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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 8, 2020 MWA Ltd c/o Inmarsat Global Ltd 6 April 6, 2020 8 Transmission of IPv6 Packets over Overlay Multilink Network (OMNI) 9 Interfaces 10 draft-templin-6man-omni-interface-11 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 8, 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. SPAN Addresses . . . . . . . . . . . . . . . . . . . . . . . 12 65 9. Address Mapping - Unicast . . . . . . . . . . . . . . . . . . 13 66 9.1. Sub-Options . . . . . . . . . . . . . . . . . . . . . . . 14 67 9.1.1. Pad1 . . . . . . . . . . . . . . . . . . . . . . . . 15 68 9.1.2. PadN . . . . . . . . . . . . . . . . . . . . . . . . 15 69 9.1.3. ifIndex-tuple (Type 1) . . . . . . . . . . . . . . . 15 70 9.1.4. ifIndex-tuple (Type 2) . . . . . . . . . . . . . . . 18 71 9.1.5. MS-Register . . . . . . . . . . . . . . . . . . . . . 18 72 9.1.6. MS-Release . . . . . . . . . . . . . . . . . . . . . 19 73 10. Address Mapping - Multicast . . . . . . . . . . . . . . . . . 19 74 11. Conceptual Sending Algorithm . . . . . . . . . . . . . . . . 19 75 11.1. Multiple OMNI Interfaces . . . . . . . . . . . . . . . . 20 76 12. Router Discovery and Prefix Registration . . . . . . . . . . 20 77 13. AR and MSE Resilience . . . . . . . . . . . . . . . . . . . . 23 78 14. Detecting and Responding to MSE Failures . . . . . . . . . . 23 79 15. Transition Considerations . . . . . . . . . . . . . . . . . . 24 80 16. OMNI Interfaces on the Open Internet . . . . . . . . . . . . 24 81 17. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25 82 18. Security Considerations . . . . . . . . . . . . . . . . . . . 26 83 19. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 26 84 20. References . . . . . . . . . . . . . . . . . . . . . . . . . 27 85 20.1. Normative References . . . . . . . . . . . . . . . . . . 27 86 20.2. Informative References . . . . . . . . . . . . . . . . . 28 87 Appendix A. Type 1 ifIndex-tuple Traffic Classifier Preference 88 Encoding . . . . . . . . . . . . . . . . . . . . . . 30 89 Appendix B. Prefix Length Considerations . . . . . . . . . . . . 32 90 Appendix C. VDL Mode 2 Considerations . . . . . . . . . . . . . 33 91 Appendix D. MN / AR Isolation Through L2 Address Mapping . . . . 34 92 Appendix E. Change Log . . . . . . . . . . . . . . . . . . . . . 34 93 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 39 95 1. Introduction 97 Mobile Nodes (MNs) (e.g., aircraft of various configurations, 98 terrestrial vehicles, seagoing vessels, mobile enterprise devices, 99 etc.) often have multiple data links for communicating with networked 100 correspondents. These data links may have diverse performance, cost 101 and availability properties that can change dynamically according to 102 mobility patterns, flight phases, proximity to infrastructure, etc. 103 MNs coordinate their data links in a discipline known as "multilink", 104 in which a single virtual interface is configured over the underlying 105 data links. 107 The MN configures a virtual interface (termed the "Overlay Multilink 108 Network (OMNI) interface") as a thin layer over the underlying Access 109 Network (ANET) interfaces. The OMNI interface is therefore the only 110 interface abstraction exposed to the IPv6 layer and behaves according 111 to the Non-Broadcast, Multiple Access (NBMA) interface principle, 112 while underlying interfaces appear as link layer communication 113 channels in the architecture. The OMNI interface connects to a 114 virtual overlay service known as the "OMNI link". The OMNI link 115 spans a worldwide Internetwork that may include private-use 116 infrastructures and/or the global public Internet itself. 118 Each MN receives a Mobile Network Prefix (MNP) for numbering 119 downstream-attached End User Networks (EUNs) independently of the 120 access network data links selected for data transport. The MN 121 performs router discovery over the OMNI interface (i.e., similar to 122 IPv6 customer edge routers [RFC7084]) and acts as a mobile router on 123 behalf of its EUNs. The router discovery process is iterated over 124 each of the OMNI interface's underlying interfaces in order to 125 register per-link parameters (see Section 12). 127 The OMNI interface provides a multilink nexus for exchanging inbound 128 and outbound traffic via the correct underlying interface(s). The 129 IPv6 layer sees the OMNI interface as a point of connection to the 130 OMNI link. Each OMNI link has one or more associated Mobility 131 Service Prefixes (MSPs) from which OMNI link MNPs are derived. If 132 there are multiple OMNI links, the IPv6 layer will see multiple OMNI 133 interfaces. 135 The OMNI interface interacts with a network-based Mobility Service 136 (MS) through IPv6 Neighbor Discovery (ND) control message exchanges 137 [RFC4861]. The MS provides Mobility Service Endpoints (MSEs) that 138 track MN movements and represent their MNPs in a global routing or 139 mapping system. 141 This document specifies the transmission of IPv6 packets [RFC8200] 142 and MN/MS control messaging over OMNI interfaces. 144 2. Terminology 146 The terminology in the normative references applies; especially, the 147 terms "link" and "interface" are the same as defined in the IPv6 148 [RFC8200] and IPv6 Neighbor Discovery (ND) [RFC4861] specifications. 149 Also, the Protocol Constants defined in Section 10 of [RFC4861] are 150 used in their same format and meaning in this document. The terms 151 "All-Routers multicast", "All-Nodes multicast" and "Subnet-Router 152 anycast" are defined in [RFC4291] (with Link-Local scope assumed). 154 The following terms are defined within the scope of this document: 156 Mobile Node (MN) 157 an end system with multiple distinct upstream data link 158 connections that are managed together as a single logical unit. 159 The MN's data link connection parameters can change over time due 160 to, e.g., node mobility, link quality, etc. The MN further 161 connects a downstream-attached End User Network (EUN). The term 162 MN used here is distinct from uses in other documents, and does 163 not imply a particular mobility protocol. 165 End User Network (EUN) 166 a simple or complex downstream-attached mobile network that 167 travels with the MN as a single logical unit. The IPv6 addresses 168 assigned to EUN devices remain stable even if the MN's upstream 169 data link connections change. 171 Mobility Service (MS) 172 a mobile routing service that tracks MN movements and ensures that 173 MNs remain continuously reachable even across mobility events. 174 Specific MS details are out of scope for this document. 176 Mobility Service Endpoint (MSE) 177 an entity in the MS (either singluar or aggregate) that 178 coordinates the mobility events of one or more MN. 180 Mobility Service Prefix (MSP) 181 an aggregated IPv6 prefix (e.g., 2001:db8::/32) advertised to the 182 rest of the Internetwork by the MS, and from which more-specific 183 Mobile Network Prefixes (MNPs) are derived. 185 Mobile Network Prefix (MNP) 186 a longer IPv6 prefix taken from an MSP (e.g., 187 2001:db8:1000:2000::/56) and assigned to a MN. MNs sub-delegate 188 the MNP to devices located in EUNs. 190 Access Network (ANET) 191 a data link service network (e.g., an aviation radio access 192 network, satellite service provider network, cellular operator 193 network, wifi network, etc.) that connects MNs. Physical and/or 194 data link level security between the MN and ANET are assumed. 196 Access Router (AR) 197 a first-hop router in the ANET for connecting MNs to 198 correspondents in outside Internetworks. 200 ANET interface 201 a MN's attachment to a link in an ANET. 203 Internetwork (INET) 204 a connected network region with a coherent IP addressing plan that 205 provides transit forwarding services for ANET MNs and INET 206 correspondents. Examples include private enterprise networks, 207 ground domain aviation service networks and the global public 208 Internet itself. 210 INET interface 211 a node's attachment to a link in an INET. 213 OMNI link 214 a virtual overlay configured over one or more INETs and their 215 connected ANETs. An OMNI link can comprise multiple INET segments 216 joined by bridges the same as for any link; the addressing plans 217 in each segment may be mutually exclusive and managed by different 218 administrative entities. 220 OMNI interface 221 a node's attachment to an OMNI link, and configured over one or 222 more underlying ANET/INET interfaces. 224 OMNI link local address (LLA) 225 an IPv6 link-local address constructed as specified in Section 7, 226 and assigned to an OMNI interface. 228 OMNI Option 229 an IPv6 Neighbor Discovery option providing multilink parameters 230 for the OMNI interface as specified in Section 9. 232 Multilink 233 an OMNI interface's manner of managing diverse underlying data 234 link interfaces as a single logical unit. The OMNI interface 235 provides a single unified interface to upper layers, while 236 underlying data link selections are performed on a per-packet 237 basis considering factors such as DSCP, flow label, application 238 policy, signal quality, cost, etc. Multilinking decisions are 239 coordinated in both the outbound (i.e. MN to correspondent) and 240 inbound (i.e., correspondent to MN) directions. 242 L2 243 The second layer in the OSI network model. Also known as "layer- 244 2", "link-layer", "sub-IP layer", "data link layer", etc. 246 L3 247 The third layer in the OSI network model. Also known as "layer- 248 3", "network-layer", "IPv6 layer", etc. 250 underlying interface 251 an ANET/INET interface over which an OMNI interface is configured. 