatible with longest-prefix-match routing determiniations. 1556 An alternate form of OMNI LLA construction could be employed by 1557 embedding the MNP beginning with the most significant bit immediately 1558 following bit 10 of the prefix fe80::/10. For example, the OMNI LLA 1559 corresponding to the MNP 2001:db8:1111:2222:3333:4444:5555::/112 1560 would be written as fe88:0043:6e04:4448:888c:ccd1:1115:5540/122. 1561 This alternate form would be compatible with longest-prefix-match 1562 determinations. It has the disadvantages of requiring an unweildy 1563 10-bit right-shift of a 16byte address, as well as presenting a non- 1564 human-readable form. 1566 As a result, the OMNI specification has elected to encode the MNP 1567 canonically beginning at bit 16 of the prefix fe80::/16. For 1568 example, the OMNI LLA corresponding to the MNP 1569 2001:db8:1111:2222:3333:4444:5555::/112 would be written as 1570 fe80:2001:db8:1111:2222:3333:4444:5555/128. This has the advantage 1571 of providing a natural coding scheme compatible with longest-prefix- 1572 match, while presenting a human readalbe form and simple address 1573 configuration through natural 16-bit word shifts. It has the 1574 disadvantage that bits 10-15 of the address are unused; hence, the 1575 longest prefix length that can be encoded is /112. 1577 Appendix C. VDL Mode 2 Considerations 1579 ICAO Doc 9776 is the "Technical Manual for VHF Data Link Mode 2" 1580 (VDLM2) that specifies an essential radio frequency data link service 1581 for aircraft and ground stations in worldwide civil aviation air 1582 traffic management. The VDLM2 link type is "multicast capable" 1583 [RFC4861], but with considerable differences from common multicast 1584 links such as Ethernet and IEEE 802.11. 1586 First, the VDLM2 link data rate is only 31.5Kbps - multiple orders of 1587 magnitude less than most modern wireless networking gear. Second, 1588 due to the low available link bandwidth only VDLM2 ground stations 1589 (i.e., and not aircraft) are permitted to send broadcasts, and even 1590 so only as compact layer 2 "beacons". Third, aircraft employ the 1591 services of ground stations by performing unicast RS/RA exchanges 1592 upon receipt of beacons instead of listening for multicast RA 1593 messages and/or sending multicast RS messages. 1595 This beacon-oriented unicast RS/RA approach is necessary to conserve 1596 the already-scarce available link bandwidth. Moreover, since the 1597 numbers of beaconing ground stations operating within a given spatial 1598 range must be kept as sparse as possible, it would not be feasible to 1599 have different classes of ground stations within the same region 1600 observing different protocols. It is therefore highly desirable that 1601 all ground stations observe a common language of RS/RA as specified 1602 in this document. 1604 Note that links of this nature may benefit from compression 1605 techniques that reduce the bandwidth necessary for conveying the same 1606 amount of data. The IETF lpwan working group is considering possible 1607 alternatives: [https://datatracker.ietf.org/wg/lpwan/documents]. 1609 Appendix D. MN / AR Isolation Through L2 Address Mapping 1611 Per [RFC4861], IPv6 ND messages may be sent to either a multicast or 1612 unicast link-scoped IPv6 destination address. However, IPv6 ND 1613 messaging should be coordinated between the MN and AR only without 1614 invoking other nodes on the ANET. This implies that MN / AR 1615 coordinations should be isolated and not overheard by other nodes on 1616 the link. 1618 To support MN / AR isolation on some ANET links, ARs can maintain an 1619 OMNI-specific unicast L2 address ("MSADDR"). For Ethernet-compatible 1620 ANETs, this specification reserves one Ethernet unicast address TBD2 1621 (see: Section 18). For non-Ethernet statically-addressed ANETs, 1622 MSADDR is reserved per the assigned numbers authority for the ANET 1623 addressing space. For still other ANETs, MSADDR may be dynamically 1624 discovered through other means, e.g., L2 beacons. 1626 MNs map the L3 addresses of all IPv6 ND messages they send (i.e., 1627 both multicast and unicast) to MSADDR instead of to an ordinary 1628 unicast or multicast L2 address. In this way, all of the MN's IPv6 1629 ND messages will be received by ARs that are configured to accept 1630 packets destined to MSADDR. Note that multiple ARs on the link could 1631 be configured to accept packets destined to MSADDR, e.g., as a basis 1632 for supporting redundancy. 