252 The OMNI interface is seen as a L3 interface by the IP layer, and 253 each underlying interface is seen as a L2 interface by the OMNI 254 interface. 256 Mobility Service Identification (MSID) 257 Each MSE and AR is assigned a unique 32-bit Identification (MSID) 258 as specified in Section 7. 260 Spanning Partitioned Administrative Networks (SPAN) 261 A means for bridging disjoint INET partitions as segments of a 262 unified OMNI link the same as for a bridged campus LAN. The SPAN 263 is a mid-layer IPv6 encapsulation service that supports a unified 264 OMNI link view for all segments. 266 3. Requirements 268 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 269 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 270 "OPTIONAL" in this document are to be interpreted as described in BCP 271 14 [RFC2119][RFC8174] when, and only when, they appear in all 272 capitals, as shown here. 274 An implementation is not required to internally use the architectural 275 constructs described here so long as its external behavior is 276 consistent with that described in this document. 278 4. Overlay Multilink Network (OMNI) Interface Model 280 An OMNI interface is a MN virtual interface configured over one or 281 more underlying interfaces, which may be physical (e.g., an 282 aeronautical radio link) or virtual (e.g., an Internet or higher- 283 layer "tunnel"). The MN receives a MNP from the MS, and coordinates 284 with the MS through IPv6 ND message exchanges. The MN uses the MNP 285 to construct a unique OMNI LLA through the algorithmic derivation 286 specified in Section 7 and assigns the LLA to the OMNI interface. 288 The OMNI interface architectural layering model is the same as in 289 [RFC7847], and augmented as shown in Figure 1. The IP layer 290 therefore sees the OMNI interface as a single L3 interface with 291 multiple underlying interfaces that appear as L2 communication 292 channels in the architecture. 294 +----------------------------+ 295 | Upper Layer Protocol | 296 Session-to-IP +---->| | 297 Address Binding | +----------------------------+ 298 +---->| IP (L3) | 299 IP Address +---->| | 300 Binding | +----------------------------+ 301 +---->| OMNI Interface | 302 Logical-to- +---->| (OMNI LLA) | 303 Physical | +----------------------------+ 304 Interface +---->| L2 | L2 | | L2 | 305 Binding |(IF#1)|(IF#2)| ..... |(IF#n)| 306 +------+------+ +------+ 307 | L1 | L1 | | L1 | 308 | | | | | 309 +------+------+ +------+ 311 Figure 1: OMNI Interface Architectural Layering Model 313 The OMNI virtual interface model gives rise to a number of 314 opportunities: 316 o since OMNI LLAs are uniquely derived from an MNP, no Duplicate 317 Address Detection (DAD) or Muticast Listener Discovery (MLD) 318 messaging is necessary. 320 o ANET interfaces do not require any L3 addresses (i.e., not even 321 link-local) in environments where communications are coordinated 322 entirely over the OMNI interface. (An alternative would be to 323 also assign the same OMNI LLA to all ANET interfaces.) 325 o as ANET interface properties change (e.g., link quality, cost, 326 availability, etc.), any active ANET interface can be used to 327 update the profiles of multiple additional ANET interfaces in a 328 single message. This allows for timely adaptation and service 329 continuity under dynamically changing conditions. 331 o coordinating ANET interfaces in this way allows them to be 332 represented in a unified MS profile with provisions for mobility 333 and multilink operations. 335 o exposing a single virtual interface abstraction to the IPv6 layer 336 allows for multilink operation (including QoS based link 337 selection, packet replication, load balancing, etc.) at L2 while 338 still permitting L3 traffic shaping based on, e.g., DSCP, flow 339 label, etc. 341 o L3 sees the OMNI interface as a point of connection to the OMNI 342 link; if there are multiple OMNI links (i.e., multiple MS's), L3 343 will see multiple OMNI interfaces. 345 Other opportunities are discussed in [RFC7847]. 347 Figure 2 depicts the architectural model for a MN connecting to the 348 MS via multiple independent ANETs. When an underlying interface 349 becomes active, the MN's OMNI interface sends native (i.e., 350 unencapsulated) IPv6 ND messages via the underlying interface. IPv6 351 ND messages traverse the ground domain ANETs until they reach an 352 Access Router (AR#1, AR#2, .., AR#n). The AR then coordinates with a 353 Mobility Service Endpoint (MSE#1, MSE#2, ..., MSE#m) in the INET and 354 returns an IPv6 ND message response to the MN. IPv6 ND messages 355 traverse the ANET at layer 2; hence, the Hop Limit is not 356 decremented. 358 +--------------+ 359 | MN | 360 +--------------+ 361 |OMNI interface| 362 +----+----+----+ 363 +--------|IF#1|IF#2|IF#n|------ + 364 / +----+----+----+ \ 365 / | \ 366 / <---- Native | IP ----> \ 367 v v v 368 (:::)-. (:::)-. (:::)-. 369 .-(::ANET:::) .-(::ANET:::) .-(::ANET:::) 370 `-(::::)-' `-(::::)-' `-(::::)-' 371 +----+ +----+ +----+ 372 ... |AR#1| .......... |AR#2| ......... |AR#n| ... 373 . +-|--+ +-|--+ +-|--+ . 374 . | | | 375 . v v v . 376 . <----- Encapsulation -----> . 377 . . 378 . +-----+ (:::)-. . 379 . |MSE#2| .-(::::::::) +-----+ . 380 . +-----+ .-(::: INET :::)-. |MSE#m| . 381 . (::::: Routing ::::) +-----+ . 382 . `-(::: System :::)-' . 383 . +-----+ `-(:::::::-' . 384 . |MSE#1| +-----+ +-----+ . 385 . +-----+ |MSE#3| |MSE#4| . 386 . +-----+ +-----+ . 387 . . 388 . . 389 . <----- Worldwide Connected Internetwork ----> . 390 ........................................................... 392 Figure 2: MN/MS Coordination via Multiple ANETs 394 After the initial IPv6 ND message exchange, the MN can send and 395 receive unencapsulated IPv6 data packets over the OMNI interface. 396 OMNI interface multilink services will forward the packets via ARs in 397 the correct underlying ANETs. The AR encapsulates the packets 398 according to the capabilities provided by the MS and forwards them to 399 the next hop within the worldwide connected Internetwork via optimal 400 routes. 402 5. Maximum Transmission Unit (MTU) and Fragmentation 404 All IPv6 interfaces are REQUIRED to configure a minimum Maximum 405 Transmission Unit (MTU) of 1280 bytes [RFC8200]. The network 406 therefore MUST forward packets of at least 1280 bytes without 407 generating an IPv6 Path MTU Discovery (PMTUD) Packet Too Big (PTB) 408 message [RFC8201]. 410 The OMNI interface configures an MTU of 9180 bytes [RFC2492]; the 411 size is therefore not a reflection of the underlying interface MTUs, 412 but rather determines the largest packet the OMNI interface can 413 forward or reassemble. 415 The OMNI interface employs mid-layer IPv6 encapsulation and 416 fragmentation/reassembly per [RFC2473] if necssary to accommodate 417 large packets. The interface returns internally-generated PTB 418 messages for packets admitted into the interface that it deems too 419 large for outbound underlying interfaces (e.g., according to 420 underlying interface performance characteristics, cost, MTU, etc). 421 For all other packets, the OMNI interface performs PMTUD even if the 422 destination appears to be on the same link since an OMNI link node on 423 the path could return a PTB message. This ensures that the path MTU 424 is adaptive and reflects the current path used for a given data flow. 426 For underlying interfaces that have sufficiently large MTUs, the MN's 427 OMNI interface sends packets according to the ANET interface L2 frame 428 format without fragmentation. For all other cases, the OMNI 429 interface encapsulates the packet in a mid-layer IPv6 header with 430 source address set to the MN's SPAN address and destination set to 431 the SPAN address corresponding to the packet's destination (see: 432 Section 8). The OMNI interface then uses IPv6 fragmentation to break 433 the encapsulated packet into a minimum number of non-overlapping 434 fragments, where the smallest fragment generated MUST be no smaller 435 than 640 bytes. For ANET interfaces that connect via ARs, the 436 largest fragment size is determined by the ANET interface MTU, while 437 for other underllying interface types the largest fragment size MUST 438 be 1280 bytes. (Note that the outbound fragments can further be 439 spread across multiple underlying interfaces, since they will be 440 reassembled by the OMNI interface closest to the final destination.) 442 When an AR receives a fragmented or whole packet from the INET 443 destined to an ANET MN, it first determines whether to forward or 444 drop and return a PTB. If the AR deems the packet to be of 445 acceptable size, it first re-adjusts fragment sizes (if necessary) 446 then forwards the packet/fragments to the MN. If the packet is no 447 larger than the ANET MTU, the AR forwards according to the ANET L2 448 frame format. If the packet is larger than the ANET MTU, the AR 449 instead uses IPv6 encapsulation and fragmentation as above. The MN 450 then reassembles and discards the encapsulation header, then forwards 451 the whole packet to the final destination. 453 In order to avoid a "tiny fragment" attack, AERO nodes 454 unconditionally drop all fragments smaller than 640 bytes. In order 455 to set the correct context for reassembly, the AERO node that inserts 456 a SPAN header MUST also be the node that inserts the IPv6 Fragment 457 Header Identification value. 459 Note also that the OMNI interface can forward large packets via 460 encapsulation and fragmentation while at the same time returning 461 advisory PTB messages, e.g., subject to rate limiting. The receiving 462 node that performs reassembly can also send advisory PTB messages if 463 reassembly conditions become unfavorable. The OMNI interface can 464 therefore continuously forward large packets without loss while 465 returning advisory messages recommending a smaller size. 467 6. Frame Format 469 The OMNI interface transmits IPv6 packets according to the native 470 frame format of each underlying interface. For example, for 471 Ethernet-compatible interfaces the frame format is specified in 472 [RFC2464], for aeronautical radio interfaces the frame format is 473 specified in standards such as ICAO Doc 9776 (VDL Mode 2 Technical 474 Manual), for tunnels over IPv6 the frame format is specified in 475 [RFC2473], etc. 477 7. Link-Local Addresses 479 OMNI interfaces assign IPv6 Link-Local Addresses (i.e., "OMNI LLAs") 480 using the following constructs: 482 o IPv6 MN OMNI LLAs encode the most-significant 112 bits of a MNP 483 within the least-significant 112 bits of the the IPv6 link-local 484 prefix fe80::/16. For example, for the MNP 485 2001:db8:1000:2000::/56 the corresponding LLA is 486 fe80:2001:db8:1000:2000::/72. See: [RFC4291], Section 2.5.6) for 487 a discussion of IPv6 link-local addresses, for which this document 488 presents an OMNI interface-specific adaptation. See Appendix B 489 for further discussion on prefix lengths. 491 o IPv4-compatible MN OMNI LLAs are assigned as fe80::ffff:[v4addr], 492 i.e., the most significant 16 bits of the prefix fe80::/16, 493 followed by 64 '0' bits, followed by 16 '1' bits, followed by a 494 32bit IPv4 address. For example, the IPv4-Compatible MN OMNI LLA 495 for 192.0.2.1 is fe80::ffff:192.0.2.1 (also written as 496 fe80::ffff:c000:0201). 498 o MS OMNI LLAs are assigned to ARs and MSEs from the range 499 fe80::/96, and MUST be managed for uniqueness. The lower 32 bits 500 of the LLA includes a unique integer "MSID" value between 501 0x00000001 and 0xfeffffff, e.g., as in fe80::1, fe80::2, fe80::3, 502 etc., fe80::feff:ffff. The MSID 0x00000000 corresponds to the 503 link-local Subnet-Router anycast address (fe80::) [RFC4291]. The 504 MSID range 0xff00000000 through 0xffffffff is reserved for future 505 use. (Note that distinct OMNI link segments can avoid overlap by 506 assigning MS OMNI LLAs from unique fe80::/96 sub-prefixes. For 507 example, a first segment could assign from fe80::1000/116, a 508 second from fe80::2000/116, a third from fe80::3000/116, etc.) 510 Since the prefix 0000::/8 is "Reserved by the IETF" [RFC4291], no 511 MNPs can be allocated from that block ensuring that there is no 512 possibility for overlap between the above OMNI LLA constructs. 514 Since MN OMNI LLAs are based on the distribution of administratively 515 assured unique MNPs, and since MS OMNI LLAs are guaranteed unique 516 through administrative assignment, OMNI interfaces set the 517 autoconfiguration variable DupAddrDetectTransmits to 0 [RFC4862]. 519 8. SPAN Addresses 521 OMNI links employ an overlay network instance called the SPAN 522 (Spanning Partitioned Administrative Networks) that supports 523 forwarding of encapsulated link-scoped messages over a private IPv6 524 routing instance that spans the entire link without decrementing the 525 (link-local) Hop Limit. The OMNI link reserves the Unique Local 526 Address (ULA) prefix fd80::/16 [RFC4193] used for mapping OMNI LLAs 527 to routable SPAN addresses. 529 SPAN addresses are configured in one-to-one correspondence with MN/MS 530 OMNI LLAs by simply zeroing bit 7 of the LLA. For example: 532 o the SPAN address corresponding to fe80:2001:db8:1:2:: is simply 533 fd80:2001:db8:1:2:: 535 o the SPAN address corresponding to fe80::ffff:192.0.2.1 is simply 536 fd80::ffff:192.0.2.1 538 o the SPAN address corresponding to fe80::1000 is simply fd80::1000 540 The SPAN address presents an IPv6 address format that is routable 541 within the OMNI link routing system and can be used to convey link- 542 scoped messages across multiple hops using IPv6 encapsulation 543 [RFC2473]. A full discussion of the SPAN appears in 544 [I-D.templin-intarea-6706bis]. 546 9. Address Mapping - Unicast 548 OMNI interfaces maintain a neighbor cache for tracking per-neighbor 549 state and use the link-local address format specified in Section 7. 550 IPv6 Neighbor Discovery (ND) [RFC4861] messages on MN OMNI interfaces 551 observe the native Source/Target Link-Layer Address Option (S/TLLAO) 552 formats of the underlying interfaces (e.g., for Ethernet the S/TLLAO 553 is specified in [RFC2464]). 555 MNs such as aircraft typically have many wireless data link types 556 (e.g. satellite-based, cellular, terrestrial, air-to-air directional, 557 etc.) with diverse performance, cost and availability properties. 558 The OMNI interface would therefore appear to have multiple L2 559 connections, and may include information for multiple underlying 560 interfaces in a single IPv6 ND message exchange. 562 OMNI interfaces use an IPv6 ND option called the "OMNI option" 563 formatted as shown in Figure 3: 565 0 1 2 3 566 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 1 567 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 568 | Type | Length | Prefix Length |R| Reserved | 569 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 570 | | 571 ~ Sub-Options ~ 572 | | 573 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 575 Figure 3: OMNI Option Format 577 In this format: 579 o Type is set to TBD. 581 o Length is set to the number of 8 octet blocks in the option. 583 o Prefix Length is set according to the IPv6 source address type. 584 For MN OMNI LLAs, the value is set to the length of the embedded 585 MNP. For IPv4-compatible MN OMNI LLAs, the value is set to 96 586 plus the length of the embedded IPv4 prefix. For MS OMNI LLAs, 587 the value is set to 128. 589 o R (the "Register/Release" bit) is set to 1/0 to request the 590 message recipient to register/release a MN's MNP. The OMNI option 591 may additionally include MSIDs for the recipient to contact to 592 also register/release the MNP. 594 o Reserved is set to the value '0' on transmission and ignored on 595 reception. 597 o Sub-Options is a Variable-length field, of length such that the 598 complete OMNI Option is an integer multiple of 8 octets long. 599 Contains one or more options, as described in Section 8.1. 601 9.1. Sub-Options 603 The OMNI option includes zero or more Sub-Options, some of which may 604 appear multiple times in the same message. Each consecutive Sub- 605 Option is concatenated immediately after its predecessor. All Sub- 606 Options except Pad1 (see below) are type-length-value (TLV) encoded 607 in the following format: 609 0 1 2 610 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 5 611 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 612 | Sub-Type | Sub-length | Sub-Option Data ... 613 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 615 Figure 4: Sub-Option Format 617 o Sub-Type is a 1-byte field that encodes the Sub-Option type. Sub- 618 Options defined in this document are: 620 Option Name Sub-Type 621 Pad1 0 622 PadN 1 623 ifIndex-tuple (Type 1) 2 624 ifIndex-tuple (Type 2) 3 625 MS-Register 4 626 MS-Release 5 628 Figure 5 630 Sub-Types 253 and 254 are reserved for experimentation, as 631 recommended in[RFC3692]]. 633 o Sub-Length is a 1-byte field that encodes the length of the Sub- 634 Option Data, in bytes 636 o Sub-Option Data is a byte string with format determined by Sub- 637 Type 639 During processing, unrecognized Sub-Options are ignored and the next 640 Sub-Option processed until the end of the OMNI option. 642 The following Sub-Option types and formats are defined in this 643 document: 645 9.1.1. Pad1 647 0 648 0 1 2 3 4 5 6 7 649 +-+-+-+-+-+-+-+-+ 650 | Sub-Type=0 | 651 +-+-+-+-+-+-+-+-+ 653 Figure 6: Pad1 655 o Sub-Type is set to 0. 657 o No Sub-Length or Sub-Option Data follows (i.e., the "Sub-Option" 658 consists of a single zero octet). 660 9.1.2. PadN 662 0 1 2 663 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 5 664 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 665 | Sub-Type=1 |Sub-length=N-2 | N-2 padding bytes ... 666 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 668 Figure 7: PadN 670 o Sub-Type is set to 1. 672 o Sub-Length is set to N-2 being the number of padding bytes that 673 follow. 675 o Sub-Option Data consists of N-2 zero-valued octets. 677 9.1.3. ifIndex-tuple (Type 1) 678 0 1 2 3 679 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 1 680 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 681 | Sub-Type=2 | Sub-length=4+N| ifIndex | ifType | 682 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 683 | Provider ID | Link |S|I|RSV| Bitmap(0)=0xff|P00|P01|P02|P03| 684 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 685 |P04|P05|P06|P07|P08|P09|P10|P11|P12|P13|P14|P15|P16|P17|P18|P19| 686 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 687 |P20|P21|P22|P23|P24|P25|P26|P27|P28|P29|P30|P31| Bitmap(1)=0xff| 688 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 689 |P32|P33|P34|P35|P36|P37|P38|P39| ... 690 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 692 Figure 8: ifIndex-tuple (Type 1) 694 o Sub-Type is set to 2. 696 o Sub-Length is set to 4+N (the number of Sub-Option Data bytes that 697 follow). 699 o Sub-Option Data contains an "ifIndex-tuple" (Type 1) encoded as 700 follows (note that the first four bytes must be present): 702 * ifIndex is set to an 8-bit integer value corresponding to a 703 specific underlying interface. OMNI options MAY include 704 multiple ifIndex-tuples, and MUST number each with an ifIndex 705 value between '1' and '255' that represents a MN-specific 8-bit 706 mapping for the actual ifIndex value assigned to the underlying 707 interface by network management [RFC2863] (the ifIndex value 708 '0' is reserved for use by the MS). Multiple ifIndex-tuples 709 with the same ifIndex value MAY appear in the same OMNI option. 