1634 Therefore, ARs must accept and process packets destined to MSADDR, 1635 while all other devices must not process packets destined to MSADDR. 1636 This model has well-established operational experience in Proxy 1637 Mobile IPv6 (PMIP) [RFC5213][RFC6543]. 1639 Appendix E. Change Log 1641 << RFC Editor - remove prior to publication >> 1643 Differences from draft-templin-6man-omni-interface-12 to draft- 1644 templin-6man-omni-interface-13: 1646 o Teredo 1648 Differences from draft-templin-6man-omni-interface-11 to draft- 1649 templin-6man-omni-interface-12: 1651 o Major simplifications and clarifications on MTU and fragmentation. 1653 o Document now udates RFC4443 and RFC8201. 1655 Differences from draft-templin-6man-omni-interface-10 to draft- 1656 templin-6man-omni-interface-11: 1658 o Removed /64 assumption, resulting in new OMNI address format. 1660 Differences from draft-templin-6man-omni-interface-07 to draft- 1661 templin-6man-omni-interface-08: 1663 o OMNI MNs in the open Internet 1665 Differences from draft-templin-6man-omni-interface-06 to draft- 1666 templin-6man-omni-interface-07: 1668 o Brought back L2 MSADDR mapping text for MN / AR isolation based on 1669 L2 addressing. 1671 o Explanded "Transition Considerations". 1673 Differences from draft-templin-6man-omni-interface-05 to draft- 1674 templin-6man-omni-interface-06: 1676 o Brought back OMNI option "R" flag, and dicussed its use. 1678 Differences from draft-templin-6man-omni-interface-04 to draft- 1679 templin-6man-omni-interface-05: 1681 o Transition considerations, and overhaul of RS/RA addressing with 1682 the inclusion of MSE addresses within the OMNI option instead of 1683 as RS/RA addresses (developed under FAA SE2025 contract number 1684 DTFAWA-15-D-00030). 1686 Differences from draft-templin-6man-omni-interface-02 to draft- 1687 templin-6man-omni-interface-03: 1689 o Added "advisory PTB messages" under FAA SE2025 contract number 1690 DTFAWA-15-D-00030. 1692 Differences from draft-templin-6man-omni-interface-01 to draft- 1693 templin-6man-omni-interface-02: 1695 o Removed "Primary" flag and supporting text. 1697 o Clarified that "Router Lifetime" applies to each ANET interface 1698 independently, and that the union of all ANET interface Router 1699 Lifetimes determines MSE lifetime. 1701 Differences from draft-templin-6man-omni-interface-00 to draft- 1702 templin-6man-omni-interface-01: 1704 o "All-MSEs" OMNI LLA defined. Also reserverd fe80::ff00:0000/104 1705 for future use (most likely as "pseudo-multicast"). 1707 o Non-normative discussion of alternate OMNI LLA construction form 1708 made possible if the 64-bit assumption were relaxed. 1710 Differences from draft-templin-atn-aero-interface-21 to draft- 1711 templin-6man-omni-interface-00: 1713 o Minor clarification on Type-2 ifIndex-tuple encoding. 1715 o Draft filename change (replaces draft-templin-atn-aero-interface). 1717 Differences from draft-templin-atn-aero-interface-20 to draft- 1718 templin-atn-aero-interface-21: 1720 o OMNI option format 1722 o MTU 1724 Differences from draft-templin-atn-aero-interface-19 to draft- 1725 templin-atn-aero-interface-20: 1727 o MTU 1729 Differences from draft-templin-atn-aero-interface-18 to draft- 1730 templin-atn-aero-interface-19: 1732 o MTU 1734 Differences from draft-templin-atn-aero-interface-17 to draft- 1735 templin-atn-aero-interface-18: 1737 o MTU and RA configuration information updated. 1739 Differences from draft-templin-atn-aero-interface-16 to draft- 1740 templin-atn-aero-interface-17: 1742 o New "Primary" flag in OMNI option. 1744 Differences from draft-templin-atn-aero-interface-15 to draft- 1745 templin-atn-aero-interface-16: 1747 o New note on MSE OMNI LLA uniqueness assurance. 1749 o General cleanup. 1751 Differences from draft-templin-atn-aero-interface-14 to draft- 1752 templin-atn-aero-interface-15: 1754 o General cleanup. 1756 Differences from draft-templin-atn-aero-interface-13 to draft- 1757 templin-atn-aero-interface-14: 1759 o General cleanup. 1761 Differences from draft-templin-atn-aero-interface-12 to draft- 1762 templin-atn-aero-interface-13: 1764 o Minor re-work on "Notify-MSE" (changed to Notification ID). 1766 Differences from draft-templin-atn-aero-interface-11 to draft- 1767 templin-atn-aero-interface-12: 1769 o Removed "Request/Response" OMNI option formats. Now, there is 1770 only one OMNI option format that applies to all ND messages. 