711 * ifType is set to an 8-bit integer value corresponding to the 712 underlying interface identified by ifIndex. The value 713 represents an OMNI interface-specific 8-bit mapping for the 714 actual IANA ifType value registered in the 'IANAifType-MIB' 715 registry [http://www.iana.org]. 717 * Provider ID is set to an OMNI interface-specific 8-bit ID value 718 for the network service provider associated with this ifIndex. 720 * Link encodes a 4-bit link metric. The value '0' means the link 721 is DOWN, and the remaining values mean the link is UP with 722 metric ranging from '1' ("lowest") to '15' ("highest"). 724 * S is set to '1' if this ifIndex-tuple corresponds to the 725 underlying interface that is the source of the ND message. Set 726 to '0' otherwise. 728 * I is set to '0' ("Simplex") if the index for each singleton 729 Bitmap byte in the Sub-Option Data is inferred from its 730 sequential position (i.e., 0, 1, 2, ...), or set to '1' 731 ("Indexed") if each Bitmap is preceded by an Index byte. 732 Figure 8 shows the simplex case for I set to '0'. For I set to 733 '1', each Bitmap is instead preceded by an Index byte that 734 encodes a value "i" = (0 - 255) as the index for its companion 735 Bitmap as follows: 737 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 738 | Index=i | Bitmap(i) |P[*] values ... 739 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 741 Figure 9 743 * RSV is set to the value 0 on transmission and ignored on 744 reception. 746 * The remainder of the Sub-Option Data contains N = (0 - 251) 747 bytes of traffic classifier preferences consisting of a first 748 (indexed) Bitmap (i.e., "Bitmap(i)") followed by 0-8 1-byte 749 blocks of 2-bit P[*] values, followed by a second Bitmap (i), 750 followed by 0-8 blocks of P[*] values, etc. Reading from bit 0 751 to bit 7, the bits of each Bitmap(i) that are set to '1'' 752 indicate the P[*] blocks from the range P[(i*32)] through 753 P[(i*32) + 31] that follow; if any Bitmap(i) bits are '0', then 754 the corresponding P[*] block is instead omitted. For example, 755 if Bitmap(0) contains 0xff then the block with P[00]-P[03], 756 followed by the block with P[04]-P[07], etc., and ending with 757 the block with P[28]-P[31] are included (as showin in 758 Figure 8). The next Bitmap(i) is then consulted with its bits 759 indicating which P[*] blocks follow, etc. out to the end of the 760 Sub-Option. The first 16 P[*] blocks correspond to the 64 761 Differentiated Service Code Point (DSCP) values P[00] - P[63] 762 [RFC2474]. If additional P[*] blocks follow, their values 763 correspond to "pseudo-DSCP" traffic classifier values P[64], 764 P[65], P[66], etc. See Appendix A for further discussion and 765 examples. 767 * Each 2-bit P[*] field is set to the value '0' ("disabled"), '1' 768 ("low"), '2' ("medium") or '3' ("high") to indicate a QoS 769 preference level for underlying interface selection purposes. 770 Not all P[*] values need to be included in all OMNI option 771 instances of a given ifIndex-tuple. Any P[*] values 772 represented in an earlier OMNI option but ommitted in the 773 current OMNI option remain unchanged. Any P[*] values not yet 774 represented in any OMNI option default to "medium". 776 9.1.4. ifIndex-tuple (Type 2) 778 0 1 2 3 779 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 1 780 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 781 | Sub-Type=3 | Sub-length=4+N| ifIndex | ifType | 782 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 783 | Provider ID | Link |S|Resvd| ~ 784 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ 785 ~ ~ 786 ~ RFC 6088 Format Traffic Selector ~ 787 ~ ~ 788 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 790 Figure 10: ifIndex-tuple (Type 2) 792 o Sub-Type is set to 3. 794 o Sub-Length is set to 4+N (the number of Sub-Option Data bytes that 795 follow). 797 o Sub-Option Data contains an "ifIndex-tuple" (Type 2) encoded as 798 follows (note that the first four bytes must be present): 800 * ifIndex, ifType, Provider ID, Link and S are set exactly as for 801 Type 1 ifIndex-tuples as specified in Section 9.1.3. 803 * the remainder of the Sub-Option body encodes a variable-length 804 traffic selector formatted per [RFC6088], beginning with the 805 "TS Format" field. 807 9.1.5. MS-Register 809 0 1 2 3 810 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 1 811 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 812 | Sub-Type=4 | Sub-length=4 | MSID (bits 0 - 15) | 813 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 814 | MSID (bits 16 - 32) | 815 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 817 Figure 11: MS-Register Sub-option 819 o Sub-Type is set to 4. 821 o Sub-Length is set to 4. 823 o MSID contains the 32 bit ID of an MSE or AR, in network byte 824 order. OMNI options contain zero or more MS-Register sub-options. 826 9.1.6. MS-Release 828 0 1 2 3 829 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 1 830 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 831 | Sub-Type=5 | Sub-length=4 | MSID (bits 0 - 15) | 832 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 833 | MSID (bits 16 - 32) | 834 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 836 Figure 12: MS-Release Sub-option 838 o Sub-Type is set to 5. 840 o Sub-Length is set to 4. 842 o MSIID contains the 32 bit ID of an MS or AR, in network byte 843 order. OMNI options contain zero or more MS-Release sub-options. 845 10. Address Mapping - Multicast 847 The multicast address mapping of the native underlying interface 848 applies. The mobile router on board the aircraft also serves as an 849 IGMP/MLD Proxy for its EUNs and/or hosted applications per [RFC4605] 850 while using the L2 address of the router as the L2 address for all 851 multicast packets. 853 11. Conceptual Sending Algorithm 855 The MN's IPv6 layer selects the outbound OMNI interface according to 856 standard IPv6 requirements when forwarding data packets from local or 857 EUN applications to external correspondents. The OMNI interface 858 maintains a neighbor cache the same as for any IPv6 interface, but 859 with additional state for multilink coordination. 861 After a packet enters the OMNI interface, an outbound underlying 862 interface is selected based on multilink parameters such as DSCP, 863 application port number, cost, performance, message size, etc. OMNI 864 interface multilink selections could also be configured to perform 865 replication across multiple underlying interfaces for increased 866 reliability at the expense of packet duplication. 868 OMNI interface multilink service designers MUST observe the BCP 869 guidance in Section 15 [RFC3819] in terms of implications for 870 reordering when packets from the same flow may be spread across 871 multiple underlying interfaces having diverse properties. 873 11.1. Multiple OMNI Interfaces 875 MNs may associate with multiple MS instances concurrently. Each MS 876 instance represents a distinct OMNI link distinguished by its 877 associated MSPs. The MN configures a separate OMNI interface for 878 each link so that multiple interfaces (e.g., omni0, omni1, omni2, 879 etc.) are exposed to the IPv6 layer. 881 Depending on local policy and configuration, an MN may choose between 882 alternative active OMNI interfaces using a packet's DSCP, routing 883 information or static configuration. Interface selection based on 884 per-packet source addresses is also enabled when the MSPs for each 885 OMNI interface are known (e.g., discovered through Prefix Information 886 Options (PIOs) and/or Route Information Options (RIOs)). 888 Each OMNI interface can be configured over the same or different sets 889 of underlying interfaces. Each ANET distinguishes between the 890 different OMNI links based on the MSPs represented in per-packet IPv6 891 addresses. 893 Multiple distinct OMNI links can therefore be used to support fault 894 tolerance, load balancing, reliability, etc. The architectural model 895 parallels Layer 2 Virtual Local Area Networks (VLANs), where the MSPs 896 serve as (virtual) VLAN tags. 898 12. Router Discovery and Prefix Registration 900 MNs interface with the MS by sending RS messages with OMNI options 901 that include MSIDs. For each underlying interface, the MN sends an 902 RS message with an OMNI option with (R,A) flags, wth MS-Register/ 903 Release suboptions, and with destination address set to All-Routers 904 multicast (ff02::2) [RFC4291]. Example MSID discovery methods are 905 given in [RFC5214], including data link login parameters, name 906 service lookups, static configuration, etc. Alternatively, MNs can 907 discover indiviual MSIDs by sending an initial RS with MS-Register 908 MSID set to 0x00000000, or associate with all MSEs by sending an RS 909 with MS-Register MSID set to 0xffffffff. 911 MNs configure OMNI interfaces that observe the properties discussed 912 in the previous section. The OMNI interface and its underlying 913 interfaces are said to be in either the "UP" or "DOWN" state 914 according to administrative actions in conjunction with the interface 915 connectivity status. An OMNI interface transitions to UP or DOWN 916 through administrative action and/or through state transitions of the 917 underlying interfaces. When a first underlying interface transitions 918 to UP, the OMNI interface also transitions to UP. When all 919 underlying interfaces transition to DOWN, the OMNI interface also 920 transitions to DOWN. 922 When an OMNI interface transitions to UP, the MN sends RS messages to 923 register its MNP and an initial set of underlying interfaces that are 924 also UP. The MN sends additional RS messages to refresh lifetimes 925 and to register/deregister underlying interfaces as they transition 926 to UP or DOWN. The MN sends initial RS messages over an UP 927 underlying interface with its OMNI LLA as the source and with 928 destination set to All-Routers multicast. The RS messages include an 929 OMNI option per Section 9 with a valid Prefix Length, (R, A) flags, 930 ifIndex-tuples appropriate for underlying interfaces and with MS- 931 Register/Release sub-options. 933 ARs process IPv6 ND messages with OMNI options and act as a proxy for 934 MSEs. ARs receive RS messages and create a neighbor cache entry for 935 the MN, then coordinate with any named MSIDs in a manner outside the 936 scope of this document. The AR returns an RA message with 937 destination address set to the MN OMNI LLA (i.e., unicast), with 938 source address set to its MS OMNI LLA, with the P(roxy) bit set in 939 the RA flags [RFC4389], with an OMNI option with (R, A) flags, 940 ifIndex tuples and MS-Register/Release sub-options, and with any 941 information for the link that would normally be delivered in a 942 solicited RA message. ARs return RA messages with configuration 943 information in response to a MN's RS messages. The AR sets the RA 944 Cur Hop Limit, M and O flags, Router Lifetime, Reachable Time and 945 Retrans Timer values, and includes any necessary options such as: 947 o PIOs with (A; L=0) that include MSPs for the link [RFC8028]. 949 o RIOs [RFC4191] with more-specific routes. 951 o an MTU option that specifies the maximum acceptable packet size 952 for this ANET interface. 954 The AR coordinates with each Register/Release MSID then sends an 955 immediate unicast RA response without delay; therefore, the IPv6 ND 956 MAX_RA_DELAY_TIME and MIN_DELAY_BETWEEN_RAS constants for multicast 957 RAs do not apply. The AR MAY send periodic and/or event-driven 958 unsolicited RA messages according to the standard [RFC4861]. 960 When the MSE processes the OMNI information, it first validates the 961 prefix registration information. The MSE then injects/withdraws the 962 MNP in the routing/mapping system and caches/discards the new Prefix 963 Length, MNP and ifIndex-tuples. The MSE then informs the AR of 964 registration success/failure, and the AR adds the MSE to the list of 965 Register/Release MSIDs to return in an RA message OMNI option per 966 Section 9. 968 When the MN receives the RA message, it creates an OMNI interface 969 neighbor cache entry with the AR's address as an L2 address and 970 records the MSIDs that have confirmed MNP registration via this AR. 971 If the MN connects to multiple ANETs, it establishes additional AR L2 972 addresses (i.e., as a Multilink neighbor). The MN then manages its 973 underlying interfaces according to their states as follows: 975 o When an underlying interface transitions to UP, the MN sends an RS 976 over the underlying interface with an OMNI option with R set to 1. 977 The OMNI option contains at least one ifIndex-tuple with values 978 specific to this underlying interface, and may contain additional 979 ifIndex-tuples specific to this and/or other underlying 980 interfaces. The option also includes any Register/Release MSIDs. 982 o When an underlying interface transitions to DOWN, the MN sends an 983 RS or unsolicited NA message over any UP underlying interface with 984 an OMNI option containing an ifIndex-tuple for the DOWN underlying 985 interface with Link set to '0'. The MN sends an RS when an 986 acknowledgement is required, or an unsolicited NA when reliability 987 is not thought to be a concern (e.g., if redundant transmissions 988 are sent on multiple underlying interfaces). 990 o When the Router Lifetime for a specific AR nears expiration, the 991 MN sends an RS over the underlying interface to receive a fresh 992 RA. If no RA is received, the MN marks the underlying interface 993 as DOWN. 995 o When a MN wishes to release from one or more current MSIDs, it 996 sends an RS or unsolicited NA message over any UP underlying 997 interfaces with an OMNI option with a Release MSID. Each MSID 998 then withdraws the MNP from the routing/mapping system and informs 999 the AR that the release was successful. 1001 o When all of a MNs underlying interfaces have transitioned to DOWN 1002 (or if the prefix registration lifetime expires), any associated 1003 MSEs withdraw the MNP the same as if they had received a message 1004 with a release indication. 1006 The MN is responsible for retrying each RS exchange up to 1007 MAX_RTR_SOLICITATIONS times separated by RTR_SOLICITATION_INTERVAL 1008 seconds until an RA is received. If no RA is received over a an UP 1009 underlying interface, the MN declares this underlying interface as 1010 DOWN. 1012 The IPv6 layer sees the OMNI interface as an ordinary IPv6 interface. 1013 Therefore, when the IPv6 layer sends an RS message the OMNI interface 1014 returns an internally-generated RA message as though the message 1015 originated from an IPv6 router. The internally-generated RA message 1016 contains configuration information that is consistent with the 1017 information received from the RAs generated by the MS. Whether the 1018 OMNI interface IPv6 ND messaging process is initiated from the 1019 receipt of an RS message from the IPv6 layer is an implementation 1020 matter. Some implementations may elect to defer the IPv6 ND 1021 messaging process until an RS is received from the IPv6 layer, while 1022 others may elect to initiate the process proactively. 1024 Note: The Router Lifetime value in RA messages indicates the time 1025 before which the MN must send another RS message over this underlying 1026 interface (e.g., 600 seconds), however that timescale may be 1027 significantly longer than the lifetime the MS has committed to retain 1028 the prefix registration (e.g., REACHABLETIME seconds). ARs are 1029 therefore responsible for keeping MS state alive on a finer-grained 1030 timescale than the MN is required to do on its own behalf. 1032 13. AR and MSE Resilience 1034 ANETs SHOULD deploy ARs in Virtual Router Redundancy Protocol (VRRP) 1035 [RFC5798] configurations so that service continuity is maintained 1036 even if one or more ARs fail. Using VRRP, the MN is unaware which of 1037 the (redundant) ARs is currently providing service, and any service 1038 discontinuity will be limited to the failover time supported by VRRP. 1039 Widely deployed public domain implementations of VRRP are available. 1041 MSEs SHOULD use high availability clustering services so that 1042 multiple redundant systems can provide coordinated response to 1043 failures. As with VRRP, widely deployed public domain 1044 implementations of high availability clustering services are 1045 available. Note that special-purpose and expensive dedicated 1046 hardware is not necessary, and public domain implementations can be 1047 used even between lightweight virtual machines in cloud deployments. 1049 14. Detecting and Responding to MSE Failures 1051 In environments where fast recovery from MSE failure is required, ARs 1052 SHOULD use proactive Neighbor Unreachability Detection (NUD) in a 1053 manner that parallels Bidirectional Forwarding Detection (BFD) 1054 [RFC5880] to track MSE reachability. ARs can then quickly detect and 1055 react to failures so that cached information is re-established 1056 through alternate paths. Proactive NUD control messaging is carried 1057 only over well-connected ground domain networks (i.e., and not low- 1058 end ANET links such as aeronautical radios) and can therefore be 1059 tuned for rapid response. 1061 ARs perform proactive NUD for MSEs for which there are currently 1062 active MNs on the ANET. If an MSE fails, ARs can quickly inform MNs 1063 of the outage by sending multicast RA messages on the ANET interface. 1064 The AR sends RA messages to the MN via the ANET interface with an 1065 OMNI option with a Release ID for the failed MSE, and with 1066 destination address set to All-Nodes multicast (ff02::1) [RFC4291]. 1068 The AR SHOULD send MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated 1069 by small delays [RFC4861]. Any MNs on the ANET interface that have 1070 been using the (now defunct) MSE will receive the RA messages and 1071 associate with a new MSE. 1073 15. Transition Considerations 1075 When a MN connects to an ANET link for the first time, it sends an RS 1076 message with an OMNI option. If the first hop AR recognizes the 1077 option, it returns an RA with its MS OMNI LLA as the source, the MN 1078 OMNI LLA as the destination, the P(roxy) bit set in the RA flags and 1079 with an OMNI option included. The MN then engages the AR according 1080 to the OMNI link model specified above. If the first hop AR is a 1081 legacy IPv6 router, however, it instead returns an RA message with no 1082 OMNI option and with a non-OMNI unicast source LLA as specified in 1083 [RFC4861]. In that case, the MN engages the ANET according to the 1084 legacy IPv6 link model and without the OMNI extensions specified in 1085 this document. 