1772 o Added new OMNI option field and supporting text for "Notify-MSE". 1774 Differences from draft-templin-atn-aero-interface-10 to draft- 1775 templin-atn-aero-interface-11: 1777 o Changed name from "aero" to "OMNI" 1779 o Resolved AD review comments from Eric Vyncke (posted to atn list) 1781 Differences from draft-templin-atn-aero-interface-09 to draft- 1782 templin-atn-aero-interface-10: 1784 o Renamed ARO option to AERO option 1786 o Re-worked Section 13 text to discuss proactive NUD. 1788 Differences from draft-templin-atn-aero-interface-08 to draft- 1789 templin-atn-aero-interface-09: 1791 o Version and reference update 1793 Differences from draft-templin-atn-aero-interface-07 to draft- 1794 templin-atn-aero-interface-08: 1796 o Removed "Classic" and "MS-enabled" link model discussion 1798 o Added new figure for MN/AR/MSE model. 1800 o New Section on "Detecting and responding to MSE failure". 1802 Differences from draft-templin-atn-aero-interface-06 to draft- 1803 templin-atn-aero-interface-07: 1805 o Removed "nonce" field from AR option format. Applications that 1806 require a nonce can include a standard nonce option if they want 1807 to. 1809 o Various editorial cleanups. 1811 Differences from draft-templin-atn-aero-interface-05 to draft- 1812 templin-atn-aero-interface-06: 1814 o New Appendix C on "VDL Mode 2 Considerations" 1816 o New Appendix D on "RS/RA Messaging as a Single Standard API" 1818 o Various significant updates in Section 5, 10 and 12. 1820 Differences from draft-templin-atn-aero-interface-04 to draft- 1821 templin-atn-aero-interface-05: 1823 o Introduced RFC6543 precedent for focusing IPv6 ND messaging to a 1824 reserved unicast link-layer address 1826 o Introduced new IPv6 ND option for Aero Registration 1828 o Specification of MN-to-MSE message exchanges via the ANET access 1829 router as a proxy 1831 o IANA Considerations updated to include registration requests and 1832 set interim RFC4727 option type value. 1834 Differences from draft-templin-atn-aero-interface-03 to draft- 1835 templin-atn-aero-interface-04: 1837 o Removed MNP from aero option format - we already have RIOs and 1838 PIOs, and so do not need another option type to include a Prefix. 1840 o Clarified that the RA message response must include an aero option 1841 to indicate to the MN that the ANET provides a MS. 1843 o MTU interactions with link adaptation clarified. 1845 Differences from draft-templin-atn-aero-interface-02 to draft- 1846 templin-atn-aero-interface-03: 1848 o Sections re-arranged to match RFC4861 structure. 1850 o Multiple aero interfaces 1852 o Conceptual sending algorithm 1853 Differences from draft-templin-atn-aero-interface-01 to draft- 1854 templin-atn-aero-interface-02: 1856 o Removed discussion of encapsulation (out of scope) 1858 o Simplified MTU section 1860 o Changed to use a new IPv6 ND option (the "aero option") instead of 1861 S/TLLAO 1863 o Explained the nature of the interaction between the mobility 1864 management service and the air interface 1866 Differences from draft-templin-atn-aero-interface-00 to draft- 1867 templin-atn-aero-interface-01: 1869 o Updates based on list review comments on IETF 'atn' list from 1870 4/29/2019 through 5/7/2019 (issue tracker established) 1872 o added list of opportunities afforded by the single virtual link 1873 model 1875 o added discussion of encapsulation considerations to Section 6 1877 o noted that DupAddrDetectTransmits is set to 0 1879 o removed discussion of IPv6 ND options for prefix assertions. The 1880 aero address already includes the MNP, and there are many good 1881 reasons for it to continue to do so. Therefore, also including 1882 the MNP in an IPv6 ND option would be redundant. 1884 o Significant re-work of "Router Discovery" section. 1886 o New Appendix B on Prefix Length considerations 1888 First draft version (draft-templin-atn-aero-interface-00): 1890 o Draft based on consensus decision of ICAO Working Group I Mobility 1891 Subgroup March 22, 2019. 1893 Authors' Addresses 1894 Fred L. Templin (editor) 1895 The Boeing Company 1896 P.O. Box 3707 1897 Seattle, WA 98124 1898 USA 1900 Email: fltemplin@acm.org 1902 Tony Whyman 1903 MWA Ltd c/o Inmarsat Global Ltd 1904 99 City Road 1905 London EC1Y 1AX 1906 England 1908 Email: tony.whyman@mccallumwhyman.com