1087 If the ANET link model is multiple access, there must be assurance 1088 that address duplication cannot corrupt the neighbor caches of other 1089 nodes on the link. When the MN sends an RS message on a multiple 1090 access ANET link with an OMNI LLA source address and an OMNI option, 1091 ARs that recognize the option ensure that the MN is authorized to use 1092 the address and return an RA with a non-zero Router Lifetime only if 1093 the MN is authorized. ARs that do not recognize the option instead 1094 return an RA that makes no statement about the MN's authorization to 1095 use the source address. In that case, the MN should perform 1096 Duplicate Address Detection to ensure that it does not interfere with 1097 other nodes on the link. 1099 An alternative approach for multiple access ANET links to ensure 1100 isolation for MN / AR communications is through L2 address mappings 1101 as discussed in Appendix D. This arrangement imparts a (virtual) 1102 point-to-point link model over the (physical) multiple access link. 1104 16. OMNI Interfaces on the Open Internet 1106 OMNI interfaces that connect to the open Internet via native and/or 1107 NATed underlying interfaces can apply symmetric security services 1108 such as VPNs to establish secured tunnels to MSEs. In environments 1109 where an explicit VPN may be too restrictive, OMNI interfaces can 1110 instead ensure neighbor cache integrity using SEcure Neighbor 1111 Discovery (SEND) [RFC3971] and Cryptographically Generated Addresses 1112 (CGAs) [RFC3972]. 1114 When SEND/CGA are used, the IPv6 ND control plane messages used to 1115 establish neighbor cache state are authenticated while data plane 1116 messages are delivered the same as for ordinary best-effort Internet 1117 traffic. Instead, data plane communications via OMNI interfaces that 1118 connect over the open Internet without an explicit VPN must emply 1119 transport- or higher-layer security to ensure integrity and/or 1120 confidentiality. 1122 In addition to secured OMNI interface RS/RA exchanges, SEND/CGA 1123 supports safe address resolution and neighbor unreachability 1124 detection as discused in Asymmetric Extended Route Optimization 1125 (AERO) [I-D.templin-intarea-6706bis]. This allows for efficient 1126 multilink operations over the open Internet with assured neighbor 1127 cache integrity. 1129 17. IANA Considerations 1131 The IANA is instructed to allocate an official Type number TBD from 1132 the registry "IPv6 Neighbor Discovery Option Formats" for the OMNI 1133 option. Implementations set Type to 253 as an interim value 1134 [RFC4727]. 1136 The OMNI option also defines an 8-bit Sub-Type field, for which IANA 1137 is instructed to create and maintain a new registry entitled "OMNI 1138 option Sub-Type values". Initial values for the OMNI option Sub-Type 1139 values registry are given below; future assignments are to be made 1140 through Expert Review [RFC8126]. 1142 Value Sub-Type name Reference 1143 ----- ------------- ---------- 1144 0 Pad1 [RFCXXXX] 1145 1 PadN [RFCXXXX] 1146 2 ifIndex-tuple (Type 1) [RFCXXXX] 1147 3 ifIndex-tuple (Type 2) [RFCXXXX] 1148 4 MS-Register [RFCXXXX] 1149 5 MS-Release [RFCXXXX] 1150 6-252 Unassigned 1151 253-254 Experimental [RFCXXXX] 1152 255 Reserved [RFCXXXX] 1154 Figure 13: OMNI Option Sub-Type Values 1156 The IANA is instructed to allocate one Ethernet unicast address TBD2 1157 (suggest 00-00-5E-00-52-14 [RFC5214]) in the registry "IANA Ethernet 1158 Address Block - Unicast Use". 1160 18. Security Considerations 1162 Security considerations for IPv6 [RFC8200] and IPv6 Neighbor 1163 Discovery [RFC4861] apply. OMNI interface IPv6 ND messages SHOULD 1164 include Nonce and Timestamp options [RFC3971] when synchronized 1165 transaction confirmation is needed. 1167 OMNI interfaces configured over secured underlying ANET interfaces 1168 inherit the physical and/or link-layer security aspects of the 1169 connected ANETs. OMNI interfaces configured over open Internet 1170 interfaces must use symmetric securing services such as VPNs or 1171 asymmetric services such as SEND/CGA [RFC3971][RFC3972]. 1173 Security considerations for specific access network interface types 1174 are covered under the corresponding IP-over-(foo) specification 1175 (e.g., [RFC2464], [RFC2492], etc.). 1177 19. Acknowledgements 1179 The first version of this document was prepared per the consensus 1180 decision at the 7th Conference of the International Civil Aviation 1181 Organization (ICAO) Working Group-I Mobility Subgroup on March 22, 1182 2019. Consensus to take the document forward to the IETF was reached 1183 at the 9th Conference of the Mobility Subgroup on November 22, 2019. 1184 Attendees and contributors included: Guray Acar, Danny Bharj, 1185 Francois D'Humieres, Pavel Drasil, Nikos Fistas, Giovanni Garofolo, 1186 Bernhard Haindl, Vaughn Maiolla, Tom McParland, Victor Moreno, Madhu 1187 Niraula, Brent Phillips, Liviu Popescu, Jacky Pouzet, Aloke Roy, Greg 1188 Saccone, Robert Segers, Michal Skorepa, Michel Solery, Stephane 1189 Tamalet, Fred Templin, Jean-Marc Vacher, Bela Varkonyi, Tony Whyman, 1190 Fryderyk Wrobel and Dongsong Zeng. 1192 The following individuals are acknowledged for their useful comments: 1193 Michael Matyas, Madhu Niraula, Greg Saccone, Stephane Tamalet, Eric 1194 Vyncke. Pavel Drasil, Zdenek Jaron and Michal Skorepa are recognized 1195 for their many helpful ideas and suggestions. 1197 This work is aligned with the NASA Safe Autonomous Systems Operation 1198 (SASO) program under NASA contract number NNA16BD84C. 1200 This work is aligned with the FAA as per the SE2025 contract number 1201 DTFAWA-15-D-00030. 1203 20. References 1205 20.1. Normative References 1207 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1208 Requirement Levels", BCP 14, RFC 2119, 1209 DOI 10.17487/RFC2119, March 1997, 1210 . 1212 [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, 1213 "Definition of the Differentiated Services Field (DS 1214 Field) in the IPv4 and IPv6 Headers", RFC 2474, 1215 DOI 10.17487/RFC2474, December 1998, 1216 . 1218 [RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander, 1219 "SEcure Neighbor Discovery (SEND)", RFC 3971, 1220 DOI 10.17487/RFC3971, March 2005, 1221 . 1223 [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)", 1224 RFC 3972, DOI 10.17487/RFC3972, March 2005, 1225 . 1227 [RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and 1228 More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191, 1229 November 2005, . 1231 [RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast 1232 Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005, 1233 . 1235 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 1236 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 1237 2006, . 1239 [RFC4727] Fenner, B., "Experimental Values In IPv4, IPv6, ICMPv4, 1240 ICMPv6, UDP, and TCP Headers", RFC 4727, 1241 DOI 10.17487/RFC4727, November 2006, 1242 . 1244 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 1245 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 1246 DOI 10.17487/RFC4861, September 2007, 1247 . 1249 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 1250 Address Autoconfiguration", RFC 4862, 1251 DOI 10.17487/RFC4862, September 2007, 1252 . 1254 [RFC6088] Tsirtsis, G., Giarreta, G., Soliman, H., and N. Montavont, 1255 "Traffic Selectors for Flow Bindings", RFC 6088, 1256 DOI 10.17487/RFC6088, January 2011, 1257 . 1259 [RFC8028] Baker, F. and B. Carpenter, "First-Hop Router Selection by 1260 Hosts in a Multi-Prefix Network", RFC 8028, 1261 DOI 10.17487/RFC8028, November 2016, 1262 . 1264 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 1265 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 1266 May 2017, . 1268 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 1269 (IPv6) Specification", STD 86, RFC 8200, 1270 DOI 10.17487/RFC8200, July 2017, 1271 . 1273 [RFC8201] McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed., 1274 "Path MTU Discovery for IP version 6", STD 87, RFC 8201, 1275 DOI 10.17487/RFC8201, July 2017, 1276 . 1278 20.2. Informative References 1280 [I-D.templin-intarea-6706bis] 1281 Templin, F., "Asymmetric Extended Route Optimization 1282 (AERO)", draft-templin-intarea-6706bis-38 (work in 1283 progress), April 2020. 1285 [RFC2225] Laubach, M. and J. Halpern, "Classical IP and ARP over 1286 ATM", RFC 2225, DOI 10.17487/RFC2225, April 1998, 1287 . 1289 [RFC2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet 1290 Networks", RFC 2464, DOI 10.17487/RFC2464, December 1998, 1291 . 1293 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 1294 IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473, 1295 December 1998, . 1297 [RFC2492] Armitage, G., Schulter, P., and M. Jork, "IPv6 over ATM 1298 Networks", RFC 2492, DOI 10.17487/RFC2492, January 1999, 1299 . 1301 [RFC2863] McCloghrie, K. and F. Kastenholz, "The Interfaces Group 1302 MIB", RFC 2863, DOI 10.17487/RFC2863, June 2000, 1303 . 1305 [RFC3692] Narten, T., "Assigning Experimental and Testing Numbers 1306 Considered Useful", BCP 82, RFC 3692, 1307 DOI 10.17487/RFC3692, January 2004, 1308 . 1310 [RFC3819] Karn, P., Ed., Bormann, C., Fairhurst, G., Grossman, D., 1311 Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L. 1312 Wood, "Advice for Internet Subnetwork Designers", BCP 89, 1313 RFC 3819, DOI 10.17487/RFC3819, July 2004, 1314 . 1316 [RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery 1317 Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April 1318 2006, . 1320 [RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick, 1321 "Internet Group Management Protocol (IGMP) / Multicast 1322 Listener Discovery (MLD)-Based Multicast Forwarding 1323 ("IGMP/MLD Proxying")", RFC 4605, DOI 10.17487/RFC4605, 1324 August 2006, . 1326 [RFC5213] Gundavelli, S., Ed., Leung, K., Devarapalli, V., 1327 Chowdhury, K., and B. Patil, "Proxy Mobile IPv6", 1328 RFC 5213, DOI 10.17487/RFC5213, August 2008, 1329 . 1331 [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site 1332 Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, 1333 DOI 10.17487/RFC5214, March 2008, 1334 . 1336 [RFC5798] Nadas, S., Ed., "Virtual Router Redundancy Protocol (VRRP) 1337 Version 3 for IPv4 and IPv6", RFC 5798, 1338 DOI 10.17487/RFC5798, March 2010, 1339 . 1341 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 1342 (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, 1343 . 1345 [RFC6543] Gundavelli, S., "Reserved IPv6 Interface Identifier for 1346 Proxy Mobile IPv6", RFC 6543, DOI 10.17487/RFC6543, May 1347 2012, . 1349 [RFC7084] Singh, H., Beebee, W., Donley, C., and B. Stark, "Basic 1350 Requirements for IPv6 Customer Edge Routers", RFC 7084, 1351 DOI 10.17487/RFC7084, November 2013, 1352 . 1354 [RFC7421] Carpenter, B., Ed., Chown, T., Gont, F., Jiang, S., 1355 Petrescu, A., and A. Yourtchenko, "Analysis of the 64-bit 1356 Boundary in IPv6 Addressing", RFC 7421, 1357 DOI 10.17487/RFC7421, January 2015, 1358 . 1360 [RFC7847] Melia, T., Ed. and S. Gundavelli, Ed., "Logical-Interface 1361 Support for IP Hosts with Multi-Access Support", RFC 7847, 1362 DOI 10.17487/RFC7847, May 2016, 1363 . 1365 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 1366 Writing an IANA Considerations Section in RFCs", BCP 26, 1367 RFC 8126, DOI 10.17487/RFC8126, June 2017, 1368 . 1370 Appendix A. Type 1 ifIndex-tuple Traffic Classifier Preference Encoding 1372 Adaptation of the OMNI option Type 1 ifIndex-tuple's traffic 1373 classifier Bitmap to specific Internetworks such as the Aeronautical 1374 Telecommunications Network with Internet Protocol Services (ATN/IPS) 1375 may include link selection preferences based on other traffic 1376 classifiers (e.g., transport port numbers, etc.) in addition to the 1377 existing DSCP-based preferences. Nodes on specific Internetworks 1378 maintain a map of traffic classifiers to additional P[*] preference 1379 fields beyond the first 64. For example, TCP port 22 maps to P[67], 1380 TCP port 443 maps to P[70], UDP port 8060 maps to P[76], etc. 1382 Implementations use Simplex or Indexed encoding formats for P[*] 1383 encoding in order to encode a given set of traffic classifiers in the 1384 most efficient way. Some use cases may be more efficiently coded 1385 using Simplex form, while others may be more efficient using Indexed. 1386 Once a format is selected for preparation of a single ifIndex-tuple 1387 the same format must be used for the entire Sub-Option. Different 1388 Sub-Options may use different formats. 1390 The following figures show coding examples for various Simplex and 1391 Indexed formats: 1393 0 1 2 3 1394 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 1395 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1396 | Sub-Type=2 | Sub-length=4+N| ifIndex | ifType | 1397 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1398 | Provider ID | Link |S|0|RSV| Bitmap(0)=0xff|P00|P01|P02|P03| 1399 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1400 |P04|P05|P06|P07|P08|P09|P10|P11|P12|P13|P14|P15|P16|P17|P18|P19| 1401 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1402 |P20|P21|P22|P23|P24|P25|P26|P27|P28|P29|P30|P31| Bitmap(1)=0xff| 1403 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1404 |P32|P33|P34|P35|P36|P37|P38|P39|P40|P41|P42|P43|P44|P45|P46|P47| 1405 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1406 |P48|P49|P50|P51|P52|P53|P54|P55|P56|P57|P58|P59|P60|P61|P62|P63| 1407 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1408 | Bitmap(2)=0xff|P64|P65|P67|P68| ... 1409 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1411 Figure 14: Example 1: Dense Simplex Encoding 1413 0 1 2 3 1414 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 1415 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1416 | Sub-Type=2 | Sub-length=4+N| ifIndex | ifType | 1417 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1418 | Provider ID | Link |S|0|RSV| Bitmap(0)=0x00| Bitmap(1)=0x0f| 1419 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1420 |P48|P49|P50|P51|P52|P53|P54|P55|P56|P57|P58|P59|P60|P61|P62|P63| 1421 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1422 | Bitmap(2)=0x00| Bitmap(3)=0x00| Bitmap(4)=0x00| Bitmap(5)=0x00| 1423 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1424 | Bitmap(6)=0xf0|192|193|194|195|196|197|198|199|200|201|202|203| 1425 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1426 |204|205|206|207| Bitmap(7)=0x00| Bitmap(8)=0x0f|272|273|274|275| 1427 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1428 |276|277|278|279|280|281|282|283|284|285|286|287| Bitmap(9)=0x00| 1429 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1430 |Bitmap(10)=0x00| ... 1431 +-+-+-+-+-+-+-+-+-+-+- 1433 Figure 15: Example 2: Sparse Simplex Encoding 1435 0 1 2 3 1436 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 1437 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1438 | Sub-Type=2 | Sub-length=4+N| ifIndex | ifType | 1439 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1440 | Provider ID | Link |S|1|RSV| Index = 0x00 | Bitmap = 0x80 | 1441 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1442 |P00|P01|P02|P03| Index = 0x01 | Bitmap = 0x01 |P60|P61|P62|P63| 1443 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1444 | Index = 0x10 | Bitmap = 0x80 |512|513|514|515| Index = 0x18 | 1445 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1446 | Bitmap = 0x01 |796|797|798|799| ... 1447 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1449 Figure 16: Example 3: Indexed Encoding 1451 Appendix B. Prefix Length Considerations 1453 The 64-bit boundary in IPv6 addresses [RFC7421] would suggest an MN 1454 OMNI LLA that encodes the most-significant 64 MNP bits into the 1455 least-significant 64 bits of the prefix fe80::/64. For example, the 1456 MNP 2001:db8:1000:2000::/56 would be encoded as the OMNI addresss 1457 fe80::2001:db8:1000:2000. However, the address juxtapositioning does 1458 not present a form compatible with natural longest-prefix-match 1459 routing. 1461 [RFC4291] defines the link-local address format as the most 1462 significant 10 bits of the prefix fe80::/10, followed by 54 unused 1463 bits, followed by the least-significant 64 bits of the address. If 1464 the 64-bit boundary is ignored for the purpose of this specification, 1465 then the 54 unused bits can be employed for extended coding of MNPs 1466 longer than /64. 1468 One possible extended coding format would continue to encode MNP bits 1469 0-63 in bits 64-127 of the OMNI LLA, while including MNP bits 64-117 1470 in bits 10-63. For example, the OMNI LLA corresponding to the MNP 1471 2001:db8:1111:2222:3333:4444:5555::/112 would be 1472 fe8c:ccd1:1115:5540:2001:db8:1111:2222/128, and would still be a 1473 valid IPv6 LLA per [RFC4291]. However, the non-sequential bit 1474 ordering would render the prefix partially unreadable and completely 1475 incompatible with longest-prefix-match routing determiniations. 1477 An alternate form of OMNI LLA construction could be employed by 1478 embedding the MNP beginning with the most significant bit immediately 1479 following bit 10 of the prefix fe80::/10. For example, the OMNI LLA 1480 corresponding to the MNP 2001:db8:1111:2222:3333:4444:5555::/112 1481 would be written as fe88:0043:6e04:4448:888c:ccd1:1115:5540/122. 1482 This alternate form would be compatible with longest-prefix-match 1483 determinations. It has the disadvantages of requiring an unweildy 1484 10-bit right-shift of a 16byte address, as well as presenting a non- 1485 human-readable form. 1487 As a result, the OMNI specification has elected to encode the MNP 1488 canonically beginning at bit 16 of the prefix fe80::/16. For 1489 example, the OMNI LLA corresponding to the MNP 1490 2001:db8:1111:2222:3333:4444:5555::/112 would be written as 1491 fe80:2001:db8:1111:2222:3333:4444:5555/128. This has the advantage 1492 of providing a natural coding scheme compatible with longest-prefix- 1493 match, while presenting a human readalbe form and simple address 1494 configuration through natural 16-bit word shifts. It has the 1495 disadvantage that bits 10-15 of the address are unused; hence, the 1496 longest prefix length that can be encoded is /112. 1498 Appendix C. VDL Mode 2 Considerations 1500 ICAO Doc 9776 is the "Technical Manual for VHF Data Link Mode 2" 1501 (VDLM2) that specifies an essential radio frequency data link service 1502 for aircraft and ground stations in worldwide civil aviation air 1503 traffic management. The VDLM2 link type is "multicast capable" 1504 [RFC4861], but with considerable differences from common multicast 1505 links such as Ethernet and IEEE 802.11. 1507 First, the VDLM2 link data rate is only 31.5Kbps - multiple orders of 1508 magnitude less than most modern wireless networking gear. Second, 1509 due to the low available link bandwidth only VDLM2 ground stations 1510 (i.e., and not aircraft) are permitted to send broadcasts, and even 1511 so only as compact layer 2 "beacons". Third, aircraft employ the 1512 services of ground stations by performing unicast RS/RA exchanges 1513 upon receipt of beacons instead of listening for multicast RA 1514 messages and/or sending multicast RS messages. 1516 This beacon-oriented unicast RS/RA approach is necessary to conserve 1517 the already-scarce available link bandwidth. Moreover, since the 1518 numbers of beaconing ground stations operating within a given spatial 1519 range must be kept as sparse as possible, it would not be feasible to 1520 have different classes of ground stations within the same region 1521 observing different protocols. It is therefore highly desirable that 1522 all ground stations observe a common language of RS/RA as specified 1523 in this document. 1525 Note that links of this nature may benefit from compression 1526 techniques that reduce the bandwidth necessary for conveying the same 1527 amount of data. The IETF lpwan working group is considering possible 1528 alternatives: [https://datatracker.ietf.org/wg/lpwan/documents]. 1530 Appendix D. MN / AR Isolation Through L2 Address Mapping 1532 Per [RFC4861], IPv6 ND messages may be sent to either a multicast or 1533 unicast link-scoped IPv6 destination address. However, IPv6 ND 1534 messaging should be coordinated between the MN and AR only without 1535 invoking other nodes on the ANET. This implies that MN / AR 1536 coordinations should be isolated and not overheard by other nodes on 1537 the link. 1539 To support MN / AR isolation on some ANET links, ARs can maintain an 1540 OMNI-specific unicast L2 address ("MSADDR"). For Ethernet-compatible 1541 ANETs, this specification reserves one Ethernet unicast address TBD2 1542 (see: Section 17). For non-Ethernet statically-addressed ANETs, 1543 MSADDR is reserved per the assigned numbers authority for the ANET 1544 addressing space. For still other ANETs, MSADDR may be dynamically 1545 discovered through other means, e.g., L2 beacons. 1547 MNs map the L3 addresses of all IPv6 ND messages they send (i.e., 1548 both multicast and unicast) to MSADDR instead of to an ordinary 1549 unicast or multicast L2 address. In this way, all of the MN's IPv6 1550 ND messages will be received by ARs that are configured to accept 1551 packets destined to MSADDR. Note that multiple ARs on the link could 1552 be configured to accept packets destined to MSADDR, e.g., as a basis 1553 for supporting redundancy. 1555 Therefore, ARs must accept and process packets destined to MSADDR, 1556 while all other devices must not process packets destined to MSADDR. 1557 This model has well-established operational experience in Proxy 1558 Mobile IPv6 (PMIP) [RFC5213][RFC6543]. 1560 Appendix E. Change Log 1562 << RFC Editor - remove prior to publication >> 1564 Differences from draft-templin-6man-omni-interface-10 to draft- 1565 templin-6man-omni-interface-11: 1567 o Removed /64 assumption, resulting in new OMNI address format. 1569 Differences from draft-templin-6man-omni-interface-07 to draft- 1570 templin-6man-omni-interface-08: 1572 o OMNI MNs in the open Internet 1574 Differences from draft-templin-6man-omni-interface-06 to draft- 1575 templin-6man-omni-interface-07: 1577 o Brought back L2 MSADDR mapping text for MN / AR isolation based on 1578 L2 addressing. 1580 o Explanded "Transition Considerations". 1582 Differences from draft-templin-6man-omni-interface-05 to draft- 1583 templin-6man-omni-interface-06: 1585 o Brought back OMNI option "R" flag, and dicussed its use. 1587 Differences from draft-templin-6man-omni-interface-04 to draft- 1588 templin-6man-omni-interface-05: 1590 o Transition considerations, and overhaul of RS/RA addressing with 1591 the inclusion of MSE addresses within the OMNI option instead of 1592 as RS/RA addresses (developed under FAA SE2025 contract number 1593 DTFAWA-15-D-00030). 1595 Differences from draft-templin-6man-omni-interface-02 to draft- 1596 templin-6man-omni-interface-03: 1598 o Added "advisory PTB messages" under FAA SE2025 contract number 1599 DTFAWA-15-D-00030. 1601 Differences from draft-templin-6man-omni-interface-01 to draft- 1602 templin-6man-omni-interface-02: 1604 o Removed "Primary" flag and supporting text. 1606 o Clarified that "Router Lifetime" applies to each ANET interface 1607 independently, and that the union of all ANET interface Router 1608 Lifetimes determines MSE lifetime. 1610 Differences from draft-templin-6man-omni-interface-00 to draft- 1611 templin-6man-omni-interface-01: 1613 o "All-MSEs" OMNI LLA defined. Also reserverd fe80::ff00:0000/104 1614 for future use (most likely as "pseudo-multicast"). 1616 o Non-normative discussion of alternate OMNI LLA construction form 1617 made possible if the 64-bit assumption were relaxed. 1619 Differences from draft-templin-atn-aero-interface-21 to draft- 1620 templin-6man-omni-interface-00: 1622 o Minor clarification on Type-2 ifIndex-tuple encoding. 1624 o Draft filename change (replaces draft-templin-atn-aero-interface). 1626 Differences from draft-templin-atn-aero-interface-20 to draft- 1627 templin-atn-aero-interface-21: 1629 o OMNI option format 1631 o MTU 1633 Differences from draft-templin-atn-aero-interface-19 to draft- 1634 templin-atn-aero-interface-20: 1636 o MTU 1638 Differences from draft-templin-atn-aero-interface-18 to draft- 1639 templin-atn-aero-interface-19: 1641 o MTU 1643 Differences from draft-templin-atn-aero-interface-17 to draft- 1644 templin-atn-aero-interface-18: 1646 o MTU and RA configuration information updated. 1648 Differences from draft-templin-atn-aero-interface-16 to draft- 1649 templin-atn-aero-interface-17: 1651 o New "Primary" flag in OMNI option. 1653 Differences from draft-templin-atn-aero-interface-15 to draft- 1654 templin-atn-aero-interface-16: 1656 o New note on MSE OMNI LLA uniqueness assurance. 1658 o General cleanup. 1660 Differences from draft-templin-atn-aero-interface-14 to draft- 1661 templin-atn-aero-interface-15: 1663 o General cleanup. 1665 Differences from draft-templin-atn-aero-interface-13 to draft- 1666 templin-atn-aero-interface-14: 1668 o General cleanup. 1670 Differences from draft-templin-atn-aero-interface-12 to draft- 1671 templin-atn-aero-interface-13: 1673 o Minor re-work on "Notify-MSE" (changed to Notification ID). 1675 Differences from draft-templin-atn-aero-interface-11 to draft- 1676 templin-atn-aero-interface-12: 1678 o Removed "Request/Response" OMNI option formats. Now, there is 1679 only one OMNI option format that applies to all ND messages. 1681 o Added new OMNI option field and supporting text for "Notify-MSE". 1683 Differences from draft-templin-atn-aero-interface-10 to draft- 1684 templin-atn-aero-interface-11: 1686 o Changed name from "aero" to "OMNI" 1688 o Resolved AD review comments from Eric Vyncke (posted to atn list) 1690 Differences from draft-templin-atn-aero-interface-09 to draft- 1691 templin-atn-aero-interface-10: 1693 o Renamed ARO option to AERO option 1695 o Re-worked Section 13 text to discuss proactive NUD. 1697 Differences from draft-templin-atn-aero-interface-08 to draft- 1698 templin-atn-aero-interface-09: 1700 o Version and reference update 1702 Differences from draft-templin-atn-aero-interface-07 to draft- 1703 templin-atn-aero-interface-08: 1705 o Removed "Classic" and "MS-enabled" link model discussion 1707 o Added new figure for MN/AR/MSE model. 1709 o New Section on "Detecting and responding to MSE failure". 1711 Differences from draft-templin-atn-aero-interface-06 to draft- 1712 templin-atn-aero-interface-07: 1714 o Removed "nonce" field from AR option format. Applications that 1715 require a nonce can include a standard nonce option if they want 1716 to. 1718 o Various editorial cleanups. 1720 Differences from draft-templin-atn-aero-interface-05 to draft- 1721 templin-atn-aero-interface-06: 1723 o New Appendix C on "VDL Mode 2 Considerations" 1725 o New Appendix D on "RS/RA Messaging as a Single Standard API" 1727 o Various significant updates in Section 5, 10 and 12. 1729 Differences from draft-templin-atn-aero-interface-04 to draft- 1730 templin-atn-aero-interface-05: 1732 o Introduced RFC6543 precedent for focusing IPv6 ND messaging to a 1733 reserved unicast link-layer address 1735 o Introduced new IPv6 ND option for Aero Registration 1737 o Specification of MN-to-MSE message exchanges via the ANET access 1738 router as a proxy 1740 o IANA Considerations updated to include registration requests and 1741 set interim RFC4727 option type value. 1743 Differences from draft-templin-atn-aero-interface-03 to draft- 1744 templin-atn-aero-interface-04: 1746 o Removed MNP from aero option format - we already have RIOs and 1747 PIOs, and so do not need another option type to include a Prefix. 1749 o Clarified that the RA message response must include an aero option 1750 to indicate to the MN that the ANET provides a MS. 1752 o MTU interactions with link adaptation clarified. 1754 Differences from draft-templin-atn-aero-interface-02 to draft- 1755 templin-atn-aero-interface-03: 1757 o Sections re-arranged to match RFC4861 structure. 1759 o Multiple aero interfaces 1761 o Conceptual sending algorithm 1763 Differences from draft-templin-atn-aero-interface-01 to draft- 1764 templin-atn-aero-interface-02: 1766 o Removed discussion of encapsulation (out of scope) 1768 o Simplified MTU section 1769 o Changed to use a new IPv6 ND option (the "aero option") instead of 1770 S/TLLAO 1772 o Explained the nature of the interaction between the mobility 1773 management service and the air interface 1775 Differences from draft-templin-atn-aero-interface-00 to draft- 1776 templin-atn-aero-interface-01: 1778 o Updates based on list review comments on IETF 'atn' list from 1779 4/29/2019 through 5/7/2019 (issue tracker established) 1781 o added list of opportunities afforded by the single virtual link 1782 model 1784 o added discussion of encapsulation considerations to Section 6 1786 o noted that DupAddrDetectTransmits is set to 0 1788 o removed discussion of IPv6 ND options for prefix assertions. The 1789 aero address already includes the MNP, and there are many good 1790 reasons for it to continue to do so. Therefore, also including 1791 the MNP in an IPv6 ND option would be redundant. 1793 o Significant re-work of "Router Discovery" section. 1795 o New Appendix B on Prefix Length considerations 1797 First draft version (draft-templin-atn-aero-interface-00): 1799 o Draft based on consensus decision of ICAO Working Group I Mobility 1800 Subgroup March 22, 2019. 1802 Authors' Addresses 1804 Fred L. Templin (editor) 1805 The Boeing Company 1806 P.O. Box 3707 1807 Seattle, WA 98124 1808 USA 1810 Email: fltemplin@acm.org 1811 Tony Whyman 1812 MWA Ltd c/o Inmarsat Global Ltd 1813 99 City Road 1814 London EC1Y 1AX 1815 England 1817 Email: tony.whyman@mccallumwhyman.com